Liver Of STZ-diabetic Rats Research Articles

Streptozotocin-Induced Adaptive Modification of Mitochondrial Supercomplexes in Liver of Wistar Rats and the Protective Effect of Moringa oleifera Lam.

The increasing prevalence of diabetes continues to be a major health issue worldwide. Alteration of mitochondrial electron transport chain is a recognized hallmark of the diabetic-associated decline in liver bioenergetics; however, the molecular events involved are only poorly understood. Moringa oleifera is used for the treatment of diabetes. However, its role on mitochondrial functionality is not yet established. This study was aimed to evaluate the effect of M. oleifera extract on supercomplex formation, ATPase activity, ROS production, GSH levels, lipid peroxidation, and protein carbonylation. The levels of lipid peroxidation and protein carbonylation were increased in diabetic group. However, the levels were decreased in Moringa-treated diabetic rats. Analysis of in-gel activity showed an increase in all complex activities in the diabetic group, but spectrophotometric determinations of complex II and IV activities were unaffected in this treatment. However, we found an oxygen consumption abolition through complex I-III-IV pathway in the diabetic group treated with Moringa. While respiration with succinate feeding into complex II-III-IV was increased in the diabetic group. These findings suggest that hyperglycemia modifies oxygen consumption, supercomplexes formation, and increases ROS levels in mitochondria from the liver of STZ-diabetic rats, whereas M. oleifera may have a protective role against some alterations.

Effect of Ganoderma lucidum polysaccharides on oxidative damage in liver of STZ-diabetic rats

In this study, the effects of exogenic application of Ganoderma lucidum polysaccharide on oxidative stress and hyperlipidemia was determined in diabetics rats. The study included 60 Wistar albino rats aged 4-5 months. Rats were divided into 6 equal groups. The groups were control, Ganoderma lucidum polysaccharide, diabetic, diabetic+60 mg/kg polysaccharides, diabetic+120 mg/kg polysaccharides and diabetic+10 mg/kg polysaccharide. Diabetes was induced by intraperitoneal injection of streptozocine at the dose rate of 50 mg/kg. The rats were fed ad-libitum throughout the experiment. At the end of the study, we took some samples out of total oxidant and total antioxidant levels and measured them with the spectrophotometer; thereafter we used the auto-analyser to measure the levels of total cholesterol, triglycerides, HDL, LDL, VLDL cholesterol and pancreatic amylase. We examined the blood of diabetic fasting rats and the effect was that their glucose level was increased significantly. (p<0.05), nonetheless the dose of 60, 120 and 180 mg/kg of Ganoderma lucidum polysaccharides did not reduce the blood glucose level (p>0.05). With the diabetic rats, the dose of 60, 120 and 180 mg/kg of Ganoderma lucidum polysaccharides rides effected in the increase of serum levels of total cholesterol, triglycerides, VLDL, and HDL cholesterol levels, although it was not a significant change (p>0.05), instead, we observed a statistically significant decrease of LDL cholesterol level (p<0.05). According to this study we concluded that polysaccharides effects in the decrease of hyperlipidaemia with regard to diabetes. During the study we applied Ganoderma lucidum polysaccharides exogenously (60, 120, 180 mg/kg) and it did not affect the level of total antioxidant in diabetes significantly (p>0.05), however with a dose of 180 mg/kg the total oxidant level in pancreas and liver tissues was reduced significantly and has been considered as crucial fact. The collected data supported our view on histopathologic examination. Based on all the information, we used one type of fungus Ganoderma lucidum polysaccharides which did not influence the blood glucose level in diabetes, whereas with regard to LDL and total oxidants it played a significant role in reducing its levels.

Quercetin prevents type 1 diabetic liver damage through inhibition of CYP2E1.

