Polystyrene Microplastics Induce Sustained Cardiovascular Redox Imbalance and Alter Mitochondrial Quality Control

Microplastic exposure is an emerging environmental risk factor for cardiovascular health; however, whether cardiovascular alterations can be detected after exposure cessation remains unclear. This study investigated subclinical cardiovascular alterations following repeated oral exposure to polystyrene microplastics (PSMPs), with particular emphasis on redox imbalance and mitochondrial function in delayed cardiovascular alterations. Male Sprague-Dawley rats were administered 0.5 μm PSMPs via oral gavage at varying dosages of 5 or 20 mg/kg every 5 days for 70 days, followed by a 35-day exposure-free period. Repeated exposure to PSMPs did not affect body or organ weights but altered cardiac serum biochemical markers. Cardiac tissue exhibited elevated NADPH oxidase 4 (NOX4) expression and decreased superoxide dismutase 1 (SOD1), SOD2, and catalase (CAT) activities, whereas malondialdehyde (MDA) levels remained unchanged, indicating a state of chronic, low-level oxidative stress. Mitochondrial respiratory chain activities, including nicotinamide adenine dinucleotide cytochrome c reductase (NCCR) and succinate cytochrome c reductase (SCCR), were significantly reduced. Ultrastructural analysis revealed mitochondrial swelling and cristae disruption. In parallel, mitochondrial biogenesis-related proteins, including peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), nuclear respiratory factor 1 (NRF-1), and mitochondrial transcription factor A (TFAM), were downregulated, while mitophagy markers, including PTEN-induced kinase 1 (PINK1), Parkin RBR E3 ubiquitin protein ligase (Parkin), microtubule-associated protein 1 light chain 3 (LC3), and sequestosome 1 (p62), were upregulated. Notably, most significant alterations were primarily observed in the high-dose group. Furthermore, the aorta showed increased oxidative stress markers without overt structural remodeling. These findings suggest that repeated exposure to PSMP is associated with subclinical cardiac redox–mitochondrial dysregulation, potentially involving redox imbalance, impaired mitochondrial respiratory chain activity, reduced mitochondrial biogenesis, and altered mitochondrial quality-control markers.