Dietary methionine imbalance, endothelial cell dysfunction and atherosclerosis

Methionine Binding to Dirhodium(II) Tetraacetate

The reaction between antitumor active dirhodium(II) tetraacetate and dl-methionine (HMet) was followed in aqueous solution and showed initially mixtures of 1:1 and 1:2 adducts [Rh2(AcO)4(HMet)(H2O)] (AcO- = CH3COO-) and [Rh2(AcO)4(HMet)2] formed at room temperature (RT), as evidenced by UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Rh K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy confirmed methionine thioether binding to the axial positions of the Rh2(AcO)4 cage structure. With excess HMet at RT, stepwise displacement of the acetate groups was observed after some time using ESI-MS. Heating the solution to 40° for 24 h accelerated the substitution reaction leading to stable dirhodium(II) species with two acetate ligands displaced by two methionine groups. The crystal structure of the purple [RhII2(AcO)2(d-Met)(l-Met)]·6H2O compound obtained from the solution revealed tridentate coordination of the methionine ligands to the Rh(II) ions, with the thioether S atoms in equatorial positions. A minor amount of a light orange monomeric [RhIII(Met)2](AcO) complex also formed in the solution was isolated by size exclusion chromatography and identified by ESI-MS. Crystals of [RhIII(d-Met)(l-Met)]Cl·3H2O were prepared by reacting RhCl3 and dl-HMet. The crystal structure showed tridentate binding of the methionine ligands to the Rh(III) ion in a trans-S, N, O arrangement.

Assessment of Serum Folic Acid and Homocysteine in Thalassemia Major Patients Before and After Folic Acid Supplement Cessation

BACKGROUND

Thalassemic patients have ineffective erythropoiesis. In recent treatment protocols, there are little data on folic acid supplementation for patients with thalassemia because it is supposed that regular blood transfusions prevent bone marrow hyperfunctioning.

OBJECTIVE

Investigators aimed to assess serum folic acid and homocysteine (Hcy) in thalassemia major patients before and after folic acid supplement cessation.

PATIENTS AND METHODS

This study was a before-after controlled clinical trial conducted in 17th Shahrivar Hospital, Rasht, North of Iran, during May to October 2016. The patients enrolled in this study had thalassemia major on regular blood transfusion and older than 2 years of age. They had at least a 6-month history of folic acid supplement consumption before enrollment in the study (1 mg/daily). Complete blood count, serum folic acid, and serum Hcy were measured before discontinuation of folic acid supplement. Then, patients did not receive folic acid for a month and after 1 month of folic acid cessation, the measurements were repeated. All data were entered in SPSS version 20.0 and analyzed.

RESULTS

Among the 40 patients in this study, 25 (62.5%) were female. The mean age of the participants was 21.39±11.17 years old. The mean of body mass index was 21.38±3.32 kg/m. Most of the participants had used folic acid supplement >5 years (29, 72.5%). The serum Hcy level was significantly increased (5.24±2.35 vs. 5.93±2.56; P=0.008) and serum folic acid level was decreased significantly (14.74±4.20 vs. 8.80±4.16; P<0.0001) from baseline.

CONCLUSIONS

Cessation of folic acid supplementations in beta thalassemia major patients can lead to a significant decrease in serum folic acid and increase in Hcy levels. According to our findings and efficacy of folic acid in patients with beta thalassemia major, it is recommended to use the supplementation in all patients.

Characterisation of Atherogenic Effects of Low Carbohydrate, High Protein Diet (LCHP) in ApoE/LDLR-/- Mice

INTRODUCTION

Low Carbohydrate High Protein diet represents a popular strategy to achieve weight loss.

OBJECTIVE

The aim of this study was to characterize effects of low carbohydrate, high protein diet (LCHP) on atherosclerotic plaque development in brachiocephalic artery (BCA) in apoE/LDLR-/- mice and to elucidate mechanisms of proatherogenic effects of LCHP diet.

