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Bai XP, Dong F, Yang GH, Zhang L. Influences of sterol regulatory element binding protein-1c silencing on glucose production in HepG2 cells treated with free fatty acid. Lipids Health Dis 2019; 18:89. [PMID: 30954075 PMCID: PMC6451783 DOI: 10.1186/s12944-019-1026-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Accepted: 03/21/2019] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Elevation of exogenous free fatty acid (FFA) level leads to insulin resistance (IR) in liver, IR is manifested by elevated hepatic glucose production. We aim to study whether inhibition of endogenous fatty acid synthesis could decrease hepatic glucose production. METHODS Low-passage HepG2 cells derived from human liver tissue were cultured in medium supplemented with FFA to induce IR, the influences of sterol regulatory element binding protein-1c (SREBP-1c) silencing on glucose production of HepG2 cells were investigated, and genes responsible for fatty acid and glucose metabolism were detected by real-time PCR. RESULTS Compared with HepG2 cells cultured in normal growth medium, glucose production of HepG2 cells treated by FFA was significantly increased {[(0.28 ± 0.01) vs (0.83 ± 0.02)] umol.ug- 1 protein, n = 6 wells, P < 0.01}; the mRNA expression of phosphoenolpyruvate carboxylase kinase (PEPCK) and glucose-6-phosphatase (G6PC) in HepG2 cells increased by more than 5-fold and 3-fold, respectively; the mRNA expression of fatty acid synthase (FAS) and stearoyl-CoA desaturase-1 (SCD1) increased by approximately 4-fold and 1.1-fold, respectively; the mRNA expression of carnitine palmitoyltransferase-1 (CPT-1) changed slightly. Compared with the scrambled siRNA control, glucose production of HepG2 cells treated by FFA significantly increased after SREBP-1c silencing {[(0.018 ± 0.001) vs (0.028 ± 0.002)] umol.ug- 1 protein, n = 6 wells, P < 0.01}; the mRNA expression of PEPCK and G6PC increased by approximately 1.5-fold and 5-fold, respectively, but the mRNA expression of FAS, SCD1 and CPT-1 changed slightly. CONCLUSIONS SREBP-1c silencing further augmented glucose production of HepG2 cells treated by FFA significantly, genes responsible for fatty acid synthesis and gluconeogenesis played an important role in this process. SREBP-1c functions not only as a lipid regulator but also plays an important role in regulation of glucose metabolism.
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Affiliation(s)
- Xiu-Ping Bai
- Endocrinology Division, The Second Hospital of ShanXi Medical University, TaiYuan, 030001, ShanXi, China.
| | - Feng Dong
- Diabetes Division, University of Texas Health Science Center, San Antonio, TX, USA
| | - Guo-Hua Yang
- Central Laboratory, The Second Hospital of ShanXi Medical University, TaiYuan, 030001, ShanXi, China
| | - Lei Zhang
- Endocrinology Division, The Second Hospital of ShanXi Medical University, TaiYuan, 030001, ShanXi, China
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Jung TW, Chung YH, Kim HC, Abd El-Aty AM, Jeong JH. Protectin DX attenuates LPS-induced inflammation and insulin resistance in adipocytes via AMPK-mediated suppression of the NF-κB pathway. Am J Physiol Endocrinol Metab 2018; 315:E543-E551. [PMID: 29584445 DOI: 10.1152/ajpendo.00408.2017] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several studies have demonstrated that protectins, ω-3 fatty acid-derived proresolution mediators, may ameliorate inflammation. Recently, protectin DX (PDX) was also reported to attenuate inflammation and insulin resistance in several cell types. However, the effects of PDX on inflammation in adipocytes remain ambiguous. In this study, we found that PDX treatment suppressed adipogenesis and lipid accumulation during 3T3-L1 differentiation. Treatment of differentiated 3T3-L1 cells with PDX stimulated AMP-activated protein kinase (AMPK) phosphorylation in a dose-dependent manner. PDX-induced AMPK phosphorylation blocked lipopolysaccharide (LPS)-induced secretion of proinflammatory cytokines, such as tumor necrosis factor-α and monocyte chemoattractant protein-1. Treatment of 3T3-L1 cells with PDX alleviated LPS-induced NF-κB and inhibitory factor κB phosphorylation. Furthermore, PDX treatment diminished LPS-induced impairment of insulin signaling and insulin-stimulated glucose uptake, as well as fatty acid oxidation. These effects were decreased by silencing AMPK expression with small-interfering RNA. In conclusion, the current findings suggest that PDX attenuates inflammation and insulin resistance in adipocytes via an AMPK-dependent pathway, which in turn provides evidence that PDX has anti-inflammatory and antidiabetic effects in adipocytes.
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Affiliation(s)
- Tae Woo Jung
- Research Administration Team, Seoul National University Bundang Hospital, Seongnam, Republic of Korea
| | - Yoon Hee Chung
- Department of Anatomy, College of Medicine, Chung-Ang University, Seoul, Republic of Korea
| | - Hyoung-Chun Kim
- Neuropsychopharmacology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon, Republic of Korea
| | - A M Abd El-Aty
- Department of Pharmacology, Faculty of Veterinary Medicine, Cairo University , Giza , Egypt
- Department of Medical Pharmacology, Medical Faculty, Ataturk University , Erzurum , Turkey
| | - Ji Hoon Jeong
- Department of Pharmacology, College of Medicine, Chung-Ang University, Seoul, Republic of Korea
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Vella V, Nicolosi ML, Giuliano S, Bellomo M, Belfiore A, Malaguarnera R. PPAR-γ Agonists As Antineoplastic Agents in Cancers with Dysregulated IGF Axis. Front Endocrinol (Lausanne) 2017; 8:31. [PMID: 28275367 PMCID: PMC5319972 DOI: 10.3389/fendo.2017.00031] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 02/06/2017] [Indexed: 12/13/2022] Open
Abstract
It is now widely accepted that insulin resistance and compensatory hyperinsulinemia are associated to increased cancer incidence and mortality. Moreover, cancer development and progression as well as cancer resistance to traditional anticancer therapies are often linked to a deregulation/overactivation of the insulin-like growth factor (IGF) axis, which involves the autocrine/paracrine production of IGFs (IGF-I and IGF-II) and overexpression of their cognate receptors [IGF-I receptor, IGF-insulin receptor (IR), and IR]. Recently, new drugs targeting various IGF axis components have been developed. However, these drugs have several limitations including the occurrence of insulin resistance and compensatory hyperinsulinemia, which, in turn, may affect cancer cell growth and survival. Therefore, new therapeutic approaches are needed. In this regard, the pleiotropic effects of peroxisome proliferator activated receptor (PPAR)-γ agonists may have promising applications in cancer prevention and therapy. Indeed, activation of PPAR-γ by thiazolidinediones (TZDs) or other agonists may inhibit cell growth and proliferation by lowering circulating insulin and affecting key pathways of the Insulin/IGF axis, such as PI3K/mTOR, MAPK, and GSK3-β/Wnt/β-catenin cascades, which regulate cancer cell survival, cell reprogramming, and differentiation. In light of these evidences, TZDs and other PPAR-γ agonists may be exploited as potential preventive and therapeutic agents in tumors addicted to the activation of IGF axis or occurring in hyperinsulinemic patients. Unfortunately, clinical trials using PPAR-γ agonists as antineoplastic agents have reached conflicting results, possibly because they have not selected tumors with overactivated insulin/IGF-I axis or occurring in hyperinsulinemic patients. In conclusion, the use of PPAR-γ agonists in combined therapies of IGF-driven malignancies looks promising but requires future developments.
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Affiliation(s)
- Veronica Vella
- Scienze delle Attività Motorie e Sportive, University Kore, Enna, Italy
| | - Maria Luisa Nicolosi
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
| | - Stefania Giuliano
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
| | - Maria Bellomo
- Scienze delle Attività Motorie e Sportive, University Kore, Enna, Italy
| | - Antonino Belfiore
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
- *Correspondence: Antonino Belfiore,
| | - Roberta Malaguarnera
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
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Malaguarnera R, Vella V, Nicolosi ML, Belfiore A. Insulin Resistance: Any Role in the Changing Epidemiology of Thyroid Cancer? Front Endocrinol (Lausanne) 2017; 8:314. [PMID: 29184536 PMCID: PMC5694441 DOI: 10.3389/fendo.2017.00314] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Accepted: 10/30/2017] [Indexed: 12/13/2022] Open
Abstract
In the past few decades, the incidence of thyroid cancer (TC), namely of its papillary hystotype (PTC), has shown a steady increase worldwide, which has been attributed at least in part to the increasing diagnosis of early stage tumors. However, some evidence suggests that environmental and lifestyle factors can also play a role. Among the potential risk factors involved in the changing epidemiology of TC, particular attention has been drawn to insulin-resistance and related metabolic disorders, such as obesity, type 2 diabetes, and metabolic syndrome, which have been also rapidly increasing worldwide due to widespread dietary and lifestyle changes. In accordance with this possibility, various epidemiological studies have indeed gathered substantial evidence that insulin resistance-related metabolic disorders might be associated with an increased TC risk either through hyperinsulinemia or by affecting other TC risk factors including iodine deficiency, elevated thyroid stimulating hormone, estrogen-dependent signaling, chronic autoimmune thyroiditis, and others. This review summarizes the current literature evaluating the relationship between metabolic disorders characterized by insulin resistance and the risk for TC as well as the possible underlying mechanisms. The potential implications of such association in TC prevention and therapy are discussed.
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Affiliation(s)
- Roberta Malaguarnera
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
| | - Veronica Vella
- School of Human and Social Sciences, “Kore” University of Enna, Enna, Italy
- *Correspondence: Veronica Vella, ; Antonino Belfiore,
| | - Maria Luisa Nicolosi
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
| | - Antonino Belfiore
- Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
- *Correspondence: Veronica Vella, ; Antonino Belfiore,
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Lackey DE, Lazaro RG, Li P, Johnson A, Hernandez-Carretero A, Weber N, Vorobyova I, Tsukomoto H, Osborn O. The role of dietary fat in obesity-induced insulin resistance. Am J Physiol Endocrinol Metab 2016; 311:E989-E997. [PMID: 27802965 PMCID: PMC5183884 DOI: 10.1152/ajpendo.00323.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 10/12/2016] [Accepted: 10/26/2016] [Indexed: 01/15/2023]
Abstract
Consumption of excess calories results in obesity and insulin resistance and has been intensively studied in mice and humans. The objective of this study was to determine the specific contribution of dietary fat rather than total caloric intake to the development of obesity-associated insulin resistance. We used an intragastric feeding method to overfeed excess calories from a low-fat diet (and an isocalorically matched high-fat diet) through a surgically implanted gastric feeding tube to generate obesity in wild-type mice followed by hyperinsulinemic-euglycemic clamp studies to assess the development of insulin resistance. We show that overfeeding a low-fat diet results in levels of obesity similar to high-fat diet feeding in mice. However, despite a similar body weight, obese high-fat diet-fed mice are more insulin resistant than mice fed an isocaloric low-fat diet. Therefore, increased proportion of calories from dietary fat further potentiates insulin resistance in the obese state. Furthermore, crossover diet studies revealed that reduction in dietary fat composition improves glucose tolerance in obesity. In the context of the current obesity and diabetes epidemic, it is particularly important to fully understand the role of dietary macronutrients in the potentiation and amelioration of disease.
