| Abstract: | Previous in vivo studies have shown that low-dose benzene exposure (10 to 28 ppm for 4 to 6 h) in mice can induce sister chromatid exchange (SCE) in peripheral blood B-lymphocytes and bone marrow as well as micronuclei in bone marrow polychromatic erythrocytes. Because benzene is metabolized to a variety of intermediate compounds and two of these, catechol and hydroquinone, have been reported to be potent SCE-inducers, it is possible that other known and proposed metabolites could have chromosome-damaging effects in lymphocytes. Induced SCE frequencies, mitotic indices, and cell cycle kinetics were quantitated in human peripheral blood T-lymphocytes exposed to benzene, phenol, catechol, 1,2,4-benzenetriol, hydroquinone, 1,4-benzoquinone, or trans,trans-muconic acid. Three proposed metabolites of phenol, 4,4'-biphenol, 4,4'-diphenoquinone, and 2,2'-biphenol, which can be generated by a phenol-horseradish peroxidase-hydrogen peroxide system were also examined. Benzene, phenol, catechol, 1,2,4-benzenetriol, hydroquinone, and 1,4-benzoquinone induced significant concentration-related increases in the SCE frequency, decreases in mitotic indices, and inhibition of cell cycle kinetics. Based on the slope of the linear regression curves for SCE induction, the relative potencies were as follows: catechol greater than 1,4-benzoquinone greater than hydroquinone greater than 1,2,4-benzenetriol greater than phenol greater than benzene. On an induced SCE per microM basis, catechol was approximately 221 times more active than benzene at the highest concentrations studied. trans,trans-Muconic acid had no significant effect on the cytogenetic parameters analyzed. 2,2'-Biphenol induced a significant increase in SCE only at the highest concentration analyzed, and 4,4'-biphenol caused a significant increase in SCE frequency that was not clearly concentration related. However, both 2,2'- and 4,4'-biphenol caused significant cell cycle delay and mitotic inhibition. 4,4'-Diphenoquinone caused only a significant decrease in mitotic activity. These data indicate that in addition to phenol, di- and trihydroxybenzene metabolites play important roles in SCE induction. Furthermore, the results suggest either that benzene alone can induce SCE or, a more likely possibility, that mononuclear leucocytes have a limited capability to activate benzene. |
