Up-regulation of heme oxygenase provides vascular protection in an animal model of diabetes through its antioxidant and antiapoptotic effects

Effect of PPARγ on oxidative stress in diabetes-related dry eye

Oxidative stress is closely associated with diabetes and can cause free radical accumulation and eventually lead to ocular surface tissue damage. The purpose of this study was to investigate peroxisome proliferator-activated receptor-γ (PPARγ) expression in the lacrimal gland (LG), meibomian gland, and cornea of diabetes-related dry eye mice and whether the PPARγ agonist rosiglitazone can alleviate the oxidative stress of the ocular surface, thereby improving the condition of diabetes-related dry eye. Quantitative RT-PCR (Q-PCR) showed that the PPARγ, catalase, glutathione peroxidase 3, and heme oxygenase-1 (HO-1) mRNA expression levels in the LG of diabetes-related dry eye mice decreased at 8 and 12 weeks. In addition, the increased levels of oxidative stress were confirmed by western blot. Although the mRNA expression levels of antioxidant enzymes in the cornea and meibomian gland decreased at 8 weeks, some of them recovered by 12 weeks. Rosiglitazone alleviated ocular surface damage and increased corneal sensitivity and tear production in diabetes-related dry eye mice. Moreover, the reactive oxygen species accumulation was reduced and the PPARγ, HO-1, and glutathione peroxidase 3 mRNA expression levels were increased in the LG. The PPARγ, HO-1, translocase of the outer membrane 20, and mitochondrial transcription factor A protein levels were also significantly increased. These results demonstrated that rosiglitazone reduced oxidative stress in the LG of diabetes-related dry eye mice, at least in part, by activating PPARγ to up-regulate antioxidant enzyme expression.

Protective actions of nuclear factor erythroid 2-related factor 2 (NRF2) and downstream pathways against environmental stressors

Environmental risk factors, including noise, air pollution, chemical agents, ultraviolet radiation (UVR) and mental stress have a considerable impact on human health. Oxidative stress and inflammation are key players in molecular pathomechanisms of environmental pollution and risk factors. In this review, we delineate the impact of environmental risk factors and the protective actions of the nuclear factor erythroid 2-related factor 2 (NRF2) in connection to oxidative stress and inflammation. We focus on well-established studies that demonstrate the protective actions of NRF2 and its downstream pathways against different environmental stressors. State-of-the-art mechanistic considerations on NRF2 signaling are discussed in detail, e.g. classical concepts like KEAP1 oxidation/electrophilic modification, NRF2 ubiquitination and degradation. Specific focus is also laid on NRF2-dependent heme oxygenase-1 induction with detailed presentation of the protective down-stream pathways of heme oxygenase-1, including interaction with BACH1 system. The significant impact of all environmental stressors on the circadian rhythm and the interactions of NRF2 with the circadian clock will also be considered here. A broad range of NRF2 activators is discussed in relation to environmental stressor-induced health side effects, thereby suggesting promising new mitigation strategies (e.g. by nutraceuticals) to fight the negative effects of the environment on our health.

Biliverdin reductase-A protein levels are reduced in type 2 diabetes and are associated with poor glycometabolic control

AIM

Biliverdin reductase-A (BVR-A) other than its canonical role in the degradation pathway of heme as partner of heme oxygenase-1 (HO1), has recently drawn attention as a protein with pleiotropic functions involved in insulin-glucose homeostasis. However, whether BVR-A expression is altered in type 2 diabetes (T2D) has never been evaluated.

MAIN METHODS

BVR-A protein levels were evaluated in T2D (n = 44) and non-T2D (n = 29) subjects, who underwent complete clinical workup and routine biochemistry. In parallel, levels HO1, whose expression is regulated by BVR-A as well as levels of tumor necrosis factor α (TNFα), which is a known repressor for BVR-A with pro-inflammatory properties, were also assessed.

KEY FINDINGS

BVR-A levels were significantly lower in T2D subjects than in non-T2D subjects. Reduced BVR-A levels were associated with greater body mass, systolic blood pressure, fasting blood glucose (FBG), glycated hemoglobin (HbA1c), triglycerides, transaminases and TNFα, and with lower high-density lipoprotein (HDL) levels. Lower BVR-A levels are associated with reduced HO1 protein levels and the multivariate analysis showed that BVR-A represented the main determinant of HO1 levels in T2D after adjustment. In addition, reduced BVR-A levels were able to predict the presence of T2D with AUROC = 0.69. for potential confounders.

SIGNIFICANCE

Our results demonstrate for the first time that BVR-A protein levels are reduced in T2D individuals, and that this alteration strictly correlates with poor glycometabolic control and a pro-inflammatory state. Hence, these observations reinforce the hypothesis that reduced BVR-A protein levels may represent a key event in the dysregulation of intracellular pathways finally leading to metabolic disorders.

Heme-oxygenase and lipid mediators in obesity and associated cardiometabolic diseases: Therapeutic implications

Obesity-mediated metabolic syndrome remains the leading cause of death worldwide. Among many potential targets for pharmacological intervention, a promising strategy involves the heme oxygenase (HO) system, specifically its inducible form, HO-1. This review collects and updates much of the current knowledge relevant to pharmacology and clinical medicine concerning HO-1 in metabolic diseases and its effect on lipid metabolism. HO-1 has pleotropic effects that collectively reduce inflammation, while increasing vasodilation and insulin and leptin sensitivity. Recent reports indicate that HO-1 with its antioxidants via the effect of bilirubin increases formation of biologically active lipid metabolites such as epoxyeicosatrienoic acid (EET), omega-3 and other polyunsaturated fatty acids (PUFAs). Similarly, HO-1and bilirubin are potential therapeutic targets in the treatment of fat-induced liver diseases. HO-1-mediated upregulation of EET is capable not only of reversing endothelial dysfunction and hypertension, but also of reversing cardiac remodeling, a hallmark of the metabolic syndrome. This process involves browning of white fat tissue (i.e. formation of healthy adipocytes) and reduced lipotoxicity, which otherwise will be toxic to the heart. More importantly, this review examines the activity of EET in biological systems and a series of pathways that explain its mechanism of action and discusses how these might be exploited for potential therapeutic use. We also discuss the link between cardiac ectopic fat deposition and cardiac function in humans, which is similar to that described in obese mice and is regulated by HO-1-EET-PGC1α signaling, a potent negative regulator of the inflammatory adipokine NOV.

Noise-Induced Vascular Dysfunction, Oxidative Stress, and Inflammation Are Improved by Pharmacological Modulation of the NRF2/HO-1 Axis

Vascular oxidative stress, inflammation, and subsequent endothelial dysfunction are consequences of traditional cardiovascular risk factors, all of which contribute to cardiovascular disease. Environmental stressors, such as traffic noise and air pollution, may also facilitate the development and progression of cardiovascular and metabolic diseases. In our previous studies, we investigated the influence of aircraft noise exposure on molecular mechanisms, identifying oxidative stress and inflammation as central players in mediating vascular function. The present study investigates the role of heme oxygenase-1 (HO-1) as an antioxidant response preventing vascular consequences following exposure to aircraft noise. C57BL/6J mice were treated with the HO-1 inducer hemin (25 mg/kg i.p.) or the NRF2 activator dimethyl fumarate (DMF, 20 mg/kg p.o.). During therapy, the animals were exposed to noise at a maximum sound pressure level of 85 dB(A) and a mean sound pressure level of 72 dB(A). Our data showed a marked protective effect of both treatments on animals exposed to noise for 4 days by normalization of arterial hypertension and vascular dysfunction in the noise-exposed groups. We observed a partial normalization of noise-triggered oxidative stress and inflammation by hemin and DMF therapy, which was associated with HO-1 induction. The present study identifies possible new targets for the mitigation of the adverse health effects caused by environmental noise exposure. Since natural dietary constituents can achieve HO-1 and NRF2 induction, these pathways represent promising targets for preventive measures.

Heme Oxygenase-1 Signaling and Redox Homeostasis in Physiopathological Conditions

Heme-oxygenase is the enzyme responsible for degradation of endogenous iron protoporphyirin heme; it catalyzes the reaction’s rate-limiting step, resulting in the release of carbon monoxide (CO), ferrous ions, and biliverdin (BV), which is successively reduced in bilirubin (BR) by biliverdin reductase. Several studies have drawn attention to the controversial role of HO-1, the enzyme inducible isoform, pointing out its implications in cancer and other diseases development, but also underlining the importance of its antioxidant activity. The contribution of HO-1 in redox homeostasis leads to a relevant decrease in cells oxidative damage, which can be reconducted to its cytoprotective effects explicated alongside other endogenous mechanisms involving genes like TIGAR (TP53-induced glycolysis and apoptosis regulator), but also to the therapeutic functions of heme main transformation products, especially carbon monoxide (CO), which has been shown to be effective on GSH levels implementation sustaining body’s antioxidant response to oxidative stress. The aim of this review was to collect most of the knowledge on HO-1 from literature, analyzing different perspectives to try and put forward a hypothesis on revealing yet unknown HO-1-involved pathways that could be useful to promote development of new therapeutical strategies, and lay the foundation for further investigation to fully understand this important antioxidant system.

