Increased lipid peroxidation and antioxidant activity in methionine-induced hepatitis in rabbits

Pathological role of methionine in the initiation and progression of biliary atresia

Methionine (Met) is an essential amino acid, and its excessive dietary intake and/or its metabolism disturbance could lead to accumulation/depletion of hepatic Met and some of the key intermediates of these pathways, which would interfere normal liver function and would be associated with liver diseases. Biliary atresia (BA) is a life-threatening disease characterized by inflammatory fibrosclerosing changes of the intrahepatic and extrahepatic biliary systems and is the primary cause of obstructive neonatal cholestasis with a rapid course of liver failure. However, its pathogenesis remains unknown. Previous studies reported elevated Met level in patients with obstructive cholestasis, suggesting a potential link between Met and BA. This paper reviews the Met metabolism in normal conditions and its dysregulation under abnormal conditions, the possible causes of hypermethioninemia, and its connection to BA pathogenesis: Abnormal hepatic level of Met could lead to a perturbation of redox homeostasis and mitochondrial functions of hepatocytes, enhancement of viral infectivity, and dysregulation of innate and adaptative immune cells in response to infection/damage of the liver contributing to the initiation/progression of BA.

Impacts of dietary supplementation with nano-iron and methionine on growth, blood chemistry, liver biomarkers, and tissue histology of heat-stressed broiler chickens

A 28-day study was done to explore the impact of nano-iron alone or combined with methionine on growth, blood chemistry, liver biomarkers, and tissue histology of heat-stressed chicken. One-day-old Ross 308 chicks were randomly allocated to three groups. Each group was divided into three replicates (13 chicks/replicate). The first group was the control one that was fed a basal diet without supplementation (T0). The second group was fed a basal diet with nano-iron 4 mg kg^-1 diet (T1). The third group was fed a basal diet with nano-iron 4 mg kg^-1 diet plus methionine 4 g kg^-1 diet (T2). The results showed that the birds in the control group had significantly (p < 0.05) higher final weights. Also, a partial relief of heat stress adverse effects was observed on growth by T1 compared to T2. The T2 showed a significantly increased (p < 0.05) free iron (Fe) level and transferrin saturation index. Likewise, T2 significantly (p < 0.05) reduced total iron-binding capacity (TIBC) and transferrin level in comparison with T0 and T1. Also, hepatic impairment and inflammatory response were observed in the T2 group when compared to T0 and T1, besides a bad lipid profile. Further, T2 showed raised levels of Fe and ferritin in their hepatic tissues compared to those T1 and T0. A significant increment of thiobarbituric acid reactive and decrement of reduced glutathione levels in the hepatic tissues of T2 and T1 versus T0 levels were recorded. It is concluded that nano-iron at the level of 4 mg kg^-1 in this study is highly absorbed, leading to harmful effects. Further investigations are needed to detect the proper supplemental level.

Severe hepatitis treated with an artificial liver support system

We designed an artificial liver support system (ALSS) including plasma exchange, charcoal hemoperfusion, plasma bilirubin absorption, charcoal plasma perfusion, hemofiltration and hemodialysis. We chose different methods or their combinations according to the patients’ conditions. We investigated the effect of ALSS in 154 patients with severe hepatitis, 72 of whom survived. All data were analyzed by SPSS. The effectiveness of ALSS treatment was compared at different stages (i.e. early, middle and end stages). After each ALSS treatment, the liver function of these patients greatly improved, serum endotoxin and HBV-DNA concentrations were significantly decreased, and the serum concentration of aromatic amino acids (AAA) such as methionine decreased while BCAA/AAA ratio increased. Patients treated with ALSS in the early or middle stages of disease had much higher survival rates than patients in the end stage of disease. Thus, we concluded that ALSS is a reliable therapy for advanced liver diseases and treatment in early or middle stages is appropriate.

