The effect of glucagon-like peptide-1 in the management of diabetes mellitus: cellular and molecular mechanisms.

Incretins, such as glucagon-like peptide-1 (GLP)-1, have been shown to elevate plasma insulin concentration. The purpose of this study is to investigate the cellular and molecular basis of the beneficial effects of GLP-1. Normal and diabetic male Wistar rats were treated with GLP-1 (50 ng/kg body weight) for 10 weeks. At the end of the experiment, pancreatic tissues were taken for immunohistochemistry, immunoelectron microscopy and real-time polymerase chain reaction studies. Samples of blood were retrieved from the animals for the measurement of enzymes and insulin. The results show that treatment of diabetic rats with GLP-1 caused significant (P < 0.05) reduction in body weight gain and blood glucose level. GLP-1 (10(-12)-10(-6) M) induced significant (P < 0.01) dose-dependent increases in insulin release from the pancreas of normal and diabetic rats compared to basal. Diabetes-induced abnormal liver (aspartate aminotransferase and alanine aminotransferase) and kidney (blood urea nitrogen and uric acid) parameters were corrected in GLP-1-treated rats compared to controls. GLP-1 treatment induced significant (P < 0.05) elevation in the expression of pancreatic duodenal homeobox-1, heat shock protein-70, glutathione peroxidase, insulin receptor and GLP-1-receptor genes in diabetic animals compared to controls. GLP-1 is present in pancreatic beta cells and significantly (P < 0.05) increased the number of insulin-, glutathione reductase- and catalase-immunoreactive islet cells. The results of this study show that GLP-1 is co-localized with insulin and seems to exert its beneficial effects by increasing cellular concentrations of endogenous antioxidant genes and other genes involved in the maintenance of pancreatic beta cell structure and function.

Pattern of distribution of calcitonin gene-related Peptide in the dorsal root ganglion of animal models of diabetes mellitus.

This article examined the pattern of distribution of calcitonin gene-related peptide (CGRP) in the dorsal root ganglion (DRG) of normal and diabetic Wistar, Zucker lean, and Goto-Kakizaki (GK) rats to determine whether there are changes in the number and pattern of distribution of CGRP-positive neurons after the onset of latent or overt diabetes. Type 1 diabetes mellitus was induced in Wistar rats by a single dose of streptozotocin (STZ) given intraperitoneally (60 mg/kg body weight). Four weeks after the induction of diabetes mellitus, diabetic (n = 6) and normal (n = 6), Zucker lean (n = 6), and GK (n = 6) rats were anesthetized with chloral hydrate and their DRGs were removed and processed for immunohistochemistry. CGRP-positive neurons were observed in the DRG of normal and diabetic Wistar, Zucker lean (nondiabetic), and GK (animal model of type 2 diabetes) rats. CGRP was present in small-, medium-, and large-sized neurons of the DRG in these three animal models. Only a small percentage of large-sized neurons contains CGRP. The number of CGRP-positive neurons was significantly (P < 0.05) reduced in STZ-induced diabetic Wistar and GK rats compared to normal Wistar and Zucker lean rats. Moreover, the quantity of CGRP-containing varicose nerves was less in diabetic Wistar and GK rats compared to control Wistar and Zucker lean rats. The reduced number of CGRP-positive neurons in the DRG of GK rats indicated that subjects with latent diabetes may already have dysfunctional CGRP metabolism and thus diabetic neuropathy.

The effect of a fat-enriched diet on the pattern of distribution of pancreatic islet cells in the C57BL/6J mice.

