Sugar- and lipid-derived aldehydes are reactive carbonyl species (RCS) frequently used as surrogate markers of oxidative stress in obesity. A pathogenic role for RCS in metabolic diseases of obesity ...remains controversial, however, partly because of their highly diffuse and broad reactivity and the lack of specific RCS-scavenging therapies. Naturally occurring histidine dipeptides (e.g., anserine and carnosine) show RCS reactivity, but their therapeutic potential in humans is limited by serum carnosinases. Here, we present the rational design, characterization, and pharmacological evaluation of carnosinol, i.e., (2S)-2-(3-amino propanoylamino)-3-(1H-imidazol-5-yl)propanol, a derivative of carnosine with high oral bioavailability that is resistant to carnosinases. Carnosinol displayed a suitable ADMET (absorption, distribution, metabolism, excretion, and toxicity) profile and was determined to have the greatest potency and selectivity toward α,β-unsaturated aldehydes (e.g., 4-hydroxynonenal, HNE, ACR) among all others reported thus far. In rodent models of diet-induced obesity and metabolic syndrome, carnosinol dose-dependently attenuated HNE adduct formation in liver and skeletal muscle, while simultaneously mitigating inflammation, dyslipidemia, insulin resistance, and steatohepatitis. These improvements in metabolic parameters with carnosinol were not due to changes in energy expenditure, physical activity, adiposity, or body weight. Collectively, our findings illustrate a pathogenic role for RCS in obesity-related metabolic disorders and provide validation for a promising new class of carbonyl-scavenging therapeutic compounds rationally derived from carnosine.
Summary
1. The heart is a highly oxidative organ in which cardiomyocyte turnover is virtually absent, making it particularly vulnerable to accumulation of lipid peroxidation products (LPP) formed as ...a result of oxidative damage.
2. Reactive oxygen and nitrogen species are the most common electrophiles formed during lipid peroxidation and lead to the formation of both stable and unstable LPP. Of the LPP formed, highly reactive aldehydes are a well‐recognized causative factor in ageing and age‐associated diseases, including cardiovascular disease and diabetes.
3. Recent studies have identified that the mitochondria are both a primary source and target of LPP, with specific emphasis on aldehydes in cardiomyocytes and how these affect the electron transport system and Ca2+ balance.
4. Numerous studies have found that there are functional consequences in the heart following exposure to specific aldehydes (acrolein, trans‐2‐hexanal, 4‐hydroxynonenal and acetaldehyde). Because these LPP are known to form in heart failure, cardiac ischaemia–reperfusion injury and diabetes, they may have an underappreciated role in the pathophysiology of these disease processes.
5. Lipid peroxidation products are involved in the transcriptional regulation of endogenous anti‐oxidant systems. Recent evidence demonstrates that transient increases in LPP may be beneficial in cardioprotection by contributing to mitohormesis (i.e. induction of anti‐oxidant systems) in cardiomyocytes. Thus, exploitation of the cardioprotective actions of the LPP may represent a novel therapeutic strategy for future treatment of heart disease.
Neutrophils form neutrophil extracellular traps (NETs), which have been implicated in microcirculatory plugging. NET formation (NETosis) involves the fusion of granule and nuclear contents, which are ...then released in the extracellular space. Myeloperoxidase (MPO) plays a major role in NETosis leading to the dissociation of DNA from histones. During neutrophil activation, MPO is released and activated to convert hydrogen peroxide and chloride to hypochlorous acid (HOCl). HOCl targets plasmalogens leading to the production of the chlorinated lipids, 2-chlorofatty aldehyde and 2-chlorofatty acid (2-ClFA). Here, we tested the hypothesis that 2-ClFAs are important lipid mediators of NETosis. Human neutrophils treated with physiological levels of 2-ClFAs formed NETs, characterized by MPO association with DNA and neutrophil elastase (NE) redistribution to the perinuclear area. 2-ClFA-induced NETs reduced Escerichia coli colony forming units. 2-ClFA-induced NETosis is calcium- and protein arginine deiminase 4-dependent. Interestingly, unlike PMA, 2-ClFA initiates the NETosis process without neutrophil activation and degranulation. Furthermore, 2-ClFA elicits NETosis in bone-marrow derived neutrophils from MPO-deficient mice. Taken together, these findings suggest 2-ClFA as an MPO product that triggers the NETosis pathway following neutrophil activation.
