The renin-angiotensin system and antihypertensive drugs in Alzheimer's disease:current standing of the angiotensin hypothesis?

There is an urgent need to improve upon Alzheimer's disease (AD) treatments. Limitations of existing drugs are that they target specific downstream neurochemical abnormalities while the upstream underlying pathology continues unchecked. Preferable treatments would be those that can target a number of the broad range of molecular and cellular abnormalities that occur in AD such as amyloid-ß (Aß) and hyperphosphorylated tau-mediated damage, inflammation, and mitochondrial dysfunction, as well more systemic abnormalities such as brain atrophy, impaired cerebral blood flow (CBF), and cerebrovascular disease. Recent pre-clinical, epidemiological, and a limited number of clinical investigations have shown that prevention of the signaling of the multifunctional and potent vasoconstrictor angiotensin II (Ang II) may offer broad benefits in AD. In addition to helping to ameliorate co-morbid hypertension, these drugs also likely improve diminished CBF which is common in AD and can contribute to focal Aß pathology. These drugs, angiotensin converting enzyme (ACE) inhibitors, or angiotensin receptor antagonists (ARAs) may also help deteriorating cognitive function by preventing Ang II-mediated inhibition of acetylcholine release as well as interrupt the upregulation of deleterious inflammatory pathways that are widely recognized in AD. Given the current urgency to find better treatments for AD and the relatively immediate availability of drugs that are already widely prescribed for the treatment of hypertension, one of the largest modifiable risk factors for AD, this article reviews current knowledge as to the eligibility of ACE-inhibitors and ARAs for consideration in future clinical trials in AD.

Application of a mechanobiological simulation technique to stents used clinically

Many cardiovascular diseases are characterised by the restriction of blood flow through arteries. Stents can be expanded within arteries to remove such restrictions; however, tissue in-growth into the stent can lead to restenosis. In order to predict the long-term efficacy of stenting, a mechanobiological model of the arterial tissue reaction to stress is required. In this study, a computational model of arterial tissue response to stenting is applied to three clinically relevant stent designs. We ask the question whether such a mechanobiological model can differentiate between stents used clinically, and we compare these predictions to a purely mechanical analysis. In doing so, we are testing the hypothesis that a mechanobiological model of arterial tissue response to injury could predict the long-term outcomes of stent design. Finite element analysis of the expansion of three different stent types was performed in an idealised, 3D artery. Injury was calculated in the arterial tissue using a remaining-life damage mechanics approach. The inflammatory response to this initial injury was modelled using equations governing variables which represented tissue-degrading species and growth factors. Three levels of inflammation response were modelled to account for inter-patient variability. A lattice-based model of smooth muscle cell behaviour was implemented, treating cells as discrete agents governed by local rules. The simulations predicted differences between stent designs similar to those found in vivo. It showed that the volume of neointima produced could be quantified, providing a quantitative comparison of stents. In contrast, the differences between stents based on stress alone were highly dependent on the choice of comparison criteria. These results show that the choice of stress criteria for stent comparisons is critical. This study shows that mechanobiological modelling may provide a valuable tool in stent design, allowing predictions of their long-term efficacy. The level of inflammation was shown to affect the sensitivity of the model to stent design. If this finding was verified in patients, this could suggest that high-inflammation patients may require alternative treatments to stenting.

Direct reprogramming of fibroblasts into endothelial cells capable of angiogenesis and reendothelialization in tissue-engineered vessels

The generation of induced pluripotent stem (iPS) cells is an important tool for regenerative medicine. However, the main restriction is the risk of tumor development. In this study we found that during the early stages of somatic cell reprogramming toward a pluripotent state, specific gene expression patterns are altered. Therefore, we developed a method to generate partial-iPS (PiPS) cells by transferring four reprogramming factors (OCT4, SOX2, KLF4, and c-MYC) to human fibroblasts for 4 d. PiPS cells did not form tumors in vivo and clearly displayed the potential to differentiate into endothelial cells (ECs) in response to defined media and culture conditions. To clarify the mechanism of PiPS cell differentiation into ECs, SET translocation (myeloid leukemia-associated) (SET) similar protein (SETSIP) was indentified to be induced during somatic cell reprogramming. Importantly, when PiPS cells were treated with VEGF, SETSIP was translocated to the cell nucleus, directly bound to the VE-cadherin promoter, increasing vascular endothelial-cadherin (VE-cadherin) expression levels and EC differentiation. Functionally, PiPS-ECs improved neovascularization and blood flow recovery in a hindlimb ischemic model. Furthermore, PiPS-ECs displayed good attachment, stabilization, patency, and typical vascular structure when seeded on decellularized vessel scaffolds. These findings indicate that reprogramming of fibroblasts into ECs via SETSIP and VEGF has a potential clinical application.

