Niilo T. Kärki

Comparison of activities of drug‐metabolizing enzymes in human fetal and adult livers

The in vitro capacity of human fetal liver to metabolize 3,4‐benzpyrene, aniline, aminopyrine, and hexobarbital was lower than that of human adult liver from patients with uncomplicated cholelithiasis. Fetal liver drug‐metabolizing capacity, expressed as percentages of adult values, was 2.4, 27.8, 32.0, and 36.1 per cent, respectively, for the four substrates studied. Cytochrome P‐450 content and nicotinamide adenine dinucleotide phosphate (NADPH)—cytochrome c reductase activity in fetal liver microsomes also reflected the lower drug‐metabolizing activity, being 27.4 and 49.2 per cent, respectively, of adult values. Microsomal protein content was about 26 mg per gram wet weight in fetal liver and about 35 mg per gram in adult liver. Recovery of microsomes was 40% to 60% in both fetal and adult livers. All parameters studied exhibited considerable variation, which ranged from three‐ to elevenfold. Fetal drug metabolism, although generally lower than in the adult, may, in some cases, be higher than maternal drug metabolism.

Effect of maternal cigarette smoking on 3,4-benzpyrene and N-methylaniline metabolism in human fetal liver and placenta☆

Abstract The effect of maternal cigarette smoking on the metabolism of 3,4-benzpyrene (BP) and N -methylaniline (MA) was studied in human fetal liver and placenta. Maternal cigarette smoking apparently had no effect on fetal hepatic drug metabolism. Placentas from smokers, unlike those from nonsmokers, were able to metabolize BP both in the first half of pregnancy and at term. The critical duration of gestation for the appearance of the effect of cigarette smoking seemed to be about 10–11 wk. Metabolism of MA by placental homogenates was very low during the pregnancy, and maternal cigarette smoking had no effect on it. No correlation was established between the level of BP hydroxylase activity in the fetal liver and the level of BP hydroxylase activity in the placenta of the same mother. The fetal hepatic and placental BP hydroxylase systems were shown to differ in their response to maternal cigarette smoking, their subcellular location and their kinetic characteristics.

Cytochrome P-450-linked monooxygenase system and drug-induced spectral interactions in human liver microsomes

Summary Human liver microsomes isolated from operation biopsy samples from patients with cholelithiasis or a malignant disease, were studied with respect to a drug-oxidizing monooxygenase system. The human liver contained about 30-40 mg of microsomal protein per gram of wet weight and about 50% of that was recovered in the microsomal fraction. The mean levels of cytochrome P-450, NADPH-cytochrome c reductase and cytochrome b5 in the livers of cholelithiatic patients were essentially similar to those in the livers of rat and guinea pig and only slightly lower than those in the rabbit liver. The cytochrome P-450-carbon monoxide difference spectrum exhibited a peak at 450 nm and, in microsomes from several smokers, no peak shift to 448 nm was evident. Studies with ethyl isocyanide as a ligand revealed a typical difference spectrum with a peak ratio at pH 7.4 of 455/430 nm of 0.46 and a pH intercept of at about 7.9. There was no correlation between cigarette smoking and a peak ratio. Drug-induced interactions of type I (SKF 525A, bromobenzene), type II (aniline, n-octylamine, KCN) and reverse type I (phenacetin, n-butanol) variety were detected in liver samples studied. Hexobarbital and aminopyrine gave either type I or reverse type I spectral changes. The spectral dissociation constant for aniline was of the same order of magnitude as in rat liver microsomes. These studies seem to indicate that although qualitative differences between hepatic monooxygenase systems in man and laboratory animals may exist, available evidence suggests that many essential differences are only quantitative in nature.

Metabolism of polycyclic hydrocarbons by a highly active aryl hydrocarbon hydroxylase system in the liver of a trout species

Summary In sharp contrast to earlier beliefs, some fish (trout) liver-microsomes are highly capable of metabolizing benzo(α)pyrene. The hydroxylating system is a typical monooxygenase system in many respects when compared with the mammalian system, needing oxygen and NADPH for full activity. The trout liver-microsomes convert benzo(α)pyrene to dihydrodiols and hydroxymetabolites at a rate 5 to 10 times higher than the male rat liver-microsomes, when measured per mg of microsomal protein. The trout liver-microsomes metabolize benzo(α)pyrene 15 to 30 times as fast as the male rat liver-microsomes if the activity is measured per unit of cytochrome P-450 and NADPH-cytochrome c reductase.

Effect of physicochemical and pharmacokinetic properties of barbiturates on the induction of drug metabolism.

Abstract In searching for possible determinants of the ability of compounds to induce microsomal drug metabolizing enzymes we studied relationships between the relative inducing activity of eleven barbiturates and their lipid solubility and pharmacokinetic behaviour. Allyl derivatives of barbituric acid were poor inducers regardless of their lipid solubility or half-life. The ability of other barbiturate derivatives to induce drug metabolism was directly related to biological half-life or time/concentration area value and inversely correlated to lipid solubility. The results suggest that the ability of a given compound to induce drug metabolism is not only related to lipid solubility and pharmacokinetic characteristics but also to the nature of chemical groups present in the molecule.

