Effects of glucagon-like peptide-1 receptor agonists on secretions of insulin and glucagon and gastric emptying in Japanese individuals with type 2 diabetes: A prospective, observational study.

AIMS/INTRODUCTION: Differences in the glucose-lowering mechanisms of glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been noted. Clarifying these differences could facilitate the choice of optimal drugs for individuals with type 2 diabetes and requires investigation in a clinical setting. MATERIALS AND METHODS: A single-arm, prospective, observational study was conducted to evaluate the effects of various GLP-1RAs on postprandial glucose excursion, secretions of insulin and glucagon as well as on the gastric emptying rate. Participants were subjected to meal tolerance tests before and 2 weeks and 12 weeks after GLP-1RA initiation. Effects on postprandial secretions of glucose-dependent insulinotropic polypeptide (GIP) and apolipoprotein B48 were also investigated. RESULTS: Eighteen subjects with type 2 diabetes received one of three GLP-1RAs, i.e., lixisenatide, n = 7; liraglutide, n = 6; or dulaglutide, n = 5. While 12-week administration of all of the GLP-1RAs significantly reduced HbA1c, only lixisenatide and liraglutide, but not dulaglutide, significantly reduced body weight. Postprandial glucose elevation was improved by all of the GLP-1RAs. Postprandial insulin levels were suppressed by lixisenatide, while insulin levels were enhanced by liraglutide. Postprandial glucagon levels were suppressed by lixisenatide. The gastric emptying rate was significantly delayed by lixisenatide, while liraglutide and dulaglutide had limited effects on gastric emptying. GIP secretion was suppressed by lixisenatide and liraglutide. Apolipoprotein B48 secretion was suppressed by all of the GLP-1RAs. CONCLUSIONS: All of the GLP-1RAs were found to improve HbA1c in a 12-week prospective observational study in Japanese individuals with type 2 diabetes. However, differences in the mechanisms of the glucose-lowering effects and body weight reduction were observed.

Carbonic anhydrase 8 (CAR8) negatively regulates GLP-1 secretion from enteroendocrine cells in response to long-chain fatty acids.

Glucagon-like peptide-1 (GLP-1) is an incretin secreted from enteroendocrine preproglucagon (PPG)-expressing cells (traditionally known as L cells) in response to luminal nutrients that potentiates insulin secretion. Augmentation of endogenous GLP-1 secretion might well represent a novel therapeutic target for diabetes treatment in addition to the incretin-associated drugs currently in use. In this study, we found that PPG cells substantially express carbonic anhydrase 8 (CAR8), which has been reported to inhibit inositol 1,4,5-trisphosphate (IP3) binding to the IP3 receptor and subsequent Ca2+ efflux from the endoplasmic reticulum in neuronal cells. In vitro experiments using STC-1 cells demonstrated that Car8 knockdown increases long-chain fatty acid (LCFA)-stimulated GLP-1 secretion. This effect was reduced in the presence of phospholipase C (PLC) inhibitor; in addition, Car8 knockdown increased the intracellular Ca2+ elevation caused by α-linolenic acid, indicating that CAR8 exerts its effect on GLP-1 secretion via the PLC/IP3/Ca2+ pathway. Car8wdl null mutant mice showed significant increase in GLP-1 response to oral corn oil administration compared with that in wild-type littermates, with no significant change in intestinal GLP-1 content. These results demonstrate that CAR8 negatively regulates GLP-1 secretion from PPG cells in response to LCFAs, suggesting the possibility of augmentation of postprandial GLP-1 secretion by CAR8 inhibition.NEW & NOTEWORTHY This study focused on the physiological significance of carbonic anhydrase 8 (CAR8) in GLP-1 secretion from enteroendocrine preproglucagon (PPG)-expressing cells. We found an inhibitory role of CAR8 in LCFA-induced GLP-1 secretion in vitro and in vivo, suggesting a novel therapeutic approach to diabetes and obesity through augmentation of postprandial GLP-1 secretion by CAR8 inhibition.

