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Yu C, Xu N, Tao X, Liu G. Chronic lead poisoning-induced budgerigar liver damage, gut microbiota dysbiosis, and metabolic disorder. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2024; 278:116388. [PMID: 38701653 DOI: 10.1016/j.ecoenv.2024.116388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 04/07/2024] [Accepted: 04/21/2024] [Indexed: 05/05/2024]
Abstract
Birds are sensitive to heavy metal pollution, and lead (Pb) contamination can negatively affect their liver and gut. Therefore, we used budgerigars to examine liver and gut toxicosis caused by Pb exposure in bird, and the possible toxic mechanisms. The findings showed Pb exposure increased liver weight and decreased body weight. Moreover, histopathological and immunofluorescence assay results demonstrated obvious liver damage and cell apoptosis increased in Pb- treated budgerigars. Quantitative polymerase chain reaction (qPCR) results also showed Pb caused an increase in apoptosis by inhibiting the PPAR-γ/PI3K/Akt pathway. The gut microbe analyses indicated Firmicutes, Proteobacteria, and Bacteroidetes were dominant microbial phyla, and Network analysis results shown Arthrobacter, Bradyrhizobium and Alloprevotella as the hubs of Modules I, II, and III, respectively. Phenylpropanoids and polyketides, Organoheterocyclic compounds, Organic oxygen compounds, and Organic nitrogen compounds were dominant metabolite superclasses. Tauroursodeoxycholic acid, taurochenodeoxycholic acid (sodium salt), and 2-[2-(5-bromo-2-pyridyl)diaz-1-enyl]-5-(diethylamino)phenol were significantly enriched in the Pb-treated group. It showed that 41 Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologues and 183 pathways differed between the Pb-treated and control budgerigars using microbial and metabolomic data. Moreover, orthogonal partial least-squares discrimination analysis (OPLS-DA) based on microbial and metabolite indicated distinct clusters in the Pb-treated and control groups. Additionally, the correlation analysis results indicated that a positive correlation for the Pb-treated and control groups between gut microbiota and metabolomic data, respectively. Furthermore, the microenvironment of the gut and liver were found to affect each other, and this study demonstrated heavy metal especially Pb may pose serious health risks to birds through the "gut-liver axis" too.
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Affiliation(s)
- Chongyang Yu
- College of Life Sciences, Anhui Medical University, China
| | - Na Xu
- College of Life Sciences, Anhui Medical University, China
| | - Xiaoyu Tao
- College of Life Sciences, Anhui Medical University, China
| | - Gang Liu
- College of Life Sciences, Anhui Medical University, China.
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2
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Riaz F, Wei P, Pan F. PPARs at the crossroads of T cell differentiation and type 1 diabetes. Front Immunol 2023; 14:1292238. [PMID: 37928539 PMCID: PMC10623333 DOI: 10.3389/fimmu.2023.1292238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 10/11/2023] [Indexed: 11/07/2023] Open
Abstract
T-cell-mediated autoimmune type 1 diabetes (T1D) is characterized by the immune-mediated destruction of pancreatic beta cells (β-cells). The increasing prevalence of T1D poses significant challenges to the healthcare system, particularly in countries with struggling economies. This review paper highlights the multifaceted roles of Peroxisome Proliferator-Activated Receptors (PPARs) in the context of T1D, shedding light on their potential as regulators of immune responses and β-cell biology. Recent research has elucidated the intricate interplay between CD4+ T cell subsets, such as Tregs and Th17, in developing autoimmune diseases like T1D. Th17 cells drive inflammation, while Tregs exert immunosuppressive functions, highlighting the delicate balance crucial for immune homeostasis. Immunotherapy has shown promise in reinstating self-tolerance and restricting the destruction of autoimmune responses, but further investigations are required to refine these therapeutic strategies. Intriguingly, PPARs, initially recognized for their role in lipid metabolism, have emerged as potent modulators of inflammation in autoimmune diseases, particularly in T1D. Although evidence suggests that PPARs affect the β-cell function, their influence on T-cell responses and their potential impact on T1D remains largely unexplored. It was noted that PPARα is involved in restricting the transcription of IL17A and enhancing the expression of Foxp3 by minimizing its proteasomal degradation. Thus, antagonizing PPARs may exert beneficial effects in regulating the differentiation of CD4+ T cells and preventing T1D. Therefore, this review advocates for comprehensive investigations to delineate the precise roles of PPARs in T1D pathogenesis, offering innovative therapeutic avenues that target both the immune system and pancreatic function. This review paper seeks to bridge the knowledge gap between PPARs, immune responses, and T1D, providing insights that may revolutionize the treatment landscape for this autoimmune disorder. Moreover, further studies involving PPAR agonists in non-obese diabetic (NOD) mice hold promise for developing novel T1D therapies.
