Combined Treatment of Tacrolimus and Everolimus Increases Target Organ Injury Via Increasing P-Glycoprotein and Cytochrome P450.

Abstract

It is not clear the influence of combined treatment of tacrolimus (TAC) and everolimus (EVR). In this study, we investigated; first, whether combined treatment of EVR and TAC affects organ dysfunction and oxidative stress; second, whether these combined treatment affect each drug level at the blood and target organ tissues and third, the mechanisms of drug-drug interaction by assessing P-glycoprotein and cytochrome P450.Rat was orally administrated with TAC (6 mg/kg/day) and EVR (1 or 2 mg/kg/day) for 4 weeks. The effect of EVR on TAC-induced organ injury was also compared with that of EVR and TAC treatment alone. Oxidative stress was measured with 8-hydroxy-2'-deoxyguanosin (8-OHdG) in serum and 24 hour urine. To confirm the drug interaction between and EVR or TAC, concentration of each drug was evaluated in the whole blood and tissue (kidney, pancreas and liver) using LC/MS/MS. The mechanism of drug interaction was evaluated by the expression of P-glycoprotein and cytochrome P450 in target organ tissues using immunoblot analysis. TAC or EVR treatment alone did not caused overt renal, pancreatic islet, and liver injury, but addition of EVR significantly increased the TAC-induced injury, as demonstrated by aggravated nephrotoxicity, pancreatic islet and liver dysfunction. In blood and target organs e.g. liver, kidney and pancreas, surprising higher TAC or EVR level were detected in combined group compared with single treated groups. And there was good correlation between two drugs in blood and target organs. The serum and urinary 8-OHdG level were significantly increased in the TAC and EVR combined treated group compared with the TAC or EVR alone group, and were well correlated with drug levels in the blood and tissues. TAC or EVR alone treated groups showed higher expression of P-glycoprotein than control, and combined treatment was further increased its expression compared to the TAC or EVR alone treatment groups. Consistently, cytochrome P450 also showed much higher level in combined group compared to the single treated groups. We conclude that addition of EVR aggravates TAC-induced organ injury and pharmacologic drug-drug interaction. The reason for drug interaction between two drugs is related to the mutual competitive interactions targeting P-glycoprotein and cytochrome P450.