Residual B-cell function and glycaemic control in diabetic pregnancy

Serum C-peptide immunoreactivity (CPR), mean blood glucose and blood glycosylated haemoglobin Hb A1c were measured in 23 insulin-dependent diabetic women at 11-12, 23-24, 33-34 and 37-38 gestational weeks in order to elucidate changes in residual B-cell function during pregnancy and their influence on the glycaemic control. CPR values generally increased at the 23-33 gestational weeks, with a significant difference between the mean of the peak values and the mean of the values at the first admission. When the subjects were divided into two groups on the basis of the residual B-cell function at the first admission, the glycaemic control during pregnancy was significantly better in those with higher residual B-cell activity. The overall prevalence of marked residual B-cell activity was higher than previously reported in non-pregnant insulin-dependent diabetic subjects. The results indicate clinically important enhancement in residual B-cell function during pregnancy. The mechanism of this improvement is poorly known although the more strict management of diabetes during gestation may be an important factor.     

Influence of B-cell impairment on pancreatic acini in NOD mice and streptozotocin-induced diabetic rats

Exocrine pancreatic function insufficiency, even of short duration, has been reported in juvenile-onset insulin dependent diabetic patients. To evaluate the status of pancreatic acini under decreased B-cell function, tissue insulin, amylase, chymotrypsinogen and trypsinogen in the pancreas were measured in streptozotocin-induced diabetic rats and non-obese diabetic mice in various conditions. In streptozotocin diabetic rats, a dissociation of three enzyme contents was demonstrated in the condition with discontinuation of insulin injection, i.e., a marked decrease in amylase, a significant increase in chymotrypsinogen, but no significant change in trypsinogen. This dissociation was markedly improved in the insulin-treated condition. In non-obese diabetic mice, these enzyme contents were not significantly changed although severe insulitis together with the marked decrease in insulin content was observed. These data show that the cessation of B-cell function alone does not cause insufficiency of exocrine pancreas.     

Allogeneic segmental pancreas transplantation in diabetic dogs with and without occlusion of the pancreatic duct

Currently the rate of complications in segmental pancreas transplantation is very high. Reasons for this come from technical failures and from the site of immunology. To prove the cause of technical complications, several methods were used for the allogeneic segmental pancreas transplantation in diabetic dogs. To influence the exocrine pancreas secretion in grafts, we applied the intraductal injection of Ethibloc and Neoprene and the intraperitoneal drainage. By all these approaches it was possible to ameliorate an experimental diabetes in the recipients. Clearly better results were achieved in the Ethibloc-injected and open-duct grafts. The longest function time was about 6 months. Main complications, especially in the Neoprene-injected group, were venous thrombosis, pancreatitis and graft rejection.     

Short- and long-term effects of dimethyl sulfoxide on mouse pancreatic islet B-cell function in vitro

Dimethylsulfoxide has been used as a cryoprotectant for the endocrine pancreas. To explore possible harmful effects of Me₂SO influenced neither glucose-stimulated insulin release, nor islet glucose oxidation. On the other hand, 1 M but not 0.25 M Me₂SO decreased glucose-stimulated (pro)insulin and total protein biosynthesis in acute experiments. In islet culture experiments with Me₂SO-supplemented culture media there was no obvious effects on glucose-stimulated (pro)insulin biosynthesis. It is suggested that Me₂SO in the range 0.01–0.5 M does not affect islet B-cell function in vitro.     

The glucose tolerance, insulin response and pancreatic exocrine function in patients after acute pancreatitis

In 25 patients having a history of acute pancreatitis (AP) in anamnesis one year ago and in 12 control subjects the insulin response to oral glucose was investigated and in some cases the exocrine function of pancreas was evaluated. The disturbances in glucose tolerance occurred in about 30% of the patients and were associated with impairment of insulin response and deterioration of exocrine pancreatic function. The double cortisone and glucose load did not influence the glucose tolerance in the patients. In persons investigated during AP and one year later only slight improvement of insulin response was noted. The results support the significance of follow-up studies of carbohydrate tolerance and insulin response in patients after AP for the evaluation of the diabetic risk in such cases.     

