Coronary and aortic vasoreactivity protection with endothelin receptor antagonist, bosentan, after ischemia and hypoxia in aged rats

Chronic matrix metalloproteinase inhibition retards age-associated arterial proinflammation and increase in blood pressure

Age-associated arterial remodeling involves arterial wall collagen deposition and elastin fragmentation, as well as an increase in arterial pressure. This arterial remodeling is linked to proinflammatory signaling, including transforming growth factor-β1, monocyte chemoattractant protein 1, and proendothelin 1, activated by extracellular matrix metalloproteinases (MMPs) and orchestrated, in part, by the transcriptional factor ets-1. We tested the hypothesis that inhibition of MMP activation can decelerate the age-associated arterial proinflammation and its attendant increase in arterial pressure. Indeed, chronic administration of a broad-spectrum MMP inhibitor, PD166739, via a daily gavage, to 16-month-old rats for 8 months markedly blunted the expected age-associated increases in arterial pressure. This was accompanied by the following: (1) inhibition of the age-associated increases in aortic gelatinase and interstitial collagenase activity in situ; (2) preservation of the elastic fiber network integrity; (3) a reduction of collagen deposition; (4) a reduction of monocyte chemoattractant protein 1 and transforming growth factor-β1 activation; (5) a diminution in the activity of the profibrogenic signaling molecule SMAD-2/3 phosphorylation; (6) inhibition of proendothelin 1 activation; and (7) downregulation of expression of ets-1. Acute exposure of cultured vascular smooth muscle cells in vitro to proendothelin 1 increased both the transcription and translation of ets-1, and these effects were markedly reduced by MMP inhibition. Furthermore, infection of vascular smooth muscle cells with an adenovirus harboring a full-length ets-1 cDNA increased activities of both transforming growth factor-β1 and monocyte chemoattractant protein 1. Collectively, our results indicate that MMP inhibition retards age-associated arterial proinflammatory signaling, and this is accompanied by preservation of intact elastin fibers, a reduction in collagen, and blunting of an age-associated increase in blood pressure.

Oxidative Stress and Microcirculatory Flow Abnormalities in the Ventricles during Atrial Fibrillation

Patients with atrial fibrillation (AF) often present with typical angina pectoris and mildly elevated levels of cardiac troponin (non-ST-segment elevation myocardial infarction) during an acute episode of AF. However, in a large proportion of these patients, significant coronary artery disease is excluded by coronary angiography, which suggests that AF itself influences myocardial blood flow. The present review summarizes the effect of AF on the occurrence of ventricular oxidative stress, redox-sensitive signaling pathways and gene expression, and microcirculatory flow abnormalities in the left ventricle.

Middle age aggravates myocardial ischemia through surprising upholding of complex II activity, oxidative stress, and reduced coronary perfusion

Aging compromises restoration of the cardiac mechanical function during reperfusion. We hypothesized that this was due to an ampler release of mitochondrial reactive oxygen species (ROS). This study aimed at characterising ex vivo the mitochondrial ROS release during reperfusion in isolated perfused hearts of middle-aged rats. Causes and consequences on myocardial function of the observed changes were then evaluated. The hearts of rats aged 10- or 52-week old were subjected to global ischemia followed by reperfusion. Mechanical function was monitored throughout the entire procedure. Activities of the respiratory chain complexes and the ratio of aconitase to fumarase activities were determined before ischemia and at the end of reperfusion. H(2)O(2) release was also evaluated in isolated mitochondria. During ischemia, middle-aged hearts displayed a delayed contracture, suggesting a maintained ATP production but also an increased metabolic proton production. Restoration of the mechanical function during reperfusion was however reduced in the middle-aged hearts, due to lower recovery of the coronary flow associated with higher mitochondrial oxidative stress indicated by the aconitase to fumarase ratio in the cardiac tissues. Surprisingly, activity of the respiratory chain complex II was better maintained in the hearts of middle-aged animals, probably because of an enhanced preservation of its membrane lipid environment. This can explain the higher mitochondrial oxidative stress observed in these conditions, since cardiac mitochondria produce much more H(2)O(2) when they oxidize FADH(2)-linked substrates than when they use NADH-linked substrates. In conclusion, the lower restoration of the cardiac mechanical activity during reperfusion in the middle-aged hearts was due to an impaired recovery of the coronary flow and an insufficient oxygen supply. The deterioration of the coronary perfusion was explained by an increased mitochondrial ROS release related to the preservation of complex II activity during reperfusion.