The C57BL/6J mice are inbred strains and develop the metabolic syndrome of obesity, hyperinsulinemia, hyperglycemia, and hypertension, when fed a high-fat diet. These features are similar to those observed in the human metabolic syndrome. This article examined the effect of fat-enriched (FE) diet on the pattern of distribution of insulin-, glucagon-, somatostatin-, and pancreatic polypeptide (PP)-positive cells in the pancreatic islets of C57BL/6J mice using immunohistochemical methods. Insulin-immunoreactive cells were observed in both the peripheral and central regions of the islets of Langerhans in both FE- and control diet-fed mice. The percentage distribution of insulin-positive cells was similar in FE (83.5 +/- 6.4) compared to control diet-fed C57BL/6J mice (83.8 +/- 6.5). Glucagon-containing cells were discerned in the periphery of pancreatic islets in both FE- and control diet-fed mice. The percentage distribution of glucagon was not statistically different in mice fed with FE (9.9 +/- 2.7) compared to control diet (11.3 +/- 4.9). Somatostatin-positive cells were seen in the outer part of the islet of Langerhans and constitute 12.1% (+/-6.3) and 10% (+/-5.5) of pancreatic islet cells in FE- and control diet-fed mice, respectively. PP-immunoreactive cells were observed in the peripheral region of the pancreatic islets of both FE- and control diet-fed mice. The percentage distribution of PP-positive cells was significantly (2.0 +/- 1.2) lower compared to control (5.1 +/- 2.4). In conclusion, the number of PP is significantly reduced in FE diet-fed mice and may play a role in the pathogenesis of diet-induced metabolic syndrome in C57BL/6J mice.

Diabetes-induced changes in the morphology and nociceptinergic innervation of the rat uterus.

The prevalence of diabetes mellitus (DM) is about 6% across the globe. This prevalence has been reported to increase in the near future. This means that the number of women with DM who would like to get pregnant and have children will also increase. The present study is aimed at investigating the morphological changes observed in the uterus after the onset of DM. The study also examined the pattern of distribution of nociceptin (NC), a neuropeptide involved in the regulation of pain, a major physiological factor during parturition. The study shows a severe atrophy of uteri as early as 15 days post DM and continued until the termination of the eight-week study. This atrophy was confirmed by light microscopy. Electron microscopy study showed atrophy of the columnar cells of the endometrium, reduced myofibril number and destruction of smooth muscle cells in the myometrium of diabetic rats compared to control. Immunofluorescence and immunoelectron microscopy studies clearly demonstrated the presence of NC in the endometrium, myometrium and on the myofibrils of the smooth muscles of both control and diabetic rat uteri. In addition, NC-positive neurons and varicose fibres were observed in the myometrium of both normal and diabetic rats. However, the expression of NC decreased after the onset of DM. Morphometric analysis showed that the number of NC-labeled cells was significantly (p < 0.05) lower in diabetic rat uteri compared to those of control. In conclusion, DM-induced uterine atrophy is associated with a decrease in the expression of NC in cells, neurons and myofibrils of the rat uterus.

Distribution of nociceptin in pancreatic islet cells of normal and diabetic rats.

OBJECTIVES: Nociceptin has been reported to play an important role in the regulation of pancreatic exocrine secretion. Most of the studies performed on nociceptin are mainly physiological rather than morphological in nature. The present study investigated the pattern of distribution of nociceptin in the endocrine pancreas of normal and diabetic rats. METHODS: Immunohistochemistry, immunofluorescence, Western blot, and double-labeled immunoelectron microscopy were used in this study. Diabetes was induced using streptozotocin (60 mg/kg body weight). RESULTS: Nociceptin-immunoreactive cells were observed in the central and peripheral regions of the islets of both normal and diabetic rat pancreas. The number of nociceptin-positive cells was significantly (P < 0.05) lower in the islet of diabetic rats compared with the control. Immunofluorescence study showed that nociceptin colocalizes with insulin in pancreatic ß-cells. The degree of colocalization of nociceptin with insulin was severely deranged after the onset of diabetes. Moreover, immunogold particles conjugated with either nociceptin or insulin were observed on the granules of pancreatic ß-cell. The number of nociceptin-labeled colloidal gold particles was significantly lower after the onset of diabetes. CONCLUSIONS: Nociceptin is present in pancreatic islets cells and colocalizes with insulin. Nociceptin may have a physiological role in the metabolism of insulin.

