Papers of the Month
By Nancy Lamontagne
Drought associated with risk of hospital admissions and mortality
In a new study, NIEHS grantees reported an association between drought conditions and increased risk of death among older adults. The researchers also observed a decreased risk of respiratory-related hospital admissions during periods of full drought. According to the authors, the work was the first to systematically analyze the risk of hospital admissions and mortality associated with drought periods in the U.S.
By analyzing 2000 to 2013 drought maps for 618 counties in the western U.S., the researchers identified periods of full droughts, nondrought, and worsening drought. They classified the days when droughts worsened as high- and low-severity droughts. Using Medicare records from the same period, the team calculated daily rates of hospital admissions and deaths among people aged 65 years old or older that were related to cardiovascular or respiratory causes.
The study showed that compared with nondrought periods, respiratory admissions decreased by a small but statistically significant amount during the full drought period but not during worsening drought conditions. The risk of dying was increased by a small but statistically significant amount during high-severity worsening drought periods but not during full drought or low-severity worsening droughts. Overall, cardiovascular-related hospital admissions did not differ significantly during either full drought or worsening drought periods. However, counties where drought occurred less frequently showed an increased risk for cardiovascular disease and death during worsening drought conditions.
In the same issue, a comment by NIEHS Senior Advisor for Public Health John Balbus, M.D., noted that the groundbreaking study helped identify future research questions about how drought affects health, and the actual severity and significance of those effects.
Citation: Berman JD, Ebisu K, Peng RD, Dominici F, Bell ML. 2017. Drought and the risk of hospital admissions and mortality in older adults in western USA from 2000 to 2013: a retrospective study. Lancet Planet Health 1(1):e17–e25.
New insights into marine sponge PBDE biosynthesis
A new study, funded in part by NIEHS, revealed that symbiotic cyanobacteria are responsible for the naturally produced polybrominated diphenyl ether (PBDE) toxins found in Dysideidae marine sponges. The researchers also identified the genes involved in PBDE production, which may help scientists find and monitor other cyanobacteria that produce PBDEs.
According to the researchers, PBDEs found throughout the marine environment are structurally similar to toxic man-made brominated flame retardants and can potentially transfer to humans through bioaccumulation in the marine food web. The researchers sought to clarify the genetic and molecular basis for PBDE production in Dysideidae sponges because they are among the most abundant sources of these natural toxins.
Using an approach called metagenome mining, the scientists searched for genes involved in PBDE production in three types of sponges and their associated microbial communities. The analysis identified PDBE biosynthetic genes in Hormoscilla spongeliae symbiotic cyanobacteria, but not in the sponges themselves or other microbial organisms. The researchers then expressed the genes in cyanobacterial hosts and confirmed that the genes were responsible for PBDE production.
Citation: Agarwal V, Blanton JM, Podell S, Taton A, Schorn MA, Busch J, Lin Z, Schmidt EW, Jensen PR, Paul VJ, Biggs JS, Golden JW, Allen EE, Moore BS. 2017. Metagenomic discovery of polybrominated diphenyl ether biosynthesis by marine sponges. Nat Chem Biol 13(5):537–543. (Story)
Traffic-related air pollution linked with lower HDL levels
An NIEHS-funded study found an association between exposure to higher levels of traffic-related air pollution and lower levels of high-density lipoprotein (HDL) cholesterol, or good cholesterol. Because low HDL cholesterol is a risk factor for cardiovascular diseases, the new findings offer possible insight into how air pollution exposure increases cardiovascular disease risk.
To examine the relationship between HDL levels and air pollution, the researchers studied 6,654 middle-aged and older participants in the Multi-Ethnic Study of Atherosclerosis Air Pollution study. Individual residential exposure to ambient fine particulate pollution exposure (PM2.5) and black carbon — both components of traffic-related air pollution — were averaged for exposure periods of 12 months, 3 months, and 2 weeks. Because HDL particle numbers have been recently shown to reflect HDL’s heart-protective qualities better than HDL cholesterol levels, the researchers measured both HDL cholesterol and particle numbers. In the body, HDL particles carry HDL cholesterol.
The analysis revealed that participants living in areas with higher levels of traffic-related air pollution tended to have lower HDL levels. Specifically, exposure to higher concentrations of black carbon over a 1-year period was associated with a 1.68 milligram per deciliter lower HDL cholesterol and a 0.55 micromole per liter lower HDL particle number. For the 3-month averaged exposure period, 5.0 milligrams per cubic meter higher exposure to PM2.5 was associated with a HDL particle number that was 0.64 micromole per liter lower, but HDL cholesterol levels dropped only 0.05 milligram per deciliter.
Citation: Bell G, Mora S, Greenland P, Tsai M, Gill E, Kaufman JD. 2017. Association of air pollution exposures with high-density lipoprotein cholesterol and particle number: the Multi-Ethnic Study of Atherosclerosis. Arterioscler Thromb Vasc Biol 37(5):976–982.
Respiratory toxicity of short and long silver nanowires in rats
NIEHS grantees reported that cells in the lungs of rats converted short and long silver nanowires into shorter lengths that were fully taken up by lung cells, which led to lung inflammation. The study provided new insights into possible health risks linked with silver nanomaterials, which have been increasingly used in industrial and domestic products, such as odor-resistant socks, personal care products, respiratory devices, food storage boxes, computers, and cleaning sprays.
To study the respiratory toxicity of short and long silver nanowires — 1.5 and 10 micrometers in length, respectively — the researchers instilled nanowires of each length into the lungs of rats. Within one day of instillation, both short and long nanowires were taken up and degraded by lung macrophages, a type of white blood cell that engulfs and digests cellular debris, and by cells that line lung alveoli, the site of oxygen exchange. Using three-dimensional scanning electron microscopy, the researchers observed a small, but significant, reduction of nanowire lengths inside cells.
The researchers also observed increased lung inflammation after instillation of both types of nanowires. Mice that received the long nanowires showed a greater and longer lasting degree of lung inflammation and bronchial hyperreactivity.
Citation: Chung KF, Seiffert J, Chen S, Theodorou IG, Goode AE, Leo BF, McGilvery CM, Hussain F, Wiegman C, Rossios C, Zhu J, Gong J, Tariq F, Yufit V, Monteith AJ, Hashimoto T, Skepper JN, Ryan MP, Zhang J, Tetley TD, Porter AE. 2017. Inactivation, clearance, and functional effects of lung-instilled short and long silver nanowires in rats. ACS Nano 11(3):2652–2664.