DNA synthesis in pancreatic islet and acinar cells in rats with streptozotocin-induced diabetes.

The rates of DNA synthesis in islet and acinar cells were compared at different intervals following streptozotocin-induced diabetes. Streptozotocin, injected I.V. at a dosage of 65 mg/kg, consistently produced a diabetic-like state in young rats, ages 33 to 42 days. At two, four, and seven days after streptozotocin administration, no significant difference in DNA synthesis per mm2 of islet and acinar tissue was evident. However, four days after streptozotocin injection, a significant increase over control values was observed in the number of cells per islet incorporating tritiated thymidine. Following streptozotocin administration, beta cells generally appeared degranulated but not necrotic. Transformation of acinar cells or ductal elements to beta cells was not observed, suggesting that proliferating beta cells are the progeny of pre-existing beta cells. This study suggests that a brief, temporary period of compensatory proliferation of beta cells follows the initial insult of the diabetogenic agent streptozotocin in young rats.     

Recovery of function and mass of endogenous beta-cells in streptozotocin-induced diabetic rats treated with islet transplantation

We found that the hepatopancreas of oyster, Crassostrea virginica, contained a sialidase capable of releasing Neu5Gc from the novel polysialic acid chain (-->5-O(glycolyl)Neu5Gcalpha2-->)n more efficiently than from the conventional type of polysialic acid chains, (-->8Neu5Acalpha2-->)n, or (-->8Neu5Gcalpha2-->)n. We have partially purified this novel sialidase and compared its reactivity with that of microbial sialidases using four different sialic acid dimers, Neu5Gcalpha2-->5-O(glycolyl)Neu5Gc (Gg2), Neu5Acalpha2-->8Neu5Ac (A2), Neu5Gcalpha2-->8Neu5Gc (G2), and KDNalpha2-->8KDN (K2) as substrates. Hydrolysis was monitored by high performance anion-exchange chromatography with a CarboPac PA-100 column and pulsed amperometric detection, the method by which we can accurately quantitate both the substrate (sialiac acid dimers) and the product (sialic acid monomers). The oyster sialidase effectively hydrolyzed Gg2 and K2, whereas A2 and G2 were poor substrates. Neu5Ac2en but not KDN2en effectively inhibited the hydrolysis of Gg2 by the oyster sialidase. Likewise, the hydrolysis of K2 by the oyster sialidase was inhibited by a cognate inhibitor, KDN2en, but not by Neu5Ac2en. Using the new analytical method we found that Gg2 was hydrolyzed less efficiently than A2 but much more readily than G2 by Arthrobacter ureafaciens sialidase. This result was at variance with the previous report using the thiobarbituric acid method to detect the released free sialic acid [Kitazume, S., et al. (1994) Biochem. Biophys. Res. Commun. 205, 893-898]. In agreement with previous results, Gg2 was a poor substrate for Clostridium perfringens sialidase, while K2 was refractory to all microbial sialidases tested. Thus, the oyster sialidase is novel and distinct from microbial sialidases with regards to glycon- and linkage-specificity. This finding adds an example of the presence of diverse sialidases, in line with the diverse sialic acids and sialic acid linkages that exist in nature. The new sialidase should become useful for both structural and functional studies of sialoglycoconjugates.     

Imatinib mesylate (Gleevec) protects against streptozotocin-induced diabetes and islet cell death in vitro

The tyrosine kinase inhibitor imatinib mesylate (Gleevec) has been demonstrated to protect various cell types from death by inhibition of Abelson tyrosine kinase (c-Abl). The aim of the present study was to establish whether imatinib protects the insulin producing beta-cell from the different apoptosis promoting agents in vitro and whether imatinib counteracts streptozotocin-induced diabetes in NMRI mice. We observe that imatinib attenuated the actions of several different death promoting substances. In addition, mice injected with streptozotocin did not develop diabetes when given imatinib. The beneficial effects of imatinib may be related to inhibition of the pro-apoptotic MAP kinase JNK. We conclude that imatinib protects against beta-cell death and that this may contribute to the previously reported anti-diabetic actions of imatinib.     