Acromegaly accompanied by diabetes mellitus and polycystic kidney disease.

Acromegaly is characterized by autonomous excessive growth hormone (GH) secretion, generally due to GH-producing pituitary adenoma, and is associated with various systemic comorbidities including diabetes mellitus. Polycystic kidney disease (PKD) is characterized by the growth of numerous cysts in the kidneys that deteriorate renal function. While possible renal effects of excessive GH exposure have been a current issue in experimental medicine, only five cases of coexisting acromegaly and PKD have been reported previously, and little is known regarding the influence of acromegaly on renal disease. We treated a 50-year-old male with diabetes mellitus who showed a sudden and rapid decline of renal function along with increasing proteinuria, which led to diagnoses of PKD and acromegaly. His urinary protein levels were increased together with excessive GH secretion and worsening glycemic control. An increase of total kidney volume was also noted. Transsphenoidal surgery for the pituitary adenoma was successfully performed. Marked improvement of hyperglycemia and proteinuria were observed after the surgery, but renal function was unchanged. The patient's clinical course suggested common aspects of excessive GH secretion as an accelerating factor of the progression of diabetic nephropathy and PKD via direct and indirect pathways. Although coexisting acromegaly and PKD is clinically rare, vigilance for early diagnosis of acromegaly is appropriate in patients with diabetes and/or PKD, especially in those showing unexpected exacerbation of renal dysfunction.

Single-Cell Transcriptome Analysis Dissects the Replicating Process of Pancreatic Beta Cells in Partial Pancreatectomy Model.

Heterogeneity of gene expression and rarity of replication hamper molecular analysis of ß-cell mass restoration in adult pancreas. Here, we show transcriptional dynamics in ß-cell replication process by single-cell RNA sequencing of murine pancreas with or without partial pancreatectomy. We observed heterogeneity of Ins1-expressing ß-cells and identified the one cluster as replicating ß-cells with high expression of cell proliferation markers Pcna and Mki67. We also recapitulated cell cycle transition accompanied with switching expression of cyclins and E2F transcription factors. Both transient activation of endoplasmic reticulum stress responders like Atf6 and Hspa5 and elevated expression of tumor suppressors like Trp53, Rb1, and Brca1 and DNA damage responders like Atm, Atr, Rad51, Chek1, and Chek2 during the transition to replication associated fine balance of cell cycle progression and protection from DNA damage. Taken together, these results provide a high-resolution map depicting a sophisticated genetic circuit for replication of the ß-cells.

Generation and Characterization of a Novel Mouse Model That Allows Spatiotemporal Quantification of Pancreatic ß-Cell Proliferation.

Pancreatic ß-cell proliferation has been gaining much attention as a therapeutic target for the prevention and treatment of diabetes. In order to evaluate potential ß-cell mitogens, accurate and reliable methods for the detection and quantification of the ß-cell proliferation rate are indispensable. In this study, we developed a novel tool that specifically labels replicating ß-cells as mVenus+ cells by using RIP-Cre; R26Fucci2aR mice expressing the fluorescent ubiquitination-based cell cycle indicator Fucci2a in ß-cells. In response to ß-cell proliferation stimuli, such as insulin receptor antagonist S961 and diet-induced obesity (DIO), the number of 5-ethynyl-2'-deoxyuridine-positive insulin+ cells per insulin+ cells and the number of mVenus+ cells per mCherry+ mVenus- cells + mCherry- mVenus+ cells were similarly increased in these mice. Three-dimensional imaging of optically cleared pancreas tissue from these mice enabled quantification of replicating ß-cells in the islets and morphometric analysis of the islets after known mitogenic interventions such as S961, DIO, pregnancy, and partial pancreatectomy. Thus, this novel mouse line is a powerful tool for spatiotemporal analysis and quantification of ß-cell proliferation in response to mitogenic stimulation.

Sphingosine kinase 1-interacting protein is a dual regulator of insulin and incretin secretion.