Thymoquinone-induced relaxation of isolated rat pulmonary artery

AIM OF THE STUDY

The effect of thymoquinone (TQ), the main constituent of the volatile oil of black seed (Nigella sativa L. family Ranunculaceae), on the isolated rat pulmonary arterial rings was investigated.

MATERIALS AND METHODS

Isolated rat pulmonary arterial rings were precontracted with phenylephrine and concentration-response curves to TQ were constructed. The effects of different receptors antagonists or enzyme inhibitors were examined.

RESULTS

TQ caused a concentration-dependent decrease in the tension of the pulmonary arterial rings precontracted by phenylephrine. The effects of TQ were not influenced by pretreatment of the rings with propranolol (a non-selective beta-blocker), atropine (a non-selective blocker for muscarinic receptors), theophylline (an adenosine receptor antagonist), indomethacin (a cyclooxygenase inhibitor), L-NAME (a NO synthase inhibitor), methylene blue (an inhibitor of soluble guanylyl cyclase) and nifedipine (a Ca(2+) channel blocker). The effects of TQ were significantly potentiated by bosentan (an ET(A)/ET(B) receptor antagonist). The effects of TQ were slightly abolished by pretreatment of the rings with glibenclamide (a non-selective blocker of ATP-sensitive K+ channels). TQ totally abolished the pressor effects of serotonin and phenylephrine on the isolated rat pulmonary arterial rings.

CONCLUSION

The results of the present study suggest that TQ-induced relaxation of the precontracted pulmonary artery is probably mediated, at least in part, by activation of ATP-sensitive potassium channels and possibly by non-competitive blocking of serotonin, alpha1 and endothelin receptors.

Mechanisms of ET-1-induced endothelial dysfunction

There is now increasing evidence that endothelial dysfunction is an early event in the pathophysiology of cardiovascular diseases and can be corrected with certain therapies such as angiotensin converting enzyme inhibitors angiotensin type I receptor antagonists and stains independently of blood pressure lowering effects. Restoring endothelial function appears to be a crucial target since endothelial dysfunction predicts cardiovascular events in various situations such as coronary artery disease peripheral artery disease, or hypertension and in patients undergoing vascular surgery. Preclinical and clinical data strongly support that endothelin receptor antagonists belong to this restricted class of pharmacological agents able to act on the endothelium, and offer a potential therapeutic approach for numerous diseases associated with endothelial dysfunction. The purpose of this review will be therefore, 1) to propose mechanisms by which ET-1 can cause endothelial dysfunction; 2) to provide an overview of pathological situations associated with endothelial dysfunction related to ET-1; and 3) to assemble evidence on efficacy of endothelin receptor antagonists for improvement of endothelial function.

Antagonism of endothelin action normalizes altered levels of VEGF and its signaling in the brain of stroke-prone spontaneously hypertensive rat

Stroke-prone spontaneously hypertensive rats (SHRSP) often suffer from spontaneous stroke, in part, due to abnormalities in the cerebrovasculature. Here, we investigate the profile of key angiogenic factors and their basic signaling molecules in the brain of SHRSP during the age-dependent stages of hypertension. The profile of VEGF and its receptor, Flk-1, was dependent on age and stage of hypertension (i.e., down regulated at pre-hypertensive and malignant hypertensive stages, but up regulated at typical hypertensive stage), while that of its downstream components, pAkt and eNOS, were down regulated in a time-dependent manner in the frontal cortex of SHRSP compared to age-matched genetic control, normotensive WKY rats. On the other hand, the expression of endothelin-1 and its type A receptor (endothelin ETA receptor) were up regulated, depending on age and stage of hypertension. In contrast, levels of endothelin type B receptor were down regulated. The regional cerebral blood flow decreased during the development of malignant hypertension. Thus, subsequent experiments were designed to investigate whether endothelin-1 receptor antagonism, using endothelin-A/-B dual receptor antagonist SB209670, could normalize the molecular profile of these factors in SHRSP brain. Interestingly, blockage of endothelin-1 receptor restored to normal, levels of cerebral endothelin-1, endothelin ETA receptor and endothelin ETB receptor; VEGF and Flk-1; endothelial nitric oxide synthase (eNOS) and pAkt, in SHRSP, compared to age-matched WKY. Endothelin receptor blocker might be important to prevent the progression in the defect in VEGF and its angiogenic signaling cascade in the pathogenesis of hypertension-induced vascular remodeling in frontal cortex of SHRSP rats.

