Impact of sub-chronic polystyrene nanoplastics exposure on hematology, histology, and endoplasmic reticulum stress-related protein expression in Nile tilapia (Oreochromis niloticus)

Nanoplastics (NPs) are one of the most hazardous marine litters, having the potential to cause far-reaching impacts on the environment and humankind. The effect of NPs on fish health has been studied, but their impact on the subcellular organelles remains unexplored. The present investigation studied the possible implications of polystyrene-nanoplastics (PS-NPs) on the hematology, tissue organization, and endoplasmic reticulum (ER) stress-related proteins in Nile tilapia (Oreochromis niloticus). Fish were exposed to ∼100 nm PS-NPs at environmentally relevant (0.1 mg/L), and sublethal (1, 10 mg/L) concentrations for 14 days through water exposure. The growth performance and hematological parameters such as erythrocytes, hemoglobin, hematocrit, and leucocytes decreased, while thrombocytes increased with PS-NPs dose-dependently. The gills, liver, kidney, and heart tissues displayed increasing degrees of pathology with increased concentrations of PS-NPs. The gills showed severe epithelial hyperplasia and lamellar fusion. The liver had an abstruse cellular framework, membrane breakage, and vacuolation. While glomerular and tubular atrophy was the most prominent pathology in the kidney tissue, the heart displayed extensive myofibrillar loss and disorderly arranged cardiac cells. The ER-stress-related genes such as bip, atf6, ire1, xbp1, pkr, and apoptotic genes such as casp3a, and bax were over-expressed, while, the anti-apoptotic bcl2 was under-expressed with increasing concentrations of PS-NPs. Immunohistochemistry and blotting results of GRP78, CHOP, EIF2S, and ATF6 in gills, liver, kidney, and heart tissues affirmed the translation to ER stress proteins. The results revealed the sub-lethal adverse effects and the activation of the ER-stress pathway in fish with sub-chronic exposure to PS-NPs.