Papers of the Month
By Sara Amolegbe
Pregnant women exposed to less secondhand nicotine after ban
Pregnant women experienced less secondhand smoke exposure after the passage of a 2009 law banning smoking inside restaurants and bars in North Carolina, according to a new study by NIEHS grantees. Although exposure lowered overall, the study identified racial and socioeconomic disparities among the women exposed to secondhand smoke.
The data comes from 668 women who enrolled in the study between 2005 and 2011. Their secondhand smoke exposure was measured by the presence of cotinine, a biomarker found in blood plasma that indicates nicotine exposure in the previous 48 to 72 hours.
The researchers found that most nonsmoking pregnant women were not exposed to nicotine in the days before having their blood tested for the study. Although some women tested after the passage of the ban still had cotinine in their blood, their average blood levels were lower than those tested before the ban. Being African American, unmarried, and having less education were each associated with increased risk for passive smoke exposure.
According to the authors, the new results indicate that banning smoking in public spaces can reduce passive smoke exposure in nonsmoking pregnant women. The findings are also informative for medical providers who may want to discuss possible prevention efforts with pregnant women who are at higher risk of exposure.
Citation: Schechter JC, Fuemmeler BF, Hoyo C, Murphy SK, Zhang JJ, Kollins SH. 2018. Impact of smoking ban on passive smoke exposure in pregnant non-smokers in the southeastern United States. Int J Environ Res Public Health 15(1):E83.
Serotonin changes linked to flame retardants in placenta
NIEHS grantees showed a connection between exposure to a flame retardant chemical mixture and disruption of normal placental function in rats, which led to altered production of the neurotransmitter serotonin. Flame retardant exposure was associated with effects related to inflammation, hormones, and neurodevelopment. Some of the effects were only observed in female offspring.
The researchers exposed pregnant rats to the chemical FireMaster 550 (FM 550), a flame-retardant mixture used in foam-based baby products and furniture. The team examined the placentas and developing brains of the offspring to identify possible pathways affected by the chemical mixture. The dose levels used were all below the 50 milligrams per day currently considered safe.
In female offspring, the researchers found increased levels of estrogen and androgen receptors in placentas with exposure. They also observed an altered ratio of serotonin and its metabolite 5-HIAA in placentas and fetal forebrains of female offspring compared with the unexposed group. This finding demonstrated disruption of neurotransmitter production in the placenta and developing brain. Increased markers of inflammation that are associated with elevated risk of behavioral disorders were observed in placentas from both sexes.
According to the authors, these findings demonstrate that environmental contaminants like FM 550 have the potential to affect the developing brain by disrupting normal placental functions. These data also show, for the first time, that flame retardants can have sex-specific effects on placental functions critical for brain development.
Citation: Rock KD, Horman B, Phillips AL, McRitchie SL, Watson S, Deese-Spruill J, Jima D, Sumner S, Stapleton HM, Patisaul HB. 2018. EDC IMPACT: Molecular effects of developmental FM 550 exposure in Wistar rat placenta and fetal forebrain. Endocr Connect 7(2):305–324.
Possible explanation for male and female cardiovascular differences
NIEHS grantees discovered that estrogen can block the function of soluble epoxide hydrolase (sEH), an enzyme in cells that degrades chemically stable fatty acid metabolites. Because inhibition of sEH can be cardioprotective, this finding may help explain why women generally have a lower incidence of cardiovascular disease than men.
Using mice and human cells, the researchers showed that estrogen is responsible for DNA methylation of the gene Ephx2, which blocks the gene’s ability to promote sEH expression. This sEH inhibition can raise levels of epoxyeicosatrienoic acids (EETs), which are omega-6 fatty acid metabolites that are generally degraded by sEH. Because EETs are cardioprotective and can lower blood pressure, increases in EETs caused by estrogen suppression of sEH can help protect against heart disease.
According to the authors, this finding also highlights the potential for using sEH inhibitors that share the same target with estrogen to prevent negative cardiovascular outcomes that may result from estrogen deficiency.
Citation: Yang YM, Sun D, Kandhi S, Froogh G, Zhuge J, Huang W, Hammock BD4, Huang A. 2018. Estrogen-dependent epigenetic regulation of soluble epoxide hydrolase via DNA methylation. Proc Natl Acad Sci U S A 115(3):613–618.
Exposure to air pollution around conception linked to birth defects
Women exposed to air pollution just before conception or during the first month of pregnancy face a slightly increased risk of their children being born with birth defects, according to a new study by NIEHS grantees.
The researchers estimated the association between abnormalities at birth and the mother’s exposure during pregnancy to increased levels of fine particulate matter, an air pollutant. The team linked the geographic coordinates of the mother’s residence for each birth with the nearest monitoring station and calculated average exposures. Birth certificate data came from the Ohio Department of Health, and particulate matter data came from the U.S. Environmental Protection Agency’s 57 monitoring stations throughout Ohio.
Exposure to increased levels of particulate matter in the air during the period around conception was modestly associated with an increased risk of birth defects, after adjustment for coexisting risk factors. The strongest influences of particulate matter on individual malformations were found with abdominal wall defects and hypospadias, in which the urinary opening on the penis is not in the usual location. They found that the most susceptible time of exposure was the one month before and after conception.
The authors added that although the increased risk is modest, the potential impact on a population basis is noteworthy because all pregnant women are exposed to some amount of particulate matter.
Citation: Ren S, Haynes E, Hall E, Hossain M, Chen A, Muglia L, Lu L, DeFranco E. 2018. Periconception exposure to air pollution and risk of congenital malformations. J Pediatr 193:76–84.
(Sara Amolegbe is a research and communication specialist for MDB Inc., a contractor for the NIEHS Division of Extramural Research and Training.)