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Abstract
Comprehensive studies support the notion that the peroxisome proliferator-activated receptors, (PPARs), PPARα, PPARβ/δ, and PPARγ, regulate cell growth, morphogenesis, differentiation, and homeostasis. Agonists of each PPAR subtype exert their effects similarly or distinctly in different tissues such as liver, muscle, fat, and vessels. It is noteworthy that PPARα or PPARγ agonists have pharmacological effects by modulating the activity of AMPK, which is a key cellular energy sensor. However, the role of AMPK in the metabolic effects of PPAR agonists has not been thoroughly focused. Moreover, AMPK activation by PPAR agonists seems to be independent of the receptor activation. This intriguing action of PPAR agonists may account in part for the mechanistic basis of the therapeutics in the treatment of metabolic disease. In this paper, the effects of PPAR agonists on metabolic functions were summarized with particular reference to their AMPK activity regulation.
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102
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Fabbrini E, Tamboli RA, Magkos F, Marks PA, Eckhauser AW, Richards WO, Klein S, Abumrad NN. Surgical removal of omental fat does not improve insulin sensitivity and cardiovascular risk factors in obese adults. Gastroenterology 2010; 139:448-55. [PMID: 20457158 PMCID: PMC2910849 DOI: 10.1053/j.gastro.2010.04.056] [Citation(s) in RCA: 148] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 04/23/2010] [Accepted: 04/30/2010] [Indexed: 01/12/2023]
Abstract
BACKGROUND & AIMS Visceral adipose tissue (VAT) is an important risk factor for the metabolic complications associated with obesity. Therefore, a reduction in VAT is considered an important target of obesity therapy. We evaluated whether reducing VAT mass by surgical removal of the omentum improves insulin sensitivity and metabolic function in obese patients. METHODS We conducted a 12-month randomized controlled trial to determine whether reducing VAT by omentectomy in 22 obese subjects increased their improvement following Roux-en-Y gastric bypass (RYGB) surgery in hepatic and skeletal muscle sensitivity to insulin study 1. Improvement was assessed by using the hyperinsulinemic-euglycemic clamp technique. We also performed a 3-month, longitudinal, single-arm study to determine whether laparoscopic omentectomy alone, in 7 obese subjects with type 2 diabetes mellitus (T2DM), improved insulin sensitivity study 2. Improvement was assessed by using the Frequently Sampled Intravenous Glucose Tolerance Test. RESULTS The greater omentum, which weighed 0.82 kg (95% confidence interval: 0.67-0.97), was removed from subjects who had omentectomy in both studies. In study 1, there was an approximate 2-fold increase in muscle insulin sensitivity (relative increase in glucose disposal during insulin infusion) and a 4-fold increase in hepatic insulin sensitivity 12 months after RYGB alone and RYGB plus omentectomy, compared with baseline values (P<.001). There were no significant differences between groups (P>.87) or group x time interactions (P>.36). In study 2, surgery had no effect on insulin sensitivity (P=.844) or use of diabetes medications. CONCLUSIONS These results demonstrate that decreasing VAT through omentectomy, alone or in combination with RYGB surgery, does not improve metabolic function in obese patients.
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Affiliation(s)
- Elisa Fabbrini
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, MO, USA, Center for Clinical and Basic Research, Department of Medical Sciences, IRCCS San Raffaele, Rome, Italy
| | - Robyn A. Tamboli
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Faidon Magkos
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, MO, USA, Department of Nutrition and Dietetics, Harokopio University, Athens, Greece
| | - Pamela A. Marks
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Aaron W. Eckhauser
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - William O. Richards
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Samuel Klein
- Center for Human Nutrition and Atkins Center of Excellence in Obesity Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Naji N. Abumrad
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA
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103
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DeFronzo RA. Insulin resistance, lipotoxicity, type 2 diabetes and atherosclerosis: the missing links. The Claude Bernard Lecture 2009. Diabetologia 2010; 53:1270-87. [PMID: 20361178 PMCID: PMC2877338 DOI: 10.1007/s00125-010-1684-1] [Citation(s) in RCA: 563] [Impact Index Per Article: 40.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 12/22/2009] [Indexed: 12/15/2022]
Abstract
Insulin resistance is a hallmark of type 2 diabetes mellitus and is associated with a metabolic and cardiovascular cluster of disorders (dyslipidaemia, hypertension, obesity [especially visceral], glucose intolerance, endothelial dysfunction), each of which is an independent risk factor for cardiovascular disease (CVD). Multiple prospective studies have documented an association between insulin resistance and accelerated CVD in patients with type 2 diabetes, as well as in non-diabetic individuals. The molecular causes of insulin resistance, i.e. impaired insulin signalling through the phosphoinositol-3 kinase pathway with intact signalling through the mitogen-activated protein kinase pathway, are responsible for the impairment in insulin-stimulated glucose metabolism and contribute to the accelerated rate of CVD in type 2 diabetes patients. The current epidemic of diabetes is being driven by the obesity epidemic, which represents a state of tissue fat overload. Accumulation of toxic lipid metabolites (fatty acyl CoA, diacylglycerol, ceramide) in muscle, liver, adipocytes, beta cells and arterial tissues contributes to insulin resistance, beta cell dysfunction and accelerated atherosclerosis, respectively, in type 2 diabetes. Treatment with thiazolidinediones mobilises fat out of tissues, leading to enhanced insulin sensitivity, improved beta cell function and decreased atherogenesis. Insulin resistance and lipotoxicity represent the missing links (beyond the classical cardiovascular risk factors) that help explain the accelerated rate of CVD in type 2 diabetic patients.
