Protective effect of zinc on liver injury induced byd-galactosamine in rats

The protective effects of zinc on liver injury induced byd-galactosamine (GalN) were investigated in rats in vivo and in vitro. Zinc supplementation (50 mg/kg/d) for 5 d of rats treated with GalN (1.5 g/kg, ip) could reduce their mortality rate, restore liver pathomorphological changes, maintain zinc content, inhibit the lipid peroxidation, hasten the protein synthesis, and improve liver function. In vitro, zinc supplement could abate the death of GalN-intoxicated hepatocytes, decrease malonaldehyde (MDA) content, and maintain reduced glutathione (GSH). It is concluded that zinc has protective effects on GalN-induced liver damage. Its effects may be owing to inhibition of lipid peroxidation and hastening of protein syntheses.     

Effect of oral methionine on blood lipid peroxidation and antioxidants in alloxan-induced diabetic rats

Supplementation of thiol compounds has been suggested to protect against the toxic effects of reduced oxygen species by contributing to the thiol pool of the cell. The present study was designed to determine whether supplementation of methionine in the diet of diabetic animals protected against the oxidative stress in diabetic pathology. Oral methionine was administered at a dosage of 330 mg/100 g feed to diabetic rats. The effect was compared with the effect of insulin administration. Levels of lipid peroxides were measured in plasma, erythrocytes, and erythrocyte membrane. Anti-oxidants were measured in plasma. Diabetic condition was associated with increased lipid peroxidation and depletion in antioxidant levels. Although methionine did not affect the level of blood glucose and some of the antioxidants, it lowered the lipid peroxide content in blood. Erythrocyte lipid peroxidation activity was unaffected by methionine treatment. Administration of insulin lowered both plasma and erythrocyte lipid peroxide levels.     

A note on the stability of conjugated diene absorption of rat liver microsomal lipids after carbon tetrachloride poisoning

Liver microsomal lipid peroxidation has been observed in fatal human CCl(4) poisoning, in rats with fatty livers induced by CCl(4) or by yellow phosphorus, and in mice poisoned with 1,1,2,2-tetrachloroethane. These observations suggest the possibility that other instances of toxic liver injury may involve lipid peroxidation. Cases of acute, fatal, toxic liver injury (e.g., from halothane anesthesia) are not likely to occur at or near laboratories equipped to determine whether any lipid peroxidation might have taken place. The data presented indicate that rat livers may be stored frozen for at least 7 days with no demonstrable diminution in CCl(4)-induced conjugated diene absorption of liver microsomal lipids.     

Restoration of antioxidants in liver by methionine feeding in experimental rat urolithiasis.

The effect of methionine or citrate on antioxidant defense system has been studied in urolithic rat. Liver weight and its protein concentration did not change in the rats fed with calculi producing diet (CPD) when compared to normal diet fed rats. Feeding rats along with citrate (c-CPD) or methionine (m-CPD) improved their body weight gain. Liver microsomes and mitochondria fractions of CPD and c-CPD fed groups showed increased susceptibility for lipid peroxidation in presence of ascorbate and t-butyl hydroperoxide when compared to either control or m-CPD fed groups. Increased superoxide dismutase and xanthine oxidase activities, decreased catalase, glutathione peroxidase and glucose-6-phosphate dehydrogenase activities, decreased concentrations of reduced glutathione, total thiols, ascorbic acid and vitamin-E and increased formation of hydroxyl radical, hydroperoxides and diene conjugates were observed in the liver of both CPD fed group as well as c-CPD fed group. Except SOD and xanthine oxidase, all other parameters were normalized in m-CPD fed group. This suggested that feeding methionine reduced the susceptibility for lipid peroxidation by restoration of the level of free radical scavengers.     

