Probucol attenuated hyperglycemia in multiple low-dose streptozotocin-induced diabetic mice.

The present studies were undertaken to examine the effects of probucol on the protection against pancreatic beta-cell damage by multiple low-dose streptozotocin (STZ: 40 mg/kg, ip). The degree of hyperglycemia at 7, 14 and 17 days after STZ injection was attenuated by probucol. Serum immunoreactive insulin (IRI) levels were increased in the rats fed probucol containing diet at Day 14 and 17. Serum IRI levels after intraperitoneal injection of 2.0 g/kg glucose was reduced in STZ mice and the reduction of serum IRI levels was attenuated in the rats fed probucol, accompanied with a significant reduction of the degree of hyperglycemia after bolus of glucose. Probucol attenuated the reduction of pancreatic IRI content by STZ. The percentage of Thy 1.2-positive splenocytes was increased by STZ and probucol reduced the percentage of Thy 1.2-positive splenocytes, although there were no differences in the populations of splenocytes, positive with Lyt 2 or L3/T4. These data suggest that probucol has a protective action against pancreatic insulitis by multiple low-dose STZ administration.     

Troglitazone can prevent development of type 1 diabetes induced by multiple low-dose streptozotocin in mice.

Recent investigations suggest that cytotoxic cytokines such as tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta or free radicals play an essential role in destruction of pancreatic beta cells in Type 1 diabetes and that, therefore, anti-oxidant or anti-TNF alpha and IL-1beta therapy could prevent the development of Type I diabetes. Troglitazone belongs to a novel class of antidiabetic agent possessing the ability to enhance insulin action provably through activating PPAR gamma and to scavenge free radicals. In the present study, we examined whether troglitazone can prevent the development of Type 1 diabetes in multiple, low-dose streptozotocin (MLDSTZ)-injected mice. In addition, effects of troglitazone on cytokine-induced pancreatic beta cell damage were examined in vitro. Type 1 diabetes was induced by MLDSTZ injection to DBA/2 mice (40 mg/kg/day for 5 days). Troglitazone was administered as a 0.2% food admixture (240 mg/kg/day) for 4 weeks from the start of or immediately after STZ injection. MLDSTZ injection elevated plasma glucose to 615 +/- 8 mg/dl 4 weeks after final STZ injection and was accompanied by infiltration of leukocytes to pancreatic islets (insulitis). Troglitazone treatment with MLDSTZ injection prevented hyperglycemia (230 +/- 30 mg/dl) and, suppressed insulitis and TNF alpha production from intraperitoneal exudate cells. TNF alpha (10 pg/ml) and IL-1beta (1 pg/ml) addition to hamster insulinoma cell line HIT-T15 for 7 days in vitro decreased insulin secretion and cell viability. Simultaneous troglitazone addition (0.03 to approximately 3 microM) significantly improved cytokine-induced decrease in insulin secretion and in cell viability. These findings suggest that troglitazone prevents the development of Type 1 diabetes in the MLDSTZ model by suppressing insulitis associated with decreasing TNF alpha production from intraperitoneal exudate cells and the subsequent TNF alpha and IL-1beta-induced beta cell damage.     

Proteomic analysis of mouse islets after multiple low-dose streptozotocin injection

The islets of Langerhans are scattered throughout the pancreas and play a major role in the control of metabolic fuel homeostasis. To get a better understanding of the mechanisms underlying type 1 diabetes mellitus, we have generated a mouse model by injections of multiple low-dose streptozotocin. The islets in the mouse pancreas were handpicked and proteins from the islets were then isolated and separated by two-dimensional gel electrophoresis. Seven proteins were found to be altered significantly at expression level. Among the seven proteins, four were up-regulated and three were down-regulated in diabetic mice as compared with controls. These proteins were successfully identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and the changes of selected protein expression were further validated by quantitative real time PCR and Western blotting. Voltage-dependent anion-selective channel protein 1 and peroxiredoxin-4 were found for the first time to be associated with type 1 diabetes mellitus in mouse islets in the current study. These results suggest that glucose transport, beta cell proliferation/death, and oxidative stress play important roles in maintaining the balance of glucose level. Our study also provides novel insight into the mechanism of type 1 diabetes mellitus.     

