CHLOROPHYLLIN IS BOTH A POSITIVE AND NEGATIVE MODIFIER OF MUTAGENICITY
CHLOROPHYLLIN IS BOTH A POSITIVE AND NEGATIVE MODIFIER OF MUTAGENICITY
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DOI：
10.1093/mutage/7.5.349
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发表时间：
1992-09-01
期刊：
影响因子：
2.7
通讯作者：
JENSSEN, D
中科院分区：
文献类型：
--
作者：
ROMERT, L;CURVALL, M;JENSSEN, D
利用不同作用机理的诱变化合物，包括单官能团烷基化试剂N-甲基-N‘-亚硝脲和乙基甲烷磺酸盐，与烟草制品有关的亚硝胺，即二甲基亚硝胺、N-亚硝基烟碱和4-(N-methyl-N-nitrosoamino)-1-(3-pyridinyl)-2-butanone，研究了叶绿素的诱变机理。多环芳烃(PAH)苯并[a]芘(B[a]P)及其两种代谢物，即(-)-7β，8α-二羟基-7，8-二氢苯并[a]芘(7，8-二醇)和(+)-7β，8α-二羟基-9α，10α-氧基-7，8，9，10-四氢苯并[a]芘(BPDE)；以及一种复杂的诱变剂混合物，瑞典润口鼻烟的提取物和亚组分(SMOS)。用Ames沙门氏菌/微粒体法(STY)和HPRT V79点突变试验(V79)检测其致突变性。在STAT试验中，叶绿素对亚硝胺致突变性的影响是复杂的。在NNN或NNK存在的情况下，低浓度的叶绿素实际上增强了2倍的诱变性。然而，在较高的但仍然无毒的浓度下，叶绿素降低了这两种化合物的致突变性。在含有DMN的V79测定系统中，对叶绿素的剂量-反应关系也是相同的，尽管其影响要弱得多。用另一种卟啉化合物氯化高铁血红素取代氯代海林，进一步证实了与STY的结果。相反，胆绿素是一种不含中心金属离子的卟啉结构，不能增强NNK的致突变性。这些发现表明，叶绿素干扰了电子传递，这一发现进一步支持了这一发现，即在叶绿素存在的情况下，葡萄糖-6-磷酸可以从生物激活的NADPH产生的S9混合物中排除，而不会改变诱变性。MNU或EMS的致突变性在两种方法中均未受到影响，这与亚硝胺致突变性的改变可能涉及代谢活化的假设是一致的。用B[a]P和BPDE在STY法和V79法用7，8-二醇和BPDE进一步研究了叶绿素的增强作用。结果表明，无毒水平的叶绿素能完全抑制两种体系中三种化合物的致突变性。低浓度的叶绿素对多环芳烃的诱变没有促进作用。由于增强只与亚硝胺发生，我们认为，叶绿素特异性地干扰催化DMN-脱甲基酶活性的细胞色素P450的形式。SMOS与多环芳烃混合物的研究结果与多环芳烃相似，表明这些提取物的主要致突变活性不是由亚硝胺引起的。到目前为止，关于叶绿素发挥抗突变活性的机制还只有一些推测。清除自由基或抑制代谢激活，以及由于与代谢激活的诱变剂或未激活的前体形成络合物而导致的失活，都已被提出。我们得出结论，叶绿素有几种作用机制，包括与多环芳烃形成络合物而产生的抗突变活性；对单官能性烷基化试剂没有影响；以及最后，干扰特定形式的细胞色素P450的电子传递。
The mechanism responsible for the modification of mutagenicity by chlorophyllin has been investigated using mutagenic compounds with different mechanisms of action, including the monofunctional alkylating agents, N-methyl-N'-nitrosourea (MNU) and ethylmethanesulphonate (EMS); nitrosamines related to tobacco products, i.e. dimethyl-nitrosamine (DMN), N-nitrosonornicotine (NNN) and 4-(N-methyl-N-nitrosoamino)-1-(3-pyridinyl)-2-butanone (NNK); the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P) and two of its metabolites, i.e. (-)-7beta,8alpha-dihydroxy-7, 8-dihydrobenzo[a]pyrene (7,8-diol) and (+)-7beta,8alpha-dihydroxy-9alpha, 10alpha-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE); and a complex mutagenic mixture, an extract and subfractions of Swedish moist oral snuff (SMOS). Mutagenicity was monitored with the Ames Salmonella/microsome assays (STY) and hprt V79 point mutation assay (V79). The effects of chlorophyllin on the mutagenicity of the nitrosamines in the STY assays were found to be complex. In the presence of either NNN or NNK, low concentrations of chlorophyllin actually potentiated the mutagenicity >2-fold. However, at higher, but still non-toxic concentrations, chlorophyllin decreased the mutagenicity of both compounds. The same type of dose - response relationship for chlorophyllin was indicated in the V79 assay system with DMN, although the effect was much weaker. The results with STY were further confirmed by replacing chlorohylin with another porphyrin compound, hemin. In contrast, biliverdin, a porphyrin structure without the central metal ion, was unable to potentiate the mutagenicity of NNK in STY. These findings suggest that chlorophyllin interferes with electron transport, which was further supported by the finding that glucose-6-phosphate can be excluded from the bioactivating NADPH-generating S9 mixture in the presence of chlorophyllin without altering the mutagenicity. The mutagenicity of MNU or EMS was not influenced in either of the assays, which is consistent with the hypothesis that the modification of nitrosamine mutagenicity may involve changes in metabolic activation. The potentiating effect of chlorophyllin was further investigated using both B[a]P and BPDE in the STY assay and 7,8-diol and BPDE in the V79 assay. The results show a complete supression of the mutagenicity of all three compounds in both systems by non-toxic levels of chlorophyllin. There was no enhancement of PAH-induced mutations with low concentrations of chlorophyllin. Since enhancement only occurs with nitrosamines we suggest that chlorophyllin specifically interferes with the form of cytochrome P450 catalyzing DMN-demethylase activity. Findings with the complex mixtures SMOS were similar to these with PAH, indicating that the major mutagenic activity in these extracts is not caused by nitrosamines. To date, only speculations, about the mechanism by which chlorophyllin exerts its antimutagenic activity have been presented. Scavenging of radicals or supression of metabolic activation, as well as inactivation due to complex formation with either the metabolically activated mutagen or a non-activated precursor, have all been suggested. We conclude that chlorophyllin has several mechanisms of action, including anti-mutagenic activity arising from complex formation with PAH; no effect on monofunctional alkylating agents; and, finally, interference with electron transport to a specific form of cytochrome P450.