Mechanism of the beneficial and protective effects of exenatide in diabetic rats.

Glucagon-like peptide 1 (GLP1) agonists are promising therapeutic agents in the treatment of diabetes mellitus. This study examines the mechanism of the protective effects of exenatide in experimental diabetes, employing four groups of ten rats each, in which two groups were streptozotocin-induced diabetic and two were control groups. One control and one diabetic group were treated with exenatide (1 µg/kg body weight (BW)) for 10 weeks. Blood plasma was taken for biochemical analyses while pancreatic tissue was taken for immunofluorescence and immunoelectron microscopy studies and real-time PCR to examine the expression of genes. The results show that exenatide improved BW gain and reduced blood glucose in diabetic rats compared with controls. Similarly, exenatide enhanced insulin release from the pancreatic fragments and improved liver and kidney functions and lipid profile in diabetic rats compared with controls. Exenatide not only induced significant increases in serum insulin level but also elevated the number of insulin-, GLP1- and exenatide-positive cells compared with untreated controls. Exenatide also elevated the number of catalase- and glutathione reductase-positive cells in diabetic rat pancreas compared with controls. Exenatide caused significant elevation in the expressions of pancreatic duodenal homeobox-1, heat shock protein-70, glutathione peroxidase, insulin receptor and GLP1 receptor genes in the pancreas of both control and diabetic rats compared with untreated animals. The results have demonstrated that exenatide can exert its beneficial and protective effects by elevating the levels of endogenous antioxidants and genes responsible for the survival, regeneration and proliferation of pancreatic ß-cell.

Diabetes mellitus is associated with an increased expression of resistin in human pancreatic islet cells.

The pattern of distribution of resistin in the pancreas of diabetic patients was investigated to determine whether diabetes mellitus influences the expression of resistin. Pancreatic tissue samples retrieved, during pancreatectomy for pancreatic cancer, from cancer patients with and without type 2 diabetes were processed for immunohistochemistry. The pancreatic tissue samples were retrieved from non-cancerous and clear margins. An immunofluorescence technique was used to examine the expression of resistin and its co-localization with insulin and glucagon in pancreatic islet cells. Resistin was observed in many cells located in the central region of pancreatic islet. The expression of resistin increased significantly (p < 0.0001) in pancreatic islet cells of type 2 diabetic patients compared to control. Resistin co-localized with insulin but not glucagon in pancreatic islet cells of both normal and diabetic patients. However, the degree of co-localization was higher in pancreata of diabetic patients compared to normal. The number of human pancreatic islet cells expressing resistin increased significantly after the onset of type 2 diabetes. In conclusion, resistin may play a role in the regulation of pancreatic ß-cell function.

Effect of diabetes mellitus on acinar morphology, peroxidase concentration, and release in isolated rat lacrimal glands.

PURPOSE: This study investigated the effect of diabetes mellitus on lacrimal gland morphology and function. MATERIALS AND METHODS: The lacrimal glands of rats (n = 6) were removed 8 weeks after the onset of diabetes and processed for electron microscopy. The lacrimal gland of control rats (n = 6) were processed similarly. Lacrimal tissue samples of diabetic rats (n = 12) were also incubated with different concentrations (10(-6)-10(-3) M) of acetylcholine and noradrenaline to investigate secretagogue-induced peroxidase release. The lacrimal glands of control rats (n = 12) were treated in a similar manner. RESULTS: Diabetic rats and their lacrimal glands gained significantly (p < 0.05) less weight compared to age-matched controls. Lacrimal acinar cells of diabetic rat have significantly (p < 0.001) smaller and more homogenous secretory granules compared to age-matched control. Lacrimal glands of diabetic rats contained significantly (p < 0.05) less peroxidase and secrete significantly less quantity (p < 0.05) of the enzyme in response to either acetylcholine or noradrenaline challenge compared to control glands. CONCLUSIONS: The results indicate that diabetes is associated with lacrimal gland insufficiency as a result of abnormal acinar morphology and reduced peroxidase content and secretion.