Polyol pathway impairs the function of SERCA and RyR in ischemic-reperfused rat hearts by increasing oxidative modifications of these proteins

Stable oxidative posttranslational modifications alter the gating properties of RyR1

The ryanodine receptor type 1 (RyR1) is a Ca2+ release channel that regulates skeletal muscle contraction by controlling Ca2+ release from the sarcoplasmic reticulum (SR). Posttranslational modifications (PTMs) of RyR1, such as phosphorylation, S-nitrosylation, and carbonylation are known to increase RyR1 open probability (Po), contributing to SR Ca2+ leak and skeletal muscle dysfunction. PTMs on RyR1 have been linked to muscle dysfunction in diseases like breast cancer, rheumatoid arthritis, Duchenne muscle dystrophy, and aging. While reactive oxygen species (ROS) and oxidative stress induce PTMs, the impact of stable oxidative modifications like 3-nitrotyrosine (3-NT) and malondialdehyde adducts (MDA) on RyR1 gating remains unclear. Mass spectrometry and single-channel recordings were used to study how 3-NT and MDA modify RyR1 and affect Po. Both modifications increased Po in a dose-dependent manner, with mass spectrometry identifying 30 modified residues out of 5035 amino acids per RyR1 monomer. Key modifications were found in domains critical for protein interaction and channel activation, including Y808/3NT in SPRY1, Y1081/3NT and H1254/MDA in SPRY2&3, and Q2107/MDA and Y2128/3NT in JSol, near the binding site of FKBP12. Though these modifications did not directly overlap with FKBP12 binding residues, they promoted FKBP12 dissociation from RyR1. These findings provide detailed insights into how stable oxidative PTMs on RyR1 residues alter channel gating, advancing our understanding of RyR1-mediated Ca2+ release in conditions associated with oxidative stress and muscle weakness.

The role of glycolytic metabolic pathways in cardiovascular disease and potential therapeutic approaches

Cardiovascular disease (CVD) is a major threat to human health, accounting for 46% of non-communicable disease deaths. Glycolysis is a conserved and rigorous biological process that breaks down glucose into pyruvate, and its primary function is to provide the body with the energy and intermediate products needed for life activities. The non-glycolytic actions of enzymes associated with the glycolytic pathway have long been found to be associated with the development of CVD, typically exemplified by metabolic remodeling in heart failure, which is a condition in which the heart exhibits a rapid adaptive response to hypoxic and hypoxic conditions, occurring early in the course of heart failure. It is mainly characterized by a decrease in oxidative phosphorylation and a rise in the glycolytic pathway, and the rise in glycolysis is considered a hallmark of metabolic remodeling. In addition to this, the glycolytic metabolic pathway is the main source of energy for cardiomyocytes during ischemia-reperfusion. Not only that, the auxiliary pathways of glycolysis, such as the polyol pathway, hexosamine pathway, and pentose phosphate pathway, are also closely related to CVD. Therefore, targeting glycolysis is very attractive for therapeutic intervention in CVD. However, the relationship between glycolytic pathway and CVD is very complex, and some preclinical studies have confirmed that targeting glycolysis does have a certain degree of efficacy, but its specific role in the development of CVD has yet to be explored. This article aims to summarize the current knowledge regarding the glycolytic pathway and its key enzymes (including hexokinase (HK), phosphoglucose isomerase (PGI), phosphofructokinase-1 (PFK1), aldolase (Aldolase), phosphoglycerate metatase (PGAM), enolase (ENO) pyruvate kinase (PKM) lactate dehydrogenase (LDH)) for their role in cardiovascular diseases (e.g., heart failure, myocardial infarction, atherosclerosis) and possible emerging therapeutic targets.

