Renoprotective effects of omapatrilat are mediated partially by bradykinin

Acute kidney injury and chronic kidney disease after cardiac surgery

Kidney dysfunction is common after cardiac surgery and predicts mortality risk and poorer long-term outcome, particularly when acute injury superimposes upon chronic kidney disease. Numerous insults contribute to perioperative renal impairment including major surgical trespass, procedure-specific interventions (eg, deep hypothermic circulatory arrest), and postoperative complications. Regardless of cause, evidence supports a role for renal impairment and accumulation of "uremic toxins" as direct contributors to adverse outcome. No one has yet characterized a loss of renal function small enough to be insignificant. Despite considerable research focus, progress in development of interventions aimed at perioperative renoprotection has been disappointing. However, practice modifications can influence the likelihood of acute kidney injury, and several recent advances provide hope for the future. We review pathophysiologic understanding of this disorder; evaluate the confusing relationship (causal v epiphenomena) among acute kidney injury, chronic kidney disease, and adverse outcome after cardiac surgery; and provide an evidence-based assessment of the conduct of cardiac surgery and renoprotection strategies.

Uric acid: Its relationship to renal hemodynamics and the renal renin-angiotensin system

Reports relating hyperuricemia and hypertension have been filed for many decades. Nevertheless, controversy remains concerning serum uric acid concentration as an independent risk factor underlying coronary heart disease (CHD) and essential hypertension or as an indirect marker of renovascular involvement. Earlier studies in normotensive subjects and hypertensive patients demonstrated that serum uric acid concentration was closely related to intrarenal hemodynamic alterations, suggesting that it is an excellent marker of vascular involvement. Our data from clinical studies and in an animal model of severe hypertensive nephrosclerosis have strengthened this concept. Conversely, other reports have suggested that uric acid may be a pathogenetic factor. Supporting arguments for this theory maintain that experimental hyperuricemia induces hypertension and renal damage. Epidemiologically, hyperuricemia is associated with hypertension, CHD, renal disease, toxemia of pregnancy, and other outcomes, although mechanisms remain unclear. Additionally, there are no available data on the effects of lowering uric acid on pressure control and organ protection.

Effects of vasopeptidase inhibition on renal function and tubuloglomerular feedback in spontaneously hypertensive rats

Vasopeptidase inhibitors are a novel class of antihypertensive agents that concomitantly inhibit angiotensin converting enzyme and neutral endopeptidase. Our purpose was to investigate the effects of omapatrilat, a vasopeptidase inhibitor, on renal function and tubuloglomerular feedback (TGF) response in anesthetized 9-10-week-old spontaneously hypertensive rats (SHR). Intravenous injection of omapatrilat at 10 micromol/kg decreased systemic blood pressure and renal vascular resistance. Renal plasma flow was unchanged, whereas glomerular filtration rate (GFR) and filtration fraction (FF) were reduced. Increased urinary sodium excretion of tubular origin was observed. These parameters remained unaltered with vehicle treatment. Micropuncture study revealed that the maximal reduction of early proximal flow rate (EPFR) induced by orthograde perfusion of Henle's loop with artificial tubular fluid (ATF) was significantly reduced by omapatrilat treatment (28.5+/-3.1% vs. 72.0+/-2.8% of control) and was not significantly changed in the vehicle-treated group (vehicle 70.8+/-1.7% vs. control 71.0+/-2.1%). EPFR at zero perfusion was comparable between omapatrilat and vehicle treatment (29.7+/-2.2 vs. 31.3+/-2.1 nl/min, respectively). Luminal perfusion of 10(-4) mol/l 7-nitroindazole in ATF abrogated the blunting of TGF response by omapatrilat but elicited no change in the vehicle-treated group. The suppression of the TGF mechanism and the reduction in FF suggest that omapatrilat respectively dilates the afferent and efferent arterioles. Under such conditions, reduction of GFR may indicate a fall in intraglomerular pressure. The restoration of nitric oxide signaling in the juxtaglomerular apparatus of SHR seems to participate in the inhibition of TGF by omapatrilat. These findings suggest that omapatrilat may provide a novel approach to the treatment of systemic and glomerular hypertension.

