Smooth muscle apoptosis during vascular regression in spontaneously hypertensive rats

Regulated vascular smooth muscle cell death in vascular diseases

Regulated cell death (RCD) is a complex process that involves several cell types and plays a crucial role in vascular diseases. Vascular smooth muscle cells (VSMCs) are the predominant elements of the medial layer of blood vessels, and their regulated death contributes to the pathogenesis of vascular diseases. The types of regulated VSMC death include apoptosis, necroptosis, pyroptosis, ferroptosis, parthanatos, and autophagy-dependent cell death (ADCD). In this review, we summarize the current evidence of regulated VSMC death pathways in major vascular diseases, such as atherosclerosis, vascular calcification, aortic aneurysm and dissection, hypertension, pulmonary arterial hypertension, neointimal hyperplasia, and inherited vascular diseases. All forms of RCD constitute a single, coordinated cell death system in which one pathway can compensate for another during disease progression. Pharmacologically targeting RCD pathways has potential for slowing and reversing disease progression, but challenges remain. A better understanding of the role of regulated VSMC death in vascular diseases and the underlying mechanisms may lead to novel pharmacological developments and help clinicians address the residual cardiovascular risk in patients with cardiovascular diseases.

Maintenance over Time of the Effect Produced by Esmolol on the Structure and Function of Coronary Arteries in Hypertensive Heart Diseases

We previously observed that esmolol treatment for 48 h reduced vascular lesions in spontaneously hypertensive rats (SHRs). Therefore, we investigated whether this beneficial effect is persistent after withdrawal. Fourteen-month-old SHRs (SHR-Es) were treated with esmolol (300 μg/kg/min) or a vehicle for 48 h. Two separate groups were also given identical treatment, but they were then monitored for a further 1 week and 1 month after drug withdrawal. We analyzed the geometry and composition of the coronary artery, vascular reactivity and plasma redox status. Esmolol significantly decreased wall thickness (medial layer thickness and cell count), external diameter and cross-sectional area of the artery, and this effect persisted 1 month after drug withdrawal. Esmolol significantly improved endothelium-dependent relaxation by ACh (10⁻⁹–10⁻⁴ mol/L); this effect persisted 1 week (10⁻⁹–10⁻⁴ mol/L) and 1 month (10⁻⁶–10⁻⁴ mol/L) after withdrawal. Esmolol reduced the contraction induced by 5-HT (3 × 10⁻⁸–3 × 10⁻⁵ mol/L), and this effect persisted 1 week after withdrawal (10⁻⁶–3 × 10⁻⁵ mol/L). Esmolol increased nitrates and reduced glutathione, and it decreased malondialdehyde and carbonyls; this enhancement was maintained 1 month after withdrawal. This study shows that the effect of esmolol on coronary remodeling is persistent after treatment withdrawal in SHRs, and the improvement in plasma oxidative status can be implicated in this effect.

Sex differences in apoptosis do not contribute to sex differences in blood pressure or renal T cells in spontaneously hypertensive rats

Apoptosis is a physiological and anti-inflammatory form of cell death that is indispensable for normal physiology and homeostasis. Several studies have reported aberrant activation of apoptosis in various tissues at the onset of hypertension. However, the functional significance of apoptosis during essential hypertension remains largely undefined. The current study was designed to test the hypothesis that apoptosis contributes to sex differences in blood pressure and the T cell profile in spontaneously hypertensive rats (SHR). Apoptosis was measured in kidney, aorta and spleen of 13-week-old adult hypertensive male and female SHR. Female SHR had greater renal and aortic apoptosis compared to age-matched males; apoptosis in the spleen was comparable between the sexes. Based on well-established sex differences in hypertension, we tested the hypothesis that greater apoptosis in female SHR contributes to the lower BP and pro-inflammatory profile compared to males. Male and female SHR were randomized to receive vehicle or ZVAD-FMK, a cell permeable pan-caspase inhibitor, in established hypertension from 13 to 15 weeks of age or at the onset of hypertension from 6 to 12 weeks or age. Treatment with ZVAD-FMK lowered renal apoptosis in both studies, yet neither BP nor renal T cells were altered in either male or female SHR. These results suggest that apoptosis does not contribute to the control or maintenance of BP in male or female SHR or sex differences in renal T cells.

Blood Pressure Correlates Asymmetrically with Neuropeptidase Activities of the Left and Right Frontal Cortices

It was suggested that the brain-heart connection is asymmetrically organized. However, evidence connecting neurochemical factors from each brain hemisphere with changes in cardio-vascular functions have not yet been reported. In order to analyze potential asymmetrical connections between brain neurochemical factors with cardio-vascular functions, we studied the level of correlations between the left and right frontal cortex (FC) soluble (Sol) and membrane-bound (MB) neuropeptide-degrading enzymes alanyl (AlaAP), cystinyl (CysAP), and glutamyl (GluAP) aminopeptidase activities, involved among others in the metabolism of angiotensins, with heart rate (HR), systolic (SBP), and diastolic (DBP) blood pressure, in rats treated or not with hypotensive or hypertensive drugs such as captopril, propranolol or L-NAME. The present study suggests the existence of a bidirectional asymmetrical connection between these brain neuropeptidases and cardio-vascular functions. Specifically, depending on treatment, in control group, Sol AlaAP from the left FC correlates negatively with SBP and DBP. In captopril-treated animals, MB CysAP and MB GluAP from the right FC correlate negatively with HR. In L-NAME treated rats, Sol CysAP from the right FC correlates negatively with DBP. No significant correlations were observed in the propranolol group. Considering together all the values obtained from the left or the right cortex of the four groups regardless of drug treatment, the results demonstrated significant negative correlations between these neuropeptidase activities, mainly from the left frontal cortex, with the levels of systolic and diastolic blood pressure. Remarkably, these findings contrast drastically with previously reported results indicating significant positive correlations between the left frontal cortex with other peripheral functions such as water intake and diuresis. Both results represent noteworthy information that strongly supports the concept of a bidirectional asymmetric organization of neurovisceral integration involving left and right brain neurochemical processes with peripheral physiological functions, most probably mediated by the autonomic nervous system. Overall, the present results suggest that cognitive functions involving the frontal cortex may be asymmetrically connected with peripheral physiological processes, and vice versa.

Perinatal taurine exerts a hypotensive effect in male spontaneously hypertensive rats and down-regulates endothelial oxide nitric synthase in the aortic arch

Essential hypertension is considered to be a result of the interaction between genetic and environmental factors, including perinatal factors. Different advantageous perinatal factors proved to have beneficial long-lasting effects against an abnormal genetic background. Taurine is a ubiquitous sulphur-containing amino acid present in foods such as seafood. The antihypertensive effects of taurine have been reported in experimental studies and in human hypertension. We aimed to investigate the effects of perinatal treatment with taurine in spontaneously hypertensive rats (SHR), a known model of genetic hypertension. Female SHR were administered with taurine (3 g/L) during gestation and lactation (SHR-TAU). Untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. Long-lasting effects in offspring were investigated. Addition of taurine to the mother's drinking water reduced blood pressure in adult offspring. No differences were observed in cardiac hypertrophy. Findings on morphometric evaluations suggest that perinatal treatment with taurine would be partially effective in improving structural alterations of the aorta. Modifications in gene expression of Bcl-2 family members and upregulation of endothelial nitric oxide synthase in the aorta of 22-week-old male offspring were found. No differences were observed on relative telomere length in different cardiovascular tissues between SHR and SHR-TAU. Altogether results suggest that taurine programming, albeit sex specific, is associated with gene expression changes which ultimately may lead to improvement of aortic remodelling and enhanced endothelial function because of augmented nitric oxide (NO) production.

