Exploring autism spectrum disorder (ASD) and attention deficit disorder (ADD/ADHD) in children exposed to polybrominated biphenyl

Background

Although the causes of attention-deficit/hyperactivity disorder (ADHD) and autism have not been identified, exposure to endocrine-disrupting chemicals, such as polybrominated biphenyl (PBB), during fetal development and early life has been suspected to impact neurological development. This study aims to investigate the association between prenatal and early life exposure to PBB and the development of ADHD and autism later in life.

Methods

Data from the Michigan PBB Registry, a cohort of Michigan residents who had been exposed to PBB in a mass contamination event in 1973, was leveraged for this nested case-control analysis among two distinct samples: (1) Those who self-reported ADHD or autism diagnosis, and (2) mothers who reported their child's ADHD or autism diagnosis. PBB exposure was measured in participants of the PBB Registry, and the mother's PBB level was used in mother-reported analyses. Cases were matched with controls by sex and year of birth. Conditional logistic regression models were used to estimate the association between PBB level and case status.

Results

PBB levels were higher among those who were exposed in early life compared with those exposed in utero (geometric mean: 0.300 ng/ml vs. 0.016 ng/ml). Among women in this cohort, a higher than expected proportion of self-reported ADHD diagnosis (11.11%), compared with population estimates. PBB was not associated with ADHD or autism in either self-reported or mother-reported analyses.

Conclusions

This study adds to the sparse literature about prenatal and early life exposure to PBB-153 and ADHD and autism. Future studies should examine potential effect modification by sex.

In-utero exposure to polybrominated biphenyl (PBB) and menstrual cycle function in adulthood

BACKGROUND

There is evidence that in-utero exposure to PBBs, and similar chemicals, are associated with several adverse reproductive health outcomes including altered pubertal timing. However, less is known about the effects of in-utero exposure to PBBs on menstrual cycle function and reproductive hormone levels in adulthood.

METHODS

For this menstrual cycle study, we recruited reproductive-aged women in the Michigan PBB Registry who were not pregnant, lactating, or taking hormonal medications (2004-2014). A total of 41 women who were born after the PBB contamination incident (1973-1974) and were prenatally exposed to PBBs, were included in this analysis. We estimated in-utero PBB exposure using maternal serum PBB measurements taken after exposure and extrapolated to time of pregnancy using a PBB elimination model. Women were followed for up to 6 months during which they provided daily urine samples and completed daily diaries. The urine samples were assayed for estrone 3-glucuronide (E13G), pregnanediol 3-glucuronide (Pd3G), and follicle stimulating hormone (FSH).

RESULTS

Women in our study were, on average, 27.5 (SD:5.3) years old and contributed 4.9 (SD:1.9) menstrual cycles of follow-up. Compared to women with low in-utero PBB exposure (≤1 ppb), women with medium (>1.0-3.0 ppb) and high (>3.0 ppb) exposure had higher maximum 3-day mean Pd3G levels during the luteal phase. Specifically, the age- and creatinine-adjusted maximum 3-day mean luteal phase Pd3G levels (95% CI) in increasing categories of in-utero PBB exposure were 9.2 (4.6,13.9), 14.8 (11.6,18.0), and 16.1 (12.9,19.3) μg/mg creatinine. There were no meaningful differences in average cycle length, follicular or luteal phase cycle length, bleed length, or creatinine-adjusted E13G or FSH levels by category of in-utero PBB exposure.

CONCLUSION

Higher exposure to PBB in-utero was associated with increased progesterone levels across the luteal phase, however, most other menstrual cycle characteristics were largely unassociated with in-utero PBB exposure. Given our modest sample size, our results require cautious interpretation.

Polybrominated biphenyls (PBBs) and prevalence of autoimmune disorders among members of the Michigan PBB registry

BACKGROUND

Polybrominated biphenyls (PBBs), a class of endocrine disrupting chemicals, were the main chemicals present in one of the largest industrial accidents in the United States. We investigated the association between serum PBB-153 levels and autoimmune disorders among members of the Michigan PBB Registry.

METHODS

Eight hundred and ninety-five members of the registry had both a serum PBB-153 measurement and had completed one or more questionnaires about autoimmune disorders. Autoimmune disorders were examined collectively and within specific organ systems. Sex-stratified unadjusted and adjusted log-binomial models were used to examine the association between tertiles of serum PBB-153 levels and autoimmune disorders. Models were adjusted by lifestage at exposure (in utero, childhood, adulthood), smoking history (never, past, current), and total serum lipid levels (continuous). We utilized cubic spline models to investigate non-linearity between serum PBB-153 levels and the prevalence of autoimmune disorders.

RESULTS

Approximately 12.9% and 20.7% of male and female participants reported having one or more autoimmune disorders, respectively. After adjustment for potential confounders, we observed no association between PBB-153 tertiles and the composite classification of 'any autoimmune disorder' in either sex. We observed some evidence for an association between serum PBB-153 levels and rheumatoid arthritis in males and females; however, this was not statistically significant in females. We also observed some evidence for an association between serum PBB-153 levels and neurological- and thyroid-related autoimmune disorders in females, but again this was not statistically significant. Additionally, we identified dose-response curves for serum PBB-153 levels and the prevalence of autoimmune disorders that differed by lifestage of exposure and sex.

CONCLUSIONS

We observed some evidence that increasing serum PBB-153 levels were associated with three specified autoimmune disorders. Studies focusing on these three autoimmune disorders and the potential non-linear trend differences by lifestage of exposure warrant further investigation.

Assessing Metabolic Differences Associated with Exposure to Polybrominated Biphenyl and Polychlorinated Biphenyls in the Michigan PBB Registry

BACKGROUND

Polybrominated biphenyls (PBB) and polychlorinated biphenyls (PCB) are persistent organic pollutants with potential endocrine-disrupting effects linked to adverse health outcomes.

OBJECTIVES

In this study, we utilize high-resolution metabolomics (HRM) to identify internal exposure and biological responses underlying PCB and multigenerational PBB exposure for participants enrolled in the Michigan PBB Registry.

METHODS

HRM profiling was conducted on plasma samples collected from 2013 to 2014 from a subset of participants enrolled in the Michigan PBB Registry, including 369 directly exposed individuals (F0) who were alive when PBB mixtures were accidentally introduced into the food chain and 129 participants exposed to PBB in utero or through breastfeeding, if applicable (F1). Metabolome-wide association studies were performed for PBB-153 separately for each generation and Σ PCB (PCB-118, PCB-138, PCB-153, and PCB-180) in the two generations combined, as both had direct PCB exposure. Metabolite and metabolic pathway alterations were evaluated following a well-established untargeted HRM workflow.

RESULTS

Mean levels were 1.75  ng / mL [standard deviation (SD): 13.9] for PBB-153 and 1.04  ng / mL (SD: 0.788) for Σ PCB . Sixty-two and 26 metabolic features were significantly associated with PBB-153 in F0 and F1 [false discovery rate (FDR) p < 0.2 ], respectively. There were 2,861 features associated with Σ PCB (FDR p < 0.2 ). Metabolic pathway enrichment analysis using a bioinformatics tool revealed perturbations associated with Σ PCB in numerous oxidative stress and inflammation pathways (e.g., carnitine shuttle, glycosphingolipid, and vitamin B9 metabolism). Metabolic perturbations associated with PBB-153 in F0 were related to oxidative stress (e.g., pentose phosphate and vitamin C metabolism) and in F1 were related to energy production (e.g., pyrimidine, amino sugars, and lysine metabolism). Using authentic chemical standards, we confirmed the chemical identity of 29 metabolites associated with Σ PCB levels (level 1 evidence).

CONCLUSIONS

Our results demonstrate that serum PBB-153 is associated with alterations in inflammation and oxidative stress-related pathways, which differed when stratified by generation. We also found that Σ PCB was associated with the downregulation of important neurotransmitters, serotonin, and 4-aminobutanoate. These findings provide novel insights for future investigations of molecular mechanisms underlying PBB and PCB exposure on health. https://doi.org/10.1289/EHP12657.

Elimination of PBB-153; findings from a cohort of Michigan adults

BACKGROUND

An industrial accident led to the widespread contamination of polybrominated biphenyl (PBB), a flame retardant, into the food system in Michigan in the 1970's. PBB continues to be detected in Michiganders' blood some forty years later. It is necessary to understand the elimination rate and half-life of PBB because it may provide clues on how to hasten the elimination of it from the human body.

