Embryotoxic effects of salicylates: role of biotransformation

The three major metabolites of salicylate, o- hydroxyhippurate ( salicylglycine , salicyluric acid), 2,5-dihydroxybenzoate (gentisic acid), and 2,3-dihydroxybenzoate, were examined for their capacities to elicit dysmorphogenesis, embryolethality , and growth retarding effects in an embryo culture system. The effects were compared with those produced by the parent salicylate. At the highest concentrations tested (1.9 mM), none of the three metabolites produced significant increases in the number of malformed embryos or in embryolethality . At the same concentration, all three agents reduced crown-rump lengths and somite numbers slightly but significantly (p less than 0.01), and the dihydroxy metabolites also reduced the embryonic protein content (p less than 0.01). In contrast, the parent salicylate produced large increases in embryolethality ( embryolethality in controls was 6% or less) and malformed embryos at equivalent or lower concentrations. Preincubation of the parent salicylate with various biotransforming systems did not affect embryotoxicity significantly. The most rapid biotransformation of salicylate in vitro was achieved with mitochondrial preparations of monkey kidney as the enzyme source but quantities metabolized were not sufficient to prevent malformations in the culture system. Increased serum protein concentration in the culture medium, however, markedly reduced the capacity of added salicylate to cause malformations. An examination of the kinetics of the dysmorphogenic effects of parent salicylate indicated that 5 hr of exposure elicited nonsignificant increases in numbers of malformations. A significant malformation rate was produced by 9 hr of exposure. In contrast, effects on embryonic growth parameters and embryolethality were greatest after a 24-hr exposure period. The results strongly suggest that the parent salicylate, rather than generated metabolites, was primarily or solely responsible for the malformations observed and that the duration of exposure of embryos to unmetabolized salicylate may be the critical factor for determining teratogenic outcome.