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Adamson SE, Hughes JW. Paracrine Signaling by Pancreatic Islet Cilia. CURRENT OPINION IN ENDOCRINE AND METABOLIC RESEARCH 2024; 35:100505. [PMID: 38524256 PMCID: PMC10956557 DOI: 10.1016/j.coemr.2024.100505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/26/2024]
Abstract
The primary cilium is a sensory and signaling organelle present on most pancreatic islet endocrine cells, where it receives and interprets a wide range of intra-islet chemical cues including hormones, peptides, and neurotransmitters. The ciliary membrane possesses a molecular composition distinct from the plasma membrane, with enrichment of signaling mediators including G protein-coupled receptors (GPCRs), tyrosine kinase family receptors, membrane transporters and others. When activated, these membrane proteins interact with ion channels and adenylyl cyclases to trigger local Ca2+ and cAMP activity and transmit signals to the cell body. Here we review evidence supporting the emerging model in which primary cilia on pancreatic islet cells play a central role in the intra-islet communication network and discuss how changes in cilia-mediated paracrine function in islet cells might lead to diabetes.
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Affiliation(s)
- Samantha E Adamson
- Division of Endocrinology, Metabolism & Lipid Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Jing W Hughes
- Division of Endocrinology, Metabolism & Lipid Research, Washington University School of Medicine, St. Louis, MO, USA
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Adamson SE, Li ZA, Hughes JW. Beta cell primary cilia mediate somatostatin responsiveness via SSTR3. Islets 2023; 15:2252855. [PMID: 37660302 PMCID: PMC10478741 DOI: 10.1080/19382014.2023.2252855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 08/23/2023] [Accepted: 08/24/2023] [Indexed: 09/05/2023] Open
Abstract
Somatostatin is a paracrine modulator of insulin secretion and beta cell function with pleotropic effects on glucose homeostasis. The mechanism of somatostatin-mediated communication between delta and beta cells is not well-understood, which we address in this study via the ciliary somatostatin receptor 3 (SSTR3). Primary cilia are membrane organelles that act as signaling hubs in islets by virtue of their subcellular location and enrichment in signaling proteins such as G-protein coupled receptors (GPCRs). We show that SSTR3, a ciliary GPCR, mediates somatostatin suppression of insulin secretion in mouse islets. Quantitative analysis of calcium flux using a mouse model of genetically encoded beta cell-specific GCaMP6f calcium reporter shows that somatostatin signaling alters beta cell calcium flux after physiologic glucose stimulation, an effect that depends on endogenous SSTR3 expression and the presence of intact primary cilia on beta cells. Comparative in vitro studies using SSTR isoform antagonists demonstrate a role for SSTR3 in mediating somatostatin regulation of insulin secretion in mouse islets. Our findings support a model in which ciliary SSTR3 mediates a distinct pathway of delta-to-beta cell regulatory crosstalk and may serve as a target for paracrine modulation.
