Exposure to Polypropylene Microplastics Causes Cardiomyocyte Apoptosis Through Oxidative Stress and Activation of the MAPK‐Nrf2 Signaling Pathway

ABSTRACT Microplastics are a growing concern as pollutants that impact both public health and the environment. However, the toxic effects of polypropylene microplastics (PP‐MPs) are not well understood. This study aimed to investigate the effects of PP‐MPs on cardiotoxicity and its underlying mechanisms. The cardiotoxicity of exposure to different amounts of PP‐MPs were investigated in both ICR mice and H9C2 cells. Our results demonstrated that sub‐chronic exposure to 5 and 50 mg/L PP‐MPs led to myocardial structural damage, apoptosis, and fibrosis in mice cardiomyocytes. Flow cytometry analysis revealed that PP‐MPs could decrease mitochondrial membrane potential and induce apoptosis in H9C2 cells. Western blotting revealed decreased expression of Bcl‐2, poly(ADP‐ribose) polymerase (PARP) and caspase 3 and increased expression of Bax, cleaved‐PARP, and cleaved‐caspase 3 in PP‐MPs‐treated cardiac tissue and H9C2 cells. These results confirmed the apoptotic effects induced by PP‐MPs. Moreover, PP‐MPs treatment triggered oxidative stress, as evidenced by the increased levels of malondialdehyde; reduction in glutathione peroxidase, superoxide dismutase, and catalase activities in mice cardiac tissues; and increased reactive oxygen species levels in H9C2 cells. Finally, western blotting demonstrated that exposure to PP‐MPs significantly reduced the expression levels of Nrf2 and p‐ERK proteins associated with MAPK‐Nrf2 pathway in both cardiac tissue and H9C2 cells. Overall, our findings indicate that PP‐MPs can induce cardiomyocyte apoptosis through MAPK‐Nrf2 signaling pathway, which is triggered by oxidative stress. This study provides a foundation for determining the effects of PP‐MPs on cardiotoxicity and their underlying mechanisms.