Transplacental exposure to tobacco smoke in human-adduct formation in placenta and umbilical cord blood vessels

Maternal Smoking during Early Pregnancy, GSTP1 and EPHX1 Variants, and Risk of Isolated Orofacial Clefts

Objective:

To examine the interactions between four fetal xenobiotic metabolizing gene polymorphisms, maternal cigarette smoking, and risk for oral cleft defects.

Design and Participants:

California population–based case-control study of 431 infants born with isolated orofacial clefts and 299 nonmalformed controls.

Main Outcome Measures:

Infants were genotyped for functional polymorphisms of the detoxification enzymes microsomal epoxide hydrolase-1 (EPHX1 T→C [Tyr113His], and A→G [His139Arg]), and glutathione-S transferase Pi-1 (GSTP1 A→G [Ile105Val] and C→T [Ala114Val]), and risks for cleft outcomes were measured for gene only and gene-maternal smoking effects.

Results:

Although smoking was associated with an increased risk for isolated cleft lip ± palate, we found no independent associations of genotypes of EPHX1-codon 113 or GSTP1-codon 105 polymorphisms for either isolated cleft lip ± palate or isolated cleft palate. The heterozygote genotype for the EPHX1-codon 139 polymorphism was associated with an increased risk of isolated cleft palate (odds ratio = 1.6 [95% confidence interval, 1.0 to 2.6]). Infant EPHX1 and GTSP1 polymorphic variants did not appreciably alter the risks for clefts associated with maternal smoking, nor were any EPHX1 combined genotype-specific risks found. Infant genotypes of the GSTP1-codon 105 polymorphism, combined with glutathione-S-transferase-μ-1 null genotypes, did not appreciably alter the risk of orofacial clefts.

Conclusions:

Our results suggest that genetic variation of the detoxification enzymes EPHX1 and GSTP1 did not increase the risks of orofacial clefting, nor do they influence the risks associated with maternal smoking.

Modelling of human transplacental transport as performed in Copenhagen, Denmark

Placenta perfusion models are very effective when studying the placental mechanisms in order to extrapolate to real-life situations. The models are most often used to investigate the transport of substances between mother and foetus, including the potential metabolism of these. We have studied the relationships between maternal and foetal exposures to various compounds including pollutants such as polychlorinated biphenyls, polybrominated flame retardants, nanoparticles as well as recombinant human antibodies. The compounds have been studied in the human placenta perfusion model and to some extent in vitro with an established human monolayer trophoblast cell culture model. Results from our studies distinguish placental transport of substances by physicochemical properties, adsorption to placental tissue, binding to transport and receptor proteins and metabolism. We have collected data from different classes of chemicals and nanoparticles for comparisons across chemical structures as well as different test systems. Our test systems are based on human material to bypass the extrapolation from animal data. By combining data from our two test systems, we are able to rank and compare the transport of different classes of substances according to their transport ability. Ultimately, human data including measurements in cord blood contribute to the study of placental transport.

Cytogenetic evaluation of pre-pregnancy smoking in maternal and newborn lymphocytes

OBJECTIVE

To study cytogenetic damage in order to estimate the effect of pre-pregnancy smoking on pregnant women and their foetuses.

STUDY DESIGN

Lymphocyte cultures were obtained from peripheral blood of 20 women who quit smoking during pregnancy, and umbilical cord blood of their newborns at delivery. Cytogenetic analyses were performed for sister chromatid exchanges (SCEs), proliferation rate index (PRI) and mitotic index (MI) using the Fluorescence Plus Giemsa staining technique. Twenty non-smoking women and their newborns were evaluated as controls. CPT-11, a known antineoplastic, was used as a positive genotoxic agent in order to correlate non-smoking women with smoking women and reveal any underlying chromosome instability. Statistical evaluation of SCE frequencies, PRI and MI was based on independent samples t-test in order to estimate the effect of pre-pregnancy smoking on mothers and their newborns.

RESULTS

SCEs were induced in the cord blood lymphocytes of newborns whose mothers smoked before pregnancy when they were exposed to the mutagenic agent CPT-11 (p<0.01). A similar increase in SCEs was observed in both non-smoking and smoking mothers exposed to CPT-11. Newborns in both groups had significantly lower SCE levels than their mothers (p<0.01).

CONCLUSION

Pre-pregnancy smoking results in cytogenetic damage for both mothers and newborns, and is an important risk factor for cancer and/or other genetic-related diseases. Smoking cessation needs to occur well before conception in order to avoid the strong cytogenetic association between pre-pregnancy smoking by mothers and their newborns.

Transplacental carcinogenesis with dibenzo[def,p]chrysene (DBC): timing of maternal exposures determines target tissue response in offspring

Dibenzo[def,p]chrysene (DBC) is a transplacental carcinogen in mice (15mg/kg; gestation day (GD) 17). To mimic residual exposure throughout pregnancy, dams received four smaller doses of DBC (3.75mg/kg) on GD 5, 9, 13 and 17. This regimen alleviated the previously established carcinogenic responses in the thymus, lung, and liver. However, there was a marked increase in ovarian tumors (females) and hyperplastic testes (males). [(14)C]-DBC (GD 17) dosing revealed transplacental distribution to fetal tissues at 10-fold lower concentrations than in paired maternal tissue and residual [(14)C] 3weeks post-dose. This study highlights the importance of developmental stage in susceptibility to environmental carcinogens.