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Affiliation(s)
- Samantha E. Adamson
- Department of Medicine, Division of Endocrinology, Metabolism & Lipid Research, Washington University School of Medicine, St. Louis, USA
| | - Zipeng A. Li
- Department of Medicine, Division of Endocrinology, Metabolism & Lipid Research, Washington University School of Medicine, St. Louis, USA
| | - Jing W. Hughes
- Department of Medicine, Division of Endocrinology, Metabolism & Lipid Research, Washington University School of Medicine, St. Louis, USA
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Ng XW, Chung YH, Piston DW. Intercellular Communication in the Islet of Langerhans in Health and Disease. Compr Physiol 2021; 11:2191-2225. [PMID: 34190340 PMCID: PMC8985231 DOI: 10.1002/cphy.c200026] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Blood glucose homeostasis requires proper function of pancreatic islets, which secrete insulin, glucagon, and somatostatin from the β-, α-, and δ-cells, respectively. Each islet cell type is equipped with intrinsic mechanisms for glucose sensing and secretory actions, but these intrinsic mechanisms alone cannot explain the observed secretory profiles from intact islets. Regulation of secretion involves interconnected mechanisms among and between islet cell types. Islet cells lose their normal functional signatures and secretory behaviors upon dispersal as compared to intact islets and in vivo. In dispersed islet cells, the glucose response of insulin secretion is attenuated from that seen from whole islets, coordinated oscillations in membrane potential and intracellular Ca2+ activity, as well as the two-phase insulin secretion profile, are missing, and glucagon secretion displays higher basal secretion profile and a reverse glucose-dependent response from that of intact islets. These observations highlight the critical roles of intercellular communication within the pancreatic islet, and how these communication pathways are crucial for proper hormonal and nonhormonal secretion and glucose homeostasis. Further, misregulated secretions of islet secretory products that arise from defective intercellular islet communication are implicated in diabetes. Intercellular communication within the islet environment comprises multiple mechanisms, including electrical synapses from gap junctional coupling, paracrine interactions among neighboring cells, and direct cell-to-cell contacts in the form of juxtacrine signaling. In this article, we describe the various mechanisms that contribute to proper islet function for each islet cell type and how intercellular islet communications are coordinated among the same and different islet cell types. © 2021 American Physiological Society. Compr Physiol 11:2191-2225, 2021.
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Affiliation(s)
- Xue W Ng
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - Yong H Chung
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
| | - David W Piston
- Department of Cell Biology and Physiology, Washington University, St Louis, Missouri, USA
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Stigmasterol prevents glucolipotoxicity induced defects in glucose-stimulated insulin secretion. Sci Rep 2017; 7:9536. [PMID: 28842702 PMCID: PMC5573401 DOI: 10.1038/s41598-017-10209-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 08/04/2017] [Indexed: 02/07/2023] Open
Abstract
Type 2 diabetes results from defects in both insulin sensitivity and insulin secretion. Elevated cholesterol content within pancreatic β-cells has been shown to reduce β-cell function and increase β-cell apoptosis. Hyperglycemia and dyslipidemia contribute to glucolipotoxicity that leads to type 2 diabetes. Here we examined the capacity of glucolipotoxicity to induce free cholesterol accumulation in human pancreatic islets and the INS-1 insulinoma cell line. Glucolipotoxicity treatment increased free cholesterol in β-cells, which was accompanied by increased reactive oxygen species (ROS) production and decreased insulin secretion. Addition of AAPH, a free radical generator, was able to increase filipin staining indicating a link between ROS production and increased cholesterol in β-cells. We also showed the ability of stigmasterol, a common food-derived phytosterol with anti-atherosclerotic potential, to prevent the increase in both free cholesterol and ROS levels induced by glucolipotoxicity in INS-1 cells. Stigmasterol addition also inhibited early apoptosis, increased total insulin, promoted actin reorganization, and improved insulin secretion in cells exposed to glucolipotoxicity. Overall, these data indicate cholesterol accumulation as an underlying mechanism for glucolipotoxicity-induced defects in insulin secretion and stigmasterol treatment as a potential strategy to protect β-cell function during diabetes progression.