MATERIALS AND METHODS

Atherosclerosis plaques in brachiocephalic artery (BCA) as well as in aortic roots, lipoprotein profile, inflammation biomarkers, expression of SREBP-1 in the liver as well as mortality were analyzed in Control diet (AIN-93G) or LCHP (Low Carbohydrate High Protein) diet fed mice.

RESULTS

Area of atherosclerotic plaques in aortic roots or BCA from LCHP diet fed mice was substantially increased as compared to mice fed control diet and was characterized by increased lipids and cholesterol contents (ORO staining, FT-IR analysis), increased macrophage infiltration (MOMA-2) and activity of MMPs (zymography). Pro-atherogenic phenotype of LCHP fed apoE/LDLR-/- mice was associated with increased plasma total cholesterol concentration, and in LDL and VLDL fractions, increased TG contents in VLDL, and a modest increase in plasma urea. LCHP diet increased SCD-1 index, activated SREBP-1 transcription factor in the liver and triggered acute phase response as evidence by an increased plasma concentration of haptoglobin, CRP or AGP. Finally, in long-term experiment survival of apoE/LDLR-/- mice fed LCHP diet was substantially reduced as compared to their counterparts fed control diet suggesting overall detrimental effects of LCHP diet on health.

CONCLUSIONS

The pro-atherogenic effect of LCHP diet in apoE/LDLR-/- mice is associated with profound increase in LDL and VLDL cholesterol, VLDL triglicerides, liver SREBP-1 upregulation, and systemic inflammation.

Effect of low carbohydrate high protein (LCHP) diet on lipid metabolism, liver and kidney function in rats

The objective of this study was to compare effects of Western diet (WD) with low carbohydrate high protein (LCHP) diet on lipid metabolism, liver and kidney function in rats. Eighteen rats were randomly assigned to three experimental groups and fed for the next 2 months. The experimental diets were: Control (7% of soybean oil, 20% protein), WD (21% of butter, 20% protein), and LCHP (21% of butter and 52.4% protein) diet. The LCHP diet significantly decreased the body weight of the rats. Diet consumption was differentiated among groups, however significant changes were observed since third week of the experiment duration. Rats fed LCHP diet ate significantly less (25.2g/animal/day) than those from Control (30.2g/animal/day) and WD (27.8 g/animal/day) groups. Additionally, food efficiency ratio (FER) tended to decrease in LCHP fed rats. Serum homocysteine concentration significantly decreased in rats fed WD and LCHP diets. Liver weights were significantly higher in rats fed WD and LCHP diets. At the end of the experiment (2 months) the triacylglycerol (TAG) was significantly decreased in animals fed LCHP compared to WD. qRT-PCR showed that SCD-1 and FAS were decreased in LCHP fed rats, but WD diet increased expression of lipid metabolism genes. Rats receiving LCHP diet had two fold higher kidney weight and 54.5% higher creatinin level compared to Control and WD diets. In conclusion, LCHP diet decreased animal's body weight and decreased TAG in rat's serum. However, kidney damage in LCHP rats was observed.

Methionine concentration in the diet has a tissue-specific effect on chromosomal stability in female mice

Inadequate nutrient intake can influence the genome. Since methionine is an essential amino acid that may influence DNA integrity due to its role in the one-carbon metabolism pathway, we were interested in whether methionine imbalance can lead to genotoxic events. Adult female Swiss mice were fed a control (0.3% dl-methionine), methionine-supplemented (2.0% DL-methionine) or methionine-deficient (0% DL-methionine) diet over a 10-week period. Chromosomal damage was assessed in peripheral blood using a micronucleus test, and DNA damage was assessed in the liver, heart and peripheral blood tissues using a comet assay. The mRNA expression of the mismatch repair genes Mlh1 and Msh2 was analyzed in the liver. The frequency of micronucleus in peripheral blood was increased by 122% in the methionine-supplemented group (p<0.05). The methionine-supplemented diet did not induce DNA damage in the heart and liver tissues, but it increased DNA damage in the peripheral blood. The methionine-deficient diet reduced basal DNA damage in liver tissue. This reduction was correlated with decreased mRNA expression of Msh2. Our results demonstrate that methionine has a tissue-specific effect because methionine-supplemented diet induced both chromosomal and DNA damage in peripheral blood while the methionine-deficient diet reduced basal DNA damage in the liver.

