Trichloroacetic acid: investigation into the mechanism of chromosomal damage in the in virto human lymphocyte cytogenetic assay and the mouse bone marrow micronucleus test

Trichloroacetic acid (TCA) was tested for its ability to induce chromosomal damage in cultured human peripheral blood lymphocytes and in bone marrow cells of male and female C57BL/6J f BL10/Alpk mice. Two in vino cytogenetic assays were conducted with TCA. In the first TCA, as free acid, was added to whole blood cultures at final concentrations of 500, 2000 and 3500 μg/ml in the presence and absence of an auxiliary metabolic activation system (rat liver S9-mix). Statistically significant increases in the percentage of aberrant cells compared with solvent control values were observed in cultures treated with TCA at 2000 and 5000 μg/ml. Investigation into the effects of TCA on the pH of the culture medium revealed significant reductions in pH at both these TCA concentrations. Neutralized TCA was then tested at concentrations of 500, 2 000 and 5000 μg/ml, also in the presence and absence of S9-mix. No statistically or biologically significant increases in the percentage of aberrant cells were observed in any of these cultures. In the mouse micronucleus test, neutralized TCA was administered in two equal intraperitoneal doses 24 h apart to C57BL/6J f BL10/Alpk mice (337, 675 and 1080 mg/kg in males; 405, 810 and 1300mg/kg in females). These dose levels represent 25%, 50% and 80% of the median lethal dose (MLD) in this strain of mouse. Bone marrow samples were taken 6 and 24 h after the second dose and the chromosomal damage assessed by analysis of the bone marrow for micronuclei. No statistically or biologically significant increases in the incidence of micronucleated polychromatic erythrocytes compared with the solvent control dosed animals were observed in either sex at the 6 h sampling time or in the females at the 24 h sampling time. A small but statistically significant increase in micronucleated polychromatic erythrocytes was observed in male mice 24 h after a dose of 675 mg/kg (50% MLD). Since no increases were noted at the 25 or 80% MLD, and the levels recorded are within the range of the concurrent solvent control values, the small increase observed in the males at the 50% MLD is considered not to be biologically significant. Flow cytometric studies on suspensions of isolated liver cell nuclei revealed that changes in FITC binding (indicating altered chromatin conformation) were induced by pH changes alone and were not caused by neutralized TCA. Consideration of all the data presented in this paper indicates that increase in chromosomal damage observed in human lymphocyte cultures treated with TCA is a result of pH changes inducing artefactual chromosomal damage rather than to any clastogenic effects of TCA. TCA is therefore considered not to be clastogenic when examined in the in vino human lymphocyte chromosomal aberration assay or in the mouse bone marrow micronucleus test