BENZOYL PEROXIDE CYTOTOXICITY EVALUATED IN-VITRO WITH THE HUMAN KERATINOCYTE CELL-LINE, RHEK-I

The human keratinocyte cell line, RHEK-1, was used to evaluate the cyt otoxicity of benzoyl peroxide (BZP). As determined with the neutral re d (NR) cytotoxicity assay, the 24-h midpoint (NR(50)) toxicity values, in mM, were 0.11 for BZP and 29.5 for benzoic acid, the stable metabo lite of BZP. Irreversible cytotoxicity occurred after a I-h exposure t o 0.15 mM BZP and greater, When exposed to BZP for 7 days, a lag in gr owth kinetics was first observed at 0.06 mM BZP, Damage to the integri ty of the plasma membrane was evident, as leakage of lactic acid dehyd rogenase occurred during a 4-h exposure to BZP at 0.05 mM and greater. Intracellular membranes were also affected, as extensive vacuolizatio n, initially perinuclear but then spreading throughout the cytoplasm, was noted in BZP-stressed cells. The generation of reactive free radic als from BZP was suggested by the following: the intracellular content of glutathione was lowered in cells exposed to BZP; cells pretreated with the glutathione-depleting agent, chlorodinitrobenzene, were hyper sensitive to a subsequent challenge with BZP; lipid peroxidation by BZ P was inducible in the presence of Fe2+; and cells previously maintain ed in a medium amended with vitamin E, an antioxidant, were more resis tant to BZP, showed less lipid peroxidation in the presence of BZP + F e2+ and did not develop the extensive intracellular vacuolization as c ompared to non-vitamin E maintained cells.