Nicotinamide restores tissue NAD+ and improves survival in rodent models of cardiac arrest

Metabolic suppression in the ischemic heart is characterized by reduced levels of NAD+ and ATP. Since NAD+ is required for most metabolic processes that generate ATP, we hypothesized that nicotinamide restores ischemic tissue NAD+ and improves cardiac function in cardiomyocytes and isolated hearts, and enhances survival in a mouse model of cardiac arrest. Mouse cardiomyocytes were exposed to 30 min simulated ischemia and 90 min reperfusion. NAD+ content dropped 40% by the end of ischemia compared to pre-ischemia. Treatment with 100 μM nicotinamide (NAM) at the start of reperfusion completely restored the cellular level of NAD+ at 15 min of reperfusion. This rescue of NAD+ depletion was associated with improved contractile recovery as early as 10 min post-reperfusion. In a mouse model of cardiac arrest, 100 mg/kg NAM administered IV immediately after cardiopulmonary resuscitation resulted in 100% survival at 4 h as compared to 50% in the saline group. In an isolated rat heart model, the effect of NAM on cardiac function was measured for 20 min following 18 min global ischemia. Rate pressure product was reduced by 26% in the control group following arrest. Cardiac contractile function was completely recovered with NAM treatment given at the start of reperfusion. NAM restored tissue NAD+ and enhanced production of lactate and ATP, while reducing glucose diversion to sorbitol in the heart. We conclude that NAM can rapidly restore cardiac NAD+ following ischemia and enhance glycolysis and contractile recovery, with improved survival in a mouse model of cardiac arrest.

Identification of pharmacokinetic markers for safflower injection using a combination of system pharmacology, multicomponent pharmacokinetics, and quantitative proteomics study

Safflower injection (SI), a water-extract preparation from safflower (Carthamus tinctorius L.), has been widely used for the treatment of cardio-cerebrovascular diseases. This work aims to develop an approach for identifying PK markers of cardiovascular herbal medicines using SI as a case study. Firstly, qualitative and quantitative analyses were performed to reveal ingredients of the preparation via HPLC-MS. Subsequently, multiple PK ingredients and integrated PK investigations were carried out to ascertain ingredients with favorable PK properties (e.g., easily detected at conventional PK time points and high system exposure) for the whole preparation. Next, ingredients against cardiovascular diseases (CVDs) in the preparation were predicted with target fishing and system pharmacology studies. Finally, ingredients with favorable PK properties, satisfactory PK representativeness for the preparation, and high relevance to CVDs were considered as potential PK markers. Their therapeutic effect was further evaluated using the H₂O₂-induced H9c2 cardiomyocyte-injured model and a proteomics study to identify objective PK markers. As results, it disclosed that SI mainly contains 11 ingredients. Among them, five ingredients, namely, hydroxysafflor yellow A (HSYA), syringin (SYR), p-coumaric acid (p-CA), scutellarin (SCU), and p-hydroxybenzaldehyde (p-HBA), showed favorable PK properties. HSYA, SYR, and rutin (RU) were predicted to show high relevance to CVDs and screened as potential PK markers. However, only HSYA and SYR were confirmed as therapeutic ingredients against CVDs. Combined with these findings, only HSYA demonstrated satisfactory representativeness on PK properties and therapeutic effects of multiple ingredients of the preparation, thereby indicating that HSYA is a potential PK marker for the SI. The results of this study can provide a reference for the characterization of PK markers for traditional Chinese medicines.

Structure-Function Relationships and Modifications of Cardiac Sarcoplasmic Reticulum Ca2+-Transport

Sarcoplasmic reticulum (SR) is a specialized tubular network, which not only maintains the intracellular concentration of Ca2+ at a low level but is also known to release and accumulate Ca2+ for the occurrence of cardiac contraction and relaxation, respectively. This subcellular organelle is composed of several phospholipids and different Ca2+-cycling, Ca2+-binding and regulatory proteins, which work in a coordinated manner to determine its function in cardiomyocytes. Some of the major proteins in the cardiac SR membrane include Ca2+-pump ATPase (SERCA2), Ca2+-release protein (ryanodine receptor), calsequestrin (Ca2+-binding protein) and phospholamban (regulatory protein). The phosphorylation of SR Ca2+-cycling proteins by protein kinase A or Ca2+-calmodulin kinase (directly or indirectly) has been demonstrated to augment SR Ca2+-release and Ca2+-uptake activities and promote cardiac contraction and relaxation functions. The activation of phospholipases and proteases as well as changes in different gene expressions under different pathological conditions have been shown to alter the SR composition and produce Ca2+-handling abnormalities in cardiomyocytes for the development of cardiac dysfunction. The post-translational modifications of SR Ca2+ cycling proteins by processes such as oxidation, nitrosylation, glycosylation, lipidation, acetylation, sumoylation, and O GlcNacylation have also been reported to affect the SR Ca2+ release and uptake activities as well as cardiac contractile activity. The SR function in the heart is also influenced in association with changes in cardiac performance by several hormones including thyroid hormones and adiponectin as well as by exercise-training. On the basis of such observations, it is suggested that both Ca2+-cycling and regulatory proteins in the SR membranes are intimately involved in determining the status of cardiac function and are thus excellent targets for drug development for the treatment of heart disease.

