Angiotensin receptor-neprilysin inhibitor improves coronary collateral perfusion

Background

We investigated the pleiotropic effects of an angiotensin receptor-neprilysin inhibitor (ARNi) on collateral-dependent myocardial perfusion in a rat model of coronary arteriogenesis, and performed comprehensive analyses to uncover the underlying molecular mechanisms.

Methods

A rat model of coronary arteriogenesis was established by implanting an inflatable occluder on the left anterior descending coronary artery followed by a 7-day repetitive occlusion procedure (ROP). Coronary collateral perfusion was measured by using a myocardial particle infusion technique. The putative ARNi-induced pro-arteriogenic effects were further investigated and compared with an angiotensin-converting enzyme inhibitor (ACEi). Expression of the membrane receptors and key enzymes in the natriuretic peptide system (NPS), renin-angiotensin-aldosterone system (RAAS) and kallikrein-kinin system (KKS) were analyzed by quantitative polymerase chain reaction (qPCR) and immunoblot assay, respectively. Protein levels of pro-arteriogenic cytokines were measured by enzyme-linked immunosorbent assay, and mitochondrial DNA copy number was assessed by qPCR due to their roles in arteriogenesis. Furthermore, murine heart endothelial cells (MHEC5-T) were treated with a neprilysin inhibitor (NEPi) alone, or in combination with bradykinin receptor antagonists. MHEC5-T proliferation was analyzed by colorimetric assay.

Results

The in vivo study showed that ARNis markedly improved coronary collateral perfusion, regulated the gene expression of KKS, and increased the concentrations of relevant pro-arteriogenic cytokines. The in vitro study demonstrated that NEPis significantly promoted MHEC5-T proliferation, which was diminished by bradykinin receptor antagonists.

Conclusion

ARNis improve coronary collateral perfusion and exert pro-arteriogenic effects via the bradykinin receptor signaling pathway.

Angiotensin-converting enzyme inhibitors stimulate cerebral arteriogenesis

AIM

Arteriogenesis constitutes the most efficient endogenous rescue mechanism in cases of cerebral ischaemia. The aim of this work was to investigate whether angiotensin-converting enzyme inhibitors (ACEi) stimulates, and angiotensin II receptor type 1 blockers (ARB) inhibits cerebral collateral growth by applying a three-vessel occlusion (3-VO) model in rat.

METHODS

Cerebral collateral growth was measured post 3-VO (1) by assessing blood flow using the cerebrovascular reserve capacity (CVRC) technique, and (2) by assessing vessel diameters in the posterior cerebral artery (PCA) via the evaluation of latex angiographies. A stimulatory effect on arteriogenesis was investigated for ACEi administration ± bradykinin receptor 1 (B1R) and 2 (B2R) blockers, and an inhibitory effect was analysed for ARB administration. Results were validated by immunohistochemical analysis and mechanistic data were collected by human umbilical vein endothelial cell (HUVEC) viability or scratch assay and monocyte (THP-1) migration assay.

RESULTS

An inhibitory effect of ARB on arteriogenesis could not be demonstrated. However, collateral growth measurements demonstrated a significantly increased CVRC and PCA diameters in the ACEi group. ACEi stimulates cell viability and migration, which could be partially reduced by additional administration of bradykinin receptor 1 inhibitor (B1Ri). ACEi inhibits the degradation of pro-arteriogenic bradykinin derivatives, but combined ACEi + B1Ri + B1Ri (BRB) treatment did not reverse the stimulatory effect. Yet, co-administration of ACEi + BRB enhances arteriogenesis and cell migration.

CONCLUSION

We demonstrate a potent stimulatory effect of ACEi on cerebral arteriogenesis in rats, presumable via B1R. However, results imply a pleiotropic and compensatory effect of ACEi on bradykinin receptor-stimulated arteriogenesis.

Cardiovascular drugs attenuated myocardial resistance against ischaemia-induced and reperfusion-induced injury in a rat model of repetitive occlusion

Objective

We investigated the impact of cardioprotective drugs on ST-elevation, arrhythmias and infarct size in a rat model of repetitive coronary artery occlusion.

Methods

Seventy Sprague-Dawley rats were randomised to two control and five treatment groups. Placebo was either implantation of a pneumatic occluder onto the left anterior descending coronary artery (LAD) without starting repetitive occlusion (SHAM) or subsequent RO of the LAD over 10 days without medication (ROP). Treatment groups underwent RO and additionally received nitroglycerin (NTG), metoprolol, verapamil (VER), ranolazine (RAN) or candesartan (CAN). Two weeks after the intervention, rats underwent a single, sustained LAD occlusion followed by reperfusion. To evaluate differences in cardiac resistance against myocardial ischaemia and reperfusion injury, cardiac surrogate parameters including maximal ST-elevation, arrhythmias and infarct size were assessed.

