Involvement of Orotic Acid in Mitochondrial Activity of Ovarian Granulosa Cells and Oocyte Meiotic Maturation

Orotic acid (OA) is a natural component of milk and is found in many biological fluids such as human ovarian follicular fluid. However, its effect on ovarian cells is unknown. Some studies suggest that OA may alter lipid metabolism and energy production in cells. In the present study, we determine the effect of OA on mitochondrial function and lipid droplet content in the human granulosa cell line. The effect of OA on in vitro mouse oocyte maturation and mitochondrial activity was also investigated. We found that repeated exposure to OA (0.01-1000 µM) did not alter the viability of human epithelial (HOSEpiC) and granulosa (HGrC1) ovarian cells. HGrC1 cells treated with a high dose of OA (500 µM) showed a more aerobic and energetic phenotype than control cells, whereas this effect was not observed after treatment with lower doses (0.01 and 100 µM) of OA. In addition, OA at a high dose (500 µM) reduced lipid droplet (LD) content without altering glucose (GLUT1, GLUT4) and fatty acid transporter (SLC27A1) gene expression in HGrC1 cells. At the same time, OA at 100 µM did not disrupt mouse in vitro oocyte maturation, whereas OA at 500 µM inhibited this process by arresting oocytes at the germinal vesicle (GV) stage with a reduction in mitochondrial activity. Our results show that OA at high doses can disrupt female reproduction, but normal dietary orotate intake does not have a negative effect on ovarian function.