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Affiliation(s)
- Farooq Riaz
- Shenzhen Institute of Advanced Technology (SIAT), Chinese Academy of Sciences (CAS), Shenzhen, China
| | - Ping Wei
- Department of Otolaryngology, Ministry of Education Key Laboratory of Child Development and Disorders, National Clinical Research Center for Child Health and Disorders (Chongqing), China International Science and Technology Cooperation base of Child Development and Critical Disorders, Children’s Hospital of Chongqing Medical University, Chongqing, China
| | - Fan Pan
- Shenzhen Institute of Advanced Technology (SIAT), Chinese Academy of Sciences (CAS), Shenzhen, China
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Takahashi I. Importance of Heparan Sulfate Proteoglycans in Pancreatic Islets and β-Cells. Int J Mol Sci 2022; 23:12082. [PMID: 36292936 PMCID: PMC9603760 DOI: 10.3390/ijms232012082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 09/20/2022] [Indexed: 12/15/2022] Open
Abstract
β-cells in the islets of Langerhans of the pancreas secrete insulin in response to the glucose concentration in the blood. When these pancreatic β-cells are damaged, diabetes develops through glucose intolerance caused by insufficient insulin secretion. High molecular weight polysaccharides, such as heparin and heparan sulfate (HS) proteoglycans, and HS-degrading enzymes, such as heparinase, participate in the protection, maintenance, and enhancement of the functions of pancreatic islets and β-cells, and the demand for studies on glycobiology within the field of diabetes research has increased. This review introduces the roles of complex glycoconjugates containing high molecular weight polysaccharides and their degrading enzymes in pancreatic islets and β-cells, including those obtained in studies conducted by us earlier. In addition, from the perspective of glycobiology, this study proposes the possibility of application to diabetes medicine.
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Affiliation(s)
- Iwao Takahashi
- Division of Molecular and Cellular Pharmacology, Department of Pathophysiology and Pharmacology, School of Pharmacy, Iwate Medical University, 1-1-1 Idaidori, Yahaba-cho, Shiwa-gun, Morioka 028-3694, Iwate, Japan
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Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm. Nutrients 2020; 12:nu12113476. [PMID: 33198317 PMCID: PMC7696073 DOI: 10.3390/nu12113476] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2020] [Revised: 11/04/2020] [Accepted: 11/09/2020] [Indexed: 02/06/2023] Open
Abstract
The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.
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Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity. Cells 2020; 9:cells9071708. [PMID: 32708786 PMCID: PMC7407644 DOI: 10.3390/cells9071708] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 07/14/2020] [Accepted: 07/14/2020] [Indexed: 02/06/2023] Open
Abstract
Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.
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Exopolysaccharides of Bacillus amyloliquefaciens modulate glycemic level in mice and promote glucose uptake of cells through the activation of Akt. Int J Biol Macromol 2020; 146:202-211. [DOI: 10.1016/j.ijbiomac.2019.12.217] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 12/14/2019] [Accepted: 12/24/2019] [Indexed: 12/12/2022]
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Abstract
Peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors with a key role in glucose and lipid metabolism. PPARs are expressed in many cell types including pancreatic beta cells and immune cells, where they regulate insulin secretion and T cell differentiation, respectively. Moreover, various PPAR agonists prevent diabetes in the non-obese diabetic (NOD) mouse model of type 1 diabetes. PPARs are thus of interest in type 1 diabetes (T1D) as they represent a novel approach targeting both the pancreas and the immune system. In this review, we examine the role of PPARs in immune responses and beta cell biology and their potential as targets for treatment of T1D.
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Zhang K, Yuan Q, Xie J, Yuan L, Wang Y. PPAR-γ activation increases insulin secretion independent of CASK in INS-1 cells. Acta Biochim Biophys Sin (Shanghai) 2019; 51:715-722. [PMID: 31168600 DOI: 10.1093/abbs/gmz052] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Indexed: 01/03/2023] Open
Abstract
Peroxisome proliferator-activated receptor-γ (PPAR-γ) is expressed in pancreatic β cells and is involved in insulin secretion. However, the precise mechanisms remain unclear. Calcium/calmodulin-dependent serine protein kinase (CASK), which plays a vital role in the anchoring of insulin granules on pancreatic β cell membrane, is probably a downstream of the transcription factor PPAR-γ. The aim of the present study was to investigate the correlation among PPAR-γ, CASK and insulin secretion. We found that rosiglitazone (RSG) had a positive effect on the expression of CASK and PPAR-γ in INS-1 cells as shown by real-time polymerase chain reaction (PCR) and western blot analysis, but did not change the cellular location of CASK as shown by immunofluorescence assay. Knockdown of PPAR-γ significantly attenuated the mRNA and protein expression levels of CASK. ChIP-qPCR and luciferase assays showed that PPAR-γ bound with the Cask promoter, and promoter activity of Cask was elevated by RSG. RSG significantly enhanced the insulin secretion with potassium stimulation, but did not alter the insulin content as shown by potassium-stimulated insulin secretion assay. In addition, with RSG pretreatment, knockdown of Cask did not significantly affect the PPAR-γ activation-mediated insulin secretion. Moreover, electron microscopy demonstrated that with RSG pretreatment, silence of Cask did not change the number of vesicles anchored on the cell membranes compared with those in siCask-treated cells. Overall, the present study identifies that CASK is one of the PPAR-γ downstream targets and PPAR-γ exerts a positive effect on the expression of CASK in INS-1 cells. PPAR-γ activation increases insulin secretion independent of the upregulation of CASK.
