Selective downregulation of hepatic cytochrome P450 expression and activity in a rat model of inflammatory pain

Purpose. This study was designed to examine the effect of Freund's complete adjuvant (FCA)-induced inflammation on liver P450 expression and activities in the first 7 days that followed a single FCA injection in the rat hindpaw. Methods. Rats were humanely sacrificed at regular time points, plasma and liver samples were collected, liver mRNA extracted, and liver microsomes prepared. Results. FCA injection led to the development of an acute inflammatory response evidenced by paw edema and increased alpha-1-acid glycoprotein (AGP) and total-nitrite (NOx) plasma concentrations. Plasma IL-6 levels were significantly higher in FCA-treated rats than in controls at 8 h post-FCA. Within 24 h, these changes were accompanied by a rapid decrease in total P450 contents in FCA-treated rat liver and the selective downregulation of specific CYP isoforms, as illustrated by decreased mRNA levels (CYP2B,CYP2C11,CYP3A1 and CYP2E1), protein contents (CYP2B, CYP2C11, and CYP2EI) or catalytic activities (CYP2C6, CYP2C11, and CYP2EI). CYP3A1 mRNA levels were severely decreased by FCA administration, whereas CYP3A2 mRNA and protein levels remained unchanged. Conclusions. These early biochemical and metabolic modifications may have pharmacokinetic and pharmacodynamic consequences when hepatically cleared drugs are administered to FCA-treated rats, especially within the first 24-72 h post-FCA.