A novel antidiabetic drug, fasiglifam/TAK-875, acts as an ago-allosteric modulator of FFAR1.

Selective free fatty acid receptor 1 (FFAR1)/GPR40 agonist fasiglifam (TAK-875), an antidiabetic drug under phase 3 development, potentiates insulin secretion in a glucose-dependent manner by activating FFAR1 expressed in pancreatic ß cells. Although fasiglifam significantly improved glycemic control in type 2 diabetes patients with a minimum risk of hypoglycemia in a phase 2 study, the precise mechanisms of its potent pharmacological effects are not fully understood. Here we demonstrate that fasiglifam acts as an ago-allosteric modulator with a partial agonistic activity for FFAR1. In both Ca(2+) influx and insulin secretion assays using cell lines and mouse islets, fasiglifam showed positive cooperativity with the FFAR1 ligand γ-linolenic acid (γ-LA). Augmentation of glucose-induced insulin secretion by fasiglifam, γ-LA, or their combination was completely abolished in pancreatic islets of FFAR1-knockout mice. In diabetic rats, the insulinotropic effect of fasiglifam was suppressed by pharmacological reduction of plasma free fatty acid (FFA) levels using a lipolysis inhibitor, suggesting that fasiglifam potentiates insulin release in conjunction with plasma FFAs in vivo. Point mutations of FFAR1 differentially affected Ca(2+) influx activities of fasiglifam and γ-LA, further indicating that these agonists may bind to distinct binding sites. Our results strongly suggest that fasiglifam is an ago-allosteric modulator of FFAR1 that exerts its effects by acting cooperatively with endogenous plasma FFAs in human patients as well as diabetic animals. These findings contribute to our understanding of fasiglifam as an attractive antidiabetic drug with a novel mechanism of action.

Overexpression of GPR40 in pancreatic beta-cells augments glucose-stimulated insulin secretion and improves glucose tolerance in normal and diabetic mice.

OBJECTIVE: GPR40 is a G protein-coupled receptor regulating free fatty acid-induced insulin secretion. We generated transgenic mice overexpressing the hGPR40 gene under control of the mouse insulin II promoter and used them to examine the role of GPR40 in the regulation of insulin secretion and glucose homeostasis. RESEARCH DESIGN AND METHODS: Normal (C57BL/6J) and diabetic (KK) mice overexpressing the hGPR40 gene under control of the insulin II promoter were generated, and their glucose metabolism and islet function were analyzed. RESULTS: In comparison with nontransgenic littermates, hGPR40 transgenic mice exhibited improved oral glucose tolerance with an increase in insulin secretion. Although islet morphologic analysis showed no obvious differences between hGPR40 transgenic and nontransgenic mice, isolated islets from hGPR40 transgenic mice had enhanced insulin secretion in response to high glucose (16 mmol/l) compared with those from nontransgenic mice, and they both had similar low glucose (3 mmol/l)-stimulated insulin secretion. In addition, hGPR40 transgenic islets significantly increased insulin secretion against a naturally occurring agonist palmitate in the presence of 11 mmol/l glucose. hGPR40 transgenic mice were also found to be resistant to high-fat diet-induced glucose intolerance, and hGPR40 transgenic mice harboring KK background showed augmented insulin secretion and improved oral glucose tolerance compared with nontransgenic littermates. CONCLUSIONS: Our results suggest that GPR40 may have a role in regulating glucose-stimulated insulin secretion and plasma glucose levels in vivo and that pharmacological activation of GPR40 may provide a novel insulin secretagogue beneficial for the treatment of type 2 diabetes.

Association of C825T polymorphism of G protein beta3 subunit with the autonomic nervous system in young healthy Japanese individuals.

