Hypermethioninemia provokes oxidative damage and histological changes in liver of rats

In the present study we evaluated the effect of chronic methionine administration on oxidative stress and biochemical parameters in liver and serum of rats, respectively. We also performed histological analysis in liver. Results showed that hypermethioninemia increased chemiluminescence, carbonyl content and glutathione peroxidase activity, decreased total antioxidant potential, as well as altered catalase activity. Hypermethioninemia increased synthesis and concentration of glycogen, besides histological studies showed morphological alterations and reduction in the glycogen/glycoprotein content in liver. Serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and glucose were increased in hypermethioninemic rats. These findings suggest that oxidative damage and histological changes caused by methionine may be related to the hepatic injury observed in hypermethioninemia.     

Experimental hyperprolinemia induces mild oxidative stress, metabolic changes, and tissue adaptation in rat liver

The present study investigated the effects of chronic hyperprolinemia on oxidative and metabolic status in liver and serum of rats. Wistar rats received daily subcutaneous injections of proline from their 6th to 28th day of life. Twelve hours after the last injection the rats were sacrificed and liver and serum were collected. Results showed that hyperprolinemia induced a significant reduction in total antioxidant potential and thiobarbituric acid-reactive substances. The activities of the antioxidant enzymes catalase and superoxide dismutase were significantly increased after chronic proline administration, while glutathione (GSH) peroxidase activity, dichlorofluorescin oxidation, GSH, sulfhydryl, and carbonyl content remained unaltered. Histological analyses of the liver revealed that proline treatment induced changes of the hepatic microarchitecture and increased the number of inflammatory cells and the glycogen content. Biochemical determination also demonstrated an increase in glycogen concentration, as well as a higher synthesis of glycogen in liver of hyperprolinemic rats. Regarding to hepatic metabolism, it was observed an increase on glucose oxidation and a decrease on lipid synthesis from glucose. However, hepatic lipid content and serum glucose levels were not changed. Proline administration did not alter the aminotransferases activities and serum markers of hepatic injury. Our findings suggest that hyperprolinemia alters the liver homeostasis possibly by induction of a mild degree of oxidative stress and metabolic changes. The hepatic alterations caused by proline probably do not implicate in substantial hepatic tissue damage, but rather demonstrate a process of adaptation of this tissue to oxidative stress. However, the biological significance of these findings requires additional investigation.     

Experimental hyperphenylalaninemia provokes oxidative stress in rat brain

Tissue accumulation of L-phenylalanine (Phe) is the biochemical hallmark of human phenylketonuria (PKU), an inherited metabolic disorder clinically characterized by mental retardation and other neurological features. The mechanisms of brain damage observed in this disorder are poorly understood. In the present study we investigated some oxidative stress parameters in the brain of rats with experimental hyperphenylalaninemia. Chemiluminescence, total radical-trapping antioxidant potential (TRAP), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities were measured in the brain of the animals. We observed that chemiluminescence is increased and TRAP is reduced in the brain of hyperphenylalaninemic rats. Similar data were obtained in the in vitro experiments using Phe at various concentrations. CAT activity was significantly inhibited by Phe in vitro and in vivo, whereas GSH-Px activity was reduced in vivo but not in vitro and SOD activity was not altered by any treatment. The results indicate that oxidative stress may be involved in the neuropathology of PKU. However, further studies are necessary to confirm and extend our findings to the human condition and also to determine whether an antioxidant therapy may be of benefit to these patients.     