Catecholamine metabolism
monoamine oxidase (MAO) contributes to cardiac injury in models of ischemia and diabetes, but the pathogenic mechanisms involved are unclear. MAO deaminates norepinephrine ...(NE) and dopamine to produce H
O
and highly reactive "catecholaldehydes," which may be toxic to mitochondria due to the localization of MAO to the outer mitochondrial membrane. We performed a comprehensive analysis of catecholamine metabolism and its impact on mitochondrial energetics in atrial myocardium obtained from patients with and without type 2 diabetes.
Content and maximal activity of MAO-A and MAO-B were higher in the myocardium of patients with diabetes and they were associated with body mass index. Metabolomic analysis of atrial tissue from these patients showed decreased catecholamine levels in the myocardium, supporting an increased flux through MAOs. Catecholaldehyde-modified protein adducts were more abundant in myocardial tissue extracts from patients with diabetes and were confirmed to be MAO dependent. NE treatment suppressed mitochondrial ATP production in permeabilized myofibers from patients with diabetes in an MAO-dependent manner. Aldehyde dehydrogenase (ALDH) activity was substantially decreased in atrial myocardium from these patients, and metabolomics confirmed lower levels of ALDH-catalyzed catecholamine metabolites. Proteomic analysis of catechol-modified proteins in isolated cardiac mitochondria from these patients identified >300 mitochondrial proteins to be potential targets of these unique carbonyls.
These findings illustrate a unique form of carbonyl toxicity driven by MAO-mediated metabolism of catecholamines, and they reveal pathogenic factors underlying cardiometabolic disease. Importantly, they suggest that pharmacotherapies targeting aldehyde stress and catecholamine metabolism in heart may be beneficial in patients with diabetes and cardiac disease.
35, 235-251.
Key points
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For reasons not completely understood, obesogenic high‐fat, high‐sucrose (HFHS) diets and exercise training both increase free fatty acid utilization and chronic oxidative stress, yet ...the former is deleterious to cardiovascular/metabolic health, whereas the latter is beneficial.
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Here, we report that the heart shows decreased mitochondrial H2O2 (mH2O2) generation following HFHS diet, while skeletal muscle shows increased mH2O2, and uncover a novel role for thioredoxin reductase‐2 (TxnRd2) underlying these differences.
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We also show that TxnRd2 is critical to controlling mH2O2 levels during mitochondrial fatty acid oxidation, especially following exercise training in skeletal muscle.
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These findings are important in that they illustrate how the heart and skeletal muscle have contrasting adaptations in antioxidant capacity in response to HFHS diet, and uncover a new role for TxnRd2 in the overall control of mH2O2 in these organs with HFHS diet and exercise training.
Increased fatty acid availability and oxidative stress are physiological consequences of exercise (Ex) and a high‐fat, high‐sugar (HFHS) diet. Despite these similarities, the global effects of Ex are beneficial, whereas HFHS diets are largely deleterious to the cardiovascular system. The reasons for this disparity are multifactorial and incompletely understood. We hypothesized that differences in redox adaptations following HFHS diet in comparison to exercise may underlie this disparity, particularly in mitochondria. Our objective in this study was to determine mechanisms by which heart and skeletal muscle (red gastrocnemius, RG) mitochondria experience differential redox adaptations to 12 weeks of HFHS diet and/or exercise training (Ex) in rats. Surprisingly, both HFHS feeding and Ex led to contrasting effects in heart and RG, in that mitochondrial H2O2 decreased in heart but increased in RG following both HFHS diet and Ex, in comparison to sedentary animals fed a control diet. These differences were determined to be due largely to increased antioxidant/anti‐inflammatory enzymes in the heart following the HFHS diet, which did not occur in RG. Specifically, upregulation of mitochondrial thioredoxin reductase‐2 occurred with both HFHS and Ex in the heart, but only with Ex in RG, and systematic evaluation of this enzyme revealed that it is critical for suppressing mitochondrial H2O2 during fatty acid oxidation. These findings are novel and important in that they illustrate the unique ability of the heart to adapt to oxidative stress imposed by HFHS diet, in part through upregulation of thioredoxin reductase‐2. Furthermore, upregulation of thioredoxin reductase‐2 plays a critical role in preserving the mitochondrial redox status in the heart and skeletal muscle with exercise.
