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

Recent Advances in Folates and Autoantibodies against Folate Receptors in Early Pregnancy and Miscarriage

Though firstly identified in cerebral folate deficiency, autoantibodies against folate receptors (FRAbs) have been implicated in pregnancy complications such as miscarriage; however, the underlying mechanism needs to be further elaborated. FRAbs can be produced via sensitization mediated by folate-binding protein as well as gene mutation, aberrant modulation, or degradation of folate receptors (FRs). FRAbs may interfere with folate internalization and metabolism through blocking or binding with FRs. Interestingly, different types of FRs are expressed on trophoblast cells, decidual epithelium or stroma, and macrophages at the maternal-fetal interface, implying FRAbs may be involved in the critical events necessary for a successful pregnancy. Thus, we propose that FRAbs may disturb pregnancy establishment and maintenance by modulating trophoblastic biofunctions, placental development, decidualization, and decidua homeostasis as well as the functions of FOLR2+ macrophages. In light of these findings, FRAbs may be a critical factor in pathological pregnancy, and deserve careful consideration in therapies involving folic acid supplementation for pregnancy complications.

Maternal metabolism influences neural tube closure

Changes in maternal nutrient availability due to diet or disease significantly increase the risk of neural tube defects (NTDs). Because the incidence of metabolic disease continues to rise, it is urgent that we better understand how altered maternal nutrient levels can influence embryonic neural tube development. Furthermore, primary neurulation occurs before placental function during a period of histiotrophic nutrient exchange. In this review we detail how maternal metabolites are transported by the yolk sac to the developing embryo. We discuss recent advances in understanding how altered maternal levels of essential nutrients disrupt development of the neuroepithelium, and identify points of intersection between metabolic pathways that are crucial for NTD prevention.

Homocysteine Metabolism in Pregnancy and Developmental Impacts

Homocysteine is a metabolite generated by methionine cycle metabolism, comprising the demethylated derivative of methionine. Homocysteine can be metabolised by the transsulphuration pathway to cystathionine, which requires vitamin B6, or can undergo remethylation to methionine. Homocysteine remethylation to methionine is catalysed by methionine synthase activity which requires vitamin B12, regenerating methionine to allow synthesis of the universal methyl donor S-adenosylmethionine required for methylation and gene transcription regulation. The methyl-group donated for homocysteine remethylation comes from 5-methyltetrahydrofolate generated by the folate cycle, which allows tetrahydrofolate to be returned to the active folate pool for nucleotide biosynthesis. Therefore the integrated actions of the methionine and folate cycles, required to metabolise homocysteine, also perpetuate methylation and nucleotide synthesis, vitally important to support embryonic growth, proliferation and development. Dysregulated activities of these two interdependent metabolic cycles, arising from maternal suboptimal intake of nutrient co-factors such as folate and vitamin B12 or gene polymorphisms resulting in reduced enzymatic activity, leads to inefficient homocysteine metabolic conversion causing elevated concentrations, known as hyperhomocysteinemia. This condition is associated with multiple adverse pregnancy outcomes including neural tube defects (NTDs). Raised homocysteine is damaging to cellular function, binding to proteins thereby impairing their function, with perturbed homocysteine metabolism impacting negatively on embryonic development. This review discusses the "cross-talk" of maternal-fetal homocysteine interrelationships, describes the placental transport of homocysteine, homocysteine impacts on pregnancy outcomes, homocysteine and methylation effects linking to NTD risk and proposes a putative pathway for embryonic provision of folate and vitamin B12, homocysteine-modulating nutrients that ameliorate NTD risk.

Maternal Inositol Status and Neural Tube Defects: A Role for the Human Yolk Sac in Embryonic Inositol Delivery?