Dapsone induces oxidative stress and impairs antioxidant defenses in rat liver

Dapsone (DDS) is currently used in the treatment of leprosy, malaria and in infections with Pneumocystis jirovecii and Toxoplasma gondii in AIDS patients. Adverse effects of DDS involve methemoglobinemia and hemolysis and, to a lower extent, liver damage, though the mechanism is poorly characterized. We evaluated the effect of DDS administration to male and female rats (30 mg/kg body wt, twice a day, for 4 days) on liver oxidative stress through assessment of biliary output and liver content of reduced (GSH) and oxidized (GSSG) glutathione, lipid peroxidation, and expression/activities of the main antioxidant enzymes glutathione peroxidase, superoxide dismutase, catalase and glutathione S-transferase. The influence of DDS treatment on expression/activity of the main DDS phase-II-metabolizing system, UDP-glucuronosyltransferase (UGT), was additionally evaluated. The involvement of dapsone hydroxylamine (DDS-NHOH) generation in these processes was estimated by comparing the data in male and female rats since N-hydroxylation of DDS mainly occurs in males. Our studies revealed an increase in the GSSG/GSH biliary output ratio, a sensitive indicator of oxidative stress, and in lipid peroxidation, in male but not in female rats treated with DDS. The activity of all antioxidant enzymes was significantly impaired by DDS treatment also in male rats, whereas UGT activity was not affected in any sex. Taken together, the evidence indicates that DDS induces oxidative stress in rat liver and that N-hydroxylation of DDS was the likely mediator. Impairment in the activity of enzymatic antioxidant systems, also associated with DDS-NHOH formation, constituted a key aggravating factor.     

Ethanol-induced changes in methionine metabolism in rat liver

The administration of alcohol to rats fed a protein-restricted diet results in significant changes in the hepatic content of four enzymes of methionine metabolism. The levels of s-adenosylmethionine synthetase, cystathionine synthase, and betaine-homocysteine methyltransferase increase while the level of methyltetrahydrofolate-homocysteine methyltransferase decreases. These changes represent a reversal of the normal adaptive response to protein-restriction. The resultant impairment in methionine conservation could explain the alcohol-induced increase in the dietary lipotrope requirement.     

Chronic ethanol feeding causes oxidative stress in rat liver mitochondria. Prevention by S-adenosyl methionine

Oxygen utilisation during tyrosinase-catalysed oxidation of 4-hydroxyanisole was investigated using an electron spin resonance technique which employs quantitative changes in the characteristics of the electron spin resonance spectrum of the spin label 3-carbamoyl-2,5-dihydro-2,2,5–5-tetramethyl-1-H-pyridoyl-1-yloxy (CTPO) to follow changes in the oxygen concentration. Reaction mixtures containing mushroom tyrosinase (15 μg ml^?1) and differing initial concentrations of 4-hydroxyanisole in aerated phosphate buffer at pH 6.8 were incubated at room temperature. The ratio of utilisation of oxygen was found to be in approximately 1:1 molar ratio with the initial 4-hydroxyanisole concentration in the reaction mixture between 50 and 200 μmol/1 4-hydroxyanisole. The results are consistent with the stoichiometry of oxygen utilisation being accounted for by the oxidation of 4-hydroxyanisole to anisyl quinone.     

Paraquat-generated oxidative stress in rat liver induces heme oxygenase-1 and aminolevulinic acid synthase

The in vivo effect of the known herbicide, paraquat, on both hepatic oxidative stress and heme metabolism was studied. A marked increase in lipid peroxidation and a decrease in reduced glutathione (GSH) content were observed 1 h after paraquat administration. The activity of liver antioxidant enzymes, superoxide dismutase, catalase and glutathione peroxidase was decreased 3 h after paraquat injection. Heme oxygenase-1 induction started 9 h after treatment, peaking at 15 h. delta-aminolevulinic acid synthase induction occurred once heme oxygenase had been enhanced, reaching its maximum (1.5-fold of control) at 16 h. delta-aminolevulinic acid dehydratase activity was 40% inhibited at 3 h showing a profile similar to that of GSH, while porphobilinogenase activity was not modified along the whole period of the assay. Administration of alpha-tocopherol (35 mmol/kg body weight) 2 h before paraquat treatment entirely prevented the increase in thiobarbituric acid reactive substances (TBARS) content, the decrease in GSH levels as well as heme oxygenase-1 and delta-aminolevulinic acid synthase induction. This study shows that oxidative stress produced by paraquat leads to an increase in delta-aminolevulinic acid synthase and heme oxygenase-1 activities, indicating that the herbicide affects both heme biosynthesis and degradation.     