Investigating autonomic control of the cardiovascular system: a battery of simple tests

Sympathetic and parasympathetic divisions of the autonomic nervous system constantly control the heart (sympathetic and parasympathetic divisions) and blood vessels (predominantly the sympathetic division) to maintain appropriate blood pressure and organ blood flow over sometimes widely varying conditions. This can be adversely affected by pathological conditions that can damage one or both branches of autonomic control. The set of teaching laboratory activities outlined here uses various interventions, namely, 1) the heart rate response to deep breathing, 2) the heart rate response to a Valsalva maneuver, 3) the heart rate response to standing, and 4) the blood pressure response to standing, that cause fairly predictable disturbances in cardiovascular parameters in normal circumstances, which serve to demonstrate the dynamic control of the cardiovascular system by autonomic nerves. These tests are also used clinically to help investigate potential damage to this control.

Nephropathy in a hypercholesterolemic mouse model with streptozotocin-induced diabetes

The contribution of preexisting hypercholesterolemia to diabetic nephropathy remains unclear. We assessed the impact of hypercholesterolemia on diabetic nephropathy using a double knockout (DKO) mouse, null for the low-density lipoprotein receptor (LDLRNDASH;/NDASH;) and the apoB mRNA editing catalytic polypeptide 1 (APOBEC1NDASH;/NDASH;).

Endothelium-derived agents in pericyte function/dysfunction

The major components of blood vessels are the vascular endothelium and its supporting smooth muscle. Significant strides have been made in the understanding of the cellular and molecular biology of these two cell types and in particular their interactions have been the subject of much interest and debate over the past two decades. The vascular endothelium is now known to profoundly influence the synthetic and motor functions of the underlying smooth muscle and participate in the pathogenesis of all the major vascular disorders. Similarly, the vascular smooth muscle has important effects on the overlying endothelium, and any disruption in the cellular physiology of either cell type can result in dysfunction with important effects on blood flow and vascular permeability The majority of this accumulated knowledge relates to the vascular cells of the macrocirculation. Pericytes are the supporting cells of the microvasculature and a body of evidence is now available to show that similar regulatory mechanisms and vessel-wall cross-talk exists between these cells and the microvascular endothelium. Nowhere are these interactions more important than in the retinal microcirculation where autoregulation is vital for the maintenance of smooth and uninterrrupted blood flow. This review focuses on the interactions between retinal microvascular endothelial cells and their associated pericytes and examines the role of the endothelial cell and the pericyte in the pathogenesis of disease.

The effect of endothelin 1 on the retinal microvascular pericyte

The effect of the highly vasoactive peptide endothelin 1 (ET1) was tested on bovine retinal microvascular pericytes propagated in vitro. Specific binding of 125I-ET1 to retinal pericytes was documented by autoradiography. ET1 caused contraction of pericytes at a concentration of 0.1 nM which was accompanied by increases in inositol phosphates. Exposure of pericytes to 10 nM ET1 resulted in the aggregation and realignment of muscle-specific actins into bundles which were oriented parallel to the long axis of the cell, and ET1 was also mitogenic to pericytes in the presence of low levels of fetal calf serum. These observations suggest that ET1 may play an important role in endothelial cell-pericyte interactions within the microvasculature of the retina and that it may be involved in the autoregulation of retinal blood flow.