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Affiliation(s)
- Kai Zhang
- Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, Medical School, Southeast University, Nanjing, China
| | - Qingzhao Yuan
- Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, Medical School, Southeast University, Nanjing, China
| | - Jinyang Xie
- Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, Medical School, Southeast University, Nanjing, China
| | - Li Yuan
- Department of Biochemistry and Molecular Biology, Nanjing Medical University, Nanjing, China
| | - Yao Wang
- Department of Endocrinology, Zhongda Hospital, Institute of Diabetes, Medical School, Southeast University, Nanjing, China
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Jin X, Jia T, Liu R, Xu S. The antagonistic effect of selenium on cadmium-induced apoptosis via PPAR-γ/PI3K/Akt pathway in chicken pancreas. JOURNAL OF HAZARDOUS MATERIALS 2018; 357:355-362. [PMID: 29909169 DOI: 10.1016/j.jhazmat.2018.06.003] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Revised: 05/31/2018] [Accepted: 06/01/2018] [Indexed: 06/08/2023]
Abstract
The animal experiment was preformed to investigate the roles of PPAR-γ/PI3K/Akt pathway in apoptosis triggered by cadmium (Cd) and in the antagonistic effects of selenium (Se) on Cd in the pancreas of chicken. The current study showed that Cd treatment obviously increased the accumulation of Cd and directly led to lower activities of amylase, trypsin and lipase in chicken pancreas. The expression of PPAR-γ, PI3K, and Akt was declined, whereas the level of Bax, Cyt C and caspase-3 were increased in Cd group. In the result of TUNEL assay and the histological examination, typical apoptosis characteristics in the pancreas of Cd group were confirmed. Cd group also showed high levels of inducible nitric oxide synthase (iNOS) activity and nitric oxide (NO) content in pancreas. However, those Cd-induced changes were obviously alleviated in Cd + Se group. Our study revealed that Cd could impact the pancreas function and induce the activation of Bax and the overproduction of NO via PPAR-γ/PI3K/Akt pathway to promote apoptosis in chicken pancreas. However, Se could reduce Cd accumulation and antagonize Cd-triggered apoptosis in chicken pancreas.
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Affiliation(s)
- Xi Jin
- College of Veterinary Medicine, Northeast Agricultural University, Harbin, PR China.
| | - Tiantian Jia
- College of Veterinary Medicine, Northeast Agricultural University, Harbin, PR China.
| | - Ruohan Liu
- College of Veterinary Medicine, Northeast Agricultural University, Harbin, PR China.
| | - Shiwen Xu
- College of Veterinary Medicine, Northeast Agricultural University, Harbin, PR China; Key Laboratory of the Provincial Education Department of Heilongjiang for Common Animal Disease Prevention and Treatment, College of Veterinary Medicine, Northeast Agricultural University, Harbin, 150030, PR China.
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Lan YL, Huang SP, Heng XP, Chen L, Li PH, Wu J, Yang LQ, Pan XD, Lin T, Cheng XL, Lin Q, Chen SX. Dan-gua Fang (丹瓜方) improves glycolipid metabolic disorders by promoting hepatic adenosine 5′-monophosphate activated protein kinase expression in diabetic Goto-Kakizaki rats. Chin J Integr Med 2014; 21:188-95. [DOI: 10.1007/s11655-014-1826-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Indexed: 01/30/2023]
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Deng R, Nie A, Jian F, Liu Y, Tang H, Zhang J, Zhang Y, Shao L, Li F, Zhou L, Wang X, Ning G. Acute exposure of beta-cells to troglitazone decreases insulin hypersecretion via activating AMPK. Biochim Biophys Acta Gen Subj 2014; 1840:577-85. [DOI: 10.1016/j.bbagen.2013.10.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2013] [Revised: 10/05/2013] [Accepted: 10/13/2013] [Indexed: 11/16/2022]
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12
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Fu A, Eberhard CE, Screaton RA. Role of AMPK in pancreatic beta cell function. Mol Cell Endocrinol 2013; 366:127-34. [PMID: 22766107 DOI: 10.1016/j.mce.2012.06.020] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 05/08/2012] [Accepted: 06/21/2012] [Indexed: 10/28/2022]
Abstract
Pharmacological activation of AMP activated kinase (AMPK) by metformin has proven to be a beneficial therapeutic approach for the treatment of type II diabetes. Despite improved glucose regulation achieved by administration of small molecule activators of AMPK, the potential negative impact of enhanced AMPK activity on insulin secretion by the pancreatic beta cell is an important consideration. In this review, we discuss our current understanding of the role of AMPK in central functions of the pancreatic beta cell, including glucose-stimulated insulin secretion (GSIS), proliferation, and survival. In addition we discuss the controversy surrounding the role of AMPK in insulin secretion, underscoring the merits and caveats of methods used to date.
