C-peptide In Response Research Articles

Pancreatic beta cell function in polycystic ovary syndrome: its relationship to body weight, serum testosterone and serum prolactin levels.

Circulating levels of insulin and C-peptide in response to oral glucose administration (75 g) were measured in 25 PCOS patients (13 were obese and 12 non-obese) without acanthosis nigricans and in 12 non-obese normal cycling women of similar age. Fasting levels of insulin and C-peptide as well as the sums of their levels in response to glucose were significantly greater in PCO patients than in controls despite similar glucose responses. Obese PCO patients had greater basal levels, maximum increments and sums of insulin and C-peptide levels than non-obese PCO patients and controls. PCO patients with increased basal total testosterone levels had significantly greater mean fasting insulin levels (p less than 0.005) than those with normal testosterone levels but their responses to glucose were not significantly different. Hyperprolactinaemic PCO patients had neither basal level nor sums of insulin and C-peptide levels in response to glucose greater than normoprolactinaemic PCO patients. In all PCO patients BMI correlated significantly with insulin (p less than 0.05) and C-peptide levels (p less than 0.001). Total serum testosterone levels correlated significantly with fasting levels and the sum of C-peptide levels in response to glucose. The correlations of total serum testosterone levels with fasting and the sum of insulin levels in response to glucose were also positive but not significant. These results clearly indicate that in PCOS there is a significant degree of hyperinsulinaemia which is mainly related to obesity.

In vivo characterization of transplanted human embryonic stem cell-derived pancreatic endocrine islet cells.

Islet-like clusters (ILCs), differentiated from human embryonic stem cells (hESCs), were characterized both before and after transplantation under the kidney capsule of streptozotocin-induced diabetic immuno-incompetent mice. Multiple independent ILC preparations (n = 8) were characterized by immunohistochemistry, flow cytometry and cell insulin content, with six preparations transplanted into diabetic mice (n = 42), compared to controls, which were transplanted with either a human fibroblast cell line or undifferentiated hESCs (n = 28). Prior to transplantation, ILCs were immunoreactive for the islet hormones insulin, C-peptide and glucagon, and for the ductal epithelial marker cytokeratin-19. ILCs also had cellular insulin contents similar to or higher than human foetal islets. Expression of islet and pancreas-specific cell markers was maintained for 70 days post-transplantation. The mean survival of recipients was increased by transplanted ILCs as compared to transplanted human fibroblast cells (P < 0.0001), or undifferentiated hESCs (P < 0.042). Graft function was confirmed by secretion of human C-peptide in response to an oral bolus of glucose. hESC-derived ILC grafts continued to contain cells that were positive for islet endocrine hormones and were shown to be functional by their ability to secrete human C-peptide. Further enrichment and maturation of ILCs could lead to generation of a sufficient source of insulin-producing cells for transplantation into patients with type 1 diabetes.

Insulin Resistance and Decreased Glucose-Stimulated Insulin Secretion After Acute Olanzapine Administration

The newer atypical antipsychotics, as a class, have been associated with an increased risk of weight gain and metabolic abnormalities. The mechanisms underlying this phenomenon are currently unclear, but there are data to suggest the possibility of an immediate (as opposed to chronic) effect of these drugs. The aim of the present study was to assess the acute effects of olanzapine on specific measures of insulin sensitivity and secretion. Healthy animals were tested in either the hyperinsulinemic-euglycemic or the hyperglycemic clamp. After reaching steady state in the hyperinsulinemic-euglycemic clamp, rats were injected with olanzapine (3 mg/kg sc) and monitored for an additional 130 minutes. In the hyperglycemic clamp, olanzapine was injected approximately 90 minutes before receiving a glucose bolus, and hyperglycemia was maintained via exogenous glucose infusion for an additional 90 minutes. Insulin and C-peptide levels were monitored throughout this clamp.Acute administration of olanzapine significantly lowered the glucose infusion rate due to an increase in hepatic glucose production and a decrease in glucose utilization. Olanzapine pretreatment induced hyperglycemia and markedly decreased plasma insulin and C-peptide in response to the glucose challenge. These findings indicate that olanzapine can directly induce metabolic changes that occur rapidly and well in advance of the changes that might be anticipated as a result of its weight-gain liability. We present novel findings highlighting an olanzapine-induced deficit in beta-cell functioning.

