Insulin Secretion In Diabetes Mellitus Research Articles

Serum C-peptide assay of patients with hyperglycemic emergencies at the Lagos State University Teaching Hospital (LASUTH), Ikeja.

IntroductionHE are common acute complications of diabetes mellitus (DM) and include diabetic ketoacidosis (DKA), normo-osmolar hyperglycemic state (NHS) and hyperosmolar hyperglycemic state (HHS). They contribute a lot to the mortality and morbidity of DM. The clinical features include dehydration, hyperglycemia, altered mental status and ketosis. The basic mechanism of HE is a reduction in the net effective action of circulating insulin, resulting in hyperglycemia and ketonemia (in DKA) causing osmotic diuresis and electrolytes loss. Infection is a common precipitating factor.Measurement of serum C-peptide provides an accurate assessment of residual β-cell function and is a marker of insulin secretion in DM patients.Aim and objectivesTo assess the level of pancreatic beta cell function in HE patients, using the serum C-peptide.MethodologyThe biodata and clinical characteristics of the 99 subjects were collated using a questionnaire. All subjects had their serum C-peptide, glucose, electrolytes, urea, creatinine levels, urine ketones determined at admission. Results of statistical analysis were expressed as mean ± standard deviation (SD). A p value <0.05 was regarded statistically significant. Correlation between levels of serum C-peptide and admission blood glucose levels and the duration of DM respectively was done.ResultsThe mean age of the subjects was 51 (SD ± 16) years and comparable in both sexes. Mean duration of DM was 6.3 (SD ± 7.1) years, with 35% newly diagnosed at admission.The types of HE in this study are: DKA (24.7%), NHS (36.1%), and HHS (39.2%). Mean blood glucose in this study was 685 mg/dL, significantly highest in HHS and lowest in NHS. Mean serum C-peptide level was 1.6 ng/dL. It was 0.9 ng/dL in subjects with DKA and NHS while 2.7 ng/dL in HHS (p>0.05).Main precipitating factors were poor drug compliance, new-onset of DM and infection.ConclusionMost (70%) of subjects had poor pancreatic beta cell function, this may be a contributory factor to developing HE. Most subjects with high C-peptide levels had HHS.Electronic supplementary materialThe online version of this article (doi:10.1186/1755-7682-7-50) contains supplementary material, which is available to authorized users.

Localization of multidomain adaptor proteins, p140Cap and vinexin, in the pancreatic islet of a spontaneous diabetes mellitus model, Otsuka Long-Evans Tokushima Fatty rats

We have shown that two multidomain adaptor proteins, p140Cap and vinexin, interact with each other and are likely to be involved in neurotransmitter release. Because the basic molecular mechanism governing neurotransmitter and insulin secretion is conserved, these two proteins may also to play pivotal roles in insulin secretion. We therefore performed some characterization of p140Cap and vinexin in pancreas of a wild-type rat or a spontaneous type 2 diabetes mellitus (DM) model, the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. These two proteins were detected in Wistar rat pancreas by Western blotting. Immunohistochemistry revealed that p140Cap and vinexin are enriched in β and α cells, respectively, in the rat pancreas. We then found that pancreatic islet structure was disorganized in the OLETF rat with hyperinsulinemia or with hyperglycemia, based on immunohistochemical analyses of vinexin. In β cells of these model rats, p140Cap was distributed in a cytoplasmic granular pattern as in the control rats, although its expression was reduced to various extents from cell to cell. These results may suggest possible involvement of p140Cap in insulin secretion, and reduction of p140Cap might be related to abnormal insulin secretion in DM.

Non-Invasive Imaging of Ferucarbotran Labeled INS-1E Cells and Rodent Islets in Vitro and in Transplanted Diabetic Rats