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B(2) receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT(1) receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B(2) receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B(2) receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B(1) receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B(1) receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B(1)/B(2) receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B(2) receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.

Evidence-based renal protection in cardiac surgery

Acute renal dysfunction is a common serious complication of cardiac surgery. Although a diversity of mechanisms exist by which the kidney can be damaged during cardiac surgery, atheroembolism, ischemia-reperfusion, and inflammation are believed to be primary contributors to perioperative renal insult. In addition, the high metabolic demands of active tubular reabsorption and the oxygen diffusion shunt characteristic of renal circulation make the kidney particularly vulnerable to ischemic injury. Remote effects of acute renal injury likely contribute to the strong association of this condition with other major postoperative morbidities and mortality and justify the search for renoprotective agents, even when dialysis is never required. Nonpharmacologic preventive strategies include procedure planning that is based on risk stratification, avoidance of nephrotoxins, and meticulous perioperative clinical care, including optimizing intravascular volume and attention to modifiable risk factors such as minimizing hemodilution. Although numerous pharmacologic interventions to prevent or treat acute renal injury have shown promise in animal models, randomized placebo-controlled clinical trials that have looked at measures of significant adverse outcomes such as death and dialysis have not confirmed a benefit.

Vasopeptidase inhibitor restores the balance of vasoactive hormones in progressive nephropathy

BACKGROUND

The mechanism(s) underlying greater renoprotection of combined blockade of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) by vasopeptidase over ACE inhibitors are ill defined. We previously found that progressive renal disease is associated with increased renal synthesis of endothelin-1 (ET-1) in the face of reduced generation of renal nitric oxide (NO) in the remnant kidney model. Here we compared changes in urinary excretion of ET-1 and nitrite/nitrate, markers of renal ET-1, and NO synthesis, respectively, and urinary cGMP, an indirect index of renal atrial natriuretic peptide (ANP) synthesis, after administration of vasopeptidase or ACE inhibitor in rats with renal mass reduction (RMR).

METHODS

Twenty-one days after 5/6 nephrectomy, after the onset of hypertension and overt proteinuria, rats were divided in 3 groups (N= 7-8) and given daily by gavage: vehicle, the vasopeptidase inhibitor AVE7688 (3 mg/kg bid), or enalapril (5 mg/kg bid) until day 90. Normal rats (N= 5) served as control rats.

RESULTS

Systolic blood pressure in RMR rats was equally controlled by AVE7688 and enalapril. AVE7688 resulted in a significant antiproteinuric effect, with urinary protein levels being reduced on average by 83% in respect to vehicle (88 +/- 28 vs. 518 +/- 27 mg/day, P < 0.0001). Enalapril achieved a 47% reduction in proteinuria (277 +/- 81 mg/day, P < 0.01 vs. vehicle) to levels that remained higher (P < 0.01), however, than those after AVE7688. Renal function impairment and glomerular and tubular changes were significantly (P < 0.05 vs. vehicle) ameliorated by AVE7688, and partially affected by enalapril. AVE7688 reduced the abnormal urinary excretion of ET-1 of RMR animals (98 +/- 8 vs. vehicle: 302 +/- 50 pg/24 h, P < 0.001) more than enalapril (159 +/- 14 pg/24 h, P < 0.05 vs. AVE7688). Consistently, AVE7688 was more effective than enalapril in augmenting renal synthesis of NO (2487 +/- 267 and 1519 +/- 217 vs. vehicle: 678 +/- 71 nmol/15 h; P < 0.001, AVE7688 vs. vehicle, P < 0.01 AVE7688 vs. enalapril). AVE7688 significantly increased urinary cGMP (78 +/- 6 vs. vehicle 45 +/- 9 nmol/24 h; P < 0.01).

