Ablation of angiotensin IV receptor attenuates hypofibrinolysis via PAI-1 downregulation and reduces occlusive arterial thrombosis

Renin-Angiotensin-Aldosterone System Inhibitions and Cardiovascular Outcomes in Acute Myocardial Infarction With Renal Impairment

OBJECTIVE

To compare the clinical outcomes of patients with acute myocardial infarction with renal impairment (AMI-RI) treated with either angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) in real-world clinical settings.

PATIENTS AND METHODS

A total of 4790 consecutive patients with AMI-RI between November 1, 2011, and December 31, 2015, were subdivided into ACEI (n=2845) and ARB (n=1945) treatment groups. The primary end points were major adverse cardiac and cerebrovascular events, including all-cause mortality, nonfatal myocardial infarction, any revascularization, cerebrovascular accident, rehospitalization, and stent thrombosis. Propensity score matching (PSM) was used to adjust for group differences.

RESULTS

The ARB group had a significantly higher incidence of major adverse cardiac and cerebrovascular events (at 3-year follow-up) than the ACEI group according to the unadjusted analysis (3-year hazard ratio [HR], 1.60; 95% CI, 1.43 to 1.78) and the PSM-adjusted analysis (3-year HR, 1.34; 95% CI, 1.15 to 1.56). However, any revascularization (3-year HR, 1.21; 95% CI, 0.95 to 1.54) and rehospitalization (3-year HR, 1.21; 95% CI, 0.88 to 1.67) were not significantly different between groups in the PSM-adjusted analysis. Compared with the ARB group, the ACEI group had lower rates of all-cause mortality at estimated glomerular filtration rates of at least 15 or less than 90 mL/min/1.73 m2 in the unadjusted data and at least 60 or less than 90 mL/min/1.73 m2 in the PSM-adjusted analysis.

CONCLUSION

Treatment with ACEIs seemed to be more beneficial than treatment with ARBs for patients with AMI-RI; further prospective studies are required to confirm these results.

Functional ACE2 deficiency leading to angiotensin imbalance in the pathophysiology of COVID-19

SARS-CoV-2, the virus responsible for COVID-19, uses angiotensin converting enzyme 2 (ACE2) as its primary cell-surface receptor. ACE2 is a key enzyme in the counter-regulatory pathway of the broader renin-angiotensin system (RAS) that has been implicated in a broad array of human pathology. The RAS is composed of two competing pathways that work in opposition to each other: the "conventional" arm involving angiotensin converting enzyme (ACE) generating angiotensin-2 and the more recently identified ACE2 pathway that generates angiotensin (1-7). Following the original SARS pandemic, additional studies suggested that coronaviral binding to ACE2 resulted in downregulation of the membrane-bound enzyme. Given the similarities between the two viruses, many have posited a similar process with SARS-CoV-2. Proponents of this ACE2 deficiency model argue that downregulation of ACE2 limits its enzymatic function, thereby skewing the delicate balance between the two competing arms of the RAS. In this review we critically examine this model. The available data remain incomplete but are consistent with the possibility that the broad multisystem dysfunction of COVID-19 is due in large part to functional ACE2 deficiency leading to angiotensin imbalance with consequent immune dysregulation and endothelial cell dysfunction.

Cytokine-induced liver injury in coronavirus disease-2019 (COVID-19): untangling the knots

Liver dysfunction manifesting as elevated aminotransferase levels has been a common feature of coronavirus disease-2019 (COVID-19) infection. The mechanism of liver injury in COVID-19 infection is unclear. However, it has been hypothesized to be a result of direct cytopathic effects of the virus, immune dysfunction and cytokine storm-related multiorgan damage, hypoxia-reperfusion injury and idiosyncratic drug-induced liver injury due to medications used in the management of COVID-19. The favored hypothesis regarding the pathophysiology of liver injury in the setting of COVID-19 is cytokine storm, an aberrant and unabated inflammatory response leading to hyperproduction of cytokines. In the current review, we have summarized the potential pathophysiologic mechanisms of cytokine-induced liver injury based on the reported literature.