Increased CYP2E1 protein and activity levels can be the main cause of stress-mediated liver damage in diabetes. In this work we investigated the quercetin properties to prevent diabetic oxidative liver injury through inhibition of CYP2E1. Animals were randomly divided into three groups (n=5 for each group): non-diabetic control, STZ-diabetic rats and STZ-diabetic rats administered with quercetin (50mg/kg bw, per day, during 30days). Markers of oxidative stress and liver injury, hepatocyte ultrastructure and levels of CYP2E1 protein and activity were examined using biochemical, electron microscopy and molecular biological methods. It was shown that symptoms of diabetes (hyperglycemia, bodyweight loss, damaged hepatocyte ultrastructure), signs of oxidative stress in liver (2-fold intensification of peroxide process and 2-fold depletion of antioxidants) and serum markers of liver damage (3.5-, 1.5- and 5-fold increase in levels of ALT, AST and GGT, respectively) were present in STZ-diabetic rats. We found 3- and 2.5-fold increase in levels of protein and activity of CYP2E1 in the liver of STZ-diabetic rats. We demonstrated that the administration of quercetin leads to significant decrease in CYP2E1 activity (5- and 2-times compared to STZ-diabetic and control group, respectively). That was accompanied by normalization of pro-oxidant-antioxidant balance, improving the ultrastructure of hepatocytes and rates of serum markers of liver injury. CYP2E1 can play a crucial role in stress-induced pathological processes in the liver in diabetes, and the inhibition of the enzyme by quercetin during the development of diabetes mainly prevents the oxidative damage in liver.

Effect of exercise training on liver antioxidant enzymes in STZ-diabetic rats.

Abstract Aims Although exercise is shown to improve the antioxidant defense in many organs and pathologies, little research has focused on the effect of chronic exercise training on diabetes-induced liver oxidative stress. We evaluated the effect of chronic treadmill exercise on the hepatic antioxidant enzymes and redox status in STZ-diabetic rats. Main methods Male Wistar rats were randomly assigned into control, trained, diabetic, and diabetic trained groups. Type 1 diabetes mellitus was induced via intraperitoneal injection of STZ. The animals were trained by running on a non-graded motorized treadmill 5 days weekly for a period of 9 weeks. The activity and mRNA levels of antioxidant enzymes, hydrogen peroxide generation, thiol content, and GSH/GSSG ratio were evaluated. Key findings Diabetes negatively affected the hepatic antioxidant defense as indicated by reduced SOD activity, downregulation of SOD1 and GPX1 mRNA levels, increased catalase activity, increased H2O2 production, reduced thiol content and GSH/GSSG ratio. Nine weeks of treadmill exercise training either prevented (SOD1 mRNA, GPX1 mRNA, and thiol content) or ameliorated (catalase activity, SOD activity, H2O2 generation, GSH/GSSG ratio) these diabetes hepatic effects. Significance Our data suggest that exercise training attenuates the diabetes-induced alterations on antioxidant enzymes in the liver of STZ-diabetic rats by improving the hepatic ROS scavenging and redox status. This result strongly implicates a positive effect of exercise training on diabetes-induced liver oxidative stress.

OXIDATIVE DAMAGE TO NUCLEAR DNA IN STREPTOZOTOCIN‐DIABETIC RAT LIVER

1. Accumulating evidence suggests that oxidative and glycative stress is enhanced in diabetes. Oxidative stress induces DNA damage. In the present study, we assessed the 8-oxo-2'-deoxyguanosine (8-oxodG) content of DNA, an indicator of oxidative DNA damage, in streptozotocin (STZ)-induced diabetic (n = 21) and control rats (n = 18). 2. Rats were rendered diabetic by intraperitoneal administration of STZ at a dose of 65 mg/kg. Glucose was determined by glucose oxidase and glycated haemoglobin (GHb), an indicator of glycative stress, was determined by agarose-boronate affinity chromatography. 8-Oxo-2'-deoxyguanosine within the DNA (ratio of 8-oxodG to deoxyguanosine (dG)) was assessed by HPLC in conjunction with both electrochemical (8-oxodG) and diode array (dG) detection. 3. Glucose, GHb and the extent of oxidative DNA damage in the liver of STZ-diabetic rats were much higher compared with control rats. There was a correlation between GHb and 8-oxodG/10(5) dG levels in control (r = 0.756, P < 0.001) and diabetic groups (r = 0.468, 0.02 < P < 0.05). 4. These results clearly show that oxidative damage to hepatic nuclear DNA increases in the diabetic state and that this increase is correlated with glycative stress.