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Wang T, Wang Y, Lv DM, Song JF, Lu Q, Gao X, Zhang F, Guo H, Li W, Yin XX. Effects of NOS1AP rs12742393 polymorphism on repaglinide response in Chinese patients with type 2 diabetes mellitus. Pharmacotherapy 2013; 34:131-9. [PMID: 24338736 DOI: 10.1002/phar.1379] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
STUDY OBJECTIVE To investigate the associations of NOS1AP rs12742393 polymorphism with the risk of type 2 diabetes mellitus (T2DM) and repaglinide therapeutic efficacy in Chinese patients with T2DM. DESIGN Prospective case-control study. SETTING Academic medical center. PATIENTS A total of 300 patients with T2DM and 200 healthy volunteers were enrolled to identify NOS1AP rs12742393 genotypes using the polymerase chain reaction-restriction fragment length polymorphism assay. Eighty-four patients with various genotypes were randomly selected to receive oral repaglinide as a single-agent therapy (3 mg/day) for 8 weeks. MEASUREMENTS AND MAIN RESULTS Anthropometric measurements and fasting plasma glucose (FPG), postprandial plasma glucose, hemoglobin A1c , fasting serum insulin (FINS), postprandial serum insulin, homeostasis model assessment for insulin resistance (HOMA-IR), triglyceride, total cholesterol, low-density lipoprotein-cholesterol, and high-density lipoprotein-cholesterol tests were obtained before and after repaglinide treatment. The risk C allelic frequency of NOS1AP rs12742393 was higher in patients with T2DM than in healthy volunteers (p<0.001). Patients with T2DM and genotypes AA and AC at NOS1AP rs12742393 had a significant reduction in FPG (mmol/l) compared with those with genotype CC (p<0.01). Patients with CC homozygotes and AC heterozygotes had a greater increase in FINS (mU/l) than those with wild-type AA (p<0.05). In addition, the carriers of genotype CC at NOS1AP rs12742393 had higher differential values of HOMA-IR compared with genotypes AC and AA carriers (p<0.001). The effects of repaglinide treatment on FPG (p<0.01), FINS (p<0.05) and HOMA-IR (p<0.001) were reduced in patients with T2DM carrying the NOS1AP rs12742393 risk C allele compared with the AA genotype carriers. CONCLUSION The NOS1AP rs12742393 polymorphism is associated with therapeutic efficacy of repaglinide in Chinese T2DM patients.
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Affiliation(s)
- Tao Wang
- Key Laboratory of New Drugs and Clinical Application, Xuzhou Medical College, Xuzhou, China; Department of Pharmacy, the Affiliated Hospital of Xuzhou Medical College, Xuzhou, China
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Mannino GC, Sesti G. Individualized therapy for type 2 diabetes: clinical implications of pharmacogenetic data. Mol Diagn Ther 2013; 16:285-302. [PMID: 23018631 DOI: 10.1007/s40291-012-0002-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance, abnormally elevated hepatic glucose production, and reduced glucose-stimulated insulin secretion. Treatment with antihyperglycemic agents is initially successful in type 2 diabetes, but it is often associated with a high secondary failure rate, and the addition of insulin is eventually necessary for many patients, in order to restore acceptable glycemic control and to reduce the risk of development and progression of disease complications. Notably, even patients who appear to have similar requirements of antidiabetic regimens show great variability in drug disposition, glycemic response, tolerability, and incidence of adverse effects during treatment. Pharmacogenomics is a promising area of investigation and involves the search for genetic polymorphisms that may explain the interindividual variability in antidiabetic therapy response. The initial positive results portend that genomic efforts will be able to shed important light on variability in pharmacologic traits. In this review, we summarize the current understanding of genetic polymorphisms that may affect the responses of subjects with T2DM to antidiabetic treatment. These genes belong to three major classes: genes involved in drug metabolism and transporters that influence pharmacokinetics (including the cytochrome P450 [CYP] superfamily, the organic anion transporting polypeptide [OATP] family, and the polyspecific organic cation transporter [OCT] family); genes encoding drug targets and receptors (including peroxisome proliferator-activated receptor gamma [PPARG], the adenosine triphosphate [ATP]-sensitive potassium channel [K(ATP)], and incretin receptors); and genes involved in the causal pathway of T2DM that are able to modify the effects of drugs (including adipokines, transcription factor 7-like 2 (T cell specific, HMG-box) [TCF7L2], insulin receptor substrate 1 [IRS1], nitric oxide synthase 1 (neuronal) adaptor protein [NOS1AP], and solute carrier family 30 (zinc transporter), member 8 [SLC30A8]). In addition to these three major classes, we also review the available evidence on novel genes (CDK5 regulatory subunit associated protein 1-like 1 [CDKAL1], insulin-like growth factor 2 mRNA binding protein 2 [IGF2BP2], potassium voltage-gated channel, KQT-like subfamily, member 1 [KCNQ1], paired box 4 [PAX4] and neuronal differentiation 1 [NEUROD1] transcription factors, ataxia telangiectasia mutated [ATM], and serine racemase [SRR]) that have recently been proposed as possible modulators of therapeutic response in subjects with T2DM.