Endothelial METTL3 (Methyltransferase-Like 3) Inhibits Fibrinolysis by Promoting PAI-1 (Plasminogen Activator Inhibitor-1) Expression Through Enhancing Jun Proto-Oncogene N6-Methyladenosine Modification

OBJECTIVE

METTL3 (methyltransferase-like protein 3)-mediated N6-methyladenosine modification is the most abundant RNA modification on eukaryote mRNAs and plays a crucial role in diverse physiological and pathological processes. However, whether N6-methyladenosine modification has function in thrombosis is unknown. This study aims to determine the role of METTL3 in the endothelial cells-mediated thrombosis. Approach and Results: RNA-sequencing and real-time quantitative PCR revealed that the expression of PAI-1 (plasminogen activator inhibitor-1) was downregulated in METTL3 knockdown human umbilical vein endothelial cells. In vitro experiments showed that METTL3 suppressed fibrinolysis. Mechanically, RNA methylation sequencing and meRIP-quantitative real-time PCR showed that METTL3 catalyzed N6-methyladenosine modification on 3' UTR of JUN mRNA. Western blotting analysis showed that METTL3 promoted JUN protein expression. Chromatin immunoprecipitation analysis demonstrated that JUN bound to the PAI-1 promoter in human umbilical vein endothelial cells. Furthermore, mice challenged with lipopolysaccharide resulted in higher METTL3 expression in vessels. Endothelial-specific knockdown of Mettl3 decreased expression of active PAI-1 in plasma and attenuated fibrin deposition in livers and lungs during endotoxemia.

CONCLUSIONS

Our study reveals that METTL3-mediated N6-methyladenosine modification plays a crucial role in fibrinolysis and is an underlying target for the therapy of thrombotic disorders.

IRAP Inhibitors: M1-Aminopeptidase Family Inspiration

The insulin regulated aminopeptidase (IRAP) has been proposed as an important therapeutic target for indications including Alzheimer’s disease and immune disorders. To date, a number of IRAP inhibitor designs have been investigated but the total number of molecules investigated remains quite small. As a member the M1 aminopeptidase family, IRAP shares numerous structural features with the other M1 aminopeptidases. The study of those enzymes and the development of inhibitors provide key learnings and new approaches and are potential sources of inspiration for future IRAP inhibitors.

Angiotensin III increases monocyte chemoattractant protein-1 expression in cultured human proximal tubular epithelial cells

BACKGROUND/AIMS

We investigated whether angiotensin III (Ang III) is involved in monocyte recruitment through regulation of the chemokine monocyte chemoattractant protein-1 (MCP-1) in cultured human proximal tubular epithelial cells (HK-2 cells).

METHODS

We measured MCP-1 levels in HK-2 cells that had been treated with various concentrations of Ang III and Ang II type-1 (AT1) receptor antagonists at various time points. The phosphorylation states of p38, c-Jun N-terminal kinases (JNK), and extracellular-signal-regulated kinases were measured in Ang III-treated cells to explore the mitogen-activated protein kinase (MAPK) pathway. MCP-1 levels in HK-2 cell-conditioned media were measured after pre-treatment with the transcription factor inhibitors curcumin or pyrrolidine dithiocarbamate.

RESULTS

Ang III increased MCP-1 protein production in dose- and time-dependent manners in HK-2 cells, which was inhibited by the AT1 receptor blocker losartan. p38 MAPK activity increased significantly in HK-2 cells exposed to Ang III for 30 minutes, and was sustained at higher levels after 60 minutes (p < 0.05). Total phosphorylated JNK protein levels tended to increase 20 minutes after stimulation with Ang III. Pre-treatment with a p38 inhibitor, a JNK inhibitor, or curcumin significantly inhibited Ang III-induced MCP-1 production.

CONCLUSIONS

Ang III increases MCP-1 synthesis via stimulation of intracellular p38 and JNK MAPK signaling activity and subsequent activated protein-1 transcriptional activity in HK-2 cells.

Roles of Coagulation and fibrinolysis in angiotensin II-enhanced microvascular thrombosis

OBJECTIVE

AngII-induced HTN is associated with accelerated thrombus development in arterioles. This study assessed the contributions of different components of the coagulation cascade and fibrinolysis to AngII-mediated microvascular thrombosis.

