Papers of the Month
By Sara Amolegbe
Heat and impaired kidney function affect worker productivity
Heat extremes may be associated with loss of agricultural worker productivity and employment, especially among workers with impaired kidney function, according to an NIEHS study. The study provides the first direct field evidence linking kidney function, heat, and agricultural productivity.
The researchers measured temperature exposure, kidney function, and productivity of 4,095 Guatemalan sugarcane cutters over a 6-month harvest. Heat stress was evaluated by measuring wet bulb globe temperature (WBGT), which accounts for temperature, humidity, wind speed, sun angle, and cloud cover. They also measured productivity, based on tons of cut sugarcane, and the job attrition of workers with normal or impaired kidney function.
The team estimated that the cumulative effect on productivity for workers with impaired kidney function was 1.16 tons less sugarcane cut over five days after exposure to a max WBGT of 34 degrees Celsius (93.2 degrees Fahrenheit) compared with exposure to 29 degrees Celsius (84.2 degrees Fahrenheit). Workers who started the harvest season with impaired kidney function were more than twice as likely to leave their employment.
According to the authors, agricultural workers who developed health conditions, such as kidney disease, were particularly vulnerable to increasing heat extremes. In light of the epidemic of work-related chronic illnesses related to heat, including chronic kidney disease of unknown origin, the researchers called for further research and interventions to address impaired kidney function and the resultant loss of employment and productivity.
Citation: Dally M, Butler-Dawson J, Krisher L, Monaghan A, Weitzenkamp D, Sorensen C, Johnson RJ, Carlton EJ, Asensio C, Tenney L, Newman LS. 2018. The impact of heat and impaired kidney function on productivity of Guatemalan sugarcane workers. PLoS One 13(10):e0205181.
Prenatal fluoride exposure linked to ADHD symptoms
NIEHS grantees discovered that higher levels of urinary fluoride during pregnancy were associated with increased incidence of attention deficit-hyperactivity disorder (ADHD)-like symptoms in school-aged children. ADHD is the most common psychiatric disorder diagnosed in childhood, affecting between five and nine percent of all school-aged children.
The study analyzed data from 213 mother-child pairs in Mexico City enrolled in a project that recruited pregnant women from 1994 to 2005 and has continued to follow the women and their children. The research team analyzed urine samples from pregnant mothers and their children between six and 12 years of age. The researchers then analyzed how levels of fluoride in urine, an indicator of exposure, were related to a child's performance on tests and questionnaires that measured inattention and hyperactivity, which provided scores related to ADHD.
These findings demonstrated that children with elevated prenatal fluoride exposure, as indicated by maternal urinary fluoride, were more likely to exhibit symptoms of ADHD. Prenatal fluoride exposure was also associated with inattentive behaviors, but not with hyperactivity or impulse control. According to the authors, these findings provided further evidence of the neurotoxic effects of prenatal fluoride exposure and warrant further investigation.
Citation: Bashash M, Marchand M, Hu H, Till C, Martinez-Mier EA, Sanchez BN, Basu N, Peterson KE, Green R, Schnaas L, Mercado-Garcia A, Hernandez-Avila M, Tellez-Rojo MM. 2018. Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6-12 years of age in Mexico City. Environ Int 121(Pt 1):658–666.
Diabetes drug may protect heart from air pollution effects
The diabetes drug metformin may reduce inflammation triggered by air pollution exposure, according to an NIEHS-funded study. The researchers reported that metformin prevented immune cells known as macrophages from releasing an inflammatory molecule called interleukin-6 (IL-6), which has been linked to heart attacks and strokes.
Mice were exposed to particulate matter air pollution and treated with or without metformin for three days. Treatment with metformin prevented the release of IL-6 in mice and reduced the susceptibility to arterial thrombosis, or blood clots, in the artery. The researchers also exposed both human and mouse lung cells to metformin treatment and found that it prevented the release of IL-6 following air pollution exposure.
Because several cellular processes in the mitochondria are required to release IL-6, the researchers tested the effects of air pollution on mice lacking certain mitochondrial proteins. Similar to mice treated with metformin, those lacking certain mitochondrial proteins were also protected against pollution-induced acceleration of arterial thrombosis, which suggested the involvement of mitochondria in this process.
Metformin is a safe and inexpensive drug used by more than 100 million diabetes patients worldwide. According to the authors, these findings suggested that metformin also has the potential to prevent inflammation caused by air pollution exposure.
Citation: Soberanes S, Misharin AV, Jairaman A, Morales-Nebreda L, McQuattie-Pimentel AC, Cho T, Hamanaka RB, Meliton AY, Walter JM, Chen CI, Chi M, Chiu S, Gonzalez-Gonzalez FJ, Antalek M, Adbala-Valencia H, Chiarella SE, Sun KA, Woods PS, Ghio AJ, Jain M, Perlman H, Ridge KM, Morimoto RI, Sznajder JI, Balch WE, Bhorade SM, Bharat A, Prakriya M, Chandel NS, Mutlu GM, Budinger GRS. 2018. Metformin targets mitochondrial electron transport to reduce air pollution-induced thrombosis. Cell Metab 29:1–13.
New method links metal mixture to reduced fetal growth
NIEHS grantees determined that exposure to a mixture of metals predominated by arsenic and cadmium was associated with reduced fetal growth. Although previous studies showed independent associations between arsenic and cadmium exposures and fetal growth restriction, this study was the first to demonstrate that the effects of these metals persist even after accounting for the presence of other metals.
The researchers used maternal toenails collected from the Rhode Island Health Study to measure a panel of 16 trace metals. Most trace metals detected in the participants were on par with levels reported in other U.S. populations. They integrated advanced bioinformatics and biostatistics methods to evaluate metal signatures associated with being small for gestational age and identified a positive association with a multimetal signature dominated by arsenic and cadmium.
They also found that this specific mixture of metals was associated with placental genes related to fetal growth, including metabolic hormone secretion. Evaluating the relationship between the multimetal signatures and placental genes highlighted potential molecular pathways through which metals might affect pregnancy outcomes.
According to the authors, the study provided a novel approach that integrated advanced bioinformatics and biostatistics methods to delineate potential placental pathways through which trace metal exposures might affect fetal growth.
Citation: Deyssenroth MA, Gennings C, Liu SH, Peng S, Hao K, Lambertini L, Jackson BP, Karagas MR, Marsit CJ, Chen J. 2018. Intrauterine multi-metal exposure is associated with reduced fetal growth through modulation of the placental gene network. Environ Int 120:373–381.
(Sara Amolegbe is a research and communication specialist for MDB Inc., a contractor for the NIEHS Division of Extramural Research and Training.)