Betaine-homocysteine S-methyltransferase (BHMT) uses betaine to catalyze the conversion of homocysteine (Hcy) to methionine. There are common genetic polymorphisms in the BHMT gene in humans that can alter its enzymatic activity. We generated the first Bhmt Histopathological analysis revealed that Bhmt ؊/؊ mice developed hepatocellular carcinoma or carcinoma precursors. These results indicate that BHMT has an important role in Hcy, choline, and one-carbon homeostasis. A lack of Bhmt also affects susceptibility to fatty liver and hepatocellular carcinoma. We suggest that functional polymorphisms in BHMT that significantly reduce activity may have similar effects in humans.Betaine-homocysteine S-methyltransferase (BHMT) 2 is a zinc-dependent cytosolic enzyme that catalyzes the transfer of a methyl group from betaine to homocysteine (Hcy) forming dimethylglycine and methionine (Met) (Fig. 5). Humans have common single nucleotide polymorphisms in the BHMT gene that alter BHMT enzyme activity and function (1). A common BHMT single nucleotide polymorphism rs3733890 (41% of NC population has 1 variant allele, and 8% have 2 alleles (2)) was associated with increased risk for having babies with neural tube defects (3), decreased risk for developing cardiovascular disease (4), and reduced risk for breast cancer-specific mortality (5). The epidemiological evidence suggests the importance of single nucleotide polymorphisms in the gene. However, the metabolic consequences of having null mutations of the BHMT gene have not been thoroughly investigated. To directly investigate the role of BHMT in vivo, we generated and characterized mice in which the gene encoding Bhmt was deleted (Bhmt Ϫ/Ϫ ). BHMT activity is found at high levels in the liver and kidney, and low levels in the brain, lenses, and other human tissues. In rodents, high levels of BHMT activity are only found in the liver (6). Betaine, the methyl donor for BHMT, comes from either dietary sources or from oxidation of choline (an irreversible reaction) by choline dehydrogenase (CHDH). Alternatively, choline can be used to form the phospholipid phosphatidylcholine (PtdCho) or the neurotransmitter acetylcholine (7). The product of BHMT, methionine, is the precursor for S-adenosylmethionine (AdoMet), the major methyl donor for most biological methylations, including DNA and histone methylation, the conversion of glycine to methylglycine (catalyzed by glycine methyltransferase (GNMT)), and the methylation of phosphatidylethanolamine (PtdEtn) to form PtdCho (catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT)).The other substrate for BHMT is Hcy, a thiol-containing amino acid, which, when elevated in plasma, is associated with cardiovascular diseases, pregnancy complications, renal insufficiency, and cognitive impairment (8). Hcy is converted to methionine by BHMT or by methionine synthase, the latter of which uses methyltetrahydrofolate (methyl-THF) as the methyl

Choline dehydrogenase (CHDH) catalyzes the conversion of choline to betaine, an important methyl donor and organic osmolyte. We have previously identified single nucleotide polymorphisms (SNPs) in the human CHDH gene that, when present, seem to alter the activity of the CHDH enzyme. These SNPs occur frequently in humans. We created a Chdh(-/-) mouse to determine the functional effects of mutations that result in decreased CHDH activity. Chdh deletion did not affect fetal viability or alter growth or survival of these mice. Only one of eleven Chdh(-/-) males was able to reproduce. Loss of CHDH activity resulted in decreased testicular betaine and increased choline and PCho concentrations. Chdh(+/+) and Chdh(-/-) mice produced comparable amounts of sperm; the impaired fertility was due to diminished sperm motility in the Chdh(-/-) males. Transmission electron microscopy revealed abnormal mitochondrial morphology in Chdh(-/-) sperm. ATP content, total mitochondrial dehydrogenase activity and inner mitochondrial membrane polarization were all significantly reduced in sperm from Chdh(-/-) animals. Mitochondrial changes were also detected in liver, kidney, heart, and testis tissues. We suggest that men who have SNPs in CHDH that decrease the activity of the CHDH enzyme could have decreased sperm motility and fertility.

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Elevated homocysteine (Hcy) concentrations are associated with increased risk of several chronic diseases. Hcy can be removed by methylating it to form methionine via either the betaine homocysteine S-methyltransferase (BHMT) or the methionine synthase (MS) pathway. BHMT uses betaine as the methyl donor, whereas MS uses 5-methyltetrahydrofolate. We previously found that mice with the gene encoding Bhmt deleted (Bhmt(-/-)) had altered Hcy metabolites in tissues. This study aimed to determine whether folate supplementation of Bhmt(-/-) mice reverses, and folate deficiency exacerbates, these metabolic changes. Bhmt(-/-) mice and their littermates (Bhmt(+/+) mice) were fed a folate-deficient (FD; 0 mg/kg diet), a folate control (FC; 2 mg/kg diet), or a folate-supplemented (FS; 20 mg/kg diet) diet for 4 wk. Bhmt(-/-) mice had higher plasma Hcy and hepatic S-adenosylhomocysteine (AdoHcy) concentrations and had lower hepatic S-adenosylmethionine (AdoMet) concentrations compared with Bhmt(+/+) mice for all diets. Although the FD diet increased plasma Hcy (P < 0.05) and hepatic AdoHcy (P < 0.001) concentrations in Bhmt(+/+) mice compared with FC and FS mice, the FD diet had no effect on the metabolites measured in Bhmt(-/-) mice. The FS diet did not ameliorate elevated plasma Hcy and elevated hepatic AdoHcy concentrations but did increase hepatic AdoMet concentrations in Bhmt(-/-) mice (P < 0.001) compared with FD and FC mice. We conclude that the BHMT pathway is a major route for the elimination of Hcy in mice and that the MS pathway has little excess capacity to methylate the Hcy that accumulates when the BHMT pathway is blocked.

The charge transfer (CT) from montmorillonite K10 (iron-containing clay) was studied by monitoring the reaction of halides (Cl-, Br-, and I-) with the intercalated photosensitizer, 10-methylacridinium (AcH+). The electrodes, which were fabricated by the AcH+-intercalated clays (denoted clay/AcH+), showed no current responses to bromide and chloride. However, there was a significant current response corresponding to the reduction of iodine and this response was enhanced by light irradiation. These differences in the electrochemical behavior suggested the electron transfer on the clay/AcH+ surface was regulated by the electrochemically active iron species in the clay. The lifetime of AcH+ is ca. 36 ns, whereas for AcH+ (clay), it is as fast as the instrumental response (<10 ns), indicating the clay can efficiently quench the excited acridinium, AcH+*. Moreover, a long-lived species, attributed to I2 -•, was recorded in KI solutions (pH 4) containing either AcH+ or clay/AcH+. In contrast, the transient species, presumed to be Br2 -•, was only observed in the solutions containing free AcH+. Both electrochemical and laser spectroscopic results indicated that the electron transfer between AcH+* and I- is mediated by the iron species in montmorillonite K10.