In a preprint under consideration at the peer-reviewed journal Particle and Fibre Toxicology, published on July 19, 2021, Haibo Jin and co-authors from Nanjing University, China, studied the effects of polystyrene (PS) microplastics on the male reproductive system of mammals. The scientists exposed mice to fluorescent PS microplastics of three sizes (0.5, 4.0, and 10 µm) for 180 days and exposed primary Leydig cells to particles of 0.5 µm for 24 hours. Leydig cells are testis cells that synthesize and secrete testosterone. According to the authors, environmentally relevant particle concentrations were used (100 and 1000 µg/L for mice exposure) which complies with requirements previous reviews emphasized as necessary to better understand potential health implications of microplastics (FPF reported).
After the exposure period, Jin and colleagues observed damage to testicular tissue structure as well as decreased sperm quality and testosterone levels, showing that chronic exposure to PS microplastics induces male reproductive toxicity in mice. They also analyzed the underlying mechanism for reduced testosterone levels and found the inhibition of the luteinizing hormone (LH)-mediated LHR/cAMP/PKA/StAR pathway to be responsible. Moreover, the researchers reported that the plastic particles attached to the Leydig cells and were subsequently internalized. The authors believe that their “findings may provide a novel insight for preventing the reproductive toxicity of MPs [microplastics].” Providing novel insights into micro- and nanoplastic impacts on human health is also the objective of five recently launched Horizon 2020 research projects (FPF reported).
In a previous study, published January 5, 2021, in the Journal of Hazardous Materials, Haibo Jin and colleagues demonstrated that even exposing mice to PS microplastics over a shorter, 28-day period reduces sperm quality and testosterone levels. In addition, the plastic particles disrupted the blood-testis barrier and induced testicular inflammation.
Recent reviews and articles have outlined the knowledge gaps hindering human health risk assessment of microplastics and stressed that research must reflect the diversity of microplastics present in the environment. These knowledge gaps can therefore be addressed by using not only pristine regularly shaped plastic particles in experiments, as reported above, but potentially even more successfully by using weathered and irregular microplastic particles most commonly present in the environment (FPF reported).
Jin et al. (2021). “Reproductive toxicity of chronic exposure to polystyrene microplastics and the molecular mechanism of decrease in testosterone levels in male mice.” Particle and Fibre Toxicology. DOI: 10.21203/rs.3.rs-689230/v1 (preprint)
Jin et al. (2021). ”Polystyrene microplastics induced male reproductive toxicity in mice.” Journal of Hazardous materials. DOI: 10.1016/j.jhazmat.2020.123430