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Affiliation(s)
- Denise E Lackey
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
| | - Raul G Lazaro
- Southern California Research Center for ALPD and Cirrhosis and Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California; and
| | - Pingping Li
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
| | - Andrew Johnson
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
| | - Angelina Hernandez-Carretero
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
| | - Natalie Weber
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California
| | - Ivetta Vorobyova
- Southern California Research Center for ALPD and Cirrhosis and Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California; and
| | - Hidekazu Tsukomoto
- Southern California Research Center for ALPD and Cirrhosis and Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California; and
- Department of Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California
| | - Olivia Osborn
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, La Jolla, California;
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Reynolds K, Novosad B, Hoffhines A, Gipson J, Johnson J, Peters J, Gonzalez F, Gimble J, Hill M. Pretreatment with troglitazone decreases lethality during endotoxemia in mice. ACTA ACUST UNITED AC 2016. [DOI: 10.1177/09680519020080040701] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Troglitazone is an oral antidiabetic drug that is a ligand for peroxisome proliferator activated receptor γ (PPARγ). Based on other studies that have implicated an immunosuppressive role for PPARγ during inflammatory responses, we hypothesized that troglitazone treatment would improve survival in a murine model of endotoxemia and that the protective effect would be mediated by decreased expression of inflammatory mediators. C57Bl/6N x Sv/129 (wild-type [WT]) or PPARα null mice treated for 2 weeks with dietary troglitazone (0.1%) had significantly fewer deaths and a higher LD 50 value compared to control-fed mice when challenged with lipopolysaccharide (LPS). PPARα null mice were more sensitive to the lethal effects of LPS as evidenced by a 2-fold lower LD 50 (6.6 mg/kg) compared to WT mice (14.6 mg/kg). Troglitazone treatment had no significant effect on LPS-induced plasma TNF, glucose, or nitric oxide levels in WT or PPARα null mice at any of the time points examined. However, troglitazone treatment significantly reduced LPS-induced plasma IL-6 levels in both WT and PPARα null mice. The results of these studies suggest that troglitazone treatment protects mice against a lethal challenge of LPS, but whether or not this effect is mediated through decreased expression of inflammatory mediators remains unclear.
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Affiliation(s)
- Karen Reynolds
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA, Department of Radiologic Technology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - Bo Novosad
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA, Department of Radiologic Technology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - Adam Hoffhines
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA
| | - Jenny Gipson
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA
| | - Jared Johnson
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA
| | - Jeffrey Peters
- Department of Veterinary Science, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Frank Gonzalez
- Laboratory of Metabolism, NCI, National Institutes of Health, Bethesda, Maryland, USA
| | - Jeffrey Gimble
- Tissue Engineering Program, Artecell Inc., Durham, North Carolina, USA
| | - Molly Hill
- Department of Natural Sciences, Oklahoma Christian University, Oklahoma City, Oklahoma, USA, , Department of Radiologic Technology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
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Meshkani R, Sadeghi A, Taheripak G, Zarghooni M, Gerayesh-Nejad S, Bakhtiyari S. Rosiglitazone, a PPARγagonist, ameliorates palmitate-induced insulin resistance and apoptosis in skeletal muscle cells. Cell Biochem Funct 2014; 32:683-91. [DOI: 10.1002/cbf.3072] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 10/04/2014] [Accepted: 10/06/2014] [Indexed: 11/06/2022]
Affiliation(s)
- Reza Meshkani
- Department of Biochemistry, Faculty of Medicine; Tehran University of Medical Sciences; Tehran IR Iran
| | - Asie Sadeghi
- Department of Biochemistry, Faculty of Medicine; Tehran University of Medical Sciences; Tehran IR Iran
| | - Gholamreza Taheripak
- Department of Biochemistry, Faculty of Medicine; Tehran University of Medical Sciences; Tehran IR Iran
| | | | - Siavash Gerayesh-Nejad
- Department of Biochemistry, Faculty of Medicine; Tehran University of Medical Sciences; Tehran IR Iran
| | - Salar Bakhtiyari
- Department of Clinical Biochemistry, Faculty of Medicine; Ilam University of Medical Sciences; Ilam IR Iran
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Yee JK, Lee WNP, Ross MG, Lane RH, Han G, Vega J, Desai M. Peroxisome proliferator-activated receptor gamma modulation and lipogenic response in adipocytes of small-for-gestational age offspring. Nutr Metab (Lond) 2012; 9:62. [PMID: 22726273 PMCID: PMC3495639 DOI: 10.1186/1743-7075-9-62] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 06/14/2012] [Indexed: 01/30/2023] Open
Abstract
Background Small-for-gestational age (SGA) at birth increases risk of development of adult obesity and insulin resistance. A model of SGA rat offspring has been shown to exhibit increased adipose tissue expression of a key adipogenic transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ), and increased fatty acid de novo synthesis during the nursing period, prior to onset of obesity. PPARγ agonists have been studied for potential use in the prevention of insulin resistance. Moreover, SGA adipocytes exhibit age-dependent differences in lipogenesis as mediated by PPARγ. The effects of PPARγ modulators on lipogenic gene expression and de novo lipogenesis on the age-dependent changes in SGA adipocytes are not known. The objectives of this study were: 1) to determine the adipogenic and lipogenic potential in SGA adipocytes at postnatal day 1 (p1) and day 21 (p21), 2) to determine how the PPARγ activator- and repressor-ligands affect the lipogenic potential, and 3) to determine the fatty acid metabolic response to PPARγ activator-ligand treatment. Methods Primary adipocyte cultures from p1 and p21 SGA and Control male offspring were established from a known maternal food-restriction model of SGA. Cell proliferation and Oil Red O (ORO) staining were quantified. Adipocytes were treated with increasing doses of rosiglitazone or bisphenol-A diglycidyl ether (BADGE). PPARγ and SREBP1 protein expression were determined. De novo lipogenesis with rosiglitazone treatment at p21 was studied using 50% U13C-glucose and gas chromatography/mass spectrometry. Results At p1 and p21, SGA demonstrated increased cell proliferation and increased ORO staining. At p21, SGA demonstrated increased lipogenic gene expression and increased glucose-mediated fatty acid de novo synthesis compared with Controls. In response to rosiglitazone, SGA adipocytes further increased glucose utilization for fatty acid synthesis. SGA lipogenic gene expression demonstrated resistance to BADGE treatment. Conclusions SGA adipocytes exhibit an enhanced adipogenic and lipogenic potential in early postnatal life. By p21, SGA demonstrated resistance to PPARγ repressor-ligand treatment, and selective response to high dose PPARγ activator-ligand treatment in adipogenic and lipogenic gene expression. p21 SGA adipocytes revealed increased fatty acid de novo synthesis through a complex relationship with glucose metabolism.
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Affiliation(s)
- Jennifer K Yee
- Department of Pediatrics, Division of Endocrinology, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, David Geffen School of Medicine at UCLA, 1000 West Carson Street, Harbor Box 446, Torrance, CA 90509, USA.
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Tran TTT, Poirier H, Clément L, Nassir F, Pelsers MMAL, Petit V, Degrace P, Monnot MC, Glatz JFC, Abumrad NA, Besnard P, Niot I. Luminal lipid regulates CD36 levels and downstream signaling to stimulate chylomicron synthesis. J Biol Chem 2011; 286:25201-10. [PMID: 21610069 DOI: 10.1074/jbc.m111.233551] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The membrane glycoprotein CD36 binds nanomolar concentrations of long chain fatty acids (LCFA) and is highly expressed on the luminal surface of enterocytes. CD36 deficiency reduces chylomicron production through unknown mechanisms. In this report, we provide novel insights into some of the underlying mechanisms. Our in vivo data demonstrate that CD36 gene deletion in mice does not affect LCFA uptake and subsequent esterification into triglycerides by the intestinal mucosa exposed to the micellar LCFA concentrations prevailing in the intestine. In rodents, the CD36 protein disappears early from the luminal side of intestinal villi during the postprandial period, but only when the diet contains lipids. This drop is significant 1 h after a lipid supply and associates with ubiquitination of CD36. Using CHO cells expressing CD36, it is shown that the digestion products LCFA and diglycerides trigger CD36 ubiquitination. In vivo treatment with the proteasome inhibitor MG132 prevents the lipid-mediated degradation of CD36. In vivo and ex vivo, CD36 is shown to be required for lipid activation of ERK1/2, which associates with an increase of the key chylomicron synthesis proteins, apolipoprotein B48 and microsomal triglyceride transfer protein. Therefore, intestinal CD36, possibly through ERK1/2-mediated signaling, is involved in the adaptation of enterocyte metabolism to the postprandial lipid challenge by promoting the production of large triglyceride-rich lipoproteins that are rapidly cleared in the blood. This suggests that CD36 may be a therapeutic target for reducing the postprandial hypertriglyceridemia and associated cardiovascular risks.
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Affiliation(s)
- Thi Thu Trang Tran
- Physiologie de la Nutrition, U866 INSERM/Université de Bourgogne, AgroSup Dijon, 21000 Dijon, France
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Hsiao G, Chapman J, Ofrecio JM, Wilkes J, Resnik JL, Thapar D, Subramaniam S, Sears DD. Multi-tissue, selective PPARγ modulation of insulin sensitivity and metabolic pathways in obese rats. Am J Physiol Endocrinol Metab 2011; 300:E164-74. [PMID: 20959535 PMCID: PMC3023199 DOI: 10.1152/ajpendo.00219.2010] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Accepted: 10/14/2010] [Indexed: 01/17/2023]
Abstract
Peroxisome proliferator-activated receptor-γ (PPARγ) ligands, including the insulin-sensitizing thiazolidinedione drugs, transcriptionally regulate hundreds of genes. Little is known about the relationship between PPARγ ligand-specific modulation of cellular mechanisms and insulin sensitization. We characterized the insulin sensitivity and multitissue gene expression profiles of lean and insulin-resistant, obese Zucker rats untreated or treated with one of four PPARγ ligands (pioglitazone, rosiglitazone, troglitazone, and AG-035029). We analyzed the transcriptional profiles of adipose tissue, skeletal muscle, and liver from the rats and determined whether ligand treatment insulin-sensitizing potency was related to ligand treatment-induced alteration of functional pathways. Ligand treatments improved insulin sensitivity in obese rats to varying degrees. Adipose tissue profiles revealed ligand treatment-selective modulation of inflammatory and branched-chain amino acid (BCAA) metabolic pathways, which correlated with ligand treatment-specific insulin-sensitizing potency. Skeletal muscle profiles showed that obese rats exhibited elevated expression of adipocyte and slow-twitch fiber markers, which further increased after ligand treatment, but the magnitude of the treatment-induced changes was not correlated with insulin sensitization. Although PPARγ ligand treatments heterogeneously improved dysregulated expression of cholesterol and fatty acid biosynthetic pathways in obese rat liver, these alterations were not correlated with ligand insulin-sensitizing potency. PPARγ ligand treatment-specific insulin-sensitizing potency correlated with modulation of adipose tissue inflammatory and BCAA metabolic pathways, suggesting a functional relationship between these pathways and whole body insulin sensitivity. Other PPARγ ligand treatment-induced functional pathway changes were detected in adipose tissue, skeletal muscle, and liver profiles but were not related to degree of insulin sensitization.
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Affiliation(s)
- Gene Hsiao
- Department of Bioengineering, University of California, San Diego, CA, USA
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Chapman J, Miles PD, Ofrecio JM, Neels JG, Yu JG, Resnik JL, Wilkes J, Talukdar S, Thapar D, Johnson K, Sears DD. Osteopontin is required for the early onset of high fat diet-induced insulin resistance in mice. PLoS One 2010; 5:e13959. [PMID: 21103061 PMCID: PMC2980483 DOI: 10.1371/journal.pone.0013959] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2010] [Accepted: 07/21/2010] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND Insulin resistance is manifested in muscle, adipose tissue, and liver and is associated with adipose tissue inflammation. The cellular components and mechanisms that regulate the onset of diet-induced insulin resistance are not clearly defined. METHODOLOGY AND PRINCIPAL FINDINGS We initially observed osteopontin (OPN) mRNA over-expression in adipose tissue of obese, insulin resistant humans and rats which was normalized by thiazolidinedione (TZD) treatment in both species. OPN regulates inflammation and is implicated in pathogenic maladies resulting from chronic obesity. Thus, we tested the hypothesis that OPN is involved in the early development of insulin resistance using a 2-4 week high fat diet (HFD) model. OPN KO mice fed HFD for 2 weeks were completely protected from the severe skeletal muscle, liver and adipose tissue insulin resistance that developed in wild type (WT) controls, as determined by hyperinsulinemic euglycemic clamp and acute insulin-stimulation studies. Although two-week HFD did not alter body weight or plasma free fatty acids and cytokines in either strain, HFD-induced hyperleptinemia, increased adipose tissue inflammation (macrophages and cytokines), and adipocyte hypertrophy were significant in WT mice and blunted or absent in OPN KO mice. Adipose tissue OPN protein isoform expression was significantly altered in 2- and 4-week HFD-fed WT mice but total OPN protein was unchanged. OPN KO bone marrow stromal cells were more osteogenic and less adipogenic than WT cells in vitro. Interestingly, the two differentiation pathways were inversely affected by HFD in WT cells in vitro. CONCLUSIONS The OPN KO phenotypes we report reflect protection from insulin resistance that is associated with changes in adipocyte biology and adipose tissue inflammatory status. OPN is a key component in the development of HFD-induced insulin resistance.
