Opposite effect of methionine-supplemented diet, a model of hyperhomocysteinemia, on plasma and liver antioxidant status in normotensive and spontaneously hypertensive rats

Hyperhomocysteinaemia-induced cardiovascular changes in rats

(1) Increased plasma homocysteine content and increased blood pressure are independently associated with higher cardiovascular risks. The present study was designed to determine the effects of hyperhomocysteinaemia (HHcys) on the activity of the cardiovascular system in rats. (2) Using male Wistar rats, the effect of moderate HHcys, induced by treating rats with dl-homocysteine thiolactone (DL-HT; 1 g/kg per day) for 15 days, on arterial blood pressure, heart rate, baroreflex and vascular reactivity was determined. (3) Hyperhomocysteinaemia was observed after 15 days of treatment. Baseline arterial blood pressure and heart rate values of HHcys animals were significantly increased after 15 days of treatment. Plasma homocysteine and cardiovascular parameters returned to control values after termination of treatment. Baroreflex gain was significantly enhanced in HHcys rats. The pressor effect of an i.v. infusion of phenylephrine (50 mg/kg per mL) was decreased in HHcys rats and returned to control values after washout of DL-HT. Hypotensive responses to i.v. infusions of sodium nitroprusside (70 mg/kg per mL) or acetylcholine (10 mg/kg per mL) were increased in HHcys animals and returned to control values after washout of DL-HT. The increase in resting arterial blood pressure associated with the moderate HHcys was reversed by treatment with the b1-adrenoceptor antagonist atenolol, suggesting that HHcys-related hypertension is related to increase in cardiac sympathetic activity. (4) The present study showed significantly increased arterial blood pressure, heart rate and baroreflex activity in the early phase of moderate HHcys. In addition, HHcys was associated with alterations of vascular responsiveness to pressor and depressor agents, as well as increased cardiac sympathetic activity. The fact that cardiovascular changes observed in HHcys were reversed after DL-HT washout indicate that moderate HHcys evokes cardiovascular changes.

Spontaneously hypertensive rats develop pronounced hepatic steatosis induced by choline-deficient diet: Evidence for hypertension as a potential enhancer in non-alcoholic steatohepatitis

AIM

  Patients with non-alcoholic steatohepatitis (NASH) frequently have many co-morbidities including essential hypertension, which is reported to increase vascular production of reactive oxygen species (ROS) and alter the hepatic anti-oxidant defense system. Since ROS play a role in the pathogenesis of NASH, it is hypothesized that hypertension modulates the hepatic oxidative status and influences the development of NASH. The aim of this study was to investigate the potential effects of hypertension on the progression of NASH.

METHODS

  Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats as normotensive controls were fed choline-deficient (CD) diet for 5 weeks. Histological changes, messenger RNA (mRNA) expression and thiobarbituric acid reactive substances (TBARS) levels in the liver were assessed in each group.

RESULTS

  Choline-deficient diet led to pronounced hepatic steatosis in SHR with an 8-fold increase of the hepatic triglyceride content, while there was no significant increase in WKY. These changes in SHR were associated with significant reduction in the expression of mRNA for peroxisome proliferator activated receptor α, acyl-CoA oxidase, microsomal triglyceride transfer protein, and apolipoprotein B100. Consistent with the significant reduction of hepatic superoxide dismutase activity and marked downregulation of the gene expression of hepatic antioxidant enzymes, the hepatic TBARS level and the plasma level of alanine aminotransferase were only increased in SHR on CD diet.

CONCLUSIONS

  Spontaneously hypertensive rats receiving CD diet showed severe hepatic steatosis associated with reduction of hepatic anti-oxidant capacity, leading to increased hepatic oxidative stress and tissue damage. Accordingly, hypertension might have a potential effect on the progression of NASH.

Effect of methionine load on homocysteine levels, lipid peroxidation and DNA damage in rats receiving ethanol

Changes in the metabolism of methionine can cause hyperhomocysteinemia, inducing a triad of atherosclerosis, hypertension, and increased oxidative stress. The generation of free radicals and oxidative damage to DNA is important in the liver damage caused by ethanol. In this study, the effect of methionine overload associated or otherwise with acute administration of ethanol on homocysteine values, damage to DNA, lipoperoxidation and vitamin E was evaluated. Thirty rats were divided into 3 groups: Group Ethanol 24 hours (EG24), Group Methionine 24 hours (MG24), and Group Methionine and Ethanol 24 hours (MEG24). TBARS, vitamin E, GS and, homocysteine values were determined and the Comet assay was carried out. Increased GSH, vitamin E and homocysteine levels were observed for MEG24, and increased TBARS were observed in EG24. The Comet assay showed an increase in DNA damage in EG24 and DNA protection in MEG24. The administration of ethanol decreased antioxidant levels and increased TBARS, indicating the occurrence of oxidative stress with possible DNA damage. The combination of methionine and ethanol had a protective effect against the ethanol-induced damage, but increased the levels of homocysteine.

Oxidative and nitrosative stress and apoptosis in the liver of rats fed on high methionine diet: protective effect of taurine

OBJECTIVE

There are few reports about the direct toxic effects of hyperhomocysteinemia on the liver. We investigated oxidative and nitrosative stresses and apoptotic and necrotic changes in the liver of rats fed a high-methionine (HM) diet (2%, w/w) for 6 mo. We also investigated whether taurine, an antioxidant amino acid, is protective against an HM-diet-induced toxicity in the liver.

