Investigation of liver binding of pentachlorophenol based upon measurement of protein adducts

Pentachlorophenol, polychlorodibenzodioxin and polychlorodibenzofuran in eggs from hens exposed to contaminated wood shavings

Laying hens may be exposed to pentachlorophenol (PCP) present in bedding materials derived from treated timber. As a result, this chemical and its contaminants or degradation products, such as polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs), may be present in eggs. The litter-to-eggs transfer and depletion of these compounds were studied in a flock of laying hens reared on contaminated wood shavings. PCP determination was carried out via high resolution gas chromatography coupled to low resolution mass spectrometry/mass spectrometry (HRGC-LRMS/MS); PCDDs and PCDFs were quantified by HRGC-HRMS (SIM). After substitution of the litter contaminated with PCDDs and PCDFs at an average of 50 pg WHO-TE g(-1) and with PCP at 15 microg g(-1), pooled eggs from six selected hens were sampled twice a month for the depletion study. At steady state, PCDDs and PCDFs showed a transfer ratio of 0.9; for PCP it was 0.03. PCP concentration in eggs (500 ng g(-1) whole weight) fell sharply the second week after exposure withdrawal; for PCDDs and PCDFs (47 pg WHO-TE g(-1) fat, at day 0), the overall TEQ half-life was estimated at an average of 3.8 weeks. Due to differences in toxicokinetics (a faster depletion), PCP does not appear to be a suitable marker of PCDD and PCDF violative levels. However, the prominent analytical contribution of H(7)CCD and O(8)CCD in the contamination profile may help to trace the source of contamination. Among congeners, 2,3,7,8 T(4)CDF exhibited a different depletion pattern, indicating a possible mechanism of active transport.

Characterization of metabolic activation of pentachlorophenol to quinones and semiquinones in rodent liver

Pentachlorophenol (PCP), a widely used biocide, induces liver tumors in mice but not in rats. Metabolic activation of PCP to chlorinated quinones and semiquinones in liver cytosol from Sprague-Dawley rats and B6C3F1 mice was investigated in vitro (1) with microsomes in the presence of either beta-nicotinamide adenine dinucleotide phosphate (NADPH) or cumene hydroperoxide (CHP), (2) with CHP in the absence of microsomes, and (3) with horseradish peroxidase (HRP) and H2O2. Mono-S- and multi-S-substituted adducts of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) and Cl4-1,2-BQ and their corresponding semiquinones [i.e. tetrachloro-1,4-benzosemiquinone (Cl4-1,4-SQ) and tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ)] were measured by gas chromatography-mass spectrometry (GC-MS). Qualitatively, the metabolites of PCP were the same in both rats and mice for all activation systems. Induction of PCP metabolism by either 3MC or PB-treated microsomes was observed in NADPH- but not in CHP-supported systems. In rats, the amount of induction was comparable with either 3MC or PB. 3MC was a stronger inducer than PB in mice and also induced a greater amount of metabolism than in rats. This suggests that induction of specific P450 isozymes may play a role in the toxicity of PCP to mice. Both HRP/H2O2 and CHP led to production of the full spectrum of chlorinated quinones and semiquinones, confirming the direct oxidation of PCP. CHP (with or without microsomes) converted PCP into much greater quantities of quinones and semiquinones than did microsomal P450/NADPH or HRP/H2O2 in both species. This implies that, under conditions of oxidative stress, endogenous lipid hydroperoxides may increase PCP metabolism sufficiently to enhance the toxicity and carcinogenicity of PCP.

Dosimetry of chlorinated quinone metabolites of pentachlorophenol in the livers of rats and mice based upon measurement of protein adducts

The dosimetry of chlorinated quinones arising from metabolism of pentachlorophenol (PCP), in the livers of male Sprague-Dawley rats and B6C3F1 mice was investigated via measurements of cysteinyl protein adducts and estimates of the second-order reaction rate constants between the quinones and the proteins. We had previously shown that adducts of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) and tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ) were observed at the highest levels in the livers of Sprague-Dawley rats to which PCP had been administered by gavage (5-40 mg/kg body wt) (Biomarkers 1, 232-243, 1996). In the current study we observed that adducts of Cl4-1,4-BQ and tetrachloro-1,2-benzoquinone (CL4-1,2-BQ) were predominant in the livers of B6C3F1 mice receiving 20 mg PCP/kg body wt. The second-order rate constants, representing in vitro reactions between Cl4-1,2-BQ and Cl4-1,4-BQ and various cysteine residues of hepatic proteins of liver cytosol and liver nuclei, were estimated to be 0.012-1.96 L(g protein)(-1) hr(-1) in rats and 0.082-1.67 L(g protein)(-1) hr(-1) in mice. The estimated tissue doses of the quinones to liver cytosol decreased in the order rat Cl4-1,4-BQ > mouse Cl4-1,4-BQ > mouse Cl4-1,2-BQ and to liver nuclei in the order mouse Cl4-1,2-BQ > mouse Cl4-1,4-BQ > rat Cl4-1,4-BQ. The corresponding doses of Cl4-1,2-SQ could not be inferred due to our inability to estimate the second-order rate constants. After aggregating the estimated contributions of all quinone species, mice had a fourfold greater dose to liver nuclei than rats, whereas rats had a threefold greater dose to liver cytosol. The increased nuclear dose to mouse liver compared to that of the rat suggests that the mouse is at greater risk to hepatic DNA damage from PCP-derived quinones. Investigation of the time course of levels of unconjugated tetrachlorohydroquinone (Cl4HQ) in the livers indicated that about 0.4% of Cl4HQ was oxidized to Cl4-1,4-BQ in both rats and mice.