Paul A. Fowler

Science and policy on endocrine disrupters must not be mixed: a reply to a “common sense” intervention by toxicology journal editors

The “common sense” intervention by toxicology journal editors regarding proposed European Union endocrine disrupter regulations ignores scientific evidence and well-established principles of chemical risk assessment. In this commentary, endocrine disrupter experts express their concerns about a recently published, and is in our considered opinion inaccurate and factually incorrect, editorial that has appeared in several journals in toxicology. Some of the shortcomings of the editorial are discussed in detail. We call for a better founded scientific debate which may help to overcome a polarisation of views detrimental to reaching a consensus about scientific foundations for endocrine disrupter regulation in the EU.

Circulating leptin in women: a longitudinal study in the menstrual cycle and during pregnancy

To investigate whether leptin is linked to reproduction, circulating levels were measured longitudinally throughout spontaneous menstrual cycles and during pregnancy in normal women.

The roles of cellular reactive oxygen species, oxidative stress and antioxidants in pregnancy outcomes.

Reactive oxygen species (ROS) are generated as by-products of aerobic respiration and metabolism. Mammalian cells have evolved a variety of enzymatic mechanisms to control ROS production, one of the central elements in signal transduction pathways involved in cell proliferation, differentiation and apoptosis. Antioxidants also ensure defenses against ROS-induced damage to lipids, proteins and DNA. ROS and antioxidants have been implicated in the regulation of reproductive processes in both animal and human, such as cyclic luteal and endometrial changes, follicular development, ovulation, fertilization, embryogenesis, embryonic implantation, and placental differentiation and growth. In contrast, imbalances between ROS production and antioxidant systems induce oxidative stress that negatively impacts reproductive processes. High levels of ROS during embryonic, fetal and placental development are a feature of pregnancy. Consequently, oxidative stress has emerged as a likely promoter of several pregnancy-related disorders, such as spontaneous abortions, embryopathies, preeclampsia, fetal growth restriction, preterm labor and low birth weight. Nutritional and environmental factors may contribute to such adverse pregnancy outcomes and increase the susceptibility of offspring to disease. This occurs, at least in part, via impairment of the antioxidant defense systems and enhancement of ROS generation which alters cellular signalling and/or damage cellular macromolecules. The links between oxidative stress, the female reproductive system and development of adverse pregnancy outcomes, constitute important issues in human and animal reproductive medicine. This review summarizes the role of ROS in female reproductive processes and the state of knowledge on the association between ROS, oxidative stress, antioxidants and pregnancy outcomes in different mammalian species.

Cyclic changes in composition and volume of the breast during the menstrual cycle, measured by magnetic resonance imaging

Summary. The volumes and spin‐lattice (T1) relaxation times of breast tissues and parenchymal water content were measured non‐invasively by magnetic resonance imaging (MRI) in eight healthy women during four to eight consecutive menstrual cycles. Total breast volume, and parenchymal volume, T1 relaxation time and water content were lowest between days 6 and 15. Between days 16 and 28, parenchymal volume, T1 relaxation time and water content rose sharply by 38·9%, 15·1% and 24·5%, respectively, and peaked after day 25. Within 5 days of the onset of menses, parenchymal volume fell sharply by 30·3%, while water content declined by 17·5%. Rising parenchymal volume in the second half of the menstrual cycle is not solely due to increased tissue water content and provides in vivo evidence for both growth and increased tissue fluid at this time.

Measurement of serum concentrations of inhibin‐A (α‐βA dimer) during human pregnancy

OBJECTIVE The alms were to measure concentrations of Inhibin‐A (α‐βA dimer) in peripheral serum during normal human pregnancy, to establish which molecular weight form(s) are present In pregnancy serum and to relate the concentrations of inhlbin‐A to those of oestradlol and progesterone.

Exposure to a complex cocktail of environmental endocrine-disrupting compounds disturbs the kisspeptin/GPR54 system in ovine hypothalamus and pituitary gland.