METHODS

Serum samples were taken from young adult and adult participants of the Michigan PBB registry from 1974 to 2019. A single compartment model was assumed for the elimination rate for PBB-153 in young adults and adults (≥16 years). Generalized linear mixed models were used to estimate the average elimination rate of PBB-153 and allowed for a random intercept and slope for the time between measurements. Models were adjusted for age at exposure, body mass index (BMI) at initial measurement, and smoking. Models were also stratified by demographic characteristics.

RESULTS

In total, 1974 participants contributed 4768 samples over a forty-year span. The median initial PBB-153 level was 1.542 parts per billion (ppb) (Range: 0.001-1442.48 ppb). The adjusted median participant-specific half-life for PBB-153 was 12.23 years. The half-life of PBB-153 was lengthened by higher initial PBB level (∼1.5 years), younger age at exposure (∼5.4 years), higher BMI (∼1.0 years), and increased gravidity (∼7.3 years). Additionally, the half-life of PBB-153 was shortened by smoking status (∼-2.8 years) and breastfeeding (∼-3.5 years).

CONCLUSIONS

Consistent with previous studies, PBB-153 has been demonstrated to have a long half-life in the human body and may be modified by some demographic characteristics. These updated estimates of half-life will further support evaluation of health effects associated with PBB exposure. Investigations into mechanisms to accelerate elimination and reduce body burdens of PBB-153, especially those related to body weight, are needed.

Birth outcomes associated with paternal polybrominated and polychlorinated biphenyl exposure

In 1973-74, a polybrominated biphenyl (PBB) flame retardant mixture was shipped to Michigan livestock feed mills in place of a nutritional supplement and contaminated the food supply. Following the accident, the Michigan PBB Registry was established to study the long-term health effects of halogenated compounds and is now led by a community-academic partnership. PBB exposure is associated with altered DNA methylation in sperm, which may lead to adverse birth outcomes in children whose fathers have increased levels of serum PBB or polychlorinated biphenyl (PCB). Paternal PBB and PCB levels of men enrolled in the Michigan PBB Registry (n = 155) were analyzed against matched offspring birthweight and gestational age (n = 336). Birthweight and gestational age were dichotomized at the 25th percentile and 37 weeks, respectively, and paternal PBB and PCB levels were examined as continuous measures and divided into tertiles. Associations of offspring birthweight and gestational age with paternal PBB and PCB serum concentrations were modeled using multivariable linear spline and log-risk regression, adjusting for family clustering, paternal health and lifestyle factors, maternal PBB, and PCB serum concentrations, sex, and offspring gestational age (for birthweight). Fathers in the middle and upper PBB and PCB tertiles had increased risks for lowest quartile birthweight compared to the first tertile, with adjusted risk ratios (aRR) = 1.67 (95% CI: 0.93, 2.99) and aRR = 2.06 (95% CI: 1.12, 3.79) for PBB, and aRR = 1.47 (95% CI: 0.79, 2.75) and aRR = 1.34 (95% CI: 0.70, 2.54) for PCB, respectively. Elevated paternal PBB levels were not associated with an increased risk for preterm birth, while PCB levels were associated with a small, but not significant, decrease in gestational age, β = -0.37 (95% CI: -0.76, 0.03) weeks per log unit increase PCB. The findings suggest that increased paternal PBB and PCB levels negatively impact offspring birthweight, and paternal PCB levels may negatively impact gestational age.

Genome-wide DNA methylation differences and polychlorinated biphenyl (PCB) exposure in a US population

Exposure to polychlorinated biphenyls (PCBs), an endocrine-disrupting compound, is ubiquitous despite decades-old bans on the manufacture and use of PCBs. Increased exposure to PCBs is associated with adverse health consequences throughout life, including type 2 diabetes and cancer. PCB exposure is also associated with alterations in epigenetic marks and gene transcription, which could lead to adverse health outcomes, but many of these are population-specific. To further investigate the association between PCB and epigenetic marks, DNA methylation was measured at 787,684 CpG sites in 641 peripheral blood samples from the Michigan Polybrominated Biphenyl (PBB) Registry. 1345 CpGs were associated with increased total PCB level after controlling for age, sex, and 24 surrogate variables (FDR < 0.05). These CpGs were enriched in active promoter and transcription associated regions (p < 0.05), and in regions around the binding sites for transcription factors involved in xenobiotic metabolism and immune function (FDR < 0.05). PCB exposure also associated with proportions of CD4T, NK, and granulocyte cell types, and with the neutrophil to lymphocyte ratio (NLR) (p < 0.05), and the estimated effect sizes of PCB on the epigenome were correlated with the effect sizes previously reported in an epigenome-wide study of C-reactive protein (r = 0.29; p = 2.22e-5), supporting previous studies on the association between PCB and immune dysfunction. These results indicate that PCB exposure is associated with differences in epigenetic marks in active regions of the genome, and future work should investigate whether these may mediate the association between PCB and health consequences.

Sex-specific DNA methylation differences in people exposed to polybrominated biphenyl

Aim: Michigan residents were exposed to polybrominated biphenyls (PBBs) when it was accidentally added to the food supply. Highly exposed individuals report sex-specific health problems, but the underlying biological mechanism behind these different health risks is not known. Materials and methods: DNA methylation in blood from 381 women and 277 men with PBB exposure was analyzed with the MethylationEPIC BeadChip. Results: 675 CpGs were associated with PBBs levels in males, while only 17 CpGs were associated in females (false discovery rate <0.05). No CpGs were associated in both sexes. These CpGs were enriched in different functional regions and transcription factor binding sites in each sex. Conclusion: Exposure to PBBs may have sex-specific effects on the epigenome that may underlie sex-specific adverse health outcomes.

Detrimental effects of flame retardant, PBB153, exposure on sperm and future generations

In 1973, the Velsicol Chemical Company, which manufactured FireMaster, a brominated flame retardant, and NutriMaster, a nutritional supplement, mistakenly shipped hundreds of pounds of FireMaster to grain mills around Michigan where it was incorporated into animal feed and then into the food chain across the state. An estimated 6.5 million Michigan residents consumed polybrominated biphenyl (PBB)-laced animal products leading to one of the largest agricultural accidents in U.S. history. To date, there have been no studies investigating the effects of PBB on epigenetic regulation in sperm, which could explain some of the endocrine-related health effects observed among children of PBB-exposed parents. Fusing epidemiological approaches with a novel in vitro model of human spermatogenesis, we demonstrate that exposure to PBB153, the primary component of FireMaster, alters the epigenome in human spermatogenic cells. Using our novel stem cell-based spermatogenesis model, we show that PBB153 exposure decreases DNA methylation at regulatory elements controlling imprinted genes. Furthermore, PBB153 affects DNA methylation by reducing de novo DNA methyltransferase activity at increasing PBB153 concentrations as well as reducing maintenance DNA methyltransferase activity at the lowest tested PBB153 concentration. Additionally, PBB153 exposure alters the expression of genes critical to proper human development. Taken together, these results suggest that PBB153 exposure alters the epigenome by disrupting methyltransferase activity leading to defects in imprint establishment causing altered gene expression, which could contribute to health concerns in the children of men exposed to PBB153. While this chemical is toxic to those directly exposed, the results from this study indicate that the epigenetic repercussions may be detrimental to future generations. Above all, this model may be expanded to model a multitude of environmental exposures to elucidate the effect of various chemicals on germline epigenetics and how paternal exposure may impact the health of future generations.

Hormonal Profiles of Menstrual Bleeding Patterns During the Luteal-Follicular Transition

CONTEXT

Menstrual cycle function is determined by a complex endocrine axis that controls the ovaries and endometrium. While the late luteal phase is characterized by declining progesterone and estrogen, how these hormonal profiles relate to menstrual bleeding patterns is not well understood.

OBJECTIVE

Characterize associations between luteal phase hormonal profiles and subsequent menstrual bleeding patterns, specifically spotting before bleeding.

DESIGN, SETTING, AND PARTICIPANTS

We examined creatinine-adjusted urinary estrone 3-glucuronide (E13G) and pregnanediol 3-glucuronide (Pd3G) levels in relation to spotting in 116 premenopausal women (ages 20-47) who kept daily menstrual diaries and collected first morning urine samples for ≥ 2 consecutive cycles or 1 luteal-follicular transition (n = 283 transitions). We used linear mixed models to estimate associations between luteal phase hormone levels and spotting before bleeding.

MAIN OUTCOME MEASURE(S) AND RESULTS

Transitions with ≥ 1 days of spotting before menstrual bleeding (n = 118) had greater luteal phase Pd3G levels vs nonspotting transitions (n = 165). Differences in Pd3G between spotting and nonspotting transitions were largest at menses onset (34.8%, 95% confidence interval, 18.9%, 52.7%). Pd3G levels for spotting transitions dropped to similar levels as nonspotting transitions an average of 1 day later, which aligned with the first day of bleeding for transitions with contiguous spotting. Spotting transitions were preceded by slower rates of Pd3G decline than nonspotting transitions, whereas E13G declines were similar.

