Lin P H, Nakamura J, Yamaguchi S, Upton P B, La D K, Swenberg J A
Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina, Chapel Hill, NC 27599-7400, USA.
Carcinogenesis. 2001 Apr;22(4):627-34. doi: 10.1093/carcin/22.4.627.
DNA damage induced by quinoid metabolites of pentachlorophenol (PCP), i.e. tetrachloro-1,4-benzoquinone (Cl(4)BQ) and tetrachlorohydroquinone (Cl(4)HQ), was investigated in calf thymus DNA. The (32)P-post-labeling assay revealed four major and several minor adducts (3.5 adducts per 10(5) total nucleotides) that were produced in calf thymus DNA treated with Cl(4)BQ (5 mM). These DNA adducts were chemically stable even after conditions that induce thermal depurination and are unlikely to undergo depurination/depyrimidination to form apurinic/apyrimidinic (AP) sites. In addition, increases in 8-hydroxy-deoxyguanosine (8-HO-dG) (5 8-HO-dG per 10(5) nucleotides) and AP sites (0.5 AP sites per 10(5) nucleotides) were observed in Cl(4)BQ-modified calf thymus DNA. Further investigation indicated that in the presence of Cu(II) and NADPH, low concentrations of Cl(4)BQ (1 microM) induced a doubling of 8-HO-dG (10 8-HO-dG per 10(5) nucleotides) and dramatic increases in AP sites (20 AP sites per 10(5) nucleotides) and DNA single-strand breaks. The types of DNA damage induced by Cl(4)HQ plus Cu(II) were similar to those by Cl(4)BQ plus Cu(II) and NADPH, whereas catalase inhibited the formation of DNA damage. These data suggest that oxidative damage is causally involved in the formation of AP sites. Concentration-dependent increases in 8-HO-dG induced by Cl(4)HQ plus Cu(II) and Cl(4)BQ plus Cu(II) and NADPH were correlated with the formation of AP sites (r(2) = 0.977) with a ratio of 8-HO-dG to AP sites at 1:1.6. The AP site-cleavage assay confirmed that approximately 85% of the AP sites induced by Cl(4)HQ and Cu(II) were detected as 5'-cleaved AP sites. Since hydrogen peroxide alone causes similar DNA damage, these results suggest the involvement of Cu(II) and hydrogen peroxide in the induction of oxidative DNA damage by Cl(4)HQ/Cl(4)BQ. The data demonstrate that PCP quinone and hydroquinone induce direct and oxidative base modifications as well as the formation of 5'-cleaved AP sites in genomic DNA. These lesions may have important implications for PCP clastogenicity and carcinogenicity.
研究了五氯苯酚（PCP）的醌类代谢物，即四氯-1,4-苯醌（Cl(4)BQ）和四氯对苯二酚（Cl(4)HQ）对小牛胸腺DNA的损伤。(32)P后标记分析显示，用Cl(4)BQ（5 mM）处理的小牛胸腺DNA产生了四种主要加合物和几种次要加合物（每10(5)个总核苷酸有3.5个加合物）。这些DNA加合物即使在诱导热脱嘌呤的条件下仍具有化学稳定性，不太可能发生脱嘌呤/脱嘧啶形成无嘌呤/无嘧啶（AP）位点。此外，在Cl(4)BQ修饰的小牛胸腺DNA中观察到8-羟基脱氧鸟苷（8-HO-dG）（每10(5)个核苷酸有5个8-HO-dG）和AP位点（每10(5)个核苷酸有0.5个AP位点）增加。进一步研究表明，在Cu(II)和NADPH存在下，低浓度的Cl(4)BQ（1 microM）可使8-HO-dG增加一倍（每10(5)个核苷酸有10个8-HO-dG），AP位点（每10(5)个核苷酸有20个AP位点）和DNA单链断裂显著增加。Cl(4)HQ加Cu(II)诱导的DNA损伤类型与Cl(4)BQ加Cu(II)和NADPH诱导的相似，而过氧化氢酶可抑制DNA损伤的形成。这些数据表明氧化损伤与AP位点的形成有因果关系。Cl(4)HQ加Cu(II)和Cl(4)BQ加Cu(II)和NADPH诱导的8-HO-dG浓度依赖性增加与AP位点的形成相关（r(2)=0.977），8-HO-dG与AP位点的比例为1:1.6。AP位点切割分析证实，Cl(4)HQ和Cu(II)诱导的AP位点中约85%被检测为5'-切割的AP位点。由于单独的过氧化氢会导致类似的DNA损伤，这些结果表明Cu(II)和过氧化氢参与了Cl(4)HQ/Cl(4)BQ诱导的氧化性DNA损伤。数据表明，PCP醌和对苯二酚可诱导基因组DNA发生直接和氧化性碱基修饰以及5'-切割的AP位点的形成。这些损伤可能对PCP的致断裂性和致癌性具有重要意义。
