Endothelial Angiotensin-converting Enzyme Research Articles

Emerging Role of Platelet-Endothelium Interactions in the Pathogenesis of Severe SARS-CoV-2 Infection-Associated Myocardial Injury.

Cardiovascular dysfunction and disease are common and frequently fatal complications of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Indeed, from early on during the SARS-CoV-2 virus pandemic it was recognized that cardiac complications may occur, even in patients with no underlying cardiac disorders, as part of the acute infection, and that these were associated with more severe disease and increased morbidity and mortality. The most common cardiac complication is acute cardiac injury, defined by significant elevation of cardiac troponins. The potential mechanisms of cardiovascular complications include direct viral myocardial injury, systemic inflammation induced by the virus, sepsis, arrhythmia, myocardial oxygen supply-demand mismatch, electrolyte abnormalities, and hypercoagulability. This review is focused on the prevalence, risk factors and clinical course of COVID-19-related myocardial injury, as well as on current data with regard to disease pathogenesis, specifically the interaction of platelets with the vascular endothelium. The latter section includes consideration of the role of SARS-CoV-2 proteins in triggering development of a generalized endotheliitis that, in turn, drives intense activation of platelets. Most prominently, SARS-CoV-2–induced endotheliitis involves interaction of the viral spike protein with endothelial angiotensin-converting enzyme 2 (ACE2) together with alternative mechanisms that involve the nucleocapsid and viroporin. In addition, the mechanisms by which activated platelets intensify endothelial activation and dysfunction, seemingly driven by release of the platelet-derived calcium-binding proteins, SA100A8 and SA100A9, are described. These events create a SARS-CoV-2–driven cycle of intravascular inflammation and coagulation, which contributes significantly to a poor clinical outcome in patients with severe disease.

Modeling the 20‐HETE Binding Site on GPR75

Recently, the cytochrome P450‐derived eicosanoid 20‐Hydroxyeicosatetraenoic acid (20‐HETE) was shown to activate the orphan receptor GPR75. The pairing of 20‐HETE and GPR75 activates a signaling pathway that elicits increases in endothelial angiotensin converting enzyme (ACE) and promotes the development of hypertension. Little is known about the critical binding sites/pockets across GPR75 involved in interacting with 20‐HETE that ultimately leads to receptor activation. Computational docking analysis of GPR75 uncovered a putative ligand binding site located between transmembranes five and six on GPR75 (SiteScore: 1.182 and Dscore: 1.303). Independent analyses of ligand‐receptor docking using 20‐HETE placed the lipid in close proximity to the putative binding pocket (Docking Score: −3.229, Glide Emodel: −29.045). Additional modeling of GPR75 alongside another proposed ligand, the chemokine CCL5 (RANTES), revealed a potential protein‐protein interaction model occurring at the top (extracellular face) between the first and seventh transmembranes of GPR75. This distant site suggests the possibility of distinct ligand‐receptor interactions that promote unique signaling cascades. In order to establish a functional assay to further investigate the significance of the proposed 20‐HETE binding site/pocket, we have adapted the PRESTO‐Tango system. This system allows for the quantification of ligand‐dependent β‐arresstin2 recruitment, a common hallmark of G‐protein coupled receptor activation, biased agonism and receptor inactivation/internalization. Preliminary studies using the GPR75‐Tango construct demonstrated a robust signal wherein 20‐HETE stimulates the recruitment of β‐arresstin2 after GPR75 activation (EC50=3μM). Further studies will be conducted to assess the significance of residues located within the putative binding pocket with respect to 20‐HETE‐mediated activation of GPR75.Support or Funding InformationThis study was supported by National Institute of Health grants HL39793(M.L. Schwartzman), HL39793‐01S1 (V. Garcia) and the Robert A. Welch Foundation (I‐0011, J.R. Falck).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Upregulation of cathepsin C expression contributes to endothelial chymase activation in preeclampsia.

