DNA methylation patterns in bladder tumors of African American patients point to distinct alterations in xenobiotic metabolism

Racial/ethnic disparities have a significant impact on bladder cancer outcomes with African American patients demonstrating inferior survival over European-American patients. We hypothesized that epigenetic difference in methylation of tumor DNA is an underlying cause of this survival health disparity. We analyzed bladder tumors from African American and European-American patients using reduced representation bisulfite sequencing (RRBS) to annotate differentially methylated DNA regions. Liquid chromatography-mass spectrometry (LC-MS/MS) based metabolomics and flux studies were performed to examine metabolic pathways that showed significant association to the discovered DNA methylation patterns. RRBS analysis showed frequent hypermethylated CpG islands in African American patients. Further analysis showed that these hypermethylated CpG islands in patients are commonly located in the promoter regions of xenobiotic enzymes that are involved in bladder cancer progression. On follow-up, LC-MS/MS revealed accumulation of glucuronic acid, S-adenosylhomocysteine, and a decrease in S-adenosylmethionine, corroborating findings from the RRBS and mRNA expression analysis indicating increased glucuronidation and methylation capacities in African American patients. Flux analysis experiments with 13C-labeled glucose in cultured African American bladder cancer cells confirmed these findings. Collectively, our studies revealed robust differences in methylation-related metabolism and expression of enzymes regulating xenobiotic metabolism in African American patients indicate that race/ethnic differences in tumor biology may exist in bladder cancer.

Development and validation of a UPLC-UV method for the quantification of thiopurine methyltransferase enzyme activity in human erythrocytes

Thiopurines are drugs widely used for the treatment of autoimmune conditions, inflammatory bowel disease or acute lymphoblastic leukemia. Determination of thiopurine methyltransferase activity (TPMT), a major determinant of thiopurines toxicity, has been suggested before implementing thiopurine treatment. An ultraperformance liquid chromatography (UPLC) method was developed and validated for the quantification of TPMT enzyme activity based on the conversion of 6-mercaptopurine (6-MP) to 6-methylmercaptopurine (6-MMP) using S-adenosyl-L-methionine (SAM) as methyl donor in red blood cell lysates (RBC). This method was improved from a previous laborious high performance liquid chromatography (HPLC) method, using a lower volume of injection and with a shorter runtime. After incubation and protein precipitation 6-MMP was separated on a HSS-T3 (2.1 × 50 mm, 1.8 μm) column and monitored by UV detection (290 nm). A change on the organic solvent used to dissolve 6-MP resulted in a reduction of interference by endogenous or non-enzymatic methylated 6-MMP. A full validation of the 6-MMP assay was performed according to the FDA and EMA guidelines. The method was linear from 0.125 to 2 nmol/mL, with acceptable values of accuracy and precision. The method was applied in 106 patients treated with thiopurines whose TPMT activity was previously quantified by HPLC. Evaluation through Bland-Altman plot showed that TPMT activities were in agreement between both methods.

Combined Mössbauer spectroscopic, multi-edge X-ray absorption spectroscopic, and density functional theoretical study of the radical SAM enzyme spore photoproduct lyase

Spore photoproduct lyase (SPL), a member of the radical S-adenosyl-L-methionine (SAM) superfamily, catalyzes the direct reversal of the spore photoproduct, a thymine dimer specific to bacterial spores, to two thymines. SPL requires SAM and a redox-active [4Fe-4S] cluster for catalysis. Mössbauer analysis of anaerobically purified SPL indicates the presence of a mixture of cluster states with the majority (40 %) as [2Fe-2S](2+) clusters and a smaller amount (15 %) as [4Fe-4S](2+) clusters. On reduction, the cluster content changes to primarily (60 %) [4Fe-4S](+). The speciation information from Mössbauer data allowed us to deconvolute iron and sulfur K-edge X-ray absorption spectra to uncover electronic (X-ray absorption near-edge structure, XANES) and geometric (extended X-ray absorption fine structure, EXAFS) structural features of the Fe-S clusters, and their interactions with SAM. The iron K-edge EXAFS data provide evidence for elongation of a [2Fe-2S] rhomb of the [4Fe-4S] cluster on binding SAM on the basis of an Fe···Fe scatterer at 3.0 Å. The XANES spectra of reduced SPL in the absence and presence of SAM overlay one another, indicating that SAM is not undergoing reductive cleavage. The X-ray absorption spectroscopy data for SPL samples and data for model complexes from the literature allowed the deconvolution of contributions from [2Fe-2S] and [4Fe-4S] clusters to the sulfur K-edge XANES spectra. The analysis of pre-edge features revealed electronic changes in the Fe-S clusters as a function of the presence of SAM. The spectroscopic findings were further corroborated by density functional theory calculations that provided insights into structural and electronic perturbations that can be correlated by considering the role of SAM as a catalyst or substrate.

S-adenosyl-L-methionine usage during climacteric ripening of tomato in relation to ethylene and polyamine biosynthesis and transmethylation capacity

S-adenosyl-L-methionine (SAM) is the major methyl donor in cells and it is also used for the biosynthesis of polyamines and the plant hormone ethylene. During climacteric ripening of tomato (Solanum lycopersicum 'Bonaparte'), ethylene production rises considerably which makes it an ideal object to study SAM involvement. We examined in ripening fruit how a 1-MCP treatment affects SAM usage by the three major SAM-associated pathways. The 1-MCP treatment inhibited autocatalytic ethylene production but did not affect SAM levels. We also observed that 1-(malonylamino)cyclopropane-1-carboxylic acid formation during ripening is ethylene dependent. SAM decarboxylase expression was also found to be upregulated by ethylene. Nonetheless polyamine content was higher in 1-MCP-treated fruit. This leads to the conclusion that the ethylene and polyamine pathway can operate simultaneously. We also observed a higher methylation capacity in 1-MCP-treated fruit. During fruit ripening substantial methylation reactions occur which are gradually inhibited by the methylation product S-adenosyl-L-homocysteine (SAH). SAH accumulation is caused by a drop in adenosine kinase expression, which is not observed in 1-MCP-treated fruit. We can conclude that tomato fruit possesses the capability to simultaneously consume SAM during ripening to ensure a high rate of ethylene and polyamine production and transmethylation reactions. SAM usage during ripening requires a complex cellular regulation mechanism in order to control SAM levels.

Role of epigenetic and miR-22 and miR-29b alterations in the downregulation of Mat1a and Mthfr genes in early preneoplastic livers in rats induced by 2-acetylaminofluorene

Carcinogenesis is a multistep sequential process of clonal expansion of initiated cells associated with the accumulation of multiple cancer-specific heritable phenotypes. The acquisition of these heritable cancer-specific alterations may be triggered by mutational and/or non-mutational changes in the genome that affect the regulation of gene expression. Currently, cancer-specific epigenetically mediated changes in gene expression are regarded as driving events in tumorigenesis. In the present study, we investigated the role of gene-specific expression changes in the mechanism of rat hepatocarcinogenesis induced by the complete hepatocarcinogen 2-acetylaminofluorene (2-AAF). The results of the present study demonstrate significant alterations in gene expression, especially of Mat1a and Mthfr genes, during early stages of rat 2-AAF-induced liver carcinogenesis. Both of these genes were downregulated in the livers of 2-AAF-treated male rats. Inhibition of Mat1a expression was associated with an increase in histone H3 lysine 27 trimethylation and a decrease in histone H3 lysine 18 acetylation at the gene promoter/first exon region. Additionally, we demonstrate for the first time a critical contribution of miR-22 and miR-29b microRNAs in the inhibition of Mat1a and Mthfr gene expression during 2-AAF-induced rat hepatocarcinogenesis. The downregulation of Mat1a and Mthfr genes was accompanied by marked functional alterations in one-carbon metabolism. The results of the present study suggest that downregulation of the Mat1a and Mthfr genes may be one of the main driver events that promote liver carcinogenesis by causing a profound accumulation of subsequent epigenetic abnormalities during progression of the carcinogenic process.