IFN-gamma induces islet cell MHC antigens and enhances autoimmune, streptozotocin-induced diabetes in the mouse

To explore the role of the lymphokine, IFN-gamma, in the development of autoimmune-mediated insulin-dependent diabetes, we examined the effects of systemically administered IFN-gamma on the clinical features and pancreatic immunohistology of CBA mice made diabetic with multiple low doses of the pancreatic islet beta-cell toxin, streptozotocin. Mice given streptozotocin and IFN-gamma were significantly more hyperglycemic than those given streptozotocin alone and had significantly decreased body weight. Mice given IFN-gamma alone did not differ in glycemia or weight from vehicle-injected mice. On day 11, Ia proteins were detected on islet cells from mice given streptozotocin and their expression was potentiated by IFN-gamma; they could not be detected on islet cells from mice given IFN-gamma alone or vehicle. H-2K protein expression was increased on islet cells from mice given streptozotocin and was potentiated by IFN-gamma. IFN-gamma alone also increased H-2K protein expression on islet cells compared with vehicle-treated mice. These findings show that IFN-gamma enhances the severity of diabetes in mice given multiple-low doses of streptozotocin, in association with enhanced expression of Ia and H-2K proteins on islet cells. They indicate an important role for IFN-gamma in amplifying the autoimmune process leading to beta-cell destruction in diabetes. The ability of IFN-gamma to worsen autoimmune disease has implications for its use in man.     

Effects of pycnogenol treatment on oxidative stress in streptozotocin-induced diabetic rats

Free radicals and oxidative stress have been implicated in the etiology of diabetes and its complications. This in vivo study has examined whether subacute administration of pycnogenol, a French pine bark extract containing procyanidins that have strong antioxidant potential, alters biomarkers of oxidative stress in normal and diabetic rats. Diabetes was induced in female Sprague-Dawley rats by a single injection of streptozotocin (90 mg/kg body weight, ip), resulting (after 30 days) in subnormal body weight, increased serum glucose concentrations, and an increase in liver weight, liver/body weight ratios, total and glycated hemoglobin, and serum aspartate aminotransferase activity. Normal and diabetic rats were treated with pycnogenol (10 mg/kg body weight/day, ip) for 14 days. Pycnogenol treatment significantly reduced blood glucose concentrations in diabetic rats. Biochemical markers for oxidative stress were assessed in the liver, kidney, and heart. Elevated hepatic catalase activity in diabetic rats was restored to normal levels after pycnogenol treatment. Additionally, diabetic rats treated with pycnogenol had significantly elevated levels of reduced glutathione and glutathione redox enzyme activities. The results demonstrate that pycnogenol alters intracellular antioxidant defense mechanisms in streptozotocin-induced diabetic rats.     

Antihypertensive treatment in spontaneously hypertensive rats with streptozotocin-induced diabetes mellitus

Recent clinical reports have suggested that hypertension accelerates the progress of diabetic nephropathy and retinopathy, whereas antihypertensive treatments may retard them. Thus, the effect of antihypertensive treatment in diabetes mellitus with hypertension was evaluated in rats. A model of diabetes mellitus with hypertension has been developed in spontaneously hypertensive (SHR) rats by unilateral nephrectomy and streptozotocin (STZ, 30 mg/kg, i.v. treatment). The rats were treated with four antihypertensive drugs orally for 12 weeks thereafter. STZ treatment induced chronic hypeglycaemia (300-400 mg/dl), decreased body weight and heart rate, and caused vascular changes of ophthalmic fundi and cataracta. The kidney of these rats showed proliferative changes such as periarteritis nodosa, hyperplasia, or fibronecrosis of the arterioles, exudative changes, mesangial proliferation, or thickening of the basement membrane of the glomeruli. Enalapril (10 mg/kg per day) and remipril (Hoe 498) (1 mg/kg per day), converting enzyme inhibitors, or arotinolol (20 mg/kg per day), a beta-adrenoceptor blocking drug, decreased blood pressure, prevented the development of renal and ocular lesions, and tended to increase creatinine clearance. Nisoldipine (3 mg/kg per day), a calcium-entry blocking drug, tended to decrease blood glucose, and prevented the decrease of body weight and development of ocular lesions. In conclusion, antihypertensive treatments were effective in preventing the progress of diabetic retinopathy and nephropathy, and renal insufficiency in this animal model.     

