The arterial wall: a new pharmacological and therapeutic target

Endothelial Dysfunction and Cardiovascular Disease: History and Analysis of the Clinical Utility of the Relationship

The endothelium is the single-cell monolayer that lines the entire vasculature. The endothelium has a barrier function to separate blood from organs and tissues but also has an increasingly appreciated role in anti-coagulation, vascular senescence, endocrine secretion, suppression of inflammation and beyond. In modern times, endothelial cells have been identified as the source of major endocrine and vaso-regulatory factors principally the dissolved lipophilic vosodilating gas, nitric oxide and the potent vascular constricting G protein receptor agonists, the peptide endothelin. The role of the endothelium can be conveniently conceptualized. Continued investigations of the mechanism of endothelial dysfunction will lead to novel therapies for cardiovascular disease. In this review, we discuss the impact of endothelial dysfunction on cardiovascular disease and assess the clinical relevance of endothelial dysfunction.

A global perspective on the epidemiology of pulmonary hypertension

The epidemiology of pulmonary hypertension (PH) is not fully determined worldwide but is believed to vary in different regions of the world, with differences determined by genetic, geographic, environmental, and socioeconomic factors, as well as sex-related practices and inequities in access to health care. This article reviews the global epidemiology of PH, with emphasis on the prevalence, causes, forms, and underlying factors in the developing world. Left ventricular heart disease is the most common cause worldwide, but the main contributors in developing countries are chronic infectious diseases, hypertensive heart disease, cardiomyopathy, and rheumatic heart disease. Despite data suggesting a high prevalence in Sub-Saharan Africa, the available literature is very limited. International registries like the Pan African Pulmonary Hypertension Cohort are essential to provide information about the causes, comorbidities, and diagnostic classification, therapeutic management, and the natural course of PH worldwide. Moreover, there is a need to track diagnostic and management practices and challenges to identify the gaps and gradients between different regions of the world. The information gained will pinpoint areas for improvement, aiming at bridging the current divide between low-income and high-income countries.

Review: Therapeutic advances in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by vasoconstriction, in situ thrombosis, and vascular remodeling of small pulmonary arteries inducing increased pulmonary arterial resistance. Conventional treatment is based on life style modification and nonspecific treatment (warfarine, diuretics, oxygen). Calcium channel blockers are vasodilatators that have been shown to be of great efficacy in a very specific subpopulation of patients with PAH. For the majority of patients, specific PAH therapies are still lacking. Numerous studies evaluating prostacyclin agonists, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors are now available to guide therapeutic choices. Despite those important advances there is still no cure for PAH. Fortunately, research is ongoing and many drugs show promises.

Time course of vascular reactivity to contracting and relaxing agents after endothelial denudation by balloon angioplasty in rat carotid artery

Endothelial injuries induced by different stimuli lead to proliferation of intimal vascular smooth muscle cells with formation of neointima. In this functional study, we evaluated the reactivity to contracting and vasorelaxing agents in Wistar rat carotid artery at different times (1, 7, 14, 21 and 28 days) after endothelial denudation with angioplastic balloon technique. Injured (IC) and uninjured carotid artery rings (UC) were placed in an isolated organ bath for isometric force displacement. IC collected at 1, 7, 14, 21 and 28 days showed a reduction in contraction to phenylephrine (0.3 microM), angiotensin II (0.1 microM), U46619 (0.1 microM), KCl (60 mM) and A23187 (1microM) at any experimental time compared to rings obtained from UC. The evaluation of endothelial-derived relaxing or hyperpolarizing factor (EDRF or EDHF), induced by acetylcholine (0.001-1 microM) in presence of indomethacin (10 microM) or indomethacin and Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) (10 and 100 microM, respectively), was carried out at 14, 21 and 28 days. The EDRF-induced relaxation was significantly (P < 0.0001) reduced at 14 days and it improved through out the observation time, indeed at 28 days it was indistinguishable from UC relaxation curve. In contrast, the EDHF-induced relaxation was significantly (P < 0.0001) reduced at all experimental time. A significant reduction in nitric oxide-induced relaxation, sodium nitroprusside (0.001-10 microM), was observed at 7, 14 and 21 days, but not at 28 days. The relaxation induced by diazoxide (3-300 microM), an opener of KATP channels, was significantly reduced only at 7 days but not at 14, 21 and 28 days. Western blot analysis of myosin heavy chain revealed that up to 28 days the re-differentiation (maturity state) of smooth muscle cells was not yet reached. In conclusion, our data showed that hyporeactivity to contracting and relaxing agents in endothelial denuded carotid of rats could be linked to a multifactorial condition in which reduction of receptors and alterations in post-receptor transductions in neointima may produce modification of protein expression and/or variation in ion flux where calcium could have a pivotal role.

