Ayse Karatug

Exendin-4 improves hepatocyte injury by decreasing proliferation through blocking NGF/TrkA in diabetic mice.

The hepatocytes express nerve growth factor (NGF) and its high affinity receptor tyrosine kinase A (TrkA). However, the link between NGF/TrkA system and hepatocyte proliferation in diabetic animals and the effects of exendin-4, a glucagon like peptide-1 (GLP-1) receptor agonist, on this system are not known. BALB/c male mice were divided into four groups. The first group was given citrate buffer only, the second group was administered exendin-4 alone, the third group received streptozotocin (STZ), and the fourth group was given both STZ and exendin-4. Exendin-4 (3μg/kg) was administered by subcutaneous injection daily for 30 days after the animals were rendered diabetic by administration of STZ (200mg/kg). With treatment of exendin-4 to the diabetic mice the following results were noted (i) NGF, TrkA and proliferating cell nuclear antigen positive hepatocytes were decreased; (ii) p75 neurotrophin receptor and caspase-3 positive hepatocyte could not be detected; (iii) liver alanine transaminase and aspartate transaminase activities, lipid peroxidation, protein carbonyl and myeloperoxidase levels were decreased; (iv) liver catalase, superoxide dismutase, glutathione peroxidase activities and glutathione levels were increased. These data suggest that exendin-4 might exerts its anti-proliferative action through blocking NGF/TrkA system and stimulating oxidative defense system in liver of diabetic mice.

Regulation of oxidative stress and somatostatin, cholecystokinin, apelin gene expressions by ghrelin in stomach of newborn diabetic rats.

The aim of the study was to determine whether ghrelin treatment has a protective effect on gene expression and biochemical changes in the stomach of newborn streptozotocin (STZ) induced diabetic rats. In this study, four groups of Wistar rats were used: control, ghrelin control, diabetic and diabetic+ghrelin. The rats were sacrificed after four weeks of treatment for diabetes. The gene expressions of: somatostatin, cholecystokinin, apelin and the altered active caspase-3, active caspase-8, proliferating cell nuclear antigen, were investigated in the pyloric region of the stomach and antioxidant parameters were measured in all the stomach. Although ghrelin treatment to diabetic rats lowered the stomach lipid peroxidation levels, the stomach glutathione levels were increased. Exogenous ghrelin caused an increased activities of stomach catalase, superoxide dismutase, glutathione reductase and glutathione peroxidase in diabetic rats. Numbers of somatostatin, cholecystokinin and proliferating cell nuclear antigen immunoreactive cells decreased in the diabetic+ghrelin group compared to the diabetic group. Apelin mRNA expressions were remarkably less in the diabetic+ghrelin rats than in diabetic rats. The results may indicate that ghrelin treatment has a protective effect to some extent on the diabetic rats. This protection is possibly accomplished through the antioxidant activity of ghrelin observed in type 2 diabetes. Consequently exogenous ghrelin may be a candidate for therapeutic treatment of diabetes.

Acute effects of methiocarb on oxidative damage and the protective effects of vitamin E and taurine in the liver and kidney of Wistar rats

Methiocarb (MC) is a widely used carbamate pesticide in agriculture and health programs. Although the main molecular mechanism of carbamate toxicity involves acetylcholinesterase inhibition, studies have also implicated the induction of oxidative stress. Therefore, the present study was aimed to evaluate the effect of acute MC exposure on lipid peroxidation, antioxidant defense systems, histological changes in Wistar rats and the protective effect of pretreatment with vitamin E and taurine. A total of 48 rats were randomly divided into six groups. Rats in group I were given corn oil, while those in group III were dosed with vitamin E (100 mg/kg body weight (b.w.)) and in group V were dosed with taurine (50 mg/kg b.w.). Rats in group II were administered with MC only (25 mg/kg b.w., 1/4 of median lethal dose (LD50)), while those in groups IV and VI were pretreated with vitamin E (100 mg/kg b.w.) and taurine (50 mg/kg b.w.) for 20 days, respectively, and then exposed to MC (25 mg/kg b.w.). The rats administered with MC showed significant increase in the levels of malondialdehyde in the liver and kidney as an index of lipid peroxidation. Levels of glutathione and activities of superoxide dismutase, catalase and glutathione peroxidase were significantly increased, while activity of glutathione reductase remained unchanged in both the tissues after MC treatment. Mild degenerative histological changes were observed in liver tissue, while the changes in kidney tissue were more severe then liver after MC treatment. Pretreatment with vitamin E and taurine resulted in a significant decrease in the lipid peroxidation and alleviating effects on antioxidant defense systems in both the tissues, while protective effects on the histological changes were shown only in kidney when compared with liver. In conclusion, the study has demonstrated that the acute MC exposure in Wistar rats caused oxidative damage on liver and kidney, which were partly ameliorated by the pretreatment of vitamin E and taurine.