Mechanistic basis of hypermethioninemia

Hypermethioninemia is a condition defined as elevated plasma methionine levels and may be a consequence of different conditions that include non-genetic and genetic causes. In severe cases, hypermethioninemia may lead to development of neurological and hepatic impairments, but mechanisms are still not well elucidated. Therefore, this review aims to reunite the knowledge acquired about the methionine-induced brain and liver toxicity focusing on the results obtained by studies from patients, in vitro experiments, and in vivo animal models. In general, some studies have shown that methionine decreases Na⁺,K⁺-ATPase activity, induces oxidative stress, increases acetylcholinesterase activity, and leads to dendritic spine downregulation in brain. Concerning to liver, hypermethioninemia seems to provoke changes in cell morphology, lipid accumulation, oxidative stress, inflammation, and ATP depletion. It is possible to infer that oxidative damage is one of the most important mechanisms responsible for methionine toxicity, since different studies showed that this amino acid induces oxidative stress in brain and liver tissues. Besides, reactive oxygen species may mediate other alterations induced by methionine, such as the reduction in brain Na⁺,K⁺-ATPase activity, and liver inflammation.

Effects of excessive dietary methionine on oxidative stress and dyslipidemia in chronic ethanol-treated rats

BACKGROUND/OBJECTIVE

The aim of this study was to examine the effect of high dietary methionine (Met) consumption on plasma and hepatic oxidative stress and dyslipidemia in chronic ethanol fed rats.

MATERIALS/METHODS

Male Wistar rats were fed control or ethanol-containing liquid diets supplemented without (E group) or with DL-Met at 0.6% (EM1 group) or 0.8% (EM2 group) for five weeks. Plasma aminothiols, lipids, malondialdehyde (MDA), alanine aminotransferase (ALT), and aspartate aminotransferase were measured. Hepatic folate, S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) were measured.

RESULTS

DL-Met supplementation was found to increase plasma levels of homocysteine (Hcy), triglyceride (TG), total cholesterol (TC), and MDA compared to rats fed ethanol alone and decrease plasma ALT. However, DL-Met supplementation did not significantly change plasma levels of HDL-cholesterol, cysteine, cysteinylglycine, and glutathione. In addition, DL-Met supplementation increased hepatic levels of folate, SAM, SAH, and SAM:SAH ratio. Our data showed that DL-Met supplementation can increase plasma oxidative stress and atherogenic effects by elevating plasma Hcy, TG, and TC in ethanol-fed rats.

CONCLUSION

The present results demonstrate that Met supplementation increases plasma oxidative stress and atherogenic effects by inducing dyslipidemia and hyperhomocysteinemia in ethanol-fed rats.

Methionine and homocysteine modulate the rate of ROS generation of isolated mitochondria in vitro

Dietary methionine restriction and supplementation in mammals have beneficial (antiaging) and detrimental effects respectively, which have been related to chronic modifications in the rate of mitochondrial ROS generation. However it is not known if methionine or its metabolites can have, in addition, direct effects on the rate of mitochondrial ROS production. This is studied here for the methionine cycle metabolites S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), homocysteine and methionine itself in isolated rat liver, kidney, heart, and brain mitochondria. The results show that methionine increases ROS production in liver and kidney mitochondria, homocysteine increases it in kidney and decreases it in the other three organs, and SAM and SAH have no effects. The variations in ROS production are localized at complexes I or III. These changes add to previously described chronic effects of methionine restriction and supplementation in vivo.

The biochemical and toxicological significance of hypermethionemia: new insights and clinical relevance

IMPORTANCE OF THE FIELD

Disrupted l-methionine (Met) metabolism can lead to hepatic, neurological and cardiovascular dysfunction in humans. Aberrant methyl group flux likely contributes to the development of these pathologies, but when patients also become hypermethionemic, additional toxicological mechanisms may be relevant.

AREAS COVERED IN THIS REVIEW

Following a discussion of the causes of hypermethionemia in humans, evidence for the toxicological roles and clinical significance of the Met transmethylation (TM), transamination (TA) and sulfoxidation (SO) pathways will be presented.

WHAT THE READER WILL GAIN

Recent data from freshly isolated mouse hepatocytes (FIMHs) confirmed previous in vivo results in rodents that Met TM is a detoxification pathway while Met TA leads to toxicity. Gender-related differences in Met accumulation and metabolism in FIMHs correlated with gender differences in toxicity. Data obtained from FIMHs also implicated Met SO in Met metabolism and toxicity. Currently, little is known about the mechanisms and biological significance of Met sulfoxidation in humans.