Our previous study demonstrated that sphingosine kinase 1-interacting protein (SKIP, or Sphkap) is expressed in pancreatic ß-cells, and depletion of SKIP enhances glucose-stimulated insulin secretion. We find here that SKIP is also expressed in intestinal K- and L-cells and that secretion of gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) as well as insulin are significantly increased, and blood glucose levels are decreased in SKIP-deficient (SKIP-/-) mice compared with those in wild-type mice. Plasma triglyceride (Tg), LDL cholesterol, and mRNA levels of proinflammatory cytokines in adipose tissues, livers, and intestines were found to be significantly decreased in SKIP-/- mice. The phenotypic characteristics of SKIP-/- mice, including adiposity and attenuation of basal inflammation, were abolished by genetic depletion of GIP. The improvement of glucose tolerance and lipid profiles in SKIP-/- mice were cancelled by GLP-1 receptor antagonist exendin-(9-39) treatment. In summary, depletion of SKIP ameliorates glucose tolerance by enhancing secretion of insulin and incretins, improves lipid metabolism, and reduces basal inflammation levels. Thus, inhibition of SKIP action may emerge as a new option for treatment of type 2 diabetes mellitus with metabolic dysfunction.-Liu, Y., Harashima, S., Wang, Y., Suzuki, K., Tokumoto, S., Usui, R., Tatsuoka, H., Tanaka, D., Yabe, D., Harada, N., Hayashi, Y., Inagaki, N. Sphingosine kinase 1-interacting protein is a dual regulator of insulin and incretin secretion.

Twincretin as a potential therapeutic for the management of type 2 diabetes with obesity.

Unimolecular peptide-based dual agonists against glucagon-like peptide-1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR) have been gaining much attention recently as novel antidiabetic agents that can potentially control glycemia and bodyweight. Although GLP-1 and GIP both enhance insulin secretion and subsequently ameliorate postprandial glucose excursion, most research has focused on GLP-1R as a therapeutic target for type 2 diabetes. This is partly because the effects of GIPR activation on glycemia and bodyweight have been controversial. GIPR-deficient mice showed impaired glucose tolerance with reduced ß-cell function and resistance to high-fat diet-induced obesity, whereas GIPR agonists improved glycemia and prevented high-fat diet-induced obesity in mice. Conflicting results in mice might be explained by pharmacological levels of GIP signal in the central nervous systems decreasing food intake and overcoming the obesogenic effects of GIP at physiological levels in adipose tissues. Thus, GIPR activation at pharmacological levels might result in bodyweight reduction. Indeed, bodyweight reduction by GIPR/GLP-1R dual agonists was greater than GLP-1R single agonists in individuals with type 2 diabetes. Thus, GLP-1R/GIPR dual agonists can add additional therapeutic efficacy to tailored diabetes care, especially among obese individuals with type 2 diabetes. However, caution should be exercised as to whether or not these drugs are appropriate for the management of Asian type 2 diabetes patients, which are primarily characterized by non-obesity and impaired ß-cell function, as well as in that of elderly adults with type 2 diabetes, who tend to develop sarcopenia and frailty as a result of poor energy intake.

Sphingosine kinase 1-interacting protein is a novel regulator of glucose-stimulated insulin secretion.

Glucose-stimulated insulin secretion (GSIS) is essential in keeping blood glucose levels within normal range. GSIS is impaired in type 2 diabetes, and its recovery is crucial in treatment of the disease. We find here that sphingosine kinase 1-interacting protein (SKIP, also called Sphkap) is highly expressed in pancreatic ß-cells but not in α-cells. Intraperitoneal glucose tolerance test showed that plasma glucose levels were decreased and insulin levels were increased in SKIP-/- mice compared to SKIP+/+ mice, but exendin-4-enhanced insulin secretion was masked. GSIS was amplified more in SKIP-/- but exendin-4-enhanced insulin secretion was masked compared to that in SKIP+/+ islets. The ATP and cAMP content were similarly increased in SKIP+/+ and SKIP-/- islets; depolarization-evoked, PKA and cAMP-mediated insulin secretion were not affected. Inhibition of PDE activity equally augmented GSIS in SKIP+/+ and SKIP-/- islets. These results indicate that SKIP modulates GSIS by a pathway distinct from that of cAMP-, PDE- and sphingosine kinase-dependent pathways.