The protective effect of dronedarone on the structure and mechanical properties of the aorta in hypertensive rats by decreasing the concentration of symmetric dimethylarginine (SDMA)

BACKGROUND AND AIMS

Dronedarone is a new multichannel-blocking antiarrhythmic for the treatment of patients with atrial fibrillation. Our group has demonstrated that dronedarone produces regression of cardiac remodeling; however, its effect on the remodeling of the elastic arteries has not yet been reported. We aim to assess the effects of dronedarone on the regression of thoracic aortic remodeling in spontaneously hypertensive rats (SHRs).

METHOD

Ten-month-old male SHRs were randomly assigned to an intervention group (SHR-D), where the animals received dronedarone treatment (100 mg/kg), to a control group (SHR) where rats were given vehicle, or to a group (SHR-A) where they were given amiodarone. A fourth group of normotensive control rats (Wistar-Kyoto rats, WKY) was also added. After two weeks of treatment, we studied the structure, the elastic fiber content of the thoracic aorta using histological techniques and confocal microscopy, and the vascular mechanical properties using an organ bath and isometric tension analysis. A mass spectrometric determination of symmetric dimethylarginine (SDMA) concentrations was performed.

RESULTS

SHR group developed the classic remodeling expected from the experimental model: outward hypertrophic remodeling, increased elastic fiber content and wall stiffness. However, the SHR-D group showed statistically significantly lower values for aortic tunica media thickness, wall to lumen ratio, external diameter, cross-sectional area, volume density of the elastic fibers, wall stiffness, and aortic SDMA concentration when compared to the SHR group. These parameters were similar in the SHR and SHR-A groups. Interestingly, the values for tunica media thickness, volume density of the elastic fibers, wall stiffness, and SDMA concentration obtained from the SHR-D group were similar to those measured in the WKY group.

CONCLUSION

These results suggest that dronedarone improves the structure and passive mechanical properties of the thoracic aorta in hypertensive rats, and that this protective effect could be associated with a reduction in the concentration of aortic SDMA.

Systematic Analysis of the Smooth Muscle Wall Phenotype of the Pharyngeal Arch Arteries During Their Reorganization into the Great Vessels and Its Association with Hemodynamics

Early outflow morphogenesis is a critical event in cardiac development. Understanding mechanical and molecular based morphogenetic relationships at early stages of cardiogenesis is essential for the advancement of cardiovascular technology related to congenital heart defects. In this study, we pair molecular changes in pharyngeal arch artery (PAA) vascular smooth muscle cells (VSMCs) with hemodynamic changes over the course of the same period. We focus on Hamburger Hamilton stage 24-36 chick embryos, using both Doppler ultrasound and histological sections to phenotype PAA VSMCs, and establish a relationship between hemodynamics and PAA composition. Our findings show that PAA VSMCs transition through a synthetic, intermediate, and contractile phenotype over time. Wall shear stress magnitude per arch varies throughout development. Despite distinct hemodynamic and fractional expression trends, no strong correlation was found between the two, indicating that WSS magnitude is not the main driver of PAA wall remodeling and maturation. While WSS magnitude was not found to be a major driver, this work provides a basic framework for investigating relationships between hemodynamic forces and tunica media during a critical period of development. Anat Rec, 302:153-162, 2019. © 2018 Wiley Periodicals, Inc.

Changes of Bax, Bcl-2, CCR-2, MCP-1, and TGF-β1 genes in the left ventricle of spontaneously hypertensive rat after losartan treatment

Purpose

Increased apoptosis was recently found in the hypertrophied left ventricle of spontaneously hypertensive rats (SHRs). Although the available evidence suggests that apoptosis can be induced in cardiac cells by various insults including pressure overload, cardiac apoptosis appears to result from an exaggerated local production of angiotensin in adult SHRs. Altered expressions of Bcl associated X (Bax), Bcl-2, chemokine receptor (CCR)-2, monocyte chemoattractant protein (MCP)-1, transforming growth factor (TGF)-β1, phosphorylated extracellular signal-regulated kinases (PERK), and connexin 43 proteins, and kallikrein mRNA were investigated to explore the effects of losartan on the SHR model.

Methods

Twelve-week-old male rats were grouped as follows: control (C), SHR (hypertension: H), and losartan (L; SHRs were treated with losartan [10 mg/kg/day] for 5 weeks). Western blot and reverse transcription polymerase chain reaction assays were performed.

Results

Expression of Bax, CCR-2, MCP-1, TGF-β1, PERK, and connexin 43 proteins, and kallikrein mRNA was significantly increased in the H group compared to that in the C group at weeks 3 and 5. Expression of Bax, CCR-2, MCP-1, TGF-β1, and connexin 43 proteins and kallikrein mRNA was significantly decreased after losartan treatment at week 5. PERK protein expression was significantly decreased after losartan treatment at weeks 3 and 5. Bcl-2 protein expression was significantly decreased in the H group compared to that in the C group at weeks 3 and 5.

Conclusion

Losartan treatment reduced expression of Bax, CCR-2, MCP-1, TGF-β1, PERK, and connexin 43 proteins, and kallikrein mRNA in SHRs, along with decreased inflammation and apoptosis.

Effects of Taurine and L-Arginine on the Apoptosis of Vascular Smooth Muscle Cells in Insulin Resistance Hypertensive Rats

OBJECTIVE

In order to find the effects and mechanism of taurine and L-arginine on the apoptosis of VSMCs in insulin resistance hypertensive rats.

METHODS

25% fructose were administered in the drinking water to Wistar rats for 12 weeks to induce the insulin resistance hypertensive model. Apoptosis of VSMCs was identified by TUNEL. The expressions of Bax protein and Bcl-2 protein were examined by immunohistochemistry.

RESULTS

High level of fructose significantly suppressed the apoptosis of VSMCs. Taurine and L-arginine promoted apoptosis of VSMCs via increasing the Bax protein expression and decreasing the Bcl-2 protein expression.

CONCLUSIONS

Taurine and L-arginine have obvious anti-hypertensive effects in insulin resistance hypertensive rats, and its mechanism might partially be associated with attenuating vascular remodeling by promoting apoptosis in VSMCs. In addition, the combined medication of taurine and L-arginine was more effective than single medication.

Vascular structural and functional changes: their association with causality in hypertension: models, remodeling and relevance

Essential hypertension is a complex multifactorial disease process that involves the interaction of multiple genes at various loci throughout the genome, and the influence of environmental factors such as diet and lifestyle, to ultimately determine long-term arterial pressure. These factors converge with physiological signaling pathways to regulate the set-point of long-term blood pressure. In hypertension, structural changes in arteries occur and show differences within and between vascular beds, between species, models and sexes. Such changes can also reflect the development of hypertension, and the levels of circulating humoral and vasoactive compounds. The role of perivascular adipose tissue in the modulation of vascular structure under various disease states such as hypertension, obesity and metabolic syndrome is an emerging area of research, and is likely to contribute to the heterogeneity described in this review. Diversity in structure and related function is the norm, with morphological changes being causative in some beds and states, and in others, a consequence of hypertension. Specific animal models of hypertension have advantages and limitations, each with factors influencing the relevance of the model to the human hypertensive state/s. However, understanding the fundamental properties of artery function and how these relate to signalling mechanisms in real (intact) tissues is key for translating isolated cell and model data to have an impact and relevance in human disease etiology. Indeed, the ultimate aim of developing new treatments to correct vascular dysfunction requires understanding and recognition of the limitations of the methodologies used.