Nicotinamide induces differentiation of embryonic stem cells into insulin-secreting cells

The poly(ADP-ribose) polymerase (PARP) inhibitor, nicotinamide, induces differentiation and maturation of fetal pancreatic cells. In addition, we have previously reported evidence that nicotinamide increases the insulin content of cells differentiated from embryonic stem (ES) cells, but the possibility of nicotinamide acting as a differentiating agent on its own has never been completely explored. Islet cell differentiation was studied by: (i) X-gal staining after neomycin selection; (ii) BrdU studies; (iii) single and double immunohistochemistry for insulin, C-peptide and Glut-2; (iv) insulin and C-peptide content and secretion assays; and (v) transplantation of differentiated cells, under the kidney capsule, into streptozotocin (STZ)-diabetic mice. Here we show that undifferentiated mouse ES cells treated with nicotinamide: (i) showed an 80% decrease in cell proliferation; (ii) co-expressed insulin, C-peptide and Glut-2; (iii) had values of insulin and C-peptide corresponding to 10% of normal mouse islets; (iv) released insulin and C-peptide in response to stimulatory glucose concentrations; and (v) after transplantation into diabetic mice, normalized blood glucose levels over 7 weeks. Our data indicate that nicotinamide decreases ES cell proliferation and induces differentiation into insulin-secreting cells. Both aspects are very important when thinking about cell therapy for the treatment of diabetes based on ES cells.

Human Islet-Derived Precursor Cells Are Mesenchymal Stromal Cells That Differentiate and Mature to Hormone-Expressing Cells In Vivo

Islet transplantation offers improved glucose homeostasis in diabetic patients, but transplantation of islets is limited by the supply of donor pancreases. Undifferentiated precursors hold promise for cell therapy because they can expand before differentiation to produce a large supply of functional insulin-producing cells. Previously, we described proliferative populations of human islet-derived precursor cells (hIPCs) from adult islets. To show the differentiation potential of hIPCs, which do not express insulin mRNA after at least 1,000-fold expansion, we generated epithelial cell clusters (ECCs) during 4 days of differentiation in vitro. After transplantation into mice, 22 of 35 ECC preparations differentiated and matured into functional cells that secreted human C-peptide in response to glucose. Transcripts for insulin, glucagon, and somatostatin in recovered ECC grafts increased with time in vivo, reaching levels approximately 1% of those in adult islets. We show that hIPCs are mesenchymal stromal cells (MSCs) that adhere to plastic, express CD73, CD90, and CD105, and can differentiate in vitro into adipocytes, chondrocytes, and osteocytes. Moreover, we find a minor population of CD105(+)/CD73(+)/CD90(+) cells in adult human islets (prior to incubation in vitro) that express insulin mRNA at low levels. We conclude that hIPCs are a specific type of pancreas-derived MSC that are capable of differentiating into hormone-expressing cells. Their ability to mature into functional insulin-secreting cells in vivo identifies them as an important adult precursor or stem cell population that could offer a virtually unlimited supply of human islet-like cells for replacement therapy in type 1 diabetes. Disclosure of potential conflicts of interest is found at the end of this article.

Glucose-regulated insulin production from genetically engineered human non-beta cells

In this report we describe development and characterization of four human cell lines that are able to secrete insulin and C-peptide in response to higher concentrations of glucose. These cell lines have been developed by stably and constitutively expressing human proinsulin with a furin-cleavable site, whereas expression of furin is regulated by glucose concentration. These cell lines have been cloned and, therefore, the transgene in each cell is located in an identical location of the genome leading to a uniform expression. Cloning has also allowed us to identify cell lines with more desirable properties such as higher basal insulin secretion and/or better glucose responsiveness. We have further shown that the insulin produced by these cells is biologically active and induces normoglycemia when injected in diabetic animals. Our objective in initiating these studies was to identify a cell line that could serve as a surrogate beta cell line for therapeutic intervention in type I diabetic patients.