Chymase is an ACE (angiotensin-converting enzyme)-independent angiotensin II-forming enzyme whose expression is increased in the maternal vascular endothelium in preeclampsia. However, mechanisms underlying chymase activation in preeclampsia remain unclear. Cathepsin C is a key enzyme in the activation of several serine proteases including chymase. In this study, we determined whether increased cathepsin C expression/activity might be responsible for the upregulation of chymase expression in preeclampsia. Maternal vascular cathepsin C, chymase and ACE expression were examined through immunohistochemical staining of subcutaneous fat tissue sections of normal and preeclamptic pregnant women. The role of cathepsin C in endothelial chymase and ACE expression was determined in cells treated with cathepsin C. Consequences of chymase activation were then determined by measurement of angiotensin II production in cells treated with the ACE inhibitor captopril and the chymase inhibitor chymostatin, separately and in combination. Expression of both cathepsin C and chymase, but not ACE expression, was markedly increased in the maternal vascular endothelium in subjects with preeclampsia compared with normal pregnant controls. Exogenous cathepsin C induced a dose-dependent increase in expression of mature cathepsin C and chymase, but not ACE, in endothelial cells. Moreover, angiotensin II production was significantly inhibited in cells treated with captopril or chymostatin alone and was further inhibited in cells treated with both inhibitors. These results suggest that cathepsin C upregulation induces chymase activation and subsequently promotes angiotensin II generation in endothelial cells. These data also provide evidence of upregulation of the cathepsin C-chymase-angiotensin signaling axis in maternal vasculature in preeclampsia.

Angiotensin II receptor blockade or deletion of vascular endothelial ACE does not prevent vascular dysfunction and remodeling in 20-HETE-dependent hypertension.

Increased vascular 20-HETE is associated with hypertension and activation of the renin-angiotensin system (RAS) through induction of vascular angiotensin-converting enzyme (ACE) expression. Cyp4a12tg mice, whose Cyp4a12-20-HETE synthase expression is under the control of a tetracycline (doxycycline, DOX) promoter, were used to assess the contribution of ACE/RAS to microvascular remodeling in 20-HETE-dependent hypertension. Treatment of Cyp4a12tg mice with DOX increased systolic blood pressure (SBP; 136 ± 2 vs. 102 ± 1 mmHg; P < 0.05), and this increase was prevented by administration of 20-HEDGE, lisinopril, or losartan. DOX-induced hypertension was associated with microvascular dysfunction and remodeling of preglomerular microvessels, which was prevented by 20-HEDGE, a 20-HETE antagonist, yet only lessened, but not prevented, by lisinopril or losartan. In ACE 3/3 mice, which lack vascular endothelial ACE, administration of 5α-dihydrotestosterone (DHT), a known inducer of 20-HETE production, increased SBP; however, the increase was about 50% of that in wild-type (WT) mice (151 ± 1 vs. 126 ± 1 mmHg). Losartan and 20-HEDGE prevented the DHT-induced increase in SBP in WT and ACE 3/3 mice. DHT treatment increased 20-HETE production and microvascular remodeling in WT and ACE 3/3 mice; however, remodeling was attenuated in the ACE 3/3 mice as opposed to WT mice (15.83 ± 1.11 vs. 22.17 ± 0.92 μm; P < 0.05). 20-HEDGE prevented microvascular remodeling in WT and ACE 3/3 mice, while losartan had no effect on microvascular remodeling in ACE 3/3. Taken together, these results suggest that RAS contributes to 20-HETE-mediated microvascular remodeling in hypertension and that 20-HETE-driven microvascular remodeling independent of blood pressure elevation does not fully rely on ACE activity in the vascular endothelium.

20‐SOLA, a Novel Water Soluble 20‐HETE Antagonist, Reduces Blood Pressure Through Regulation of Vascular ACE Expression via an IKK Dependent Pathway

Increased vascular 20‐HETE has been associated with hypertension and activation of the renin‐angiotensin system through induction of vascular angiotensin converting enzyme (ACE) expression. CYP4a14 knockout (KO) mice exhibit male‐specific androgen‐sensitive 20‐HETE‐dependent hypertension. A novel water‐soluble 20‐HETE antagonist, 2,5,8,11,14,17‐hexaoxanonadecan‐19‐yl 20‐hydroxyeicosa‐6(Z),15(Z)‐dienoate (20‐SOLA) was administered to CYP4a14 KO male and female mice (10mg/kg/day in drinking water). 20‐SOLA normalized blood pressure in hypertensive CYP4a14 KO male mice over the course of 10 days (124±1 vs 153 ±2 mmHg in untreated littermates) and had no effect on blood pressure of CYP4a14 KO female mice (126±1 vs 124±1 mmHg). Renal preglomerular microvessel (PGMV) ACE expression was significantly elevated in CYP4a14 KO males (3.57 ± 0.6 fold) compared to normotensive female mice and treatment with 20‐SOLA normalized vascular ACE expression. 20‐HETE‐mediated induction of vascular endothelial ACE expression has been demonstrated to be IKK‐dependent. PGMV of CYP4a14 KO male mice expressed a 2.6‐fold increase in phospho‐IKK compared to female KO mice and this increase was significantly reduced by 20‐SOLA (2.6±0.2 vs. 1.3±0.3 fold, respectively). These results suggest that the water soluble 20‐HETE antagonist 20‐SOLA reduces blood pressure in the male CYP4a14 KO mice, at least in part, through regulation of vascular ACE expression.