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Affiliation(s)
- Justin Chapman
- Pfizer Inc., San Diego, California, United States of America
| | - Philip D. Miles
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Jachelle M. Ofrecio
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Jaap G. Neels
- Inserm U907, University of Nice-Sophia Antipolis, Nice, France
| | - Joseph G. Yu
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Jamie L. Resnik
- Department of Reproductive Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Jason Wilkes
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Saswata Talukdar
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Divya Thapar
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Kristen Johnson
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Dorothy D. Sears
- Division of Endocrinology & Metabolism, Department of Medicine, University of California San Diego, La Jolla, California, United States of America
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Kiilerich K, Gudmundsson M, Birk JB, Lundby C, Taudorf S, Plomgaard P, Saltin B, Pedersen PA, Wojtaszewski JFP, Pilegaard H. Low muscle glycogen and elevated plasma free fatty acid modify but do not prevent exercise-induced PDH activation in human skeletal muscle. Diabetes 2010; 59:26-32. [PMID: 19833896 PMCID: PMC2797931 DOI: 10.2337/db09-1032] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
OBJECTIVE To test the hypothesis that free fatty acid (FFA) and muscle glycogen modify exercise-induced regulation of PDH (pyruvate dehydrogenase) in human skeletal muscle through regulation of PDK4 expression. RESEARCH DESIGN AND METHODS On two occasions, healthy male subjects lowered (by exercise) muscle glycogen in one leg (LOW) relative to the contra-lateral leg (CON) the day before the experimental day. On the experimental days, plasma FFA was ensured normal or remained elevated by consuming breakfast rich (low FFA) or poor (high FFA) in carbohydrate, 2 h before performing 20 min of two-legged knee extensor exercise. Vastus lateralis biopsies were obtained before and after exercise. RESULTS PDK4 protein content was approximately 2.2- and approximately 1.5-fold higher in LOW than CON leg in high FFA and low FFA, respectively, and the PDK4 protein content in the CON leg was approximately twofold higher in high FFA than in low FFA. In all conditions, exercise increased PDHa (PDH in the active form) activity, resulting in similar levels in LOW leg in both trials and CON leg in high FFA, but higher level in CON leg in low FFA. PDHa activity was closely associated with the PDH-E1alpha phosphorylation level. CONCLUSIONS Muscle glycogen and plasma FFA attenuate exercise-induced PDH regulation in human skeletal muscle in a nonadditive manner. This might be through regulation of PDK4 expression. The activation of PDH by exercise independent of changes in muscle glycogen or plasma FFA suggests that exercise overrules FFA-mediated inhibition of PDH (i.e., carbohydrate oxidation), and this may thus be one mechanism behind the health-promoting effects of exercise.
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Affiliation(s)
- Kristian Kiilerich
- Copenhagen Muscle Research Centre, University of Copenhagen, Copenhagen, Denmark.
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14
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Abstract
The function and survival of all organisms is dependent on the dynamic control of energy metabolism, when energy demand is matched to energy supply. The AMP-activated protein kinase (AMPK) alphabetagamma heterotrimer has emerged as an important integrator of signals that control energy balance through the regulation of multiple biochemical pathways in all eukaryotes. In this review, we begin with the discovery of the AMPK family and discuss the recent structural studies that have revealed the molecular basis for AMP binding to the enzyme's gamma subunit. AMPK's regulation involves autoinhibitory features and phosphorylation of both the catalytic alpha subunit and the beta-targeting subunit. We review the role of AMPK at the cellular level through examination of its many substrates and discuss how it controls cellular energy balance. We look at how AMPK integrates stress responses such as exercise as well as nutrient and hormonal signals to control food intake, energy expenditure, and substrate utilization at the whole body level. Lastly, we review the possible role of AMPK in multiple common diseases and the role of the new age of drugs targeting AMPK signaling.
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Affiliation(s)
- Gregory R Steinberg
- Protein Chemistry and Metabolism, St. Vincent's Institute of Medical Research, University of Melbourne, Fitzroy, Victoria, Australia.
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15
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Hoy AJ, Brandon AE, Turner N, Watt MJ, Bruce CR, Cooney GJ, Kraegen EW. Lipid and insulin infusion-induced skeletal muscle insulin resistance is likely due to metabolic feedback and not changes in IRS-1, Akt, or AS160 phosphorylation. Am J Physiol Endocrinol Metab 2009; 297:E67-75. [PMID: 19366875 PMCID: PMC2711668 DOI: 10.1152/ajpendo.90945.2008] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Type 2 diabetes is characterized by hyperlipidemia, hyperinsulinemia, and insulin resistance. The aim of this study was to investigate whether acute hyperlipidemia-induced insulin resistance in the presence of hyperinsulinemia was due to defective insulin signaling. Hyperinsulinemia (approximately 300 mU/l) with hyperlipidemia or glycerol (control) was produced in cannulated male Wistar rats for 0.5, 1 h, 3 h, or 5 h. The glucose infusion rate required to maintain euglycemia was significantly reduced by 3 h with lipid infusion and was further reduced after 5 h of infusion, with no difference in plasma insulin levels, indicating development of insulin resistance. Consistent with this finding, in vivo skeletal muscle glucose uptake (31%, P < 0.05) and glycogen synthesis rate (38%, P < 0.02) were significantly reduced after 5 h compared with 3 h of lipid infusion. Despite the development of insulin resistance, there was no difference in the phosphorylation state of multiple insulin-signaling intermediates or muscle diacylglyceride and ceramide content over the same time course. However, there was an increase in cumulative exposure to long-chain acyl-CoA (70%) with lipid infusion. Interestingly, although muscle pyruvate dehydrogenase kinase 4 protein content was decreased in hyperinsulinemic glycerol-infused rats, this decrease was blunted in muscle from hyperinsulinemic lipid-infused rats. Decreased pyruvate dehydrogenase complex activity was also observed in lipid- and insulin-infused animals (43%). Overall, these results suggest that acute reductions in muscle glucose metabolism in rats with hyperlipidemia and hyperinsulinemia are more likely a result of substrate competition than a significant early defect in insulin action or signaling.
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Affiliation(s)
- Andrew J Hoy
- Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, University of New South Wales, Sydney, New South Wales, Australia.
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Anti-diabetic effects of pumpkin and its components, trigonelline and nicotinic acid, on Goto-Kakizaki rats. Biosci Biotechnol Biochem 2009; 73:1033-41. [PMID: 19420712 DOI: 10.1271/bbb.80805] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The effects of a pumpkin paste concentrate and its components on oral glucose tolerance and serum lipid levels were determined in non-obese type 2 diabetic Goto-Kakizaki (GK) rats. In the oral glucose tolerance test, the pumpkin paste concentrate-fed group maintained a lower glucose level than the control group between 15 and 60 min. The compounds considered to be effective in improving glucose tolerance and contained in the methanol extract of the pumpkin in relatively abundant amounts were isolated and identified as trigonelline (TRG) and nicotinic acid (NA).Feeding a diet containing TRG and NA respectively improved and tended to improve glucose tolerance. The insulin level increased after 15 min in the TRG-fed GK rats and then gradually decreased over the next 120 min. In contrast, a gradual increase was seen in the insulin level over 120 min in the control GK rats not fed with TRG, suggesting that TRG could improve the insulin resistance. The serum and liver triglyceride (TG) levels in the TRG- and NA-fed GK rats were lower than those in the control GK rats. Lower activity of liver fatty acid synthase (FAS), and higher activity of liver carnitine palmitoyl transferase (CPT) and glucokinase (GLK) in the TRG- and NA-fed GK rats than in the control GK rats were observed. This suggests that the regulation of these enzyme activities by TRG and NA was closely related to the suppression of both TG accumulation and the progression of diabetes.
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Sohn KAK, Cruciani-Guglielmacci C, Kassis N, Clément L, Ouali F, Caüzac M, Lebègue N, Berthelot P, Caignard DH, Pégorier JP, Renard P, Dacquet C, Ktorza A, Magnan C. S26948, a new specific peroxisome proliferator activated receptor gamma modulator improved in vivo hepatic insulin sensitivity in 48 h lipid infused rats. Eur J Pharmacol 2009; 608:104-11. [PMID: 19250932 DOI: 10.1016/j.ejphar.2009.02.033] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 01/21/2009] [Accepted: 02/12/2009] [Indexed: 11/19/2022]
Abstract
We examined whether S26948, a new specific peroxisome proliferator activated receptor gamma modulator prevented insulin-resistance induced by a 48 h intralipid-infusion in normal rat (IL rats). The effect of S26948 (30 mg/kg) was compared to rosiglitazone (10 mg/kg). Rats were catheterized in the right jugular vein 4 days before the beginning of the 48 h lipid or saline infusions. Animals were intraperitoneally injected once daily with vehicle, S26948 or rosiglitazone. At the end of the infusion the rats underwent either a glucose tolerance test or a euglycemic-hyperinsulinemic clamp. Finally isolation and incubation of hepatocytes in another series of rats were performed. Intralipid infusion leads to a 4-fold increase in plasma free fatty acid concentration compared to controls (C). Both S26948 and rosiglitazone decreased plasma free fatty acid concentration in IL rats compared to vehicle treated IL rats. Glucose-induced insulin secretion was significantly increased in IL compared to C and was associated with insulin resistance. Both S26948 and rosiglitazone treatments normalized glucose-induced insulin secretion and improved insulin action in IL rats. However, S26948 specifically improved hepatic insulin sensitivity whereas rosiglitazone improved both hepatic insulin sensitivity and insulin-stimulated glucose utilization. Finally, studies on isolated hepatocytes showed differential effect of both compounds on gene expression of key enzymes of glucose metabolism. Our data show that non thiazolidinedione S26948 may represent an alternative way for the management of dysregulated hepatic insulin sensitivity.
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18
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Wang H, Li H, Hou Z, Pan L, Shen X, Li G. Role of oxidative stress in elevated blood pressure induced by high free fatty acids. Hypertens Res 2009; 32:152-8. [PMID: 19262475 DOI: 10.1038/hr.2008.35] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The aim of the study is to investigate the possible mechanism of oxidative stress in the high free fatty acids (FFAs)-induced hypertension. Male Sprague-Dawley rat models were established and classified into three groups, namely the control group (NC group), the FFA group, and the N-acetylcysteine (NAC) group. Blood pressure (BP) was recorded. An organ chamber experiment was performed to determine endothelium-dependent/-independent vasodilation (EDV/EIV). Reactive oxygen species (ROS), nitrotyrosine, reduced glutathione hormone (GSH) and NO(2)(-)/NO(3)(-) levels were measured in plasma. Endothelial nitric oxide synthase (eNOS) mRNA expression in endothelial cells was evaluated by real-time PCR. The following results were observed: (1) In the FFA group, BP increased after 4 h infusion of Intralipid+heparin. In the NAC group, systolic and diastolic BP remained the same. (2) In the FFA group, the aortic rings tended to show impaired EDV in response to acetylcholine (ACh). There was no difference of EDV response in the NAC and NC groups. (3) In the FFA group, NO(2)(-)/NO(3)(-) levels were significantly reduced, and eNOS mRNA expression and activity were significantly decreased compared with the NC group. NAC administration increased eNOS mRNA expression and activity. (4) ROS and nitrotyrosine concentrations in the FFA group were higher than in the NC group, and GSH concentrations in the FFA group were lower than in the NC group. Elevated FFAs can induce elevated BP, potentially through FFA-induced impairment of EDV resulting from decreased eNOS mRNA expression and activity. Oxidative stress may also play an important role in potential mechanisms of this high FFA-induced elevated BP.