METHODS

Light/dye-induced thrombus formation (the time of onset and flow cessation) was quantified in cremaster muscle arterioles of AngII infused (two weeks) WT/AngII mice, EPCR-TgN, and mice deficient in PAI-1. WT/AngII mice were also treated with either tissue factor antibody, antithrombin III, heparin, hirudin, or murine APC.

RESULTS

TF immunoblockade or hirudin treatment did not prevent the AngII-induced acceleration of thrombosis. While antithrombin III treatment prevented the acceleration in both thrombus onset and flow cessation, heparin only improved the time for blood flow cessation. Neither WT mice treated with murine APC nor EPCR-TgN were protected against AngII-induced thrombus development. A similar lack of protection was noted in PAI-1deficient mice.

CONCLUSION

These findings implicate a role for thrombin generation pathway in the accelerated thrombosis induced by AngII and suggest that an impaired protein C pathway and increased PAI-1 do not make a significant contribution to this model of microvascular thrombosis.

The evolving landscape of RAAS inhibition: from ACE inhibitors to ARBs, to DRIs and beyond

Chronic renin-angiotensin-aldosterone system (RAAS) activation has far-reaching effects on cardiometabolic risk and is a substantial contributor to cardiovascular (CV) disease and renal dysfunction. The vascular effects of sustained RAAS activation are associated with hemodynamic imbalances, as well as inflammatory stimulation and prothrombotic processes that lead to fibrosis, endothelial dysfunction and cellular remodeling. RAAS inhibition therapies, which include the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and more recently, direct renin inhibitors, have been used in clinical practice for more than 30 years. Our understanding of how these drugs work, alone and in combination, has contributed to an expanding landscape of treatment options and established RAAS inhibition as essential for reducing the risk of CV and renal disease. This perspective provides a historical overview of how RAAS inhibitors have evolved to their present-day status and will discuss recently discovered functions for components of this complicated and powerful regulatory system.

Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract

BACKGROUND

The renin-angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

AIM

To elicit the anatomical distribution and physiological significance of the components of the RAS in the gastrointestinal tract.

METHODS

An extensive online literature review including Pubmed and Medline.

RESULTS

There is evidence for RAS involvement in gastrointestinal physiology and pathophysiology, with all the components required for autonomous regulation identified throughout the gastrointestinal tract. The RAS is implicated in the regulation of glucose, amino acid, fluid and electrolyte absorption and secretion, motility, inflammation, blood flow and possibly malignant disease within the gastrointestinal tract. Animal studies investigating the effects of RAS blockade in a range of conditions including inflammatory bowel disease, functional gut disorders, gastrointestinal malignancy and even intestinal ischaemia have been encouraging to date. Given the ready availability of drugs that modify the RAS and their excellent safety profile, an opportunity exists for investigation of their possible therapeutic role in a variety of human gastrointestinal diseases.

CONCLUSIONS

The gastrointestinal renin-angiotensin system appears to be intricately involved in a number of physiological processes, and provides a possible target for novel investigative and therapeutic approaches.

Angiotensin IV protects against angiotensin II-induced cardiac injury via AT4 receptor

Angiotensin II (Ang II) is an important regulator of cardiac function and injury in hypertension. The novel Ang IV peptide/AT4 receptor system has been implicated in several physiological functions and has some effects opposite to those of Ang II. However, little is known about the role of this system in Ang II-induced cardiac injury. Here we studied the effect of Ang IV on Ang II-induced cardiac dysfunction and injury using isolated rat hearts, neonatal cardiomyocytes and cardiac fibroblasts. We found that Ang IV significantly improved Ang II-induced cardiac dysfunction and injury in the isolated heart in response to ischemia/reperfusion (I/R). Moreover, Ang IV inhibited Ang II-induced cardiac cell apoptosis, cardiomyocyte hypertrophy, and proliferation and collagen synthesis of cardiac fibroblasts; these effects were mediated through the AT4 receptor as confirmed by siRNA knockdown. These findings suggest that Ang IV may have a protective effect on Ang II-induced cardiac injury and dysfunction and may be a novel therapeutic target for hypertensive heart disease.

