Surgical stress-induced alterations in retinoid metabolism in the small intestine: role of oxygen free radicals

Oxidative stress in the small intestine can result in altered cell proliferation, migration, and differentiation of villus-crypt cells. Retinoid metabolism is recognized as an important mediator of cellular differentiation in the intestine. This study examined the effect of oxidative stress in retinoid metabolism in a surgical stress model. Surgical stress was performed by handling the intestine as done during laparotomy. Villus-crypt cells were isolated at different time periods and various retinoid concentrations in the cell homogenate and the retinoic acid forming enzymes were quantitated using HPLC. Surgical stress resulted in altered retinoid levels in various cell populations in the small intestine at 1 and 12h. The activity of alkaline phosphatase and retinal oxidase was also altered at these time points and all these changes were prevented by inhibiting superoxide generation using xanthine oxidase inhibitor, allopurinol. These studies suggest that alterations seen in enterocytes during surgical stress may be mediated by changes in retinoid metabolism.     

Copper-deficient rat embryos are characterized by low superoxide dismutase activity and elevated superoxide anions

The teratogenicity of copper (Cu) deficiency may result from increased oxidative stress and oxidative damage. Dams were fed either control (8.0 microg Cu/g) or Cu-deficient (0.5 microg Cu/g) diets. Embryos were collected on Gestational Day 12 for in vivo studies or on Gestational Day 10 and cultured for 48 h in Cu-deficient or Cu-adequate media for in vitro studies. Superoxide dismutase (SOD), glutathione peroxidase (GPX), and glutathione reductase (GR) activities were measured in control and Cu-deficient embryos as markers of the oxidant defense system. Superoxide anions were measured as an index of exposure to reactive oxygen species (ROS). No differences were found in GPX or GR activities among treatment groups. However, SOD activity was lower and superoxide anion concentrations higher in Cu-deficient embryos cultured in Cu-deficient serum compared to control embryos cultured in control serum. Even so, Cu-deficient embryos had similar CuZnSOD protein levels as controls. In the in vitro system, Cu-deficient embryos had a higher frequency of malformations and increased staining for superoxide anions in the forebrain, heart, forelimb, and somites compared to controls. When assessed for lipid and DNA oxidative damage, conjugated diene concentrations were similar among the groups, but a tendency was observed for Cu-deficient embryos to have higher 8-hydroxy-2'-deoxyguanosine concentrations than controls. Thus, Cu deficiency resulted in embryos with malformations and reduced SOD enzyme activity. Increased ROS concentrations in the Cu-deficient embryo may cause oxidative damage and contribute to the occurrence of developmental defects.     

Alterations in cardiac membrane Ca2+ transport during oxidative stress

Although cardiac dysfunction due to ischemia-reperfusion injury is considered to involve oxygen free radicals, the exact manner by which this oxidative stress affects the myocardium is not clear. As the occurrence of intracellular Ca²⁺ overload has been shown to play a critical role in the genesis of cellular damage due to ischemia-reperfusion, this study was undertaken to examine whether oxygen free radicals are involved in altering the sarcolemmal Ca²⁺-transport activities due to reperfusion injury. When isolated rat hearts were made globally ischemic for 30 min and then reperfused for 5 min, the Ca²⁺ -pump and Na⁺-Ca²⁺ exchange activities were depressed in the purified sarcolemmal fraction; these alterations were prevented when a free radical scavenger enzymes (superoxide dismutase plus catalase) were added to the reperfusion medium. Both the Ca²⁺- pump and Na⁺- Ca²⁺ exchange activities in control heart sarcolemmal preparations were depressed by activated oxygen-generating systems containing xanthine plus xanthine oxidase and H₂O₂; these changes were prevented by the inclusion of superoxide dismutase and catalase in the incubation medium. These results support the view that oxidative stress during ischemia-reperfusion may contribute towards the occurrence of intracellular Ca²⁺ overload and subsequent cell damage by depressing the sarcolemmal mechanisms governing the efflux of Ca²⁺ from the cardiac cell.     

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.     

