Estrogenic activity of alkylcyclohexanones and alkylcyclohexanols in rainbow trout estrogen receptor binding and liver slices Vtg mRNA expression assays.

Alkylcyclohexanones and alkylcyclohexanols are industrial chemicals produced in large volumes. Little is known regarding the estrogenic activity of these chemicals in aquatic species. A series of para-alkyl substituted hexanones and hexanols with varying chain length and branching were tested in a suite of in vitro rainbow trout binding assays and in an ex vivo rainbow trout liver slice/vitellogenin (Vtg) expression assay to assess estrogenic potential. Furthermore, the extent of biotransformation of these chemicals under test conditions was monitored. Cyclohexane, cyclohexanol, and 4-ethylcyclohexanol had no detectable estrogenic activity in these assays. Para substituted alkylcyclohexanones and alkylcyclohexanols with side chains containing three to six carbons were active in both assays. Alkylcyclohexanones and alkylcyclohexanols with other than para substitution were also estrogenic when tested in these assays. The binding affinity relative to estradiol in cytosol of active chemicals was low, ranging from 0.0016% to 0.000029%. Biotransformation of alkylcyclohexanones to alkylcyclohexanols occurred in the cytosol binding assay and in the liver slice assay, thus making those exposures a mixture of alcohol and ketone forms. Biotransformation did not occur in rainbow trout nuclear extract and recombinant binding assays; thus, the exposure in these assays was to only the dosed chemical. Both alkylcyclohexanones and alkylcyclohexanols bound to the estrogen receptor in these metabolically limited assays. Significant induction of Vtg mRNA expression was seen in slice exposed to chemicals with measurable binding affinities. Often the induction levels were below maximum efficacy and occurred at concentrations slightly lower than toxic concentrations. Therefore, while these chemicals produced an estrogenic effect, it is considerably weaker than that of the endogenous hormone and occurred at concentrations close to those which produce toxicity.