Lead-dependent effects on arachidonic acid accumulation and the proliferation of vascular smooth muscle

Lead (Pb(2+)) has been implicated in the development of hypertension and atherosclerosis. The proliferation of vascular smooth muscle cells (VSMC) is a central feature of both conditions and there is evidence that Pb(2+) potentiates serum-dependent cell growth. The aim of this work was to examine the role of phospholipase A(2) in mitogen-dependent VSMC proliferation and determine if Pb(2+) interacts with this system in order to potentiate mitotic events. It was observed that cell proliferation induced by angiotensin II, or fetal bovine serum, required the activation of a Ca(2+)-dependent cytosolic phospholipase A(2) and the subsequent release of unesterified arachidonic acid. This path was affected by Pb(2+) as the metal increased the amount of arachidonic acid accumulation induced by either mitogen. In addition, Pb(2+) potentiated mitogen-induced DNA synthesis when present at lower doses (0.02 or 0.2 mg%), but had no effect on DNA synthesis, or cell numbers, in unstimulated cells. However, a high dose (2 mg%) of Pb(2+) attenuated the DNA synthesis stimulated by angiotensin II, or serum, but induced the accumulation of unesterified arachidonic acid in unstimulated cells. A biphasic effect of Pb(2+) on cell numbers and viability was also observed as 0.02 or 0.2 mg% Pb(2+) did not affect cell numbers or trypan blue exclusion in unstimulated cells, while 2 mg% Pb(2+) reduced cell numbers and viability. It appeared, therefore, that the lower concentrations of Pb(2+) increased arachidonic acid release and DNA synthesis only in stimulated VSMC, perhaps due to further activation of a Ca(2+)-dependent processes. In contrast, the high dose of Pb(2+) reduced DNA synthesis in stimulated cells and reduced cell numbers and viability in unstimulated cells, which may relate to the noted increase in unesterified arachidonic acid.

Vessel-specific stimulation of protein synthesis by nitric oxide synthase inhibition: role of extracellular signal-regulated kinases 1/2

Although conduit arteries develop hypertrophy after chronic NO synthesis blockade, resistance arteries remodel without hypertrophy under the same conditions. Similar findings have been described in essential hypertension. We postulated that this regional difference may be related to a heterogeneous effect of endogenous NO on proliferation along the vascular tree. Newly synthesized proteins were radiolabeled in vivo with [(3)H]L-leucine in basal conditions and during NO synthase inhibition, with or without PD98059 (inhibitor of the extracellular signal-regulated kinases [ERK] 1/2). Blocking the generation of NO by 3 different L-arginine analogues increased protein synthesis by an average of 75% in the aorta, in association with enhanced ERK 1/2 phosphorylation. PD98059 significantly reduced L-arginine analogue-induced protein synthesis and ERK 1/2 phosphorylation, confirming the involvement of ERK 1/2 as an important signaling element. In small arteries, L-arginine analogues did not influence the extent of protein synthesis, although phosphorylation of ERK 1/2 was also enhanced. To determine the role of NO in a condition of enhanced protein synthesis, angiotensin II was infused for 24 hours. Angiotensin II augmented protein synthesis in mesenteric arteries and the aorta, and was additive to NO synthase blockade in the aorta. In conclusion, endogenous NO exerts a tonic inhibitory influence on aortic growth, with limited impact on small arteries in basal and hypertrophic conditions. This heterogeneous role of NO on vascular growth may explain the heterogeneity of vascular remodeling observed in essential hypertension, a condition associated with endothelial dysfunction.

Norepinephrine-induced aortic hyperplasia and extracellular matrix deposition are endothelin-dependent

BACKGROUND

Sympathetic hyperactivity is observed in several disease states and may contribute to cardiovascular hypertrophic remodeling. Endothelin has been suggested to be a mediator of hypertrophy.

OBJECTIVE

To examine the involvement of endothelin in maintaining the growth response induced by exogenous norepinephrine.

DESIGN AND METHODS

Rats were treated with norepinephrine (2.5 microg/Kg per min subcutaneously) for 2 and 4 weeks, alone or in association with the selective endothelin-A (ETA) receptor antagonist, darusentan (LU135252, 30 mg/Kg per day orally) for weeks 3 and 4.