Plasma glucose-lowering action of Hon-Chi in streptozotocin-induced diabetic rats.

Hon-Chi was used for anti-hyperglycemic activity screening in streptozotocin-induced diabetic rats (STZ-diabetic rats) in an attempt to develop new substances for handling diabetes. Mandarin Hon-Chi is red yeast rice fermented with Monascus pilous and Monascus purpureus. Single oral administration of Hon-Chi decreased plasma glucose in STZ-diabetic rats in a dose-dependent manner from 50 mg/kg to 350 mg/kg. Similar treatment with Hon-Chi also lowered the plasma glucose in normal rats as effectively as that produced in STZ-diabetic rats. In addition, oral administration of Hon-Chi at the highest dose (350 mg/kg) attenuated the elevation of plasma glucose induced by an intravenous glucose challenge test in normal rats. Moreover, mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) in liver from STZ-diabetic rats were reversed in a dose-dependent manner by the repeated oral treatment of Hon-Chi three times daily for two weeks. Otherwise, hyperphagia in STZ-diabetic rats was markedly reversed by similar repeated treatment of Hon-Chi. The obtained results suggest that oral administration of Hon-Chi could decrease hepatic gluconeogenesis to lower plasma glucose in diabetic rats lacking insulin.     

Plasma glucose-lowering effect of beta-endorphin in streptozotocin-induced diabetic rats.

The effect of beta-endorphin on plasma glucose levels was investigated in streptozotocin-induced diabetic rats (STZ-diabetic rats). A dose-dependent lowering of plasma glucose was observed in the fasting STZ-diabetic rat fifteen minutes after intravenous injection of beta-endorphin. The plasma glucose-lowering effect of beta-endorphin was abolished by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptors. Also, unlike wild-type diabetic mice, beta-endorphin failed to induce its plasma glucose-lowering effect in the opioid mu-receptor knock-out diabetic mice. In isolated soleus muscle, beta-endorphin enhanced the uptake of radioactive glucose in a concentration-dependent manner. Stimulatory effects of beta-endorphin on glycogen synthesis were also seen in hepatocytes isolated from STZ-diabetic rats. The blockade of these actions by naloxone and naloxonazine indicated the mediation of opioid mu-receptors. In the presence of U73312, the specific inhibitor of phospholipase C (PLC), the uptake of radioactive glucose into isolated soleus muscle induced by beta-endorphin was reduced in a concentration-dependent manner, but it was not affected by U73343, the negative control of U73312. Moreover, chelerythrine and GF 109203X diminished the stimulatory action of beta-endorphin on the uptake of radioactive glucose at a concentration sufficient to inhibit protein kinase C (PKC). The data obtained suggest that activating opioid mu-receptors by beta-endorphin may increase glucose utilization in peripheral tissues via the PLC-PKC pathway to lower plasma glucose in diabetic rats lacking insulin.     

microRNA deficiency in pancreatic islet cells exacerbates streptozotocin-induced murine autoimmune diabetes

Recent studies have demonstrated that gene expression is regulated not only by protein-coding genes, but also by non-protein-coding small RNA molecules, microRNAs (miRNAs). miRNAs have emerged as important regulators involved in many biological processes, including cell proliferation and differentiation, apoptosis and metabolism, and disease development. Here we report that specific miRNA deficiency in pancreatic islet cells exacerbates multiple low-dose streptozotocin-induced murine autoimmune type 1 diabetes, suggesting that miRNAs expressed in islet β cells regulate their susceptibility to immune-mediated β cell destruction.     