CONCLUSIONS

Self-reported bleeding patterns may provide insight into luteal phase Pd3G levels. First bleed appears to be the best choice for defining the end of the luteal phase and achieving hormonal consistency across transitions.

Serum concentrations of polybrominated biphenyls (PBBs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the Michigan PBB Registry 40 years after the PBB contamination incident

Widespread polybrominated biphenyls (PBBs) contamination occurred in Michigan from 1973 to 1974, when PBBs were accidentally substituted for a nutritional supplement in livestock feed. People who lived in the state were exposed to PBBs via several routes including ingestion, inhalation and skin absorption. PBBs sequestered in lipid-rich matrices such as adipose tissue, are slowly eliminated after entering the human body, and can also be transferred from a mother to her offspring through the placenta and breastfeeding. Due to the long biological half-lives of PBBs, as well as concerns from the exposed community, biomonitoring measurements were conducted from 2012 to 2015. Because of their similar structures, serum PBBs, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were all measured 40 years after the PBB contamination incident (N = 862). The serum PBB-153 levels among the original highly-exposed groups (i.e., chemical workers, the family of chemical workers, and individuals who lived on or received food from the contaminated farms) remains significantly higher than other Michigan residents. Several predictors such as sampling age, sex, and smoking status were significantly associated with the serum levels of some persistent organic pollutants (POPs). Higher average values and also wider ranges of serum POP levels were found in this study compared to the National Health and Nutrition Examination Survey (NHANES), with the most substantial difference in serum PBB-153. This was true for all groups of Michigan residents including those who were not part of the above-described highly-exposed groups. Moreover, the people born after the contamination incident began also have higher serum PBB-153 levels when compared with more recent NHANES data (2010-2014), which suggests potential intergenerational exposure and/or continued environmental exposure following the contamination period.

Endometriosis, endocrine disrupters, and epigenetics: an investigation into the complex interplay in women with polybrominated biphenyl exposure and endometriosis

PURPOSE

Endocrine disrupting compounds (EDCs) have been shown to affect multiple biologic processes especially steroid-hormone processes. We sought to determine differences in DNA methylation exists between women with and without endometriosis following exposure to polybrominated biphenyl (PBB).

METHODS

Cross-sectional study of 305 females in the Michigan PBB Registry. DNA was extracted, and DNA methylation was interrogated using the MethylationEPIC BeadChip (Illumina, San Diego, California). Demographic data was analyzed using Chi-squared and T tests. Linear regressions were performed for each cytosine-guanine dinucleotide (CpG) site, modeling the logit transformation of the β value as a linear function of the presence of endometriosis. Sensitivity analyses were conducted controlling for estradiol levels and menopausal status. Replication study performed evaluating for any association between CpGs reported in the literature and our findings.

RESULTS

In total, 39,877 CpGs nominally associated with endometriosis (p < 0.05) after adjusting for age and cellular heterogeneity, although none remained significant after correction for multiple comparisons (FDR < 0.05). Pathway analysis of these CpGs showed enrichment in 68 biologic pathways involved in various endocrine, immunologic, oncologic, and cell regulation processes as well as embryologic reproductive tract development and function (FoxO, Wnt, and Hedgehog signaling). We identified 42,261 CpG sites in the literature reported to be associated with endometriosis; 2012 of these CpG sites were also significant in our cohort.

CONCLUSION

We found 39,877 CpG sites that nominally associated with endometriosis (p < 0.05) after adjusting for age and cellular heterogeneity; however, none remained significant after correction for multiple comparisons (FDR < 0.05).

Thyroid hormone levels associate with exposure to polychlorinated biphenyls and polybrominated biphenyls in adults exposed as children

BACKGROUND

Michigan residents were directly exposed to endocrine-disrupting compounds, polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB). A growing body of evidence suggests that exposure to certain endocrine-disrupting compounds may affect thyroid function, especially in people exposed as children, but there are conflicting observations. In this study, we extend previous work by examining age of exposure's effect on the relationship between PBB exposure and thyroid function in a large group of individuals exposed to PBB.

METHODS

Linear regression models were used to test the association between serum measures of thyroid function (total thyroxine (T4), total triiodothyronine (T3), free T4, free T3, thyroid stimulating hormone (TSH), and free T3: free T4 ratio) and serum PBB and PCB levels in a cross-sectional analysis of 715 participants in the Michigan PBB Registry.

RESULTS

Higher PBB levels were associated with many thyroid hormones measures, including higher free T3 (p = 0.002), lower free T4 (p = 0.01), and higher free T3: free T4 ratio (p = 0.0001). Higher PCB levels were associated with higher free T4 (p = 0.0002), and higher free T3: free T4 ratio (p = 0.002). Importantly, the association between PBB and thyroid hormones was dependent on age at exposure. Among people exposed before age 16 (N = 446), higher PBB exposure was associated with higher total T3 (p = 0.01) and free T3 (p = 0.0003), lower free T4 (p = 0.04), and higher free T3: free T4 ratio (p = 0.0001). No significant associations were found among participants who were exposed after age 16. No significant associations were found between TSH and PBB or PCB in any of the analyses conducted.

CONCLUSIONS

This suggests that both PBB and PCB are associated with thyroid function, particularly among those who were exposed as children or prenatally.

Environmental exposure to polybrominated biphenyl (PBB) associates with an increased rate of biological aging

Advanced age increases risk for cancer, cardiovascular disease, and all-cause mortality. However, people do not age at the same rate, and biological age (frequently measured through DNA methylation) can be older than chronological age. Environmental factors have been associated with the rate of biological aging, but it is not known whether persistent endocrine-disrupting compounds (EDCs) like polybrominated biphenyl (PBB) would associate with age acceleration. Three different epigenetic age acceleration measures (intrinsic, extrinsic, and phenotypic) were calculated from existing epigenetic data in whole blood from a population highly exposed to PBB (N=658). Association between serum PBB concentration and these measures was tested, controlling for sex, lipid levels, and estimated cell type proportions. Higher PBB levels associated with increased age acceleration (intrinsic: β=0.24, 95%CI=0.01-0.46, p = 0.03; extrinsic: β=0.39, 95%CI=0.12-0.65, p = 0.004; and phenotypic: β=0.30, 95%CI=0.05-0.54, p = 0.01). Neither age when exposed to PBB nor sex statistically interacted with PBB to predict age acceleration, but, in stratified analyses, the association between PBB and age acceleration was only in people exposed before finishing puberty and in men. This suggests that EDCs can associate with the biological aging process, and further studies are warranted to investigate other environmental pollutants' effect on aging.

Exposure to polybrominated biphenyl and stochastic epigenetic mutations: application of a novel epigenetic approach to environmental exposure in the Michigan polybrominated biphenyl registry

Endocrine-disrupting compounds are associated with altered epigenetic regulation and adverse health outcomes, although inconsistent results suggest that people have varied responses to the same exposure. Interpersonal variation in response to environmental exposures is not identified using standard, population-based methods. However, methods that capture an individual's response, such as analyzing stochastic epigenetic mutations (SEMs), may capture currently missed effects of environmental exposure. To test whether polybrominated biphenyl (PBB) was associated with SEMs, DNA methylation was measured using Illumina's MethylationEPIC array in PBB-exposed individuals, and SEMs were identified. Association was tested using a linear regression with robust sandwich variance estimators, controlling for age, sex, lipids, and cell types. The number of SEMs was variable (range: 119-18,309), and positively associated with age (p = 1.23e-17), but not with sex (p = 0.97). PBBs and SEMs were only positively associated in people who were older when they were exposed (p = 0.02 vs. p = 0.91). Many subjects had SEMs enriched in biological pathways, particularly in pathways involved with xenobiotic metabolism and endocrine function. Higher number of SEMs was also associated with higher age acceleration (intrinsic: p = 1.70e-3; extrinsic: p = 3.59e-11), indicating that SEMs may be associated with age-related health problems. Finding an association between environmental contaminants and higher SEMs may provide insight into individual differences in response to environmental contaminants, as well as into the biological mechanism behind SEM formation. Furthermore, these results suggest that people may be particularly vulnerable to epigenetic dysregulation from environmental exposures as they age.