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Affiliation(s)
- Accalia Fu
- Children's Hospital of Eastern Ontario Research Institute, Ottawa, Canada
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13
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Kim HS, Hwang YC, Koo SH, Park KS, Lee MS, Kim KW, Lee MK. PPAR-γ activation increases insulin secretion through the up-regulation of the free fatty acid receptor GPR40 in pancreatic β-cells. PLoS One 2013; 8:e50128. [PMID: 23372643 PMCID: PMC3553172 DOI: 10.1371/journal.pone.0050128] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Accepted: 10/16/2012] [Indexed: 11/18/2022] Open
Abstract
Background It has been reported that peroxisome proliferator-activated receptor (PPAR)-γ and their synthetic ligands have direct effects on pancreatic β-cells. We investigated whether PPAR-γ activation stimulates insulin secretion through the up-regulation of GPR40 in pancreatic β-cells. Methods Rat insulinoma INS-1 cells and primary rat islets were treated with rosiglitazone (RGZ) and/or adenoviral PPAR-γ overexpression. OLETF rats were treated with RGZ. Results PPAR-γ activation with RGZ and/or adenoviral PPAR-γ overexpression increased free fatty acid (FFA) receptor GPR40 expression, and increased insulin secretion and intracellular calcium mobilization, and was blocked by the PLC inhibitors, GPR40 RNA interference, and GLUT2 RNA interference. As a downstream signaling pathway of intracellular calcium mobilization, the phosphorylated levels of CaMKII and CREB, and the downstream IRS-2 and phospho-Akt were significantly increased. Despite of insulin receptor RNA interference, the levels of IRS-2 and phospho-Akt was still maintained with PPAR-γ activation. In addition, the β-cell specific gene expression, including Pdx-1 and FoxA2, increased in a GPR40- and GLUT2-dependent manner. The levels of GPR40, phosphorylated CaMKII and CREB, and β-cell specific genes induced by RGZ were blocked by GW9662, a PPAR-γ antagonist. Finally, PPAR-γ activation up-regulated β-cell gene expressions through FoxO1 nuclear exclusion, independent of the insulin signaling pathway. Based on immunohistochemical staining, the GLUT2, IRS-2, Pdx-1, and GPR40 were more strongly expressed in islets from RGZ-treated OLETF rats compared to control islets. Conclusion These observations suggest that PPAR-γ activation with RGZ and/or adenoviral overexpression increased intracellular calcium mobilization, insulin secretion, and β-cell gene expression through GPR40 and GLUT2 gene up-regulation.
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Affiliation(s)
- Hyo-Sup Kim
- Division of Endocrinology and Metabolism, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - You-Cheol Hwang
- Division of Endocrinology and Metabolism, Department of Medicine, Kyung Hee University Hospital at Gangdong, Kyung Hee University School of Medicine, Seoul, Korea
| | - Seung-Hoi Koo
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Kyong Soo Park
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
| | - Myung-Shik Lee
- Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Kwang-Won Kim
- Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Moon-Kyu Lee
- Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
- * E-mail:
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Düfer M, Noack K, Edalat A, Krippeit-Drews P, Drews G. Glitazones exert multiple effects on β-cell stimulus-secretion coupling. Mol Pharmacol 2012; 83:51-60. [PMID: 23024191 DOI: 10.1124/mol.112.081638] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Earlier studies suggest that glitazones exert beneficial effects in patients with type 2 diabetes by directly affecting insulin secretion of β-cells, besides improving the effectiveness of insulin in peripheral tissues. The effects of glitazones on stimulus-secretion coupling (SSC) are poorly understood. We tested the influence of troglitazone and pioglitazone on different parameters of SSC, including insulin secretion (radioimmunoassay), cell membrane potential, various ion currents (patch-clamp), mitochondrial membrane potential (ΔΨ), and cytosolic Ca(2+) concentration (fluorescence). Troglitazone exerted stimulatory, inhibitory, or no effects on insulin secretion depending on the drug and glucose concentration. It depolarized the ΔΨ, thus lowering ATP production, which resulted in opening of ATP-dependent K(+) channels (K(ATP) channels) and reduced insulin secretion. However, it also exerted direct inhibitory effects on K(ATP) channels that can explain enhanced insulin secretion. Troglitazone also inhibited the currents through voltage-dependent Ca(2+) and K(+) channels. Pioglitazone was less effective than troglitazone on all parameters tested. The effects of both glitazones were markedly reduced in the presence of bovine serum albumin. Glitazones exert multiple actions on β-cell SSC that have to be considered as undesired side effects because the influence of these compounds on β-cells is not controllable. The final effect on insulin secretion depends on many parameters, including the actual glucose and drug concentration, protein binding of the drug, and the drug by itself. Troglitazone and pioglitazone differ in their influence on SSC. It can be assumed that the effects of pioglitazone on β-cells are negligible under in vivo conditions.
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Affiliation(s)
- Martina Düfer
- Institute of Pharmacy, Department of Pharmacology, University of Tübingen, Auf der Morgenstelle 8, D-72076 Tübingen, Germany
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Activation of SIRT1 protects pancreatic β-cells against palmitate-induced dysfunction. Biochim Biophys Acta Mol Basis Dis 2012; 1822:1815-25. [PMID: 22968147 DOI: 10.1016/j.bbadis.2012.08.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 08/08/2012] [Accepted: 08/13/2012] [Indexed: 01/23/2023]
Abstract
Sirtuin 1 (SIRT1), a nicotinamide adenosine dinucleotide-dependent histone deacetylase, is an important regulator of energy homeostasis in response to nutrient availability. In pancreatic β-cells, SIRT1 has been shown to up-regulate insulin secretion in response to glucose stimulation. However, the potential roles of SIRT1 in islet β-cells against lipotoxicity remain poorly understood. Here, we demonstrated that SIRT1 mRNA and protein expressions were markedly reduced in the islets isolated from rats infused with 20% Intralipid for 24h. Long-term exposure to 0.4mmol/L palmitate also decreased SIRT1 expression in cultured INS-1 cells and isolated rat islets, which was prevented by 10μmol/L resveratrol, a SIRT1 agonist. In addition, resveratrol improved glucose-stimulated insulin secretion decreased by palmitate, which was abrogated by EX527, a specific SIRT1 inhibitor. Furthermore, inhibition of SIRT1 activity by EX527 or a knockdown of SIRT1 suppressed insulin promoter activity, along with decreased insulin, v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA), and NK6 homeodomain 1 (NKX6.1) mRNA expressions. Activation of SIRT1 by resveratrol or overexpression of SIRT1 antagonized palmitate-inhibited insulin transcriptional activity. SIRT1 overexpression exerted an additive effect on pancreatic and duodenal homeobox 1 (PDX1)-stimulated insulin promoter activity and abolished forkhead box O1 protein (FOXO1)-decreased insulin transcriptional activity. Resveratrol reversed FOXO1 nuclear translocation induced by palmitate. Our findings indicate that SIRT1 protects against palmitate-induced β-cell dysfunction.