Effect of telmisartan on cardiovascular complications associated with streptozotocin diabetic rats

Angiotensin receptor blockers provide cardiovascular protection in heart failure patients. We have studied the effect of 8 weeks treatment with telmisartan (5 mg kg(-1) day(-1)) on cardiovascular complications associated with streptozotocin (STZ) diabetic rats. Wistar rats were made diabetic with STZ (45 mg kg(-1), iv). Various biochemical and cardiac parameters were measured at the end of 8 weeks. STZ produced hyperglycemia, hypoinsulinemia, hyperlipidemia, increased blood pressure, increased creatinine, cardiac enzyme and C-reactive protein (CRP) levels, reduction in heart rate and cardiac hypertrophy. Chronic treatment with telmisartan significantly (P < 0.05) prevented STZ induced hypertension and elevated fasting glucose level with simultaneous increase in serum insulin levels. It significantly (P < 0.05) reduced the elevated cholesterol, very low density lipoprotein (VLDL) and triglyceride levels in diabetic rats and increased the lower high density lipoprotein (HDL)-cholesterol levels. Further, telmisartan produced a significant (P < 0.05) reduction in the elevated creatinine levels, CRP and levels of other cardiac enzyme markers like Lactate de-hydrogenase and creatinine kinase of diabetic rats. STZ-induced bradycardia was also prevented by telmisartan treatment and it also produced beneficial effect by preventing cardiac hypertrophy as evident from left ventricular collagen levels, cardiac hypertrophy index and left ventricular hypertrophy index of diabetic rats. Our data suggest that telmisartan prevents not only the STZ-induced metabolic abnormalities, but also cardiovascular complications.     

Effect of chronic treatment with losartan on streptozotocin induced diabetic rats

Treatment of rats with streptozotocin (STZ, 45mg/kg, i.v.,single dose) produced cardinal symptoms of diabetes mellitus including hyperglycemia, hypoinsulinemia and increase in blood pressure. Treatment with losartan--an angiotensin (AT1) receptor antagonist, 2 mg/kg, po for 6 weeks decreased the blood glucose levels by 16.5%. There was 190% increase in AUCglucose and 59.4% decrease in AUCinsulin in STZ-diabetic rats as compared to control rats. Treatment with losartan caused slight decrease in AUCglucose and slight increase in AUCinsulin. There was no significant difference in insulin sensitivity (K(ITT)) index of STZ-diabetic group as compared to control. Losartan treatment failed to alter these levels significantly. Serum cholesterol and creatinine levels were found to be increased significantly in STZ-diabetic rats. Treatment with losartan significantly prevented the rise in cholesterol and creatinine levels by 20.1 and 81% respectively. The results suggest that losartan produces some beneficial effects in STZ-diabetic rats.     

Recovery from diabetes in neonatal mice after a low-dose streptozotocin treatment

Administration of streptozotocin (STZ) induces destruction of β-cells and is widely used as an experimental animal model of type I diabetes. In neonatal rat, after low-doses of STZ-mediated destruction of β-cells, β-cells regeneration occurs and reversal of hyperglycemia was observed. However, in neonatal mice, β-cell regeneration seems to occur much slowly compared to that observed in the rat. Here, we described the time dependent quantitative changes in β-cell mass during a spontaneous slow recovery of diabetes induced in a low-dose STZ mice model. We then investigated the underlying mechanisms and analyzed the cell source for the recovery of β-cells. We showed here that postnatal day 7 (P7) female mice treated with 50 mg/kg STZ underwent the destruction of a large proportion of β-cells and developed hyperglycemia. The blood glucose increased gradually and reached a peak level at 500 mg/dl on day 35–50. This was followed by a spontaneous regeneration of β-cells. A reversal of non-fasting blood glucose to the control value was observed within 150 days. However, the mice still showed impaired glucose tolerance on day 150 and day 220, although a significant improvement was observed on day 150. Quantification of the β-cell mass revealed that the β-cell mass increased significantly between day 100 and day 150. On day 150 and day 220, the β-cell mass was approximately 23% and 48.5% of the control, respectively. Of the insulin-positive cells, 10% turned out to be PCNA-positive proliferating cells. Our results demonstrated that, β-cell duplication is one of the cell sources for β-cell regeneration.     

