Tissue differences in the modulation of rat cytochromes P450 and phase II conjugation systems by dietary doses of phenethyl isothiocyanate

Rats were fed diets supplemented with phenethyl isothiocyanate (PEITC) at 0.06 (low dose, dietary intake level), 0.6 (medium dose) and 6.0 μmole/g (high dose), and xenobiotic-metabolising enzymes were monitored in liver, lung and kidney. At the low dose, inhibition of the hepatic O-dealkylation of ethoxy- and methoxyresorufin was noted, whereas at the high dose increases in the O-depentylation of pentoxyresorufin and O-debenzylation of benzyloxyquinoline were observed, whereas p-nitrophenol hydroxylase was inhibited. Hepatic bioactivation of 2-amino-3-methylimidazo-[4,5-f]quinoline to mutagens was not influenced by the PEITC-treatment. In the lung, at the high dose, ethoxyresorufin dealkylation was elevated and that of pentoxyresorufin suppressed; no significant changes were seen in the kidney. Quinone reductase was markedly elevated at all doses in liver, but the lung enzyme was refractive whereas in the kidney a modest rise was observed at the high dose. Hepatic glutathione S-transferase activity was stimulated by PEITC-treatment, but no effect was evident in the lung or kidney. It is concluded that the effects of PEITC on xenobiotic-metabolising systems are dose- and tissue-dependent, with the liver being the most sensitive and the lung generally resistant. Increased detoxication rather than cytochrome P450 inhibition is the likely mechanism of the chemopreventive activity of PEITC.