Neural tube defects induced by folate deficiency in mutant curly tail (Grhl3) embryos are associated with alteration in folate one-carbon metabolism but are unlikely to result from diminished methylation

BACKGROUND

Folate one-carbon metabolism has been implicated as a determinant of susceptibility to neural tube defects (NTDs), owing to the preventive effect of maternal folic acid supplementation and the higher risk associated with markers of diminished folate status.

METHODS

Folate one-carbon metabolism was compared in curly tail (ct/ct) and genetically matched congenic (+(ct)/+(ct)) mouse strains using the deoxyuridine suppression test in embryonic fibroblast cells and by quantifying s-adenosylmethionine (SAM) and s-adenosylhomocysteine (SAH) in embryos using liquid chromatography tandem mass spectrometry. A possible genetic interaction between curly tail and a null allele of 5,10-methylenetetrahydrofolate reductase (MTHFR) was investigated by generation of compound mutant embryos.

RESULTS

There was no deficit in thymidylate biosynthesis in ct/ct cells, but incorporation of exogenous thymidine was lower than in +(ct)/+(ct) cells. In +(ct)/+(ct) embryos the SAM/SAH ratio was diminished by dietary folate deficiency and normalized by folic acid or myo-inositol treatment, in association with prevention of NTDs. In contrast, folate deficiency caused a significant increase in the SAM/SAH ratio in ct/ct embryos. Loss of MTHFR function in curly tail embryos significantly reduced the SAM/SAH ratio but did not cause cranial NTDs or alter the frequency of caudal NTDs.

CONCLUSIONS

Curly tail fibroblasts and embryos, in which Grhl3 expression is reduced, display alterations in one-carbon metabolism, particularly in the response to folate deficiency, compared to genetically matched congenic controls in which Grhl3 is unaffected. However, unlike folate deficiency, diminished methylation potential appears to be insufficient to cause cranial NTDs in the curly tail strain, nor does it increase the frequency of caudal NTDs.

Determination of S-adenosyl-l-methionine in fruits by capillary electrophoresis

INTRODUCTION

S-adenosyl-l-methionine (SAM) plays an important role in many biochemical reactions in plants. It is mainly used as a methyl donor for methylation reactions, but it also participates in, for example, the biosynthesis of polyamines and the plant hormone ethylene.

OBJECTIVE

To develop a fast capillary electrophoresis technique to separate SAM in fruits and fruit juices without any pre-purification steps.

METHODOLOGY

Four different extraction solutions and two extraction times were tested, of which 5% trichloroacetic acid (TCA) for 10 min was found most suited. A glycine : phosphate buffer (200 : 50 mm, pH 2.5) was found optimal to analyse SAM in TCA extracts. Analyses were preformed on different climacteric and non-climacteric fruits and fruit juices. The calibration curve was created in degraded tomato extract. The CE-method was compared with a more conventional HPLC method described in literature.

RESULTS

The CE technique made it possible to completely separate the S,S- and R,S-diastereoisomeric forms of SAM. The CE method proved to be very fast (20 min total running time instead of 42 min) and more sensitive (limit of detection of 0.5 µm instead of 1 µm) compared with the conventional HPLC method.

CONCLUSION

Fast measurements of SAM in fruits and juices are favoured by capillary electrophoresis in a 200 : 50 mm glycine : phosphate (pH 2.5) buffer system.

Dietary intake of S-(alpha-carboxybutyl)-DL-homocysteine induces hyperhomocysteinemia in rats

Betaine homocysteine S-methyltransferase (BHMT) catalyzes the transfer of a methyl group from betaine to homocysteine (Hcy), forming dimethylglycine and methionine. We previously showed that inhibiting BHMT in mice by intraperitoneal injection of S-(alpha-carboxybutyl)-DL-homocysteine (CBHcy) results in hyperhomocysteinemia. In the present study, CBHcy was fed to rats to determine whether it could be absorbed and cause hyperhomocysteinemia as observed in the intraperitoneal administration of the compound in mice. We hypothesized that dietary administered CBHcy will be absorbed and will result in the inhibition of BHMT and cause hyperhomocysteinemia. Rats were meal-fed every 8 hours an L-amino acid-defined diet either containing or devoid of CBHcy (5 mg per meal) for 3 days. The treatment decreased liver BHMT activity by 90% and had no effect on methionine synthase, methylenetetrahydrofolate reductase, phosphatidylethanolamine N-methyltransferase, and CTP:phosphocholine cytidylyltransferase activities. In contrast, cystathionine beta-synthase activity and immunodetectable protein decreased (56% and 26%, respectively) and glycine N-methyltransferase activity increased (52%) in CBHcy-treated rats. Liver S-adenosylmethionine levels decreased by 25% in CBHcy-treated rats, and S-adenosylhomocysteine levels did not change. Furthermore, plasma choline decreased (22%) and plasma betaine increased (15-fold) in CBHcy-treated rats. The treatment had no effect on global DNA and CpG island methylation, liver histology, and plasma markers of liver damage. We conclude that CBHcy-mediated BHMT inhibition causes an elevation in total plasma Hcy that is not normalized by the folate-dependent conversion of Hcy to methionine. Furthermore, metabolic changes caused by BHMT inhibition affect cystathionine beta-synthase and glycine N-methyltransferase activities, which further deteriorate plasma Hcy levels.

Analysis of S-adenosylmethionine and related sulfur metabolites in bacterial isolates of Pseudomonas aeruginosa (BAA-47) by liquid chromatography/electrospray ionization coupled to a hybrid linear quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometry

A comprehensive and highly selective method for detecting in bacterial supernatants a modified sulfur nucleoside, S-adenosyl-L-methionine (SAM), and its metabolites, i.e., S-adenosylhomocysteine (SAH), adenosine (Ado), 5'-deoxy-5'-methylthioadenosine (MTA), adenine (Ade), S-adenosyl-methioninamine (dcSAM), homocysteine (Hcy) and methionine (Met), was developed. The method is based on reversed-phase liquid chromatography with positive electrospray ionization (ESI+) coupled to a hybrid linear quadrupole ion trap (LTQ) and 7-T Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). A gradient elution was employed with a binary solvent of 0.05 M ammonium formate at pH 4 and acetonitrile. The assay involves a simultaneous cleanup of cell-free bacterial broths by solid-phase extraction and trace enrichment of metabolites with a 50-fold concentration factor by using immobilized phenylboronic and anion-exchange cartridges. While the quantitative determination of SAM was performed using stable-isotope-labeled SAM-d3 as an internal standard, in the case of Met and Ade, Met-13C and Ade-15N2 were employed as isotope-labeled internal standards, respectively. This method enabled the identification of SAM and its metabolites in cell-free culture of Pseudomonas aeruginosa grown in Davis minimal broth (formulation without sulphur organic compounds), with routine sub-ppm mass accuracies (-0.27 +/- 0.68 ppm). The resulting contents of S(C)S(S)-SAM, S(S)-dcSAM, MTA, Ado and Met in the free-cell supernatant of P. aeruginosa was 56.4 +/- 2.1 nM, 32.2 +/- 2.2 nM, 0.91 +/- 0.10 nM, 19.6 +/- 1.2 nM and 1.93 +/- 0.02 microM (mean +/- SD, n = 4 extractions), respectively. We report also the baseline separation (Rs > or = 1.5) of both diastereoisomeric forms of SAM (S(C)S(S) and S(C)R(S)) and dcSAM (S(S) and R(S)), which can be very useful to establish the relationship between the biologically active versus the inactive species, S(C)S(S)/S(C)R(S) and S(S)/R(S) of SAM and dcSAM, respectively. An additional confirmation of SAM-related metabolites was accomplished by a systematic study of their MS/MS spectra.

Homocysteine affects cardiomyocyte viability: concentration-dependent effects on reversible flip-flop, apoptosis and necrosis

BACKGROUND

Hyperhomocysteinaemia (HHC) is thought to be a risk factor for cardiovascular disease including heart failure. While numerous studies have analyzed the role of homocysteine (Hcy) in the vasculature, only a few studies investigated the role of Hcy in the heart. Therefore we have analyzed the effects of Hcy on isolated cardiomyocytes.