Effect of ethanol ingestion on tryptophan metabolism in streptozotocin diabetic rats

Ingestion of ethanol by albino rats affected brain liver and plasma tryptophan contents in both normal and diabetic animals, although at different rates. Liver tryptophan was increased in both the groups, whereas tryptophan levels in brain and plasma of normal group were decreased and those of diabetic group were increased after the treatment. Similarly, while hepatic tryptophan dioxygenase activity was decreased in both the groups, activity of hepatic 3-hydroxykynureninase was increased only in normal rats and that of liver picolinic carboxylase was significantly decreased only in the diabetic group after ethanol administration.     

Insulinotropic effect of ovarian steroid hormones in streptozotocin diabetic female mice

To investigate the protective effect of ovarian sex steroids against streptozotocin diabetes, groups of ovariectomized streptozotocin diabetic female mice were treated orally with estradiol-17 beta (5 and 500 ug/kg/day) or progesterone (1 mg/kg/day) for 10 weeks. Streptozotocin produced a more severe hyperglycaemia and a greater fall in plasma insulin concentrations in ovariectomized mice than intact female mice. The estradiol-17 beta and progesterone treatments reduced both the severity of the hyperglycaemia and the fall in plasma insulin. Loss of pancreatic insulin after streptozotocin administration was reduced in intact mice and in mice treated with estradiol-17 beta. These observations suggest that ovarian sex steroids reduce the severity of streptozotocin diabetes at least partly by countering the cytotoxic effect of the drug on the islet B-cells, thereby reducing the fall in pancreatic and plasma insulin.     

Effect of clofibrate on lipid metabolism in streptozotocin diabetic rats.

The effect of clofibrate (CPIB) on lipid metabolism was studied in male rats rendered diabetic by intravenous injection of 80 mg/kg of streptozotocin. After 1 wk, the rats received by gastric intubation 242 mg/kg/day of CPIB for 7 days. Liver lipid concentration remained unchanged in experimental diabetes and after treatment with CPIB; however, due to decreased liver weight, total liver lipids were lower in diabetic rats. Elevation of cholesterol, phospholipids, and triglycerides in the serum of diabetic rats was reversed by CPIB treatment. Hepatic cholesterol synthesis in diabetic rats was suppressed to approximately 1/10 of that in normal rats. Treatment with CPIB abolished this residual cholesterogenic activity. Diabetes had no effect on intestinal cholesterol synthesis; a slight increase was noted after CPIB treatment. Basal and norepinephrine-induced lipolysis in fat pads was elevated in diabetic rats; CPIB had no effect on these changes. The data show that the elevated serum lipids in diabetic rats are lowered by treatment with C-IB. It was concluded that the hypocholesterolemic activity of clofibrate in rats is not caused by its suppression of hepatic cholesterol synthesis.     

Effect of vanadate on tryptophan metabolism in streptozotocin diabetic rats.

Administration of sodium orthovanadate (0.3 mg/ml) through drinking water for 20 days to streptozotocin-induced diabetic rats resulted in reversal of markedly elevated activities of some of the key enzymes of tryptophan-niacin pathway, viz. hepatic and renal aminocarboxymuconate semialdehyde decarboxylase and hepatic tryptophan oxygenase, to normal levels without restoring the elevated blood sugar level to normal state. However vanadate administration to normal rats did not cause any significant change.     

