Exposição ao nanoplástico de poliestireno durante os períodos juvenil e puberal: impacto sobre a morfofisiologia testicular e funcionalidade espermática

Abstract

Global plastic production has increased significantly each year. Once discarded, plastic items undergo environmental degradation, resulting in the formation of small particles known as nanoplastics (NP). These NP are contaminants found in water and food and accumulate throughout the trophic chain. In this context, polystyrene (PS) is a type of plastic widely used in the manufacture of various products, including disposable packaging, toys, and toothbrushes. In addition to affecting adult health, it is well established that exposure to environmental contaminants during critical developmental windows can lead to long-lasting impairments. Since the postnatal period encompasses essential cellular and molecular events required for the acquisition of reproductive capacity, the aim of this study was to evaluate whether exposure to polystyrene nanoplastics (PS-NP) during the juvenile and pubertal periods influences postnatal testicular development and sperm function in male mice. A total of 45 male C57BL/6 mice aged 21 days were divided into three experimental groups: a Control group, which received only the vehicle (phosphate-buffered saline, PBS), and two groups that received PS-NP solutions at doses of 1 mg/day and 0.1 mg/day. Animals received the compound daily by gavage for 50 days. The experimental period occurred between postnatal day (PND) 21 and PND 71. After treatment, animals were euthanized for collection of the testes and vas deferens (for sperm retrieval). Body weight, testis and epididymis weights were measured, and testicular histopathology, morphometry, and spermatogenesis dynamics were evaluated. Serum testosterone and estradiol levels were quantified. Sperm were analyzed for morphology, mitochondrial activity, motility, viability, and chromatin maturation. Data were statistically analyzed, assuming significance at p < 0.05. A reduction in the proportion of normal seminiferous tubules was observed in mice exposed to PS-NP, regardless of dose. Additionally, exposure to the higher dose increased seminiferous tubule diameter, while both doses increased germinal epithelium thickness compared with the control group. Spermatogenesis dynamics, as well as serum testosterone and estradiol levels, were not affected by PS-NP exposure. Regarding sperm parameters, the number of motile sperm decreased in the higher-dose group, and the proportion of sperm with normal morphology decreased in both exposed groups. The percentage of sperm lacking mitochondrial activity (unstained sheath) increased in both treated groups. No differences were found in the number of dead sperm or in chromatin maturation between exposed and control groups. Body weight and testis and epididymis weights were also unaffected by PS-NP exposure. In conclusion, exposure to PS-NP during the postnatal developmental period compromises testicular structure and impairs sperm functionality in male mice.