Epoxyeicosatrienoic acid agonist rescues the metabolic syndrome phenotype of HO-2-null mice

Heme Oxygenase-1, Cardiac Senescence, and Myocardial Infarction: A Critical Review of the Triptych

PURPOSE

Heme oxygenase-1 (HO-1) is a crucial enzyme in heme metabolism, facilitating the breakdown of heme into biliverdin, carbon monoxide, and free iron. Renowned for its potent cytoprotective properties, HO-1 showcases notable antioxidant, anti-inflammatory, and anti-apoptotic effects. In this review, the authors aim to explore the profound impact of HO-1 on cardiac senescence and its potential implications in myocardial infarction (MI).

RESULTS

Recent research has unveiled the intricate role of HO-1 in cellular senescence, characterized by irreversible growth arrest and functional decline. Notably, cardiac senescence has emerged as a pivotal factor in the development of various cardiovascular conditions, including MI. Notably, cardiac senescence has emerged as an important factor in the development of various cardiovascular conditions, including myocardial infarction (MI). The accumulation of senescent cells, spanning vascular endothelial cells, vascular smooth muscle cells, cardiomyocytes, and progenitor cells, poses a significant risk for cardiovascular diseases such as vascular aging, atherosclerosis, myocardial infarction, and ventricular remodeling. Inhibition of cardiomyocyte senescence not only reduces senescence-associated inflammation but also impacts other myocardial lineages, hinting at a broader mechanism of propagation in pathological remodeling. HO-1 has been shown to improve heart function and mitigate cardiomyocyte senescence induced by ischemic injury and aging. Furthermore, HO-1 induction has been found to alleviate H2O2-induced cardiomyocyte senescence. As we grow in our understanding of antiproliferative, antiangiogenic, anti-aging, and vascular effects of HO-1, we see the potential to exploit potential links between individual susceptibility to cardiac senescence and myocardial infarction.

CONCLUSIONS

This review investigates strategies for upregulating HO-1, including gene targeting and pharmacological agents, as potential therapeutic approaches. By synthesizing compelling evidence from diverse experimental models and clinical investigations, this study elucidates the therapeutic potential of targeting HO-1 as an innovative strategy to mitigate cardiac senescence and improve outcomes in myocardial infarction, emphasizing the need for further research in this field.

Heme metabolism in nonerythroid cells

Heme is an iron-containing prosthetic group necessary for the function of several proteins termed "hemoproteins." Erythrocytes contain most of the body's heme in the form of hemoglobin and contain high concentrations of free heme. In nonerythroid cells, where cytosolic heme concentrations are 2 to 3 orders of magnitude lower, heme plays an essential and often overlooked role in a variety of cellular processes. Indeed, hemoproteins are found in almost every subcellular compartment and are integral in cellular operations such as oxidative phosphorylation, amino acid metabolism, xenobiotic metabolism, and transcriptional regulation. Growing evidence reveals the participation of heme in dynamic processes such as circadian rhythms, NO signaling, and the modulation of enzyme activity. This dynamic view of heme biology uncovers exciting possibilities as to how hemoproteins may participate in a range of physiologic systems. Here, we discuss how heme is regulated at the level of its synthesis, availability, redox state, transport, and degradation and highlight the implications for cellular function and whole organism physiology.

Heme oxygenase 2 genetic variants alter hormonal and metabolic traits in polycystic ovary syndrome

Oxidative stress and metabolic disorders are involved in the pathogenesis of polycystic ovary syndrome (PCOS). Heme oxygenase 2 (HMOX2) plays a critical role in preserving heme metabolism as well as in modulating glycolipid metabolism, oxidative stress, and inflammation. This study examined the correlation between HMOX2 G554A (rs1051308) and A-42G (rs2270363) genetic variants with the risk of PCOS and assessed the effects of these genotypes on clinical, hormonal, metabolic, and oxidative stress indices using a case-control design that included 1014 patients with PCOS and 806 control participants. We found that the allelic and genotypic frequencies of the HMOX2 G554A and A-42G polymorphisms were comparable between the PCOS and control groups in Chinese women (P > 0.05). Nevertheless, it was discovered that patients with the AA or AG genotype of A-42G polymorphism had notably elevated levels of estradiol (E2), follicle-stimulating hormone (FSH), luteinizing hormone (LH), LH/FSH ratio, high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apolipoprotein (apo)B, and/or apoB/apoA1 ratio than those with the GG genotypes (P < 0.05). Patients with the GG or AG genotype of G554A polymorphism had elevated serum levels of LH, FSH, E2, LH/FSH ratio, TC, HDL-C, LDL-C, apoB, and/or apoB/apoA1 ratio and lower 2-h glucose concentration compared with those with the AA genotype (P < 0.05). Our findings indicate a potential association between the genetic variants and endocrine abnormalities in the reproductive system and metabolic irregularities in glycolipid levels in patients, thus suggesting their potential role in the pathogenesis of PCOS.

Is Environmental Cadmium Exposure Causally Related to Diabetes and Obesity?

Cadmium (Cd) is a pervasive toxic metal, present in most food types, cigarette smoke, and air. Most cells in the body will assimilate Cd, as its charge and ionic radius are similar to the essential metals, iron, zinc, and calcium (Fe, Zn, and Ca). Cd preferentially accumulates in the proximal tubular epithelium of the kidney, and is excreted in urine when these cells die. Thus, excretion of Cd reflects renal accumulation (body burden) and the current toxicity of Cd. The kidney is the only organ other than liver that produces and releases glucose into the circulation. Also, the kidney is responsible for filtration and the re-absorption of glucose. Cd is the least recognized diabetogenic substance although research performed in the 1980s demonstrated the diabetogenic effects of chronic oral Cd administration in neonatal rats. Approximately 10% of the global population are now living with diabetes and over 80% of these are overweight or obese. This association has fueled an intense search for any exogenous chemicals and lifestyle factors that could induce excessive weight gain. However, whilst epidemiological studies have clearly linked diabetes to Cd exposure, this appears to be independent of adiposity. This review highlights Cd exposure sources and levels associated with diabetes type 2 and the mechanisms by which Cd disrupts glucose metabolism. Special emphasis is on roles of the liver and kidney, and cellular stress responses and defenses, involving heme oxygenase-1 and -2 (HO-1 and HO-2). From heme degradation, both HO-1 and HO-2 release Fe, carbon monoxide, and a precursor substrate for producing a potent antioxidant, bilirubin. HO-2 appears to have also anti-diabetic and anti-obese actions. In old age, HO-2 deficient mice display a symptomatic spectrum of human diabetes, including hyperglycemia, insulin resistance, increased fat deposition, and hypertension.

Mitigation of Cadmium Toxicity through Modulation of the Frontline Cellular Stress Response

Cadmium (Cd) is an environmental toxicant of public health significance worldwide. Diet is the main Cd exposure source in the non-occupationally exposed and non-smoking populations. Metal transporters for iron (Fe), zinc (Zn), calcium (Ca), and manganese (Mn) are involved in the assimilation and distribution of Cd to cells throughout the body. Due to an extremely slow elimination rate, most Cd is retained by cells, where it exerts toxicity through its interaction with sulfur-containing ligands, notably the thiol (-SH) functional group of cysteine, glutathione, and many Zn-dependent enzymes and transcription factors. The simultaneous induction of heme oxygenase-1 and the metal-binding protein metallothionein by Cd adversely affected the cellular redox state and caused the dysregulation of Fe, Zn, and copper. Experimental data indicate that Cd causes mitochondrial dysfunction via disrupting the metal homeostasis of this organelle. The present review focuses on the adverse metabolic outcomes of chronic exposure to low-dose Cd. Current epidemiologic data indicate that chronic exposure to Cd raises the risk of type 2 diabetes by several mechanisms, such as increased oxidative stress, inflammation, adipose tissue dysfunction, increased insulin resistance, and dysregulated cellular intermediary metabolism. The cellular stress response mechanisms involving the catabolism of heme, mediated by heme oxygenase-1 and -2 (HO-1 and HO-2), may mitigate the cytotoxicity of Cd. The products of their physiologic heme degradation, bilirubin and carbon monoxide, have antioxidative, anti-inflammatory, and anti-apoptotic properties.

