Swimming in Plastamination: Poly-lactic Acid Nanoplastics and Sperm Functions

The increasing demand of plastic-goods and the accumulation of plastic-waste in the environment make plastic contamination (PLASTAMINATION) one of the main troubles of XXI century. Recently, attention has been focused on microplastics (MPs, 5mm-1µm) and nanoplastics (NPs, <1µm) that can be intentionally produced or originate from the environmental degradation of larger plastic-waste. MNPs enter the food chain, bypass the biological barriers, and enter cells exerting toxic/inflammatory effects. The presence of MNPs has been demonstrated in the tissues of aquatic and terrestrial organisms, included human, and also in biological fluids like blood, breastmilk, follicular fluid, and semen. Recent studies linked MNPs exposure to higher rate of chronic diseases, miscarriage or poor semen production. Nevertheless, the use of biodegradable polymers like the the poly-lactic acid (PLA) does not guarantee they are safe for health. Since the ability of PLA-NPs to enter cells (i.e., C6, HT29, Caco-2, hPBMCs), we investigated their possible internalization in mammalian spermatozoa (SPZ). Hence, rat SPZ collected from caput/cauda epididymis and seminal material from bulls were incubated with increasing concentrations of Rhodamine B conjugated-PLA-NPs (0-300 µg/mL); PLA-NPs internalization was investigated by immunofluorescence (IFL) analysis. In bovine, the effects on sperm kinetics was evaluated using a computerized semen analyzer (CASA). Additionally, flow cytometry was used to determine if the PLA-NPs could increase cytoplasmic membrane permeability, alter membrane organization, and whether PLA-NPs affects mitochondrial function by assessing the bioenergetic state. PLA-NPs entry in SPZ was investigated by IFL and further confirmed by co-localization with α-tubulin, used as a marker for the sperm flagellum. PLA-NPs enter rat and bovine SPZ. In bovine SPZ PLA-NPs affects progressive motility, mitochondrial metabolism and plasma membrane destabilization mainly at the highest doses. In conclusion, PLASTAMINATION warrant consideration. The development of strategies to mitigate PLASTAMINATION and further studies on the biological effects of biodegradable plastics are recommended. Funding: NGEU, MUR, PRIN-PNRR2022, CODE: P2022AA47Y- CUP I53D23007130001, Project title: Poly(Lactic Acid) plastics contamination (PLASTAMINATION): organ injuries and underlying molecular mechanisms