Methotrexate (MTX) belongs to a group of medicines known as antimetabolites. It is commonly used in the treatment of malignant diseases and is prescribed in autoimmune and chronic inflammatory disorders. Along with its effective therapeutic power, MTX has adverse effects on several organs, including the kidney. The organic anion transporter 5 (Oat5) is exclusively localized in the renal apical membrane. Oat5 urinary excretion was proposed as an early biomarker in ischemic and nephrotoxic-induced kidney injury and in renal damage due to vascular calcification in preclinical models. The aim of this study was to evaluate Oat5 renal expression and urinary excretion in rats 48 h after the exposure to different doses of MTX, in comparison with traditional markers of renal injury, such as creatinine and urea plasma levels, protein urinary levels, urinary alkaline phosphatase (AP) activity, fractional excretion of water (FE) and renal histology. Male Wistar rats were treated with a single intraperitoneal injection of MTX at different dosages: 40-80-120-180-360 mg per kg b.w. (M40, M80, M120, M180, M360, = 4, respectively) and experiments were carried out 48 h after MTX administration. Oat5 renal expression was evaluated by western blotting and immunohistochemistry. Traditional parameters were only modified at the higher MTX dose (M360). Conversely, Oat5 urinary excretion was elevated at the middle dose of 80 mg per kg b.w. Oat5 renal expression was modified at the highest dose as well, both in homogenates and in apical membranes. These results suggest that Oat5 urinary excretion might serve as an early biomarker of MTX-induced kidney injury.

Obstructive nephropathy is characterized by alterations in renal function that depends on the degree and type of obstruction. To increase the knowledge about the physiopathological mechanisms involved in the renal damage associated with bilateral ureteral obstruction (BUO), we studied the renal expression and function (as urinary citrate excretion) of sodium-dependent dicarboxylate cotransporter (NaDC1) in rats. In addition, we evaluated the urinary excretion of NaDC1 as a candidate biomarker for this pathology. Male Wistar rats underwent bilateral ureteral obstruction for 1 (BUO1), 2 (BUO2), 5 (BUO5), and 24 (BUO24) h or sham operation. After 24 h of ureteral releasing, traditional parameters of renal function and citrate levels were determined, and NaDC1 levels were evaluated in total renal homogenates, apical plasma membranes, and urine by electrophoresis and Western blotting. Traditional parameters of renal function were only modified in BUO5 and BUO24. The renal expression of NaDC1 was decreased in BUO5 and BUO24, with a concomitant increase in urinary excretion of citrate. Moreover, the urinary excretion of NaDC1 increased after short times of ureteral obstruction (BUO1 and BUO2) and was positively correlated with the time elapsed after obstruction. The results obtained from the renal expression of NaDC1 could explain an adaptive mechanism to prevent the formation of kidney stones by increasing the levels of citrate, a calcium chelator. The urinary excretion of NaDC1 could be postulated as an early biomarker of obstructive nephropathy that also gives information about the duration of the obstruction.