Aliskiren: beyond blood pressure reduction

The role of direct renin inhibitors in the treatment of the hypertensive diabetic patient

Hypertensive patients with diabetes exhibit an increased risk for cardiovascular complications, such as acute coronary syndrome, stroke, heart failure and chronic kidney disease (CKD). These two chronic diseases are linked to a high rate of morbidity and mortality and for this reason it is important for the clinician to recognize the need for effective treatment of hypertension, which can require combination therapy to achieve blood pressure (BP) goals. Direct renin inhibitors (DRIs) may be useful in combination with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs) as they provide a more complete blockade of the renin-angiotensin-aldosterone system (RAAS), effectively suppressing residual angiotensin II production and the counter-regulatory increase in plasma renin activity observed in patients receiving monotherapy with ACEIs or ARBs. Some questions regarding the action of aliskiren in cardiovascular and renal disorders are open. In particular, the combination therapy of aliskiren and a RAAS blocker in diabetic hypertensive patients with CKD is controversial. Several published studies demonstrated that aliskiren is suitable for once-daily administration and its antihypertensive effect is comparable or superior to that of other antihypertensive agents at recommended doses, with a good tolerability profile. At the moment the association with ACEIs and ARBs is not recommended in patients with type 2 diabetes mellitus (T2DM) and renal impairment even if a recent published open-label study of low-dose aliskiren (150 mg/daily) in association with ACEIs or ARBs has demonstrated a good tolerability profile without the adverse events found in other studies. This review provides a brief overview of RAAS blocking, in particular the rationale and clinical evidence supporting the use of the DRI aliskiren, in high-risk patients with T2DM.

Inhibition of the renin-angiotensin system for lowering coronary artery disease risk

The renin-angiotensin system when activated exerts proliferative and pro-inflammatory actions and thereby contributes to progression of atherosclerosis, including that occurring in the coronary arteries. It thus contributes as well to coronary artery disease (CAD). Several clinical trials have examined effects of renin-angiotensin system inhibition for primary and secondary prevention of coronary heart disease. These include important trials such as HOPE, EUROPA and PEACE using angiotensin converting enzyme inhibitors, VALIANT, OPTIMAAL and TRANSCEND using angiotensin receptor blockers, and the ongoing TOPCAT study in patients with preserved ejection fraction heart failure, many of who also have coronary artery disease. Data are unavailable as yet of effects of either direct renin inhibitors or the new angiotensin receptor/neprilysin inhibitor agents. Today, inhibition of the renin-angiotensin system is standard-of-care therapy for lowering cardiovascular risk in secondary prevention in high cardiovascular risk subjects.

Aliskiren improves insulin resistance and ameliorates diabetic renal vascular complications in STZ-induced diabetic rats

Aliskiren, a direct renin inhibitor (DRI), has therapeutic effects in patients with hypertension and associated complications, but its potential mechanism in diabetic nephropathy is lacking. The effects of aliskiren in Streptozotocin (STZ)-induced renal complication in diabetic rats were investigated. Aliskiren treatment for eight weeks at the dose of 10 mg/kg/day, via osmotic mini-pump, induced improvement in blood glucose levels, systolic blood pressure (BP) and serum creatinine. Improvement of insulin resistance by aliskiren was confirmed by increased glucose translocation in liver and muscle and hence insulin levels. The treated group also showed improvement in glomerulosclerosis and tubulointerstitial injury. Aliskiren treatment also improved albumin levels in plasma, suppressed profibrotic and proinflammatory cytokine synthesis viz TNF-α and TGF-β and angiogenesis by a decrease in VEGF. In addition, the level of total proteins and GFR via cystatin c and beta-2microglobulin along with adiponectin and erythropoietin were also improved. These results suggest that the beneficial organ protective effect of aliskiren is mediated by improvement in insulin resistance as well as a direct anti-fibrotic effect in the target organ in STZ-induced diabetic rats with a slight effect on blood pressure. Aliskiren may be a useful therapeutic agent in the treatment of type 2 diabetes and diabetic nephropathy.

Angiotensin II Type 1 Receptors and Systemic Hemodynamic and Renal Responses to Stress and Altered Blood Volume in Conscious Rabbits

We examined how systemic blockade of type 1 angiotensin (AT(1)-) receptors affects reflex control of the circulation and the kidney. In conscious rabbits, the effects of candesartan on responses of systemic and renal hemodynamics and renal excretory function to acute hypoxia, mild hemorrhage, and plasma volume expansion were tested. Candesartan reduced resting mean arterial pressure (MAP, -8 ± 2%) without significantly altering cardiac output (CO), increased renal blood flow (RBF, +38 ± 9%) and reduced renal vascular resistance (RVR, -32 ± 6%). Glomerular filtration rate (GFR) was not significantly altered but sodium excretion (U(Na+)V) increased fourfold. After vehicle treatment, hypoxia (10% inspired O(2) for 30 min) did not significantly alter MAP or CO, but reduced heart rate (HR, -17 ± 6%), increased RVR (+33 ± 16%) and reduced GFR (-46 ± 16%) and U(Na+)V (-41 ± 17%). Candesartan did not significantly alter these responses. After vehicle treatment, plasma volume expansion increased CO (+35 ± 7%), reduced total peripheral resistance (TPR, -26 ± 5%), increased RBF (+62 ± 23%) and reduced RVR (-32 ± 9%), but did not significantly alter MAP or HR. It also increased U(Na+)V (803 ± 184%) yet reduced GFR (-47 ± 9%). Candesartan did not significantly alter these responses. After vehicle treatment, mild hemorrhage did not significantly alter MAP but increased HR (+16 ± 3%), reduced CO (-16 ± 4%) and RBF (-18 ± 6%), increased TPR (+18 ± 4%) and tended to increase RVR (+18 ± 9%, P = 0.1), but had little effect on GFR or U(Na+)V. But after candesartan treatment MAP fell during hemorrhage (-19 ± 1%), while neither TPR nor RVR increased, and GFR (-64 ± 18%) and U(Na+)V (-83 ± 10%) fell. AT(1)-receptor activation supports MAP and GFR during hypovolemia. But AT(1)-receptors appear to play little role in the renal vasoconstriction, hypofiltration, and antinatriuresis accompanying hypoxia, or the systemic and renal vasodilatation and natriuresis accompanying plasma volume expansion.