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16
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Doliba NM, Qin W, Najafi H, Liu C, Buettger CW, Sotiris J, Collins HW, Li C, Stanley CA, Wilson DF, Grimsby J, Sarabu R, Naji A, Matschinsky FM. Glucokinase activation repairs defective bioenergetics of islets of Langerhans isolated from type 2 diabetics. Am J Physiol Endocrinol Metab 2012; 302:E87-E102. [PMID: 21952036 PMCID: PMC3328091 DOI: 10.1152/ajpendo.00218.2011] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Accepted: 09/20/2011] [Indexed: 12/31/2022]
Abstract
It was reported previously that isolated human islets from individuals with type 2 diabetes mellitus (T2DM) show reduced glucose-stimulated insulin release. To assess the possibility that impaired bioenergetics may contribute to this defect, glucose-stimulated respiration (Vo(2)), glucose usage and oxidation, intracellular Ca(2+), and insulin secretion (IS) were measured in pancreatic islets isolated from three healthy and three type 2 diabetic organ donors. Isolated mouse and rat islets were studied for comparison. Islets were exposed to a "staircase" glucose stimulus, whereas IR and Vo(2) were measured. Vo(2) of human islets from normals and diabetics increased sigmoidally from equal baselines of 0.25 nmol/100 islets/min as a function of glucose concentration. Maximal Vo(2) of normal islets at 24 mM glucose was 0.40 ± 0.02 nmol·min(-1)·100 islets(-1), and the glucose S(0.5) was 4.39 ± 0.10 mM. The glucose stimulation of respiration of islets from diabetics was lower, V(max) of 0.32 ± 0.01 nmol·min(-1)·100 islets(-1), and the S(0.5) shifted to 5.43 ± 0.13 mM. Glucose-stimulated IS and the rise of intracellular Ca(2+) were also reduced in diabetic islets. A clinically effective glucokinase activator normalized the defective Vo(2), IR, and free calcium responses during glucose stimulation in islets from type 2 diabetics. The body of data shows that there is a clear relationship between the pancreatic islet energy (ATP) production rate and IS. This relationship was similar for normal human, mouse, and rat islets and the data for all species fitted a single sigmoidal curve. The shared threshold rate for IS was ∼13 pmol·min(-1)·islet(-1). Exendin-4, a GLP-1 analog, shifted the ATP production-IS curve to the left and greatly potentiated IS with an ATP production rate threshold of ∼10 pmol·min(-1)·islet(-1). Our data suggest that impaired β-cell bioenergetics resulting in greatly reduced ATP production is critical in the molecular pathogenesis of type 2 diabetes mellitus.
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Affiliation(s)
- Nicolai M Doliba
- Department of Biochemistry and Biophysics, University of Pennsylvania, 415 Curie Blvd., Philadelphia, PA 19104-6140, USA
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Krause MS, McClenaghan NH, Flatt PR, de Bittencourt PIH, Murphy C, Newsholme P. L-arginine is essential for pancreatic β-cell functional integrity, metabolism and defense from inflammatory challenge. J Endocrinol 2011; 211:87-97. [PMID: 21784771 DOI: 10.1530/joe-11-0236] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In this work, our aim was to determine whether L-arginine (a known insulinotropic amino acid) can promote a shift of β-cell intermediary metabolism favoring glutathione (GSH) and glutathione disulfide (GSSG) antioxidant responses, stimulus-secretion coupling and functional integrity. Clonal BRIN-BD11 β-cells and mouse islets were cultured for 24 h at various L-arginine concentrations (0-1.15 mmol/l) in the absence or presence of a proinflammatory cytokine cocktail (interleukin 1β, tumour necrosis factor α and interferon γ). Cells were assessed for viability, insulin secretion, GSH, GSSG, glutamate, nitric oxide (NO), superoxide, urea, lactate and for the consumption of glucose and glutamine. Protein levels of NO synthase-2, AMP-activated protein kinase (AMPK) and the heat shock protein 72 (HSP72) were also evaluated. We found that L-arginine at 1.15 mmol/l attenuated the loss of β-cell viability observed in the presence of proinflammatory cytokines. L-arginine increased total cellular GSH and glutamate levels but reduced the GSSG/GSH ratio and glutamate release. The amino acid stimulated glucose consumption in the presence of cytokines while also stimulating AMPK phosphorylation and HSP72 expression. Proinflammatory cytokines reduced, by at least 50%, chronic (24 h) insulin secretion, an effect partially attenuated by L-arginine. Acute insulin secretion was robustly stimulated by L-arginine but this effect was abolished in the presence of cytokines. We conclude that L-arginine can stimulate β-cell insulin secretion, antioxidant and protective responses, enabling increased functional integrity of β-cells and islets in the presence of proinflammatory cytokines. Glucose consumption and intermediary metabolism were increased by L-arginine. These results highlight the importance of L-arginine availability for β-cells during inflammatory challenge.
