Specific alterations of endothelial signal transduction pathways of porcine epicardial coronary arteries in left ventricular hypertrophy

Large animal models of pressure overload-induced cardiac left ventricular hypertrophy to study remodelling of the human heart with aortic stenosis

Pathologic cardiac hypertrophy is a common consequence of many cardiovascular diseases, including aortic stenosis (AS). AS is known to increase the pressure load of the left ventricle, causing a compensative response of the cardiac muscle, which progressively will lead to dilation and heart failure. At a cellular level, this corresponds to a considerable increase in the size of cardiomyocytes, known as cardiomyocyte hypertrophy, while their proliferation capacity is attenuated upon the first developmental stages. Cardiomyocytes, in order to cope with the increased workload (overload), suffer alterations in their morphology, nuclear content, energy metabolism, intracellular homeostatic mechanisms, contractile activity, and cell death mechanisms. Moreover, modifications in the cardiomyocyte niche, involving inflammation, immune infiltration, fibrosis, and angiogenesis, contribute to the subsequent events of a pathologic hypertrophic response. Considering the emerging need for a better understanding of the condition and treatment improvement, as the only available treatment option of AS consists of surgical interventions at a late stage of the disease, when the cardiac muscle state is irreversible, large animal models have been developed to mimic the human condition, to the greatest extend. Smaller animal models lack physiological, cellular and molecular mechanisms that sufficiently resemblance humans and in vitro techniques yet fail to provide adequate complexity. Animals, such as the ferret (Mustello purtorius furo), lapine (rabbit, Oryctolagus cunigulus), feline (cat, Felis catus), canine (dog, Canis lupus familiaris), ovine (sheep, Ovis aries), and porcine (pig, Sus scrofa), have contributed to research by elucidating implicated cellular and molecular mechanisms of the condition. Essential discoveries of each model are reported and discussed briefly in this review. Results of large animal experimentation could further be interpreted aiming at prevention of the disease progress or, alternatively, at regression of the implicated pathologic mechanisms to a physiologic state. This review summarizes the important aspects of the pathophysiology of LV hypertrophy and the applied surgical large animal models that currently better mimic the condition.

The Novel Inodilator ORM-3819 Relaxes Isolated Porcine Coronary Arteries: Role of Voltage-Gated Potassium Channel Activation

Relaxation and changes in the transmembrane potential of vascular smooth muscle induced by ORM-3819, a novel inodilating compound, were investigated in isolated porcine coronary arteries. Isometric tone was studied on arterial rings precontracted by KCl (30 mM), and resting membrane potential was investigated by a conventional microelectrode technique. ORM-3819 in the concentration range 0.38-230.6 µM evoked concentration-dependent relaxation with a maximum value of 58.1% and an effective concentration of the relaxing substance that caused 50% of maximum relaxation of 72.2 µM. The maximum hyperpolarization produced by ORM-3819 at a concentration of 120 µM (-2.6 ± 0.81 mV, N = 10) did not differ significantly from that induced by C-type natriuretic peptide (CNP), an endogenous hyperpolarizing mediator, at a concentration of 1.4 µM (-3.6 ± 0.38 mV, N = 17). The same effect elicited by the known inodilator levosimendan was less pronounced at a concentration of 3.7 µM: -1.82 ± 0.44 mV, N = 22 (P < 0.05 vs. CNP). The voltage-gated potassium channel inhibitor 4-aminopyridine, at a concentration of 5 mM, attenuated the relaxation induced by ORM-3819 at concentrations of 41.6 or 117.2 µM. These results suggest that ORM-3819 is a potent vasodilating agent able to relieve coronary artery vasospasm by causing hyperpolarization of vascular smooth muscle cells through processes involving activation of voltage-gated potassium channels.

Uridine Adenosine Tetraphosphate-Induced Coronary Relaxation Is Blunted in Swine With Pressure Overload: A Role for Vasoconstrictor Prostanoids