Modification of the xanthine-converting enzyme of perfused rat heart during ischemia and oxidative stress

The reversible and irreversible conversion of xanthine dehydrogenase to xanthine oxidase during ischemia/reperfusion and oxidative stress induced by hydrogen peroxide or diamide and its relationship with glutathione and protein SH groups were studied. The direct spectrophotometric measurement of the various forms of the xanthine-converting enzyme indicates that, in the fresh rat heart or after normoxic perfusion, there always is a basal level of 80% xanthine dehydrogenase and 20% of xanthine oxidase (15% irreversible and 5% reversible) that could contribute to the background production of free radicals. There is no significant increase of irreversible xanthine oxidase during ischemia nor during reperfusion. After global ischemia the reversible oxidase shows almost no increase while, when ischemia is followed by reperfusion, there is a limited increase (less then 9%) of the reversible xanthine oxidase. In the latter conditions there is a decrease of glutathione and of SH groups of about 70% and 25%, respectively. Perfusion for 1 h with oxidizing agents like hydrogen peroxide (60 microM) or diamide (100 microM) determines a marked conversion of xanthine dehydrogenase to reversible xanthine oxidase of about 40% and 60%, respectively; this oxidase activity partially reconverts to the dehydrogenase after withdrawing the oxidizing agents from the perfusion medium. The level of irreversible xanthine oxidase remains unchanged in all the conditions tested. Both hydrogen peroxide and diamide induce a strong decrease in SH groups and depletion of glutathione. The xanthine dehydrogenase----xanthine oxidase conversion thus appears to be sensitive to the redox state of thiol groups.     

Beneficial effects of Murraya koenigii leaves on antioxidant defense system and ultra structural changes of pancreatic beta-cells in experimental diabetes in rats

Oxidative stress and oxidative damage to tissues are common end points of chronic diseases such as atherosclerosis, diabetes, and rheumatoid arthritis. Oxidative stress in diabetes coexists with a reduction in the antioxidant status, which can further increase the deleterious effects of free radicals. The aim of the present study was to evaluate the possible protective effects of Murraya koenigii leaves extract against beta-cell damage and antioxidant defense systems of plasma and pancreas in streptozotocin induced diabetes in rats. The levels of glucose and glycosylated hemoglobin in blood and insulin, Vitamin C, Vitamin E, ceruloplasmin, reduced glutathione and TBARS were estimated in plasma of control and experimental groups of rats. To assess the changes in the cellular antioxidant defense system such as the level of reduced glutathione and activities of superoxide dismutase, catalase and glutathione peroxidase were assayed in pancreatic tissue homogenate. The levels of glucose, glycosylated hemoglobin, insulin, TBARS, enzymatic and non-enzymatic antioxidants were altered in diabetic rats. These alterations were reverted back to near control levels after the treatment of M. koenigii leaves extract. Transmission electron microscopic studies also revealed the protective nature of M. koenigii leaves on pancreatic beta-cells. These findings suggest that M. koenigii treatment exerts a therapeutic protective nature in diabetes by decreasing oxidative stress and pancreatic beta-cell damage. The antioxidant effect of the M. koenigii extract was compared with glibenclamide, a well-known hypoglycemic drug.     

Tamarix gallica ameliorates thioacetamide-induced hepatic oxidative stress and hyperproliferative response in Wistar rats

Tamarix gallica, a hepatic stimulant and tonic, was examined for its ability to inhibit thioacetamide (TAA)-induced hepatic oxidative stress, toxicity and early tumor promotion response in male Wistar rats. TAA (6.6 mmol/kg body wt. i.p) enhanced lipid peroxidation, hydrogen peroxide content, glutathione S-transferase and xanthine oxidase with reduction in the activities of hepatic antioxidant enzymes viz., glutathione peroxidase, superoxide dismutase and caused depletion in the level of hepatic glutathione content. A marked increase in liver damage markers was also observed. TAA treatment also enhanced tumor promotion markers, ornithine decarboxylase (ODC) activity and [3H] thymidine incorporation into hepatic DNA. Pretreatment of rats orally with Tamarix gallica extract (25 and 50 mg/kg body weight) prevented TAA-promoted oxidative stress and toxicity. Prophylaxis with Tamarix gallica significantly reduced the susceptibility of the hepatic microsomal membrane for iron-ascorbate induced lipid peroxidation, H2O2 content, glutathione S-transferase and xanthine oxidase activities. There was also reversal of the elevated levels of liver marker parameters and tumor promotion markers. Our data suggests that Tamarix gallica is a potent chemopreventive agent and may suppress TAA-mediated hepatic oxidative stress, toxicity, and tumor promotion response in rats.     