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Affiliation(s)
- Mauricio S Krause
- Biomedical Research Group, Department of Science, Institute of Technology Tallaght, Dublin, Ireland
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Abstract
AMP-activated protein kinase AMP-activated protein kinase (AMPK AMPK ), a phylogenetically conserved serine/threonine protein kinase, is a major regulator of cellular and whole-body energy homeostasis that coordinates metabolic pathways in order to balance nutrient supply with energy demand. It is now recognized that pharmacological activation of AMPK improves blood glucose homeostasis, lipid profile, and blood pressure in insulin-resistant rodents. Indeed, AMPK activation mimics the beneficial effects of physical activity or those of calorie restriction calorie restriction by acting on multiple cellular targets. In addition, it is now demonstrated that AMPK is one of the probable (albeit indirect) targets of major antidiabetic drugs drugs including the biguanides (metformin metformin ) and thiazolidinedione thiazolidinedione s, as well as of insulin-sensitizing adipokines (e.g., adiponectin adiponectin ). Taken together, such findings highlight the logic underlying the concept of targeting the AMPK pathway for the treatment of metabolic syndrome and type 2 diabetes.
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Brandon AE, Hoy AJ, Wright LE, Turner N, Hegarty BD, Iseli TJ, Julia Xu X, Cooney GJ, Saha AK, Ruderman NB, Kraegen EW. The evolution of insulin resistance in muscle of the glucose infused rat. Arch Biochem Biophys 2011; 509:133-41. [PMID: 21420928 DOI: 10.1016/j.abb.2011.03.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2011] [Revised: 03/14/2011] [Accepted: 03/15/2011] [Indexed: 11/17/2022]
Abstract
Glucose infusion into rats causes skeletal muscle insulin resistance that initially occurs without changes in insulin signaling. The aim of the current study was to prolong glucose infusion and evaluate other events associated with the transition to muscle insulin resistance. Hyperglycemia was produced in rats by glucose infusion for 3, 5 and 8 h. The rate of infusion required to maintain hyperglycemia was reduced at 5 and 8 h. Glucose uptake into red quadriceps (RQ) and its incorporation into glycogen decreased between 3 and 5 h, further decreasing at 8 h. The earliest observed change in RQ was decreased AMPKα2 activity associated with large increases in muscle glycogen content at 3 h. Activation of the mTOR pathway occurred at 5 h. Akt phosphorylation (Ser(473)) was decreased at 8 h compared to 3 and 5, although no decrease in phosphorylation of downstream GSK-3β (Ser(9)) and AS160 (Thr(642)) was observed. White quadriceps showed a similar but delayed pattern, with insulin resistance developing by 8 h and decreased AMPKα2 activity at 5 h. These results indicate that, in the presence of a nutrient overload, alterations in muscle insulin signaling occur, but after insulin resistance develops and appropriate changes in energy/nutrient sensing pathways occur.
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Affiliation(s)
- Amanda E Brandon
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Darlinghurst, NSW 2010, Australia.
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Chang CI, Tseng HI, Liao YW, Yen CH, Chen TM, Lin CC, Cheng HL. In vivo and in vitro studies to identify the hypoglycaemic constituents of Momordica charantia wild variant WB24. Food Chem 2011. [DOI: 10.1016/j.foodchem.2010.09.043] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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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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Kanda Y, Shimoda M, Hamamoto S, Tawaramoto K, Kawasaki F, Hashiramoto M, Nakashima K, Matsuki M, Kaku K. Molecular mechanism by which pioglitazone preserves pancreatic beta-cells in obese diabetic mice: evidence for acute and chronic actions as a PPARgamma agonist. Am J Physiol Endocrinol Metab 2010; 298:E278-86. [PMID: 19920213 PMCID: PMC2822485 DOI: 10.1152/ajpendo.00388.2009] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Pioglitazone preserves pancreatic beta-cell morphology and function in diabetic animal models. In this study, we investigated the molecular mechanisms by which pioglitazone protects beta-cells in diabetic db/db mice. In addition to the morphological analysis of the islets, gene expression profiles of the pancreatic islet were analyzed using laser capture microdissection and were compared with real-time RT-PCR of db/db and nondiabetic m/m mice treated with or without pioglitazone for 2 wk or 2 days. Pioglitazone treatment (2 wk) ameliorated dysmetabolism, increased islet insulin content, restored glucose-stimulated insulin secretion, and preserved beta-cell mass in db/db mice but had no significant effects in m/m mice. Pioglitazone upregulated genes that promote cell differentiation/proliferation in diabetic and nondiabetic mice. In db/db mice, pioglitazone downregulated the apoptosis-promoting caspase-activated DNase gene and upregulated anti-apoptosis-related genes. The above-mentioned effects of pioglitazone treatment were also observed after 2 days of treatment. By contrast, the oxidative stress-promoting NADPH oxidase gene was downregulated, and antioxidative stress-related genes were upregulated, in db/db mice treated with pioglitazone for 2 wk, rather than 2 days. Morphometric results for proliferative cell number antigen and 4-hydroxy-2-noneal modified protein were consistent with the results of gene expression analysis. The present results strongly suggest that pioglitazone preserves beta-cell mass in diabetic mice mostly by two ways; directly, by acceleration of cell differentiation/proliferation and suppression of apoptosis (acute effect); and indirectly, by deceleration of oxidative stress because of amelioration of the underlying metabolic disorder (chronic effect).
