Signaling Aptamer Optimization through Selection Using RNA-Capturing Microsphere Particles.

An RNA signaling aptamer is composed of two units: a sensing aptamer that binds the input target molecule and a working aptamer that binds the output target molecule to result in a detectable signal. A conformational change of the signaling aptamer that induces an allosteric interaction with the output target molecule in response to the input target molecule depends on a junction region, which connects the two aptamer units. Efficient and effective optimization of the junction region remains a technical challenge. In this study, we demonstrate a simple strategy for optimizing the junction region through functional RNA selection using RNA-capturing microsphere particles. From approximately 0.2 million sequence variants, a signaling aptamer that enabled intracellular detection of S-adenosyl methionine with a high signal-to-noise ratio, which is approximately 2-fold higher relative fluorescence increment compared to the previously reported signaling aptamer, was obtained after single round of selection. The technology demonstrated here can be used to select RNA sequences that carry out specific functions in response to particular stimuli.

Engineering Pichia pastoris to improve S-adenosyl- l-methionine production using systems metabolic strategies.

S-adenosyl-l-methionine (SAM) is a highly valued chemical that can be used as a dietary supplement and has been used to treat depression, osteoarthritis, and liver problems as well. We adopted systems metabolic engineering strategies to improve SAM production in a high-producing strain (GS115/DS56). First, the cystathionine ß-synthase gene CYS4 was downregulated using a weak promoter PG12 to reduce the removal of homocysteine from SAM cycle, thus leading to a 48.8% increase in the SAM titer (1.68 g/L) from the strain G12-CBS, while preventing cysteine auxotrophy induced by deletion of this essential gene. Subsequently, the SAM titer of G12-CBS was improved to 13.01 g/L in 15-L fed-batch fermentation using the optimal l-methionine feeding strategy. Finally, based on comparative transcriptomics, five genes were chosen and overexpressed for further enhancement of SAM production. Among them, GDH2 and ACS2 exhibited positive effects, and the additional overexpression of GDH2 led to a 52.3% increase of titer (2.71 g/L) in shake flask culture. Therefore, the engineered Pichia pastoris strains can be utilized in industrial production of SAM using a simple and cost-effective process, and these approaches could be employed for improving the production of other chemicals by P. pastoris.

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.

Disruption of por1 gene in Candida utilis improves co-production of S-adenosylmethionine and glutathione.

The por1 gene encoding one of the mitochondrial porin channels in C. utilis CCTCC M 209298 was disrupted using a homologous recombination method. The co-production of S-adenosylmethionine (SAM) and glutathione (GSH) in the mutant C. utilis Δpor1 increased by 34.9% and 25.1%, respectively, during batch and fed-batch fermentation, relative to the parental strain. The average oxygen consumption rate, activities of key enzymes involved in SAM and GSH biosynthesis, levels of intracellular cofactors such as NADH and ATP, and carbon fluxes of key metabolites were compared between the parental strain and the Δpor1 mutant. The disruption of por1 gene increased the rate of mitochondrial respiration, increased the activities of both methionine adenosyltransferase and γ-glutamylcysteine synthetase, and enhanced the supply of energy and substrates for SAM and GSH biosynthesis, all of which favored the overproduction of SAM and GSH in the Δpor1 mutant.

Identification of (2S,3S)-ß-Methyltryptophan as the Real Biosynthetic Intermediate of Antitumor Agent Streptonigrin.

Streptonigrin is a potent antitumor antibiotic, active against a wide range of mammalian tumor cells. It was reported that its biosynthesis relies on (2S,3R)-ß-methyltryptophan as an intermediate. In this study, the biosynthesis of (2S,3R)-ß-methyltryptophan and its isomer (2S,3S)-ß-methyltryptophan by enzymes from the streptonigrin biosynthetic pathway is demonstrated. StnR is a pyridoxal 5'-phosphate (PLP)-dependent aminotransferase that catalyzes a transamination between L-tryptophan and ß-methyl indolepyruvate. StnQ1 is an S-adenosylmethionine (SAM)-dependent C-methyltransferase and catalyzes ß-methylation of indolepyruvate to generate (R)-ß-methyl indolepyruvate. Although StnR exhibited a significant preference for (S)-ß-methyl indolepyruvate over the (R)-epimer, StnQ1 and StnR together catalyze (2S,3R)-ß-methyltryptophan formation from L-tryptophan. StnK3 is a cupin superfamily protein responsible for conversion of (R)-ß-methyl indolepyruvate to its (S)-epimer and enables (2S,3S)-ß-methyltryptophan biosynthesis from L-tryptophan when combined with StnQ1 and StnR. Most importantly, (2S,3S)-ß-methyltryptophan was established as the biosynthetic intermediate of the streptonigrin pathway by feeding experiments with a knockout mutant, contradicting the previous proposal that stated (2S,3R)-ß-methyltryptophan as the intermediate. These data set the stage for the complete elucidation of the streptonigrin biosynthetic pathway, which would unlock the potential of creating new streptonigrin analogues by genetic manipulation of the biosynthetic machinery.

