Methionine In Rats Research Articles

Intramolecular Disulfide Bridges in Voltage-Dependent Anion Channel 2 (VDAC2) Protein from Rattus norvegicus Revealed by High-Resolution Mass Spectrometry.

Voltage-Dependent Anion Channel isoforms (VDAC1, VDAC2, and VDAC3) are relevant components of the outer mitochondrial membrane (OMM) and play a crucial role in regulation of metabolism and in survival pathways. As major players in the regulation of cellular metabolism and apoptosis, VDACs can be considered at the crossroads between two broad families of pathologies, namely, cancer and neurodegeneration, the former being associated with elevated glycolytic rate and suppression of apoptosis in cancer cells, the latter characterized by mitochondrial dysfunction and increased cell death. Recently, we reported the characterization of the oxidation pattern of methionine and cysteines in rat and human VDACs showing that each cysteine in these proteins is present with a preferred oxidation state, ranging from the reduced to the trioxidized form, and such an oxidation state is remarkably conserved between rat and human VDACs. However, the presence and localization of disulfide bonds in VDACs, a key point for their structural characterization, have so far remained undetermined. Herein we have investigated by nanoUHPLC/High-Resolution nanoESI-MS/MS the position of intramolecular disulfide bonds in rat VDAC2 (rVDAC2), a protein that contains 11 cysteines. To this purpose, extraction, purification, and enzymatic digestions were carried out at slightly acidic or neutral pH in order to minimize disulfide bond interchange. The presence of six disulfide bridges was unequivocally determined, including a disulfide bridge linking the two adjacent cysteines 4 and 5, a disulfide bridge linking cysteines 9 and 14, and the alternative disulfide bridges between cysteines 48, 77, and 104. A disulfide bond, which is very resistant to reduction, between cysteines 134 and 139 was also detected. In addition to the previous findings, these results significantly extend the characterization of the oxidation state of cysteines in rVDAC2 and show that it is highly complex and presents unusual features. Data are available via ProteomeXchange with the identifier PXD044041.

Cholestyramine Modulates Non-Alcoholic Steatohepatitis Induced by Methionine and Choline Deficiency in Rats: Cross-linking AGEs, MIP2, EMR1 and Adiponectin.

Cholestyramine Modulates Non-Alcoholic Steatohepatitis Induced by Methionine and Choline Deficiency in Rats: Cross-linking AGEs, MIP2, EMR1 and Adiponectin.

Role of folic acid in reducing the renal damage induced by amino acid methionine in male rats

Methionine is an essential amino acid. When the metabolic pathway of methionine are interrupted, Homocysteine (Hcy) level will be elevated ,and this elevation is pathogenic. Folic acid can effectively reduce blood Hcy levels. The thirty adult male rats were randomly divided in to three equal groups and were treated daily as follows for 42 days. first (T1) served as control group. Rats of the second group (T2) were intubated orally 100 mg / kg B.W. of methionine . rats of the third group (T3) were intubated same doses of methionine plus 5mg of folic acid supplementation . Fasting blood samples were collected at 21, and 42 days of experiment to study the following parameters: Serum creatinine (SC) concentration, Blood urea nitrogen (BUN) concentration and Serum uric acid (SUA) concentration . Furthermore; section of kidney was assessed for histopathological studies. The resulted revealed significant increase (P< 0.05)of methionine group in SC , BUN and SUA concentrations in 12 , 42 day of treatment as comparing to control (T1). On the other hand that animals treated with folic acid plus methionine (T3) showed significant decline in SC , BUN and SUA concentrations in 42 day of treatment . Histological section of rat kidney received methionine showed monocyte cells around collected renal tubules ,while folic acid supplementation in groups T3caused regression of renal damage induced by methionine. It seems that methionine was effective in induction of oxidative stress and change in some biological markers related to kidney disease. Also it seems that folic acid exert protective actions against the damaging effect of methionine.