Mechanisms of Physical Fatigue and its Applications in Nutritional Interventions

Physical fatigue during exercise can be defined as an impairment of physical performance. Multiple factors have been found contributing to physical fatigue, including neurotransmitter-mediated defense action, insufficient energy supply, and induction of oxidative stress. These mechanistic findings provide a sound theoretical rationale for nutritional intervention since most of these factors can be modulated by nutrient supplementation. In this review, we summarize the current evidence regarding the functional role of nutrients supplementation in managing physical performance and propose the issues that need to be addressed for better utilization of nutritional supplementation approach to improve physical performance.

Inactivation of cysteine 674 in the sarcoplasmic/endoplasmic reticulum calcium ATPase 2 causes retinopathy in the mouse

Diabetic retinopathy is a multifactorial microvascular complication, and its pathogenesis hasn't been fully elucidated. The irreversible oxidation of cysteine 674 (C674) in the sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2) was increased in the type 1 diabetic retinal vasculature. SERCA2 C674S knock-in (SKI) mouse line that half of C674 was replaced by serine 674 (S674) was used to study the effect of C674 inactivation on retinopathy. Compared with wild type (WT) mice, SKI mice had increased number of acellular capillaries and pericyte loss similar to those in type 1 diabetic WT mice. In the retina of SKI mice, pro-apoptotic proteins and intracellular Ca²⁺-dependent signaling pathways increased, while anti-apoptotic proteins and vessel density decreased. In endothelial cells, C674 inactivation increased the expression of pro-apoptotic proteins, damaged mitochondria, and induced cell apoptosis. These results suggest that a possible mechanism of retinopathy induced by type 1 diabetes is the interruption of calcium homeostasis in the retina by oxidation of C674. C674 is a key to maintain retinal health. Its inactivation can cause retinopathy similar to type 1 diabetes by promoting apoptosis. SERCA2 might be a potential target for the prevention and treatment of diabetic retinopathy.

Inactivation of Cys674 in SERCA2 increases BP by inducing endoplasmic reticulum stress and soluble epoxide hydrolase

BACKGROUND AND PURPOSE

The kidney is essential in regulating sodium homeostasis and BP. The irreversible oxidation of Cys⁶⁷⁴ (C674) in the sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2) is increased in the renal cortex of hypertensive mice. Whether inactivation of C674 promotes hypertension is unclear. Here we have investigated the effects on BP of the inactivation of C674, and its role in the kidney.

EXPERIMENTAL APPROACH

We used heterozygous SERCA2 C674S knock-in (SKI) mice, where half of C674 was substituted by serine, to represent partial irreversible oxidation of C674. The BP, urine volume, and urine composition of SKI mice and their littermate wild-type (WT) mice were measured. The kidneys were collected for cell culture, Na⁺ /K⁺ -ATPase activity, protein expression, and immunohistological analysis.

KEY RESULTS

Compared with WT mice, SKI mice had higher BP, lower urine volume and sodium excretion, up-regulated endoplasmic reticulum (ER) stress markers and soluble epoxide hydrolase (sEH), and down-regulated dopamine D₁ receptors in renal cortex and cells from renal proximal tubule. ER stress and sEH were mutually regulated, and both upstream of D₁ receptors. Inhibition of ER stress or sEH up-regulated expression of D₁ receptors, decreased the activity of Na⁺ /K⁺ -ATPase, increased sodium excretion, and lowered BP in SKI mice.

