What type of cell death occurs in chronic cerebral hypoperfusion? A review focusing on pyroptosis and its potential therapeutic implications

Chronic cerebral hypoperfusion (CCH) is a major global disease with chronic cerebral blood flow reduction. It is also the main cause of cognitive impairment and neurodegenerative diseases. Pyroptosis, a novel form of cell death, is characterized by the rupture of the cell membrane and the release of pro-inflammatory mediators. In recent years, an increasing number of studies have identified the involvement of pyroptosis and its mediated inflammatory response in the pathological process of CCH. Therefore, preventing the activation of pyroptosis following CCH is beneficial to inhibit the inflammatory cascade and reduce brain injury. In this review, we discuss the research progress on the relationship between pyroptosis and CCH, in order to provide a reference for research in related fields.

Indazole and its Derivatives in Cardiovascular Diseases: Overview, Current Scenario, and Future Perspectives

Indazoles are a class of heterocyclic compounds with a bicyclic ring structure composed of a pyrazole ring and a benzene ring. Indazole-containing compounds with various functional groups have important pharmacological activities and can be used as structural motifs in designing novel drug molecules. Some of the indazole-containing molecules are approved by FDA and are already in the market. However, very few drugs with indazole rings have been developed against cardiovascular diseases. This review aims to summarize the structural and pharmacological functions of indazole derivatives which have shown efficacy against cardiovascular pathologies in experimental settings.

Tetrahydrobiopterin paradoxically mediates cardiac oxidative stress and mitigates ethanol-evoked cardiac dysfunction in conscious female rats

Oxidation of tetrahydrobiopterin (BH4), a cofactor of nitric oxide synthase (NOS), by reactive oxidative species (ROS), leads to NOS uncoupling and superoxide production instead of NO. Further, oxidative stress plays a major role in ethanol-evoked cardiac dysfunction in proestrus female rats, and acute ethanol administration reduces brain BH4 level. Therefore, we discerned the unknown role of BH4 in ethanol-evoked cardiac dysfunction by pharmacologically increasing BH4 levels or inhibiting its effect in proestrus female rats. Acute ethanol (1.5 g/kg, i.v, 30 min) caused myocardial dysfunction (lowered dP/dtmax and LVDP) and hypotension, along with increases in myocardial: (i) levels of NO, ROS and malondialdehyde (MDA), (ii) activities of catalase, ALDH2 and NADPH oxidase (Nox), and (iii) phosphorylation of eNOS, nNOS. Further, ethanol suppressed myocardial arginase and superoxide dismutase (SOD) activities and enhanced eNOS uncoupling. While ethanol had no effect on cardiac BH4 levels, BH4 (19 mg/kg, i.v) supplementation paradoxically caused cardiac oxidative stress, but mitigated the cardiac dysfunction/hypotension and most of the adverse molecular responses caused by ethanol. Equally important, the BH4 inhibitor DAHP (1 g/kg, i.p) exacerbated the adverse molecular and cardiovascular effects caused by ethanol. Our pharmacological studies support a protective role for the NOS co-factor BH4 against ethanol-evoked cardiac dysfunction and hypotension in female rats.

Pharmacological Treatment of Vascular Dementia: A Molecular Mechanism Perspective

Vascular dementia (VaD) is a neurodegenerative disease, with cognitive dysfunction attributable to cerebrovascular factors. At present, it is the second most frequently occurring type of dementia in older adults (after Alzheimer's disease). The underlying etiology of VaD has not been completely elucidated, which limits its management. Currently, there are no approved standard treatments for VaD. The drugs used in VaD are only suitable for symptomatic treatment and cannot prevent or reduce the occurrence and progression of VaD. This review summarizes the current status of pharmacological treatment for VaD, from the perspective of the molecular mechanisms specified in various pathogenic hypotheses, including oxidative stress, the central cholinergic system, neuroinflammation, neuronal apoptosis, and synaptic plasticity. As VaD is a chronic cerebrovascular disease with multifactorial etiology, combined therapy, targeting multiple pathophysiological factors, may be the future trend in VaD.