The Pivotal Role of Adipocyte-Na K peptide in Reversing Systemic Inflammation in Obesity and COVID-19 in the Development of Heart Failure

This review summarizes data from several laboratories that have demonstrated a role of the Na/K-ATPase, specifically its α1 subunit, in the generation of reactive oxygen species (ROS) via the negative regulator of Src. Together with Src and other signaling proteins, the Na/K-ATPase forms an oxidant amplification loop (NKAL), amplifies ROS, and participates in cytokines storm in obesity. The development of a peptide fragment of the α1 subunit, NaKtide, has been shown to negatively regulate Src. Several groups showed that the systemic administration of the cell permeable modification of NaKtide (pNaKtide) or its selective delivery to fat tissue—adipocyte specific expression of NaKtide—ameliorate the systemic elevation of inflammatory cytokines seen in chronic obesity. Severe acute respiratory syndrome – coronavirus 2 (SARS-CoV-2), the RNA Coronavirus responsible for the COVID-19 global pandemic, invades cells via the angiotensin converting enzyme 2 (ACE-2) receptor (ACE2R) that is appended in inflamed fat tissue and exacerbates the formation of the cytokines storm. Both obesity and heart and renal failure are well known risks for adverse outcomes in patients infected with COVID-19. White adipocytes express ACE-2 receptors in high concentration, especially in obese patients. Once the virus invades the white adipocyte cell, it creates a COVID19–porphyrin complex which degrades and produces free porphyrin and iron and increases ROS. The increased formation of ROS and activation of the NKAL results in a further potentiated formation of ROS production, and ultimately, adipocyte generation of more inflammatory mediators, leading to systemic cytokines storm and heart failure. Moreover, chronic obesity also results in the reduction of antioxidant genes such as heme oxygenase-1 (HO-1), increasing adipocyte susceptibility to ROS and cytokines. It is the systemic inflammation and cytokine storm which is responsible for many of the adverse outcomes seen with COVID-19 infections in obese subjects, leading to heart failure and death. This review will also describe the potential antioxidant drugs and role of NaKtide and their demonstrated antioxidant effect used as a major strategy for improving obesity and epicardial fat mediated heart failure in the context of the COVID pandemic.

Irisin ameliorates high glucose-induced cardiomyocytes injury via AMPK/mTOR signal pathway

High glucose (HG)-induced cardiomyocytes (CMs) injury is a leading cause of diabetic cardiomyopathy with little treatment options. Irisin, a new myokine, which is cleaved from its precursor fibronectin type III domain-containing protein 5 (FNDC5), has aroused great attention as an essential cardioprotective factor and glucose metabolism regulator but little was known on diabetic cardiomyopathy yet. Here, we aim to clarify the role of irisin in the HG-induced CMs injury. Neonatal Sprague-Dawley rat CMs were cultured in a normal or HG medium for 12, 24, and 48 hr, respectively before exposing to irisin. The apoptosis level was determined by terminal-deoxynucleotidyl transferase-mediated-dUTP nick end-labeling assay. Cell viability was measured with the conventional methyl thiazolyl tetrazolium assay. Moreover, reactive oxygen species production was evaluated by dihydroethidium staining. Inflammatory factors, namely tumor necrosis factor-α, interleukin-6, interleukin-1β were determined by enzyme-linked immunosorbent assay kits. Furthermore, protein and messenger RNA (mRNA) expressions were measured by western blot and quantitative real-time polymerase chain reaction, respectively. HG increases the apoptosis of CMs and activated the inflammatory responses and oxidative stress in CMs. Meanwhile, the mRNA and protein expressions of FNDC5 are decreased after HG exposure. Nevertheless, the increased apoptosis is alleviated by irisin treatment. Notably, irisin suppresses the inflammatory responses and oxidative stress in injured CMs. Mechanically, after the administration of Compound C, AMP-activated protein kinase (AMPK) inhibitor, these cardioprotective effects resulting from irisin are reversed. Irisin plays a significant role in antiapoptosis, anti-inflammation, antioxidative stress in HG-induced CMs via AMPK/mammalian target of the rapamycin signaling pathway.

Therapeutic Efficacy of Antioxidants in Ameliorating Obesity Phenotype and Associated Comorbidities

Obesity has been a worldwide epidemic for decades. Despite the abundant increase in knowledge regarding the etiology and pathogenesis of obesity, the prevalence continues to rise with estimates predicting considerably higher numbers by the year 2030. Obesity is characterized by an abnormal lipid accumulation, however, the physiological consequences of obesity are far more concerning. The development of the obesity phenotype constitutes dramatic alterations in adipocytes, along with several other cellular mechanisms which causes substantial increase in systemic oxidative stress mediated by reactive oxygen species (ROS). These alterations promote a chronic state of inflammation in the body caused by the redox imbalance. Together, the systemic oxidative stress and chronic inflammation plays a vital role in maintaining the obese state and exacerbating onset of cardiovascular complications, Type II diabetes mellitus, dyslipidemia, non-alcoholic steatohepatitis, and other conditions where obesity has been linked as a significant risk factor. Because of the apparent role of oxidative stress in the pathogenesis of obesity, there has been a growing interest in attenuating the pro-oxidant state in obesity. Hence, this review aims to highlight the therapeutic role of antioxidants, agents that negate pro-oxidant state of cells, in ameliorating obesity and associated comorbidities. More specifically, this review will explore how various antioxidants target unique and diverse pathways to exhibit an antioxidant defense mechanism.

Therapeutic approaches to diabetic cardiomyopathy: Targeting the antioxidant pathway

The global epidemic of cardiovascular disease continues unabated and remains the leading cause of death both in the US and worldwide. We hereby summarize the available therapies for diabetes and cardiovascular disease in diabetics. Clearly, the current approaches to diabetic heart disease often target the manifestations and certain mediators but not the specific pathways leading to myocardial injury, remodeling and dysfunction. Better understanding of the molecular events determining the evolution of diabetic cardiomyopathy will provide insight into the development of specific and targeted therapies. Recent studies largely increased our understanding of the role of enhanced inflammatory response, ROS production, as well as the contribution of Cyp-P450-epoxygenase-derived epoxyeicosatrienoic acid (EET), Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1α (PGC-1α), Heme Oxygenase (HO)-1 and 20-HETE in pathophysiology and therapy of cardiovascular disease. PGC-1α increases production of the HO-1 which has a major role in protecting the heart against oxidative stress, microcirculation and mitochondrial dysfunction. This review describes the potential drugs and their downstream targets, PGC-1α and HO-1, as major loci for developing therapeutic approaches beside diet and lifestyle modification for the treatment and prevention of heart disease associated with obesity and diabetes.

P38 MAPK and Nrf2 Activation Mediated Naked Gold Nanoparticle Induced Heme Oxygenase-1 Expression in Rat Aortic Vascular Smooth Muscle Cells

BACKGROUND AND AIMS

Heme oxygenase 1 (HO-1) is mainly regulated by the redox-sensitive transcription factor, namely nuclear factor erythroid 2-related factor 2 (Nrf2). We previously found a physically-made gold nanoparticle (GNP) can affect migration, adhesion, and proliferation of rat aortic vascular smooth muscle cells (VSMCs). This study was sought to investigate whether the GNP can affect HO-1 expression level in VSMCs.

METHODS

Cellular fractionation, Western blotting, and immunofluorescence microscopy were used to determine Nrf2 translocation and phosphorylation. SiRNA interference was used to examine role of Nrf2 in GNP-induced HO-1 expression.

RESULTS

The GNP concentration- and time-dependently enhanced HO-1 protein and mRNA expression; however, the mRNA induction was declined after 16 h treatment. The GNP treatment caused Nrf2 expression level and phosphorylation. In addition, it induced cytosolic Nrf2 translocation into nucleus. The HO-1 induction was inhibited by a ROS scavenger N-acetylcysteine (NAC), thiol-containing antioxidants (glutathione [GSH] and dithiothreitol [DTT]), JNK and p38 MAPK inhibitors, and nuclear transport inhibitor leptomycin. Meanwhile, the GNP-induced Nrf2 translocation (activation) was also reduced by NAC, JNK and p38 MAPK inhibitors, and nuclear transport inhibitor. Intriguingly, the GNP only enhanced activation of p38 MAPK but not JNK1/2. Finally, introduction of Nrf2 siRNA to cells to knockdown Nrf2 expression significantly inhibited GNP-induced HO-1 protein expression.

CONCLUSIONS

This study elucidates the action mechanism that the naked physically-made GNP can enhance HO-1 expression in rat aortic VSMCs by inducing Nrf2 expression and phosphorylation and translocation into nucleus. The Nrf2 activation is mediated through a redox-related reaction and p38 MAPK activation.

Heme Oxygenase-1 Upregulation: A Novel Approach in the Treatment of Cardiovascular Disease

Significance: Heme oxygenase (HO) plays a pivotal role in both vascular and metabolic functions and is involved in many physiological and pathophysiological processes in vascular endothelial cells (ECs) and adipocytes. Recent Advances: From the regulation of adipogenesis in adipose tissue to the adaptive response of vascular tissue in the ECs, HO plays a critical role in the capability of the vascular system to respond and adjust to insults in homeostasis. Recent studies show that HO-1 through regulation of adipocyte and adipose tissue functions ultimately aid not only in local but also in systemic maintenance of homeostasis. Critical Issues: Recent advances have revealed the existence of a cross talk between vascular ECs and adipocytes in adipose tissue. In the pathological state of obesity, this cross talk contributes to the condition's adverse chronic effects, and we propose that specific targeting of the HO-1 gene can restore signaling pathways and improve both vascular and adipose functions. Future Directions: A complete understanding of the role of HO-1 in regulation of cardiovascular homeostasis is important to comprehend the homeostatic regulation as well as in cardiovascular disease. Efforts are required to highlight the effects and the ability to target the HO-1 gene in models of obesity with an emphasis on the role of pericardial fat on cardiovascular health.

