Therapeutic targeting of mitochondrial superoxide in hypertension

Mitochondrial Dysfunction: Metabolic Drivers of Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is a progressive disease characterized by pulmonary vascular remodeling and lung vasculopathy. The disease displays progressive dyspnea, pulmonary artery uncoupling and right ventricular (RV) dysfunction. The overall survival rate is ranging from 28-72%. Recent Advances: The molecular events that promote the development of PH are complex and incompletely understood. Metabolic impairment has been proposed to contribute to the pathophysiology of PH with evidence for mitochondrial dysfunction involving the electron transport chain proteins, antioxidant enzymes, apoptosis regulators, and mitochondrial quality control. Critical Issues: It is vital to characterize the mechanisms by which mitochondrial dysfunction contribute to PH pathogenesis. This review focuses on the currently available publications that supports mitochondrial mechanisms in PH pathophysiology. Future Directions: Further studies of these metabolic mitochondrial alterations in PH could be viable targets of diagnostic and therapeutic intervention.

NADPH oxidases and oxidase crosstalk in cardiovascular diseases: novel therapeutic targets

Reactive oxygen species (ROS)-dependent production of ROS underlies sustained oxidative stress, which has been implicated in the pathogenesis of cardiovascular diseases such as hypertension, aortic aneurysm, hypercholesterolaemia, atherosclerosis, diabetic vascular complications, cardiac ischaemia-reperfusion injury, myocardial infarction, heart failure and cardiac arrhythmias. Interactions between different oxidases or oxidase systems have been intensively investigated for their roles in inducing sustained oxidative stress. In this Review, we discuss the latest data on the pathobiology of each oxidase component, the complex crosstalk between different oxidase components and the consequences of this crosstalk in mediating cardiovascular disease processes, focusing on the central role of particular NADPH oxidase (NOX) isoforms that are activated in specific cardiovascular diseases. An improved understanding of these mechanisms might facilitate the development of novel therapeutic agents targeting these oxidase systems and their interactions, which could be effective in the prevention and treatment of cardiovascular disorders.

A neutral water-soluble mitochondria-targeting polymer

We report the first neutral and water-soluble polymer capable of strong mitochondrial targeting in vitro and in vivo, zwitterionic poly[2-(N-oxide-N,N-diethylamino)ethyl methacrylate] (OPDEA). OPDEA is quickly internalized via macropinocytosis by various cancer cells and transferred into the mitochondria, which slightly lowers the mitochondrial membrane potential as determined by the JC-1 assay.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

Crosstalk Between Mitochondrial Hyperacetylation and Oxidative Stress in Vascular Dysfunction and Hypertension

Significance: Vascular dysfunction plays a key role in the development of arteriosclerosis, heart disease, and hypertension, which causes one-third of deaths worldwide. Vascular oxidative stress and metabolic disorders contribute to vascular dysfunction, leading to impaired vasorelaxation, vascular hypertrophy, fibrosis, and aortic stiffening. Mitochondria are critical in the regulation of metabolic and antioxidant functions; therefore, mitochondria-targeted treatments could be beneficial. Recent Advances: Vascular dysfunction is crucial in hypertension pathophysiology and exhibits bidirectional relationship. Metabolic disorders and oxidative stress contribute to the pathogenesis of vascular dysfunction and hypertension, which are associated with mitochondrial impairment and hyperacetylation. Mitochondrial deacetylase Sirtuin 3 (Sirt3) is critical in the regulation of metabolic and antioxidant functions. Clinical studies show that cardiovascular disease risk factors reduce Sirt3 level and Sirt3 declines with age, paralleling the increased incidence of cardiovascular disease and hypertension. An imbalance between mitochondrial acetylation and reduced Sirt3 activity contributes to mitochondrial dysfunction and oxidative stress. We propose that mitochondrial hyperacetylation drives a vicious cycle between metabolic disorders and mitochondrial oxidative stress, promoting vascular dysfunction and hypertension. Critical Issues: The mechanisms of mitochondrial dysfunction are still obscure in human hypertension. Mitochondrial hyperacetylation and oxidative stress contribute to mitochondrial dysfunction; however, regulation of mitochondrial acetylation, the role of GCN5L1 (acetyl-CoA-binding protein promoting acetyltransferase protein acetylation) acetyltransferase, Sirt3 deacetylase, and acetylation of specific proteins require further investigations. Future Directions: There is an urgent need to define molecular mechanisms and the pathophysiological role of mitochondrial hyperacetylation, identify novel pharmacological targets, and develop therapeutic approaches to reduce this phenomenon.

Prenatal high-salt diet impaired vasodilatation with reprogrammed renin-angiotensin system in offspring rats

AIMS

High-salt diet is linked to hypertension, and prenatal high-salt diet increases the risk of cardiovascular diseases in the offspring. The present study investigated whether and how prenatal high-salt diet influenced nitric oxide-mediated vasodilatation in the offspring.

METHODS AND RESULTS

Pregnant rats were fed either normal-salt (1% sodium chloride) or high-salt (8% sodium chloride) diet during gestation. Experiments were conducted in 5-month-old male offspring. Sodium nitroprusside (SNP, nitric oxide donor)-induced hypotensive responses (in vivo) and vascular dilatation (in vitro) was significantly attenuated (Emax: 84 ± 2 vs. 51 ± 2, high-salt vs. control, P < 0.001) in the high-salt offspring, indicating reduced vascular relaxations. Pretreatment with Tempol (reactive oxygen species scavenger) alleviated this attenuation. The high-salt offspring showed an increased level of oxidative stress markers in both mesenteric arteries and plasma samples. The antioxidant activity, serum superoxide dismutase and catalase were significantly reduced, whereas malondialdehyde was increased in the high-salt offspring. O2 production, and protein expression of Nox2 and Nox4 in mesenteric arteries was significantly increased in the high-salt offspring whereas Nox1 showed no changes. The local renin-angiotensin system in mesenteric arteries was activated, associated with an increased NADPH oxidase. DNA methylation at the proximal promoter of angiotensin-converting enzyme gene in the lung was significantly increased in the high-salt offspring (P = 0.004).

CONCLUSION

The results suggest that prenatal high-salt diet impairs nitric oxide-mediated vasodilatation because of the increased oxidative stress-affected renin-angiotensin system in the high-salt offspring, providing new information for understanding, and early prevention of cardiovascular diseases in fetal origins.

Chemoptogenetic damage to mitochondria causes rapid telomere dysfunction

Reactive oxygen species (ROS) play important roles in aging, inflammation, and cancer. Mitochondria are an important source of ROS; however, the spatiotemporal ROS events underlying oxidative cellular damage from dysfunctional mitochondria remain unresolved. To this end, we have developed and validated a chemoptogenetic approach that uses a mitochondrially targeted fluorogen-activating peptide (Mito-FAP) to deliver a photosensitizer MG-2I dye exclusively to this organelle. Light-mediated activation (660 nm) of the Mito-FAP-MG-2I complex led to a rapid loss of mitochondrial respiration, decreased electron transport chain complex activity, and mitochondrial fragmentation. Importantly, one round of singlet oxygen produced a persistent secondary wave of mitochondrial superoxide and hydrogen peroxide lasting for over 48 h after the initial insult. By following ROS intermediates, we were able to detect hydrogen peroxide in the nucleus through ratiometric analysis of the oxidation of nuclear cysteine residues. Despite mitochondrial DNA (mtDNA) damage and nuclear oxidative stress induced by dysfunctional mitochondria, there was a lack of gross nuclear DNA strand breaks and apoptosis. Targeted telomere analysis revealed fragile telomeres and telomere loss as well as 53BP1-positive telomere dysfunction-induced foci (TIFs), indicating that DNA double-strand breaks occurred exclusively in telomeres as a direct consequence of mitochondrial dysfunction. These telomere defects activated ataxia-telangiectasia mutated (ATM)-mediated DNA damage repair signaling. Furthermore, ATM inhibition exacerbated the Mito-FAP-induced mitochondrial dysfunction and sensitized cells to apoptotic cell death. This profound sensitivity of telomeres through hydrogen peroxide induced by dysregulated mitochondria reveals a crucial mechanism of telomere-mitochondria communication underlying the pathophysiological role of mitochondrial ROS in human diseases.

