ACE inhibition accelerates endothelial regrowth in vivo: a possible explanation for the benefit observed with ACE inhibitors following arterial injury

"Amyloid-beta accumulation cycle" as a prevention and/or therapy target for Alzheimer's disease

The cell cycle and its regulators are validated targets for cancer drugs. Reagents that target cells in a specific cell cycle phase (e.g., antimitotics or DNA synthesis inhibitors/replication stress inducers) have demonstrated success as broad-spectrum anticancer drugs. Cyclin-dependent kinases (CDKs) are drivers of cell cycle transitions. A CDK inhibitor, flavopiridol/alvocidib, is an FDA-approved drug for acute myeloid leukemia. Alzheimer's disease (AD) is another serious issue in contemporary medicine. The cause of AD remains elusive, although a critical role of latent amyloid-beta accumulation has emerged. Existing AD drug research and development targets include amyloid, amyloid metabolism/catabolism, tau, inflammation, cholesterol, the cholinergic system, and other neurotransmitters. However, none have been validated as therapeutically effective targets. Recent reports from AD-omics and preclinical animal models provided data supporting the long-standing notion that cell cycle progression and/or mitosis may be a valid target for AD prevention and/or therapy. This review will summarize the recent developments in AD research: (a) Mitotic re-entry, leading to the "amyloid-beta accumulation cycle," may be a prerequisite for amyloid-beta accumulation and AD pathology development; (b) AD-associated pathogens can cause cell cycle errors; (c) thirteen among 37 human AD genetic risk genes may be functionally involved in the cell cycle and/or mitosis; and (d) preclinical AD mouse models treated with CDK inhibitor showed improvements in cognitive/behavioral symptoms. If the "amyloid-beta accumulation cycle is an AD drug target" concept is proven, repurposing of cancer drugs may emerge as a new, fast-track approach for AD management in the clinic setting.

Influence of valsartan-eluting stent on neointima formation

OBJECTIVE

#ENTITYSTARTX02014; This study is to explore the effect of valsartan-eluting stents on neointima formation after stenting and to elucidate possible mechanisms how locally used valsartan prevents in-stent restenosis (ISR).

METHOD

valsartan- and carriereluting stents were manufactured by using multi-layer-coated technology. Bare stents, carrier-eluting stents and valsartan- eluting stents were implanted into the abdominal aortas of the rabbits respectively. Quantitative angiography (QA) before, immediately after and 3 months after stent implantation were compared between the groups of bare (n=8), carrier-eluting (n=8) and valsartan-eluting stent (n=10), which allows the comparison of vascular diameters of aortas as well as indices of vascular neointimal formation, i.e. luminal area (LA), neointimal area (NIA), inner elastic membrane luminal area (IELA) and the maximal inner-membrane thickness (MIT) in 15 rabbits. α-Actin protein expression were detected by Envision two-step immunohistochemistry. Mean positive indices (MPI) of the above protein were analyzed semi-quantatively by IMS(Information Management System) cell image analysis system. MPI=positive area×OD (optical density). Collagen deposition in neointima was observed through MASSON stain among the three groups.

RESULT

#ENTITYSTARTX02014; the mean aortic diameters were similar in the three groups:bare stents group(n=8), carrier-eluting stents group(n=8) and valsartan eluting stents group(n=10) measured by QA at different time. A larger luminal area and a less neointimal hyperplasia in valsartan eluting-stents group was found compared with the other two groups. The mean luminal areas were 4345548±125822um(2); 4302061±167952 um(2); 5016269±207934um(2) respectively. The mean neointimal areas were 1119635±163503um(2); 1135636±136555um(2); 441577±74099um(2) and the mean maximal inner-membrane thickness were 210±30um;192±21um; 116±12um respectively. α-Actin protein expression was significantly lower in neointima of valsartan eluting-stents group than the other two groups. Through MASSON stain we found that Collagen was much richer in neointima of bare stents group and carrier-eluting stents group than valsartan eluting-stents group.

CONCLUSION

#ENTITYSTARTX02014; Valsartan eluting-stents inhibited neointimal hyperplasia after stenting by decreasing collagen deposition and smooth muscle cell proliferation. Therefore it would be potentially effective in preventing in-stent restenosis.

ABBREVIATIONS

#ENTITYSTARTX02014; Quantitative angiography (QA), luminal area (LA), neointimal area (NIA), inner elastic membrane luminal area (IELA), the maximal inner-membrane thickness (MIT), Mean positive indices (MPI), optical density (OD), Drugeluting stents (DES), in-stent restenosis(ISR), percutaneous transluminal coronary angioplasty (PTCA), angiotensin α type 2 receptor (AT2).

