In Vivo and in Vitro Interaction of 1,2-Dichlorobenzene with Nucleic Acids and Proteins of Mice and Rats

Micronuclei induction and chromosomal aberrations in Rattus norvegicus by chloroacetic acid and chlorobenzene

Chloroacetic acid (CAA) and chlorobenzene (CB) have been evaluated for in vivo mutagenic potential in Rattus norvegicus, employing the following criteria : (i) chromosomal aberrations (CAs) such as breaks, gaps, exchanges, rings, and multiple aberrations and (ii) micronuclei (MN) induction. Three sublethal doses, 0.008, 0.01, and 0.012 mg/g b. wt. of CAA and 0.75, 1.0, and 1.25 mg/g b. wt. of rat of CB were administered and the bone marrow cells evaluated in each of the three treated groups at 12, 24, and 48 h, respectively. Mean MN frequencies of 4.40+/-0.2 and 5.42+/-0.3, obtained respectively for CAA and CB. The higher induction of MN by CAA and CB was dose- and time-dependent. Most significant impact (P<0.05) for either of the compounds was observed at 24h post administration, when the recorded mean frequency of CAs was maximum for CAA (4.33+/-0.6) as well as for CB (4.66+/-0.5).

Cytochrome P450 catalyzed oxidation of monochlorobenzene, 1,2- and 1,4-dichlorobenzene in rat, mouse, and human liver microsomes

We studied metabolism of monochlorobenzene (MCB), 1,2-dichlorobenzene (1,2-DCB) and 1,4-DCB in liver microsomes from untreated male and female Wistar rats and B6C3F1 mice or in those after the induction of CYP3A or 2E1 as well as in human male liver microsomes. MCB and 1,2-DCB were oxidised mainly by rat and human CYP2E1. It was found that 1,4-DCB was oxidised by rat and human CYP2E1 at a several-fold lower rate than 1,2-DCB, but a greater part to covalently binding products. In contrast to previous studies showing rat CYP3A1 as the main CYP form oxidising both DCBs, our experiments indicate only a certain role of rat and human CYP3A in MCB, 1,2-DCB and 1,4-DCB oxidation to covalently bound products. The relative roles of human liver CYP2E1 and 3A4 in the metabolism of 1,4-DCB seem to be individually different. Metabolic rates of MCB, 1,2-DCB and 1,4-DCB correlated with CYP2E1 immunochemical level in microsomes from 11 different human livers and with metabolic rates of CYP2E1 substrates. These rates in different human livers were up to 10-fold different and were generally several-fold higher than those in untreated rats or mice. Metabolic activation of MCB and 1,2-DCB to products binding covalently to microsomal proteins and to calf-thymus DNA, respectively, mostly corresponded to production of water-soluble metabolites. Significant species and sex differences in the oxidation of MCB, 1,2-DCB and 1,4-DCB were reflected in a markedly higher oxidation in male mice than male rats and higher oxidation in male than female mice. The formation of covalently bound products generally corresponded to production of soluble metabolites, but female rats formed significantly less covalently bound products of 1,4-DCB (and also of 1,2-DCB and MCB) than male rats and mice of both sexes, in possible reflection of the fact that 1,4-DCB is not carcinogenic in female rats despite its carcinogenicity for male rats and both sexes of mice.

Demonstration of chlorobenzene-induced DNA damage in mouse lymphocytes using the single cell gel electrophoresis assay

The DNA damaging effect of chlorobenzene was investigated in peripheral lymphocytes and bone marrow cells from C57BL/6 female mice using a gel electrophoresis assay for DNA from single cells ('the single cell gel electrophoresis assay') under alkaline conditions. The effect of chlorobenzene was studied both after single and repeated intraperitoneal injections of 750 mg/kg body weight. The cytostatic agent cyclophosphamide (150 mg/kg, i.p.) was used as a reference substance, and vehicle-treated mice as controls. DNA damage was recorded 16 h after the (last) injection, using an automated computerized image analysis system specifically designed for the single cell gel electrophoresis assay. There was evidence of chlorobenzene-induced DNA damage after 3 days of repeated exposure in peripheral lymphocytes, but no indications of such an effect in bone marrow cells. Cyclophosphamide induced significant damage to DNA both in bone marrow cells and lymphocytes, the effect being most pronounced in the latter cells. It is concluded that high-dose exposure to chlorobenzene is associated with genotoxicity to peripheral lymphocytes. However, this solvent is apparently not a major hazard to bone marrow cells, even after repeated high-dose exposure.