Effects of streptozotocin-induced long-term diabetes on parietal cell function and morphology in rats

Gastric pathology is a common complication in diabetes mellitus. The aim of the study was to evaluate the functions and morphological changes of the parietal cells of the rat stomach after streptozotocin-induced diabetes. Diabetes mellitus was induced in Wistar rats by a single intraperitoneal injection of streptozotocin (60 mg/kg body weight). The rats were weighed weekly and sacrificed after 6 months. The glandular portion of the stomach was removed and processed for H⁺-K⁺-ATPase immunohistochemistry and light and electron microscopy studies. Acid secretion was measured in vivo. After 6 months of diabetes, the mean weight of the rats was significantly lower (P < 0.001) compared to control. The mean weight of the stomach to body weight percentage increased significantly (P < 0.001) compared to control. The blood glucose level in diabetic rats was significantly higher (P < 0.001) than in normal control. Diabetic rats showed significant (P < 0.001) decrease in basal and stimulated acid secretion when compared to control. Electron micrographs of the parietal cells of glandular stomach of diabetic rats revealed significant (P < 0.0002) reduction in the number of mitochondria and a small though not significant increase in the number of canaliculi in the parietal cells compared with normal. Immunohistochemistry showed reduced H⁺-K⁺-ATPase (P < 0.00001) compared to control. Long-term diabetes induces morphological as well as functional changes in gastric parietal cells. The decrease in the number of mitochondria accompanied by reduced in H⁺-K⁺-ATPase in parietal cells may explain the reduced acid secretion observed in diabetics.     

Antioxidant effect of carnosine treatment on renal oxidative stress in streptozotocin-induced diabetic rats

Nitric oxide (NO) plays a significant role in the development of diabetic nephropathy. We investigated the effects of an antioxidant, carnosine, on streptozotocin (STZ)-induced renal injury in diabetic rats. We used four groups of eight rats: group 1, control; group 2, carnosine treated; group 3, untreated diabetic; group 4, carnosine treated diabetic. Kidneys were removed and processed, and sections were stained with periodic acid-Schiff (PAS) and subjected to eNOS immunohistochemistry. Examination by light microscopy revealed degenerated glomeruli, thickened basement membrane and glycogen accumulation in the tubules of diabetic kidneys. Carnosine treatment prevented the renal morphological damage caused by diabetes. Moreover, administration of carnosine decreased somewhat the oxidative damage of diabetic nephropathy. Appropriate doses of carnosine might be a useful therapeutic option to reduce oxidative stress and associated renal injury in diabetes mellitus.     

Effect of prolonged treatment with tyramine on glucose tolerance in streptozotocin-induced diabetic rats

The biogenic amine tyramine has been reported to stimulate in vitro glucose transport in adipocytes, cardiomyocytes and skeletal muscle, and to improve in vivo glucose utilization in rats. These effects were dependent on amine oxidation, since they were blocked by inhibitors of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO). We thus tested in this work whether a prolonged treatment with tyramine could improve glucose tolerance in streptozotocin-induced diabetic rats. First, tyramine content of standard rodent chow was determined by HPLC and daily tyramine intake of control rats was estimated to be around 26 micromol/kg body weight. Then, tyramine was administred during 3 weeks in streptozotocin-induced diabetic rats at 29 micromol/kg by daily i.p. injection alone or together with vanadate 0.02 micromol/kg. In another group of diabetic rats, tyramine was subcutaneously delivered at 116 micromol/kg/day by osmotic minipumps. All tyramine treatments resulted in a decrease of the hyperglycemic responses to an i.p. glucose load. Adipocytes isolated from either untreated or treated diabetic rats were sensitive to the stimulation of glucose uptake by tyramine. However, diabetic animals receiving tyramine for three weeks did not recover from their hyperglycemia, hypoinsulinemia and glucosuria. These results show that the improvement of glucose tolerance induced by prolonged tyramine administration occurs in an insulin-depleted model and probably results from peripheral insulin-like actions of the oxidation of MAO/SSAO substrates, such as the stimulation of glucose uptake into adipocytes.     

