Guo Huang

A Novel Gymnema sylvestre Extract Stimulates Insulin Secretion from Human Islets In Vivo and In Vitro

Many plant‐based products have been suggested as potential antidiabetic agents, but few have been shown to be effective in treating the symptoms of Type 2 diabetes mellitus (T2DM) in human studies, and little is known of their mechanisms of action. Extracts of Gymnema sylvestre (GS) have been used for the treatment of T2DM in India for centuries. The effects of a novel high molecular weight GS extract, Om Santal Adivasi, (OSA®) on plasma insulin, C‐peptide and glucose in a small cohort of patients with T2DM are reported here. Oral administration of OSA® (1 g/day, 60 days) induced significant increases in circulating insulin and C‐peptide, which were associated with significant reductions in fasting and post‐prandial blood glucose. In vitro measurements using isolated human islets of Langerhans demonstrated direct stimulatory effects of OSA® on insulin secretion from human ?‐cells, consistent with an in vivo mode of action through enhancing insulin secretion. These in vivo and in vitro observations suggest that OSA® may provide a potential alternative therapy for the hyperglycemia associated with T2DM. Copyright

Cannabinoid receptor agonists and antagonists stimulate insulin secretion from isolated human islets of Langerhans

Aims: The role of cannabinoid receptors in human islets of Langerhans has not been investigated in any detail, so the current study examined CB1 and CB2 receptor expression by human islets and the effects of pharmacological cannabinoid receptor agonists and antagonists on insulin secretion.

Islet cell transplantation

People with type 1 diabetes have normal exocrine pancreatic function, making islet cell rather than whole organ transplantation an attractive option. Achieving insulin independence in type 1 diabetes was the perceived goal of islet cell transplantation. The success of the Edmonton group in achieving this in a selected group of type 1 patients has led to renewed optimism that this treatment could eventually replace whole organ pancreas transplantation. However the long-term results of this treatment indicate that insulin independence is lost with time in a significant proportion of patients, although they may retain glycaemic stability. In this context, the indications for islet cell transplantation, which have evolved over the last 5 years, indicate that the patients who benefit most are those who experience severe hypoglycaemic reactions despite optimal insulin therapy. This review will summarise the history of islet cell transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, indications for islet cell transplantation, current clinical trials, the early UK islet cell transplant experience using the Edmonton protocol, and some of the challenges that lie ahead.

Insulin-producing cells derived from human pancreatic non-endocrine cell cultures reverse streptozotocin-induced hyperglycaemia in mice

Aims/hypothesisThe aim of the study was to investigate the potential of human pancreatic non-endocrine cells to transdifferentiate into endocrine cells that would be capable of secreting insulin in response to glucose and ameliorating insulin-deficient diabetes after transplantation.Materials and methodsCell fractions enriched with exocrine cells after human islet isolation were treated with streptozotocin to remove residual beta cells, grown in monolayer culture to allow de-differentiation, transferred to cluster culture for redifferentiation in the presence of activin A, betacellulin, nicotinamide and glucose, supplemented with 10% FCS, and administered to streptozotocin-induced diabetic SCID mice. A subset of cells was transfected with the IPF1 gene (also known as PDX1) before transdifferentiation.ResultsNo insulin was detectable in cell preparations after 5 days of treatment with streptozotocin. In monolayer culture, 90% of the streptozotocin-treated pancreatic cells co-expressed cytokeratin-19 and vimentin at 2 weeks and 60% expressed nestin at 4 weeks. Cell cultures with a high proportion of nestin-expressing cells had greater plasticity for transdifferentiation into cells with phenotypic and functional markers of beta cells, this property being significantly enhanced by transfection with IPF1 gene and leading to 15±6.7% insulin-positive cells after transplantation vs. 0.01% of cells transplanted after streptozotocin treatment alone. These cells improved glucose control in all of 42 diabetic mice after transplantation, restoring normoglycaemia in 40%.Conclusions/interpretationHuman pancreatic cells are a potential source of new glucose-responsive insulin-producing cells that may be developed further for clinical use.

Human Islets Derived From Donors After Cardiac Death Are Fully Biofunctional

Islets from brain‐dead donors (BDDs) are being used in the treatment of Type 1 diabetes. However, both donor numbers and islet survival are limited. We explored the clinical potential for islets from non‐heart‐beating donors (NHBDs), who have lower circulating cytokines, by comparing islets from 10 NHBDs against 12 identically‐isolated islets from BDDs over the same time period. The quantity and quality of islets from NHBDs was good. NHBD yielded ∼12.6% more islets than those of BDDs (505 000 ± 84 230 vs. 400 970 ± 172 430 islet equivalent number [IEQ]/pancreas, p = 0.01) with comparable viability. ATP and GTP contents were lower (6.026 ± 3.076 vs. 18.105 ± 7.8 nM/mg protein, p = 0.01 and 1.52 ± 0.87 vs. 3.378 ± 0.83 nM/mg protein, p = 0.04) and correlated negatively to warm ischemia time (R2= 0.8022 and R2= 0.7996, respectively). Islets from NHBDs took longer to control hyperglycemia in diabetic mice, but were equally able to sustain euglycemia. With a warm ischemia time (WIT) of ≤25 min, islets from NHBDs are at least as competent as islets from BDDs and should be suitable for clinical use.