Clinical relevance of local Renin Angiotensin systems.

The concept of a “local” renin angiotensin system (RAS) can mean different things to different people. Its main purpose is to differentiate the “local” RAS operating in tissues from the classical “circulating” RAS, but it is difficult to differentiate between the two systems because of their extensive overlap. The circulating RAS comprises kidney-derived renin acting on liver-derived angiotensinogen to generate angiotensin (Ang) I that is converted to Ang II by angiotensin converting enzyme (ACE). However, tissues are the main site of production of angiotensin peptides by the circulating RAS, whereby plasma-derived renin acts on plasma-derived angiotensinogen to generate Ang I, which is converted to Ang II by endothelial ACE (1–4). Local RAS refers to tissue-based mechanisms of Ang peptide formation that operate separately from the circulating RAS. Although many different concepts of local RAS have been described, a key feature is the local synthesis of RAS components including angiotensinogen and enzymes such as renin that cleave angiotensinogen to produce Ang peptides independently of the circulating RAS. ACE and Ang II type 1 (AT1) and type 2 (AT2) receptors are invariably locally synthesized, but these are also components of the circulating RAS. Many other potential components of local RAS have been described that may contribute to tissue-specific mechanisms of Ang peptide formation, and that may either participate in disease processes or contribute to mechanisms that protect from tissue injury. These include the (pro)renin receptor (5), renin-independent mechanisms of Ang peptide generation from Ang- (1-12) (6), intracellular (or intracrine) RAS that may contribute to cardiovascular disease (7, 8), and AT2 receptors (7) and the ACE2/Ang-(1-7)/Mas receptor pathway (6–8) that may mediate therapeutic benefit in cardiovascular disease. In addition, novel Ang peptides with novel pharmacology, including Ang IV, Ang A, alamandine, and angioprotectin (6, 8), have the potential to contribute to disease or to protective mechanisms. Moreover, the brain RAS, including the ACE2/Ang-(1-7)/Mas receptor and the Ang IV/insulin regulated aminopeptidase pathways may play a role in Alzheimer’s and Parkinson’s diseases (9). Local production of aldosterone may have a pathogenic role (7, 10), ACE, AT2 receptors, Ang-(1-7) and acetyl-Ser-Asp-Lys-Pro may have a role in hematopoiesis (11), and the ACE2/Ang-(1-7)/Mas receptor pathway may contribute to fetal programing, reproduction, and cancer (6, 12). This short opinion piece discusses the potential clinical relevance of local RAS. The challenge in demonstrating the independence of local from circulating RAS, and the potential interaction of ACE inhibitor and AT1 receptor blocker (ARB) therapies with local RAS are discussed. Attempts to define local RAS that are independent of the circulating RAS have been primarily based on animal models and the clinical relevance of local RAS is uncertain. However, this area of research continues to evolve, and today’s opinions may change as we gain better understanding of how these novel components and mechanisms impact on clinical medicine.

20-HETE and Blood Pressure Regulation

20-Hydroxy-5, 8, 11, 14-eicosatetraenoic acid (20-HETE) is a cytochrome P450 (CYP)-derived omega-hydroxylation metabolite of arachidonic acid. 20-HETE has been shown to play a complex role in blood pressure regulation. In the kidney tubules, 20-HETE inhibits sodium reabsorption and promotes natriuresis, thus, contributing to antihypertensive mechanisms. In contrast, in the microvasculature, 20-HETE has been shown to play a pressor role by sensitizing smooth muscle cells to constrictor stimuli and increasing myogenic tone, and by acting on the endothelium to further promote endothelial dysfunction and endothelial activation. In addition, 20-HETE induces endothelial angiotensin-converting enzyme, thus, setting forth a potential feed forward prohypertensive mechanism by stimulating the renin-angiotensin-aldosterone system. With the advancement of gene sequencing technology, numerous polymorphisms in the regulatory coding and noncoding regions of 20-HETE-producing enzymes, CYP4A11 and CYP4F2, have been associated with hypertension. This in-depth review article discusses the biosynthesis and function of 20-HETE in the cardiovascular system, the pharmacological agents that affect 20-HETE action, and polymorphisms of CYP enzymes that produce 20-HETE and are associated with systemic hypertension in humans.

Gene polymorphism of endothelial NO-synthase, angiotensin-converting enzyme and receptors of angiotensin II type 1 in patients with coronary artery disease and type II diabetes.