Impact of losartan and angiotensin II on the expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 in rat vascular smooth muscle cells

The present study aimed to investigate the impact of losartan and angiotensin II (AngII) on the expression of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1), secreted by rat vascular smooth muscle cells (VSMCs). Rat VSMCs were isolated and cultured in different concentrations of AngII and losartan for 24 h and western blot analysis and quantitative polymerase chain reaction were performed to observe the subsequent impact on the gene and protein expression of MMP-9 and TIMP-1. AngII was shown to promote the protein and gene expression of MMP-9 in VSMCs in a concentration-dependent manner. No effect was observed on the expression of TIMP-1, therefore, an increase in the MMP-9/TIMP-1 ratio was observed. Losartan was shown to be able to inhibit MMP-9 protein and gene expression in a concentration-dependent manner, whilst promoting an increase in TIMP-1 expression, thus decreasing the ratio of MMP-9/TIMP-1. The combined action of losartan and AngII resulted in the same directional changes in MMP-9 and TIMP-1 expression as observed for losartan alone. The comparison of AngII, losartan and the combinatory effect on the expression of MMP-9 and TIMP-1 in VSMCs indicated that losartan inhibited the effects of AngII, therefore reducing the MMP-9/TIMP-1 ratio, which may contribute to the molecular mechanism of losartan in preventing atherosclerosis. In atherosclerosis, the development of the extracellular matrix of plaque is closely correlated with the evolution of AS. The balance between MMPs and TIMPs is important in maintaining the dynamic equilibrium between the ECM, and the renin-angiotensin-aldosterone system, which is involved in the pathologenesis of AS, and in which AngII has a central role.

Effect of Angiotensin converting enzyme inhibitors on soluble tumor-necrosis-factor-related apoptosis-inducing ligand levels - association with neointimal hyperplasia in drug eluting stents

OBJECTIVE

To test the hypothesis that angiotensin converting enzyme inhibitors (ACEi) affect soluble tumor-necrosis-factor-related apoptosis-inducing ligand (sTRAIL) and this interaction is associated with less in-drug-eluting-stent (DES) neointimal hyperplasia following percutaneous coronary intervention (PCI).

METHODS

From our database of patients with elective PCI and baseline intravascular ultrasound (IVUS) evaluation of the implanted DES, we randomly selected 60 patients who were prescribed an ACEi and 60 matched controls, who did not receive an ACEi following PCI. All patients underwent coronary angiography and IVUS. sTRAIL was measured in samples from the stented coronary artery and a peripheral vein.

RESULTS

sTRAIL concentration was higher in the ACEi group, both in coronary and peripheral samples: 104 [78-139] pg/ml versus 63 [45-100] pg/ml (P < 0.001) and 99 [73-135] pg/ml versus 69 [49-103] pg/ml (P = 0.002), respectively. There was an inverse association (standardized beta -0.760; P < 0.001) between sTRAIL and lumen area loss in both treatment groups. In the multivariable analysis, log(sTRAIL) was an independent negative predictor of lumen area loss (standardized beta -0.660, adjusted 95% confidence interval -0.722 to -0.466).

CONCLUSIONS

Treatment with ACEi was associated with higher sTRAIL levels and lower lumen area loss in the IVUS evaluation of implanted DES. sTRAIL levels were negatively associated with in-stent neointima hyperplasia in these post-PCI patients.

Remodeling of aorta extracellular matrix as a result of transient high oxygen exposure in newborn rats: implication for arterial rigidity and hypertension risk

Neonatal high-oxygen exposure leads to elevated blood pressure, microvascular rarefaction, vascular dysfunction and arterial (aorta) rigidity in adult rats. Whether structural changes are present in the matrix of aorta wall is unknown. Considering that elastin synthesis peaks in late fetal life in humans, and early postnatal life in rodents, we postulated that transient neonatal high-oxygen exposure can trigger premature vascular remodelling. Sprague Dawley rat pups were exposed from days 3 to 10 after birth to 80% oxygen (vs. room air control) and were studied at 4 weeks. Blood pressure and vasomotor response of the aorta to angiotensin II and to the acetylcholine analogue carbachol were not different between groups. Vascular superoxide anion production was similar between groups. There was no difference between groups in aortic cross sectional area, smooth muscle cell number or media/lumen ratio. In oxygen-exposed rats, aorta elastin/collagen content ratio was significantly decreased, the expression of elastinolytic cathepsin S was increased whereas collagenolytic cathepsin K was decreased. By immunofluorescence we observed an increase in MMP-2 and TIMP-1 staining in aortas of oxygen-exposed rats whereas TIMP-2 staining was reduced, indicating a shift in the balance towards degradation of the extra-cellular matrix and increased deposition of collagen. There was no significant difference in MMP-2 activity between groups as determined by gelatin zymography. Overall, these findings indicate that transient neonatal high oxygen exposure leads to vascular wall alterations (decreased elastin/collagen ratio and a shift in the balance towards increased deposition of collagen) which are associated with increased rigidity. Importantly, these changes are present prior to the elevation of blood pressure and vascular dysfunction in this model, and may therefore be contributory.

Brain, heart and kidney correlate for the control of blood pressure and water balance: role of angiotensinases

The renin-angiotensin system (RAS) plays a major role in the control of blood pressure (BP) and water balance by coordinating brain, heart and kidney functions, connected with each other by hormonal and neural mechanisms through the autonomic nervous system (ANS). RAS function may be monitored by the study of the enzymes (angiotensinases) involved in the metabolism of its active peptides. In order to study the relationship between the brain-heart-kidney axis and the control of BP and water balance, we analyzed the correlation of angiotensinase activities, assayed as arylamidase activities, between hypothalamus, left ventricle, renal cortex and renal medulla, collected from Wistar-Kyoto and spontaneously hypertensive rats, treated or not treated with L-NAME [N(G)-nitro-L-arginine methyl ester]. This compound not only inhibits the formation of nitric oxide but also disrupts the normal function of the ANS activating the sympathetic nervous system (SNS) to increase BP. In addition, to assess the influence of the SNS, we studied the effect of its blockade by treatment of both strains with propranolol. The present results support the notion that RAS function of the brain-heart-kidney axis, as reflected by the activities of angiotensinases, is reciprocally connected by afferent and efferent mechanisms between these locations, presumably through the ANS. These results reveal new aspects of neuroendocrine regulation possibly involving the ANS.

Antioxidant effect of doxycycline decreases MMP activity and blood pressure in SHR

Increased matrix metalloproteinase (MMP) levels are involved in vascular remodeling of hypertension. In this study, we hypothesized that doxycycline (a MMP inhibitor) could exert antioxidant effects, reverse establish vascular remodeling, and lower blood pressure in spontaneously hypertensive rats (SHR). SHR and Wistar-Kyoto rats received either doxycycline at 30 mg/kg/day by gavage or vehicle. Systolic blood pressure (SBP) was assessed weekly by tail cuff. After 5 weeks of treatment, morphologic changes in the aortic wall were studied in hematoxylin/eosin sections. MMP activity and expression were determined by in situ zymography using DQ gelatin and immunofluorescence for MMP-2. Dihydroethidium was used to evaluate aortic reactive oxygen species (ROS) production by fluorescence microscopy. Doxycycline reduced SBP by 25 mmHg. However, the antihypertensive effects were not associated with significant reversal of hypertension-induced vascular hypertrophy. SHR showed increased aortic MMP-2 levels which co-localized with higher aortic MMP activity and ROS levels, and all those biochemical alterations associated with hypertension were blunted by treatment with doxycycline. These results show that MMP inhibition with doxycycline in SHR with established hypertension resulted in antioxidant effects, lower gelatinolytic activity, and antihypertensive effects which were not associated with reversal of hypertension-induced vascular remodeling.

