BIOTRANSFORMATION OF ESTRADIOL IN THE HUMAN KERATINOCYTE CELL-LINE HACAT - METABOLISM KINETICS AND THE INHIBITORY EFFECT OF ETHANOL

Purpose. The aim of our study was to investigate the kinetics of beta- estradiol (E-2) metabolism in the human keratinocyte cell line HaCaT a nd to estimate the effect of the potential inhibitor ethanol on the bi otransformation reaction. Methods. The formation rates of estrone (E-1 ) in dependence on substrate concentrations were determined in HaCaT c ells using tritium labelled E-2. Experiments were conducted with and w ithout addition of dehydroepiandrosterone (DHEA) and ethanol. Possible toxic effects on the cells due to ethanol were investigated by cytoto xicity tests. Results. The metabolism of E-2 in HaCaT cells exhibited Michaelis-Menten kinetics with K-m and V-max values of 3.5 mu M and 21 6 pmol x mg(-1) protein x h(-1), respectively. The reaction was inhibi ted by DHEA and ethanol. The alcohol showed a reversible competitive i nhibition mechanism for concentrations of 4 to 8% (v/v). Lower ethanol concentrations had no effect, whereas levels greater than or equal to 10% significantly decreased cell viability leading to a different inh ibition mechanism. Conclusions. The HaCaT cell line seems to be a suit able model for studying enzyme kinetics equivalent to the human skin. The concentration dependent inhibitory effect of ethanol observed in t his cell line may be relevant for the transdermal E-2 application in p atients.