ENZYMES INVOLVED IN THE BIOACTIVATION OF 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE IN PATAS MONKEY LUNG AND LIVER-MICROSOMES

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent tobac co-specific carcinogen in animals, Our previous studies indicated that there are differences between rodents and humans for the enzymes invo lved in the activation of NNK. To determine if the patas monkey is a b etter animal model for the activation of NNK in humans, we investigate d the metabolism of NNK in patas monkey Lung and liver microsomes and characterized the enzymes involved in the activation, In lung microsom es, the formation of 4-oxo-1-(3-pyridyl)-1-butanone (keto aldehyde), e thylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanone (NNK-N-oxide), 4-hyd roxy-1-(3-pyridyl)-1-butanone (keto alcohol), and 4-(methylnitrosamino )-1-(3-pyridyl)-1-butanol (NNAL) was observed, displaying apparent K-m values of 10.3, 5.4, 4.9, and 902 mu M, respectively, NNK metabolism in liver microsomes resulted in the formation of keto aldehyde, keto a lcohol, and NNAL, displaying apparent K-m values of 8.1, 8.2, and 474 mu M, respectively, The low K-m values for NNK oxidation in the patas monkey lung and Liver microsomes are different from those in human lun g and liver microsomes showing K-m values of 400-653 mu M, although lo ss of low K-m forms from human tissue as a result of disease, surgery or anesthesia cannot be ruled out, Carbon monoxide (90%) significantly inhibited NNK metabolism in the patas monkey lung and liver microsome s by 38-66% and 82-91%, respectively, Nordihydroguaiaretic acid (a lip oxygenase inhibitor) and aspirin (a cyclooxygenase inhibitor) decrease d the rate of formation of keto aldehyde and keto alcohol by 10-20% in the monkey lung microsomes, alpha-Napthoflavone and coumarin markedly decreased the oxidation of NNK in monkey lung and liver microsomes, s uggesting the involvement of p450s 1A and 2A6. An antibody against hum an P450 2A6 decreased the oxidation of NNK hy 12-16% and 22-24% in the patas monkey lung and liver microsomes, respectively, These results a re comparable to that obtained with human lung and liver microsomes. C oumarin hydroxylation was observed in the patas monkey lung and liver microsomes at a rate of 16 and 4000 pmol/min/mg protein, respectively, which was 5-fold higher than human lung and liver microsomes, respect ively, Immunoblot analysis demonstrated that the P450 2A level in the individual patas monkey liver microsomal sample was 6-fold greater tha n in an individual human liver microsomal sample. Phenethyl isothiocya nate, an inhibitor of NNK activation in rodents and humans, decreased NNK oxidation in the monkey lung and liver microsomes displaying inhib itor concentration resulting in 50% inhibition of the activity (IC50) values of 0.28-0.8 mu M and 4.2-6.8 mu M, respectively, The results de monstrate the similarities and differences between species in the meta bolic activation of NNK, The patas monkey microsomes appear to more cl osely resemble human microsomes than mouse or rat enzymes and may bett er reflect the activation of NNK in humans.