Aliskiren-Binding Increases the Half Life of Renin and Prorenin in Rat Aortic Vascular Smooth Muscle Cells

Abstract

Objective-Renin inhibition with aliskiren has been reported to cause a greater rise in renin than other types of renin-angiotensin system blockade, thereby potentially leading to angiotensin generation or stimulation of the human (pro)renin receptor (h(P)RR). Here we studied whether this rise in renin is attributable to an aliskiren-induced change in the prorenin conformation, allowing its detection in renin assays, or a change in renin/prorenin clearance. We also investigated whether aliskiren affects (pro)renin binding to its receptors, using rat aortic vascular smooth muscle cells (VSMCs) overexpressing the h(P)RR. Methods and Results-A 48-hour incubation with aliskiren at 4°C converted the prorenin conformation from "closed" to "open," thus allowing its recognition in active site-directed renin assays. VSMCs accumulated (pro)renin through binding to mannose 6-phosphate receptors (M6PRs) and h(P)RRs. Aliskiren did not affect binding at 4°C. At 37°C, aliskiren increased (pro)renin accumulation up to 40-fold, and M6PR blockade prevented this. Aliskiren increased the intracellular half life of prorenin 2 to 3 times. Conclusion-Aliskiren allows the detection of prorenin as renin, and decreases renin/prorenin clearance. Both phenomena may contribute to the "renin" surge during aliskiren treatment, but because they depend on aliskiren binding, they will not result in angiotensin generation.

Comparative efficacy and safety of aliskiren and irbesartan in patients with hypertension and metabolic syndrome

“…11 It should be noted, however, that at least part of the increase in PRC observed during aliskiren treatment may be the result of an assay artefact related to the ability of aliskiren to bind to and alter the conformation of prorenin, which would then be measured as renin by the standard PRC immunoassay. [27][28][29] This artefact does not occur with ARBs and might account for some of the observed between-treatment differences in PRC. Levels of prorenin were significantly increased from baseline to a similar extent with both irbesartan and aliskiren treatments, an expected consequence of any chronic stimulus of renin release.…”

New insights into the renoprotective actions of the renin inhibitor aliskiren in experimental renal disease

“…109 Furthermore, on binding to the (P)RR, prorenin, which is normally inactive, becomes catalytically active (it can cleave Aogen to form Ang I), possibly because of a conformational change induced by the binding. 109,[114][115][116] The Ang IIindependent effects of (P)RR stimulation include activation of extracellular signal-regulated kinase1/2, 109,117,118 and heat shock protein 27 119 and phosphatidylinositol-3 kinase p85a 120 pathways. The production of TGF-b and plasminogen-activator-1 is also increased, as are gene expression and production of collagen I and fibronectin, respectively.…”

“…123 In vitro studies showed that when incubated with prorenin, aliskiren binds to the active site of the enzyme 87 and can inhibit Ang I formation that would normally occur from nonproteolytic [(P)RR-mediated] activation of prorenin. 116 This finding is significant because activation of prorenin at tissue sites might occur by (P)RR-mediated mechanisms or by proteolytic cleavage of the prosegment. The latter may occur in tissues in which inflammatory or dead/dying parenchymal cells may release proteases such as cathepsin G or elastase, 124 which are capable of cleaving the prosegment.…”

“…Inhibition of Ang II formation on cell surface (116) Persistent tissue RAAS blockade (91) Long renal residence time (90) • Decreased (P)RR synthesis • No activation of prorenin when it binds to (P)RR (116) • No gain in catalytic activity when renin binds to (P)RR Renal protection (71,72,75,86,87,88) Incorporates into renin granules (101) (Pro)renin secreted as inhibited enzyme (101) Efficient renin inhibition (101) No chance to cleave Aogen Inhibition of Ang II formation (71) In tissue & plasma Glomerular localization (87) Inhibition of mesangial, podocyte (25) RAAS JG cells ( * ) Figure 3 In this working model of the renoprotective actions of aliskiren, outcomes for which in vitro or in vivo evidence exists are referenced (see References); no reference indicates a logical, but still speculative outcome. Solid arrows indicate the existence of in vitro or in vivo evidence to support a causal link between the events.…”

Signal transduction of the (pro)renin receptor as a novel therapeutic target for preventing end-organ damage

“…59,63,64 The 34-fold increase might be overestimated because of an assay artefact: by binding to prorenin, aliskiren causes a conformational change in this molecule, which is then detected as (immuno-re)active renin, that is, aliskiren allows the false detection of prorenin as renin. [65][66][67] Nevertheless, renin inhibition can cause a greater increase in plasma renin compared with AT1R blockade at dosages with comparable antihypertensive effects. 68 It has been reported that the plasma renin concentration under 300 mg aliskiren is almost doubled compared with 320 mg valsartan.…”