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Affiliation(s)
- Hui Wang
- Department of Endocrinology, China-Japan Friendship Hospital, Beijing, China
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19
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Basu R, Basu A, Chandramouli V, Norby B, Dicke B, Shah P, Cohen O, Landau BR, Rizza RA. Effects of pioglitazone and metformin on NEFA-induced insulin resistance in type 2 diabetes. Diabetologia 2008; 51:2031-40. [PMID: 18769904 PMCID: PMC2701394 DOI: 10.1007/s00125-008-1138-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/21/2008] [Accepted: 07/23/2008] [Indexed: 11/26/2022]
Abstract
AIMS/HYPOTHESIS We sought to determine whether pioglitazone and metformin alter NEFA-induced insulin resistance in type 2 diabetes and, if so, the mechanism whereby this is effected. METHODS Euglycaemic-hyperinsulinaemic clamps (glucose approximately 5.3 mmol/l, insulin approximately 200 pmol/l) were performed in the presence of Intralipid-heparin (IL/H) or glycerol before and after 4 months of treatment with pioglitazone (n = 11) or metformin (n = 9) in diabetic participants. Hormone secretion was inhibited with somatostatin in all participants. RESULTS Pioglitazone increased insulin-stimulated glucose disappearance (p < 0.01) and increased insulin-induced suppression of glucose production (p < 0.01), gluconeogenesis (p < 0.05) and glycogenolysis (p < 0.05) during IL/H. However, glucose disappearance remained lower (p < 0.05) whereas glucose production (p < 0.01), gluconeogenesis (p < 0.05) and glycogenolysis (p < 0.05) were higher on the IL/H study day than on the glycerol study day, indicating persistence of NEFA-induced insulin resistance. Metformin increased (p < 0.001) glucose disappearance during IL/H to rates present during glycerol treatment, indicating protection against NEFA-induced insulin resistance in extrahepatic tissues. However, glucose production and gluconeogenesis (but not glycogenolysis) were higher (p < 0.01) during IL/H than during glycerol treatment with metformin, indicating persistence of NEFA-induced hepatic insulin resistance. CONCLUSIONS/INTERPRETATION We conclude that pioglitazone improves both the hepatic and the extrahepatic action of insulin but does not prevent NEFA-induced insulin resistance. In contrast, whereas metformin prevents NEFA-induced extrahepatic insulin resistance, it does not protect against NEFA-induced hepatic insulin resistance.
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Affiliation(s)
- R. Basu
- Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic College of Medicine, 200 1st Street SW, Room 5-194 Joseph, Rochester, MN 55905, USA
| | - A. Basu
- Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic College of Medicine, 200 1st Street SW, Room 5-194 Joseph, Rochester, MN 55905, USA
| | - V. Chandramouli
- Division of Clinical and Molecular Endocrinology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - B. Norby
- Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic College of Medicine, 200 1st Street SW, Room 5-194 Joseph, Rochester, MN 55905, USA
| | - B. Dicke
- Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic College of Medicine, 200 1st Street SW, Room 5-194 Joseph, Rochester, MN 55905, USA
| | - P. Shah
- Department of Endocrine Neoplasia and Hormonal Disorders, University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - O. Cohen
- Institute of Endocrinology, Chaim Sheba Medical Center, Tel Hashomer, Israel
| | - B. R. Landau
- Division of Clinical and Molecular Endocrinology, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - R. A. Rizza
- Division of Endocrinology, Diabetes, Metabolism and Nutrition, Mayo Clinic College of Medicine, 200 1st Street SW, Room 5-194 Joseph, Rochester, MN 55905, USA
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Kim HS, Noh JH, Hong SH, Hwang YC, Yang TY, Lee MS, Kim KW, Lee MK. Rosiglitazone stimulates the release and synthesis of insulin by enhancing GLUT-2, glucokinase and BETA2/NeuroD expression. Biochem Biophys Res Commun 2008; 367:623-9. [DOI: 10.1016/j.bbrc.2007.12.192] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2007] [Accepted: 12/29/2007] [Indexed: 11/16/2022]
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21
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Watt MJ, Steinberg GR. Pathways involved in lipid-induced insulin resistance in obesity. ACTA ACUST UNITED AC 2007. [DOI: 10.2217/17460875.2.6.659] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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22
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Mittermayer F, Schaller G, Pleiner J, Krzyzanowska K, Kapiotis S, Roden M, Wolzt M. Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction. J Clin Endocrinol Metab 2007; 92:2574-80. [PMID: 17473072 DOI: 10.1210/jc.2006-2130] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation. OBJECTIVE We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans. DESIGN AND SETTING We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital. PATIENTS AND INTERVENTIONS Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations. MAIN OUTCOME MEASURES Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion. RESULTS Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline). CONCLUSIONS Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.
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Affiliation(s)
- Friedrich Mittermayer
- Department of Clinical Pharmacology, Medical University Vienna, AKH-Wien, Währinger Gürtel 18-20, A-1090 Vienna, Austria
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Schenk S, Horowitz JF. Acute exercise increases triglyceride synthesis in skeletal muscle and prevents fatty acid-induced insulin resistance. J Clin Invest 2007; 117:1690-8. [PMID: 17510709 PMCID: PMC1866251 DOI: 10.1172/jci30566] [Citation(s) in RCA: 281] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2006] [Accepted: 02/19/2007] [Indexed: 12/24/2022] Open
Abstract
Fatty acid oversupply is a key mediator of skeletal muscle insulin resistance in obesity, primarily via accumulation of fatty acid metabolites and activation of proinflammatory pathways. Herein, we demonstrate that fatty acid-induced insulin resistance in humans is completely prevented the day after 1 session of endurance exercise. Because skeletal muscle is the primary site for systemic glucose disposal and is highly susceptible to impaired insulin action by elevated fatty acid availability, we obtained skeletal muscle samples to investigate possible mechanisms mediating this protective effect of exercise. Prevention of fatty acid-induced insulin resistance after exercise accompanied enhanced skeletal muscle protein expression of key lipogenic enzymes and an increase in muscle triglyceride synthesis. Partitioning more fatty acids toward triglyceride synthesis within muscle reduced the accumulation of fatty acid metabolites and suppressed the proinflammatory response in skeletal muscle, as evidenced by decreased phosphorylation and activation of JNK and increased abundance of inhibitor of NF-kappaB alpha (I kappa B-alpha) and I kappa B-beta. We believe this is the first study to demonstrate that 1 session of exercise completely reverses fatty acid-induced insulin resistance in humans. Reversal of insulin resistance accompanied enhanced lipogenic capacity within skeletal muscle, reduced accumulation of highly bioactive fatty acid metabolites, and suppressed activation of proinflammatory pathways known to impair insulin action.
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Affiliation(s)
- Simon Schenk
- Substrate Metabolism Laboratory, Division of Kinesiology, University of Michigan, Ann Arbor, Michigan 48109-2214, USA
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Abstract
Insulin resistance typically reflects multiple defects of insulin receptor and post-receptor signalling that impair a diverse range of metabolic and vascular actions. Many potential intervention targets and compounds with therapeutic activity have been described. Proof of principle for a non-peptide insulin mimetic has been demonstrated by specific activation of the intracellular B-subunit of the insulin receptor. Potentiation of insulin action has been achieved with agents that enhance phosphorylation and prolong the tyrosine kinase activity of the insulin receptor and its protein substrates after activation by insulin. These include inhibitors of phosphatases and serine kinases that normally prevent or terminate tyrosine kinase signalling. Additional approaches involve increasing the activity of phosphatidylinositol 3-kinase and other downstream components of the insulin signalling pathways. Experimental interventions to remove signalling defects caused by cytokines, certain adipocyte hormones, excess fatty acids, glucotoxicity and negative feedback by distal signalling steps have also indicated therapeutic possibilities. Several hormones, metabolic enzymes, minerals, co-factors and transcription co-activators have shown insulin-sensitising potential. Since insulin resistance affects many metabolic and cardiovascular diseases, it provides an opportunity for simultaneous therapeutic attack on a broad front.
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Affiliation(s)
- Clifford J Bailey
- Deabetes Research Group, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
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Todd MK, Watt MJ, Le J, Hevener AL, Turcotte LP. Thiazolidinediones enhance skeletal muscle triacylglycerol synthesis while protecting against fatty acid-induced inflammation and insulin resistance. Am J Physiol Endocrinol Metab 2007; 292:E485-93. [PMID: 17003244 DOI: 10.1152/ajpendo.00080.2006] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In the present investigation, we studied the effects of thiazolidinedione (TZD) treatment on insulin-stimulated fatty acid (FA) and glucose kinetics in perfused muscle from high-fat (HF)-fed rats. We tested the hypothesis that TZDs prevent FA-induced insulin resistance by attenuating proinflammatory signaling independently of myocellular lipid levels. Male Wistar rats were assigned to one of three 3-wk dietary groups: control chow fed (CON), 65% HF diet (HFD), or TZD- (troglitazone or rosiglitazone) enriched HF diet (TZD + HFD). TZD treatment led to a significant increase in plasma membrane content of CD36 protein in muscle (red: P = 0.01, and white: P = 0.001) that correlated with increased FA uptake (45%, P = 0.002) and triacylglycerol (TG) synthesis (46%, P = 0.03) during the perfusion. Importantly, whereas HF feeding caused increased basal TG (P = 0.047), diacylglycerol (P = 0.002), and ceramide (P = 0.01) levels, TZD treatment only prevented the increase in muscle ceramide. In contrast, all of the muscle inflammatory markers altered by HF feeding ( upward arrowNIK protein content, P = 0.009; upward arrowIKKbeta activity, P = 0.006; downward arrowIkappaB-alpha protein, P = 0.03; and upward arrowJNK phosphorylation, P = 0.003) were completely normalized by TZD treatment. Consistent with this, HFD-induced decrements in insulin action were also prevented by TZD treatment. Thus our findings support the notion that TZD treatment causes increased FA uptake and TG accumulation in skeletal muscle under insulin-stimulated conditions. Despite this, TZDs suppress the inflammatory response to dietary lipid overload, and it is this mechanism that correlates strongly with insulin sensitivity.
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Affiliation(s)
- Mark K Todd
- Department of Kinesiology, University of Southern California, Los Angeles, California, USA
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Serlie MJ, Allick G, Groener JE, Ackermans MT, Heijligenberg R, Voermans BC, Aerts JM, Meijer AJ, Sauerwein HP. Chronic treatment with pioglitazone does not protect obese patients with diabetes mellitus type II from free fatty acid-induced insulin resistance. J Clin Endocrinol Metab 2007; 92:166-71. [PMID: 17062758 DOI: 10.1210/jc.2006-1518] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Thiazolidinediones increase peripheral insulin sensitivity and decrease plasma free fatty acids (FFA). However, their exact mechanism of action has not been fully elucidated. OBJECTIVE We studied the protective effect of pioglitazone on FFA-induced insulin resistance and the effects on intramyocellular glycosphingolipids. DESIGN We studied glucose metabolism in the basal state and during a hyperinsulinemic euglycemic clamp by using stable isotopes. Studies were performed at baseline and after 4 months of treatment with pioglitazone. Patients were then studied on a third occasion during infusion of a lipid emulsion to increase plasma FFA to pretreatment levels. All studies were combined with muscle biopsies to measure intramyocellular ceramide and glycosphingolipids. PATIENTS Patients were obese with poorly controlled type 2 diabetes mellitus. INTERVENTION Patients were treated with 30 mg pioglitazone once daily. MAIN OUTCOME MEASURE The change in peripheral insulin sensitivity after treatment with pioglitazone and during the infusion of the lipid emulsion was the main outcome measure. RESULTS Peripheral glucose uptake (Rd) increased significantly, but returned to baseline levels after increasing plasma FFA to pretreatment levels. Insulin-mediated suppression of FFA was increased significantly. Intramyocellular ceramide concentrations were higher during the hyperinsulinemic clamp after treatment with pioglitazone, but not in the basal state. The intramyocellular content of glycosphingolipids and plasma concentrations of ceramide and glycosphingolipids did not change. CONCLUSIONS Pioglitazone increases Rd and insulin-mediated suppression of plasma FFA, but does not protect patients with type 2 diabetes mellitus from FFA-induced insulin resistance. This effect of pioglitazone is not attained via a decrease in intramyocellular concentrations of ceramide or glycosphingolipids.
