1. The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsomes and the effect of maternal cigarette smoking on placental 7-alkoxyquinoline metabolism was studied. 2. None of several monoclonal antibodies to isoenzymes of cytochrome P450 had a clear effect on metabolism of the compounds by liver microsomes. 3. Maternal cigarette smoking induced the O-dealkylation of all of the 7-alkoxyquinoline derivatives, being greatest for 7-butoxy- and 7-benzyloxyquinoline. 4. Placental 7-alkoxyquinoline metabolism induced by smoking was partially inhibited by the monoclonal antibody 1-7-1 raised against 3-methylcholanthrene-induced rat liver P450. 5. None of the 7-alkoxyquinoline O-dealkylations could be assigned specifically to any known P450 isoenzyme in human liver or placenta.
The role of the glutathione-dependent antioxidant system in the prooxidant-antioxidant balance support was studied in the experiments with Wistar male rat under single gamma-irradiation (8 Gr dose), fed with unbalanced (as to animal proteins and antioxidant vitamins) diet and with addition of Aronia melanocarpa. Single gamma-irradiation of animals led to the decrease of selenium-dependent glutathione-peroxidase activity in the blood plasma and glutathione-S-transferase activity decrease in rat liver mitochondria. Animals which received the unbalanced food allowance under irradiation showed more expressed change of glutathione-dependent antioxidant enzymes activity, namely--proved decrease of glutathione-peroxidase and glutathione-S-transferase activity in liver microsomes and less expressed activation of selenium-dependent glutathione-peroxidase activity in the postmitochondrial fraction of laboratory animals liver. Introduction of the A. melanocarpa food supplement in the unbalanced diet of the laboratory animals which in vitro demonstrated expressed antioxidant and antiradical activity had no effect upon glutathione-peroxidase activity in the investigated tissues. Obtained data concerning significant decrease of the activity of glutathione-dependent antioxidant system and, particularly, of the selenium-dependent glutathione-peroxidase activity under the unbalanced diet condition may be useful in maintenance of prooxidant-antioxidant balance in the tissues of irradiated animals. Allowing for the above stated it is advisable to seek for new food additives which increase activity of the endogenous glutathione-dependent antioxidant enzymes for human tolerance improvement, especially under the unbalanced food allowance condition.
The involvement of cytochrome P-450 isozymes in the activation of benzo[a]pyrene (BP) by human placental and liver microsomes was studied in vitro using monoclonal antibodies (Mab) toward the major 3-methylcholanthrene (MC)-inducible and phenobarbital-inductible rat liver P-450 isozymes (Mab 1-7-1 and Mab 2-66-3, respectively). Microsomes from human placenta and liver and rat liver were incubated with BP and DNA, and BP-diolepoxide-DNA (BPDE-DNA) adducts were measured by synchronous fluorescence spectrophotometry (SFS). The only BP metabolite giving the same fluorescence peak as chemically modified BPDE-DNA was BP-7,8-dihydrodiol. Five (smokers) out of 29 human placentas (smokers and nonsmokers), and five out of nine human livers were able to metabolically activate BP to BPDE-DNA adducts in this system. The Mab 1-7-1 totally inhibited the formation of BPDE-DNA adducts in placental microsomal incubations. Inhibition using rat or human liver microsomes was 50-60% and about 90%, respectively. The Mab 2-66-3 had no effect in any of the microsome types. Adduct formation was inhibited more strongly and at lower concentrations of Mab 1-7-1 compared with the inhibition of AHH activity. This study is a clear indication of the major role of P-450IA1 (P-450c) in human placenta and probably P-450IA2 (P-450d) in human liver in BP activation, while other isozymes also take part in the activation in rat liver. Furthermore, this clearly indicates that AHH activity and BP activation are not necessarily associated.
Placental and hepatic xenobiotic-metabolising activities were studied in smokers and non-smokers, who were classified by anamnestic interview, plasma thiocyanate and plasma cotinine determinations. Plasma thiocyanate assay is inadequate in the classification of smokers and non-smokers. Plasma cotinine levels reflect more accurately the smoking status. The anamnestic smokers remained smokers and several self-declared non-smokers proved to be smokers. On the basis of plasma cotinine determination all real smokers had higher 7-ethoxyresorufin 0-deethylase (ERDE) activities measured either in placental microsomes or liver biopsy homogenates than non-smokers. Classification based on plasma cotinine levels showed a statistically significant (P less than 0.001) difference between smokers and non-smokers in liver homogenate ERDE activity. However, cotinine levels did not correlate with any of the xenobiotic-metabolising activities tested. An objective biochemical marker, such as cotinine determination seems to be necessary when evaluating the effect of smoking on drug metabolism in man.
Studied in vitro, lipophen (in contrast to essentiale) did not separate the oxidation and phosphorylation processes in intact mitochondria. The antioxidant effect of lipophen with respect to enzymatic or ascorbate-dependent lipid peroxidation in intact microsomes from rat liver was higher by two-three orders of magnitude as compared to the effect of essentiale. In rats with a toxic hepatitis model induced by ethanol, lipophen restored the activity of mitochondria on a level characteristic of intact animals. In the case of CCl4-induced hepatitis, lipophen significantly increased the hydroxylase activity.
The effects of five calcium antagonists, verapamil, diltiazem, nifedipine, darodipine and isradipine, on rat liver microsomal drug metabolism in vitro and in vivo were studied. All compounds prolonged hexobarbital-induced sleeping time in a dose-dependent manner (doses 3.0 and 30.0 mg/kg, except nifedipine 0.3 and 3.0 mg/kg) and inhibited cytochrome P450-dependent N-demethylation of aminopyrine in vitro in rat liver microsomes. The incubation of all compounds with microsomes resulted in the apparent formation of formaldehyde, suggesting either N- or O-demethylation. Diltiazem, isradipine and darodipine gave rise to a type I spectral change. Nifedipine seemed to produce a type II spectral change. A spectrum of verapamil changed from a type I to a type II as concentration increased. These results indicate that all calcium antagonists studied interact with P450 and are in vitro inhibitors of microsomal drug metabolism in the rat and the inhibition brings out pharmacokinetic drug-drug interactions in vivo.