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Affiliation(s)
- Gaia Chiara Mannino
- Department of Medical and Surgical Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy
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Keenan DM, Basu R, Liu Y, Basu A, Bock G, Veldhuis JD. Logistic model of glucose-regulated C-peptide secretion: hysteresis pathway disruption in impaired fasting glycemia. Am J Physiol Endocrinol Metab 2012; 303:E397-409. [PMID: 22669243 PMCID: PMC3423124 DOI: 10.1152/ajpendo.00494.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present analysis tests the hypothesis that quantifiable disruption of the glucose-stimulated insulin-secretion dose-response pathway mediates impaired fasting glycemia (IFG) and type 2 diabetes mellitus (DM). To this end, adults with normal and impaired fasting glycemia (NFG, n = 30), IFG (n = 32), and DM (n = 14) were given a mixed meal containing 75 g glucose. C-peptide and glucose were measured over 4 h, 13 times in NFG and IFG and 16 times in DM (age range 50-57 yr, body mass index 28-32 kg/m(2)). Wavelet-based deconvolution analysis was used to estimate time-varying C-peptide secretion rates. Logistic dose-response functions were constructed analytically of the sensitivity, potency, and efficacy (in the pharmacological sense of slope, one-half maximal stimulation, and maximal effect) of glucose's stimulation of prehepatic insulin (C-peptide) secretion. A hysteresis changepoint time, demarcating unequal glucose potencies for onset and recovery pathways, was estimated simultaneously. According to this methodology, NFG subjects exhibited distinct onset and recovery potencies of glucose in stimulating C-peptide secretion (6.5 and 8.5 mM), thereby defining in vivo hysteresis (potency shift -2.0 mM). IFG patients manifested reduced glucose onset potency (8.6 mM), and diminished C-peptide hysteretic shift (-0.80 mM). DM patients had markedly decreased glucose potency (18.8 mM), reversal of C-peptide's hysteretic shift (+4.5 mM), and 30% lower C-peptide sensitivity to glucose stimulation. From these data, we conclude that a dynamic dose-response model of glucose-dependent control of C-peptide secretion can identify disruption of in vivo hysteresis in patients with IFG and DM. Pathway-defined analytic models of this kind may aid in the search for prediabetes biomarkers.
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Affiliation(s)
- Daniel M Keenan
- Department of Statistics, University of Virginia, Charlottesville, VA, USA
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Misler S, Gillis KD. Modes of exocytosis and electrogenesis underlying canine biphasic insulin secretion. Front Biosci (Elite Ed) 2012. [PMID: 22201903 DOI: 10.2741/408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Biphasic insulin secretion in response to glucose consists of a transient first phase followed by a progressive second phase. It is a well described feature of whole perfused pancreases as well as isolated pancreatic islets of Langerhans. Applying to single cell assays of exocytosis (capacitance monitoring and amperometry) to single canine Beta-cells we have examined the time courses of granule exocytosis in response to voltage-clamp depolarizations that mimic two modes of glucose-induced electrical activity, and then compared these to biphasic insulin secretion. Action potentials evoked in short trains at frequencies similar those recorded during first phase insulin secretion trigger phasic exocytosis from a small pool of insulin granules that are likely docked near voltage-activated Ca²⁺ channels. In contrast, prolonged voltage-clamp pulses mimicking plateau depolarizations occur during second phase insulin secretion and trigger tonic or continuous exocytosis. Comparing the latter results with ones obtained using photorelease of caged Ca²⁺ in other insulin-secreting cells, we suggest that tonic exocytosis likely results from granule release from a highly Ca²⁺-sensitive pool of insulin granules, likely located further from Ca²⁺ channels. Both phasic and tonic modes of exocytosis are enhanced by glucose, via its metabolism. Hence, in canine Beta-cells we propose that two distinct modes of exocytosis, tuned to two types of electrical activity, may underlay biphasic insulin secretion.
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Affiliation(s)
- Stanley Misler
- Department of Medicine, Washington University School of Medicine, St. Louis MO 63110, USA.
