Mutagenic activity of structurally related oxiranes and siloranes in Salmonella typhimurium

Ring-opening molecules like oxiranes (epoxides) maybe suitable for the development of non-shrinking dental composite materials. Since oxiranes are reactive molecules, they can cause adverse biological effects in living organisms. The introduction of siloranes, a merger of silane and oxirane, may solve this problem. Here, new oxiranes and siloranes were analyzed for the induction of mutations in Salmonella typhimurium (TA97a, TA98, TA100, and TA102), and a reactive oxirane molecule served as a reference. This chemical, epoxy cyclohexyl methyl-epoxy cyclohexane carboxylate (Est-Ep) tested positive in S. typhimurium TA100. The numbers of mutants were about 3-10-fold higher than controls in the presence of a metabolically active S9 fraction isolated from rat liver. Only a weak mutagenic effect was observed after direct testing (without S9). Di(cyclohexene-epoxidemethyl)ether (Eth-Ep) also caused a slight increase of mutant numbers in TA100 both in the presence and absence of S9. In contrast, no effects were detected with the large oxirane molecules, 2,2-bis(4,1-phenylenoxy-3,1-propanediyl-3-oxatricyclo [3.2.1.0(2,4)]octylcarboxy) propylidene (Nor-BP-Ep) and 2,2-bis(4,1-phenylenoxy-3,1-propanediyl-3,4-epoxycyclo-hexylcarboxylic-acid) propylidene (Est-BP-Ep). As to the siloranes, 1,4-bis(2,3-epoxypropyloxypropyl-dimethylsilyl)-benzene (Phen-Glyc) was a direct mutagen in S. typhimurium TA100 and TA102. This weak but dose-related increase of revertants was even enhanced by S9. Other siloranes, like di-3,4-epoxy cyclohexylmethyl-dimethyl-silane (DiMe-Sil), methyl-bis[2-(7-oxabicyclo[4.1.0]hept-3-yl)phenyl silane (Ph-Sil), and 1,3,5,7-tetrakis(ethyl cyclohexane epoxy)-1,3,5,7-tetramethyl-cyclotetrasiloxane (TET-Sil) tested negative in all S. typhimurium strains. All compounds will be further analyzed for the formation of chromosomal aberrations in mammalian cell cultures.