Prenatal exposure to cigarette smoke and benign breast disease

BACKGROUND

Experimental studies have indicated that cigarette smoke contains potential human breast toxins and that the toxic influence during the prenatal period is greater than that of later life.

METHODS

The study sample includes 810 women whose mothers enrolled in the Collaborative Perinatal Project between 1959 and 1966 in Boston and Providence. These women have been followed from gestation until middle-age. Information on maternal smoking during pregnancy was prospectively collected during prenatal visits. We identified 146 women who had been told by a health professional that they had benign breast disease. Log-binomial regression models with Generalized Estimating Equation methods were employed to quantify the association between maternal smoking and benign breast disease among offspring.

RESULTS

There was a positive association between maternal smoking during pregnancy and the risk of benign breast disease among offspring. In particular, women whose mother smoked 1 pack or more per day were 1.7 times more likely to develop benign breast disease (relative risk = 1.7 [95% confidence interval = 1.2-2.5]) in comparison with women whose mother never smoked during pregnancy. The association was independent of women's age, race, education, age at menarche, parity, obesity, birth weight, and maternal age at pregnancy.

CONCLUSIONS

Exposure to heavy cigarette smoking during the prenatal period was associated with an increased risk of benign breast disease in adulthood.

Morphological and biological effects of maternal exposure to tobacco smoke on the feto-placental unit

Active and passive maternal smoking has a damaging effect in every trimester of human pregnancy. Cigarette smoke contains scores of toxins which exert a direct effect on the placental and fetal cell proliferation and differentiation and can explain the increased risk of miscarriage, fetal growth restriction (FGR) stillbirth, preterm birth and placental abruption reported by epidemiological studies. In the placenta, smoking is associated from early in pregnancy, with a thickening of the trophoblastic basement membrane, an increase in collagen content of the villous mesenchyme and a decrease in vascularisation. These anatomical changes are associated with changes in placental enzymatic and synthetic functions. In particular, nicotine depresses active amino-acid (AA) uptake by human placental villi and trophoblast invasion and cadmium decreases the expression and activity of 11 beta-hydroxysteroid dehydrogenase type 2 which is causally linked to FGR. Maternal smoking also dysregulates trophoblast expression of molecules that govern cellular responses to oxygen tension. In the fetus, smoking is associated with a reduction of weight, fat mass and most anthropometric parameters and as in the placenta with alterations in protein metabolism and enzyme activity. These alterations are the results of a direct toxic effect on the fetal cells or an indirect effect through damage to, and/or functional disturbances of the placenta. In particular, smoking interferes strongly with the fetal brain and pancreas biological parameters and induces chromosomal instability, which is associated with an increase in the risk of cancer, especially childhood malignancies.

Early childhood lower respiratory illness and air pollution

BACKGROUND

Few studies of air pollutants address morbidity in preschool children. In this study we evaluated bronchitis in children from two Czech districts: Teplice, with high ambient air pollution, and Prachatice, characterized by lower exposures.

OBJECTIVES

Our goal was to examine rates of lower respiratory illnesses in preschool children in relation to ambient particles and hydrocarbons.

METHODS

Air monitoring for particulate matter < 2.5 microm in diameter (PM(2.5)) and polycyclic aromatic hydrocarbons (PAHs) was conducted daily, every third day, or every sixth day. Children born May 1994 through December 1998 were followed to 3 or 4.5 years of age to ascertain illness diagnoses. Mothers completed questionnaires at birth and at follow-up regarding demographic, lifestyle, reproductive, and home environmental factors. Longitudinal multivariate repeated-measures analysis was used to quantify rate ratios for bronchitis and for total lower respiratory illnesses in 1,133 children.

RESULTS

After adjustment for season, temperature, and other covariates, bronchitis rates increased with rising pollutant concentrations. Below 2 years of age, increments in 30-day averages of 100 ng/m(3) PAHs and of 25 microg/m(3) PM(2.5) resulted in rate ratios (RRs) for bronchitis of 1.29 [95 % confidence interval (CI), 1.07-1.54] and 1.30 (95% CI, 1.08-1.58), respectively; from 2 to 4.5 years of age, these RRs were 1.56 (95% CI, 1.22-2.00) and 1.23 (95% CI, 0.94-1.62), respectively.

CONCLUSION

Ambient PAHs and fine particles were associated with early-life susceptibility to bronchitis. Associations were stronger for longer pollutant-averaging periods and, among children > 2 years of age, for PAHs compared with fine particles. Preschool-age children may be particularly vulnerable to air pollution-induced illnesses.