Regional variations in intestinal brush border membrane fluidity and function during diabetes and the role of oxidative stress and non-enzymatic glycation

The physical state (fluidity) of lipids modulates the activities of several membrane bound enzymes and transport proteins. Alteration of brush border membrane (BBM) fluidity is one of the several changes exhibited by the small intestine during diabetes. In the present study, an investigation of the diabetes induced regional changes in fluidity, oxidative damage, non-enzymatic glycation as well as the activities and the kinetic parameters of the enzymes alkaline phosphatase and -glutamyl transpeptidase was carried out on the intestinal BBM. At the end of 6 weeks of diabetes, significant increases in the extent of both oxidative damage and non-enzymatic glycation were observed along the length of the intestine along with a simultaneous decrease in membrane fluidity. A significant correlation between the decrease in BBM fluidity and increase in non-enzymatic glycation was observed in the duodenum and jejunum. Additionally regional variations in the activities and kinetic parameters of both the enzymes were observed.     

Development of oxidative stress and cell damage in the liver of rats with water-immersion restraint stress

We examined how oxidative stress and cell damage develop in the liver of rats subjected to water-immersion stress (WIRS). In rats subjected to WIRS for 1.5, 3 or 6 h, serum alanine aminotransferase and aspartate aminotransferase activities increased time-dependently. In the liver tissue, vacuolization and apoptosis occurred at 1.5 h of WIRS and vacuolization further developed without further appearance of apoptosis at 3 h or 6 h. Serum lipid peroxide (LPO) and NOx (nitrite/nitrate) concentrations increased at 3 h of WIRS and these increases were enhanced at 6 h. In liver tissue, increases in LPO and NOx concentrations and myeloperoxidase activity and decreases in ascorbic acid and reduced glutathione concentrations and superoxide dismutase activity occurred at 3 h of WIRS and these changes were enhanced at 6 h, although vitamin E concentration and xanthine oxidase activity were unchanged. These results indicate that oxidative stress in the liver of rats with WIRS develops after the appearance of cell damage in the tissue, and suggests that oxidative stress is caused through disruption of the antioxidant defense system and increases in NO generation and neutrophil infiltration in the liver, which may contribute to the progression of cell damage in the tissue.     

Effects of piperine on antioxidant pathways in tissues from normal and streptozotocin-induced diabetic rats

Using diabetes mellitus as a model of oxidative damage, this study investigated whether subacute treatment (10 mg/kg/day, intraperitoneally for 14 days) with the compound piperine would protect against diabetes-induced oxidative stress in 30-day streptozotocin-induced diabetic Sprague-Dawley rats. Liver, kidney, brain, and heart were assayed for degree of lipid peroxidation, reduced and oxidized glutathione (GSH and GSSG, respectively) content, and activities of the free-radical detoxifying enzymes catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase. Piperine treatment of normal rats enhanced hepatic GSSG concentration by 100% and decreased renal GSH concentration by 35% and renal glutathione reductase activity by 25% when compared to normal controls. All tissues from diabetic animals exhibited disturbances in antioxidant defense when compared with normal controls. Treatment with piperine reversed the diabetic effects on GSSG concentration in brain, on renal glutathione peroxidase and superoxide dismutase activities, and on cardiac glutathione reductase activity and lipid peroxidation. Piperine treatment did not reverse the effects of diabetes on hepatic GSH concentrations, lipid peroxidation, or glutathione peroxidase or catalase activities; on renal superoxide dismutase activity; or on cardiac glutathione peroxidase or catalase activities. These data indicate that subacute treatment with piperine for 14 days is only partially effective as an antioxidant therapy in diabetes.     

Evaluation of the fluidity and functionality of the renal cortical brush border membrane in experimental diabetes in rats

The present study was aimed at addressing the effect of hyperglycemia on the renal cortical brush border membrane. The fluidity and the functionality of the renal cortical brush border membrane have been evaluated after 6 weeks of streptozotocin-induced diabetes in rats. Lipid peroxidation and protein oxidation were first performed to confirm a state of oxidative stress. The fluidity of the brush border membrane of diabetic rats decreased significantly by 15.76%. There was an increase in the amount of early (19.39%) and advanced (42.23%) glycation end-products suggesting the accumulation of significant amount of non-enzymic glycation products at 6 weeks of diabetes. Although, the activities of both gamma-glutamyl transpeptidase and alkaline phosphatase of the brush border membrane decreased, that of the latter decreased to a significant extent with an increase in K(m) (81%) and no change in the V(max). A study of the activities of glutathione-dependent antioxidant enzymes in the renal cortical homogenates showed that the activities of glutathione peroxidase and glyoxalase II were altered significantly. Our study seems to suggest that increased free radical generation accompanied by non-enzymic glycation may be responsible for oxidative stress and an increased rigidity of the diabetic brush border membrane. Alkaline phosphatase may thus serve as a potentially useful marker of free radical induced damage to the renal cortical brush border membrane. The results also suggest that enhanced susceptibility to oxidative stress during early stages may be an important factor in the development of secondary complications of diabetes.     