Background Ubiquitous environmental chemicals, including endocrine-disrupting chemicals (EDCs), are associated with declining human reproductive health, as well as an increasing incidence of cancers of the reproductive system. Verifying such links requires animal models exposed to “real-life,” environmentally relevant concentrations/mixtures of EDC, particularly in utero, when sensitivity to EDC exposure is maximal. Objectives We evaluated the effects of maternal exposure to a pollutant cocktail (sewage sludge) on the ovine fetal reproductive neuroendocrine axes, particularly the kisspeptin (KiSS-1)/GPR54 (G-protein–coupled receptor 54) system. Methods KiSS-1, GPR54, and ERα (estrogen receptor α) mRNA expression was quantified in control (C) and treated (T) maternal and fetal (110-day) hypothalami and pituitary glands using semiquantitative reverse transcription polymerase chain reaction, and colocalization of kisspeptin with LHβ (luteinizing hormone β) and ERα in C and T fetal pituitary glands quantified using dual-labeling immunohistochemistry. Results Fetuses exposed in utero to the EDC mixture showed reduced KiSS-1 mRNA expression across three hypothalamic regions examined (rostral, mid, and caudal) and had fewer kisspetin immunopositive cells colocalized with both LHβ and ERα in the pituitary gland. In contrast, treatment had no effect on parameters measured in the adult ewe hypothalamus or pituitary. Conclusions This study demonstrates that the developing fetus is sensitive to real-world mixtures of environmental chemicals, which cause significant neuroendocrine alterations. The important role of kisspeptin/GPR54 in regulating puberty and adult reproduction means that in utero disruption of this system is likely to have long-term consequences in adulthood and represents a novel, additional pathway through which environmental chemicals perturb human reproduction.

In utero exposure to low doses of environmental pollutants disrupts fetal ovarian development in sheep

Epidemiological studies of the impact of environmental chemicals on reproductive health demonstrate consequences of exposure but establishing causative links requires animal models using ‘real life’ in utero exposures. We aimed to determine whether prolonged, low-dose, exposure of pregnant sheep to a mixture of environmental chemicals affects fetal ovarian development. Exposure of treated ewes (n = 7) to pollutants was maximized by surface application of processed sewage sludge to pasture. Control ewes (n = 10) were reared on pasture treated with inorganic fertilizer. Ovaries and blood were collected from fetuses (n = 15 control and n = 8 treated) on Day 110 of gestation for investigation of fetal endocrinology, ovarian follicle/oocyte numbers and ovarian proteome. Treated fetuses were 14% lighter than controls but fetal ovary weights were unchanged. Prolactin (48% lower) was the only measured hormone significantly affected by treatment. Treatment reduced numbers of growth differentiation factor (GDF9) and induced myeloid leukaemia cell differentiation protein (MCL1) positive oocytes by 25–26% and increased pro-apoptotic BAX by 65% and 42% of protein spots in the treated ovarian proteome were differently expressed compared with controls. Nineteen spots were identified and included proteins involved in gene expression/transcription, protein synthesis, phosphorylation and receptor activity. Fetal exposure to environmental chemicals, via the mother, significantly perturbs fetal ovarian development. If such effects are replicated in humans, premature menopause could be an outcome.

Body fat in lean and overweight women estimated by six methods

Body fat content of seven lean women (body mass index (BMI) 20.6 (SD 1.8) kg/m2) and seven overweight women (BMI 31.1 (SD 3.3) kg/m2) was estimated by six different methods: underwater weighing (UWW), body-water dilution (BWD), whole-body counting (40K), skinfold thickness (SFT), bioelectrical impedance (BEI) and magnetic resonance imaging (MRI). Using UWW as the reference method, the differences between percentage fat by each other method and the percentage fat by UWW were calculated for each subject. The mean difference was lowest for SFT and highest for BWD. MRI showed the lowest variability in individual results, and 40K the highest. 40K and BWD methods used in combination gave better agreement with UWW results than either 40K or BWD methods alone. There was a weak negative correlation between the difference from the UWW results and percentage fat in the SFT measurements, but not in the BWD, 40K, BEI or MRI measurements, suggesting that for these methods the assumptions involved produced no greater inaccuracy in the overweight women than in the lean women. In all subjects the BEI offered little improvement over the traditional SFT measurements. The agreement between MRI and UWW estimates in both lean and overweight women suggests that MRI may be a satisfactory substitute for the more established methods of body fat estimation in adult women.