Transfer of folic acid inside the first-trimester gestational sac and the effect of maternal smoking

OBJECTIVE

The objective of the study was to investigate the transfer pathways of folic acid inside the first-trimester gestational sac and to evaluate the impact of maternal smoking.

STUDY DESIGN

Folate and cotinine levels were evaluated in maternal serum (n = 125) and coelomic fluid (n = 42), and immunostaining was used to identify folate receptors in placental villi, decidual tissue, and secondary yolk sacs from normal pregnancies at 6-12 weeks' gestation.

RESULTS

Folate receptors-alpha were found on the apical surface of syncytiotrophoblast, uterine glandular epithelial cells, and mesothelial layer of the yolk sac. Significantly higher (P < .05) median folate levels were found in maternal serum than in coelomic fluid. The median folate maternal serum and coelomic levels were significantly (P < .0001 and P < .005) lower in smokers, compared with nonsmokers.

CONCLUSION

Uterine glands and the secondary yolk sac play key roles in supplying folic acid to the developing fetus before the placental circulations are established, and maternal smoking does not seem to impair directly its transfer mechanism in early pregnancy.

Biomarkers of intermediate endpoints in environmental and occupational health

The use of biomarkers in environmental and occupational health is increasing due to increasing demands on information about health risks from unfavourable exposures. Biomarkers provide information about individual loads. Biomarkers of intermediate endpoints benefit in comparison with biomarkers of exposure from the fact that they are closer to the adverse outcome in the pathway from exposure to health effects and may provide powerful information for intervention. Some biomarkers are specific, e.g., DNA and protein adducts, while others are unspecific like the cytogenetic biomarkers of chromosomal aberrations (CA), sister chromatid exchanges and micronuclei (MN). The validation of biomarkers includes measurements of sensitivity and specificity of biomarkers and round robin tests to ensure reproducible protocols within different laboratories. The predictive value of biomarkers with respect to adverse health effect from the result of the measurement has been performed for the cytogenetic biomarkers showing a predictive value of high levels of CA and increased risk of cancer. The use of CA in future studies is, however, limited by the laborious and sensitive procedure of the test and lack of trained cytogeneticists. Less time consuming, but robust biomarkers, sensitive to environmental exposures are suggested. From the selection of developed biomarkers, the comet assay is highly sensitive to lifestyle exposures, often confounding the output, while MN in lymphocytes seem promising with respect to laboratory and health effect (cancer) validity. Also, new biomarkers exploiting the new 'omics' technologies are being developed. A number of ethical issues arise from the use of biomarkers with a predictive value aiming at respecting the autonomy of the study person in participation (only upon written informed consent and with obligations of withdrawal at any time), access to personal information (right to know and right not to know the study result) and securing proper data management (data protection to avoid misuse in employment, insurance, loaning and learning opportunities).

Maternal smoking during pregnancy and risk of brain tumors in the offspring. A prospective study of 1.4 million Swedish births

OBJECTIVE

Studies of the effect of maternal smoking during pregnancy on development of brain tumors in the offspring generally have found no increase in risk but most have mainly relied on retrospective exposure assessment. We conducted a prospective study on a large birth cohort in Sweden.

METHODS

Women giving birth during 1983-1997 were classified as smokers or non-smokers based on information ascertained at the first prenatal visit and recorded in the Swedish Birth Register. Follow-up of brain tumor incidence among offspring through 1997 was achieved by linkage with the Swedish Cancer Register. Hazard ratios were estimated using Cox proportional hazard regression, adjusting for demographic characteristics available in the Birth Register.

RESULTS

Brain tumors (n=480) occurred at a rate of 4.5 cases per 100,000 person-years. Children of women who smoked during pregnancy had an increased incidence of brain tumors (hazard ratio = 1.24; 95% confidence interval: 1.01-1.53). The increase in risk was similar for benign and malignant tumors, and was most apparent for astrocytoma. The effect of smoking on the occurrence of brain tumors was seen most strongly among 2-4 year-old children.

CONCLUSIONS

These results support a role for maternal smoking during pregnancy in the etiology of childhood brain tumors. Our findings should be confirmed in other prospective studies.

Epidemiology of brain tumors in childhood--a review

Malignant brain tumors are the leading cause of cancer death among children and the second most common type of pediatric cancer. Despite several decades of epidemiologic investigation, the etiology of childhood brain tumors (CBT) is still largely unknown. A few genetic syndromes and ionizing radiation are established risk factors. Many environmental exposures and infectious agents have been suspected of playing a role in the development of CBT. This review, based on a search of the medical literature through August 2003, summarizes the epidemiologic evidence to date. The types of exposures discussed include ionizing radiation, N-nitroso compounds (NOC), pesticides, tobacco smoke, electromagnetic frequencies (EMF), infectious agents, medications, and parental occupational exposures. We have chosen to focus on perinatal exposures and review some of the recent evidence indicating that such exposures may play a significant role in the causation of CBT. The scientific community is rapidly learning more about the molecular mechanisms by which carcinogenesis occurs and how the brain develops. We believe that advances in genetic and molecular biologic technology, including improved histologic subtyping of tumors, will be of huge importance in the future of epidemiologic research and will lead to a more comprehensive understanding of CBT etiology. We discuss some of the early findings using these technologies.