Role of T lymphocytes in angiotensin II-mediated microvascular thrombosis

Clinical trials and animal studies have revealed a role for the renin-angiotensin system in the enhanced thrombus development that is associated with hypertension. Because T lymphocytes have been implicated in the vascular dysfunction and blood pressure elevation associated with increased angiotensin II (Ang II) levels, we evaluated the role of the adaptive immune system in mediating the enhanced thrombosis during Ang II-induced hypertension. Light/dye-induced thrombosis was induced in cremaster arterioles of wild-type, immunodeficient Rag-1(-/-), CD8(+), or CD4(+) lymphocyte-deficient and NADPH oxidase (gp91(phox))-deficient mice implanted with an Ang II-loaded pump for 2 weeks. Chronic Ang II infusion enhanced arteriolar thrombosis in wild-type mice but not in Rag-1(-/-), CD4(+) T-cell-deficient, or gp91(phox-/-) mice. CD8(+) T-cell(-/-) mice exhibited partial protection. Adoptive transfer of T cells derived from wild-type or gp91(phox-/-) mice into Rag-1(-/-) restored the prothrombotic phenotype induced by Ang II. T lymphocytes (CD4(+) and, to a lesser extent, CD8(+)) play a major role in mediating the accelerated microvascular thrombosis associated with Ang II-induced hypertension. NADPH oxidase-derived reactive oxygen species, produced by cells other than T lymphocytes, also appear critical for the Ang II-enhanced, T cell-dependent thrombosis response.

Role of angiotensin II in plasma PAI-1 changes induced by imidapril or candesartan in hypertensive patients with metabolic syndrome

To evaluate the relationship between plasma plasminogen activator inhibitor-1 (PAI-1) and angiotensin II (Ang II) changes during treatment with imidapril and candesartan in hypertensive patients with metabolic syndrome. A total of 84 hypertensive patients with metabolic syndrome were randomized to imidapril 10 mg or candesartan 16 mg for 16 weeks. At weeks 4 and 8, there was a dose titration to imidapril 20 mg and candesartan 32 mg in nonresponders (systolic blood pressure (SBP) >140 and/or diastolic blood pressure (DBP) >90 mm Hg). We evaluated, at baseline and after 2, 4, 8, 12 and 16 weeks, clinic blood pressure, Ang II and PAI-1 antigen. Both imidapril and candesartan induced a similar SBP/DBP reduction (-19.4/16.8 and -19.5/16.3 mm Hg, respectively, P<0.001 vs. baseline). Both drugs decreased PAI-1 antigen after 4 weeks of treatment, but only the PAI-1 lowering effect of imidapril was sustained throughout the 16 weeks (-9.3 ng ml(-1), P<0.01 vs. baseline), whereas candesartan increased PAI-1 (+6.5 ng ml(-1), P<0.05 vs. baseline and P<0.01 vs. imidapril). Imidapril significantly decreased Ang II levels (-14.6 pg ml(-1) at week 16, P<0.05 vs. baseline), whereas candesartan increased them (+24.2 pg ml(-1), P<0.01 vs. baseline and vs. imidapril). In both groups there was a positive correlation between Ang II and PAI-1 changes (r=0.61, P<0.001 at week 16 for imidapril, and r=0.37, P<0.005 at week 16 for candesartan). Imidapril reduced plasma PAI-1 and Ang II levels, whereas candesartan increased them. This suggests that the different effect of angiotensin-converting enzyme inhibitors and Ang II blockers on Ang II production has a role in their different influence on fibrinolysis.

Use of mouse models to study plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and therefore plays an important role in the plasminogen/plasmin system. PAI-1 is involved in a variety of cardiovascular diseases (mainly through inhibition of t-PA) as well as in cell migration and tumor development (mainly through inhibition of u-PA and interaction with vitronectin). PAI-1 is a unique member of the serpin superfamily, exhibiting particular unique conformational and functional properties. Since its involvement in various biological and pathophysiological processes PAI-1 has been the subject of many in vivo studies in mouse models. We briefly discuss structural and physiological differences between human and mouse PAI-1 that should be taken into account prior to extrapolation of data obtained in mouse models to the human situation. The current review provides an overview of the various models, with a focus on cardiovascular disease and cancer, using wild-type mice or genetically modified mice, either deficient in PAI-1 or overexpressing different variants of PAI-1.