Supplementation with myo-inositol during the periconceptional period of pregnancy may ameliorate the recurrence risk of having a fetus affected by a neural tube defect (NTD; e.g., spina bifida). This could be of particular importance in providing a means for preventing NTDs that are unresponsive to folic acid. This review highlights the characteristics of inositol and describes the role of myo-inositol in the prevention of NTDs in rodent studies and the evidence for its efficacy in reducing NTD risk in human pregnancy. The possible reduction in NTD risk by maternal myo-inositol implies functional and developmentally important maternal-embryonic inositol interrelationships and also suggests that embryonic uptake of myo-inositol is crucial for embryonic development. The establishment of active myo-inositol cellular uptake mechanisms in the embryonic stages of human pregnancy, when the neural tube is closing, is likely to be an important determinant of normal development. We draw attention to the generation of materno-fetal inositol concentration gradients and relationships, and outline a transport pathway by which myo-inositol may be delivered to the early developing human embryo. These considerations provide novel insights into the mechanisms that may underpin inositol's ability to confer embryonic developmental benefit.

Maternal Cotinine Levels and Red Blood Cell Folate Concentrations in the Periconceptual Period

OBJECTIVES

Studies have examined the association between tobacco use and folate levels in pregnancy, yet few have assessed this relation using objective and accurate measures of both smoking and folate. In this study, we evaluated the association between maternal cotinine levels and periconceptional red blood cell (RBC) folic acid reserves in a cohort of low-income pregnant mothers.

METHODS

Smoking information, based on salivary cotinine, a highly sensitive and specific tobacco smoke exposure biomarker, was used. Furthermore, folate was assessed using RBC folate, an indicator of long-term folate storage. Participants were early to mid-trimester pregnant women who received antenatal care between 2011 and 2015 at the Genesis Clinic of Tampa (Florida). A total of 496 women were enrolled in the study. Associations between smoking status/maternal salivary cotinine concentrations, sociodemographic factors, and folate concentrations were investigated using Tobit regression analyses.

RESULTS

The mean folate level of the participants was 718.3 ± 183.2 ng/mL, and only 2 (0.4%) participants were deficient in folate. We observed no significant difference in folate levels by smoking status. In contrast, salivary cotinine levels were significantly associated with decreased RBC folate concentrations (β -11.43, standard error 5.45, P = 0.032). Prepregnancy maternal body mass index, gestational age, stress, and depression also were associated with folate levels.

CONCLUSIONS

Low RBC folate is associated with perinatal factors, including high maternal cotinine levels, body mass index, stress, and depression. The effect of low folate levels among smokers cannot be overemphasized, considering that tobacco products not only reduce folate levels but also decrease the bioutilization of folate.

Folic Acid Intake, Fetal Brain Growth, and Maternal Smoking in Pregnancy: A Randomized Controlled Trial

BACKGROUND

Folic acid supplementation during pregnancy plays an important role in fetal growth and development. To our knowledge, no experimental study has examined the effect of folic acid on fetal brain growth in women who smoke cigarettes during pregnancy.

OBJECTIVES

The aim of this study was to investigate the efficacy of higher-dose compared with standard-dose folic acid supplementation on prenatal fetal brain growth, measured by head circumference, brain weight, and brain-body weight ratio (BBR).

DESIGN

In this randomly assigned, double-blind, controlled clinical trial, we recruited 345 smoking pregnant women attending a community health center in Tampa, FL between 2010 and 2014. Participants were randomly assigned in a 1:1 ratio to receive either 0.8 mg folic acid/d (standard of care at the study center) or 4 mg folic acid/d (higher strength). Participants were also enrolled in a smoking cessation program. A 2-level linear growth model was used to assess treatment effect and factors that predict intrauterine growth in head circumference over time. Multiple linear regression analyses were conducted to estimate the effect of higher-strength folic acid on head circumference at birth, fetal brain weight, and fetal BBRs.

RESULTS

Mothers who received the higher dose of folic acid had infants with a 1.18 mm larger mean head circumference compared with infants born to mothers who received the standard dose, but this difference was not statistically significant (P = 0.2762). Higher-dose folic acid also had no significant effect on brain weight. The BBR of infants of mothers who received higher-dose folic acid was, however, 0.33 percentage points lower than that for infants of mothers who received the standard dose of folic acid (P = 0.044).