Plasma levels of the vasoactive substance uridine adenosine tetraphosphate (Up₄A) are elevated in hypertensive patients and Up₄A-induced vascular contraction is exacerbated in various arteries isolated from hypertensive animals, suggesting a potential role of Up₄A in development of hypertension. We previously demonstrated that Up₄A produced potent and partially endothelium-dependent relaxation in the porcine coronary microvasculature. Since pressure-overload is accompanied by structural abnormalities in the coronary microvasculature as well as by endothelial dysfunction, we hypothesized that pressure-overload blunts the coronary vasodilator response to Up₄A, and that the involvement of purinergic receptors and endothelium-derived factors is altered. The effects of Up₄A were investigated using wire-myography in isolated coronary small arteries from Sham-operated swine and swine with prolonged (8 weeks) pressure overload of the left ventricle induced by aortic banding (AoB). Expression of purinergic receptors and endothelium-derived factors was assessed in isolated coronary small arteries using real-time PCR. Up₄A (10^-9 to 10^-5 M) failed to produce contraction in isolated coronary small arteries from either Sham or AoB swine, but produced relaxation in preconstricted arteries, which was significantly blunted in AoB compared to Sham. Blockade of purinergic P1, and P2 receptors attenuated Up₄A-induced coronary relaxation more, while the effect of P2X₁-blockade was similar and the effects of A_2A- and P2Y₁-blockade were reduced in AoB as compared to Sham. mRNA expression of neither A1, A2, A3, nor P2X₁, P2X₇, P2Y₁, P2Y₂, nor P2Y₆-receptors was altered in AoB as compared to Sham, while P2Y₁₂ expression was higher in AoB. eNOS inhibition attenuated Up₄A-induced coronary relaxation in both Sham and AoB. Additional blockade of cyclooxygenase enhanced Up₄A-induced coronary relaxation in AoB but not Sham swine, suggesting the involvement of vasoconstrictor prostanoids. In endothelium-denuded coronary small arteries from normal swine, thromboxane synthase (TxS) inhibition enhanced relaxation to Up₄A compared to endothelium-intact arteries, to a similar extent as P2Y₁₂ inhibition, while the combination inhibition of P2Y₁₂ and TxS had no additional effect. In conclusion, Up₄A-induced coronary relaxation is blunted in swine with AoB, which appears to be due to the production of a vasoconstrictor prostanoid, likely thromboxane A₂.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Atorvastatin worsens left ventricular diastolic dysfunction and endothelial dysfunction of epicardial coronary arteries in normocholesterolemic porcine with left ventricular hypertrophy

Statins have pleiotropic effects that can reverse endothelial dysfunction and prevent the development of left ventricular hypertrophy (LVH). The goal of this study was to assess the effect of treatment with atorvastatin on the endothelial dysfunction of epicardial coronary arteries and the development of LVH in a porcine model. LVH was induced through 2 months of aortic banding (AB) of the ascending aorta. Experimental groups were (1) sham untreated: without AB, (2) LVH untreated: with AB, and (3,4) LVH treated: with AB treated with 40 and 80 mg of atorvastatin, respectively, for 60 days, and (5) sham treated: without AB treated with 80 mg of atorvastatin for 60 days. Vascular reactivity studies were performed in organ chambers experiments. NO bioavailability was assessed using cyclic guanosine monophosphate quantification. Oxidative stress levels were measured by quantifying angiotensin II) and nitrite/nitrate levels. LVH and LV diastolic function were evaluated using echocardiography. Atorvastatin decreased endothelium-dependent relaxations and cyclic guanosine monophosphate levels in all treated animals. Angiotensin II levels were increased, whereas nitrite levels were similar among groups (P > 0.05). LV diastolic dysfunction and LVH were significantly greater in all treated animals (P < 0.01). High-density lipoprotein levels and low-density lipoprotein levels were significantly decreased in animals receiving atorvastatin (P < 0.05). In this swine model of LVH, atorvastatin did not prevent LVH development or coronary endothelial dysfunction and resulted in worsening of the LV diastolic dysfunction.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Large animal models for diastolic dysfunction and diastolic heart failure-a review of the literature

Diastolic heart failure (DHF) or heart failure with preserved systolic left ventricular function is estimated to account for approximately 40% of heart failure cases. Medical treatment of patients with DHF is limited and mainly empirical. Device-based therapy has an increasing role in the treatment of systolic heart failure and may have a future role in the treatment of DHF patients. Diastolic dysfunction and DHF are associated with anatomical and physiological characteristics, which need to be modeled in large animals in order to allow evaluation of device-based therapies, prior to clinical studies. In this article, we will review the large animal models for diastolic dysfunction and heart failure.

Coronary endothelial dysfunction and hyperlipidemia are independently associated with diastolic dysfunction in humans

BACKGROUND

Coronary endothelial dysfunction (CED) and DHF are both associated with myocardial ischemia and CAD risk factors. The objective of the this study was to determine if CED and CAD factors are associated with diastolic dysfunction before the development of occlusive CAD or clinical heart failure.

METHODS

Patients with normal ejection fraction and nonocclusive CAD who underwent coronary endothelial function studies were identified. Left ventricular relaxation was assessed by tissue Doppler assessment of early diastolic ascent of the septal mitral annulus (Ea). Multiple linear regression was used to investigate whether coronary risk factors influenced diastolic function after adjusting for the presence of CED.

RESULTS

A total of 160 patients had adequate assessment of diastolic relaxation. With multiple linear regression models, %deltaCBF (P = .018) was associated with a higher Ea; in contrast, older age (P < .001), female sex (P = .028), higher left ventricular mass index (P = .016), and higher nonhigh-density lipoprotein cholesterol (P = .022) were associated with a lower Ea.