Exposure to polybrominated biphenyl (PBB) associates with genome-wide DNA methylation differences in peripheral blood

In 1973, Michigan residents were exposed to polybrominated biphenyl (PBB) when it was accidentally added to farm animal feed. Highly exposed individuals and their children have experienced endocrine-related health problems, though the underlying mechanism behind these remains unknown. We investigated whether PBB exposure is associated with variation in DNA methylation in peripheral blood samples from 658 participants of the Michigan PBB registry using the MethylationEPIC BeadChip, as well as investigated what the potential function of the affected regions are and whether these epigenetic marks are known to associate with endocrine system pathways. After multiple test correction (FDR <0.05), 1890 CpG sites associated with total PBB levels. These CpGs were not enriched in any particular biological pathway, but were enriched in enhancer and insulator regions, and depleted in regions near the transcription start site or in CpG islands (p < 0.05). They were also more likely to be in ARNT and ESR2 transcription factor binding sites (p = 3.27e-23 and p = 1.62e-6, respectively), and there was significant overlap between CpGs associated with PBB and CpGs associated with estrogen (p < 2.2e-16). PBB-associated CpGs were also enriched for CpGs known to be associated with gene expression in blood (eQTMs) (p < 0.05). These eQTMs were enriched for pathways related to immune function and endocrine-related autoimmune disease (FDR <0.05). These results indicate that exposure to PBB is associated with differences in epigenetic marks that suggest that it is acting similarly to estrogen and is associated with dysregulated immune system pathways.

Intergenerational effects of endocrine-disrupting compounds: a review of the Michigan polybrominated biphenyl registry

Endocrine-disrupting compounds (EDCs) are a broad class of chemicals present in many residential products that can disrupt hormone signaling and cause health problems in humans. Multigenerational cohorts, like the Michigan polybrominated biphenyl registry, are ideal for studying the effects of intergenerational exposure. Registry participants report hormone-related health problems, particularly in those exposed before puberty or those in the second generation exposed through placental transfer or breastfeeding. However, more research is needed to determine how EDCs cause health problems and the mechanisms underlying intergenerational exposure. Utilizing existing data in this registry, along with genetic and epigenetic approaches, could provide insight to how EDCs cause human disease and help to determine the risk to exposed populations and future generations.

Thyroid hormones and menstrual cycle function in a longitudinal cohort of premenopausal women

BACKGROUND

Previous studies have reported that hyperthyroid and hypothyroid women experience menstrual irregularities more often compared with euthyroid women, but reasons for this are not well-understood and studies on thyroid hormones among euthyroid women are lacking. In a prospective cohort study of euthyroid women, this study characterised the relationship between thyroid hormone concentrations and prospectively collected menstrual function outcomes.

METHODS

Between 2004-2014, 86 euthyroid premenopausal women not lactating or taking hormonal medications participated in a study measuring menstrual function. Serum thyroid hormones were measured before the menstrual function study began. Women then collected first morning urine voids and completed daily bleeding diaries every day for three cycles. Urinary oestrogen and progesterone metabolites (estrone 3-glucuronide (E₁ 3G) and pregnanediol 3-glucuronide (Pd3G)) and follicle-stimulating hormone were measured and adjusted for creatinine (Cr).

RESULTS

Total thyroxine (T₄ ) concentrations were positively associated with Pd3G and E₁ 3G. Women with higher (vs lower) T₄ had greater luteal phase maximum Pd3G (Pd3G = 11.7 μg/mg Cr for women with high T₄ vs Pd3G = 9.5 and 8.1 μg/mg Cr for women with medium and low T₄ , respectively) and greater follicular phase maximum E₁ 3G (E₁ 3G = 41.7 ng/mg Cr for women with high T₄ vs E₁ 3G = 34.3 and 33.7 ng/mg Cr for women with medium and low T₄ , respectively).

CONCLUSIONS

Circulating thyroid hormone concentrations were associated with subtle differences in menstrual cycle function outcomes, particularly sex steroid hormone levels in healthy women. Results contribute to the understanding of the relationship between thyroid function and the menstrual cycle, and may have implications for fertility and chronic disease.

Serum Polybrominated Biphenyls (PBBs) and Polychlorinated Biphenyls (PCBs) and Thyroid Function among Michigan Adults Several Decades after the 1973-1974 PBB Contamination of Livestock Feed

BACKGROUND

In 1973-1974, Michigan residents were exposed to polybrominated biphenyls (PBBs) through an accidental contamination of the food supply. Residents were enrolled in a registry assembled after the incident, and they and their children participated in follow-up studies to assess subsequent health outcomes.

OBJECTIVES

We evaluated associations between serum PBBs and polychlorinated biphenyls (PCBs) and markers of thyroid function among Michigan adults.

METHODS

Serum concentrations of four PBB and four PCB congeners were measured at least once in 753 adults, including 79 women who participated in a 2004-2006 study and 683 women and men with follow-up during 2012-2015. Participants completed questionnaires on health conditions (including physician-diagnosed thyroid disease), behaviors, and demographics. Thyroid hormones were measured in a subset without thyroid disease (n=551). In multivariable linear regression models, PBB and PCB congener concentrations, on both the volume (nanogram/milliliter) and lipid (nanogram/gram lipid) basis, were assessed in relation to thyroid hormones. Logistic regression models were used to estimate associations between serum PBBs and PCBs and thyroid disease.

RESULTS

Thyroid disease was common (18% overall; 25% among women). Among women, all odds ratios (ORs) for PBB-153 and thyroid disease were positive for quintiles above the reference level, but estimates were imprecise and were without a monotonic increase. For an interquartile range (IQR) increase in PBB-153 (0.43 ng/mL), the OR (any thyroid disease)=1.12; (95% CI: 0.83, 1.52) (n=105 cases); for hypothyroidism, OR=1.35 (95% CI: 0.86, 2.13) (n=49 cases). There were 21 cases of thyroid disease in men [OR=0.69 (95% CI: 0.33); 1.44 for an IQR increase (0.75 ng/mL) in serum PBB-153]. PCB congeners were statistically significantly associated with greater total and free thyroxine and total triiodothyronine among women and with total and free triiodothyronine among men in lipid-standardized models.

CONCLUSIONS

We found some evidence to support associations of PBBs and PCBs with thyroid disease and thyroid hormone levels. https://doi.org/10.1289/EHP1302.

Breast cancer among women in Michigan following exposure to brominated flame retardants

In this updated follow-up, we investigated the breast cancer experience among women in Michigan exposed to brominated flame retardants, some 30 years following exposure. Michigan residents were enrolled in a study cohort after exposure to polybrominated biphenyls (PBBs) through the consumption of contaminated food products. PBB concentrations were measured in serum at the time of enrolment. Cancer experience was determined by linkage to the Michigan Cancer Registry. We conducted a nested case-control study that included 51 women diagnosed with breast cancer during 1974-2004 and 202 age-matched controls. While the data suggest an increase in breast cancer risk with higher PBB exposure, this did not reach statistical significance. The OR of having breast cancer among women with PBB concentrations ≥10 ng/mL compared to women with PBB concentrations at or below the limit of detection of 1 ng/mL was 2.60, 95% CI 0.93 to 7.27, (p=0.07), when adjusted for age and family history of cancer in a first-degree female relative. It remains important to examine exposure to brominated chemicals and possible health effects, and to continue following the cancer experience of participants in this study.

Maternal exposure to brominated flame retardants and infant Apgar scores

Brominated flame retardants (BFRs) and other persistent organic pollutants have been associated with adverse health outcomes in humans and may be particularly toxic to the developing fetus. We investigated the association between in utero polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB) exposures and infant Apgar scores in a cohort of Michigan residents exposed to PBB through contaminated food after an industrial accident. PBB and PCB concentrations were measured in serum at the time the women were enrolled in the cohort. PBB concentrations were also estimated at the time of conception for each pregnancy using a validated elimination model. Apgar scores, a universal measure of infant health at birth, measured at 1 and 5min, were taken from birth certificates for 613 offspring born to 330 women. Maternal PCB concentrations at enrollment were not associated with below-median Apgar scores in this cohort. However, maternal PBB exposure was associated with a dose-related increase in the odds of a below-median Apgar score at 1min and 5min. Among infants whose mothers had an estimated PBB at conception above the limit of detection of 1 part per billion (ppb) to <2.5ppb, the odds ratio=2.32 (95% CI: 1.22-4.40); for those with PBB⩾2.5ppb the OR=2.62 (95% CI: 1.38-4.96; test for trend p<0.01). Likewise, the odds of a below-median 5min Apgar score increased with higher maternal PBB at conception. It remains critical that future studies examine possible relationships between in utero exposures to brominated compounds and adverse health outcomes.