Oral Administration of Apple Procyanidins Ameliorates Insulin Resistance via Suppression of Pro-Inflammatory Cytokine Expression in Liver of Diabetic ob/ob Mice.

Procyanidins, the main ingredient of apple polyphenols, are known to possess antioxidative and anti-inflammatory effects associated closely with the pathophysiology of insulin resistance and type 2 diabetes. We investigated the effects of orally administered apple procyanidins (APCs) on glucose metabolism using diabetic ob/ob mice. We found no difference in body weight or body composition between mice treated with APCs and untreated mice. A 4 week oral administration of APCs containing water [0.5% (w/v)] ameliorated glucose tolerance, insulin resistance, and hepatic gluconeogenesis in ob/ob mice. APCs also suppressed the increase in the level of the pancreatic ß-cell. Insulin-stimulated Akt phosphorylation was significantly enhanced; pro-inflammatory cytokine expression levels were significantly decreased, and c-Jun N-terminal kinase phosphorylation was downregulated in the liver of those mice treated with APCs. In conclusion, APCs ameliorate insulin resistance by improving hepatic insulin signaling through suppression of hepatic inflammation in ob/ob mice, which may be a mechanism with possible beneficial health effects of APCs in disturbed glucose metabolism.

Src regulates insulin secretion and glucose metabolism by influencing subcellular localization of glucokinase in pancreatic ß-cells.

AIMS/INTRODUCTION: Src, a non-receptor tyrosine kinase, regulates a wide range of cellular functions, and hyperactivity of Src is involved in impaired glucose metabolism in pancreatic ß-cells. However, the physiological role of Src in glucose metabolism in normal, unstressed ß-cells remains unclear. In the present study, we investigated the role of Src in insulin secretion and glucose metabolism. MATERIALS AND METHODS: Src was downregulated using small interfering ribonucleic acid in INS-1 cells, and glucose-induced insulin secretion, adenosine triphosphate content, intracellular calcium concentration, glucose utilization and glucokinase activity were measured. Expression levels of messenger ribonucleic acid and protein of glucokinase were examined by semiquantitative real-time polymerase chain reaction and immunoblotting, respectively. Cells were fractionated by digitonin treatment, and subcellular localization of glucokinase was examined by immunoblotting. Interaction between glucokinase and neuronal nitric oxide synthase was estimated by immunoprecipitation. RESULTS: In Src downregulated INS-1 cells, glucose-induced insulin secretion was impaired, whereas insulin secretion induced by high K(+) was not affected. Intracellular adenosine triphosphate content and elevation of intracellular calcium concentration by glucose stimulation were suppressed by Src downregulation. Src downregulation reduced glucose utilization in the presence of high glucose, which was accompanied by a reduction in glucokinase activity without affecting its expression. However, Src downregulation reduced glucokinase in soluble, cytoplasmic fraction, and increased it in pellet containing intaracellular organelles. In addition, interaction between glucokinase and neuronal nitric oxide synthase was facilitated by Src downregulation. CONCLUSIONS: Src plays an important role in glucose-induced insulin secretion in pancreatic ß-cells through maintaining subcellular localization and activity of glucokinase.

Enhanced glucagon-like peptide-1 secretion in a patient with glucagonoma: implications for glucagon-like peptide-1 secretion from pancreatic α cells in vivo.

We examined GLP-1 secretion from the pancreas of a patient with glucagonoma and pancreatic resection by measuring GLP-1 after meal ingestion or selective arterial calcium injection, and immunohistochemical analysis. Our findings support the notion that GLP-1 is secreted from pancreatic α cells in humans.