Direct renin inhibition with aliskiren improves ischemia-induced neovascularization: blood pressure-independent effect

Influence of Hypoxia Inducible Factor-1α of Endothelial Progenitor Cells on Left Ventricular Function in Experimental Myocardial Infarction

Based on the promotion of myocardial activity via endothelial progenitor cells (EPCs) subsequent to acute myocardial infarction (AMI), our research was designed to explore the influence of excessive HIF-1α expression in expanded EPCs (eEPCs) on promotion of the activity of left ventricle subsequent to MI. Isolation of EPCs from cord blood was performed before transduction with the help of retroviral vector with or without HIF-1α expression. Transplantation was performed subsequent to ligation of the left anterior descending coronary artery in mice. Ejection fraction (EF) of left ventricle was promoted via transplantation after 2 weeks. Excessive HIF-1α expression enhanced EF of left ventricle and decreased the extent of MI. It was revealed via functional studies that excessive HIF-1α expression enhanced proliferation of EPCs triggered by low oxygen concentration and suppressed cell death in the region of infarction. Moreover, markers of endothelium CD31, VEGF, and eNOS were upregulated. Transplantation of eEPCs with excessive HIF-1α expression in AMI can promote myocardial activities by increasing differentiation, generation of vessels, proliferation of eEPCs, and suppressing cell death. The above findings propose that regulation of EPCs via HIF-1α enhances the activity as well as mobilization of EPCs, indicating that reinforcement of expression of HIF-1α is beneficial for coronary heart disease.

Tyrosine-Protein Phosphatase Non-receptor Type 9 (PTPN9) Negatively Regulates the Paracrine Vasoprotective Activity of Bone-Marrow Derived Pro-angiogenic Cells: Impact on Vascular Degeneration in Oxygen-Induced Retinopathy

Background and Aim

Insufficient post-ischemic neovascularization is an initial key step in the pathogenesis of Oxygen-Induced Retinopathy (OIR). During neovascularization, pro-angiogenic cells (PACs) are mobilized from the bone marrow and integrate into ischemic tissues to promote angiogenesis. However, the modulation of PAC paracrine activity during OIR and the specific mechanisms involved remain to be explored. Because Tyrosine-protein phosphatase non-receptor type 9 (PTPN9) is reported to be a negative regulator of stem cell differentiation and angiogenesis signaling, we investigated its effect on PAC activity in the context of OIR.

Methods and Results

In a rat model of OIR, higher levels of PTPN9 in the retina and in bone marrow derived PACs are associated with retinal avascular areas, lower levels of the mobilization factor SDF-1 and decreased number of CD34⁺/CD117⁺/CD133⁺ PACs. PACs exposed ex vivo to hyperoxia display increased PTPN9 expression, which is associated with impaired ability of PAC secretome to promote angiogenesis ex vivo (choroidal vascular sprouting) and in vitro (endothelial cell tubule formation) compared to the secretome of PACs maintained in normoxia. Suppression of PTPN9 (using siRNA) increases VEGF and SDF-1 expression to normalize PAC secretome during hyperoxia, leading to restored angiogenic ability of PAC secretome. Moreover, endothelial cells exposed to the secretome of siPTPN9-treated PACs expressed increased levels of activated form of VEGF receptor 2 (VEGFR2). In the rat model of OIR, intravitreal injection of secretome from siPTPN9-treated PACs significantly reduced retinal vaso-obliteration; this was associated with higher retinal levels of VEGF/SDF-1, and increased recruitment of PACs (CD34⁺ cells) to the retinal and choroidal vessels.

Conclusion

Our results suggest that hyperoxia alters the paracrine proangiogenic activity of BM-PACs by inducing PTPN9, which can contribute to impair post-ischemic revascularization in the context of OIR. Targeting PTPN9 restores PAC angiogenic properties, and provide a new target for vessel integrity in ischemic retinopathies.

Aliskiren Improved the Endothelial Repair Capacity of Endothelial Progenitor Cells from Patients with Hypertension via the Tie2/PI3k/Akt/eNOS Signalling Pathway

Background

Studies show that aliskiren exerts favourable effects not only on endothelial progenitor cells (EPCs) but also on endothelial function. However, the mechanism of the favourable effect of aliskiren on EPCs from patients with hypertension is unclear and remains to be further studied.

Methods

The object of this study was to investigate and assess the in vitro function of EPCs pretreated with aliskiren. After treated with aliskiren, the human EPCs were transplanted into a nude mouse model of carotid artery injury, and the in vivo reendothelialization of injured artery was estimated by staining denuded areas with Evans blue dye via tail vein injection.

Results

We found that aliskiren increased the in vitro migration, proliferation, and adhesion of EPCs from patients with hypertension in a dose-dependent manner and improved the reendothelialization capability of these EPCs. Furthermore, aliskiren increased the phosphorylation of Tie2, Akt, and eNOS. After the blockade of the Tie2 signalling pathway, the favourable effects of aliskiren on the in vitro function and in vivo reendothelialization capability of EPCs were suppressed.