TAKE HOME MESSAGE

In hypermethionemic patients, clinical and dietary interventions should focus on increasing Met TM and decreasing Met TA and SO. Novel biomarkers of hypermethionemia in humans that correlate with pathological end points are needed to better understand the impact of the condition.

Effect of methionine dietary supplementation on mitochondrial oxygen radical generation and oxidative DNA damage in rat liver and heart

Methionine restriction without energy restriction increases, like caloric restriction, maximum longevity in rodents. Previous studies have shown that methionine restriction strongly decreases mitochondrial reactive oxygen species (ROS) production and oxidative damage to mitochondrial DNA, lowers membrane unsaturation, and decreases five different markers of protein oxidation in rat heart and liver mitochondria. It is unknown whether methionine supplementation in the diet can induce opposite changes, which is also interesting because excessive dietary methionine is hepatotoxic and induces cardiovascular alterations. Because the detailed mechanisms of methionine-related hepatotoxicity and cardiovascular toxicity are poorly understood and today many Western human populations consume levels of dietary protein (and thus, methionine) 2-3.3 fold higher than the average adult requirement, in the present experiment we analyze the effect of a methionine supplemented diet on mitochondrial ROS production and oxidative damage in the rat liver and heart mitochondria. In this investigation male Wistar rats were fed either a L-methionine-supplemented (2.5 g/100 g) diet without changing any other dietary components or a control (0.86 g/100 g) diet for 7 weeks. It was found that methionine supplementation increased mitochondrial ROS generation and percent free radical leak in rat liver mitochondria but not in rat heart. In agreement with these data oxidative damage to mitochondrial DNA increased only in rat liver, but no changes were observed in five different markers of protein oxidation in both organs. The content of mitochondrial respiratory chain complexes and AIF (apoptosis inducing factor) did not change after the dietary supplementation while fatty acid unsaturation decreased. Methionine, S-AdenosylMethionine and S-AdenosylHomocysteine concentration increased in both organs in the supplemented group. These results show that methionine supplementation in the diet specifically increases mitochondrial ROS production and mitochondrial DNA oxidative damage in rat liver mitochondria offering a plausible mechanism for its hepatotoxicity.

Methionine-induced hyperhomocysteinemia modulates lipoprotein profile and oxidative stress but not progression of atherosclerosis in aged apolipoprotein E knockout mice

It is documented that hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis, but whether elevated plasma homocysteine contributes to the progression of atherosclerosis in aged animals with hypercholesterolemia is still unknown. HHcy was induced in apolipoprotein E (ApoE) knockout mice (male, 32 weeks old) by feeding 2% methionine/low folate (1 mg/kg) diet for 20 weeks. HHcy induced by methionine feeding significantly increased oxidative stress, as measured by thiobarbituric-reactive substances in livers (P < .05) and genetic expression of Cu,Zn-superoxide dismutase, in methionine-fed animals compared with controls (P < .05). Furthermore, lipoprotein profiles were changed, in that low-density lipoprotein-cholesterol was shifted to very low-density lipoprotein in the methionine-supplemented group. However, nuclear factor kappaB activity, atherosclerotic lesions, hepatic glutathione level, lipid profiles, and activities of aspartate aminotransferase and alanine aminotransferase were not significantly different. These findings suggest that HHcy induced by methionine may promote disturbances in lipid peroxidation and modify lipoprotein metabolism but not contribute to the progression of atherosclerotic lesion in aged ApoE knockout mice.

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.

Methionine, folic acid and vitamin B12 in growing-finishing pigs: impact on growth performance and meat quality

Growth performance, metabolic variables, and meat quality were measured in 78 growing-finishing pigs using supplements of 0 (C), or 0.2% of DL-methionine (M), and three combinations of folic acid [mg/kg] and cyanocobalamin [microg/kg], respectively 0 and 0 (V0), 10 and 25 (V1), and 10 and 150 (V2) in a 2 x 3 factorial arrangement. Feed conversion was lower (p = 0.05) in M than in C pigs during the growing period (0-4 weeks). Both V1 and V2 treatments increased plasma vitamin B12 (p < 0.01) and decreased plasma homocysteine (p < 0.01). Plasma 5-methyl-tetrahydrofolates were the lowest, highest and intermediate in V0, V1 and V2 pigs (p < 0.04), respectively. In V2 meat, folates were 32% higher, vitamin B12, 55% higher and homocysteine, 28% lower than in V0 (p < 0.01). Oxidative stability of the fresh meat was similar among treatments during a storage period of 42 days. Therefore, methionine supplements improved growth performance during the growing period. Vitamin supplements interacted with the methionine cycle pathway, increased vitamin content of pork meat but did not improve oxidative stability of the fresh meat during storage.

