Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Endothelial dysfunction in COVID-19: Current findings and therapeutic implications

Coronavirus disease 2019 (COVID-19) increases the risk of several non-pulmonary complications such as acute myocardial injury, renal failure or thromboembolic events. A possible unifying explanation for these phenomena may be the presence of profound endothelial dysfunction and injury. This review provides an overview on the association of endothelial dysfunction with COVID-19 and its therapeutic implications. Endothelial dysfunction is a common feature of the key comorbidities that increase risk for severe COVID-19 such as hypertension, obesity, diabetes mellitus, coronary artery disease or heart failure. Preliminary studies indicate that vascular endothelial cells can be infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and evidence of widespread endothelial injury and inflammation is found in advanced cases of COVID-19. Prior evidence has established the crucial role of endothelial cells in maintaining and regulating vascular homeostasis and blood coagulation. Aggravation of endothelial dysfunction in COVID-19 may therefore impair organ perfusion and cause a procoagulatory state resulting in both macro- and microvascular thrombotic events. Angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs) and statins are known to improve endothelial dysfunction. Data from smaller observational studies and other viral infections suggests a possible beneficial effect in COVID-19. Other treatments that are currently under investigation for COVID-19 may also act by improving endothelial dysfunction in patients. Focusing therapies on preventing and improving endothelial dysfunction could improve outcomes in COVID-19. Several clinical trials are currently underway to explore this concept.

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New evidence implicates endothelial dysfunction in the pathophysiology of COVID-19.

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It may explain complications such as multi-organ damage or thrombotic events.

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Targeted interventions such as RAS inhibitors or statins may improve outcomes.

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Studies on interventions that affect endothelial dysfunction are underway in COVID-19.

Angiotensin-converting enzyme 2, the complement system, the kallikrein-kinin system, type-2 diabetes, interleukin-6, and their interactions regarding the complex COVID-19 pathophysiological crossroads

Because of the current COVID-19-pandemic, the world is currently being held hostage in various lockdowns. ACE2 facilitates SARS-CoV-2 cell-entry, and is at the very center of several pathophysiological pathways regarding the RAAS, CS, KKS, T2DM, and IL-6. Their interactions with severe COVID-19 complications (e.g. ARDS and thrombosis), and potential therapeutic targets for pharmacological intervention, will be reviewed.

The Importance of Redox Status in the Frame of Lifestyle Approaches and the Genetics of the Lung Innate Immune Molecules, SP-A1 and SP-A2, on Differential Outcomes of COVID-19 Infection

The pandemic of COVID-19 is of great concern to the scientific community. This mainly affects the elderly and people with underlying diseases. People with obesity are more likely to experience unpleasant disease symptoms and increased mortality. The severe oxidative environment that occurs in obesity due to chronic inflammation permits viral activation of further inflammation leading to severe lung disease. Lifestyle affects the levels of inflammation and oxidative stress. It has been shown that a careful diet rich in antioxidants, regular exercise, and fasting regimens, each and/or together, can reduce the levels of inflammation and oxidative stress and strengthen the immune system as they lead to weight loss and activate cellular antioxidant mechanisms and reduce oxidative damage. Thus, a lifestyle change based on the three pillars: antioxidants, exercise, and fasting could act as a proactive preventative measure against the adverse effects of COVID-19 by maintaining redox balance and well-functioning immunity. Moreover, because of the observed diversity in the expression of COVID-19 inflammation, the role of genetics of innate immune molecules, surfactant protein A (SP-A)1 and SP-A2, and their differential impact on the local lung microenvironment and host defense is reviewed as genetics may play a major role in the diverse expression of the disease.

Diminazene aceturate extenuate the renal deleterious consequences of angiotensin-II induced by γ-irradiation through boosting ACE2 signaling cascade

AIM

This work aims to explore the role of diminazene aceturate (DIZE) in the enhancement of angiotensin-converting enzyme-2 (ACE2) to prevent the inflammatory and fibrotic response induced by γ-irradiation through activating the protective axis ACE2/angiotensin (1-7)/Mas receptor (ACE2/Ang(1-7)/Mas).