Pathophysiology and Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy is traditionally viewed as a disease of the retinal blood vessels, although there is increasing evidence that retinal neurons and glial cells are also affected. This article describes the changes in the diabetic retina that precede the development of clinical diabetic retinopathy, including changes in the rate of retinal blood flow, alterations in the electroretinogram and breakdown of the integrity of the blood-retinal barrier. The long term lesions of diabetic retinopathy are characterised by a complex array of vasodegenerative changes that lead directly to areas of retinal ischaemia. This frequently triggers the onset of macular oedema and/or the proliferative stages of diabetic retinopathy with risk of visual impairment and blindness. Neurodegeneration has also been reported in the retina during both human and experimental diabetic retinopathy, although presently it remains unclear to what extent such changes contribute to visual loss in diabetic retinopathy.

Contractile properties of human renal cell carcinoma recruited arteries and their response to nicotinamide

Background and purpose: The manipulation of tumour blood supply and thus oxygenation is a potentially important strategy for improving the treatment of solid tumours by radiation. Increased knowledge about the characteristics that distinguish the tumour vasculature from its normal counterparts may enable tumour blood flow to be more selectively modified, Nicotinamide (NA) causes relaxation of preconstricted normal and tumour-supply arteries in rats. It has also been shown to affect microregional blood flow in human tumours. Direct effects of NA on human tumour supply arteries have not previously been reported. This paper describes our evaluation of the effects of NA on two parameters: 'spontaneous', oscillatory contractile activity and agonist (phenylephrine)-induced constriction in the arteries supplying human renal cell carcinomas.

Materials and methods: Isolated renal cell carcinoma feeder vessels were perfused in an organ bath with the alpha(1)-adrenoceptor agonist phenylephrine (PE). When the arteries had reached a plateau of constriction, nicotinamide (8.2 mM) was added to the perfusate and changes in perfusion pressure were measured.

Results: PE (10 mu M) induced a sustained constriction in the majority of the renal cell carcinoma feeder vessels examined, demonstrating that they retain contractile characteristics, at least in response to this alpha(1)-adrenoceptor agonist. In combination with NA (8.2 mM) the constriction was significantly attenuated in half of the preparations. In addition, seven arteries exhibited spontaneous contractile activity which was significantly attenuated by NA in six of them.

Conclusions: NA can significantly attenuate both 'spontaneous' and agonist-induced constrictions in tumour-recruited human arteries, though not all arteries are sensitive. Published by Elsevier Science Ireland Ltd.

PKC-β exacerbates in vitro brain barrier damage in hyperglycemic settings via regulation of RhoA/Rho-kinase/MLC2 pathway

Stroke patients with hyperglycemia (HG) develop higher volumes of brain edema emerging from disruption of blood-brain barrier (BBB). This study explored whether inductions of protein kinase C-β (PKC-β) and RhoA/Rho-kinase/myosin-regulatory light chain-2 (MLC2) pathway may account for HG-induced barrier damage using an in vitro model of human BBB comprising human brain microvascular endothelial cells (HBMEC) and astrocytes. Hyperglycemia (25 mmol/L D-glucose) markedly increased RhoA/Rho-kinase protein expressions (in-cell westerns), MLC2 phosphorylation (immunoblotting), and PKC-β (PepTag assay) and RhoA (Rhotekin-binding assay) activities in HBMEC while concurrently reducing the expression of tight junction protein occludin. Hyperglycemia-evoked in vitro barrier dysfunction, confirmed by decreases in transendothelial electrical resistance and concomitant increases in paracellular flux of Evan's blue-labeled albumin, was accompanied by malformations of actin cytoskeleton and tight junctions. Suppression of RhoA and Rho-kinase activities by anti-RhoA immunoglobulin G (IgG) electroporation and Y-27632, respectively prevented morphologic changes and restored plasma membrane localization of occludin. Normalization of glucose levels and silencing PKC-β activity neutralized the effects of HG on occludin and RhoA/Rho-kinase/MLC2 expression, localization, and activity and consequently improved in vitro barrier integrity and function. These results suggest that HG-induced exacerbation of the BBB breakdown after an ischemic stroke is mediated in large part by activation of PKC-β.