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.

Ligularia fischeri leaf extract prevents the oxidative stress in DBA/1J mice with type II collagen-induced arthritis

The generation of free radicals has been implicated in the causation of several diseases and compounds that can scavenge free radicals have great potential in ameliorating these disease processes. The present study was aimed to investigate the possible antioxidant potential of Ligularia fischeri leaves on collagen type II induced arthritis (CIA) in DBA/1J mice. Ligularia fischeri extracts (100 and 200 mg kg(-1)) were orally administered to DBA/1J mice once daily for 49 days after initial immunization with type II collagen. The levels of oxidant products and the activities of antioxidant enzymes were determined in the serum and organs obtained at day 50. The induction of arthritis significantly increased malondialdehyde (MDA) in the serum and kidney, and oxidized proteins such as protein carbonyl (PCO) and advanced glycation end-products (AGE) in the serum, liver, spleen and kidney. Oral administration of Ligularia fischeri extract at doses of 100 and 200 mg kg(-1) reduced the levels of MDA in the serum and kidney, and PCO and AGE in the serum, liver, and kidney compared with CIA mice. Moreover, treatment with Ligularia fischeri extract dose-dependently increased the activities of superoxide dismutase, glutathione peroxidase and glutathione reductase in the spleen compared with CIA mice. These results suggest that Ligularia fischeri exerts antioxidant actions in the CIA mouse model.

Effect of artificial liver support system on patients with severe viral hepatitis: A study of four hundred cases

AIM: To assess the effect of artificial liver support system (ALSS) on patients with severe viral hepatitis, who were divided into treatment group and control group.

METHODS: Four hundred in-hospital patients enrolled during 1995-2003 who received ALSS therapy were studied as the treatment group. Four hundred in-hospital patients enrolled during 1986-1994 who received other medical therapies served as the control group. The methods of ALSS used included plasma exchange, hemoperfusion, hemofiltration, continuous hemodiafiltration (CHDF). The effect of ALSS treatment was studied in patients at different stages of the disease.

RESULTS: The cure rate of acute and subacute severe hepatitis in the treatment group was 78.9% (30/38), and was 11.9% (5/42) in the control group. The improved rate of chronic severe hepatitis in the treatment group was 43.4% (157/362), and was 15.4% (55/358) in the control group. We found that patients treated with ALSS in the early or middle stage of the disease had much higher survival rates than patients in the end stage of the disease.

CONCLUSION: ALSS is an effective and safe therapy for severe viral hepatitis.

Methionine-induced hyperhomocysteinemia promotes superoxide anion generation and NFkappaB activation in peritoneal macrophages of C57BL/6 mice

It is well documented that hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis. This study was designed to investigate whether some of the atherosclerotic effects ascribed to HHcy are mediated by oxidative stress and nuclear factor kappa B (NFkappaB) activation in peritoneal macrophages of C57BL/6 mice fed a high (2%) methionine/low (1 mg/kg) folate diet for 12 weeks. Plasma homocysteine concentrations in mice fed methionine averaged 49 mol/L after 12 weeks of feeding, five times higher than that of controls. HHcy induced by methionine feeding significantly elevated oxidative stress, as measured by superoxide anion radical level (P <.05) in peritoneal macrophages. Furthermore, NFkappaB binding activities of peritoneal macrophages were higher in the methionine group than in the control group. These results suggest that HHcy induced by methionine may intensify disturbances in peroxidation and inflammatory mediator activation in peritoneal macrophages, and is a possible mechanism of its atherogenic effects.