Aortic-banding induces myocardial oxidative stress and changes in concentration and activity of antioxidants in male Wistar rats

Myocardial activity and gene expression of antioxidant defenses and oxidative damage were examined in an experimental model of pressure overload hypertrophy. Male Wistar rats were divided into abdominal aortic-banded or sham-operated groups. After 30 days, arterial pressure and heart rate were measured. Heart, lung, and liver were extracted and weighted to evaluate cardiac hypertrophy and pulmonary and hepatic congestion. Heart homogenates were prepared to quantify lipid peroxidation (LPO); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and glutathione reductase (GR); and Cu-Zn SOD and GST concentrations. Total glutathione (GSH) myocardial content was also measured. Arterial pressure (142 +/- 17 mmHg) and cardiac hypertrophy index (3.4 +/- 0.45 mg/g) were significantly increased (by 38% and 22%, respectively, p<0.0001) in the aortic-banded group. LPO was enhanced by 55% in the aortic-banded group (11891 +/- 766 cps/mg protein, p<0.001) compared with that in the controls. SOD activity and concentration were higher (40% and 38%, 15.15 +/- 1.03 U/mg protein, 49.187 pixels, respectively, p<0.05) in the aortic-banded group than in the controls. Aortic-banding induced a decrease by 28% in GST (48 +/- 10 pmol/min/mg protein, p<0.005), by 36% in GPx (38.2 +/- 9.5 nmol/min/mg protein, p<0.005), by 31% in GR activities (1.55 +/- 0.23 nmol/mg protein, p<0.0005), and by 43% in GSH content (0.13 +/- 0.02 nmol/mg protein, p<0.005). In conclusion, in this model it was observed that myocardial oxidative stress induces alterations in antioxidant enzyme activities and protein expression. The follow up of these parameters could afford an early therapeutical window to avoid heart failure progression.     

Investigation of the protective effects of crocin on acrylamide induced small and large intestine damage in rats

We investigated repair of acrylamide (AA) induced damage in intestines by administration of crocin. We used 40 male Wistar rats in four groups of 10 animals: control, AA, crocin, and AA + crocin groups. We investigated biochemical and histological changes to small and large intestine. AA ingestion decreased glutathione (GSH) levels and total antioxidant status (TAS) in the intestine compared to the control group, while superoxide dismutase (SOD) and catalase (CAT) activities, and total oxidant status (TOS) and malondialdehyde (MDA) levels were increased. Villi were shortened and villus degeneration was observed in ileum of the AA group. Degeneration of surface epithelium and Liberkühn crypts were observed in colon sections. GSH and TAS levels increased after administration of AA together with crocin, while SOD and CAT levels and TOS and MDA levels decreased; significant recovery of histological damage also was observed. We found that crocin exhibits protective effects on AA induced small and large intestine damage by inhibiting oxidative stress.     

Oxidative stress occurs during soybean nodule senescence

Several markers of oxidative stress were measured in 2- to 10-week-old soybean (Glycine max [L.] Merr.) nodules. There were increases in peroxides, protein carbonyls and modified DNA base concentrations with nodule age. The catalytic iron content also increased significantly during nodule ageing. Iron contained in the peribacteroid space was effective in promoting lipid peroxidation and this might contribute to the degradation of the peribacteroid membrane in senescing nodules. The concentration of the oxidized forms of glutathione and homoglutathione increased significantly during nodule development and the concentration of reduced glutathione and homoglutathione decreased during senescence. Taken together, these results are consistent with the development of oxidative stress in senescing nodules. Significant DNA and protein damage also occurred in the first days of nodule development, suggesting that an earlier period of oxidative stress might occur in the period over which the symbiosis becomes established. Received: 7 July 1998 / Accepted: 30 November 1998     