METHODS

Male rats were injected i.p. with 15 mg/kg DIZE daily for 7 days pre and post-irradiation, where 7.5 Gy of γ-radiation as a single dose was used.

KEY FINDINGS

Gamma radiation induced a significant elevation of renal biochemical parameters: urea, creatinine and blood urea nitrogen (BUN) in serum with a significant disturbance in oxidative stress markers: elevation in malondialdehyde (MDA) associated with a depletion of reduced glutathione (GSH) and superoxide dismutase (SOD). Beside elevation in the level of angiotensin II (AngII) that lead to remarkably increases in the levels of the renal inflammatory mediators: tumor necrosis factor-α (TNF-α), nuclear factor kappa B (NF-κB) and interleukin-1β (IL-1β) as well as renal fibrogenic markers: transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), and hydroxyproline content in the renal tissues. DIZE caused marked expansion in the expression of ACE2 consequently decreased the expression of AngII and increased the expression of Ang(1-7) which through its Mas receptor ameliorates the biochemical and histopathological damage induced by radiation.

SIGNIFICANCE

DIZE-induced stimulation of ACE2 subdues the renal deleterious consequences induced by γ-radiation via activation of ACE2/Ang(1-7)/Mas axis in rats.

Dipeptidyl peptidase 3 modulates the renin-angiotensin system in mice

Dipeptidyl peptidase 3 (DPP3) is a zinc-dependent hydrolase involved in degrading oligopeptides with 4-12 amino acid residues. It has been associated with several pathophysiological processes, including blood pressure regulation, pain signaling, and cancer cell defense against oxidative stress. However, the physiological substrates and the cellular pathways that are potentially targeted by DPP3 to mediate these effects remain unknown. Here, we show that global DPP3 deficiency in mice (DPP3^-/-) affects the renin-angiotensin system (RAS). LC-MS-based profiling of circulating angiotensin peptides revealed elevated levels of angiotensin II, III, IV, and 1-5 in DPP3^-/- mice, whereas blood pressure, renin activity, and aldosterone levels remained unchanged. Activity assays using the purified enzyme confirmed that angiotensin peptides are substrates for DPP3. Aberrant angiotensin signaling was associated with substantially higher water intake and increased renal reactive oxygen species formation in the kidneys of DPP3^-/- mice. The metabolic changes and altered angiotensin levels observed in male DPP3^-/- mice were either absent or attenuated in female DPP3^-/- mice, indicating sex-specific differences. Taken together, our observations suggest that DPP3 regulates the RAS pathway and water homeostasis by degrading circulating angiotensin peptides.

Prognostic Value of Cardiovascular Biomarkers in COVID-19: A Review

In early December 2019, the coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first emerged in Wuhan, China. As of May 10th, 2020, a total of over 4 million COVID-19 cases and 280,000 deaths have been reported globally, reflecting the raised infectivity and severity of this virus. Amongst hospitalised COVID-19 patients, there is a high prevalence of established cardiovascular disease (CVD). There is evidence showing that COVID-19 may exacerbate cardiovascular risk factors and preexisting CVD or may lead to cardiovascular complications. With intensive care units operating at maximum capacity and such staggering mortality rates reported, it is imperative during this time-sensitive COVID-19 outbreak to identify patients with an increased risk of adverse outcomes and/or myocardial injury. Preliminary findings from COVID-19 studies have shown the association of biomarkers of acute cardiac injury and coagulation with worse prognosis. While these biomarkers are recognised for CVD, there is emerging prospect that they may aid prognosis in COVID-19, especially in patients with cardiovascular comorbidities or risk factors that predispose to worse outcomes. Consequently, the aim of this review is to identify cardiovascular prognostic factors associated with morbidity and mortality in COVID-19 and to highlight considerations for incorporating laboratory testing of biomarkers of cardiovascular performance in COVID-19 to optimise outcomes.