The Effects of Heme Oxygenase Upregulation on Obesity and the Metabolic Syndrome

Significance: Obesity is a chronic condition that is characterized by inflammation and oxidative stress with consequent cardiovascular complications of hypertension, dyslipidemia, and vascular dysfunction. Obesity-induced metabolic syndrome remains an epidemic of global proportions. Recent Advances: Gene targeting of the endothelium with a retrovirus using an endothelium-specific promoter vascular endothelium cadherin (VECAD)-HO-1 offers a potential long-term solution to adiposity by targeting the endothelium. This has resulted in improvements of both vascular function and adiposity attenuation. Critical Issues: Heme oxygenase plays an ever-increasing role in the understanding of human biology in the complex conditions of obesity and the metabolic syndrome. The heme oxygenase 1 (HO-1) system creates biliverdin/bilirubin, which functions as an antioxidant, and carbon monoxide, which has antiapoptotic properties. Future Directions: Upregulation of HO-1 has been shown to improve adiposity as well as vascular function in both animal and human studies.

Bcl-2 expression in a diabetic embryopathy model in presence of polyamines

The frequency of congenital malformations is 3-5 times higher in mothers with pregestational diabetes mellitus than in general population. Apparently, this problem is due to change in the expression of apoptotic and antiapoptotic genes induced by the oxidative stress derived from the diabetes/hyperglycemia. One of these genes is Bcl-2, which is associated with the control and inhibition of apoptosis. The purpose of the present work was to study the effect of polyamine addition over expression of Bcl-2 gene in a model of diabetic embryopathy. For this, gestational day 10.5 (GD10.5) rat embryos were incubated at 37°C for 24 h in control medium, medium with high glucose, or medium with high glucose and supplemented with spermidine or spermine. Post-cultured embryos were harvested and observed to obtain morphological scores; some of them were subjected to molecular biology studies: DNA isolation plus conventional PCR or RNA isolation plus RT-PCR; other embryos were fixed with paraformaldehyde and used for immunohistochemical detection of Bcl-2 protein. Although Bcl-2 mRNA was similarly expressed in all rat embryo treatments, Bcl-2 protein was found only in control-incubated embryos. In conclusion, it seems that the inhibition of Bcl-2 gene expression induced by glucose was not reversed by polyamines.

HO-1 overexpression and underexpression: Clinical implications

In this review we examine the effects of both over- and under-production of heme oxygenase-1 (HO-1) and HO activity on a broad spectrum of biological systems and on vascular disease. In a few instances e.g., neonatal jaundice, overproduction of HO-1 and increased HO activity results in elevated levels of bilirubin requiring clinical intervention with inhibitors of HO activity. In contrast HO-1 levels and HO activity are low in obesity and the HO system responds to mitigate the deleterious effects of oxidative stress through increased levels of bilirubin (anti-inflammatory) and CO (anti-apoptotic) and decreased levels of heme (pro-oxidant). Site specific HO-1 overexpression diminishes adipocyte terminal differentiation and lipid accumulation of obesity mediated release of inflammatory molecules. A series of diverse strategies have been implemented that focus on increasing HO-1 and HO activity that are central to reversing the clinical complications associated with diseases including, obesity, metabolic syndrome and vascular disease.

Reduced biliverdin reductase-A levels are associated with early alterations of insulin signaling in obesity

Biliverdin reductase-A (BVR-A) is a serine/threonine/tyrosine kinase involved in the regulation of insulin signaling. In vitro studies have demonstrated that BVR-A is a substrate of the insulin receptor and regulates IRS1 by avoiding its aberrant activation, and in animal model of obesity the loss of hepatic BVR-A has been associated with glucose/insulin alterations and fatty liver disease. However, no studies exist in humans. Here, we evaluated BVR-A expression levels and activation in peripheral blood mononuclear cells (PBMC) from obese subjects and matched lean controls and we investigated the related molecular alterations of the insulin along with clinical correlates. We showed that BVR-A levels are significantly reduced in obese subjects and associated with a hyper-activation of the IR/IRS1/Akt/GSK-3β/AS160/GLUT4 pathway. Low BVR-A levels also associate with the presence of obesity, metabolic syndrome, NASH and visceral adipose tissue inflammation. These data suggest that the reduction of BVR-A may be responsible for early alterations of the insulin signaling pathway in obesity and in this context may represent a novel molecular target to be investigated for the comprehension of the process of insulin resistance development in obesity.

Oxidized HDL, Adipokines, and Endothelial Dysfunction: A Potential Biomarker Profile for Cardiovascular Risk in Women with Obesity

OBJECTIVE

High BMI predicts adverse cardiovascular outcomes and positively correlates with increased levels of adipokines. The relationship among BMI, IL-6, TNFα, adiponectin, and oxidized high-density lipoprotein (Ox-HDL) with circulating endothelial cells (CECs) and endothelial progenitor cells (EPCs) has not been well studied. Elevated CEC levels have been described in both humans and mice with obesity and diabetes. Ox-HDL has been shown to be a potent driver of adipogenesis in vivo and in vitro. In this study, elevated BMI was examined in 2 groups of women studied in Brooklyn, New York, and Huntington, West Virginia, respectively.

METHODS

Twenty-six females with obesity and five lean controls without overt cardiovascular disease were enrolled, 13 from Huntington and 13 from Brooklyn. Cytokine levels, EPCs, and CECs were determined.

RESULTS

Females with obesity had elevated levels of leptin, IL-6, and Ox-HDL, increased CEC levels, and decreased EPC and adiponectin levels (all P < 0.01). The Ox-HDL levels were higher in women from Brooklyn versus Huntington (P < 0.01), possibly from higher TNFα levels in Brooklyn or higher adiponectin levels in Huntington. Seventy-five percent of the variance in Ox-HDL levels could be predicted in this population (P < 0.01).

CONCLUSIONS

This study reveals a unique inflammatory biomarker profile in females with obesity.

Development of NASH in Obese Mice is Confounded by Adipose Tissue Increase in Inflammatory NOV and Oxidative Stress

AIM

Nonalcoholic steatohepatitis (NASH) is the consequence of insulin resistance, fatty acid accumulation, oxidative stress, and lipotoxicity. We hypothesize that an increase in the inflammatory adipokine NOV decreases antioxidant Heme Oxygenase 1 (HO-1) levels in adipose and hepatic tissue, resulting in the development of NASH in obese mice.

METHODS

Mice were fed a high fat diet (HFD) and obese animals were administered an HO-1 inducer with or without an inhibitor of HO activity to examine levels of adipose-derived NOV and possible links between increased synthesis of inflammatory adipokines and hepatic pathology.

RESULTS

NASH mice displayed decreased HO-1 levels and HO activity, increased levels of hepatic heme, NOV, MMP2, hepcidin, and increased NAS scores and hepatic fibrosis. Increased HO-1 levels are associated with a decrease in NOV, improved hepatic NAS score, ameliorated fibrosis, and increases in mitochondrial integrity and insulin receptor phosphorylation. Adipose tissue function is disrupted in obesity as evidenced by an increase in proinflammatory molecules such as NOV and a decrease in adiponectin. Importantly, increased HO-1 levels are associated with a decrease of NOV, increased adiponectin levels, and increased levels of thermogenic and mitochondrial signaling associated genes in adipose tissue.

CONCLUSIONS

These results suggest that the metabolic abnormalities in NASH are driven by decreased levels of hepatic HO-1 that is associated with an increase in the adipose-derived proinflammatory adipokine NOV in our obese mouse model of NASH. Concurrently, induction of HO-1 provides protection against insulin resistance as seen by increased insulin receptor phosphorylation. Pharmacological increases in HO-1 associated with decreases in NOV may offer a potential therapeutic approach in preventing fibrosis, mitochondrial dysfunction, and the development of NASH.

Tin protoporphyrin activates the oxidant-dependent NRF2-cytoprotective pathway and mitigates acute kidney injury

Tin protoporphyrin (SnPP), a heme oxygenase (HO) inhibitor, can paradoxically protect against diverse forms of acute kidney injury (AKI). This study sought potential underlying mechanisms. CD-1 mice received intravenous SnPP, followed 4-18 hours later by a variety of renal biochemical, histologic, and genomic assessments. Renal resistance to ischemic-reperfusion injury (IRI) was also sought. SnPP was rapidly taken up by kidney and was confined to proximal tubules. Transient suppression of renal heme synthesis (decreased δ aminolevulinic acid synthase expression), a 2.5-fold increase in "catalytic" Fe levels and oxidant stress resulted (decreased glutathione; increased malondialdehyde, and protein carbonyl content). Nrf2 nuclear translocation (∼2x Nrf2 increase; detected by enzyme-linked immunosorbent assay, Western blotting), with corresponding activation of ∼20 Nrf2-sensitive genes (RNA-Seq) were observed. By 18 hours after SnPP injection, marked protection against IRI emerged. This represented "preconditioning", not a direct SnPP effect, given that SnPP administered at the time of IRI exerted no protective effect. The importance of transient oxidant stress in SnPP "preconditioning" was exemplified by the following: (1) oxidant stress induced by a different mechanism (myoglobin injection) recapitulated SnPP's protective action; (2) GSH treatment blunted SnPP's protective influence; (3) SnPP raised cytoprotective heavy chain ferritin (Fhc), a response enhanced by exogenous Fe injection; and (4) SnCl₂, a ∼35- to 50-fold HO-1 inducer (not inhibitor) evoked neither oxidant stress nor mitigated IRI (seemingly excluding HO-1 activity in SnPP's protective effect). SnPP specifically accumulates within proximal tubule cells; transient "catalytic" Fe overload and oxidative stress result; Nrf2-cytoprotective pathways are upregulated; and these changes help protect against ischemic AKI.