Central pharmacological activity of a quaternary ammonium compound in streptozotocin diabetic mice

Possible changes in blood-brain barrier (BBB) function as a result of diabetes were investigated by assessing antagonism of morphine analgesia in diabetic mice by methylnaltrexone (MeNTX), an opioid receptor blocker that does not cross the BBB when administered subcutaneously (SC). In streptozotocin (STZ)-treated diabetic mice--but not vehicle-treated, non-diabetic mice--treatment with SC MeNTX significantly reduced morphine analgesia. In vehicle-treated, non-diabetic mice, morphine analgesia was antagonized by MeNTX administered intracerebroventricularly and by SC naltrexone, which crosses the BBB. Reduction of STZ-induced hyperglycemia by insulin reversed the effectiveness of SC MeNTX in antagonizing morphine analgesia. We hypothesize that in STZ diabetic mice, MeNTX was able to cross the BBB and block brain opioid receptors.     

Prevention of multiple low-dose streptozotocin (MLD-STZ) diabetes in mice by an extract from gum resin of Boswellia serrata (BE)

Type 1-diabetes is an autoimmune disease, where a chronic inflammatory process finally causes β-cell death and insulin deficiency. Extracts from gum resin of Boswellia serrata (BE) have been shown to posses anti-inflammatory properties especially by targeting factors/mediators related to autoimmune diseases. Multiple low dose-streptozotocin (MLD-STZ) treatment is a method to induce diabetes in animals similar to Type 1 diabetes in humans.It was aimed to study whether or not a BE could prevent hyperglycemia, inflammation of pancreatic islets and increase of proinflammatory cytokines in the blood in MLD-STZ treated mice.In BK+/+ wild type mice, 5 days of daily treatment with 40 mg/kg STZ i.p. produced permanent increase of blood glucose, infiltration of lymphocytes into pancreatic islets (CD3-stain), apoptosis of periinsular cells (staining for activated caspase 3) after 10 days as well as shrinking of islet tissue after 35 days (H&E staining). This was associated with an increase of granulocyte colony stimulating factor (G-CSF), granulocyte/macrophage colony stimulating factor (GM-CSF) and proinflammatory cytokines (IL-1A, IL-1B, IL-2, IL-6, IFN-γ, TNF-α) in the blood. Whereas BE alone did not affect blood glucose in non diabetic mice, in STZ treated mice simultaneous i.p. injection of 150 mg/kg of BE over 10 days prevented animals from increase of blood glucose levels. Histochemical studies showed, that i.p. injection of 150 mg/kg BE for 10 days starting with STZ treatment, avoided lymphocyte infiltration into islets, apoptosis of periinsular cells and shrinking of islet size 35 days after STZ. As far as the cytokines tested are concerned, there was a significant inhibition of the increase of G-CSF and GM-CSF. BE also significantly prevented the increase of IL-1A, IL-1B, IL-2, IL-6, IFN-γ and TNF-α. It is concluded that extracts from the gum resin of Boswellia serrata prevent islet destruction and consequent hyperglycemia in an animal model of type 1 diabetes probably by inhibition of the production/action of cytokines related to induction of islet inflammation in an autoimmune process.     

Cardiac overexpression of hormone-sensitive lipase inhibits myocardial steatosis and fibrosis in streptozotocin diabetic mice

Intracellular lipid accumulation (steatosis) and resultant lipotoxicity are key features of diabetic cardiomyopathy. Since cardiac hormone-sensitive lipase (HSL) is activated in diabetic mice, we sought to explore a pathophysiological function of cardiac HSL in the development of diabetic cardiomyopathy. Transgenic (Tg) mice with heart-specific HSL overexpression were generated, and cardiac histology, function, lipid profile, and gene expressions were analyzed after induction of diabetes by streptozotocin. Electron microscopy showed numerous lipid droplets in wild-type (Wt) hearts after 3 wk of diabetes, whereas Tg mice showed no lipid droplet accumulation. Cardiac content of acylglycerides was increased approximately 50% with diabetes in Wt mice, whereas this was blunted in Tg hearts. Cardiac lipid peroxide content was twofold lower in Tg hearts than in Wt hearts. The mRNA expressions for peroxisome proliferator-activated receptor-alpha, genes for triacylglycerol synthesis, and lipoprotein lipase were increased with diabetes in Wt hearts, whereas this induction was absent in Tg hearts. Expression of genes associated with lipoapoptosis was decreased, whereas antioxidant protein metallothioneins were increased in diabetic Tg hearts. Diabetic Wt hearts showed interstitial fibrosis and increased collagen content. However, Tg hearts displayed no overt fibrosis, concomitant with decreased expression of collagens, transforming growth factor-beta, and matrix metalloproteinase 2. Notably, mortality during the experimental period was approximately twofold lower in diabetic Tg mice compared with Wt mice. In conclusion, since HSL overexpression inhibits cardiac steatosis and fibrosis by apparently hydrolyzing toxic lipid metabolites, cardiac HSL could be a therapeutic target for regulating diabetic cardiomyopathy.     