N-mustard analogs of S-adenosyl-L-methionine as biochemical probes of protein arginine methylation.

Nucleosomes, the fundamental building blocks of eukaryotic chromatin, undergo post-synthetic modifications and play a major role in the regulation of transcriptional processes. Combinations of these modifications, including methylation, regulate chromatin structure, determining its different functional states and playing a central role in differentiation. The biological significance of cellular methylation, particularly on chromatin, is widely recognized, yet we know little about the mechanisms that link biological methylation events. To characterize and fully understand protein methylation, we describe here novel N-mustard analogs of S-adenosyl-l-methionine (SAM) as biochemical tools to better understand protein arginine methylation events using protein arginine methyltransferase 1 (PRMT1). Specifically, azide- and alkyne-functionalized N-mustard analogs serve as cofactor mimics of SAM and are enzymatically transferred to a model peptide substrate in a PRMT1-dependent fashion. Once incorporated, the resulting alkynes and azides can be modified through chemoselective ligations, including click chemistry and the Staudinger ligation. These results readily demonstrate the feasibility of utilizing N-mustard analogs as biochemical tools to site-specifically label substrates of PRMT1 and serve as an alternative approach to study protein methylation events.

Measurement of the S-adenosyl methionine (SAMe) content in a range of commercial veterinary SAMe supplements.

OBJECTIVES: To measure the percentage of the stated amount of S-adenosyl methionine present in a range of commercially available S-adenosyl methionine supplements for veterinary use. METHOD: Sixty-four samples of products containing S-adenosyl methionine marketed to support liver function were obtained from five manufacturers via three commercial wholesalers. The amount of S-adenosyl methionine in each product was measured using high-pressure liquid chromatography. RESULTS: There were greater than threefold variation in the percentage of measured S-adenosyl methionine compared to the stated amount on the packaging which was significantly (P < 0 · 001) related to the product group being measured. CLINICAL SIGNIFICANCE: Differences in received dose of S-adenosyl methionine between different products were marked and this could have a profound influence on studies that evaluate any variation in absorption of S-adenosyl methionine between different product formulations, the effectiveness of S-adenosyl methionine-based products in clinical cases or when translating the results of studies that have used a specific S-adenosyl methionine product to those produced by a different manufacturer.

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.

Synthetic gene circuit-mediated monitoring of endogenous metabolites: identification of GAL11 as a novel multicopy enhancer of s-adenosylmethionine level in yeast.

Monitoring levels of key metabolites in living cells comprises a critical step in various investigations. The simplest approach to this goal is a fluorescent reporter gene using an endogenous promoter responsive to the metabolite. However, such a promoter is often not identified or even present in the species of interest. An alternative can be a synthetic gene circuit based on a heterologous pair consisting of a promoter and a transcription factor known to respond to the metabolite. We exploited the met operator and MetJ repressor of Escherichia coli, the interaction between which depends on S-adenosylmethionine (SAM), to construct synthetic gene circuits that report SAM levels in Saccharomyces cerevisiae. Using a dual-input circuit that outputs selection marker genes in a doxycycline-tunable manner, we screened a genomic library to identify GAL11 as a novel multicopy enhancer of SAM levels. These results demonstrate the potential and utility of synthetic gene circuit-mediated metabolite monitoring.

Low dietary folate and methylenetetrahydrofolate reductase deficiency may lead to pregnancy complications through modulation of ApoAI and IFN-γ in spleen and placenta, and through reduction of methylation potential.

SCOPE: Genetic or nutritional disturbances in folate metabolism lead to hyperhomocysteinemia and adverse reproductive outcomes. Folate-dependent homocysteine remethylation is required for methylation reactions and may influence choline/betaine metabolism. Hyperhomocysteinemia has been suggested to play a role in inflammation. The goal of this study was to determine whether folate-related pregnancy complications could be due to altered expression of some inflammatory mediators or due to disturbances in methylation intermediates. METHODS AND RESULTS: Pregnant mice with or without a deficiency of methylenetetrahydrofolate reductase (MTHFR) were fed control diets or folate-deficient (FD) diets; tissues were collected at embryonic day 14.5. FD decreased plasma phosphocholine and increased plasma glycerophosphocholine and lysophosphatidylcholine. Liver betaine, phosphocholine, and S-adenosylmethionine:S-adenosylhomocysteine ratios were reduced in FD. In liver, spleen, and placenta, the lowest levels of apolipoprotein AI (ApoAI) were observed in Mthfr(+/-) mice fed FD. Increased interferon-gamma (IFN-γ) was observed in spleen and placentae due to FD or Mthfr genotype. Plasma homocysteine correlated negatively with liver and spleen ApoAI, and positively with IFN-γ. CONCLUSION: Low dietary folate or Mthfr deficiency during pregnancy may result in adverse pregnancy outcomes by altering expression of the inflammatory mediators ApoAI and IFN-γ in spleen and placenta. Disturbances in choline metabolism or methylation reactions may also play a role.

