Protective Effects of Rosmarinic Acid Against Microplastic-Induced Oxidative Stress in RTgill-W1 Fish Gill Cell Culture: A Pharmacological In Vitro Study

Abstract

Microplastic contamination has emerged as a significant environmental threat to aquatic ecosystems, contributing to oxidative stress, inflammation, and cellular toxicity in aquatic organisms. This study investigated the protective effects of rosmarinic acid (RA) against microplastic-induced cytotoxicity and oxidative stress using RTgill-W1 fish gill cells as an in vitro aquatic toxicology model. Cells were exposed to polystyrene microplastics (PS-MPs; 100 µg/mL) either alone or in combination with low-dose (25 µM) or high-dose (50 µM) RA for 24 h. Cell viability was determined using the MTT assay, while oxidative stress biomarkers including reactive oxygen species (ROS), malondialdehyde (MDA), glutathione (GSH), and catalase activity were evaluated. Inflammatory responses were assessed through quantitative PCR analysis of TNF-α and IL-1β expression. PS-MP exposure significantly reduced cell viability from 100.0 ± 2.4% to 52.6 ± 4.1% (p < 0.05), accompanied by marked increases in ROS production (248 ± 12%), MDA levels (6.8 ± 0.5 nmol/mg protein), TNF-α expression (4.86 ± 0.31-fold), and IL-1β expression (5.42 ± 0.40-fold). Simultaneously, antioxidant defenses were impaired, as evidenced by reductions in catalase activity (21.4 ± 1.8 U/mg protein) and GSH content (3.1 ± 0.3 µmol/g protein). Co-treatment with RA significantly attenuated these effects in a dose-dependent manner. The high-dose RA treatment restored cell viability to 88.4 ± 3.2%, reduced ROS and MDA levels to 122 ± 7% and 3.1 ± 0.3 nmol/mg protein, respectively, and increased catalase activity and GSH content to 43.7 ± 1.9 U/mg protein and 7.0 ± 0.3 µmol/g protein. Furthermore, RA markedly suppressed TNF-α and IL-1β expression to 1.42 ± 0.11-fold and 1.66 ± 0.13-fold, respectively. These findings demonstrate that RA effectively protects RTgill-W1 cells against microplastic-induced oxidative and inflammatory injury and highlight its potential as a natural pharmacological strategy for mitigating aquatic pollutant toxicity.