Conclusions

This study demonstrates that aliskiren can improve the in vitro function and in vivo reendothelialization capability of EPCs from patients with hypertension via the activation of the Tie2/PI3k/Akt/eNOS signalling pathway. These findings further indicate that aliskiren is an effective pharmacological treatment for cell-based repair in hypertension-related vascular injury.

Computational and Pharmacogenomic Insights on Hypertension Treatment: Rational Drug Design and Optimization Strategies

Background::

Hypertension is a prevalent cardiovascular complication caused by genetic and nongenetic factors. Blood pressure (BP) management is difficult because most patients become resistant to monotherapy soon after treatment initiation. Although many antihypertensive drugs are available, some patients do not respond to multiple drugs. Identification of personalized antihypertensive treatments is a key for better BP management.

Objective::

This review aimed to elucidate aspects of rational drug design and other methods to develop better hypertension management.

Results::

Among hypertension-related signaling mechanisms, the renin-angiotensin-aldosterone system is the leading genetic target for hypertension treatment. Identifying a single drug that acts on multiple targets is an emerging strategy for hypertension treatment, and could be achieved by discovering new drug targets with less mutated and highly conserved regions. Extending pharmacogenomics research to include patients with hypertension receiving multiple antihypertensive drugs could help identify the genetic markers of hypertension. However, available evidence on the role of pharmacogenomics in hypertension is limited and primarily focused on candidate genes. Studies on hypertension pharmacogenomics aim to identify the genetic causes of response variations to antihypertensive drugs. Genetic association studies have identified single nucleotide polymorphisms affecting drug responses. To understand how genetic traits alter drug responses, computational screening of mutagenesis can be utilized to observe drug response variations at the protein level, which can help identify new inhibitors and drug targets to manage hypertension.

Conclusions::

Rational drug design facilitates the discovery and design of potent inhibitors. However, further research and clinical validation are required before novel inhibitors can be clinically used as antihypertensive therapies.

Central Application of Aliskiren, a Renin Inhibitor, Improves Outcome After Experimental Stroke Independent of Its Blood Pressure Lowering Effect

Epidemiological studies suggest that pharmacological reduction of systemic hypertension lowers incidence and severity of stroke. However, whether the reduction of blood pressure per se or the compounds used to reduce hypertension are responsible for this effect received little attention. In the current study we therefore aimed to investigate whether Aliskiren, a renin-inhibitor used to treat arterial hypertension, may improve outcome in a mouse model of ischemic stroke when applied centrally and in a dose not affecting blood pressure. Male C57BL/6 mice received 0.6, 2.0, or 6.0 μg Aliskiren or vehicle by intracerebroventricular injection as a pre-treatment and were then subjected to 60 min of middle cerebral artery occlusion (MCAo). Infarct volume, brain edema formation, mortality, antioxidant effects, and functional outcome were assessed up to seven days after MCAo. Central administration of Aliskiren (0.6 or 2.0 μg) had no effect on systemic blood pressure but significantly reduced infarct volume and brain edema formation, blunted mortality, and improved neurological outcome up to 1 week after MCAo. Due to the central and prophylactic administration of the compound, we cannot make any conclusions about the potency of Aliskiren for acute stroke treatment, however, our study clearly demonstrates, that in addition to lowering blood pressure Aliskiren seems to have a direct neuroprotective effect. Hence, renin-inhibitors may be an effective addition to prophylactic treatment regimens in stroke patients.

Normalizing Plasma Renin Activity in Experimental Dilated Cardiomyopathy: Effects on Edema, Cachexia, and Survival

Heart failure (HF) patients frequently have elevated plasma renin activity. We examined the significance of elevated plasma renin activity in a translationally-relevant model of dilated cardiomyopathy (DCM), which replicates the progressive stages (A–D) of human HF. Female mice with DCM and elevated plasma renin activity concentrations were treated with a direct renin inhibitor (aliskiren) in a randomized, blinded fashion beginning at Stage B HF. By comparison to controls, aliskiren treatment normalized pathologically elevated plasma renin activity (p < 0.001) and neprilysin levels (p < 0.001), but did not significantly alter pathological changes in plasma aldosterone, angiotensin II, atrial natriuretic peptide, or corin levels. Aliskiren improved cardiac systolic function (ejection fraction, p < 0.05; cardiac output, p < 0.01) and significantly reduced the longitudinal development of edema (extracellular water, p < 0.0001), retarding the transition from Stage B to Stage C HF. The normalization of elevated plasma renin activity reduced the loss of body fat and lean mass (cachexia/sarcopenia), p < 0.001) and prolonged survival (p < 0.05). In summary, the normalization of plasma renin activity retards the progression of experimental HF by improving cardiac systolic function, reducing the development of systemic edema, cachexia/sarcopenia, and mortality. These data suggest that targeting pathologically elevated plasma renin activity may be beneficial in appropriately selected HF patients.