Effect of oral methionine and vitamin E on blood lipid peroxidation in vitamin B6 deficient rats

Lipid peroxidation in blood of vitamin B6 deficient rats was significantly increased when compared to pair-fed controls. The observed increased lipid peroxidation in vitamin B6 deficiency was correlated with high levels of lipids, metal ions and low levels of antioxidants, alpha-tocopherol, ascorbic acid and reduced GSH. Supplementation of methionine or vitamin E along with the vitamin B6 deficient diet restored the levels of antioxidants to near normal and also protected against oxidative stress. However plasma TBARS level as well as total lipids were still elevated in M-B6 diet fed rats and normalized in E-B6-d rats.     

Enhanced lipid peroxidation is not necessary for induction of metallothionein-I by oxidative stress

A study has been made of factors which may influence the induction of metallothionein-I (MT-I) synthesis by the superoxide radical generating agent, paraquat (PQ). Hepatic concentrations of zinc (Zn) and MT-I increased in rats injected with PQ (40 mg/kg, s.c.) or fasting, but were greater in the former. Renal concentration of MT-I increased in fasted rats but not in PQ-treated rats. The data suggest that the increase in MT-I concentrations in PQ-treated rats is not caused by reduction in food intake. Administration of PQ increased hepatic concentrations of Zn, MT-I and thiobarbituric acid-reactive substances (TBA-RS), indicating the occurrence of lipid peroxidation. Treatment of rats with vitamin E (400 mg/kg, s.c.) on 4 successive days before injection of PQ prevented only the enhancement of lipid peroxidation. The data indicate that the induction of MT synthesis by PQ is not correlated with enhancement of lipid peroxidation. Similar results were obtained in the liver of rats subjected to the radical-generating conditions, such as fasting and exposure to carbon tetrachloride. Free radicals may induce MT synthesis by direct or indirect mechanisms.     

Increased methionine synthetase activity in zinc-deficient rat liver

To study the effect of zinc deficiency on folate metabolism, three groups of male Sprague-Dawley rats (zinc deficient (ZD), restricted-fed (RF + Zn), and ad libitum-fed control (control] were given a semipurified 25% egg white protein diet. The ZD group received less than 10.3 nmol zinc/g of diet, while the RF + Zn and control groups were given 1620 nmol zinc/g of diet. After 6-7 weeks of feeding, severe zinc deficiency developed in ZD rats. Hepatic methionine synthetase activity was increased in the ZD group compared to both the RF + Zn and control groups, but hepatic 5,10-CH2-H4folate reductase activity was similar in all groups. This increased methionine synthetase activity found in zinc-deficient rats might induce secondary alterations in folate metabolism. These changes include significantly lowered plasma folate levels, decreased 5-CH3-H4folate in liver, and increased rates of histidine and formate oxidation. The latter two findings suggest that the available non-5-CH3-H4folate is increased in zinc deficiency.     

Modulation of CYP4502E1 and oxidative stress by testosterone in liver and kidney of benzene treated rats

Bilateral castration increased lipid peroxidation and consequently reduced glutathione in both liver and kidney. Testosterone administration reduced lipid peroxidation in the liver of castrated and benzene treated rats, however, reduced glutathione status could not be restored. Benzene depleted CYP4502E1 in castrated rats, however, the enzyme was restored in liver and kidney both after testosterone treatment. The results suggest that testosterone affects the metabolism and disposition of benzene by influencing CYP4502E1. Other hormonal and cellular/molecular factors may also alter the actions of testosterone. Testosterone dependent mechanism of toxicity of benzene in the liver and kidney has been discussed.     

