Global plastic production has led to widespread contamination by micro- and nanoplastics, with polystyrene nanoplastics (PSNPs) increasingly being detected in human biological samples, including blood and cardiac tissue. Given the critical role of mitochondria in cardiac energy metabolism, this study investigated whether 100 nm PSNPs interact with mitochondria and affect mitochondrial function in H9c2 cardiomyoblasts. Cellular uptake and intracellular distribution were examined, followed by an evaluation of mitochondrial ultrastructure, intracellular and mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential, mitochondrial dynamics and mitophagy-related gene expression, mitochondrial DNA copy number, and metabolic function. PSNPs were internalized but did not directly localize to mitochondria within 24 h. No significant cytotoxicity, increase in intracellular or mitochondrial ROS production, or alteration in basal metabolic activity was observed. However, PSNP exposure resulted in intracellular accumulation, an altered mitochondrial ultrastructure characterized by crista loosening and vacuole-like structural changes. These changes were accompanied by reduced mitochondrial membrane potential; the upregulation of mitochondrial dynamics-related genes, including optic atrophy 1 (Opa1) and dynamin-related protein 1 (Drp1); the suppression of PTEN-induced kinase 1 (PINK1)/Parkin RBR E3 ubiquitin protein ligase (Parkin)-mediated mitophagy-related genes; and decreased maximal respiratory capacity. Lactate production and the extracellular acidification rate remained unchanged, suggesting that compensatory glycolysis was not activated. These findings indicate that PSNP exposure induces early mitochondrial structural and functional alterations without substantial cell damage, suggesting a potential reduction in cardiac adaptive capacity under PSNP-induced stress conditions.

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.