Trpm2 enhances physiological bioenergetics and protects against pathological oxidative cardiac injury: Role of Pyk2 phosphorylation

The mechanisms by which Trpm2 channels enhance mitochondrial bioenergetics and protect against oxidative stress-induced cardiac injury remain unclear. Here, the role of proline-rich tyrosine kinase 2 (Pyk2) in Trpm2 signaling is explored. Activation of Trpm2 in adult myocytes with H₂ O₂ resulted in 10- to 21-fold increases in Pyk2 phosphorylation in wild-type (WT) myocytes which was significantly lower (~40%) in Trpm2 knockout (KO) myocytes. Pyk2 phosphorylation was inhibited (~54%) by the Trpm2 blocker clotrimazole. Buffering Trpm2-mediated Ca²⁺ increase with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) resulted in significantly reduced pPyk2 in WT but not in KO myocytes, indicating Ca²⁺ influx through activated Trpm2 channels phosphorylated Pyk2. Part of phosphorylated Pyk2 translocated from cytosol to mitochondria which has been previously shown to augment mitochondrial Ca²⁺ uptake and enhance adenosine triphosphate generation. Although Trpm2-mediated Ca²⁺ influx phosphorylated Ca²⁺ -calmodulin kinase II (CaMKII), the CaMKII inhibitor KN93 did not significantly affect Pyk2 phosphorylation in H₂ O₂ -treated WT myocytes. After ischemia/reperfusion (I/R), Pyk2 phosphorylation and its downstream prosurvival signaling molecules (pERK1/2 and pAkt) were significantly lower in KO-I/R when compared with WT-I/R hearts. After hypoxia/reoxygenation, mitochondrial membrane potential was lower and superoxide level was higher in KO myocytes, and were restored to WT values by the mitochondria-targeted superoxide scavenger MitoTempo. Our results suggested that Ca²⁺ influx via tonically activated Trpm2 phosphorylated Pyk2, part of which translocated to mitochondria, resulting in better mitochondrial bioenergetics to maintain cardiac health. After I/R, Pyk2 activated prosurvival signaling molecules and prevented excessive increases in reactive oxygen species, thereby affording protection from I/R injury.

Targeting of reactive isolevuglandins in mitochondrial dysfunction and inflammation

Inflammation is a major cause of morbidity and mortality in Western societies. Despite use of multiple drugs, both chronic and acute inflammation still represent major health burdens. Inflammation produces highly reactive dicarbonyl lipid peroxidation products such as isolevuglandins which covalently modify and cross-link proteins via lysine residues. Mitochondrial dysfunction has been associated with inflammation; however, its molecular mechanisms and pathophysiological role are still obscure. We hypothesized that inflammation-induced isolevuglandins contribute to mitochondrial dysfunction and mortality. To test this hypothesis, we have (a) investigated the mitochondrial dysfunction in response to synthetic 15-E2-isolevuglandin (IsoLG) and its adducts; (b) developed a new mitochondria-targeted scavenger of isolevuglandins by conjugating 2-hydroxybenzylamine to the lipophilic cation triphenylphosphonium, (4-(4-aminomethyl)-3-hydroxyphenoxy)butyl)-triphenylphosphonium (mito2HOBA); (c) tested if mito2HOBA protects from mitochondrial dysfunction and mortality using a lipopolysaccharide model of inflammation. Acute exposure to either IsoLG or IsoLG adducts with lysine, ethanolamine or phosphatidylethanolamine inhibits mitochondrial respiration and attenuates Complex I activity. Complex II function was much more resistant to IsoLG. We confirmed that mito2HOBA markedly accumulates in isolated mitochondria and it is highly reactive with IsoLGs. To test the role of mitochondrial IsoLGs, we studied the therapeutic potential of mito2HOBA in lipopolysaccharide mouse model of sepsis. Mito2HOBA supplementation in drinking water (0.1 g/L) to lipopolysaccharide treated mice increased survival by 3-fold, improved complex I-mediated respiration, and histopathological analyses supported mito2HOBA-mediated protection of renal cortex from cell injury. These data support the role of mitochondrial IsoLG in mitochondrial dysfunction and inflammation. We conclude that reducing mitochondrial IsoLGs may be a promising therapeutic target in inflammation and conditions associated with mitochondrial oxidative stress and dysfunction.

Biochemical basis and metabolic interplay of redox regulation

Accumulated evidence strongly indicates that oxidative stress, characterized by an imbalance between reactive oxygen species (ROS) production and antioxidants in favor of oxidants, plays an important role in disease pathogenesis. However, ROS can act as signaling molecules and fulfill essential physiological functions at basal levels. Each ROS would be different in the extent to stimulate and contribute to different pathophysiological effects. Importantly, multiple ROS generators can be activated either concomitantly or sequentially by relevant signaling molecules for redox biological functions. Here, we summarized the current knowledge related to chemical and biochemical features of primary ROS species and corresponding antioxidants. Metabolic pathways of five major ROS generators and five ROS clearance systems were described, including their ROS products, specific ROS enriched tissue, cell and organelle, and relevant functional implications. We provided an overview of ROS generation and induction at different levels of metabolism. We classified 11 ROS species into three types based on their reactivity and target selectivity and presented ROS homeostasis and functional implications in pathological and physiological status. This article intensively reviewed and refined biochemical basis, metabolic signaling and regulation, functional insights, and provided guidance for the identification of novel therapeutic targets.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

IDH2 deficiency impairs cutaneous wound healing via ROS-dependent apoptosis

Dermal fibroblasts are mesenchymal cells found between the skin epidermis and subcutaneous tissue that play a pivotal role in cutaneous wound healing by synthesizing fibronectin (a component of the extracellular matrix), secreting angiogenesis factors, and generating strong contractile forces. In wound healing, low concentrations of reactive oxygen species (ROS) are essential in combating invading microorganisms and in cell-survival signaling. However, excessive ROS production impairs fibroblasts. Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) is a key enzyme that regulates the mitochondrial redox balance and reduces oxidative stress-induced cell injury through the generation of NADPH. In the present study, the downregulation of IDH2 expression resulted in an increase in cell apoptosis in mouse skin through ROS-dependent ATM-mediated p53 signaling. IDH2 deficiency also delayed cutaneous wound healing in mice and impaired dermal fibroblast function. Furthermore, pretreatment with the mitochondria-targeted antioxidant mito-TEMPO alleviated the apoptosis induced by IDH2 deficiency both in vitro and in vivo. Together, our findings highlight the role of IDH2 in cutaneous wound healing in association with mitochondrial ROS.

New opportunities for targeting redox dysregulation in cardiovascular disease

Despite substantial promise, the use of antioxidant therapy to improve cardiovascular outcomes has been disappointing. Whilst the fundamental biology supporting their use continues to build, the challenge now is to differentially target dysregulated redox signalling domains and to identify new ways to deliver antioxidant substances. Looking further afield to other disciplines, there is an emerging ‘tool-kit’ containing sophisticated molecular and drug delivery applications. Applying these to the cardiovascular redox field could prove a successful strategy to combat the increasing disease burden. Excessive reactive oxygen species production and protein modifications in the mitochondria has been the target of successful drug development with several positive outcomes emerging in the cardiovascular space, harnessing both improved delivery mechanisms and enhanced understanding of the biological abnormalities. Using this as a blueprint, similar strategies could be applied and expanded upon in other redox-hot-spots, such as the caveolae sub-cellular region, which houses many of the key cardiovascular redox proteins such as NADPH oxidase, endothelial nitric oxide synthase, angiotensin II receptors, and beta adrenoceptors. The expanded tool kit of drug development, including gene and miRNA therapies, nanoparticle technology and micropeptide targeting, can be applied to target dysregulated redox signalling in subcellular compartments of cardiovascular cells. In this review, we consider the opportunities for improving cardiovascular outcomes by utilizing new technology platforms to target subcellular ‘bonfires’ generated by dysregulated redox pathways, to improve clinical outcomes.

Lipoprotein modulation of proteinuric renal injury

High-density lipoprotein (HDL) and its main protein, apolipoprotein AI (apoAI), have established benefits in various cells, but whether these cytoprotective effects of HDL pertain to renal cells is unclear. We investigated the in vitro consequences of exposing damaged podocytes to normal apoAI, HDL, and apoAI mimetic (L-4F), and the in vivo effects of L-4F on kidney and atherosclerotic injury in a podocyte-specific injury model of proteinuria. In vitro, primary mouse podocytes were injured by puromycin aminonucleoside (PAN). Cellular viability, migration, production of reactive oxygen species (ROS), apoptosis, and the underlying signaling pathway were assessed. In vivo, we used a proteinuric model, Nphs1-hCD25 transgenic (NEP25⁺) mice, which express human CD25 on podocytes. Podocyte injury was induced by using immunotoxin (LMB2) and generated a proteinuric atherosclerosis model, NEP25⁺:apoE^-/- mice, was generated by mating apoE-deficient (apoE^-/-) mice with NEP25⁺ mice. Animals received L-4F or control vehicle. Renal function, podocyte injury, and atherosclerosis were assessed. PAN reduced podocyte viability, migration, and increased ROS production, all significantly lessened by apoAI, HDL, and L-4F. L-4F attenuated podocyte apoptosis and diminished PAN-induced inactivation of Janus family protein kinase-2/signal transducers and activators of transcription 3. In NEP25⁺ mice, L-4F significantly lessened overall proteinuria, and preserved podocyte expression of synaptopodin and cell density. Proteinuric NEP25⁺:apoE^-/- mice had more atherosclerosis than non-proteinuric apoE^-/- mice, and these lesions were significantly decreased by L-4F. Normal human apoAI, HDL, and apoAI mimetic protect against podocyte damage. ApoAI mimetic provides in vivo beneficial effects on podocytes that culminate in reduced albuminuria and atherosclerosis. The results suggest supplemental apoAI/apoAI mimetic may be a novel candidate to lessen podocyte damage and its complications.