Results

Compared with sham, RO alone and RO plus nitroglycerin were associated with significantly lower maximal ST-elevation and percentage of infarcted myocardium (SHAM 0.12 mV, ROP 0.06 mV (p=0.004), NTG 0.05 mV (p=0.005); SHAM 16.2%, ROP 6.6% (p=0.008), NTG 5.9% (p=0.006). Compared with RO alone, RO plus RAN was accompanied by increased ST-elevation (0.13 mV, p=0.018) and RO plusVER or CAN by more infarcted myocardium (14.2%, p=0.004% and 15.5%, p=0.003, respectively). Rats treated with VER, RAN or CAN tended to severe arrhythmias more frequently than those of the control groups.

Conclusions

RO led to an increased myocardial resistance against ischaemia and reperfusion injury. Concomitant administration of nitroglycerin did not affect the efficacy of RO. Cardiovascular channel or receptor blockers reduced the efficacy of RO.

Nitroglycerin application and coronary arteriogenesis

BACKGROUND

In the presence of a coronary occlusion, pre-existing small collateral vessels (arterioles) develop into much larger arteries (biological bypasses) that have the potential to allow a certain level of perfusion distal to the blockage. Termed arteriogenesis, this phenomenon proceeds via a complex combination of events, with nitric oxide (NO) playing an essential role. The aim of this study was to investigate the effects of supplemental administration of NO donors, i.e., short-acting nitroglycerin (NTG) or slow-release pelleted isosorbide dinitrate (ISDN), on collateral development in a repetitive coronary artery occlusion model in rats.

METHODS

Coronary collateral growth was induced via a repetitive occlusion protocol (ROP) of the left anterior descending coronary artery (LAD) in rats. The primary endpoints were the histological evaluation of rat heart infarct size and ST-segment elevation (ECG-analysis) upon final permanent occlusion of the LAD (experimentally induced myocardial infarction). The effects of NTG or ISDN were also evaluated by administration during 5 days of ROP. We additionally investigated whether concomitant application of NTG can compensate for the anti-arteriogenic effect of acetylsalicylic acid (ASA).

RESULTS

After 5 days of ROP, the mean infarct size and degree of ST-elevation were only slightly lower than those of the SHAM group; however, after 10 days of the protocol, the ROP group displayed significantly less severe infarct damage, indicating enhanced arteriogenesis. Intermittent NTG application greatly decreased the ST-elevation and infarct size. The ISDN also had a positive effect on arteriogenesis, but not to the same extent as the NTG. Administration of ASA increased the infarct severity; however, concomitant dosing with NTG somewhat attenuated this effect.

CONCLUSION

Intermittent treatment with the short-acting NTG decreased the size of an experimentally induced myocardial infarct by promoting coronary collateral development. These new insights are of great relevance for future clinical strategies for the treatment of occlusive vascular diseases.

PPARγ activation inhibits cerebral arteriogenesis in the hypoperfused rat brain

AIMS

PPARγ stimulation improves cardiovascular (CV) risk factors, but without improving overall clinical outcomes. PPARγ agonists interfere with endothelial cell (EC), monocyte and smooth muscle cell (SMC) activation, function and proliferation, physiological processes critical for arterial collateral growth (arteriogenesis). We therefore assessed the effect of PPARγ stimulation on cerebral adaptive and therapeutic collateral growth.

METHODS

In a rat model of adaptive cerebral arteriogenesis (3-VO), collateral growth and function were assessed (i) in controls, (ii) after PPARγ stimulation (pioglitazone 2.8 mg kg(-1); 10 mg kg(-1) compared with metformin 62.2 mg kg(-1) or sitagliptin 6.34 mg kg(-1)) for 21 days or (iii) after adding pioglitazone to G-CSF (40 μg kg(-1) every other day) to induce therapeutic arteriogenesis for 1 week. Pioglitazone effects on endothelial and SMC morphology and proliferation, monocyte activation and migration were studied.

RESULTS

PPARγ stimulation decreased cerebrovascular collateral growth and recovery of hemodynamic reserve capacity (CVRC controls: 12 ± 7%; pio low: -2 ± 9%; pio high: 1 ± 7%; metformin: 9 ± 13%; sitagliptin: 11 ± 12%), counteracted G-CSF-induced therapeutic arteriogenesis and interfered with EC activation, SMC proliferation, monocyte activation and migration.

CONCLUSION

Pharmacologic PPARγ stimulation inhibits pro-arteriogenic EC activation, monocyte function, SMC proliferation and thus adaptive as well as G-CSF-induced cerebral arteriogenesis. Further studies should evaluate whether this effect may underlie the CV risk associated with thiazolidinedione use in patients.