CYP450 Epoxygenase Metabolites, Epoxyeicosatrienoic Acids, as Novel Anti-Inflammatory Mediators

Inflammation plays a crucial role in the initiation and development of a wide range of systemic illnesses. Epoxyeicosatrienoic acids (EETs) are derived from arachidonic acid (AA) metabolized by CYP450 epoxygenase (CYP450) and are subsequently hydrolyzed by soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs), which are merely biologically active. EETs possess a wide range of established protective effects on many systems of which anti-inflammatory actions have gained great interest. EETs attenuate vascular inflammation and remodeling by inhibiting activation of endothelial cells and reducing cross-talk between inflammatory cells and blood vessels. EETs also process direct and indirect anti-inflammatory properties in the myocardium and therefore alleviate inflammatory cardiomyopathy and cardiac remodeling. Moreover, emerging studies show the substantial roles of EETs in relieving inflammation under other pathophysiological environments, such as diabetes, sepsis, lung injuries, neurodegenerative disease, hepatic diseases, kidney injury, and arthritis. Furthermore, pharmacological manipulations of the AA-CYP450-EETs-sEH pathway have demonstrated a contribution to the alleviation of numerous inflammatory diseases, which highlight a therapeutic potential of drugs targeting this pathway. This review summarizes the progress of AA-CYP450-EETs-sEH pathway in regulation of inflammation under different pathological conditions and discusses the existing challenges and future direction of this research field.

Heme Oxygenase Modulation Drives Ferroptosis in TNBC Cells

The term ferroptosis refers to a peculiar type of programmed cell death (PCD) mainly characterized by extensive iron-dependent lipid peroxidation. Recently, ferroptosis has been suggested as a potential new strategy for the treatment of several cancers, including breast cancer (BC). In particular, among the BC subtypes, triple negative breast cancer (TNBC) is considered the most aggressive, and conventional drugs fail to provide long-term efficacy. In this context, our study's purpose was to investigate the mechanism of ferroptosis in breast cancer cell lines and reveal the significance of heme oxygenase (HO) modulation in the process, providing new biochemical approaches. HO's effect on BC was evaluated by MTT tests, gene silencing, Western blot analysis, and measurement of reactive oxygen species (ROS), glutathione (GSH) and lipid hydroperoxide (LOOH) levels. In order to assess HO's implication, different approaches were exploited, using two distinct HO-1 inducers (hemin and curcumin), a well-known HO inhibitor (SnMP) and a selective HO-2 inhibitor. The data obtained showed HO's contribution to the onset of ferroptosis; in particular, HO-1 induction seemed to accelerate the process. Moreover, our results suggest a potential role of HO-2 in erastin-induced ferroptosis. In view of the above, HO modulation in ferroptosis can offer a novel approach for breast cancer treatment.

Carbon monoxide and β-cell function: Implications for type 2 diabetes mellitus

Carbon monoxide (CO), a member of the multifunctional gasotransmitters family produced by heme oxygenases (i.e., HO-1 and HO-2), has received significant attention because of its involvement in carbohydrate metabolism. Experimental evidence indicates that both HO-2- and HO-1-derived CO stimulate insulin secretion, but the latter mainly acts as a compensatory response in pre-diabetes conditions. CO protects pancreatic β-cell against cytokine- and hypoxia-induced apoptosis and promotes β-cell regeneration. CO cross-talks with nitric oxide (NO) and hydrogen sulfide (H₂S), other important gasotransmitters in carbohydrate metabolism, in regulating β-cell function and insulin secretion. These data speak in favor of the potential therapeutic application of CO in type 2 diabetes mellitus (T2DM) and preventing the progression of pre-diabetes to diabetes. Either CO (as both gaseous form and CO-releasing molecule) or pharmacological formulations made of natural HO inducers (i.e., bioactive components originating from plant-based foods) are potential candidates for developing CO-based therapeutics in T2DM. Future studies are needed to assess the safety/efficacy and potential therapeutic applications of CO in T2DM.

Orally active epoxyeicosatrienoic acid analogs in hypertension and renal injury

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites synthesized by cytochrome P450 epoxygenases. Biological activities for EETs include vasodilation, decreasing inflammation, opposing apoptosis, and inhibiting renal sodium reabsorption. These actions are beneficial in lowering blood pressure and slowing kidney disease progression. Furthermore, evidence in human and experimental animal studies have found that decreased EET levels contribute to hypertension and kidney diseases. Consequently, EET mimics/analogs have been developed as a potential therapeutic for hypertension and acute and chronic kidney diseases. Their development has resulted in EET analogs that are orally active with favorable pharmacological profiles. Analogs for 8,9-EET, 11,12-EET, and 14,15-EET have been tested in several hypertension and kidney disease animal models. More recently, kidney targeted EET analogs have been synthesized and tested against drug-induced nephrotoxicity. Experimental evidence has demonstrated compelling therapeutic potential for EET analogs to oppose cardiovascular and kidney diseases. These EET analogs lower blood pressure, decrease kidney inflammation, improve vascular endothelial function, and decrease kidney fibrosis and apoptosis. Overall, these preclinical studies support the likelihood that EET analogs will advance to clinical trials for hypertension and associated comorbidities or acute and chronic kidney diseases.

EET Analog Treatment Improves Insulin Signaling in a Genetic Mouse Model of Insulin Resistance

We previously showed that global deletion of the cytochrome P450 epoxygenase Cyp2c44, a major epoxyeicosatrienoic acid (EET) producing enzyme in mice, leads to impaired hepatic insulin signaling resulting in insulin resistance. This finding led us to investigate whether administration of a water soluble EET analog restores insulin signaling in vivo in Cyp2c44(-/-) mice and investigated the underlying mechanisms by which this effect is exerted. Cyp2c44(-/-) mice treated with the analog EET-A for 4 weeks improved fasting glucose and glucose tolerance compared to Cyp2c44(-/-) mice treated with vehicle alone. This beneficial effect was accompanied by enhanced hepatic insulin signaling, decreased expression of gluconeogenic genes and increased expression of glycogenic genes. Mechanistically, we show that insulin-stimulated phosphorylation of insulin receptor β (IRβ) is impaired in primary Cyp2c44(-/-) hepatocytes and this can be restored by cotreatment with EET-A and insulin. Plasma membrane fractionations of livers indicated that EET-A enhances the retention of IRβ in membrane rich fractions, thus potentiating its activation. Altogether, EET analogs ameliorate insulin signaling in a genetic model of hepatic insulin resistance by stabilizing membrane-associated IRβ and potentiating insulin signaling.

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.

GSK2256294 Decreases sEH (Soluble Epoxide Hydrolase) Activity in Plasma, Muscle, and Adipose and Reduces F2-Isoprostanes but Does Not Alter Insulin Sensitivity in Humans

[Figure: see text].

Treatment of Primary Aldosteronism Increases Plasma Epoxyeicosatrienoic Acids

[Figure: see text].

