Chronic vasopeptidase inhibition restores endothelin-converting enzyme activity and normalizes endothelin levels in salt-induced hypertension

Comparison of pharmacological activity of macitentan and bosentan in preclinical models of systemic and pulmonary hypertension

AIMS

The endothelin (ET) system is a tissular system, as the production of ET isoforms is mostly autocrine or paracrine. Macitentan is a novel dual ETA/ETB receptor antagonist with enhanced tissue distribution and sustained receptor binding properties designed to achieve a more efficacious ET receptor blockade. To determine if these features translate into improved efficacy in vivo, a study was designed in which rats with either systemic or pulmonary hypertension and equipped with telemetry were given macitentan on top of maximally effective doses of another dual ETA/ETB receptor antagonist, bosentan, which does not display sustained receptor occupancy and shows less tissue distribution.

MAIN METHODS

After establishing dose-response curves of both compounds in conscious, hypertensive Dahl salt-sensitive and pulmonary hypertensive bleomycin-treated rats, macitentan was administered on top of the maximal effective dose of bosentan.

KEY FINDINGS

In hypertensive rats, macitentan 30 mg/kg further decreased mean arterial blood pressure (MAP) by 19 mm Hg when given on top of bosentan 100 mg/kg (n=9, p<0.01 vs. vehicle). Conversely, bosentan given on top of macitentan failed to induce an additional MAP decrease. In pulmonary hypertensive rats, macitentan 30 mg/kg further decreased mean pulmonary artery pressure (MPAP) by 4 mm Hg on top of bosentan (n=8, p<0.01 vs. vehicle), whereas a maximal effective dose of bosentan given on top of macitentan did not cause any additional MPAP decrease.

SIGNIFICANCE

The add-on effect of macitentan on top of bosentan in two pathological models confirms that this novel compound can achieve a superior blockade of ET receptors and provides evidence for greater maximal efficacy.

Optimizing Dose Selection with Modeling and Simulation: Application to the Vasopeptidase Inhibitor M100240

Dual inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE) has gained increasing interest in the treatment of hypertension, heart failure, and renoprotection. Specifically, M100240, the thioester of the dual ACE/NEP inhibitor MDL100,173, has been evaluated in the management of hypertension. A model-based analysis, including simulations, was employed to characterize the relationship between individual M100240 drug exposure and neurohormonal response and to optimize the dose selection for future clinical studies. Sixty-two healthy subjects and 189 hypertensive patients were studied after oral once-daily administration of 2.5, 5, 10, 25, or 50 mg M100240. Pharmacokinetic-biomarker and blood pressure response models were fitted to the data with the computer program NONMEM. A direct inhibitory E(max) model adequately described the relationship between MDL100,173 concentration and ACE activity. No clear concentration or dose-dependent NEP or blood pressure responses were evident. Given a target 90% ACE inhibition, simulation reveals that (1). 50 mg M100240 once daily produces adequate ACE inhibition 24 hours postdose in only 20% of subjects, and (2). higher and/or more frequent doses on the order of 25 mg three times daily or 50 mg twice daily are required to achieve the target ACE inhibition in at least 50% of patients over 24 hours. Insufficient blood pressure-lowering effects were observed in healthy subjects and hypertensive patients due to inadequate ACE and NEP inhibition with once-daily oral doses of up to 50 mg of M100240. Divided doses might provide target ACE inhibition in more patients.

Plasma volume and arterial stiffness in the cardiac alterations associated with long-term high sodium feeding in rats

BACKGROUND

Rats fed an early and long-term high-salt diet (HS, NaCl 8%) developed significant cardiovascular hypertrophy without major changes in blood pressure. The mechanism of this cardiac hypertrophy has not been yet elucidated.

METHODS

In the present work, we assessed the influence of volume overload and arterial stiffness on the structural and functional cardiac changes induced by a high salt feeding from weaning to 5 months of age in Sprague-Dawley rats.

RESULTS

Cardiac hypertrophy in HS rats was associated with clear augmentation in the size of left ventricular (LV) cardiomyocyte as compared with rats fed regular diet (NS). Echocardiography revealed a marked increase in relative wall thickness. Of note, no alteration of global and regional systolic and diastolic function was detected in HS rats. High sodium consumption was associated with a slight increase in aortic mean and pulse pressure (PP) without effect on pulse wave velocity (PWV) and elastic modulus. Plasma volume and central venous pressure were higher in HS than NS rats. Whereas plasma endothelin level was twofold higher in HS than in NS rats, LV endothelin level was similar in both groups. Treatment by the endothelin receptors blocker bosentan had no detectable effect on the changes induced by HS diet.

CONCLUSIONS

High sodium intake was associated with concentric cardiac hypertrophy without change of systolic and diastolic function. Aortic rigidity was not a determinant of cardiac hypertrophy. Beside a likely direct effect of sodium on cardiovascular system the slight increase in arterial pressure and plasma volume play a role.

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.