METHODS

H9c2 cells (rat cardiomyoblast cells) and adult rat cardiomyocytes were incubated with Hcy and were analyzed for cell viability. Furthermore, we determined the effects of Hcy on intracellular mediators related to cell viability in cardiomyocytes, namely NOX2, reactive oxygen species (ROS), mitochondrial membrane potential (DeltaPsi (m)) and ATP concentrations.

RESULTS

We found that incubation of H9c2 cells with 0.1 mM D,L-Hcy (= 60 microM L-Hcy) resulted in an increase of DeltaPsi (m) as well as ATP concentrations. 1.1 mM D,L-Hcy (= 460 microM L-Hcy) induced reversible flip-flop of the plasma membrane phospholipids, but not apoptosis. Incubation with 2.73 mM D,L-Hcy (= 1.18 mM L-Hcy) induced apoptosis and necrosis. This loss of cell viability was accompanied by a thread-to-grain transition of the mitochondrial reticulum, ATP depletion and nuclear NOX2 expression coinciding with ROS production as evident from the presence of nitrotyrosin residues. Notably, only at this concentration we found a significant increase in S-adenosylhomocysteine which is considered the primary culprit in HHC.

CONCLUSION

We found concentration-dependent effects of Hcy in cardiomyocytes, varying from induction of reversible flip-flop of the plasma membrane phospholipids, to apoptosis and necrosis.

Supranormal dietary folic acid supplementation: effects on methionine metabolism in weanling rats

There are nationwide folic acid (FA) fortification programmes of staple foods established or under consideration in order to prevent neural tube defects. Universal FA fortification still remains controversial because of the concern that additional FA in the diets of population groups (e.g. children and elderly) not initially targeted for fortification may suffer adverse effects. However, dietary surveys regarding folate generally deal with adults and little is known about the consumption and long-term effects of fortified food and supplements in growing individuals. Recent reports from our laboratory show several effects of high-dose folate supplementation in rats. In the present work, we studied the effect of FA on the methionine cycle in weanling (3-week-old) male rats after 4 weeks of supplementation with 40 mg FA/kg dietv.control (1 mg FA/kg diet). FA supplementation resulted in a reduction of homocysteine and creatinine concentrationsv.control group. FA supplementation did not alterS-adenosylmethionine/S-adenosylhomocysteine ratio, DNA methylation, enzymatic activities or concentrations of vitamins involved in the nutritional regulation of the methionine cycle, except for folate. FA supplementation of 40 mg/kg did not lead to hepatic or renal damage. In conclusion, there were no apparent adverse effects on one-carbon metabolism after FA supplementation in the studied conditions.

Abnormal folate metabolism in foetuses affected by neural tube defects

Folic acid supplementation can prevent many cases of neural tube defects (NTDs), whereas suboptimal maternal folate status is a risk factor, suggesting that folate metabolism is a key determinant of susceptibility to NTDs. Despite extensive genetic analysis of folate cycle enzymes, and quantification of metabolites in maternal blood, neither the protective mechanism nor the relationship between maternal folate status and susceptibility are understood in most cases. In order to investigate potential abnormalities in folate metabolism in the embryo itself, we derived primary fibroblastic cell lines from foetuses affected by NTDs and subjected them to the dU suppression test, a sensitive metabolic test of folate metabolism. Significantly, a subset of NTD cases exhibited low scores in this test, indicative of abnormalities in folate cycling that may be causally linked to the defect. Susceptibility to NTDs may be increased by suppression of the methylation cycle, which is interlinked with the folate cycle. However, reduced efficacy in the dU suppression test was not associated with altered abundance of the methylation cycle intermediates, s-adenosylmethionine and s-adenosylhomocysteine, suggesting that a methylation cycle defect is unlikely to be responsible for the observed abnormality of folate metabolism. Genotyping of samples for known polymorphisms in genes encoding folate-associated enzymes did not reveal any correlation between specific genotypes and the observed abnormalities in folate metabolism. These data suggest that as yet unrecognized genetic variants result in embryonic abnormalities of folate cycling that may be causally related to NTDs.

Betaine attenuates alcoholic steatosis by restoring phosphatidylcholine generation via the phosphatidylethanolamine methyltransferase pathway

BACKGROUND/AIMS

Previous studies in our laboratory implicated ethanol-induced decreases in hepatocellular S-adenosylmethionine to S-adenosylhomocysteine (SAM:SAH) ratios in lowering the activity of phosphatidylethanolamine methyltransferase (PEMT), which is associated with the generation of steatosis. Further in vitro studies showed that betaine supplementation could correct these alterations in the ratio as well as attenuate alcoholic steatosis. Therefore, we sought to determine whether the protective effect of betaine is via its effect on PEMT activity.

METHODS

Male Wistar rats were fed the Lieber DeCarli control or ethanol diet with or without 1% betaine supplementation for 4 weeks.

RESULTS

We observed that ethanol feeding resulted in decreased phosphatidylcholine (PC) production by a PEMT-catalyzed reaction. Betaine supplementation corrected the ethanol-induced decrease in hepatic SAM:SAH ratios and by normalizing PC production via the PEMT-mediated pathway, significantly reduced fatty infiltration associated with ethanol consumption. This restoration of hepatocellular SAM:SAH ratio by betaine supplementation was associated with increases in the activity, enzyme mass and gene expression of the enzyme, betaine homocysteine methyltransferase (BHMT), that remethylates homocysteine.

CONCLUSIONS

Betaine, by virtue of promoting an alternate remethylation pathway, restores SAM:SAH ratios that, in turn, correct the defective cellular methylation reaction catalyzed by PEMT resulting in protection against the generation of alcoholic steatosis.

Adenosine metabolism and its effect on methylation potential in cultured cells: methodological considerations

Cell culture models are frequently used to study the role of adenosine in several physiological and pathological processes. In the present study, we have shown that adenosine deaminase activity in medium supplemented with calf serum significantly reduces adenosine concentration in culture medium. In the presence of HepG2 cells, the adenosine concentration in culture medium is decreased much faster, because a large amount of exogenous adenosine is metabolized by cellular enzyme. In order to measure intracellular adenosine, inosine, adenine nucleotides, S-adenosylhomocysteine (AdoHcy) and Sadenosylmethionine (AdoMet) contents, two methods for cell harvesting were compared. First, cells were removed with trypsin/EDTA, second, cells were lysed in cell culture dishes immediately after removing culture medium. Our results show that exact determination of adenosine metabolites requires immediate inactivation of metabolism by cell lysis in culture dishes. Application of adenosine (1mM) resulted in a time-dependent increase in intracellular adenosine, inosine, AMP, ATP, AdoHcy and AdoMet concentration. Since AdoHcy levels increased to a larger extent than AdoMet, the methylation potential, expressed as the ratio of AdoMet/AdoHcy, was reduced from 51.8 (control) to 2.9 (adenosine 1 mM, 2 hrs), suggesting that AdoMet-dependent methylation reactions might be impaired. In conclusion our data demonstrate that extracellular adenosine concentration and intracellular metabolite concentration strongly depend on the methods used to culture and harvest the cells.