Effect of zinc supplementation on type 2 diabetes parameters and liver metallothionein expressions in Wistar rats

Zinc is a trace metal and acts as an active component of various enzymes. Zinc deficiency has been suggested to be associated with the development of diabetes. The present study investigated the role of zinc supplementation on prevention of diabetic conditions. A double-disease model mimicking hyperlipidemia and type 2 diabetes was created by applying high-fat diet and streptozotocin (STZ) to Wistar rats. We demonstrated that zinc supplementation improved symptoms of diabetes such as polydipsia and increased serum level of high-density lipoprotein cholesterol, indicating that zinc supplementation has a potential beneficial effect on diabetic conditions. The level of maldondialdehyde (MDA), an oxidative stress marker, was reduced in liver by zinc supplementation in high fat-fed rats with or without STZ injection. Meanwhile, we observed an increase in the expression of metallothioneins (MTs) in liver of rats treated with zinc. This suggests that the induction of MTs in liver, which has been shown to be important in scavenging free radicals, could be one of the underlying mechanisms of zinc supplementation on reducing MDA levels in liver. Finally, we found that zinc levels in liver were increased while there was no change in serum zinc levels, indicating that local zinc level might be a critical factor for the induction of MTs. Also, the level of MTs could potentially be an index of zinc bioavailability. Taken together, these results suggest that both zinc and MT could play an important role in balancing nutrition and metabolism to prevent diabetic development.     

Hepatic glutathione concentrations linked to ethionine toxicity in rats

1. The effect of injected ethionine on liver GSH concentrations was studied in male and female rats. 2. Liver GSH concentrations were markedly and consistently decreased in 5hr. and elevated within 24-44hr. By 72hr. the amount of liver GSH of ethionine-poisoned rats had the same values as saline-injected control rats. At no time was erythrocyte GSH concentration affected by ethionine. 3. The concentrations of non-protein thiol compounds, glycogen and ATP were also significantly decreased when the rats were killed 5hr. after ethionine injection. 4. ATP, adenine or methionine did not prevent the decrease of liver GSH produced by ethionine. From these and other observations we conclude that ethionine is not an antagonist of methionine with respect to GSH metabolism. 5. The metabolic relationship between ethionine toxicity and liver GSH concentration is briefly discussed.     

Protective antioxidant effect of vitamins C and E in streptozotocin induced diabetic rats

We have investigated the protective effect of vitamin C and E together supplementation on oxidative stress and antioxidant enzyme activities in the liver of streptozotocin-induced diabetic rats, unsupplemented diabetic and control rats. We also determined the levels of both the vitamins and oxidative stress in plasma. Vitamin supplementation in diabetic rats lowered plasma and liver lipid peroxidation, normalised plasma vitamin C levels and raised vitamin E above normal levels. In liver, the activity of glutathione peroxidase was raised significantly and that of glutathione-S-transferase was normalised by vitamin supplementation in diabetic rats. The levels of lipid peroxidation products in plasma and liver of vitamin-supplemented diabetic rats and activities of antioxidant enzymes in liver suggest that these vitamins reduce lipid peroxidation by quenching free radicals.     

Phosphine-induced oxidative damage in rats: attenuation by melatonin

Phosphine (PH(3)), from hydrolysis of aluminum, magnesium and zinc phosphide, is an insecticide and rodenticide. Earlier observations on PH(3)-poisoned insects, mammals and a mammalian cell line led to the proposed involvement of oxidative damage in the toxic mechanism. This investigation focused on PH(3)-induced oxidative damage in rats and antioxidants as candidate protective agents. Male Wistar rats were treated ip with PH(3) at 2 mg/kg. Thirty min later the brain, liver, and lung were analyzed for glutathione (GSH) levels and lipid peroxidation (as malondialdehyde and 4-hydroxyalkenals) and brain and lung for 8-hydroxydeoxyguanosine (8-OH-dGuo) in DNA. PH(3) caused a significant decrease in GSH concentration and elevation in lipid peroxidation in brain (36-42%), lung (32-38%) and liver (19-25%) and significant increase of 8-OH-dGuo in DNA of brain (70%) and liver (39%). Antioxidants administered ip 30 min before PH(3) were melatonin, vitamin C, and beta-carotene at 10, 30, and 6 mg/kg, respectively. The PH(3)-induced changes were significantly or completely blocked by melatonin while vitamin C and beta-carotene were less effective or inactive. These findings establish that PH(3) induces and melatonin protects against oxidative damage in the brain, lung and liver of rats and suggest the involvement of reactive oxygen species in the genotoxicity of PH(3).     