Ablation of adipose-HO-1 expression increases white fat over beige fat through inhibition of mitochondrial fusion and of PGC1α in female mice

Background Hmox1 plays an important role in the regulation of mitochondrial bioenergetics and function by regulating cellular heme-derived CO and bilirubin. Previous studies have demonstrated that global disruption of HO-1 in humans and mice resulted in severe organ dysfunction. Methods We investigated the potential role of adipose-specific-HO-1 genetic ablation on adipose tissue function, mitochondrial quality control and energy expenditure by generating an adipo-HO-1 knockout mouse model (Adipo-HO-1-/-) and, in vitro, adipocyte cells in which HO activity was inhibited. Adiposity, signaling proteins, fasting glucose and oxygen consumption were determined and compared to adipocyte cultures with depressed levels of both HO-1/HO-2. Results Adipo-HO-1-/- female mice exhibited increased adipocyte size, and decreases in the mitochondrial fusion to fission ratio, PGC1, and SIRT3. Importantly, ablation of HO-1 in adipose tissue resulted in fat acquiring many properties of visceral fat such as decreases in thermogenic genes including pAMPK and PRDM16. Deletion of HO-1 in mouse adipose tissue led to complete metabolic dysfunction, an increase in white adipose tissue, a reduction of beige fat and associated increases in FAS, aP2 and hyperglycemia. Mechanistically, genetic deletion of HO-1 in adipose tissues decreased the mitochondrial fusion to fission ratio; disrupted the activity of the PGC1 transcriptional axis and thermogenic genes both in vitro and in vivo. Conclusion Ablation of adipose tissue-HO-1 abridged PGC1 expression promoted mitochondrial dysfunction and contributed to an increase of pro-inflammatory visceral fat and abrogated beige-cell like phenotype.

Butein induction of HO-1 by p38 MAPK/Nrf2 pathway in adipocytes attenuates high-fat diet induced adipose hypertrophy in mice

Adipose tissue inflammation and oxidative stress are key components in the development of obesity and insulin resistance. Heme oxygenase (HO)-1 in adipocytes protects against obesity and adipose dysfunction. In this study, we report the identification of butein, a flavonoid chalcone, as a novel inducer of HO-1 expression in adipocytes in vitro and in vivo. Butein upregulated HO-1 mRNA and protein expression in 3T3-L1 adipocytes, accompanied by Kelch-Like ECH-Associated Protein (Keap) 1 degradation and increase in the nuclear level of nuclear factor erythroid 2-related factor 2 (Nrf2). Butein modulation of Keap1 and Nrf2 as well as HO-1 upregulation was reversed by pretreatment with p38 MAPK inhibitor SB203580, indicating the involvement of p38 MAPK in butein activation of Nrf2 in adipocytes. In addition, HO-1 activation by butein led to the inhibitions of reactive oxygen species and adipocyte differentiation, as evidenced by the fact that butein repression of reactive oxygen species and adipogenesis was reversed by pretreatment with HO-1 inhibitor SnPP. Induction of HO-1 expression by butein was also demonstrated in the adipose tissue of C57BL/6 mice fed a high-fat diet administered along with butein for three weeks, and correlated with the inhibitions of adiposity and adipose tissue inflammation, which were reversed by co-administration of SnPP. Altogether, our results demonstrate that butein activates the p38 MAPK/Nrf2/HO-1 pathway to act as a potent inhibitor of adipose hypertrophy and inflammation in a diet-induced obesity model and thus has potential for suppressing obesity-linked metabolic syndrome.

Heme oxygenase (HO)-1 induction prevents Endoplasmic Reticulum stress-mediated endothelial cell death and impaired angiogenic capacity

Most of diabetic cardiovascular complications are attributed to endothelial dysfunction and impaired angiogenesis. Endoplasmic Reticulum (ER) and oxidative stresses were shown to play a pivotal role in the development of endothelial dysfunction in diabetes. Hemeoxygenase-1 (HO-1) was shown to protect against oxidative stress in diabetes; however, its role in alleviating ER stress-induced endothelial dysfunction remains not fully elucidated. We aim here to test the protective role of HO-1 against high glucose-mediated ER stress and endothelial dysfunction and understand the underlying mechanisms with special emphasis on oxidative stress, inflammation and cell death. Human Umbilical Vein Endothelial Cells (HUVECs) were grown in either physiological or intermittent high concentrations of glucose for 5days in the presence or absence of Cobalt (III) Protoporphyrin IX chloride (CoPP, HO-1 inducer) or 4-Phenyl Butyric Acid (PBA, ER stress inhibitor). Using an integrated cellular and molecular approach, we then assessed ER stress and inflammatory responses, in addition to apoptosis and angiogenic capacity in these cells. Our results show that HO-1 induction prevented high glucose-mediated increase of mRNA and protein expression of key ER stress markers. Cells incubated with high glucose exhibited high levels of oxidative stress, activation of major inflammatory and apoptotic responses [nuclear factor (NF)-κB and c-Jun N-terminal kinase (JNK)] and increased rate of apoptosis; however, cells pre-treated with CoPP or PBA were fully protected. In addition, high glucose enhanced caspases 3 and 7 cleavage and activity and augmented cleaved poly ADP ribose polymerase (PARP) expression whereas HO-1 induction prevented these effects. Finally, HO-1 induction and ER stress inhibition prevented high glucose-induced reduction in NO release and impaired the angiogenic capacity of HUVECs, and enhanced vascular endothelial growth factor (VEGF)-A expression. Altogether, we show here the critical role of ER stress-mediated cell death in diabetes-induced endothelial dysfunction and impaired angiogenesis and underscore the role of HO-1 induction as a key therapeutic modulator for ER stress response in ischemic disorders and diabetes. Our results also highlight the complex interplay between ER stress response and oxidative stress.

Immunoregulatory networks in sickle cell alloimmunization

Red blood cell (RBC) transfusions are critical for treatment and prevention of complications of sickle cell disease (SCD), and most SCD patients will receive 1 or more transfusions by age 20. However, SCD alloimmunization remains a serious complication of transfusions that can lead to life-threatening acute and delayed transfusion reactions. Alloimmunization rates are higher in SCD patients most likely due to RBC antigenic differences between largely white donors vs mainly African-American recipients and frequency of transfusions. However, it remains unclear why some but not all SCD patients develop alloantibodies. Cellular immune responses that differ between alloimmunized and nonalloimmunized SCD patients are beginning to be characterized. Altered CD4⁺ T helper cell responses, known to control immunoglobulin G production, have been identified in alloimmunized SCD patients, including abnormalities in regulatory T cells, as well as helper type 1 (T_H1), T_H17, and follicular helper T cells. Furthermore, heightened innate immune cell responses to cell free heme with cell polarization toward proinflammatory T cell profiles were recently reported in SCD antibody responders, suggesting that the ongoing hemolytic state in SCD may impair the ability of innate immune cells in these already alloimmunized patients to counter alloimmunization. Identification of molecular pathways in key cellular components that differ between alloimmunized and nonalloimmunized SCD patients is likely to lead to identification of biomarkers of alloimmunization and future design of targeted therapies to prevent or even dampen alloantibody responses in these highly susceptible patients.

Resveratrol prevents endothelial progenitor cells from senescence and reduces the oxidative reaction via PPAR‑γ/HO‑1 pathways

Increasing evidence suggests endothelial progenitor cells (EPCs) improve neovascularization and endothelium regeneration. Resveratrol (RSV) is a natural polyphenolic compound, which has been demonstrated to exert multiple protective effects on the cardiovascular system, including inhibition of platelet adhesion and aggregation, reduction of myocardial ischemia-reperfusion injury, and suppression of neointimal hyperplasia of injured vascular tissue. The present study investigated the role of RSV on levels of oxidative stress and senescence of EPCs, and the effects of RSV on vascular-promoting and/or vascular-healing capacity of EPCs. It was demonstrated that EPCs could promote the repair of endothelium of the injured artery. RSV reduced the oxidative reaction of EPCs and inhibited EPC senescence, and these effects may occur via the peroxisome proliferator-activated receptor-γ/heme oxygenase-1 signaling pathways.

Omeprazole induces heme oxygenase-1 in fetal human pulmonary microvascular endothelial cells via hydrogen peroxide-independent Nrf2 signaling pathway

Omeprazole (OM) is an aryl hydrocarbon receptor (AhR) agonist and a proton pump inhibitor that is used to treat humans with gastric acid related disorders. Recently, we showed that OM induces NAD (P) H quinone oxidoreductase-1 (NQO1) via nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent mechanism. Heme oxygenase-1 (HO-1) is another cytoprotective and antioxidant enzyme that is regulated by Nrf2. Whether OM induces HO-1 in fetal human pulmonary microvascular endothelial cells (HPMEC) is unknown. Therefore, we tested the hypothesis that OM will induce HO-1 expression via Nrf2 in HPMEC. OM induced HO-1 mRNA and protein expression in a dose-dependent manner. siRNA-mediated knockdown of AhR failed to abrogate, whereas knockdown of Nrf2 abrogated HO-1 induction by OM. To identify the underlying molecular mechanisms, we determined the effects of OM on cellular hydrogen peroxide (H₂O₂) levels since oxidative stress mediated by the latter is known to activate Nrf2. Interestingly, the concentration at which OM induced HO-1 also increased H₂O₂ levels. Furthermore, H₂O₂ independently augmented HO-1 expression. Although N-acetyl cysteine (NAC) significantly decreased H₂O₂ levels in OM-treated cells, we observed that OM further increased HO-1 mRNA and protein expression in NAC-pretreated compared to vehicle-pretreated cells, suggesting that OM induces HO-1 via H₂O₂-independent mechanisms. In conclusion, we provide evidence that OM transcriptionally induces HO-1 via AhR - and H₂O₂ - independent, but Nrf2 - dependent mechanisms. These results have important implications for human disorders where Nrf2 and HO-1 play a beneficial role.

