GIP contributes to islet trihormonal abnormalities in type 2 diabetes.

CONTEXT: Research and clinical treatments on type 2 diabetes mainly focus on insulin deficiency with little attention paid to other islet hormones. OBJECTIVE: This study tested the hypothesis that glucose-dependent insulinotropic polypeptide (GIP) is involved in diabetes-associated multiislet hormone dysregulation. DESIGN: This paper included a case-control study involving 92 community-based volunteers from the Baltimore Longitudinal Study of Aging (BLSA): 23 with type 2 diabetes on glucose-lowering agents, 25 with newly diagnosed drug-naïve type 2 diabetes, 19 with prediabetes, and 25 with normal glucose tolerance; a separate intervention study with 13 non-BLSA volunteers with type 2 diabetes treated with diet alone, metformin, and/or metformin/sulfonylurea combination; a rodent study; and an in vitro cell line study. INTERVENTIONS: An oral glucose tolerance test was performed in the BLSA participants. For the intervention study, saline (0.9% NaCl) or synthetic human GIP (20 ng · kg(-1) · min(-1)) was administered to type 2 diabetes subjects for 180 minutes together with a meal, and plasma samples were obtained at predetermined intervals for 360 minutes. A bolus of GIP or placebo was given to C57BL/6 mice. MAIN OUTCOME MEASURES: Plasma glucose, insulin, glucagon, pancreatic polypeptide (PP), glucagon-like peptide-1 (GLP-1), and GIP were measured. RESULTS: After an oral glucose tolerance test, glucose, glucagon, PP, GLP-1, and GIP levels were significantly elevated in type 2 diabetes groups, compared with normal and prediabetes groups. GIP infusion in type 2 diabetes subjects was associated with significantly elevated PP levels compared with placebo. The GIP bolus given to C57BL/6 mice was followed by increased PP levels. GIP receptors were found in both human and mouse PP cells. CONCLUSIONS: Up-regulation of GIP production may play an important role in multihormonal dysregulation in type 2 diabetes, most likely through interaction with GIP receptors on islets.

Insulin and glucagon regulate pancreatic α-cell proliferation.

Type 2 diabetes mellitus (T2DM) results from insulin resistance and ß-cell dysfunction, in the setting of hyperglucagonemia. Glucagon is a 29 amino acid peptide hormone, which is secreted from pancreatic α cells: excessively high circulating levels of glucagon lead to excessive hepatic glucose output. We investigated if α-cell numbers increase in T2DM and what factor (s) regulate α-cell turnover. Lepr(db)/Lepr(db) (db/db) mice were used as a T2DM model and αTC1 cells were used to study potential α-cell trophic factors. Here, we demonstrate that in db/db mice α-cell number and plasma glucagon levels increased as diabetes progressed. Insulin treatment (EC50 = 2 nM) of α cells significantly increased α-cell proliferation in a concentration-dependent manner compared to non-insulin-treated α cells. Insulin up-regulated α-cell proliferation through the IR/IRS2/AKT/mTOR signaling pathway, and increased insulin-mediated proliferation was prevented by pretreatment with rapamycin, a specific mTOR inhibitor. GcgR antagonism resulted in reduced rates of cell proliferation in αTC1 cells. In addition, blockade of GcgRs in db/db mice improved glucose homeostasis, lessened α-cell proliferation, and increased intra-islet insulin content in ß cells in db/db mice. These studies illustrate that pancreatic α-cell proliferation increases as diabetes develops, resulting in elevated plasma glucagon levels, and both insulin and glucagon are trophic factors to α-cells. Our current findings suggest that new therapeutic strategies for the treatment of T2DM may include targeting α cells and glucagon.

High-dose isoflavones do not improve metabolic and inflammatory parameters in androgen-deprived men with prostate cancer.

The profound hypogonadism that occurs with androgen deprivation therapy (ADT) for prostate cancer (PCa) results in complications such as diabetes and metabolic syndrome that predispose to cardiovascular disease. Because phytoestrogens have been associated with an improvement in metabolic parameters, we evaluated their role in men undergoing ADT. Our objective was to evaluate the effects of high-dose isoflavones on metabolic and inflammatory parameters in men undergoing ADT. This was a randomized, double-blind, placebo-controlled, 12-week pilot study. Participants were randomly assigned to receive 20 g of soy protein containing 160 mg of total isoflavones vs taste-matched placebo (20 g whole milk protein). The study was conducted at a tertiary care center in the United States. Thirty-three men (isoflavones = 17, placebo = 16) undergoing ADT for PCa completed this pilot study. Mean age in the 2 groups was 69 years and the majority of men were Caucasians. Mean duration of ADT in both groups was approximately 2 years (P = .70). The 2 groups were well matched at baseline. After 12 weeks of intervention, there was no significant difference in either metabolic or inflammatory parameters between the 2 groups. We found that high-dose isoflavones over a course of 12 weeks do not improve metabolic or inflammatory parameters in androgen-deprived men.