Acetazolamide enhances the release of urinary exosomal aquaporin-1

BACKGROUND: Renal aquaporin-1 (AQP1), a water channel protein, is known to be secreted into urine, conveyed by nano-sized extracellular vesicles called exosomes. A previous study has demonstrated that acetazolamide (AZ), a diuretic that inhibits carbonic anhydrases, alters the expression level of AQP1 in cultured cells. Here we investigated whether AZ alters the release of urinary exosomal AQP1 in vivo. METHODS: The effect of AZ on urinary exosomal AQP1 secretion was examined in rats and compared with furosemide (another diuretic), NaHCO3 (an alkalizing agent) and NH4Cl (an acidifying agent). Urine, blood and kidney samples were obtained 2 h after each treatment. Urinary exosomes were isolated by a differential centrifugation technique and urinary exosomal proteins were analyzed by immunoblotting. RESULTS: The release of exosomal AQP1 into urine was markedly increased after treatment with AZ, accompanied by alkaluria and metabolic acidosis. Immunohistochemistry clearly demonstrated that AZ increased the apical membrane expression of AQP1 in the proximal tubules. AZ did not affect the release of exosomal marker proteins (tumor susceptibility gene 101 protein and apoptosis-linked gene 2 interacting protein X). Treatment with furosemide did not change, whereas NaHCO3 and NH4Cl decreased the exosomal release of AQP1. CONCLUSION: The present findings indicate that AZ increases the release of exosomal AQP1 into urine in association with enhanced apical membrane expression of AQP1.