Protective role of zinc in nickel induced hepatotoxicity in rats

This study was planned to determine the protective role of zinc, if any, in attenuating the toxicity induced by nickel sulfate in rat liver. Female Sprague Dawley (SD) rats received either nickel alone in the dose of 800 mg/l in drinking water, zinc alone in the dose of 227 mg/l in drinking water, and nickel plus zinc or drinking water alone for a total duration of eight weeks. The effects of different treatments were studied on various parameters in rat liver which include antioxidant enzymes, levels of nickel and zinc and histoarchitecture at the light microscopic level. Further, the activities of hepatic marker enzymes AST and ALT were also studied in rat serum. Nickel treatment to the normal control animals, resulted in a significant increase in lipid peroxidation and enzyme activities of catalase and glutathione-S-transferase. On the contrary, nickel treatment to normal rats caused a significant inhibition in the levels of reduced glutathione. Superoxide dismutase activity was found to be decreased which however was not significant. Interestingly, when Zn was supplemented to nickel treated rats, the activities of catalase, and glutathione-S-transferase and the levels of GSH and lipid peroxidation came back to within normal limits. Activities of serum AST and ALT were increased significantly following nickel treatment to normal rats. Simultaneous zinc administration to nickel treated rats tended to restore the altered levels of AST and ALT. Normal control and zinc treated animals revealed normal histology of liver. On the other hand, nickel treated animals showed alterations in normal hepatic histoarchitecture which comprise of vacuolization of the hepatocytes and dilatation of sinusoids as well as increase in the number of bi-nucleated cells. Administration of zinc to nickel treated rats resulted in marked improvement in the structure of hepatocytes, thus emphasizing the protective potential of zinc in restoring the altered hepatic histoarchitecture. The nickel administration to normal rats indicated increased concentrations of nickel and decreased concentrations of zinc. However, zinc effectively brought the altered levels of nickel and zinc to within normal range. The study concludes that zinc has the potential in alleviating the toxic effects of nickel in rat liver because of its property to induce metallothionein (S-rich protein) as a free radical scavenger, or its indirect action in reducing the levels of oxygen reactive species.     

Antioxidant status and mineral contents in tissues of rutin and baicalin fed rats

The versatile benefit effects of flavonoids lead some nutritionists to believe that they are micronutrients. However, excess intake of flavonoids may cause side effects. In this paper, the effects produced by a higher intake of rutin and baicalin on antioxidant status as well as trace minerals such as iron, copper and zinc in rat tissues were studied. When rats were fed a rutin or baicalin containing diet (1%) for 20 days, the body weight gain was lower than that of the control group. Both rutin and baicalin caused significant a decrease of catalase activity and a moderate increase of total superoxide dismutase activity in the liver. The total antioxidant status of flavonoid fed rats was increased in the liver but decreased in the serum. In comparison to the control group, the lipid peroxidation level in the liver of the rutin fed group was significantly decreased; however, there was no statistical significance in the liver of the baicalin fed group and the brain of both flavonoids groups. The liver homogenates of both flavonoid fed rats significantly inhibited alkyl radical-induced lipid peroxidation. The iron contents in the liver of flavonoid fed rats were significantly decreased; rutin also caused zinc and copper decrease in the liver. These results indicated that high flavonoid intake can improve rat antioxidant systems in the liver; while it can also cause a trace mineral decrease and, in turn, reduce the activities of some metal-containing enzymes and may cause harmful effects on health.     