Copper-mediated oxidative stress in rat liver

Copper is an essential trace element with various biological functions. Excess copper, however, is extremely toxic, leading to many pathological conditions that are consistent with oxidative damage to membranes and molecules. Exposure to high levels of copper results in various changes in the tissues. In liver, hypertrophy of hepatocytes, hepatitis, hepatocellular necrosis, and hepatocellular death are the results. Lipid peroxidation causes dysfunction in the cell membrane, decreased fluidity, inactivation of receptors and enzymes, and changes ion permeability. In this study, we aimed to determine the effect of copper on oxidative and antioxidative substances in plasma and liver tissue in a rat model. Sixteen male Sprague—Dawley rats were divided into two groups: Group 1 rats included control rats given tap water. Group 2 rats were given water containing copper in a dose of 100 μg/mL. All rats were sacrificed at 4 wk under ether anesthesia. Plasma and liver superoxide dismutase (SOD) activities, plasma and liver MDA (malondialdehyde) levels, and liver glutathione (GSH) levels were studied. Plasma and liver SOD activities were found to be higher in group 2 than those in group 1. Although plasma MDA levels were higher in group 2, MDA levels in liver tissues were comparable. Liver tissue glutathione levels were lower in group 2. It was concluded that although copper is needed in trace amounts, an excess amount is toxic for the organism. It increases lipid peroxidation and depletes GSH reserves, which makes the organism more vulnerable to other oxidative challenges.     

Hypobaric hypoxia induces oxidative stress in rat brain

High altitude exposure results in decreased partial pressure of oxygen and an increased formation of reactive oxygen and nitrogen species (RONS), which causes oxidative damage to lipids, proteins and DNA. Exposure to high altitude appears to decrease the activity and effectiveness of antioxidant enzyme system. The antioxidant system is very less in brain tissue and is very much susceptible to hypoxic stress. The aim of the present study was to investigate the time dependent and region specific changes in cortex, hippocampus and striatum on oxidative stress markers on chronic exposure to hypobaric hypoxia. The rats were exposed to simulated high altitude equivalent to 6100 m in animal decompression chamber for 3 and 7 days. Results indicate an increase in oxidative stress as seen by increase in free radical production, nitric oxide level, lipid peroxidation and lactate dehydrogenase levels. The magnitude of increase in oxidative stress was more in 7 days exposure group as compared to 3 days exposure group. The antioxidant defence system such as reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD) and reduced/oxidized glutathione (GSH/GSSG) levels were significantly decreased in all the three regions. The observation suggests that the hippocampus is more susceptible to hypoxia than the cortex and striatum. It may be concluded that hypoxia differentially affects the antioxidant status in the cortex, hippocampus and striatum.     

Aortic coarctation induces oxidative stress in rat tissues

The purpose of this study was to evaluate the induction of oxidative stress in heart and erythrocytes from rats with abdominal aorta coarctation (Coa) compared with sham-operated normotensive controls (Sham). The group of Coa animals developed myocardial hypertrophy, showing heart homogenates markedly increased levels of reduced glutathione (48%), lipid peroxidation (148%) and activation of superoxide dismutase and glutathione peroxidase (189% and 37%, respectively), compared with controls. Other oxidative stress indicators were also altered in erythrocytes from Coa rats: increased protein carbonyl content (141%) and total glutathione level (349%) were determined. Inactivation of the antioxidant enzymes catalase (27%), superoxide dismutase (58%) and glutathione peroxidase (25%) was observed in erythrocytes from the Coa group. Taken jointly our results provide strong evidence for the production of oxidative stress in heart and erythrocytes from aortic coarcted rats.     