Transplacental lung carcinogenesis: molecular mechanisms and pathogenesis

A wide variety of studies in both animal models and human populations have demonstrated age-related differences in the susceptibility of the developing organism to environmentally prevalent toxicants. While this differential susceptibility has been clearly established, the mechanistic basis for these age-related differences is still poorly understood. The developing fetus utilizes many of the same metabolic and signaling pathways as adult organisms in responding to environmental agents. However, it is becoming increasingly evident that the fetus is not a "little adult" and exhibits unique biochemical responses and gene expression profiles to chemical and physical agents. Because of the rapid growth and developmental changes that occur during gestation, the fetus represents a particularly challenging research subject as a result of the dynamic alterations that occur in gene expression pathways as gene systems are activated or repressed during specific stages of development. Thus, an understanding of the mechanism(s) that render the developing organism more or less susceptible to specific carcinogenic agents is crucial for both regulatory decisions regarding the determination of safe levels of toxic chemicals released into the environment and also for determining the effects of therapeutic compounds in younger age groups and pregnant women. Concentrating on studies from the author's laboratory, this review will highlight recent research on the molecular pathogenesis of transplacentally induced tumors. While focusing on the lung, other animal models and recent human epidemiological studies will also be discussed to contrast similarities and differences in the developing and adult organisms in terms of responses to toxic chemicals, including metabolism of environmentally prevalent toxicants and alterations in gene systems at the molecular level.

Genomic and transcriptional alterations in mouse fetus liver after transplacental exposure to cigarette smoke

The transplacental exposure of fetuses to maternal cigarette smoke may increase the risk of developmental impairments, congenital diseases, and childhood cancer. The whole-body exposure of Swiss mice to environmental cigarette smoke (ECS) during pregnancy decreased the number of fetuses per dam, placenta weight, and fetus weight. ECS increased DNA adducts, oxidative nucleotide alterations, and cytogenetic damage in fetus liver. Evaluation by cDNA array of 746 genes showed that 61 of them were expressed in fetus liver under basal conditions. The oral administration of N-acetylcysteine (NAC) during pregnancy enhanced the expression of three genes only, including two glutathione S-transferases and alpha1-antitrypsin precursor, whose deficiency plays a pathogenetic role in congenital emphysema. Transplacental ECS upregulated the expression of 116 genes involved in metabolism, response to oxidative stress, DNA and protein repair, and signal transduction. NAC inhibited the ECS-related genetic damage and upregulation of most genes. ECS stimulated pro-apoptotic genes and genes downregulating the cell cycle, which may justify growth impairments in the developing fetus. Thus, both genetic and epigenetic mechanisms were modulated by ECS. Moreover, hypoxia-related genes and several oncogenes and receptors involved in proliferation and differentiation of leukocytes were induced in the fetal liver, which also bears hematopoietic functions.

Fibrin-type fibrinoid in placentae from pregnancies associated with maternal smoking: association with villous trophoblast and impact on intervillous porosity

Smoking during pregnancy perturbs maternal haemostasis via activated coagulation which could include greater coagulation (fibrin-type fibrinoid deposition) in the placental intervillous space. This might affect intervillous haemodynamics and transport of oxygen and nutrients to the fetus. Fibrin deposits could influence the sizes and numbers of intervillous spaces ('pores') and perivillous fibrin could reflect changes in the nature or activity of trophoblast. Here, we test whether or not smoking is associated with differences in the composition of villous trophoblast, the amounts and patterns of fibrin and, hence, the dimensions and numbers of intervillous pores. Random samples of placentae were taken from pregnancies classified according to smoking status (non-smokers, light smokers, heavy smokers). Stereology was used to estimate volumes of intervillous space and fibrin, test for differences in trophoblast composition and patterns of fibrin deposition at the villous surface, and determine the impact of deposits on the mean volumes and theoretical numbers of intervillous pores. No group differences were found in total volumes or surfaces of trophoblast or total volume of intervillous fibrin. However, the total surfaces of syncytial knots declined in smokers and the surfaces of syncytial bridges increased. Particularly in heavy smokers, this was associated with reduced deposits of perivillous fibrin at syncytial knots. In all placentae, the greatest deposits occurred where there was trophoblast denudation. Little fibrin was seen on thin regions of syncytium. Regardless of smoking status, intervillous fibrin reduced intervillous pore size and increased pore number. However, heavy smokers had larger pores. Reductions in syncytial knots are consistent with reports that smoking reduces the incidence of trophoblast apoptosis whilst increases in syncytial bridges are consistent with enhanced branching angiogenesis. Results confirm that perivillous fibrin accumulates preferentially at denudation sites. They also suggest that smoking perturbs the normal pattern of fibrin deposition, that the impact is greater in heavy smokers and that the placental site is privileged or active in terms of fibrinolytic or anti-coagulatory activity. This activity seems to reside in thin regions of syncytium.