Proteasome activity in experimental diabetes

Numerous studies have indicated that oxidative stress contributes to the development and progression of diabetes and other related complications. Since the ubiquitin-proteasome pathway is involved in degradation of oxidized proteins, it is to be expected that alterations in proteasome-dependent proteolysis accompany diabetes. This paper focuses on the role of the proteasome in alloxan-induced experimental diabetes. The changes in proteasomal activity and oxidative stress indices (protein oxidation and lipid peroxidation) were evaluated. The obtained results revealed increased protein oxidation and lipid peroxidation, as well as alterations in proteasomal activities in diabetic rats. Our data indicates a significant decrease in chymotryptic-like activity; increased tryptic-like activity; and unchanged post-glutamyl peptide hydrolytic-like activity. These findings suggest the presence of oxidative stress in diabetes that appears to result in changes to the ubiquitin-proteasome pathway.     

Caffeic acid phenethyl ester (CAPE) protects brain against oxidative stress and inflammation induced by diabetes in rats

Diabetic patients reveal significant disorders, such as nephropathy, cardiomyopathy, and neuropathy. As oxidative stress and inflammation seem to be implicated in the pathogenesis of diabetic brain, we aimed to investigate the effects of caffeic acid phenethyl ester (CAPE) on oxidative stress and inflammation in diabetic rat brain. Diabetes was induced by a single dose of streptozotocin (45 mg kg⁻¹, i.p.) injection into rats. Two days after streptozotocin treatment 10 μM kg⁻¹ day⁻¹ CAPE was administrated and continued for 60 days. Here, we demonstrate that CAPE significantly decreased the levels of nitric oxide and malondialdehyde induced by diabetes, and the activities of catalase, glutathione peroxidase, and xanthine oxidase in the brain. However, glutathione levels were increased by CAPE. The mRNA expressions of tumor necrosis factor (TNF)-α and interferon (IFN)-γ, and inducible nitric oxide synthase (iNOS) were remarkably enhanced in brain by diabetes. CAPE treatments significantly suppressed these inflammatory cytokines (about 70% for TNF-α, 26% for IFN-γ) and NOS (completely). Anti-inflammatory cytokine IL-10 mRNA expression was not affected by either diabetes or CAPE treatments. In conclusion, diabetes induces oxidative stress and inflammation in the brain, and these may be contributory mechanisms involved in this disorder. CAPE treatment may reverse the diabetic-induced oxidative stress in rat brains. Moreover, CAPE reduces the mRNA expressions of TNF-α and IFN-γ in diabetic brain; suggesting CAPE suppresses inflammation as well as oxidative stress occurred in the brain of diabetic patients.     

Does selenium exert cardioprotective effects against oxidative stress in myocardial ischemia?

In the mid-1960s, a small number of scientists postulated the role of oxidative stress and oxygen-derived free radicals in the pathophysiological mechanisms underlying ischemic heart disease. However, because of the technical difficulty of measuring free radicals and quantitating oxidative damage, it was very difficult to prove that free radicals could contribute to cell pathology. The role of oxidative stress in biological systems was not definitely recognized until the early 1980s when measurement of short-lived oxygen-derived reactive species was made possible by the advent of sophisticated techniques such as EPR spectroscopy or fluorescent probes. These enabled both the study of free radical biochemistry and the acquisition of useful information about the nature and consequences of free radical-induced protein and lipid oxidation. The hypothesis that reactive oxygen species mediate cellular damage produced upon reperfusion of ischemic myocardium has gained considerable support during the past 10-15 years. Several experimental studies indicated that the administration of antioxidant enzymes or non-enzymatic antioxidants offers a significant degree of protection against ischemic damage, improving functional recovery and reducing morphological alterations to cardiomyocytes. In this context, selenium, as an essential component of glutathione peroxidase, plays a critical role in protecting aerobic tissues from oxygen radical-initiated cell injury.     

Decreased enzymic protection and increased sensitivity to oxidative damage in erythrocytes as a function of cell and donor aging.

