The inhibitory effect of newly synthesized ethnyl- derivatives on the activity of cytochrome P450 isoenzymes in rat liver microsomes in-vitro

The inhibitory effect of six newly synthesized ethnyl-derivatives on the activity of cytochrome P450 isoenzymes were investigated in rat liver microsomes. 6 μM concentration of each compound against different concentrations of the substrates (1, 2, 4, 8 and 16 μM) was used: 7-ethoxy resorufin "EROD" in β-Naphthoflavone "β-NF"induced CYP 1A isoenzyme and 7-pentoxy resorufin "PROD" in phenobarbital "PB"induced CYP 2B were used. It was found that all the compounds inhibited the activity of CYP 1A at the high concentration. CYP 2B was inhibited by the same compounds except for the first one. The binding experiments was carried out to delineate the exact nature of binding between these compounds and CYPisoenzymes (CYP 2B; 1A; 3A; 2E1 and 2D1) in PB, β-NF, DEX, pyrazol-induced and control rat liver microsomes respectively. It was found that, only compounds III and IV at high concentration "80 μM" revealed an interaction with the active site of CYP450. A type I binding for compound IV was obtained. In contrast, compound III showed a type II or reverse type I binding. The enzyme kinetics "Vmax and Km" of the different inhibitors were investigated. The inhibitory effect of the compounds III and IV at different concentrations (10, 20, 40 and 80 μM) in untreated rat liver microsomes on the Dex-O-demethylation was studied. It was found that neither compound III nor IV had no effect except the concentration of 80 μM 0f compound IV which exert a complete inhibition, as well as, the effect of these compounds at the concentration on of 6 μM against different concentrations of erythromycin (2.5, 5,10,15, 20 and 25 m ( indicative CYP 3A1 activity on the dealkylation reaction in Dex-induced rat liver microsomes. Also, the results revealed that compounds III, IV, V, VI and VII inhibited the activity of CYP 2E1. It was concluded that these derivatives proved to be variable potential inhibition on CYP450 isoformes in rat liver microsomes.