Transplantation of pancreatic islets is a promising strategy for restoring insulin secretion in diabetes mellitus. To monitor transplanted islets, a method to evaluate the distribution in a non-invasive manner in vivo is needed. INS-1E, a stable differentiated insulin secreting cell line, and rodent islets were used to monitor cell transplantation by MRI. For labeling INS-1E cells in vitro, increasing concentrations of Resovist in culture medium were tested. For MR imaging in a clinical 3T scanner, we placed a layer of labeled INS-1E cells between two layers of 4% gelatin. Viability assay was performed. Cell function was evaluated by static incubation assay to assess insulin secretion. For in vivo imaging, iron labeled rodent islets were transplanted into the liver of streptozotocin induced diabetic rats and visualized by MRI. Blood sugar values were controlled and liver tissue was removed for histological analysis. SPIO labeled INS-1E cells did not show altered viability or reduced glucose stimulated insulin secretion in vitro. Double staining of labeled and unlabeled INS-1E cells showed no difference in the staining pattern. Labeling of rodent islets with SPIOs does not reduce their secretory activity or alter their viability. We visualized SPIO-labeled INS-1E cells and rat islets in vitro using a clinical 3T scanner. Diabetic rats transplanted with SPIO-labeled islets became normoglycemic. MR imaging successfully verified the distribution of labeled transplanted cells in vivo. Labeling INS-1E cells and rat islets with SPIOs does not alter their viability, while enabling MR imaging of labeled cells in vitro and within the living organism.

Noncoding miRNAs as key controllers of pancreatic β-cell functions

miRNAs, a recently discovered family of small noncoding RNAs, are emerging as major controllers of gene expression and key determinants of pancreatic β-cell function. These 19–22-nucleotide molecules govern gene expression by partially pairing to 3´-untranslated regions of target mRNAs and by inhibiting their translation. The elucidation of the role of miRNAs promises to unravel new aspects of β-cell biology and to clarify the mechanisms leading to defective insulin secretion in diabetes mellitus. This information is expected to favor the design of new approaches for preserving functional β-cells in prediabetic stages and the development of strategies for engineering insulin-secreting cells capable of replacing endogenous β-cells in diabetic patients.

Ascorbic acid recycling by cultured β cells: effects of increased glucose metabolism

Ascorbic acid is necessary for optimal insulin secretion from pancreatic islets. We evaluated ascorbate recycling and whether it is impaired by increased glucose metabolism in the rat β-cell line INS-1. INS-1 cells, engineered with the potential for overexpression of glucokinase under the control of a tetracycline-inducible gene expression system, took up and reduced dehydroascorbic acid to ascorbate in a concentration-dependent manner that was optimal in the presence of physiologic d-glucose concentrations. Ascorbate uptake did not affect intracellular GSH concentrations. Whereas depletion of GSH in culture to levels about 25% of normal also did not affect the ability of the cells to reduce dehydroascorbic acid, more severe acute GSH depletion to less than 10% of normal levels did impair dehydroascorbic acid reduction. Culture of inducible cells in 11.8 mM d-glucose and doxycycline for 48 h enhanced glucokinase activity, increased glucose utilization, abolished d-glucose-dependent insulin secretion, and increased generation of reactive oxygen species. The latter may have contributed to subsequent decreases in the ability of the cells both to maintain intracellular ascorbate and to recycle it from dehydroascorbic acid. Cultured β cells have a high capacity to recycle ascorbate, but this is sensitive to oxidant stress generated by increased glucose metabolism due to culture in high glucose concentrations and increased glucokinase expression. Impaired ascorbate recycling as a result of increased glucose metabolism may have implications for the role of ascorbate in insulin secretion in diabetes mellitus and may partially explain glucose toxicity in β cells.

Membrane phospholipid turnover as an intermediary step in insulin secretion: Putative roles of phospholipases in cell signaling