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Affiliation(s)
- Yukiko Kanda
- Diabetes and Endocrine Division, Kawasaki Medical School, Kurashiki, Japan
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Davies G, Ross A, Arnason T, Juurlink B, Harkness T. Troglitazone inhibits histone deacetylase activity in breast cancer cells. Cancer Lett 2010; 288:236-50. [DOI: 10.1016/j.canlet.2009.07.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Revised: 07/09/2009] [Accepted: 07/10/2009] [Indexed: 10/20/2022]
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Affiliation(s)
- Joohun Ha
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Korea
| | - Sooho Lee
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Korea
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Lamontagne J, Pepin E, Peyot ML, Joly E, Ruderman NB, Poitout V, Madiraju SRM, Nolan CJ, Prentki M. Pioglitazone acutely reduces insulin secretion and causes metabolic deceleration of the pancreatic beta-cell at submaximal glucose concentrations. Endocrinology 2009; 150:3465-74. [PMID: 19406947 PMCID: PMC2717855 DOI: 10.1210/en.2008-1557] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Thiazolidinediones (TZDs) have beneficial effects on glucose homeostasis via enhancement of insulin sensitivity and preservation of beta-cell function. How TZDs preserve beta-cells is uncertain, but it might involve direct effects via both peroxisome proliferator-activated receptor-gamma-dependent and -independent pathways. To gain insight into the independent pathway(s), we assessed the effects of short-term (<or=90 min) exposure to pioglitazone (Pio) (10 to 50 microM) on glucose-induced insulin secretion (GIIS), AMP-activated protein kinase (AMPK) activation, and beta-cell metabolism in INS 832/13 beta-cells and rat islets. Pio caused a right shift in the dose-dependence of GIIS, such that insulin release was reduced at intermediate glucose but unaffected at either basal or maximal glucose concentrations. This was associated in INS 832/13 cells with alterations in energy metabolism, characterized by reduced glucose oxidation, mitochondrial membrane polarization, and ATP levels. Pio caused AMPK phosphorylation and its action on GIIS was reversed by the AMPK inhibitor compound C. Pio also reduced palmitate esterification into complex lipids and inhibited lipolysis. As for insulin secretion, the alterations in beta-cell metabolic processes were mostly alleviated at elevated glucose. Similarly, the antidiabetic agents and AMPK activators metformin and berberine caused a right shift in the dose dependence of GIIS. In conclusion, Pio acutely reduces glucose oxidation, energy metabolism, and glycerolipid/fatty acid cycling of the beta-cell at intermediate glucose concentrations. We suggest that AMPK activation and the metabolic deceleration of the beta-cell caused by Pio contribute to its known effects to reduce hyperinsulinemia and preserve beta-cell function and act as an antidiabetic agent.
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Affiliation(s)
- Julien Lamontagne
- Department of Nutrition and Biochemistry, Molecular Nutrition Unit and Montreal Diabetes Research Center, Université de Montréal, Montréal, Québec, Canada
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When hypothermia meets hypotension and hyperglycemia: the diverse effects of adenosine 5'-monophosphate on cerebral ischemia in rats. J Cereb Blood Flow Metab 2009; 29:1022-34. [PMID: 19319149 PMCID: PMC2726621 DOI: 10.1038/jcbfm.2009.28] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mild hypothermia renders potent neuroprotection against acute brain injury. Recent reports show that adenosine 5'-monophosphate (AMP) plays a role in thermoregulation and induces hypothermia in mice. Therefore, this study sought to determine whether AMP induces hypothermia in rats and to study its collective effects on cerebral ischemia induced by 2-h middle cerebral artery occlusion. An intraperitoneal injection of AMP induced hypothermia dose-dependently. At the dose of 4 mmol/kg, AMP induced promising mild hypothermia for 2.5 h. Unexpectedly, the AMP-induced hypothermia failed to reduce infarct volume after brain ischemia; instead, it exaggerated the ischemic damage, indicated by an increased infarct volume, as well as increased incidences of hemorrhagic transformation, seizure, and animal death. Physiologic parameter monitoring revealed that AMP causes profound hypotension, leading to cerebral hypoperfusion. Furthermore, AMP administration resulted in severe hyperglycemia, metabolic acidosis, and hypocalcemia. In addition, western blots showed early dephosphorylation and degradation of AMP-activated kinase in the ischemic cortex in AMP-treated rats. Taken together, our findings suggest that AMP induces hypothermia in rats, probably by limiting cellular access to glucose. However, the potential neuroprotection of AMP-mediated hypothermia against ischemia was overwhelmed by the detrimental effects of hypotension and hyperglycemia, thus making AMP an unlikely agent for inducing hypothermia to protect the brain against ischemic injury.