Endogenous endothelin attenuates the pressor response to acute environmental stress via the ETA receptor

Clinical studies have documented an abrupt rise in plasma endothelin-1 (ET-1) coincident with an increase in mean arterial pressure (MAP) during the response to acute stress. We therefore examined the ET(A) and ET(B) receptor-dependent effects of ET-1 on the pressor response to acute environmental stress in ET-1-dependent hypertension. Stress was induced by administration of air jet pulses (3 min) in ET(B) receptor-deficient (ET(B) sl/sl) rats fed normal salt (NS; 0.8% NaCl), high salt (HS; 8% NaCl), and HS plus the ET(A) receptor antagonist ABT-627 (5 mg.kg(-1).day(-1)) on successive weeks. MAP was chronically monitored by telemetry. Total pressor response (area under the curve) was significantly reduced in ET(B) sl/sl rats maintained on a HS vs. NS diet [-6.8 mmHg (SD 18.7) vs. 29.3 mmHg (SD 8.1) x 3 min, P < 0.05]. Conversely, the total pressor response was augmented in both wild-type [34.2 mmHg (SD 29.2) x 3 min, P < 0.05 vs. NS] and ET(B) sl/sl rats [49.1 mmHg (SD 11.8) x 3 min, P < 0.05 vs. NS] by ABT-627. Blockade of ET(B) receptors in Sprague-Dawley rats caused an increase in basal MAP that was enhanced by HS and lowered by mixed ET(A)/ET(B) receptor antagonism; none of these treatments, however, had any effect on the pressor response. These data demonstrate that increasing endogenous ET-1 suppresses the pressor response to acute stress through ET(A) receptor activation in a genetic model of ET-1-dependent hypertension. These results are consistent with reports that ET-1 can attenuate sympathetically mediated responses.

Comparison of the cardiovascular protection by omapatrilat and lisinopril treatments in DOCA-salt hypertension

OBJECTIVE

To compare the cardiovascular protection provided by omapatrilat and lisinopril in an experimental model of hypertension.

METHODS

Four-week deoxycorticosterone acetate (DOCA)-salt hypertensive (HT) and age-matched normotensive (NT) rats were treated either with omapatrilat (40 mg/kg per day) or lisinopril (20 mg/kg per day) for 2 weeks before sacrifice, and compared with untreated HT and NT rats sacrificed at ages corresponding to either before or after the drug regimens.

RESULTS

Systolic arterial pressure (SAP) of 2 and 4 week HT rats was increased in comparison to age-matched NT rats (P <0.05). Treatment with omapatrilat or lisinopril reduced SAP in HT (P <0.05) similarly by about 10%. Cardiac interstitial collagen, perivascular collagen and media/lumen ratio of coronary arterioles were increased in HT rats. Both treatments partially prevented the rise in perivascular collagen and completely corrected the increased media/lumen ratio in small arterioles from HT (P <0.05). In contrast to NT rats, only a weak coronary dilatation to bradykinin was observed in Langendorff hearts isolated from untreated-HT. This response was slightly improved by lisinopril and markedly improved by omapatrilat (P <0.05). The coronary dilatation to SNP which was reduced in 4-week HT (P <0.05), was partially improved by omapatrilat treatment but not by lisinopril. The enhanced superoxide anion production in aorta from HT rats was partially corrected with omapatrilat and lisinopril. Finally, omapatrilat, unlike lisinopril, markedly reduced mortality in a more severe form of DOCA-salt hypertension.

CONCLUSIONS

Omapatrilat and lisinopril regressed coronary remodelling and cardiac collagen deposition, and reduced vascular oxidative stress in DOCA-salt hypertensive rats. However, despite similar antihypertensive efficacy, omapatrilat was superior to lisinopril in improving the endothelial-dependent coronary dilatation, suggesting a better vascular protection in the DOCA-salt model of hypertension.

Vasopeptidase inhibition: effective blood pressure control for vascular protection

Angiotensin converting enzyme (ACE) inhibition is a well-established principle in the treatment of hypertension, and numerous large scale clinical studies have clearly demonstrated the beneficial effects of inhibiting the renin-angiotensin-aldosterone system (RAS) in hypertension. The clinical success of ACE inhibitors encouraged attempts to inhibit other key enzymes in the regulation of vascular tone, such as the neutral endopeptidase (NEP). Similar to ACE, NEP is an endothelial cell surface metalloproteinase, which is involved in the degradation of several regulatory peptides including the natriuretic peptides, and augments vasodilatation and natriuresis through increased levels of atrial natriuretic peptide. By inhibiting the RAS and potentiating the natriuretic peptide system at the same time, combined NEP/ACE inhibitors, the so-called "vasopeptidase inhibitors," reduce vasoconstriction and enhance vasodilatation, and in turn decrease peripheral vascular resistance and blood pressure. Within the vessel wall this may lead to a reduction of vasoconstrictor and proliferative mediators such as angiotensin II and endothelin-1, and may increase local levels of bradykinin as well as natriuretic peptides. Based on these considerations, numerous preclinical studies with vasopeptidase inhibitors have been performed and reveal promising results in experimental hypertension. Correspondingly, large-scale clinical studies in patients with hypertension are on the way, to transfer the principle of vasopeptidase inhibition from bench to bedside.

Vasopeptidase inhibition and endothelial function in hypertension

Vasopeptidase inhibitors are a new class of drugs capable of inhibiting both angiotensin-converting enzyme and neutral endopeptidase 24.11. This involves simultaneous inhibition with a single molecule of two key enzymes, ACE and NEP, which are both involved in the regulation of cardiovascular homeostasis in many ways. This includes metabolism of several vasoactive peptides and their clearance from the circulation, therefore contributing to neurohumoral modulation, which might have therapeutic advantages in the prevention of endothelial dysfunction in hypertension.