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Affiliation(s)
- R A DeFronzo
- Diabetes Division, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive-MSC 7886, San Antonio, TX, 78229, USA.
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104
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Shaul ME, Bennett G, Strissel KJ, Greenberg AS, Obin MS. Dynamic, M2-like remodeling phenotypes of CD11c+ adipose tissue macrophages during high-fat diet--induced obesity in mice. Diabetes 2010; 59:1171-81. [PMID: 20185806 PMCID: PMC2857897 DOI: 10.2337/db09-1402] [Citation(s) in RCA: 283] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
OBJECTIVE To identify, localize, and determine M1/M2 polarization of epidydimal adipose tissue (eAT) macrophages (Phis) during high-fat diet (HFD)-induced obesity. RESEARCH DESIGN AND METHODS Male C57BL/6 mice were fed an HFD (60% fat kcal) or low-fat diet (LFD) (10% fat kcal) for 8 or 12 weeks. eATMPhis (F4/80(+) cells) were characterized by in vivo fluorescent labeling, immunohistochemistry, fluorescence-activated cell sorting, and quantitative PCR. RESULTS Recruited interstitial macrophage galactose-type C-type lectin (MGL)1(+)/CD11c(-) and crown-like structure-associated MGL1(-)/CD11c(+) and MGL1(med)/CD11c(+) eATMPhis were identified after 8 weeks of HFD. MGL1(med)/CD11c(+) cells comprised approximately 65% of CD11c(+) eATMPhis. CD11c(+) eATMPhis expressed a mixed M1/M2 profile, with some M1 transcripts upregulated (IL-12p40 and IL-1beta), others downregulated (iNOS, caspase-1, MCP-1, and CD86), and multiple M2 and matrix remodeling transcripts upregulated (arginase-1, IL-1Ra, MMP-12, ADAM8, VEGF, and Clec-7a). At HFD week 12, each eATMPhi subtype displayed an enhanced M2 phenotype as compared with HFD week 8. CD11c(+) subtypes downregulated IL-1beta and genes mediating antigen presentation (I-a, CD80) and upregulated the M2 hallmark Ym-1 and genes promoting oxidative metabolism (PGC-1alpha) and adipogenesis (MMP-2). MGL1(med)/CD11c(+) eATMPhis upregulated additional M2 genes (IL-13, SPHK1, CD163, LYVE-1, and PPAR-alpha). MGL1(med)/CD11c(+) ATMPhis expressing elevated PGC-1alpha, PPAR-alpha, and Ym-1 transcripts were selectively enriched in eAT of obese mice fed pioglitazone for 6 days, confirming the M2 features of the MGL1(med)/CD11c(+) eATMPhi transcriptional profile and implicating PPAR activation in its elicitation. CONCLUSIONS These results 1) redefine the phenotypic potential of CD11c(+) eATMPhis and 2) suggest previously unappreciated phenotypic and functional commonality between murine and human ATMPhis in the development of obesity and its complications.
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Affiliation(s)
- Merav E. Shaul
- From the Obesity and Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Grace Bennett
- From the Obesity and Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Katherine J. Strissel
- From the Obesity and Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
| | - Andrew S. Greenberg
- From the Obesity and Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
- Corresponding authors: Martin S. Obin, , or Andrew S. Greenberg,
| | - Martin S. Obin
- From the Obesity and Metabolism Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts
- Corresponding authors: Martin S. Obin, , or Andrew S. Greenberg,
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105
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Cross-Talk between PPARgamma and Insulin Signaling and Modulation of Insulin Sensitivity. PPAR Res 2010; 2009:818945. [PMID: 20182551 PMCID: PMC2826877 DOI: 10.1155/2009/818945] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2009] [Revised: 10/30/2009] [Accepted: 12/02/2009] [Indexed: 12/25/2022] Open
Abstract
PPARγ activation in type 2 diabetic patients results in a marked improvement in insulin and glucose parameters, resulting from an improvement of whole-body insulin sensitivity. Adipose tissue is the major mediator of PPARγ action on insulin sensitivity. PPARγ activation in mature adipocytes induces the expression of a number of genes involved in the insulin signaling cascade, thereby improving insulin sensitivity. PPARγ is the master regulator of adipogenesis, thereby stimulating the production of small insulin-sensitive adipocytes. In addition to its importance in adipogenesis, PPARγ plays an important role in regulating lipid, metabolism in mature adipocytes by increasing fatty acid trapping. Finally, adipose tissue produces several cytokines that regulate energy homeostasis, lipid and glucose metabolism. Disturbances in the production of these factors may contribute to metabolic abnormalities, and PPARγ activation is also associated with beneficial effects on expression and secretion of a whole range of cytokines.