Propofol ameliorates hyperglycemia-induced cardiac hypertrophy and dysfunction via heme oxygenase-1/signal transducer and activator of transcription 3 signaling pathway in rats

OBJECTIVES

Heme oxygenase-1 is inducible in cardiomyocytes in response to stimuli such as oxidative stress and plays critical roles in combating cardiac hypertrophy and injury. Signal transducer and activator of transcription 3 plays a pivotal role in heme oxygenase-1-mediated protection against liver and lung injuries under oxidative stress. We hypothesized that propofol, an anesthetic with antioxidant capacity, may attenuate hyperglycemia-induced oxidative stress in cardiomyocytes via enhancing heme oxygenase-1 activation and ameliorate hyperglycemia-induced cardiac hypertrophy and apoptosis via heme oxygenase-1/signal transducer and activator of transcription 3 signaling and improve cardiac function in diabetes.

DESIGN

Treatment study.

SETTING

Research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

In vivo and in vitro treatments.

MEASUREMENTS AND MAIN RESULTS

At 8 weeks of streptozotocin-induced type 1 diabetes in rats, myocardial 15-F2t-isoprostane was significantly increased, accompanied by cardiomyocyte hypertrophy and apoptosis and impaired left ventricular function that was coincident with reduced heme oxygenase-1 activity and signal transducer and activator of transcription 3 activation despite an increase in heme oxygenase-1 protein expression as compared to control. Propofol infusion (900 μg/kg/min) for 45 minutes significantly improved cardiac function with concomitantly enhanced heme oxygenase-1 activity and signal transducer and activator of transcription activation. Similar to the changes seen in diabetic rat hearts, high glucose (25 mmol/L) exposure for 48 hours led to cardiomyocyte hypertrophy and apoptosis, both in primary cultured neonatal rat cardiomyocytes and in H9c2 cells compared to normal glucose (5.5 mmol/L). Hypertrophy was accompanied by increased reactive oxygen species and malondialdehyde production and caspase-3 activity. Propofol, similar to the heme oxygenase-1 inducer cobalt protoporphyrin, significantly increased cardiomyocyte heme oxygenase-1 and p-signal transducer and activator of transcription protein expression and heme oxygenase-1 activity and attenuated high-glucose-mediated cardiomyocyte hypertrophy and apoptosis and reduced reactive oxygen species and malondialdehyde production (p < 0.05). These protective effects of propofol were abolished by heme oxygenase-1 inhibition with zinc protoporphyrin and by heme oxygenase-1 or signal transducer and activator of transcription 3 gene knockdown.

CONCLUSIONS

Heme oxygenase-1/signal transducer and activator of transcription 3 signaling plays a critical role in propofol-mediated amelioration of hyperglycemia-induced cardiomyocyte hypertrophy and apoptosis, whereby propofol improves cardiac function in diabetic rats.

MicroRNA-218 promotes high glucose-induced apoptosis in podocytes by targeting heme oxygenase-1

Emerging evidence has demonstrated that microRNAs (miRNAs) play a mediatory role in the pathogenesis of diabetic nephropathy. In this study, we found that miR-218 was upregulated in high glucose (HG) treated podocytes, which are essential components of the glomerular filtration barrier and a major prognostic determinant in diabetic nephropathy. Additionally, up-regulation of miR-218 was accompanied by an increased rate of podocyte death and down-regulation in the level of nephrin, a key marker of podocytes. However, inhibition of miR-218 exerted the opposite effect. In addition, the dual-luciferase reporter assay showed that miR-218 directly targeted the 3'-untranslated region of heme oxygenase-1 (HO-1), and further study confirmed an increase of HO-1 in HG-treated podocytes transfected with anti-miR-218. Knockdown of HO-1 blocked the anti-apoptotic effect of anti-miR-218. Furthermore, inhibition of miR-218 was associated with decreased expression of the known pro-apoptotic molecule p38-mitogen-activated protein kinase (p38-MAPK) activation. Following preconditioning with SB203580, an inhibitor of p38-MAPK, the stimulatory effect of HG on podocyte apoptosis was strikingly ameliorated. These findings suggested that miR-218 accelerated HG-induced podocyte apoptosis through directly down-regulating HO-1 and facilitating p38-MAPK activation.

Redox modulation of adipocyte differentiation: hypothesis of "Redox Chain" and novel insights into intervention of adipogenesis and obesity

In view of the global prevalence of obesity and obesity-associated disorders, it is important to clearly understand how adipose tissue forms. Accumulating data from various laboratories implicate that redox status is closely associated with energy metabolism. Thus, biochemical regulation of the redox system may be an attractive alternative for the treatment of obesity-related disorders. In this work, we will review the current data detailing the role of the redox system in adipocyte differentiation, as well as identifying areas for further research. The redox system affects adipogenic differentiation in an extensive way. We propose that there is a complex and interactive "redox chain," consisting of a "ROS-generating enzyme chain," "combined antioxidant chain," and "transcription factor chain," which contributes to fine-tune the regulation of ROS level and subsequent biological consequences. The roles of the redox system in adipocyte differentiation are paradoxical. The redox system exerts a "tridimensional" mechanism in the regulation of adipocyte differentiation, including transcriptional, epigenetic, and posttranslational modulations. We suggest that redoxomic techniques should be extensively applied to understand the biological effects of redox alterations in a more integrated way. A stable and standardized "redox index" is urgently needed for the evaluation of the general redox status. Therefore, more effort should be made to establish and maintain a general redox balance rather than to conduct simple prooxidant or antioxidant interventions, which have comprehensive implications.

Translational Significance of Heme Oxygenase in Obesity and Metabolic Syndrome

The global epidemic of obesity continues unabated with sequelae of diabetes and metabolic syndrome. This review reflects the dramatic increase in research on the role of increased expression of heme oxygenase (HO)-1/HO-2, biliverdin reductase, and HO activity on vascular disease. The HO system engages with other systems to mitigate the deleterious effects of oxidative stress in obesity and cardiovascular disease (CVD). Recent reports indicate that HO-1/HO-2 protein expression and HO activity have several important roles in hemostasis and reactive oxygen species (ROS)-dependent perturbations associated with metabolic syndrome. HO-1 protects tissue during inflammatory stress in obesity through the degradation of pro-oxidant heme and the production of carbon monoxide (CO) and bilirubin, both of which have anti-inflammatory and anti-apoptotic properties. By contrast, repression of HO-1 is associated with increases of cellular heme and inflammatory conditions including hypertension, stroke, and atherosclerosis. HO-1 is a major focus in the development of potential therapeutic strategies to reverse the clinical complications of obesity and metabolic syndrome.

The HO-1/CO system regulates mitochondrial-capillary density relationships in human skeletal muscle

The heme oxygenase-1 (HO-1)/carbon monoxide (CO) system induces mitochondrial biogenesis, but its biological impact in human skeletal muscle is uncertain. The enzyme system generates CO, which stimulates mitochondrial proliferation in normal muscle. Here we examined whether CO breathing can be used to produce a coordinated metabolic and vascular response in human skeletal muscle. In 19 healthy subjects, we performed vastus lateralis muscle biopsies and tested one-legged maximal O2 uptake (V̇o2max) before and after breathing air or CO (200 ppm) for 1 h daily for 5 days. In response to CO, there was robust HO-1 induction along with increased mRNA levels for nuclear-encoded mitochondrial transcription factor A (Tfam), cytochrome c, cytochrome oxidase subunit IV (COX IV), and mitochondrial-encoded COX I and NADH dehydrogenase subunit 1 (NDI). CO breathing did not increase V̇o2max (1.96 ± 0.51 pre-CO, 1.87 ± 0.50 post-CO l/min; P = not significant) but did increase muscle citrate synthase, mitochondrial density (139.0 ± 34.9 pre-CO, 219.0 ± 36.2 post-CO; no. of mitochondrial profiles/field), myoglobin content and glucose transporter (GLUT4) protein level and led to GLUT4 localization to the myocyte membrane, all consistent with expansion of the tissue O2 transport system. These responses were attended by increased cluster of differentiation 31 (CD31)-positive muscle capillaries (1.78 ± 0.16 pre-CO, 2.37 ± 0.59 post-CO; capillaries/muscle fiber), implying the enrichment of microvascular O2 reserve. The findings support that induction of the HO-1/CO system by CO not only improves muscle mitochondrial density, but regulates myoglobin content, GLUT4 localization, and capillarity in accordance with current concepts of skeletal muscle plasticity.