Levosimendan prevents doxorubicin-induced cardiotoxicity in time- and dose-dependent manner: implications for inotropy

AIMS

Levosimendan (LEVO) a clinically-used inodilator, exerts multifaceted cardioprotective effects. Case-studies indicate protection against doxorubicin (DXR)-induced cardiotoxicity, but this effect remains obscure. We investigated the effect and mechanism of different regimens of levosimendan on sub-chronic and chronic doxorubicin cardiotoxicity.

METHODS AND RESULTS

Based on preliminary in vivo experiments, rats serving as a sub-chronic model of doxorubicin-cardiotoxicity and were divided into: Control (N/S-0.9%), DXR (18 mg/kg-cumulative), DXR+LEVO (LEVO, 24 μg/kg-cumulative), and DXR+LEVO (acute) (LEVO, 24 μg/kg-bolus) for 14 days. Protein kinase-B (Akt), endothelial nitric oxide synthase (eNOS), and protein kinase-A and G (PKA/PKG) pathways emerged as contributors to the cardioprotection, converging onto phospholamban (PLN). To verify the contribution of PLN, phospholamban knockout (PLN-/-) mice were assigned to PLN-/-/Control (N/S-0.9%), PLN-/-/DXR (18 mg/kg), and PLN-/-/DXR+LEVO (ac) for 14 days. Furthermore, female breast cancer-bearing (BC) mice were divided into: Control (normal saline 0.9%, N/S 0.9%), DXR (18 mg/kg), LEVO, and DXR+LEVO (LEVO, 24 μg/kg-bolus) for 28 days. Echocardiography was performed in all protocols. To elucidate levosimendan's cardioprotective mechanism, primary cardiomyocytes were treated with doxorubicin or/and levosimendan and with N omega-nitro-L-arginine methyl ester (L-NAME), DT-2, and H-89 (eNOS, PKG, and PKA inhibitors, respectively); cardiomyocyte-toxicity was assessed. Single bolus administration of levosimendan abrogated DXR-induced cardiotoxicity and activated Akt/eNOS and cAMP-PKA/cGMP-PKG/PLN pathways but failed to exert cardioprotection in PLN-/- mice. Levosimendan's cardioprotection was also evident in the BC model. Finally, in vitro PKA inhibition abrogated levosimendan-mediated cardioprotection, indicating that its cardioprotection is cAMP-PKA dependent, while levosimendan preponderated over milrinone and dobutamine, by ameliorating calcium overload.

CONCLUSION

Single dose levosimendan prevented doxorubicin cardiotoxicity through a cAMP-PKA-PLN pathway, highlighting the role of inotropy in doxorubicin cardiotoxicity.

Protein kinase D activation induces mitochondrial fragmentation and dysfunction in cardiomyocytes

KEY POINTS

Abnormal mitochondrial morphology and function in cardiomyocytes are frequently observed under persistent Gq protein-coupled receptor (Gq PCR) stimulation. Cardiac signalling mechanisms for regulating mitochondrial morphology and function under pathophysiological conditions in the heart are still poorly understood. We demonstrate that a downstream kinase of Gq PCR, protein kinase D (PKD) induces mitochondrial fragmentation via phosphorylation of dynamin-like protein 1 (DLP1), a mitochondrial fission protein. The fragmented mitochondria enhance reactive oxygen species generation and permeability transition pore opening in mitochondria, which initiate apoptotic signalling activation. This study identifies a novel PKD-specific substrate in cardiac mitochondria and uncovers the role of PKD on cardiac mitochondria, with special emphasis on the molecular mechanism(s) underlying mitochondrial injury with abnormal mitochondrial morphology under persistent Gq PCR stimulation. These findings provide new insights into the molecular basis of cardiac mitochondrial physiology and pathophysiology, linking Gq PCR signalling with the regulation of mitochondrial morphology and function.