Role of lipids in the early developmental stages of experimental immune diabetes induced by multiple low-dose streptozotocin.

The present work examines the role of lipids in the development of the Type 1 diabetes induced by the administration of multiple low doses of streptozotocin (STZ) in C57BL/6J mice. The study was performed before and after the onset of clear hyperglycemia, and the results were as follows. First, 6 days after the first dose of STZ, while plasma glucose and insulin levels remained similar to those observed in the control mice, plasma free fatty acid (FFA) levels were significantly increased (P < 0.05). At that time, a marked increase of triglyceride content in gastronemius muscle was accompanied by a diminished activity of pyruvate dehydrogenase complex, suggesting an impaired glucose oxidation. Furthermore, a decrease of both triglyceride content and lipoprotein lipase activity was observed in the epididymal fat tissue. Second, 12 days after the first injection of STZ, hyperglycemia was accompanied by hypertriglyceridemia, a more pronounced increase of plasma FFA, and a significant (P < 0.05) reduction of insulinemia. At this time, both the adipose tissue and the gastrocnemius muscle showed a further deterioration of all parameters mentioned after 6 days. Moreover, in the gastrocnemius muscle, an impaired nonoxidative pathway of glucose metabolism was observed [significant reduction (P < 0.05) of glycogen mass, glucose-6-phosphate content, and glycogen synthase activities] at this time point. Finally, the data suggest for the first time that, in mice, Type 1 diabetes induced by multiple low doses of STZ and enhanced lipolysis of fat pads leads to an increase in the availability of plasma FFA, which seems to play a role in the early steps of diabetes evolution.     

Influences of crude extract of tea leaves,Camellia sinensis,on streptozotocin diabetic male albino mice

Natural remedies from medicinal plants are considered to be effective and safe alternative treatment for diabetes mellitus. The aim of the present study was to investigate the hypoglycemic activity of the crude tea leaves extract on streptozotocin (STZ)-induced diabetic mice. The average body weight of animals with diabetes and their percentage changes of body weight gain after 15 and 30 days were significantly lower than that of the normal control mice. In diabetic mice, supplementation with tea leaves extract decreased the loss of body weight. After 15 and 30 days, significant increases in the levels of serum glucose, triglycerides, cholesterol, creatinine, urea, uric acid, glutamic pyruvic acid transaminase (GPT) and glutamic oxaloacetic acid transaminase (GOT) were noted in STZ-diabetic mice fed with normal diet. Also, the values of total protein in this group were statistically declined after 15 and 30 days. The levels of serum glucose and GPT were significantly elevated after 15 and 30 days in diabetic mice supplemented with tea leaves extract. Moreover, the level of serum GOT was notably increased after 30 days. Insignificant alterations were observed in the levels of serum triglycerides, cholesterol, total protein, creatinine, urea and uric acid in diabetic mice supplemented with tea leaves extract. Thus, the present results have shown that tea leaves extract has the antihyperglycemic, antihyperlipidemic, and antihyperproteinemic effects and consequently may alleviate liver and kidney damage associated with STZ-induced diabetes in mice.     