Purpose: to study the clinical manifestations of coronary artery disease (CAD) in patients with diabetes mellitus (DM) II type and the possible association of mutations in the genes of endothelial NO-synthase (eNOS), angiotensin-converting enzyme (ACE) and receptor of angiotensin II type 1 (AT2R1) with the development of type II diabetes in these patients. Mate­rials and methods. The study involved 318 patients with CAD, of whom 54 (17,0%) patients had type II DM and 264 (83,0%) patients -without diabetes. Study of allelic polymorphism of T-786S of eNOS gene promoter, insertion-deletion (I/D) polymorphism of ACE gene and polymorphism A1166S of AT2R1 gene was performed by polymerase chain reaction. Results. In patients with CAD and DM type II such risk factors as hypertension, obesity, family history with early onset of cardiovascular disease were significantly more common; CAD manifestation occurs at a younger age, myocardial ischemia more often has silent nature. In the presence of type II DM, coronary artery lesions were of diffuse and multivessel character, other vascular pools are often involved in the atherosclerotic process. An independent as­sociation of type II diabetes with hypertension, obesity, and CC genotype of eNOS gene T-786S polymorphism was identified in patients with CAD. Negative independent influence of ACE gene I/D polymorphism of D allele and AT2R1 gene A1166S polymorphism C allele on renal function in patients with CAD and type II DM was proved.

AMP-Activated Protein Kinase Regulates Endothelial Cell Angiotensin-Converting Enzyme Expression via p53 and the Post-Transcriptional Regulation of microRNA-143/145

High-angiotensin-converting enzyme (ACE)-levels are associated with cardiovascular disease, but little is known about the regulation of its expression. To assess the molecular mechanisms regulating endothelial ACE expression focusing on the role of the AMP-activated protein kinase (AMPK) and miR-143/145. Shear stress decreased ACE expression in cultured endothelial cells, an effect prevented by downregulating AMPKα2 but not AMPKα1. AMPKα2(-/-) mice expressed higher ACE levels than wild-type littermates resulting in impaired hindlimb vasodilatation to the ACE substrate, bradykinin. The latter response was also evident in animals lacking the AMPKα2 subunit only in endothelial cells. In cultured endothelial cells, miR-143/145 levels were increased by shear stress in an AMPKα2-dependent manner, and miR-143/145 overexpression decreased ACE expression. The effect of shear stress was unrelated to an increase in miR-143/145 promoter activity and transcription but could be attributed to post-transcriptional regulation of precursor-miR-143/145 by AMPKα2. The AMPK substrate, p53, can enhance the post-transcriptional processing of several microRNAs, including miR-143/145. We found that shear stress elicited the AMPKα2-dependent phosphorylation of p53 (on Ser15), and that p53 downregulation prevented the shear stress-induced decrease in ACE expression. Streptozotocin-induced diabetes mellitus in mice was studied as a pathophysiological model of altered AMPK activity. Diabetes mellitus increased tissue phosphorylation of the AMPK substrates, p53 and acetyl-coenzyme A carboxylase, changes that correlated with increased miR-143/145 levels and decreased ACE expression. AMPKα2 suppresses endothelial ACE expression via the phosphorylation of p53 and upregulation of miR-143/145. Post-transcriptional regulation of miR-143/145 may contribute to the vascular complications associated with diabetes mellitus.

Abstract 105: 20-HETE: An Inducer of ACE in Human Microvascular Endothelial Cells (HMVEC).

20-hydroxyeicosatetraenoic acid (20-HETE), a cytochrome P450 derived arachidonic acid metabolite, is manufactured in the microcirculation and shown to sensitize the smooth muscle to constrictor stimuli and cause endothelial activation and dysfunction. Increased vascular production of 20-HETE promotes hypertension that is dependent, in part, on the renin angiotensin system. Microarray analysis of endothelial cells treated with 20-HETE revealed a five-fold upregulation of angiotensin converting enzyme (ACE). In cultured human microvascular endothelial cells (HMVEC), 20-HETE (5 nM) induced ACE mRNA by 3.1-fold (± 0.16 p&lt;0.05), increased ACE protein levels by 4.2-fold (±0.99 p&lt;0.05) and ACE activity by 2-fold (±0.23 p&lt;0.05). These effects were abrogated by co-treatment with 20-HEDE, a 20-HETE antagonist. 20-HETE induction of ACE mRNA was abolished by inhibitors of EGFR-tyrosine kinase, MAPK and IKKβ activation but was not affected by PKC inhibition. Moreover, transfection of cells with IKKβ siRNA prevented 20-HETE from inducing ACE mRNA. Collectively, theses results suggest a role for 20-HETE as a regulator of endothelial ACE. This regulatory activity impacts vascular function since downregulation of ACE in endothelial cells treated with siRNA exogenous 20-HETE from inhibiting NO synthesis and stimulating O 2 - production. This study demonstrates that induction of ACE expression and activity is critical to the actions of 20-HETE on endothelial cell function, further implicating the induction of ACE and activation of RAS as a key mechanism by which excessive production of 20-HETE within the vasculature leads to hypertension.

