Tacrolimus diffusion across the peripheral mononuclear blood cell membrane: impact of drug transporters.

Measuring tacrolimus (TAC) concentration in peripheral blood mononuclear cells (PBMC) could better reflect the drug effect on its target (calcineurin (CaN) in lymphocytes) than whole blood concentrations. Mechanisms influencing TAC diffusion into PBMC are not well characterized. This work aimed at describing, ex-vivo, TAC diffusion kinetics into PBMC and investigating the contribution of membrane transporters to regulate TAC intracellular concentration as well as the impact on CaN activity. PBMC were incubated with TAC for 5 min to 4h and under several experimental conditions: 37°C (physiological conditions) 4°C (inhibition of influx and efflux active transport), 37°C + transporter inhibitors (verapamil, carvedilol, probenecid, bromosulphophtalein respectively inhibitors of P-gp, OAT, OATP). TAC concentration and CaN activity were measured in PBMC using liquid chromatography coupled with mass spectrometry. TAC intra-PBMC concentration was maximal after 1h of incubation. Mean TAC PMBC concentrations were significantly lower in samples incubated at 4°C compared to the 37°C groups. Addition of verapamil slightly increased TAC accumulation in PBMC while other inhibitors had no effect. A significant correlation was found between TAC intra-PBMC concentration and the level of inhibition of CaN. Using an ex-vivo cellular model, these results suggest that P-gp is involved in the drug efflux from PBMC while influx active transporters likely to regulate TAC intra-PBMC disposition remain to be identify. TAC concentration in PBMC is correlated with its pharmacodynamic effect. Then, TAC intra-PBMC concentration appears to be a promising biomarker to refine TAC therapeutic drug monitoring. This article is protected by copyright. All rights reserved.