Maternal concentrations of polyfluoroalkyl compounds during pregnancy and fetal and postnatal growth in British girls

BACKGROUND

Prenatal exposures to polyfluoroalkyl compounds (PFCs) may be associated with adverse changes in fetal and postnatal growth.

OBJECTIVE

We explored associations of prenatal serum concentrations of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and perfluorohexane sulfonate (PFHxS) with fetal and postnatal growth in girls.

METHODS

We studied a sample of 447 singleton girls and their mothers participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Data on weight and length were obtained at birth and at 2, 9, and 20 months. Serum samples were obtained in 1991-1992, from mothers during pregnancy. We explored associations between prenatal PFC concentrations and weight at birth as well as longitudinal changes in weight-for-age SD scores between birth and 20 months.

RESULTS

PFOS (median, 19.6 ng/mL), PFOA (median, 3.7 ng/mL), and PFHxS (median, 1.6 ng/mL) were detected in 100% of samples. On average, girls born to mothers with prenatal concentrations of PFOS in the upper tertile weighed 140 g less [95% confidence interval (CI): -238, -42] at birth than girls born to mothers with concentrations in the lower tertile in adjusted models. Similar patterns were seen for PFOA (-133 g; 95% CI: -237, -30) and PFHxS (-108 g; 95% CI: -206, -10). At 20 months, however, girls born to mothers with prenatal concentrations of PFOS in the upper tertile weighed 580 g more (95% CI: 301, 858) when compared with those in the lower tertile. No differences in weight were found for PFOA and PFHxS.

CONCLUSIONS

Girls with higher prenatal exposure to each of the PFCs examined were smaller at birth than those with lower exposure. In addition, those with higher exposure to PFOS were larger at 20 months.

Dietary exposure to brominated flame retardants and abnormal Pap test results

OBJECTIVE

This study examined a possible association of dietary exposure to polybrominated biphenyls (PBBs), a brominated flame retardant, and self-reported abnormal Pap test results and cervical dysplasia as a precursor to cervical cancer.

METHODS

Women in Michigan who ingested contaminated poultry, beef, and dairy products in the early 1970s were enrolled in a population-based cohort study in Michigan. Serum PBB and serum polychlorinated biphenyl (PCB) concentrations were measured. Reproductive history and health information, including Pap test results, were self-reported by participants.

RESULTS

Of the women, 23% (223 of 956) reported an abnormal Pap test. In unadjusted analyses, self-reporting an abnormal Pap test was associated with younger age, current smoking (hazard ratio [HR] 1.61, 95% confidence interval [CI] 1.19-2.17), and longer duration of lifetime use of oral contraceptives (≥10 years; HR 1.92, 95% CI 1.21-3.06). When adjusting for PCB exposure, age at the interview, and smoking history, there was a slightly elevated risk of self-reporting an abnormal Pap test among the highly exposed women compared to women with nondetectable PBB concentrations (PBB≥13 μg/L, HR 1.23, 95% CI 0.74-2.06); however, the CI was imprecise. When breastfeeding duration after the initial PBB measurement was taken into account, there was a reduced risk of self-reporting an abnormal Pap test among the highly exposed women who breastfed for ≥12 months (HR 0.41, 95% CI 0.06-3.03; referent group: women with nondetectable PBB concentrations who did not breastfeed).

CONCLUSIONS

It remains important to evaluate the potential reproductive health consequences of this class of chemicals as well as other potential predictors of abnormal Pap tests.

Incidence of thyroid disease following exposure to polybrominated biphenyls and polychlorinated biphenyls, Michigan, 1974-2006

Thyroid hormones, which influence body metabolism and development, could be affected by persistent organic pollutants. We sought to examine the relationship between polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) and thyroid disease. We employed incidence density sampling to perform a nested case control analysis of the Michigan Long-Term PBB Cohort. Cohort members (n=3333) were exposed to PBBs through contaminated cattle feed in 1973-1974 and to PCBs through daily life. Those with detectable serum PBB and PCB concentrations at enrollment were categorized into tertiles of PBB and PCB exposure. Case-patients were cohort members answering "Yes" to "Has a healthcare provider ever told you that you had a thyroid problem?" during follow-up interviews; control-patients were cohort members answering "No". We used odds ratios (OR) with 95% confidence intervals (CI) to compare odds of thyroid disease by PBB and PCB exposure and by various risk factors. Total cumulative thyroid disease incidence after 33 years was 13.9% among women and 2.6% among men. After adjusting for body mass index, we found no statistically significant differences in odds of any type of thyroid disease among women or men with elevated PBB or PCB exposure. Compared to control-patients, women with thyroid disease had increased odds of being overweight/obese (OR=2.82, 95% CI: 1.94-4.11) and developing infertility (OR=1.71, 95% CI: 1.08-2.69), diabetes (OR=1.61, 95% CI: 1.04-2.51), or arthritis (OR=1.71, 95% CI: 1.18-2.50) during follow-up. Additional research should explore potential associations between PBBs/PCBs and thyroid disease among children exposed in utero.

Can environmental or occupational hazards alter the sex ratio at birth? A systematic review

More than 100 studies have examined whether environmental or occupational exposures of parents affect the sex ratio of their offspring at birth. For this review, we searched Medline and Web of Science using the terms ‘sex ratio at birth’ and ‘sex ratio and exposure’ for all dates, and reviewed bibliographies of relevant studies to find additional articles. This review focuses on exposures that have been the subject of at least four studies including polychlorinated biphenyls (PCBs), dioxins, pesticides, lead and other metals, radiation, boron, and g-forces. For paternal exposures, only dioxins and PCBs were consistently associated with sex ratios higher or lower than the expected 1.06. Dioxins were associated with a decreased proportion of male births, whereas PCBs were associated with an increased proportion of male births. There was limited evidence for a decrease in the proportion of male births after paternal exposure to DBCP, lead, methylmercury, non-ionizing radiation, ionizing radiation treatment for childhood cancer, boron, or g-forces. Few studies have found higher or lower sex ratios associated with maternal exposures. Studies in humans and animals have found a reduction in the number of male births associated with lower male fertility, but the mechanism by which environmental hazards might change the sex ratio has not yet been established.

Reproductive outcomes among women exposed to a brominated flame retardant in utero

The authors studied 194 women exposed to polybrominated biphenyls (PBB) in utero when their mothers consumed products accidentally contaminated in Michigan in 1973. Generalized estimating equations were used to examine the effect of in utero PBB exposure on adult pregnancy-related outcomes. Compared to those with the lowest exposure (≤1 ppb), those with mid-range (>1-3.16 ppb) and high (≥3.17 ppb) PBB exposure had increased odds of spontaneous abortion with wide confidence intervals (odds ratio [OR] = 2.75, 95% confidence interval [CI] = 0.64-11.79, OR = 4.08, 95% CI = 0.94-17.70; respectively; p for trend = .05). Exposure during infancy to PBB-contaminated breast milk further increased this risk. Time to pregnancy and infertility were not associated with in utero exposure to PBB. Future studies should examine the suggested relationship between spontaneous abortion and other brominated flame retardants.

A cohort study of the association between secondary sex ratio and parental exposure to polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB)

BACKGROUND

Polybrominated biphenyl (PBB), a brominated flame retardant, was accidently mixed into animal feed in Michigan (1973-1974) resulting in human exposure through consumption of contaminated meat, milk and eggs. Beginning in 1976 individuals who consumed contaminated products were enrolled in the Michigan Long-Term PBB Study. This cohort presents a unique opportunity to study the association between parental exposures to PBB and offspring sex ratio.

METHODS

We identified offspring of female PBB cohort participants (born 1975-1988) and obtained electronic birth records for those born in the state of Michigan. We linked this information to parental serum PBB and PCB concentrations collected at enrollment into the cohort. We modeled the odds of a male birth with generalized estimating equations accounting for the non-independence of siblings born to the same parents. We explored potential confounders: parental age and education at offspring's birth, parental body mass index at cohort enrollment, birth order, gestational age and year of offspring's birth.

RESULTS

The overall proportion of male offspring among 865 live births to cohort mothers was 0.542. This was higher than the national male proportion of 0.514 (binomial test: p = 0.10). When both parents were in the cohort (n = 300), we found increased odds of a male birth with combined parents' enrollment PBB exposure > or = the median concentrations (3 microg/L for mothers; 6 microg/L for fathers) compared to combined parents' PBB exposure < the median concentrations (AOR = 1.43, 95% CI: 0.89-2.29), although this did not reach statistical significance. In addition, there was a suggestion of increased odds of a male birth for combined parents' enrollment PCB exposure > or = the median concentrations (6 microg/L for mothers; 8 microg/L for fathers) compared to combined parents' enrollment PCB exposure < the median concentrations (AOR = 1.53, 95% CI: 0.93-2.52).