Induction of Angiotensin-Converting Enzyme and Activation of the Renin–Angiotensin System Contribute to 20-Hydroxyeicosatetraenoic Acid–Mediated Endothelial Dysfunction

20-hydroxyeicosatetraenoic acid (20-HETE) promotes endothelial dysfunction by uncoupling endothelial NO synthase, stimulating O(2)(-) production, and reducing NO bioavailability. Moreover, 20-HETE-dependent vascular dysfunction and hypertension are associated with upregulation of the renin-angiotensin system This study was undertaken to examine the contribution of renin-angiotensin system to 20-HETE actions in the vascular endothelium. In endothelial cells, 20-HETE induced angiotensin-converting enzyme (ACE) mRNA levels and increased ACE protein and activity by 2- to 3-fold; these effects were negated with addition of the 20-HETE antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20 HEDE). 20-HETE induced ACE expression was protein kinase C independent and epidermal growth factor receptor tyrosine kinase and IκB kinase β dependent. ACE short interfering RNA abolished 20-HETE-mediated inhibition of NO production and stimulation of O(2)(-) generation, whereas angiotensin II type 1 receptor short interfering RNA attenuated these effects by 40%. 20-HETE-stimulated O(2)(-) production was negated by 20-HEDE and was attenuated by lisinopril and losartan. Importantly, 20-HETE-mediated impairment of acetylcholine-induced relaxation in rat renal interlobar arteries was also attenuated by lisinopril and losartan. These results indicate that ACE and angiotensin II type 1 receptor activation contribute to 20-HETE-mediated endothelial cell and vascular dysfunction and further enforce the notion that excessive production of 20-HETE within the vasculature leads to hypertension via mechanisms that include the induction of endothelial ACE, thus, perpetuating an increase in vascular angiotensin which, together with 20-HETE, promotes vascular dysfunction.

Hypertensive effects of the iv administration of picomoles of ouabain

Ouabain, an endogenous digitalis compound, has been detected in nanomolar concentrations in the plasma of several mammals and is associated with the development of hypertension. In addition, plasma ouabain is increased in several hypertension models, and the acute or chronic administration of ouabain increases blood pressure in rodents. These results suggest a possible association between ouabain and the genesis or development and maintenance of arterial hypertension. One explanation for this association is that ouabain binds to the α-subunit of the Na(+) pump, inhibiting its activity. Inhibition of this pump increases intracellular Na(+), which reduces the activity of the sarcolemmal Na(+)/Ca(2+) exchanger and thereby reduces Ca(2+) extrusion. Consequently, intracellular Ca(2+) increases and is taken up by the sarcoplasmic reticulum, which, upon activation, releases more calcium and increases the vascular smooth muscle tone. In fact, acute treatment with ouabain enhances the vascular reactivity to vasopressor agents, increases the release of norepinephrine from the perivascular adrenergic nerve endings and promotes increases in the activity of endothelial angiotensin-converting enzyme and the local synthesis of angiotensin II in the tail vascular bed. Additionally, the hypertension induced by ouabain has been associated with central mechanisms that increase sympathetic tone, subsequent to the activation of the cerebral renin-angiotensin system. Thus, the association with peripheral mechanisms and central mechanisms, mainly involving the renin-angiotensin system, may contribute to the acute effects of ouabain-induced elevation of arterial blood pressure.

A ligand-based approach to investigate the expression and function of angiotensin converting enzyme in intact human umbilical vein endothelial cells

Angiotensin converting enzyme (ACE) is a drug target and an effective bradykinin (BK)-inactivating ectopeptidase. We exploited a recently described [ 3H]enalaprilat binding assay to quantify the full dynamic range of ACE expression in intact human umbilical vein endothelial cells (HUVECs) stimulated with known or novel modulators of ACE expression. Further, the affinities for ACE of a set of physiological substrates were determined using the same assay. BK has the highest affinity ( K i 525 nM) among known substrates to displace [ 3H]enalaprilat binding from ACE. Tumor necrosis factor (TNF)-α repressed the expression of ACE in HUVECs while phorbol 12-myristate 13-acetate (PMA) upregulated it in 24 h (∼12-fold dynamic range by [ 3H]enalaprilat binding, corroborated by ACE immunoblotting). Intermediate levels of ACE expression were seen in cells stimulated with both PMA and a cytokine. In contrast, high glucose, insulin or EGF failed to affect ACE expression. The effect of TNF-α was abated by etanercept, the IKK2 inhibitor TPCA-1, or a p38 inhibitor while that of PMA was reduced by inhibitors of PKC isoforms sensitive to phorbol esters and calcium. The short-term PKC- and MEK1-dependent increase of c-Fos expression was best correlated to PMA-induced ACE upregulation. The [ 3H]enalaprilat binding assay applied to HUVECs supports that ACE is a particularly active kininase and that endothelial ACE expression is dynamically and specifically regulated. This has potential importance in inflammatory diseases and diabetes.