Abstract Objective Lipid peroxides and their reactive aldehyde derivatives (LPPs) have been linked to obesity-related pathologies, but whether they have a causal role has remained unclear. ...Glutathione peroxidase 4 (GPx4) is a selenoenzyme that selectively neutralizes lipid hydroperoxides, and human gpx4 gene variants have been associated with obesity and cardiovascular disease in epidemiological studies. This study tested the hypothesis that LPPs underlie cardio-metabolic derangements in obesity using a high fat, high sucrose (HFHS) diet in gpx4 haploinsufficient mice (GPx4+/− ) and in samples of human myocardium. Methods Wild-type (WT) and GPx4+/− mice were fed either a standard chow (CNTL) or HFHS diet for 24 weeks, with metabolic and cardiovascular parameters measured throughout. Biochemical and immuno-histological analysis was performed in heart and liver at termination of study, and mitochondrial function was analyzed in heart. Biochemical analysis was also performed on samples of human atrial myocardium from a cohort of 103 patients undergoing elective heart surgery. Results Following HFHS diet, WT mice displayed moderate increases in 4-hydroxynonenal (HNE)-adducts and carbonyl stress, and a 1.5-fold increase in GPx4 enzyme in both liver and heart, while gpx4 haploinsufficient (GPx4+/− ) mice had marked carbonyl stress in these organs accompanied by exacerbated glucose intolerance, dyslipidemia, and liver steatosis. Although normotensive, cardiac hypertrophy was evident with obesity, and cardiac fibrosis more pronounced in obese GPx4+/− mice. Mitochondrial dysfunction manifesting as decreased fat oxidation capacity and increased reactive oxygen species was also present in obese GPx4+/− but not WT hearts, along with up-regulation of pro-inflammatory and pro-fibrotic genes. Patients with diabetes and hyperglycemia exhibited significantly less GPx4 enzyme and greater HNE-adducts in their hearts, compared with age-matched non-diabetic patients. Conclusion These findings suggest LPPs are key factors underlying cardio-metabolic derangements that occur with obesity and that GPx4 serves a critical role as an adaptive countermeasure.
Consequences of oxidative stress may be beneficial or detrimental in physiological systems. An organ system's position on the "hormetic curve" is governed by the source and temporality of reactive ...oxygen species (ROS) production, proximity of ROS to moieties most susceptible to damage, and the capacity of the endogenous cellular ROS scavenging mechanisms. Most importantly, the resilience of the tissue (the capacity to recover from damage) is a decisive factor, and this is reflected in the disparate response to ROS in cardiac and skeletal muscle. In myocytes, a high oxidative capacity invariably results in a significant ROS burden which in homeostasis, is rapidly neutralized by the robust antioxidant network. The up-regulation of key pathways in the antioxidant network is a central component of the hormetic response to ROS. Despite such adaptations, persistent oxidative stress over an extended time-frame (e.g., months to years) inevitably leads to cumulative damages, maladaptation and ultimately the pathogenesis of chronic diseases. Indeed, persistent oxidative stress in heart and skeletal muscle has been repeatedly demonstrated to have causal roles in the etiology of heart disease and insulin resistance, respectively. Deciphering the mechanisms that underlie the divergence between adaptive and maladaptive responses to oxidative stress remains an active area of research for basic scientists and clinicians alike, as this would undoubtedly lead to novel therapeutic approaches. Here, we provide an overview of major types of ROS in striated muscle and the divergent adaptations that occur in response to them. Emphasis is placed on highlighting newly uncovered areas of research on this topic, with particular focus on the mitochondria, and the diverging roles that ROS play in muscle health (e.g., exercise or preconditioning) and disease (e.g., cardiomyopathy, ischemia, metabolic syndrome).