Estrogen receptor alpha expression in both endothelium and hematopoietic cells is required for the accelerative effect of estradiol on reendothelialization

OBJECTIVE

E2 accelerates reendothelialization through estrogen receptor alpha (ER alpha), and we now aimed at defining the precise local and systemic cellular actors of this process.

METHODS AND RESULTS

The respective roles of endothelial and hematopoietic targets of E2 were investigated in a mouse carotid injury model, using confocal microscopy, to follow endothelium repair. Grafting ER alpha(-/-) mice with ER alpha(+/+) bone marrow (BM) was not sufficient to restore the accelerative effect of E2 on reendothelialization, demonstrating the necessary role of extrahematopoietic ER alpha. Using an endothelial-specific inactivation of ER alpha (Cre-Lox system), we showed that endothelial ER alpha plays a pivotal role in this E2 action. Conversely, in ER alpha(+/+) grafted with ER alpha(-/-) BM, the E2 regenerative effect was abolished, demonstrating that ER alpha-expressing hematopoietic cells are also needed. As eNOS expression in BM was required for this action, both endothelial progenitor cells and platelets could be the hematopoietic targets that participate to this beneficial E2 effect.

CONCLUSIONS

We demonstrate that endothelial ER alpha plays a pivotal role in E2-mediated reendothelialization. However, endothelial targeting alone is not sufficient because the concomitant stimulation of a subpopulation of BM ER alpha is necessary. This cooperation should be taken into account in strategies aimed at optimizing in-stent reendothelialization.

ACE inhibition in hypertension: focus on perindopril

Ongoing developments in our understanding of cardiovascular disease, together with the introduction of new drugs to treat these conditions, has led to much debate over the optimal management of hypertension. The ALLHAT study showed no major differences in cardiovascular outcome among three major classes of antihypertensive drugs. Indeed, large meta-analyses have substantiated this view, and most experts would agree that BP reduction matters more than the choice of antihypertensive agent. However, recently published data from the ASCOT-BPLA trial for hypertensive patients at moderate risk of cardiac events have caused some experts to re-evaluate this view. The recent Blood Pressure Lowering Treatment Trialists' Collaboration publication confirmed this change. In the ASCOT-BPLA trial, antihypertensive therapy based on amlodipine+perindopril significantly reduced total and cardiovascular mortality as well as other clinically relevant outcomes in comparison with a traditional strategy based on atenolol and a thiazide diuretic, despite both regimens producing nonsignificantly different reductions in brachial BP. These findings suggest that amlodipine/perindopril may exert a beneficial effect by acting on other parameters such as central BP or BP variability. ACE inhibitors have been shown to have antiatherosclerotic and antithrombogenic effects, to improve endothelial dysfunction, and to prevent cardiac remodeling in patients with coronary heart disease. In this regard, perindopril, which has relatively high affinity for ACE and true 24-hour duration of action, is one of the most extensively studied ACE inhibitors. More recent data suggest that ACE inhibitors reduce arterial stiffness, an independent risk factor for cardiovascular events, and have a beneficial effect on central aortic BP, thus providing a possible explanation for the findings of ASCOT-BPLA and confirming that ACE inhibitors are an appropriate first choice for patients with hypertension.

Renin-Angiotensin System Intervention to Prevent In-Stent Restenosis

The occurrence of in-stent restenosis is a major drawback of percutaneous transluminal coronary angioplasty with stent placement. Target vessel revascularization is necessary in 15% of patients who receive a stent. Recent advances in the development of drug-eluting stents have reduced these numbers tremendously. However refinement of antirestenotic therapies remains obligatory. The emerging interest in more physiological antirestenotic therapies might unchain an interest in the well-known inhibitors of the rennin-angiotensin system (RAS), the angiotensin-converting enzyme inhibitors, and the angiotensin II type I receptor blockers. Contradictory results overshadow the discussion of whether intervention in the RAS could prevent in-stent restenosis. This review discusses the pathophysiology of in-stent restenosis, the role of the RAS in in-stent restenosis, and the possible role of RAS intervention in the prevention of in-stent restenosis.

The relevance of tissue angiotensin-converting enzyme: manifestations in mechanistic and endpoint data

Angiotensin-converting enzyme (ACE) is primarily localized (>90%) in various tissues and organs, most notably on the endothelium but also within parenchyma and inflammatory cells. Tissue ACE is now recognized as a key factor in cardiovascular and renal diseases. Endothelial dysfunction, in response to a number of risk factors or injury such as hypertension, diabetes mellitus, hypercholesteremia, and cigarette smoking, disrupts the balance of vasodilation and vasoconstriction, vascular smooth muscle cell growth, the inflammatory and oxidative state of the vessel wall, and is associated with activation of tissue ACE. Pathologic activation of local ACE can have deleterious effects on the heart, vasculature, and the kidneys. The imbalance resulting from increased local formation of angiotensin II and increased bradykinin degradation favors cardiovascular disease. Indeed, ACE inhibitors effectively reduce high blood pressure and exert cardio- and renoprotective actions. Recent evidence suggests that a principal target of ACE inhibitor action is at the tissue sites. Pharmacokinetic properties of various ACE inhibitors indicate that there are differences in their binding characteristics for tissue ACE. Clinical studies comparing the effects of antihypertensives (especially ACE inhibitors) on endothelial function suggest differences. More comparative experimental and clinical studies should address the significance of these drug differences and their impact on clinical events.