Vascular Inflammation and Oxidative Stress: Major Triggers for Cardiovascular Disease

Cardiovascular disease is a leading cause of death and reduced quality of life, proven by the latest data of the Global Burden of Disease Study, and is only gaining in prevalence worldwide. Clinical trials have identified chronic inflammatory disorders as cardiovascular risks, and recent research has revealed a contribution by various inflammatory cells to vascular oxidative stress. Atherosclerosis and cardiovascular disease are closely associated with inflammation, probably due to the close interaction of inflammation with oxidative stress. Classical therapies for inflammatory disorders have demonstrated protective effects in various models of cardiovascular disease; especially established drugs with pleiotropic immunomodulatory properties have proven beneficial cardiovascular effects; normalization of oxidative stress seems to be a common feature of these therapies. The close link between inflammation and redox balance was also supported by reports on aggravated inflammatory phenotype in the absence of antioxidant defense proteins (e.g., superoxide dismutases, heme oxygenase-1, and glutathione peroxidases) or overexpression of reactive oxygen species producing enzymes (e.g., NADPH oxidases). The value of immunomodulation for the treatment of cardiovascular disease was recently supported by large-scale clinical trials demonstrating reduced cardiovascular mortality in patients with established atherosclerotic disease when treated by highly specific anti-inflammatory therapies (e.g., using monoclonal antibodies against cytokines). Modern antidiabetic cardiovascular drugs (e.g., SGLT2 inhibitors, DPP-4 inhibitors, and GLP-1 analogs) seem to share these immunomodulatory properties and display potent antioxidant effects, all of which may explain their successful lowering of cardiovascular risk.

Inhibition of Mitochondrial Oxidative Damage Improves Reendothelialization Capacity of Endothelial Progenitor Cells via SIRT3 (Sirtuin 3)-Enhanced SOD2 (Superoxide Dismutase 2) Deacetylation in Hypertension

OBJECTIVE

Dysfunction of endothelial progenitor cells (EPCs) leads to impaired endothelial repair capacity in patients with hypertension, but the mechanisms remain incompletely understood. Mitochondrial oxidative stress is involved in endothelial injury in hypertension. In this study, we aim to investigate the role of mitochondrial oxidative stress in the deficient endothelial reparative capacity of EPCs and identify enhanced SIRT3 (sirtuin 3)-mediated SOD2 (superoxide dismutase 2) deacetylation as a novel endothelial protective mechanism in hypertension. Approach and Results: Hypertension-EPCs displayed increased mitochondrial reactive oxygen species and mitochondrial damage, including loss of mitochondrial membrane potential, abnormal mitochondrial ultrastructure, and mtDNA oxidative injury, which was coincided with impaired in vitro function and in vivo reendothelialization capacity. The harmful effects of hypertension on mitochondrial function of EPCs were in vitro mimicked by angiotensin II coincubation. Scavenging of mitochondrial reactive oxygen species with mitoTEMPO attenuated mitochondrial oxidative damage and rescued reendothelialization capacity. Enzymatic activity and deacetylation level of SOD2 were significantly reduced in hypertension-EPCs, which was accompanied with decreased SIRT3 expression. Knockdown of SIRT3 in EPCs resulted in mitochondrial oxidative damage, hyperacetylation of SOD2, and suppression of reendothelialization capacity. SIRT3 physically interacted with SOD2 and eliminated excess mitochondrial reactive oxygen species, restored mitochondrial function through enhancing SOD2 activity by deacetylation of K68. Upregulation of SIRT3/SOD2 signaling improved reendothelialization capability of EPCs.

CONCLUSIONS

The present study demonstrated for the first time that mitochondrial oxidative damage because of deficient SIRT3/SOD2 signaling contributes to the decline in reendothelialization capacity of EPCs in hypertension. Maintenance of mitochondrial redox homeostasis in EPCs may be a novel therapeutic target for endothelial injury.

Differential impacts of brain stem oxidative stress and nitrosative stress on sympathetic vasomotor tone

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

BA6 Induces Apoptosis via Stimulation of Reactive Oxygen Species and Inhibition of Oxidative Phosphorylation in Human Lung Cancer Cells

Lung cancer is the leading cause of cancer deaths in the world, with a five-year survival rate of less than 30%. Clinically effective chemotherapeutic treatments at the initial stage may eventually face the dilemma of no drug being effective due to drug resistance; therefore, finding new effective drugs for lung cancer treatment is a necessary and important issue. Compounds capable of further increasing the oxidative stress of cancer cells are considered to have anticancer potential because they possessed the ability to induce apoptosis. This study mainly investigated the effects of BA6 (heteronemin), the marine sponge sesterterpene, on lung cancer cell apoptosis, via modulation of mitochondrial reactive oxygen species (mtROS) and oxidative phosphorylation (OXPHOS). BA6 has cellular cytotoxic activities against a variety of cancer cell lines, but it has no effect on nontumor cells. The BA6-treated lung cancer cells show a significant increase in both cellular ROS and mtROS, which in turn caused the loss of mitochondrial membrane potential (MMP). The increase of oxidative stress in lung cancer cells treated with BA6 was accompanied by a decrease in the expression of antioxidant enzymes Cu/Zn SOD, MnSOD, and catalase. In addition, OXPHOS performed in the mitochondria and glycolysis in the cytoplasm were inhibited, which subsequently reduced downstream ATP production. Pretreatment with mitochondria-targeted antioxidant MitoTEMPO reduced BA6-induced apoptosis through the mitochondria-dependent apoptotic pathway, which was accompanied by increased cell viability, decreased mtROS, enhanced MMP, and suppressed expression of cleaved caspase-3 and caspase-9 proteins. In conclusion, the results of this study clarify the mechanism of BA6-induced apoptosis in lung cancer cells via the mitochondrial apoptotic pathway, suggesting that it is a potentially innovative alternative to the treatment of human lung cancer.

Mitigation of cocaine-mediated mitochondrial damage, defective mitophagy and microglial activation by superoxide dismutase mimetics

Although cocaine exposure has been shown to potentiate neuroinflammation by upregulating glial activation in the brain, the role of mitophagy in this process remains an enigma. In the present study, we sought to examine the role of impaired mitophagy in cocaine-mediated activation of microglia and to determine the ameliorative potential of superoxide dismutase mimetics in this context. Our findings demonstrated that exposure of mouse primary microglial cells (mPMs) to cocaine resulted in decreased mitochondrial membrane potential, that was accompanied by increased expression of mitophagy markers, PINK1 and PRKN. Exposure of microglia to cocaine also resulted in increased expression of DNM1L and OPTN with a concomitant decrease in the rate of mitochondrial oxygen consumption as well as impaired mitochondrial functioning. Additionally, in the presence of cocaine, microglia also exhibited upregulated expression of autophagosome markers, BECN1, MAP1LC3B-II, and SQSTM1. Taken together, these findings suggested diminished mitophagy flux and accumulation of mitophagosomes in the presence of cocaine. These findings were further confirmed by imaging techniques such as transmission electron microscopy and confocal microscopy. Cocaine-mediated activation of microglia was further monitored by assessing the expression of the microglial marker (ITGAM) and the inflammatory cytokine (Tnf, Il1b, and Il6) mRNAs. Pharmacological, as well as gene-silencing approaches aimed at blocking both the autophagy/mitophagy and SIGMAR1 expression, underscored the role of impaired mitophagy in cocaine-mediated activation of microglia. Furthermore, superoxide dismutase mimetics such as TEMPOL and MitoTEMPO were shown to alleviate cocaine-mediated impaired mitophagy as well as microglial activation.Abbreviations: 3-MA: 3-methyladenine; Δψm: mitochondrial membrane potential; ACTB: actin, beta; AIF1: allograft inflammatory factor 1; ATP: adenosine triphosphate; BAF: bafilomycin A₁; BECN1: beclin 1, autophagy related; CNS: central nervous system; DNM1L: dynamin 1 like; DMEM: Dulbecco modified Eagle medium; DAPI: 4,6-Diamidino-2-phenylindole; DRD2: dopamine receptor D2; ECAR: extracellular acidification rate; FBS: fetal bovine serum; FCCP: Trifluoromethoxy carbonylcyanide phenylhydrazone; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; IL1B: interleukin 1, beta; IL6: interleukin 6; ITGAM: integrin subunit alpha M; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; mPMs: mouse primary microglial cells; MRC: maximal respiratory capacity; NFKB: nuclear factor kappa B; NLRP3: NLR family pyrin domain containing 3; NTRK2: neurotrophic receptor tyrosine kinase 2; OCR: oxygen consumption rate; OPTN: optineurin; PBS: phosphate buffered saline; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; siRNA: small interfering RNA; SQSTM1: sequestosome 1; TNF: tumor necrosis factor.

