Methionine Metabolites Research Articles

Elevated Serum Homocysteine in Patients with Coronary Vasospasm

Background: Homocysteine is a metabolite of methionine with atherogenic properties via endothelial dysfunction. Endothelial dysfunction is one of main pathophysiologic mechanisms of coronary vasospasm. We examined the relationship between the risk of patients with coronary vasospasm and serum total homocysteine (tHcy), folate, vitamin B12, and plasma vitamin B6. Methods: Fasting serum tHcy, folate, vitamin B12, and plasma vitamin B6 concentrations were measured in 25 patients (15 men, age 52.8±10.1) with coronary vasospasm and compared with 22 healthy control subjects matching in age and sex (10 men, age 52.7±9.2). Serum tHcy concentration was higher in the vasospasm group than in the control group (14.8±5.3 vs 10.1±2.5 μmol/L, p<0.001). Results: Serum folate (6.3±1.0 vs 10.2±4.5 ng/mL, p<0.001) and vitamin B12 concentration (544.8±181.7 vs 1004.9±567.1 pg/mL, p<0.001) were lower in vasospasm group. There was no significant difference in plasma vitamin B6 concentration between the two groups (77.8±44.3 and 95.8±63.4 nmol/L). Conclusions: These data support the hypothesis that elevated serum tHcy is a risk factor for coronary vasospasm. Low folate and vitamin B12 levels in patients with coronary vasospasm suggest that these agents contribute therapeutically to the treat

Hepatic transmethylation reactions in micropigs with alcoholic liver disease.

Alcoholic liver disease is associated with abnormal hepatic methionine metabolism, including increased levels of homocysteine and S-adenosylhomocysteine (SAH) and reduced levels of S-adenosylmethionine (SAM) and glutathione (GSH). The concept that abnormal methionine metabolism is involved in the pathogenesis of alcoholic liver disease was strengthened by our previous findings in a micropig model where combining dietary folate deficiency with chronic ethanol feeding produced maximal changes in these metabolites together with early onset of microscopic steatohepatitis and an eightfold increase in plasma aspartate aminotransferase. The goal of the present study was to determine potential mechanisms for abnormal levels of these methionine metabolites by analyzing the transcripts and activities of transmethylation enzymes in the livers of the same micropigs. Ethanol feeding or folate deficiency, separately or in combination, decreased transcript levels of methylenetetrahydrofolate reductase (MTHFR), methionine adenosyltransferase (MAT1A), glycine-N-methyltransferase (GNMT) and S-adenosylhomocysteine hydrolase (SAHH). Ethanol feeding alone reduced the activities of methionine synthase (MS) and MATIII and increased the activity of GNMT. Each diet, separately or in combination, decreased the activities of MTHFR and SAHH. In conclusion, the observed abnormal levels of methionine metabolites in this animal model of accelerated alcoholic liver injury can be ascribed to specific effects of ethanol with or without folate deficiency on the expressions and activities of hepatic enzymes that regulate transmethylation reactions. These novel effects on transmethylation reactions may be implicated in the pathogenesis of alcoholic liver disease.

Increased plasma homocysteine and S-adenosylhomocysteine and decreased methionine is associated with altered phosphatidylcholine and phosphatidylethanolamine in cystic fibrosis

ObjectiveWe used a novel approach based on the intersection of phospholipid and methionine metabolism at the S-adenosylmethionine (SAM)-dependent methylation of phosphatidylethanolamine (PE) to study potential alterations in phospholipid metabolism in children with cystic fibrosis (CF). Methyl groups from methionine via SAM are used for sequential methylation of PE to form phosphatidylcholine (PC) with the generation of S-adenosylhomocysteine (SAH) and homocysteine. Study designPlasma phospholipids and methionine metabolites and plasma and red blood cell phospholipid fatty acids were determined in 53 children with CF and 18 control children. ResultsPlasma methionine and the PC/PE ratio was lower and homocysteine, SAH, and PE were higher in children with CF than in control children (P<.001). Plasma methionine was inversely (P<.05) and SAH and homocysteine were positively (P<.001) correlated with the plasma PE. Docosahexaenoic acid (22:6n-3) was significantly lower in plasma phospholipids and triglycerides and in red blood cell PC and PE of children with CF than in control children (P<.05). ConclusionsThese studies demonstrate that methionine metabolism is altered and associated with alteration of the plasma PC/PE ratio in CF. Altered phospholipid and methionine metabolism may contribute to the clinical complications associated with CF.