CONCLUSION

The superior renoprotection achieved by AVE7688 over enalapril in progressive renal injury is due to the correction of the altered balance of vasoconstrictor/vasodilator mediators in the kidney.

Dual angiotensin-converting enzyme/neutral endopeptidase inhibition on cardiac and renal fibrosis and inflammation in DOCA-salt hypertensive rats

OBJECTIVES

The relative roles of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) inhibition on cardiac and renal fibrosis in deoxycorticosterone acetate (DOCA)-salt hypertensive rats were studied.

METHODS

The ACE/NEP inhibitor omapatrilat (40 mg/kg per day), the ACE inhibitor enalapril (10 mg/kg per day) and the NEP inhibitor CGS 25462(100 mg/kg per day) were administrated for 3 weeks to DOCA rats. Collagen was stained with Sirius red, and mediators of inflammation were identified by immunolabeling (vascular cell adhesion molecule, nuclear factor-kappaB, infiltrating ED-1-positive macrophages and monocyte chemotactic protein-1) or by western blot (platelet-endothelial cell adhesion molecule-1).

RESULTS

Elevated systolic blood pressure of DOCA rats was significantly reduced (P < 0.05) by omapatrilat and CGS 25462. Omapatrilat and CGS 25462 significantly (P < 0.05) decreased interstitial collagen density in the left ventricle of DOCA rats compared with untreated DOCA rats. Enalapril only decreased the subepicardial collagen of DOCA rats. Omapatrilat significantly (P < 0.05) decreased renal mesangial collagen deposition in DOCA rats. Cardiac and renal expression of surface adhesion molecules, nuclear factor-kappaB, monocyte chemotactic protein and ED-1-positive cells were decreased in omapatrilat-treated DOCA rats compared with untreated DOCA rats. Enalapril and CGS 25462 did not alter mesangial collagen of DOCA rats.

CONCLUSIONS

Dual ACE/NEP inhibition was more effective than ACE or NEP inhibition in decreasing inflammatory mediators, and improving cardiac and renal fibrosis. This suggests a role for NEP inhibition added to blockade of the renin-angiotensin system that may explain the greater efficacy of omapatrilat.

Imidapril improves l-NAME-exacerbated nephrosclerosis with TGF-β1 inhibition in spontaneously hypertensive rats

OBJECTIVE

This study was designed to investigate whether chronic angiotensin-converting enzyme (ACE) inhibition prevents hypertensive glomerular injury and inhibits increases in the mRNA levels and immunohistological expression of the apoptosis inducer caspase-3, and transforming growth factor (TGF)-beta 1 during prolonged nitric oxide synthase (NOS) inhibition with N-nitro-L-arginine methyl ester (L-NAME) in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

For 3 weeks, we studied three groups of 20-week-old male SHR: a control group, a l-NAME group, and a group treated with L-NAME and the ACE inhibitor imidapril. L-NAME rats developed severe hypertensive nephrosclerosis with significantly elevated blood pressure, markedly increased urinary protein excretion and serum creatinine levels, and more severe glomerulosclerosis and tubulo-interstitial changes. Levels of TGF-beta 1 mRNA in the renal tissue was also significantly increased in L-NAME rats compared with control SHR. Addition of imidapril significantly lowered blood pressure, inhibited nephrosclerosis and attenuated the mRNA level of TGF-beta 1 in comparison with L-NAME/SHR. Histologically, the glomerular cell apoptosis labeling index, terminal doxynucleotidil transferase-mediated dUTP nick-end labeling of fragmented DNA (TUNEL) and active caspase-3, and TGF-beta 1 positive areas were also reduced by imidapril.

CONCLUSION

These data suggest that imidapril prevents glomerular and arteriolar damages and renal functions, through inhibiting both TGF-beta 1 production and apoptosis induction.