A mathematical model gives insights into nutritional and genetic aspects of folate-mediated one-carbon metabolism

Impaired folate-mediated 1-carbon metabolism has been linked to multiple disease outcomes. A better understanding of the nutritional and genetic influences on this complex biochemical pathway is needed to comprehend their impact on human health. To this end, we created a mathematical model of folate-mediated 1-carbon metabolism. The model uses published data on folate enzyme kinetics and regulatory mechanisms to simulate the impact of genetic and nutritional variation on critical aspects of the pathway. We found that the model predictions match experimental data, while providing novel insights into pathway kinetics. Our primary observations were as follows: 1) the inverse association between folate and homocysteine is strongest at very low folate concentrations, but there is no association at high folate concentrations; 2) the DNA methylation reaction rate is relatively insensitive to changes in folate pool size; and 3) as folate concentrations become very high, enzyme velocities decrease. With regard to polymorphisms in 5,10-methylenetetrahydrofolate reductase (MTHFR), the modeling predicts that decrease MTHFR activity reduces concentrations of S-adenosylmethionine and 5-methyltetrahydrofolate, as well as DNA methylation, while modestly increasing S-adenosylhomocysteine and homocysteine concentrations and thymidine or purine synthesis. Decreased folate together with a simulated vitamin B-12 deficiency results in decreases in DNA methylation and purine and thymidine synthesis. Decreased MTHFR activity superimposed on the B-12 deficiency appears to reverse the declines in purine and thymidine synthesis. These mathematical simulations of folate-mediated 1-carbon metabolism provide a cost-efficient approach to in silico experimentation that can complement and help guide laboratory studies.

Exogenous glycine partially attenuates homocysteine-induced apoptosis and membrane peroxidation in chick embryos

The effects of exogenous glycine on homocysteine (HoCys)-induced reductions in chick (Gallus gallus) embryo viability, HoCys-induced increases in brain and hepatic membrane lipid peroxidation, HoCys-induced apoptosis (caspase-3 activities) in brain and hepatic tissues, and HoCys-induced reductions in brain and hepatic S-adenosylemethionine (SAM)/S-adenosylhomocysteine (SAH) levels were studied. Exogenous HoCys caused reductions in percent living embryos and reductions in embryo masses. Exogenous glycine attenuated these HoCys-induced reductions in embryo viability. Brain and liver tissues of HoCys-treated embryos exhibited increased caspase-3 activities, increased lipid hydroperoxide (LPO) levels, and reduced levels of long-chain polyunsaturated membrane fatty acids. While exogenous glycine attenuated HoCys-induced changes in brain caspase-3 activities, brain LPO levels, and brain membrane PUFA levels, exogenous glycine was less effective in attenuating HoCys-induced changes in hepatic caspase-3 activities and hepatic membrane PUFA levels. HoCys-induced reductions in SAM/SAH ratios were observed in brains and livers. Exogenous glycine attenuated HoCys-induced reductions in brain SAM/SAH. However, glycine was unable to attenuate HoCys-induced reductions in hepatic SAM/SAH levels.

Quantitative analysis of s-adenosylmethionine and s-adenosylhomocysteine in neurulation-stage mouse embryos by liquid chromatography tandem mass spectrometry

The potential importance of the methylation cycle during embryonic development necessitates the establishment of methodology to detect alterations in the relative abundance of s-adenosylmethionine (SAM) and s-adenosylhomocysteine (SAH) in an embryonic experimental system. We have developed a precise and sensitive method for measurement of SAM and SAH based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in single neurulation-stage mouse embryos. Use of a penta-fluorinated high-performance liquid chromatography (HPLC) stationary phase gave enhanced sensitivity due to optimal ionisation in organic mobile phase and increased retention time compared to standard reversed-phase separation. Calibration curves suitable for the analysis of neurulation-stage mouse embryos (SAM 0.02-25.0microM, SAH 0.01-10.0microM) were linear (r(2)>0.997) with limits of detection for SAM and SAH of 10 and 2.5nmol/L, respectively.

The sulfur-containing amino acids: an overview

Methionine, cysteine, homocysteine, and taurine are the 4 common sulfur-containing amino acids, but only the first 2 are incorporated into proteins. Sulfur belongs to the same group in the periodic table as oxygen but is much less electronegative. This difference accounts for some of the distinctive properties of the sulfur-containing amino acids. Methionine is the initiating amino acid in the synthesis of virtually all eukaryotic proteins; N-formylmethionine serves the same function in prokaryotes. Within proteins, many of the methionine residues are buried in the hydrophobic core, but some, which are exposed, are susceptible to oxidative damage. Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways. Methionine metabolism begins with its activation to S-adenosylmethionine. This is a cofactor of extraordinary versatility, playing roles in methyl group transfer, 5'-deoxyadenosyl group transfer, polyamine synthesis, ethylene synthesis in plants, and many others. In animals, the great bulk of S-adenosylmethionine is used in methylation reactions. S-Adenosylhomocysteine, which is a product of these methyltransferases, gives rise to homocysteine. Homocysteine may be remethylated to methionine or converted to cysteine by the transsulfuration pathway. Methionine may also be metabolized by a transamination pathway. This pathway, which is significant only at high methionine concentrations, produces a number of toxic endproducts. Cysteine may be converted to such important products as glutathione and taurine. Taurine is present in many tissues at higher concentrations than any of the other amino acids. It is an essential nutrient for cats.

Quantification of S-adenosyl Methionine in Microbial Cell Extracts

A sensitive method for quantification of S-adenosyl methionine (SAM) in microbial cell extracts was developed and applied to Corynebacterium glutamicum. The method is based on SAM being completely hydrolyzed into (18)O-homoserine when extracted in boiling H(2) (18)O and thus can be clearly distinguished by GC-MS analysis from naturally labeled homoserine present in the cell extract. Additional quantification of the total homoserine pool, representing both SAM and homoserine, via HPLC allows separate determination of both metabolites.

Stable isotope dilution-based accurate comparative quantification of nitrogen-containing metabolites in Arabidopsis thaliana T87 cells using in vivo (15)N-isotope enrichment

Stable isotope dilution-based comparative quantification of nitrogen-containing metabolites for highly sensitive and selective metabolomics was developed using liquid chromatography/mass spectrometry (LC/MS) and (15)N-isotope enrichment. We produced metabolically stable isotope-labeled Arabidopsis T87 cells by culturing with (15)N-labeled medium. We found that the growth of cells maintained in (15)N-labeled medium is very similar to the growth in normal medium, as evidenced by cell morphology, doubling time, and measurement of chlorophyll and carotenoid contents. Complete incorporation of (15)N in folate, S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) in T87 cells was accomplished after culturing for 21 d. Accurate comparative quantification of folate, SAM, and SAH was established by means of LC/MS using the isotopomers of the target metabolites as internal standards. The within- and between-run assay coefficients of variation for the folate, SAM, and SAH levels were all less than 8.5%. Stable isotope labeling by nitrogen source in Arabidopsis T87 cell culture provided simple, inexpensive, and accurate amino acid profiling. This interesting new protocol is valuable for the study of dynamic changes in N-compound pools in cultured cells.

Evaluation of chemical and diastereoisomeric stability of S-adenosylmethionine in aqueous solution by capillary electrophoresis

Capillary electrophoresis was used for monitoring the stability of S-adenosylmethionine in aqueous solution under different conditions of storage and incubation used for "in vitro" and "in vivo" experiments, by evaluating both the entity of degradation and the possibility of epimerization at the sulfonium group. The determination of S,S-S-adenosylmethionine in presence of its R,S-epimer and degradation products was performed in uncoated capillary of 50 microm ID using 150 mM sodium phosphate buffer at pH 2.5. The analyses were performed in short or long-end injection modes depending if a fast monitoring of the degradation products or the evaluation of the diastereoisomeric ratio were carried out, respectively. In the long-end injection mode the baseline separation of S-adenosylmethionine diastereoisomeric forms and degradation products was obtained in less than 10 min with efficiency values in the range of 172,520-311,439 number of theoretical plates per meter. The results showed that freezing was the optimum storage mode for S-adenosylmethionine aqueous solutions preserving from degradation and diastereoisomeric ratio alterations. Under incubation conditions at 38 degrees C during 14 days period S-adenosylmethionine showed a strong degradation and the formation of three main increasing degradation products. After 7 and 14 days only the 52% and 32% of the initial drug concentration were available and the active S,S-S-adenosylmethionine form was the most affected.

