Metabolites of benzo(a) pyrene produced by placental microsomes from cigarette smokers and nonsmokers

The expression and environmental regulation of P450 enzymes in human placenta

The human placenta oxidizes several xenobiotics, although the spectrum of substrates and metabolic activities when compared with the liver appears somewhat restricted. Maternal cigarette smoking or PCB exposure increases the expression of CYP1A1. This induced activity is able to catalyze the activation of benzo(a)pyrene (B(a)P) into DNA-bound products, both in vitro and in vivo. Studies on adult human liver bolster the concept that CYP1A1 and -1A2 are differentially expressed in hepatic and extrahepatic tissues. Studies with cDNA probe or enzyme specific antibodies and substrates for CYP2A, -2B, -2C, -2D, and -2E gene products have yielded negative results. There are only minimal activities that can be found in substantial quantities in placentas without maternal smoking; one example is 7-ethoxycoumarin O-deethylase (ECOD). Aromatase and cholesterol side-chain cleaving P450 mRNAs, proteins, and activities are measurable in human placentas and do not seem to be affected by maternal cigarette smoking.

Placental aryl hydrocarbon hydroxylase activity and placental calcifications

Induction of aryl hydrocarbon hydroxylase (AHH) activity in the placenta as a result of maternal exposure to polycyclic aromatic hydrocarbons contained in cigarette smoke has been well documented. Furthermore, calcifications are more prevalent in the placentas of pregnant smokers than in those of non-smokers. The present study examines whether this latter relationship could be explained by the induction of AHH activity in the placenta. AHH levels were determined at birth in 141 unselected pregnant women admitted for delivery. Macroscopic placental examination was performed for vascular lesions, abnormalities of placental shape, of the cord and parameters of placental maturity such as basal and parenchymatous calcifications. Significant increases in the prevalence of calcifications of the placental basal plates and parenchyma with the induction of placental AHH were found. A similar significant association between smoking and AHH activation was also observed. These findings remained unchanged when controlling for smoking status assessed both by questionnaire and presence of cotinine in mother's urine. Moreover, the apparent association between smoking 'factor' and calcifications disappeared when controlling for AHH induction. Therefore, the association between smoking and placental calcifications previously related could be mediated by the AHH induction.

Immunohistochemical detection of human placental cytochrome P-450-associated mono-oxygenase system inducible by maternal cigarette smoking

Several xenobiotic-metabolizing mono-oxygenase activities, in conjunction with the immunohistochemical localization of the respective cytochrome P-450 forms, were investigated in placentae from smoking and non-smoking women. The antibodies used in the immunohistochemical analyses were monoclonal antibodies (MAbs) 1-7-1 and 2-66-3, prepared against the 3-methylcholanthrene-induced and phenobarbital-induced rat liver P-450, respectively. The mono-oxygenase activities were higher in placental microsomes from smokers, although no difference was observed in microsomal P-450 content. A distinct positive staining with MAb 1-7-1 was detectable in the trophoblastic layer of all placentae from smokers. In placentae from non-smokers, minimal cytoplasmic staining was observed in large villi in a few trophoblastic cells. The staining reaction was negative when MAb 2-66-3 or non-specific antibody were used. These results demonstrate that maternal cigarette smoking induces in the trophoblastic layer of the placenta a cytochrome P-450 form which is detectable immunohistochemically with the monoclonal antibody to 3-methylcholanthrene-inducible P-450 in rat liver.

The effect of maternal smoke exposure on the ultrastructure of fetal peripheral blood vessels in the mouse

Ultrastructural changes have been found in umbilical blood vessels, placental blood vessels, and peripheral blood vessels of human fetuses whose mothers smoked during pregnancy. This study was undertaken to determine if similar changes could be found in peripheral blood vessels of mice fetuses whose mothers were exposed to cigarette smoke during pregnancy. Breeding mice of the C57BL/KsJ strain were placed in a smoking box similar to that described by Younoszai and exposed to cigarette smoke intermittently. This produces carbon monoxide levels in the adult mice similar to that found in human adults smoking one pack of cigarettes per day. Similarly caged mice of the same strain were used as controls. The female mice were not removed from their cage from pre-conception time until after delivery. Upon delivery each pup was sacrificed via neck fracture and the entire pup was immersed in a solution of 2.5% glutaraldehyde in 0.1 M cacodylate buffer at pH 7.3. While still under solution, the rear leg muscles were dissected free, sliced, and immersed in the same preservative for four to five hours. They were then placed in fresh 2.5% glutaraldehyde mixture overnight. The tissues were post-fixed in osmium ferrocyanide and en-block stained with uranyl acetate in a graded series of alcohol. The tissues were infiltrated with and embedded in Spurr. Sections were taken via an ultramicrotome and post-stained with uranyl acetate and lead citrate. The sections were examined in a Philips 201 electron microscope at 60 KV. In the peripheral vessels of the fetuses from smoke-exposed mothers, endothelial blebbing (both surface-type and vacuole-type) was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent induction of human placental mono-oxygenase activity by previous dietary exposure to polychlorinated biphenyls and their thermal degradation products

Placental tissues were obtained from women in Taiwan who had ingested rice oil contaminated with aromatic polychlorinated hydrocarbons 3-4 years before conception. Known contaminants in the rice oil were polychlorinated biphenyls and their thermal degradation products, including polychlorinated dibenzofurans and polychlorinated quaterphenyls. Placental homogenates showed large increases in mono-oxygenase enzymes, including aryl hydrocarbon hydroxylase, 7-ethoxycoumarin O-de-ethylase, and diol, quinone, and phenolic metabolites of benzo(a)pyrene (analysed by high performance liquid chromatography). The findings suggest that exposure to these widespread, environmental pollutants may exert substantial and persistent metabolic effects.

