INHIBITION OF THE CONVERSION OF PRE-INTERLEUKINS-1-ALPHA AND 1-BETA TO MATURE CYTOKINES BY P-BENZOQUINONE, A METABOLITE OF BENZENE

Chronic exposure of humans to benzene causes severe bone marrow cell d epression leading to aplastic anemia. Marrow stromal macrophage dysfun ction and deficient interleukin-1 production has been reported for pat ients with severe aplastic anemia. The stromal macrophage, a target of benzene toxicity, is involved in hematopoietic regulation through the synthesis of several cytokines including interleukin-1, which is requ ired for production by stromal fibroblasts of a number of cytokines re quired for the survival of hematopoietic progenitor cells. We have pre viously demonstrated that hydroquinone, a major toxic metabolite of be nzene in marrow, prevents the proteolytic conversion of 31 kDa pre-int erleukin-1 alpha to the 17 kDa cytokine by calpain in purified murine stromal macrophages. Furthermore, stromal macrophages from benzene-tre ated mice produce the 31 kDa pre-interleukin-1 alpha when stimulated i n culture with endotoxin, but cannot convert the precursor to interleu kin-1 alpha. In this report, we show that 1,4-benzoquinone, the oxidat ion product of hydroquinone in the cell, causes a concentration-depend ent inhibition of highly purified human platelet calpain with an IC50 of 3 mu M. Hydroquinone also inhibits the processing of pre-interleuki n-1 beta by interleukin-1 beta convertase, The addition of 2 mu M hydr oquinone to B1 cells that undergo autocrine stimulation by interleukin -1 beta resulted in the cessation of autocrine cell. growth and interl eukin-1 beta secretion into the culture medium, as determined by Weste rn immunoblots of the culture supernatants, Purified converting enzyme treated with 3 mu M benzoquinone was incapable of converting 31 kDa r ecombinant pre-interleukin-1 beta to the 17 kDa mature cytokine as ana lyzed by polyacrylamide gel electrophoresis and Western immunoblotting . These findings support our observations in a mouse model that benzen e-induced bone marrow cell depression results from a lack of interleuk in-1 alpha subsequent to an inhibition by benzoquinone of calpain, the protease required for converting pre-interleukin-1 alpha to active cy tokine. The results may provide a basis for studying benzene-induced a plastic anemia in a mouse model.