Two sensitive in vitro tests have been developed to determine the toxicity of chemicals applied to full-thickness skin explants from fresh human surgical specimens and sacrificed guinea pigs and rabbits. Before incubation, dinitrochlorobenzene (DNCB), sulfur mustard, or resorcinol was topically applied to the exposed top surface of each explant. The explants were then organ-cultured for 24 hr in shallow Petri dishes. Toxicity to skin was assessed by two methods. The first was histologic and morphometric. Paranuclear vacuoles in the basal epidermal cells were counted microscopically in tissue sections prepared from the cultured ex-plants. The number of these vacuoles was found to increase with the toxicant concentration, in the range from low to full toxicity. The DNCB (0.5% caused fewer vacuoles in guinea pigs than in the other two species. Resorcinol (50% caused more vacuoles in rabbits than in the other two species. Control skin explants (normal skin and skin exposed only to diluents) contained very few paranuclear vacuoles. Examination of these vacuoles under the electron microscope suggests they might be blebs in the cell's nuclear membrane. The second method to assess skin toxicity was biochemical and functional. The toxicant-exposed skin explants were cultured in the presence of [14C]leucine for 24 hr, along with unexposed explants and with explants exposed to the diluents. The incorporation of [14C]leucine into the proteins of the skin explants was found to decrease as above with the toxicant concentration. These tests for in vitro toxicity to skin proved to be the most sensitive and reliable among the various histochemical and biochemical tests for lysosomal and oxidative enzymes that we performed.
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