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.

Hepatic metabolism of sulfur amino acids in db/db mice.

To determine the effect of type-2 diabetes and obesity on the hepatic metabolism of sulfur amino acids, hepatic sulfur amino acid metabolism was determined in db/db mice. Hepatic methionine was markedly decreased in db/db mice, although the hepatic activity of betaine homocysteine methyltransferase was increased. The decrease in hepatic methionine was reflected by decreased sulfur-containing methionine metabolites, including S-adenosylmethionine, homocysteine, cysteine, and hypotaurine in liver and plasma. In contrast, S-adenosylhomocysteine, putrescine, and spermidine were increased in db/db mice. The hepatic level and activity of methionine adenosyltransferase I/III, an S-adenosylmethionine synthesizing enzyme, were significantly increased. These results suggest that increased polyamine synthesis, in conjunction with decreased hepatic methionine levels, is partly responsible for the reduction in hepatic S-adenosylmethionine. Decreased homocysteine in liver and plasma may be attributable to the decrease in hepatic methionine and upregulation of hepatic betaine homocysteine methyltransferase. Glutathione in liver and plasma did not change despite decreased γ-glutamylcysteine ligase activity. The decreased hepatic hypotaurine may be attributable to the downregulation of cysteine dioxygenase. The major finding of this study is that db/db mice exhibited decreases in hepatic methionine and its sulfurcontaining metabolites.

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.

DNA methylase and demethylase activities are modulated by one-carbon metabolism in Alzheimer's disease models.

Late-onset Alzheimer's disease seems to be a multi-factorial disease with both genetic and non-genetic, environmental, possible causes. Recently, epigenomics is achieving a major role in Alzheimer's research due to its involvement in different molecular pathways leading to neurodegeneration. Among the different epigenetic modifications, DNA methylation is one of the most relevant to the disease. We previously demonstrated that presenilin1 (PSEN1), a gene involved in amyloidogenesis, is modulated by DNA methylation in neuroblastoma cells and Alzheimer's mice in an experimental model of nutritionally altered one-carbon metabolism. This alteration, obtained by nutritional deficiency of B vitamins (folate, B12 and B6) hampered S-adenosylmethionine (SAM)-dependent methylation reactions. The aim of the present paper was to investigate the regulation of DNA methylation machinery in response to hypomethylating (B vitamin deficiency) and hypermethylating (SAM supplementation) alterations of the one-carbon metabolism. We found that DNA methylases (DNMT1, 3a and 3b) and a putative demethylase (MBD2) were differently modulated, in line with the previously observed changes of PSEN1 methylation pattern in the same experimental conditions.

Spermine synthase activity affects the content of decarboxylated S-adenosylmethionine.

dcAdoMet (decarboxylated S-adenosylmethionine) is an essential intermediate in the synthesis of polyamines. Its content is normally very low, amounting to less than 5% of that of S-adenosylmethionine itself. It was found that in mice lacking spermine synthase there was a large increase in dcAdoMet and that overexpression of spermine synthase reduced the amount of this nucleoside. There was also an increase in dcAdoMet in cells derived from patients with Snyder-Robinson syndrome, a rare X-linked recessive human disease caused by SMS gene mutations that greatly reduce the content of spermine synthase. These results suggest that there is an inverse relationship between the amount of spermine synthase protein and the content of dcAdoMet and raise the possibility that some of the abnormalities seen in mammals deficient in spermine synthase might be due to changes in dcAdoMet pools.

Analysis of trace degradation products (decarboxylated diastereoisomers) of S-adenosylmethionine by electrophoresis in capillaries with cationic coatings (N-methylpolyvinylpyridinium or divalent barium).

Commercial preparations of S-adenosylmethionine (SAM) when analyzed in uncoated capillaries show a minute impurity believed to be decarboxylated (dc) SAM. By using two types of cationic coatings, thus reducing the electro-endo-osmotic flow (EOF), it was possible to separate this impurity into two diastereoisomers of dcSAM. The coatings evaluated for this purpose were: (i) N-methylpolyvinylpyridinium, used under reversed EOF at acidic conditions (pH 4.0) and (ii) deposition of divalent barium at alkaline pH values (pH 9.4), providing reduced EOF. Under these conditions, it was possible to separate this impurity into two diastereoisomers, which by chemical synthesis were indeed proven to be dcSAM. It was further demonstrated that, in the alkylation of 5'-methylthioadenosine by 3-bromopropylamine in bromidric acid to dcSAM, another minute impurity was present, proven, via mass spectrometry, to consist of S-(5'-adenosyl)-3-thiopropylamine (decarboxylated and demethylated (dc-SAH)). The LOD for the two dcSAM diastereoisomers was assessed as 17.5 µg/mL and their LOQ as 25.5 µg/mL. By the barium-based protocol it was possible to quantify the dcSAM, present in a commercial sample of SAM, as a 0.1% impurity.

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.

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.