CONCLUSIONS

Infants of smokers in pregnancy may benefit from higher-strength maternal folic acid supplementation. We noted a decrease in the proportion of infants with impaired BBR among those on higher-dose folic acid. This trial was registered at clinicaltrials.gov as NCT01248260.

Folate, vitamin B12, and homocysteine in smoking-exposed pregnant women: A systematic review

Smoking exposure is associated with pregnancy complications, as are levels of folate, vitamin B12, and homocysteine. In nonpregnant adults, smoking exposure is associated negatively with folate and vitamin B12 levels and positively with homocysteine levels. A complete overview of the literature on this topic in pregnant women is lacking. To evaluate evidence of associations of maternal smoking exposure during pregnancy and levels of folate, homocysteine, and vitamin B12 in pregnancy and in cord blood, we searched MEDLINE, Embase, CINAHL, Cochrane, Scopus, Web of Science, and reference lists of relevant studies until August 2017. We selected studies in pregnant women describing the association of passive or active smoking and levels of folate, homocysteine, and/or vitamin B12. Data were extracted by two independent reviewers. We included 32 studies of 2,015 identified references with a total of 37,822 participants and more than 6,000 smokers. Twenty‐eight studies measured folate, 14 measured vitamin B12, and 13 measured homocysteine. Nineteen out of 28 studies assessing folate reported significantly lower levels in pregnant women exposed to smoking compared with those unexposed. Vitamin B12 levels were lower in smoking mothers in eight out of 14 studies. Homocysteine levels tended to be higher in mothers exposed to smoking. Smoking exposure during pregnancy is generally associated with lower folate and vitamin B12 levels and higher homocysteine levels. This may help raise further awareness about the consequences of smoking and the need to encourage stopping smoking in all, especially in pregnant women.

Placental Origins of Chronic Disease

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.

Association between interpregnancy interval and the risk of recurrent loss after a midtrimester loss

STUDY QUESTION

After an initial midtrimester loss, is the interval to the next conception associated with the risk of a recurrent loss?

SUMMARY ANSWER

Among women who had a pregnancy loss at 14-19 weeks gestation, conception at least 3 months after this initial loss was associated with a reduced risk of a recurrent loss.

WHAT IS KNOWN ALREADY

A short interpregnancy interval (IPI) has been thought to increase risk but recent studies of pregnancy after a loss have found no effect; however, these studies have been based almost entirely on an initial first trimester (<14 weeks) loss.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study drawing on over 997 000 linked birth and hospital records from New South Wales, Australia for 2003-2011. Index pregnancies were those of women who had a first recorded pregnancy loss of 14-23 weeks gestation (miscarriage, termination and perinatal death). The study population was 4290 women who conceived again within 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The index loss was categorized by subgroups: 14-19 weeks gestation versus 20-23 weeks, and by whether spontaneous or a termination. The primary outcome was any loss or perinatal death before 24 weeks in the subsequent pregnancy.

MAIN RESULTS AND THE ROLE OF CHANCE

After a 14-19 weeks index loss, an IPI of ≤3 months had an increased rate of recurrent loss compared with an IPI of >9-12 months: 21.9% versus 11.3% (adjusted relative risk (aRR) = 2.02, 95% CI 1.44-2.83). For women who had a spontaneous index loss of 20-23 weeks, there was no evidence that a short IPI increased or decreased the risk of recurrent loss. For any gestational age group of index losses, an IPI of >18-24 months increased the risk of a recurrent loss; the risk was highest after a 20-23 weeks index loss (aRR = 2.15, 95% CI 1.18-3.91).

LIMITATIONS, REASONS FOR CAUTION

We do not know how many cycles were required to achieve conception. Pregnancies resulting in early first trimester losses are unlikely to have resulted in hospitalization so would not have been identified.