Role of angiotensin II type 2 receptor during regression of cardiac hypertrophy in spontaneously hypertensive rats

We previously reported that the AT1 receptor antagonist valsartan and the angiotensin converting enzyme (ACE) inhibitor enalapril decrease DNA synthesis and stimulate apoptosis in interstitial fibroblasts and epicardial mesothelial cells during regression of ventricular hypertrophy in spontaneously hypertensive rats (SHR). To examine the role of the AT2 receptor in this model, we studied hearts from SHR treated with valsartan or enalapril either alone or combined with the AT2 antagonist PD123319 for 1 or 2 weeks. Apoptosis was evaluated by quantification of DNA fragmentation or by TUNEL labeling. At 1 week, valsartan significantly increased ventricular DNA fragmentation, increased apoptosis in epicardial mesothelial cells, and decreased DNA synthesis. At 2 weeks, ventricular DNA content and cardiomyocyte cross-sectional area were significantly reduced. These valsartan-induced changes were attenuated by PD123319 co-administration. However, valsartan-induced increases in apoptosis of left ventricular interstitial non-cardiomyocytes was unaffected by the AT2 blocker. Enalapril-induced changes were similar to those observed with valsartan but were not affected by co-treatment with PD123319. These results demonstrate that AT1 and AT2 receptors act in a coordinated yet cell-specific manner to regulate cell growth and apoptosis in the left ventricle of SHR during AT1 receptor blockade but not ACE inhibition.

Protection against L-NAME-induced reduction in cardiac output persists even after cessation of angiotensin-converting enzyme inhibitor treatment

AIM

We have demonstrated that short-term angiotensin-converting enzyme (ACE) inhibition in adult spontaneously hypertensive rats produces cardiac changes that persist following cessation of treatment that result in a reduced inflammatory, proliferative and fibrotic response to the nitric oxide synthase inhibitor N(ω) -Nitro-l-arginine methyl ester (L-NAME). The present study examines whether prior ACE inhibition with enalapril also protects against L-NAME-induced cardiac dysfunction.

METHODS

Rats were treated with enalapril (Enal + L) or tap water (Con, Con + L) for 2 weeks followed by a 2-week washout period. At this point, Con + L and Enal + L rats were treated with L-NAME for 10 days. Hearts were perfused in the working mode, mean arterial pressure (MAP) was assessed via radiotelemetry, and myocardial injury was evaluated in hematoxylin and eosin-stained sections.

RESULTS

L-NAME increased MAP by a similar magnitude in Con + L and Enal + L. L-NAME-induced statistically significant decreases in flow-mediated functional parameters in Con + L rats including cardiac output, stroke volume and coronary flow. This was prevented by prior enalapril treatment. Prior enalapril did not prevent L-NAME-induced myocardial injury, but may have lessened the degree of it. Regardless of treatment, changes in cardiac function did not correlate with myocardial injury.

CONCLUSION

Despite equivalent impact on MAP and incidence of myocardial infarction, prior enalapril treatment resulted in the preservation of cardiac function following L-NAME. Understanding the mechanisms by which transient ACE inhibition protects against reductions in cardiac function in the absence of ongoing treatment may reveal novel targets for heart failure treatment.

The vascular phenotypes in hypertension: Relation with the natural history of hypertension

The different vascular phenotypes found in hypertension comprise different aspects. They may be clinical, diagnostic, structural, mechanical, functional, cellular and extracellular, signaling and molecular, proteomic, and gene expression phenotypes. In this manuscript the emphasis will be on the various structure, mechanics, dysfunction, and cell and signaling changes that can be demonstrated in hypertension, and particularly in human hypertension. The phenotype relates to the natural history of hypertension, increasingly elucidated on the basis of cohort studies. The evolution from pre-hypertension to diastolic, systolic, and systo-diastolic hypertension may have a vascular substratum that could explain, in part, the prevalence of each of these phenotypes. The potential for intervention to prevent the passage from pre-hypertension to hypertension thanks to therapies that modulate the development of vascular remodeling is highlighted.

Ginsenoside-Rd potentiates apoptosis induced by hydrogen peroxide in basilar artery smooth muscle cells through the mitochondrial pathway

Our previous studies showed that ginsenoside-Rd, a purified component from Panax notoginseng, inhibited cell proliferation and reversed basilar artery remodeling. The aim of this study was to investigate whether ginsenoside- Rd influences H(2)O(2)-induced apoptosis in basilar artery smooth muscle cells (BASMCs). The results showed that ginsenoside-Rd significantly potentiated H(2)O(2)-induced cell death and cell apoptosis. This resulted in a concentration-dependent reduction of the cell viability. Ginsenoside-Rd further increased cytochrome C release and caspase-9/caspase-3 activations, and reduced the stability of mitochondrial membrane potential (MMP) and the ratio of Bcl-2/Bax. Cyclosporine A, an inhibitor of mitochondrial-permeability transition, inhibited alteration of mitochondrial permeability induced by H(2)O(2) and reversed the effect of ginsenoside-Rd on MMP. Our data strongly suggest that ginsenoside-Rd potentiated H(2)O(2)-induced apoptosis of BASMCs through the mitochondria-dependent pathway.

Short-term ACE inhibition confers long-term protection against target organ damage

Angiotensin converting enzyme (ACE) inhibitors reduce left ventricular (LV) hypertrophy and cardiovascular-renal fibrosis. Experimentally, changes in the LV and kidney persist even after cessation of treatment. The present study investigates whether brief ACE inhibition in spontaneously hypertensive rats (SHR) provides long-term protection against the LV and kidney damage induced by the nitric oxide synthase inhibitor N-ω-nitro-L-arginine-methyl ester (L-NAME). SHR received the ACE inhibitor enalapril (n = 36) or tap water (n = 36). In all, 12 control and treated SHR were sacrificed after 2 weeks and remaining rats were taken off-treatment. After a 2-week washout, 12 controls or previously treated SHR were sacrificed and remaining rats were treated with L-NAME ((control (Con)+L, enalapril (Enal)+L) for 10 days. At sacrifice, blood pressure was recorded via carotid artery cannulation in anesthetized rats, and blood, the kidney and LV were isolated for analysis. LV mass and arterial pressure were significantly reduced by enalapril. LV mass showed a persistent reduction throughout the study. In LV, prior enalapril treatment provided significant (P<0.05) protection against L-NAME-induced increases in proliferating cells (Con+L: 11 ± 10.0 mm(2) vs. Enal+L: 4 ± 4.4 mm(2)), interstitial fibrosis (Con+L: 3 ± 2.5% vs. Enal+L: 1 ± 1.0%) and tissue macrophages (Con+L: 12 ± 9 mm(2) vs. Enal+L: 5 ± 3.6 mm(2)). In the kidney, prior enalapril treatment protected against L-NAME-induced interstitial fibrosis and vascular injury. There was no difference in glomerular size or glomerulosclerosis regardless of prior treatment. Plasma creatinine and urea were significantly increased in L-NAME treated rats. This study suggests that brief ACE inhibition confers protection against future heart and kidney injury, even in the absence of continued antihypertensive treatment.

Signalling from dead cells drives inflammation and vessel remodelling

Death of vascular smooth muscle cells (VSMCs) has been demonstrated in vessel development and in disease, most notably in atherosclerosis, but also after injury and remodelling. VSMC death promotes multiple features of vulnerable plaques, but also induces features of normal vessel ageing and cystic medial necrosis, including loss of VSMCs, elastin fragmentation and loss, increased glycosaminoglycans and speckled calcification. VSMC apoptosis in the absence of efficient phagocytosis also produces inflammation due to secondary necrosis; in contrast, VSMC apoptosis in normal vessels can be silent. We have investigated the consequences of VSMC apoptosis in both disease and during vessel remodelling. We find that VSMCs release specific cytokines dependent upon the mode of cell death; IL-1β predominates during apoptosis, whilst IL-1α predominates during necrosis. Both IL-1α and β promote release of further cytokines from adjacent live cells, in particular IL-6 and MCP-1. The balance of cytokines results in pathology with differing compositions, including inflammation or neointima formation/vascular repair, via direct promotion of VSMC proliferation and migration. Thus, VSMC death can promote either pathology or repair, depending upon the context and cytokine signalling.

