Protection against Trp-P-2 mutagenicity by purpurin: mechanism of in vitro antimutagenesis
作者:T. Marczylo
DOI:10.1093/mutage/15.3.223
日期:2000.5.1
Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a natural pigment isolated from madder root (Rubia tinctorum) which inhibits the mutagenicity of a number of heterocyclic amines in the Ames mutagenicity test. Two effects were observed in the presence of purpurin. The rate of degradation of 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole [Trp-P-2(NHOH)] at neutral pH was increased. The major product of this purpurin-dependent degradation was identified as the parent amine 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2). Secondly, the rate of Trp-P-2 N-hydroxylation, the major route of bioactivation, by PCB-treated rat hepatic microsomes was markedly decreased. Cytochrome P450-dependent O-dealkylation of methoxy-, ethoxy- and pentoxyresorufin by these microsomes was also significantly inhibited by purpurin. The nature of this inhibition was competitive. Spectrophotometric investigations suggest no direct interaction between Trp-P-2 and purpurin. Furthermore, no evidence for Trp-P-2 binding was observed with carminic acid, a structural analog of purpurin, when it was immobilized on ω-aminohexyl agarose. Therefore, in vitro the proposed mechanism by which purpurin protects against heterocyclic amine-induced mutagenesis involves competitive inhibition of cytochrome P450-dependent bioactivation and accelerated degradation of the N-hydroxylamine to the parent amine.
紫嘌呤(1,2,4-三羟基-9,10-蒽醌)是从茜草根(Rubia tinctorum)中分离出来的一种天然色素,在艾姆斯致突变试验中可抑制多种杂环胺的致突变性。在紫丁香素的作用下,观察到两种效应。在中性 pH 值下,3-羟基氨基-1-甲基-5H-吡啶并[4,3-b]吲哚[Trp-P-2(NHOH)]的降解率增加。经鉴定,这种紫癜素依赖性降解的主要产物是母胺 3-氨基-1-甲基-5H-吡啶并[4,3-b]吲哚(Trp-P-2)。其次,经多氯联苯处理的大鼠肝脏微粒体的 Trp-P-2 N- 羟基化速率(生物活化的主要途径)明显降低。这些微粒体依赖细胞色素 P450 对甲氧基、乙氧基和戊氧基resorufin 进行的 O-脱烷基化反应也受到紫嘌呤的显著抑制。这种抑制的性质是竞争性的。分光光度法研究表明,Trp-P-2 和紫嘌呤之间没有直接的相互作用。此外,将紫嘌呤的结构类似物卡明酸固定在ω-氨基己基琼脂糖上时,也没有观察到与 Trp-P-2 结合的证据。因此,在体外,紫草素防止杂环胺诱变的拟议机制包括竞争性抑制依赖细胞色素 P450 的生物活化和加速 N-羟胺降解为母胺。