The relation among NGF, EGF and insulin is important for triggering pancreatic β cell apoptosis.

Nerve growth factor (NGF) is a well‐known mediator for maintaining the survival of neurons, while recent studies report that its absence induces apoptosis in cultured β cells of humans and rats. However, its relationship with other growth factors that have important roles in the survival and function of β cells such as epidermal growth factor (EGF) has not yet been elucidated. The aim of this study was to investigate the effects of NGF withdrawal on the synthesis and secretion of EGF, insulin with respect to β cell apoptosis in hyperglycemic rats.

Alterations in kidney tissue following zinc supplementation to STZ-induced diabetic rats.

Diabetes mellitus is a chronic disease characterized by anomalies forming in carbohydrate, lipid, protein metabolisms and the incidence of this disease varies widely throughout the world. Zinc is an important element which is essential for life and is present in nature. In this study, the animals were divided into four groups. These groups were named as untreated; zinc sulfate; streptozotocin (STZ); STZ and zinc sulfate. STZ (65 mg/kg) was dissolved in a freshly prepared 0.01 M pH 4.5 citrate buffer and given with intraperitoneal injection in a single dose. Zinc sulfate (100mg/kg) was dissolved in distilled water and given to the animals by gavage at a daily dose for 60 days. The rats were sacrificed under ether anesthesia. This study was aimed to investigate histological and biochemical changes of zinc supplementation on the kidney tissue in STZ-induced diabetic rats. In the current study, histological and histochemical observations showed that the occurred degenerative changes decreased after giving zinc in the kidney tissue of diabetic group. Kidney glutathione (GSH) levels decreased and lipid peroxidation (LPO), nonenzymatic glycosylation (NEG), urea and creatinine levels increased in diabetic rats. GSH levels increased, while LPO, NEG, urea and creatinine levels decreased in the kidney with administration of zinc to diabetic rats. As a result, we observed curative effects of zinc given to diabetic rats. We can say that zinc may be an important antioxidant for the treatment of secondary complications of diabetes in kidney tissue.

Regulation of gene expression and biochemical changes in small intestine of newborn diabetic rats by exogenous ghrelin

The aim of this study was to investigate (i) the cholecystokinin, somatostatin and apelin mRNA levels, (ii) the changes in levels and localization of these peptides, (iii) relation between these peptides, (iv) antiapoptotic effects and (v) antioxidant effects of ghrelin. The rats were divided into four groups second day after birth. These groups were respectively treated with physiological saline, ghrelin (100μg/kg/day), streptozotocin (100mg/kg), ghrelin and streptozotocin. After four weeks, small intestine and blood samples were taken from rats. Cholecystokinin mRNA and peptide, somatostatin mRNA, release to duodenal lumen of apelin peptide and apelin mRNA signals decreased in ghrelin-treated diabetic rats compared to the diabetic group. There was no statistically significant difference among the four groups for somatostatin and apelin peptides. Caspase-3 signals were not observed only in diabetic group treated with ghrelin. Caspase-8 signals were increased while PCNA signals were decreased in diabetic group given ghrelin compared to diabetic group. Small intestine CAT, SOD, GP(x) and GST activities and GSH levels were decreased and LPO, PC levels were increased in diabetic rats. Administration of ghrelin to diabetic rats caused an increase in intestinal CAT, SOD, GP(x) and GST activities and GSH levels, while PC levels decreased. As a result, we observed positive changes in diabetic rats treated with ghrelin in both microscopic and biochemical studies. We can suggest that ghrelin may be an important hormone for the treatment of diabetes.

