Novel drugs targeting hypertension: renin inhibitors and beyond

The direct renin inhibitor aliskiren improves vascular remodelling in transgenic rats harbouring human renin and angiotensinogen genes

In the present study, we tested the hypothesis that chronic treatment with the direct rennin inhibitor aliskiren improves the remodelling of resistance arteries in dTGR (double-transgenic rats). dTGR (5 weeks) were treated with aliskiren (3 mg/kg of body mass per day) or ramipril (1 mg/kg of body mass per day) for 14 days and compared with age-matched vehicle-treated dTGR. BP (blood pressure) was similarly reduced in both aliskiren-treated and ramipril-treated rats compared with control dTGR (167±1 and 169±2 mmHg compared with 197±4 mmHg respectively; P<0.05). The M/L (media-to-lumen) ratio assessed on pressurized preparations was equally reduced in aliskiren-treated and ramipril-treated rats compared with controls (6.3±0.5 and 6.4±0.2% compared with 9.8±0.4% respectively; P<0.05). Endothelium-dependent and -independent relaxations were similar among the groups. L-NAME (NG-nitro-L-arginine methyl ester) significantly reduced acetylcholine-induced dilation in drug-treated dTGR. This effect was significantly more prominent in aliskiren-treated rats. eNOS (endothelial NO synthase) expression showed a 2-fold increase only in aliskiren-treated dTGR as compared with controls (P<0.01) and ramipril-treated dTGR (P<0.05). Plasma nitrite, as an index of NO production, was significantly increased in dTGR treated with either aliskiren or ramipril compared with controls. Only aliskiren induced a 2-fold increase in plasma nitrite, which was significantly greater than that induced by ramipril (P<0.05). gp91phox expression and ROS (reactive oxygen species) production in aorta were significantly and similarly reduced by both drugs. In conclusion, equieffective hypotensive doses of aliskiren or ramipril reduced the M/L ratio of mesenteric arteries and improved oxidative stress in dTGR. However, only aliskiren increased further NO production in the vasculature. Hence, in dTGR, direct renin inhibition induces favourable effects similar to that induced by ACE (angiotensin-converting enzyme) inhibition in improving vascular remodelling through different mechanisms.

Renin inhibition in the treatment of diabetic kidney disease

Inhibition of the RAAS (renin–angiotensin–aldosterone system) plays a pivotal role in the prevention and treatment of diabetic nephropathy and a spectrum of other proteinuric kidney diseases. Despite documented beneficial effects of RAAS inhibitors in diabetic patients with nephropathy, reversal of the progressive course of this disorder or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. Incomplete inhibition of the RAAS has been postulated as one of reasons for unsatisfactory therapeutic responses to RAAS inhibition in some patients. Inhibition of renin, a rate-limiting step in the RAAS activation cascade, could overcome at least some of the abovementioned problems associated with the treatment with traditional RAAS inhibitors. The present review focuses on experimental and clinical studies evaluating the two principal approaches to renin inhibition, namely direct renin inhibition with aliskiren and inhibition of the (pro)renin receptor. Moreover, the possibilities of renin inhibition and nephroprotection by interventions primarily aiming at non-RAAS targets, such as vitamin D, urocortins or inhibition of the succinate receptor GPR91 and cyclo-oxygenase-2, are also discussed.

What is the role of renin inhibition in the treatment of diabetic kidney disease?

Inhibition of the renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in preventing and treating diabetic nephropathy. However, despite documented beneficial effects of RAAS inhibitors in diabetic patients with nephropathy, reversal of the progressive course of this disorder or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. Incomplete inhibition of the RAAS has been postulated as one of the reasons for unsatisfactory therapeutic responses to RAAS inhibition in some patients. Inhibition of renin, a rate-limiting step in the RAAS activation cascade, is the logical approach to overcome at least some of the above-mentioned problems associated with the treatment with traditional RAAS inhibitors. This article focuses on experimental and clinical studies evaluating the two principal approaches to renin inhibition: direct renin inhibition with competitive inhibitors (eg, aliskiren) and inhibition of the (pro)renin receptor.

Renin-angiotensin system revisited

New components and functions of the renin-angiotensin system (RAS) are still being unravelled. The classical RAS as it looked in the middle 1970s consisted of circulating renin, acting on angiotensinogen to produce angiotensin I, which in turn was converted into angiotensin II (Ang II) by angiotensin-converting enzyme (ACE). Ang II, still considered the main effector of RAS was believed to act only as a circulating hormone via angiotensin receptors, AT1 and AT2. Since then, an expanded view of RAS has gradually emerged. Local tissue RAS systems have been identified in most organs. Recently, evidence for an intracellular RAS has been reported. The new expanded view of RAS therefore covers both endocrine, paracrine and intracrine functions. Other peptides of RAS have been shown to have biological actions; angiotensin 2-8 heptapeptide (Ang III) has actions similar to those of Ang II. Further, the angiotensin 3-8 hexapeptide (Ang IV) exerts its actions via insulin-regulated amino peptidase receptors. Finally, angiotensin 1-7 (Ang 1-7) acts via mas receptors. The discovery of another ACE2 was an important complement to this picture. The recent discovery of renin receptors has made our view of RAS unexpectedly complex and multilayered. The importance of RAS in cardiovascular disease has been demonstrated by the clinical benefits of ACE inhibitors and AT1 receptor blockers. Great expectations are now generated by the introduction of renin inhibitors. Indeed, RAS regulates much more and diverse physiological functions than previously believed.