Growth Inhibition and DNA Damage Induced by X‑Phenols in Yeast: A Quantitative Structure–Activity Relationship Study

Phenolic
compounds and their derivatives are ubiquitous constituents
of numerous synthetic and natural chemicals that exist in the environment.
Their toxicity is mostly attributed to their hydrophobicity and/or
the formation of free radicals. In a continuation of the study of
phenolic toxicity in a systematic manner, we have examined the biological
responses of Saccharomyces cerevisiae to a series of mostly monosubstituted phenols utilizing a quantitative
structure–activity relationship (QSAR) approach. The biological
end points included a growth assay that determines the levels of growth
inhibition induced by the phenols as well as a yeast deletion (DEL)
assay that assesses the ability of X-phenols to induce DNA damage
or DNA breaks. The QSAR analysis of cell growth patterns determined
by IC50 and IC80 values indicates that toxicity
is delineated by a hydrophobic, parabolic model. The DEL assay was
then utilized to detect genomic deletions in yeast. The increase in
the genotoxicity was enhanced by the electrophilicity of the phenolic
substituents that were strong electron donors as well as by minimal
hydrophobicity. The electrophilicities are represented by Brown’s
sigma plus values that are a variant of the Hammett sigma constants.
A few mutant strains of genes involved in DNA repair were separately
exposed to 2,6-di-tert-butyl-4-methyl-phenol (BHT)
and butylated hydroxy anisole (BHA). They were subsequently screened
for growth phenotypes. BHA-induced growth defects in most of the DNA
repair null mutant strains, whereas BHT was unresponsive.

酚类化合物及其衍生物广泛存在于环境中的各类合成与天然化学物质内。其毒性主要源于疏水性以及/或自由基的生成。本研究延续了酚类毒性的系统性研究工作，采用定量构效关系（quantitative structure–activity relationship, QSAR）方法，探究了酿酒酵母（Saccharomyces cerevisiae）对一系列以单取代酚类为主的化合物的生物学响应。本研究设置的生物学终点包含两类实验：其一为生长抑制实验，用于测定酚类物质诱导的生长抑制水平；其二为酵母缺失（deletion, DEL）实验，用以评估X-取代酚类诱导DNA损伤或DNA断裂的能力。基于IC50与IC80值得到的细胞生长模式的QSAR分析表明，酚类毒性符合疏水性抛物线模型。随后利用缺失实验检测酵母的基因组缺失情况：遗传毒性的增强受到酚类取代基的亲电性（强电子给体）以及低疏水性的共同促进。亲电性可由布朗σ+值表征，该参数是哈米特σ常数的变体。我们将数株参与DNA修复的基因敲除突变菌株分别暴露于2,6-二叔丁基对甲酚（2,6-di-tert-butyl-4-methyl-phenol, BHT）与丁基羟基茴香醚（butylated hydroxy anisole, BHA）中，随后对这些菌株的生长表型进行筛选。结果显示，丁基羟基茴香醚（BHA）在多数DNA修复功能缺失突变菌株中会引发生长缺陷，而2,6-二叔丁基对甲酚（BHT）则未表现出此类作用。