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Misler S, Gillis KD. Modes of exocytosis and electrogenesis underlying canine biphasic insulin secretion. Front Biosci (Elite Ed) 2012; 4:669-76. [PMID: 22201903 PMCID: PMC5868347 DOI: 10.2741/e408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Biphasic insulin secretion in response to glucose consists of a transient first phase followed by a progressive second phase. It is a well described feature of whole perfused pancreases as well as isolated pancreatic islets of Langerhans. Applying to single cell assays of exocytosis (capacitance monitoring and amperometry) to single canine Beta-cells we have examined the time courses of granule exocytosis in response to voltage-clamp depolarizations that mimic two modes of glucose-induced electrical activity, and then compared these to biphasic insulin secretion. Action potentials evoked in short trains at frequencies similar those recorded during first phase insulin secretion trigger phasic exocytosis from a small pool of insulin granules that are likely docked near voltage-activated Ca²⁺ channels. In contrast, prolonged voltage-clamp pulses mimicking plateau depolarizations occur during second phase insulin secretion and trigger tonic or continuous exocytosis. Comparing the latter results with ones obtained using photorelease of caged Ca²⁺ in other insulin-secreting cells, we suggest that tonic exocytosis likely results from granule release from a highly Ca²⁺-sensitive pool of insulin granules, likely located further from Ca²⁺ channels. Both phasic and tonic modes of exocytosis are enhanced by glucose, via its metabolism. Hence, in canine Beta-cells we propose that two distinct modes of exocytosis, tuned to two types of electrical activity, may underlay biphasic insulin secretion.
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Affiliation(s)
- Stanley Misler
- Department of Medicine, Washington University School of Medicine, St. Louis MO 63110, USA.
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Cho HJ, Lee SY, Kim YG, Oh SY, Kim JW, Huh W, Huh WS, Ko JW, Kim HG. Effect of genetic polymorphisms on the pharmacokinetics and efficacy of glimepiride in a Korean population. Clin Chim Acta 2011; 412:1831-4. [PMID: 21704609 DOI: 10.1016/j.cca.2011.06.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 06/10/2011] [Accepted: 06/11/2011] [Indexed: 12/31/2022]
Abstract
BACKGROUNDS Glimepiride is a commonly used sulfonylurea hypoglycemic agent. There is considerable interindividual variation in the response to sulfonylurea for patients with type 2 diabetes. The purpose of this study was to investigate whether genetic variations influence the efficacy of glimepiride in healthy Korean subjects. METHODS A single 2-mg oral dose of glimepiride was administered to 46 healthy volunteers. Serial blood sampling for 12h after oral dosing was performed for determination of plasma glimepiride, glucose and insulin levels. We tested the association of seven single nucleotide polymorphisms (SNPs) in four candidate genes with the efficacy of glimepiride. RESULTS Pharmacodynamic profiles for plasma glucose and insulin showed no statistically significant differences among genotype groups, and parameters were not different from one another. There were no association of the KCNJ11, NOS1AP, TCF7L2 and ABCC8 gene polymorphisms and the efficacy of glimepiride. CONCLUSIONS Knowledge of these polymorphisms provides no clinical useful information for the pharmacogenetic therapeutic approach for Korean patients with type 2 diabetes.
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Affiliation(s)
- Hyun-Jung Cho
- Department of Laboratory Medicine, Konyang University Hospital, College of Medical Science Konyang University, Daejon, Republic of Korea
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Aquilante CL. Sulfonylurea pharmacogenomics in Type 2 diabetes: the influence of drug target and diabetes risk polymorphisms. Expert Rev Cardiovasc Ther 2010; 8:359-72. [PMID: 20222815 DOI: 10.1586/erc.09.154] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The sulfonylureas stimulate insulin release from pancreatic beta cells, and have been a cornerstone of Type 2 diabetes pharmacotherapy for over 50 years. Although sulfonylureas are effective antihyperglycemic agents, interindividual variability exists in drug response (i.e., pharmacodynamics), disposition (i.e., pharmacokinetics) and adverse effects. The field of pharmacogenomics has been applied to sulfonylurea clinical studies in order to elucidate the genetic underpinnings of this response variability. Historically, most studies have sought to determine the influence of polymorphisms in drug-metabolizing enzyme genes on sulfonylurea pharmacokinetics in humans. More recently, polymorphisms in sulfonylurea drug target genes and diabetes risk genes have been implicated as important determinants of sulfonylurea pharmacodynamics in patients with Type 2 diabetes. As such, the purpose of this review is to discuss sulfonylurea pharmacogenomics in the setting of Type 2 diabetes, specifically focusing on polymorphisms in drug target and diabetes risk genes, and their relationship with interindividual variability in sulfonylurea response and adverse effects.