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Kidney-Targeted Epoxyeicosatrienoic Acid Analog, EET-F01, Reduces Inflammation, Oxidative Stress, and Cisplatin-Induced Nephrotoxicity

Although epoxyeicosatrienoic acid (EET) analogs have performed well in several acute and chronic kidney disease models, targeted delivery of EET analogs to the kidney can be reasonably expected to reduce the level of drug needed to achieve a therapeutic effect and obviate possible side effects. For EET analog kidney-targeted delivery, we conjugated a stable EET analog to folic acid via a PEG-diamine linker. Next, we compared the kidney targeted EET analog, EET-F01, to a well-studied EET analog, EET-A. EET-A or EET-F01 was infused i.v. and plasma and kidney tissue collected. EET-A was detected in the plasma but was undetectable in the kidney. On the other hand, EET-F01 was detected in the plasma and kidney. Experiments were conducted to compare the efficacy of EET-F01 and EET-A for decreasing cisplatin nephrotoxicity. Cisplatin was administered to WKY rats treated with vehicle, EET-A (10 mg/kg i.p.) or EET-F01 (20 mg/kg or 2 mg/kg i.p.). Cisplatin increased kidney injury markers, viz., blood urea nitrogen (BUN), N-acetyl-β-(D)-glucosaminidase (NAG), kidney injury molecule-1 (KIM-1), and thiobarbituric acid reactive substances (TBARS). EET-F01 was as effective as EET-A in decreasing BUN, NAG, KIM-1, TBARS, and renal histological injury caused by cisplatin. Despite its almost 2×-greater molecular weight compared with EET-A, EET-F01 was comparably effective in decreasing renal injury at a 10-fold w/w lower dose. EET-F01 decreased cisplatin nephrotoxicity by reducing oxidative stress and inflammation. These data demonstrate that EET-F01 targets the kidney, allows for a lower effective dose, and combats cisplatin nephrotoxicity. In conclusion, we have developed a kidney targeted EET analog, EET-F01, that demonstrates excellent potential as a therapeutic for kidney diseases.

Discovery of Soluble Epoxide Hydrolase Inhibitors from Chemical Synthesis and Natural Products

Soluble epoxide hydrolase (sEH) is an α/β hydrolase fold protein and widely distributed in numerous organs including the liver, kidney, and brain. The inhibition of sEH can effectively maintain endogenous epoxyeicosatrienoic acids (EETs) levels and reduce dihydroxyeicosatrienoic acids (DHETs) levels, resulting in therapeutic potentials for cardiovascular, central nervous system, and metabolic diseases. Therefore, since the beginning of this century, the development of sEH inhibitors is a hot research topic. A variety of potent sEH inhibitors have been developed by chemical synthesis or isolated from natural sources. In this review, we mainly summarized the interconnected aspects of sEH with cardiovascular, central nervous system, and metabolic diseases and then focus on representative inhibitors, which would provide some useful guidance for the future development of potential sEH inhibitors.

Changes and sex- and age-related differences in the expression of drug metabolizing enzymes in a KRAS-mutant mouse model of lung cancer

Background

This study aimed to systematically profile the alterations and sex- and age-related differences in the drug metabolizing enzymes (DMEs) in a KRAS-mutant mouse model of lung cancer (KRAS mice).

Methodology

In this study, the LC-MS/MS approach and a probe substrate method were used to detect the alterations in 21 isoforms of DMEs, as well as the enzymatic activities of five isoforms, respectively. Western blotting was applied to study the protein expression of four related receptors.

Results

The proteins contents of CYP2C29 and CYP3A11, were significantly downregulated in the livers of male KRAS mice at 26 weeks (3.7- and 4.4-fold, respectively, p < 0.05). SULT1A1 and SULT1D1 were upregulated by 1.8- to 7.0- fold at 20 (p = 0.015 and 0.017, respectively) and 26 weeks (p = 0.055 and 0.031, respectively). There were positive correlations between protein expression and enzyme activity for CYP2E1, UGT1A9, SULT1A1 and SULT1D1 (r² ≥ 0.5, p < 0.001). Western blotting analysis revealed the downregulation of AHR, FXR and PPARα protein expression in male KRAS mice at 26 weeks. For sex-related differences, CYP2E1 was male-predominant and UGT1A2 was female-predominant in the kidney. UGT1A1 and UGT1A5 expression was female-predominant, whereas UGT2B1 exhibited male-predominant expression in liver tissue. For the tissue distribution of DMEs, 21 subtypes of DMEs were all expressed in liver tissue. In the intestine, the expression levels of CYP2C29, CYP27A1, UGT1A2, 1A5, 1A6a, 1A9, 2B1, 2B5 and 2B36 were under the limitation of quantification. The subtypes of CYP7A1, 1B1, 2E1 and UGT1A1, 2A3, 2B34 were detected in kidney tissue.

Conclusions

This study, for the first time, unveils the variations and sex- and age-related differences in DMEs in C57 BL/6 (WT) mice and KRAS mice.

Heme Oxygenase 1 and 2 Differentially Regulate Glucose Metabolism and Adipose Tissue Mitochondrial Respiration: Implications for Metabolic Dysregulation

Heme oxygenase (HO) consists of inducible (HO-1) and constitutive (HO-2) isoforms that are encoded by Hmox1 and Hmox2 genes, respectively. As an anti-inflammatory and antioxidant molecule, HO participates in the development of metabolic diseases. Whether Hmox deficiency causes metabolic abnormalities under basal conditions remains unclear. We hypothesized that HO-1 and HO-2 differentially affect global and adipose tissue metabolism. To test this hypothesis, we determined insulin sensitivity, glucose tolerance, energy expenditure, and respiratory exchange ratio in global Hmox1^-/- and Hmox2^-/- mice. Body weight was reduced in female but not male Hmox1^-/- and Hmox2^-/- mice. Reduced insulin sensitivity and physical activity were observed in Hmox1^-/- but not Hmox2^-/- mice. Deletion of either Hmox1 or Hmox2 had no effects on glucose tolerance, energy expenditure or respiratory exchange ratio. Mitochondrial respiration was unchanged in gonadal fat pads (white adipose tissue, WAT) of Hmox1^-/- mice. Hmox2 deletion increased proton leak and glycolysis in gonadal, but not interscapular fat tissues (brown adipose tissue, BAT). Uncoupling protein and Hmox1 genes were unchanged in gonadal fat pads of Hmox2^-/- mice. Conclusively, HO-1 maintains insulin sensitivity, while HO-2 represses glycolysis and proton leak in the WAT under basal condition. This suggests that HO-1 and HO-2 differentially modulate metabolism, which may impact the metabolic syndrome.

The Peroxisome Proliferator-Activated Receptor-Gamma Coactivator-1α-Heme Oxygenase 1 Axis, a Powerful Antioxidative Pathway with Potential to Attenuate Diabetic Cardiomyopathy

Significance: From studies of diabetic animal models, the downregulation of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α)-heme oxygenase 1 (HO-1) axis appears to be a crucial event in the development of obesity and diabetic cardiomyopathy (DCM). In this review, we discuss the role of metabolic and biochemical stressors in the rodent and human pathophysiology of DCM. A crucial contributor for many cardiac pathologies is excessive production of reactive oxygen species (ROS) pathologies, which lead to extensive cellular damage by impairing mitochondrial function and directly oxidizing DNA, proteins, and lipid membranes. We discuss the role of ROS production and inflammatory pathways with multiple contributing and confounding factors leading to DCM. Recent Advances: The relevant biochemical pathways that are critical to a therapeutic approach to treat DCM, specifically caloric restriction and its relation to the PGC-1α-HO-1 axis in the attenuation of DCM, are elucidated. Critical Issues: The increased prevalence of diabetes mellitus type 2, a major contributor to unique cardiomyopathy characterized by cardiomyocyte hypertrophy with no effective clinical treatment. This review highlights the role of mitochondrial dysfunction in the development of DCM and potential oxidative targets to attenuate oxidative stress and attenuate DCM. Future Directions: Targeting the PGC-1α-HO-1 axis is a promising approach to ameliorate DCM through improvement in mitochondrial function and antioxidant defenses. A pharmacological inducer to activate PGC-1α and HO-1 described in this review may be a promising therapeutic approach in the clinical setting.