Transamination of 3-phenylpyruvate in pancreatic B-cell mitochondria

High aminotransferase activities catalyzing the reaction between L-glutamate and the aromatic ketomonocarboxylic acid, 3-phenylpyruvate, were observed in the mitochondria from pancreatic B-cells. At very low concentrations of 3-phenylpyruvate, L-glutamine was an effective amino group donor. The aminotransferase activities for the aliphatic ketomonocarboxylic acids, pyruvate and 2-ketoisovalerate, were lower in B-cell mitochondria. High rates of transamination of 2-ketoisocaproate with L-glutamine were observed and may be an important prerequisite for the insulin secretory potency of this 2-keto acid. Since B-cell mitochondria are well supplied with L-glutamine and L-glutamate, 3-phenylpyruvate-induced 2-ketoglutarate production may explain the insulin secretory potency of 3-phenylpyruvate which is not a fuel for pancreatic islet cells.     

Observations on the morphology of pancreatic secretory capillaries

Summary The fine morphology of, and the light microscopic distribution of ATPase in, pancreatic secretory capillaries suggest that they may be absorptive channels receiving material from the general blood circulation rather than secretory channels communicating with the duct system. This assumption is based upon many observations; 1. The pattern of microvilli of their wall differs from that of acinar lumen. 2. The material retained by them in ultrathin sections differs from that retained by acinar lumen. 3. They ramify, basally, to the level of Golgi region. 4. The lack of release of zymogen droplets in them. 5. Their points of origin from acinar lumen are controlled by zonulae occludentes. 6. Gulf-like extensions from the basal surface of acinar cell communicate with them. 7. Fenestrated blood capillaries run in their vicinity. 8. Blood capillaries and acinar cells share a joint basement lamina. 9. Light microscopically, ATPase activity is associated with their wall and not with the basal acinar cell surface.Publication No. 932 of the Division of Basic Health Sciences of Emory University; which was supported by the McCandless Research Funds and the School of Dentistry Fellowship Funds, of Emory University. The technical assistance of Miss Brenda Callahan, Mr. Peter Daly and Mr. Hugo Greiner is acknowledged. The use of the facilities of Dr. Wallace G. Campbell Jr. is appreciated.     

Thiazolidinediones improve beta-cell function in type 2 diabetic patients

Thiazolidinediones (TZDs) improve glycemic control and insulin sensitivity in patients with type 2 diabetes mellitus (T2DM). There is growing evidence from in vivo and in vitro studies that TZDs improve pancreatic beta-cell function. The aim of this study was to determine whether TZD-induced improvement in glycemic control is associated with improved beta-cell function. We studied 11 normal glucose-tolerant and 53 T2DM subjects [age 53+/-2 yr; BMI 29.4+/-0.8 kg/m2; fasting plasma glucose (FPG) 10.3+/-0.4 mM; Hb A1c 8.2+/-0.3%]. Diabetic patients were randomized to receive placebo or TZD for 4 mo. Subjects received 1) 2-h OGTT with determination of plasma glucose, insulin, and C-peptide concentrations and 2) two-step euglycemic insulin (40 and 160 mU.m-2.min-1) clamp with [3-(3)H]glucose. T2DM patients were then randomized to receive 4 mo of treatment with pioglitazone (45 mg/day), rosiglitazone (8 mg/day), or placebo. Pioglitazone and rosiglitazone similarly improved FPG, mean plasma glucose during OGTT, Hb A1c, and insulin-mediated total body glucose disposal (Rd) and decreased mean plasma FFA during OGTT (all P<0.01, ANOVA). The insulin secretion/insulin resistance (disposition) index [DeltaISR(AUC)/Deltaglucose(AUC)/IR] was significantly improved in all TZD-treated groups: +1.8+/-0.7 (PIO+drug-na?ve diabetics), +0.7+/-0.3 (PIO+sulfonylurea-treated diabetics), and 0.7+/-0.2 (ROSI+sulfonylurea-withdrawn diabetics) vs. -0.2+/-0.3 in the two placebo groups (P<0.01, all TZDs vs. placebo, ANOVA). Improved insulin secretion correlated positively with increased body weight, fat mass, and Rd and inversely with decreased plasma glucose and FFA during the OGTT. In T2DM patients, TZD treatment leads to improved beta-cell function, which correlates strongly with improved glycemic control.     

Protective effects of probucol treatment on pancreatic beta-cell function of SZ-induced diabetic APA hamsters.