Glucose responsive insulin production from human embryonic germ (EG) cell derivatives

Type 1 diabetes mellitus subjects millions to a daily burden of disease management, life threatening hypoglycemia and long-term complications such as retinopathy, nephropathy, heart disease, and stroke. Cell transplantation therapies providing a glucose-regulated supply of insulin have been implemented clinically, but are limited by safety, efficacy and supply considerations. Stem cells promise a plentiful and flexible source of cells for transplantation therapies. Here, we show that cells derived from human embryonic germ (EG) cells express markers of definitive endoderm, pancreatic and β-cell development, glucose sensing, and production of mature insulin. These cells integrate functions necessary for glucose responsive regulation of preproinsulin mRNA and expression of insulin C-peptide in vitro. Following transplantation into mice, cells become insulin and C-peptide immunoreactive and produce plasma C-peptide in response to glucose. These findings suggest that EG cell derivatives may eventually serve as a source of insulin producing cells for the treatment of diabetes.

Production of pancreatic hormone–expressing endocrine cells from human embryonic stem cells

Of paramount importance for the development of cell therapies to treat diabetes is the production of sufficient numbers of pancreatic endocrine cells that function similarly to primary islets. We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, gut-tube endoderm, pancreatic endoderm and endocrine precursor--en route to cells that express endocrine hormones. The hES cell-derived insulin-expressing cells have an insulin content approaching that of adult islets. Similar to fetal beta-cells, they release C-peptide in response to multiple secretory stimuli, but only minimally to glucose. Production of these hES cell-derived endocrine cells may represent a critical step in the development of a renewable source of cells for diabetes cell therapy.

Glucose Stimulation of Cytochrome C Reduction and Oxygen Consumption as Assessment of Human Islet Quality

An in vitro method to assess human islets could prevent transplantation of nonviable islets and facilitate the optimization of islet preparation. We hypothesize that glucose-stimulated cytochrome c reduction and oxygen consumption by human islets can be used as predictors of transplant success. Isolated human islets were obtained from research-grade pancreata. Using a previously developed islet flow culture system, the response of cytochrome c reduction and oxygen consumption to glucose was compared to the ability of islets transplanted into nondiabetic NOD-SCID mice to secrete C-peptide in response to a glucose tolerance test conducted 7 days following transplant (n=10). In vitro responses by human islets were qualitatively similar to those seen in rat islets: glucose increased both oxygen consumption and cytochrome c reduction. However, the responses were smaller in magnitude and quite variable. Scatter plots of C-peptide and quantiles for ln(C-peptide) indicated that 12 ng/ml could be used as threshold of transplant success with which to evaluate the diagnostic potential of cytochrome c and oxygen consumption. Data was analyzed by generating receiver operating curves and the area under the curve was 0.889 (95% CI: 0.645-1.000) and 0.738 (95% CI: 0.413-1.000) for cytochrome c reduction and oxygen consumption respectively (1 indicates absolute predictive capability and 0.5 indicates no predictive capability). The detection of glucose-stimulated cytochrome c reduction and oxygen consumption may have utility as criteria for the assessment of human islet quality.

Islet autotransplantation combined with pancreatectomy for treatment of pancreatic adenocarcinoma: a case report