BACKGROUND: The T allele of the C825T polymorphism of the G protein beta3 subunit gene (GNB3) is reported to be associated with increased intracellular signal transduction and the prevalence of essential hypertension. Because the two major receptors in the autonomic nervous system (ANS), the adrenergic and muscarinic acetylcholine receptors, are G protein-coupled receptors, it was expected that the GNB3 C825T polymorphism was associated with ANS function. In the present study, we have investigated the association of this polymorphism with ANS in young, healthy Japanese male individuals. METHODS: A total of 94 young, healthy subjects underwent the genotyping for the GNB3 C825T polymorphism and electrocardiogram R-R interval power spectral analysis in supine rest and standing positions. RESULTS: There were no significant differences among genotypes in any of the characteristics investigated (body mass index, blood pressure, plasma glucose, insulin, lipids, and family history of hypertension, diabetes, or obesity). However, in power spectral analysis of heart rate variability, the very-low-frequency component when standing was higher in TT carriers than in CC carriers, and TT and CT carriers had a significantly higher sympathetic nervous system (SNS) index and lower parasympathetic nervous system (PNS) index when standing than CC carriers. In addition, we found that TT carriers showed no chronological variations in either SNS or PNS index after postural change. CONCLUSIONS: These observations suggested that GNB3 C825T polymorphism is associated with ANS in youth. These findings raise the possibility that individuals who are T allele carriers are at increased risk for developing hypertension in relation to ANS function.

T393C polymorphism of GNAS1 associated with the autonomic nervous system in young, healthy Japanese subjects.

1. T393C polymorphism of the gene encoding the Gs-protein alpha-subunit (GNAS1) has been reported recently to be associated with hypertension in which dysfunctions of the autonomic nervous system (ANS) are closely involved. In the present study, the association of this polymorphism with ANS activity was investigated in young, healthy Japanese males. 2. Four hundred and one subjects were genotyped for the T393C polymorphism of GNAS1 by polymerase chain reaction-restriction fragment length polymorphism. Autonomic nervous system activity during supine rest and when standing was assessed in 137 subjects by electrocardiogram R-R interval power spectral analysis. 3. One hundred and fifty-four subjects (38.4%) were homozygous for the T allele (TT), 188 (46.9%) were heterozygous (TC) and 59 (14.7%) were homozygous for the C allele (CC). There were no significant differences as to genotype among the clinical characteristics investigated. In power spectral analysis of heart rate variability, the high-frequency component and parasympathetic nervous system (PNS) index during supine rest were significantly lower in TT and TC carriers than in CC carriers. Furthermore, the increase in heart rate and the responsiveness of sympathetic nervous system index and PNS index to postural change from supine rest to standing were significantly lower in TT and TC carriers than in CC carriers. 4. These observations suggest that the GNAS1 T393C polymorphism is associated with ANS activity in youth, so that it may be useful as a genetic marker for future pathogenesis of hypertension. Follow-up studies are necessary to clarify the prevalence rates of hypertension among 393T allele carriers in the present study.

Alpha(2B)-adrenergic receptor deletion polymorphism associates with autonomic nervous system activity in young healthy Japanese.

Several polymorphisms of genes involved in autonomic nervous system (ANS) function have been reported to affect metabolic regulation. We have investigated the association of an alpha(2B)-adrenergic receptor (alpha(2B)AR) three-amino acid deletion polymorphism with ANS activity in young healthy subjects by means of electrocardiogram R-R interval power spectral analysis. Three hundred eighty-one young healthy Japanese males (mean +/- SE, 20.6 +/- 0.1 yr) were studied. One hundred sixty-eight (44.1%) were homozygotes of Long allele (Long/Long), 162 (42.5%) were heterozygotes (Long/Short), and 51 (13.4%) were homozygotes of Short allele (Short/Short). The allele frequency of Short allele was 0.35. No significant differences were observed in any of the characteristics investigated: body mass index, plasma glucose, plasma insulin, or family history of diabetes and obesity. In R-R spectral analysis of heart rate variability, carriers of Short/Short had significantly greater low frequency and very low frequency than Long/Long, as well as a higher sympathetic nervous system index. These findings suggest that the alpha(2B)AR deletion polymorphism might result in metabolic disorder by altering ANS function.