CONCLUSIONS AND IMPLICATIONS

The inactivation of SERCA2 C674 promotes the development of hypertension by inducing ER stress and sEH. Our study highlights the importance of C674 redox status in BP control and the contribution of SERCA2 to sodium homeostasis and BP in the kidney.

Keeping heart homeostasis in check through the balance of iron metabolism

Highly active cardiomyocytes need iron for their metabolic activity. In physiological conditions, iron turnover is a delicate process which is dependent on global iron supply and local autonomous regulatory mechanisms. Though less is known about the autonomous regulatory mechanisms, data suggest that these mechanisms can preserve cellular iron turnover even in the presence of systemic iron disturbance. Therefore, activity of local iron protein machinery and its relationship with global iron metabolism is important to understand cardiac iron metabolism in physiological conditions and in cardiac disease. Our knowledge in this respect has helped in designing therapeutic strategies for different cardiac diseases. This review is a synthesis of our current knowledge concerning the regulation of cardiac iron metabolism. In addition, different models of cardiac iron dysmetabolism will be discussed through the examples of heart failure (cardiomyocyte iron deficiency), myocardial infarction (acute changes in cardiac iron turnover), doxorubicin-induced cardiotoxicity (cardiomyocyte iron overload in mitochondria), thalassaemia (cardiomyocyte cytosolic and mitochondrial iron overload) and Friedreich ataxia (asymmetric cytosolic/mitochondrial cardiac iron dysmetabolism). Finally, future perspectives will be discussed in order to resolve actual gaps in knowledge, which should be helpful in finding new treatment possibilities in different cardiac diseases.

Acute exposure to organic and inorganic sources of copper: Differential response in intestinal cell lines

SCOPE

Copper supplementation in nutrition has evolved from using inorganic mineral salts to organically chelated minerals but with limited knowledge of the impact at the cellular level.

METHODS

Here, the impact of inorganic and organic nutrient forms (glycinate, organic acid, and proteinate) of copper on the cellular level is investigated on intestinal cell lines, HT29 and Caco-2, after a 2-hr acute exposure to copper compounds and following a 10-hr recovery.

RESULTS

Following the 10-hr recovery, increases were observed in proteins involved in metal binding (metallothioneins) and antioxidant response (sulfiredoxin 1 and heme oxygenase 1), and global proteomic analysis suggested recruitment of the unfolded protein response and proteosomal overloading. Copper organic acid chelate, the only treatment to show striking and sustained reactive oxygen species generation, had the greatest impact on ubiquitinated proteins, reduced autophagy, and increased aggresome formation, reducing growth in both cell lines. The least effect was noted in copper proteinate with negligible impact on aggresome formation or extended growth for either cell line.

CONCLUSION

The type and source of copper can impact significantly at the cellular level.

Aldo-keto reductases-mediated cytotoxicity of 2-deoxyglucose: A novel anticancer mechanism

2‐Deoxyglucose (2DG) is a non‐metabolizable glucose analog currently in clinical trials to determine its efficacy in enhancing the therapeutic effects of radiotherapy and chemotherapy of several types of cancers. It is thought to preferentially kill cancer cells by inhibiting glycolysis because cancer cells are more dependent on glycolysis for their energy needs than normal cells. However, we found that the toxicity of 2DG in cancer cells is mediated by the enzymatic activities of AKR1B1 and/or AKR1B10 (AKR1Bs), which are often overexpressed in cancer cells. Our results show that 2DG kills cancer cells because, in the process of being reduced by AKR1Bs, depletion of their cofactor NADPH leads to the depletion of glutathione (GSH) and cell death. Furthermore, we showed that compounds that are better substrates for AKR1Bs than 2DG are more effective than 2DG in killing cancer cells that overexpressed these 2 enzymes. As cancer cells can be induced to overexpress AKR1Bs, the anticancer mechanism we identified can be applied to treat a large variety of cancers. This should greatly facilitate the development of novel anticancer drugs.