Adiponectin ameliorates hyperglycemia-induced cardiac hypertrophy and dysfunction by concomitantly activating Nrf2 and Brg1

Hyperglycemia-induced oxidative stress is implicated in the development of cardiomyopathy in diabetes that is associated with reduced adiponectin (APN) and heme oxygenase-1 (HO-1). Brahma-related gene 1 (Brg1) assists nuclear factor-erythroid-2-related factor-2 (Nrf2) to activate HO-1 to increase myocardial antioxidant capacity in response to oxidative stress. We hypothesized that reduced adiponectin (APN) impairs HO-1 induction which contributes to the development of diabetic cardiomyopathy, and that supplementation of APN may ameliorate diabetic cardiomyopathy by activating HO-1 through Nrf2 and Brg1 in diabetes. Control (C) and streptozotocin-induced diabetic (D) rats were untreated or treated with APN adenovirus (1×10(9) pfu) 3 weeks after diabetes induction and examined and terminated 1 week afterward. Rat left ventricular functions were assessed by a pressure-volume conductance system, before the rat hearts were removed to perform histological and biochemical assays. Four weeks after diabetes induction, D rats developed cardiac hypertrophy evidenced as increased ratio of heart weight to body weight, elevated myocardial collagen I content, and larger cardiomyocyte cross-sectional area (all P<0.05 vs C). Diabetes elevated cardiac oxidative stress (increased 15-F2t-isoprostane, 4-hydroxynonenal generation, 8-hydroxy-2'-deoxyguanosine, and superoxide anion generation), increased myocardial apoptosis, and impaired cardiac function (all P<0.05 vs C). In D rats, myocardial HO-1 mRNA and protein expression were reduced which was associated with reduced Brg1 and nuclear Nrf2 protein expression. All these changes were either attenuated or prevented by APN. In primarily cultured cardiomyocytes (CMs) isolated from D rats or in the embryonic rat cardiomyocytes cell line H9C2 cells incubated with high glucose (HG, 25 mM), supplementation of recombined globular APN (gAd, 2μg/mL) reversed HG-induced reductions of HO-1, Brg1, and nuclear Nrf2 protein expression and attenuated cellular oxidative stress, myocyte size, and apoptotic cells. Inhibition of HO-1 by ZnPP (10μM) or small interfering RNA (siRNA) canceled all the above gAd beneficial effects. Moreover, inhibition of Nrf2 (either by the Nrf2 inhibitor luteolin or siRNA) or Brg1 (by siRNA) canceled gAd-induced HO-1 induction and cellular protection in CMs and in H9C2 cells incubated with HG. In summary, our present study demonstrated that APN reduced cardiac oxidative stress, ameliorated cardiomyocyte hypertrophy, and prevented left ventricular dysfunction in diabetes by concomitantly activating Nrf2 and Brg1 to facilitate HO-1 induction.

HO-1 Upregulation Attenuates Adipocyte Dysfunction, Obesity, and Isoprostane Levels in Mice Fed High Fructose Diets

Background. Fructose metabolism is an unregulated metabolic pathway and excessive fructose consumption is known to activate ROS. HO-1 is a potent antioxidant gene that plays a key role in decreasing ROS and isoprostanes. We examined whether the fructose-mediated increase in adipocyte dysfunction involves an increase in isoprostanes and that pharmacological induction of HO-1 would decrease both isoprostane levels and adipogenesis. Methods and Results. We examined the effect of fructose, on adipogenesis in human MSCs in the presence and absence of CoPP, an inducer of HO-1. Fructose increased adipogenesis and the number of large lipid droplets while decreasing the number of small lipid droplets (P < 0.05). Levels of heme and isoprostane in fructose treated MSC-derived adipocytes were increased. CoPP reversed these effects and markedly increased HO-1 and the Wnt signaling pathway. The high fructose diet increased heme levels in adipose tissue and increased circulating isoprostane levels (P < 0.05 versus control). Fructose diets decreased HO-1 and adiponectin levels in adipose tissue. Induction of HO-1 by CoPP decreased isoprostane synthesis (P < 0.05 versus fructose). Conclusion. Fructose treatment resulted in increased isoprostane production and adipocyte dysfunction, which was reversed by the increased expression of HO-1.

Induction of heme oxygenase I (HMOX1) by HPP-4382: a novel modulator of Bach1 activity

Oxidative stress is generated by reactive oxygen species (ROS) produced in response to metabolic activity and environmental factors. Increased oxidative stress is associated with the pathophysiology of a broad spectrum of inflammatory diseases. Cellular response to excess ROS involves the induction of antioxidant response element (ARE) genes under control of the transcriptional activator Nrf2 and the transcriptional repressor Bach1. The development of synthetic small molecules that activate the protective anti-oxidant response network is of major therapeutic interest. Traditional small molecules targeting ARE-regulated gene activation (e.g., bardoxolone, dimethyl fumarate) function by alkylating numerous proteins including Keap1, the controlling protein of Nrf2. An alternative is to target the repressor Bach1. Bach1 has an endogenous ligand, heme, that inhibits Bach1 binding to ARE, thus allowing Nrf2-mediated gene expression including that of heme-oxygenase-1 (HMOX1), a well described target of Bach1 repression. In this report, normal human lung fibroblasts were used to screen a collection of synthetic small molecules for their ability to induce HMOX1. A class of HMOX1-inducing compounds, represented by HPP-4382, was discovered. These compounds are not reactive electrophiles, are not suppressed by N-acetyl cysteine, and do not perturb either ROS or cellular glutathione. Using RNAi, we further demonstrate that HPP-4382 induces HMOX1 in an Nrf2-dependent manner. Chromatin immunoprecipitation verified that HPP-4382 treatment of NHLF cells reciprocally coordinated a decrease in binding of Bach1 and an increase of Nrf2 binding to the HMOX1 E2 enhancer. Finally we show that HPP-4382 can inhibit Bach1 activity in a reporter assay that measures transcription driven by the human HMOX1 E2 enhancer. Our results suggest that HPP-4382 is a novel activator of the antioxidant response through the modulation of Bach1 binding to the ARE binding site of target genes.

Gas what: NO is not the only answer to sexual function

The ability to get and keep an erection is important to men for several reasons and the inability is known as erectile dysfunction (ED). ED has started to be accepted as an early indicator of systemic endothelial dysfunction and subsequently of cardiovascular diseases. The role of NO in endothelial relaxation and erectile function is well accepted. The discovery of NO as a small signalling gasotransmitter led to the investigation of the role of other endogenously derived gases, carbon monoxide (CO) and hydrogen sulphide (H2 S) in physiological and pathophysiological conditions. The role of NO and CO in sexual function and dysfunction has been investigated more extensively and, recently, the involvement of H2 S in erectile function has also been confirmed. In this review, we focus on the role of these three sister gasotransmitters in the physiology, pharmacology and pathophysiology of sexual function in man, specifically erectile function. We have also reviewed the role of soluble guanylyl cyclase/cGMP pathway as a common target of these gasotransmitters. Several studies have proposed alternative therapies targeting different mechanisms in addition to PDE-5 inhibition for ED treatment, since some patients do not respond to these drugs. This review highlights complementary and possible coordinated roles for these mediators and treatments targeting these gasotransmitters in erectile function/ED.

Hemin controls T cell polarization in sickle cell alloimmunization

Patients with sickle cell disease (SCD) often require transfusions to treat and prevent worsening anemia and other SCD complications. However, transfusions can trigger alloimmunization against transfused RBCs with serious clinical sequelae. Risk factors for alloimmunization in SCD remain poorly understood. We recently reported altered regulatory T cell (Treg) and Th responses with higher circulating Th1 (IFN-γ(+)) cytokines in chronically transfused SCD patients with alloantibodies as compared with those without alloantibodies. Because monocytes play a critical role in polarization of T cell subsets and participate in clearance of transfused RBCs, we tested the hypothesis that in response to the RBC breakdown product hemin, monocyte control of T cell polarization will differ between alloimmunized and non-alloimmunized SCD patients. Exogenous hemin induced Treg polarization in purified T cell/monocyte cocultures from healthy volunteers through the monocyte anti-inflammatory heme-degrading enzyme heme oxygenase-1. Importantly, hemin primarily through its effect on CD16+ monocytes induced an anti-inflammatory (higher Treg/lower Th1) polarization state in the non-alloimmunized SCD group, whereas it had little effect in the alloimmunized group. Non-alloimmunized SCD CD16+ monocytes expressed higher basal levels of heme oxygenase-1. Furthermore, IL-12, which contributed to a proinflammatory polarization state (low Treg/high Th1) in SCD, was dampened in hemin-treated stimulated monocytes from non-alloimmunized SCD patients, but not in the alloimmunized group. These data suggest that unlike alloimmunized patients, non-alloimmunized SCD CD16+ monocytes in response to transfused RBC breakdown products promote an anti-inflammatory state that is less conducive to alloimmunization.

Antioxidants condition pleiotropic vascular responses to exogenous H(2)O(2): role of modulation of vascular TP receptors and the heme oxygenase system

AIMS

Hydrogen peroxide (H(2)O(2)), a nonradical oxidant, is employed to ascertain the role of redox mechanisms in regulation of vascular tone. Where both dilation and constriction have been reported, we examined the hypothesis that the ability of H(2)O(2) to effect vasoconstriction or dilation is conditioned by redox mechanisms and may be modulated by antioxidants.

RESULTS

Exogenous H(2)O(2) (0.1-10.0 μM), dose-dependently reduced the internal diameter of rat renal interlobular and 3rd-order mesenteric arteries (p<0.05). This response was obliterated in arteries pretreated with antioxidants, including tempol, pegylated superoxide dismutase (PEG-SOD), butylated hydroxytoluene (BHT), and biliverdin (BV). However, as opposed to tempol or PEG-SOD, BHT & BV, antioxidants targeting radicals downstream of H(2)O(2), also uncovered vasodilation.