The potential role of combined antioxidant treatment on pancreas of STZ-diabetic mice

In diabetes, cells and tissues are damaged due to the imbalance between production of free radicals and removal of them. The effective biologic antioxidants for oxidative stress such as α-lipoic acid, vitamin E and selenium are effective in diminishing oxidative damage such as membrane lipid peroxidation. The experiment aimed to investigate the oxidative stress occurring in mitochondrial and cytoplasmic fraction of pancreatic tissues in streptozotocin-diabetic mice and the possible effects of α-lipoic acid + vitamin E + selenium combination on oxidative damage and antioxidative system by using microscopic and biochemical methods. The mice were divided into five groups. These groups were treated by citrate buffer, the solvents of the antioxidants, combined the antioxidants [α-lipoic acid (50 mg/kg), vitamin E (100 mg/kg), selenium (0.25 mg/kg)], streptozotocin (40 mg/kg × 5), combined the antioxidants and streptozotocin. The mice were sacrificed by cervical dislocation. In the experimental group given combined antioxidants following results were observed compared to diabetic group: increased percent insulin-positive cell area; decreased blood glucose levels; increased manganase superoxide dismutase activities and unsignificantly increased superoxide dismutase activities; unsignificantly decreased lipid peroxidase levels in both of fraction; unsignificantly decreased in mitochondrial fraction and unsignificantly increased in cytosolic fraction for catalase levels; not any alteration glutathione levels; not any activity in both of fraction for glutathione peroxidase. We can say that by taking the blood glucose levels and immunohistochemical results into account, the combination of triple antioxidants has a partly positive effect on diabetes. This positive effect could increase when trying different doses of combined antioxidant treatment.

Nerve growth factor neutralization suppresses β-cell proliferation through activin A and betacellulin.

Objective The aim of this study was to investigate the effects of nerve growth factor (NGF) neutralization on synthesis and secretion of activin A (Act-A) and betacellulin (BTC) from primary &bgr; cells and the importance of these relations for &bgr;-cell proliferation. Methods &bgr; Cells were isolated from euglycemic and streptozotocin-induced (75 mg/kg) hyperglycemic rats and treated with NGF neutralization antibody. The gene expression levels of Act-A and BTC in the primary &bgr; cells were evaluated using quantitative real-time polymerase chain reaction. The cellular and secreted levels of Act-A and BTC proteins were estimated using Western blot analysis. Results Nerve growth factor neutralization (1) reduced &bgr;-cell proliferation, (2) decreased Act-A at gene expression and protein levels while increasing its secretion from &bgr; cells, and (3) increased BTC at gene expression level while mildly decreasing its cellular protein level and secretion from &bgr; cells. Nerve growth factor neutralization specifically affected &bgr; cells of hyperglycemic rats. Conclusions These findings indicate that NGF is an important regulator for the synthesis and secretion of Act-A and BTC from the &bgr; cells. Moreover, the results suggested that &bgr;-cell proliferation decreased through NGF neutralization is possibly related to decreased BTC and increased Act-A secretion from &bgr; cells of hyperglycemic rats.

Carbon tetrachloride-induced kidney damage and protective effect of Amaranthus lividus L. in rats.

This study was designed to evaluate the protective effect of water extract of Amaranthus lividus L. (A. lividus) (Amaranthaceae) on carbon tetrachloride (CCl4)-induced toxicity in kidneys of rats. For this purpose, male albino Wistar rats were pretreated with A. lividus (250 and 500 mg/kg body weight (b.w.)) daily for 9 days and a single dose of CCl4 was applied intraperitoneally (50% in olive oil; 1.5 mL/kg b.w.) on the 10th day. All rats were killed 24 h after CCl4 administration, and kidneys were excised and used for determination of histopathological and biochemical parameters. CCl4 administration caused a remarkable increase in lipid peroxidation (LPO) and glutathione levels and glutathione-S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, myeloperoxidase (MPO) activities and a decrease in catalase (CAT) activity when compared to the control group. Pretreatment with A. lividus (250 and 500 mg/kg b.w.) significantly prevented the elevation in LPO level and MPO activity as well as protected the decrease in CAT activity but did not alter other biochemical parameters. The protective effect of A. lividus was further evident through the decreased histological alterations in kidneys. In conclusion, this study has indicated that A. lividus possesses protective and antioxidant effects against CCl4-induced oxidative kidney damage.