Changes critical to persistent lowering of arterial pressure in spontaneously hypertensive rat occur early in antihypertensive treatment

OBJECTIVES

Angiotensin-converting enzyme inhibition (ACEI) in adult spontaneously hypertensive rats (SHRs) produces reductions in mean arterial pressure (MAP) and vascular structure that persist after treatment cessation. This study used an intermittent treatment strategy to determine the time course of changes in MAP, vascular resistance properties, and the tissue levels of endothelin.

METHODS

Adult SHRs were treated with enalapril and low sodium diet for three 2-week treatment cycles, each separated by 2-week washout periods. MAP was measured via radiotelemetry. Hindlimb structurally based vascular resistance properties were assessed after two treatment cycles. Endothelin was measured in mesenteric vessels, renal cortex and medulla in untreated SHR (Con), and at day 10 of the first and third treatment cycles.

RESULTS

Treatment produced a persistent reduction in MAP; however, the magnitude of change in the 'off-treatment' level decreased following successive treatments (cycle 1: -15 ± 1.7%, cycle 2: -8 ± 1.9%, and cycle 3: -1 ± 1.7%). Reduction in hindlimb vascular structure after two cycles of treatment was not different from that previously observed after one cycle. Endothelin levels were significantly elevated during the third cycle in renal medulla (Con: 797 ± 102 pg/g tissue, cycle 1: 767 ± 81 pg/g tissue, cycle 3: 1097 ± 205 pg/g tissue) and mesenteric vessels (Con: 711 ± 226 pg/g tissue, cycle 1: 696 ± 231 pg/g tissue, cycle 3: 1063 ± 741 pg/g tissue). Concomitant treatment with an endothelin antagonist did not impact arterial pressure.

CONCLUSION

These findings demonstrate that during ACEI treatment, most of the changes that confer persistent changes in MAP and vascular structure occur within the first 2 weeks. Elevation in endothelin levels is likely unrelated to arterial pressure.

Pharmacological inhibition of Axl affects smooth muscle cell functions under oxidative stress

We previously demonstrated that reactive oxygen species (ROS) activate Axl, a receptor tyrosine kinase, resulting in increased survival of rat aortic smooth muscle cells (RASMs). Our experiments in Axl knockout mice showed significant reduction in vascular pathologies. We hypothesize that selective pharmacological inhibitors of Axl could prove beneficial in treating vascular diseases associated with oxidative stress. We investigated a role for two novel compounds specific for Axl (R428 and R572) on ligand independent activation of Axl mediated cell survival and migration. Stimulation of RASMs with H(2)O(2) for 5 min significantly increased Akt phosphorylation (p-Akt). Inhibition at 50% (IC(50)) of p-Akt was calculated at lower concentrations in R428 (100 nM) and R572 (10 nM) compared to Fc-Axl (2 microg/mL). Flow cytometry staining with Annexin V showed a 2-fold increase in apoptosis with R428 and R572 compared to Fc-Axl after H(2)O(2), which was validated by concomitant increases in cleaved caspase-3. Pretreatment with R428 and R572 decreased cell migration by approximately 50% in response to 20% serum (similar to that after Fc-Axl). R428 and R572 decreased intracellular production of ROS in comparison to Fc-Axl. In conclusion, R428 and R572 are more potent inhibitors of ligand independent mediated Axl signaling compared to Fc-Axl in RASMs under oxidative stress.

Effect of quinapril on in-stent restenosis and relation to plasma apoptosis signaling molecules

Angiotensin-converting enzyme inhibitors have been reported to inhibit in-stent restenosis. To assess the effect of angiotensin-converting enzyme inhibition on in-stent restenosis and its relation to apoptosis, 86 patients with chronic coronary artery disease who required stent implantation in the left anterior descending coronary artery or a major diagonal branch were studied. Patients were randomized to receive quinapril 40 mg/day orally (n = 43) or a placebo (n = 43). Drug therapy was initiated 1 week before initial stenting and continued for 6 months. Plasma levels of the apoptotic signaling molecules soluble Fas and soluble Fas ligand obtained from blood drawn from the left anterior descending coronary artery were measured just before initial stenting and 6 months later, at the time of repeat coronary angiography. In-stent restenosis was present in 9.3% of patients in the quinapril group and 25.6% of patients in the placebo group (p = 0.047). Mean late luminal loss was 0.56 +/- 0.51 mm in the quinapril group and 0.95 +/- 0.95 mm in the placebo group (p = 0.003). There were no significant differences in plasma soluble Fas or soluble Fas ligand levels at baseline. At 6 months, the change in plasma soluble Fas level was significantly higher in the quinapril group (0.72 +/- 1.24 ng/ml) than in the placebo group (0.28 +/- 0.72 ng/ml) (p = 0.024). The change in plasma soluble Fas ligand levels at 6 months was significantly higher in the quinapril group (7.43 +/- 12.2 pg/ml) than in the placebo group (0.06 +/- 6.8 pg/ml) (p = 0.002). In conclusion, the angiotensin-converting enzyme inhibitor quinapril inhibits in-stent restenosis by stimulating apoptosis after percutaneous intervention.

Neointimal-specific induction of apoptosis by losartan results in regression of vascular lesion in rat aorta

We previously reported that initiating treatment with the angiotensin II receptor antagonist losartan, prior to and immediately after balloon injury, attenuates neointimal hyperplasia via induction of smooth muscle cell (SMC) apoptosis in the aorta of spontaneously hypertensive rats (SHR). The present study examines whether losartan can induce regression of an established neointima. Balloon angioplasty was performed in the aorta of 1 1 week-old SHR. Five weeks were allowed for neointima formation before rats received placebo or losartan (30 mg/kg/day) for 1 to 4 weeks. Blood pressure was measured by tail cuff plethysmography. Losartan significantly reduced blood pressure (16%) versus placebo within 2 weeks of treatment. In situ labeling with terminal deoxynucleotidyl transferase among neointimal SMC was transiently increased with losartan (10-fold at 2 weeks; P=0.004) in correlation with internucleosomal fragmentation of vascular DNA. Accordingly, losartan reversed neointimal hyperplasia by 43% (P=0.002) and 61% (P=0.007) at weeks 2 and 4, respectively, and neointimal mass by 63% (P<0.001) and 75% (P<0.001) at weeks 2 and 4, respectively, as compared to pre-treatment values. No change in aortic medial hyperplasia or mass was observed during losartan treatment. Taken together, endothelial denudation rendered the underlying media resistant to drug-induced remodeling, while losartan treatment induced vascular lesion regression by inducing apoptosis selectively in neointimal SMC, an effect that may contribute to the reduction of cardiovascular complications in hypertension.

Smooth muscle apoptosis and vascular remodeling

PURPOSE OF REVIEW

The present review is to summarize recent advances in molecular mechanisms that regulate vascular smooth muscle cell apoptosis during vascular remodeling. In normal blood vessels apoptosis counteracts cell division, whereas apoptosis is especially crucial for regulating vascular remodeling during cardiovascular diseases.