Parental smoking and childhood cancer: results from the United Kingdom Childhood Cancer Study

There are strong a priori reasons for considering parental smoking behaviour as a risk factor for childhood cancer but case - control studies have found relative risks of mostly only just above one. To investigate this further, self-reported smoking habits in parents of 3838 children with cancer and 7629 control children included in the United Kingdom Childhood Cancer Study (UKCCS) were analysed. Separate analyses were performed for four major groups (leukaemia, lymphoma, central nervous system tumours and other solid tumours) and more detailed diagnostic subgroups by logistic regression. In the four major groups, after adjustment for parental age and deprivation there were nonsignificant trends of increasing risk with number of cigarettes smoked for paternal preconception smoking and nonsignificant trends of decreasing risk for maternal preconception smoking (all P-values for trend >0.05). Among the diagnostic subgroups, a statistically significant increased risk of developing hepatoblastoma was found in children whose mothers smoked preconceptionally (OR=2.68, P=0.02) and strongest (relative to neither parent smoking) for both parents smoking (OR=4.74, P=0.003). This could be a chance result arising from multiple subgroup analysis. Statistically significant negative trends were found for maternal smoking during pregnancy for all diagnoses together (P<0.001) and for most individual groups, but there was evidence of under-reporting of smoking by case mothers. In conclusion, the UKCCS does not provide significant evidence that parental smoking is a risk factor for any of the major groups of childhood cancers.

Placental transfer of cotinine at 12-17 weeks of gestation and at term in heavy smokers

The objective of this study was to compare the placental transfer of cotinine from maternal to fetal circulation in heavy chronic smokers during the second trimester of pregnancy and at term. Maternal and fetal cotinine concentrations were evaluated in 26 women requesting surgical termination for psychosocial reasons at 12-17 weeks gestation and 26 women with uncomplicated pregnancies at 37-40 weeks gestation, and delivered vaginally. Cotinine concentrations were measured by radioimmunoassay. At 12-17 weeks, the median cotinine concentration was significantly (P = 0.009) lower in fetal than in maternal serum. At term fetal and maternal cotinine concentrations were similar. The feto-maternal ratio was significantly (P < 0.001) lower in second trimester pregnancies than in term pregnancies. In both groups, positive linear correlations were found between maternal and fetal serum cotinine concentration and between maternal serum cotinine concentration and the number of cigarettes smoked per day. These data indicate that placental cotinine transfer increases with advancing gestation. This may be secondary to increased placental permeability in the third trimester, which could be linked to progressive placental damage in heavy chronic smokers.

Detection of DNA adducts in developing CD4+ CD8+ thymocytes and splenocytes following in utero exposure to benzo[a]pyrene

Environmental carcinogen exposure may play an important role in the incidence of cancer in children. In addition to environmental pollutants, maternal smoking during pregnancy may be a contributing factor. Major carcinogenic components of cigarette smoke and other combustion by-products in the environment include polycyclic aromatic hydrocarbons (PAH). Mouse offspring exposed during midpregnancy to the PAH, benzo[a]pyrene (B[a]P), show significant deficiencies in their immune functions, observed in late gestation which persist for at least 18 months. Tumor incidences in these progeny are 8 to 10-fold higher than in controls. We have demonstrated a significant reduction in thymocytes (CD4+ CD8+, CD4+ CD8+ Vbeta8+, CD4+ CD8+ Vgamma2+) from newborn and splenocytes (CD4+ CD8+) from 1-week-old mouse progeny exposed to B[a]P in utero. To investigate possible causes of the observed T cell reduction, we analyzed the thymocytes and splenocytes from progeny and maternal tissues for the presence of B[a]P-DNA adducts. Adducts were detected in maternal, placental and offspring lymphoid tissues at day 19 of gestation, at birth and 1-wk after birth. The presence of B[a]P-DNA adducts in immature T cells may, in part, explain the previously observed T cell immunosuppression and tumor susceptibility in mice exposed to B[a]P in utero. The effects of DNA lesions on progeny T cells may include interference with normal T-cell development. These results provide a possible explanation for the relationship between maternal smoking during pregnancy and childhood carcinogenesis.

Biomonitoring of tobacco smoke carcinogenicity by dosimetry of DNA adducts and genotyping and phenotyping of biotransformational enzymes: a review on polycyclic aromatic hydrocarbons

In this review article, we summarize the data on tobacco smoke carcinogenicity in relation to DNA adduct dosimetry and genotyping and phenotyping of biotransformational enzymes. A major class of carcinogens, polycyclic aromatic hydrocarbons, present in substantial quantities in tobacco smoke, is discussed. The historical background and an overview of the metabolic pathways are given. The epidemiological and biological data in particular on dosimetry of the representative DNA adducts and genotyping and phenotyping of the respective activating and detoxifying enzymes are presented. The salient findings are highlighted, the uncertainties are underlined and, finally, recommendations for future research are made.