WIDER IMPLICATIONS OF THE FINDINGS

The risk of recurrent loss after an initial midtrimester loss may differ from the risk after an initial first trimester loss.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by an Australian National Health and Medical Research Council (NHMRC) Centre for Research Excellence Grant (1001066). C.L.R. is supported by an NHMRC Senior Research Fellowship (#APP1021025). J.B.F. is supported by an ARC Future Fellowship (#120100069). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Mono-2-ethylhexyl phthalate (MEHP) alters histiotrophic nutrition pathways and epigenetic processes in the developing conceptus

Histiotrophic nutrition pathways (HNPs) are processes by which the organogenesis-stage conceptus obtains nutrients, amino acids, vitamins and cofactors required for protein biosynthesis and metabolic activities. Nutrients are captured from the maternal milieu as whole proteins and cargoes via receptor-mediated endocytosis in the visceral yolk sac (VYS), degraded by lysosomal proteolysis and delivered to the developing embryo (EMB). Several nutrients obtained by HNPs are required substrates for one-carbon (C1) metabolism and supply methyl groups required for epigenetic processes, including DNA and histone methylation. Increased availability of methyl donors has been associated with reduced risk for neural tube defects (NTDs). Here, we show that mono-2-ethylhexyl phthalate (MEHP) treatment (100 or 250μM) alters HNPs, C1 metabolism and epigenetic programming in the organogenesis-stage conceptus. Specifically, 3-h MEHP treatment of mouse EMBs in whole culture resulted in dose-dependent reduction of HNP activity in the conceptus. To observe nutrient consequences of decreased HNP function, C1 components and substrates and epigenetic outcomes were quantified at 24h. Treatment with 100-μM MEHP resulted in decreased dietary methyl donor concentrations, while treatment with 100- or 250-μM MEHP resulted in dose-dependent elevated C1 products and substrates. In MEHP-treated EMBs with NTDs, H3K4 methylation was significantly increased, while no effects were seen in treated VYS. DNA methylation was reduced in MEHP-treated EMB with and without NTDs. This research suggests that environmental toxicants such as MEHP decrease embryonic nutrition in a time-dependent manner and that epigenetic consequences of HNP disruption may be exacerbated in EMB with NTDs.

Fetal and neonatal exposure to nicotine leads to augmented hepatic and circulating triglycerides in adult male offspring due to increased expression of fatty acid synthase

While nicotine replacement therapy is assumed to be a safer alternative to smoking during pregnancy, the long-term consequences for the offspring remain elusive. Animal studies now suggest that maternal nicotine exposure during perinatal life leads to a wide range of adverse outcomes for the offspring including increased adiposity. The focus of this study was to investigate if nicotine exposure during pregnancy and lactation leads to alterations in hepatic triglyceride synthesis. Female Wistar rats were randomly assigned to receive daily subcutaneous injections of saline (vehicle) or nicotine bitartrate (1mg/kg/day) for two weeks prior to mating until weaning. At postnatal day 180 (PND 180), nicotine exposed offspring exhibited significantly elevated levels of circulating and hepatic triglycerides in the male offspring. This was concomitant with increased expression of fatty acid synthase (FAS), the critical hepatic enzyme in de novo triglyceride synthesis. Given that FAS is regulated by the nuclear receptor Liver X receptor (LXRα), we measured LXRα expression in both control and nicotine-exposed offspring. Nicotine exposure during pregnancy and lactation led to an increase in hepatic LXRα protein expression and enriched binding to the putative LXRE element on the FAS promoter in PND 180 male offspring. This was also associated with significantly enhanced acetylation of histone H3 [K9,14] surrounding the FAS promoter, a hallmark of chromatin activation. Collectively, these findings suggest that nicotine exposure during pregnancy and lactation leads to an increase in circulating and hepatic triglycerides long-term via changes in the transcriptional and epigenetic regulation of the hepatic lipogenic pathway.

