Co-exposure to Microplastics and Cadmium: Effects on DNA Damage in Mytilus Galloprovincialis

The issue of plastic pollution has become a critical global issue of the 21st century. Microplastics (MPs) have emerged as a pervasive contaminant in ecosystems worldwide, affecting both marine and terrestrial ecosystems.1 Depending on the specific context and how they interact, MPs can have a positive or negative effect on the impact of heavy metals. Heavy metals can be transported by MPs as vectors, with their bioavailability and toxicity potentially being increased. Nevertheless, microplastics have the capacity to absorb heavy metals, thereby diminishing their mobility and availability in the environment. We have already demonstrated that polystyrene microplastics (PS-MPs) induce alterations to the normal function of protamine-like proteins (PLs).2 These proteins are critical in DNA packaging and are the main basic components of the sperm chromatin in Mytilus galloprovincialis. Taking into account that DNA damage is one of the main causes of male infertility, this study examined the potential damage to DNA, the ability of PLs to protect DNA from oxidative damage after exposure for 24 hours of Mytilus galloprovincialis to PS-MPs (1 µg/L) in combination with three concentrations of cadmium chloride (1, 10 and 100 nM), compared to exposure to cadmium chloride alone at these three doses. In addition, activity and automodification by poly(ADPR) of PARP, a well known marker of DNA damage were also determined. Our investigation revealed that, despite acetic urea polyacrylamide electrophoresis (AU-PAGE) and SDS-PAGE did not demonstrate significant alterations in the patterns of PL proteins under all exposure conditions, protection assays revealed that PLs lose their ability to protect DNA from oxidative damage when mussels were exposed to 10 and 100nM of CdCl₂, while co-exposure to cadmium and microplastics restores this ability. In line with these results, PARP activity and its automodification decrease after exposure to all three doses of CdCl₂, while the co-exposure with microplastics partially restore PARP activity and auto-modification levels. Moreover, the expression of γH2Ax, a marker of double strand breakage, was also investigated. The results indicate that microplastics could reduce the detrimental effects of cadmium in our experimental conditions. The results highlight the detrimental impact of cadmium on the reproductive health of Mytilus galloprovincialis, shedding new light on the mechanisms of action of microplastics.