CONCLUSION

Coronary endothelial dysfunction and hyperlipidemia are independently associated with impaired relaxation in patients with normal ejection fraction in the absence of occlusive CAD and heart failure. The current study suggests a new potential mechanism for the development of endothelial and diastolic dysfunction in humans.

Role of probucol on endothelial dysfunction of epicardial coronary arteries associated with left ventricular hypertrophy

The lipid-lowering agent probucol may be efficacious, through its antioxidant properties, to limit and reverse the vascular endothelial dysfunction associated with left ventricular hypertrophy (LVH). LVH was induced by performing an aortic banding (AB) on swine, except for controls (group 1). The untreated AB group received a placebo (group 2) whereas the treated groups received probucol (1000 mg/d orally); the third group began its treatment on the day of the banding (for 60 d), the fourth began on day 30 and the fifth on day 60 after AB (both for 30 d). Hypertrophy was assessed by echocardiography and histology. Coronary vascular reactivity was evaluated in organ chambers and endothelial function by quantification of NO2/NO3 and cyclic guanosine-3',5'-monophosphate. To assess oxidative stress, hydroperoxides and angiotensin II levels as well as superoxide dismutase activity were evaluated. After treatment with probucol, a significant decrease in left ventricle/body weight ratio was observed compared with the untreated group. Dose-response curves of the probucol groups showed an improvement in endothelium-dependent relaxations, associated with increased nitric oxide bioavailability and decreased angiotensin II and hydroperoxide levels. In conclusion, the antioxidant probucol limited the development and induced the regression of LVH and the associated coronary endothelial dysfunction.

Alterations in the endothelial G-protein coupled receptor pathway in epicardial arteries and subendocardial arterioles in compensated left ventricular hypertrophy

The present study was designed to compare alterations of endothelium-dependent vasorelaxation in coronary epicardial arteries and subendocardial arterioles occurring in left ventricular hypertrophy (LVH) secondary to 60 days of aortic banding in a porcine model. Development of LVH was documented by echocardiogram and the endothelial function of subendocardial and epicardial vessels was studied by constructing concentration-response curves in a pressure myograph and standard organ chambers, respectively. 5-HT induced relaxations were reduced (p<0.05) in both vessel types isolated from pigs with LVH. Dilations of subendocardial arterioles and epicardial vessels to UK14304 were depressed by LVH. In the presence of Nomega-nitro-L-arginine (L-NNA), EDHF solely accounts for BK-induced relaxations; it fully compensates for the loss of NO in arterioles, but only partially in epicardial arteries isolated from LVH swine. Endothelium-independent relaxations induced by SNP were not altered in both vessel types from the LVH group. In a porcine model of LVH secondary to 60 days of aortic banding, the associated coronary endothelial dysfunction preferentially involves Gi-protein mediated relaxations in arterioles and arteries but also affects Gq-protein mediated relaxations in epicardial coronary arteries.

Decrease of Endothelin Receptor Subtype ETB and Release of COX-Derived Products Contribute to Endothelial Dysfunction of Porcine Epicardial Coronary Arteries in Left Ventricular Hypertrophy

Alterations in the regulation of coronary circulation play a major role in the enhanced susceptibility to ischemic injury of the myocardium in left ventricular hypertrophy (LVH). The present study was designed to assess the role of endothelium-dependent contracting factors and endothelin receptors in the coronary endothelial dysfunction in LVH, occurring 2 months after aortic banding in a swine model. Hemodynamic and morphologic analyses were performed in LVH and control groups. Vascular reactivity studies were performed in rings from control and aortic banding groups to assess the contribution of endothelin (ET-1) receptor subtypes to the contraction induced by ET-1 and IRL-1620 (an ETB receptor agonist), with and without endothelium. The effects of cyclooxygenase (COX)-derived products induced by ET-1, serotonin (5-HT), and bradykinin (BK) were evaluated, with or without indomethacin (a COX antagonist). ET-1 receptor density was assessed by confocal microscopy and Western blot experiments. The wall-to-lumen ratio, determined in digital planimetry, was increased in the LVH group with no significant changes in coronary perfusion pressures. There was a significant increase in contractions to ET-1 in the LVH group, which were reduced by exposure to indomethacin and daltroban (thromboxane A2 [TXA2] receptor antagonist). Relaxations to 5-HT and BK were improved by indomethacin in the LVH group. There was no significant change in ETA receptor density (3.113 +/- 0.389 vs 3.594 +/- 0.314) but a decrease in ETB receptor density (6.435 +/- 0.265 vs 4.588 +/- 0.089; P < 0.001) in the LVH group. The coronary endothelial dysfunction of swine epicardial coronary arteries in LVH secondary to 2 months of aortic banding involves both relaxing and contracting factors. ETA receptors and COX-derived products are preferentially implicated in the increased contractions to ET-1. Strategies aimed at decreasing ET-1 effects with ET-1 antagonists selective for ETA receptors could improve the coronary endothelial dysfunction in LVH.