Methods in Assessing Homocysteine Metabolism

Homocysteine, a sulfur-containing amino acid, is a metabolite of the essential amino acid methionine. High blood levels of homocysteine result in far-reaching biochemical and life-threatening consequences. Homocysteine exists at a critical biochemical intersection in the methionine cycle between S-adenosylmethionine, the ubiquitous methyl donor, and vitamins B(12) and folic acid. Indirect and direct vascular damage can be caused by homocysteine, a putative atherothrombotic risk factor. Homocysteine has been associated with vascular disease, particularly in subjects with significant carotid stenosis. Increasing evidence for a connection between homocysteine metabolism and cognitive function is surfacing, and this includes from mild cognitive decline (age-related memory loss) to vascular dementia and Alzheimer's disease. In the elderly population increase in homocysteine is commonly seen due to significant deficiencies in cobalamin (B(12)), folate and vitamin B(6.) All of these disease associations are thought to be interrelated via increased homocysteine and S-adenosylhomocysteine and subsequent hypomethylation of numerous substances, including DNA and proteins, rendering vascular structures more susceptible to damage. Decreasing plasma homocysteine, by providing nutritional cofactors for its metabolism has been shown to reduce the risk of cardiovascular events. The current methods of evaluation of homocysteine metabolism include assessment of cobalamin (B(12)) and folate and vitamin B(6) status and screening for mutations in the genes encoding the enzymes of metabolism. An accurate method for the estimation of plasma and tissue levels of homocysteine would contribute greatly to a proper understanding of the metabolism. In the current review emphasis will be on the estimation of homocysteine, and evaluation of one of the common mutations encountered in the metabolism of this amino acid.

Altered methionine metabolism in long living Ames dwarf mice

Ames dwarf mice (df/df) are deficient in growth hormone, prolactin, and thyroid-stimulating hormone and live significantly longer than their normal siblings. In the current study, we found that the hormone deficiencies affect methionine metabolism. We previously reported that the dwarf mice exhibit enzyme activities and levels that combat oxidative stress more efficiently than those of normal mice. Moreover, methionine or metabolites of methionine are involved in antioxidative processes. Thus, we performed an experiment that compared various parameters of methionine metabolism between 18-month old male dwarf ( N=6) and wild type ( N=5) mice. The specific activity of liver methionine adenosyltransferase (MAT) was significantly elevated (205%, p<0.0001) in the dwarf mice, as were cystathionine synthase (50%, p<0.01), cystathionase (83%, p<0.001), and glycine N-methyltransferase (GNMT, 91%, p<0.001) activities. Even though the activities of MAT and GNMT were elevated, the concentration of liver S-adenosylmethionine was decreased (24%, p<0.001) and S-adenosylhomocysteine increased (113%, p<0.001) in the dwarf mice. These data indicate that dwarf mice, compared to wild type mice, have a markedly different metabolism of methionine. Altered methionine metabolism may partially explain earlier reports indicating less oxidative damage to proteins in dwarf mice. Taken together, the data suggest that methionine metabolism may play a role in oxidative defense in the dwarf mouse and should be studied as a potential mechanism of extended lifespan.