The lactotripeptides isoleucine-proline-proline and valine-proline-proline do not inhibit the N-terminal or C-terminal angiotensin converting enzyme active sites in humans

The potential blood pressure lowering effect of fermented milk may involve inhibition of angiotensin-converting enzyme (ACE) by dairy lactotripeptides generated during milk fermentation, such as isoleucine-proline-proline (IPP) and valine-proline-proline (VPP). These peptides are weak ACE inhibitors in vitro but it remains unclear whether they inhibit ACE in vivo in humans. To assess in vivo ACE inhibition in individuals given fermented milk over a 7-day period. Twelve healthy normotensive men were given 330 ml of fermented milk once daily from day 1 to day 7 (IPP: 4.5 mg and VPP: 6.6 mg) and a single dose of 50 mg captopril on day 8. ACE inhibition was assessed in vivo by measuring plasma and urine AcSDKP and plasma active renin and in vitro by measuring plasma ACE activity using hippuryl-histidine-leucine. Plasma IPP/VPP concentrations were measured by LC/MS/MS. Plasma IPP concentrations increased slightly and very transiently after fermented milk administration. Plasma VPP concentrations were below the limit of quantification. Fermented milk had no effect on plasma AcSDKP, ACE activity or active renin concentrations on days 1 or 7. Urine AcSDKP excretion underwent a small transient increase. In contrast, plasma and urine AcSDKP increased 7.7-fold and 70-fold, respectively, and plasma ACE activity decreased by 82.3 +/- 16.1% following captopril administration; plasma active renin concentration increased four-fold. IPP and VPP were poorly absorbed and rapidly eliminated. They did not inhibit plasma or endothelial ACE in vivo at the selected doses and had no specific effect on the N-terminal or C-terminal ACE domains.

Hypoxemic resuscitation prevents pulmonary capillary endothelial dysfunction induced by normoxemic resuscitation from hemorrhagic shock

Hypoxemic reperfusion attenuates brain injury secondary to severe cerebral ischemia, myocardial, and intestinal injury occurring in intestinal postischemic shock, and offers hemodynamic stabilization and attenuation of inflammatory response when applied in the resuscitation from hemorrhagic shock. In this study, we sought to investigate the effect of hypoxemic resuscitation on pulmonary endothelium. Prospective, randomized, controlled animal study. Experimental laboratory of a university intensive care unit. Male New Zealand White rabbits weighting 3-3.5 kg. Hemorrhagic shock at mean arterial pressure of 40 mm Hg was induced by exsanguinations in anesthetized, mechanically ventilated animals for 60 minutes and thereafter rabbits were resuscitated by homologous blood and Ringer's lactate infusion under normoxemia (Normox-Res group, Pao2 = 95-105 mm Hg, n = 9) or hypoxemia (Hypox-Res group, Pao2 = 35-40 mm Hg, n = 7). Using indicator-dilution techniques we measured at baseline and post resuscitation pulmonary capillary endothelial angiotensin converting enzyme activity expressed as percentage of metabolism (%M) and hydrolysis (v) of the substrate H-benzoyl-Phe-Ala-Pro. Normox-Res rabbits exhibited decreased %M (p < 0.05) and v (p < 0.05) post resuscitation as compared with baseline, while no differences occurred in the Hypox-Res group. Myeloperoxidase was measured in lung tissue and was higher in Normox-Res than Hypox-Res animals (p < 0.01). Lung injury was estimated microscopically, whereas the expression of the intercellular adhesion molecule-1 and the vascular cell adhesion molecule-1 were assessed by immunohistochemistry on sections coming from the same tissue block. Compared with Normox-Res, Hypox-Res animals exhibited lower lung injury histopathological score (p < 0.01) and lung malondialdehyde concentration (p < 0.01), and lower intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expressions in both the inflammatory cells (p < 0.01) and the blood vessels (p < 0.05). Normoxemic resuscitation of hemorrhagic shock is associated with pulmonary endothelial dysfunction and lung injury that may be attenuated by hypoxemic resuscitation.

