title: Tacrolimus, a calcineurin inhibitor, overcomes treatment unresponsiveness mediated by P-glycoprotein on lymphocytes in refractory rheumatoid arthritis.
abstract: OBJECTIVE
  Tacrolimus, a calcineurin inhibitor, is used for treatment of rheumatoid arthritis (RA). It also inhibits functions of P-glycoprotein, which is involved in drug resistance. We examined the mechanisms of early response to 2-week tacrolimus treatment in patients with RA.
  
  
  METHODS
  One hundred thirteen patients with refractory RA despite at least 3 antirheumatic agents, including methotrexate, were treated with tacrolimus (1.5-3 mg/day) and the response was assessed at 2 weeks. Expression of the multidrug resistance (MDR-1) gene and P-glycoprotein was assessed in peripheral blood mononuclear cells (PBMC) collected from 113 patients and 40 healthy subjects. The drug exclusion function by the P-glycoprotein was measured by the residual amount of intracellular tritium-labeled dexamethasone cell/medium ratio (C/M ratio).
  
  
  RESULTS
  The disease activity of enrolled patients was 5.8 +/- 1.2 (mean +/- SD) by DAS28 erythrocyte sedimentation rate. A good response to tacrolimus was noted at 2 weeks in 22 of 113 patients. At baseline, PBMC of patients with RA showed upregulated expression of MDR-1 gene and P-glycoprotein and low C/M ratio. The response to tacrolimus correlated with P-glycoprotein expression and C/M ratio. A significant improvement in C/M ratio was noted after 2 weeks of treatment. The C/M ratio correlated significantly with P-glycoprotein expression on CD4+ lymphocytes.
  
  
  CONCLUSIONS
  Early efficacy of tacrolimus treatment depended on its inhibitory effect on the drug exclusion function of P-glycoprotein, leading to restoration of intracellular therapeutic levels of corticosteroids and clinical improvement. Evaluation of P-glycoprotein expression on lymphocytes is potentially useful for predicting the response to RA treatment.
authors.affiliation: First Department of Internal Medicine, University of Occupational and Environmental Health, Japan.
authors.forename: Katsunori
authors.initials: K
authors.lastname: Suzuki
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Saito
authors.forename: Shizuyo
authors.initials: S
authors.lastname: Tsujimura
authors.forename: Shingo
authors.initials: S
authors.lastname: Nakayamada
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Yamaoka
authors.forename: Norifumi
authors.initials: N
authors.lastname: Sawamukai
authors.forename: Shigeru
authors.initials: S
authors.lastname: Iwata
authors.forename: Masao
authors.initials: M
authors.lastname: Nawata
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Nakano
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Tanaka
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000473:pathology; D065095:Calcineurin Inhibitors; D016022:Case-Control Studies; D004351:Drug Resistance / Q000187:drug effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D016559:Tacrolimus / Q000494:pharmacology / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D065095:Calcineurin Inhibitors; D007166:Immunosuppressive Agents; D016559:Tacrolimus