EVALUATION OF P-GLYCOPROTEIN EXPRESSION AND FUNCTION IN PERIPHERAL-LYMPHOCYTES OF RENAL TRANSPLANT RECIPIENTS: RELATIONSHIP WITH LYMPHOCYTE-SENSITIVITY TO IMMUNOSUPPRESSIVE DRUGS AND CLINICAL STATUS.

Abstract

P719 Aims: P-glycoprotein (P-gp) is reported to mediate the efflux of several lipophilic drugs from mammalian cells. Overexpression of P-gp in immune cells may result in the insufficient efficacy of immunosuppressive drugs in renal transplantation patients. With this in mind, we evaluated P-gp expression and function in peripheral-blood mononuclear cells (PBMCs) to examine their influence on PBMC-sensitivity to immunosuppressive drugs and the clinical status of renal transplant recipients. Methods: Seventeen renal transplant recipients, nine patients with chronic renal failure, and 16 healthy subjects were included in the study. The basic characteristics of these subject groups did not differ significantly. Out of the 17 transplant recipients, 14 had received cyclosporine-based immunosuppressive therapy, while two patients received tacrolimus and one a steroid without calcineurin inhibitors. P-gp expressed in PBMCs was stained with FITC-labeled anti-P-gp monoclonal antibodies and subsequently analyzed with flow cytometry. P-gp function was evaluated with incorporation and efflux of rhodamine 123 (R123) in the presence or absence of cyclosporine, followed by flow cytometry analysis. PBMC-sensitivity to the suppressive effects of prednisolone, methylprednisolone, cyclosporine or tacrolimus was evaluated by measuring the IC50s (ng/ml) of these agents against concanavalin A-induced blastogenesis of PBMCs in vitro. Results: The incidence of transplant recipients with PBMCs exhibiting high-rates of P-gp expression was significantly higher than that of the healthy subjects (p=0.0035). However, percentages of P-gp expressing PBMCs and P-gp function evaluated by R123-efflux ability of the cells did not correlate significantly in either of the subject groups. The IC50s of the immunosuppressive drugs did not correlate with the percentage of cells expressing P-gp or P-gp function in the PBMCs of the transplant recipients. In addition, we found no statistically significant correlation between these P-gp parameters and other clinical characteristics of the recipients such as the incidence of rejection episodes or adverse effects of the immunosuppressive drugs administered. In contrast, the amount of R123 incorporated and retained in the PBMCs significantly correlated with either serum creatinine or blood urea nitrogen (BUN) concentrations in transplant recipients (p=0.021 and p=0.0014, respectively). Conclusions: We conclude that P-gp expression and its function in PBMCs had little influence on the cellular and clinical pharmacodynamics of immunosuppressive drugs in the renal transplant recipients. Increases in concentrations of serum creatinine, BUN, and/or possibly other uremic toxin(s) due to the impairment of renal graft function results from chronic allograft rejection or cyclosporine side effects may have suppressed the P-gp function in the PBMCs of these recipients.