Development of steroid signaling pathways during primordial follicle formation in the human fetal ovary.

CONTEXT Ovarian primordial follicle formation is critical for subsequent human female fertility. It is likely that steroid, and especially estrogen, signaling is required for this process, but details of the pathways involved are currently lacking. OBJECTIVE The aim was to identify and characterize key members of the steroid-signaling pathway expressed in the second trimester human fetal ovary. DESIGN We conducted an observational study of the female fetus, quantifying and localizing steroid-signaling pathway members. SETTING The study was conducted at the Universities of Aberdeen, Edinburgh, and Glasgow. PATIENTS/PARTICIPANTS Ovaries were collected from 43 morphologically normal human female fetuses from women undergoing elective termination of second trimester pregnancies. MAIN OUTCOME MEASURES We measured mRNA transcript levels and immunolocalized key steroidogenic enzymes and steroid receptors, including those encoded by ESR2, AR, and CYP19A1. RESULTS Levels of mRNA encoding the steroidogenic apparatus and steroid receptors increased across the second trimester. CYP19A1 transcript increased 4.7-fold during this period with intense immunostaining for CYP19A detected in pregranulosa cells around primordial follicles and somatic cells around oocyte nests. ESR2 was localized primarily to germ cells, but androgen receptor was exclusively expressed in somatic cells. CYP17A1 and HSD3B2 were also localized to oocytes, whereas CYP11A1 was detected in oocytes and some pregranulosa cells. CONCLUSIONS The human fetal ovary expresses the machinery to produce and detect multiple steroid signaling pathways, including estrogenic signaling, with the oocyte acting as a key component. This study provides a step-change in our understanding of local dynamics of steroid hormone signaling during the key period of human primordial follicle formation.

Maternal Smoking and Fetal Sex Significantly Affect Metabolic Enzyme Expression in the Human Fetal Liver

CONTEXT Pollutants and toxicants passing from the mother to the fetus may damage developing organ systems. The human fetal liver is both a potential target organ and a critical defense against exposure to such xenochemicals. OBJECTIVE The aim of the study was to determine the effects of human fetal toxicant exposure, via maternal smoking, on metabolic enzyme transcripts in the fetal liver. DESIGN AND SETTING We conducted an observational study of mRNA transcripts and proteins in livers from second trimester fetuses at the Universities of Aberdeen and Glasgow. PATIENTS/PARTICIPANTS Liver samples were taken from 55 normal fetuses from women undergoing second trimester elective termination. MAIN OUTCOME MEASURES Housekeeping genes for normalization were identified by GeNorm and NormFinder. Levels of mRNA transcripts encoding 15 metabolic enzymes and three xenobiotic receptors were measured. Expression of representative proteins was shown by Western blotting. RESULTS Eighty-nine percent of measured transcripts were detectable in the human fetal liver. Eight transcripts showed significant sex-specific differences in expression levels (EPHX1, GSTA1, GSTT1, AHR, AS3MT, GLRX2, GGT1, CAR). In male fetuses, maternal smoking was associated with a decrease in expression of three transcripts (GGT1, CYP2R1, CAR) and an increase in eight transcripts (CYP1A1, EPHX1, NQO1, GSTP1, GSTT1, AHR, AS3MT, GLRX2). In the female, CYP3A7 and EPHX1 were increased in smoke-exposed fetuses. CONCLUSIONS The human fetal liver expresses a wide array of metabolic enzymes, with sex differences apparent in 44% of the transcripts measured. Exposure of the fetus to pollutants/toxicants is associated with significantly altered transcript expression, with the more marked response in the male potentially affecting levels of endogenous factors involved in fetal growth.