An Update on the Pathophysiology and Treatment of Cardiorenal Syndrome

Cardiorenal syndrome (CRS) encompasses various disorders of the heart and kidneys; dysfunction of one organ leads to acute or chronic dysfunction of the other. It incorporates the intersection of heart-kidney interactions across several mediums, hemodynamically, through the alterations in neurohormonal markers, and increased venous and renal pressure, all of which are hallmarks of its clinical phenotypes. This article explores the epidemiology, pathology, classification and treatment of each type of CRS.

Telomerase Deficiency Predisposes to Heart Failure and Ischemia-Reperfusion Injury

Introduction: Elevated levels of mitochondrial reactive oxygen species (ROS) contribute to the development of numerous cardiovascular diseases. TERT, the catalytic subunit of telomerase, has been shown to translocate to mitochondria to suppress ROS while promoting ATP production. Acute overexpression of TERT increases survival and decreases infarct size in a mouse model of myocardial infarct, while decreased telomerase activity predisposes to mitochondrial defects and heart failure. In the present study, we examined the role of TERT on cardiac structure and function under basal conditions and conditions of acute or prolonged stress in a novel rat model of TERT deficiency. Methods: Cardiac structure and function were evaluated via transthoracic echocardiogram. Langendorff preparations were used to test the effects of acute global ischemia reperfusion injury on cardiac function and infarction. Coronary flow and left ventricular pressure were measured during and after ischemia/reperfusion (I/R). Mitochondrial DNA integrity was measured by PCR and mitochondrial respiration was assessed in isolated mitochondria using an Oxygraph. Angiotensin II infusion was used as an established model of systemic stress. Results: No structural changes (echocardiogram) or coronary flow/left ventricle pressure (isolated hearts) were observed in TERT-/- rats at baseline; however, after I/R, coronary flow was significantly reduced in TERT-/- compared to wild type (WT) rats, while diastolic Left Ventricle Pressure was significantly elevated (n = 6 in each group; p < 0.05) in the TERT-/-. Interestingly, infarct size was less in TERT-/- rats compared to WT rats, while mitochondrial respiratory control index decreased and mitochondrial DNA lesions increased in TERT-/- compared to WT. Angiotensin II treatment did not alter cardiac structure or function; however, it augmented the infarct size significantly more in TERT-/- compared to the WT. Conclusion: Absence of TERT activity increases susceptibility to stress like cardiac injury. These results suggest a critical role of telomerase in chronic heart disease.

Immunoproteasome Subunit β5i Promotes Ang II (Angiotensin II)–Induced Atrial Fibrillation by Targeting ATRAP (Ang II Type I Receptor–Associated Protein) Degradation in Mice

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and increases the risk of stroke, heart failure, and death. Ang II (angiotensin II) triggers AF, mainly through stimulation of the AT1R (Ang II type I receptor). The immunoproteasome is a highly efficient proteolytic machine derived from the constitutive proteasome, but the role it plays in regulating AT1R activation and triggering AF remains unknown. Here, we show that among the catalytic subunits, β5i (PSMB8) expression, and chymotrypsin-like activity were the most significantly upregulated in atrial tissue of Ang II–infused mice or serum from patients with AF. β5i KO (β5i knockout) in mice markedly attenuated Ang II-induced AF incidence, atrial fibrosis, inflammatory response, and oxidative stress compared with WT (wild type) animals, but injection with recombinant adeno-associated virus serotype 9–β5i increased these effects. Moreover, we found that ATRAP (AT1R-associated protein) was a target of β5i. Overexpression of ATRAP significantly attenuated Ang II-induced atrial remodeling and AF in recombinant adeno-associated virus serotype 9–β5i-injected mice. Mechanistically, Ang II upregulated β5i expression to promote ATRAP degradation, which resulted in activation of AT1R-mediated NF-κB signaling, increased NADPH oxidase activity, increased TGF (transforming growth factor)-β1/Smad signaling, and altered the expression of Kir2.1 and CX43 (connexin 43) in the atria, thereby affecting atrial remodeling and AF. In summary, this study identifies β5i as a negative regulator of ATRAP stability that contributes to AT1R activation and to AF, highlighting that targeting β5i activity may represent a potential therapeutic approach for the treatment of hypertensive AF.