Active and passive smoking during pregnancy and risk of central nervous system tumours in children

The effects of maternal active and passive smoking during pregnancy on childhood central nervous system (CNS) tumours were assessed in a population-based case-control study. The mothers of 244 children aged 0-15 years with CNS tumours and 502 control mothers were interviewed about their smoking habits. All families were resident in the region of Lombardy, Italy. Risk estimates were calculated by unconditional logistic regression, adjusted for age, sex and area of residence. Active smoking by the parents before pregnancy was not associated with increased risk of CNS tumours in the children. Active smoking by the mother during early pregnancy (approximately the first 5 weeks) was associated with a slightly increased risk of the child developing a CNS tumour (odds ratio [OR] 1.5 [95% CI 1.0, 2.3]). An increased risk of CNS tumours was found in the children of non-smoking mothers exposed regularly to tobacco smoke both in early pregnancy (OR 1.8 [95% CI 1.2, 2.6]) and in late pregnancy (OR 1.7 [95% CI 1.2, 2.5]). Although this study was retrospective, the results confirm our previous findings and suggest an association between the risk of developing CNS tumours in children and regular passive smoking by the mother during pregnancy.

Maternal exposure to benzo[a]pyrene alters development of T lymphocytes in offspring

Childhood cancer has been increasing significantly over the past two decades in the United States, suggesting that environmental exposures may be playing a causative role. One such cause may be maternal smoking during pregnancy. Suspected carcinogens in cigarette smoke and environmental pollution include N-nitrosamines and polycyclic aromatic hydrocarbons, which may be several micrograms per exposure. Previously, we have shown that mouse progeny of mothers exposed to benzo[a]pyrene (B[a]P) during midpregnancy had abnormalities in their humoral and cell-mediated immune response. Immunodeficiency was detectable during gestation, at one week after birth and persisted for 18 months. Tumor incidences in progeny were eight to 10-fold higher than in controls. The present study compared frequencies of CD4+, CD8+, V gamma 2+, and V beta 8+ T cells in progeny following in utero exposure to B[a]P. The significant reduction in newborn CD4+CD8+, CD4+CD8+V beta 8+ thymocytes and CD4+ splenocytes from 1-week-old progeny, suggests that B[a]P induces abnormal changes in developing T cells. These early alterations may lead to postnatal T cell suppression, thus providing a more suitable environment for the growth of tumors later in life. These results suggest that developmental immunosuppression mediated by B[a]P may play a critical role in the relationship between maternal exposures and childhood carcinogenesis.

Metabolites of a tobacco-specific carcinogen in urine from newborns

BACKGROUND

Cigarette smoking during pregnancy can result in fetal exposure to carcinogens that are transferred from the mother via the placenta, but little information is available on fetal uptake of such compounds. We analyzed samples of the first urine from newborns whose mothers did or did not smoke cigarettes for the presence of metabolites of the potent tobacco-specific transplacental carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

METHODS

The urine was collected and analyzed for two metabolites of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). Gas chromatography and nitrosamine-selective detection, with confirmation by mass spectrometry, were used in the analyses, which were performed without knowledge of the origin of the urine samples.

RESULTS

NNAL-Gluc was detected in 22 (71%) of 31 urine samples from newborns of mothers who smoked; NNAL was detected in four of these 31 urine samples. Neither compound was detected in the 17 urine samples from newborns of mothers who did not smoke. The arithmetic mean level of NNAL plus NNAL-Gluc in the 27 newborns of smokers for which both analytes were quantified was 0.14 (95% confidence interval [CI] = 0.083-0.200) pmol/mL. The levels of NNAL plus NNAL-Gluc in the urine from these babies were statistically significantly higher than those in the urine from newborns of nonsmoking mothers (geometric means = 0.062 [95% CI = 0.035-0.110] and 0.010 [considered as not detected; no confidence interval], respectively; two-sided P<.001). NNAL plus NNAL-Gluc levels in the 18 positive urine samples in which both analytes were quantified ranged from 0.045 to 0.400 pmol/mL, with an arithmetic mean level of 0.20 (95% CI = 0.14-0.26) pmol/mL, about 5%-10% of the levels of these compounds detected in the urine from adult smokers.

CONCLUSIONS

Two metabolites of the tobacco-specific transplacental carcinogen NNK can be detected in the urine from newborns of mothers who smoked cigarettes during pregnancy.

