title: Multidrug resistance-1 (MDR-1) in autoimmune disorders IV. P-glycoprotein overfunction in lymphocytes from myasthenia gravis patients.
abstract: Multidrug resistance (MDR) mechanisms have been widely studied in cancer. Among them, P-glycoprotein (P-gp) overfunction has been associated with resistance to several antineoplastic agents. The physiological role of P-gp involves hormone and metabolite secretion, bacterial product detoxification, and transport of several drugs to the extracellular space, thus inhibiting their toxic or therapeutic effects. The study of MDR-1 in diseases of autoimmune origin has just recently emerged. Corticosteroids remain the mainstay therapy for autoimmune diseases. As prednisone (PDN) is transported by P-gp, the aim of this study was to evaluate the P-gp function in lymphocytes from myasthenia gravis (MG) patients. Thirty MG patients and 25 healthy controls were studied. Peripheral blood mononuclear cells were isolated by gradient centrifugation and incubated with daunorubicin (DNR) (a fluorescent drug extruded by P-gp). Functional activity of P-gp was analyzed by flow cytometry. Results were expressed as percentage of gated lymphocytes able to efflux DNR. Overall, MG patients showed increased numbers of lymphocytes with functional P-gp activity when compared with controls (x = 4.92 +/- 5.26% vs. x = 0.7 +/- 0.48%, respectively) (P < 0.0001). When patients were classified as responders (n = 21) or refractory (n = 9) to treatment, the latter group exhibited higher values of functional P-gp (x = 10.18 +/- 6.39%) when compared to the responder group (x = 2.66 +/- 2.45%) (P = 0.0076). These data suggest, on the one hand, that drug resistance may be induced by long-term treatment or by high PDN doses and, on the other, emphasize the need for the study of P-gp antagonists in order to improve the current therapeutical schemes for the treatment of MG.
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Vasco de Quiroga # 15, Tlalpan 14000, Mexico City, D.F., Mexico.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Richaud-Patin
authors.forename: Felipe
authors.initials: F
authors.lastname: Vega-Boada
authors.forename: Antonio
authors.initials: A
authors.lastname: Vidaller
authors.forename: Luis
authors.initials: L
authors.lastname: Llorente
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000097:blood*; D000293:Adolescent; D000328:Adult; D001379:Azathioprine / Q000627:therapeutic use; D003630:Daunorubicin / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000494:pharmacology; D005938:Glucocorticoids / Q000627:therapeutic use; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism*; D011239:Prednisolone / Q000627:therapeutic use
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005456:Fluorescent Dyes; D005938:Glucocorticoids; D007166:Immunosuppressive Agents; D011239:Prednisolone; D001379:Azathioprine; D003630:Daunorubicin