Pulmonary capillary endothelial metabolic dysfunction: Severity in pulmonary arterial hypertension related to connective tissue disease versus idiopathic pulmonary arterial hypertension

Pulmonary endothelial dysfunction is intertwined with the development and progression of pulmonary arterial hypertension (PAH). Pulmonary endothelium is an active metabolic tissue in healthy human subjects. This study was undertaken to determine the effects of PAH on pulmonary endothelial angiotensin-converting enzyme (ACE) activity and to identify differences between common PAH types, i.e., PAH related to connective tissue disease (PAH-CTD) versus idiopathic PAH (IPAH). Nineteen patients with PAH-CTD, 25 patients with IPAH, and 23 control subjects were evaluated. The single-pass transpulmonary percent metabolism (%M) and hydrolysis (both reflecting enzyme activity per capillary) of an ACE synthetic substrate were determined. In addition, the calculated functional capillary surface area (FCSA), normalized to body surface area (BSA), was determined. The %M values in patients with PAH-CTD (mean+/-SEM 53.6+/-3.6%) were significantly reduced compared with those in control subjects (P<0.01) and those in patients with IPAH (P<0.03), but were similar between the IPAH and control groups (mean+/-SEM 66.2+/-3.6% and 74.7+/-2.7%, respectively). Substrate hydrolysis was also significantly reduced in patients with PAH-CTD. The FCSA/BSA was significantly reduced in patients with PAH-CTD (mean+/-SEM 1,068+/-118 ml/minute/m2) and in patients with IPAH (1,443+/-186 ml/minute/m2) compared with that in controls (2,948+/-245 ml/minute/m2; P<0.01 for both). At a given cardiac index, the FCSA/BSA tended to be lower in the PAH-CTD group than in the IPAH group. Moreover, unlike in IPAH, a linear relationship between the FCSA/BSA and the diffusing capacity for carbon monoxide (DLCO) was observed in PAH-CTD (r=0.54, P<0.03). The metabolically functional pulmonary capillary bed appears to be reduced to an equal extent in PAH-CTD and IPAH. However, %M and hydrolysis appear to be reduced in PAH-CTD but not in IPAH, reflecting relatively diminished ACE activity on the pulmonary capillary endothelial cells of patients with PAH-CTD, and showing that pulmonary endothelial metabolic function differs between PAH types. This study also provides the first functional evidence that a reduced DLCO value in patients with PAH-CTD is related to the degree of FCSA loss.

Angiotensin-converting enzyme (ACE) inhibitors have different selectivity for bradykinin binding sites of human somatic ACE

The angiotensin-converting enzyme (ACE) has two natural substrates and two catalytic domains: one cleaving angiotensin I and one inactivating bradykinin. The aim of this study was to investigate the comparative binding affinity of ACE inhibitors for the two binding sites of human endothelial ACE. In vitro binding assays were performed to test the ability of bradykinin, angiotensin I, or various ACE inhibitors (enalaprilat, perindoprilat, quinaprilat, ramiprilat, and trandolaprilat) to displace a saturating concentration of [ 125I]351A, a radiolabeled lisinopril analogue, from ACE binding sites. The calculated IC 50 values for the ACE inhibitors were in the nanomolar range, while those for the natural substrates were in the micromolar range. The bradykinin/angiotensin I selectivity ratios calculated from double displacement experiments were: perindoprilat, 1.44; ramiprilat, 1.16; quinaprilat, 1.09; trandolaprilat, 1.08; enalaprilat, 1.00. The ACE inhibitors generally had higher affinity for the bradykinin than the angiotensin I binding sites, supporting the idea that these agents are primarily inhibitors of bradykinin degradation, and secondarily inhibitors of angiotensin II production. Perindoprilat had the highest selectivity for bradykinin versus angiotensin I binding sites, and enalaprilat has the lowest. These results indicate that there are differences in the affinity of ACE inhibitors toward sites for bradykinin degradation, which could lead to differences in efficacy in cardiovascular disease.

