Effect of the benzene metabolite, hydroquinone, on interleukin-1 secretion by human monocytes in vitro

Decreased interleukin-1 (IL-1) production by mononuclear phagocytes has been shown to contribute to benzene myelotoxicity in animals. The study presented here was designed to examine the relevance of this mechanism in humans. Fresh human blood monocytes were exposed to 0.001-10 microM hydroquinone (HQ) and assessed for their ability to release IL-1 alpha and IL-1 beta in response to a stimulation with endotoxin. Both cytokines were measured by specific ELISA. Exposure of human monocytes to micromolar concentrations of HQ for 2 hr resulted in a dose-dependent reduction of IL-1 secretion. For both IL-1 alpha and IL-1 beta, the decreases were statistically significant at concentrations of 5 microM and above. HQ also inhibited RNA and protein synthesis in a dose-dependent manner, with 50% inhibitory concentrations of 21 +/- 11 and 10 +/- 9 microM, respectively. Furthermore, monocytes treated with 5 microM HQ also displayed a reduced total protein content when compared with control cells. These data suggest that the reduction of IL-1 production caused by HQ results from a global impairment of monocyte essential functions such as transcription or translation. Taken as a whole, our results support a mechanism whereby HQ may contribute to the myelotoxicity of benzene in humans by inhibiting the production by mononuclear phagocytes of cytokines involved in the regulation of hematopoiesis.