Neuroinflammation in hypertension: the renin-angiotensin system versus pro-resolution pathways

Overstimulation of the pro-inflammatory pathways within brain areas responsible for sympathetic outflow is well evidenced as a primary contributing factor to the establishment and maintenance of neurogenic hypertension. However, the precise mechanisms and stimuli responsible for promoting a pro-inflammatory state are not fully elucidated. Recent work has unveiled novel compounds derived from omega-3 polyunsaturated fatty acids (ω-3 PUFAs), termed specialized pro-resolving mediators (SPMs), which actively regulate the resolution of inflammation. Failure or dysregulation of the resolution process has been linked to a variety of chronic inflammatory and neurodegenerative diseases. Given the pathologic role of neuroinflammation in the hypertensive state, SPMs and their associated pathways may provide a link between hypertension and the long-standing association of dietary ω-3 PUFAs with cardioprotection. Herein, we review recent progress in understanding the RAS-driven pathophysiology of neurogenic hypertension, particularly in regards to the chronic low-grade neuroinflammatory response. In addition, we examine the potential for an impaired resolution of inflammation process in the context of hypertension.

IL-1 Inhibition and Function of the HDL-Containing Fraction of Plasma in Patients with Stages 3 to 5 CKD

BACKGROUND AND OBJECTIVES

Systemic inflammation modulates cardiovascular disease risk and functionality of HDL in the setting of CKD. Whether interventions that modify systemic inflammation can improve HDL function in CKD is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a post hoc analysis of two randomized, clinical trials, IL-1 trap in participants with GFR 15-59 ml/min per 1.73 m² (study A) and IL-1 receptor antagonist in participants on maintenance hemodialysis (study B), to evaluate if IL-1 blockade had improved the anti-inflammatory activity (IL-6, TNF-α, and Nod-like receptor protein 3), antioxidant function (superoxide production), and net cholesterol efflux capacity of HDL. HDL function was measured using LPS-stimulated THP-1 macrophages or peritoneal macrophages of apoE-deficient mice exposed to the apoB-depleted, HDL-containing fraction obtained from the plasma of the study participants, collected before and after the interventions to block IL-1 effects. Analysis of covariance was used for between group comparisons.

RESULTS

The mean age of the participants was 60±13 years, 72% (n=33) were men, and 39% (n=18) were black. There were 32 CKD (16 IL-1 trap and 16 placebo) and 14 maintenance hemodialysis (7 IL-1 receptor antagonist and 7 placebo) participants. Compared with placebo, IL-1 inhibition, in study A and B reduced cellular expression of TNF-α by 15% (P=0.05) and 64% (P=0.02), IL-6 by 38% (P=0.004) and 56% (P=0.08), and Nod-like receptor protein 3 by 16% (P=0.01) and 25% (P=0.02), respectively. The intervention blunted superoxide production in the treated arm compared with placebo, with the values being higher by 17% in the placebo arm in study A (P<0.001) and 12% in the placebo arm in study B (P=0.004). Net cholesterol efflux capacity was not affected by either intervention.

CONCLUSIONS

IL-1 blockade improves the anti-inflammatory and antioxidative properties of the HDL-containing fraction of plasma in patients with stages 3-5 CKD, including those on maintenance hemodialysis.

Effect of mito-TEMPO, a mitochondria-targeted antioxidant, in rats with neuropathic pain

The therapeutic effects of mitochondria-targeted antioxidants have been demonstrated in many pathological conditions, but their effect on neuropathic pain remains unclear. The objective was to study the therapeutic effects and mechanisms of mito-TEMPO (MT), as a nitroxide conjugated with a triphenylphosphonium moiety, on neuropathic pain in rats. Rats were randomly assigned to sham control (sham), chronic constrictive injury (CCI) or MT treatment groups (sham+MT and CCI+MT). All animals received CCI of the left sciatic nerve except those in the sham group. Overall, 0.7 mg/kg of MT was intraperitoneally injected once daily for 14 consecutive days starting from day 7 after surgery. Mechanical paw withdrawal threshold and thermal paw withdrawal latency were detected to assess pain behavior. Malondialdehyde and reduced glutathione content and total superoxide dismutase activity of serum and spinal cord tissues were estimated to assess oxidative stress levels. Mitochondrial morphology and dynamin-related proteins were used to evaluate mitochondrial function, such as fusion [Mitofusin (Mfn) and optic atrophy 1 gene protein (OPA1)] and fission [dynamin-related protein (DRP1) and Fis1]. Paw withdrawal threshold and thermal paw withdrawal latency were significantly increased in the CCI+MT group compared with the CCI group. The malondialdehyde content was decreased whereas glutathione content and superoxide dismutase activity were increased in the serum of CCI+MT rats. Furthermore, MT substantially attenuated the elevated number and decreased size of mitochondria induced by CCI. Finally, MT significantly increased expressions of Mfn1 and OPA1 and significantly decreased expression of DRP1 and Fis1. The mitochondria-targeted antioxidant MT relieved neuropathic pain induced by CCI by protecting mitochondria against oxidative stress injury.

Comparative Genotoxicity of TEMPO and 3 of Its Derivatives in Mouse Lymphoma Cells

TEMPO (2, 2, 6, 6-tetramethylphiperidine-1-oxyl) and its derivatives are stable free radical nitroxides widely used in the field of chemistry, biology, and pharmacology. TEMPO was previously found to be mutagenic and to induce micronuclei in mammalian cells. In this study, we investigated and quantified the genotoxicity of 4 structurally similar nitroxides, TEMPO and 3 of its derivatives (4-hydroxy-TEMPO, 4-oxo-TEMPO, and 4-methoxy-TEMPO), using the mouse lymphoma assay (MLA) and Comet assay in L5178Y Tk+/- cells. The results showed that all tested nitroxides were cytotoxic and mutagenic in the MLA, both in the presence and absence of S9, with metabolic activation significantly enhancing the cytotoxicity and/or mutagenicity. In addition, the 4 nitroxides caused DNA-strand breakage. The mutagenicity and DNA damaging dose-responses of the test articles were compared using the PROAST benchmark dose software package. The potency ranking of the 4 nitroxides for mutagenicity was different from the ranking of the DNA damaging effects. The mode of action analysis by a multi-endpoint DNA damage pathway assay classified all 4 nitroxides as clastogens. In addition, the majority of the induced Tk mutants showed loss of heterozygosity at the Tk and D11Mit42 loci (ie, chromosome damage <31 Mbp). These results suggest that TEMPO and its 3 derivatives are cytotoxic and mutagenic in mouse lymphoma cells through a mechanism that involves strand breakage and large alterations to DNA. The potency rankings indicate that the different TEMPO derivatives vary in their mutagenic and DNA damaging potential.