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-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.

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.

Influence of hyperhomocysteinemia on the cellular redox state--impact on homocysteine-induced endothelial dysfunction

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. An increasing body of evidence has implicated oxidative stress as being contributory to homocysteine's deleterious effects on the vasculature. Elevated levels of homocysteine may lead to increased generation of superoxide by a biochemical mechanism involving nitric oxide synthase, and, to a lesser extent, by an increase in the chemical oxidation of homocysteine and other aminothiols in the circulation. The resultant increase in superoxide levels is further amplified by homocysteine-dependent alterations in the function of cellular antioxidant enzymes such as cellular glutathione peroxidase or extracellular superoxide dismutase. One direct clinical consequence of elevated vascular superoxide levels is the inactivation of the vasorelaxant messenger nitric oxide, leading to endothelial dysfunction. Scavenging of superoxide anion by either superoxide dismutase or 4,5-dihydroxybenzene 1,3-disulfonate (Tiron) reverses endothelial dysfunction in hyperhomocysteinemic animal models and in isolated aortic rings incubated with homocysteine. Similarly, homocysteine-induced endothelial dysfunction is also reversed by increasing the concentration of the endogenous antioxidant glutathione or overexpressing cellular glutathione peroxidase in animal models of mild hyperhomocysteinemia. Taken together, these findings strongly suggest that the adverse vascular effects of homocysteine are at least partly mediated by oxidative inactivation of nitric oxide.

Endothelial dysfunction and atherothrombosis in mild hyperhomocysteinemia

Mildly elevated plasma homocysteine levels are an independent risk factor for atherothrombotic vascular disease in the coronary, cerebrovascular, and peripheral arterial circulation. Endothelial dysfunction as manifested by impaired endothelium-dependent regulation of vascular tone and blood flow, by increased recruitment and adhesion of circulating inflammatory cells to the endothelium, and by a loss of endothelial cell antithrombotic function contributes to the vascular disorders linked to hyperhomocysteinemia. Increased vascular oxidant stress through imbalanced thiol redox status and inhibition of important antioxidant enzymes by homocysteine results in decreased bioavailability of the endothelium-derived signaling molecule nitric oxide via oxidative inactivation. This plays a central role in the molecular mechanisms underlying the effects of homocysteine on endothelial function. Supplementation of folic acid and vitamin B12 has been demonstrated to be efficient in lowering mildly elevated plasma homocysteine levels and in reversing homocysteine-induced impairment of endothelium-dependent vasoreactivity. Results from ongoing intervention trials will determine whether homocysteine-lowering therapies contribute to the prevention and reduction of atherothrombotic vascular disease and may thereby provide support for the causal relationship between hyperhomocysteinemia and atherothrombosis.

The relation between plasma cysteine, plasma homocysteine and coronary atherosclerosis