Extensive pancreatectomy (EP) may increase the resection rate of pancreatic adenocarcinoma (PA). Unfortunately, EP often results in unstable diabetes. Recently, islet autotransplantation (auto-Tx) has offered the potential to prevent this metabolic disorder. Because of the fear of contamination of prepared islets by malignant cells, this procedure has so far not been used as a treatment for PA. We herein report a case of a 63-year-old nondiabetic patient who underwent EP combined with islet auto-Tx in an emergency operation following histologically proved R 0-resection for PA (pT 3pN 1G 2). Islets were isolated from the excised pancreas using a continuous digestion filtration device. The resultant preparation was injected into the portal vein. Owing to the moderate fasting hyperglycemia, postoperative exogenous insulin therapy was necessary (26 U/d). After discharge, the patient's daily insulin dose was gradually reduced. At 1-year follow-up the fasting C-peptide level was 0.66 ng/mL, and an oral glucose tolerance test (oGTT) and an intravenous (IV) glucagon stimulation (GS) showed functioning engrafted islets. The K- ras mutations were detected in the paraffin-embedded PA, but not in the prepared islets or in the peripheral blood. Computed tomographic (CT) imaging revealed neither local tumor recurrence nor liver metastases. At 2-year follow-up, the patient was on a balanced food regimen and gaining weight. Although he remains insulin-dependent (16 U/d), he is metabolically stable (HbA 1 c 5.9%). The fasting C-peptide level is 0.68 ng/mL. The peak value of C-peptide in response to oGTT was 0.92 ng/mL and to GS 0.89 ng/mL. At this time Ca19-9 and CEA are increased to 35.3 U/mL and 19.2 ng/mL, respectively. The patient died 2.5 years after operation owing to tumor recurrence. There was no evidence for liver metastases. We postulate that histologic evaluation (R 0-resection) and detection of K- ras mutations may be useful techniques. However, islet auto-Tx after EP for adenocarcinoma should only be regarded for rescue therapy. Studies on strategies to exclude possible contamination of islet tissue with carcinoma cells are critically important.

Lowering of blood glucose to nondiabetic levels in a hyperglycemic pig by allografting of fetal pig isletlike cell clusters.

Fetal pig isletlike cell clusters (ICCs) will differentiate when grafted into the thymus gland of outbred immunosuppressed nondiabetic pigs for up to 3 months. Whether these cells will survive for a similar period in a diabetic recipient and will mature with secretion of insulin to ameliorate the hyperglycemia is unknown. Between 40,000 and 125,000 ICCs (7,000 to 11,400 ICCs/kg) were injected into the thymus gland of five juvenile pigs immunosuppressed with cyclosporine and deoxyspergualin, and the animals were subsequently made diabetic by the injection of streptozotocin. Insulin was administered subcutaneously, with one pig dying from hypoglycemia. The animal with the least number of ICCs transplanted was killed 81 days later, and the graft was analyzed histologically. Blood glucose levels and porcine C-peptide in the remaining animals were monitored for a median of 101 days. Histological analysis of the graft showed numerous epithelial cell clusters; the percentage of cells that contained insulin, glucagon, somatostatin, and pancreatic polypeptide were 61%, 64%, 25%, and 18%, respectively. Some cells contained more than one hormone. Porcine C-peptide was detected from 21 days after induction of diabetes but not before. In the pig receiving the most ICCs, blood glucose levels were lowered to nondiabetic levels 109 days after transplantation. Plasma C-peptide levels in response to glucagon in this pig steadily increased after grafting; peak levels were 0, 0.21, 0.45, and 0.52 ng/ml at 4, 21, 49, and 80 days after induction of diabetes compared to 0.09 ng/ml in control diabetic pigs. The secretion of C-peptide in response to oral and intravenous glucose and arginine also was greater than in untransplanted diabetic pigs, the pattern of secretion being consistent with developing fetal beta cells as the source of the C-peptide. Pancreatic insulin content was 0.1 mU/mg, 4% of that in nondiabetic pigs, and the number of beta cells per islet was 3 to 6 compared to 90 in nondiabetic controls. ICCs will differentiate and function for up to 111 days when transplanted into outbred immunosuppressed pigs rendered diabetic. Blood glucose levels can be lowered to nondiabetic levels when sufficient numbers of ICCs are grafted.