Comparative mammalian choline metabolism with emphasis on the high-yielding dairy cow

The present review examines the importance of choline in dairy cow nutrition. Choline is an essential nutrient for mammals when excess methionine and folate are not available in the diet. The requirement for choline can be met by dietary choline and by transmethylation reactions. Two types of functions for choline are known: functions of choline per se; functions as a methyl donor. The two principal methyl donors in animal metabolism are betaine, a metabolite of choline, and S-adenosyl-methionine, a metabolite of methionine. Choline and methionine are interchangeable with regard to their methyl group-furnishing functions. In adult ruminants, choline is extensively degraded in the rumen; for this reason dietary choline contributes insignificantly to the choline body pool and methyl group metabolism is generally conservative with a relatively low rate of methyl catabolism and an elevated rate of de novo synthesis of methyl groups via the tetrahydrofolate system. In dairy ruminants, the dietary availability of choline is still low, but the output of methylated compounds in milk is high, and precursors from the tetrahydrofolate pathway are limiting, especially at the onset of lactation. Therefore choline may be a limiting nutrient for milk production in high-yielding dairy cows.

The Effects of Diet, Genetics and Chemicals on Toxicity and Aberrant DNA Methylation: an Introduction

In the early 1930s, the group of Banting and Best showed that the choline moiety of lecithin was responsible for the prevention of the fatty livers produced in pancreatectomized dogs treated with insulin. This was the first study linking abnormal methyl metabolism with disease. Since then, deficiencies of each of the four essential dietary sources of methyl groups (choline, methionine, vitamin B-12 and folic acid) have been associated with increased risk of a number of diseases. Choline-deficient diets were shown to enhance liver tumor formation in rats, and such diets frequently were found to lead to atherosclerosis. Although methionine deficiency per se was not extensively studied in vivo, its metabolic antagonist ethionine did cause liver cancer and pancreatic toxicity in rodents. Deficiencies of vitamin B-12 and of folic acid have long been shown to cause neurological disturbances and birth defects both in humans and in experimental animals. In 1969 inborn errors of metabolism leading to the accumulation of the demethylated metabolite of methionine, homocysteine, were proposed as contributing to the early onset of atherosclerosis. Before 1990, numerous studies described the abnormal methylation of DNA in tumors and transformed cells. Less frequently investigated, however, were the exogenous and endogenous agents leading to such abnormal methylation. These included genetic variants among rodent strains and the methyl-deficient diets that caused liver cancer. In addition, several chemicals, particularly carcinogens, were shown to alter DNA methylation. The possible links between chemically induced alterations in DNA methylation and development of other diseases were little explored. However, by 1990, a chain of causality had been established in experimental carcinogenesis linking dietary methyl deficiency with methyl insufficiency in vivo, as well as with the abnormal methylation of DNA and of specific genes. Also during this period, the diminished activity of the enzyme methylenetetrahydrofolate reductase (EC 1.5.1.20), which is responsible for the actual de novo synthesis of methyl groups, was shown to be associated with increased risk of developing atherosclerosis, neurological disorders and birth defects. The exponential rise in studies on methyl metabolism and DNA methylation since then enables us to examine here the extent to which the mechanisms by which abnormal methylation processes seem to exert their toxic effects in one disease may be applicable to other pathologies.

Effects of atorvastatin on oxidized low-density lipoprotein, low-density lipoprotein subfraction distribution, and remnant lipoprotein in patients with mixed hyperlipoproteinemia

