Exposure to low-dose polystyrene nanoplastics impairs the estrous cycle by decreasing ovarian levels of steroidogenic acute regulatory protein and serum progesterone levels in rats

Plastic can be fragmented into smaller pieces referred to as microplastics (< 5 mm), or nanoplastics (< 1 µm). These particles have been reported to cross biological barriers and cause oxidative stress damage in several tissue types. Given that female reproductive tissues are considered a target for such particles, our study aimed to evaluate the effects of polystyrene nanoplastics (PS-NP, 500 nm) at a low concentration (0.015 mg/d), on reproductive parameters of adult female Wistar rats. Animals (n = 10/group) were treated by gavage for 25 days with PS-NP diluted in distilled water at a concentration of 0.015 mg/d. The Control group received only distilled water (vehicle). We assessed weight gain, estrous cyclicity, sexual behavior and fertility, morphology of ovaries and uteri, immunostaining for StAR in the ovaries, and serum levels of the steroid hormones: estradiol and progesterone. Data was evaluated by Student's t-test, Mann-Whitney test, or Fisher's Exact test. Results were considered significantly different when P ≤ 0.05. The PS-NP group showed estrous cycle dysregulation, uterine inflammatory infiltration, increased uterus and pituitary weight, and decreased thyroid weight in the experimental conditions utilized. These findings are potentially due to the decrease in StAR expression in luteal cells, and consequent reduction of progesterone serum levels. These results indicate that nanoplastics act as endocrine disruptors impairing female endocrine and reproductive function, in a rodent model, and raise concern about outcomes after exposure to nanoplastics in other females and in adult women's reproductive health.