Differential expression of α-like glutathione S-transferase (GST) isoforms in catfish intestine

Previous studies suggested that dietary composition affected glutathione S-transferase (GST) activity in catfish intestine, and this activity varied along the intestine. In this study, catfish were fed a semi-purified diet or a commercial chow for at least 2 weeks. GST activity, percent protein cross-reacting with anti-catfish GST π antibody, and immuno-cross-reactivity with antibodies specific for human α, μ, π and θ class GSTs were determined in cytosol prepared from sections of proximal, medial, and distal intestine. The bulk of GST activity with 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid, and the percent protein cross-reacting with anti-catfish GST π were in the more proximal segments and dropped off distally in the two diet groups. The percent of cross-reacting GST protein in the proximal section of fish fed on commercial chow was significantly higher (4.3±1.7%) than in fish fed purified diet (2.3±0.2%). Further Western blot analysis revealed a differential expression of GST isoforms only in the distal segment of fish fed commercial chow that recognized human anti-α GST antibody. Distal intestinal segments of catfish exposed to 3,3′,4,4′-tetrachlorobiphenyl (TCB) and β-naphthoflavone (BNF) also revealed expression of distinct α-like GST isoforms. Results strongly suggest the distal segment as a site for potential biomarkers for polycyclic aromatic hydrocarbon (PAH)- and co-planar polychlorinated biphenyl (PCB)-type contaminants.