Anthropometric, socioeconomic, and maternal health determinants of placental transfer of organochlorine compounds

The aim of this study was to relate placental transfer, quantified by the cord to maternal serum concentration ratio (C/M), of five organochlorine pesticides (OCP) hexachlorobenzene (HCB), β-hexachlorocyclohexane (β-HCH), γ-hexachlorocyclohexane (γ-HCH) , p,p'-DDT, p,p'-DDE and 15 polychlorinated biphenyl (PCB) congeners (28, 52, 101, 105, 114, 118, 123(+149), 138(+163), 153, 156(+171), 157, 167, 170, 180, and 189) to anthropometric, socioeconomic, and maternal health characteristics. We included into the study 1,134 births during the period 2002-2004 from two districts in eastern Slovakia with high organochlorine concentrations relative to other areas of the world. Only concentrations >LOD were taken into account. Variables as age, weight and height of mothers, parity, ethnicity, alcohol consumption, illness during pregnancy, smoking during pregnancy, hypertension, respiratory diseases, rheumatoid arthritis and diabetes mellitus, and birth weight were related to C/M. Results of regression analyses showed that C/M was predicted by several factors studied. Positive associations were observed for gestational alcohol consumption, fewer illnesses during pregnancy, maternal age, and maternal weight. Caucasians had a greater C/M compared to Romani for wet weight data of congeners 170 and 180 and in contrast C/M for HCB was greater in Romani. Our results show that drinking mothers compared to abstaining expose their fetuses not only to alcohol but to an increased level of several PCB congeners. A straightforward explanation of associations between C/M shifts and factors studied is very difficult, however, with regard to the high lipophilicity of OCPs and PCBs, changes in their kinetics probably reflect lipid kinetics.

Expression and immunolocalisation of the endocytic receptors megalin and cubilin in the human yolk sac and placenta across gestation

Megalin and cubilin are multifunctional endocytic receptors associated with many transporting epithelia. They play an essential role in transport of nutrients through the visceral yolk sac of rodents during embryogenesis. Here, we immunolocalise them to the endodermal layer of the human yolk sac, and to the syncytiotrophoblast and cytotrophoblast cells of placental villi. In villi, the protein level of both receptors increased with gestation. The mRNA for megalin remained constant, while that encoding cubilin increased with gestation. These results suggest megalin and cubilin may be important in human maternal–fetal transfer, and that they increase across gestation to facilitate this function.

Placental adaptations to the maternal-fetal environment: implications for fetal growth and developmental programming

The placenta is a transient organ found in eutherian mammals that evolved primarily to provide nutrients for the developing fetus. The placenta exchanges a wide array of nutrients, endocrine signals, cytokines and growth factors with the mother and the fetus, thereby regulating intrauterine development. Recent studies show that the placenta is not just a passive organ mediating maternal-fetal exchange. It can adapt its capacity to supply nutrients in response to intrinsic and extrinsic variations in the maternal-fetal environment. These dynamic adaptations are thought to occur to maximize fetal growth and viability at birth in the prevailing conditions in utero. However, some of these adaptations may also affect the development of individual fetal tissues, with patho-physiological consequences long after birth. Here, this review summarizes current knowledge on the causes, possible mechanisms and consequences of placental adaptive responses, with a focus on the regulation of transporter-mediated processes for nutrients. This review also highlights the emerging roles that imprinted genes and epigenetic mechanisms of gene regulation may play in placental adaptations to the maternal-fetal environment.

Effects of maternal 5,10-methylenetetrahydrofolate reductase C677T and A1298C Polymorphisms and tobacco smoking on infant birth weight in a Japanese population

Background

Intracellular folate hemostasis depends on the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene. Because 5,10-MTHFR 677TT homozygosity and tobacco smoking are associated with low folate status, we tested the hypothesis that smoking in mothers with 5,10-MTHFR C677T or A1298C polymorphisms would be independently associated with lower birth weight among their offspring.

Methods

We assessed 1784 native Japanese mother-child pairs drawn from the ongoing birth cohort of The Hokkaido Study on Environment and Children’s Health. Data (demographic information, hospital birth records, and biological specimens) were extracted from recruitments that took place during the period from February 2003 to March 2006. Maternal serum folate were assayed by chemiluminescent immunoassay, and genotyping of 5,10-MTHFR C677T/A1298C polymorphisms was done using a TaqMan allelic discrimination assay.