Subchronic exposure to high-dose ACE-inhibitor moexipril induces catalase activity in rat liver

The long-term clinical effects of ACE-inhibitors have similarities with those of both fibrates and glitazones, activators of peroxisome proliferator activator receptor (PPAR) alpha and gamma, respectively. The antioxidant enzyme catalase, a heme protein that degrades hydrogen peroxide, is found at high concentrations in peroxisomes. Catalase activity is one of the recognized surrogate markers indicative of PPAR activation in the rat liver. The purpose of the study was to establish the effect of moexipril on catalase activity and to compare it with the effect of both saline controls and that of the known PPAR agonist clofibrate (positive control). Three groups of seven rats were used. All substances were applied i.p. daily for 5 days, followed by a 2-day break. The cycle was repeated eight times. After the final cycle (day 56) the animals were sacrificed and liver tissue collected. The number of catalase positive cells in both moexipril group (95% CI 57–61) and clofibrate group (95% CI 72–80) is higher than in controls (95% CI 3–16) (p ≤ 0.01). The number of catalase positive cells in the clofibrate group is higher than in the moexipril group (p ≤ 0.01). High-dose subchronic exposure to the ACE-inhibitor moexipril induces catalase activity in the rat liver to an extent comparable to fibrates. We suggest that some of the long-term advantages of ACE inhibitor use – beyond mere BP lowering – might be due to a PPAR mediated effect. (Mol Cell Biochem xxx: 159–163, 2005)     

Lipid accumulation in the rat liver: a histological and biochemical study.

The sequential pattern of lipid accumulation and associated biochemical changes were studied in two commonly used experimental models of nutritional fatty liver in rats. Female rats were maintained for 8 weeks on high fat, low protein diets containing adequate methionine and choline, and drinking water ad libitum (Diet 1), or deficient in methionine and choline and containing 20% ethanol as a substitute for drinking water (Diet 2). Histologically, there was a progressive increase in liver lipids, mainly in the periportal areas. Occasional foci of liver cell necrosis with lipogranuloma formation occurred in areas of severe fatty change. These changes appeared earlier and were more marked in rats maintained on Diet 2. Electron micrographs revealed large lipid droplets in the liver cells, which sometimes contained myelin figures. The mitochondria were enlarged, distorted and appeared as amorphous structures with disorientated cristae in rats on Diet 1, whereas they had a condensed conformation in rats maintained on Diet 2. Rough endoplasmic reticulum was fragmented and degranulated particularly in rats on Diet 1, and smooth endoplasmic reticulum showed hyperplasia and vesiculation in rats on Diet 2. There was a progressive increase in the total liver lipids and triglycerides in both the groups of rats. This fatty change was accompanied by a significant increase in hepatic 3-hydroxybutyrate, acetoacetate, malate, 2-oxoglutarate, citrate, lactate, ammonia, glutamate, alanine and aspartate, and a significant decrease in oxaloacetate, urea and glucose concentrations. The mass action ratios for alanine aminotransferase, aspartate amino transferase, and glutamate dehydrogenase, generally moved in a parallel direction. Hepatic ATP content was considerably reduced accompanied by a decrease in [ATP]/[ADP] ratios and a significant increased in [lactate]/[pyruvate] and [3-hydroxybutyrate]/[acetoacetate] ratios. There was a corresponding decrease in the [NAD+]/[NADH] ratios both in the cytoplasmic and mitochondrial compartments. These biochemical changes were particularly severe in rats maintained on Diet 1 and Diet 2 for 8 weeks. There was a very good relationship between impaired mitochondrial and endoplasmic reticulum functions, redox and phosphorylation states, and the relevance of their changes to the fate of fatty liver cells.     