Molecular pathogenesis of transplacentally induced mouse lung tumors

Previous studies from this and other laboratories have shown that treatment of pregnant mice with 3-methylcholanthrene (MC) caused lung tumors in the offspring, the incidence of which correlated with fetal inducibility of Cyp1a1. Analysis of paraffin-embedded lung tissue for Ki-ras-2 mutations indicated that 79% of the lesions examined contained point mutations in codons 12 and 13 of the Ki-ras-2 gene locus, the majority of which (84%) were G-->T transversions. The mutational spectrum was dependent on the tumor stage, as both the incidence of mutation and type of mutation produced correlated with malignant progression of the tumor. Mutations occurred in 60% of the hyperplasias, 80% of the adenomas, and 100% of the adenocarcinomas. In the tumors with mutations, GLY12-->CYS12 transversions occurred in 100% of the hyperplasias, 42% of the adenomas, and 14% of the adenocarcinomas. GLY12-->VAL12 transversions were not observed in hyperplasias and occurred in 42% of the adenomas and 57% of the adenocarcinomas. The remaining ASP12 and ARG13 mutations occurred only in adenomas (17%) and adenocarcinomas (29%). The tumors were also analyzed for alterations in the structure or function of the tumor suppressor genes Rb, p53, and Cdkn2a. No mutations were observed in exons 5-8 of the p53 gene. SSCP analysis demonstrated that 2 of 15 lung tumors contained shifted bands at the Cdkn2a gene locus. Sequence analysis had identified these as mutations in exon 2, with a CAC-->TAC transition at base 301 (HIS74-->TYR74) in tumor 23-1 and GGG-->GAG transition at base 350 (GLY90-->GLU90) in tumor 36-1. Northern blot analysis of the larger tumors revealed that 14 of 14 of these large lung tumors exhibited markedly decreased expression of Rb gene transcripts. These results were confirmed by immunohistochemistry. The larger tumors, which exhibited features of adenocarcinomas, showed a marked reduction or almost complete absence of nuclear pRb staining compared with smaller adenomas and normal lung tissue. The results suggest that Ki-ras-2 mutations are an early and frequent event in lung tumorigenesis, and that the type of mutation produced by environmental chemicals can influence the carcinogenic potential of the tumor. The results obtained with the Cdkn2a and Rb genes suggest that alterations in the Rb regulatory axis may play a key role in the pathogenesis of the pulmonary tumors and appear to occur later in the neoplastic process. It appears from these experiments that the combination of mutated Ki-ras-2 and alterations in the Rb regulatory gene locus, which are frequent alterations in human lung tumors, may be the preferred pathway for lung tumor pathogenesis in mice exposed transplacentally to environmental carcinogens.

Role of tumor suppressor genes in transplacental lung carcinogenesis

Most human cancers involve multiple genetic changes, including activation of oncogenes such as Ki-ras-2 (Kras2) and inactivation of any one of a number of tumor suppressor genes such as p53 and members of the retinoblastoma (Rb) regulatory axis. As part of an ongoing project to determine how in utero exposure to chemical carcinogens affects the molecular pathogenesis of murine lung tumors, the p53 and p16Cdkn2a genes were analyzed by using paraffin-embedded lung tissues from mice treated transplacentally with 3-methylcholanthrene. Single-strand conformation polymorphism analysis of exons 5-8 of the p53 gene, as well as their flanking introns, demonstrated an absence of mutations at this gene locus. However, a genetic polymorphism was identified at nt 708 in intron 4 of the DBA/2 strain of mice 5 bp downstream of a 3' branching-point splice signal. Analysis of exons 1 and 2 of the Cdkn2a gene by single-strand conformation polymorphism and sequence analyses revealed mutations in exon 2 in 7% of the tumors examined. Tumor 23-1 exhibited a CAC-->TAC transition at nt 301 (His74-->Tyr74), and tumor 36-1 exhibited a GGG-->GAG transition at nucleotide 350 (Gly90-->Glu90). Northern blot analysis of 14 of the larger tumors showed a marked decrease in the levels of Rb RNA expression. Immunohistochemical analysis revealed a spectrum of pRb expression, with the smaller adenomas showing moderate numbers of nuclei with heterogeneous staining for pRb in contrast with a highly reduced or near-complete absence of expression in the nuclei of larger tumors with features of adenocarcinomas. The low incidence of mutations at tumor suppressor loci suggested that inactivation of tumor suppressor genes was a late event in murine lung tumor pathogenesis. The identification of both mutations at the Cdkn2a gene locus and reduced levels of Rb expression combined with previous studies demonstrating a high incidence of mutated Kras2 alleles in these tumors implies that alterations of the Rb regulatory axis, in combination with mutation of Kras2, may be the preferred pathway for the pathogenesis of pulmonary tumors in transplacentally exposed mice.

Xenobiotic-metabolizing cytochrome P450 enzymes in the human feto-placental unit: role in intrauterine toxicity