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Affiliation(s)
- Mireille J Serlie
- Department of Endocrinology and Metabolism, Academic Medical Center, F5-169, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
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Li L, Yang G, Li Q, Tang Y, Li K. High-fat- and lipid-induced insulin resistance in rats: the comparison of glucose metabolism, plasma resistin and adiponectin levels. ANNALS OF NUTRITION AND METABOLISM 2006; 50:499-505. [PMID: 17191023 DOI: 10.1159/000098141] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 08/08/2006] [Indexed: 11/19/2022]
Abstract
AIMS In animal models, both an acute elevation in plasma free fatty acid (FFA) via intravenous infusion of a lipid emulsion and a chronic elevation in plasma FFA via high-fat feeding have been shown to induce skeletal muscle and liver insulin resistance. However, there have been very few studies comparing the effects of high-fat- and lipid-induced insulin resistance on glucose metabolism and adipocytokines. METHODS In the current study, we used lipid infusion and a high-fat feed in combination with the hyperinsulinemic-euglycemic clamp technique to assess the impact of acute and chronically elevated FFA levels on overall glucose metabolism and insulin action; two adipocytokines, resistin and adiponectin, were used. RESULTS At baseline, plasma FFA levels were significantly increased in the high-fat diet (HF) group compared to the control group (p < 0.05). During clamp steady-state, the FFA levels were reduced by approximately 25% in the control and approximately 48% in the HF groups. In contrast, there was a significant increase in the plasma FFA level in the lipid-infused group (from 0.82 +/- 0.03 to 2.87 +/- 0.18 mmol/l). The glucose infusion rates (GIRs) in the HF and lipid groups were obviously lower than in the control group (p < 0.01). Moreover, GIR was lower in the lipid group compared with the HF group (p < 0.05). The rate of glucose disappearance (G(Rd)) was significantly lower in the lipid group compared with the control group. Hepatic glucose production in the control group was suppressed by approximately 15% compared with the HF and lipid groups where it was suppressed by only approximately 72 and approximately 91%, respectively. The resistin level of muscle tissues in the lipid group was significantly higher compared with the control and HF groups (both p < 0.05). After the insulin clamp, the circulating adiponectin level was significantly decreased in the lipid group compared with the control and HF groups (p < 0.05). CONCLUSIONS Lipid infusion, which was more effective than a high-fat diet, can induce peripheral and hepatic insulin resistance in rats. Insulin-induced resistance might be associated with elevated resistin and decreased adiponectin.
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Affiliation(s)
- Ling Li
- Department of Clinical Biochemistry and Key Laboratory of Laboratory Medical Diagnostics, Ministry of Education, Chongqing University of Medical Sciences, Chongqing, China.
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Haider DG, Mittermayer F, Schaller G, Artwohl M, Baumgartner-Parzer SM, Prager G, Roden M, Wolzt M. Free fatty acids normalize a rosiglitazone-induced visfatin release. Am J Physiol Endocrinol Metab 2006; 291:E885-90. [PMID: 16735449 DOI: 10.1152/ajpendo.00109.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The detrimental effect of elevated free fatty acids (FFAs) on insulin sensitivity can be improved by thiazolidinediones (TZDs) in patients with type 2 diabetes mellitus. It is unknown whether this salutary action of TZD is associated with altered release of the insulin-mimetic adipocytokine visfatin. In this study, we investigated whether visfatin concentrations are altered by FFA and TZD treatment. In a randomized, double-blind, placebo-controlled, parallel-group study 16 healthy volunteers received an infusion of triglycerides/heparin to increase plasma FFA after 3 wk of treatment with rosiglitazone (8 mg/day, n = 8) or placebo (n = 8), and circulating plasma visfatin was measured. As a corollary, human adipocytes were incubated with synthetic fatty acids and rosiglitazone to assess visfatin release in vitro. The results were that rosiglitazone treatment increased systemic plasma visfatin concentrations from 0.6 +/- 0.1 to 1.7 +/- 0.2 ng/ml (P < 0.01). Lipid infusion caused a marked elevation of plasma FFA but had no effect on circulating visfatin in controls. In contrast, elevated visfatin concentrations in subjects receiving rosiglitazone were normalized by lipid infusion. In isolated adipocytes, visfatin was released into supernatant medium by acute addition and long-term treatment of rosiglitazone. This secretion was blocked by synthetic fatty acids and by inhibition of phosphatidylinositol 3-kinase or Akt. In conclusion, release of the insulin-mimetic visfatin may represent a major mechanism of metabolic TZD action. The presence of FFA antagonizes this action, which may have implications for visfatin bioactivity.
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Affiliation(s)
- Dominik G Haider
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
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Bandyopadhyay GK, Yu JG, Ofrecio J, Olefsky JM. Increased malonyl-CoA levels in muscle from obese and type 2 diabetic subjects lead to decreased fatty acid oxidation and increased lipogenesis; thiazolidinedione treatment reverses these defects. Diabetes 2006; 55:2277-85. [PMID: 16873691 DOI: 10.2337/db06-0062] [Citation(s) in RCA: 209] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Increased accumulation of fatty acids and their derivatives can impair insulin-stimulated glucose disposal by skeletal muscle. To characterize the nature of the defects in lipid metabolism and to evaluate the effects of thiazolidinedione treatment, we analyzed the levels of triacylglycerol, long-chain fatty acyl-coA, malonyl-CoA, fatty acid oxidation, AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), malonyl-CoA decarboxylase, and fatty acid transport proteins in muscle biopsies from nondiabetic lean, obese, and type 2 subjects before and after an euglycemic-hyperinsulinemic clamp as well as pre-and post-3-month rosiglitazone treatment. We observed that low AMPK and high ACC activities resulted in elevation of malonyl-CoA levels and lower fatty acid oxidation rates. These conditions, along with the basal higher expression levels of fatty acid transporters, led accumulation of long-chain fatty acyl-coA and triacylglycerol in insulin-resistant muscle. During the insulin infusion, muscle fatty acid oxidation was reduced to a greater extent in the lean compared with the insulin-resistant subjects. In contrast, isolated muscle mitochondria from the type 2 subjects exhibited a greater rate of fatty acid oxidation compared with the lean group. All of these abnormalities in the type 2 diabetic group were reversed by rosiglitazone treatment. In conclusion, these studies have shown that elevated malonyl-CoA levels and decreased fatty acid oxidation are key abnormalities in insulin-resistant muscle, and, in type 2 diabetic patients, thiazolidinedione treatment can reverse these abnormalities.
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Affiliation(s)
- Gautam K Bandyopadhyay
- Department of Medicine, Division of Endocrinology and Metabolism, University of California at San Diego, 9500 Gilman Dr., La Jolla, 92093, USA
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Shadid S, Jensen MD. Pioglitazone increases non-esterified fatty acid clearance in upper body obesity. Diabetologia 2006; 49:149-57. [PMID: 16323003 DOI: 10.1007/s00125-005-0051-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Accepted: 09/05/2005] [Indexed: 10/25/2022]
Abstract
AIMS/HYPOTHESIS Plasma NEFA concentrations are largely determined by adipose tissue lipolysis. Insulin suppression of lipolysis is commonly impaired with insulin resistance and improves with thiazolidinedione treatment of type 2 diabetes. The present studies were designed to assess the effects of thiazolidinedione on NEFA (oleate) metabolism that are independent of improved glycaemic control. MATERIALS AND METHODS We measured plasma oleate concentration and flux ([(3)H]oleate), glucose kinetics ([6-(2)H(2)]glucose) and substrate oxidation (indirect calorimetry) before and after pioglitazone (30 mg/day for approximately 20 weeks) in 20 non-diabetic adults with upper body obesity. To assess the effects of improved insulin sensitivity per se we performed the same measurements in a matched group of volunteers treated with diet/exercise. Half of the two groups underwent these measurements during a hyperinsulinaemic-euglycaemic clamp, and the other half had their measurements taken during a (control) saline infusion before and after the intervention. RESULTS Both interventions increased insulin-stimulated glucose disposal and reduced plasma oleate concentrations during the insulin clamp. After diet/exercise, oleate flux decreased (p=0.03) during the insulin clamp and oleate clearance remained unchanged (p=0.55), whereas in the pioglitazone group, oleate flux during the clamp was unchanged (p=0.97) and oleate clearance increased (p=0.003). Oleate clearance in the saline control condition was increased in the pioglitazone group compared with the diet/exercise group (p=0.02). CONCLUSIONS/INTERPRETATION In insulin-resistant, non-diabetic adults, pioglitazone increases NEFA clearance during physiological hyperinsulinaemia, whereas improved insulin sensitivity achieved by diet/exercise does not alter NEFA clearance but enhances insulin suppression of NEFA release. This action of pioglitazone may contribute to improved glucose metabolism in type 2 diabetes.
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Affiliation(s)
- S Shadid
- Endocrine Research Unit, Mayo Clinic, 5-194 Joseph, 200 1st Street SW, Rochester, MN 55905, USA
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31
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Yang G, Li L, Tang Y, Boden G. Short-term pioglitazone treatment prevents free fatty acid-induced hepatic insulin resistance in normal rats: Possible role of the resistin and adiponectin. Biochem Biophys Res Commun 2006; 339:1190-6. [PMID: 16338222 DOI: 10.1016/j.bbrc.2005.11.143] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2005] [Accepted: 11/25/2005] [Indexed: 10/25/2022]
Abstract
We have evaluated the effects of a 2 week treatment with pioglitazone (Pio, 4mg/kg x d) on hepatic and peripheral insulin sensitivity, plasma adiponectin, and resistin concentrations in lipid-infused rats. Lipid infusion caused a large (60% in 4h) decrease in whole-body insulin sensitivity. Hepatic and peripheral insulin resistance contributed about equally to the whole-body insulin resistance. Pio treatment significantly improved whole-body insulin sensitivity due to normalization of hepatic insulin action, whereas peripheral insulin action remained unchanged and inhibited. Basal plasma resistin levels were approximately 4-fold lower in Pio-treated than in untreated rats. During lipid infusion, resistin levels rose in both Pio-treated and untreated rats, but remained significantly lower in Pio-treated than in untreated rats (P<0.01). Dot-blot analyses revealed a marked decrease in resistin protein levels in the liver of Pio-treated rats. Resistin levels were higher in muscle tissue in lipid group compared with control and Pio-treated rats (P<0.05). Fasting plasma adiponectin levels were 1.5-fold higher in Pio-treated than in untreated rats. We conclude that short-term treatment of rats with Pio prevented lipid-induced hepatic insulin resistance and that Pio mediated lowering of blood resistin and raising of adiponectin levels may have contributed to that effect.
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Affiliation(s)
- Gangyi Yang
- Department of Endocrinology, The Second Affiliated Hospital, Chongqing University of Medical Sciences, Chongqing 400010, China.
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32
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Hirabara SM, Silveira LR, Abdulkader F, Carvalho CRO, Procopio J, Curi R. Time-dependent effects of fatty acids on skeletal muscle metabolism. J Cell Physiol 2006; 210:7-15. [PMID: 17013887 DOI: 10.1002/jcp.20811] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Increased plasma levels of free fatty acids (FFA) occur in states of insulin resistance such as type 2 diabetes mellitus, obesity, and metabolic syndrome. These high levels of plasma FFA seem to play an important role for the development of insulin resistance but the mechanisms involved are not known. We demonstrated that acute exposure to FFA (1 h) in rat incubated skeletal muscle leads to an increase in the insulin-stimulated glycogen synthesis and glucose oxidation. In conditions of prolonged exposure to FFA, however, the insulin-stimulated glucose uptake and metabolism is impaired in skeletal muscle. In this review, we discuss the differences between the effects of acute and prolonged exposure to FFA on skeletal muscle glucose metabolism and the possible mechanisms involved in the FFA-induced insulin resistance.