Atorvastatin (10 to 20 mg/day) was administered for 3 months to 15 outpatients (average age 58 ± 4 years) with hypercholesterolemia accompanied by hypertriglyceridemia without hypolipemic treatment. Changes in lipid profile, particularly oxidized low-density lipoprotein (LDL) (malondialdehyde LDL), subfractions of LDL, and remnant lipoprotein (RLP) cholesterol, were examined before and after administration. In addition, the influence of atorvastatin on lipoprotein(a) (known to be an independent risk factor for atherosclerosis), asymmetric dimethylarginine (known to be an endogenous inhibitor of nitric oxide synthase), and homocysteine (methionine metabolite) was also investigated. Administration of atorvastatin significantly decreased serum total cholesterol, LDL cholesterol, and triglycerides. Conversely, a significant increase in high-density lipoprotein cholesterol was shown. In LDL subfractions, large, buoyant LDL fractions were not influenced by treatment with atorvastatin (before administration, 99 ± 14 mg/dl; after administration, 91 ± 6 mg/dl, shown as a cholesterol content in each subfraction), but a marked decrease in small, dense LDL fractions (p <0.001) (before administration, 119 ± 17 mg/dl; after administration, 43 ± 10 mg/dl) was shown. Moreover, oxidized LDL was significantly decreased (p <0.01) (before administration, 169 ± 13 U/L; after administration, 119 ± 10 U/L) and RLP cholesterol also was significantly decreased (p <0.01) (before administration, 11.9 ± 2.0 mg/dl; after administration, 6.0 ± 0.9 mg/dl) with atorvastatin treatment. No significant change was observed in fasting plasma glucose, hemoglobin A1c, lipoprotein(a), asymmetric dimethylarginine, homocysteine, and so on. These data suggest that administration of relatively low doses of atorvastatin to patients with hypercholesterolemia accompanied with hypertriglyceridemia results in a decrease not only in LDL cholesterol and triglycerides, but also in oxidized LDL and RLP cholesterol, with an increase in high-density lipoprotein cholesterol. Furthermore, small, dense LDL decreased with a shift in LDL subfractions to large, buoyant fractions, and these changes are considered to be involved in the inhibition of the onset and progression of atherosclerosis.

Basal and Post-Methionine Serum Homocysteine and Lipoprotein Abnormalities in Patients With Chronic Liver Disease

BackgroundLipoprotein abnormalities are commonly found in chronic liver diseases (CLDs), particularly hypercholesterolemia in primary biliary cirrhosis (PBC). However, affected patients may not be at increased risk of coronary heart disease....

Homocysteine Predicts Incident Isolated Systolic Hypertension in Older Adults

0019 Untreated isolated systolic hypertension (ISH) indicates arterial stiffening and carries a risk for both stroke and cardiovascular disease. Elevated plasma homocysteine, a metabolite of the essential amino acid methionine, has been linked to vascular stiffness. 187 normotensive (defined as systolic blood pressure (SBP) &lt; 160 mmHg and diastolic blood pressure &lt; 90 mmHg) men and women (mean age 71.29 + 6.3 yrs) were followed for an average of 7 years for incident ISH. ISH was defined as a SBP ≥160 mmHg (while maintaining a DBP of &lt; 90 mmHg) at least one time at 3 year follow-up visits, or the initiation of antihypertensive therapy. The mean baseline systolic and diastolic blood pressures (DBP) were 127 and 69 mmHg, respectively. Over the 7 year period, 59(31.5%) participants developed ISH, 76% qualified by antihypertensive use, and 24% by blood pressure values. The Kaplan Meier Estimate of 7 year survival free from ISH was 67% (95% CI: 61%, 74%). The relationship between incident ISH and the traditional cardiovascular risk factors, creatinine, homocysteine, and carotid artery intima-media wall thickness (IMT) was assessed by Cox proportional hazards regression. The strongest predictor of incident ISH was baseline SBP. For participants with baseline SBPs of &lt; 130, 130-139, and 140+ mmHg, the corresponding 7 year survival free from ISH was 80% (95% CI: 73%, 88% ), 53% (95%CI: 38%, 67%), and 44% (95% CI: 26%, 62%). Factors independently associated with time to ISH were higher triglycerides (upper tertile,RR=2.0, p=0.012), homocysteine levels (&gt; 12.0 μmol/l, RR=2.2, p=0.005), and baseline SBP (per 10 mmHg,RR=1.4, p=0.003). The results were similar when the analysis was restricted to the 157 participants with a baseline SBP of &lt; 140 mmHg. Baseline IMT was found to be univariately related to time to ISH (RR per each 1.0 mm increment=3.0; p=0.016). In multivariate analysis, this association remained independent of triglycerides and homocysteine, but not baseline SBP (RR per each 1.0 mm increment=2.5; p=0.049). In conclusion, among normotensive older adults, 32% can be expected to develop ISH over a 7 year period, and higher triglyceride and homocysteine levels are risk factors.