Hyperhomocysteinemia increases susceptibility to cortical spreading depression associated with photophobia, mechanical allodynia, and anxiety in rats

Epidemiological data suggest that elevated homocysteine is associated with migraine with aura. However, how homocysteine contributes to migraine is still unclear. Here, we tested whether hyperhomocysteinemia (hHCY) promotes cortical spreading depression (CSD), a phenomenon underlying migraine with aura, and whether hHCY contributes to pain behavior. hHCY was induced by dietary methionine in female rats while the testing was performed on their 6–8week-old offspring. CSD and multiple unit activity (MUA) induced by KCl were recorded from the primary somatosensory cortex, S1, using multichannel electrodes. In hHCY rats, compared to control, we found: i) higher probability of CSD occurrence; ii) induction of CSD by lower concentrations of KCl; iii) faster horizontal propagation of CSD; iv) smaller CSD with longer duration; v) higher frequency of MUA at CSD onset along with slower reappearance. Rats with hHCY demonstrated high level of locomotor activity and grooming while spent less time in the central area of the open field, indicating anxiety. These animals showed light sensitivity and facial mechanical allodinia. Thus, hHCY acquired at birth promotes multiple features of migraine such as higher cortical excitability, mechanical allodynia, photophobia, and anxiety. Our results provide the first experimental explanation for the higher occurrence of migraine with aura in patients with hHCY.

Exploring Neuroprotective Properties of Centella Asiatica Extract on Metabolic Change in Chronic Stress-Induced Rats

Stress is a mode of adaptive response towards external demands, and prolonged exposure to stress is known to promote aging and neurodegeneration. Several therapies promote neuroprotection but are usually accompanied by adverse consequences. Traditional medicine has been proven as an effective alternative for promoting pharmacological health benefits such as wound healing, boosting memory function and reducing oxidative stress. Centella asiatica (CeA) has also gaining attention as an alternative option in promoting neuroprotective activities against neurodegenerative disorders and neuronal injuries. In this study, the neurodegenerative condition of rats was achieved using chronic stress through movement restraint and forced swimming for 21 consecutive days. Here, the neuroprotective properties of three different dosage of CeA (200 mg/kg/day, 400 mg/kg/day and 800 mg/kg/day) was evaluated using metabolomics approach. The administration of CeA shown distinction between untreated group and treated group; and reducing the effect of chronic stress in rats. The extract also demonstrated a significant elevation in several metabolites (lactate, isoleucine, proline, methionine, valine, leucine and glutamine) in rats treated with CeA, particularly in rats administered with 800 mg/kg of CeA. These significant metabolites play important roles in variety of biochemical function of the brain such as the synthesis of protein, energy metabolism, synthesis of neurotransmitter, protection against oxidative stress and compartmentalisation of glutamate. The results of this study may contribute towards greater understanding of molecular mechanism of CeA in promoting neuroprotective properties against neurodegeneration from exposure to chronic stress.
 
 Keywords: Centella asiatica, Chronic Stress, NMR-based metabolomics, Serum Metabolites

Hypoxic Adaptation of Mitochondrial Metabolism in Rat Cerebellum Decreases in Pregnancy.

Function of brain amino acids as neurotransmitters or their precursors implies changes in the amino acid levels and/or metabolism in response to physiological and environmental challenges. Modelling such challenges by pregnancy and/or hypoxia, we characterize the amino acid pool in the rat cerebellum, quantifying the levels and correlations of 15 amino acids and activity of 2-oxoglutarate dehydrogenase complex (OGDHC). The parameters are systemic indicators of metabolism because OGDHC limits the flux through mitochondrial TCA cycle, where amino acids are degraded and their precursors synthesized. Compared to non-pregnant state, pregnancy increases the cerebellar content of glutamate and tryptophan, decreasing interdependence between the quantified components of amino acid metabolism. In response to hypoxia, the dependence of cerebellar amino acid pool on OGDHC and the average levels of arginine, glutamate, lysine, methionine, serine, phenylalanine, and tryptophan increase in non-pregnant rats only. This is accompanied by a higher hypoxic resistance of the non-pregnant vs. pregnant rats, pointing to adaptive significance of the hypoxia-induced changes in the cerebellar amino acid metabolism. These adaptive mechanisms are not effective in the pregnancy-changed metabolic network. Thus, the cerebellar amino acid levels and OGDHC activity provide sensitive markers of the physiology-dependent organization of metabolic network and its stress adaptations.

Methionine attenuates the intensity of rheumatoid arthritis by downregulating NF-κB and iNOS expression in neonatal rats.