Early administration of empagliflozin preserved heart function in cardiorenal syndrome in rat

This study tested the hypothesis that early administration of empagliflozin (Empa), an inhibitor of glucose recycling in renal tubules, could preserve heart function in cardiorenal syndrome (CRS) in rat. Chronic kidney disease (CKD) was caused by 5/6 subtotal nephrectomy and dilated cardiomyopathy (DCM) by doxorubicin (DOX) treatment. In vitro results showed that protein expressions of cleaved-caspase3 and autophagy activity at 24 h/48 h in NRK-52P cells were significantly upregulated by para-Creso treatment; these were significantly downregulated by Empa treatment. Flow cytometric analysis showed that annexin-V (i.e., early/late apoptosis) in NRK-52P cells expressed an identical pattern to cleaved-caspase3 between the two groups (all p < 0.001). Adult-male-SD rats (n = 18) were equally categorized into group 1 (sham-control), group 2 (CRS) and group 3 [CRS + Empa; 20 mg/kg/day]. By day-42 after CRS induction, left-ventricular ejection fraction (LVEF) level exhibited an opposite pattern, whereas LV end-diastolic dimension and creatinine level displayed the same pattern, to cleaved-caspase3 among the three groups (all p < 0.0001). In LV tissues, protein expressions of inflammatory (tumor-necrosis factor-α/nuclear-factor-κB/interleukin-1ß/matrix-metalloprotianse-9), oxidative stress (NOX-1/NOX-2/oxidized protein), apoptotic (mitochondrial-Bax/cleaved-caspase-3/cleaved-PARP), fibrotic (transforming-growth factor-ß/Smad3), DNA/mitochondrial-damage (γ-H2AX/cytosolic-cytochrome-C) and heart failure (brain natriuretic peptide (BNP) levels displayed an opposite pattern to LVEF among the three groups (all p < 0.0001). Additionally, cellular expressions of DNA-damage/heart-failure (γ-H2AX+//XRCC1+CD90+//BNP+) biomarkers and histopathological findings of fibrotic/condensed collagen-deposition areas and apoptotic nuclei showed an identical pattern, whereas connexin43 and small-vessel number exhibited an opposite pattern, to inflammation among the three groups (all p < 0.0001). In conclusion, Empa therapy protected heart and kidney against CRS injury.

XPO1-mediated nuclear export of RNF146 protects from angiotensin II-induced endothelial cellular injury

Endothelial cells death induced by angiotensin II (Ang II) plays a role in vascular injury. RNF146 is identified as a E3 ubiquitin ligase, which promotes cell survival under many types of stresses. However, the role of RNF146 in endothelial cellular injury is unknown. In human umbilical vein endothelial cells (HUVECs), Ang II treatment led to cell death by oxidative stress and promoted RNF146 to accumulate in nucleus in time dependent manner. Nuclear export signal was found in the RNF146's sequence. The interaction between RNF146 and XPO1 was further confirmed by co-immunoprecipitation. Inhibition of XPO1 with KPT-185 increased the level of RNF146 in nucleus. The expression of XPO1 was suppressed responding to Ang II treatment. Overexpression of XPO1 facilitated the nuclear shuttling of RNF146, which protected from Ang II-induced cell death. Moreover, overexpression of RNF146 in HUVECs reduced the cell death induced by Ang II, whereas inhibition of XPO1 abolished the protective effect of RNF146. Therefore, our data demonstrated that RNF146 was a protective factor against cell death induced by AngII in human endothelial cells, which was dependent on XPO1-mediated nuclear export.