Acetylsalicylic acid, but not clopidogrel, inhibits therapeutically induced cerebral arteriogenesis in the hypoperfused rat brain

This study investigated the effects of acetylsalicylic acid (ASA) and clopidogrel, standardly used in the secondary prevention of vascular occlusions, on cerebral arteriogenesis in vivo and in vitro. Cerebral hypoperfusion was induced by three-vessel occlusion (3-VO) in rats, which subsequently received vehicle, ASA (6.34 mg/kg), or clopidogrel (10 mg/kg). Granulocyte colony-stimulating factor (G-CSF), which enhanced monocyte migration in an additional cell culture model, augmented cerebrovascular arteriogenesis in subgroups (40 μg/kg). Cerebrovascular reactivity and vessel diameters were assessed at 7 and 21 days. Cerebrovascular reserve capacity was completely abolished after 3-VO and remained severely compromised after 7 (-14±14%) and 21 (-5±11%) days in the ASA groups in comparison with controls (4±5% and 10±10%) and clopidogrel (4±13% and 10±8%). It was still significantly decreased when ASA was combined with G-CSF (1±4%) compared with G-CSF alone (20±8%). Posterior cerebral artery diameters confirmed these data. Monocyte migration into the vessel wall, improved by G-CSF, was significantly reduced by ASA. Acetylsalicylic acid, but not clopidogrel, inhibits therapeutically augmented cerebral arteriogenesis.

Arteriogenesis Is Modulated By Bradykinin Receptor Signaling

Rationale:

Positive outward remodeling of pre-existing collateral arteries into functional conductance arteries, arteriogenesis, is a major endogenous rescue mechanism to prevent cardiovascular ischemia. Collateral arterial growth is accompanied by expression of kinin precursor. However, the role of kinin signaling via the kinin receptors (B1R and B2R) in arteriogenesis is unclear.

Objective:

The purpose of this study was to elucidate the functional role and mechanism of bradykinin receptor signaling in arteriogenesis.

Methods and Results:

Bradykinin receptors positively affected arteriogenesis, with the contribution of B1R being more pronounced than B2R. In mice, arteriogenesis upon femoral artery occlusion was significantly reduced in B1R mutant mice as evidenced by reduced microspheres and laser Doppler flow perfusion measurements. Transplantation of wild-type bone marrow cells into irradiated B1R mutant mice restored arteriogenesis, whereas bone marrow chimeric mice generated by reconstituting wild-type mice with B1R mutant bone marrow showed reduced arteriogenesis after femoral artery occlusion. In the rat brain 3-vessel occlusion arteriogenesis model, pharmacological blockade of B1R inhibited arteriogenesis and stimulation of B1R enhanced arteriogenesis. In the rat, femoral artery ligation combined with arterial venous shunt model resulted in flow-driven arteriogenesis, and treatment with B1R antagonist R715 decreased vascular remodeling and leukocyte invasion (monocytes) into the perivascular tissue. In monocyte migration assays, in vitro B1R agonists enhanced migration of monocytes.

Conclusions:

Kinin receptors act as positive modulators of arteriogenesis in mice and rats. B1R can be blocked or therapeutically stimulated by B1R antagonists or agonists, respectively, involving a contribution of peripheral immune cells (monocytes) linking hemodynamic conditions with inflammatory pathways.

Pulsatile shear and Gja5 modulate arterial identity and remodeling events during flow-driven arteriogenesis

In the developing chicken embryo yolk sac vasculature, the expression of arterial identity genes requires arterial hemodynamic conditions. We hypothesize that arterial flow must provide a unique signal that is relevant for supporting arterial identity gene expression and is absent in veins. We analyzed factors related to flow, pressure and oxygenation in the chicken embryo vitelline vasculature in vivo. The best discrimination between arteries and veins was obtained by calculating the maximal pulsatile increase in shear rate relative to the time-averaged shear rate in the same vessel: the relative pulse slope index (RPSI). RPSI was significantly higher in arteries than veins. Arterial endothelial cells exposed to pulsatile shear in vitro augmented arterial marker expression as compared with exposure to constant shear. The expression of Gja5 correlated with arterial flow patterns: the redistribution of arterial flow provoked by vitelline artery ligation resulted in flow-driven collateral arterial network formation and was associated with increased expression of Gja5. In situ hybridization in normal and ligation embryos confirmed that Gja5 expression is confined to arteries and regulated by flow. In mice, Gja5 (connexin 40) was also expressed in arteries. In the adult, increased flow drives arteriogenesis and the formation of collateral arterial networks in peripheral occlusive diseases. Genetic ablation of Gja5 function in mice resulted in reduced arteriogenesis in two occlusion models. We conclude that pulsatile shear patterns may be central for supporting arterial identity, and that arterial Gja5 expression plays a functional role in flow-driven arteriogenesis.