NADPH oxidases are in part responsible for increased cardiovascular superoxide production during aging

The aim of our study was to examine in rats, age-related differences in myocardial ischemic recovery and to determine the possible relationship with modification of cardiac and vascular oxidative stress. Isolated perfused hearts from young (2 months), adult (6 months), and old (21 months) Wistar rats were subjected to a ischemia-reperfusion sequence. Vascular histomorphological analyses were performed and NADPH oxidase was studied. The expression of angiotensin AT(1) receptors was evaluated using immunostaining. During the preischemic period, but also after ischemia, an aged-related decrease in myocardial functional parameters was observed, and was associated with an increased release of reactive oxygen species. In aortas, the activity and expression of NADPH oxidase increased with age according to the ESR, fluorescence microscopy, and immunohistochemistry; the NADPH oxidase involved was localized in endothelial cells. We found an age-related increase in the expression of endothelial angiotensin AT(1). Our study suggests that myocardial function and adaptation to ischemia-reperfusion declined during aging and are related to a higher level of oxidative stress. Endothelial NADPH oxidase is a major contributor to age-related cardiovascular deterioration. One of the regulators of vascular NADPH oxidase activity, the renin-angiotensin system, may be involved in the modulation of vascular superoxide production during the aging process.

Protection of endothelial-derived vasorelaxation with cariporide, a sodium-proton exchanger inhibitor, after prolonged hypoxia and hypoxia–reoxygenation: Effect of age

Calcium overload during hypoxia and reoxygenation exerts deleterious effects in endothelial and smooth muscle cells but potential effects of sodium-proton exchanger (NHE) inhibitors have never been investigated in both adult and senescent vessels. Isolated aortic rings from adult and senescent rats were submitted to hypoxia (50 min) or to hypoxia/reoxygenation (20/30 min) without or with cariporide (10(-6) M) and aortic vasoreactivity was recorded. After hypoxia, relaxation to acetylcholine was preserved in adult rings treated with cariporide (-22.3% vs. -9.3% of baseline value in control and treated groups respectively, P<0.05) but not in senescents. Cariporide treatment restored relaxation to acetylcholine after hypoxia-reoxygenation in adult rings (-32.04% vs. -0.03% of baseline value in control and treated groups respectively, P<0.01) and to a lesser extent, in senescent rings (-30.8% vs. -24.4% of baseline value in control and treated groups respectively, P<0.01). These results suggested that hypoxia induced lower acidosis and/or involved other mechanisms of proton extrusion than NHE in senescent aorta. Improvement of endothelial function with cariporide after reoxygenation in senescent aorta, but in a lesser extent than in adult aorta, suggests a lower role of NHE in pH regulation and subsequent calcium overload during aging.

Cardioprotection with cariporide, a sodium-proton exchanger inhibitor, after prolonged ischemia and reperfusion in senescent rats

This study investigated the effects of cariporide, an inhibitor of sodium-proton exchanger (NHE), during myocardial ischemia and reperfusion in senescence. Isolated Langendorff perfused hearts from 4 (adult) and 24 (senescent) month old male Wistar rats were submitted to prolonged low-flow ischemia (LFI) at 15% of initial coronary flow (180 min) or to 45 min of LFI (15% of initial coronary flow) followed by 30 min of reperfusion, without or with cariporide (10(-6)M). In senescent hearts, but not in adults, treatment with cariporide during prolonged LFI attenuated the elevation of coronary resistances (578 +/- 84 vs 1020 +/- 129% of baseline value after 180 min, P < 0.05) and delayed the decrease in active tension (35.6 +/- 5.1 vs 22.2 +/- 3.4% of baseline value after 60 min; P < 0.05). During reperfusion following LFI, the coronary flow impairment was more pronounced in senescents than in adults (48.4 +/- 9.4 and 75.3 +/- 4.9% of baseline value, respectively; P < 0.05) but was fully prevented in senescent hearts by cariporide treatment (95.6 +/- 17.0% of baseline value; P < 0.05 vs untreated group). This beneficial effect of cariporide on coronary tone was associated with an improvement of active and resting tensions and lower LDH release. Such functional protective effects of cariporide suggest an operative NHE during LFI at both coronary and myocardial levels in senescent heart. In addition, cariporide-associated improvement of post-ischemic recovery of coronary and contractile function as well as the limitation of cellular injury suggests a major role of calcium overload via NHE activation during reperfusion of senescent ischemic heart.