Practically all lipid-soluble xenobiotics enter the conceptus through placental transfer. Many xenobiotics, including a number of clinically used drugs, are known to cause unwanted effects in the embryo or fetus, including in utero death, initiation of birth defects, and production of functional abnormalities. It is well established that numerous xenobiotics are not necessarily toxic as such, but are enzymatically transformed in the body to reactive and toxic intermediates. The cytochrome P450 (CYP) enzymes are known to catalyze oxidative metabolism of a vast number of compounds, including many proteratogens, procarcinogens, and promutagens. About 20 xenobiotic-metabolizing CYP forms are known to exist in humans. Most of these forms are most abundant in the liver, but examples of exclusively extrahepatic CYP forms also exist. Unlike rodents, the liver of the human fetus and even embryo possesses relatively well-developed metabolism of xenobiotics. There is experimental evidence for the presence of CYP1A1, CYP1B1, CYP2C8, CYP2D6, CYP2E1, CYP3A4, CYP3A5, and CYP3A7 in the fetal liver after the embryonic phase (after 8 to 9 weeks of gestation). Significant xenobiotic metabolism occurs also during organogenesis (before 8 weeks of gestation). Also, some fetal extrahepatic tissues, most notably the adrenal, contain substantial levels of CYP enzymes. The full-term human placenta is devoid of many CYP activities present in liver. Placental CYP1A1 is highly inducible by maternal cigarette smoking. Other forms present in full-term placenta include CYP4B1 and CYP19 (steroid aromatase), which also contribute to the oxidation of some xenobiotics. At earlier stages of pregnancy, the placenta may express a wider array of CYP genes, including CYP2C, CYP2D6, and CYP3A7. Due to the small size of the fetus and low abundance of CYPs in placenta, the contribution of feto-placental metabolism to overall gestational pharmacokinetics of drugs is probably minor. In contrast, several toxic outcomes have been ascribed to altered metabolic patterns in the feto-placental unit, including a putative association between reduced placental oxidative capacity and birth defects. Examples of human teratogens that are substrates for CYP enzymes include thalidomide, phenytoin, ethanol, and several hormonal agents. Recent studies have improved our understanding of the expression and regulation of individual CYP genes in the fetus and placenta, and the stage is set for applying this knowledge with more precision to the role of xenobiotic metabolism in abnormal intrauterine development in humans.

Detection of benzo[a]pyrene-DNA adducts in human placenta and umbilical cord blood

Placenta constitutes a vital organ of exchange between mother and foetus. In addition to this favourable effect for foetal development, placenta indirectly may allow transfer of several maternal blood xenobiotics. Human placenta and umbilical cord blood are interesting models for investigating maternal environment and the metabolism, the bioactivation and the transfer of carcinogens such as polycyclic aromatic hydrocarbons. We used them to assess the effect of a woman's smoking on the foetus. Few studies cover this subject. In pregnant women who have continued to smoke, benzo[a]pyrene compound of cigarette smoke is metabolically activated to diol-epoxide derivative: benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide, ultimate carcinogen (BPDE-I). This derivative is covalently fixed on DNA and gives BPDE-I-DNA adducts. By a competitive immunoassay technique, we determined BDPE-I-DNA adducts in 20 samples of placenta and umbilical cord blood from women who smoked (n = 15) and who did not (n = 10). Tobacco consumption was checked by urinary cotinine determination. In the group of smokers levels of adducts were found in 13 specimens of placenta (from 10 to 60 fmol/50 micrograms of DNA) and 12 umbilical cord blood (from 10 to 22.15 fmol/50 micrograms of DNA) samples. These results indicate that a mother's tobacco consumption is linked to the accumulation of BPDE-I-DNA adducts in the placenta, which are seen in smaller quantities in the umbilical cord blood, probably because of the metabolic capacity of the placenta and the transfer of B[a]P from the mother to the foetus.

Transplacental transfer of environmental genotoxins--polycyclic aromatic hydrocarbon-albumin in nonsmoking women

Transplacental transfer of genotoxic material has been determined by measuring the polycyclic aromatic hydrocarbon-albumin adduct level in serum isolated from the mother and the umbilical cord blood using a competitive enzyme-linked immunoadsorbent assay (ELISA) and the antibody (8E11( against benzo[a]pyrene (B[a]P) tetrols. Smoking women (median = 5.54 fmol B[a]P eq/micrograms albumin; n = 21 cases) and nonsmoking women living in rural areas (median = 4.99; n = 30) had higher adduct levels than nonsmoking women living in suburbia (median = 4.09; n = 37), whereas nonsmoking women living in the city of Aarhus had an intermediate level (median = 4.82; n = 40). The median adduct level in umbilical cord blood was significantly lower than in maternal blood, the maternal/fetal ratio being approximately 1.3. A positive association between the adduct levels in the mother and umbilical cord blood was observed. This study indicates that the competitive ELISA to detect B[a]P bound to serum albumin is sensitive enough to detect differences in the burden of genotoxic compounds in nonoccupationally exposed individuals. The lower adduct level in people living in suburbia suggests that local production of incomplete combustion products, like vehicle exhaust or heat generation, is a contributing factor to genotoxic compounds in the general environment.

The effect of smoking on sister chromatid exchange rate of newborn infants born to smoking mothers

Sister chromatid exchange (SCE) frequencies in lymphocytes of 21 smoking mothers and their 21 newborns were compared to those that of 10-infants whose mothers had never smoked and to those of 8 infants whose mothers were passive smokers and reported high exposure to tobacco smoke by living or working with smokers. Mothers in the first group also smoked throughout their pregnancy. Results confirm our earlier study on smoking effects reported for adults. Additionally, we saw that neonates have consistently lower SCE frequencies than adults.