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.

Crossing signals: bioactive lipids in the microvasculature

The primary function of the arterial microvasculature is to ensure that regional perfusion of blood flow is matched to the needs of the tissue bed. This critical physiological mechanism is tightly controlled and regulated by a variety of vasoactive compounds that are generated and released from the vascular endothelium. Although these substances are required for modulating vascular tone, they also influence the surrounding tissue and have an overall effect on vascular, as well as parenchymal, homeostasis. Bioactive lipids, fatty acid derivatives that exert their effects through signaling pathways, are included in the list of vasoactive compounds that modulate the microvasculature. Although lipids were identified as important vascular messengers over three decades ago, their specific role within the microvascular system is not well defined. Thorough understanding of these pathways and their regulation is not only essential to gain insight into their role in cardiovascular disease but is also important for preventing vascular dysfunction following cancer treatment, a rapidly growing problem in medical oncology. The purpose of this review is to discuss how biologically active lipids, specifically prostanoids, epoxyeicosatrienoic acids, sphingolipids, and lysophospholipids, contribute to vascular function and signaling within the endothelium. Methods for quantifying lipids will be briefly discussed, followed by an overview of the various lipid families. The cross talk in signaling between classes of lipids will be discussed in the context of vascular disease. Finally, the potential clinical implications of these lipid families will be highlighted.

Soluble epoxide hydrolase inhibitor protects against blood-brain barrier dysfunction in a mouse model of type 2 diabetes via the AMPK/HO-1 pathway

Diabetes mellitus is a metabolic disorder that can lead to blood-brain barrier (BBB) disruption and cognitive decline. However, the mechanisms of BBB breakdown in diabetes are still unclear. Soluble epoxide hydrolase (sEH) is an enzyme that degrades epoxyeicosatrienoic acids (EETs), which have multiple protective effects on vascular structure and functions. In the current study, we showed increased vascular permeability of the BBB, which was accompanied by upregulation of sEH and downregulation of 14,15-EET. Moreover, the sEH inhibitor t-AUCB restored diabetic BBB integrity in vivo, and 14,15-EET prevented ROS accumulation and MEC injury in vitro. t-AUCB or 14,15-EET treatment provoked AMPK/HO-1 activation under diabetic conditions in vivo and in vitro. Thus, we suggest that decreased EET degradation by sEH inhibition might be a potential therapeutic approach to attenuate the progression of BBB injury in diabetic mice via AMPK/HO-1 pathway activation.

A synthetic epoxyeicosatrienoic acid analogue prevents the initiation of ischemic acute kidney injury

AIM

Imbalances in cytochrome P450 (CYP)-dependent eicosanoid formation may play a central role in ischemic acute kidney injury (AKI). We reported previously that inhibition of 20-hydroxyeicosatetraenoic acid (20-HETE) action ameliorated ischemia/reperfusion (I/R)-induced AKI in rats. Now we tested the hypothesis that enhancement of epoxyeicosatrienoic acid (EET) actions may counteract the detrimental effects of 20-HETE and prevent the initiation of AKI.

METHODS

Male Lewis rats underwent right nephrectomy and ischemia was induced by 45 min clamping of the left renal pedicle followed by up to 48 h of reperfusion. Circulating CYP-eicosanoid profiles were compared in patients who underwent cardiac surgery with (n = 21) and without (n = 38) developing postoperative AKI.

RESULTS

Ischemia induced an about eightfold increase of renal 20-HETE levels, whereas free EETs were not accumulated. To compensate for this imbalance, a synthetic 14,15-EET analogue was administered by intrarenal infusion before ischemia. The EET analogue improved renal reoxygenation as monitored by in vivo parametric MRI during the initial 2 h reperfusion phase. The EET analogue improved PI3K- as well as mTORC2-dependent rephosphorylation of Akt, induced inactivation of GSK-3β, reduced the development of tubular apoptosis and attenuated inflammatory cell infiltration. The EET analogue also significantly alleviated the I/R-induced drop in creatinine clearance. Patients developing postoperative AKI featured increased preoperative 20-HETE and 8,9-EET levels.

CONCLUSIONS

Pharmacological interventions targeting the CYP-eicosanoid pathway could offer promising new options for AKI prevention. Individual differences in CYP-eicosanoid formation may contribute to the risk of developing AKI in clinical settings.

Loss of hepatic PPARα promotes inflammation and serum hyperlipidemia in diet-induced obesity

Agonists for PPARα are used clinically to reduce triglycerides and improve high-density lipoprotein (HDL) cholesterol levels in patients with hyperlipidemia. Whether the mechanism of PPARα activation to lower serum lipids occurs in the liver or other tissues is unknown. To determine the function of hepatic PPARα on lipid profiles in diet-induced obese mice, we placed hepatocyte-specific peroxisome proliferator-activated receptor-α (PPARα) knockout (Ppara^HepKO) and wild-type (Ppara^fl/fl) mice on high-fat diet (HFD) or normal fat diet (NFD) for 12 wk. There was no significant difference in weight gain, percent body fat mass, or percent body lean mass between the groups of mice in response to HFD or NFD. Interestingly, the Ppara^HepKO mice on HFD had worsened hepatic inflammation and a significant shift in the proinflammatory M1 macrophage population. These changes were associated with higher hepatic fat mass and decreased hepatic lean mass in the Pparα^HepKO on HFD but not in NFD as measured by Oil Red O and noninvasive EchoMRI analysis (31.1 ± 2.8 vs. 20.2 ± 1.5, 66.6 ± 2.5 vs. 76.4 ± 1.5%, P < 0.05). We did find that this was related to significantly reduced peroxisomal gene function and lower plasma β-hydroxybutyrate in the Ppara^HepKO on HFD, indicative of reduced metabolism of fats in the liver. Together, these provoked higher plasma triglyceride and apolipoprotein B100 levels in the Ppara^HepKO mice compared with Ppara^fl/fl on HFD. These data indicate that hepatic PPARα functions to control inflammation and liver triglyceride accumulation that prevent hyperlipidemia.

Impact of diabetes on male sexual function in streptozotocin-induced diabetic rats: Protective role of soluble epoxide hydrolase inhibitor

Diabetes-induced male sexual dysfunction is associated with endothelial dysfunction. Inhibition of soluble epoxide hydrolase (sEH) is known to improve endothelial function in diabetes. Therefore, we hypothesized that sEH inhibitor (sEHI), [trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]cyclohexyloxy}benzoic acid] / t-TUCB can restore the male sexual function in diabetic rat. After one week of administration of diabetogenic agent STZ (52 mg/kg i.p) injection, diabetic rats were treated with t-TUCB (0.1 and 0.3 mg/kg, p.o) or vehicle for 8 weeks. The sexual behaviour parameters of the animals were evaluated at the end of dosing period. The levels of testosterone and glucose in serum, and sperm were quantified. Effect of treatment on weight of reproductive organs and histopathology of penile tissue was evaluated. Diabetes had a negative effect on male sexual function, weight of sexual organs and production of sperm with a parallel decrease in the level of testosterone. The sEHI, t-TUCB, significantly preserved the sexual function and minimized an increase in the level of blood glucose in diabetic rats. It also prevented a decrease in the level of testosterone and sperm in diabetic rats, in comparison to diabetic control rats. Further, diabetes induced distortion of corpus cavernosum was attenuated by t-TUCB. Based on our findings, sEHI may delay the development of sexual dysfunction in diabetes.