Conduit artery structure and function in lowlanders and native highlanders: relationships with oxidative stress and role of sympathoexcitation

Research detailing the normal vascular adaptions to high altitude is minimal and often confounded by pathology (e.g. chronic mountain sickness) and methodological issues. We examined vascular function and structure in: (1) healthy lowlanders during acute hypoxia and prolonged (∼2 weeks) exposure to high altitude, and (2) high-altitude natives at 5050 m (highlanders). In 12 healthy lowlanders (aged 32 ± 7 years) and 12 highlanders (Sherpa; 33 ± 14 years) we assessed brachial endothelium-dependent flow-mediated dilatation (FMD), endothelium-independent dilatation (via glyceryl trinitrate; GTN), common carotid intima–media thickness (CIMT) and diameter (ultrasound), and arterial stiffness via pulse wave velocity (PWV; applanation tonometry). Cephalic venous biomarkers of free radical-mediated lipid peroxidation (lipid hydroperoxides, LOOH), nitrite (NO₂^–) and lipid soluble antioxidants were also obtained at rest. In lowlanders, measurements were performed at sea level (334 m) and between days 3–4 (acute high altitude) and 12–14 (chronic high altitude) following arrival to 5050 m. Highlanders were assessed once at 5050 m. Compared with sea level, acute high altitude reduced lowlanders’ FMD (7.9 ± 0.4 vs. 6.8 ± 0.4%; P = 0.004) and GTN-induced dilatation (16.6 ± 0.9 vs. 14.5 ± 0.8%; P = 0.006), and raised central PWV (6.0 ± 0.2vs. 6.6 ± 0.3 m s⁻¹; P = 0.001). These changes persisted at days 12–14, and after allometrically scaling FMD to adjust for altered baseline diameter. Compared to lowlanders at sea level and high altitude, highlanders had a lower carotid wall:lumen ratio (∼19%, P ≤ 0.04), attributable to a narrower CIMT and wider lumen. Although both LOOH and NO₂^– increased with high altitude in lowlanders, only LOOH correlated with the reduction in GTN-induced dilatation evident during acute (n = 11, r = −0.53) and chronic (n = 7, r = −0.69; P ≤ 0.01) exposure to 5050 m. In a follow-up, placebo-controlled experiment (n = 11 healthy lowlanders) conducted in a normobaric hypoxic chamber (inspired O₂ fraction () = 0.11; 6 h), a sustained reduction in FMD was evident within 1 h of hypoxic exposure when compared to normoxic baseline (5.7 ± 1.6 vs. 8.0 ±1.3%; P < 0.01); this decline in FMD was largely reversed following α₁-adrenoreceptor blockade. In conclusion, high-altitude exposure in lowlanders caused persistent impairment in vascular function, which was mediated partially via oxidative stress and sympathoexcitation. Although a lifetime of high-altitude exposure neither intensifies nor attenuates the impairments seen with short-term exposure, chronic high-altitude exposure appears to be associated with arterial remodelling.

CaV3.1 T-Type Ca2+ Channels Contribute to Myogenic Signalling in Rat Retinal Arterioles

Purpose: Although L-type Ca2+ channels are known to play a key role in the myogenic reactivity of retinal arterial vessels, the involvement of other types of voltage-gated Ca2+ channels in this process remains unknown. In the present study we have investigated the contribution of T-type Ca2+ channels to myogenic signalling in arterioles of the rat retinal microcirculation.

Methods: Confocal immunolabelling of wholemount preparations was used to investigate the localisation of CaV3.1-3 channels in retinal arteriolar smooth muscle cells. T-type currents and the contribution of T-type channels to myogenic signalling were assessed by whole-cell patch-clamp recording and pressure myography of isolated retinal arteriole segments.

Results: Strong immunolabelling for CaV3.1 was observed on the plasma membrane of retinal arteriolar smooth muscle cells. In contrast, no expression of CaV3.2 or CaV3.3 could be detected in retinal arterioles, although these channels were present on glial cell end feet surrounding the vessels and retinal ganglion cells, respectively. TTA-A2 sensitive T-type currents were recorded in retinal arteriolar myocytes with biophysical properties distinct from those of the L-type currents present in these cells. Inhibition of T-type channels using TTA-A2 or ML-218 dilated isolated, myogenically active, retinal arterioles.

Conclusions: CaV3.1 T-type Ca2+ channels are functionally expressed on arteriolar smooth muscle cells of retinal arterioles and play an important role in myogenic signalling in these vessels. The work has important implications concerning our understanding of the mechanisms controlling blood flow autoregulation in the retina and its disruption during ocular disease.