Effect of Azathioprine on Na+/H+ Exchanger Activity in Dendritic Cells

Abstract

Azathioprine is a powerful immunosuppressive drug, which is partially effective by interfering with the maturation and function of dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity. DCs are stimulated by bacterial lipopolysaccharides (LPS), which trigger the formation of reactive oxygen species (ROS), paralleled by activation of the Na⁺/H⁺ exchanger. The carrier is involved in the regulation of cytosolic pH, cell volume and migration. The present study explored whether azathioprine influences Na⁺/H⁺ exchanger activity in DCs. DCs were isolated from murine bone marrow, cytosolic pH (pH_i) was estimated utilizing 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF-AM) fluorescence, Na⁺/H⁺ exchanger activity from the Na⁺-dependent realkalinization following an ammonium pulse, cell volume from forward scatter in FACS analysis, ROS production from 2′,7′-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, TNFα release utilizing ELISA, and migration utilizing transwell migration assays. Exposure of DCs to lipopolysaccharide (LPS, 1 µg/ml) led to a transient increase of Na⁺/H⁺ exchanger activity, an effect paralleled by ROS formation, increased cell volume, TNFα production and stimulated migration. Azathioprine (10 µM) did not significantly alter the Na⁺/H⁺ exchanger activity, cell volume and ROS formation prior to LPS exposure but significantly blunted the LPS-induced stimulation of Na⁺/H⁺ exchanger activity, ROS formation, cell swelling, TNFα production and cell migration. In conclusion, azathioprine interferes with the activation of dendritic cell Na⁺/H⁺ exchanger by bacterial lipopolysaccharides, an effect likely participating in the anti-inflammatory action of the drug.