Preconception urinary phthalate concentrations and sperm DNA methylation profiles among men undergoing IVF treatment: a cross-sectional study.

STUDY QUESTION: Are preconception phthalate and phthalate replacements associated with sperm differentially methylated regions (DMRs) among men undergoing IVF?

SUMMARY ANSWER: Ten phthalate metabolites were associated with 131 sperm DMRs that were enriched in genes related to growth and development, cell movement and cytoskeleton structure.

WHAT IS KNOWN ALREADY: Several phthalate compounds and their metabolites are known endocrine disrupting compounds and are pervasive environmental contaminants. Rodent studies report that prenatal phthalate exposures induce sperm DMRs, but the influence of preconception phthalate exposure on sperm DNA methylation in humans is unknown.

STUDY DESIGN, SIZE, DURATION: An exploratory cross-sectional study with 48 male participants from the Sperm Environmental Epigenetics and Development Study (SEEDS).

PARTICIPANTS/MATERIALS, SETTING, METHODS: The first 48 couples provided a spot urine sample on the same day as semen sample procurement. Sperm DNA methylation was assessed with the HumanMethylation 450 K array. Seventeen urinary phthalate and 1,2-Cyclohexane dicarboxylic acid diisononyl ester (DINCH) metabolite concentrations were measured from spot urine samples. The A-clust algorithm was employed to identify co-regulated regions. DMRs associated with urinary metabolite concentrations were identified via linear models, corrected for false discovery rate (FDR).

MAIN RESULTS AND ROLE OF CHANCE: Adjusting for age, BMI, and current smoking, 131 DMRs were associated with at least one urinary metabolite. Most sperm DMRs were associated with anti-androgenic metabolites, including mono(2-ethylhexyl) phthalate (MEHP, n = 83), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP, n = 16), mono-n-butyl phthalate (MBP, n = 22) and cyclohexane-1,2-dicarboxylic acid-monocarboxy isooctyl (MCOCH, n = 7). The DMRs were enriched in lincRNAs as well as in regions near coding regions. Functional analyses of DMRs revealed enrichment of genes related to growth and development as well as cellular function and maintenance. Finally, 13% of sperm DMRs were inversely associated with high quality blastocyst-stage embryos after IVF.

LIMITATIONS, REASONS FOR CAUTION: Our modest sample size only included 48 males and additional larger studies are necessary to confirm our observed results. Non-differential misclassification of exposure is also a concern given the single spot urine collection.

WIDER IMPLICATIONS OF THE FINDINGS: To our knowledge, this is the first study to report that preconception urinary phthalate metabolite concentrations are associated with sperm DNA methylation in humans. These results suggest that paternal adult environmental conditions may influence epigenetic reprogramming during spermatogenesis, and in turn, influence early-life development.

STUDY FUNDING/COMPETING INTEREST(S): This work was supported by grant K22-ES023085 from the National Institute of Environmental Health Sciences. The authors declare no competing interests.