CONCLUSION

This study adds to the body of literature on secondary sex ratio and exposure to environmental contaminants. In this population, combined parental exposure to PBBs or PCBs increased the odds of a male birth. Further research is needed to corroborate these findings and shed light on the biological mechanisms by which these types of chemicals may influence the secondary sex ratio.

Maternal exposure to a brominated flame retardant and genitourinary conditions in male offspring

BACKGROUND

The upward trend in industrial nations in the incidence of male genitourinary (GU) conditions may be attributed to increased exposure to endocrine disruptors. Polybrominated biphenyl (PBB), a brominated flame retardant, is one such suspected endocrine disruptor.

OBJECTIVE

We investigated the relationship between maternal serum levels of PBBs and GU conditions among male offspring exposed in utero.

METHODS

In this cohort study of sons born to women accidentally exposed to PBBs during 1973-1974, we examined self-reported data on GU conditions among male offspring in relation to maternal serum PBB levels. We used generalized estimating equations to calculate odds ratios (ORs), controlling for gestational age at birth.

RESULTS

Of 464 sons, 33 reported any GU condition (13 hernias, 10 hydroceles, 9 cryptorchidism, 5 hypospadias, and 1 varicocele). Four reported both hernia and hydrocele, and one both hernia and cryptorchidism. After adjustment for gestational age at birth, sons of highly exposed women (> 5 ppb) were twice as likely to report any GU condition compared with sons of the least exposed women [< or =1 ppb; OR = 2.0; 95% confidence interval (CI), 0.8-5.1]. This risk was increased when we excluded sons born after the exposure but before the mother's serum PBB measurement (OR = 3.1; 95% CI, 1.0-9.1). We found evidence of a 3-fold increase in reported hernia or hydrocele among sons with higher PBB exposure (test of trend p-value = 0.04). Neither hypospadias nor cryptorchidism was individually associated with PBB exposure.

CONCLUSIONS

Although cryptorchidism and hypospadias were not associated with in utero PBB exposure, this study suggests that other GU conditions may be associated with exposure to endocrine-disrupting chemicals during development.

Assessing inter-generational transfer of a brominated flame retardant

Studies have shown that the lipophilic nature of polybrominated biphenyl (PBB) causes it to preferentially accumulate in breast milk posing a potential hazard for suckling infants. The purpose of this study was to examine the inter-generational transfer of PBB from mother to child and whether this association was modified by maternal breast-feeding patterns. One hundred and forty-five mother-child pairs that were participants of the Michigan Long-Term PBB Study were included in this analysis. Mothers were exposed to PBB via contaminated food between 1973 and 1974 and children were exposed in utero and for some, through breast-feeding. Seventy-three percent of children had a non-detectable serum PBB concentration (limit of detection (LOD) = 1 microg L(-1)). Mothers' serum PBB concentration at enrollment ranged from <LOD to 933 microg L(-1). The following variables were associated with the child having a detectable serum PBB concentration: maternal serum PBB > or =8 microg L(-1), breast-feeding > or =5.5 months, maternal age at child's birth > or =28 years, and being born during the PBB exposure period. Among mothers with a detectable serum PBB concentration, those who breast-fed > or =5.5 months were 6 times more likely to have a child with a detectable serum PBB concentration, compared to a non-breast-fed child (95% C.I., 2.0-19.6).

In utero exposure to a brominated flame retardant and male growth and development

Whether environmental exposures alter the timing of puberty is the subject of increasing interest as pubertal age may have consequences for long term health. This study examines the association between exposure to a brominated flame retardant, polybrominated biphenyl (PBB), and puberty and growth. The population consists of sons born to women accidentally exposed to PBBs during 1973-74. Sons 5 to 17 years reported Tanner Stages and answered questions regarding current growth in a mailed questionnaire. Sons 18 to 30 years of age participated in a telephone interview in which they reported retrospective measures of development. Among sons 5-17 years, those with highest exposure (>3 ppb) were less likely to report advanced Tanner stage genital development (OR=0.4, 95% CI: 0.2-0.9) and were less likely to report advanced pubic hair development (OR=0.5; 95% CI: 0.2-1.0), after adjusting for current age, compared to those with lowest exposure (<= 1 ppb). No differences were seen in growth among sons 5-17. However, among sons 18-30 years, those with higher exposure were more likely to weigh less and have lower BMI as adults (test of trend p=0.01 and 0.04, respectively). They were less likely to recall being tall (OR=0.5; 95% CI 0.2-0.9) or heavy (OR=0.6; 95% CI 0.3-1.1) compared to their peers at age 11 years. These results suggest that sons exposed to PBBs in utero may be more likely to have delayed puberty. Further research is needed to corroborate these findings among structurally related compounds and shed light on the biological mechanisms that may be disrupted during puberty and development.

A decay model for assessing polybrominated biphenyl exposure among women in the Michigan Long-Term PBB Study

The Michigan Long-Term PBB Study was established following exposure to polybrominated biphenyls (PBBs) in the early 1970s. Serum samples from cohort members were analyzed for PBB during 1976-1993. More than 20 years following this industrial incident, some participants still had measurable serum PBB concentration levels. Thus, there is continuing interest in understanding the elimination of PBB from the body. In the present study, we estimated serum PBB decay and investigated the effects of covariates on serum PBB decay rates among 406 female cohort members. We developed a decay model using a general linear mixed model, which attributes unique intercept and slope estimates for each individual while borrowing information across individuals for predicting these quantities. Age at exposure and body mass index (BMI) at the initial measurement were time-independent covariates. Time since exposure, smoking history, pregnancy status, and breast-feeding status were time-dependent covariates. Higher BMI was associated with a slower decay rate; smokers had a faster decay rate than nonsmokers; and increasing age at exposure was marginally associated with a slower decay rate. Our results suggest a faster serum PBB decay rate for women who breast-fed during the interval between serum PBB measurements. To evaluate the predictive performance of our modeling approach, we compared the results from this model with those from a previously developed ordinary least squares (OLS) two-stage decay model. The mixed-effects decay model predicted the observed serum PBB concentration levels significantly better than the OLS two-stage decay model (mixed-effects model, r=0.93; OLS two-stage model, r=0.86; P<0.0001).

Maternal exposure to polybrominated and polychlorinated biphenyls: infant birth weight and gestational age

Understanding the influence of maternal exposures on gestational age and birth weight is essential given that pre-term and/or low birth weight infants are at risk for increased mortality and morbidity. We performed a retrospective analysis of a cohort exposed to polybrominated biphenyls (PBB) through accidental contamination of cattle feed and polychlorinated biphenyls (PCB) through residual contamination in the geographic region. Our study population consisted of 444 mothers and their 899 infants born between 1975 and 1997. Using restricted maximum likelihood estimation, no significant association was found between estimated maternal serum PBB at conception or enrollment PCB levels and gestational age or infant birth weight in unadjusted models or in models that adjusted for maternal age, smoking, parity, infant gender, and decade of birth. For enrollment maternal serum PBB, no association was observed for gestational age. However, a negative association with high levels of enrollment maternal serum PBB and birth weight was suggested. We also examined the birth weight and gestational age among offspring of women with the highest (10%) PBB or PCB exposure, and observed no significant association. Because brominated compounds are currently used in consumer products and therefore, are increasingly prevalent in the environment, additional research is needed to better understand the potential relationship between in utero exposure to brominated compounds and adverse health outcomes.

The impact of the demand for clinical productivity on student teaching in academic emergency departments

OBJECTIVE

Because many emergency medicine (EM) attending physicians believe the time demands of clinical productivity limit their ability to effectively teach medical students in the emergency department (ED), the purpose of this study was to determine if there is an inverse relationship between clinical productivity and teaching evaluations.

METHODS

The authors conducted a prospective, observational, double-blind study. They asked senior medical students enrolled in their EM clerkship to evaluate each EM attending physician who precepted them at three academic EDs. After each shift, students anonymously evaluated 10 characteristics of clinical teaching by their supervising attending physician. Each attending physician's clinical productivity was measured by calculating their total relative value units per hour (RVUs/hr) during the nine-month study interval. The authors compared the total RVUs/hr for each attending physician to the medians of their teaching evaluation scores at each ED using a Spearman rank correlation test.

RESULTS

Seventy of 92 students returned surveys, evaluating 580 shifts taught by 53 EM attending physicians. Each attending physician received an average of 11 evaluations (median score, 5 of 6) and generated a mean of 5.68 RVUs/hr during the study period. The correlation between evaluation median scores and RVUs/hr was -0.08 (p = 0.44).