Dioxygen and Metabolism; Dangerous Liaisons in Cardiac Function and Disease

The heart must consume a significant amount of energy to sustain its contractile activity. Although the fuel demands are huge, the stock remains very low. Thus, in order to supply its daily needs, the heart must have amazing adaptive abilities, which are dependent on dioxygen availability. However, in myriad cardiovascular diseases, “fuel” depletion and hypoxia are common features, leading cardiomyocytes to favor low-dioxygen-consuming glycolysis rather than oxidation of fatty acids. This metabolic switch makes it challenging to distinguish causes from consequences in cardiac pathologies. Finally, despite the progress achieved in the past few decades, medical treatments have not improved substantially, either. In such a situation, it seems clear that much remains to be learned about cardiac diseases. Therefore, in this review, we will discuss how reconciling dioxygen availability and cardiac metabolic adaptations may contribute to develop full and innovative strategies from bench to bedside.

Mitochondrial Bioenergetics During Ischemia and Reperfusion

During ischemia and reperfusion (I/R) mitochondria suffer a deficiency to supply the cardiomyocyte with chemical energy, but also contribute to the cytosolic ionic alterations especially of Ca²⁺. Their free calcium concentration ([Ca²⁺]m) mainly depends on mitochondrial entrance through the uniporter (UCam) and extrusion in exchange with Na⁺ (mNCX) driven by the electrochemical gradient (ΔΨm). Cardiac energetic is frequently estimated by the oxygen consumption, which determines metabolism coupled to ATP production and to the maintaining of ΔΨm. Nevertheless, a better estimation of heart energy consumption is the total heat release associated to ATP hydrolysis, metabolism, and binding reactions, which is measurable either in the presence or the absence of oxygenation or perfusion. Consequently, a mechano-calorimetrical approach on isolated hearts gives a tool to evaluate muscle economy. The mitochondrial role during I/R depends on the injury degree. We investigated the role of the mitochondrial Ca²⁺ transporters in the energetic of hearts stunned by a model of no-flow I/R in rat hearts. This chapter explores an integrated view of previous and new results which give evidences to the mitochondrial role in cardiac stunning by ischemia o hypoxia, and the influence of thyroid alterations and cardioprotective strategies, such as cardioplegic solutions (high K-low Ca, pyruvate) and the phytoestrogen genistein in both sex. Rat ventricles were perfused in a flow-calorimeter at either 30 °C or 37 °C to continuously measure the left ventricular pressure (LVP) and total heat rate (Ht). A pharmacological treatment was done before exposing to no-flow I and R. The post-ischemic contractile (PICR as %) and energetical (Ht) recovery and muscle economy (Eco: P/Ht) were determined during stunning. The functional interaction between mitochondria (Mit) and sarcoplasmic reticulum (SR) was evaluated with selective mitochondrial inhibitors in hearts reperfused with Krebs-10 mM caffeine-36 mM Na⁺. The caffeine induced contracture (CIC) was due to SR Ca²⁺ release, while relaxation mainly depends on mitochondrial Ca²⁺ uptake since neither SL-NCX nor SERCA are functional under this media. The ratio of area-under-curves over ischemic values (AUC-ΔHt/AUC-ΔLVP) estimates the energetical consumption (EC) to maintain CIC. Relaxation of CIC was accelerated by inhibition of mNCX or by adding the aerobic substrate pyruvate, while both increased EC. Contrarily, relaxation was slowed by cardioplegia (high K-low Ca Krebs) and by inhibition of UCam. Thus, Mit regulate the cytosolic [Ca²⁺] and SR Ca²⁺ content. Both, hyperthyroidism (HpT) and hypothyroidism (HypoT) reduced the peak of CIC but increased EC, in spite of improving PICR. Both, CIC and PICR in HpT were also sensitive to inhibition of mNCX or UCam, suggesting that Mit contribute to regulate the SR store and Ca²⁺ release. The interaction between mitochondria and SR and the energetic consequences were also analyzed for the effects of genistein in hearts exposed to I/R, and for the hypoxia/reoxygenation process. Our results give evidence about the mitochondrial regulation of both PICR and energetic consumption during stunning, through the Ca²⁺ movement.