Naproxen-induced oxidative stress in the isolated perfused rat liver

We previously showed that naproxen induced the oxidative stress in the liver microsomes and the isolated hepatocytes of rats. In this study, the in situ effect of naproxen on the rat liver tissue was investigated, using the isolated perfused liver from the view-point of the naproxen-induced hepatotoxicity. The leakage of glutamic-oxaloacetic transaminase (GOT) from the perfused liver and appearance of thiobarbituric acid reactive substances (TBARS) in the perfusate increased with the progress of perfusion after a lag time of about 1h. The naproxen-perfusion of the liver decreased the biliary excretion of glutathione (GSH) and oxidized glutathione, glutathione disulfide (GSSG) prior to TBARS production and GOT leakage. GSSG content in the naproxen-perfused liver was significantly higher than in the control. TBARS appeared in the perfusate of the naproxen-perfused liver for 30 min, but not in the control. The biliary excretion clearance (CL(bile)) of indocyanine green (ICG), a reagent for testing the liver function, in the liver perfused with naproxen decreased to a half of that in the liver perfused without naproxen. Thus, the naproxen-induced oxidative stress in the liver was shown to affect the physiological function of liver through the impairment of biliary excretion, which is recognized as a detoxification system.     

Carnosine and taurine treatments decreased oxidative stress and tissue damage induced by d-galactose in rat liver

d-galactose (GAL) causes aging-related changes and oxidative stress in the organism. We investigated the effect of carnosine (CAR) or taurine (TAU), having antioxidant effects, on hepatic injury and oxidative stress in GAL-treated rats. Rats received GAL (300 mg/kg; s.c.; 5 days/week) alone or together with CAR (250 mg/kg/daily; i.p.; 5 days/week) or TAU (2.5 % w/w; in rat chow) for 2 months. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities and hepatic malondialdehyde (MDA), protein carbonyl (PC) and glutathione (GSH) levels and superoxide dismutase (SOD), glutathione peroxidase (GSH-0050x), and glutathione transferase (GST) activities were determined. Hepatic expressions of B cell lymphoma-2 (Bcl-2), Bax and Ki-67 were evaluated. Serum ALT, AST, hepatic MDA, and PC levels were observed to increase in GAL-treated rats. Hepatic Bax expression, but not Bcl-2, increased, Ki-67 expression decreased. GAL treatment caused decreases in GSH levels, SOD and GSH-Px activities in the liver. Hepatic mRNA expressions of SOD, but not GSH-Px, also diminished. CAR or TAU treatments caused significant decreases in serum ALT and AST activities. These treatments decreased apoptosis and increased proliferation and ameliorated histopathological findings in the livers of GAL-treated rats. Both CAR and TAU reduced MDA and PC levels and elevated GSH levels, SOD and GSH-Px (non significant in TAU?+?GAL group) activities. These treatments did not alter hepatic mRNA expressions of SOD and GSH-Px enzymes. Our results indicate that CAR and TAU restored liver prooxidant status together with histopathological amelioration in GAL-induced liver damage.     

Developmental changes of the sensitivity of cardiac and liver mitochondrial permeability transition pore to calcium load and oxidative stress

Opening of the mitochondrial membrane permeability transition pore (MPTP) is an important factor in the activation of apoptotic and necrotic processes in mammalian cells. In a previous paper we have shown that cardiac mitochondria from neonatal rats are more resistant to calcium load than mitochondria from adult animals. In this study we have analyzed the ontogenetic development of this parameter both in heart and in liver mitochondria. We found that the high resistance of heart mitochondria decreases from day 14 to adulthood. On the other hand, we did not observe a similar age-dependent sensitivity in liver mitochondria, particularly in the neonatal period. Some significant but relatively smaller increase could be observed only after day 30. When compared with liver mitochondria cardiac mitochondria were more resistant also to the peroxide activating effect on calcium-induced mitochondrial swelling. These data thus indicate that the MPTP of heart mitochondria is better protected against damaging effects of the calcium load and oxidative stress. We can only speculate that the lower sensitivity to calcium-induced swelling may be related to the higher ischemic tolerance of the neonatal heart.     