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Affiliation(s)
- Christina L Aquilante
- School of Pharmacy, Department of Pharmaceutical Sciences, University of Colorado-Denver, 12700 East 19th Avenue, Aurora, CO 80045, USA.
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Common variation in the NOS1AP gene is associated with reduced glucose-lowering effect and with increased mortality in users of sulfonylurea. Pharmacogenet Genomics 2008; 18:591-7. [PMID: 18551039 DOI: 10.1097/fpc.0b013e328300e8c5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE The single nucleotide polymorphism rs10494366 in the nitric oxide synthase 1 adaptor protein (NOS1AP) gene is associated with QTc prolongation, through an effect on the intracellular Ca levels. As sulfonylurea stimulate insulin secretion by an increased influx of Ca, we hypothesized that this polymorphism is associated with the glucose-lowering effect and mortality risk in sulfonylurea users. METHODS Associations between the NOS1AP polymorphism, prescribed doses, and mortality rates in sulfonylurea, metformin, and insulin users were assessed in the Rotterdam Study, a population-based cohort study of 7983 elderly people. RESULTS We identified 619 participants who were prescribed oral antidiabetic drugs during follow-up. In glibenclamide users carrying the TG genotype, the prescribed doses were higher compared with the glibenclamide users carrying the TT genotype [0.38 defined daily dose units, 95% confidence interval (CI) 0.14-0.63]. Glibenclamide users with the TG or GG genotype had an increased mortality risk compared with glibenclamide users with the TT genotype [hazard ratio (HR) 2.80, 95% CI: 1.09-7.22]. Tolbutamide users with the TG or GG genotype (HR: 0.30, 95% CI: 0.14-0.63) and glimepiride users with the TG or GG genotype (HR: 0.18, 95% CI: 0.04-0.74) had a decreased mortality risk compared with tolbutamide and glimepiride users with the TT genotype. CONCLUSION In participants with the TG or GG genotype at rs10494366 in the NOS1AP gene, glibenclamide is less effective in reducing glucose levels and mortality rates were higher compared with glibenclamide users with the TT genotype. In tolbutamide and glimepiride users, the TG and GG genotype were associated with a reduced mortality rate.
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Gunawardana SC, Head WS, Piston DW. Dimethyl amiloride improves glucose homeostasis in mouse models of type 2 diabetes. Am J Physiol Endocrinol Metab 2008; 294:E1097-108. [PMID: 18413672 PMCID: PMC7170306 DOI: 10.1152/ajpendo.00748.2007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Dimethyl amiloride (DMA) enhances insulin secretion in the pancreatic beta-cell. DMA also enhances time-dependent potentiation (TDP) and enables TDP to occur in situations where it is normally absent. As we have demonstrated before, these effects are mediated in part through inhibition of neuronal nitric oxide synthase (nNOS), resulting in increased availability of arginine. Thus both DMA and arginine have the potential to correct the secretory defect in diabetes by enabling or enhancing TDP. In the current study we have demonstrated the ability of these agents to improve blood glucose homeostasis in three mouse models of type 2 diabetes. The pattern of TDP under different conditions indicates that inhibition of NOS is not the only mechanism through which DMA exerts its positive effects. Thus we also have explored another possible mechanism through which DMA enables/enhances TDP, via the activation of mitochondrial alpha-ketoglutarate dehydrogenase.
