PLATELET MONOAMINE-OXIDASE-B ACTIVITY IN WORKERS EXPOSED TO STYRENE

A cross-sectional study was conducted to evaluate monoamine oxidase type B (MAO-B) activity in platelets as a biomarker of effect of styrene and perchloroethylene exposures. MAO-B is an enzyme system involved in dopamine catabolism, the impairment of which has been postulated as a mechanism of styrene-induced neurotoxicity. We previously observed an inverse association between blood styrene and MAO-B among reinforced plastics manufacturing workers. The present study included 59 male boat plant workers exposed to styrene (exposure range <1-144 ppm, 8-h TWA). Two comparison groups comprised six male dry cleaning workers exposed to perchloroethylene (PCE; exposure range <2-37 ppm) and 14 male laundry workers not exposed to either agent. Respiratory protection was not used by any of the styrene- or PCE-exposed workers; thus, air concentrations were regarded as valid exposure indicators. MAO-B activity (pmol/10(8) cells/h) was measured in peripheral blood platelets, using phenylethylamine as substrate. Only small overall mean differences in MAO-B were observed among the three groups; mean Values were 4.21, 4.51, and 4.12 for the styrene-exposed, PCE-exposed, and laundry workers, respectively. Despite the absence of gross differences among the groups, styrene exposure was inversely related to MAO-B. Mean values for four increasing exposure group quartiles were: 5.60, 4.13, 3.69, and 3.44. The Spearman rank correlation coefficient for styrene with MAO-B was -0.41. Adjustment for age, medication use, smoking, and alcohol consumption had only a minimal effect on this trend. Duration of exposure to styrene bore a weak positive relation to MAO-B (Spearman r = + 0.29), which was nearly entirely explained by collinearity with age. The results from this study are in close quantitative agreement with previous findings of an inverse association between styrene exposure and MAO-B. More agents need to be evaluated to establish specificity, and longitudinal analyses of styrene-exposed workers will be required before confident conclusions can be reached about the predictive value of MAO-B as a biomarker of styrene-related neurotoxicity.