Prospective for cytochrome P450 epoxygenase cardiovascular and renal therapeutics

Therapeutics for arachidonic acid pathways began with the development of non-steroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX). The enzymatic pathways and arachidonic acid metabolites and respective receptors have been successfully targeted and therapeutics developed for pain, inflammation, pulmonary and cardiovascular diseases. These drugs target the COX and lipoxygenase pathways but not the third branch for arachidonic acid metabolism, the cytochrome P450 (CYP) pathway. Small molecule compounds targeting enzymes and CYP epoxy-fatty acid metabolites have evolved rapidly over the last two decades. These therapeutics have primarily focused on inhibiting soluble epoxide hydrolase (sEH) or agonist mimetics for epoxyeicosatrienoic acids (EET). Based on preclinical animal model studies and human studies, major therapeutic indications for these sEH inhibitors and EET mimics/analogs are renal and cardiovascular diseases. Novel small molecules that inhibit sEH have advanced to human clinical trials and demonstrate promise for cardiovascular diseases. Challenges remain for sEH inhibitor and EET analog drug development; however, there is a high likelihood that a drug that acts on this third branch of arachidonic acid metabolism will be utilized to treat a cardiovascular or kidney disease in the next decade.

Ablation of soluble epoxide hydrolase reprogram white fat to beige-like fat through an increase in mitochondrial integrity, HO-1-adiponectin in vitro and in vivo

We have shown that epoxyeicosatrienoic acids (EETs), specifically 11,12- and 14,15-EETs, reduce adipogenesis in human mesenchymal stem cells and mouse preadipocytes (3T-3L1). In this study, we explore the effects of soluble epoxide hydrolase (sEH) deletion on various aspects of adipocyte-function, including programing for white vs. beige-like fat, and mitochondrial and thermogenic gene-expressions. We further hypothesize that EETs and heme-oxygenase 1 (HO-1) form a synergistic, functional module whose effects on adipocyte and vascular function is greater than the effects of sEH deletion alone. In in vitro studies, we examined the effect of sEH inhibitors on MSC-derived adipocytes. MSC-derived adipocytes exposed to AUDA, an inhibitor of sEH, exhibit an increased number of small and healthy adipocytes, an effect reproduced by siRNA for sEH. in vivo studies indicate that sEH deletion results in a significant decrease in adipocyte size, inflammatory adipokines NOV, TNFα, while increasing adiponectin (p < 0.05). These findings are associated with a decrease in body weight (p < 0.05), and visceral fat (p < 0.05). Importantly, sEH deletion was associated with a significant increase in Mfn1, COX 1, UCP1 and adiponectin (p < 0.03). sEH deletion was manifested by a significant increase in EETs isomers 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET and an increased EETs/DHETEs ratio. Notably, activation of HO-1 gene expression further increased the levels of EETs, suggesting that the antioxidant HO-1 system protects EETs from degradation by ROS. These results are novel in that sEH deletion, while increasing EET levels, resulted in reprograming of white fat to express mitochondrial and thermogenic genes, a phenotype characteristic of beige-fat. Thus, EETs agonist(s) and sEH inhibitors may have therapeutic potential in the treatment of metabolic syndrome and obesity.

EET enhances renal function in obese mice resulting in restoration of HO-1-Mfn1/2 signaling, and decrease in hypertension through inhibition of sodium chloride co-transporter

BACKGROUND

We have previously reported that epoxyeicosatrienoic acid (EET) has multiple beneficial effects on renal and adipose tissue function, in addition to its vasodilatory action; it increases insulin sensitivity and inhibits inflammation. In an examination of the signaling mechanisms by which EET reduces renal and peri-renal fat function, we hypothesized that EET ameliorates obesity-induced renal dysfunction by improving sodium excretion, reducing the sodium-chloride cotransporter NCC, lowering blood pressure, and enhancing mitochondrial and thermogenic gene levels in PGC-1α dependent mice.

METHODS

EET-agonist treatment normalized glucose metabolism, renal ENaC and NCC protein expression, urinary sodium excretion and blood pressure in obese (db/db) mice. A marked improvement in mitochondrial integrity, thermogenic genes, and PGC-1α-HO-1-adiponectin signaling occurred. Knockout of PGC-1α in EET-treated mice resulted in a reversal of these beneficial effects including a decrease in sodium excretion, elevation of blood pressure and an increase in the pro-inflammatory adipokine nephroblastoma overexpressed gene (NOV). In the elucidation of the effects of EET on peri-renal adipose tissue, EET increased adiponectin, mitochondrial integrity, thermogenic genes and decreased NOV, i.e. "Browning' peri-renal adipose phenotype that occurs under high fat diets. Taken together, these data demonstrate a critical role of an EET agonist in the restoration of healthy adipose tissue with reduced release of inflammatory molecules, such as AngII and NOV, thereby preventing their detrimental impact on sodium absorption and NCC levels and the development of obesity-induced renal dysfunction.

Endothelium-specific CYP2J2 overexpression attenuates age-related insulin resistance

Ample evidences demonstrate that cytochrome P450 epoxygenase‐derived epoxyeicosatrienoic acids (EETs) exert diverse biological activities, which include potent vasodilatory, anti‐inflammatory, and cardiovascular protective effects. In this study, we investigated the effects of endothelium‐specific CYP2J2 overexpression on age‐related insulin resistance and metabolic dysfunction. Endothelium‐specific targeting of the human CYP epoxygenase, CYP2J2, transgenic mice (Tie2‐CYP2J2‐Tr mice) was utilized. The effects of endothelium‐specific CYP2J2 overexpression on aging‐associated obesity, inflammation, and peripheral insulin resistance were evaluated by assessing metabolic parameters in young (3 months old) and aged (16 months old) adult male Tie2‐CYP2J2‐Tr mice. Decreased insulin sensitivity and attenuated insulin signaling in aged skeletal muscle, adipose tissue, and liver were observed in aged adult male mice, and moreover, these effects were partly inhibited in 16‐month‐old CYP2J2‐Tr mice. In addition, CYP2J2 overexpression‐mediated insulin sensitization in aged mice was associated with the amelioration of inflammatory state. Notably, the aging‐associated increases in fat mass and adipocyte size were only observed in 16‐month‐old wild‐type mice, and CYP2J2 overexpression markedly prevented the increase in fat mass and adipocyte size in aged Tie2‐CYP2J2‐Tr mice, which was associated with increased energy expenditure and decreased lipogenic genes expression. Furthermore, these antiaging phenotypes of Tie2‐CYP2J2‐Tr mice were also associated with increased muscle blood flow, enhanced active‐phase locomotor activity, and improved mitochondrial dysfunction in skeletal muscle. Collectively, our findings indicated that endothelium‐specific CYP2J2 overexpression alleviated age‐related insulin resistance and metabolic dysfunction, which highlighted CYP epoxygenase‐EET system as a potential target for combating aging‐related metabolic disorders.

CYP2J2 Expression in Adult Ventricular Myocytes Protects Against Reactive Oxygen Species Toxicity

Cytochrome P450 2J2 isoform (CYP2J2) is a drug-metabolizing enzyme that is highly expressed in adult ventricular myocytes. It is responsible for the bioactivation of arachidonic acid (AA) into epoxyeicosatrienoic acids (EETs). EETs are biologically active signaling compounds that protect against disease progression, particularly in cardiovascular diseases. As a drug-metabolizing enzyme, CYP2J2 is susceptible to drug interactions that could lead to cardiotoxicity. CYP2J2 has been shown to be resistant to induction by canonical CYP inducers such as phenytoin and rifampin. It is, however, unknown how cellular stresses augment CYP2J2 expression. Here, we determine the effects of oxidative stress on gene expression in adult ventricular myocytes. Further, we assess the consequences of CYP2J2 inhibition and CYP2J2 silencing on cells when levels of reactive oxygen species (ROS) are elevated. Findings indicate that CYP2J2 expression increases in response to external ROS or when internal ROS levels are elevated. In addition, cell survival decreases with ROS exposure when CYP2J2 is chemically inhibited or when CYP2J2 expression is reduced using small interfering RNA. These effects are mitigated with external addition of EETs to the cells. Finally, we determined the results of external EETs on gene expression and show that only two of the four regioisomers cause an increase in HMOX1 expression. This work is the first to determine the consequence of cellular stress, specifically high ROS levels, on CYP2J2 expression in human ventricular myocytes and discusses how this enzyme may play an important role in response to cardiac oxidative stress.