Effect of dietary fibres on constituents of complex carbohydrates in streptozotocin induced diabetic rat tissues

The effect of dietary fibres on constituents of complex carbohydrates in various tissues of streptozotocin induced diabetic rats is presented by analysing different constituents of complex carbohydrates in presence and absence of dietary fibre. Wheat bran was effective in preventing the decrease (14%) in total sugars in spleen and an increase in total sugars in stomach (33%) during diabetes. Decrease in uronic acid content during diabetes in spleen was prevented to the extent of 25% by the presence of wheat bran in the diet. The other parameters which were affected by the presence of wheat bran in the diet during diabetes are amino sugar (brain and stomach), sulphates (liver) and protein (lungs and stomach). Guar gum was effective in preventing the decrease in total sugar content in spleen by 28% and sulphate content in liver by 14% during diabetes. Variation in protein content in lungs was observed in diabetes. The results indicated beneficial role of dietary fibres like wheat bran and guar gum on complex carbohydrates to varying extents in different tissues.     

Immune responsiveness and phagocytic activity of macrophages in streptozotocin (SZ)-induced diabetic mice

We succeeded in inducing different severities of diabetic state in C3H male mice by repeated intraperitoneal injections of various doses of SZ. SZ-induced diabetic mice were divided into four groups as follows: Group A, B, C and D. SZ, respectively, 3, 5 doses of 45 mg/kg, 5 doses of 60 mg/kg on consecutive days and one of a dose of 200 mg/kg BW. The degree of hyperglycemia and glycosuria were mild in group A and D. Group B was moderate and group C severe with ketonuria and loss of body weight. We investigated the immune response to anti-sheep red blood cells (SRBC) and the phagocytic activity of macrophages in the above mentioned various SZ-induced mice. Antibody forming activities (values of anti-SRBC plaque-forming cells (PFC) and serum agglutinin) were markedly depressed in all of SZ-diabetic groups. The degree of the suppression of antibody response to SRBC in SZ-diabetic mice corresponded with the severity of the diabetic state (C greater than B greater than A = D). However, the phagocytic activity of peritoneal macrophages in SZ-diabetic mice was as high as or higher than that in normal controls, using both latex beads and immune complex as test particles. Moreover, we observed that insulin treatment reversed the defect in the immune response in SZ-diabetic mice. These results indicate that the phagocytic activity of peritoneal macrophages was retained but the antibody response was impaired in the SZ-diabetic mice, and this suggested that the impaired antibody response may be a contributing cause of increased susceptibility to infections in a diabetic state.     

Testicular lesions of streptozotocin diabetic rats.

Diabetes was induced in adult male albino rats by a single intravenous injection of streptozotocin (75 mg/kg body weight). The diabetes was allowed to stabilize for at least 15 days, whereafter the testicular and seminal vesicle histology was studied at various time intervals. Reduction in testis weights and tubule diameters was significant after 2 weeks of diabetes. The changes in seminiferous tubules ranged from premature sloughing of epithelium to total cessation of spermatogenesis. The testicular histology of diabetic animals frequently greatly simulated the situation described following hypophysectomy. By subjective visual assessment the number of Leydig cells was found to be normal or reduced in all of the diabetic animals. Diabetes was also demonstrated to induce seminal vesicle atrophy, which did not show any correlation with the degree of testicular lesions. The possible etiology of testicular damage in diabetic animals is discussed.     

Heligmosomoides polygyrus infection reduces severity of type 1 diabetes induced by multiple low-dose streptozotocin in mice via STAT6- and IL-10-independent mechanisms

Some parasitic helminths are known to protect their hosts from allergic and autoimmune disorders. Here, we tested the effects of a gastrointestinal nematode, Heligmosomoides polygyrus (Hp), on streptozotocin (STZ)-induced type 1 diabetes (T1D) in mice. Hp infection significantly suppressed hyperglycemia induced by multiple low-dose administration of STZ, but did not affect hyperglycemia induced by single high-dose administration of STZ. In the multiple low dose model, Hp infection prevented a decrease in pancreatic islet size. The augmentation of TNF-α and IL-1β expression in the pancreas was abrogated by Hp infection. The genetic absence of IL-10 or STAT6 did not abrogate the anti-hyperglycemic effect of Hp. Hp has a suppressive effect on immune mechanism-mediated experimental T1D via Th2 polarization-independent mechanisms.