Human populations are exposed to a variety of pesticides. Much of the research documenting the detrimental effects of pesticide exposure on sperm quality has been extrapolated on laboratory and animal models with limited results from studies of direct human pesticide exposure. Many of the human studies focus on the use of persistent pesticides, such as DDT (dichlorodiphenyltrichloroethane), whose use is thankfully decreasing in the developed world. However, increasing studies suggest deleterious effects of contemporary, non-persistent pesticides on human semen parameters, including decreased sperm concentration and motility. Latino immigrant farmworkers, most of whom are men, are a health disparate population with direct and frequent exposure to pesticides. These men provide an opportunity to examine the mechanisms and effects of exposure to contemporary, non-persistent pesticides on human sperm quality. A promising new area of reproductive research relates the epigenetic state of spermatozoa to sperm quality. In humans, clinic-based studies indicate that levels of DNA methylation are abnormal in spermatozoa of men with reduced fertility. A significant gap exists in our understanding of the genes that are epigenetically alterd following exposure to non-persistent pesticides. Data documenting the association of exposure to contemporary, non-persistent pesticides on the reproductive health of male farmworkers is needed to inform prevention strategies and public health policy surrounding the use of agricultural pesticides. The goal of this project is to document the association of pesticide exposure with epigenetic changes in spermatogenesis. We will compare 50 male immigrant Latino farmworkers, a group that experiences repeated pesticide exposure, with 50 immigrant Latinos living in urban, non-agricultural communities, without occupational exposure to pesticides. The proposed project will address three specific aims: 1. Methylation binding protein precipitation will be used to enrich imprinted DNA and Next Generation sequencing will be used for genome wide annotation of spermatozoa genes in high- (farmworkers) and low- (non-farmworker) pesticide exposed Latino men. 2. We will correlate biomarkers of non-persistent pesticide exposure (urinary metabolites of organophosphorus pesticides [3,5,6-trichloropyridinol, TCPy/chlorpyrifos], pyrethroid insecticides [3-phenoxybenzoic acid, 3PBA], and herbicides [2,4- dichlorophenoxyacetic acid, 2,4-D]) with the methylation status of spermatozoa genes. 3. Associations among clinically relevant semen parameters (sperm concentration, motility and morphology), urinary pesticide metabolite concentrations and DNA methylation patterns within spermatozoa genes in both groups of men will be determined. This research will combine epidemiology, andrology and epigenomics. The unique longitudinal design of this study will allow us to evaluate cross-sectional differences between high- and low-exposure groups, and changes within populations and individuals across an agricultural season.
Chronic pesticide exposure is pervasive in the United States, and it is particularly prevalent among Latino immigrant and seasonal farmworkers. Substantial research has documented the detrimental effects of pesticide exposure on human reproductive health. Using data collected from immigrant farmworkers, as well as socioeconomically- and ethnically-matched non-farmworker controls, this study will annotate methylated spermatozoa genes and determine their association with pesticide exposure and male reproductive health, to begin to define the underlying biological mechanisms.