The effect of methionine and S-adenosylmethionine on S-adenosylmethionine levels in the rat brain

OBJECTIVE

S-Adenosylmethionine (SAMe) is a major methyl donor in the brain and is also an antidepressant with few reported side effects; however, SAMe is relatively expensive and unstable. Brain SAMe can be increased by giving methionine to rats, raising the possibility that methionine may be an antidepressant. We aimed to study whether SAMe and methionine, when given orally to rats, could raise levels of SAMe in the central nervous system (CNS). We also aimed to test the relative abilities of SAMe and methionine to increase tail-flick latency after a thermal stimulus. This test was used to measure changes in CNS function.

METHODS

Rats were given SAMe and methionine orally at various doses, and biochemical and behavioural testing was carried out at intervals up to 6 hours later.

RESULTS

Methionine raised SAMe levels in various regions of the CNS and increased tail-flick latency, both at lower doses than SAMe.

CONCLUSION

Methionine should be tested for antidepressant properties in humans.

Effect of Fasting on Methionine Adenosyltransferase Expression and the Methionine Cycle in the Mouse Liver

The effect of fasting on mouse liver methionine adenosyltransferase (MAT I/ III) expression and the regulation of methionine metabolism were investigated. The mRNA level, protein level, and activity of MAT I/III were increased by fasting for 10 or 16 h. In spite of the increase of MAT I/III activity, S-adenosylmethionine, the product of methionine due to MAT I/III, decreased. S-Adenosylhomocysteine, which is made from S-adenosylmethionine by its coupling to methyltransferase, increased as a result of fasting for 16 h. These results suggest that the total methylation reactions using S-adenosylmethionine are stimulated in the fasting mouse liver. However, the DNA methylation level was not changed by fasting for 16 h. Glutathione, which is made by the transsulfuration pathway from homocysteine, decreased due to fasting. Regulation of supplementation of S-adenosylmethionine may occur in the fasting mouse because MAT I/III activity increases and the flow to glutathione is decreased.

S-Adenosyl methionine/S-adenosyl-L-homocysteine ratio determination by capillary electrophoresis employed as a monitoring tool for the antiviral effectiveness of adenosine analogs

S-Adenosyl-L-homocysteine hydrolase (SAHh) inhibitors have long been used as broad-range antivirals and have been recently evaluated as an experimental therapy of filovirus infections. In response to the need for a rapid laboratory testing method that could assess antiviral potency in vivo, our group developed a capillary electrophoresis (CE) method for the determination of the S-adenosyl-L-homocysteine (SAH) to S-adenosyl-L-methionine (SAM) ratio. After chloroacetaldehyde derivatization, SAH and SAM were detected using laser-induced fluorescence detection with a HeCd laser. Separation and quantitation of both SAH and SAM in human plasma were achieved in less than 1 min. The proposed method is rapid and reliable, and could be easily applied to routine monitoring of clinical and preclinical trials subjects.

NMR regulatory analysis: determination and characterization of S-adenosyl-L-methionine in dietary supplements

1H NMR methodology is described for the determination and characterization of the dietary supplement S-adenosyl-L-methionine (SAM), recently introduced to the US market, utilizing a 400 MHz spectrometer without the need of pure reference standards. The developed methodology is able to assess chemical structure, differentiate between biologically-active (S)-diastereomer and biologically-inactive (R)-diastereomer, and determine the ratio of each in the dietry supplement formulation. The determination of the percentage of declared SAM was based on the integrals for the methyl proton of 2-methyl-2-propanol served as an internal standard at delta 1.24 and the methine proton H1' of SAM ribose ring at delta 6.06. The percentage of the active diastereomer was calculated from the relative intensities of the sulfonium methyl singlets corresponding to the major component (S)-diastereomer at delta 2.98 and the minor (R)-counterpart at delta 2.93. The accuracy was established by analyzing synthetic mixtures of the analyte and the internal standard. Excellent agreement was verified between the assay results and the quantities of analyte in the mixture. The mean +/- SD recovery values for SAM and its (R)-diastereomer impurity from a set of 10 synthetic mixtures were 99.6 +/- 0.8% and 22.5 +/- 0.1%, respectively. Using 10 lots, the percentage of SAM ranged from 0 to 110.7% of the declared value and the percentage of the active (S)-diastereomer ranged from 0 to 82.3%.

Rapid screening for S-adenosylmethionine-dependent methylation products by enzyme-transferred isotope patterns analysis

We report here an isotopic labeling and mass spectrometric method to rapidly identify S-adenosylmethionine (AdoMet)-dependent methylation products. In the presence of CH(3)- and CD(3)-labeled AdoMet, a methyl transfer product appears as a doublet separated by 3 Da in a mass spectrum, while other compounds show their normal isotopic distribution. Based on this unique isotopic pattern, methylation product(s) can be easily detected even from a mixture of cellular components. To validate our method, the product of human thiopurine methyltransferase (TPMT, EC 2.1.1.67) has been successfully identified from both an in vitro assay and a whole-cell assay. This method is generally applicable to AdoMet-dependent transmethylation and other group-transfer reactions, and constitutes the first example of a general strategy of enzyme-transferred isotope patterns (ETIPs) analysis.

RXRalpha-regulated liver SAMe and GSH levels influence susceptibility to alcohol-induced hepatotoxicity

Retinoids influence the pathogenesis of alcohol liver disease (ALD). To analyze the impact of retinoid X receptor alpha (RXRalpha) on ALD, alcohol-induced hepatotoxicity was studied using mice fed ethanol intragastrically for 25 days. Alcohol-induced microvesicular fat around the central vein and drug-induced morphological changes (loss of rough endoplasmic reticulum, pinkish cytoplasm, and enlarged hepatocyte) in the pericentral area were observed in the liver of wild-type mice. In the hepatocyte RXRalpha-deficient mouse liver, alcohol induced fat accumulation, mitosis, acute inflammation, and necrosis. The histology score after alcohol treatment was significantly higher in mutant mice than in wild-type mice. However, drug-induced morphological changes were not apparent in alcohol-treated hepatocyte RXRalpha-deficient mice. Northern analysis showed that the basal and alcohol-induced CYP2B, CYP2A, and CYP3A mRNA levels were lower in hepatocyte RXRalpha-deficient mice than in wild-type mice, which in turn may protect mutant mice from morphological changes. Compared with wild-type mice, hepatocyte RXRalpha-deficient mice have significant lower levels of S-adenosylmethionine and glutathione, which is further reduced after alcohol treatment, and that may account for severe liver injury induced by alcohol. The overall result suggests an important role of RXRalpha in preventing alcohol-induced liver injury.

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.

Insertional inactivation of the methionine s-methyltransferase gene eliminates the s-methylmethionine cycle and increases the methylation ratio

Methionine (Met) S-methyltransferase (MMT) catalyzes the synthesis of S-methyl-Met (SMM) from Met and S-adenosyl-Met (Ado-Met). SMM can be reconverted to Met by donating a methyl group to homocysteine (homo-Cys), and concurrent operation of this reaction and that mediated by MMT sets up the SMM cycle. SMM has been hypothesized to be essential as a methyl donor or as a transport form of sulfur, and the SMM cycle has been hypothesized to guard against depletion of the free Met pool by excess Ado-Met synthesis or to regulate Ado-Met level and hence the Ado-Met to S-adenosylhomo-Cys ratio (the methylation ratio). To test these hypotheses, we isolated insertional mmt mutants of Arabidopsis and maize (Zea mays). Both mutants lacked the capacity to produce SMM and thus had no SMM cycle. They nevertheless grew and reproduced normally, and the seeds of the Arabidopsis mutant had normal sulfur contents. These findings rule out an indispensable role for SMM as a methyl donor or in sulfur transport. The Arabidopsis mutant had significantly higher Ado-Met and lower S-adenosylhomo-Cys levels than the wild type and consequently had a higher methylation ratio (13.8 versus 9.5). Free Met and thiol pools were unaltered in this mutant, although there were moderate decreases (of 30%-60%) in free serine, threonine, proline, and other amino acids. These data indicate that the SMM cycle contributes to regulation of Ado-Met levels rather than preventing depletion of free Met.