Mediation of Endogenous beta-endorphin by Tetrandrine to Lower Plasma Glucose in Streptozotocin-induced Diabetic Rats.

The role of β-endorphin in the plasma glucose-lowering action of tetrandrine in streptozotocin-induced diabetic rats (STZ-diabetic rats) was investigated. The plasma glucose concentration was assessed by the glucose oxidase method. The enzyme-linked immunosorbent assay was used to determine the plasma level of β-endorphin-like immunoreactivity (BER). The mRNA levels of glucose transporter subtype 4 (GLUT4) in soleus muscle and phosphoenolpyruvate carboxykinase (PEPCK) in the liver of STZ-diabetic rats were detected by Northern blotting analysis. The expressed protein of GLUT4 or PEPCK was characterized by Western blotting analysis. Tetrandrine dose-dependently increased plasma BER in a manner parallel to the decrease of plasma glucose in STZ-diabetic rats. Moreover, the plasma glucose-lowering effect of tetrandrine was inhibited by naloxone and naloxonazine at doses sufficient to block opioid μ-receptors. Further, tetrandrine failed to produce plasma glucose-lowering action in opioid μ-receptor knockout diabetic mice. Bilateral adrenalectomy eliminated the plasma glucose-lowering effect and plasma BER-elevating effect of tetrandrine in STZ-diabetic rats. Both effects were abolished by treatment with hexamethonium or pentolinium at doses sufficient to block nicotinic receptors. Tetrandrine enhanced BER release directly from the isolated adrenal medulla of STZ-diabetic rats and this action was abolished by the blockade of nicotinic receptors. Repeated intravenous administration of tetrandrine (1.0 mg/kg) to STZ-diabetic rats for 3 days resulted in an increase in the mRNA and protein levels of the GLUT4 in soleus muscle, in addition to the lowering of plasma glucose. Similar treatment with tetrandrine reversed the elevated mRNA and protein levels of PEPCK in the liver of STZ-diabetic rats. The obtained results suggest that tetrandrine may induce the activation of nicotinic receptors in adrenal medulla to enhance the secretion of β-endorphin, which could stimulate opioid μ-receptors to increase glucose utilization or/and reduce hepatic gluconeogenesis to lower plasma glucose levels in STZ-diabetic rats.

Antihyperglycemic action of angiotensin II receptor antagonist, valsartan, in streptozotocin-induced diabetic rats.