Terminating the Stress: Peripheral Peptidolysis of Proopiomelanocortin-Derived Regulatory Hormones by the Dermal Microvascular Endothelial Cell Extracellular Peptidases Neprilysin and Angiotensin-Converting Enzyme

The skin including the microvascular endothelium is an established peripheral source and target of the immunomodulatory proopiomelanocortin (POMC) peptides ACTH and alpha-MSH. Whereas intracellular POMC peptide generation is well characterized, less is known on their extracellular processing in peripheral tissues by the neuropeptide-specific zinc metalloproteases neprilysin (NEP) and angiotensin-converting enzyme (ACE). This may locally control POMC peptide bioavailability and activation of ACTH/alpha-MSH-specific melanocortin receptors (MCs). In a cell-free system, endothelial cell (EC) membranes prepared from ACE(high)/NEP(low)-expressing primary human dermal microvascular ECs and the ACE(low)/NEP(high) expressing EC line HMEC-1 degraded ACTH(1-39) over time, resulting in temporary increased alpha-MSH immunoreactivity. Matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy peptide mapping and electrospray ionization-mass spectroscopy sequencing identified several stable fragments generated from ACTH(1-39), ACTH(1-24), and alpha-MSH by EC membranes or recombinant NEP and ACE. Whereas some fragments could be assigned to a cell-specific NEP or ACE activity, other degradation products require additional enzyme activity. Pharmacological NEP inhibition enhanced the ACTH and alpha-MSH-mediated activation of EC ectopically expressing MC(1). Likewise, selected peptides such as alpha-MSH(2-12) generated from ACTH(1-39) and alpha-MSH by recombinant NEP displayed equipotent MC(1)-activating properties in vitro and antiinflammatory activity in murine allergic contact dermatitis in vivo as compared with the parental peptides. Thus, NEP and ACE significantly contribute to the EC processing of stress hormones (ACTH) and antiinflammatory peptides (alpha-MSH), which modulates MC(1) activation but does not completely inactivate the peptide ligand. Because NEP and ACE are regulated by inflammatory mediators and UV light, this may be important for ACTH/MSH-modulated skin inflammation.

EFFECTS OF PLASMA FREE HEMOGLOBIN (Hb) ON THE RENIN ANGIOTENSIN SYSTEM (RAS)

A growing body of evidence suggests that the presence of plasma free Hb, even in extremely low concentrations, may be associated with adverse clinical signs and symptoms. Hb is linked to vasoconstrictive, pro-oxidative and pro-inflammatory events. While Hb’s oxidative and inflammatory effects are well established, the complete pathomechanism of Hb-induced vasoconstriction has not yet been fully elucidated. The hemodynamic disturbances mediated by Hb are of rapid onset, occurring within minutes, and sustained, lasting hours. Recently, we discovered that Hb, in its ferryl form, possesses angiotensin converting enzyme (ACE)-like activity, being able to convert, within minutes, angiotensin (Ang)-I to Ang-II and other active Ang fragments. This present study evaluated further the effect of Hb on RAS, focusing on the impact of ferrous- and ferryl-Hb on angiotensinogen (AGT) and ACE. The possible renin-like activity of Hb toward AGT was evaluated by reversed phase C-18 HPLC. The effect of Hb on ACE was investigated by monitoring changes in activity of purified and human lung microvascular endothelial ACE. Results indicate that both forms of Hb had no impact on AGT. However, incubation of purified ACE with ferryl-Hb increased its enzymatic activity. Hb also activated lung microvascular ACE. These events occurred within hours and could contribute to the sustained vasoconstrictive episodes associated with the presence of free Hb. Based on this study, it can be concluded that Hb has an impact on various elements of RAS, which could be an important factor in the not yet fully understood Hb-mediated vasoconstriction.

Improved Endothelium Dependent Vasodilation in Endurance Athletes and Its Relation With ACE I/D Polymorphism

Aerobic exercise enhances endothelium-dependent vasodilation in healthy individuals. It is thought that exercise increases nitric oxide (NO) production and decreases NO inactivation, leading to an increase in NO bioavailability. Angiotensin II and NO have important roles in maintaining vascular tone. There are polymorphisms of the angiotensin converting enzyme (ACE) gene and the presence of the deletion (D) allele has been associated with higher concentrations of circulating and tissue ACE. In this study, the relationship between endothelial function and ACE gene polymorphisms was investigated in athletes and sedentary subjects. The study group comprised 56 endurance athletes and 46 sedentary subjects who underwent brachial artery ultrasonographic examination. ACE insertion (I) and D allele frequencies were analyzed in all patients. Baseline brachial artery diameter and resting blood flow were similar in athletes and controls (p > 0.05). The flow-mediated dilation (FMD) was 8.48+/-3.65% in athletes and 5.16+/-2.5% in controls (p = 0.0001). FMD was significantly different between ACE genotypes in the athletes (p < 0.0001): it was higher in ACE II (10.5+/-1.6%) subjects than in the DI (8.4+/-2.3%) or DD (7+/-1.2%) subgroups. Regular isotonic exercise can improve endothelium-dependent vasodilation especially in those with the ACE II genotype.