Ubbink J B, van der Merwe A, Delport R, Allen R H, Stabler S P, Riezler R, Vermaak W J
Department of Chemistry Pathology, University of Pretoria, South Africa.
J Clin Invest. 1996 Jul 1;98(1):177-84. doi: 10.1172/JCI118763.
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.
同型半胱氨酸是一种致动脉粥样硬化氨基酸，它可通过再甲基化作用转化为蛋氨酸，或通过转硫途径代谢为半胱氨酸。同型半胱氨酸向半胱氨酸的生化转化依赖于两个连续的、维生素B6依赖的反应。为了研究选择性维生素B6缺乏对转硫作用的影响，我们对22名接受茶碱（一种维生素B6拮抗剂）治疗的维生素B6缺乏哮喘患者和24名年龄及性别匹配、维生素B6状态正常的对照者进行了口服蛋氨酸负荷试验。两组的循环维生素B12和叶酸浓度均正常。与对照组相比，蛋氨酸负荷导致维生素B6缺乏患者的循环总同型半胱氨酸（P < 0.01）和胱硫醚（P < 0.05）浓度显著升高。对缺乏维生素B6的受试者补充6周维生素B6（20 mg/d）可显著（P < 0.05）降低蛋氨酸负荷后循环总同型半胱氨酸浓度的升高，但对对照组总同型半胱氨酸浓度的升高无显著影响。补充维生素后，两组蛋氨酸负荷后循环胱硫醚浓度的升高均显著（P < 0.01）降低。结论是，维生素B6缺乏可能导致转硫作用受损和蛋氨酸负荷试验异常，这与过早发生的血管疾病有关。
