Renoprotective effect of long-term combined treatment with adrenomedullin and omapatrilat in hypertensive rats

Adrenomedullin: Continuing to explore cardioprotection

Adrenomedullin (AM), a peptide isolated from an extract of human pheochromocytoma, comprises 52 amino acids with an intramolecular disulfide bond and amidation at the carboxy-terminus. AM is present in various tissues and organs in rodents and humans, including the heart. The peptide concentration increases with cardiac hypertrophy, acute myocardial infarction, and overt heart failure in the plasma and the myocardium. The principal function of AM in the cardiovascular system is the regulation of the vascular tone by vasodilation and natriuresis via cyclic adenosine monophosphate-dependent or -independent mechanism. In addition, AM may possess unique properties that inhibit aldosterone secretion, oxidative stress, apoptosis, and stimulation of angiogenesis, resulting in the protection of the structure and function of the heart. The AM receptor comprises a complex between calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein (RAMP) 2 or 3, and the AM-CLR/RAMP2 system is essential for heart development during embryogenesis. Small-scale clinical trials have proven the efficacy and safety of recombinant AM peptide therapy for heart failure. Gene delivery and a modified AM peptide that prolongs the half-life of the native peptide could be an innovative method to improve the efficacy and benefit of AM in clinical settings. In this review, we focus on the pathophysiological roles of AM and its receptor system in the heart and describe the advances in AM and proAM-derived peptides as diagnostic biomarkers as well as the therapeutic application of AM and modified AM for cardioprotection.

Effects of neutral endopeptidase (neprilysin) inhibition on the response to other vasoactive peptides in small human resistance arteries: studies with thiorphan and omapatrilat

PURPOSE

New compounds with neprilysin or neutral endopeptidase (NEP) inhibiting activity are under clinical investigation in heart failure and hypertension. We investigated the effect of NEP inhibition on the functional vasomotor responses to a range of vasoactive peptides in human blood vessels.

METHODS

Small human resistance arteries from patients with coronary artery disease and preserved left ventricular systolic function were studied. Thiorphan (a NEP inhibitor) was compared with captopril (an ACE inhibitor) and omapatrilat (a dual NEP-ACE inhibitor) with regard to their effects on the response of human arteries to key vasoactive peptides.

RESULTS

As expected, both captopril and omapatrilat (but not thiorphan) inhibited the vasoconstrictor effect of angiotensin I (maximal response [SEM]: 27 ± 8% vehicle, 6 ± 2% captopril, 39 ± 10% thiorphan, 8 ± 7% omapatrilat, P < 0.05). Thiorphan, captopril, and omapatrilat all enhanced the vasodilator response to bradykinin (all P < 0.01). Omapatrilat markedly augmented the vasodilator action of adrenomedullin (P < 0.05), whilst thiorphan and captopril did not. None of the three inhibitors studied affected the vasodilator action of c-type natriuretic peptide, calcitonin gene-related peptide, vasoactive intestinal polypeptide or substance P.

CONCLUSIONS

NEP inhibition with thiorphan modestly augmented the vasodilator action of bradykinin, but did not potentiate the response to adrenomedullin; dual ACE and NEP inhibition with omapatrilat, as expected, markedly augmented the response to bradykinin and also potentiated the effect of adrenomedullin. Thiorphan weakly enhanced the vasoconstrictor response to angiotensin I. Neither omapatrilat nor thiorphan had any effect on the action of a range of other vasoactive peptides including CNP.

Relationship of increased circulating adrenomedullin with cardiac dysfunction, inflammation, oxidative stress and volume overload in hemodialysis patients

Adrenomedullin (AM) is a peptide involved in cardiovascular homeostasis. The aim of our study was to investigate whether circulating AM might be related to cardiac function, volume overload, oxidative stress and inflammation in hemodialysis patients. Plasma adrenomedullin, C-reactive protein (CRP), oxidized LDL (ox-LDL), lipoprotein (a), systolic and diastolic cardiac functions were assessed before hemodialysis in 80 patients as well as in 40 healthy control subjects. Plasma adrenomedullin levels were significantly higher in the hemodialysis group compared to the control group. Plasma adrenomedullin levels were negatively correlated with systolic and diastolic blood pressure, S/D ratio, deceleration time, left ventricular ejection fraction, ox-LDL and lipoprotein (a). However, it was positively correlated with CRP, delta body weight, mitral E/A wave, and inferior vena cava diameter. Higher plasma adrenomedullin levels may provide a possible index of cardiac dysfunction, systemic inflammation, and volume overload conditions in haemodialysis patients with concomitant cardiovascular disease. In addition, the negative correlation between ox-LDL, lipoprotein (a) and adrenomedullin may suggest that endogenous AM is an important protective factor in anti-atherosclerosis and might be useful as a new target for prevention and therapy for the disease.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Vasopeptidase inhibition normalizes blood pressure and restores endothelial function in renovascular hypertension

