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Extracellular vesicles (EVs) are involved in intercellular communication and are a topic of increasing interest due to their therapeutic potential. The aim of this study was to determine whether human islet-derived EVs contain insulin, and if so, what role do they play in glucose stimulated insulin secretion. We isolated EVs from human islets culture and plasma to probe for insulin. Plasma from hyperglycemic glucose clamp experiments were also used to isolate and measure EV insulin content in response to a secretory stimulus. We performed immunogold electron microscopy for insulin presence in EVs. Co-culture experiments of isolated EVs with fresh islets were performed to examine the effect of EV cargo on insulin receptor signaling. EVs isolated from culture medium contained insulin. Glucose treatment of islets increased the level of EV insulin. Hyperglycemic glucose clamp experiments in humans also lead to increased levels of insulin in plasma-derived EVs. Immunogold electron microscopy and proteinase K-digestion experiments demonstrated that insulin in EVs predominantly associated with the exterior surface of EVs while western blot analyses uncovered the presence of only preproinsulin in EVs. Membrane-bound preproinsulin in EVs was capable of activating insulin signaling pathway in an insulin receptor-dependent manner. The physiological relevance of this finding was observed in priming of human naïve islets by EVs during glucose stimulated insulin secretion. Our data suggest that (1) human islets secret insulin via an alternate pathway (EV-mediated) other than conventional granule-mediated insulin secretion, and (2) EV membrane bound preproinsulin is biologically active. [ABSTRACT FROM AUTHOR]

Aims: Abdominal fat is a major determinant of metabolic diseases in older individuals. Obesity and diabetes are associated with low serum amylase (SA) levels, but the association between SA and metabolic disease is poorly understood. We investigated the association of low SA with diabetes and sex-specific associations of serum amylase with abdominal fat in older adults.Methods: In community-dwelling volunteers from the Baltimore Longitudinal Study of Aging (778 participants, age 66.8±13.6years), we assessed abdominal fat by computed tomography and diabetes status using the American Diabetes Association criteria. Linear regression analyses assessed the cross-sectional associations between abdominal fat and SA, and logistic regression assessed the odds of diabetes, given low SA.Results: In unadjusted analyses, individuals in the lowest SA quartile (<48μ/L) had 1.97 greater odds of diabetes, (95%CI, 1.01-3.83) than those in the highest quartile (⩾80μ/L). This association was no longer significant after adjusting for visceral adipose tissue area (VAT, dm(2)), abdominal subcutaneous adipose tissue (SAT, dm(2)) or BMI. In adjusted analyses, VAT and SAT were significantly associated with SA in both sexes. Among women, SA was more strongly associated with VAT than with SAT or BMI; VAT (β=-0.117±0.048, P<0.001), SAT (β=-0.023±0.025, P=0.346) and BMI (β=-0.0052±0.075, P=0.49).Conclusions: The association between SA and diabetes was explained mainly by abdominal visceral fat. In women, SA was more strongly associated with VAT than with BMI or SAT. These findings provide motivation for future mechanistic studies on SA's role in metabolic diseases. [ABSTRACT FROM AUTHOR]

We have previously demonstrated in human subjects who under euglycemic clamp conditions GLP-1(9–36)amide infusions inhibit endogenous glucose production without substantial insulinotropic effects. An earlier report indicates that GLP-1(9–36)amide is cleaved to a nonapeptide, GLP-1(28–36)amide and a pentapeptide GLP-1(32–36)amide (LVKGR amide). Here we study the effects of the pentapeptide on whole body glucose disposal during hyperglycemic clamp studies. Five dogs underwent indwelling catheterizations. Following recovery, the dogs underwent a 180 min hyperglycemic clamp (basal glucose +98 mg/dl) in a cross-over design. Saline or pentapeptide (30 pmol kg −1 min −1 ) was infused during the last 120 min after commencement of the hyperglycemic clamp in a primed continuous manner. During the last 30 min of the pentapeptide infusion, glucose utilization ( M ) significantly increased to 21.4 ± 2.9 mg kg −1 min −1 compared to M of 14.3 ± 1.1 mg kg −1 min −1 during the saline infusion ( P = 0.026, paired t -test; P = 0.062, Mann–Whitney U test). During this interval, no significant differences in insulin (26.6 ± 3.2 vs. 23.7 ± 2.5 μU/ml, P = NS) or glucagon secretion (34.0 ± 2.1 vs. 31.7 ± 1.8 pg/ml, P = NS) were observed. These findings demonstrate that under hyperglycemic clamp studies the pentapeptide modulates glucose metabolism by a stimulation of whole-body glucose disposal. Further, the findings suggest that the metabolic benefits previously observed during GLP-1(9–36)amide infusions in humans might be due, at least in part, to the metabolic effects of the pentapeptide that is cleaved from the pro-peptide, GLP-1(9–36)amide in the circulation. [ABSTRACT FROM AUTHOR]