The present study investigated the anti-arthritic effects of methionine in neonatal rats. Rats were divided into four groups, with six rats in each group. The rats were administered methionine (150- or 300-mg/kg body weight) orally for 45 consecutive days. The expression levels of catalase, superoxide dismutase (SOD), reduced glutathione (GSH), lipid peroxidation, glutathione peroxidase (Gpx), prostaglandin E2 (PGE2), matrix metalloproteinase-3, uric acid, nitric oxide (NO), ceruloplasmin, inducible nitric oxide synthase (iNOS), and nuclear factor (NF)-κB were determined in rheumatoid arthritis-induced neonatal rats. The levels of SOD, catalase, Gpx, and GSH were substantially reduced in control rats, while the levels of other parameters were increased in control neonatal rats. However, methionine supplementation significantly increased (more than 40%) the levels of SOD, catalase, Gpx, and GSH in neonatal rats. The levels of lipid peroxidation, uric acid, ceruloplasmin, NO, and PGE2 were significantly reduced following methionine supplementation. Furthermore, NF-κB mRNA expression was substantially reduced up to 51.7% in the 300-mg/kg methionine group, whereas the mRNA expression of iNOS was reduced up to 43.5% in the 300-mg/kg methionine group. NF-κB protein expression was substantially reduced up to 45.8% in the 300-mg/kg methionine group, whereas the protein expression of iNOS was reduced up to 45.4% in the 300-mg/kg methionine group. Taken together, these data suggest that methionine supplementation was effective against rheumatoid arthritis.

Methionine and Choline Deficient Diet-induced Non-Alcoholic Steatohepatitis in Rats: Role of Melatonin

Methionine and Choline Deficient Diet-induced Non-Alcoholic Steatohepatitis in Rats: Role of Melatonin

Comparative investigation of methionine and novel formulation Metovitan protective effects in Wistar rats with testicular and epididymal toxicity induced by anti-tuberculosis drugs co-administration

Despite clear beneficial effects, studies on the efficacy of different formulations of micronutrients and vitamins in the treatment of male infertility are still very limited. The aim of the study was to compare the efficacy of methionine and novel formulation Metovitan based on the combination of methionine, thiamine, nicotinamide, α-tocopherol acetate and zinc salt as remedies for prevention of anti-tuberculosis drugs (ATD) anti-fertility effects in male rats. ATD co-administration resulted in testicular CYP2E1, CYP2C23 and CYP3A2 transcriptional activation. Methionine and Metovitan regulated the level of CYP2E1 and CYP3A2 mRNA expression. Methionine unaffected CYP2C23 mRNA level, while Metovitan effectively normalized this parameter. The use of methionine did not allow normalizing of DNA fragmentation processes in testes, while Metovitan provided decrease in the number of DNA fragments to the control level. Both substances significantly decreased p-nitrophenol hydroxylase activity and prevented pro/antioxidant parameters imbalance in testes of ATD-treated rats. The end results of methionine and Metovitan application were partial or complete restoration of altered spermatogenesis parameters with subsequent increase in sperm count and fertility. Ameliorating effects may be attributed to antioxidant properties and modulating effects on testicular CYPs. More pronounced beneficial Metovitan effects might be due to synergic effects of its components.

Modulatory role of Co-enzyme Q10 on methionine and choline deficient diet-induced non-alcoholic steatohepatitis (NASH) in albino rats.

The present study aimed to evaluate the hepato-protective and neuro-protective activity of Co-enzyme Q10 (CoQ10) on non-alcoholic steatohepatitis (NASH) in albino rats induced by methionine and choline-deficient (MCD) diet. Rats were fed an MCD diet for 8 weeks to induce non-alcoholic steatohepatitis. CoQ10 (10 mg/(kg·day)-1) was orally administered for 2 consecutive weeks. Twenty-four hours after the last dose of the drug, the behavioral test, namely the activity cage test, was performed and the activity counts were recorded. Serum alanine transaminase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyl transferase, total/direct bilirubin, and albumin were valued to assess liver function. Moreover, hepatic cytokines interleukin-6 as well as its modulator nuclear factor kappa-light-chain-enhancer of activated B cells were determined. In addition, brain biomarkers, viz ammonia, nitric oxide, and brain-derived neurotrophic factor (BDNF), were measured as they are reliable indices to assess brain damage. Histopathological and immunohistochemical examination of brain proliferating cell nuclear antigen in brain and liver tissues were also evaluated. Results revealed that MCD-induced NASH showed impairment in the liver functions with an increase in the liver inflammatory markers. Moreover, NASH resulted in pronounced brain dysfunction as evidenced by hyper-locomotor activity, a decrease in the BDNF level, as well as an increase in the brain nitric oxide and ammonia contents. Oral treatment of MCD-diet-fed rats with CoQ10 for 14 days showed a marked improvement in all the assigned parameters. Finally, it can be concluded that CoQ10 has a hepatoprotective and neuroprotective role in MCD-diet-induced NASH in rats.

Body composition in gene knockouts of sulfur amino acid-metabolizing enzymes.