Role of Mitochondrial Dysfunction and Reactive Oxygen Species in Mediating Hypertension in the Reduced Uterine Perfusion Pressure Rat Model of Preeclampsia

Placental ischemia is believed to be the initial event in the development of preeclampsia. Mitochondrial dysfunction is a cause of reactive oxygen species (ROS) generation and oxidative stress, however, there are not many studies examining the role of mitochondrial ROS in the pathology of preeclampsia. The purpose of this study was to not only examine the effect of placental ischemia on mitochondrial-mediated oxidative stress in reduced uterine perfusion pressure (RUPP) rat model of preeclampsia but to also examine the role of mitochondrial ROS in contributing to hypertension in response to placental ischemia. Female pregnant Sprague Dawley rats were used in this study. On gestational day 14, RUPP surgery was performed. On gestational day 19, blood pressure (mean arterial pressure) was measured, placentas and kidneys were collected from normal pregnant and RUPP rats and processed for mitochondrial respiration, ROS, and oxidative phosphorylation enzyme activities. Renal and placental complex activities, expressions and respiration rates were significantly reduced and mitochondrial ROS was increased in RUPP versus normal pregnant mitochondria. Mean arterial pressure was elevated in RUPP (n=6) compared with normal pregnant rats (n=5; 126±4 versus 103±4 mm Hg; P<0.05) and treatment with mitochondrial-specific antioxidants (MitoQ/MitoTEMPO) significantly reduced mean arterial pressure in RUPPs (n=5-10). Mitochondrial ROS was significantly elevated in endothelial cells incubated with RUPP serum compared from with normal pregnant rats, whereas serum from mito antioxidant-treated RUPP rats attenuated this response. Impaired mitochondrial function and vascular, placental, and renal mitochondrial ROS play an important role in hypertension and reduced fetal weight in response to placental ischemia during pregnancy.

Cancer-associated fibroblasts promote prostate cancer malignancy via metabolic rewiring and mitochondrial transfer

Cancer-associated fibroblasts (CAFs) are the major cellular stromal component of many solid tumors. In prostate cancer (PCa), CAFs establish a metabolic symbiosis with PCa cells, contributing to cancer aggressiveness through lactate shuttle. In this study, we report that lactate uptake alters the NAD⁺/NADH ratio in the cancer cells, which culminates with SIRT1-dependent PGC-1α activation and subsequent enhancement of mitochondrial mass and activity. The high exploitation of mitochondria results in tricarboxylic acid cycle deregulation, accumulation of oncometabolites and in the altered expression of mitochondrial complexes, responsible for superoxide generation. Additionally, cancer cells hijack CAF-derived functional mitochondria through the formation of cellular bridges, a phenomenon that we observed in both in vitro and in vivo PCa models. Our work reveals a crucial function of tumor mitochondria as the energy sensors and transducers of CAF-dependent metabolic reprogramming and underscores the reliance of PCa cells on CAF catabolic activity and mitochondria trading.

Knockout of dihydrofolate reductase in mice induces hypertension and abdominal aortic aneurysm via mitochondrial dysfunction

Hypertension and abdominal aortic aneurysm (AAA) are severe cardiovascular diseases with incompletely defined molecular mechanisms. In the current study we generated dihydrofolate reductase (DHFR) knockout mice for the first time to examine its potential contribution to the development of hypertension and AAA, as well as the underlying molecular mechanisms. Whereas the homozygote knockout mice were embryonically lethal, the heterozygote knockout mice had global reduction in DHFR protein expression and activity. Angiotensin II infusion into these animals resulted in substantially exaggerated elevation in blood pressure and development of AAA, which was accompanied by excessive eNOS uncoupling activity (featured by significantly impaired tetrahydrobiopterin and nitric oxide bioavailability), vascular remodeling (MMP2 activation, medial elastin breakdown and adventitial fibrosis) and inflammation (macrophage infiltration). Importantly, scavenging of mitochondrial reactive oxygen species with Mito-Tempo in vivo completely abrogated development of hypertension and AAA in DHFR knockout mice, indicating a novel role of mitochondria in mediating hypertension and AAA downstream of DHFR deficiency-dependent eNOS uncoupling. These data for the first time demonstrate that targeting DHFR-deficiency driven mitochondrial dysfunction may represent an innovative therapeutic option for the treatment of AAA and hypertension.

SIRT3 promotes antimycobacterial defenses by coordinating mitochondrial and autophagic functions

SIRT3 (sirtuin 3), a mitochondrial protein deacetylase, maintains respiratory function, but its role in the regulation of innate immune defense is largely unknown. Herein, we show that SIRT3 coordinates mitochondrial function and macroautophagy/autophagy activation to promote anti-mycobacterial responses through PPARA (peroxisome proliferator activated receptor alpha). SIRT3 deficiency enhanced inflammatory responses and mitochondrial dysfunction, leading to defective host defense and pathological inflammation during mycobacterial infection. Antibody-mediated depletion of polymorphonuclear neutrophils significantly increased protection against mycobacterial infection in sirt3^-/- mice. In addition, mitochondrial oxidative stress promoted excessive inflammation induced by Mycobacterium tuberculosis infection in sirt3^-/- macrophages. Notably, SIRT3 was essential for the enhancement of PPARA, a key regulator of mitochondrial homeostasis and autophagy activation in the context of infection. Importantly, overexpression of either PPARA or TFEB (transcription factor EB) in sirt3^-/- macrophages recovered antimicrobial activity through autophagy activation. Furthermore, pharmacological activation of SIRT3 enhanced antibacterial autophagy and functional mitochondrial pools during mycobacterial infection. Finally, the levels of SIRT3 and PPARA were downregulated and inversely correlated with TNF (tumor necrosis factor) levels in peripheral blood mononuclear cells from tuberculosis patients. Collectively, these data demonstrate a previously unappreciated function of SIRT3 in orchestrating mitochondrial and autophagic functions to promote antimycobacterial responses. Abbreviations: Ab: antibody; BCG: M. bovis Bacillus Calmette-Guérin; Baf-A₁: bafilomycin A₁; BMDMs: bone marrow-derived macrophages; CFU: colony forming unit; CXCL5: C-X-C motif chemokine ligand 5; EGFP: enhanced green fluorescent protein; ERFP: enhanced red fluorescent protein; FOXO3: forkhead box O3; HC: healthy controls; H&E: haematoxylin and eosin; HKL: honokiol; IHC: immunohistochemistry; IL1B: interleukin 1 beta; IL6: interleukin 6; IL12B: interleukin 12B; MDMs: monocyte-derived macrophages; MMP: mitochondrial membrane potential; Mtb: Mycobacterium tuberculosis; PBMC: peripheral blood mononuclear cells; PBS: phosphate buffered saline; PMN: polymorphonuclear neutrophil; PPARA: peroxisome proliferator activated receptor alpha; ROS: reactive oxygen species; SIRT3: sirtuin 3; TB: tuberculosis; TEM: transmission electron microscopy; TFEB: transcription factor EB; TNF: tumor necrosis factor.

Reactive oxygen species modulate Na+-coupled neutral amino acid transporter 1 expression in piglet pulmonary arterial endothelial cells

We have previously shown that Na⁺-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in pulmonary arterial endothelial cells (PAECs) from newborn piglets. Specifically, the ability to increase NO production in response to the l-arginine-NO precursor l-citrulline is dependent on SNAT1 expression. Elucidating factors that regulate SNAT1 expression in PAECs could provide new insights and therapeutic targets relevant to NO production. Our major goals were to determine if reactive oxygen species (ROS) modulate SNAT1 expression in PAECs from newborn piglets and to evaluate the role of NADPH oxidase 1 (NOX1) and uncoupled endothelial NO synthase, enzymatic sources of ROS, in hypoxia-induced increases in SNAT1 expression. Treatment with either H₂O₂ or xanthine plus xanthine oxidase increased SNAT1 expression in PAECs from newborn piglets cultured under normoxic conditions. Hypoxia-induced increases in SNAT1 expression were inhibited by treatments with the ROS-removing agents catalase and superoxide dismutase, NOX1 siRNA, and the NO synthase inhibitor N^G-nitro-l-arginine methyl ester. Both tetrahydropbiopterin (BH₄) and l-citrulline, two therapies that decrease ROS by recoupling endothelial NO synthase, reduced the hypoxia-induced increase in SNAT1 expression. BH₄ and l-citrulline treatment improved NO production in hypoxic PAECs despite a reduction in SNAT1 expression. In conclusion, SNAT1 expression is modulated by ROS in PAECs from newborn piglets. However, ROS-mediated decreases in SNAT1 expression per se do not implicate a reduction in NO production. Although SNAT1 may be critical to l-citrulline-induced increases in NO production, therapies designed to alter SNAT1 expression may not lead to a concordant change in NO production. NEW & NOTEWORTHY Na⁺-coupled neutral amino acid transporter 1 (SNAT1) modulates nitric oxide (NO) production in piglet pulmonary arterial endothelial cells. Factors that regulate SNAT1 expression in pulmonary arterial endothelial cells are unclear. Here, we show that ROS-reducing strategies inhibit hypoxia-induced increases in SNAT1 expression. l-Citrulline and tetrahydropbiopterin decrease SNAT1 expression but increase NO production. Although SNAT1 is modulated by ROS, changes in SNAT1 expression may not cause a concordant change in NO production.

