Dioxin, an endocrine disruptor, induces long term effects on DNA methylation in men after in-utero exposure

Prenatal exposure to dioxin, a known endocrine disruptor, after the Seveso accident of 1976 has been associated with thyroid dysfunction, metabolic syndrome and semen quality reduction. Experimental exposure to dioxin in utero produced epigenetic endocrine modifications associated with reduction of semen quality, while in men epigenetic effects are not known. Our objective was to study, by a case control approach, the long-term epigenetic effects of prenatal dioxin exposure in 38 men whose mothers had been exposed to high doses of dioxin, serum median 52.0 ppt at exposure, and therefore who were exposed in utero, median 24.7 ppt at pregnancy, vs. 41 unexposed men.

Bisulfite-converted DNA was hybridized onto illumina Infinium Methylation EPIC BeadChip and methylation differences were studied at both individual probe (DMPs) and gene region (DMRs) levels.

We identified hypomethylation of the SPAG1 gene region and a slightly hypermethylated region containing genes of the HOXA family associated with thyroid and skeletal development. An elevated level of epigenetic drift was noted in the exposed group potentially contributing to disease risk. Epigenetic age acceleration did not show significant association with in-utero dioxin exposure. Additionally, we found heightened neutrophils and diminished natural killer cells in blood of dioxin exposed men.

These observations are the first in the literature and align with the long-term semen quality reduction and alteration of thyroid homeostasic mechanisms reported in children exposed in utero to dioxin in Seveso. The actual dioxin background serum levels, 1.0-2.0 ppt, are much lower than those associated to these effects.