In the present study, we use valsartan, a highly selective antagonist for angiotensin(1) (AT(1)) receptor subtype, to investigate the effect of AT(1) receptor on the plasma glucose metabolism in streptozotocin-induced diabetic rats (STZ-diabetic rats). The plasma glucose concentration was assessed by glucose oxidase method and plasma insulin was measured using enzyme-linked immunosorbent assay. Systolic blood pressure (SBP) was determined by the tail-cuff method. The intravenous glucose challenge test (IVGCT) was carried out to evaluate the effect of valsartan on the glucose utilization in vivo. The mRNA levels of the subtype 4 form of glucose transporter (GLUT4) in soleus muscle and phosphoenolpyruvate carboxykinase (PEPCK) in the liver were detected by Northern blotting analysis. Moreover, the protein levels of GLUT4 in isolated soleus muscle and hepatic PEPCK were investigated using Western blotting analysis. A single intravenous injection of valsartan decreased the plasma glucose concentrations in a dose-dependent manner in STZ-diabetic rats. Plasma glucose-lowering action of valsartan also observed in normal rats although in a way not so effective as that in STZ-diabetic rats. Valsartan at the dose of 0.2 mg/kg that produced the maximal plasma glucose-lowering activity in STZ-diabetic rats is also effective to lower the SBP. However, oral treatment with nifedipine or nicorandil in STZ-diabetic rats at the dose sufficient to decrease SBP showed no change of plasma glucose. Otherwise, infusion of saralasin (10 microg/kg per min) into STZ-diabetic rats produced a plasma glucose-lowering activity similar to that by valsartan at 0.2 mg/kg. Moreover, valsartan (0.2 mg/kg) significantly attenuated the raise of plasma glucose induced by IVGCT in normal rats. Repeated intravenous administration of valsartan (0.2 mg/kg) in STZ-diabetic rats resulted in the lowering of plasma glucose after 3 days. The mRNA and protein levels of GLUT4 in the soleus muscle were increased after repeated intravenous administration of valsartan in STZ-diabetic rats for 3 days. Moreover, similar repeated treatment with valsartan reversed the elevated mRNA and protein levels of PEPCK in the liver of STZ-diabetic rats. These results suggest that the plasma glucose-lowering activity of AT(1) receptor antagonism was associated with an increase in the glucose utilization in peripheral tissue and/or a reduction in hepatic gluconeogenesis in the absence of insulin.

Increase in adenosine A1 receptor gene expression in the liver of streptozotocin‐induced diabetic rats

Adenosine A1 receptor (A1-AR) activation can lower plasma glucose in diabetic rats lacking insulin. We investigated the change in A1-AR gene expression in diabetic rats. The incorporation of [U-(14)C]-glucose into glycogen was carried out to evaluate the effect of N(6)-cyclopentyladenosine (CPA) on glucose utilization in vitro. The plasma glucose concentration was assessed by the glucose oxidase method. The mRNA and protein levels of A1-AR in isolated liver were detected by Western blotting analysis and Northern blotting analysis, respectively. The effect of CPA, an agonist of A1-AR, on glycogen incorporation in hepatocytes isolated from streptozotocin-induced diabetic rats (STZ-diabetic rats) was more marked than that from the normal rats. However, similar glycogen synthesis was not modified by 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, in the isolated hepatocytes from both the normal and the STZ-diabetic rats. A change in response at the receptor level can thus be considered. The mean level of liver mRNA transcripts encoding A1-AR was increased in STZ-diabetic rats to about 250% of that in normal rats. Exogenous insulin at a dose sufficient to normalize the plasma glucose of STZ-diabetic rats reversed the mRNA level of A1-AR in the liver after a four-day treatment. Similar results were also observed in STZ-diabetic rats that received treatment with phlorizin for four days. Moreover, the protein level of A1-AR was higher in the liver of STZ-diabetic rats than that in the normal rats. Similar treatment with exogenous insulin or phlorizin reversed the elevated protein level of A1-AR in the liver of STZ-diabetic rats to near the normal level. Therefore, correction of hyperglycemia in STZ-diabetic rats can reverse the higher gene expression of A1-AR in liver. The obtained results suggest that an increase in plasma glucose is responsible for the higher gene expression of A1-AR in the liver of STZ-diabetic rats.

Arginine Stimulated Insulin and Glucagon Release from Islets Transplanted into the Liver of Diabetic Rats

We investigated the ability of intraportal transplanted islets to release insulin and glucagon after stimulation with arginine. Furthermore, the islet volume and hormone content of the recipient pancreas were analyzed. Three months after syngeneic portal islet transplantation the liver of STZ-diabetic rats was perfused in vitro in the presence of different arginine concentrations. Transplanted islets preserve their functional integrity for at least three months indicated by a stimulus adequate insulin release and contribute substantially to the observed amelioration of the diabetic state. The islet and B-cell volume as well as the insulin and glucagon content of the recipient pancreas are still markedly decreased three months after islet transplantation when compared with healthy controls.