Proteolytic activation of the epithelial sodium channel and therapeutic application of a serine protease inhibitor for the treatment of salt-sensitive hypertension

Proteases are involved in numerous essential biological processes including blood clotting, controlled cell death, and tissue differentiation. Prostasin, a glycosylphosphatidylinositol-anchored serine protease, has been identified as a potential regulator of the epithelial sodium channel (ENaC) function in the kidney, lung, and airways. ENaC is composed of three homologous subunits α, β, and, γ. The dual cleavage of α subunit by furin and γ subunit by prostasin and furin releases inhibitory segments from ENaC, leading to the channel activation. Protease nexin-1, an endogenous prostasin inhibitor, inhibits ENaC activity through the suppression of prostasin activity, strongly suggesting the possibility that a coordinated regulation of serine proteases and serine protease inhibitors plays a key role in the sodium handling in the kidney. Camostat mesilate (CM), a synthetic serine protease inhibitor, reduced prostasin activity and subsequently decreased ENaC current. Oral administration of CM to Dahl salt-sensitive rats resulted in a significant decrease in blood pressure with an elevation of the urinary sodium/potassium ratio. These findings suggest that synthetic serine protease inhibitors such as CM might represent a new class of antihypertensive drugs in patients with salt-sensitive hypertension.