Population distribution of placental benzo(a)pyrene metabolism in smokers

Human placental microsomes isolated from term placentas derived from nonsmoking women and women smoking 1 to 40 cigarettes a day were analyzed for the metabolism of benzo(a)pyrene measured as various metabolites by HPLC and/or as aryl hydrocarbon hydroxylase (AHH)6 activity. In accordance with other reports, AHH activity was several times higher in smokers than in nonsmokers. Regression analysis on 13 different placental tissues from women smoking from 1 to 40 cigarettes demonstrated a high correlation (r = 0.8 to 0.9) between AHH activity (or the formation of benzo(a)pyrene phenols resolved by HPLC) versus the formation of the procarcinogenic benzo(a)pyrene-7,8-diol. Subsequent studies on placentas derived from 67 women who smoked 10 to 40 cigarettes per day demonstrated a definite dose-response relationship between AHH activity and the number of cigarettes smoked/day. The dose-response curve was sigmoidal in shape; however, when the data were plotted on a semi-log scale the curve assumed a linear shape, reaching saturation of AHH induction beyond 20 to 25 cigarettes/day. While mean AHH activity was dependent upon the number of cigarettes smoked/day, considerable interindividual variability in AHH (ranging more than 1,000-fold in some cases) was observed among individuals with comparable smoking histories, i.e. smoking the same number of cigarettes. Population distribution suggested clustering of the population in the low-AHH-activity region while cord-blood thiocyanate analysis and twin studies suggested that genetic factors contributed to a major portion of the inter-individual variability in AHH activity observed among smokers.

Placental toxicology

A review is presented of the literature concerning the placenta as a target organ for chemical- and drug-induced injuries that can ultimately lead to teratogenesis or reproductive defects. Such defects can result from the effects of xenobiotics on placental transport, blood flow or pathology, from the metabolism by the placenta of xenobiotics to harmful substances, or from the alteration by xenobiotics of placental endocrine function. Although it is clear that drug- or chemical-induced placental toxicity should be considered as a possible mechanism of teratogenicity, it is an area of research that has been comparatively neglected and is in need of extensive investigation.

Influence of liver disease and environmental factors on hepatic monooxygenase activity in vitro

The effects of liver disease and environmental factors on hepatic microsomal cytochrome P-450 content, NADPH-cytochrome c reductase (reductase) activity and aryl hydrocarbon hydroxylase (AHH) activity have been simultaneously investigated in 70 patients undergoing diagnostic liver biopsy. The activity of reductase was not significantly affected by the presence of liver disease or any of the environmental factors studied. Cytochrome P-450 content decreased with increasing severity of liver disease whereas AHH activity was only significantly reduced in biopsies showing hepatocellular destruction. None of the parameters of monooxygenase activity varied significantly with the age or sex of the patients. Alcohol excess was associated with decreased cytochrome P-450 content and AHH activity and this effect was independent of the histological status of the biopsy. Both high caffeine intake and cigarette smoking increased AHH activity in the absence of any change in cytochrome P-450 content. There was a positive correlation between the number of meat meals eaten per week and cytochrome P-450 content. Chronic treatment with enzyme-inducing anticonvulsants appeared to increase both cytochrome P-450 content and AHH activity. Despite differential effects of liver disease and environmental influences on cytochrome P-450 content and AHH activity there was a highly significant correlation between the two parameters. The results of the present study correlate well with the known effects of disease and environment on drug metabolism in vivo.

Unusual patterns of benzo[a]pyrene metabolites and DNA-benzo[a]pyrene adducts produced by human placental microsomes in vitro

Human placental microsomes were incubated with [3H]benzo[a]pyrene (BP) and Salmon sperm DNA and the resulting metabolite-nucleoside complexes resolved by Sephadex LH-20 chromatography. The metabolite pattern was analyzed by high-pressure liquid chromatography (HPLC). The incubates were also co-chromatographed with extracts obtained from incubates with rat liver microsomes and [14C] BP. Phenols, quinones and 7,8-dihydrodiol were detected in the placental incubates. Both 9,10- and 4,5-dihydrodiols were very low as compared with control rat liver samples. Placental microsomes catalyzed the binding of BP metabolites to DNA in vitro, giving rise to two main complexes which co-chromatographed with rat liver-produced peaks attributable to 7,8-diol-9,10-epoxide and 7,8-oxide and/or quinones when metabolized further. The nucleoside metabolite peaks attributable to 4,5-oxide and 9-phenol-4,5-oxide were lacking when compared with the binding pattern catalyzed by rat liver. Both the total binding and specific metabolite-nucleoside adducts in the placenta correlated with fluorometrically measured aryl hydrocarbon hydroxylase (AHH) activity and with the amount of dihydrodiol formed. The results demonstrate that both the metabolite pattern and the nucleoside-metabolite complexes formed by the placental microsomes in vitro differed greatly from thos produced by rat liver microsomes. These sstudies also suggest that it is not possible to predict specific patterns of DNA binding from AHH measurements or even from BP metabolite patterns, especially when comparing different tissues and species.