RESULTS

Increases in medial cell number and accumulation of collagen and elastin characterized norepinephrine-induced aortic remodeling. These effects occurred without marked changes of mean arterial pressure, but may be related to enhanced pressure variability in addition to direct effects of norepinephrine. Inhibition of ETA receptors by darusentan reversed aortic alterations produced by infusion of norepinephrine. Evaluation of medial apoptosis did not reveal any significant change in any group at 4 weeks.

CONCLUSIONS

Antagonism of ETA receptors effectively and rapidly reversed norepinephrine-induced aortic structural and compositional changes, suggesting a central role of endothelin in mediating this response. Thus, ETA receptor antagonists may help to regress large artery remodeling in conditions of increased circulating catecholamine concentrations.

Protective effects of delapril combined with indapamide or hydrochlorothiazide in spontaneously hypertensive stroke-prone rats: a comparative dose-response analysis

In previous articles, we have shown that the combination of the angiotensin-converting enzyme (ACE) inhibitor delapril (12 mg/kg/day) and the diuretic indapamide (1 mg/kg/ day) was able to prolong the life span significantly in salt-loaded stroke-prone spontaneously hypertensive rats (SHRsp). Because this finding was partly dependent on the antagonism of salt-loading effects by pharmacologic induction of diuresis, which prevented any increase in blood pressure values, we decided to evaluate whether lower doses of the combination could be equally protective without changing the progression of hypertension. Thus, we studied several treatments with progressively lower doses of delapril (6, 3, or 1.5 mg/kg/day) combined with indapamide (0.5, 0.25, or 0.125 mg/kg/day) or hydrochlorothiazide (2.5, 1.25, or 0.625 mg/kg/day) in salt-loaded SHRsp. Salt-loaded untreated animals were considered to be the control group. In agreement with previous experiments, control rats reached 50% mortality approximately 7 weeks after the beginning of salt loading. The combination of delapril and hydrochlorothiazide at the two lowest doses was not able to delay animal death significantly, whereas treatment with delapril and indapamide at the lowest dose was effective (50% survival rate, 15 weeks). The groups treated with the highest dose of delapril and hydrochlorothiazide or with the intermediate or highest dose of delapril and indapamide did not reach 50% mortality by the end of the experiment, at 44 weeks of treatment (i.e., when animals reached age 1 year). Only the highest delapril and indapamide doses were able to increase diuresis, but for a relatively short period. None of the treatments was able to lower or control blood pressure levels adequately. Therefore, blood pressure levels by themselves were not predictive of rat mortality. In contrast, the maximal value of proteinuria in the weeks preceding death was inversely correlated with the survival time. In conclusion, this study shows that low doses of an ACE inhibitor in combination with a diuretic can be effectively protective in a model of severe hypertension, independent of any change in blood pressure levels.

Non-invasive evaluation of arterial abnormalities in hypertensive patients

ARTERIAL ABNORMALITIES IN HYPERTENSION: Morbidity and mortality in hypertension are mainly determined by arterial lesions which may occur in different regional circulations (e.g. kidney, cerebral, coronary circulations, causing nephro-angiosclerosis, stroke or myocardial infarction, respectively). Despite arterial heterogeneity, structural and functional abnormalities are usually observed at an early stage of hypertension in both large and small arteries. These alterations modify physiological and mechanical properties of the arterial wall, which may become clinically evident by increasing arterial pulsatility or pulse pressure; the alterations facilitate the establishment and progression of atherosclerosis and arteriosclerosis.

METHODS OF ASSESSING ARTERIAL ABNORMALITIES

Several non-invasive techniques can be used to assess haemodynamic properties of arteries: (1) casual and ambulatory blood pressure measurements can be used to evaluate pulse pressure; (2) pulse pressure can be measured directly in different sites of the arterial tree using the Tonometer device; (3) ultrasound techniques can be applied, including Doppler signals to assess the arterial flow, video-echo signals to analyse the arterial structure such as the intimal-medial thickness and echo-tracking systems for direct measurements of arterial wall distension and thickness; (4) pulse wave velocity is widely used as index of arterial distensibility; this parameter, assessed by the Complior device, has shown that hypertensive patients have decreased arterial distensibility and that antihypertensive treatment does not always reverse this abnormality.

TREATMENT

It is important to evaluate the effect of cardiovascular risk-reduction measures on the arterial wall. Large therapeutic trials are necessary to show whether an evaluation of arterial abnormalities can identify patients with a high cardiovascular risk and contribute to their treatment and prognostic improvement.