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Affiliation(s)
- Subhadra C Gunawardana
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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Hao M, Head WS, Gunawardana SC, Hasty AH, Piston DW. Direct effect of cholesterol on insulin secretion: a novel mechanism for pancreatic beta-cell dysfunction. Diabetes 2007; 56:2328-38. [PMID: 17575085 DOI: 10.2337/db07-0056] [Citation(s) in RCA: 231] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Type 2 diabetes is often accompanied by abnormal blood lipid and lipoprotein levels, but most studies on the link between hyperlipidemia and diabetes have focused on free fatty acids (FFAs). In this study, we examined the relationship between cholesterol and insulin secretion from pancreatic beta-cells that is independent of the effects of FFAs. RESEARCH DESIGN AND METHODS Several methods were used to modulate cholesterol levels in intact islets and cultured beta-cells, including a recently developed mouse model that exhibits elevated cholesterol but normal FFA levels. Acute and metabolic alteration of cholesterol was done using pharmacological reagents. RESULTS We found a direct link between elevated serum cholesterol and reduced insulin secretion, with normal secretion restored by cholesterol depletion. We further demonstrate that excess cholesterol inhibits secretion by downregulation of metabolism through increased neuronal nitric oxide synthase dimerization. CONCLUSIONS This direct effect of cholesterol on beta-cell metabolism opens a novel set of mechanisms that may contribute to beta-cell dysfunction and the onset of diabetes in obese patients.
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Affiliation(s)
- Mingming Hao
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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Bibliography. Current world literature. Diabetes and the endocrine pancreas II. Curr Opin Endocrinol Diabetes Obes 2007; 14:329-57. [PMID: 17940461 DOI: 10.1097/med.0b013e3282c3a898] [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: 11/25/2022]
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Attali V, Parnes M, Ariav Y, Cerasi E, Kaiser N, Leibowitz G. Regulation of insulin secretion and proinsulin biosynthesis by succinate. Endocrinology 2006; 147:5110-8. [PMID: 16916949 DOI: 10.1210/en.2006-0496] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Succinate stimulates insulin secretion and proinsulin biosynthesis. We studied the effects of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-modulating pathways on glucose- and succinate-stimulated insulin secretion and proinsulin biosynthesis in the rat and the insulin-resistant Psammomys obesus. Disruption of the anaplerotic pyruvate/malate shuttle by phenylacetic acid inhibited glucose- and succinate-stimulated insulin secretion and succinate-stimulated proinsulin biosynthesis in both species. In contrast, phenylacetic acid failed to inhibit glucose-stimulated proinsulin biosynthesis in P. obesus islets. Inhibition of the NADPH-consuming enzyme neuronal nitric oxide synthase (nNOS) with l-N(G)-nitro-l-arginine methyl ester or with N(G)-monomethyl-l-arginine(G) doubled succinate-stimulated insulin secretion in rat islets, suggesting that succinate- and nNOS-derived signals interact to regulate insulin secretion. In contrast, nNOS inhibition had no effect on succinate-stimulated proinsulin biosynthesis in both species. In P. obesus islets, insulin secretion was not stimulated by succinate in the absence of glucose, whereas proinsulin biosynthesis was increased 5-fold. Conversely, under stimulating glucose levels, succinate doubled insulin secretion, indicating glucose-dependence. Pyruvate ester and inhibition of nNOS partially mimicked the permissive effect of glucose on succinate-stimulated insulin secretion, suggesting that anaplerosis-derived signals render the beta-cells responsive to succinate. We conclude that beta-cell anaplerosis via pyruvate carboxylase is important for glucose- and succinate-stimulated insulin secretion and for succinate-stimulated proinsulin biosynthesis. In P. obesus, pyruvate/malate shuttle dependent and independent pathways that regulate proinsulin biosynthesis coexist; the latter can maintain fuel stimulated biosynthetic activity when the succinate-dependent pathway is inhibited. nNOS signaling is a negative regulator of insulin secretion, but not of proinsulin biosynthesis.
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Affiliation(s)
- Veronique Attali
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, P.O. Box 12000, Jerusalem 91120, Israel
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