RECENT FINDINGS

Recent results have expanded our knowledge regarding the signaling pathways and molecules that regulate vascular smooth muscle cell death in postnatal vascular remodeling. Compelling data from genetic disorders associated with vascular smooth muscle cell loss (e.g., Hutchinson-Gilford progeria syndrome) and experimental studies suggest that changes in hemodynamic and mechanical forces are major modulators for vascular smooth muscle cell apoptosis. Furthermore, understanding the therapeutic effects of antihypertensive drugs related to apoptosis may identify pathways that can improve outcomes independent of the blood pressure fall.

SUMMARY

Regulation of vascular smooth muscle cell apoptosis is a potential target to modify pathological vascular remodeling and new drugs development.

Induction of vascular atrophy as a novel approach to treating restenosis. A review

Regardless of the type of arterial reconstruction, luminal narrowing (stenosis or restenosis) develops in approximately one third of the vessels. In the past, the focus of research has been on the mechanisms of stenosis (intimal hyperplasia, pathologic remodeling) and pharmacologic approaches to prevention. An alternative approach is to induce intimal atrophy after luminal narrowing has developed, thus limiting treatment to only those patients that develop a problem. This approach to treat established disease by reducing wall mass through induction of cell death and extracellular matrix removal would be particularly useful for treating stenosis in synthetic bypass grafts or stented vessels, in which intimal hyperplasia is the primary mechanism of stenosis. This approach may be applicable as well to other vascular proliferative disorders, such as pulmonary hypertension and chronic transplant arteriopathy. Proof of principle has been shown in experiments with antibodies to platelet-derived growth factor (PDGF) receptors that cause neointimal regression in baboon polytetrafluoroethylene (PTFE) grafts and with angiotensin-converting enzyme inhibitors that induce medial atrophy in hypertensive arteries. Possible molecular targets could include PDGF receptors, A20, and BMP4. Further studies are needed to determine the utility of such a therapeutic approach to vascular disease.

Differential regulation of Akt, caspases and MAP kinases underlies smooth muscle cell apoptosis during aortic remodelling in SHR treated with amlodipine

BACKGROUND AND PURPOSE

The regression of aortic hypertrophy is initiated by a transient wave of smooth muscle cell (SMC) apoptosis in spontaneously hypertensive rats (SHR) treated with antihypertensive drugs, although the molecular pathways remain unclear.

EXPERIMENTAL APPROACH

Enzymes involved in apoptosis regulation were examined daily during onset aortic remodelling in SHR treated with amlodipine (20 mg kg(-1) day(-1)).

KEY RESULTS

Significant reduction of aortic SMC number occurred by day 3 of amlodipine, reaching -13% at 28 days, followed by a significant regression of medial hypertrophy by day 5, reaching -13% at 28 days. ISOL-positive (apoptotic) SMC nuclei increased by 4.6-fold between days 2 and 4, in temporal correlation with the activation of caspase-8 (2.7-fold) at day 2 only, caspase-3 at days 3 and 4 (1.7-fold) and caspase-9 at day 3 only (3.1-fold). Akt phosphorylation, a pro-survival pathway, was reduced prior to apoptosis at day 1 (-52%) and until day 3. During the first 6 days of amlodipine treatment, significant reduction in phosphorylation of mitogen-activated protein (MAP) kinases was transient for p38 (-46% at day 3 only) but continuous for ERK1/2 after 3 days (-40%), and for JNK after 4 days (>-50%).

CONCLUSIONS AND IMPLICATIONS

Amlodipine inhibition of Akt occurred prior to and during SMC apoptosis induction, a process mediated by the early activation of caspase-8 followed by caspase-9 and -3 and associated with MAP kinase inhibition. These findings provide insights about the molecular pathways underlying SMC apoptosis leading to vascular remodelling during amlodipine treatment of hypertension.

Accumulation of 8-oxo-deoxyguanosine in cardiovascular tissues with the development of hypertension

Accumulation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in DNA is associated with mutagenesis and cell death. Little attention has been given to the biological significance of 8-oxo-dG accumulation in cardiovascular tissues during the different stage of hypertension and its prevention. We thus investigated the levels and localization of both 8-oxo-dG accumulation and expression of MTH1, which hydrolyzes 8-oxo-dGTP to prevent its incorporation into DNA, in the thoracic aorta prepared from stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wister-Kyoto rats (WKY), aged 5-32 weeks. HPLC-MS/MS analysis revealed that the levels of nuclear 8-oxo-dG in the aorta increased significantly in SHRSP, but not WKY, with aging. Immunohistochemical study revealed that both TUNEL reactivity and 8-oxo-dG immunoreactivity were increased in smooth muscle cells (SMC) and endothelial cells (EC) of the aorta with aging, and they exhibited similar distributions in serial sections. The number of 8-oxo-dG and TUNEL positive cells in EC, but not in SMC, was significantly higher in SHRSP than WKY at 32 weeks of age. In contrast, the expression levels of Mth1mRNA and MTH1 protein in the aorta were similarly decreased both in SHRSP and WKY with aging. However, the number of MTH1 expressing EC was remarkably increased in the older SHRSP compared to the younger ones or age-matched WKY. Hypertension significantly increased not only 8-oxo-dG accumulation but also the expression of MTH1 in EC of the aorta during aging. While accumulation of 8-oxo-dG in SMC of the aorta was slightly increased, the expression of MTH1 protein in SMC was rather decreased by hypertension. We thus suggest that MTH1 may protect EC in the aorta from the oxidative damage increased by hypertension.

The protective effects of 17beta-estradiol on hepatic ischemia-reperfusion injury in rat model, associated with regulation of heat-shock protein expression

BACKGROUND

Ischemia-reperfusion (I/R) injury, which was commonly seen in the field of hepatic surgical intervention, impaired liver regeneration and predisposed to liver failure. Previous studies have shown gender dimorphic response of the liver for various hepatic stresses including I/R injury, hemorrhagic shock-resuscitation, liver cirrhosis, endotoxemia, and chronic alcoholic consumption, and demonstrated gender dimorphism in hepatocellular dysfunction after experimental trauma and hemorrhage. The objective of this study was to examine the hypothesis that the protective effects of 17beta-estradiol (E2) in hepatic I/R injury were associated with increasing heat-shock protein 70 expression.

MATERIALS AND METHODS

Sprague-Dawley male and female rats were randomly divided into male and female sham, I/R, and E2 + I/R groups. The model of reduced-size liver ischemia and reperfusion was used. Except for the sham-operated groups, all rats were subjected to 70% liver ischemia for 45 min followed by resection of the remaining 30% nonischemic lobes and reperfusion of ischemic tissue. For each group, five rats were used to investigate the survival during a week after operation; blood samples and liver tissues were obtained in the remaining animals after 3, 12, and 24 h of reperfusion to assess serum alanine aminotransferase, aspartate aminotransferase, liver tissue NO(2)(-) + NO(3)(-), malondialdehyde content, superoxide dismutase, nitric oxide synthase, and myeloperoxidase activity, Hsp70 expression, and apoptosis ratio.

RESULTS

Compared with I/R groups, male and female E2 + I/R groups showed less I/R-induced injury, and SOD and eNOS activity and Hsp70 expression were increased significantly (P < 0.01). A higher rate of apoptosis was observed in the I/R group versus the E2 + I/R group, a significant increase of MDA, NO(2)(-) + NO(3)(-), and MPO of liver tissues and serum transaminase were also observed in the I/R group versus the E2 + I/R group. The survival rate was significantly higher in the male E2 + I/R group than in the male I/R group.

CONCLUSION

E2 pretreatment had protective effects on liver in hepatic I/R injury. The mechanism of this protection might be related to overexpression of Hsp70.