Selenomethionine induces polyamine biosynthesis in regenerating rat liver tissue

Summary. Our study was undertaken to elucidate the effects of selenomethionine (SeMet) on polyamine metabolism in regenerating rat liver tissue, as useful model of rapidly growing normal tissue. We have examined the levels of spermine, spermidine and putrescine in liver tissue. At the same time we have evaluated the activities of polyamine oxidase (PAO) and diamine oxidase (DAO), the catabolic enzymes of polyamine metabolism. The obtained results suggest that polyamine levels in regenerating liver tissue, at 7^th day after two-thirds partial hepatectomy, were higher in comparison with control group. The administration of selenomethionine to hepatectomized animals during seven days, in a single daily dose of 2.5 μg/100 g body weight, increases the amount of spermine and spermidine; the level of putrescine does not change under the influence of SeMet in regenerating rat liver tissue. PAO activity is lower in regenerating hepatic tissue than in control group. Supplementation of hepatectomized animals with SeMet significantly decreases the activity of this enzyme. DAO activity was significantly higher in hepatectomized and in operated animals treated with SeMet compared to the sham-operated and control ones. The differential sensitivity observed in our model of highly proliferating normal tissue to SeMet, compared with the reported anticancer activity of this molecule is discussed.     

Systemic administration of d-amphetamine induces long-lasting oxidative stress in the rat striatum

The long-term effect of d-amphetamine (AMPH) on the induction of oxidative stress was examined in vivo in the rat brain. In this study, 2,3-dihydroxybenzoic acid (2,3-DHBA) and malonaldehyde (MDA) were used as the index of the hydroxyl radical and lipid peroxidation, respectively. The levels of 2,3-DHBA, MDA and dopamine (DA) in striatal homogenates were examined 7 days following injection of a single large dose of AMPH (7.5 mg/kg, i.p.) in rats pretreated with desipramine (10 mg/kg, i.p.), an agent that inhibits the metabolism of AMPH. Our results showed that 2,3-DHBA and MDA levels were significantly increased by AMPH, whereas DA and its metabolites, DOPAC and HVA were depleted in the striatum. Pretreatment with the glutamate NMDA receptor subtype antagonist MK-801 (1 mg/kg, i.p.) attenuated the increases of 2,3-DHBA and MDA, and provided partial protection against the long-lasting loss of DA produced by AMPH. Overall, the results demonstrate that AMPH could induce sustained production of free radical and oxidative damage, and lead to DA terminal degeneration in the striatum of the rat.     

High-fat diet induces metabolic changes and reduces oxidative stress in female mouse hearts

After an acute myocardial infarction, obese patients generally have a better prognosis than their leaner counterparts, known as the “obesity paradox”. In addition, female sex is associated with a lower risk of cardiac ischemic events and smaller infarct size compared to males. The objective of the present work was to study the metabolic phenotype and mitochondrial function associated to female sex and short-term high-fat diet. ¹H NMR spectra of mice heart extracts were analysed by mRMR variable selection and linear discriminant analysis was used to evaluate metabolic changes. In separate experiments, O₂ consumption and H₂O₂ production were measured from isolated mitochondria as well as serum oxidation susceptibility. Fingerprinting showed that male hearts contained more myo-inositol, taurine and glutamate than female hearts. HFD reduced the levels of creatine, taurine citrate and acetate. Profiling showed increased alanine and fumarate in HFD suggesting altered glycolitic and Krebs cycle pathways. Female mice contained less glucose than males. Female sex nor HFD altered mitochondria oxygen consumption but both conditions reduced the amount of H₂O₂ produced in an additive manner. Serum of females had lower oxidation susceptibility than serum from males but there were no differences associated with HFD. In conclusion, female sex and short-term HFD have an effect on the myocardial metabolic pattern and reduce the amount of H₂O₂ produced by mitochondria in an additive manner suggesting different mechanisms of action. This could explain, at least in part, the protection afforded by female sex and the “obesity paradox”.