Increased response of liver microsomal delta 6-desaturase activity to dietary methionine in rats

The effects of dietary casein level (5-40%) on the liver microsomal phospholipid profile, delta 6-desaturase activity and related variables were investigated in rats to examine whether the dietary protein level affected the delta 6-desaturase activity through an alteration of the liver microsomal phospholipid profile. The effects of supplementing a 10% casein diet with certain amino acids were also investigated. The concentration of hepatic S-adenosylmethionine (SAM), the ratio of phosphatidylcholine (PC) to phosphatidylethanolamine (PE) and the delta 6-desaturase activity in liver microsomes, and the ratio of arachidonate to linoleate of microsomal PC increased with increasing dietary casein level. There were significant correlations between the dietary methionine content and hepatic SAM concentration, hepatic SAM concentration and microsomal PE concentration, and microsomal PE concentration and delta 6-desaturase activity. Supplementation of the 10% casein diet with methionine significantly increased the hepatic SAM concentration, PC/PE ratio, delta 6-desaturase activity, and arachidonate/linoleate ratio, whereas cystine supplementation had no or little effect on these variables. These increases induced by methionine were significantly suppressed by additional glycine. The results obtained here, together with those in our previous report, suggest that quantity and type of dietary protein might affect the delta 6-desaturase activity through an alteration of the liver microsomal profile of phospholipids, especially PE, and that the alteration of phospholipid profile might be mediated by a hepatic SAM concentration that reflects the dietary methionine level.

A stereospecific colorimetric assay for (S,S)-adenosylmethionine quantification based on thiopurine methyltransferase-catalyzed thiol methylation

S-Adenosyl-L-methionine (AdoMet) which is biologically synthesized by AdoMet synthetase bears an S configuration at the sulfur atom. The chiral sulfonium spontaneously racemizes to form a mixture of S and R isomers of AdoMet under physiological conditions or normal storage conditions. The chirality of AdoMet greatly affects its activity; the R isomer is not accepted as a substrate for AdoMet-dependent methyltransferases. We report a stereospecific colorimetric assay for (S,S)-adenosylmethionine quantification based on an enzyme-coupled reaction in which (S,S)-AdoMet reacts with 2-nitro-5-thiobenzoic acid to form AdoHcy and 2-nitro-5-methylthiobenzoic acid. The transformation is catalyzed by recombinant human thiopurine S-methyltransferase (TPMT, EC 2.1.1.67) and is associated with a large spectral change at 410 nm. Accumulation of the S-adenosylhomocysteine (AdoHcy) product, a feedback inhibitor of TPMT, slows the assay. AdoHcy nucleosidase (EC 3.2.2.9) irreversibly cleaves AdoHcy to adenine and S-ribosylhomocysteine, significantly shortening the assay time to less than 10 min. The assay is linear from 5 to at least 60 microM (S,S)-AdoMet.

Liquid chromatographic determination of S-adenosyl-L-methionine in dietary supplement tablets

A simple and reliable liquid chromatographic method was developed for the determination of S-adenosyl-L-methionine (SAM) in dietary supplement tablets. SAM in products was extracted with a phosphate buffer and separated from the mixture on a reversed-phase C8 column by ion-pair chromatography. A gradient mobile phase containing phosphate buffer, sodium octanesulfonate as the ion-pair reagent, and acetonitrile at a flow rate of 1.2 mL/min was used in the analysis. The UV detection wavelength was set at 257 nm. The calibration curve was linear over a range of 75-375 microg/mL for the SAM active ion with R2 = 0.9999. Replicate tests indicated good reproducibility of the method with a relative standard deviation of 0.9% (n = 8). The multiple extractions and recoveries from fortified products showed the high accuracy of the analysis. The use of the acidic buffer for SAM extraction and elution and the use of a fresh standard for each calibration to counteract the instability of the SAM compound significantly improved the accuracy of the method.

NO sensitizes rat hepatocytes to proliferation by modifying S-adenosylmethionine levels

BACKGROUND & AIMS

Liver regeneration is a fundamental response of this organ to injury. Hepatocyte proliferation is triggered by growth factors, such as hepatocyte growth factor. However, hepatocytes need to be primed to react to mitogenic signals. It is known that nitrous oxide (NO), generated after partial hepatectomy, plays an important role in hepatocyte growth. Nevertheless, the molecular mechanisms behind this priming event are not completely known. S-adenosylmethionine (AdoMet) synthesis by methionine adenosyltransferase is the first step in methionine metabolism, and NO regulates hepatocyte S-adenosylmethionine levels through specific inhibition of this enzyme. We have studied the modulation of hepatocyte growth factor-induced proliferation by NO through the regulation of S-adenosylmethionine levels.

METHODS

Studies were conducted in cultured rat hepatocytes isolated by collagenase perfusion, which triggers NO synthesis.

RESULTS

The mitogenic response to hepatocyte growth factor was blunted when inducible NO synthase was inhibited; this process was overcome by the addition of an NO donor. This effect was dependent on methionine concentration in culture medium and intracellular S-adenosylmethionine levels. Accordingly, we found that S-adenosylmethionine inhibits hepatocyte growth factor-induced cyclin D1 and D2 expression, activator protein 1 induction, and hepatocyte proliferation.

CONCLUSIONS

Together our findings indicate that NO may switch hepatocytes into a hepatocyte growth factor-responsive state through the down-regulation of S-adenosylmethionine levels.

Reversed-phase high-performance liquid chromatography procedure for the simultaneous determination of S-adenosyl-L-methionine and S-adenosyl-L-homocysteine in mouse liver and the effect of methionine on their concentrations

An improved reversed-phase high-performance liquid chromatography (HPLC) procedure with ultraviolet detection is described for the simultaneous determination of S-adenosyl-L-methionine (SAM) and S-adenosyl-L-homocysteine (SAH) in mouse tissue. The method provides rapid resolution of both compounds in a 25-microl perchloric acid extract of the tissue. The limits of detection in 25-microl injection volumes were 22 and 20 pmol for SAM and SAH, respectively. The limits of quantitation in 25-microl injection volumes were 55 and 50 pmol for SAM and SAH, respectively, with recovery consistently >98%. The assay was validated over linear ranges of 55-11000 pmol for SAM and 50-10000 pmol for SAH. The intra-day precision and accuracy were < or =6.4% relative standard deviation (RSD) and 99.9-100.0% for SAH and < or =6.7% RSD and 100.0-100.1% for SAM. The inter-day precision and accuracy were < or =5.9% RSD and 99.9-100.6% for SAH and < or =7.0% RSD and 99.5-100.1% for SAM. Compared to earlier procedures, the HPLC method demonstrated significantly better separation, detection limit and linear range for SAM and SAH determination. The assay demonstrated applicability to monitoring in mice the time-course of the effect of methionine on SAM and SAH levels in the liver. Administering methionine to mice increased by 10-fold the liver concentration of SAM and SAH within 2 h, which then rapidly decreased to the control levels by 8 h. This indicated that methionine was promptly converted to SAM and then rapidly catabolized into SAH. Thus, the metabolism of methionine to SAM should be considered in the supplementation of methionine to maintain SAM levels in the body.

HPLC analysis of S-adenosyl-L-methionine in pharmaceutical formulations

A validated analytical method of S-adenosyl-L-methionine (SAM) in pharmaceutical preparations by reversed phase high performance liquid chromatography (RP-HPLC) is described. The compound is separated by a 2.1 mm x 15 cm, 5 microns--Discovery C18 column with isocratic elution. The effect of different anionic surface active agents with different molarity on the separation was studied. A direct relationship between the molarity of the surface active agents and the capacity factor (k') was found. The limit of detection was 0.49 mmol/ml and the linearity was r = 0.999 in the concentration range 20-100 micrograms/ml. Inter- and intra-assay variation was determined for three selected concentrations (20, 60, 100 micrograms/ml) by calculating the analytical recoveries with a range of 97.0-99.9%. The procedure was also suitable to check the stability of S-adenosyl-L-methionine in solution at room temperature.