Cell death in drug-induced liver injury

Drug-induced liver injury (DILI) is an important cause of liver toxicity which can have varying clinical presentations, the most severe of which being acute liver failure. Hepatocyte death as a cause of drug toxicity is a feature of DILI. There are multiple cell death subroutines; some, like apoptosis, necroptosis, autophagy, and necrosis have been extensively studied, while others such as pyroptosis and ferroptosis have been more recently described. The mode of cell death in DILI depends on the culprit drug, as it largely dictates the mechanism and extent of injury. The main cell death subroutines in DILI are apoptosis and necrosis, with mitochondrial involvement being pivotal for the execution of both. A few drugs such as acetaminophen (APAP) can cause direct, dose-dependent toxicity, while the majority of drugs cause idiosyncratic DILI (IDILI). IDILI is an unpredictable form of liver injury that is not dose dependent, occurs in individuals with a genetic predisposition, and presents with variable latency. APAP-induced programmed necrosis has been extensively studied. However, the mechanisms and pathogenesis of cell death from drugs causing IDILI are harder to elucidate due to the complex and multifactorial nature of the disease. Cell death in IDILI is likely death receptor-mediated apoptosis and the result of an activated innate and adaptive immune system, compounded by other host factors such as genetics, gender, age, and capacity for immune tolerance. This chapter will review the different modes of cell death, namely apoptosis, necrosis, necroptosis, autophagy, pyroptosis, and ferroptosis and their pertinence to DILI.

Endothelium structure and function in kidney health and disease

The kidney harbours different types of endothelia, each with specific structural and functional characteristics. The glomerular endothelium, which is highly fenestrated and covered by a rich glycocalyx, participates in the sieving properties of the glomerular filtration barrier and in the maintenance of podocyte structure. The microvascular endothelium in peritubular capillaries, which is also fenestrated, transports reabsorbed components and participates in epithelial cell function. The endothelium of large and small vessels supports the renal vasculature. These renal endothelia are protected by regulators of thrombosis, inflammation and complement, but endothelial injury (for example, induced by toxins, antibodies, immune cells or inflammatory cytokines) or defects in factors that provide endothelial protection (for example, regulators of complement or angiogenesis) can lead to acute or chronic renal injury. Moreover, renal endothelial cells can transition towards a mesenchymal phenotype, favouring renal fibrosis and the development of chronic kidney disease. Thus, the renal endothelium is both a target and a driver of kidney and systemic cardiovascular complications. Emerging therapeutic strategies that target the renal endothelium may lead to improved outcomes for both rare and common renal diseases.

Angiotensin II and vascular damage in hypertension: Role of oxidative stress and sympathetic activation

Reactive oxygen species (ROS) are oxygen derivates and play an active role in vascular biology. These compounds are generated within the vascular wall, at the level of endothelial and vascular smooth muscle cells, as well as by adventitial fibroblasts. Physiologically, ROS generation is counteracted effectively by the rate of elimination. In hypertension, a ROS excess occurs, which is not counterbalanced by the endogenous antioxidant mechanisms, leading to a state of oxidative stress. Angiotensin II, the active peptide of the renin-angiotensin-system (RAS), is a significant stimulus for ROS generation within the vasculature. It was also documented that at the level of subfornical cerebral regions an inappropriate RAS stimulation may lead to an increased vascular sympathetic activity. More recently, in conditions of fetal undernutrition, it was also proposed an increased vascular sympathetic activity secondary to inappropriate RAS activation, leading to the development of hypertension in adult life. The present review will discuss the complex interaction between RAS activation, vascular ROS generation and increased sympathetic outflow in hypertension.

Ferroptosis as a target for protection against cardiomyopathy

Nonapoptotic cell death-induced tissue damage has been implicated in a variety of diseases, including neurodegenerative disorder, inflammation, and stroke. In this study, we demonstrate that ferroptosis, a newly defined iron-dependent cell death, mediates both chemotherapy- and ischemia/reperfusion-induced cardiomyopathy. RNA-sequencing analysis revealed up-regulation of heme oxygenase 1 by doxorubicin as a major mechanism of ferroptotic cardiomyopathy. As a result, heme oxygenase 1 degrades heme and releases free iron in cardiomyocytes, which in turn leads to generation of oxidized lipids in the mitochondria membrane. Most importantly, both iron chelation therapy and pharmacologically blocking ferroptosis could significantly alleviate cardiomyopathy in mice. These findings suggest targeting ferroptosis as a strategy for treating deadly heart disease.

Heart disease is the leading cause of death worldwide. A key pathogenic factor in the development of lethal heart failure is loss of terminally differentiated cardiomyocytes. However, mechanisms of cardiomyocyte death remain unclear. Here, we discovered and demonstrated that ferroptosis, a programmed iron-dependent cell death, as a mechanism in murine models of doxorubicin (DOX)- and ischemia/reperfusion (I/R)-induced cardiomyopathy. In canonical apoptosis and/or necroptosis-defective Ripk3^−/−, Mlkl^−/−, or Fadd^−/−Mlkl^−/− mice, DOX-treated cardiomyocytes showed features of typical ferroptotic cell death. Consistently, compared with dexrazoxane, the only FDA-approved drug for treating DOX-induced cardiotoxicity, inhibition of ferroptosis by ferrostatin-1 significantly reduced DOX cardiomyopathy. RNA-sequencing results revealed that heme oxygenase-1 (Hmox1) was significantly up-regulated in DOX-treated murine hearts. Administering DOX to mice induced cardiomyopathy with a rapid, systemic accumulation of nonheme iron via heme degradation by Nrf2-mediated up-regulation of Hmox1, which effect was abolished in Nrf2-deficent mice. Conversely, zinc protoporphyrin IX, an Hmox1 antagonist, protected the DOX-treated mice, suggesting free iron released on heme degradation is necessary and sufficient to induce cardiac injury. Given that ferroptosis is driven by damage to lipid membranes, we further investigated and found that excess free iron accumulated in mitochondria and caused lipid peroxidation on its membrane. Mitochondria-targeted antioxidant MitoTEMPO significantly rescued DOX cardiomyopathy, supporting oxidative damage of mitochondria as a major mechanism in ferroptosis-induced heart damage. Importantly, ferrostatin-1 and iron chelation also ameliorated heart failure induced by both acute and chronic I/R in mice. These findings highlight that targeting ferroptosis serves as a cardioprotective strategy for cardiomyopathy prevention.

mTOR-Dependent Oxidative Stress Regulates oxLDL-Induced Trained Innate Immunity in Human Monocytes

Introduction: Cells of the innate immune system particularly monocytes and macrophages have been recognized as pivotal players both during the initial insult as well as the chronic phase of atherosclerosis. It has recently been shown that oxidized low-density lipoprotein (oxLDL) induces a long-term pro-inflammatory response in monocytes due to epigenetic and metabolic reprogramming, an emerging new concept called trained innate immunity. Changes in the cellular redox state are crucial events in the regulation of many physiologic functions in macrophages including transcription, differentiation and inflammatory response. Here we have analyzed the role of reactive oxygen species (ROS) in regulating this proinflammatory monocyte priming in response to oxLDL-treatment.

Methods and Results: Human monocytes were isolated and incubated with oxLDL for 24 h. After 5 days of resting, oxLDL treated cells produced significantly more inflammatory cytokines upon restimulation with the TLR2-agonist Pam3cys. Furthermore, oxLDL incubation induced persistent mTOR activation, ROS formation, HIF1α accumulation and HIF1α target gene expression, while pharmacologic mTOR inhibition or siRNA mediated inhibition of the mTORC1 subunit Raptor prevented ROS formation and proinflammatory priming. mTOR dependent ROS formation was associated with increased expression of NAPDH oxidases and necessary for the emergence of the primed phenotype as antioxidant treatment blocked oxLDL priming. Inhibition of cytosolic ROS formation could also block mTOR activation and HIF1α accumulation suggesting a positive feedback loop between mTOR and cytosolic ROS. Although mitochondrial ROS scavenging did not block HIF1α-accumulation at an early time point (24 h), it was persistently reduced on day 6. Therefore, mitochondrial ROS formation appears to occur initially downstream of the mTOR-cytoROS-HIF1α feedback loop but seems to be a crucial factor that controls the long-term activation of the mTOR-HIF1α-axis.

Conclusion: In summary, our data demonstrate that mTOR dependent ROS production controls the oxLDL-induced trained innate immunity phenotype in human monocyte derived macrophages. Pharmacologic modulation of these pathways might provide a potential approach to modulate inflammation, associated with aberrant monocyte activation, during atherosclerosis development.