Maternal cigarette smoking, placental aryl hydrocarbon hydroxylase and neonatal size

Abstract Aryl hydrocarbon hydroxylase (AHH) activity was determined in placental samples from smokers and non-smokers. The offspring from pregnancies in which placental AHH was elevated weighed about 400 g less and were over 1 cm shorter than those from non-smoking mothers, whereas those from AHH-negative pregnancies were of the same size as those from non-smoking mothers. It is suggested that placental AHH be used as a measure of foetal exposure to maternal cigarette smoking.

Induction of aryl hydrocarbon hydroxylase in human fetal liver cell and fibroblast cultures by polycyclic hydrocarbons

Abstract Cells originating from the human fetal liver and grown as a primary monolayer culture for 4 to 11 days contain an enzyme system that metabolizes benzo(α) pyrene. The basal level of the enzyme varied about three-fold. The activity was increased from 1.4- to 5.1-fold by the exposure of cells for 24 hours to benz(α) anthracene, the magnitude of increase depending on the amount of inducer, on the individual cell batch studied and on the stage of cell growth. Also 3-methylcholanthrene, but not benzo(α)pyrene, induced the enzyme activity in fetal liver cell cultures at concentrations used. Fibroblast cultures derived from the human fetal lung or skin exhibited less benzo(α)pyrene metabolism and the inducibility of the enzyme activity was less marked than in hepatic cell cultures.

Genetic and Environmental Regulation of Aryl Hydrocarbon Hydroxylase in Man: Studies with Liver, Lung, Placenta, and Lymphocytes

Properties and response smoking of aryl hydrocarbon hydroxylase (AHH) activity in various human tissues are reviewed. In the placenta, induction of AHH by smoking can be demonstrated unequivocally. AHH activity in lung samples is variable, but the relation to current or past smoking is unclear. The effect of cigarette smoking can be readily shown in the rate of antipyrine elimination, although there is no change in AHH activity in liver biopsy samples. The reason for this discrepancy is not known. In peripheral lymphocytes a sort of “memory-effect” of cigarette smoking is retained even after culturing, the nature of this phenomenon remaining unclear. Furthermore, there seem to be many factors affecting AHH induction in peripheral lymphocytes in culture. These data suggest that regulation of AHH activity and induction is tissue-specific, i.e. no systemic regulation is discernible. It is also possible that the P-450 isozyme composition in some tissues masks the induction. Reasons for discrepancies between animal and human data are not clear; however, genuine biological differences and technical difficulties in human studies can be postulated.

Cerebrospinal fluid and serum transaminases and lactic dehydrogenase after head injury.

It is well known that central nervous tissue contains much glutamic oxaloacetic transaminase (G.O.T.), less lactic dehydrogenase (L.D.H.) and only little glutamic pyruvic transaminase (G.P.T.) (Cohen 1951, Wroblewski h LaDue 1955). Experimental cerebral infarction in laboratory animals has been demonstrated to increase serum and cerebrospinal fluid G.O.T. activity (Wakim et al. 1956). Clinical observations also show that serum and cerebrospinal fluid G.O.T. and L.D.H. activities increase in some neurological diseases and cerebral infarctions (Fleisher et al. 1957, Green et al. 1957, Mellick h Bassett 1964). The purpose of the present study was to determine whether there are any changes in cerebrospinal fluid and sernm G.O.T., G.P.T. and L.D.H. activities after traumatic head injuries.

Dose-dependent effects of medroxyprogesterone acetate on the hepatic drug-metabolizing enzyme system in rats

Abstract The activity of the hepatic microsomal drug metabolism was examined in vitro in rats pretreated with 10–600 mg/kg medroxyprogesterone acetate intraperitoneally daily for seven days. In both sexes there was a significant increase in the liver weight, amount of cytochrome P-450, activity of NADPH-cytochrome c reductase, benzo[ a ]pyrene hydroxylase and 2,5-diphenyloxazole hydroxylase. The increase in 7-ethoxycoumarin- O -deethylase activity was also significant in female rats, but not in male rats. In the female rats pretreated with medroxyprogesterone acetate, the ability of α-naphtho-flavone and SKF 525A to inhibit benzo[ a ]pyrene hydroxylase was decreased and slightly increased, respectively. The results show that medroxyprogesterone acetate has a dose-dependent inducing effect on the hepatic drug metabolism in rats. Female rats seem to be more sensitive to the inducing effect of medroxyprogesterone acetate than the males. The characteristics of medroxyprogesterone acetate induction resemble mostly those caused by phenobarbital and pregnenolone-16α-carbonitrile.