Physiological and Molecular Responses of the Cichlid Fish Cichlasoma dimerus to Diclofenac Exposure: Oxidative Stress, Histological Alterations, and Detoxification Mechanisms

Abstract:
One of the most ubiquitous and widely prescribed pharmaceuticals currently present in aquatic environments is diclofenac (DCF), a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase enzymes, reducing prostaglandin levels. DCF primarily enters water bodies through inadequately treated sewage effluents, causing poorly understood harmful effects on aquatic organisms. This study aimed to evaluate the impact of waterborne DCF (sodium salt) on biochemical, histological, and molecular biomarkers in the native freshwater cichlid Cichlasoma dimerus. Adult fish were exposed to 0 (control), 1, 10, or 100 µg/L DCF for 14 or 28 days, under a semi-static renewal regime, every 48 hours. The two lowest concentrations represent environmentally relevant levels. Biochemical and oxidative stress biomarkers analyzed included lipid peroxidation (TBARs), glutathione-S-transferase (GST) activity, antioxidant capacity against peroxy radicals (ACAP), catalase (CAT) activity, and reduced glutathione (GSH) content in the liver, gills, and brain. Additionally, histological changes in gills and liver after both times of exposure were measured, as well as the hepatic mRNA expression of cyclooxygenase-2 (COX-2) and the detoxification enzyme P-glycoprotein (P-gp). After 14 days of exposure, oxidative stress-related damage (↑TBARs) was observed in gills from all treatment groups. Although no statistically significant differences were detected in the histological alteration index (HAI), both structural and circulatory changes were observed in gills. After 28 days, increased hepatic GSH levels (1 µg/L DCF), together with a reduction in gill antioxidant capacity (↑ACAP) (10 µg/L DCF), were observed. Histological analysis of the gills revealed alterations similar to those seen after 14 days, while in the liver, an increase in pyknotic nuclei in hepatocytes of exposed fish was observed. Hepatic P-gp gene expression tended to increase in DCF-exposed groups. These findings suggest that DCF exposure disrupts physiological homeostasis in C. dimerus, triggering alterations of biomarkers at different levels of organization, including an upregulation of detoxification enzymes to counteract these imbalances.

Author(s):
Gabriela Chalimoniuk National Scientific and Technical Research Council (CONICET) Argentina  This Author Is the Presenter
Ismael Lozano National Scientific and Technical Research Council (CONICET) Argentina 
Cristina Czuchlej National Scientific and Technical Research Council (CONICET) Argentina 
Rodrigo Da Cuña University of Buenos Aires (UBA) Argentina 
Giovana Branco University of São Paulo (USP) Brazil 
Renata Guimaraes Moreira Whitton University of São Paulo (USP) Brazil 
Enrique Rodriguez University of Buenos Aires (UBA) Argentina 
Fabiana Lo Nostro University of Buenos Aires (UBA) Argentina 
Ariadna Battista University of Buenos Aires Argentina