Time course effects of methotrexate on renal handling of water and electrolytes in rats. Role of aquaporin-2 and Na-K-2Cl-cotransporter.

Methotrexate (MTX) is a derivate of folic acid, commonly used as an anchor drug for the treatment and management of malignant diseases and autoimmune disorders. However, nephrotoxicity is an important drawback of MTX therapy. Unfortunately, there are not enough studies reporting the nature of the renal failure induced by MTX. Thus, the aim of this study was to evaluate the time course of renal handling of water and electrolytes in male Wistar rats, after the exposure to a unique dose of MTX (80 mg/kg b.w.). Experiments were carried out at day 2, day 4, day 8 and day 14 after MTX administration. Several parameters of kidney function related to water and electrolytes handling were evaluated. Renal expression and urinary excretion of aquaporin-2 (AQP2) and Na-K-2Cl-cotransporter (NKCC2) were determined by Western blotting. MTX produced alterations on water handling on the second day after treatment, showing a significant increase in solute free water reabsorption which might be mediated by the increased expression of AQP2 in apical membranes. On the other hand, MTX produced alterations on electrolytes handling on the fourth day after treatment, showing a significant decrease of sodium chloride excretion, mediated at least in part, by the increase renal expression of NKCC2. These results provide valuable information to clinical practice in order to be able to find therapeutic targets that diminish adverse effects and health deterioration. Moreover, MTX treatment altered AQP2 and NKCC2 urinary excretion allowing postulating these transporters as potential biomarkers of MTX induced nephrotoxicity.