One or more phospholipases of the C and A 2 types exist in rodent islets and may play a pivotal role in the cell signaling cascade culminating in exocytotic insulin release. Phospholipase C generates myo-inositol-1,4,5-trisphosphate, which mobilizes a “pool” of calcium in the endoplasmic reticulum and which may also secondarily facilitate calcium (Ca ++) influx from the extracellular space to replenish that pool. Diacylglycerol is also generated by phospholipase C action and activates protein kinase C; it may thereby potentiate the cellular response to elevations in cytosolic free Ca ++ concentration. Arachidonic acid may be released during the degradation of diacylglycerol and may also contribute to islet activation. Phospholipase C is activated by glucose, cholinergic agonists, and probably by Ca ++ fluxes. Phospholipase A 2 action generates arachidonic acid and lysophospholipids. Certain lysophospholipids mobilize cellular Ca ++, at least in part from superficial, plasmalemmal stores. Native (unoxygenated) arachidonic acid also has the capability of mobilizing cellular Ca ++ from membrane-bound stores; it may, in addition, activate protein kinase C, as suggested by recent indirect studies. The further metabolism of arachidonic acid via lipoxygenase and cyclo-oxygenase appears to provide positive and negative modulation, respectively, of stimulated insulin secretion. Many pieces of the puzzle remain, however, to be supplied. For example, it has not yet been unequivocally demonstrated that phospholipase A 2 is activated by physiologic stimuli in intact islets. Furthermore, the absence of truly specific pharmacologic stimulators or inhibitors of these processes currently precludes precise delineation of the respective physiologic roles of each potential mediator in stimulus-secretion coupling. When such roles are elucidated, it can be asked whether the defects in insulin secretion in diabetes mellitus may be due in part to abnormalities in the turnover of beta-cell membrane phospholipids and the generation of intracellular lipid-derived signals.

Beta-endorphin infusion restores acute insulin responses to glucose in type-2 diabetes mellitus.

To address the possibility that an abnormality in pancreatic beta-endorphin activity might contribute to abnormal insulin secretion in diabetes mellitus, we studied the effects of beta-endorphin infusion on islet function in diabetic patients. The iv infusion of human beta-endorphin at a dose of 0.5 mg/h for 2 h in type-2 non-insulin-dependent diabetic patients (n = 12) raised plasma insulin and glucagon levels and slightly but significantly lowered plasma glucose concentrations. beta-Endorphin infusion also resulted in reappearance of a clear-cut acute insulin response to glucose, while second phase insulin release was increased and glucose disposal accelerated. Acute insulin and glucagon responses to arginine were not increased by beta-endorphin, suggesting that the effect of the opioid on the B cells of the diabetic patients is specific for glucose. An intraislet abnormality of opioid peptides action and/or secretion may play a role in the disturbances of insulin secretion in patients with type-2 diabetes mellitus.

Insulin as a Growth Factor

Insulin is a potent mitogen for many cell types in vitro. During tissue culture, supraphysiological concentrations of insulin are necessary to promote cell replication in connective or musculoskeletal tissues. Insulin promotes the growth of these cells by binding, with low affinity, to the type I insulin-like growth factor (IGF) receptor, not through the high affinity insulin receptor. In other cell types, such as hepatocytes, embryonal carcinoma cells, or mammary tumor cells, the type I IGF receptor is virtually absent, and insulin stimulates the growth of these cells at physiological concentrations by binding to the high affinity insulin receptor. Both receptor systems activate phosphorylation reactions within the cell which extend to ribosomal proteins. Insulin acts synergistically with other factors, such as platelet-derived growth factor and epidermal growth factor, to stimulate the progression of cells through the cycle of proliferation. Abnormal insulin secretion or action, before or after birth, often is associated with disordered growth suggesting that insulin may function as a growth factor in vivo. Poor growth follows impaired insulin secretion in diabetes mellitus. This is associated with reduced circulating levels of IGF's which may be partly responsible for the growth failure. Insulin has a direct action on release of IGF's from the liver in vitro, but during experimental diabetes there is a reduced number of hepatic somatotropic receptors which could limit the ability of growth hormone to regulate IGF release. Diabetic children, treated conventionally, have normal circulating IGF levels, but both growth rate and serum IGF concentration may increase dramatically when diabetic control is optimized.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of labour in pregnant diabetics using vaginal prostaglandin E2pessaries

SummaryProstaglandin E2 pessaries for the induction of labour are being used more in ‘high-risk' cases and may have advantages for the diabetic patient. Prostaglandin E2 is known to cause decreased glucose-induced insulin secretion in diabetes mellitus. We did not detect adverse effects of clinical importance in a preliminary study of diabetic patients using prostaglandin E2 vaginal pessaries before induction of labour.

A role for alpha-adrenergic receptors in abnormal insulin secretion in diabetes mellitus.