To clarify whether oxidative stress is involved in the pathogenesis of islet lesions of diabetic animals, the effects of probucol (PB), an antioxidant and anti-hyperlipidemia agent, on the islets in streptozotocin (SZ)-induced diabetic APA hamsters in the acute and chronic phases of diabetes were examined. The control (CB group) and diabetic (SZ group) hamsters were treated with PB (1% in the diet) for 4 weeks from several days after SZ injection as the acute diabetic group, or 8 weeks from 6 weeks after SZ injection as the chronic diabetic group. Glucose tolerance test revealed that PB treatment decreased the high serum glucose level after glucose injection in the diabetic APA hamsters in the acute diabetic phase. Immunohistochemistry revealed that PB treatment significantly increased the percentage of the insulin positive area in the diabetic hamsters pancreata in both the acute and chronic phases. In addition, 4-hydroxy-2-nonenal (4HNE; an oxidative stress marker) positive cells were slightly reduced by PB treatment in the acute diabetic phase. Double-immunostaining for insulin and PCNA (proliferating cell nuclear antigen) revealed that elevation of the percentage of insulin and PCNA double-positive cells against insulin-positive cells was seen in the islets of PB-treated diabetic hamsters, but the difference was not significant compared with untreated diabetic hamsters (p = 0.07). In semi-quantitative RT-PCR, the expression of two genes, Reg (Regenerating gene) and INGAP (islet neogenesis associated protein), in the diabetic APA hamsters was significantly increased compared to the control groups in both diabetic phases. PB treatment significantly reduced Reg expression in the chronic diabetic phase. These data suggest that PB treatment in SZ-injected diabetic hamsters partially restored beta-cell function through acting as an antioxidant and induced higher expression of Reg and INGAP genes in the pancreas of hamsters.     

Silymarin induces recovery of pancreatic function after alloxan damage in rats

Alloxan has been widely used to produce experimental diabetes mellitus syndrome. This compound causes necrosis of pancreatic beta-cells and, as is well known, induces oxidant free radicals which play a relevant role in the etiology and pathogenesis of both experimental and human diabetes mellitus. Previously we have reported hypoglycemic and antilipoperoxidative actions of silymarin in serum and pancreatic tissue respectively. The aim of this study was to test whether silymarin could reduce the hyperglycemia and revert the pancreatic damage in alloxan treated rats, tested with silymarin in two protocols: using both compounds simultaneously for four or eight doses, or using the compound 20 days after alloxan administration for 9 weeks. Serum glucose and insulin were determined, and pancreatic fragments were used for histology and insulin immunohistochemistry. Pancreatic islets were isolated to assess insulin and Pdx1 mRNA expression by RT-PCR. Our results showed that 72 hours after alloxan administration, serum glucose increased and serum insulin decreased significantly, whereas pancreatic tissue presented morphological abnormalities such as islet shrinkage, necrotic areas, loss of cell organization, widespread lipoid deposits throughout the exocrine tissue, and loss of beta cells, but insulin and glucagon immunoreactivity was scattered if any. In contrast the pancreatic tissue and both insulin and glucose serum levels of rats treated with silymarin were similar to those of control animals. In addition, insulin and glucagon immunoreactive cells patterns in Langerhans islets were also normal, and normal insulin and Pdx1 mRNA expression patterns were detected during pancreatic recovery in Langerhans islets. The overall results suggest that silymarin induces pancreatic function recovery demonstrated by insulin and glucagon expression protein and normoglycemia after alloxan pancreatic damage in rats.     

Magnesium uptake by pancreatic islet cells is modulated by stimulators and inhibitors of the B-cell function

28Mg2+ uptake by rat islets was measured during incubation with various stimulators or inhibitors of insulin release. D-Glucose induced a dose-dependent increase in 28Mg2+ uptake after 10 min or 120 min. The threshold concentration was around 6 mM and the maximum effect was observed with 15-20 mM glucose. After 120 min 28Mg2+ uptake was also stimulated by the metabolized sugars mannose, N-acetylglucosamine or glyceraldehyde, was unaffected by the non-metabolized or poorly metabolized L-glucose, galactose, 3-O-methylglucose, 2-deoxyglucose, fructose or mannoheptulose and was inhibited by glucosamine. The effect of glucose was markedly impaired by mannoheptulose, glucosamine, aminooxyacetate and NH4Cl, but was only partially decreased by D600 or diazoxide, which were ineffective in a glucose-free medium. Tolbutamide or KCl slightly increased 28Mg2+ uptake. Alanine, leucine alone or with glutamine, and ketoisocaproate also stimulated 28Mg2+ uptake, whereas arginine and lysine decreased it. These changes in 28Mg2+ uptake, brought about by various modifiers of the B-cell function, are thus similar but not identical to the changes in Ca2+ uptake, and are not the consequence of insulin release. The stimulatory effect of glucose requires glucose metabolism by islet cells, but is only partially due to depolarization of the B-cell membrane.