Inhibition of neointima by angiotensin-converting enzyme inhibitor in porcine coronary artery balloon-injury model

Because hepatocyte growth factor (HGF) stimulates growth of endothelial cells exclusively without replication of vascular smooth muscle cells, we hypothesized that HGF may play a role in cardiovascular disease. In human vascular smooth muscle cells, angiotensin II suppressed local vascular HGF production in a dose-dependent manner. Using a rat balloon-injury carotid artery model, we demonstrated that blockade of angiotensin II inhibited neointimal formation, accompanied by a significant increase in local HGF production. However, the relation of vascular HGF to endothelial function was not clarified. Moreover, it is important to test the hypothesis in animal models that are more similar to human restenosis. Thus, in the present study, we used a porcine coronary artery balloon-injury model to study the role of angiotensin II in regulation of the local HGF system in vivo. Expression of HGF mRNA was significantly decreased in balloon-injured coronary arteries versus intact vessels. An angiotensin-converting enzyme (ACE) inhibitor (perindopril) significantly inhibited neointimal formation after balloon injury compared with vehicle (P:<0.05). In addition, vasodilator response of balloon-injured coronary arteries to bradykinin was restored by perindopril treatment, whereas no vasodilator response was observed in balloon-injured vessels treated with vehicle. Vasodilator response of balloon-injured arteries induced by perindopril was completely abolished by N:(w)-nitro-L-arginine methyl ester. Of particular interest, vascular HGF mRNA was significantly increased in balloon-injured vessels treated with perindopril as compared with vehicle. Overall, the present study demonstrated that ACE inhibitor significantly inhibited neointimal formation, accompanied by significant improvement of endothelial dysfunction and a significant increase in local vascular HGF mRNA in vivo in a porcine coronary artery balloon-injury model. Given the strong mitogenic activity of HGF on endothelial cells, improvement of endothelial dysfunction by perindopril might be due to increased local HGF expression through enhancement of reendothelialization after balloon injury, in addition to its direct effect, ACE inhibition. Downregulation of the local vascular HGF system may play an important role in the pathogenesis of cardiovascular disease.

Angiotensin-converting enzyme inhibitor ramiprilat interferes with the sequestration of the B2 kinin receptor within the plasma membrane of native endothelial cells

BACKGROUND

ACE (kininase II) inhibitors have been shown to exert their beneficial cardiovascular effects via the inhibition of both angiotensin II formation and bradykinin breakdown. Because recent evidence suggests that ACE inhibitors may also interfere with B2 kinin receptor signaling and thus enhance the vascular response to bradykinin, we examined whether the distribution of B2 kinin receptors within the plasma membrane of native endothelial cells is affected by an ACE inhibitor.

METHODS AND RESULTS

Localization of the B2 kinin receptor in membranes prepared from native porcine aortic endothelial cells was evaluated by means of specific [3H]bradykinin binding and immunoprecipitation of the B2 receptor from isolated membranes. Effects of bradykinin and ramiprilat on intracellular signaling were determined by monitoring the activation of the extracellularly regulated kinases Erk1 and Erk2 as well as [Ca2+]i increases in fura 2-loaded endothelial cells. Stimulation of native endothelial cells with bradykinin 100 nmol/L resulted in the time-dependent sequestration of the B2 receptor to caveolin-rich (CR) membranes, which was maximal after 5 minutes. Pretreatment with ramiprilat 100 nmol/L for 15 minutes significantly attenuated the recovery of B2 kinin receptors in CR membranes while increasing that from membranes lacking caveolin. This effect was not due to the inhibition of bradykinin degradation, because no effect was seen in the presence of an inhibitory concentration of the synthetic ACE substrate hippuryl-L-histidyl-L-leucine. Ramiprilat also decreased [3H]bradykinin binding to CR membranes when applied either before or after bradykinin stimulation. Moreover, ramiprilat resulted in reactivation of the B2 receptor in bradykinin-stimulated cells and induced a second peak in [Ca2+]i and reactivation of Erk1/2.

CONCLUSIONS

The ACE inhibitor ramiprilat interferes with the targeting of the B2 kinin receptor to CR membrane domains in native endothelial cells. Therefore, effects other than the inhibition of kininase II may account for the effects of ramiprilat and other ACE inhibitors on the vascular system.