Plasma concentrations of several amino acids are elevated in human obesity and insulin resistance, but there is no conclusive evidence on whether the amino acid alterations are causal. Dietary restriction of the essential SAA methionine (MR) in rats produces a hypermetabolic phenotype, with an integrated set of transcriptional changes in lipid enzymes in liver and adipose tissue. MR also induces an array of changes in methionine metabolites, including elevated plasma homocysteine and decreased cystathionine, cysteine, glutathione, and taurine. Several knockouts of enzymes acting downstream of methionine recapitulate the phenotypic results of MR, suggesting that the MR phenotype may be driven by changes distal to methionine. Here we review the changes in SAA and body composition in seven relevant knockout mouse models. All seven models feature decreased body weight, which in five of these have been further explored and shown to result from predominantly decreased fat mass. Common to several models is increased energy expenditure, enhanced insulin sensitivity, and protection against dietary obesity, as occurs in MR. A decrease in plasma total cysteine concentrations is also seen in most models. The lean phenotype could often be reversed by dietary supplementation of cysteine or choline, but not taurine, betaine or a H2S donor. Importantly, the plasma concentrations of both cysteine and choline are positively associated with fat mass in large populations studies, while taurine, betaine, and H2S are not. Collectively, the emerging data from dietary and knockout models are in harmony with human epidemiologic data, suggesting that the availability of key nutrients in the SAA pathway regulates fat storage pathways.

Design, synthesis, and enzyme kinetics of novel benzimidazole and quinoxaline derivatives as methionine synthase inhibitors

Methionine synthase catalyzes the transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine, producing methionine and tetrahydrofolate. Benzimidazole and deazatetrahydrofolates derivatives have been shown to inhibit methionine synthase by competing with the substrate 5-methyltetrahydrofolate. In this study, a novel series of substituted benzimidazoles and quinoxalines were designed and assessed for inhibitory activity against purified rat liver methionine synthase using a radiometric enzyme assay. Compounds 3g, 3j, and 5c showed the highest activity against methionine synthase (IC50: 20μM, 18μM, 9μM, respectively). Kinetic analysis of these compounds using Lineweaver–Burk plots revealed characteristics of mixed inhibition for 3g and 5c; and uncompetitive inhibition for 3j. Docking study into a homology model of the rat methionine synthase gave insights into the molecular determinants of the activity of this class of compounds. The identification of these drug-like inhibitors could lead the design of the next generation modulators of methionine synthase.

S-Adenosylmethionine-dependent Protein Methylation Is Required for Expression of Selenoprotein P and Gluconeogenic Enzymes in HepG2 Human Hepatocytes

Cellular methylation processes enable expression of gluconeogenic enzymes and metabolism of the nutrient selenium. Selenium status has been proposed to relate to type II diabetes risk, and plasma levels of selenoprotein P (SEPP1) have been positively correlated with insulin resistance. Increased expression of gluconeogenic enzymes glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase 1 (PCK1) has negative consequences for blood glucose management in type II diabetics. Transcriptional regulation of SEPP1 is directed by the same transcription factors that control the expression of G6PC and PCK1, and these factors are activated by methylation of arginine residues. We sought to determine whether expression of SEPP1 and the aforementioned glucoconeogenic enzymes are regulated by protein methylation, the levels of which are reliant upon adequate S-adenosylmethionine (SAM) and inhibited by S-adenosylhomocysteine (SAH). We treated a human hepatocyte cell line, HepG2, with inhibitors of adenosylhomocysteine hydrolase (AHCY) known to increase concentration of SAH before analysis of G6PC, PCK1, and SEPP1 expression. Increasing SAH decreased 1) the SAM/SAH ratio, 2) protein-arginine methylation, and 3) expression of SEPP1, G6PC, and PCK1 transcripts. Furthermore, hormone-dependent induction of gluconeogenic enzymes was reduced by inhibition of protein methylation. When protein-arginine methyltransferase 1 expression was reduced by siRNA treatment, G6PC expression was inhibited. These findings demonstrate that hepatocellular SAM-dependent protein methylation is required for both SEPP1 and gluconeogenic enzyme expression and that inhibition of protein arginine methylation might provide a route to therapeutic interventions in type II diabetes.