Linkage analysis of neointimal hyperplasia and vascular wall transformation after balloon angioplasty

Neointimal hyperplasia (NIH), a result of vascular injury, is due to the migration and proliferation of smooth muscle cells through the media and internal elastic lamina leading to vascular occlusion. We used a rat model to find the genetic regions controlling NIH after endothelial denudation in two divergent inbred strains of rats. The Brown Norway (BN) and spontaneously hypertensive rat (SHR) strains have a 2.5-fold difference in injury-induced NIH. A population of 301 F2(SHR × BN) rats underwent a standard vascular injury followed by phenotyping 8 wk after injury to identify quantitative trait loci (QTL) responsible for this strain difference. Interval mapping identified two %NIH QTL on rat chromosomes 3 and 6 [logarithm of odds (LOD) scores 2.5, 2.2] and QTL for other injured vascular wall changes on rat chromosomes 3, 4, and 15 (LOD scores 2.0–4.6). Also, QTL for control vessel media width (MW) and media area (MA) were found on chromosome 6 with LOD scores of 2.3 and 2.5, suggesting that linkage exists between these control vessel parameters and NIH production. These results represent the first genetic analysis for the identification of NIH QTL and QTL associated with the vascular injury response.

Adverse interactions of rofecoxib with lisinopril in spontaneously hypertensive rats

BACKGROUND

Hypertension and arthritis are frequent comorbidities. Nonsteroidal anti-inflammatory drugs (NSAIDs) are well known to produce hypertension or attenuate the effects of antihypertensive agents in a few patients. The influence of selective NSAIDs on blood pressure and the cardiovascular and renal effects of coxibs have still to be investigated. The purpose of this study was to test the hypothesis that rofecoxib interferes with antihypertensive activity and cardiorenal protective effects of lisinopril in spontaneously hypertensive rats (SHRs).

METHODS

Twenty-one unanaesthetised, male spontaneously hypertensive rats (SHRs), 16 weeks old, were randomized to receive lisinopril (LS) 15 mg/kg/d or rofecoxib (RF) 20 mg/kg/d or combination of lisinopril (LS) and rofecoxib (RF) for 2 weeks. The arterial blood pressure changes were recorded each week. The Sodium Hydrogen Exchange (NHE) activity of erythrocytes was determined 2 weeks after the study. The surviving animals were sacrificed 24 h after the last dose, and the sections of their hearts and kidneys were assessed histologically for injury by a pathologist masked to the treatment.

RESULTS

RF completely prevented the hypotensive effects of LS during the first week of treatment but the antihypertensive efficacy of LS was restored during the second week of treatment. The NHE in erythrocytes of 18-week-old SHRs was found to be significantly lower than the age-matched Wistar rats (P < 0.05), and LS treatment reversed these values to Wistar control in SHRs. RF was devoid of any effect on NHE of erythrocytes. The histological examination revealed that the myocardial and renal protection induced by LS was attenuated by concomitant RF therapy.

CONCLUSIONS

These results indicate that COX-2 inhibitors should be used judiciously in patients with history of hypertension, ischemic heart disease, or chronic renal failure.

The effects of quinapril and atorvastatin on artery structure and function in adult spontaneously hypertensive rats

We studied the combined treatment effects of quinapril and atorvastatin on blood pressure and structure and function of resistance arteries from adult spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY rats). Apoptotic cells were identified by in situ end labeling using the terminal deoxynucleotide transferase-mediated dUTP nick end labeling method. Vascular structure was measured using a morphometric protocol and confocal microscopy and a pressurized artery system was used to study vascular functions. We found that a combined treatment with quinapril and atorvastatin lowered systolic blood pressure in both adult SHR and WKY rats and decreased medial thickness and volume and the number of smooth muscle cell layers in mesenteric arteries, as well as media-to-lumen ratio in the interlobular arteries from SHR but not in those from WKY rats. The number of apoptotic smooth muscle cells was higher in the mesenteric arteries from control WKY rats than control SHR and treatment increased the number of apoptotic smooth muscle cells in the arteries from both SHR and WKY rats. Treatment with quinapril and atorvastatin reduced ventricular weight in SHR and normalized the augmented contractile responses to norepinephrine but did not alter the contraction to electric field stimulation. Relaxation responses to acetylcholine and sodium nitroprusside were not affected by the treatment. We conclude that a combined treatment with quinapril and atorvastatin lowered blood pressure and improved cardiac and vessel hypertrophy and vessel function. An increase in apoptotic smooth muscle cells may be one of the mechanisms underlying the structural improvement.

Exercise training attenuates blood pressure elevation and adverse remodeling in the aorta of spontaneously hypertensive rats

OBJECTIVE

To observe the extracellular matrix modifications and quantify the structural alterations of the aortic wall in spontaneously hypertensive rats (SHR) submitted to an aerobic physical activity (PA) protocol.

MATERIAL AND METHODS

Three groups of five rats each were studied: sedentary normotensive Wistar rats (SED-Wistar) and SHR (divided in SHR that underwent a 1 h/day 5 days/week PA for 20 weeks (EX-SHR) and those that were restricted to cage-bound activity (SED-SHR).

RESULTS

BP was lower in EX-SHRs and SED-Wistar rats (-35%) than in SED-SHRs. This difference became significant from the 3rd week of PA. The wall thickness was smaller in the EX-SHR and SED-Wistar (-45%) than in the SED-SHR (p<0.0001). In EX-SHR group, oxytalan and elaunin fibers were more pronounced than in the other groups, while SED-SHR and SED-Wistar rats showed an equivalent appearance of aortic elaunin fibers. EX-SHR and SED-Wistar rats showed more than 65% greater smooth muscle nuclei numerical density per unit area than SED-SHRs while SED-SHRs showed more than 45% smaller surface density of lamellae than both EX-SHR and SED-Wistar rats. However, no quantitative differences were found in the aortic wall comparing EX-SHR and SED-Wistar rats.

CONCLUSION

PA might alter the aortic wall remodeling to adapt the artery to a hyperkinetic blood flow resulting in alterations of the extracellular matrix modulation and vascular resistance.

A quantitative trait locus for aortic smooth muscle cell number acting independently of blood pressure: implicating the angiotensin receptor AT1B gene as a candidate

Vascular hyperplasia may be involved in the remodeling of vasculature. It was unknown whether there were genetic determinants for aortic smooth muscle cell number (SMCN) and, if so, whether they acted independently of those for blood pressure (BP). To unravel this issue, we utilized congenic strains previously constructed for BP studies. These strains were made by replacing various chromosome 2 segments of the Dahl salt-sensitive (S) rat with those of the Milan normotensive rat (MNS). We measured and compared SMCN in aortic cross-sectional areas and BPs of these strains. Consequently, a quantitative trait locus (QTL) for SMCN was localized to a chromosome region not containing a BP QTL, but harboring the locus for the angiotensin II receptor AT1B (Agtr1b). Agtr1b became a candidate for the SMCN QTL because 1) two significant mutations were found in the coding region between S and all congenic strains possessing the MNS alleles, and 2) contractile responses to angiotensin II were significantly and selectively reduced in congenic rats harboring the MNS alleles of the SMCN QTL compared with S rats. The current investigation presents the first line of evidence that a QTL for aortic SMCN exists, and it acts independently of QTLs for BP. The relevant congenic strains developed therein potentially provide novel mammalian models for the studies of vascular remodeling disorders.

