Dose-dependent genotoxic effects of styrene on human blood lymphocytes and the relationship to its oxidative and metabolic effects.

Although the genotoxic potential of styrene is known, very limited information is available regarding its dose-dependent genotoxic response to human blood lymphocytes and how such response correlates with different metabolic events in whole blood lymphocytes. The present study was therefore carried out to study such a relationship using in vitro human blood lymphocytes from healthy volunteers. To study genotoxic response to styrene, sister chromatid exchanges (SCEs), cell cycle, and cell survival were analyzed. Lymphocytes were cultured for 72 hr in the presence of different concentrations of styrene (0-1,000 microM). Twenty-four hr before harvest, BrdU (5 micrograms/ml) was added to assess the increase in SCEs and cell cycle delay. Both the SCE frequency and the cell cycle length were increased linearly with increasing concentrations of styrene up to 200 microM, without addition of any exogenous metabolizing system. Above 200 microM, no further increase in genotoxic response occurred. The range of concentrations (10-200 microM) at which increase of cell cycle length due to styrene was observed did not impair the viability of the cells, suggesting that such cell cycle delay is a genotoxic-related event and not caused by cytotoxicity. In vitro metabolic transformation of styrene in whole-blood lymphocyte cultures without the presence of any exogenous metabolic activation system showed the formation of a reactive intermediate, styrene 7,8-oxide, to be capacity-limited, as verified from a nonlinear increase in the formation of styrene glycol. The value of such metabolic parameter reached a plateau above 200 microM styrene. The same phenomenon of saturation has also been observed with regard to other metabolic effects due to styrene in whole blood lymphocytes in culture, such as dose-dependent increase in lipid peroxidation and depletion of blood lymphocyte glutathione. Based on the relationship between the formation of different metabolic events and the genotoxicity of styrene, it may be possible that the genotoxic properties of styrene in human blood lymphocytes may be mediated initially not only by the formation of the presumably reactive styrene 7,8-oxide, but also by that of a reactive oxygen species as well. However, the present data are not sufficient enough to definitely identify the role of reactive oxygen species in such toxicity and therefore it warrants further study.