Influence of Fluoride on Rat Kidney Antioxidant System: Effects of Methionine and Vitamin E

The aim of the study has been to determine and compare the influence upon the kidney antioxidative system, exercised by administration of vitamin E, and vitamin E in combination with methionine, under conditions of oxidative stress induced by sodium fluoride. The experiment was carried out on Wistar FL rats (adult males) that, for 35 days, were administered water, NaF, NaF with vitamin E, or vitamin E with methionine (doses: 10 mg NaF/kg of body mass/24 h, 3 mg vitamin E per 10 μl per rat for 24 h, 2 mg methionine per rat for 24 h). The influence of administered sodium fluoride and antioxidants upon the antioxidative system in kidney was examined by analyzing the concentration of malondialdehyde (MDA) and the activity of the most important antioxidative enzymes (SOD, total and both its isoenzymes, GPX, GST, GR, and CAT). The studies carried out confirmed the disadvantageous effect of the administered dose of NaF upon the antixodiative system in rats (increase in the concentration MDA, decrease activity of all antioxidative enzymes). The administration of vitamin E increased the activity of studied enzymes with the exception of glutathione reductase GR; it also reduced the procesess of lipid peroxidation. It has been found that combined doses of vitamin E and methionine were most effective in inhibiting lipid peroxidation processes. The results confirmed the antioxidative properties of methionine.     

A decrease in S-adenosyl-L-methionine potentiates arachidonic acid cytotoxicity in primary rat hepatocytes enriched in CYP2E1

Previous studies show that treatment with a polyunsaturated fatty acid, arachidonic acid (AA), or high concentrations of cycloleucine, an inhibitor of methionine adenosyltransferase (MAT), which lowers levels of S-adenosyl-L-methionine (SAM), increased toxicity in hepatocytes from pyrazole-treated rats which expressed high levels of cytochrome P450 2E1 (CYP2E1). In this study, I used concentrations of cycloleucine or AA, which by themselves do not produce any toxicity, to evaluate whether a decrease in SAM sensitizes hepatocytes to AA toxicity, especially in hepatocytes enriched in CYP2E1. Levels of SAM were lower by 50% in hepatocytes from pyrazole- compared to saline-treated rats. Cycloleucine treatment caused a 50% decline in SAM levels with both hepatocyte preparations and SAM levels were lowest in the pyrazole-treated hepatocytes. The combination of cycloleucine plus AA produced some toxicity and apoptosis in hepatocytes from saline-treated rats but increased toxicity and apoptosis was found in the hepatocytes from pyrazole-treated rats. Cytotoxicity could be prevented by incubation with SAM, the antioxidant trolox, and the mitochondrial permeability transition inhibitor trifluoperazine. The enhanced cytotoxicity could also be protected by treating rats with chlormethiazole, a specific inhibitor of CYP2E1, thus validating the role of CYP2E1. Cycloleucine plus AA treatment elevated production of reactive oxygen species (ROS) and lipid peroxidation to greater extents with the hepatocytes from pyrazole-treated rats than that from the saline-treated rats. I hypothesize that increased production of ROS by hepatocytes enriched in CYP2E1 potentiates AA-induced lipid peroxidation and toxicity when hepatoprotective levels of SAM are lowered. Such interactions, e.g. induction of CYP2E1, decline in SAM and polyunsaturated fatty acid-induced lipid peroxidation, may contribute to alcohol-induced liver injury.     

Antioxidative enzymes in the liver and kidney of alloxan induced diabetic rats and their implications in cadmium toxicity

The influence of insulin-dependent diabetes mellitus on the oxidative stress caused by cadmium in the liver and kidney of laboratory rats has been studied. The results suggest that cadmium and alloxan diabetes independently promote lipid peroxidation in both liver and kidney. However, lipid peroxidation diminished in the diabetic rats fed cadmium. Administration of cadmium to normal and diabetic rats depleted glutathione in liver only. No significant change was observed in the activity of glutathione peroxidase in kidney, whereas administration of cadmium to diabetic rats stimulated catalase activity when compared to cadmium-fed rats. The actual mechanism of these effects still remains to be confirmed, but an antagonistic relationship between cytotoxic mechanisms of diabetes mellitus and cadmium is speculated upon. The insulin-dependent activity of a unique form of cytochrome 450j may be involved.     