Therapeutic Options Targeting Oxidative Stress, Mitochondrial Dysfunction and Inflammation to Hinder the Progression of Vascular Complications of Diabetes

Type 2 diabetes mellitus is a leading cause of morbidity and mortality worldwide, given its serious associated complications. Despite constant efforts and intensive research, an effective, ubiquitous treatment still eludes the scientific community. As such, the identification of novel avenues of research is key to the potential discovery of this evasive "silver bullet." We focus on this review on the matter of diabetic injury to endothelial tissue and some of the pivotal underlying mechanisms, including hyperglycemia and hyperlipidemia evoked oxidative stress and inflammation. In this sense, we revisited the most promising therapeutic interventions (both non-pharmacological and antidiabetic drugs) targeting oxidative stress and inflammation to hinder progression of vascular complications of diabetes. This review article gives particular attention to the relevance of mitochondrial function, an often ignored and understudied organelle in the vascular endothelium. We highlight the importance of mitochondrial function and number homeostasis in diabetic conditions and discuss the work conducted to address the aforementioned issue by the use of various therapeutic strategies. We explore here the functional, biochemical and bioenergetic alterations provoked by hyperglycemia in the endothelium, from elevated oxidative stress to inflammation and cell death, as well as loss of tissue function. Furthermore, we synthetize the literature regarding the current and promising approaches into dealing with these alterations. We discuss how known agents and therapeutic behaviors (as, for example, metformin, dietary restriction or antioxidants) can restore normality to mitochondrial and endothelial function, preserving the tissue's function and averting the aforementioned complications.

Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K

The accurate and specific detection of reactive oxygen species (ROS) in different cellular and tissue compartments is essential to the study of redox-regulated signaling in biological settings. Electron paramagnetic resonance spectroscopy (EPR) is the only direct method to assess free radicals unambiguously. Its advantage is that it detects physiologic levels of specific species with a high specificity, but it does require specialized technology, careful sample preparation, and appropriate controls to ensure accurate interpretation of the data. Cyclic hydroxylamine spin probes react selectively with superoxide or other radicals to generate a nitroxide signal that can be quantified by EPR spectroscopy. Cell-permeable spin probes and spin probes designed to accumulate rapidly in the mitochondria allow for the determination of superoxide concentration in different cellular compartments. In cultured cells, the use of cell permeable 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) along with and without cell-impermeable superoxide dismutase (SOD) pretreatment, or use of cell-permeable PEG-SOD, allows for the differentiation of extracellular from cytosolic superoxide. The mitochondrial 1-hydroxy-4-[2-triphenylphosphonio)-acetamido]-2,2,6,6-tetramethyl-piperidine,1-hydroxy-2,2,6,6-tetramethyl-4-[2-(triphenylphosphonio)acetamido] piperidinium dichloride (mito-TEMPO-H) allows for measurement of mitochondrial ROS (predominantly superoxide). Spin probes and EPR spectroscopy can also be applied to in vivo models. Superoxide can be detected in extracellular fluids such as blood and alveolar fluid, as well as tissues such as lung tissue. Several methods are presented to process and store tissue for EPR measurements and deliver intravenous 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CPH) spin probe in vivo. While measurements can be performed at room temperature, samples obtained from in vitro and in vivo models can also be stored at -80 °C and analyzed by EPR at 77 K. The samples can be stored in specialized tubing stable at -80 °C and run at 77 K to enable a practical, efficient, and reproducible method that facilitates storing and transferring samples.

Tobacco smoking induces cardiovascular mitochondrial oxidative stress, promotes endothelial dysfunction, and enhances hypertension

Tobacco smoking is a major risk factor for cardiovascular disease and hypertension. It is associated with the oxidative stress and induces metabolic reprogramming, altering mitochondrial function. We hypothesized that cigarette smoke induces cardiovascular mitochondrial oxidative stress, which contributes to endothelial dysfunction and hypertension. To test this hypothesis, we studied whether the scavenging of mitochondrial H₂O₂ in transgenic mice expressing mitochondria-targeted catalase (mCAT) attenuates the development of cigarette smoke/angiotensin II-induced mitochondrial oxidative stress and hypertension compared with wild-type mice. Two weeks of exposure of wild-type mice with cigarette smoke increased systolic blood pressure by 17 mmHg, which was similar to the effect of a subpresssor dose of angiotensin II (0.2 mg·kg^-1·day^-1), leading to a moderate increase to the prehypertensive level. Cigarette smoke exposure and a low dose of angiotensin II cooperatively induced severe hypertension in wild-type mice, but the scavenging of mitochondrial H₂O₂ in mCAT mice completely prevented the development of hypertension. Cigarette smoke and angiotensin II cooperatively induced oxidation of cardiolipin (a specific biomarker of mitochondrial oxidative stress) in wild-type mice, which was abolished in mCAT mice. Cigarette smoke and angiotensin II impaired endothelium-dependent relaxation and induced superoxide overproduction, which was diminished in mCAT mice. To mimic the tobacco smoke exposure, we used cigarette smoke condensate, which induced mitochondrial superoxide overproduction and reduced endothelial nitric oxide (a hallmark of endothelial dysfunction in hypertension). Western blot experiments indicated that tobacco smoke and angiotensin II reduce the mitochondrial deacetylase sirtuin-3 level and cause hyperacetylation of a key mitochondrial antioxidant, SOD2, which promotes mitochondrial oxidative stress. NEW & NOTEWORTHY This work demonstrates tobacco smoking-induced mitochondrial oxidative stress, which contributes to endothelial dysfunction and development of hypertension. We suggest that the targeting of mitochondrial oxidative stress can be beneficial for treatment of pathological conditions associated with tobacco smoking, such as endothelial dysfunction, hypertension, and cardiovascular diseases.

Neuropilin-1 Controls Endothelial Homeostasis by Regulating Mitochondrial Function and Iron-Dependent Oxidative Stress

The transmembrane protein neuropilin-1 (NRP1) promotes vascular endothelial growth factor (VEGF) and extracellular matrix signaling in endothelial cells (ECs). Although it is established that NRP1 is essential for angiogenesis, little is known about its role in EC homeostasis. Here, we report that NRP1 promotes mitochondrial function in ECs by preventing iron accumulation and iron-induced oxidative stress through a VEGF-independent mechanism in non-angiogenic ECs. Furthermore, NRP1-deficient ECs have reduced growth and show the hallmarks of cellular senescence. We show that a subcellular pool of NRP1 localizes in mitochondria and interacts with the mitochondrial transporter ATP-binding cassette B8 (ABCB8). NRP1 loss reduces ABCB8 levels, resulting in iron accumulation, iron-induced mitochondrial superoxide production, and iron-dependent EC senescence. Treatment of NRP1-deficient ECs with the mitochondria-targeted antioxidant compound mitoTEMPO or with the iron chelator deferoxamine restores mitochondrial activity, inhibits superoxide production, and protects from cellular senescence. This finding identifies an unexpected role of NRP1 in EC homeostasis.

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A subcellular pool of NRP1 localizes in the mitochondria of endothelial cells (ECs)

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NRP1 regulates mitochondrial function via ABCB8 transporter

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NRP1 loss induces iron accumulation and iron-dependent oxidative stress in ECs

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NRP1 protects ECs from iron-dependent premature cellular senescence

Targeting mitochondrial dysfunction and oxidative stress in heart failure: Challenges and opportunities

Mitochondrial dysfunction characterized by impaired bioenergetics, oxidative stress and aldehydic load is a hallmark of heart failure. Recently, different research groups have provided evidence that selective activation of mitochondrial detoxifying systems that counteract excessive accumulation of ROS, RNS and reactive aldehydes is sufficient to stop cardiac degeneration upon chronic stress, such as heart failure. Therefore, pharmacological and non-pharmacological approaches targeting mitochondria detoxification may play a critical role in the prevention or treatment of heart failure. In this review we discuss the most recent findings on the central role of mitochondrial dysfunction, oxidative stress and aldehydic load in heart failure, highlighting the most recent preclinical and clinical studies using mitochondria-targeted molecules and exercise training as effective tools against heart failure.

Mitochondria as a therapeutic target for common pathologies

Although the development of mitochondrial therapies has largely focused on diseases caused by mutations in mitochondrial DNA or in nuclear genes encoding mitochondrial proteins, it has been found that mitochondrial dysfunction also contributes to the pathology of many common disorders, including neurodegeneration, metabolic disease, heart failure, ischaemia-reperfusion injury and protozoal infections. Mitochondria therefore represent an important drug target for these highly prevalent diseases. Several strategies aimed at therapeutically restoring mitochondrial function are emerging, and a small number of agents have entered clinical trials. This Review discusses the opportunities and challenges faced for the further development of mitochondrial pharmacology for common pathologies.