Effects of methionine loading on plasma and erythrocyte sulphur amino acids and sulph-hydryls before and after co-factor supplementation in haemodialysis patients.

Hyperhomocysteinaemia, which is potentially atherogenic, is common in chronic haemodialysis (HD) patients but the reason for this is not yet known. The methionine (Met) loading test (MLT) is used to test the capacity of homocysteine (Hcy) disposal by the trans-sulphuration pathway and thus may provide information on the metabolism of sulphur amino acids. The availability of vitamin B(6) and folic acid, as co-factors for Hcy metabolism may affect the response to MLT. In the present study, we compared the effect of Met loading on plasma and erythrocyte (RBC) sulphur amino acids and sulph-hydryls before and after co-factor supplementation in healthy subjects and HD patients. In 10 HD patients and 10 healthy subjects the effect of Met loading, 0.1 g/kg BW, on plasma and RBC methionine metabolites was studied over 7 h, before and after 4 weeks supplementation with high daily doses of vitamin B(6) (200 mg) and folic acid (15 mg). MLT before vitamin supplementation in HD patients, compared to the healthy subjects, caused significantly greater increases in plasma Hcy levels (43+/-12 vs 15+/-5 micromol/l), cysteinesulphinic acid (CSA) (1.34 vs 0.36 micromol/l) and gamma-glutamylcysteine (0.98+/-0.83 vs -01+/-0.42 micromol/l) and no decline in plasma cysteine (Cys) (0.5+/-33.9 vs -31+/-26 micromol/l), but no significant differences in plasma taurine, cysteinylglycine, and glutathione concentrations. In RBCs there was a small increase in Hcy levels and a more marked increase in Tau levels, with no difference between the healthy subjects and HD patients. Vitamin supplementation in pharmacological doses failed to correct the abnormal responses to MLT in the HD patients. Oral methionine loading in HD patients leads to higher accumulation of Hcy and other Met metabolites in plasma and RBCs than in healthy subjects, indicating impaired metabolism of sulphur amino acids via the trans-sulphuration pathway. Supplementation with high doses of vitamin B(6) and folic acid does not correct this impairment, suggesting that it most probably is not due to lack of these co-factors.

Effects of parenteral cysteine and glutathione feeding in a baboon model of severe prematurity

The availability of cysteine for glutathione synthesis is low in premature infants with respiratory distress. The effects of gestational age, oxygen delivery, and cysteine infusion or glutathione infusion, or both, on plasma total cysteine and other methionine metabolites were studied in a baboon model of severe premature birth with respiratory distress. Premature baboons were studied as part of the multiinvestigator National Institutes of Health Collaborative Project on Bronchopulmonary Dysplasia. Premature baboons, 125 d (69% of term) or 140 d (78% of term) of gestational age, were maintained in neonatal intensive care units for </=14 d. Parenteral feeding with or without supplemental cysteine and glutathione infusions was given. Plasma total cysteine, methionine, N:-methylglycine, cystathionine, and the other methionine metabolites were monitored by capillary gas chromatography-mass spectrometry. Cord blood plasma total cysteine was the lowest in the 125-d-old premature baboons. Plasma total cysteine decreased in the first 3 d after delivery in the 125-d-old (but not in the 140-d-old) premature baboons even when cysteine was infused. Supplementation with glutathione from the first day of life raised plasma total cysteine markedly. Plasma cystathionine increased in all animals after birth but increased 4-fold in 125-d-old animals with glutathione infusion. At 6 and 10 d postdelivery, the arterial-alveolar oxygen gradient was significantly higher in the 125-d-old animals that received glutathione infusions. Glutathione, but not supplemental cysteine, infusions prevented the postdelivery decline in plasma cysteine concentrations in premature baboons. Glutathione infusions resulted in marked elevations of plasma cystathionine concentration.

