The objective of this study was to identify the possible role of stem cell and myeloperoxidase (MPO) in the metabolic activation of styrene, hydroquinone and trichloroethylene, by investigating the effects of stem cell from umbilical cord blood and MPO on the frequency of sister chromatid exchange (SCE) and micronuclei (MN) induction in cultured human peripheral lymphocytes exposed to these chemicals.

Isolated lymphocytes from whole blood were cultured for 72 hours. The cells were treated with 1.50 mM styrene, 50 microM hydroquinone and 1.50 mM trichloroethylene dissolved with acetone (30 microl in total volume) at 24 hours after the beginning of culture. Control group was treated with acetone only. Immediately after adding these chemicals, 1.3X1 06 cells/ml and 2.6X1 06 cells/ml stem cell or 1.0 and 2.0 unit MPO with H2O2 (for substrate) were added to the cultures. Slides were stained with Giemsa's solution, and acridine orange for sister chromatid exchange, and for micronucleus analysis, respectively.

The results were as follows: 1) Myeloperoxidase and stem cell did not significantly affect the frequencies of SCE or MN in the control group. 2) The frequency of SCE or MN with exposure to styrene did not different from control in the absence of stem cell or MPO. Sister chromatid exchange induced by styrene was significantly increased by adding stem cell or MPO in dose-dependent relationship. The frequency of MN induced by styrene significantly increased in the presence of 2.0 unit MPO. 3) The frequency of SCE was significantly increased with exposure to hydroquinone than acetone treated control in the absence of stem cell or MPO. Sister chromatid exchange induction by hydroquinone significantly increased dose-dependently in the presence of stem cell or MPO. There was a tendency of increase of the MN frequency induced by hydroquinone in the presence of stem cell or MPO, but not significant. 4) It was found that trichloroethylene itself did not increase SCE or MN frequency. Frequency of SCE induced by trichloroethylene was significantly increased with adding stem cell (low and high) and 2.0 unit MPO. Even though stem cell or MPO increased the frequency of MN of lymphocyte exposed to trichloroethylene, the difference was not significant.

Authors found that the frequencies of both sister chromatid exchange and micronucleus induced by styrene, hydroquinone, and trichloroethylene were increased significantly with the treatment of stem cell or myeloperoxidase. It was suggested that myeloperoxidase may therefore play an important role in the metabolic activation of styrene, hydroquinone, and trichloroethylene and myeloperoxidase probably be involved in the myelotoxicity of these chemicals.