Tacrolimus induces remission in refractory and relapsing lupus nephritis by decreasing P-glycoprotein expression and function on peripheral blood lymphocytes

P-glycoprotein (P-gp)-mediated efflux of corticosteroids (CS) may contribute to treatment unresponsiveness in Lupus Nephritis (LN) patients. Tacrolimus is a P-gp inhibitor and hence, may overcome this resistance. We aimed to study the response to tacrolimus, along with the expression and function of P-gp on peripheral blood lymphocytes (PBL) in patients with refractory and relapsing proliferative Lupus Nephritis. We enrolled 12 refractory/relapsing LN patients and treated them with corticosteroids and tacrolimus for 6 months. Expression and function of P-gp on PBL was measured by flow cytometry (as relative fluorescence index, RFI and Rhodamine dye efflux assay) before and 3 months after tacrolimus therapy. Renal response was assessed according to ACR response criteria after 3 and 6 months of tacrolimus therapy. 8 out of 12 refractory/relapsing LN patients achieved renal response (5 partial response, PR and 3 complete responses, CR) as early as 3 months, and 11 patients achieved renal response (7 PR and 4 CR) at 6 months from start of tacrolimus therapy. Proteinuria decreased from median urine protein creatinine ratio (UPCR) of 2.80 (2.00–3.40) at baseline to 1.20 (0.66–1.73) at 3 months (p < 0.001) and to 0.80 (0.19–1.30) at 6 months (p < 0.01). There was significant decrease in P-gp expression [RFI, 3.33 (2.87–4.97) vs 2.03 (1.25–3.86), p < 0.05) and P-gp function (RFI, 55.7 (29.7–84.1) vs 26.8 (16.1–37.0), p < 0.01) after 3 months of tacrolimus therapy. Tacrolimus achieves renal response in refractory/relapsing proliferative LN patients which may be partly related to overcoming P-glycoprotein mediated treatment unresponsiveness.