Discovery and pharmacological study of a novel diuretic
© Yang et al; licensee BioMed Central Ltd. 2012
Published: 17 October 2012
Diuretics are used widely to raise renal salt and water clearance in a variety of conditions, such as oedema, as well in non-edematous states such as hypertension, which can reduce morbidity and mortality of cardiovascular and cerebrovascular diseases, especially the frequency of stroke and congestive heart failure. However, long-term use of conventional diuretics has several adverse effects including electrolyte disorders, hyperuricemia, hyperlipidemia, and glucose tolerance decrease. Electrolyte abnormalities can induce cardiac arrythmias and sudden death. Therefore, discovering a new diuretic that does not cause electrolyte disturbance becomes a hot issue. Phenotype analysis of knockout mice lacking urea transporter UT-B or various UT-A isoforms has provided evidence for the involvement of UTs in the urinary concentrating mechanism. Functional deletion of UT-B or UT-A isoforms markedly caused polyuria and urea selective low urine concentrating ability. However, deletion of UT-B or UT-As did not affect GFR and clearance rate of the principal solutes (Na+, K+, Cl-) in urine except for urea. Therefore, we suggested a hypothesis that UT inhibitors might be novel diuretics to excrete water without disturbing electrolyte metabolism.
Present study discovered a potent small-molecular urea transporter inhibitor, UT-A4, using an erythrocyte osmotic lysis assay. Stopped flow light scattering experiment, a classical assay for measuring water and urea permeability, confirmed that UT-A4 reversibly inhibited UT-B activity. The experiments also showed that UT-A4 targeted the intracellular part of UT-B protein and had the same inhibition activity on influx and efflux of urea across membrane. UTinh-14 has inhibition activity on human, rabbit, rat and mouse UT-B. We used rats as an in vivo test model for determining the diuretic activity of UT-A4. Interestingly, UT-A4 caused dose-dependent polyuria, low urinary osmolality and urea concentration in rats. 18-h water deprivation raised urine concentrating ability in rats with or without UT-A4 treatment. However, urine osmolality and urea concentration remained significantly less in UT-A4 treated rats than that in control rats, except of unchanged non-urea solutes. Osmolality and urea concentration was significantly decreased in inner medullary tissue of UTinh-14 treated rats, but not in HCTZ treated rats. All these results suggest that UTinh-14 caused urea selective diuresis.
The excretion of osmoles, urea and non-urea solutes had no significant difference between control and UTinh-14 treated rats. However, HCTZ treated rats had significant higher excretion of osmole and non-urea solutes than control and UTinh-14 treated rats, which made lower blood Na+, K+ and Cl-. These results indicate that UT-A4 is a selective UT inhibitor and has urea selective diuretic activity without disturbing excretion of electrolytes. It might have potential value on drug discovery as a new diuretic without electrolyte imbalance and metabolic disorder. It might also be used as a tool drug to study the physiological roles of UTs in big animal models.
This work was supported by National Natural Science Foundation of China grants 30870921 and 81170632, Drug Discovery Program grant 2009ZX09301-010-30, Doctoral Training Fund 20100001110047.
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