Angiotensin II-mediated microvascular thrombosis

Hypertension is associated with an increased risk of thrombosis that appears to involve an interaction between the renin-angiotensin system and hemostasis. In this study we determined whether angiotensin II-mediated thrombosis occurs in arterioles and/or venules and assessed the involvement of type 1 (AT₁), type 2 (AT₂), and type 4 (AT₄) angiotensin II receptors, as well as receptors for endothelin 1 and bradykinin 1 and 2 in angiotensin II-enhanced microvascular thrombosis. Thrombus development in mouse cremaster microvessels was quantified after light/dye injury using the time of onset of the thrombus and time to blood flow cessation. Wild-type and AT₁ receptor-deficient mice were implanted with an angiotensin II-loaded ALZET pump for 2 weeks. Angiotensin II administration in both wild-type and ATAT₁ receptor-deficient mice significantly accelerated thrombosis in arterioles. Genetic deficiency and pharmacological antagonism of AT₁ receptors did not alter the thrombosis response to angiotensin II. Isolated murine platelets aggregated in response to low (picomolar) but not high (nanomolar) concentrations of angiotensin II. The platelet aggregation response to angiotensin II depended on AT₁ receptors. Antagonism of AT₂ receptors in vivo significantly prolonged the onset of angiotensin II-enhanced thrombosis, whereas an AT₄ receptor antagonist prolonged the time to flow cessation. Selective antagonism of either endothelin 1 or bradykinin 1 receptors largely prevented both the onset and flow cessation responses to chronic angiotensin II infusion. Our findings indicate that angiotensin II induced hypertension is accompanied by enhanced thrombosis in arterioles, and this response is mediated by a mechanism that involves AT₂, AT₄, bradykinin 1, and endothelin 1 receptor-mediated signaling.

Ischemia-induced angiogenesis is impaired in aminopeptidase A deficient mice via down-regulation of HIF-1α

Aminopeptidase A (APA; EC 3.4.11.7) is a transmembrane metalloprotease with several functions in tumor angiogenesis. To investigate the role of APA in the process of ischemia-induced angiogenesis, we evaluated the cellular angiogenic responses under hypoxic conditions and the process of perfusion recovery in the hindlimb ischemia model of APA-deficient (APA-KO; C57Bl6/J strain) mice. Western blotting of endothelial cells (ECs) isolated from the aorta of APA-KO mice revealed that the accumulation of hypoxia-inducible factor-1α (HIF-1α) protein in response to hypoxic challenge was blunted. Regarding the proteasomal ubiquitination, a proteasome inhibitor MG-132 restored the reduced accumulation of HIF-1α in ECs from APA-KO mice similar to control mice under hypoxic conditions. These were associated with decreased growth factor secretion and capillary formation in APA-KO mice. In the hindlimb ischemia model, perfusion recovery in APA-KO mice was decreased in accordance with a significantly lower capillary density at 2weeks. Regarding vasculogenesis, no differences were observed in cell populations and distribution patterns between wild type and APA-KO mice in relation to endothelial progenitor cells. Our results suggested that Ischemia-induced angiogenesis is impaired in APA-KO mice partly through decreased HIF-1α stability by proteasomal degradation and subsequent suppression of HIF-1α-driven target protein expression such as growth factors. APA is a functional target for ischemia-induced angiogenesis.

Review: Therapeutic potential of plasminogen activator inhibitor-1 inhibitors

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of fibrinolysis and regulates cell migration and fibrosis. Preclinical studies using genetically altered mice and biological or small molecule inhibitors have elucidated a role for PAI-1 in the pathogenesis of thrombosis, vascular remodeling, renal injury, and initiation of diabetes. Inhibition of PAI-1 is a potential therapeutic strategy in these diseases.