To determine whether endogenous alpha-adrenergic activity contributes to abnormal insulin secretion in nonketotic, hyperglycemic, diabetic patients, alpha-adrenergic blockade was produced in normal and diabetic subjects. The diabetics had a significantly (P less than 0.01) greater increase in circulating insulin 1 h after an intravenous phentolamine infusion than did the normal subjects. During the phentolamine infusion, there was also a significant augmentation of acute insulin responses to intravenous glucose (20 g) pulses in normal subjects (P less than 0.05) and diabetics (P less than 0.02); this augmentation was fivefold greater in the diabetics. Simultaneous treatment with the beta-adrenergic blocking agent, propranolol, did not alter these findings. Thus a role for exaggerated endogenous alpha-adrenergic activity in abnormal insulin secretion of the diabetic subjects is suggested. To determine whether this alpha-adrenergic activity might be related to elevated circulating catecholamines, total plasma-catecholamine levels were compared in normal and nonketotic diabetic subjects given intravenous glucose pulses. These levels were significantly greater (P less than 0.02) in the diabetic compared to the normal group before the glucose pulse, and increased significantly in both groups (P less than 0.02 and less than 0.001, respectively) after the pulse. These data suggest that excessive catecholamine secretion may lead to an abnormal degree of endogenous alpha-adrenergic activity, which contributes to defective insulin secretion in diabetic subjects.

The glucose receptor. A defective mechanism in diabetes mellitus distinct from the beta adrenergic receptor.

Acute serum insulin responses in 10 normal subjects after rapid intravenous injection of glucose (5 g) or isoproterenol (2 mug) were of similar magnitude and timing (glucose: 431+/-349%; mean Delta3-5' insulin (IRI)+/-SD, per cent basal and isoproterenol: 359+/-216%; mean Delta2-4' IRI+/-SD, per cent basal). To elucidate the relationship of glucose-induced insulin secretion to pancreatic beta adrenergic receptors and the implications of this relationship with regards to abnormal insulin secretion in diabetes mellitus, two questions were studied. (a) To determine whether glucose-induced insulin secretion is dependent upon beta adrenergic activity, the effect of beta adrenergic blockade with intravenous propranolol (0.08 mg/min) upon acute insulin responses to isoproterenol and glucose were compared in normal subjects. (b) To determine whether acute insulin responses to beta adrenergic stimulation were intact in diabetes mellitus, the effect of isoproterenol upon serum insulin levels was studied in diabetic subjects. Beta adrenergic blockade in the normal subjects obliterated acute insulin responses to isoproterenol (before: 361+/-270%, during: - 31+/-15%; n = 6, P < 0.001) but did not significantly affect responses to glucose (before; 311+/-270%; during: 284+/-206%; n = 5). The mean acute insulin response after isoproterenol in the diabetic group was significantly elevated over basal levels (152+/-74%; n = 10, P < 0.001) but the response after glucose was not (- 11+/-11%). These data suggest that insulin responses to glucose in normal subjects are mediated by specific pancreatic glucose receptors which are independent from beta adrenergic receptors and that abnormal glucose-induced insulin secretion in diabetics is due to defects within glucose receptors and not beta adrenergic receptors as has been previously hypothesized.

Early phase of insulin release.

The early phase of insulin release in the first five minutes after intravenous administration of glucose, glucagon, and glucose-plus-glucagon was investigated systematically in various clinical conditions. In normal subjects there is an immediate release of insulin after glucose, glucagon, and glucose-plus-glucagon infusions. The latter combination produced the highest insulin levels. Of a group of nonobese subjects with diabetic heritage, some had impaired early release of insulin, but0 their mean response did not differ significantly from the normal group. Investigation of nonobese potential diabetics (offspring of two diabetic parents) revealed that as a group average they had decreased insulin levels during the early phase of insulin release, even though intravenous glucose tolerance was normal. Four of ten subjects had a normal response. Nonobese, noninsulin-dependent diabetics had no insulin response to infused glucose, but when glucagon was added to glucose a significant and rapid insulin discharge was observed. However, the magnitude of this response was about half that seen in normal subjects after glucose-plusglucagon. Finally, the early phase of insulin release was studied in obese nondiabetic subjects who demonstrated an exaggerated insulin release to each stimulus. Again, glucose-plusglucagon was the most potent stimulator of insulin release. It is postulated that impairment in the early phase of insulin release may be the first detectable abnormality of insulin secretion in diabetes mellitus and that glucagon has the capability of restoring this toward normal.