ABSTRACT

Regulation of mitochondrial morphology is crucial for the maintenance of physiological functions in many cell types including cardiomyocytes. Small and fragmented mitochondria are frequently observed in pathological conditions, but it is still unclear which cardiac signalling pathway is responsible for regulating the abnormal mitochondrial morphology in cardiomyocytes. Here we demonstrate that a downstream kinase of Gq protein-coupled receptor (Gq PCR) signalling, protein kinase D (PKD), mediates pathophysiological modifications in mitochondrial morphology and function, which consequently contribute to the activation of apoptotic signalling. We show that Gq PCR stimulation induced by α1 -adrenergic stimulation mediates mitochondrial fragmentation in a fission- and PKD-dependent manner in H9c2 cardiac myoblasts and rat neonatal cardiomyocytes. Upon Gq PCR stimulation, PKD translocates from the cytoplasm to the outer mitochondrial membrane (OMM) and phosphorylates a mitochondrial fission protein, dynamin-like protein 1 (DLP1), at S637. PKD-dependent phosphorylation of DLP1 initiates DLP1 association with the OMM, which then enhances mitochondrial fragmentation, mitochondrial superoxide generation, mitochondrial permeability transition pore opening and apoptotic signalling. Finally, we demonstrate that DLP1 phosphorylation at S637 by PKD occurs in vivo using ventricular tissues from transgenic mice with cardiac-specific overexpression of constitutively active Gαq protein. In conclusion, Gq PCR-PKD signalling induces mitochondrial fragmentation and dysfunction via PKD-dependent DLP1 phosphorylation in cardiomyocytes. This study is the first to identify a novel PKD-specific substrate, DLP1 in mitochondria, as well as the functional role of PKD in cardiac mitochondria. Elucidation of these molecular mechanisms by which PKD-dependent enhanced fission mediates cardiac mitochondrial injury will provide novel insight into the relationship among mitochondrial form, function and Gq PCR signalling.

Gender and tachycardia: independent modulation of platelet reactivity in patients with atrial fibrillation

Background

Female patients with atrial fibrillation (AF) experience increased risk of thromboembolism compared to males, an observation that is reflected by its inclusion in the CHA₂DS₂VASc score. New onset AF (often associated with tachycardia) also confers upon patients increased thromboembolic risk. The mechanisms underlying this risk are uncertain, but new onset AF is associated with profound impairment of platelet nitric oxide (NO) signalling. Given that cardiovascular responses to catecholamines are gender-dependent, and that the presence of tachycardia in new onset AF may represent a response to catecholaminergic stimulation, we explored the potential impact of gender and tachycardia on platelet aggregation and NO signalling.

Methods

Interactions were sought in 87 AF patients between the extent of adenosine diphosphate (ADP)-induced platelet aggregation, the anti-aggregatory effects of the NO donor, sodium nitroprusside, gender, and admission heart rate. The potential impact of platelet expression of thioredoxin-interacting protein (Txnip) was also evaluated.

Results

Analysis of covariance confirmed the presence of physiological antagonism between platelet ADP and NO responses [F (1, 74) = 12.212, P < 0.01], while female sex correlated with impaired NO responses independent of platelet aggregability [F (2, 74) = 8.313, P < 0.01]. Admission heart rate correlated directly with platelet aggregation (r = 0.235, P < 0.05), and inversely with NO response (r = −0.331, P < 0.01). Txnip expression varied neither with gender nor with heart rate.

Conclusions

These results indicate that gender and heart rate are independent determinants of platelet function. Prospective studies of the putative benefit of reversal of tachycardia on restoration of normal platelet function are therefore a priority.

