title: The effect of a subnormal vitamin B-6 status on homocysteine metabolism.
abstract: Homocysteine, an atherogenic amino acid, is either remethylated to methionine or metabolized to cysteine by the transsulfuration pathway. The biochemical conversion of homocysteine to cysteine is dependent upon two consecutive, vitamin B-6-dependent reactions. To study the effect of a selective vitamin B-6 deficiency on transsulfuration, we performed oral methionine load tests on 22 vitamin B-6-deficient asthma patients treated with theophylline (a vitamin B-6 antagonist) and 24 age- and sex-matched controls with a normal vitamin B-6 status. Both groups had normal circulating vitamin B-12 and folate concentrations. Methionine loading resulted in significantly higher increases in circulating total homocyst(e)ine (P < 0.01) and cystathionine (P < 0.05) concentrations in vitamin B-6-deficient patients compared with controls. 6 wk of vitamin B-6 supplementation (20 mg/d) significantly (P < 0.05) reduced post-methionine load increases in circulating total homocyst(e)ine concentrations in deficient subjects, but had no significant effect on the increase in total homocyst(e)ine concentrations in controls. The increases in post-methionine load circulating cystathionine concentrations were significantly (P < 0.01) reduced in both groups after vitamin supplementation. It is concluded that a vitamin B-6 deficiency may contribute to impaired transsulfuration and an abnormal methionine load test, which is associated with premature vascular disease.
authors.affiliation: Department of Chemistry Pathology, University of Pretoria, South Africa. jubbink@medic.up.ac.za
authors.forename: J B
authors.initials: JB
authors.lastname: Ubbink
authors.forename: A
authors.initials: A
authors.lastname: van der Merwe
authors.forename: R
authors.initials: R
authors.lastname: Delport
authors.forename: R H
authors.initials: RH
authors.lastname: Allen
authors.forename: S P
authors.initials: SP
authors.lastname: Stabler
authors.forename: R
authors.initials: R
authors.lastname: Riezler
authors.forename: W J
authors.initials: WJ
authors.lastname: Vermaak
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001249:Asthma / Q000188:drug therapy; D001993:Bronchodilator Agents / Q000627:therapeutic use; D003540:Cystathionine / Q000097:blood; D005260:Female; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism*; D008875:Middle Aged; D011736:Pyridoxine / Q000494:pharmacology*; D013806:Theophylline / Q000627:therapeutic use; D026681:Vitamin B 6 Deficiency / Q000139:chemically induced / Q000378:metabolism*
chemical_list: D001993:Bronchodilator Agents; D006710:Homocysteine; D003540:Cystathionine; D008715:Methionine; D013806:Theophylline; D011736:Pyridoxine