Effects of 3-tert-Butyl-4-hydroxyanisole and its hydroquinone and quinone metabolites on rat and human embryonic cells in culture.

3-tert-Butyl-4-hydroxyanisole (BHA), tert-butyl hydroquinone (BHQ), 3-tert-butyl-4,5-dihydroxyanisole (BHAOH), tert-butylquinone (BQ) and 3-tert-butyl-5-methoxy-1,2-benzoquinone (BHAoQ) were assayed using cell-culture methods for assessing potential teratogenicity. In the rat embryonic cell differentiation assay, BQ had the greatest inhibitory effect on the differentiation of both limb-bud (LB) and midbrain (MB) cells. From the dose-response curves, the concentrations of BHA, BHQ, BHAOH, BHAoQ and BQ that inhibited the production of differentiated foci by 50% (IC(50)) in LB cells were 533, 105, 25, 21 and 16 μm, respectively, and the IC(50) values for MB cells were 466, 67, 24, 18 and 14 μm, respectively. BQ also showed the most potent inhibitory action in the human embryonic palatal mesenchymal (HEPM) cell-growth assay. The concentrations of BHA, BHQ, BHAOH, BHAoQ and BQ that inhibited cell growth by 50% (IC(50)) were 244, 48, 23, 15 and 3.3 μm, respectively. Therefore in these assays, the quinone and hydroquinone metabolites of BHA showed greater teratogenic potential than did BHA itself. The inhibitory action of BHA on HEPM cell growth was greater in the presence of S-9 mix prepared using livers from rats treated with phenobarbital and 5,6-benzoflavone. In the HEPM cell-growth assay, rat (F344) S-9 was more effective in inducing the metabolic activation of BHA than was S-9 from hamsters or mice.