Vascular endothelial growth factor recovers suppressed cytochrome c oxidase activity by restoring copper availability in hypertrophic cardiomyocytes

Cardiomyocyte hypertrophy induced by phenylepherine (PE) is accompanied by depression of cytochrome c oxidase (COX) activity. Vascular endothelial growth factor (VEGF) recovers the suppressed COX activity and reverses cardiomyocyte hypertrophy. Because PE causes intracellular copper (Cu) depletion and COX activity is Cu-dependent, the present study was undertaken to test the hypothesis that VEGF recovers suppressed COX activity by restoring Cu availability. Primary cultures of neonatal rat cardiomyocytes were treated with PE at a final concentration of 100 µmol/L in cultures for 48 h to induce cell hypertrophy. The hypertrophic cardiomyocytes were exposed to VEGF at a final concentration of 20 ng/mL in cultures for 24 h. Atomic absorption spectrometry analysis revealed that VEGF restored PE-depleted Cu concentrations in hypertrophic cardiomyocytes along with the recovery of COX activity. Western blot analysis showed that protein contents of COX subunit COX-IV and Cu chaperones for COX (COX17, COX11, and SCO2) were decreased in response to PE treatment, and recovered after VEGF treatment. In addition, VEGF treatment suppressed PE-induced accumulation of reactive oxygen species (ROS) and the relevant elevation of homocysteine, which has been shown to form complexes with Cu to restrict Cu availability. This study thus demonstrates that VEGF recovers PE-suppressed COX activity by restoring Cu availability and VEGF suppression of ROS accumulation and homocysteine elevation would contribute to the increased Cu availability.

Early NADPH oxidase-2 activation is crucial in phenylephrine-induced hypertrophy of H9c2 cells

Reactive oxygen species (ROS) produced by different NADPH oxidases (NOX) play a role in cardiomyocyte hypertrophy induced by different stimuli, such as angiotensin II and pressure overload. However, the role of the specific NOX isoforms in phenylephrine (PE)-induced cardiomyocyte hypertrophy is unknown. Therefore we aimed to determine the involvement of the NOX isoforms NOX1, NOX2 and NOX4 in PE-induced cardiomyocyte hypertrophy. Hereto rat neonatal cardiomyoblasts (H9c2 cells) were incubated with 100 μM PE to induce hypertrophy after 24 and 48h as determined via cell and nuclear size measurements using digital imaging microscopy, electron microscopy and an automated cell counter. Digital-imaging microscopy further revealed that in contrast to NOX1 and NOX4, NOX2 expression increased significantly up to 4h after PE stimulation, coinciding and co-localizing with ROS production in the cytoplasm as well as the nucleus. Furthermore, inhibition of NOX-mediated ROS production with apocynin, diphenylene iodonium (DPI) or NOX2 docking sequence (Nox2ds)-tat peptide during these first 4h of PE stimulation significantly inhibited PE-induced hypertrophy of H9c2 cells, both after 24 and 48h of PE stimulation. These data show that early NOX2-mediated ROS production is crucial in PE-induced hypertrophy of H9c2 cells.

Homocysteine restricts copper availability leading to suppression of cytochrome C oxidase activity in phenylephrine-treated cardiomyocytes

Cardiomyocyte hypertrophy induced by phenylephrine (PE) is accompanied by suppression of cytochrome c oxidase (CCO) activity, and copper (Cu) supplementation restores CCO activity and reverses the hypertrophy. The present study was aimed to understand the mechanism of PE-induced decrease in CCO activity. Primary cultures of neonatal rat cardiomyocytes were treated with PE at a final concentration of l00 µM in cultures for 72 h to induce cell hypertrophy. The CCO activity was determined by enzymatic assay and changes in CCO subunit COX-IV as well as copper chaperones for CCO (COX17, SCO2, and COX11) were determined by Western blotting. PE treatment increased both intracellular and extracellular homocysteine concentrations and decreased intracellular Cu concentrations. Studies in vitro found that homocysteine and Cu form complexes. Inhibition of the intracellular homocysteine synthesis in the PE-treated cardiomyocytes prevented the increase in the extracellular homocysteine concentration, retained the intracellular Cu concentration, and preserved the CCO activity. PE treatment decreased protein concentrations of the COX-IV, and the Cu chaperones COX17, COX11, and SCO2. These PE effects were prevented by either inhibition of the intracellular homocysteine synthesis or Cu supplementation. Therefore, PE-induced elevation of homocysteine restricts Cu availability through its interaction with Cu and suppression of Cu chaperones, leading to the decrease in CCO enzyme activity.