Loss of endothelial KATP channel-dependent, NO-mediated dilation of endocardial resistance coronary arteries in pigs with left ventricular hypertrophy

The influence of left ventricular hypertrophy (LVH) on the endothelial function of resistance endocardial arteries is not well established. The aim of this study was to characterise the mechanisms responsible for UK-14,304 (alpha(2)-adrenoreceptor agonist)-induced endothelium-dependent dilation in pig endocardial arteries isolated from hearts with or without LVH. LVH was induced by aortic banding 2 months before determining endothelial function. Following euthanasia, hearts were harvested and endocardial resistance arteries were isolated and pressurised to 100 mmHg in no-flow conditions. Vessels were preconstricted with acetylcholine (ACh) or high external K(+) (40 mmol l(-1) KCl). Results are expressed as mean+/-s.e.m. UK-14,304 induced a maximal dilation representing 79+/-6% (n=8) of the maximal diameter. NO synthase (l-NNA, 10 micromol l(-1), n=7) or guanylate cyclase (ODQ, 10 micromol l(-1), n=4) inhibition reduced (P<0.05) UK-14,304-dependent dilation to 35+/-6 and 18+/-7%, respectively. Apamin and charybdotoxin reduced (P<0.05) to 39+/-8% (n=4) the dilation induced by UK-14,304. In depolarised conditions, however, this dilation was prevented (P<0.05). UK-14,304-induced dilation was reduced (P<0.05) by glibenclamide (Glib, 1 micromol l(-1)), a K(ATP) channel blocker, either alone (35+/-10%, n=5) or in combination with l-NNA (34+/-9%, n=4). In LVH, UK-14,304-induced maximal dilation was markedly reduced (25+/-4%, P<0.05) compared to control; it was insensitive to l-NNA (21+/-5%) but prevented either by the combination of l-NNA, apamin and charybdotoxin, or by 40 mmol l(-1) KCl. Activation of endothelial alpha(2)-adrenoreceptor induces an endothelium-dependent dilation of pig endocardial resistance arteries. This dilation is in part dependent on NO, the release of which appears to be dependent on the activation of endothelial K(ATP) channels. This mechanism is blunted in LVH, leading to a profound reduction in UK-14,304-dependent dilation.

Inhibiting the NO pathway with intracoronary L-NAME infusion increases endothelial dysfunction and intimal hyperplasia after heart transplantation

BACKGROUND

The endothelium protects the vascular wall through the nitric oxide (NO) release. Coronary endothelial dysfunction occurs early after heart transplantation and predicts the development of intimal thickening typical of graft coronary vasculopathy.

OBJECTIVE

We designed this study to examine the effect of endothelial NO synthase (eNOS) inhibition on the endothelial dysfunction caused by rejection and on the development of accelerated atherosclerosis after heart transplantation.

METHODS

To study the effect on these 2 end-points of inhibiting eNOS with intracoronary L-nitro arginine methyl ester (L-NAME; 1 mg/kg/day), infused with an osmotic pump for 30 days, we used a porcine model of heterotopic heart transplantation with pre-operative immunologic typing, to permit slow rejection without the need for immunosuppression. The endothelium-dependent relaxations of allografted coronary arteries, allografted arteries infused with L-NAME, allografted arteries mounted with the pump, and vehicle and native coronary arteries were compared 30 days after graft implantation using standard organ chamber experiments. We evaluated intimal thickening using a semi-quantitative scale (0-4+ grading).

RESULTS

A significant decrease in relaxations to serotonin (5-HT) occurred in allografted arteries infused directly with L-NAME compared with allografted arteries from swine receiving 5-HT, and relaxations in the latter were decreased compared with those of swine receiving the vehicle and native coronary arteries (p < 0.05). We found no significant differences in endothelium-dependent relaxations to bradykinin among coronary rings from all groups. We observed a significant increase in the prevalence and severity of intimal thickening in allografted coronary arteries infused with L-NAME compared with allografts not infused (p < 0.05), which had significantly more intimal thickening compared with native coronary arteries (p < 0.05).

CONCLUSION

These results demonstrate that inhibiting the NO pathway worsens the endothelial dysfunction caused by rejection after heart transplantation and accelerates the intimal thickening process, leading to graft coronary vasculopathy. Strategies designed to preserve endothelial integrity and function of the endothelial NO pathway should be used to prevent graft coronary vasculopathy.