Homocysteine and risk of cardiovascular disease.

This pictorial introduction to homocysteine illustrates at a glance the nature of homocysteine and its role in cardiovascular disease by means of eight simple figures and an essential bibliography. Homocysteine is a sulfur-containing metabolite of methionine. Conversion back to methionine or transsulfuration to cysteine are the two major metabolic pathways that reduce total homocysteine (tHcy) concentrations in cells and blood. B vitamins are essential cofactors in homocysteine metabolism. Median fasting total homocysteine levels in adult males are approximately 10 micromol/L. Increased plasma tHcy concentrations are found with methionine-rich diets, low vitamin B intake, male gender, age, impaired renal function, and genetically determined defects of the enzymes involved in homocysteine metabolism. An inverse relation exists between plasma tHcy and circulating folate or vitamin B(6) concentrations, and folic acid supplements of 0.5 mg/d can reduce tHcy levels by approximately 25%. Homocystinuric patients, who have severe hyperhomocysteinemia, die prematurely of atherothrombotic disease. Many (but not all) cross-sectional and prospective studies indicate, on average, that plasma tHcy levels <.10 micromol/L are associated with, or predict the development of, coronary, cerebral, and peripheral vascular disease. The risk conferred by hyperhomocysteinemia is graded and is independent of traditional risk factors, with an estimated odds ratio for ischemic heart disease of 1.4 for every 5 micromol/L increase in plasma tHcy. In vitro and in vivo, tHcy has been found to impair endothelial function. It is now well established that tHcy represents a marker of current or subsequent ischemic vascular disease. However, irrefutable proof that hyperhomocysteinemia actually causes atherothrombosis will come only if interventions to lower plasma tHcy will produce concomitant reductions in cardiovascular events.

Methionine infusion reproduces liver injury of parenteral nutrition cholestasis.

Cholestatic jaundice is the major complication of total parenteral nutrition (TPN) in infancy. We have previously shown that the TPN solution is directly toxic to the liver, and that this toxicity appears to be mediated by one or more amino acids. Elevated serum methionine levels, without corresponding increases in its metabolites, suggest that accumulation of this toxic amino acid may cause TPN cholestasis. Nine-week-old rabbits (n = 28) were divided into three groups. The FED group was fed standard rabbit chow ad libitum. The TPN group was not fed and received only i.v. TPN (including methionine 121 mg.kg-1.d-1), and lipids. The EXP group was fed chow ad libitum and received i.v. methionine (121 mg.kg-1.d-1). After 14 d, we evaluated bile flow, bromosulfophthalein excretion, serum liver enzymes, liver histology, and serum amino acid levels. Bile flow was significantly depressed in the TPN and EXP groups compared with FED controls (32.9 +/- 9.4 and 45.7 +/- 14.4 versus 82.9 +/- 13.8). Excretion of the bilirubin analog bromosulfophthalein tended to be delayed by methionine infusion (p = 0.15). Serum liver enzymes (aspartate transaminase, alanine aminotransferase, gamma-glutamyltransferase, and alkaline phosphatase) were normal in all groups. Histologic liver injury in the EXP group was similar to that caused by TPN. Balloon degeneration, and portal inflammation were seen in both groups. Homocysteine, an early metabolite of methionine, was elevated in the TPN and EXP groups compared with FED controls. Intravenous methionine is hepatotoxic. Despite full oral feeding, it produces a depression of bile flow and histologic liver injury similar to that seen with TPN. Elevated homocysteine levels suggests an enzymatic block early in the pathway of methionine metabolism. We believe that methionine may be an important factor in the pathogenesis of TPN cholestasis.

Effect of methionine loading on 5-methyltetrahydrofolate, S-adenosylmethionine and S-adenosylhomocysteine in plasma of healthy humans.