Stimulation of σ1-receptor restores abnormal mitochondrial Ca²⁺ mobilization and ATP production following cardiac hypertrophy

BACKGROUND

We previously reported that the σ1-receptor (σ1R) is down-regulated following cardiac hypertrophy and dysfunction in transverse aortic constriction (TAC) mice. Here we address how σ1R stimulation with the selective σ1R agonist SA4503 restores hypertrophy-induced cardiac dysfunction through σ1R localized in the sarcoplasmic reticulum (SR).

METHODS

We first confirmed anti-hypertrophic effects of SA4503 (0.1-1μM) in cultured cardiomyocytes exposed to angiotensin II (Ang II). Then, to confirm the ameliorative effects of σ1R stimulation in vivo, we administered SA4503 (1.0mg/kg) and the σ1R antagonist NE-100 (1.0mg/kg) orally to TAC mice for 4weeks (once daily).

RESULTS

σ1R stimulation with SA4503 significantly inhibited Ang II-induced cardiomyocyte hypertrophy. Ang II exposure for 72h impaired phenylephrine (PE)-induced Ca(2+) mobilization from the SR into both the cytosol and mitochondria. Treatment of cardiomyocytes with SA4503 largely restored PE-induced Ca(2+) mobilization into mitochondria. Exposure of cardiomyocytes to Ang II for 72h decreased basal ATP content and PE-induced ATP production concomitant with reduced mitochondrial size, while SA4503 treatment completely restored ATP production and mitochondrial size. Pretreatment with NE-100 or siRNA abolished these effects. Chronic SA4503 administration also significantly attenuated myocardial hypertrophy and restored ATP production in TAC mice. SA4503 administration also decreased hypertrophy-induced impairments in LV contractile function.

CONCLUSIONS

σ1R stimulation with the specific agonist SA4503 ameliorates cardiac hypertrophy and dysfunction by restoring both mitochondrial Ca(2+) mobilization and ATP production via σ1R stimulation.

GENERAL SIGNIFICANCE

Our observations suggest that σ1R stimulation represents a new therapeutic strategy to rescue the heart from hypertrophic dysfunction.

CaMKIIδB mediates aberrant NCX1 expression and the imbalance of NCX1/SERCA in transverse aortic constriction-induced failing heart

Ca²⁺/calmodulin-dependent protein kinase II δB (CaMKIIδB) is one of the predominant isoforms of CaMKII in the heart. The precise role of CaMKIIδB in the transcriptional cross-talk of Ca²⁺-handling proteins during heart failure remains unclear. In this work, we aim to determine the mechanism of CaMKIIδB in modulating the expression of sarcolemmal Na⁺–Ca²⁺ exchange (NCX1). We also aim to address the potential effects of calmodulin antagonism on the imbalance of NCX1 and sarcoendoplasmic reticulum Ca²⁺ ATPase (SERCA) during heart failure. Eight weeks after transverse aortic constriction (TAC)-induced heart failure in mice, we found that the heart weight/tibia length (HW/TL) ratio and the lung weight/body weight (LW/BW) ratio increased by 59% and 133%, respectively. We further found that the left ventricle-shortening fraction decreased by 40% compared with the sham-operated controls. Immunoblotting revealed that the phosphorylation of CaMKIIδB significantly increased 8 weeks after TAC-induced heart failure. NCX1 protein levels were also elevated, whereas SERCA2 protein levels decreased in the same animal model. Moreover, transfection of active CaMKIIδB significantly increased NCX1 protein levels in adult mouse cardiomyocytes via class IIa histone deacetylase (HDAC)/myocyte enhancer factor-2 (MEF2)-dependent signaling. In addition, pharmacological inhibition of calmodulin/CaMKIIδB activity improved cardiac function in TAC mice, which partially normalized the imbalance between NCX1 and SERCA2. These data identify NCX1 as a cellular target for CaMKIIδB. We also suggest that the CaMKIIδB-induced imbalance between NCX1 and SERCA2 is partially responsible for the disturbance of intracellular Ca²⁺ homeostasis and the pathological process of heart failure.