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Affiliation(s)
- Sandro M Hirabara
- Department of Physiology and Biophysics, University of São Paulo, São Paulo, SP, Brazil.
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Dhindsa S, Tripathy D, Sanalkumar N, Ravishankar S, Ghanim H, Aljada A, Dandona P. Free fatty acid-induced insulin resistance in the obese is not prevented by rosiglitazone treatment. J Clin Endocrinol Metab 2005; 90:5058-63. [PMID: 15985490 DOI: 10.1210/jc.2005-0223] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
OBJECTIVE Elevation of free fatty acids (FFAs) by the infusion of triglyceride-heparin emulsion infusion (TG-Hep) causes insulin resistance (IR). We examined the effect of insulin sensitizer (rosiglitazone) on FFA-induced IR. DESIGN Nine obese subjects underwent a 6-h infusion of TG-Hep before and after 6 wk of rosiglitazone (8 mg/d) treatment. Hyperinsulinemic euglycemic clamps were performed during 0-2 and 4-6 h of TG-Hep. RESULTS After rosiglitazone for 6 wk, fasting FFA concentration fell, but not significantly (489 +/- 63 at 0 wk; 397 +/- 58 micromol/liter at 6 wk; P = 0.16), whereas C-reactive protein (4.26 +/- 0.95 at 0 wk; 2.03 +/- 0.45 microg/ml at 6 wk) and serum amyloid A (17.36 +/- 4.63 at 0 wk; 8.77 +/- 1.63 microg/ml at 6 wk) decreased significantly. At 0 wk, TG-Hep infusion caused a decrease in glucose infusion rate (GIR) from 4.49 +/- 0.95 mg/kg.min to 3.02 +/- 0.59 mg/kg.min (P = 0.018). Rosiglitazone treatment resulted in an increase in baseline GIR to 6.29 +/- 0.81 mg/kg.min (P = 0.03 vs. 0 wk), which decreased to 4.52 +/- 0.53 mg/kg.min (P = 0.001) after 6 h of TG-Hep infusion. The decrease in GIR induced by TG-Hep infusion was similar before and after rosiglitazone therapy [1.47 +/- 0.50 vs. 1.77 0.3 mg/kg.min (28.9 +/- 6.5 vs. 26.4 +/- 3.7%); P = 0.51]. The rise in FFAs and triglycerides after TG-Hep infusion was significantly lower at 6 wk (P = 0.006 for FFAs; P = 0.024 for triglycerides). CONCLUSIONS We conclude that rosiglitazone: 1) causes a significant increase in GIR; 2) induces a decrease in inflammatory mediators, C-reactive protein, and serum amyloid A; 3) decreases the rise in FFAs and triglycerides after TG-Hep infusion; and 4) does not prevent FFA-induced IR.
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Affiliation(s)
- Sandeep Dhindsa
- Diabetes-Endocrinology Center of Western New York, Distinguished Chief of Endocrinology, State University of New York at Buffalo, 3 Gates Circle, Buffalo, New York 14209, USA
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Flordellis CS, Ilias I, Papavassiliou AG. New therapeutic options for the metabolic syndrome: what's next? Trends Endocrinol Metab 2005; 16:254-60. [PMID: 16002303 DOI: 10.1016/j.tem.2005.06.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2005] [Revised: 04/11/2005] [Accepted: 06/23/2005] [Indexed: 11/21/2022]
Abstract
The metabolic syndrome (MSX), characterized by obesity, insulin resistance, dyslipidemia and hypertension, increases the risk of cardiovascular morbidity and mortality. It has recently been hypothesized that MSX and type 2 diabetes are caused by triglyceride and long-chain fatty acid accumulation in liver, muscle, pancreatic islets and selected brain areas. This lipocentric approach is integrated with analysis of inflammation associated with end-organ damage, including the vascular wall. Genes and proteins contributing to insulin resistance, beta cell dysfunction and vascular wall damage have been identified. Transcription factors and coactivators, including peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1 are crucial in mediating insulin resistance and accelerating vascular wall inflammation, and represent promising therapeutic targets. New pharmacological strategies include dual PPARalpha/gamma agonists, drugs with pleiotropic effects or combination therapies.
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35
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Summers SA, Nelson DH. A role for sphingolipids in producing the common features of type 2 diabetes, metabolic syndrome X, and Cushing's syndrome. Diabetes 2005; 54:591-602. [PMID: 15734832 DOI: 10.2337/diabetes.54.3.591] [Citation(s) in RCA: 136] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Metabolic syndrome X and type 2 diabetes share many metabolic and morphological similarities with Cushing's syndrome, a rare disorder caused by systemic glucocorticoid excess. Pathologies frequently associated with these diseases include insulin resistance, atherosclerosis, susceptibility to infection, poor wound healing, and hypertension. The similarity of the clinical profiles associated with these disorders suggests the influence of a common molecular mechanism for disease onset. Interestingly, numerous studies identify ceramides and other sphingolipids as potential contributors to these sequelae. Herein we review studies demonstrating that aberrant ceramide accumulation contributes to the development of the deleterious clinical manifestations associated with these diseases.
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Affiliation(s)
- Scott A Summers
- Division of Endocrinology, Metabolism and Diabetes, Department of Internal Medicine, University of Utah, Salt Lake City, UT 84132, USA.
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36
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Wilkes JJ, Nelson E, Osborne M, Demarest KT, Olefsky JM. Topiramate is an insulin-sensitizing compound in vivo with direct effects on adipocytes in female ZDF rats. Am J Physiol Endocrinol Metab 2005; 288:E617-24. [PMID: 15536205 DOI: 10.1152/ajpendo.00437.2004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have studied the in vivo and in vitro effects of Topiramate (TPM) in female Zucker diabetic fatty (ZDF) rats. After weight matching, drug treatment had a marked effect to lower fasting glucose levels of relatively normoglycemic animals as well as during an oral glucose tolerance test. The glucose clamp studies revealed a approximately 30% increased glucose disposal, increased hepatic glucose output (HGO) suppression from approximately 30 to 60%, and an increased free fatty acid suppression from 40 to 75%. Therefore, TPM treatment led to enhanced insulin sensitivity at the level of tissue glucose disposal (increased ISGDR), liver (increased inhibition of HGO), and adipose tissue (enhanced suppression of lipolysis). When soleus muscle strips of control or TPM-treated ZDF rats were studied ex vivo, insulin-stimulated glucose transport was not enhanced in the drug-treated animals. In contrast, when isolated adipocytes were studied ex vivo, a marked increase (+55%) in insulin-stimulated glucose transport was observed. In vitro treatment of muscle strips and rat adipocytes showed no effect on glucose transport in muscle with a 40% increase in insulin-stimulated adipocyte glucose transport. In conclusion, 1) TPM treatment leads to a decrease in plasma glucose and increased in vivo insulin sensitivity; 2) insulin sensitization was observed in adipocytes, but not muscle, when tissues were studied ex vivo or in vitro; and 3) TPM directly enhances insulin action in insulin-resistant adipose cells in vitro. Thus the in vivo effects of TPM treatment appear to be exerted through adipose tissue.
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Affiliation(s)
- Jason J Wilkes
- Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, USA.
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37
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Noushmehr H, D'Amico E, Farilla L, Hui H, Wawrowsky KA, Mlynarski W, Doria A, Abumrad NA, Perfetti R. Fatty acid translocase (FAT/CD36) is localized on insulin-containing granules in human pancreatic beta-cells and mediates fatty acid effects on insulin secretion. Diabetes 2005; 54:472-81. [PMID: 15677505 DOI: 10.2337/diabetes.54.2.472] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The membrane receptor FAT/CD36 facilitates the major fraction of long-chain fatty acid (FA) uptake by muscle and adipose tissues. In line with the well-known effects of FA metabolism on carbohydrate utilization and insulin responsiveness, altered expression of CD36 has been linked to phenotypic features of the metabolic syndrome including insulin resistance and dyslipidemia. FA metabolism is also known to significantly affect insulin secretion. However, the role of CD36 in this process remains unknown, since its expression levels and function in the pancreas have not been explored. In the present study, freshly isolated human islets and a mouse-derived beta-cell line (MIN6) were shown positive for CD36 expression by RT-PCR, Western blot, and immunofluorescence. The identity of the PCR product was confirmed by microsequencing. The identified transcript was translated and the protein was expressed and subjected to the known posttranslational glycosylation. Fluorescence resonance energy transfer analysis and subcellular protein fractionation indicated that insulin and CD36 are colocalized in the secretory granules of beta-cells. Islet CD36 functioned in FA uptake because this process was blocked by the irreversible CD36 inhibitor sulfosuccinimidyl-oleate. More importantly, sulfosuccinimidyl-oleate reversed enhancing and inhibiting effects, respectively, of acute and long-term palmitate incubations on glucose-dependent insulin secretion. In conclusion, our study demonstrates that human islets express CD36 in the plasma membrane as well as in the insulin secretory granules. CD36 activity appears important for uptake of FA into beta-cells as well as for mediating their modulatory effects on insulin secretion.
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Affiliation(s)
- Houtan Noushmehr
- Division Endocrinology & DiabetesMetabolism, Cedars-Sinai Medical Center, 8723 Alden Dr., SSB #290, Los Angeles, CA 90048, USA
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38
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Cleasby ME, Dzamko N, Hegarty BD, Cooney GJ, Kraegen EW, Ye JM. Metformin prevents the development of acute lipid-induced insulin resistance in the rat through altered hepatic signaling mechanisms. Diabetes 2004; 53:3258-66. [PMID: 15561958 DOI: 10.2337/diabetes.53.12.3258] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Metformin reduces the incidence of progression to type 2 diabetes in humans with obesity or impaired glucose tolerance. We used an animal model to investigate whether metformin could prevent acute lipid-induced insulin resistance and the mechanisms involved. Metformin or vehicle was administered to rats daily for 1 week. Rats were studied basally, after 3.75 h of intralipid-heparin or glycerol infusion, or after 5 h of infusion with a hyperinsulinemic-euglycemic clamp between 3 and 5 h. Metformin had no effect on plasma triacylglycerol or nonesterified fatty acid concentrations and did not alter glucose turnover or gluconeogenic enzyme mRNA after lipid infusion. However, metformin normalized hepatic glucose output and increased liver glycogen during lipid infusion and clamp. Basal liver (but not muscle or fat) AMP-activated protein kinase activity was increased by metformin (by 310%; P < 0.01), associated with increased phosphorylation of acetyl CoA carboxylase. Postclamp liver but not muscle phosphorylated/total Akt protein was increased, whereas basal c-Jun NH2-terminal kinase-1 and -2 protein expression were reduced (by 39 and 53%, respectively; P < 0.05). Metformin also increased hepatic basal IkappaBalpha levels (by 260%; P < 0.001) but had no effect on tyrosine phosphorylation or expression of insulin receptor substrate-1 (IRS-1). In summary, metformin opposes the development of acute lipid-induced insulin resistance in the liver through alterations in multiple signaling pathways.
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Affiliation(s)
- Mark E Cleasby
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, Australia
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39
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Li L, Yang GY. Effect of hepatic glucose production on acute insulin resistance induced by lipid-infusion in awake rats. World J Gastroenterol 2004; 10:3208-11. [PMID: 15457577 PMCID: PMC4611275 DOI: 10.3748/wjg.v10.i21.3208] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
AIM: To explore the influence of hepatic glucose production on acute insulin resistance induced by a lipid infusion in awake rats.
METHODS: A hyperinsulinaemic-euglycaemic clamp was established in awake chronically catheterized rats. Two groups of rats were studied either with a 4-h intraarterial infusion of lipid/heparin or saline. Insulin-mediated peripheral and hepatic glucose metabolism was assessed by hyperinsulinaemic-euglycaemic clamp combined with [3-3H]-glucose infusion.