The Role of Oxidative Stress in the Development of Systemic Sclerosis Related Vasculopathy

Systemic sclerosis (SSc) is a rare connective tissue disease characterized by autoimmunity, vasculopathy, and progressive fibrosis typically affecting multiple organs including the skin. SSc often is a lethal disorder, because effective disease-modifying treatment still remains unavailable. Vasculopathy with endothelial dysfunction, perivascular infiltration of mononuclear cells, vascular wall remodeling and rarefaction of capillaries is the hallmark of the disease. Most patients present with vasospastic attacks of the digital arteries referred to as 'Raynaud's phenomenon,' which is often an indication of an underlying widespread vasculopathy. Although autoimmune responses and inflammation are both found to play an important role in the pathogenesis of this vasculopathy, no definite initiating factors have been identified. Recently, several studies have underlined the potential role of oxidative stress in the pathogenesis of SSc vasculopathy thereby proposing a new aspect in the pathogenesis of this disease. For instance, circulating levels of reactive oxygen species (ROS) related markers have been found to correlate with SSc vasculopathy, the formation of fibrosis and the production of autoantibodies. Excess ROS formation is well-known to lead to endothelial cell (EC) injury and vascular complications. Collectively, these findings suggest a potential role of ROS in the initiation and progression of SSc vasculopathy. In this review, we present the background of oxidative stress related processes (e.g., EC injury, autoimmunity, inflammation, and vascular wall remodeling) that may contribute to SSc vasculopathy. Finally, we describe the use of oxidative stress related read-outs as clinical biomarkers of disease activity and evaluate potential anti-oxidative strategies in SSc.

Downregulation of microRNA‑34a inhibits oxidized low‑density lipoprotein‑induced apoptosis and oxidative stress in human umbilical vein endothelial cells

Oxidized low‑density lipoprotein (ox‑LDL) promotes endothelial cell dysfunction, which is a primary risk factor for the development of atherosclerosis. A previous study reported that microRNA (miRNA/miR)‑34a is upregulated in atherosclerotic samples. However, its function and underlying mechanisms remain to be fully elucidated. In the present study, miRNA microarray analysis was performed to investigate the miRNA expression profile in atherosclerotic plaque tissues and examine the role of miR‑34a in ox‑LDL‑induced apoptosis of human umbilical vein endothelial cells (HUVECs). Cell viability, apoptosis and protein expression was determined by a cell counting kit‑8 assay, flow cytometry and western blot analysis, respectively. It was observed that miR‑34a was upregulated in atherosclerotic plaque tissues and that ox‑LDL treatment significantly increased the levels of miR‑34a in a dose‑dependent manner in the HUVECs. The knockdown of miR‑34a increased the protein expression of B‑cell lymphoma 2 (Bcl‑2) and cell viability, improved mitochondrial membrane potential, and decreased the activity of caspase‑3, number of apoptotic cells and release of cytochrome c from mitochondria in the ox‑LDL‑treated HUVECs. The results also demonstrated that the knockdown of miR‑34a suppressed the levels of ox‑LDL‑induced reactive oxygen species (ROS) in HUVECs. Additionally, it was found that Bcl‑2 was a target of miR‑34a in HUVECs, and that silencing Bcl‑2 abrogated the protective effects of the downregulation of miR‑34a on ox‑LDL‑induced apoptosis. These data indicated that the knockdown of miR‑34a protected against ox‑LDL apoptosis and ROS in HUVECs via inhibiting the mitochondrial apoptotic pathway, suggesting it may offer potential as a biomarker in the clinical diagnosis and as a target for the treatment of atherosclerosis.