Age-related endothelial dysfunction : potential implications for pharmacotherapy

Aging per se is associated with abnormalities of the vascular wall linked to both structural and functional changes that can take place at the level of the extracellular matrix, the vascular smooth muscle and the endothelium of blood vessels. Endothelial dysfunction is generally defined as a decrease in the capacity of the endothelium to dilate blood vessels in response to physical and chemical stimuli. It is one of the characteristic changes that occur with age, independently of other known cardiovascular risk factors. This may account in part for the increased incidence of cardiovascular events in elderly people that can be reversed by restoring endothelial function. A better understanding of the mechanisms involved and the aetiopathogenesis of this process will help in the search for new therapeutic agents.Age-dependent alteration of endothelium-dependent relaxation seems to be a widespread phenomenon both in conductance and resistance arteries from several species. In the course of aging, there is an alteration in the equilibrium between relaxing and contracting factors released by the endothelium. Hence, there is a progressive reduction in the participation of nitric oxide and endothelium-derived hyperpolarising factor associated with increased participation of oxygen-derived free radicals and cyclo-oxygenase-derived prostanoids. Also, the endothelin-1 and angiotensin II pathways may play a role in age-related endothelial dysfunction. The use of drugs acting at different levels of these signalling cascades, including antioxidant therapy, lipid-lowering drugs and estrogens, seems to be promising.

The therapeutic potential of endothelin-1 receptor antagonists and endothelin-converting enzyme inhibitors on the cardiovascular system

Clinical trials have established bosentan, an orally active non-selective endothelin (ET) receptor antagonist, as a beneficial treatment in pulmonary hypertension. Trials have also shown short-term benefits of bosentan in systemic hypertension and congestive heart failure. However, bosentan also increased plasma levels of ET-1, probably by inhibiting the clearance of ET-1 by endothelin type B (ET(B)) receptors, and this may mean its effectiveness is reduced with long-term clinical use. Preliminary data suggests that selective endothelin type A (ET(A)) receptor antagonists (BQ-123, sitaxsentan) may be more beneficial than the non-selective ET receptor antagonists in heart failure, especially when the failure is associated with pulmonary hypertension. Experimental evidence in animal disease models suggests that non-selective ET or selective ET(A) receptor antagonism may have a role in the treatment of atherosclerosis, restenosis, myocarditis, shock and portal hypertension. In animal models of myocardial infarction and/or reperfusion injury, non-selective ET or selective ET(A) receptor antagonists have beneficial or detrimental effects depending on the conditions and agents used. Thus clinical trials of the non-selective ET or selective ET(A) receptor antagonists in these conditions are not presently warranted. Several selective endothelin-converting enzyme inhibitors have been synthesised recently, and these are only beginning to be tested in animal models of cardiovascular disease, and thus the clinical potential of these inhibitors is still to be defined.

Reduction of bFGF-induced smooth muscle cell proliferation and endothelin receptor mRNA expression by mevastatin and atorvastatin

The anti-atherosclerosis mechanisms of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) occur via both cholesterol-dependent and cholesterol-independent mechanisms. The present study used aortic and cerebral vascular smooth muscle cells (SMC) from rat to investigate whether atorvastatin and mevastatin affect basic fibroblast growth factor (bFGF)-induced SMC proliferation and the mRNA expression of endothelin A (ET(A)) and endothelin B (ET(B)) receptors. Cell proliferation was assessed by MTT and real-time PCR was used to quantify ET(A) and ET(B) receptor mRNA. bFGF-induced concentration and time dependent SMC proliferation and up-regulation of the mRNA expression of ET(A) and ET(B) receptors. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors inhibited bFGF-induced proliferation of SMC (P<0.01). In aortic SMC atorvastatin and mevastatin significantly inhibited bFGF-induced mRNA expression of endothelin ET(A) and ET(B) receptors (P<0.05). Although in cerebral SMC the inhibitory effect of the statins was comparable in size with that seen in aortic SMC, only reached borderline significance (P=0.06) for ET(A) receptor mRNA but not for ET(B). The findings suggested a direct effect of statins on the vascular wall beyond their well-known lipid lowering effect in anti-atherosclerosis. Furthermore, the specific antagonists of ET(A) and ET(B) receptors (FR139317 and BQ788, respectively) significantly inhibited bFGF-induced SMC proliferation (P<0.001). The results suggested that endothelin receptors and the mevalonate pathway were involved in bFGF-induced SMC proliferation.