Erythrocytes from young and old rats were separated into four age fractions by density-gradient centrifugation. The specific activities per cell were determined for glucose-6-phosphate dehydrogenase (EC 1.1.1.49), glutathione peroxidase (EC 1.11.1.9), glutathione reductase (EC 1.6.4.2) and catalase (EC 1.11.1.6). Decreased specific activities were observed with increasing cell age for all four enzymes in both young and old animals. In addition, significant differences in the activities of these enzymes were observed between cells of the same age fraction from young and old donors. Susceptibility of fractionated erythrocytes to oxidative attack in vitro generated by incubation with xanthine/xanthine oxidase increased with both cell and animal age. The amount of membrane-lipid peroxidation also increased with cell and animal aging, as measured by both thiobarbituric acid and fluorescent chromolipid assays. Increases of 2-3-fold in the contents of lipid peroxides were observed between the youngest and oldest age fractions of young rats. Lipid peroxide contents in young cells of old animals were equal to those in old erythrocytes from young rats and increased by 30% with cell aging in the old donors. These results suggest that the extent of enzymic protection against oxidative and peroxidative damage decreases with erythrocyte aging. More importantly, enzymic protection in cells of old rats is considerably decreased already in the early stages of their lifespan.     

Antioxidant capacity responsible for a hypocholesterolemia is independent of dietary cholesterol in adult rats fed rice protein

Dietary cholesterol and aging are major risk factors to accelerate oxidation process for developing hypercholesterolemia. The major aim of this study is to elucidate the effects of rice protein on cholesterol level and oxidative stress in adult rats fed with and without cholesterol. After 2 weeks of feeding, hepatic and plasma contents of cholesterol, reduced glutathione (GSH), oxidized glutathione (GSSG), malondialdehyde (MDA) and protein carbonyl (PCO) were measured. In liver, total antioxidative capacity (T-AOC), activities of antioxidant enzymes (total superoxide dismutase, T-SOD; catalase, CAT), glutathione metabolizing enzyme activities and gene expression levels (γ-glutamylcysteine synthetase, γ-GCS; glutathione reductase, GR; glutathione peroxidase, GPx) were determined. Under cholesterol-free/enriched dietary condition, T-AOC, activities of T-SOD and CAT, glutathione metabolism related enzymes' activities and mRNA levels (γ-GCS, GR and GPx) were effectively stimulated by rice proteins as compared to caseins. Compared with caseins, rice proteins significantly increased hepatic and plasma GSH contents, whereas hepatic and plasma accumulations of MDA, PCO and GSSG were significantly reduced by rice protein-feedings. As a result, the marked reductions of cholesterol in the plasma and in the liver were observed in adult rats fed rice proteins with and without cholesterol. The present study demonstrates that the hypocholesterolemic effect of rice protein is attributable to inducing antioxidative response and depressing oxidative damage in adult rats fed cholesterol-free/enriched diets. Results suggest that the antioxidant capability involved in the hypocholesterolemic action exerted by rice protein is independent of dietary cholesterol during adult period.     

Testis glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase activities in aminoguanidine-treated diabetic rats

Severe steroidogenic and spermatogenic alterations are reported in association with diabetic manifestations in humans and experimental animals. This study was planned to determine whether oxidative stress is involved in diabetes-induced alterations in the testes. Diabetes was induced in male rats by injection of 50 mg/kg of streptozotocin (STZ). Ten weeks after injection of STZ, levels of selenium and activities of selenium dependent-glutathione peroxidase (GPx) and phospholipid hydroperoxide glutathione peroxidase (PHGPx) were measured in rat testis. Lipid and protein oxidations were evaluated as measurements of testis malondialdehyde (MDA) and protein carbonyl levels, respectively. Testis sulfydryl (SH) levels were also determined. The control levels of GPx and PHGPx activities were found to be 46.5 +/- 6.2 and 108.8 +/- 19.8 nmol GSH/mg protein/min, respectively. Diabetes caused an increase in testis GPx (65.0 +/- 21.1) and PHGPx (155.9 +/- 43.1) activities but did not affect the levels of selenium or SH. However, the testis MDA and protein carbonyl levels as markers of lipid and protein oxidation, respectively, did not increase in the diabetic group. Aminoguanidine (AG) treatment of diabetic rats returned the testis PHGPx activity (136.5 +/- 24.9) to the control level but did not change the value of GPx activity (69.2 +/- 17.4) compared with diabetic group. MDA and protein carbonyl levels in testis were not affected by AG treatment of diabetic rats, but interestingly AG caused SH levels to increase. The results indicate that reactive oxygen radicals were not involved in possible testicular complications of diabetes because diabetes-induced activations of GPx and PHGPx provided protection against oxidative stress, which was reported to be related to some diabetic complications.