The Renin-Angiotensin-Aldosterone System as a Therapeutic Target in Late Injury Caused by Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a well-known phenomenon that involves different pathophysiological processes. Connection in diverse systems of survival brings about cellular dysfunction or even apoptosis. One of the survival systems of the cells, to the assault caused by ischemia, is the activation of the renin-angiotensin-aldosterone system (also known as an axis), which is focused on activating diverse signaling pathways to favor adaptation to the decrease in metabolic supports caused by the hypoxia. In trying to adapt to the I/R event, great changes occur that unchain cellular dysfunction with the capacity to lead to cell death, which translates into a poor prognosis due to the progression of dysfunction of the cellular activity. The search for the understanding of the diverse therapeutic alternatives in molecular coupling could favor the prognosis and evolution of patients who are subject to the I/R process.

S1P receptor 1-Mediated Anti-Renin-Angiotensin System Cardioprotection: Pivotal Role of Mast Cell Aldehyde Dehydrogenase Type 2

In the ischemic-reperfused (I/R) heart, renin-containing mast cells (MC) release enzymatically active renin, activating a local renin-angiotensin system (RAS), causing excessive norepinephrine release and arrhythmic dysfunction. Activation of Gi-receptors on MC and/or ischemic preconditioning (IPC) prevent renin release, thus providing anti-RAS cardioprotection. We questioned whether sphingosine-1-phosphate (S1P), a sphingolipid produced in the I/R heart, might afford anti-RAS cardioprotection by activating Gi-coupled S1P1 receptors (S1P1R) on MC. We report that activation of Gi-coupled S1P1R in cardiac MC confers IPC-like anti-RAS cardioprotection due to S1P1R-mediated inhibition of I/R-induced cardiac MC degranulation and renin release. This results from an initial translocation of protein kinase C subtype-ε and subsequent activation of aldehyde dehydrogenase type 2 (ALDH2), culminating in the elimination of the MC-degranulating effects of acetaldehyde and other toxic species produced during I/R. Inhibition of toxic aldehydes-induced MC-renin release prevents local RAS activation, reduces infarct size, and alleviates arrhythmias. Notably, these cardioprotective effects are lacking in hearts and MC from gene-targeted knock-in mice (ALDH2*2) in which ALDH2 enzymatic activity is maximally reduced. Thus, ALDH2 appears to play a pivotal role in this protective process. Our findings suggest that MC S1P1R may represent a new pharmacologic and therapeutic target for the direct alleviation of RAS-induced cardiac dysfunctions, including ischemic heart disease and congestive heart failure.

Atorvastatin has a protective effect in a mouse model of bronchial asthma through regulating tissue transglutaminase and triggering receptor expressed on myeloid cells-1 expression

Airway remodeling in asthma contributes to airway hyperreactivity, loss of lung function and persistent symptoms. Current therapies do not adequately treat the structural airway changes associated with asthma. Statin drugs have improved respiratory health and their therapeutic potential in asthma has been tested in clinical trials. However, the mechanism of action of statins in this context has remained elusive. The present study hypothesized that atorvastatin treatment of ovalbumin-exposed mice attenuates early features of airway remodeling via a mevalonate-dependent mechanism. BALB/c mice were sensitized with ovalbumin and atorvastatin was delivered via oral gavage prior to each ovalbumin exposure. Reverse transcription-semi-quantitative polymerase chain reaction (RT-semi-qPCR), ELISA and western blot analysis were used to assess the expression of a number of relevant genes, including tissue transglutaminase (tTG), triggering receptor expressed on myeloid cells (TREM)-1, nuclear factor erythroid 2-related factor (Nrf) 2, hypoxia-inducible factor (HIF)-1α, transforming growth factor (TGF)-β1, matrix metalloproteinase (MMP)-9 and tissue inhibitors of metalloproteinases (TIMP)-1 in lung tissue. α-Smooth muscle actin (α-SMA) activity was measured by immunohistochemistry. Airway hyperresponsiveness, lung collagen deposition, airway wall area, airway smooth muscle thickness and lung pathology were also assessed. Atorvastatin treatment led to downregulation of tTG and TREM-1 expression in lung tissue after ovalbumin sensitization, blocked the activity of MMP-9, vascular endothelial growth factor, nuclear factor-κB p65, α-SMA, HIF-α and TGF-β1 and up-regulated Nrf2 expression. Furthermore, the number of lymphocytes and eosinophils in the atorvastatin group was significantly lower than that in the control group. In addition, airway hyperresponsiveness, lung collagen deposition, airway wall area, airway smooth muscle thickness and pathological changes in the lung were significantly decreased in the atorvastatin group, and tumor necrosis factor-α, interleukin (IL)-8, IL-13 and IL-17 in serum were significantly decreased. Histological results demonstrated the attenuating effect of atorvastatin on ovalbumin-induced airway remodeling in asthma. In conclusion, the present study indicated that atorvastatin significantly alleviated ovalbumin-induced airway remodeling in asthma by downregulating tTG and TREM-1 expression. The marked protective effects of atorvastatin suggest its therapeutic potential in ovalbumin-induced airway remodeling in asthma treatment.