Biophysical properties and functional consequences of reactive oxygen species (ROS)-induced ROS release in intact myocardium

Reactive oxygen species (ROS)-induced ROS release (RIRR) is a fundamental mechanism by which cardiac mitochondria respond to elevated ROS levels by stimulating endogenous ROS production in a regenerative, autocatalytic process that ultimately results in global oxidative stress (OS), cellular dysfunction and death. Despite elegant studies describing the phenomenon of RIRR under artificial conditions such as photo-induced oxidation of discrete regions within cardiomyocytes, the existence, biophysical properties and functional consequences of RIRR in intact myocardium remain unclear. Here, we used a semi-quantitative approach of optical superoxide (O(2)(-)) mapping using dihydroethidium (DHE) fluorescence to explore RIRR, its arrhythmic consequences and underlying mechanisms in intact myocardium. Initially, perfusion of rat hearts with 200 μM H(2)O(2) for 40 min (n = 4) elicited two distinct O(2)(-) peaks that were readily distinguished by their timing and amplitude. The first peak (P1), which was generated rapidly (within 5-8 min of H(2)O(2) perfusion) was associated with a relatively limited (10 ± 2%) rise in normalized O(2)(-) levels relative to baseline. In contrast, the second peak (P2) occurred 19-26 min following onset of H(2)O(2) perfusion and was associated with a significantly greater amplitude compared to P1. Spatio-temporal ROS mapping during P2 revealed active O(2)(-) propagation across the myocardium at a velocity of ~20 μm s(-1). Exposure of hearts (n = 18) to a short (10 min) episode of H(2)O(2) perfusion revealed consistent generation of P2 by high (≥200 μM, 8/8) but not lower (≤100 μM, 3/8) H(2)O(2) concentrations (P < 0.03). In these hearts, onset of P2 occurred following, not during, the 10 min OS protocol, consistent with RIRR. Importantly, P2 (+) hearts exhibited a markedly greater (by 3.8-fold, P < 0.001) arrhythmia score compared to P2 (-) hearts. To explore the mechanism underlying RIRR in intact myocardium, hearts were perfused with either cyclosporin A (CsA) or 4-chlorodiazepam (4-Cl-DZP) to inhibit the mitochondrial permeability transition pore (mPTP) or the inner membrane anion channel (IMAC), respectively. Surprisingly, perfusion with CsA failed to suppress (P = 0.75, n.s.) or even delay H(2)O(2)-induced P2 or the incidence of arrhythmias compared to untreated hearts. In sharp contrast, perfusion with 4-Cl-DZP markedly blunted O(2)(-) levels during P2, and suppressed the incidence of sustained ventricular tachycardia or ventricular fibrillation (VT/VF). Finally, perfusion of hearts with the synthetic superoxide dismutase/catalase mimetic EUK-134 completely abolished the H(2)O(2)-mediated RIRR response as well as the incidence of arrhythmias. These findings extend the concept of RIRR to the level of the intact heart, establish regenerative O(2)(-) production as the mediator of RIRR-related arrhythmias and reveal their strong dependence on IMAC and not the mPTP in this acute model of OS.