Bitter Melon (Momordica charantia) is a widely used traditional remedy for hyperglycemia. While the medicinal properties of this plant have been studied extensively using in vitro and animal models, ...the clinical efficacy and safety in humans is largely unknown. This review discusses the benefits and limitations of bitter melon supplementation in the context of epidemic levels of insulin resistance and pre-diabetes throughout the world.
Background
Onset of postoperative atrial fibrillation (POAF) is a common and costly complication of heart surgery despite major improvements in surgical technique and quality of patient care. The ...etiology of POAF, and the ability of clinicians to identify and therapeutically target high‐risk patients, remains elusive.
Methods and Results
Myocardial tissue dissected from right atrial appendage (RAA) was obtained from 244 patients undergoing cardiac surgery. Reactive oxygen species (ROS) generation from multiple sources was assessed in this tissue, along with total glutathione (GSHt) and its related enzymes GSH‐peroxidase (GPx) and GSH‐reductase (GR). Monoamine oxidase (MAO) and NADPH oxidase were observed to generate ROS at rates 10‐fold greater than intact, coupled mitochondria. POAF risk was significantly associated with MAO activity (Quartile 1 Q1: adjusted relative risk ARR=1.0; Q2: ARR=1.8, 95% confidence interval CI=0.84 to 4.0; Q3: ARR=2.1, 95% CI=0.99 to 4.3; Q4: ARR=3.8, 95% CI=1.9 to 7.5; adjusted Ptrend=0.009). In contrast, myocardial GSHt was inversely associated with POAF (Quartile 1 Q1: adjusted relative risk ARR=1.0; Q2: ARR=0.93, 95% confidence interval CI=0.60 to 1.4; Q3: ARR=0.62, 95% CI=0.36 to 1.1; Q4: ARR=0.56, 95% CI=0.34 to 0.93; adjusted Ptrend=0.014). GPx also was significantly associated with POAF; however, a linear trend for risk was not observed across increasing levels of the enzyme. GR was not associated with POAF risk.
Conclusions
Our results show that MAO is an important determinant of redox balance in human atrial myocardium, and that this enzyme, in addition to GSHt and GPx, is associated with an increased risk for POAF. Further investigation is needed to validate MAO as a predictive biomarker for POAF, and to explore this enzyme's potential role in arrhythmogenesis.
The prevalence of smoking in Aboriginal Canadians is higher than non-Aboriginal Canadians, a behavior that also tends to alter dietary patterns. Compared with the general Canadian population, ...maternal smoking rates are almost twice as high. The aim of this study was to compare dietary adequacy of Inuvialuit women of childbearing age comparing smokers versus non-smokers.
A cross-sectional study, where participants completed a culturally specific quantitative food frequency questionnaire. Non-parametric analysis was used to compare mean nutrient intake, dietary inadequacy and differences in nutrient density among smokers and non-smokers. Multiple logistic regression analyses were performed for key nutrients inadequacy and smoking status. Data was collected from three communities in the Beaufort Delta region of the Northwest Territories, Canada from randomly selected Inuvialuit women of childbearing age (19-44 years).
Of 92 participants, 75% reported being smokers. There were no significant differences in age, BMI, marital status, education, number of people in household working and/or number of self employed, and physical activity between smokers and non-smokers. Non-parametric analysis showed no differences in nutrient intake between smokers and non-smokers. Logistic regression however revealed there was a positive association between smoking and inadequacies of vitamin C (OR = 2.91, 95% CI, 1.17-5.25), iron (OR = 3.16, 95% CI, 1.27-5.90), and zinc (OR = 2.78, 95% CI, 1.12-4.94). A high percentage of women (>60%), regardless of smoking status, did not meet the dietary recommendations for fiber, vitamin D, E and potassium.
This study provides evidence of inadequate dietary intake among Inuvialuit of childbearing age regardless of smoking behavior.
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