Extramural papers of the month
By Nancy Lamontagne
- Prenatal exposure to PAHs linked to childhood obesity
- BPA associated with IVF implantation failure
- Guidelines for risk of illness from beach sand
- DNA mismatch repair introduces mutations in non-dividing cells
Prenatal exposure to PAHs linked to childhood obesity
An NIEHS grantee reports that pregnant women exposed to higher concentrations of polycyclic aromatic hydrocarbons (PAHs) were more than twice as likely to have children who were obese by age 7 than women with lower levels of exposure. PAHs are a common urban air pollutant, and this study provides evidence that prenatal exposure to PAHs can influence childhood obesity.
The study involved 702 non-smoking African-American and Hispanic pregnant women, 18-35 years old, living in predominantly low-income areas. A personal air monitor recorded PAH exposure for two days during the mothers’ third trimester.
Compared with children of mothers with lower levels of exposure to PAHs during pregnancy, the children of women exposed to high levels were 1.79 times more likely to be obese at age 5 and 2.26 times more likely to be obese at age 7. The 7-year-olds, whose mothers had the highest exposures, had an average of 2.4 pounds of more fat mass than children of mothers with the least exposure.
Citation: Rundle A, Hoepner L, Hassoun A, Oberfield S, Freyer G, Holmes D, Reyes M, Quinn J, Camann D, Perera F, Whyatt R. 2012. Association of childhood obesity with maternal exposure to ambient air polycyclic aromatic hydrocarbons during pregnancy. Am J Epidemiol; doi:10.1093/aje/kwr455 [Online 13 April 2012].
BPA associated with IVF implantation failure
A study funded by NIEHS showed an association between bisphenol A (BPA) urinary concentrations and embryo implantation failure in women undergoing in vitro fertilization (IVF). The carefully synchronized hormonal signals and feedback loops involved in an embryo implanting to the uterus make this stage of prenatal development potentially vulnerable to endocrine disruptors such as BPA, which is found in many consumer products.
The researchers measured the urinary BPA levels of 137 women undergoing 180 IVF cycles at the Massachusetts General Hospital Fertility Center. Overall, 75 IVF cycles (42 percent) resulted in implantation failure. The investigators found that implantation failure was almost twice as likely for women with urinary BPA concentrations of 3.80 to 26.48 micrograms per liter than for women with the lowest concentration of less than 1.69 micrograms per liter.
Citation: Ehrlich S, Williams PL, Missmer SA, Flaws JA, Berry KF, Calafat AM, Ye X, Petrozza JC, Wright D, Hauser R. 2012. Urinary bisphenol A concentrations and implantation failure among women undergoing in vitro fertilization. Environ Health Perspect; doi:10.1289/ehp.1104307 [Online 6 April 2012].
Guidelines for risk of illness from beach sand
An NIEHS-funded researcher recently published reference levels for the risk of human illness from pathogens in beach sand. There are no U.S. federal guidelines for assessing when pathogens make beach sand unsafe.
The researchers used quantitative microbial risk assessment and Monte Carlo simulations to calculate beach sand pathogen levels corresponding to the 1.9 percent EPA reference risk for marine water, which is equivalent to 19 illnesses per 1000 swimmers. For beach sand, they calculated reference levels of about 10 oocysts per gram of Cryptosporidium, about five most probable number (MPN) per gram for enterovirus, and less than 1,000,000 colony forming units per gram for S. aureus.
They also measured pathogen levels in sand at a recreational beach in Miami that is affected by nonpoint sources of contamination and found that pathogen levels were lower than the calculated reference levels. The researchers say that more research is needed to evaluate the risk for skin infections associated with exposure to pathogens in beach sand.
Citation: Shibata T, Solo-Gabriele HM. 2012. Quantitative microbial risk assessment of human illness from exposure to marine beach sand. Environ Sci Technol 46(5):2799-2805.
DNA mismatch repair introduces mutations in non-dividing cells
NIEHS grantees report a role for DNA mismatch repair in creating mutations in non-dividing cells. These mutations can lead to cancer or create beneficial new phenotypes.
DNA mismatch repair removes replication errors by removing mismatched nucleotides. It is a strand-specific process, meaning the process removes only nucleotides on the newly replicated strand of DNA. How eukaryotic cells distinguish the strands is not fully understood, but the cells likely lose the ability to distinguish the strands as replication proceeds.
The researchers introduced specific mispairs into the DNA of yeast cells in a way that let them observe the very rare event of non-strand dependent DNA repair. They found that mispairs, not repaired during replication, sometimes underwent mismatch repair later when the cells were no longer dividing. This repair was not strand dependent and sometimes introduced mutations into the DNA sequence that allowed cells to resume growth. In one case, they observed such mutations arising in cells that had been in a non-dividing state for several days.
Citation: Rodriguez GP, Romanova NV, Bao G, Rouf NC, Kow YW, Crouse GF. 2012. Mismatch repair-dependent mutagenesis in nondividing cells. Proc Natl Acad Sci U S A 109(16):6153-6158.
(Nancy Lamontagne is a science writer with MDB, Inc., a contractor for the NIEHS Division of Extramural Research and Training, Superfund Research Program, and Worker Education and Training Program.)