Results

The prevalence of folate deficiency (<6.8 nmol/L) was 0.3%. The 5,10-MTHFR 677CT genotype was independently associated with an increase of 36.40 g (95% CI: 2.60 to 70.30, P = 0.035) in mean infant birth weight and an increase of 90.70 g (95% CI: 6.00 to 175.50, P = 0.036) among male infants of nonsmokers. Female infants of 677TT homozygous passive smokers were 99.00 g (95% CI: −190.26 to −7.56, P = 0.034) lighter. The birth weight of the offspring of smokers with 5,10-MTHFR 1298AA homozygosity was lower by 107.00 g (95% CI: −180.00 to −33.90, P = 0.004).

Conclusions

The results suggest that, in this population, maternal 5,10-MTHFR C677T polymorphism, but not the 5,10-MTHFR A1298C variant, is independently associated with improvement in infant birth weight, especially among nonsmokers. However, 5,10-MTHFR 1298AA might be associated with folate impairment and could interact with tobacco smoke to further decrease birth weight.

Hepcidin and iron species distribution inside the first-trimester human gestational sac

We have investigated factors affecting iron distribution in the first-trimester gestational sac, by the measurement of transferrin, non-transferrin-bound iron (NTBI) and pro-hepcidin (Hep) in maternal serum, coelomic fluid (CF) and amniotic fluid (AF) and by immunostaining for Hep in villous and secondary yolk sac biopsies. These samples were obtained from 15 first-trimester pregnancies at 8-11 weeks gestation. Transferrin concentrations were significantly lower in fetal (0.56 mg/ml) than maternal serum (1.71 mg/ml), with very low concentrations in CF and AF (0.09 mg/ml). In contrast, transferrin saturations were significantly higher in fetal (77%) than maternal serum (33%). NTBI was present in fetal serum, CF and AF, presumably as a consequence of low transferrin concentrations in these compartments. Pro-Hep was present at lower levels in fetal (140.0 ± 11.1) than maternal serum (206.2 ± 9.2) and at low concentrations in CF (19.4 ± 3.1) and AF (21.8 ± 5.2). Immunostaining with Hep antibody was found in the syncytiotrophoblast of first-trimester placenta as well as in mesothelial and endodermal layers of the secondary yolk sac at 10 weeks. The presence of Hep in syncytiotrophoblast cells of first-trimester placenta as well as in mesothelial and endodermal layers of the secondary yolk sac suggest a key regulatory role for this protein in iron transfer to the first-trimester fetus. The low transferrin concentrations and the presence of NTBI in CF and AF suggest that transferrin-independent iron transfer is important in early gestation.

Folate pathway and nonsyndromic cleft lip and palate

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common complex birth defect. Periconceptional supplementation with folic acid, a key component in DNA synthesis and cell division, has reduced the birth prevalence of neural tube defects and may similarly reduce the birth prevalence of other complex birth defects including NSCLP. Past studies investigating the role of two common methylenetetrahydrofolate reductase (MTHFR) single-nucleotide polymorphisms (SNPs), C677T (rs1801133) and A1298C (rs1801131), in NSCLP have produced conflicting results. Most studies of folate pathway genes have been limited in scope, as few genes/SNPs have been interrogated. Here, we asked whether variations in a more comprehensive group of folate pathway genes were associated with NSCLP, and were there detectable interactions between these genes and environmental exposures?

METHODS

Fourteen folate metabolism-related genes were interrogated using 89 SNPs in multiplex and simplex non-Hispanic white and Hispanic NSCLP families.

RESULTS

Evidence for a risk association between NSCLP and SNPs in NOS3 and TYMS was detected in the non-Hispanic white group, whereas associations with MTR, BHMT2, MTHFS, and SLC19A1 were detected in the Hispanic group. Evidence for over-transmission of haplotypes and gene interactions in the methionine arm was detected.

CONCLUSIONS

These results suggest that perturbations of the genes in the folate pathway may contribute to NSCLP. There was evidence for an interaction between several SNPs and maternal smoking, and for one SNP with gender of the offspring. These results provide support for other studies that suggest that high maternal homocysteine levels may contribute to NSCLP and should be further investigated.

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.