Diadenosine phosphates and S-adenosylmethionine: novel boron binding biomolecules detected by capillary electrophoresis

There is evidence that boron has a physiological role in animals and humans, but the search for boron binding biomolecules has been difficult because useful radioactive boron isotopes do not exist. To overcome this limitation we used capillary electrophoresis to identify and quantify boron binding to biomolecules by detecting the negative charge boron imparts to ligands. The effect of molecular structure and proximal electronic charges of adenosine and molecules with adenosine moieties including S-adenosylmethionine (SAM) and diadenosine polyphosphates (Ap(n)A) were compared. The boron affinity of the test species varied with the rank order SAM congruent with Ap(6)A congruent with Ap(5)A>Ap(4)A>Ap(3)A congruent with NAD(+)>Ap(2)A>NADH congruent with 5'ATP>5'ADP>5'AMP>adenosine>3'AMP congruent with 2'AMP congruent with cAMP congruent with adenine. Test species with vicinal cis-diols bound boron; species without those moieties did not. Boron binding affinity increased when proximal cationic moieties were present. Anionic moieties remote from the cis-hydroxyl binding site also positively influenced boron binding affinity. In the Ap(n)A species, cooperative complexing of boron between the terminal ribose moieties apparently occurred. In these species boron affinity greater than expected for two monocomplexes was observed and binding affinities increased as more phosphate groups (beyond three) were present separating the terminal moieties. Our results indicate that Ap(6)A, Ap(5)A, Ap(4)A, Ap(3)A, and SAM have higher affinities for boron than any other currently recognized boron ligand present in animal tissues including NAD(+).

Homocysteine: a history in progress

This paper shows that the linkage between basic science and clinical research has characterized the field of sulfur amino acid metabolism since 1810, when Wollaston isolated cystine from a human bladder stone. The nature and consequences of this relationship are discussed.

S-adenosylmethionine synthesis in Leishmania infantum promastigotes

Methionine adenosyltransferase (MAT), S -adenosylmethionine (AdoMet), and S -adenosylhomocysteine (AdoHcy), have been analysed at different time-points during the growth curve of Leishmania infantum. MAT activity and AdoMet content peaked in the lag and early log phases, whereas higher levels of AdoHcy were found in stationary phase cells. MAT activity of cell extracts displayed hyperbolic kinetics for both its substrates, l -methionine and ATP, with km values of 35 microm and 5 m m, respectively. MAT has an absolute requirement for divalent cations, and is dependent on sulfydryl protective agents. Unlike other sources, L. infantum MAT activity seems to be transcriptionally regulated, with an accumulation of MAT-mRNA during rapid growth periods of promastigotes.

Measurement of plasma and intracellular S-adenosylmethionine and S-adenosylhomocysteine utilizing coulometric electrochemical detection: alterations with plasma homocysteine and pyridoxal 5'-phosphate concentrations

BACKGROUND

The relative changes in plasma and intracellular concentrations of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) may be important predictors of cellular methylation potential and metabolic alterations associated with specific genetic polymorphisms and/or nutritional deficiencies. Because these metabolites are present in nanomolar concentrations in plasma, methods of detection generally require time-consuming precolumn processing or metabolite derivatization.

METHODS

We used HPLC with coulometric electrochemical detection for the simultaneous measurement of SAM and SAH in 200 microL of plasma, 10(6) lymphocytes, or 10 mg of tissue. Filtered trichloroacetic acid extracts were injected directly into the HPLC system without additional processing and were eluted isocratically.

RESULTS

The limits of detection were 200 fmol/L for SAM and 40 fmol/L SAH. In plasma extracts, the interassay CV was 3.4-5.5% and the intraassay CV was 2.8-5.6%. The analytical recoveries were 96.8% and 97.3% for SAM and SAH, respectively. In a cohort of healthy adult women with mean total homocysteine concentrations of 7.3 micromol/L, the mean plasma value was 156 nmol/L for SAM and 20 nmol/L for SAH. In women with increased homocysteine concentrations (mean, 12.1 micromol/L), plasma SAH, but not SAM, was increased (P <0.001), and plasma pyridoxal 5'-phosphate concentrations were reduced (P <0.001). Plasma SAM/SAH ratios were inversely correlated with homocysteine concentrations (r = 0.73; P <0.01), and the SAM/SAH ratio in plasma was directly correlated with the intracellular SAM/SAH ratio in lymphocytes (r = 0.70; P <0.01).

CONCLUSIONS

Increased homocysteine in serum is associated with an increase in SAH and a decrease in the SAM/SAH ratio that could negatively affect cellular methylation potential. Accurate and sensitive detection of these essential metabolites in plasma and in specific tissues should provide new insights into the regulation of one-carbon metabolism under different nutritional and pathologic conditions.

Simultaneous determination of S-adenosylmethionine and S-adenosylhomocysteine by capillary zone electrophoresis

A reproducible, rapid procedure for the simultaneous quantitative separation of S-adenosylmethionine and S-adenosylhomocysteine by capillary zone electrophoresis has been developed. Separations were performed by using an uncoated capillary of 60 cm effective length and 50 microm ID, 40 mM sodium phosphate buffer, pH 2.50, as background electrolyte solution, and 30 kV. On-line detection was carried out at 254 nm. Under the conditions selected we resolved a standard solution containing S-adenosylmethionine and S-adenosylhomocysteine in a run time shorter than 8 min. A mass detection limit in the range of 10 fmol was achieved. Adenosyl-L-methionine, S[methyl-3H] has also been assayed under the same experimental conditions. Other related compounds did not show interference, including those derived from the hydrolysis of S-adenosylmethionine. The present method allows simultaneous determination of these compounds, which play an important role in many microbiological and enzymatic research studies.

Measuring S-adenosylmethionine in whole blood, red blood cells and cultured cells using a fast preparation method and high-performance liquid chromatography

The physiological methyl donor S-adenosylmethionine (SAM) plays a key role in the maintenance of human health and in the prevention of disease. A convenient clinical test for blood SAM does not exist, even though blood SAM is increasingly seen as an important indicator of health. We have developed a simple procedure to extract SAM from small amounts of blood or cells. The extracted SAM is then measured by high-performance liquid chromatography (HPLC). This measurement is sensitive, precise and uses as little as 200 microliters of blood or 0.5-10(6) cultured cells per determination. SAM, as tested with this method, under acidic conditions, is stable for hours and can be frozen for later analysis. The method has been used to show that blood SAM varies with species, sex and treatment. We have also measured the SAM levels in cultured cells, and have been able to detect wide variations depending upon treatments administered during the growth of those cells. In conclusion, this is a very rapid and easy method to measure SAM in biological fluids and cell culture and which could be adapted to the clinical setting.

Dietary folate protects against the development of macroscopic colonic neoplasia in a dose responsive manner in rats

BACKGROUND AND AIMS

Diminished folate status is associated with enhanced colorectal carcinogenesis. This study investigated the potential chemopreventive role of dietary folate in the dimethylhydrazine colorectal cancer model.

SUBJECTS AND METHODS

Sprague-Dawley rats were fed diets containing either 0, 2 (daily dietary requirement), 8 or 40 mg folate/kg diet for 20 weeks. After five weeks of diet, rats were injected with dimethyl-hydrazine (44 mg/kg) weekly for 15 weeks. Fifteen weeks after the first injection of dimethylhydrazine, all rats were killed. Folate status was determined, and the entire colorectum from each rat was analysed for macroscopic and microscopic neoplasms.

RESULTS

Plasma and colonic folate concentrations correlated directly with dietary folate levels (p < 0.005). The incidence of microscopic neoplasms was similar among the four groups. However, the incidence and the average number of macroscopic tumours per rat decreased progressively with increasing dietary folate levels up to 8 mg/kg diet (p < 0.05). In the strongly procarcinogenic milieu used in this study, folate supplementation at 20 times the basal requirement was associated with rates of macroscopic tumour development that were intermediate, and not statistically distinct, from rates observed at either 0 or 8 mg/kg diet.

CONCLUSIONS

These data indicate that in this rat model, (a) increasing dietary folate up to four times the basal requirement leads to a progressive reduction in the evolution of macroscopic neoplasms from microscopic foci; and (b) folate supplementation beyond four times the requirement does not convey further benefit.

