Aryl hydrocarbon (benzo[a]pyrene) mono-oxygenase activity in human primary amnion cell cultures

Abstract

Amnion cells were isolated from placenta at term of healthy women and grown in monolayer cultures. The amnion cells formed dense sheets of cells of epithelial appearance after several days of growth. To evaluate these cells as targets for xenobiotics which have to be metabolically activated we have investigated their level and inducibility of the primary drug-metabolizing enzyme, aryl hydrocarbon (benzo[a]pyrene) mono-oxygenase (AHM). Amnion cells were found to contain very low levels of AHM which were highly inducible by addition of benz[a]anthracence to the growth medium. The inducibility of the enzyme was greatest during the first days of culture and declined by about two-thirds during the 5th and 8th day. After addition of the inducer, AHM activity increased several fold within 3 hr and reached a maximum at 16–24 hr. The culture age had no significant effect on the time course of induction. Constitutive and benz[a]anthracene-induced AHM were strongly inhibited by 7,8-benzoflavone suggesting that amnion cells in culture contain predominantly a cytochrome P-448-dependent mono-oxygenase form. Induced AHM activities in cultured amnion cells from 13 healthy donors ranged from 0.6 to 8.0 pmole of phenolic benzo[a]pyrene products/ min/ mg protein. The results indicate that primary amnion monolayer cultures offer a valuable model to study in human epithelial cells the activation and inactivation of cytotoxic and mutagenic substances which are metabolized by cytochrome P-448-dependent mono-oxygenase(s).