Effects of quercetin on antioxidant defense in streptozotocin-induced diabetic rats.

In light of evidence that some complications of diabetes mellitus may be caused or exacerbated by oxidative damage, we investigated the effects of subacute treatment with the antioxidant quercetin on tissue antioxidant defense systems in streptozotocin-induced diabetic Sprague-Dawley rats (30 days after streptozotocin induction). Quercetin, 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benzopyran-4-one, was administered at a dose of 10mg/kg/day, ip for 14 days, after which liver, kidney, brain, and heart were assayed for degree of lipid peroxidation, reduced and oxidized glutathione content, and activities of the free-radical detoxifying enzymes catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase. Treatment of normal rats with quercetin increased serum AST and increased hepatic concentration of oxidized glutathione. All tissues from diabetic animals exhibited disturbances in antioxidant defense when compared with normal controls. Quercetin treatment of diabetic rats reversed only the diabetic effects on brain oxidized glutathione concentration and on hepatic glutathione peroxidase activity. By contrast, a 20% increase in hepatic lipid peroxidation, a 40% decline in hepatic glutathione concentration, an increase in renal (23%) and cardiac (40%) glutathione peroxidase activities, and a 65% increase in cardiac catalase activity reflect intensified diabetic effects after treatment with quercetin. These results call into question the ability of therapy with the antioxidant quercetin to reverse diabetic oxidative stress in an overall sense.     

Ramipril treatment suppresses islet fibrosis in Otsuka Long-Evans Tokushima fatty rats

We evaluated whether ramipril, one of long-acting ACEIs, has a direct effect on pancreas islets in animal model of type 2 diabetes. OLETF rats were treated with ramipril for 24 weeks. We assessed the body weight, glucose tolerance, and the amount of islet fibrosis. RT-PCR and Western blot analysis of transforming growth factor-beta with its downstream signals were performed from the pancreas. Ramipril treatment remarkably reduced weight gain and the area under the curve of glucose. Islet fibrosis and the expression of TGF-beta with its downstream signal molecules were significantly reduced in the pancreas of ramipril-treated group than in control and paired-feeding group. These beneficial effects of ramipril might be related to the downregulation of TGF-beta and its downstream signals in OLETF rats. To our knowledge, this is the first report suggesting the potential effect of ramipril on the prevention of islet destruction by fibrosis in the animal model of type 2 diabetes mellitus.     

Studies on rats with islet beta cell tumors induced by nicotinamide and streptozotocin.

Islet beta cell adenomata were induced in rats by combined treatment with nicotinamide and streptozotocin. Three weeks after treatment marked alterations in glucose tolerance were noted in animals which later exhibited large beta cell tumors. Eight months after treatment, the rats known to have beta cell tumors on the basis of marked hypoglycemia and later confirmed by autopsy showed variable response to a glucose load. Some tumor-bearing rats showed fast response to glucose load, their blood sugar levels were elevated moderately and returned to normal or below normal levels rapidly; these animals are described as having "fast-acting tumors". Rats with "slow-acting tumors" responded sluggishly to a glucose load; their blood glucose pattern was similar to that of subdiabetic animals. Animals with beta cell tumors exhibited elevated serum insulin levels 30 min after glucose administration. Insulin biosynthesis by beta cell adenomata was demonstrated by in vitro incorporation of [14C]leucine into proinsulin and insulin. In the small number of tumor samples studied, a stimulatory effect of glucose on insulin biosynthesis was observed.