Carbon flow through the hepatic folate-dependent one-carbon pool is not altered in vitamin A-deficient rats

Vitamin A status can influence a number of enzymes and coenzymes involved in folate-dependent one-carbon metabolism as well as subsequent methyl group metabolism. Tracer kinetic techniques were used in the present study to assess the physiological importance of vitamin A deficiency on the de novo synthesis of methionine via the hepatic folate-dependent one-carbon pool. Vitamin A-deficient (0 retinol equivalents (RE) retinyl palmitate/g diet) rats were fed their respective diet for 11 wk, whereas control rats (1.2 RE retinyl palmitate/g diet) were food restricted to match the growth rate exhibited by the vitamin A-deficient group. After the dietary treatment period, duodenal cannulated rats were continuously infused with L-[3-(14)C] serine and L-[methyl-(3)H] methionine until a plateau specific radioactivity was exhibited with respect to the hepatic serine and methionine pools, indicating a steady state had been achieved. The hepatic concentration of both S-adenosylmethionine a S-adenosylhomocysteine were elevated in vitamin A-deficient rats. However, Vitamin A-deficient rats exhibited similar kinetic values compared with control rats fed a vitamin A-sufficient diet. The irreversible loss rate of hepatic serine and methionine, the transfer quotient from serine to methionine and the folate-dependent flow of carbon to methionine from serine were unaffected by vitamin A status. These studies demonstrate that vitamin A deficiency does not affect the reductive carbon flow from serine to methionine because the ability to generate methionine via remethylation of homocysteine with the carbon group originating from serine was not altered in vitamin A-deficient rats. Furthermore, the data illustrate the importance of using tracer kinetic techniques to quantify metabolic flux under steady-state conditions in vivo, thereby evaluating the consequences of an abnormal condition on a physiological and functional basis.

Moderate folate deficiency does not cause global hypomethylation of hepatic and colonic DNA or c-myc-specific hypomethylation of colonic DNA in rats

Global and gene-specific DNA hypomethylation is considered to be an important early epigenetic event in several human neoplasms. A growing body of evidence has suggested that DNA methylation can be altered by dietary manipulation of methyl group donors. This study investigated whether moderate depletion of folate, a dietary component needed for the synthesis of methyl groups, would cause decreased hepatic and colonic S-adenosylmethionine concentrations, and thereby lead to global and/or protooncogene-specific DNA hypomethylation. Weanling rats were fed an amino acid-defined diet containing either 0 or 8 mg folate/kg diet for 15 or 24 wk. Significantly lower systemic, hepatic and colonic folate concentrations were observed in the moderately folate-depleted rats than in controls at both 15 and 24 wk (P < 0.005). Although hepatic S-adenosylmethionine was significantly lower in the moderately folate-depleted rats than in controls at the two time points (P < 0.03), colonic S-adenosylmethionine concentrations were not significantly different between the two groups at either time point. No significant differences between the folate-depleted and control animals could be detected with regard to global DNA methylation in the liver or colonic mucosa. Furthermore, c-myc protooncogene-specific DNA methylation in the colonic mucosa was not significantly different between these two groups of animals. These results indicate that moderate folate depletion does not cause a significant reduction in global DNA methylation in liver or colonic mucosa or in c-myc-specific colonic mucosal DNA methylation in this rat model.

Stability-indicating proton nuclear magnetic resonance spectroscopic method for determination of S-adenosyl-L-methionine in tablets

We present a simple, accurate, stability-indicating nuclear magnetic resonance (NMR) method for determining active (S,S) and inactive (R,S) epimers of S-adenosyl-L-methionine (SAM) in tablets. The SCH3 resonances of SAM epimers were well resolved at 300 MHz. Individual assays of 5 SAM tablets gave SAM values of 101.3 +/- 1.7% of declared amounts. Tablet solutions were assayed at a level of 8.0 mg/mL, but the method was linear for SAM concentrations ranging from 64 to 1 mg/mL (correlation coefficient, 0.9996). Reproducibility was indicated by a relative standard deviation of 0.33% for 6 replicate assays for total SAM at a concentration of 8 mg/mL. In contrast to the propietary liquid chromatographic (LC) method, which requires SAM as an external standard, the NMR method uses sodium trimethylsilylpropionate-d4 (TSP) both as an internal standard and as a chemical shift reference. The method was used to test the stability of SAM analytes under various pH levels and temperatures. We found 8% inactivation of SAM due to epimerization over a 24 h period at room temperature and pH 5. SAM solutions showed no detectable inactivation after 14 days when stored below 0 degrees C.

Mechanism of erythrocyte accumulation of methylation inhibitor S-adenosylhomocysteine in uremia

We have recently demonstrated that methyl esterification of erythrocyte membrane proteins, a reaction involved in recognition and repair of specifically damaged proteins, is impaired in uremia. This is accompanied by a significant increase in intracellular S-adenosylhomocysteine (AdoHcy), a potent inhibitor of methyltransferases. AdoHcy accumulation is normally prevented by its enzymatic hydrolysis to homocysteine (Hcy) and adenosine, a reversible reaction catalyzed by AdoHcy hydrolase. To assess the contribution that Hcy offers in the elevation of AdoHcy, we measured plasma and red blood cell Hcy, AdoHcy, adenosine, and S-adenosylmethionine (AdoMet) intracellular concentrations, as well as RBC AdoHcy hydrolase specific activity, in standard hemodialysis patients and normal subjects. Plasma and red blood cell Hcy levels are significantly higher in the dialysis group, and are positively correlated to AdoHcy levels. Adenosine and AdoMet levels, and AdoHcy hydrolase specific activity are not significantly different between the two groups. The enzymatic formation of labeled AdoHcy from Hcy and tracer adenosine appears to be significantly increased, in vitro, in erythrocytes from both control and uremic patients, when 50 microM Hcy (concentration comparable to plasma levels actually found in vivo in uremic patients) is added to the incubation medium. When erythrocytes from uremic patients are incubated in vitro in absence of Hcy, a significant reduction of intracellular AdoHcy is observed with time compared to identical samples incubated in presence of 50 microM Hcy, with a T1/2 of approximately 270 minutes. The results allow us to conclude that plasma and red cell Hcy levels actually found in uremia can be effectively responsible for the intracellular accumulation of the toxic compound AdoHcy.

Two-dimensional high-performance liquid chromatographic method for assaying S-adenosyl-L-methionine and its related metabolites in tissues

S-Adenosyl-L-methionine (SAM) is a methyl-donor compound which is actively involved in a variety of biochemical reactions. An assay has been developed permitting the quantitative measurement of SAM and its related metabolites (S-adenosylhomocysteine, decarboxylated SAM, methylthioadenosine, adenosine and adenine) in liver and cell cultures. As gradient reversed-phase chromatographic or cation-exchange chromatographic methods often resulted in overlapping peaks, a two-dimensional high-performance liquid chromatographic (HPLC) procedure was developed involving gradient reversed-phase chromatographic separation followed by ion-exchange chromatography. After precipitating large molecules in the sample by perchloric acid, gel permeation was carried out on a Sephadex G 25 column to separate small water-soluble metabolites from proteins and membrane fragments. The freeze-dried sample was injected onto an ODS column and a 0-10% acetonitrile gradient in 10 mM ammonium formate buffer (pH 2.9) (20 min, linear) was applied. The relevant fractions were collected and injected onto a cation-exchange column (Partisil SCX, 10 microns, 250 mm x 4.6 mm I.D.). Elution and quantification were carried out using ammonium formate buffers of various concentration (15-400 mM), pH 2.9. The detector response (254 nm) as a function of concentration was linear over the concentration range 30-500 pmol. The detection limits of the compounds after the two-dimensional chromatographic procedure ranged from 10 to 60 pmol and the recovery was higher than 70%. The reproducibility of the results obtained from given samples was within 9-22% for rat liver and 6-24% for mast cells.