Orally Active Epoxyeicosatrienoic Acid Analogs

Biologically active epoxyeicosatrienoic acid (EET) regioisomers are synthesized from arachidonic acid by cytochrome P450 epoxygenases of endothelial, myocardial, and renal tubular cells. EETs relax vascular smooth muscle and decrease inflammatory cell adhesion and cytokine release. Renal EETs promote sodium excretion and vasodilation to decrease hypertension. Cardiac EETs reduce infarct size after ischemia-reperfusion injury and decrease fibrosis and inflammation in heart failure. In diabetes, EETs improve insulin sensitivity, increase glucose tolerance, and reduce the renal injury. These actions of EETs emphasize their therapeutic potential. To minimize metabolic inactivation, 14,15-EET agonist analogs with stable epoxide bioisosteres and carboxyl surrogates were developed. In preclinical rat models, a subset of agonist analogs, termed EET-A, EET-B, and EET-C22, are orally active with good pharmacokinetic properties. These orally active EET agonists lower blood pressure and reduce cardiac and renal injury in spontaneous and angiotensin hypertension. Other beneficial cardiovascular actions include improved endothelial function and cardiac antiremodeling actions. In rats, EET analogs effectively combat acute and chronic kidney disease including drug- and radiation-induced kidney damage, hypertension and cardiorenal syndrome kidney damage, and metabolic syndrome and diabetes nephropathy. The compelling preclinical efficacy supports the prospect of advancing EET analogs to human clinical trials for kidney and cardiovascular diseases.

EET intervention on Wnt1, NOV, and HO-1 signaling prevents obesity-induced cardiomyopathy in obese mice

We have previously reported that epoxyeicosatrienoic acid (EET) has multiple beneficial effects on vascular function; in addition to its antiapoptotic action, it increases insulin sensitivity and inhibits inflammation. To uncover the signaling mechanisms by which EET reduces cardiomyopathy, we hypothesized that EET infusion might ameliorate obesity-induced cardiomyopathy by improving heme oxygenase (HO)-1, Wnt1, thermogenic gene levels, and mitochondrial integrity in cardiac tissues and improved pericardial fat phenotype. EET reduced levels of fasting blood glucose and proinflammatory adipokines, including nephroblastoma overexpressed (NOV) signaling, while increasing echocardiographic fractional shortening and O₂ consumption. Of interest, we also noted a marked improvement in mitochondrial integrity, thermogenic genes, and Wnt 1 and HO-1 signaling mechanisms. Knockout of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in EET-treated mice resulted in a reversal of these beneficial effects including a decrease in myocardial Wnt1 and HO-1 expression and an increase in NOV. To further elucidate the effects of EET on pericardial adipose tissues, we observed EET treatment increases in adiponectin, PGC-1α, phospho-AMP-activated protein kinase, insulin receptor phosphorylation, and thermogenic genes, resulting in a "browning" pericardial adipose phenotype under high-fat diets. Collectively, these experiments demonstrate that an EET agonist increased Wnt1 and HO-1 signaling while decreasing NOV pathways and the progression of cardiomyopathy. Furthermore, this report presents a portal into potential therapeutic approaches for the treatment of heart failure and metabolic syndrome.NEW & NOTEWORTHY The mechanism by which EET acts on obesity-induced cardiomyopathy is unknown. Here, we describe a previously unrecognized function of EET infusion that inhibits nephroblastoma overexpressed (NOV) levels and activates Wnt1, hence identifying NOV inhibition and enhanced Wnt1 expression as novel pharmacological targets for the prevention and treatment of cardiomyopathy and heart failure.Listen to this article's corresponding podcast at http://ajpheart.physiology.org/content/early/2017/05/31/ajpheart.00093.2017.

Cytochrome P450 epoxygenase-derived epoxyeicosatrienoic acids contribute to insulin sensitivity in mice and in humans

AIMS/HYPOTHESIS

Insulin resistance is frequently associated with hypertension and type 2 diabetes. The cytochrome P450 (CYP) arachidonic acid epoxygenases (CYP2C, CYP2J) and their epoxyeicosatrienoic acid (EET) products lower blood pressure and may also improve glucose homeostasis. However, the direct contribution of endogenous EET production on insulin sensitivity has not been previously investigated. In this study, we tested the hypothesis that endogenous CYP2C-derived EETs alter insulin sensitivity by analysing mice lacking CYP2C44, a major EET producing enzyme, and by testing the association of plasma EETs with insulin sensitivity in humans.

METHODS

We assessed insulin sensitivity in wild-type (WT) and Cyp2c44 -/- mice using hyperinsulinaemic-euglycaemic clamps and isolated skeletal muscle. Insulin secretory function was assessed using hyperglycaemic clamps and isolated islets. Vascular function was tested in isolated perfused mesenteric vessels. Insulin sensitivity and secretion were assessed in humans using frequently sampled intravenous glucose tolerance tests and plasma EETs were measured by mass spectrometry.

RESULTS

Cyp2c44 -/- mice showed decreased glucose tolerance (639 ± 39.5 vs 808 ± 37.7 mmol/l × min for glucose tolerance tests, p = 0.004) and insulin sensitivity compared with WT controls (hyperinsulinaemic clamp glucose infusion rate average during terminal 30 min 0.22 ± 0.02 vs 0.33 ± 0.01 mmol kg-1 min-1 in WT and Cyp2c44 -/- mice respectively, p = 0.003). Although glucose uptake was diminished in Cyp2c44 -/- mice in vivo (gastrocnemius Rg 16.4 ± 2.0 vs 6.2 ± 1.7 μmol 100 g-1 min-1, p < 0.01) insulin-stimulated glucose uptake was unchanged ex vivo in isolated skeletal muscle. Capillary density was similar but vascular KATP-induced relaxation was impaired in isolated Cyp2c44 -/- vessels (maximal response 39.3 ± 6.5% of control, p < 0.001), suggesting that impaired vascular reactivity produces impaired insulin sensitivity in vivo. Similarly, plasma EETs positively correlated with insulin sensitivity in human participants.

CONCLUSIONS/INTERPRETATION

CYP2C-derived EETs contribute to insulin sensitivity in mice and in humans. Interventions to increase circulating EETs in humans could provide a novel approach to improve insulin sensitivity and treat hypertension.

Hepatocyte MyD88 affects bile acids, gut microbiota and metabolome contributing to regulate glucose and lipid metabolism

OBJECTIVE

To examine the role of hepatocyte myeloid differentiation primary-response gene 88 (MyD88) on glucose and lipid metabolism.

DESIGN

To study the impact of the innate immune system at the level of the hepatocyte and metabolism, we generated mice harbouring hepatocyte-specific deletion of MyD88. We investigated the impact of the deletion on metabolism by feeding mice with a normal control diet or a high-fat diet for 8 weeks. We evaluated body weight, fat mass gain (using time-domain nuclear magnetic resonance), glucose metabolism and energy homeostasis (using metabolic chambers). We performed microarrays and quantitative PCRs in the liver. In addition, we investigated the gut microbiota composition, bile acid profile and both liver and plasma metabolome. We analysed the expression pattern of genes in the liver of obese humans developing non-alcoholic steatohepatitis (NASH).

