RT Journal Article
SR Electronic
T1 Inhibition of Aquaporin-1 and Aquaporin-4 Water Permeability by a Derivative of the Loop Diuretic Bumetanide Acting at an Internal Pore-Occluding Binding Site
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 105
OP 112
DO 10.1124/mol.108.053744
VO 76
IS 1
A1 Elton Migliati
A1 Nathalie Meurice
A1 Pascale DuBois
A1 Jennifer S. Fang
A1 Suma Somasekharan
A1 Elizabeth Beckett
A1 Gary Flynn
A1 Andrea J. Yool
YR 2009
UL http://molpharm.aspetjournals.org/content/76/1/105.abstract
AB Aquaporin (AQP) water channels, essential for fluid homeostasis, are expressed in perivascular brain end-feet regions of astroglia (AQP4) and in choroid plexus (AQP1). At a high concentration, the loop diuretic bumetanide has been shown to reduce rat brain edema after ischemic stroke by blocking Na+-K+-2Cl- cotransport. We hypothesized that an additional inhibition of AQP contributes to the protection. We show that osmotic water flux in AQP4-expressing Xenopus laevis oocytes is reduced by extracellular bumetanide (≥100 μM). The efficacy of block by bumetanide is increased by injection intracellularly. Forty-five synthesized bumetanide derivatives were tested on oocytes expressing human AQP1 and rat AQP4. Of these, one of the most effective was the 4-aminopyridine carboxamide analog, AqB013, which inhibits AQP1 and AQP4 (IC50 ∼20 μM, applied extracellularly). The efficacy of block was enhanced by mutagenesis of intracellular AQP4 valine-189 to alanine (V189A, IC50 ∼8 μM), confirming the aquaporin as the molecular target of block. In silico docking of AqB013 supported an intracellular candidate binding site in rat AQP4 and suggested that the block involves occlusion of the AQP water pore at the cytoplasmic side. AqB013 at 2 μM had no effect, and 20 μM caused 20% block of human Na+-K+-2Cl- cotransporter activity, in contrast to >90% block of the transporter by bumetanide. AqB013 did not affect X. laevis oocyte Cl- currents and did not alter rhythmic electrical conduction in an ex vivo gastric muscle preparation. The identification of AQP-selective pharmacological agents opens opportunities for breakthrough strategies in the treatment of edema and other fluid imbalance disorders.