CONCLUSIONS

The authors found no statistically significant relationship between clinical productivity and teaching evaluations. While many EM attending physicians perceive patient care responsibilities to be too time consuming to allow them to be good teachers, the authors found that a subset of our more productive attending physicians are also highly rated teachers. Determining what characteristics distinguish faculty who are both clinically productive and highly rated teachers should help drive objectives for faculty development programs.

The impact of the demand for clinical productivity on student teaching in academic emergency departments

OBJECTIVE

Because many emergency medicine (EM) attending physicians believe the time demands of clinical productivity limit their ability to effectively teach medical students in the emergency department (ED), the purpose of this study was to determine if there is an inverse relationship between clinical productivity and teaching evaluations.

METHODS

The authors conducted a prospective, observational, double-blind study. They asked senior medical students enrolled in their EM clerkship to evaluate each EM attending physician who precepted them at three academic EDs. After each shift, students anonymously evaluated 10 characteristics of clinical teaching by their supervising attending physician. Each attending physician's clinical productivity was measured by calculating their total relative value units per hour (RVUs/hr) during the nine-month study interval. The authors compared the total RVUs/hr for each attending physician to the medians of their teaching evaluation scores at each ED using a Spearman rank correlation test.

RESULTS

Seventy of 92 students returned surveys, evaluating 580 shifts taught by 53 EM attending physicians. Each attending physician received an average of 11 evaluations (median score, 5 of 6) and generated a mean of 5.68 RVUs/hr during the study period. The correlation between evaluation median scores and RVUs/hr was -0.08 (p = 0.44).

CONCLUSIONS

The authors found no statistically significant relationship between clinical productivity and teaching evaluations. While many EM attending physicians perceive patient care responsibilities to be too time consuming to allow them to be good teachers, the authors found that a subset of our more productive attending physicians are also highly rated teachers. Determining what characteristics distinguish faculty who are both clinically productive and highly rated teachers should help drive objectives for faculty development programs.

Central interactions between angiotensin II and PGD(2) in the regulation of vasopressin and oxytocin secretion in dehydrated rats

Brain-derived angiotensin II (ANG II) and prostaglandins have important roles in the regulation of body fluid and blood pressure homeostasis. In the present studies we investigated the central interactions between these two neurochemical products in regulating the hypothalamo-neurohypophysial system during dehydration. Intracerebroventricular (icv) administration of prostaglandin D(2) (PGD(2); 20 microg/5 microl) to conscious adult male Sprague-Dawley rats deprived of water for 24 h did not alter significantly the already elevated plasma levels of vasopressin or oxytocin. When PGD(2) was administered in combination with losartan, an antagonist of ANG II AT(1)-receptor subtype, however, concentrations of both hormones in plasma became further elevated. Icv administration of ANG II (50 ng/5 microl) increased further the enhanced plasma levels of vasopressin and oxytocin, as expected. Pretreatment with indomethacin (200 microg/5 microl; icv), an inhibitor of cyclo-oxygenase, significantly attenuated the ANG II-induced increase in oxytocin secretion only. Independent of the presence of ANG II, however, indomethacin decreased plasma levels of vasopressin, but not oxytocin. These results indicate that a prostaglandin is required for the stimulated release of vasopressin during dehydration and that the elevation of oxytocin secretion in response to ANG II depends largely on activation of cyclo-oxygenase and production of prostaglandins. The oxytocin response to exogenously administered PGD(2), however, can be negatively modulated by a mechanism dependent upon ANG II AT(1) receptors.

Indomethacin prevents the L-NAME-induced increase in plasma levels of oxytocin in dehydrated rats

Inhibiting NO synthase (NOS) with N(G)-nitro-L-arginine methyl ester (L-NAME, 250 microg/5 microl of artificial cerebrospinal fluid (aCSF)) injected intracerebroventricularly (i.c.v.) increased already enhanced levels of oxytocin, but not vasopressin, in conscious adult male Sprague-Dawley rats dehydrated for 24 h. Intracerebroventricular pretreatment with indomethacin (200 microg/5 microl aCSF), an inhibitor of cyclo-oxygenase, but not with losartan (25 microg/5 microl aCSF), an antagonist of angiotensin II (ANG II) AT(1)-receptor subtype, nearly prevented the elevation in oxytocin levels after L-NAME. Thus, NO inhibits prostaglandin (but not ANG II) mediated the modulatory actions of NO on oxytocin secretion from the hypothalamo-neurohypophysial system (HNS) during water deprivation.

Angiotensin II does not mediate the pressor response to PGD2 (icv)

The objective of the present studies was to examine the interaction between brain-derived angiotensin II (Ang II) and prostaglandins in order to identify the mechanisms mediating the pressor response produced by these neuroregulators. Inhibiting synthesis of prostaglandins with indomethacin [indocin, 200 microg/ 5 microl artificial cerebrospinal fluid (aCSF)], administered intracerebroventricularly (icv) to conscious adult male Sprague-Dawley rats, reduced blood pressure to values below basal levels. When injected prior to Ang II (50 ng/5 microl aCSF; icv), indomethacin completely abolished the pressor response induced by the octapeptide. The increase in blood pressure produced by prostaglandin D(2) (PGD(2), 20 microg/5 microl; icv), the most prominent prostaglandin in the rat brain, however, was not prevented by losartan (25 microg/5 microl; icv), an Ang II AT(1)-receptor antagonist. Collectively, these results indicate that prostaglandins produced tonically in the brain maintain resting arterial blood pressure and that the pressor action of Ang II is dependent on de novo synthesis of a prostaglandin.

Effects of central injection of kyotorphin and L-arginine on oxytocin and vasopressin release and blood pressure in conscious rats

Intracerebroventricular (I.C.V.) administration of an inhibitor of nitric oxide synthase (NOS) increases oxytocin but not vasopressin secretion, in dehydrated rats [38]. Surprisingly, central injection of L-arginine, the substrate for NOS, caused a similar effect. Kyotorphin (L-tyrosyl-L-arginine), a dipeptide formed from L-arginine by kyotorphin synthetase in the brain may mediate this magnocellular response. Therefore, the dose and time responses of hormone release were compared following I.C.V. injection of kyotorphin and L-arginine to conscious rats that were normally hydrated or deprived of water for 24 h. In water-sated rats, both L-arginine and kyotorphin increased blood pressure and plasma glucose levels coincident with elevating circulating levels of oxytocin, but not vasopressin. In dehydrated animals, both L-arginine and kyotorphin increased plasma oxytocin levels with a similar time course but only kyotorphin decreased vasopressin release. D-arginine, like L-arginine, stimulated secretion of oxytocin, indicating a nonstereospecific effect. A kyotorphin receptor antagonist (L-leucyl-L-arginine) given I.C.V. to dehydrated animals elevated plasma oxytocin and prevented the decrease in vasopressin levels after kyotorphin. Thus, kyotorphin, but not L-arginine, appears to attenuate release of vasopressin either directly from magnocellular neurons or indirectly via modulating compensatory reflexes activated by the pressor response. On the other hand, an excess of L-arginine and kyotorphin within the CNS may mimic the stress response by augmenting release of oxytocin and activating the sympathetic nervous system to increase blood pressure and plasma glucose levels.

Effects of L-NAME on cerebral metabolic, vasopressin, oxytocin, and blood pressure responses in hemorrhaged rats

NG-nitro-L-arginine methyl ester (L-NAME; 250 micrograms/5 microliters), an inhibitor of NO synthase, or the vehicle artificial cerebrospinal fluid (aCSF; 5 microliters) was administered intracerebroventricularly to conscious rats hemorrhaged (0.7 ml/min) to a 20% volume depletion. Hypotension was maximal 5 min after hemorrhage ended, with compensatory recovery to basal levels 20 min later, regardless of drug treatment. L-NAME, however, elevated (P < 0.05) blood pressure (vs. aCSF controls) 40-45 min after intracerebroventricular administration. In normovolemic rats, L-NAME produced a significant pressor response and increased plasma levels of vasopressin (VP) and oxytocin (OT). After hemorrhage, both hormone levels increased, but only OT was further enhanced by L-NAME. Thus centrally produced NO tonically inhibits OT and VP secretion under basal normovolemic conditions and selectively inhibits OT release during hypovolemia. Hemorrhage increased the rates of glucose utilization in the neural lobe, indicative of enhanced efferent neural functional activity. L-NAME further enhanced the metabolic activity in the entire hypothalamoneurohypophysial system of hemorrhaged animals. Several other brain structures involved in the regulation of blood pressure and the stress response were also metabolically affected by the hemorrhage and L-NAME.