METHODS

Lipid peroxide levels, nitrotyrosine formation, and non-enzymatic and enzymatic antioxidants were determined in livers of rats fed an HM diet. In addition, apoptosis-related proteins, proapoptotic Bax and antiapoptotic B-cell lymphoma-2 expressions, apoptotic cell count, histopathologic appearance in the liver, and alanine transaminase and aspartate transaminase activities in the serum were investigated.

RESULTS

Plasma homocysteine levels and serum alanine transaminase and aspartate transaminase activities were increased after the HM diet. This diet resulted in increases in lipid peroxide and nitrotyrosine levels and decreases in non-enzymatic and enzymatic antioxidants in liver homogenates in rats. Bax expression increased, B-cell lymphoma-2 expression decreased, and apoptotic cell number increased in livers of rats fed an HM diet. Inflammatory reactions, microvesicular steatosis, and hepatocyte degeneration were observed in the liver after the HM diet. Taurine (1.5%, w/v, in drinking water) administration and the HM diet for 6 mo was found to decrease serum alanine transaminase and aspartate transaminase activities, hepatic lipid peroxide levels, and nitrotyrosine formation without any change in serum homocysteine levels. Decreases in Bax expression, increases in B-cell lymphoma-2 expression, decreases in apoptotic cell number, and amelioration of histopathologic findings were observed in livers of rats fed with the taurine plus HM diet.

CONCLUSION

Our results indicate that taurine has protective effects on hyperhomocysteinemia-induced toxicity by decreasing oxidative and nitrosative stresses, apoptosis, and necrosis in the liver.

Cystathionine beta synthase deficiency induces catalase-mediated hydrogen peroxide detoxification in mice liver

Cystathionine beta synthase deficiency induces hyperhomocysteinemia which is considered as a risk factor for vascular diseases. Studies underlined the importance of altered cellular redox reactions in hyperhomocysteinemia-induced vascular pathologies. Nevertheless, hyperhomocysteinemia also induces hepatic dysfunction which may accelerate the development of vascular pathologies by modifying cholesterol homeostasis. The aim of the present study was to analyze the modifications of redox state in the liver of heterozygous cystathionine beta synthase-deficient mice, a murine model of hyperhomocysteinemia. In this purpose, we quantified levels of reactive oxygen and nitrogen species and we assayed activities of main antioxidant enzymes. We found that cystathionine beta synthase deficiency induced NADPH oxidase activation. However, there was no accumulation of reactive oxygen (superoxide anion, hydrogen peroxide) and nitrogen (nitrite, peroxynitrite) species. On the contrary, hepatic hydrogen peroxide level was decreased independently of an activation of glutathione-dependent mechanisms. In fact, cystathionine beta synthase deficiency had no effect on glutathione peroxidase, glutathione reductase and glutathione S-transferase activities. However, we found a 50% increase in hepatic catalase activity without any variation of expression. These findings demonstrate that cystathionine beta synthase deficiency initiates redox disequilibrium in the liver. However, the activation of catalase attenuates oxidative impairments.

Methionine-supplemented diet augments hepatotoxicity and prooxidant status in chronically ethanol-treated rats

The purpose of this study was to investigate whether high methionine (HM) diet may influence the development of ethanol-induced hepatotoxicity and prooxidant-antioxidant balance in the liver. Rats received drinking water containing ethanol (20% v/v) and/or methionine supplemented diet (2% w/w) for 75 days. Although prooxidant-antioxidant balance did not change in the liver of rats in HM group, ethanol treatment was observed to increase plasma transaminase activities, and malondialdehyde (MDA) and protein carbonyl (PC) levels, but not glutathione (GSH), vitamin E and vitamin C levels, and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and glutathione transferase (GST) activities in the liver of rats as compared to controls. However, ethanol plus HM diet caused further increases in plasma transaminase activities and hepatic MDA and PC levels. In addition, SOD, GSH-Px and GST activities were observed to decrease, but GSH, vitamin E and vitamin C levels remained unchanged in the liver as compared to ethanol, HM and control groups. Our results show that HM diet may augment hepatotoxicity and oxidative stress in the liver of chronically ethanol-treated rats.

Thiol compounds metabolism in mice, rats and humans: comparative study and potential explanation of rodents protection against vascular diseases

BACKGROUND

Rodents are often used as animal models to dissect mechanisms underlying hyperhomocysteinemia atherogenicity in humans. However, neither wild-type rodents nor cystathionine beta-synthase deficient mice develop spontaneous atherosclerosis. We investigated whether species-specific differences in thiols metabolism may explain the respective sensitivity of rodents and humans to hyperhomocysteinemia.

METHODS

Thiols and vitamins B levels were determined in normohomocysteinemic humans and rodents, and in hyperhomocysteinemic mice.

RESULTS

In basal status, although plasma homocysteine, cysteine and cysteinylglycine levels were lower, glutathione levels were higher in mice than in humans (4.0+/-1.6 vs. 7.9+/-2.2, P<0.0005; 147.4+/-40.3 vs. 278.5+/-50.0, P<0.0001; 2.3+/-0.7 vs. 36.6+/-7.3, P<0.0001; and 70.9+/-20.1 vs. 4.6+/-1.6, P<0.0001). Serum vitamin B12 and folate levels were 2.5- and 7.7-fold higher in rats than in humans. In wild-type mice, the increase in plasma Hcy levels induced by methionine-enriched diet was accompanied by a proportional increase in GSH levels.

CONCLUSION

GSH levels are enough to modulate Hcy effects in normo- and hyperhomocysteinemic mice but not in humans. This rodents characteristic, likely supported by species differences in the relative contribution of remethylation and transsulfuration pathways, may partly explain their protection against atherosclerosis.