INNOVATIONS

Redox-dependent vasoconstriction to H(2)O(2) was blocked by inhibitors of cyclooxygenase (COX) (indomethacin-10 μM), thromboxane (TP) synthase (CGS13080-10 μM), and TP receptor antagonist (SQ29548-1 μM). However, H(2)O(2) did not increase vascular thromboxane B(2) release; instead, it sensitized the vasculature to a TP agonist, U46619, an effect reversed by PEG-SOD. Antioxidant-conditioned dilatory response to H(2)O(2) was accompanied by enhanced vascular heme oxygenase (HO)-dependent carbon monoxide generation and was abolished by HO inhibitors or by HO-1 & 2 antisense oligodeoxynucleotides treatment of SD rats.

CONCLUSION

These results demonstrate that H(2)O(2) has antioxidant-modifiable pleiotropic vascular effects, where constriction and dilation are brought about in the same vascular segment. H(2)O(2)-induced oxidative stress increases vascular TP sensitivity and predisposes these arterial segments to constrictor prostanoids. Conversely, vasodilation is reliant upon HO-derived products whose synthesis is stimulated only in the presence of antioxidants targeting radicals downstream of H(2)O(2).

Heme oxygenase-1 induction protects against hypertension associated with diabetes: effect on exaggerated vascular contractility

Disturbances in vascular reactivity are important components of diabetes-evoked hypertension. Heme oxygenase-1 (HO-1) is a homeostatic enzyme upregulated in stress. This study aims to investigate the protective effect of HO-1 against diabetes-evoked hypertension. Rats were left 8 weeks after diabetes induction with streptozotocin to induce vascular dysfunction in the diabetic groups. HO-1 inducers, hemin and curcumin, were daily administrated in the last 6 weeks in the treated groups after 2 weeks of induction. Then, at the end of the study (8 weeks), HO-1 protein level was assessed by immunofluorescence; blood pressure (BP) was recorded; isolated aorta reactivity to phenylephrine (PE) and KCl was studied; reactive oxygen species (ROS) generation was determined; and serum level of glucose, advanced glycation end products (AGEs), and tumor necrosis factor alpha (TNF-α) were determined. While not affected by diabetes, HO-1 protein expression was strongly induced by hemin or curcumin administration. Compared with control animals, diabetes increased systolic and pulse BP. Induction of HO-1 by hemin or curcumin significantly reduced elevated systolic BP and abolished elevated pulse BP without affecting the developed hyperglycemia or AGEs level. The possibility that alterations in vascular reactivity contributed to diabetes-HO-1 BP interaction was investigated. Diabetes increased contractile response of the aorta to PE and KCl, while HO-1 induction by curcumin or hemin prevented aorta-exaggerated response to PE and KCl. Furthermore, the competitive HO inhibitor, tin protoporphyrin, abolished the protective effect of hemin. Diabetes was accompanied with elevated level of TNF-α and ROS generation, while HO-1 induction abrogated increased TNF-α and ROS generation. Collectively, induction of HO-1 protects against hypertension associated with diabetes via ameliorating exaggerated vascular contractility by reducing TNF-α and aortic ROS levels.

Redox regulation of mitochondrial biogenesis

The cell renews, adapts, or expands its mitochondrial population during episodes of cell damage or periods of intensified energy demand by the induction of mitochondrial biogenesis. This bigenomic program is modulated by redox-sensitive signals that respond to physiological nitric oxide (NO), carbon monoxide (CO), and mitochondrial reactive oxygen species production. This review summarizes our current ideas about the pathways involved in the activation of mitochondrial biogenesis by the physiological gases leading to changes in the redox milieu of the cell, with an emphasis on the responses to oxidative stress and inflammation. The cell's energy supply is protected from conditions that damage mitochondria by an inducible transcriptional program of mitochondrial biogenesis that operates in large part through redox signals involving the nitric oxide synthase and the heme oxygenase-1/CO systems. These redox events stimulate the coordinated activities of several multifunctional transcription factors and coactivators also involved in the elimination of defective mitochondria and the expression of counterinflammatory and antioxidant genes, such as IL10 and SOD2, as part of a unified damage-control network. The redox-regulated mechanisms of mitochondrial biogenesis schematically outlined in the graphical abstract link mitochondrial quality control to an enhanced capacity to support the cell's metabolic needs while improving its resistance to metabolic failure and avoidance of cell death during periods of oxidative stress.

Heme oxygenase-1, oxidation, inflammation, and atherosclerosis

Atherosclerosis is an inflammatory process of the vascular wall characterized by the infiltration of lipids and inflammatory cells. Oxidative modifications of infiltrating low-density lipoproteins and induction of oxidative stress play a major role in lipid retention in the vascular wall, uptake by macrophages and generation of foam cells, a hallmark of this disorder. The vasculature has a plethora of protective resources against oxidation and inflammation, many of them regulated by the Nrf2 transcription factor. Heme oxygenase-1 (HO-1) is a Nrf2-regulated gene that plays a critical role in the prevention of vascular inflammation. It is the inducible isoform of HO, responsible for the oxidative cleavage of heme groups leading to the generation of biliverdin, carbon monoxide, and release of ferrous iron. HO-1 has important antioxidant, antiinflammatory, antiapoptotic, antiproliferative, and immunomodulatory effects in vascular cells, most of which play a significant role in the protection against atherogenesis. HO-1 may also be an important feature in macrophage differentiation and polarization to certain subtypes. The biological effects of HO-1 are largely attributable to its enzymatic activity, which can be conceived as a system with three arms of action, corresponding to its three enzymatic byproducts. HO-1 mediated vascular protection may be due to a combination of systemic and vascular local effects. It is usually expressed at low levels but can be highly upregulated in the presence of several proatherogenic stimuli. The HO-1 system is amenable for use in the development of new therapies, some of them currently under experimental and clinical trials. Interestingly, in contrast to the HO-1 antiatherogenic actions, the expression of its transcriptional regulator Nrf2 leads to proatherogenic effects instead. This suggests that a potential intervention on HO-1 or its byproducts may need to take into account any potential alteration in the status of Nrf2 activation. This article reviews the available evidence that supports the antiatherogenic role of HO-1 as well as the potential pathways and mechanisms mediating vascular protection.

Heme oxygenase-1, oxidation, inflammation, and atherosclerosis

Atherosclerosis is an inflammatory process of the vascular wall characterized by the infiltration of lipids and inflammatory cells. Oxidative modifications of infiltrating low-density lipoproteins and induction of oxidative stress play a major role in lipid retention in the vascular wall, uptake by macrophages and generation of foam cells, a hallmark of this disorder. The vasculature has a plethora of protective resources against oxidation and inflammation, many of them regulated by the Nrf2 transcription factor. Heme oxygenase-1 (HO-1) is a Nrf2-regulated gene that plays a critical role in the prevention of vascular inflammation. It is the inducible isoform of HO, responsible for the oxidative cleavage of heme groups leading to the generation of biliverdin, carbon monoxide, and release of ferrous iron. HO-1 has important antioxidant, antiinflammatory, antiapoptotic, antiproliferative, and immunomodulatory effects in vascular cells, most of which play a significant role in the protection against atherogenesis. HO-1 may also be an important feature in macrophage differentiation and polarization to certain subtypes. The biological effects of HO-1 are largely attributable to its enzymatic activity, which can be conceived as a system with three arms of action, corresponding to its three enzymatic byproducts. HO-1 mediated vascular protection may be due to a combination of systemic and vascular local effects. It is usually expressed at low levels but can be highly upregulated in the presence of several proatherogenic stimuli. The HO-1 system is amenable for use in the development of new therapies, some of them currently under experimental and clinical trials. Interestingly, in contrast to the HO-1 antiatherogenic actions, the expression of its transcriptional regulator Nrf2 leads to proatherogenic effects instead. This suggests that a potential intervention on HO-1 or its byproducts may need to take into account any potential alteration in the status of Nrf2 activation. This article reviews the available evidence that supports the antiatherogenic role of HO-1 as well as the potential pathways and mechanisms mediating vascular protection.

Heme oxygenase gene targeting to adipocytes attenuates adiposity and vascular dysfunction in mice fed a high-fat diet

We examined the hypothesis that adipocyte dysfunction in mice fed a high-fat (HF) diet can be prevented by lentiviral-mediated and adipocyte specific-targeting delivery of the human heme oxygenase-1 (aP2-HO-1). A bolus intracardial injection of aP2-HO-1 resulted in expression of human HO-1 for up to 9.5 months. Transduction of aP2-HO-1 increased human HO-1 expression in fat tissues without affecting murine HO-1. In mice fed a HF diet, aP2-HO-1 transduction attenuated the increases in body weight, blood glucose, blood pressure, and inflammatory cytokines, as well as the content of both visceral and subcutaneous fat. Transduction of aP2-HO-1 increased the numbers of adipocytes of small cell size (P<0.05), insulin sensitivity (P<0.05), adiponectin levels, as well as vascular relaxation to acetylcholine compared with HF mice administered the aP2-green fluorescent protein. Adipocytes of mice fed a HF diet expressed high levels of peroxisome proliferator activator receptor, aP2, C/EBP, and Wnt5b proteins and displayed marked increases in Peg1/Mesoderm specific transcript (P<0.03). Transduction of aP2-HO-1 lowered the elevated levels of these proteins and increased Sonic hedgehog, Wnt10b, and β-catenin (P<0.05). Inhibition of HO activity by administration of tin mesoporphyrin to HF-fed mice transduced with the aP2-HO-1 reversed the decrease in Peg1/Mesoderm-specific transcript, TNFα, and MCP-1 levels. Collectively, this novel study demonstrates that adipocyte-specific overexpression of HO-1 attenuates HF-mediated adiposity and vascular dysfunction; increases insulin sensitivity; and improves adipocyte function by increasing adiponectin, Shh, and WNT10b, and by decreasing inflammatory cytokines. These effects are reversed by the HO activity inhibitor, stannous mesoporphyrin.