Regulation of therapeutic apoptosis: a potential target in controlling hypertensive organ damage

Cell growth and survival are potential therapeutic targets for the control of complications associated with hypertension. In most cardiovascular disorders, cardiac fibroblasts and large-vessel smooth muscle cells can replicate and thus contribute to the disease. We propose that cardiovascular hyperplasia may be reversed via therapeutic apoptosis induction with drugs that are safe and already used in the clinic. We first reported that, irrespective of the drug class, those drugs that are able to induce regression of cardiovascular hypertrophy are also able to reverse cardiovascular hyperplasia via apoptosis. Drugs active in this regard include inhibitors of the renin-angiotensin system, calcium channel blockers, and beta-blockers. Moreover, the effects of these drugs on cell survival is not merely secondary to blood pressure reduction. Therapeutic apoptosis in the cardiovascular system of the spontaneously hypertensive rat is characterized by a rapid and transient onset following initiation of antihypertensive treatment. Herein, the induction and termination of therapeutic apoptosis during drug treatment of hypertension will be briefly reviewed and supported by novel data suggesting that reversal of cardiovascular hyperplasia is associated with reduced cell growth and a resistance to further induction of therapeutic apoptosis, as shown in spontaneously hypertensive rats receiving an intermittent regime of nifedipine therapy. We propose that the presence of a cell subpopulation with defective cell cycle regulation may determine organ susceptibility to undergo therapeutic apoptosis.Key words: apoptosis, hypertension, hyperplasia, growth, nifedipine.

Quinapril effects on resistance artery structure and function in hypertension

The effects of chronic treatment with quinapril on blood pressure, vascular reactivity and structure of resistance arteries were examined in adult, male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. SHR and WKY at 15 weeks of age were treated with quinapril (10 mg/kg per day) for 10 weeks. Structural changes in the mesenteric arteries were measured by optical sectioning with confocal microscopy and in renal arteries by light microscopic measurements. Apoptotic cells in the mesenteric vessel wall were identified using the terminal deoxynucleotide transferase-mediated dUTP-nick end-labelling (TUNEL) method. The response of mesenteric arteries to noradrenaline, electrical stimulation, acetylcholine and sodium nitroprusside was studied using a pressure myograph system. Treatment with quinapril significantly lowered systolic blood pressure and ventricular weight in both SHR and WKY. It reduced wall thickness and medial volume in mesenteric arteries from SHR and WKY and media-to-lumen ratio in interlobular arteries of SHR. It also decreased the number of smooth muscle layers in SHR and increased the number of apoptotic smooth muscle cells in both SHR and WKY. In addition, treatment normalized the augmented contractile responses and improved the impaired relaxation response of SHR mesenteric arteries to the level of WKY. We conclude that treatment with quinapril lowered blood pressure and improved cardiac and vessel structure and vessel function. An increase in apoptotic process of medial smooth muscle cells is one of the mechanisms underlying the vascular structural improvement.

Synergistic interaction between enalapril, L-arginine and tetrahydrobiopterin in smooth muscle cell apoptosis and aortic remodeling induction in SHR

Smooth muscle cell (SMC) apoptosis occurs at the onset of enalapril-induced regression of aortic hypertrophy in SHR. A potential mechanism is the correction of endothelial dysfunction (ED) leading to reduced production of reactive oxygen species and enhanced bioavailability of nitric oxide (NO), a potent apoptosis inducer. Stimulants of NO include the precursor L-arginine and the NO synthase cofactor tetrahydrobiopterin (BH(4)), which correct ED in several models. The objective was to examine the relationships between ED and the cell growth/death balance during vascular remodeling induced by enalapril in SHR. SHR, 10-week-old, received enalapril (ENA: 30 mg x kg(-1) x day(-1) p.o.) for 1 or 2 weeks, or a co-treatment of L-arginine (2.0 g x kg(-1) x day(-1) p.o.) and BH(4) (5.4 mg x kg(-1) x day(-1) i.p. twice daily) administered alone (group: LB) or in combination with enalapril (ENA+LB) for 1 week. Controls received vehicle. After 1 week, ED was completely corrected with LB but not affected significantly by ENA, whereas both treatments failed to induce SMC apoptosis or aortic remodeling. The correction of ED and the induction of SMC apoptosis (3.3-fold increase in TUNEL labeling) required 2 weeks of ENA treatment. The combination of LB with ENA for 1 week, however, was additive for the reduction of SMC proliferation, and synergistic for the induction of apoptosis and regression of vascular hypertrophy. These interactions were independent of blood pressure regulation. Our results suggest that the correction of ED is not sufficient to induce SMC apoptosis and vascular remodeling, although it facilitates these responses during enalapril treatment.

Kinin B2 receptor is not involved in enalapril-induced apoptosis and regression of hypertrophy in spontaneously hypertensive rat aorta: possible role of B1 receptor

1. Treatment with enalapril induces smooth muscle cell apoptosis and regression of aortic hypertrophy in spontaneously hypertensive rats (SHRs), whereas combined blockade of angiotensin II AT(1) and AT(2) receptors does not. We postulated that vascular apoptosis with enalapril involves enhanced half-life of bradykinin (BK) and kinin B(2) receptor stimulation. 2. SHR, 11-weeks old, were treated for 4 weeks with enalapril (30 mg kg(-1) day(-1)), Hoe 140 (500 microg kg(-1) day(-1); B(2) receptor antagonist), alone or in combination. Controls received vehicle. 3. The half-life of hypotensive responses to intra-arterial bolus injections of BK were significantly increased in SHR anesthetized after 4 weeks of enalapril, an effect prevented by Hoe 140. The magnitude of BK-induced hypotension was significantly attenuated in all rats treated with Hoe 140. 4. As compared to placebo, enalapril treatment significantly reduced blood pressure (-34+/-2%), aortic hypertrophy (-20+/-3%), hyperplasia (-37+/-5%) and DNA synthesis (-61+/-8%), while it increased aortic DNA fragmentation by two-fold. Hoe 140 given alone or in combination with enalapril affected none of these parameters. 5. As a possible alternative mechanism, aortae isolated during the second week of enalapril treatment showed a transient upregulation of contractile responses to des-Arg(9)BK (EC(50)<1 nM), which were significantly reduced by [Leu(8)]des-Arg(9)BK (10 microM). Moreover, in vitro receptor autoradiography revealed an increase in expression of B(1) and B(2) receptor binding sites by 8-11 days of enalapril treatment. 6. Aortic apoptosis induction and hypertrophy regression with enalapril do not involve kinin B(2) receptors in SHR. Kinins acting via B(1) receptors remains a candidate mechanism.

Calphostin-C induction of vascular smooth muscle cell apoptosis proceeds through phospholipase D and microtubule inhibition

Calphostin-C, a protein kinase C inhibitor, induces apoptosis of cultured vascular smooth muscle cells. However, the mechanisms are not completely defined. Because apoptosis of vascular smooth muscle cells is critical in several proliferating vascular diseases such as atherosclerosis and restenosis after angioplasty, we decided to investigate the mechanisms underlying the calphostin-C-induced apoptotic pathway. We show here that apoptosis is inhibited by the addition of exogenous phosphatidic acid, a metabolite of phospholipase D (PLD), and that calphostin-C inhibits completely the activities of both isoforms of PLD, PLD1 and PLD2. Overexpression of either PLD1 or PLD2 prevented the vascular smooth muscle cell apoptosis induced by serum withdrawal but not the calphostin-C-elicited apoptosis. These data suggest that PLDs have anti-apoptotic effects and that complete inhibition of PLD activity by calphostin-C induces smooth muscle cell apoptosis. We also report that calphostin-C induced microtubule disruption and that the addition of exogenous phosphatidic acid inhibits calphostin-C effects on microtubules, suggesting a role for PLD in stabilizing the microtubule network. Overexpressing PLD2 in Chinese hamster ovary cells phenocopies this result, providing strong support for the hypothesis. Finally, taxol, a microtubule stabilizer, not only inhibited the calphostin-C-induced microtubule disruption but also inhibited apoptosis. We therefore conclude that calphostin-C induces apoptosis of cultured vascular smooth muscle cells through inhibiting PLD activity and subsequent microtubule polymerization.