RESULTS

Hepatocyte-specific deletion of MyD88 predisposes to glucose intolerance, inflammation and hepatic insulin resistance independently of body weight and adiposity. These phenotypic differences were partially attributed to differences in gene expression, transcriptional factor activity (ie, peroxisome proliferator activator receptor-α, farnesoid X receptor (FXR), liver X receptors and STAT3) and bile acid profiles involved in glucose, lipid metabolism and inflammation. In addition to these alterations, the genetic deletion of MyD88 in hepatocytes changes the gut microbiota composition and their metabolomes, resembling those observed during diet-induced obesity. Finally, obese humans with NASH displayed a decreased expression of different cytochromes P450 involved in bioactive lipid synthesis.

CONCLUSIONS

Our study identifies a new link between innate immunity and hepatic synthesis of bile acids and bioactive lipids. This dialogue appears to be involved in the susceptibility to alterations associated with obesity such as type 2 diabetes and NASH, both in mice and humans.

The time-dependent effects of St John's wort on cytochrome P450, uridine diphosphate-glucuronosyltransferase, glutathione S-transferase, and NAD(P)H-quinone oxidoreductase in mice

Hypericum perforatum [St. John’s wort (SJW)] is known to cause a drug interaction with the substrates of cytochrome P450 (P450, CYP) isoforms, mainly CYP3A. This study aims to determine the dose response and time course of the effects of SJW extract on P450s, UDP-glucuronosyltransferase (UGT), glutathione S-transferase (GST), and NAD(P)H-quinone oxidoreductase (NQO) in mice. The oral administration of SJW extract to male mice at 0.6 g/kg/d for 21 days increased hepatic oxidation activity toward a Cyp3a substrate nifedipine. By extending the SJW treatment to 28 days, hepatic nifedipine oxidation (NFO) and warfarin 7-hydroxylation (WOH) (Cyp2c) activities were increased by 95% and 34%, respectively. Immunoblot analysis of liver microsomal proteins revealed that the Cyp2c protein level was elevated by the 28-day treatment. However, the liver microsomal activities of the oxidation of the respective substrates of Cyp1a, Cyp2a, Cyp2b, Cyp2d, and Cyp2e1 remained unchanged. In the kidney, SJW increased the NFO, but not the WOH activity. The extended 28-day treatment did not alter mouse hepatic and renal UGT, GST, and NQO activities. These findings demonstrate that SJW stimulates hepatic and renal Cyp3a activity and hepatic Cyp2c activity and expression. The induction of hepatic Cyp2c requires repeated treatment for a period longer than the initial induction of Cyp3a.

Reciprocal regulation of carbon monoxide metabolism and the circadian clock

Circadian clocks are cell-autonomous oscillators regulating daily rhythms in a wide range of physiological, metabolic and behavioral processes. Feedback of metabolic signals, such as redox state, NAD+/NADH and AMP/ADP ratios, or heme, modulate circadian rhythms and thereby optimize energy utilization across the 24-h cycle. We show that rhythmic heme degradation, which generates the signaling molecule carbon monoxide (CO), is required for normal circadian rhythms as well as circadian metabolic outputs. CO suppresses circadian transcription by attenuating CLOCK-BMAL1 binding to target promoters. Pharmacological inhibition or genetic depletion of CO-producing heme oxygenases abrogates normal daily cycles in mammalian cells and Drosophila. In mouse hepatocytes, suppression of CO production leads to a global upregulation of CLOCK-BMAL1-dependent circadian gene expression and dysregulated glucose metabolism. Together, our findings show that CO metabolism is an important link between the basic circadian-clock machinery, metabolism and behavior.

The Role of Cytochrome P450 Epoxygenases, Soluble Epoxide Hydrolase, and Epoxyeicosatrienoic Acids in Metabolic Diseases

Metabolic diseases are associated with an increased risk of developing cardiovascular disease. The features comprising metabolic diseases include obesity, insulin resistance, hyperglycemia, hyperlipidemia, and hypertension. Recent evidence has emerged showcasing a role for cytochrome P450 epoxygenases, soluble epoxide hydrolase, and epoxyeicosatrienoic acids (EETs) in the development and progression of metabolic diseases. This review discusses the current knowledge related to the modulation of cytochrome P450 epoxygenases and soluble epoxide hydrolase to alter concentrations of biologically active EETs, resulting in effects on insulin resistance, lipid metabolism, obesity, and diabetes. Future areas of research to address current deficiencies in the understanding of these enzymes and their eicosanoid metabolites in various aspects of metabolic diseases are also discussed.

Combined Angiotensin Receptor Modulation in the Management of Cardio-Metabolic Disorders

Cardiovascular and metabolic disorders, such as hypertension, insulin resistance, dyslipidemia or obesity are linked with chronic low-grade inflammation and dysregulation of the renin–angiotensin system (RAS). Consequently, RAS inhibition by ACE inhibitors or angiotensin AT1 receptor (AT1R) blockers is the evidence-based standard for cardiovascular risk reduction in high-risk patients, including diabetics with albuminuria. In addition, RAS inhibition reduces the new onset of diabetes mellitus. Yet, the high and increasing prevalence of metabolic disorders, and the high residual risk even in properly treated patients, calls for additional means of pharmacological intervention. In the past decade, the stimulation of the angiotensin AT2 receptor (AT2R) has been shown to reduce inflammation, improve cardiac and vascular remodeling, enhance insulin sensitivity and increase adiponectin production. Therefore, a concept of dual AT1R/AT2R modulation emerges as a putative means for risk reduction in cardio-metabolic diseases. The approach employing simultaneous RAS blockade (AT1R) and RAS stimulation (AT2R) is distinct from previous attempts of double intervention in the RAS by dual blockade. Dual blockade abolishes the AT1R-linked RAS almost completely with subsequent risk of hypotension and hypotension-related events, i.e. syncope or renal dysfunction. Such complications might be especially prominent in patients with renal impairment or patients with isolated systolic hypertension and normal-to-low diastolic blood pressure values. In contrast to dual RAS blockade, the add-on of AT2R stimulation does not exert significant blood pressure effects, but it may complement and enhance the anti-inflammatory and antifibrotic/de-stiffening effects of the AT1R blockade and improve the metabolic profile. Further studies will have to investigate these putative effects in particular for settings in which blood pressure reduction is not primarily desired.

A dual COX-2/sEH inhibitor improves the metabolic profile and reduces kidney injury in Zucker diabetic fatty rat

Cyclooxygenase (COX) and soluble epoxide hydrolase (sEH) inhibitors have therapeutic potential. The present study investigated efficacy of a novel dual acting COX-2/sEH inhibitor, PTUPB in type 2 diabetic Zucker Diabetic Fatty (ZDF) rats. Male ZDF rats were treated with vehicle or PTUPB (10mg/kg/d, i.p.) for 8 weeks. At the end of the 8-week experimental period, ZDF rats were diabetic (fasting blood glucose, 287±45mg/dL) compared to Zucker Diabetic Lean rats (ZDL, 99±6mg/dL), and PTUPB treatment improved glycemic status in ZDF rats (146±6mg/dL). Kidney injury was evident in ZDF compared to ZDL rats with elevated albuminurea (44±4 vs 4±2mg/d) and nephrinurea (496±127 vs 16±4μg/d). Marked renal fibrosis, tubular cast formation and glomerular injury were also present in ZDF compared to ZDL rats. In ZDF rats, PTUPB treatment reduced kidney injury parameters by 30-80% compared to vehicle. The ZDF rats also demonstrated increased inflammation and oxidative stress with elevated levels of urinary monocyte chemoattractant protein-1 excretion (862±300 vs 319±75ng/d), renal macrophage infiltration (53±2 vs 37±4/mm(2)) and kidney malondialdehyde/protein ratio (10±1 vs 5±1μmol/mg). PTUPB treatment decreased these inflammatory and oxidative stress markers in the kidney of ZDF rats by 25-57%. These data demonstrate protective actions of a novel dual acting COX-2/sEH inhibitor on the metabolic abnormalities and kidney function in ZDF rat model of type 2 diabetes.