Apo A1 Mimetic Rescues the Diabetic Phenotype of HO-2 Knockout Mice via an Increase in HO-1 Adiponectin and LKBI Signaling Pathway

Insulin resistance, with adipose tissue dysfunction, is one of the hallmarks of metabolic syndrome. We have reported a metabolic syndrome-like phenotype in heme oxygenase (HO)-2 knockout mice, which presented with concurrent HO-1 deficiency and were amenable to rescue by an EET analog. Apo A-I mimetic peptides, such as L-4F, have been shown to induce HO-1 expression and decrease oxidative stress and adiposity. In this study we aimed to characterize alleviatory effects of HO-1 induction (if any) on metabolic imbalance observed in HO-2 KO mice. In this regard, HO-2((-/-)) mice were injected with 2 mg/kg/day L-4F, or vehicle, i.p., for 6 weeks. As before, compared to WT animals, the HO-2 null mice were obese, displayed insulin resistance, and had elevated blood pressure. These changes were accompanied by enhanced tissue (hepatic) oxidative stress along with attenuation of HO-1 expression and activity and reduced adiponectin, pAMPK, and LKB1 expression. Treatment with L-4F restored HO-1 expression and activity and increased adiponectin, LKB1, and pAMPK in the HO-2((-/-)) mice. These alterations resulted in a decrease in blood pressure, insulin resistance, blood glucose, and adiposity. Taken together, our results show that a deficient HO-1 response, in a state with reduced HO-2 basal levels, is accompanied by disruption of metabolic homeostasis which is successfully restored by an HO-1 inducer.

Oxidative stress and heme oxygenase-1 regulated human mesenchymal stem cells differentiation

This paper describes the effect of increased expression of HO-1 protein and increased levels of HO activity on differentiation of bone-marrow-derived human MSCs. MSCs are multipotent cells that proliferate and differentiate into many different cell types including adipocytes and osteoblasts. HO, the rate-limiting enzyme in heme catabolism, plays an important role during MSCs differentiation. HO catalyzes the stereospecific degradation of heme to biliverdin, with the concurrent release of iron and carbon monoxide. Upregulation of HO-1 expression and increased HO activity are essential for MSC growth and differentiation to the osteoblast lineage consistent with the role of HO-1 in hematopoietic stem cell differentiation. HO-1 participates in the MSC differentiation process shifting the balance of MSC differentiation in favor of the osteoblast lineage by decreasing PPARγ and increasing osteogenic markers such as alkaline phosphatase and BMP-2. In this paper, we define HO-1 as a target molecule in the modulation of adipogenesis and osteogenesis from MSCs and examine the role of the HO system in diabetes, inflammation, osteoporosis, hypertension, and other pathologies, a burgeoning area of research.

ApoA1: mimetic peptide reverses adipocyte dysfunction in vivo and in vitro via an increase in heme oxygenase (HO-1) and Wnt10b

Insulin resistance is a risk factor in the development of type 2 diabetes and is a major cause of atherosclerosis. Reduction in heme oxygenase (HO-1) has been shown to exacerbate vascular dysfunction and insulin resistance in obese mice and involves a decrease in adiponectin levels. Adiponectin is released from mesenchymal stem cell (MSC)-derived adipocytes, its levels are decreased in type 2 diabetes. We hypothesized that the apoA1 mimetic peptide, L-4F, will target the expression of the HO-1-adiponectin axis and reverse adipocyte dysfunction both in vivo and in vitro. The administration of L-4F [2 mg/Kg/daily (i.p.) for 4-week to 8-week-old obese (ob) mice restored adipocyte function, increased adiponectin release (p < 0.05) and decreased the levels of IL-1 and IL-6 (p < 0.05)]. These perturbations were associated with an increase in insulin sensitivity (p < 0.01 vs. untreated ob mice) and decreased glucose levels (309 + 42 vs. 201 + 8 mg/d after L-4F treatment). Treatment of both mesenchymal stem cell (MSC)-derived adipocytes with L-4F (50 μg/ml) increased adiponectin (p < 0.05), decreased IL-1 and IL-6 (p < 0.05) levels and increased MSC-derived adipocyte cell numbers by 50% in S phase (p < 0.05). MSC-derived adipocytes treated with L-4F increased WNT10b and decreased Peg 1/Mest. Inhibition of HO activity reversed the decrease in the adipogenic response gene, Peg 1/Mest. An increase of HO-1 expression by L-4F increased insulin-receptor phosphorylation. These findings support the hypothesis that L-4F increases early adipocyte markers, HO-1-adiponectin, WNT10b and decreases Peg1/Mest, negative regulators of adipocyte differentiation.

Transcriptional control of mitochondrial biogenesis and its interface with inflammatory processes

BACKGROUND

Cells avoid major mitochondrial damage and energy failure during systemic inflammatory states, such as severe acute infections, by specific targeting of the inflammatory response and by inducing anti-inflammatory and anti-oxidant defenses. Recent evidence indicates that these cell defenses also include mitochondrial biogenesis and the clearance of damaged mitochondria through autophagy.

SCOPE OF REVIEW

This review addresses a group of transcriptional signaling mechanisms that engage mitochondrial biogenesis, including energy-sensing and redox-regulated transcription factors and co-activators, after major inflammatory events.

MAJOR CONCLUSIONS

Stimulation of the innate immune system by activation of toll-like receptors (TLR) generates pro-inflammatory mediators, such as tumor necrosis factor-α (TNF-α)and interleukin-1β (IL-1β), necessary for optimal host defense, but which also contribute to mitochondrial damage through oxidative stress and other mechanisms. To protect its energy supply, host cells sense mitochondrial damage and initiate mitochondrial biogenesis under the control of an inducible transcriptional program that also activates anti-oxidant and anti-inflammatory gene expression. This multifunctional network not only increases cellular resistance to metabolic failure, oxidative stress, and cell death, but promotes immune tolerance as shown in the graphical abstract.

GENERAL SIGNIFICANCE

The post-inflammatory induction of mitochondrial biogenesis supports metabolic function and cell viability while helping to control inflammation. In clinical settings, patients recovering from severe systemic infections may develop transient immune suppression, placing them at risk for recurrent infection, but there may be therapeutic opportunities to enhance mitochondrial quality control that would improve the resolution of life-threatening host responses to such infections.

Reciprocal Effects of Oxidative Stress on Heme Oxygenase Expression and Activity Contributes to Reno-Vascular Abnormalities in EC-SOD Knockout Mice

Heme oxygenase (HO) system is one of the key regulators of cellular redox homeostasis which responds to oxidative stress (ROS) via HO-1 induction. However, recent reports have suggested an inhibitory effect of ROS on HO activity. In light of these conflicting reports, this study was designed to evaluate effects of chronic oxidative stress on HO system and its role in contributing towards patho-physiological abnormalities observed in extracellular superoxide dismutase (EC-SOD, SOD3) KO animals. Experiments were performed in WT and EC-SOD((-/-)) mice treated with and without HO inducer, cobalt protoporphyrin (CoPP). EC-SOD((-/-)) mice exhibited oxidative stress, renal histopathological abnormalities, elevated blood pressure, impaired endothelial function, reduced p-eNOS, p-AKT and increased HO-1 expression; although, HO activity was significantly (P < 0.05) attenuated along with attenuation of serum adiponectin and vascular epoxide levels (P < 0.05). CoPP, in EC-SOD((-/-)) mice, enhanced HO activity (P < 0.05) and reversed aforementioned pathophysiological abnormalities along with restoration of vascular EET, p-eNOS, p-AKT and serum adiponectin levels in these animals. Taken together our results implicate a causative role of insufficient activation of heme-HO-adiponectin system in pathophysiological abnormalities observed in animal models of chronic oxidative stress such as EC-SOD((-/-)) mice.

Epoxyeicosatrienoic acids and heme oxygenase-1 interaction attenuates diabetes and metabolic syndrome complications

MSCs are considered to be the natural precursors to adipocyte development through the process of adipogenesis. A link has been established between decreased protective effects of EETs or HO-1 and their interaction in metabolic syndrome. Decreases in HO-1 or EET were associated with an increase in adipocyte stem cell differentiation and increased levels of inflammatory cytokines. EET agonist (AKR-I-27-28) inhibited MSC-derived adipocytes and decreased the levels of inflammatory cytokines. We further describe the role of CYP-epoxygenase expression, HO expression, and circulating cytokine levels in an obese mouse, ob/ob(-/-) mouse model. Ex vivo measurements of EET expression within MSCs derived from ob/ob(-/-) showed decreased levels of EETs that were increased by HO induction. This review demonstrates that suppression of HO and EET systems exist in MSCs prior to the development of adipocyte dysfunction. Further, adipocyte dysfunction can be ameliorated by induction of HO-1 and CYP-epoxygenase, i.e. EET.