Thioredoxin Activates MKK4-NFκB Pathway in a Redox-dependent Manner to Control Manganese Superoxide Dismutase Gene Expression in Endothelial Cells

The mitogen-activated protein kinase kinase 4 (MKK4) is activated via phosphorylation of Ser-257 and Thr-261 by upstream MAP3Ks and activates JNK and p38 MAPKs in response to cellular stress. We show that thioredoxin (Trx), a cellular redox protein, activates MKK4 via Cys-246 and Cys-266 residues as mutation of these residues renders MKK4 insensitive to phosphorylation by MAP3Ks, TNFα, or Trx. MKK4 is activated in vitro by reduced Trx but not oxidized Trx in the absence of an upstream kinase, suggesting that autophosphorylation of this protein occurs due to reduction of Cys-246 and Cys-266 by Trx. Additionally, mutation of Cys-246 and Cys-266 resulted in loss of kinase activity suggesting that the redox state of Cys-246 and Cys-266 is a critical determinant of MKK4 activation. Trx induces manganese superoxide dismutase (MnSOD) gene transcription by activating MKK4 via redox control of Cys-246 and Cys-266, as mutation of these residues abrogates MKK4 activation and MnSOD expression. We further show that MKK4 activates NFκB for its binding to the MnSOD promoter, which leads to AP-1 dissociation followed by MnSOD transcription. Taken together, our studies show that the redox status of Cys-246 and Cys-266 in MKK4 controls its activities independent of MAP3K, demonstrating integration of the endothelial redox environment to MAPK signaling.

Essential hypertension and oxidative stress: New insights

Essential hypertension is a highly prevalent pathological condition that is considered as one of the most relevant cardiovascular risk factors and is an important cause of morbidity and mortality around the world. Despite the fact that mechanisms underlying hypertension are not yet fully elucidated, a large amount of evidence shows that oxidative stress plays a central role in its pathophysiology. Oxidative stress can be defined as an imbalance between oxidant agents, such as superoxide anion, and antioxidant molecules, and leads to a decrease in nitric oxide bioavailability, which is the main factor responsible for maintaining the vascular tone. Several vasoconstrictor peptides, such as angiotensin II, endothelin-1 and urotensin II, act through their receptors to stimulate the production of reactive oxygen species, by activating enzymes like NADPH oxidase and xanthine oxidase. The knowledge of the mechanism described above has allowed generating new therapeutic strategies against hypertension based on the use of antioxidants agents, including vitamin C and E, N-Acetylcysteine, polyphenols and selenium, among others. These substances have different therapeutic targets, but all represent antioxidant reinforcement. Several clinical trials using antioxidants have been made. The aim of the present review is to provide new insights about the key role of oxidative stress in the pathophysiology of essential hypertension and new clinical attempts to demonstrate the usefulness of antioxidant therapy in the treatment of hypertension.