Detection of toxic effects of Cd2+ on different fish species via liver cytochrome P450-dependent monooxygenase activities and FTIR spectroscopy

The in vivo and in vitro effects of Cd²⁺ and the CYP1A inductor β-naphthoflavone(β-NF) on the hepatic cytochrome P450 (Cyt 450) monooxygenases were studied in silver carp (Hypophthalmichtys molitrix V.), wels (Silurus glanis L.), and carp (Cyprinus carpio). In vivo treatment of carp with a high dose of Cd²⁺ (10 mg kg⁻¹, for 3 days) caused a strong inhibition of 7-ethoxyresorufin-O-deethylase (EROD) and a lower inhibition of 7-ethoxycoumarin-O-deethylase (ECOD) activity. The low-dose cadmium treatment (2 mg kg⁻¹ Cd²⁺, for 6+3 days) resulted in 4-fold increase in EROD and a 3-fold increase in ECOD activity. The combined treatment with Cd²⁺ and β-NF in both cases led to a loss of EROD inducibility. The silver carp and wels were treated with 10 mg L⁻¹ Cd²⁺ for 72 h in water. The Cyt P450 content in the wels liver microsomes was increased significantly after treatment for 48 h, whereas there was only a slight, not significant increase in Cyt P450 content in the silver carp microsomes. While the Cd²⁺ treatment resulted in inhibition of the CYP1A isoenzymes (EROD and ECOD), the APND (aminopyrene-N-demethylase, CYP2B or CYP3A isoenzyme) activity was increased 3- to 4-fold in both fish species. In vitro experiments of the effect of Cd²⁺ led to a concentration-dependent inhibition in all three investigated fish species. The ECOD isoenzyme of silver carp was the most sensitive to Cd²⁺. The lowest concentration of Cd²⁺ resulted in 50% inhibition. The APND isoenzyme was similarly sensitive to Cd²⁺ in all three investigated fish species. The most sensitive species was the wels, and the least sensitive were the carp isoenzyme. FTIR spectroscopy confirmed that cadmium caused damage to the protein structure. These results support the enzyme activity measurements measured in vivo and in vitro.