RESULTS: During hyperinsulinaemic-euglycaemic clamp, there was a significant increase in plasma free fatty acid (FFA, from 741.9 ± 50.6 to 2346.4 ± 238.5 μmol/L, P < 0.01) in lipid-infused group. The glucose infusion rates (GIR) in the lipid infusion rats, compared to control rats, were significantly reduced (200-240 min average: Lipid infusion; 12.6 ± 1.5 vs control; 34.0 ± 1.6 mg/kg.min, P < 0.01), declining to - 35% of the corresponding control values during the last time of the clamp (240 min: Lipid infusion; 12.0 ± 1.9 vs control; 34.7 ± 1.7 mg/kg·min, P < 0.0001). At the end of clamp study, the hepatic glucose production (HGP) in control rats was significantly suppressed (88%) from 19.0 ± 4.5 (basal) to 2.3 ± 0.9 mg/kg.min (P < 0.01). The suppressive effect of insulin on HGP was significantly blunted in the lipid-infused rats (200-240 min: From 18.7 ± 3.0 to 23.2 ± 3.1 mg/kg·min (P < 0.05). The rate of glucose disappearance (GRd) was a slight decrease in the lipid-infused rats compared with controls during the clamp.
CONCLUSION: These data suggest that lipid infusion could induces suppression of hepatic glucose production, impairs the abilities of insulin to suppress lipolysis and mediate glucose utilization in peripheral tissue. Therefore, we conclude that lipid-infusion induces an acute insulin resistance in vivo.
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Affiliation(s)
- Ling Li
- Department of Endocrinology, The Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China
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40
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Héron-Milhavet L, Haluzik M, Yakar S, Gavrilova O, Pack S, Jou WC, Ibrahimi A, Kim H, Hunt D, Yau D, Asghar Z, Joseph J, Wheeler MB, Abumrad NA, LeRoith D. Muscle-specific overexpression of CD36 reverses the insulin resistance and diabetes of MKR mice. Endocrinology 2004; 145:4667-76. [PMID: 15231693 DOI: 10.1210/en.2003-1543] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Insulin resistance is one of the primary characteristics of type 2 diabetes. Mice overexpressing a dominant-negative IGF-I receptor specifically in muscle (MKR mice) demonstrate severe insulin resistance with high levels of serum and tissue lipids and eventually develop type 2 diabetes at 5-6 wk of age. To determine whether lipotoxicity plays a role in the progression of the disease, we crossed MKR mice with mice overexpressing a fatty acid translocase, CD36, in skeletal muscle. The double-transgenic MKR/CD36 mice showed normalization of the hyperglycemia and the hyperinsulinemia as well as a marked improvement in liver insulin sensitivity. The MKR/CD36 mice also exhibited normal rates of fatty acid oxidation in skeletal muscle when compared with the decreased rate of fatty acid oxidation in MKR. With the reduction in insulin resistance, beta-cell function returned to normal. These and other results suggest that the insulin resistance in the MKR mice is associated with increased muscle triglycerides levels and that whole-body insulin resistance can be, at least partially, reversed in association with a reduction in muscle triglycerides levels, although the mechanisms are yet to be determined.
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Affiliation(s)
- Lisa Héron-Milhavet
- Diabetes Branch, NIDDK, Room 8D12, Building 10, National Institutes of Health, Bethesda, Maryland 20892-1758, USA
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41
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Al-Rasheed NM, Chana RS, Baines RJ, Willars GB, Brunskill NJ. Ligand-independent activation of peroxisome proliferator-activated receptor-gamma by insulin and C-peptide in kidney proximal tubular cells: dependent on phosphatidylinositol 3-kinase activity. J Biol Chem 2004; 279:49747-54. [PMID: 15375153 DOI: 10.1074/jbc.m408268200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Peroxisome proliferator-activated receptor gamma (PPARgamma) has key roles in the regulation of adipogenesis, inflammation, and lipid and glucose metabolism. C-peptide is believed to be inert and without appreciable biological functions. Recent studies suggest that C-peptide possesses multiple functions. The present study investigated the effects of insulin and C-peptide on PPARgamma transcriptional activity in opossum kidney proximal tubular cells. Both insulin and C-peptide induced a concentration-dependent stimulation of PPARgamma transcriptional activity. Both agents substantially augmented thiazolidinedione-stimulated PPARgamma transcriptional activity. Neither insulin nor C-peptide had any effect on the expression levels of PPARgamma. GW9662, a PPARgamma antagonist, blocked PPARgamma activation by thiazolidinediones but had no effect on either insulin- or C-peptide-stimulated PPARgamma transcriptional activity. Co-transfection of opossum kidney cells with dominant negative mitogen-activated protein kinase kinase significantly depressed basal PPARgamma transcriptional activity but had no effect on that induced by either insulin or C-peptide. Both insulin- and C-peptide-stimulated PPARgamma transcriptional activity were attenuated by wortmannin and by expression of a dominant negative phosphatidylinositol (PI) 3-kinase p85 regulatory subunit. In addition PI 3-kinase-dependent phosphorylation of PPARgamma was observed after stimulation by C-peptide or insulin. C-peptide effects but not insulin on PPARgamma transcriptional activity were abolished by pertussis toxin pretreatment. Finally both C-peptide and insulin positively control the expression of the PPARgamma-regulated CD36 scavenger receptor in human THP-1 monocytes. We concluded that insulin and C-peptide can stimulate PPARgamma activity in a ligand-independent fashion and that this effect is mediated by PI 3-kinase. These results support a new and potentially important physiological role for C-peptide in regulation of PPARgamma-related cell functions.
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Affiliation(s)
- Nawal M Al-Rasheed
- Department of Cell Physiology and Pharmacology, University of Leicester, Leicester LE1 9HN, United Kingdom
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42
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Wakino S, Hayashi K, Kanda T, Tatematsu S, Homma K, Yoshioka K, Takamatsu I, Saruta T. Peroxisome Proliferator-Activated Receptor γ Ligands Inhibit Rho/Rho Kinase Pathway by Inducing Protein Tyrosine Phosphatase SHP-2. Circ Res 2004; 95:e45-55. [PMID: 15308580 DOI: 10.1161/01.res.0000142313.68389.92] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have an antihypertensive effect in vivo, the precise mechanism has not been fully elucidated. We examined their effects on Rho/Rho kinase pathway, a key regulator of vascular tone. In cultured rat aortic smooth muscle cells (RASMC), Rho kinase stimulated by angiotensin II was suppressed by the pretreatment with pioglitazone and troglitazone, and these effects were explained by the inhibition of the Rho translocation to the cell membrane. We evaluated the role of Vav, a GTP/GDP exchange factor upregulating Rho kinase activity, and Src homology region 2-containing protein tyrosine phosphatase-2 (SHP-2), a protein tyrosine phosphatase that dephosphorylated Vav and subsequently inactivated Rho kinase. Both pioglitazone and troglitazone upregulated SHP-2, particularly in the cytosolic fraction, and the SHP-2-bound Vav, and reduced the phosphorylation of Vav. Furthermore, 4-week treatment with pioglitazone lowered systolic blood pressure in spontaneously hypertensive rats (SHR) and suppressed the Rho/Rho kinase activity in aortic tissues isolated from SHR. Consistently, the expression of SHP-2 was upregulated in vascular tissues from pioglitazone-treated SHR. The phosphorylated Vav was increased in SHR, compared with that in normotensive Wistar-Kyoto rats (WKY), which was mitigated by pioglitazone. Finally, both basal and angiotensin II-stimulated levels of Rho kinase activity were greater in RASMC from SHR than those from WKY, and the enhanced Rho kinase activity was blocked by pioglitazone or troglitazone in both strains. Collectively, PPARgamma ligands inhibit the Rho/Rho kinase pathway through upregulation of cytosolic SHP-2 expression and inactivation of Vav, and may contribute to the hemodynamic, in addition to metabolic, action in hypertensive metabolic syndrome. The full text of this article is available online at http://circres.ahajournals.org.
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MESH Headings
- Angiotensin II/antagonists & inhibitors
- Animals
- Blood Pressure/drug effects
- Cell Cycle Proteins/metabolism
- Cells, Cultured
- Chromans/pharmacology
- Hypertension/enzymology
- Hypertension/physiopathology
- Intracellular Signaling Peptides and Proteins
- Ligands
- Male
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/enzymology
- PPAR gamma/agonists
- Pioglitazone
- Platelet-Derived Growth Factor/antagonists & inhibitors
- Protein Phosphatase 2
- Protein Serine-Threonine Kinases/antagonists & inhibitors
- Protein Tyrosine Phosphatase, Non-Receptor Type 11
- Protein Tyrosine Phosphatases/biosynthesis
- Protein Tyrosine Phosphatases/metabolism
- Proto-Oncogene Proteins/metabolism
- Proto-Oncogene Proteins c-vav
- Rats
- Rats, Inbred SHR
- Rats, Inbred WKY
- Rats, Sprague-Dawley
- Signal Transduction
- Thiazolidinediones/pharmacology
- Troglitazone
- rho GTP-Binding Proteins/antagonists & inhibitors
- rho-Associated Kinases
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Affiliation(s)
- Shu Wakino
- Department of Internal Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
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43
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Affiliation(s)
- S Del Prato
- Department of Endocrinology and Metabolism, Section of Diabetes, University of Pisa, Pisa, Italy
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Bastie CC, Hajri T, Drover VA, Grimaldi PA, Abumrad NA. CD36 in myocytes channels fatty acids to a lipase-accessible triglyceride pool that is related to cell lipid and insulin responsiveness. Diabetes 2004; 53:2209-16. [PMID: 15331529 DOI: 10.2337/diabetes.53.9.2209] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
High levels of intramyocellular triglycerides are linked to insulin resistance and reflect conditions in which fatty acid uptake exceeds the myocyte oxidative capacity. CD36 facilitates fatty acid uptake by myocytes, and its level is increased in diabetic muscle. We examined whether high CD36 levels would increase lipid content and susceptibility of myocytes to fatty acid-induced insulin resistance. C2C12 myoblasts with stable fivefold overexpression of CD36 (+CD36) were generated and differentiated into myotubes. CD36 expression increased palmitate uptake, oxidation, and lipid incorporation but had no effect on cell triglyceride content. Importantly, glycerol release increased fourfold, indicating enhanced triglyceride turnover and suggesting that CD36 promotes futile cycling of fatty acids into triglyceride. When +CD36 myotubes were incubated with excess palmitate, CD36 enhancement of glycerol release was blunted, triglyceride content increased above wild-type cells, and insulin resistance of glucose metabolism was observed. In contrast to palmitate, oleate-treated +CD36 cells exhibited enhanced glycerol release and no alteration in triglyceride content or insulin responsiveness. Furthermore, increased expression of hormone-sensitive lipase was measured with CD36 expression and with oleate treatment. In conclusion, high futile cycling of fatty acids is important for maintaining low triglyceride content and insulin responsiveness of myocytes. The findings provide a new perspective related to the etiology of lipid accumulation and insulin resistance in myocytes.