Investigation of Drug Interaction Potentials and Binding Modes on Direct Renin Inhibitors: A Computational Modeling Studies

Background:

Hypertension is one of the key risk factors for cardiovascular disease, it is regulated through Renin Angiotensin Aldosterone System (RAAS) cascade. Renin catalyzes the initial rate-limiting step in RAAS system, that influences the synthesis of angiotensin I from precursor angiotensin. Renin inhibition could be a potential step for the blood pressure lowering mechanism as well as for organ protection.

Methods:

In order to understand the structure-activity association of direct renin inhibitors (DRIs), we have carried out three-dimensional quantitative structure activity relationship (3D-QSAR), molecular docking studies and Density Functional Theory (DFT) analysis to identify the attractive compounds. Five-point pharmacophore model of one acceptor, three hydrophobic groups and one aromatic ring was chosen for the dataset of 40 compounds.

Results:

The generated 3D-QSAR model shows that the alignment has a good correlation coefficient for the training set compounds, which comprise the value of R2 = 0.96, SD = 0.1, and F = 131.3. The test compounds had Q2 = 0.91, RMSE = 0.25, and Pearson-R = 0.97, which describes the predicted model was reliable.

Discussion:

External validations were carried out to validate the predicted QSAR model. Further, the significant compounds were studied using different in silico approaches in order to explore the difference in the atomic configuration and binding mechanism of the identified compounds.

Conclusion:

The molecular dynamics simulation of the complex was analyzed and confirmed the stability of the compounds in the protein. The outcome of the result could be useful to improve the safety and efficacy of DRIs that can be projected to clinical trials.

Neonatal exposure to high oxygen levels leads to impaired ischemia-induced neovascularization in adulthood

Adverse perinatal conditions can lead to developmental programming of cardiovascular diseases. Prematurely born infants are often exposed to high oxygen levels, which in animal models has been associated with endothelial dysfunction, hypertension, and cardiac remodeling during adulthood. Here we found that adult mice that have been transiently exposed to O₂ after birth show defective neovasculariation after hindlimb ischemia, as demonstrated by impaired blood flow recovery, reduced vascular density in ischemic muscles and increased tissue damages. Ischemic muscles isolated from mice exposed to O₂ after birth exhibit increased oxidative stress levels and reduced expression of superoxide dismutase 1 (SOD1) and vascular endothelial growth factor (VEGF). Pro-angiogenic cells (PACs) have been shown to have an important role for postnatal neovascularisation. We found that neonatal exposure to O₂ is associated with reduced number of PACs in adults. Moreover, the angiogenic activities of both PACs and mature mouse aortic endothelial cells (MAECs) are significantly impaired in mice exposed to hyperoxia after birth. Our results indicate that neonatal exposure to high oxygen levels leads to impaired ischemia-induced neovascularization during adulthood. The mechanism involves deleterious effects on oxidative stress levels and angiogenic signals in ischemic muscles, together with dysfunctional activities of PACs and mature endothelial cells.

Renin inhibitor aliskiren exerts beneficial effect on trabecular bone by regulating skeletal renin-angiotensin system and kallikrein-kinin system in ovariectomized mice

SUMMARY

The skeletal renin-angiotensin system contributes to the development of osteoporosis. The renin inhibitor aliskiren exhibited beneficial effects on trabecular bone of osteoporotic mice, and this action might be mediated through angiotensin and bradykinin receptor pathways. This study implies the potential application of renin inhibitor in the management for postmenopausal osteoporosis.

INTRODUCTION

The skeletal renin-angiotensin system plays key role in the pathological process of osteoporosis. The present study is designed to elucidate the effect of renin inhibitor aliskiren on trabecular bone and its potential action mechanism in ovariectomized (OVX) mice.

METHODS

The OVX mice were treated with low dose (5 mg/kg) or high dose (25 mg/kg) of aliskiren or its vehicle for 8 weeks. The bone turnover markers were measured by ELISA. The structural parameters of trabecular bone at lumbar vertebra (LV) and distal femoral metaphysis were measured by micro-CT. The expression of messenger RNA (mRNA) and protein was studied by RT-PCR and immunoblotting, respectively.

RESULTS

Aliskiren treatment reduced urinary excretion of calcium and serum level of tartrate-resistant acid phosphatase in OVX mice. The treatment with aliskiren significantly increased bone volume (BV/TV) and connectivity density (Conn.D) of trabecular bone at LV-2 and LV-5 as well as dramatically enhanced BV/TV, Conn.D, bone mineral density (BMD/BV) and decreased bone surface (BS/BV) at the distal femoral end. Aliskiren significantly down-regulated the expression of angiotensinogen, angiotensin II (Ang II), Ang II type 1 receptor, bradykinin receptor (BR)-1, and osteocytic-specific gene sclerostin as well as the osteoclast-specific genes, including carbonic anhydrase II, matrix metalloproteinase-9, and cathepsin K.

CONCLUSIONS

This study revealed that renin inhibitor aliskiren exhibited the beneficial effects on trabecular bone of ovariectomy-induced osteoporotic mice, and the underlying mechanism for this action might be mediated through Ang II and BR signaling pathways in bone.