Dimethomorph exposure alters human granulosa cells and mouse ovarian physiology.

Dimethomorph (DMM), a widely used fungicide recently classified as a reproductive toxicant, has unknown impacts on human ovarian function. Here, mass spectrometry identified DMM in human plasma (up to 3.5 ng/mL) and in follicular fluid (up to 1 ng/mL) for the first time, although at a low concentration. Investigating its effects in primary human granulosa cells (hGCs) and the KGN cell line, we found that DMM significantly reduced cell proliferation (BrdU incorporation) across all tested doses while sparing cell viability at non-cytotoxic concentrations, as measured by the CCK-8 assay. At a concentration relevant to follicular fluid (1 ng/mL), representing direct exposure of the target organ, DMM impaired basal and IGF-1-stimulated progesterone and estradiol secretion, reduced IGF-1-induced ERK1/2 and Akt phosphorylation, and induced oxidative stress, as indicated by increased total oxidant status and oxidative stress index. Transcriptomic analysis of hGCs by RNA sequencing revealed alterations in cholesterol biosynthesis, steroidogenesis, and glucocorticoid receptor signaling pathways, marked by downregulation of key steroidogenic genes (CYP11A1, HSD17B1 and CYP19A1) and strong induction of IL11. In vivo, chronic oral exposure to a low exploratory concentration of DMM (1 µg/kg/day) in mice prolonged diestrus, reduced circulating LH and FSH, altered gonadotropin receptor and steroidogenic gene expression, decreased growing follicles and corpora lutea, and induced systemic and ovarian oxidative stress. Overall, DMM, identified for the first time in human fluid, although at a low concentration, alters granulosa cell function, steroidogenesis, oxidative balance, and folliculogenesis, raising concerns regarding its reproductive toxicity.