Comparison of different methods for measuring the superoxide radical by EPR spectroscopy in buffer, cell lysates and cells

As superoxide anion is of keen interest in biomedical research, it is highly desirable to have a technique allowing its detection sensitively and specifically in biological media. If electron paramagnetic resonance (EPR) techniques and probes have been individually described in the literature, there is actually no comparison of these techniques in the same conditions that may help guiding researchers for selecting the most appropriate approach. The aim of the present study was to compare different EPR strategies in terms of sensitivity and specificity to detect superoxide (vs. hydroxyl radical). Three main classes of EPR probes were used, including paramagnetic superoxide scavengers (such as nitroxides TEMPOL and mitoTEMPO as well as trityl CT-03), a spin trap (DIPPMPO), and diamagnetic superoxide scavengers (such as cyclic hydroxylamines CMH and mitoTEMPO-H). We analysed the reactivity of the different probes in the presence of a constant production of superoxide or hydroxyl radical in buffers and in cell lysates. We also assessed the performances of the different probes to detect superoxide produced by RAW264.7 macrophages stimulated by phorbol 12-myristate 13-acetate. In our conditions and models, we found that nitroxides were not specific for superoxide. CT-03 was specific, but the sensitivity of detection was low. Comparatively, we found that nitrone DIPPMPO and cyclic hydroxylamine CMH were good candidates to sensitively and specifically detect superoxide in complex biological media, CMH offering the best sensitivity.

A mitochondrial ROS pathway controls matrix metalloproteinase 9 levels and invasive properties in RAS-activated cancer cells

Matrix metalloproteinases (MMPs) are tissue‐remodeling enzymes involved in the processing of various biological molecules. MMPs also play important roles in cancer metastasis, contributing to angiogenesis, intravasation of tumor cells, and cell migration and invasion. Accordingly, unraveling the signaling pathways controlling MMP activities could shed additional light on cancer biology. Here, we report a molecular axis, comprising the molecular adaptor hydrogen peroxide‐inducible clone‐5 (HIC‐5), NADPH oxidase 4 (NOX4), and mitochondria‐associated reactive oxygen species (mtROS), that regulates MMP9 expression and may be a target to suppress cancer metastasis. We found that this axis primarily downregulates mtROS levels which stabilize MMP9 mRNA. Specifically, HIC‐5 suppressed the expression of NOX4, the source of the mtROS, thereby decreasing mtROS levels and, consequently, destabilizing MMP9 mRNA. Interestingly, among six cancer cell lines, only EJ‐1 and MDA‐MB‐231 cells exhibited upregulation of NOX4 and MMP9 expression after shRNA‐mediated HIC‐5 knockdown. In these two cell lines, activating RAS mutations commonly occur, suggesting that the HIC‐5–mediated suppression of NOX4 depends on RAS signaling, a hypothesis that was supported experimentally by the introduction of activated RAS into mammary epithelial cells. Notably, HIC‐5 knockdown promoted lung metastasis of MDA‐MB‐231 cancer cells in mice. The tumor growth of HIC‐5–silenced MDA‐MB‐231 cells at the primary sites was comparable to that of control cells. Consistently, the invasive properties of the cells, but not their proliferation, were enhanced by the HIC‐5 knockdown in vitro. We conclude that NOX4‐mediated mtROS signaling increases MMP9 mRNA stability and affects cancer invasiveness but not tumor growth.

Mitochondria-targeting drug conjugates for cytotoxic, anti-oxidizing and sensing purposes: current strategies and future perspectives

Mitochondrial targeting is a promising approach for solving current issues in clinical application of chemotherapy and diagnosis of several disorders. Here, we discuss direct conjugation of mitochondrial-targeting moieties to anticancer drugs, antioxidants and sensor molecules. Among them, the most widely applied mitochondrial targeting moiety is triphenylphosphonium (TPP), which is a delocalized cationic lipid that readily accumulates and penetrates through the mitochondrial membrane due to the highly negative mitochondrial membrane potential. Other moieties, including short peptides, dequalinium, guanidine, rhodamine, and F16, are also known to be promising mitochondrial targeting agents. Direct conjugation of mitochondrial targeting moieties to anticancer drugs, antioxidants and sensors results in increased cytotoxicity, anti-oxidizing activity and sensing activity, respectively, compared with their non-targeting counterparts, especially in drug-resistant cells. Although many mitochondria-targeted anticancer drug conjugates have been investigated in vitro and in vivo, further clinical studies are still needed. On the other hand, several mitochondria-targeting antioxidants have been analyzed in clinical phases I, II and III trials, and one conjugate has been approved for treating eye disease in Russia. There are numerous ongoing studies of mitochondria-targeted sensors.

Hypertension and increased endothelial mechanical stretch promote monocyte differentiation and activation: roles of STAT3, interleukin 6 and hydrogen peroxide

Aims

Monocytes play an important role in hypertension. Circulating monocytes in humans exist as classical, intermediate, and non-classical forms. Monocyte differentiation can be influenced by the endothelium, which in turn is activated in hypertension by mechanical stretch. We sought to examine the role of increased endothelial stretch and hypertension on monocyte phenotype and function.

Methods and results

Human monocytes were cultured with confluent human aortic endothelial cells undergoing either 5% or 10% cyclical stretch. We also characterized circulating monocytes in normotensive and hypertensive humans. In addition, we quantified accumulation of activated monocytes and monocyte-derived cells in aortas and kidneys of mice with Angiotensin II-induced hypertension. Increased endothelial stretch enhanced monocyte conversion to CD14++CD16+ intermediate monocytes and monocytes bearing the CD209 marker and markedly stimulated monocyte mRNA expression of interleukin (IL)-6, IL-1β, IL-23, chemokine (C-C motif) ligand 4, and tumour necrosis factor α. STAT3 in monocytes was activated by increased endothelial stretch. Inhibition of STAT3, neutralization of IL-6 and scavenging of hydrogen peroxide prevented formation of intermediate monocytes in response to increased endothelial stretch. We also found evidence that nitric oxide (NO) inhibits formation of intermediate monocytes and STAT3 activation. In vivo studies demonstrated that humans with hypertension have increased intermediate and non-classical monocytes and that intermediate monocytes demonstrate evidence of STAT3 activation. Mice with experimental hypertension exhibit increased aortic and renal infiltration of monocytes, dendritic cells, and macrophages with activated STAT3.

Conclusions

These findings provide insight into how monocytes are activated by the vascular endothelium during hypertension. This is likely in part due to a loss of NO signalling and increased release of IL-6 and hydrogen peroxide by the dysfunctional endothelium and a parallel increase in STAT activation in adjacent monocytes. Interventions to enhance bioavailable NO, reduce IL-6 or hydrogen peroxide production or to inhibit STAT3 may have anti-inflammatory roles in hypertension and related conditions.

Subplasmalemmal hydrogen peroxide triggers calcium influx in gonadotropes

Gonadotropin-releasing hormone (GnRH) stimulation of its eponymous receptor on the surface of endocrine anterior pituitary gonadotrope cells (gonadotropes) initiates multiple signaling cascades that culminate in the secretion of luteinizing and follicle-stimulating hormones, which have critical roles in fertility and reproduction. Enhanced luteinizing hormone biosynthesis, a necessary event for ovulation, requires a signaling pathway characterized by calcium influx through L-type calcium channels and subsequent activation of the mitogen-activated protein kinase extracellular signal-regulated kinase (ERK). We previously reported that highly localized subplasmalemmal calcium microdomains produced by L-type calcium channels (calcium sparklets) play an essential part in GnRH-dependent ERK activation. Similar to calcium, reactive oxygen species (ROS) are ubiquitous intracellular signaling molecules whose subcellular localization determines their specificity. To investigate the potential influence of oxidant signaling in gonadotropes, here we examined the impact of ROS generation on L-type calcium channel function. Total internal reflection fluorescence (TIRF) microscopy revealed that GnRH induces spatially restricted sites of ROS generation in gonadotrope-derived αT3-1 cells. Furthermore, GnRH-dependent stimulation of L-type calcium channels required intracellular hydrogen peroxide signaling in these cells and in primary mouse gonadotropes. NADPH oxidase and mitochondrial ROS generation were each necessary for GnRH-mediated stimulation of L-type calcium channels. Congruently, GnRH increased oxidation within subplasmalemmal mitochondria, and L-type calcium channel activity correlated strongly with the presence of adjacent mitochondria. Collectively, our results provide compelling evidence that NADPH oxidase activity and mitochondria-derived hydrogen peroxide signaling play a fundamental role in GnRH-dependent stimulation of L-type calcium channels in anterior pituitary gonadotropes.