Altered d-methionine kinetics in rats with renal impairment

D: -Amino acids are now recognized to be widely present in mammals. In rats, exogenously administered D: -methionine is almost converted into the L: -enantiomer via 2-oxo-4-methylthiobutylic acid as an intermediate. D: -Amino acid oxidase is associated with conversion of D: -methionine into the 2-oxo acid. Since D: -amino acid oxidase is present at the highest activity in the kidney compared to other organ, kidney injury is suggested to cause accumulation of D: -methionine. The purpose of the present study is to assess the role of kidney in the elimination of D: -methionine and metabolic conversion into L: -methionine in rats using a stable isotope methodology. After a bolus i.v. administration of D: -[²H₃)]methionine to 5/6-nephrectomized rats, plasma concentrations of D: -[²H₃]methionine, L: -[²H₃]methionine, and endogenous L: -methionine were determined by a stereoselective GC-MS method. Renal mass reduction slowed down the elimination of D: -[²H₃]methionine. The clearance values of conversion of D: -[²H₃]methionine into the L: -enantiomer in 5/6-nephrectomized rats were one-sixth of those in sham-operated rats. The elimination behavior of D: -[²H₃]methionine observed in rats demonstrated that kidney was the principal organ responsible for chiral inversion of D: -methionine.

Sulfur amino acids in methionine-restricted rats: Hyperhomocysteinemia

Objective Dietary methionine restriction in Fischer-344 rats favorably influences visceral fat mass, insulin sensitivity, metabolic parameters, and longevity. However, little is known about the effects of methionine restriction on serum methionine and its downstream sulfur amino acids. We investigated the serum sulfur amino acid profile of male Fischer-344 rats fed a methionine-restricted diet for 3 mo. Methods and results Using tandem mass spectrometry, we observed marked reduction in serum concentrations of methionine, cystathionine, cysteine, and taurine in methionine-restricted rats compared with control ( P < 0.001) and a 2.5-fold elevation of homocysteine ( P < 0.001). Conclusion This suggests that homocysteine trans-sulfuration may be inhibited by methionine restriction, and that some of the effects of methionine restriction may be mediated by changes in sulfur amino acids downstream of methionine.

Effect of Rosuvastatin on Methionine‐Induced Hyperhomocysteinaemia and Haematological Changes in Rats

The present study was designed to investigate the protective effect of rosuvastatin on methionine-induced hyperhomocysteinaemia and haematological changes in albino rats. Methionine (1 g/kg, orally) administration to pathogenic control rats (i.e. group II) for 30 days significantly (P < 0.01) increased the levels of homocysteine, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL-C) and triglycerides (TGs) and decreased the levels of high-density lipoprotein cholesterol (HDL-C) in serum. Haematological observations of the peripheral blood smears of pathogenic rats (i.e. group II) fed with methionine also showed crenation of red blood cells cell membrane and significant (P < 0.01) increase in total leucocyte count, differential leucocyte count and platelet counts with significant (P < 0.01) decrease in the mean haemoglobin levels as compared to vehicle control rats (group I). Administration of rosuvastatin (0.5 mg/kg/day, orally) to hyperhomocysteinaemic rats for 30 days significantly (P < 0.01) decreased the levels of homocysteine, TC, TGs, LDL-C, VLDL-C and increased the levels of HDL-C in serum. The present results provide clear evidence that oral treatment with rosuvastatin produces homocysteine and lipid lowering activity and also reversal of haematological changes induced by methionine in rats.

Distinct effects of folate and choline deficiency on plasma kinetics of methionine and homocysteine in rats

Both folate and betaine, a choline metabolite, play essential roles in the remethylation of homocysteine to methionine. We have studied the effects of folate and choline deficiency on the plasma kinetics of methionine, especially remethylation of homocysteine to methionine, by means of stable isotope methodology. After a bolus intravenous administration of [ 2H 7]methionine (5 mg/kg body weight) into the rats fed with folate-, choline-, folate + choline–deficient or control diets, the plasma concentrations of [ 2H 7]methionine, demethylated [ 2H 4]homocysteine, and remethylated [ 2H 4]methionine were determined simultaneously with endogenous methionine and homocysteine by gas chromatography-mass spectrometry–selected ion monitoring. The total plasma clearance of [ 2H 7]methionine was not significantly different among groups, suggesting that the formation of [ 2H 4]homocysteine from [ 2H 7]methionine was not influenced by deficiencies of folate and choline. The area under concentration-time curve of [ 2H 4]homocysteine significantly increased in the folate- and folate + choline–deficient group as compared with the control, but not in the choline-deficient group. The time profile of plasma concentrations of [ 2H 4]methionine in the folate-deficient group was the same as the control group, whereas the appearance of [ 2H 4]methionine in plasma was delayed in the choline- and folate + choline–deficient group. These results suggested plasma levels of remethylated methionine were influenced by choline deficiency rather than folate deficiency.