The effect of folic acid, vitamin B6 and vitamin B12 on the homocysteine levels in rabbits fed by methionine-enriched diets

Atherosclerosis is an important cause of cardiovascular morbidity and mortality in recent years. Hyperhomocysteinemia is recognized as an independent risk factor for premature atherosclerosis and venous thrombosis. It is suggested that administration of folic acid, vitamin B6 and vitamin B12 may decrease homocysteine levels. In our study, we induced hyperhomocysteinemia in rabbits by giving methionine and studied the effects of folic acid, vitamin B6 and vitamin B12 on homocysteine levels. A total of 40 (20 female, 20 male New Zealand rabbits) were divided into four groups, each consisting of 10 rabbits. Methionine (100 mg/kg/day), methionine (100 mg/kg/day) plus vitamin B6 (30 mg/kg/day), methionine (100 mg/kg/day) plus vitamin B12 (80 mg/kg/day) and methionine (100 mg/kg/day) plus folic acid (20 mg/kg/day) were given to the first, second, third and forth groups respectively. These rabbits were followed up for two months. We studied homocysteine levels on the 0, 20th, 40th and 60th days in all groups. In rabbits we induced hyperhomocysteinemia by giving methionine for 2 months. The decreases of homocysteine levels in the forth group were significant with respect to the second and third groups. Folic acid supplementation clearly resulted in a reduction of plasma homocysteine levels, whereas vitamin B12 was little effective and vitamin B6 failed to show an effect. We conclude that even folic acid treatment alone may be sufficient for decreasing negative effects of homocysteine.

Long-term consumption of a methionine-supplemented diet increases iron and lipid peroxide levels in rat liver

Methionine is a protective factor against various types of liver damage, but excessive dietary methionine is hepatotoxic. Because the mechanisms of L-methionine-related hepatotoxicity are poorly understood, the effect of long-term excessive L-methionine intake on the metabolism of iron and antioxidants was studied in rat liver to determine whether oxidative stress is involved. Wistar male rats were fed either an L-methionine-supplemented (16.0 g/kg) diet or a control diet for 1, 3, 6 and 9 mo. The growth rate of L-methionine-supplemented rats was significantly slower than that of controls. Iron, ferritin and thiobarbituric acid-reactive substances (TBARS) levels in the liver were greater in supplemented rats than in controls. Serum iron and transferrin levels were significantly lower in L-methionine-treated rats compared with controls. Serum ferritin did not differ between the two groups. Hepatic glutathione peroxidase activity, catalase activity and total glutathione concentrations were higher in rats fed the L-methionine-supplemented diet at 1 and 3 mo, but not at 6 and 9 mo. These results indicate that long-term consumption of excess L-methionine by rats may affect primarily iron metabolism rather than the antioxidant defense system and, consequently, induce an accumulation of iron.

Addition of arginine but not glycine to lysine plus methionine-enriched diets modulates serum cholesterol and liver phospholipids in rabbits

Previous experiments from our laboratory showed that in rabbits fed an amino acid diet corresponding to 30% casein, enrichment of the diet with L-lysine and L-methionine caused a marked increase in serum total and LDL cholesterol levels as well as a substantial body weight loss. Both effects were partially prevented by supplementation with L-arginine. The present studies were designed to extend this earlier observation by assessing the role of different dietary amino acids in modulation of cholesterolemic responses and body weights. In the first experiment, the original lysine and methionine-enriched diet was supplemented with glycine in an attempt to modify methionine metabolism, and thus to reduce body weight loss. In addition, the mechanism of action of lysine and methionine was investigated by quantitation of major liver phospholipids. The results showed that glycine addition had no effect on weight loss or hypercholesterolemia, nor did it alter plasma levels of homocyst(e)ine, an intermediate in methionine metabolism. However, enrichment of the diet with lysine and methionine (with or without glycine) significantly increased liver levels of phosphatidylcholine and the ratio of phosphatidylcholine to phosphatidylethanolamine, apparently through increased enzymatic conversion. These changes were consistent with higher lipoprotein levels and thus may explain the hypercholesterolemia. A second experiment showed that similar effects on body weights and serum cholesterol could be obtained by adding lysine and methionine to a diet containing amino acids equivalent to only 15% casein, or 15% intact casein. This approach is more physiologic and also reduces the expense of experiments designed to study the effects of lysine and methionine in more detail.