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Zhang F, Dey D, Bränström R, Forsberg L, Lu M, Zhang Q, Sjöholm A. BLX-1002, a novel thiazolidinedione with no PPAR affinity, stimulates AMP-activated protein kinase activity, raises cytosolic Ca2+, and enhances glucose-stimulated insulin secretion in a PI3K-dependent manner. Am J Physiol Cell Physiol 2008; 296:C346-54. [PMID: 19052259 DOI: 10.1152/ajpcell.00444.2008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BLX-1002 is a novel small thiazolidinedione with no apparent affinity to peroxisome proliferator-activated receptors (PPAR) that has been shown to reduce glycemia in type 2 diabetes without adipogenic effects. Its precise mechanisms of action, however, remain elusive, and no studies have been done with respect to possible effects of BLX-1002 on pancreatic beta-cells. We have investigated the influence of the drug on beta-cell function in mouse islets in vitro. BLX-1002 enhanced insulin secretion stimulated by high, but not low or intermediate, glucose concentrations. BLX-1002 also augmented cytoplasmic free Ca2+ concentration ([Ca2+](i)) at high glucose, an effect that was abolished by pretreatment with the Ca2+-ATPase inhibitor thapsigargin. In contrast, BLX-1002 did not interfere with voltage-gated Ca2+ channel or ATP-sensitive K+ channel activities. In addition, cellular NAD(P)H stimulated by glucose was not affected by the drug. The stimulatory effect of BLX-1002 on insulin secretion at high glucose was completely abolished by treatment with the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY-294002. Stimulation of the beta-cells with BLX-1002 also induced activation of AMP-activated protein kinase (AMPK) at high glucose. Our study suggests that BLX-1002 potentiates insulin secretion only at high glucose in beta-cells in a PI3K-dependent manner. This effect of BLX-1002 is associated with an increased [Ca2+](i) mediated through Ca2+ mobilization, and an enhanced activation of AMPK. The glucose-sensitive stimulatory impact of BLX-1002 on beta-cell function may translate into substantial clinical benefits of the drug in the management of type 2 diabetes, by avoidance of hypoglycemia.
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Affiliation(s)
- Fan Zhang
- Diabetes Research Center, Dept. of Internal Medicine, Karolinska Institutet, South Hospital, SE-11883 Stockholm, Sweden
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Zhou L, Wang X, Shao L, Yang Y, Shang W, Yuan G, Jiang B, Li F, Tang J, Jing H, Chen M. Berberine acutely inhibits insulin secretion from beta-cells through 3',5'-cyclic adenosine 5'-monophosphate signaling pathway. Endocrinology 2008; 149:4510-8. [PMID: 18511510 DOI: 10.1210/en.2007-1752] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Berberine, a hypoglycemic agent, has recently been shown to activate AMP-activated protein kinase (AMPK) contributing to its beneficial metabolic effects in peripheral tissues. However, whether berberine exerts a regulatory effect on beta-cells via AMPK or other signaling pathways and counteracts glucolipotoxicity remains uncertain. In the present study, the impact of berberine on beta-cell function was investigated in vivo and in vitro. In high-fat-fed rats, berberine treatment for 6 wk significantly decreased plasma glucose and insulin levels before and after an oral glucose challenge along with the reduction of body weight and improvement of blood lipid profile. In accordance with the in vivo results, berberine acutely decreased glucose-stimulated insulin secretion (GSIS) and palmitate-potentiated insulin secretion in MIN6 cells and rat islets. However, pretreated with berberine for 24 h augmented the response of MIN6 cells and rat islets to glucose and attenuated the glucolipotoxicity. Berberine acutely increased AMPK activity in MIN6 cells. However, compound C, an AMPK inhibitor, completely reversed troglitazone-suppressed GSIS, not berberine-suppressed GSIS. Otherwise, berberine decreased cAMP-raising agent-potentiated insulin secretion in MIN6 cells and rat islets. These results suggest that the activation of AMPK is required for troglitazone-suppressed GSIS, whereas cAMP signaling pathway contributes, at least in part, to the regulatory effect of berberine on insulin secretion.
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Affiliation(s)
- Libin Zhou
- Shanghai Institute of Endocrine and Metabolic Diseases, Department of Endocrine and Metabolic Diseases, Shanghai Clinical Center for Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai 200025, People's Republic of China
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Palmitate-induced beta-cell dysfunction is associated with excessive NO production and is reversed by thiazolidinedione-mediated inhibition of GPR40 transduction mechanisms. PLoS One 2008; 3:e2182. [PMID: 18478115 PMCID: PMC2366067 DOI: 10.1371/journal.pone.0002182] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2008] [Accepted: 03/13/2008] [Indexed: 11/19/2022] Open
Abstract
Background Type 2 diabetes often displays hyperlipidemia. We examined palmitate effects on pancreatic islet function in relation to FFA receptor GPR40, NO generation, insulin release, and the PPARγ agonistic thiazolidinedione, rosiglitazone. Principal Findings Rosiglitazone suppressed acute palmitate-stimulated GPR40-transduced PI hydrolysis in HEK293 cells and insulin release from MIN6c cells and mouse islets. Culturing islets 24 h with palmitate at 5 mmol/l glucose induced β-cell iNOS expression as revealed by confocal microscopy and increased the activities of ncNOS and iNOS associated with suppression of glucose-stimulated insulin response. Rosiglitazone reversed these effects. The expression of iNOS after high-glucose culturing was unaffected by rosiglitazone. Downregulation of GPR40 by antisense treatment abrogated GPR40 expression and suppressed palmitate-induced iNOS activity and insulin release. Conclusion We conclude that, in addition to mediating acute FFA-stimulated insulin release, GPR40 is an important regulator of iNOS expression and dysfunctional insulin release during long-term exposure to FFA. The adverse effects of palmitate were counteracted by rosiglitazone at GPR40, suggesting that thiazolidinediones are beneficial for β-cell function in hyperlipidemic type 2 diabetes.
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