Dehydroepiandrosterone protects tissues of streptozotocin-treated rats against oxidative stress

Chronic hyperglycemia in diabetes determines the overproduction of free radicals, and evidence is increasing that these contribute to the development of diabetic complications. It has recently been reported that dehydroepiandrosterone possesses antioxidant properties; this study evaluates whether, administered daily for three weeks per os, it may provide antioxidant protection in tissues of rats with streptozotocin-induced diabetes. Lipid peroxidation was evaluated on liver, brain and kidney homogenates from diabetic animals, measuring both steady-state concentrations of thiobarbituric acid reactive substances and fluorescent chromolipids. Hyperglycemic rats had higher thiobarbituric acid reactive substances formation and fluorescent chromolipids levels than controls. Dehydroepiandrosterone-treatment (4 mg/day for 3 weeks) protected tissues against lipid peroxidation: liver, kidney and brain homogenates from dehydroepiandrosterone-treated animals showed a significant decrease of both thiobarbituric acid reactive substances and fluorescent chromolipids formation. The effect of dehydroepiandrosterone on the cellular antioxidant defenses was also investigated, as impaired antioxidant enzyme activities were considered proof of oxygen-dependent toxicity. In kidney and liver homogenates, dehydroepiandrosterone treatment restored to near-control values the cytosolic level of reduced glutathione, as well as the enzymatic activities of superoxide-dismutase, glutathione-peroxidase, catalase. In the brain, only an increase of catalase activity was evident (p < .05), which reverted with dehydroepiandrosterone treatment. The results demonstrate that DHEA treatment clearly reduces oxidative stress products in the tissues of streptozotocin-treated rats.     

Methylthioadenosine phosphorylase gene expression is impaired in human liver cirrhosis and hepatocarcinoma

Methylthioadenosine phosphorylase (MTAP) is a key enzyme in the methionine and adenine salvage pathways. In mammals, the liver plays a central role in methionine metabolism, and this essential function is lost in the progression from liver cirrhosis to hepatocarcinoma. Deficient MTAP gene expression has been recognized in many transformed cell lines and tissues. In the present work, we have studied the expression of MTAP in human and experimental liver cirrhosis and hepatocarcinoma. We observe that MTAP gene expression is significantly reduced in human hepatocarcinoma tissues and cell lines. Interestingly, MTAP gene expression was also impaired in the liver of CCl4-cirrhotic rats and cirrhotic patients. We provide evidence indicating that epigenetic mechanisms, involving DNA methylation and histone deacetylation, may play a role in the silencing of MTAP gene expression in hepatocarcinoma. Given the recently proposed tumor suppressor activity of MTAP, our observations can be relevant to the elucidation of the molecular mechanisms of multistep hepatocarcinogenesis.     

Effect of thiols on lipid peroxidation in rat liver microsomes

The stimulatory or inhibitory effects of various thiol compounds on in vitro lipid peroxidation by iron-ascorbate in rat liver microsomes were determined. Glutathione had no measurable pro-oxidant capacity, in contrast, it protected against lipid peroxidation. N-Acetyl l-cysteine and S-methyl-glutathione had no effect on in vitro lipid peroxidation. l-Cysteine stimulated lipid peroxidation and also of d-penicillamine and dl-dithiothreitol the pre-oxidant capacity predominated the anti-oxidant capacity. Cysteamine afforded a pronounced protection against in vitro lipid peroxidation. In contrast to the labile character of the glutathione dependent protection, the protection by cysteamine was not affected by heat-pretreatment of the liver microsomes or alkylating protein sulfhydryl groups by N-ethyl maleimide. Again in contrast to glutathione, the protection against in vitro microsomal lipid peroxidation by cysteamine was not reduced after in vivo lipid peroxidation induced by CC14. This suggests that even after the process of lipid peroxidation has been started, administration of cysteamine might still be beneficial.