1. Elevated plasma homocysteine concentration, either in the fasting state or after methionine loading, is an independent risk factor for vascular disease in man. Methionine loading has been used to investigate impaired methionine metabolism, especially of the trans-sulphuration pathway, but most studies have focused on changes in homocysteine. 2. We investigated the effect of methionine excess on total plasma homocysteine, 5-methyltetrahydrofolate (which is the active form of folate in the remethylation of homocysteine to methionine), S-adenosyl-methionine (the first metabolite of methionine) and S-adenosylmethionine) (the demethylated product of S-adenosylmethionine) over 24h in 12 healthy subjects. 3. As well as the expected increase in homocysteine (from 8.0 +/- 1.3 to 32.6 +/- 10.3 mumol/l, mean +/- SD, P < 0.001), S-adenosylmethionine showed a significant transient increase (from 37.9 +/- 25.0 to 240.3 +/- 109.2 nmol/l, P < 0.001), which correlated well with homocysteine (r2 = 0.92, P < 0.001). 5-Methyltetrahydrofolate values decreased significantly (from 23.2 +/- 7.2 to 13.1 +/- 2.9 nmol/l, P < 0.01), and gradually returned to baseline levels after 24h. No significant change over the time of measurement was found for S-adenosylhomocysteine. 4. The sequence of metabolic changes observed in this study strongly suggests that a change in either homocysteine or S-adenosylmethionine may cause a reduction in 5-methyltetrahydrofolate. This must be considered in evaluating the relationship between folate and homocysteine in vascular disease. The metabolic relationships illustrated in this study should be evaluated in the search for pathogenetic mechanisms of mild hyperhomocysteinaemia and vascular disease.

L'homocystéine: ses liens avec les maladies cardiovasculaires ischémiques

Homocysteine, a sulfur-containing amino acid, is an intermediate metabolite of methionine. Patients with homocystinuria and severe hyperhomocysteinemia develop premature arteriosclerosis and arterial thrombotic events, and venous thromboembolism. Studies suggest that moderate hyperhomocysteinemia can be considered as an independent risk factor in the development of premature cardiovascular disease. In vitro, homocysteine has toxic effects on endothelial cells. Homocysteine can promote lipid peroxidation and damage vascular endothelial cells. Moreover, homocysteine interferes with the natural anticoagulant system and the fibrinolytic system. Homocysteinemia should be known in patients with premature vascular diseases, especially in subjects with no risk factors. Folic acid, vitamin B6 can lower homocysteine levels.

Placebo-Controlled Trials of Antioxidant Therapy Including S-Adenosylmethionine in Patients with Recurrent Nongallstone Pancreatitis

Having shown in a 20-week placebo-controlled double-blind crossover trial that ‘global’ antioxidant supplementation - including selenium, β-carotene, vitamin C (ascorbic acid), vitamin E (tocopherol) and methionine - curbs symptoms while correcting oxidative stress in patients with recurrent nongallstone pancreatitis, we have investigated through two further trials the relative importance of methionine versus that of the other antioxidants in effecting this good outcome. 30 consecutive patients were entered into the second study in which therapeutic intervention involved only the active metabolite of methionine, S-adenosyl-methionine (SAMe), 2.4g per day in divided doses. Blood analysis showed that subnormal baseline levels of selenium, β-carotene and vitamins E and C were unchanged throughout and that drug treatment resulted in supranormal levels of SAMe in plasma. SAMe proved to be ineffective clinically as judged by attack rate and background pain, as well as biochemically as gauged by the percentages of oxidatively altered vitamin C and linoleic acid. The coadministration of selenium and β-carotene with SAMe was tested in the third study. This was abandoned when 3 patients had a clearcut attack of pancreatitis while on subsequent ‘open’ treatment. Analysis of clinical and biochemical information from 14 patients who had completed the 20-week trial confirmed the inefficacy of the combination, although active treatment normalised serum selenium and β-carotene concentrations while SAMe levels were again pushed into the supranormal range. The results show that SAMe on its own, or with additional selenium and β-carotene, is ineffective in patients with recurrent nongallstone pancreatitis. By a process of elimination with reference to biochemical measurements during the 3 trials, and considering experimental evidence of the importance of methionine for pancreatic integrity, we cautiously suggest that an effective antioxidant prescription should include SAMe (or methionine) as well as vitamin C, with additional compounds as indicated by blood measurements.

