The novel function of a key enzyme regulating tryptophan-NAD metabolism

在体外实验中，吡啶甲酸酯与免疫系统有关。另一方面，喹啉酸盐是一种强效的神经细胞内源性兴奋毒素。α-氨基-β-羧酸盐-ε-半醛脱羧酶（ACMSD; EC 4.1.1.45）是调节色氨酸-烟酸代谢的重要酶之一。ACMSD似乎能够直接影响吡啶酸盐和喹啉酸盐的生产。本研究探讨急性免疫刺激对大鼠ACMSD活性及mRNA表达的影响。RT-PCR结果显示，对照组和lps处理组大鼠肝脏和肾脏中均有ACMSD mRNA表达，而脑、肺、脾和胸腺中均无。对照组与LPS处理大鼠ACMSD活性及mRNA水平无显著差异。此外，我们还测量了大鼠饲喂亚油酸后色氨酸分解物喹啉酸的水平。饲粮中添加10%或20%亚油酸的大鼠肝脏ACMSD mRNA被强烈抑制，血清喹啉酸显著升高。这些结果表明ACMSD活性与色氨酸转化为喹啉酸的产量呈反比关系。

Picolinate has been implicated in immune system in vitro experiments. On the other hand, quinolinate is a potent endogenous excitotoxin of neuronal cells. α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD ; EC 4.1.1.45) is one of the important enzymes regulating tryptophan-niacin metabolism. ACMSD seems to be able to influence directly the production of picolinate and quinolinate. In this study, we investigated the effect of acute immune stimulation on ACMSD activity and mRNA expression in rats. ACMSD mRNA was expressed in the liver and kidney, but not in the brain, lung, spleen and thymus by RT-PCR in control and LPS-treated groups. There were no significant difference between control and LPS treated rats in ACMSD activity and mRNA. Moreover we measured the tryptophan catabolite quinolinic acid level in rats fed on linoleic acid. In rats fed with 10 or 20% linoleic acid diet, ACMSD mRNA in the liver was strongly suppressed and serum quinolinic acid was significantly increased as compared with the rats fed on a fat-free diet. These results suggest that there is an inverse relationship between ACMSD activity and the production of quinolinic acid converted from tryptophan.