Epoxyeicosatrienoic acids and glucose homeostasis in mice and men

Epoxyeicosatrienoic acids (EETs) are formed from arachidonic acid by the action of P450 epoxygenases (CYP2C and CYP2J). Effects of EETs are limited by hydrolysis by soluble epoxide hydrolase to less active dihydroxyeicosatrienoic acids. Studies in rodent models provide compelling evidence that epoxyeicosatrienoic acids exert favorable effects on glucose homeostasis, either by enhancing pancreatic islet cell function or by increasing insulin sensitivity in peripheral tissues. Specifically, the tissue expression of soluble epoxide hydrolase appears to be increased in rodent models of obesity and diabetes. Pharmacological inhibition of epoxide hydrolase or deletion of the gene encoding soluble epoxide hydrolase (Ephx2) preserves islet cells in rodent models of type 1 diabetes and enhances insulin sensitivity in models of type 2 diabetes, as does administration of epoxyeicosatrienoic acids or their stable analogues. In humans, circulating concentrations of epoxyeicosatrienoic acids correlate with insulin sensitivity, and a loss-of-function genetic polymorphism in EPHX2 is associated with insulin sensitivity.

PGC-1 alpha regulates HO-1 expression, mitochondrial dynamics and biogenesis: Role of epoxyeicosatrienoic acid

BACKGROUND/OBJECTIVES

Obesity is a risk factor in the development of type 2 diabetes mellitus (DM2), which is associated with increased morbidity and mortality, predominantly as a result of cardiovascular complications. Increased adiposity is a systemic condition characterized by increased oxidative stress (ROS), increased inflammation, inhibition of anti-oxidant genes such as HO-1 and increased degradation of epoxyeicosatrienoic acids (EETs). We previously demonstrated that EETs attenuate mitochondrial ROS. We postulate that EETs increase peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), which controls mitochondrial function, oxidative metabolism and induction of HO-1.

METHODS

Cultured murine adipocytes and mice fed a high fat (HF) diet were used to assess functional relationship between EETs, HO-1 and (PGC-1α) using an EET analogue (EET-A) and lentivirus to knock down the PPARGC1A gene.

RESULTS

EET-A increased PGC-1α and HO-1 in cultured adipocytes and increased the expression of genes involved in thermogenesis and adipocyte browning (UCP1 and PRDM16, respectively). PGC-1α knockdown prevented EET-A-induced HO-1expression, suggesting that PGC-1α is upstream of HO-1. MRI data obtained from fat tissues showed that EET-A administration to mice on a HF diet significantly reduced total body fat content, subcutaneous and visceral fat deposits and reduced the VAT: SAT ratio. Moreover EET-A normalized the VO2 and RQ (VCO2/VO2) in mice fed a HF diet, an effect that was completely prevented in PGC-1α deficient mice. In addition, EET-A increased mitochondrial biogenesis and function as measured by OPA1, MnSOD, Mfn1, Mfn2, and SIRT3, an effect that was inhibited by knockdown of PGC-1α.

CONCLUSION

Taken together, our findings show that EET-A increased PGC-1α thereby increasing mitochondrial viability, increased fusion potential thereby providing metabolic protection and increased VO2 consumption in HF-induced obesity in mice, thus demonstrating that the EET-mediated increase in HO-1 levels require PGC-1α expression.

EETs/sEH in diabetes and obesity-induced cardiovascular diseases

Despite the optimization of blood glucose control and the therapeutic management of risk factors, obesity- and diabetes-induced cardiovascular diseases are still major health problems in the United States. Arachidonic acid (AA), an endogenous 20-carbon polyunsaturated fatty acid, is metabolized by cytochrome P450 (CYP) epoxygenases into epoxyeicosatrienoic acids (EETs), which are important lipid mediators with many beneficial effects in type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), and obesity- and diabetes-induced cardiovascular diseases. EETs can be further metabolized to less active dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). It has been demonstrated that the use of sEH blockers, which prevent EET degradation, is a promising pharmacological approach to promoting insulin secretion, preventing endothelial dysfunction, decreasing blood pressure, and protecting against target organ damage in obesity and metabolic diseases. This review will focus on biochemistry of CYP monooxygenase system as well as the pharmacology and physiological significance of EETs and sEH. We will also discuss the role of EETs/sEH in T1DM, T2DM, and obesity- and diabetes-induced cardiovascular diseases.

Epoxyeicosatrienoic Acids and 20-Hydroxyeicosatetraenoic Acid on Endothelial and Vascular Function

Endothelial and vascular smooth cells generate cytochrome P450 (CYP) arachidonic acid metabolites that can impact endothelial cell function and vascular homeostasis. The objective of this review is to focus on the physiology and pharmacology of endothelial CYP metabolites. The CYP pathway produces two types of eicosanoid products: epoxyeicosatrienoic acids (EETs), formed by CYP epoxygenases, and hydroxyeicosatetraenoic acids (HETEs), formed by CYP hydroxylases. Advances in CYP enzymes, EETs, and 20-HETE by pharmacological and genetic means have led to a more complete understanding of how these eicosanoids impact on endothelial cell function. Endothelial-derived EETs were initially described as endothelial-derived hyperpolarizing factors. It is now well recognized that EETs importantly contribute to numerous endothelial cell functions. On the other hand, 20-HETE is the predominant CYP hydroxylase synthesized by vascular smooth muscle cells. Like EETs, 20-HETE acts on endothelial cells and impacts importantly on endothelial and vascular function. An important aspect for EETs and 20-HETE endothelial actions is their interactions with hormonal and paracrine factors. These include interactions with the renin-angiotensin system, adrenergic system, puringeric system, and endothelin. Alterations in CYP enzymes, 20-HETE, or EETs contribute to endothelial dysfunction and cardiovascular diseases such as ischemic injury, hypertension, and atherosclerosis. Recent advances have led to the development of potential therapeutics that target CYP enzymes, 20-HETE, or EETs. Thus, future investigation is required to obtain a more complete understanding of how CYP enzymes, 20-HETE, and EETs regulate endothelial cell function.

Fragment Screening of Soluble Epoxide Hydrolase for Lead Generation-Structure-Based Hit Evaluation and Chemistry Exploration

Soluble epoxide hydrolase (sEH) is involved in the regulation of many biological processes by metabolizing the key bioactive lipid mediator, epoxyeicosatrienoic acids. For the development of sEH inhibitors with improved physicochemical properties, we performed both a fragment screening and a high-throughput screening aiming at an integrated hit evaluation and lead generation. Followed by a joint dose-response analysis to confirm the hits, the identified actives were then effectively triaged by a structure-based hit-classification approach to three prioritized series. Two distinct scaffolds were identified as tractable starting points for potential lead chemistry work. The oxoindoline series bind at the right-hand side of the active-site pocket with hydrogen bonds to the protein. The 2-phenylbenzimidazole-4-sulfonamide series bind at the central channel with significant induced fit, which has not been previously reported. On the basis of the encouraging initial results, we envision that a new lead series with improved properties could be generated if a vector is found that could merge the cyclohexyl functionality of the oxoindoline series with the trifluoromethyl moiety of the 2-phenylbenzimidazole-4-sulfonamide series.