BACKGROUND/AIMS

Vasopeptidase inhibitors by definition inhibit both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), therefore they may exceed the effect of ACE inhibitors in the treatment of hypertension. The present study investigated the effect of the vasopeptidase inhibitor AVE7688 in comparison to the ACE inhibitor ramipril on systolic blood pressure (SBP) and endothelial function in renovascular hypertension.

METHODS

Wistar-Kyoto rats with renovascular hypertension (two-kidney one-clamp-model) were randomized 2 weeks after unilateral clamping of the right renal artery for 3 weeks' oral treatment with either AVE7688 (30 mg/kg/day), ramipril (1 mg/kg/day) or placebo. SBP was measured by the tail-cuff method and endothelium-dependent and -independent vascular function was assessed in isolated preconstricted (norepinephrine 10(-7) mol/l) aortic rings as relaxation to acetylcholine (10(-10)-10(-4) mol/l) and sodium nitroprusside (10(-10)-10(-4) mol/l), respectively.

RESULTS

Two weeks after clamping, SBP was significantly elevated (196 +/- 16 vs. 145 +/- 8 mm Hg for sham-operated rats; p < 0.01) and further increased in placebo-treated animals to 208 +/- 19 mm Hg. Treatment with AVE7688 and ramipril had a similar blood pressure-lowering effect (119 +/- 8 and 124 +/- 10 mm Hg, respectively; p < 0.01 vs. placebo). Maximum endothelium-dependent relaxation was reduced in hypertensive rats (72 +/- 6 vs. 99 +/- 7% in control rats; p < 0.05). Endothelium-dependent relaxation was restored by AVE7688 (101 +/- 6%) and ramipril (94 +/- 8%), respectively, whereas endothelium-independent relaxation was comparable in all groups.

CONCLUSION

In renovascular hypertension the vasopeptidase inhibitor AVE7688 exhibited similar blood pressure-lowering and endothelial protective properties as compared to the ACE inhibitor ramipril. Therefore, in high renin models of hypertension, vasopeptidase inhibition may be considered an alternative treatment option to ACE inhibition.

Cardiac diastolic dysfunction in renal-transplant recipients is associated with increased circulating Adrenomedullin

BACKGROUND

Renal transplantation is an excellent therapeutic alternative for end-stage renal diseases. Nevertheless, the cardiac function is often impaired in renal-transplant patients (RTR) and importantly determines their prognosis. Adrenomedullin (ADM), a peptide involved in cardiovascular homeostasis, is believed to protect both cardiac and renal functions - by increasing local blood flows, attenuating the progression of vascular damage and remodelling and by reducing glomerular injury - and might be involved in renal-transplantation physiopathology. This work was performed to investigate whether an increase in circulating ADM might be related to RTR cardiac function.

METHODS

Twenty-nine subjects, 19 RTR and 10 healthy subjects, participated in the study. After 15 min rest in supine position, heart rate and systemic blood pressure were measured together with cyclosporine through levels, creatinine and ADM. Systolic and diastolic cardiac functions were assessed, using Doppler echocardiography.

RESULTS

Subjects were similar concerning age, weight, heart rate and blood pressure. Creatinine and ADM (53.8 +/- 6.9 vs. 27.2 +/- 4.1 pmol/L, p = 0.02) were significantly increased in RTR (73 +/- 10 months after transplantation). Cardiac systolic function was normal, but a reduced mitral E:A ratio was observed in RTR (0.90 +/- 0.06 vs. 1.38 +/- 0.10, p < 0.001), reflecting their impaired left ventricular relaxation. Such a ratio was negatively correlated with ADM (r = -0.55, p = 0.002).

CONCLUSIONS

RTR present with an increased ADM is likely related to cardiac diastolic dysfunction. In view of its protective effect on the cardiovascular system, these data support further studies to better define the role and the therapeutic potential of ADM after renal transplantation.