The effect of cigarette smoking on 7‐ethoxyresorufin O‐deethylase and other monooxygenase activities in human liver: analyses with monoclonal antibodies.

Abstract

1 Four cytochrome P-450 enzyme activities, 7-ethoxyresorufin O-deethylase (ERDE), coumarin 7-hydroxylase (CH), 7-ethoxycoumarin 0-deethylase (ECDE) and aryl hydrocarbon hydroxylase (AHH) were measured in human liver needle biopsy samples from smokers and non-smokers. Cigarette smoking was verified and quantitated by measuring plasma cotinine levels.3 Enzyme inhibitory monoclonal antibodies (MAb) to a 3-methylcholanthrene-induced (MAb 1-7-1) and phenobarbitone-induced (MAb 2-66-3) rat hepatic cytochrome P-450 were used to measure the contribution of MAb-defined, epitope-specific cytochromes P-450 to the total reaction measured for each of the above activities. 3 ERDE activity was significantly elevated in the livers of cigarette smokers, whereas AHH, CH or ECDE activities were not affected by cigarette smoking. No correlation was observed between plasma cotinine concentration and ERDE activity. 4 MAb 1-7-1 inhibited hepatic ERDE activity to a variable extent (from 0 to 65%), but had very little or no effect on AHH, CH or ECDE activities. The inhibitory effect of MAb 1-7-1 on ERDE activity was greater than 50% in the non-smokers. MAb 2-66-3 had no inhibitory effect on any of the enzyme activities studied. 5 In contrast to liver both ERDE and AHH on human placental microsomes from cigarette smokers were inhibited by MAb 1-7-1. The MAb 2-66-3 was without effect. 6 Cigarette smoking induces a form of P-450 in human liver, responsible for ERDE activity, that contains an epitope recognized by MAb 1-7-1. This form of cytochrome P-450 is insensitive to MAb 2-66-3 and is not contributing to AHH, CH or ECDE activities of human liver.

4-Hydroxylation of Debrisoquine by Human CYP1A1 and Its Inhibition by Quinidine and Quinine

“…4A). 7-ER (Pelkonen et al, 1986;Rodrigues and Prough, 1991), a putative substrate for CYP1A1, inhibited the formation of 4-hydroxydebrisoquine in a concentration-dependent manner in microsomes expressing CYP1A1 (Fig. 4B).…”

A form of cytochrome P450 in man, orthologous to form d in the rat, catalyses the O‐deethylation of phenacetin and is inducible by cigarette smoking.

“…However, it has proved more difficult to demonstrate such an effect in vitro, with microsomal fractions from human liver. Differences in hepatic aryl hydrocarbon hydroxylaste activity (which is highly inducible in rat liver by PAH) between smokers and nonsmokers are low or non-existent (Boobis et al, 1980;Pelkonen et al, 1986). In contrast, the high affinity components of the O-deethylation of both phenacetin (Kahn et al, 1985) and 7-ethoxyresorufin (Pelkonen et al, 1986) are two to three-fold greater in liver samples from smokers than in those from non-smokers.…”

“…Cigarette smoke is a complex mixture of organic and inorganic compounds, and in animals it has inducing properties similar to PAH (Uotila et al, 1977;Conney, 1982Conney, , 1986. Whereas treatment of animals with PAH results in considerable elevation of hepatic aryl hydrocarbon hydroxylase activity, such a change has never been observed in man following cigarette smoking (Boobis et al, 1980;Pelkonen et al, 1986). However, cigarette smoking does cause a profound induction of phenacetin oxidation in man determined both in vivo and in vitro (Pantuck et al, 1972(Pantuck et al, , 1974Boobis et al, 1981;Kahn et al, 1985).…”

Comparative effects of two antimycotic agents, ketoconazole and terbinafine on the metabolism of tolbutamide, ethinyloestradiol, cyclosporin and ethoxycoumarin by human liver microsomes in vitro.

“…The final substrate we used, ethoxycoumarin, is metabolised (at least at high concentrations) substantially by isozyme(s) distinct from those responsible for the metabolism of ethoxyresorufin. Thus ethoxyresorufin metabolism, but not that of ethoxycoumarin, is inhibited by an antibody to a 3-MC-induced rat hepatic cytochrome P-450 and is also increased in the livers of cigarette smokers (Pelkonen et al, 1986). Ryan et al (1984) found that ethoxycoumarin was only poorly metabolised by purified rat cytochromes P-450, g and h. It is not clear what the major isozyme(s) responsible for ethoxycoumarin dealkylation are.…”