Several studies have reported that elevated plasma levels of total homocysteine (tHcy) are related to an increased risk of cardiovascular disease. Only a few studies have looked at the effect of cysteine, another amino thiol, on cardiovascular disease risk. Therefore, in the present case-control study we compared plasma total cysteine (tCys) levels and plasma tHcy levels among subjects with severe coronary atherosclerosis (cases, n=131), subjects without severe coronary atherosclerosis (coronary controls, n=88) and healthy subjects (population-based controls, n=101). Cases were defined as those having > or =90% occlusion in one and > or =40% occlusion in a second coronary artery, while coronary controls had a maximum of 50% occlusion in only one coronary artery. Both males and females, aged 26--64 years were studied. We have previously reported that plasma tHcy is an independent risk factor for coronary atherosclerosis in this study population. In the present analysis, we found that cases had statistically significant higher mean plasma tCys levels than coronary controls and population-based controls (295.8+/-40.2, 279.0+/-35.5 and 282.6+/-32.4 micromol/l, respectively). The odds ratio (OR) of coronary atherosclerosis for the upper tertile of tCys compared with the bottom tertile was 2.5 (95% confidence interval (CI), 1.4--4.3). However, the association between tCys and coronary atherosclerosis was confounded to a great extent by risk factors (OR, 1.0; 95% CI, 0.5--2.0). The multivariate adjusted OR of coronary atherosclerosis per 1 S.D. increase in plasma tCys was 1.0 (95% CI, 0.8--1.3). The corresponding OR per 1 S.D. increase in plasma tHcy was 1.4 (95% CI, 1.1--1.8). We conclude that plasma tCys, unlike plasma tHcy, is not an independent risk factor for atherosclerosis.

Impaired homocysteine metabolism and atherothrombotic disease

Based on recent retrospective, prospective, and experimental studies, mild to moderate elevation of fasting or postmethionine-load plasma homocysteine is accepted as an independent risk factor for cardiovascular disease and thrombosis in both men and women. Hyperhomocysteinemia results from an inhibition of the remethylation pathway or from an inhibition or a saturation of the transsulfuration pathway of homocysteine metabolism. The involvement of a high dietary intake of methionine-rich animal proteins has not yet been investigated and cannot be ruled out. However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia. Recent experimental studies have suggested that moderately elevated homocysteine levels are a causal risk factor for atherothrombotic disease because they affect both the vascular wall structure and the blood coagulation system. The oxidant stress that results from impaired homocysteine metabolism, which modifies the intracellular redox status, might play a central role in the molecular mechanisms underlying moderate hyperhomocysteinemia-mediated vascular disorders. Because folate supplementation can efficiently reduce plasma homocysteine levels, both in the fasting state and after methionine loading, results from further prospective cohort studies and from on-going interventional trials will determine whether homocysteine-lowering therapies can contribute to the prevention and reduction of cardiovascular risk. Additionally, these studies will provide unequivocal arguments for the independent and causal relationship between hyperhomocysteinemia and atherothrombotic disease.

Fluctuations in dietary methionine intake do not alter plasma homocysteine concentration in healthy men

A moderate elevation in plasma total homocysteine (tHcy) has been established as an independent risk factor for vascular disease. An important exogenous source of homocysteine is methionine found in foods rich in animal protein. We investigated the response of tHcy to fluctuations in methionine intake in a cross-over intervention trial (two arms). Healthy men (n = 52; 19-29 y) were screened for habitual methionine intake using a food-frequency questionnaire. Subjects in the top quartile for methionine intake (n = 13), with a baseline fasting tHcy of 7.01 +/- 1.84 micromol/L (mean +/- SD), were randomly assigned to receive either a low-methionine intervention diet for 1 wk followed by a control diet for 1 wk or vice-versa. Simultaneously, those in the bottom quartile for methionine intake (n = 11), with a fasting plasma tHcy of 9.79 +/- 7. 20 micromol/L (mean +/- SD), received either a high methionine intervention diet for 1 wk followed by a control diet or vice-versa. All subjects had serum folate, red-cell folate, serum vitamin B-12 and plasma pyridoxal phosphate (PLP) concentrations within normal ranges. During the intervention, subjects in the top quartile for methionine intake reduced their daily methionine intake 79%, from 1969 +/- 639 to 407 +/- 83 mg/d (P: </= 0.001), and those in the bottom quartile almost doubled their methionine intake, from 1155 +/- 401 to 2112 +/- 379 mg/d (P: </= 0.001). Despite these changes in methionine intake, no corresponding changes in plasma tHcy were observed. These results suggest that in the absence of an obvious deficiency of relevant B-vitamins, fasting plasma tHcy is unaffected by intermediate-term fluctuations (up to 100% of usual intake) in dietary methionine.