Benzoyl peroxide cytotoxicity evaluated in vitro with the human keratinocyte cell line, RHEK-1.

The human keratinocyte cell line, RHEK-1, was used to evaluate the cytotoxicity of benzoyl peroxide (BZP). As determined with the neutral red (NR) cytotoxicity assay, the 24-h midpoint (NR50) toxicity values, in mM, were 0.11 for BZP and 29.5 for benzoic acid, the stable metabolite of BZP. Irreversible cytotoxicity occurred after a 1-h exposure to 0.15 mM BZP and greater. When exposed to BZP for 7 days, a lag in growth kinetics was first observed at 0.06 mM BZP. Damage to the integrity of the plasma membrane was evident, as leakage of lactic acid dehydrogenase occurred during a 4-h exposure to BZP at 0.05 mM and greater. Intracellular membranes were also affected, as extensive vacuolization, initially perinuclear but then spreading throughout the cytoplasm, was noted in BZP-stressed cells. The generation of reactive free radicals 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 hypersensitive to a subsequent challenge with BZP; lipid peroxidation by BZP was inducible in the presence of Fe2+; and cells previously maintained in a medium amended with vitamin E, an antioxidant, were more resistant to BZP, showed less lipid peroxidation in the presence of BZP+Fe2+ and did not develop the extensive intracellular vacuolization as compared to non-vitamin E maintained cells.

An in vitro study on the cytotoxicity of chlorhexidine digluconate to human gingival cells.

Chlorhexidine digluconate is the active ingredient in mouthrinses used to prevent dental plaque and gingivitis. The in vitro cytotoxicity of chlorhexidine was evaluated with the Smulow-Glickman (S-G) gingival epithelial cell line. The potency of chlorhexidine was dependent on the length of exposure and composition of the exposure medium. The midpoint cytotoxicity values for 1-, 24-, and 72-h exposures were 0.106, 0.011, and 0.0045 mmol/L, respectively. S-G cells exposed for 2 h to chlorhexidine and then maintained for 48 h in chlorhexidine-free medium were unable to recover from the initial insult. The adverse effects of chlorhexidine on the plasma membrane were suggested by the leakage of lactic acid dehydrogenase from chlorhexidine-treated S-G cells and by the increased permeability of chlorhexidine-treated liposomes to Ca2+. The toxicity of a 24-h exposure to chlorhexidine to the S-G cells was progressively lessened as the content of fetal bovine serum (FBS) in the exposure medium was increased from 2% to 8%. The potency of a 1-h exposure to chlorhexidine was reduced in medium amended with albumin, lecithin, and heat-killed Escherichia coli. These reductions in toxicity were presumably due to the binding of the cationic chlorhexidine to the negatively charged chemical moieties of the components of FBS and of albumin and lecithin and of sites on the surfaces of bacteria. Combinations of chlorhexidine and carbamide peroxide were additive in their cytotoxicities.