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106
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Current world literature. Curr Opin Lipidol 2009; 20:512-9. [PMID: 19935200 DOI: 10.1097/mol.0b013e328334096a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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107
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Stein LL, Dong MH, Loomba R. Insulin sensitizers in nonalcoholic fatty liver disease and steatohepatitis: Current status. Adv Ther 2009; 26:893-907. [PMID: 19921118 PMCID: PMC6659744 DOI: 10.1007/s12325-009-0072-z] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Indexed: 12/21/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD), first described in 1980, is now recognized as one of the most common causes of elevated liver enzymes and chronic liver disease in Western countries. The incidence of NAFLD in both adults and children is rising, in conjunction with the burgeoning epidemics of obesity and type 2 diabetes mellitus. NAFLD often coexists with other sequelae of the metabolic syndrome: central obesity, type 2 diabetes, hypertension, and hyperlipidemia. NAFLD encompasses a spectrum of pathologic liver diseases ranging from simple hepatic steatosis to a predominant lobular necro-inflammation, with or without centrilobular fibrosis (called nonalcoholic steatohepatitis or NASH). NASH can progress to cirrhosis, decompensated liver disease, and hepatocellular carcinoma. Though the natural history of NASH is still not clearly defined, it has been observed to progress to cirrhosis in 15%-220% of those affected. Insulin resistance is nearly universal in NASH and is thought to play an important role in its pathogenesis leading to dysregulated lipid metabolism. The prevalence of insulin resistance is reported in the general population to be approaching 45%, suggesting that NAFLD and NASH will contin nue to be an important public health concern. To date, NASH has proven to be a difficult disease to treat. Front-line therapy with lifestyle modifications resulting in weight loss through decreased caloric intake and moderate exercise is generally believed to be beneficial in patients with NASH, but is often difficult to maintain long term. Given that insulin resistance plays a dominant role in the pathogenesis, many studies have examined the use of insulin sensitizers: the biguanides (metformin), thiazolidinediones (pioglitazone, troglitazone, and rosiglitazone), glucagon-like peptide-1-receptor agonists, or incretins (exenatide)in NASH. This review will provide an overview of insulin resistance in NAFLD and provide a detailed summary on the clinical data regarding the use of insulin sensitizers in NASH.
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Affiliation(s)
- Lance L Stein
- Center for Liver Disease and Transplantation, New York Presbyterian Hospital, Columbia University College of Physicians and Surgeons, New York, USA
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108
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Gruzman A, Babai G, Sasson S. Adenosine Monophosphate-Activated Protein Kinase (AMPK) as a New Target for Antidiabetic Drugs: A Review on Metabolic, Pharmacological and Chemical Considerations. Rev Diabet Stud 2009; 6:13-36. [PMID: 19557293 DOI: 10.1900/rds.2009.6.13] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In view of the epidemic nature of type 2 diabetes and the substantial rate of failure of current oral antidiabetic drugs the quest for new therapeutics is intensive. The adenosine monophosphate-activated protein kinase (AMPK) is an important regulatory protein for cellular energy balance and is considered a master switch of glucose and lipid metabolism in various organs, especially in skeletal muscle and liver. In skeletal muscles, AMPK stimulates glucose transport and fatty acid oxidation. In the liver, it augments fatty acid oxidation and decreases glucose output, cholesterol and triglyceride synthesis. These metabolic effects induced by AMPK are associated with lowering blood glucose levels in hyperglycemic individuals. Two classes of oral antihyperglycemic drugs (biguanidines and thiazolidinediones) have been shown to exert some of their therapeutic effects by directly or indirectly activating AMPK. However, side effects and an acquired resistance to these drugs emphasize the need for the development of novel and efficacious AMPK activators. We have recently discovered a new class of hydrophobic D-xylose derivatives that activates AMPK in skeletal muscles in a non insulin-dependent manner. One of these derivatives (2,4;3,5-dibenzylidene-D-xylose-diethyl-dithioacetal) stimulates the rate of hexose transport in skeletal muscle cells by increasing the abundance of glucose transporter-4 (GLUT-4) in the plasma membrane through activation of AMPK. This compound reduces blood glucose levels in diabetic mice and therefore offers a novel strategy of therapeutic intervention strategy in type 2 diabetes. The present review describes various classes of chemically-related compounds that activate AMPK by direct or indirect interactions and discusses their potential for candidate antihyperglycemic drug development.
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Affiliation(s)
- Arie Gruzman
- Department of Pharmacology, School of Pharmacy, Faculty of Medicine, The Hebrew University, Jerusalem 91120, Israel
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109
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Defronzo RA. Banting Lecture. From the triumvirate to the ominous octet: a new paradigm for the treatment of type 2 diabetes mellitus. Diabetes 2009; 58:773-95. [PMID: 19336687 PMCID: PMC2661582 DOI: 10.2337/db09-9028] [Citation(s) in RCA: 1834] [Impact Index Per Article: 122.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Ralph A Defronzo
- Diabetes Division, University of Texas Health Science Center, San Antonio, Texas, USA.
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