The kinetics and dynamics of three kinds of radioactive methionine after i.v. administration in mice

In C57BL mice, a tracer amount of methionine (Met) at a concentration approximate to that in the blood was administered in the tail vein (i.v.). The rates of endogenous metabolic decomposition of methionine were obtained by using three specifically labelled compounds, [1-14C]-Met, [m-14C]-Met and [35S]-Met. Results on the kinetics and dynamics after i.v. administration suggested that 5 min after administration, most of the labelled compounds were taken up into the organs and tissues, and only a small portion was excreted in the expired air as CO2, the final metabolite of methionine. At 30 min the radioactive concentration in blood was minimal and was consistent with the maximum of the 14CO2 excretion in expired air. Gradual increase of the radioactive concentration in blood after 30 min might be due to the contribution of the metabolite in the blood. Methionine taken up was endogenously utilized by more than 40% during 48 h and it maintained the order of [1-14C]:[m-14C]:[35S]. Out of the remaining 60%, 40% was metabolized in 6 h after administration, the [1-14C] moiety being excreted mainly into expired air, the [m-14C] moiety into expired air and urine, and the [35S] moiety mainly into urine and partly into faeces. Microautoradiograms revealed that a part of the last 20% was taken up into the enzyme proteins contained in the pancreatic juice and intestinal juice, and was decomposed within 48 h.

Metabolism, cellular actions, and cytotoxicity of selenomethionine in cultured cells

Selenomethionine metabolism and the biochemical basis for its cytotoxicity were analyzed in cultured human and murine lymphoid cells. The metabolic pathways were also addressed, using purified mammalian enzymes and crude tissue extracts. Selenomethionine was found to be effectively metabolized to S-adenosylmethionine analog, and that analog was further metabolized in transmethylation reactions and in polyamine synthesis, similarly to the corresponding sulphur metabolites of methionine. Selenomethionine did not block these pathways, nor was there a specific block on the synthesis of DNA, RNA, or proteins when added to the culture medium. Selenomethionine showed cytotoxicity at above 40 microM levels. Yet, low selenomethionine levels (10 microM) could replace methionine and support cell growth in the absence of methionine. Selenomethionine toxicity took place concomitantly with changes in S-adenosylmethionine pools. D-form was less cytotoxic than L-form. Methionine concentration modified the cytotoxicity. Together, this indicates that selenomethionine uptake and enzymic metabolism are involved in the cytotoxicity in a yet unknown way.

Effects of Dietary Protein Degradability and Casein or Amino Acid Infusions on Production and Plasma Amino Acids in Dairy Cows

Responses to daily abomasal infusions of 400g sodium caseinate, 400g hydrolyzed casein, or 11.3g L-methionine plus 30.1g L-lysine were compared in eight Holstein cows fed diets with estimated ruminal protein degradabilities of 70 and 60.5%. Basal diets contained corn silage and corn with either soybean meal or 66.7:33.3 soybean meal:corn gluten meal added. Infusion with Methionine plus lysine increased milk protein content when cows were fed either diet but increased milk fat content and yield only when the soybean meal diet was fed. Sodium caseinate increased milk and milk protein production and decreased milk fat percentage. Concentration of total essential amino acids, branched chain amino acids, and urea cycle amino acids were increased by the infusion of both casein sources. Methionine-lysine infusion increased plasma lysine and taurine, a metabolite of methionine, suggesting that absorbed methionine was extensively metabolized. Results demonstrate an impact of both ruminal degradability of dietary protein and form of infused protein on amino acid nutrition of lactaring dairy cows.