Brain ANG II and prostaglandins mediate the pressor response after central blockade of nitric oxide synthase

Central inhibition of nitric oxide synthase (NOS) by intracerebroventricular (i.c.v.) administration of NG-nitro-l-arginine methyl ester (L-NAME; 150 microg/5 microl) to conscious rats produced a biphasic pressor response characterized by an initial transient increase within 5 min, and a delayed response starting between 60-90 min. The effect was stereospecific, as D-NAME (250 microg/5 microl) did not modify the resting arterial blood pressure, nor did L-arginine (323 microg/5 microl, i.c.v.), indicating the substrate for NOS is not rate-limiting. Intracerebroventricular pretreatment with losartan (25 microg/5 microl), a non-peptide antagonist of the angiotensin II AT1 receptor subtype, or indomethacin (100 microg/5 microl), a blocker of cyclooxygenase, however, prevented the initial increase in blood pressure without affecting the delayed pressor response. In contrast, neither intravenous losartan (10 mg/kg b.wt) nor prazosin, an alpha1 adrenergic receptor antagonist, at doses of 5 microg/5 microl (i.c.v.) or 0.3 mg/kg b.wt (i.v.) were effective in altering the pressor responses. These results indicate that centrally produced NO maintains the resting arterial blood pressure at least partially through modulation of the brain angiotensin system and prostaglandins.

Nitric oxide control of drinking, vasopressin and oxytocin release and blood pressure in dehydrated rats

Intracerebroventricular (i.c.v.) injection of the inhibitor of NO synthase (NOS), N(G)-nitro-L-arginine methyl ester (L-NAME) (250 microg/5 microL) attenuated the drinking response in rats deprived of water for 24 h. Moreover, oxytocin (OT) levels in plasma increased after 2 min, whereas both oxytocin and vasopressin levels were elevated at 120 min after intracerebroventricular injection. The delayed effect of L-NAME on both hormones was not observed in dehydrated animals allowed to drink water. Blood pressure remained stable after injection of artificial cerebrospinal fluid (aCSF) in dehydrated rats not allowed to drink. In rats having access to water, however, there was an immediate but transient pressor response (0-5 min) with a delayed hypotension from 45 to 120 min. L-NAME consistently increased blood pressure in a biphasic mode, whether the animals drank or not, with an early peak at 5 min that decayed after 15-30 min and a second pressor response beginning at 30-45 min and remaining elevated at 120 min when the experiment ended. These pressor responses were independent of the adrenal glands. Thus, centrally produced nitric oxide facilitates drinking, inhibits release of vasopressin and oxytocin from the magnocellular system, and maintains resting arterial blood pressure in normally hydrated and dehydrated rats.

Role of NO on vasopressin and oxytocin release and blood pressure responses during osmotic stimulation in rats

NG-nitro-L-arginine methyl ester (L-NAME, 250 micrograms/5 microliters), an inhibitor of nitric oxide (NO) synthase, or artificial cerebrospinal fluid (5 microliters) was administered intracerebroventricularly to conscious naive rats or to rats treated subcutaneously (15 microliters/kg) with NaCl (0.15, 0.45, or 1.0 M) or given a needle prick only. Intracerebroventricular injection of L-NAME increased plasma concentration of vasopressin (VP) and oxytocin (OT) in control naive rats, indicating that NO tonically inhibits basal secretion of both hormones during isosmotic isovolemic conditions. Osmotic stimulation with hypertonic saline (0.45 and 1.0 M NaCl) elevated plasma levels of both hormones as expected. Central blockade of NO synthase further enhanced secretion of OT during mild, but not strong, osmotic stimulation, whereas the high levels of VP remained unaffected by L-NAME. In animals treated with the needle prick or 0.15 M NaCl, only OT levels were increased after L-NAME. Therefore, NO selectively inhibits OT release in response to a painful stimulus (needle prick) and moderate osmotic stimulation to promote a preferential release of VP. A transient pressor response was observed after subcutaneous injection of 0.15 and 0.45 M NaCl, but a sustained response was obtained after 1.0 M NaCl. Regardless of whether the animals received NaCl solutions, however, treatment with L-NAME elevated blood pressure in all animals. Thus NO-induced vasodilation maintains basal arterial blood pressure and limits the pressor response to osmotic stimulation.

NO and angiotensin II effects on blood pressure and fluid homeostasis

Angiotensin II (50 ng/5 microl) and L-NAME (250 microg/5 microl), an inhibitor of NO synthase (NOS), were administered intracerebroventricularly alone or in combination to conscious rats. Mean arterial blood pressure (MABP) increased reaching a peak within 5 min in all groups compared to controls treated with the vehicle, artificial CSF (5 microl). MABP returned to basal levels at 30 min after angiotensin II and remained stable for the following 90 min. In animals treated with L-NAME alone, after the initial pressor response, MABP declined but began to increase progressively from 30 min until the end of the experiment at 120 min. When administered with angiotensin II, however, the initial pressor response was prolonged. Angiotensin II-induced drinking was significantly attenuated by L-NAME. In control rats, inhibiting NOS elevated plasma levels of oxytocin and vasopressin but in angiotensin II-stimulated animals, only oxytocin was further elevated after L-NAME. Thus, NO formed centrally inhibits basal secretion of oxytocin and vasopressin as well as the resting blood pressure. During stimulation with angiotensin II, NO facilitates drinking, limits the pressor response and selectively inhibits oxytocin release.

[14C]deoxyglucose labelling of functional activity in the cephalopod central nervous system

For the first time, the [14C]deoxyglucose radioautographic technique has been successfully used to map physiological activity in cephalopod brains. In unilaterally blinded octopus and cuttlefish, the optic lobe of the deprived side showed a decreased uptake of the labelled tracer. This suggests that the uptake is related to functional activity. The potential of the [14C]deoxyglucose technique as a powerful tool in studying the functional organization of cephalopod brains is discussed.

Osmoregulation of the magnocellular neuroendocrine system during lactation

Glucose utilization and Fos expression were used to compare responses of cerebral structures involved in osmoregulation in virgin and lactating rats given 0.15, 0.85, or 1.5 M NaCl subcutaneously. In virgin animals, glucose utilization increased (P < 0.05) in the supraoptic nuclei (SON), paraventricular nuclei (PVN), and neural lobe (NL) proportionally to the osmotic stimulus (0.15 M NaCl < 0.85 M NaCl < 1.5 M NaCl), whereas metabolism in the median preoptic nucleus (MPO) and median eminence (ME) increased only after 1.5 M NaCl. In lactating rats, enhanced utilization of glucose in response to osmotic stimulation was absent in the PVN (0.85 M NaCl), MPO, and ME or significantly (P < 0.01) reduced (SON, PVN, NL) compared with virgin animals. Glucose utilization in each structure correlated linearly with plasma osmolality but with a lower slope (P < 0.05) in lactating animals. Magnocellular neurons expressing Fos in the SON increased linearly with plasma osmolality and were more numerous (P < 0.05) in control lactating animals but increased less (P < 0.05) than in virgin rats after 0.85 M NaCl. The attenuated magnocellular response during lactation results from reduced afferent activation from osmosensitive forebrain sites.

Drinking and blood pressure responses to central injection of L-NAME in conscious rats

The drinking behavior and blood pressure responses to i.c.v. administration of artificial cerebrospinal fluid (aCSF) or NG-nitro-L-arginine methyl ester (L-NAME, 10, 250, or 500 micrograms), an inhibitor of nitric oxide synthase, were examined in conscious rats following either osmotic stimulation (1.0 M NaCl, 15 ml/kg, s.c.) or induction of hemorrhage (0.7 ml/min to a 20% blood volume loss). Water intake increased in all animals. L-NAME at doses of 250 and 500 micrograms, but not 10 micrograms, significantly attenuated water consumption induced by both stimuli. The mean arterial blood pressure (MABP), which increased after osmotic stimulation, was maintained at pressor levels by 250 and 500 micrograms of L-NAME, but decreased progressively and reached basal levels after treatment with aCSF and the lowest dose of L-NAME (i.e., 10 micrograms). Hemorrhage significantly decreased MABP in all rats. The fall in blood pressure associated with hemorrhage returned to control levels in animals treated with 250 and 500 micrograms of L-NAME but not in those treated with aCSF or 10 micrograms of L-NAME. These results indicate that nitric oxide is involved in the regulation of drinking behavior and may play an important role in the central control of blood pressure during osmotic stimulation and hypotensive hemorrhage.