All-trans-Retinoic Acid Rapidly Induces Glycine N-methyltransferase in a Dose-Dependent Manner and Reduces Circulating Methionine and Homocysteine Levels in Rats

Glycine N-methyltransferase (GNMT) regulates the methyl group supply for S-adenosylmethionine-dependent transmethylation reactions. Retinoids have been shown to perturb methyl group metabolism by increasing the abundance and activity of GNMT, thereby leading to the loss of methyl groups. Previous studies used pharmacologic doses (30 micro mol/kg body weight) of various retinoids administered daily for a total of 10 d. Here, we examined the dose- and time-dependent relationships between all-trans-retinoic acid (ATRA) administration and induction of GNMT, as well as determining additional indices of methyl group and folate metabolism. For the dose-response study, rats were administered 0, 1, 5, 10, 15 or 30 micro mol ATRA/kg body weight for 10 d. For the time-course study, rats were given 30 micromol ATRA/kg body weight for 0, 1, 2, 4, or 8 d. A significant increase (105%) in GNMT activity was observed with doses as low as 5 micromol/kg body weight, whereas maximal induction (231%) of GNMT activity was achieved at 30 micromol/kg body weight. Induction of hepatic GNMT by ATRA was rapid, exhibiting a 31% increase after a single dose (1 d) and achieving maximal induction (95%) after 4 d. Plasma methionine and homocysteine concentrations were decreased 42 and 53%, respectively, in ATRA-treated rats compared with controls. In support of this finding, the hepatic activity of methionine synthase, the folate-dependent enzyme required for homocysteine remethylation, was elevated 40% in ATRA-treated rats. This work demonstrates that ATRA administration exerts a rapid effect on hepatic methyl group, folate and homocysteine metabolism at doses that are within the therapeutic range used by humans.

Hepatic Glycine N-Methyltransferase Is Up-Regulated by Excess Dietary Methionine in Rats

Glycine N-methyltransferase (GNMT) regulates S-adenosylmethionine (SAM) levels and the ratio of SAM:S-adenosylhomocysteine (SAH). In liver, methionine availability, both from the diet and via the folate-dependent one-carbon pool, modulates GNMT activity to maintain an optimal SAM:SAH ratio. The regulation of GNMT activity is accomplished via posttranslational and allosteric mechanisms. We more closely examined GNMT regulation in various tissues as a function of excess dietary methyl groups. Sprague Dawley rats were fed either a control diet (10% casein plus 0.3% L-methionine) or the control diet supplemented with graded levels (0.5-2%) of L-methionine. Pair-fed control groups of rats were included due to the toxicity associated with high methionine consumption. As expected, the hepatic activity of GNMT was significantly elevated in a dose-dependent fashion after 10 d of feeding the diets containing excess methionine. Moreover, the abundance of hepatic GNMT protein was similarly increased. The kidney had a significant increase in GNMT as a function of dietary methionine, but to a much lesser extent than in the liver. For pancreatic tissue, neither the activity of GNMT nor the abundance of the protein was responsive to excess dietary methionine. These data suggest that additional mechanisms contribute to regulation of GNMT such that synthesis of the protein is greater than its degradation. In addition, methionine-induced regulation of GNMT is dose dependent and appears to be tissue specific, the latter suggesting that the role it plays in the kidney and pancreas may in part differ from its hepatic function.

Pharmacokinetic studies of methionine in rats using deuterium-labeled methionine: Quantitative assessment of remethylation

The pharmacokinetics of methionine has been studied in rats by means of stable isotope methodology. After the i.v. bolus injection of [ 2H 7]methionine (5 mg/kg body wt.), the plasma concentrations of [ 2H 7]methionine, demethylated [ 2H 4]homocysteine and remethylated [ 2H 4]methionine were determined simultaneously with endogenous methionine and homocysteine by gas chromatography-mass spectrometry. The half-life for [ 2H 7]methionine were 35.0 ± 6.9 min. The appearance of the metabolites, [ 2H 4]homocysteine and [ 2H 4]methionine, in the plasma was very rapid. The fraction of [ 2H 7]methionine that remethylated to [ 2H 4]methionine through [ 2H 4]homocysteine were 0.185 ± 0.028. The administered [ 2H 7]methionine did not influence the plasma levels of endogenous methionine and homocysteine. The present stable isotope methodology has made it possible to evaluate the pharmacokinetics of methionine, including the estimation of remethylation.