DRUG-METABOLIZING ENZYMES AND GILL MORPHOLOGY ARE SENSITIVE TARGETS OF TNT TOXICITY IN FISH

The aim of the present study was to evaluate TNT toxicity in fish related to its presence in the marine environment. Phase I and II drug-metabolizing enzymes and gills morphology were investigated using the European eel as model species. First eels were exposed for 6 and 24 h to 0.5, 1 and 2.5 mg/L nominal concentrations of TNT then re-exposed again for 24h and left in clean seawater for 72 h as a recovery period. CYP1A1, UGT and GST genes EROD, UGT and GST activities were measured. An in vitro study was also performed on EROD activity. Gill morphology was investigated by light microscopy. No modulation of the CYP1A1 gene was observed in TNTexposed eels while the compound resulted an inhibitor of EROD both in vivo and in vitro. On the contrary UGT and GST resulted significantly induced indicating their involvement in TNT and biodegradation products metabolism. Moreover GST gene and activity remained induced after the recovery period suggesting also the activation of the antioxidant defence. TNT determined structural lesions such as epithelial lifting, dilation of lamellar capillaries, hyperplasia and lamellar fusion. After the recovery period gill epithelium presented lamellar hypertrophy, swelling and necrosis at 2.5 mg/L TNT. The presence of TNT in marine environment may be of ecotoxicological concern as the the compound could affect seriously biochemical and physiological mechanisms regulating fish health. Finally EROD, GST and gill morphology resulted sensitive markers which could be applied in monitoring studies in TNT impacted areas.