Compensatory upregulation of the adenosine system following phenylephrine-induced hypertrophy in cultured rat ventricular myocytes

Adenosine has been shown to exert direct antihypertrophic effects on the heart, and plasma adenosine levels have been shown to be elevated in patients with heart failure. It has therefore been proposed that endogenously synthesized adenosine may function as a cardiac antihypertrophic factor. The present study was aimed to determine whether the adenosine system is altered in a potential adaptive manner following phenylephrine-induced hypertrophy in cultured neonatal rat ventricular myocytes. Phenylephrine produced significant hypertrophy as determined by cell size and atrial natriuretic peptide gene expression, which was accompanied by significantly increased gene and protein expression of adenosine A1, A2a, and A3 receptors. These effects and the hypertrophic response were prevented by the α1-adrenoceptor antagonist prazosin as well as pharmacological agonists for all adenosine receptor subtypes. The upregulation of adenosine receptors by phenylephrine was also abrogated by adenosine 5′-(α,β-methylene)diphosphate, an inhibitor of ectosolic 5′-nucleotidase. Moreover, phenylephrine significantly increased production of adenosine from myocytes in the presence of a nucleoside transport and adenosine deaminase inhibitor, the combination of which abrogated the hypertrophic effect of phenylephrine. The latter effect was reversed by adenosine receptor antagonists. Phenylephrine also produced a significant upregulation in expression levels of equilibrative nucleoside transporter 1 although expression levels of equilibrative nucleoside transporter 2 were unaffected. Taken together, our results suggest an adaptive upregulation of the adenosine system to phenylephrine-induced cardiomyocyte hypertrophy that serves to limit the hypertrophic effect of α1-adrenoceptor activation.

Novel strategies and targets for the management of hypertension

Hypertension, as the sole or comorbid component of a constellation of disorders of the cardiovascular (CV) system, is present in over 90% of all patients with CV disease and affects nearly 74 million individuals in the United States. The number of medications available to treat hypertension has dramatically increased during the past 3 decades to some 50 medications as new targets involved in the normal regulation of blood pressure have been identified, resulting in the development of new agents in those classes with improved therapeutic profiles (e.g., renin-angiotensin-aldosterone system; RAAS). Despite these new agents, hypertension is not adequately managed in approximately 30% of patients, who are compliant with prescriptive therapeutics, suggesting that new agents and/or strategies to manage hypertension are still needed. Some of the newest classes of agents have targeted other components of the RAS, for example, the selective renin inhibitors, but recent advances in vascular biology have provided novel potential targets that may provide avenues for new agent development. These newer targets include downstream signaling participants in pathways involved in contraction, growth, hypertrophy, and relaxation. However, perhaps the most unique approach to the management of hypertension is a shift in strategy of using existing agents with respect to the time of day at which the agent is taken. This new strategy, termed "chronotherapy," has shown considerable promise in effectively managing hypertensive patients. Therefore, there remains great potential for future development of safe and effective agents and strategies to manage a disorder of the CV system of epidemic proportion.

Beta-amyloid accumulation in neurovascular units following brain embolism

Nitric oxide (NO) toxicity is in part mediated by generation of peroxynitrite with concomitant production of superoxide under pathological brain conditions such as ischemia and Alzheimer's disease. The pathophysiological relevance of endothelial nitric oxide synthase (eNOS) to brain embolism-induced neurovascular injury has not been documented. We found that microsphere embolism (ME)-induced aberrant eNOS expression in vascular endothelial cells likely mediates blood-brain barrier (BBB) disruption via peroxynitrite formation and in turn causes brain edema. We also demonstrated that a mild ME model was useful for investigating the sequential events of neurovascular injury followed by beta-amyloid accumulation and tau hyperphosphorylation. Indeed, immunoblotting of purified brain microvessels revealed that beta-amyloid accumulation significantly increased one week after ME induction and remained elevated for twelve weeks in those animals. Moreover, we also confirmed that peroxynitrite formation and eNOS uncoupling-mediated superoxide generation in microvessels are inhibited by a novel calmodulin inhibitor. Thus, peroxynitrite formation via elevated eNOS is associated with endothelial cell injury with concomitant beta-amyloid accumulation in microvessels of aged rats. In this review, we focus on the detrimental effects of eNOS expression following brain embolism and introduce an attractive model representing progressive Alzheimer's disease pathology in brain.