Salinity-Dependent Modulation of Antioxidant Defense, Apoptosis Enzymes, and Molecular Complexes Interaction in Tilapia Exposed to Polystyrene Nanoplastics

Nanoplastics (NPs) are emerging contaminants due to their persistence, bioaccumulation, and small particle size. These pollutants are derived from the breakdown of larger plastic debris and frequently enter aquatic environments through runoff from unmanaged landfills and illegal dumping sites. Based on the habitat, fish could be found in some ecosystem actually, such as in fresh water, breakish water, and marine water. Moreover, NPs can affect the physiology and biochemistry of fish, potentially altering oxidative balance and triggering apoptosis. The information about the effects of NP exposure on fish in different salinity level was still limited, therefore this study aimed to examine the effects of polystyrene nanoplastics (PS-NPs) on antioxidant activity and apoptosis-inducing enzymes in tilapia’s strain Jatimbulan (Oreochromis niloticus) under varying salinity levels. Tilapia were divided into control groups (without NPs) and treatment groups exposed to PS-NPs (2 µL/kg) at salinities of 0, 2.5, 5, 10, and 15 ppt for 25 days. Antioxidant enzymes (catalase (CAT) and superoxide dismutase (SOD)) and apoptosis-related enzymes (caspase-3 and caspase-9) were quantified using ELISA test. Molecular docking was conducted using the styrene monomer (CID: 7501) as the ligand, and CAT, SOD, caspase-3, and caspase-9 as target receptors. Docking analysis and validation revealed that exposure of PS-NPs significantly reduced antioxidant levels and increased activity of apoptosis-related enzymes, particularly in fish reared at higher salinities. The results showed that exposure to PS-NPs on 0 ppt significantly reduced concentration of antioxidant enzymes and increased apoptosis-related enzymes levels. On different salinity level, it showed that salinity modulates NP toxicity by influencing antioxidant enzymes and apoptosis-related enzymes. Moreover, the molecular docking experiment revealed that CAT (−5.3 kcal/mol) and caspase-9 (−4.6 kcal/mol) proteins were found to be most affected by the presence of PS-NPs in cells, as evidenced by highest binding affinity compared to other test proteins. Molecular docking indicates direct interactions of styrene monomers with catalase and caspase-9, suggesting disruption of oxidative stress regulation and apoptosis pathways. In conclusion, this study highlighted the risk of NP pollution in different salinity level, representative of some aquatic ecosystems, persuading to be care and find mitigation solution to reduce the impact of NP pollution, such as remediation.