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Affiliation(s)
- Claire C Bastie
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
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Satoh H, Nguyen MTA, Miles PDG, Imamura T, Usui I, Olefsky JM. Adenovirus-mediated chronic "hyper-resistinemia" leads to in vivo insulin resistance in normal rats. J Clin Invest 2004; 114:224-31. [PMID: 15254589 PMCID: PMC449745 DOI: 10.1172/jci20785] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2003] [Accepted: 04/14/2004] [Indexed: 01/20/2023] Open
Abstract
We investigated the chronic in vivo effect of resistin on insulin sensitivity and glucose metabolism by overexpressing resistin protein in male Wistar rats using intravenous administration of an adenovirus encoding mouse resistin. After 7 days of elevated resistin levels at a supraphysiological concentration, the animals displayed glucose intolerance and hyperinsulinemia during glucose tolerance tests, and insulin tolerance tests demonstrated an impaired glucose-lowering effect of insulin. The glucose clamp studies were performed at submaximal (4 mU/kg/min) and maximal (25 mU/kg/min) insulin infusion rates and demonstrated the presence of insulin resistance induced by elevated resistin levels. Indeed, the insulin-stimulated glucose infusion rate was decreased by 12-31%; suppression of hepatic glucose output was attenuated by 28-55%; and insulin suppression of circulating FFA levels was inhibited by 7%. Insulin receptor substrate-1 and -2 phosphorylation and Akt activation were impaired in muscle and adipose tissue. Interestingly, activation of AMP-activated protein kinase in skeletal muscle, liver, and adipose tissue was also significantly downregulated. Together, these results indicate that chronic "hyper-resistinemia" leads to whole-body insulin resistance involving impaired insulin signaling in skeletal muscle, liver, and adipose tissue, resulting in glucose intolerance, hyperinsulinemia, and hypertriglyceridemia. Thus elevated resistin levels in normal rats fed a regular chow diet produce many of the features of human syndrome X.
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Affiliation(s)
- Hiroaki Satoh
- Department of Medicine, Division of Endocrinology and Metabolism, University of California, San Diego, La Jolla 92093-0673, USA
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46
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Ye JM, Dzamko N, Cleasby ME, Hegarty BD, Furler SM, Cooney GJ, Kraegen EW. Direct demonstration of lipid sequestration as a mechanism by which rosiglitazone prevents fatty-acid-induced insulin resistance in the rat: comparison with metformin. Diabetologia 2004; 47:1306-1313. [PMID: 15232684 DOI: 10.1007/s00125-004-1436-1] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2003] [Accepted: 03/10/2004] [Indexed: 01/24/2023]
Abstract
AIMS/HYPOTHESIS Thiazolidinediones can enhance clearance of whole-body non-esterified fatty acids and protect against the insulin resistance that develops during an acute lipid load. The present study used [(3)H]-R-bromopalmitate to compare the effects of the thiazolidinedione, rosiglitazone, and the biguanide, metformin, on insulin action and the tissue-specific fate of non-esterified fatty acids in rats during lipid infusion. METHODS Normal rats were treated with rosiglitazone or metformin for 7 days. Triglyceride/heparin (to elevate non-esterified fatty acids) or glycerol (control) were then infused for 5 h, with a hyperinsulinaemic clamp being performed between the 3rd and 5th hours. RESULTS Rosiglitazone and metformin prevented fatty-acid-induced insulin resistance (reduced clamp glucose infusion rate). Both drugs improved insulin-mediated suppression of hepatic glucose output but only rosiglitazone enhanced systemic non-esterified fatty acid clearance (plateau plasma non-esterified fatty acids reduced by 40%). Despite this decrease in plateau plasma non-esterified fatty acids, rosiglitazone increased fatty acid uptake (two-fold) into adipose tissue and reduced fatty acid uptake into liver (by 40%) and muscle (by 30%), as well as reducing liver long-chain fatty acyl CoA accumulation (by 30%). Both rosiglitazone and metformin increased liver AMP-activated protein kinase activity, a possible mediator of the protective effects on insulin action, but in contrast to rosiglitazone, metformin had no significant effect on non-esterified fatty acid kinetics or relative tissue fatty acid uptake. CONCLUSIONS/INTERPRETATION These results directly demonstrate the "lipid steal" mechanism, by which thiazolidinediones help prevent fatty-acid-induced insulin resistance. The contrasting mechanisms of action of rosiglitazone and metformin could be beneficial when both drugs are used in combination to treat insulin resistance.
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Affiliation(s)
- J-M Ye
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - N Dzamko
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - M E Cleasby
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - B D Hegarty
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - S M Furler
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - G J Cooney
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia
| | - E W Kraegen
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, Sydney, NSW 2010, Australia.
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47
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Tonelli J, Li W, Kishore P, Pajvani UB, Kwon E, Weaver C, Scherer PE, Hawkins M. Mechanisms of early insulin-sensitizing effects of thiazolidinediones in type 2 diabetes. Diabetes 2004; 53:1621-9. [PMID: 15161771 DOI: 10.2337/diabetes.53.6.1621] [Citation(s) in RCA: 191] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Whereas thiazolidinediones (TZDs) are known to rapidly improve insulin action in animals, short durations of TZD therapy have never been studied in humans. Among the many known actions of TZDs, increased circulating levels of the high molecular weight (HMW) multimer of adiponectin may be an important insulin-sensitizing mechanism. We examined the effects of only 21 days of 45 mg of pioglitazone (P+) versus placebo (P-) in nine subjects with type 2 diabetes (HbA(1c), 10.9 +/- 0.6%; BMI, 31.9 +/- 1.5 kg/m(2)). Total adiponectin levels increased by approximately twofold in P+ in association with increased adipose tissue gene expression. However, plasma free fatty acid and glucose levels were unchanged, and there were only minimal changes in other "adipokines." Glucose fluxes ([3-(3)H]glucose infusion) were measured during 6-h euglycemic (5 mmol/l) "pancreatic clamp" studies (somatostatin/glucagon/growth hormone) with stepped insulin levels. Pioglitazone induced marked decreases in endogenous glucose production (P+ = 0.9 +/- 0.1 vs. P- = 1.7 +/- 0.3 mg. kg(-1). min(-1); P < 0.05) at physiologic hyperinsulinemia ( approximately 50 microU/ml), which was highly correlated with an increased ratio of HMW adiponectin/total levels (r(2) = 0.90). Maximal insulin stimulation ( approximately 400 microU/ml) revealed pioglitazone-associated increases in glucose uptake (P+ = 10.5 +/- 0.9 vs. P- = 8.9 +/- 0.8 mg. kg(-1). min(-1); P < 0.05), which did not correlate with HMW or total adiponectin levels. Thus, only 21 days of pioglitazone therapy improved insulin action in humans with type 2 diabetes. Increased abundance of the HMW adiponectin multimer may contribute to the hepatic insulin-sensitizing effects of these agents.
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Affiliation(s)
- Julia Tonelli
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA
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48
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Koo SH, Satoh H, Herzig S, Lee CH, Hedrick S, Kulkarni R, Evans RM, Olefsky J, Montminy M. PGC-1 promotes insulin resistance in liver through PPAR-alpha-dependent induction of TRB-3. Nat Med 2004; 10:530-4. [PMID: 15107844 DOI: 10.1038/nm1044] [Citation(s) in RCA: 438] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2004] [Accepted: 04/06/2004] [Indexed: 01/11/2023]
Abstract
Insulin resistance is a major hallmark in the development of type 2 diabetes, which is characterized by an impaired ability of insulin to inhibit glucose output from the liver and to promote glucose uptake in muscle. The nuclear hormone receptor coactivator PGC-1 (peroxisome proliferator-activated (PPAR)-gamma coactivator-1) has been implicated in the onset of type 2 diabetes. Hepatic PGC-1 expression is elevated in mouse models of this disease, where it promotes constitutive activation of gluconeogenesis and fatty acid oxidation through its association with the nuclear hormone receptors HNF-4 and PPAR-alpha, respectively. Here we show that PGC-1-deficient mice, generated by adenoviral delivery of PGC-1 RNA interference (RNAi) to the liver, experience fasting hypoglycemia. Hepatic insulin sensitivity was enhanced in PGC-1-deficient mice, reflecting in part the reduced expression of the mammalian tribbles homolog TRB-3, a fasting-inducible inhibitor of the serine-threonine kinase Akt/PKB (ref. 6). We show here that, in the liver, TRB-3 is a target for PPAR-alpha. Knockdown of hepatic TRB-3 expression improved glucose tolerance, whereas hepatic overexpression of TRB-3 reversed the insulin-sensitive phenotype of PGC-1-deficient mice. These results indicate a link between nuclear hormone receptor and insulin signaling pathways, and suggest a potential role for TRB-3 inhibitors in the treatment of type 2 diabetes.
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Affiliation(s)
- Seung-Hoi Koo
- Peptide Biology Laboratories, Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, California 92037-1002, USA
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Seo JB, Noh MJ, Yoo EJ, Park SY, Park J, Lee IK, Park SD, Kim JB. Functional characterization of the human resistin promoter with adipocyte determination- and differentiation-dependent factor 1/sterol regulatory element binding protein 1c and CCAAT enhancer binding protein-alpha. Mol Endocrinol 2003; 17:1522-33. [PMID: 12730330 DOI: 10.1210/me.2003-0028] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Recent studies with murine models propose that resistin would be a possible mediator to link between obesity and insulin resistance. Although it has been reported that resistin is highly expressed and secreted by adipocytes, transcription factors that are involved in resistin gene expression have not been well characterized. To investigate the molecular mechanisms of resistin gene expression, we cloned and characterized the human resistin promoter. Sequence analysis of the resistin promoter revealed several putative binding sites for adipogenic transcription factors including adipocyte determination- and differentiation-dependent factor 1 (ADD1)/sterol regulatory element binding protein 1c (SREBP1c) and CCAAT enhancer binding protein-alpha (C/EBP alpha). EMSA and chromatin immunoprecipitation assays demonstrated that ADD1/SREBP1c binds to the human resistin promoter in vitro and in vivo. Expression of ADD1/SREBP1c transactivated the luciferase reporter gene activity, the promoter region of which contains a human resistin promoter in a sterol regulatory element (SRE)-dependent manner. Furthermore, ectopic expression of ADD1/SREBP1c by adenovirus significantly increased the expression of resistin mRNA in adipocytes. Human resistin promoter was also activated by C/EBP alpha expression, although ectopic expression of both transcription factors did not show any synergistic effects on the activation of resistin promoter. Together, these data suggest that ADD1/SREBP1c and C/EBP alpha may play discrete roles in the regulation of the resistin gene expression.
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Affiliation(s)
- Jong Bae Seo
- School of Biological Sciences, Seoul National University, NS-70, San 56-1, Seoul 151-742, Korea
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50
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Norris AW, Chen L, Fisher SJ, Szanto I, Ristow M, Jozsi AC, Hirshman MF, Rosen ED, Goodyear LJ, Gonzalez FJ, Spiegelman BM, Kahn CR. Muscle-specific PPARgamma-deficient mice develop increased adiposity and insulin resistance but respond to thiazolidinediones. J Clin Invest 2003; 112:608-18. [PMID: 12925701 PMCID: PMC171387 DOI: 10.1172/jci17305] [Citation(s) in RCA: 312] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2002] [Accepted: 06/03/2003] [Indexed: 12/12/2022] Open
Abstract
Activation of peroxisome proliferator-activated receptor gamma (PPARgamma) by thiazolidinediones (TZDs) improves insulin resistance by increasing insulin-stimulated glucose disposal in skeletal muscle. It remains debatable whether the effect of TZDs on muscle is direct or indirect via adipose tissue. We therefore generated mice with muscle-specific PPARgamma knockout (MuPPARgammaKO) using Cre/loxP recombination. Interestingly, MuPPARgammaKO mice developed excess adiposity despite reduced dietary intake. Although insulin-stimulated glucose uptake in muscle was not impaired, MuPPARgammaKO mice had whole-body insulin resistance with a 36% reduction (P < 0.05) in the glucose infusion rate required to maintain euglycemia during hyperinsulinemic clamp, primarily due to dramatic impairment in hepatic insulin action. When placed on a high-fat diet, MuPPARgammaKO mice developed hyperinsulinemia and impaired glucose homeostasis identical to controls. Simultaneous treatment with TZD ameliorated these high fat-induced defects in MuPPARgammaKO mice to a degree identical to controls. There was also altered expression of several lipid metabolism genes in the muscle of MuPPARgammaKO mice. Thus, muscle PPARgamma is not required for the antidiabetic effects of TZDs, but has a hitherto unsuspected role for maintenance of normal adiposity, whole-body insulin sensitivity, and hepatic insulin action. The tissue crosstalk mediating these effects is perhaps due to altered lipid metabolism in muscle.
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Affiliation(s)
- Andrew W Norris
- Research Division, Joslin Diabetes Center, One Joslin Place, Boston, Massachusetts 02215, USA
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