Zinc supplementation improves glucose disposal in patients with cirrhosis

Zinc deficiency is common in cirrhosis, and was proved to affect nitrogen metabolism. In experimental animals, zinc status may also affect glucose disposal, and acute zinc supplementation improves glucose tolerance in healthy subjects. This study was aimed at measuring the effects of long-term oral zinc supplements on glucose tolerance in cirrhosis. The time courses of glucose, insulin, and C-peptide in response to an intravenous (IV) glucose load were analyzed by the minimal-model technique before and after long-term oral zinc supplements (200 mg three times per day for 60 days) in 10 subjects with advanced cirrhosis and impaired glucose tolerance or diabetes. The test was performed using a simplified procedure, based on 20 blood samples collected within 4 hours from the glucose load. Normal values were obtained in 25 age-matched healthy subjects. Zinc levels were low to normal or reduced before treatment, and were normalized by oral zinc. Glucose disappearance improved by greater than 30% in response to treatment. There were no changes in pancreatic insulin secretion and systemic delivery, or in the hepatic extraction of insulin. Insulin sensitivity (S I), which was reduced by 80% before treatment, did not change. Glucose effectiveness (S G) was nearly halved in cirrhosis before treatment (0.013 [SD 0.007] min −1 v. 0.028 [SD 0.009] in controls; P < .001), and increased to 0.017 (SD 0.009) after zinc ( P < .05 v. baseline). The return to normal of plasma zinc levels after long-term zinc treatment in advanced cirrhosis improves glucose tolerance via an increase of the effects of glucose per se on glucose metabolism. Poor zinc status may contribute to the impaired glucose tolerance and diabetes of cirrhosis.

Minidiab test to assess the function of pancreatic beta-cells in the children of diabetics

The levels of glucose, insulin, and C-peptide in the blood serum were measured in 38 subjects with normal and impaired glucose tolerance whose parents suffered from insulin-dependent and noninsulin-dependent diabetes mellitus (IDDM and NIDDM, respectively) and in 12 normal subjects without hereditary aggravation for diabetes mellitus in order to specify the peculiarities of development of diabetes mellitus of various types. Reliably increased levels of glucose, insulin, and C-peptide on an empty stomach and absence of adequate secretion of insulin and C-peptide in response to stimulation with 5 mg of minidiab, expressed by a later and less manifest release of insulin and C-peptide, were observed in the test group, in contrast to healthy controls. The detected changes augment with the progress of carbohydrate metabolism disorders, being more marked in the subjects whose parents suffered from IDDM. The findings permit a conclusion that function of the insular system is changed during early disorders of carbohydrate metabolism in subjects whose parents suffered from both forms of diabetes mellitus. Minidiab test is recommended to specify the function of the pancreatic insular system.

The beta cell glucose stimulus-response curve in normal humans assessed by insulin and C-peptide secretion rates

Insulin and C-peptide secretion rates have been measured and compared in 12 nondiabetic subjects to characterize the glucose stimulus-response of B cell secretion in man. On three different days, glucose concentrations were clamped for 150 minutes at 7.5, 10, and 15 mmol/L, respectively. Plasma samples taken during the clamps were assayed for C-peptide and insulin. C-peptide secretion rates were estimated by the technique of deconvolution. Model-based estimation of insulin secretion rates from insulin concentrations yielded concordant results. In response to glucose, C-peptide concentrations rose less quickly than did insulin concentrations, but the estimated first- and second-phase secretion rates were similar when assessed from either the C-peptide or insulin concentrations. First-phase secretion peaks were larger than inspection of the plasma concentration data might suggest, with median values of 1.3, 2.0, and 2.9 nmol/min for C-peptide in response to 7.5, 10, and 15 mmol/L glucose clamp levels, respectively. The second-phase reached steady state by 90 to 120 minutes, with median C-peptide secretion rates of 0.31, 0.56, and 0.85 nmol/min after 120 minutes at 7.5, 10, and 15 mmol/L, respectively. The slopes of the curves of steady-state insulin and C-peptide secretion rates v the four glucose levels (basal plus the three clamp levels) were maximally steep between 7.5 and 10 mmol/L in the majority of subjects, consistent with in vitro sigmoidal responses. A characterization of the secretory response of the B cell of normal humans at different glucose concentrations has been obtained. With appropriate models, insulin secretion rates may be estimated from either plasma insulin or C-peptide concentration data.