Attainment of metabolic goals in the integrated UK islet transplant program with locally isolated and transported preparations

The objective was to determine whether metabolic goals have been achieved with locally isolated and transported preparations over the first 3 years of the UKs nationally funded integrated islet transplant program. Twenty islet recipients with C‐peptide negative type 1 diabetes and recurrent severe hypoglycemia consented to the study, including standardized meal tolerance tests. Participants received a total of 35 infusions (seven recipients: single graft; 11 recipients: two grafts: two recipients: three grafts). Graft function was maintained in 80% at [median (interquartile range)] 24 (13.5–36) months postfirst transplant. Severe hypoglycemia was reduced from 20 (7–50) episodes/patient‐year pretransplant to 0.3 (0–1.6) episodes/patient‐year posttransplant (p < 0.001). Resolution of impaired hypoglycemia awareness was confirmed [pretransplant: Gold score 6 (5–7); 24 (13.5–36) months: 3 (1.5–4.5); p < 0.03]. Target HbA1c of <7.0% was attained/maintained in 70% of recipients [pretransplant: 8.0 (7.0–9.6)%; 24 (13.5–36) months: 6.2 (5.7–8.4)%; p < 0.001], with 60% reduction in insulin dose [pretransplant: 0.51 (0.41–0.62) units/kg; 24 (13.5–36) months: 0.20 (0–0.37) units/kg; p < 0.001]. Metabolic outcomes were comparable 12 months posttransplant in those receiving transported versus only locally isolated islets [12 month stimulated C‐peptide: transported 788 (114–1764) pmol/L (n = 9); locally isolated 407 (126–830) pmol/L (n = 11); p = 0.32]. Metabolic goals have been attained within the equitably available, fully integrated UK islet transplant program with both transported and locally isolated preparations.

Gene expression heterogeneity in human islet endocrine cells in vitro: the insulin signalling cascade

Aims/hypothesisInsulin secretion is a highly regulated mechanism involving a complex insulin-dependent network of communication between alpha, beta and delta cells. However, whereas the role of insulin in beta cells has been well documented, very little is known about its role in alpha and delta cells. Having recently demonstrated heterogeneity of insulin receptor (INSR) isoform expression in these three endocrine cell types, our current study aimed to characterise the expression pattern of the multiple isoforms involved in the insulin signal transduction cascade in human alpha, beta and delta cells in vitro.Materials and methodscDNA samples prepared from single human islet cells were subjected to nested PCRs.ResultsOf 706 cells analysed, 15% were alpha cells, 28% beta cells, 8% delta cells and 46% non-endocrine cells. Profiling of expression of the insulin signalling cascade elements showed a heterogeneity between islet cell types, although at least one member of each protein family was expressed in the three populations of endocrine cells. Thus, the mRNAs coding for INSR-B, phosphoinositide-dependent protein kinase-1 and the human homologue of v-akt murine thymoma viral oncogene homologue 1 (AKT1) could not be detected in alpha cells, but were expressed by beta and delta cells. In addition, while the insulin receptor substrates IRS1 and IRS2, phosphoinositide-3-kinase, catalytic, beta polypeptide (PIK3CB) and AKT2 were expressed with relatively low frequencies in alpha and delta cells (<17% for IRS1, IRS2, PIK3CB; <25% for AKT2), their frequencies of expression in beta cells were 50, 33, 33 and 100%, respectively.Conclusions/interpretationOur results suggest that insulin signalling cascade elements in human alpha, beta and delta cells have distinct expression patterns.

Investigation of intracellular signalling cascades mediating stimulatory effect of a Gymnema sylvestre extract on insulin secretion from isolated mouse and human islets of Langerhans

Traditional plant‐based remedies such as Gymnema sylvestre (GS) extracts have been used to treat diabetes mellitus for many centuries. We have shown previously that a novel GS extract, OSA®, has a direct effect on insulin secretion but its mode of action has not been studied in detail Thus this study investigated the possible underlying mechanism(s) by which OSA® exerts its action.

Modification of human islet preparation: an effective approach to improve graft outcome after islet transplantation?

Revascularisation of transplanted islets is an essential prerequisite for graft survival and function. However, current islet isolation procedures deprive the islets of endothelial tubulets. This may have a detrimental effect on the revascularisation process of islets following transplantation. We hypothesise that modification of the isolation procedure that preserves islet endothelial vessels may improve the islet revascularisation process following transplantation. Here, we present a modified islet isolation method by which a substantial amount of endothelial cells still attached to the islets could be preserved. The islets with preserved endothelial cells isolated by this method were revascularised within 3 days, not observed in islets isolated by standard methods. Further, we observed that grafts of islets isolated by standard methods had more patches of dead tissue than islet grafts obtained by the modified method, indicating that attached endothelial cells may play an important role in the islet revascularisation process and potentially help to improve the transplantation outcome.