Testicular Injury to Rats Fed on Soybean Protein-Based Vitamin B12-Deficient Diet Can Be Reduced by Methionine Supplementation

Abstract

SummaryWe have previously reported that rats fed on a vitamin B 12 (B 12 )-deficient diet containing 180 g soybean protein per kg diet showed marked histologic damage in their testes. In this paper, we report the effect of B 12 -deficiency on B 12 -dependent methionine synthase in the rats' testes and the effect of methionine supplementation of the diet on testicular damage. Rats were fed the soybean protein-based B 12 -deficient diet for 120 d. We confirmed that those rats were in serious B 12 -deficiency by measuring urinary methylmalonic acid excretion and B 12 content in tissues. Methionine synthase activity in the testis of the B 12 -deficient rats was less than 2% of that in B 12 -supplemented (control) rats. To complement disrupted methionine biosynthesis, methionine was supplied in the diet. A supplement of 5 g D,L-methionine per kg diet to the B 12 -deficient diet did not affect urinary methylmalonic acid excretion of B 12 -deficient rats. The testicular histology of rats fed the methioninesupplemented B 12 -deficient diet was almost indistinguishable from that of control rats. Thus, we conclude that the lowered testicular methionine synthase activity is the primary cause of the histologic damage due to B 12 -deficiency and that methionine supplementation to the diet can reduce the damage. These findings would indicate the importance of the methionine synthase activity, especially for testicular function. Key Words vitamin B 12 -deficiency, rat, testis, methionine synthase In mammals, vitamin B 12 (B 12 ) acts as a cofactor for two enzymes, methylmalonyl-CoA mutase and methionine synthase. Adenosylcobalamin is required for methylmalonyl-CoA mutase, which catalyzes a reaction that interconverts succinyl-CoA and methylmalonylCoA. Dysfunction of methylmalonyl-CoA mutase causes methylmalonic aciduria. Methylcobalamin (MeB 12 ) binding to methionine synthase serves as an intermediary in methyl transfer from methyltetrahydrofolate to homocysteine, donating the methyl group to homocysteine to form methionine, and then accepting a methyl group from methyltetrahydrofolate to form tetrahydrofolate. Methionine synthase is important both to resynthesize methionine and to metabolize methyltetrahydrofolate. Tetrahydrofolate accepts C1-groups from serine or formate. Then, the C1-group can be donated to either homocysteine to form methionine or deoxyuridine monophosphate to form deoxythymidine monophosphate. The C1-group also is precursor in de novo purine biosynthesis. Methionine is one of the amino acids that are building blocks for protein. In addition, methionine is activated to S -adenosylmethionine (AdoMet), which is well known as a major methyldonor for numerous substrates and an allosteric regulator for methylenetetrahydrofolate reductase (MTHFR) and cystathionine-␤ -synthase. While causal of symptoms related with dysfunction of methionine synthase, such as megaloblastic anemia and neuropathy, might be explained by the "Methyl trap" hypothesis ( 1-4 ), the biochemical mechanism has not yet been fully understoo...

Vitamin B12 deficiency in Caenorhabditis elegans results in loss of fertility, extended life cycle, and reduced lifespan

“…Furthermore, methionine is one of the amino acid building blocks of protein and acts as the universal methyl group donor ( S ‐adenosylmethionine) for a large number of methylation reactions. Yamada et al [29] reported that reduced testicular MS activity is the primary cause of pathological impairment of spermatogenesis owing to B 12 deficiency and that methionine supplementation to the diet can reduce this impairment. Bennet [30] has reported that B 12 deficiency may lead to recurrent fetal death owing to the elevated Hcy levels.…”

Vitamin B₁₂ Supplement Exerts a Beneficial Effect on the Seminiferous Epithelium of Cimetidine-Treated Rats

“…In cases of vitamin B 12 deficiency, the metabolic conversion is not performed and homocysteine levels are elevated in the blood [Yamada et al, 2007]. Therefore, to verify if the treatment with cimetidine leads to vitamin B 12 deficiency, plasma concentrations of vitamin B 12 and total homocysteine were evaluated by electrochemiluminescence and chemiluminescence assays, respectively (São Lucas Clinical and Microbiological Laboratory).…”

“…Vitamin B 12 stimulates DNA synthesis, contributing to cellular division [Beck et al, 1965;Oh and Brown, 2003]. In the testis, vitamin B 12 has demonstrated to play a role in the maintenance of testicular functions [Hata et al, 2002;Webster et al, 2005;Yamada et al, 2007]. In vitamin B 12 -deficient rodents, testicular pathological disorders have been demonstrated, such as significant reduction of testis weight, atrophy of the seminiferous tubules and aplasia of spermatids and sperm [Kawata et al, 1992[Kawata et al, , 1997[Kawata et al, , 2004.…”

Change of Epigenetic Control of Cystathionine Beta-Synthase Gene Expression through Dietary Vitamin B₁₂ Is Not Recovered by Methionine Supplementation

“…C and CM group rats received 1 g of cyanocobalamin (Wako Pure Chemicals) per day by oral administration. The composition of experimental diets was previously described [9,11] . At the end of the breeding period, blood was collected from the hearts of rats under anesthesia, and the liver was removed.…”