In Vitro Nano-Polystyrene Toxicity: Metabolic Dysfunctions and Cytoprotective Responses of Human Spermatozoa

SIMPLE SUMMARY: The question of emerging pollutants, among which nanoplastics occupy a predominant position, requires further investigation regarding their interaction with different biological systems, including reproductive cells. In the present evaluation, deleterious effects on sperm cells have been correlated with polystyrene nanoparticle size. Indeed, the decline of fundamental parameters such as motility, acrosome and DNA integrity, and ROS physiological production, has been associated with the action of nanoparticles with a diameter of 50 nm, compared to particles with larger size (100 nm). In addition, the expression of protective biomarkers, such as HSP70s, has been shown to contribute to damage recovery. The results warn about persistent and chronic contamination of plastics with a focus on infertility to elucidate the metabolic and biochemical changes of sperm cells in the presence of stressful xenobiotics. ABSTRACT: The ubiquitous spread of Polystyrene nanoplastics (PS-NPs) has rendered chronic human exposure an unavoidable phenomenon. The biodistribution of such particles leads to bioaccumulation in target organs including the testis, the site of sperm maturation. The purpose of this research has been to estimate the impact of PS-NPs (50 and 100 nm) on the metabolism of mature spermatozoa. The analysis of the semen parameters has revealed a higher toxicity of the smaller sized PS-NPs, which have negatively affected major organelles, leading to increased acrosomal damage, oxidative stress with the production of ROS, DNA fragmentation, and decreased mitochondrial activity. PS-NPs of 100 nm, on the other hand, have mainly affected the acrosome and induced a general state of stress. An attempt has also been made to highlight possible protective mechanisms such as the expression of HSP70s and their correlation among various parameters. The results have evinced a marked production of HSP70s in the samples exposed to the smaller PS-NPs, negatively correlated with the worsening in oxidative stress, DNA fragmentation, and mitochondrial anomalies. In conclusion, our results have confirmed the toxicity of PS-NPs on human spermatozoa but have also demonstrated the presence of mechanisms capable of counteracting at least in part these injuries.