Corticosteroids and aldose reductase inhibitor Epalrestat modulates cardiac action potential via Kvβ1.1 (AKR6A8) subunit of voltage-gated potassium channel

We previously demonstrated the role of Kvβ1.1 subunit of voltage-activated potassium channel in heart for its sensory roles in detecting changes in NADH/NAD and modulation of ion channel. However, the pharmacological role for the association of Kvβ1 via its binding to ligands such as cortisone and its analogs remains unknown. Therefore, we investigated the significance of Kvβ1.1 binding to cortisone analogs and AR inhibitor epalrestat. In addition, the aldose reductase (AR) inhibitor epalrestat was identified as a pharmacological target and modulator of cardiac activity via binding to the Kvβ1 subunit. Using a combination of ex vivo cardiac electrophysiology and in silico binding, we identified that Kvβ1 subunit binds and interacts with epalrestat. To identify the specificity of the action potential changes, we studied the sensitivity of the action potential prolongation by probing the electrical changes in the presence of 4-aminopyridine and evaluated the specificity of pharmacological effects in the hearts from Kvβ1.1 knock out mouse. Our results show that pharmacological modulation of cardiac electrical activity by cortisone analogs and epalrestat is mediated by Kvβ1.1.

Insights for Oxidative Stress and mTOR Signaling in Myocardial Ischemia/Reperfusion Injury under Diabetes

Diabetes mellitus (DM) displays a high morbidity. The diabetic heart is susceptible to myocardial ischemia/reperfusion (MI/R) injury. Impaired activation of prosurvival pathways, endoplasmic reticulum (ER) stress, increased basal oxidative state, and decreased antioxidant defense and autophagy may render diabetic hearts more vulnerable to MI/R injury. Oxidative stress and mTOR signaling crucially regulate cardiometabolism, affecting MI/R injury under diabetes. Producing reactive oxygen species (ROS) and reactive nitrogen species (RNS), uncoupling nitric oxide synthase (NOS), and disturbing the mitochondrial quality control may be three major mechanisms of oxidative stress. mTOR signaling presents both cardioprotective and cardiotoxic effects on the diabetic heart, which interplays with oxidative stress directly or indirectly. Antihyperglycemic agent metformin and newly found free radicals scavengers, Sirt1 and CTRP9, may serve as promising pharmacological therapeutic targets. In this review, we will focus on the role of oxidative stress and mTOR signaling in the pathophysiology of MI/R injury in diabetes and discuss potential mechanisms and their interactions in an effort to provide some evidence for cardiometabolic targeted therapies for ischemic heart disease (IHD).

The Role of Oxidative Stress in Myocardial Ischemia and Reperfusion Injury and Remodeling: Revisited

Oxidative and reductive stress are dual dynamic phases experienced by the cells undergoing adaptation towards endogenous or exogenous noxious stimulus. The former arises due to the imbalance between the reactive oxygen species production and antioxidant defenses, while the latter is due to the aberrant increase in the reducing equivalents. Mitochondrial malfunction is the common denominator arising from the aberrant functioning of the rheostat that maintains the homeostasis between oxidative and reductive stress. Recent experimental evidences suggest that the maladaptation during oxidative stress could play a pivotal role in the pathophysiology of major cardiovascular diseases such as myocardial infraction, atherosclerosis, and diabetic cardiovascular complications. In this review we have discussed the role of oxidative and reductive stress pathways in the pathogenesis of myocardial ischemia/reperfusion injury and diabetic cardiomyopathy (DCM). Furthermore, we have provided impetus for the development of subcellular organelle targeted antioxidant drug therapy for thwarting the deterioration of the failing myocardium in the aforementioned cardiovascular conditions.

Mitochondrial oxidative metabolism and uncoupling proteins in the failing heart

Despite significant progress in cardiovascular medicine, myocardial ischemia and infarction, progressing eventually to the final end point heart failure (HF), remain the leading cause of morbidity and mortality in the USA. HF is a complex syndrome that results from any structural or functional impairment in ventricular filling or blood ejection. Ultimately, the heart's inability to supply the body's tissues with enough blood may lead to death. Mechanistically, the hallmarks of the failing heart include abnormal energy metabolism, increased production of reactive oxygen species (ROS) and defects in excitation-contraction coupling. HF is a highly dynamic pathological process, and observed alterations in cardiac metabolism and function depend on the disease progression. In the early stages, cardiac remodeling characterized by normal or slightly increased fatty acid (FA) oxidation plays a compensatory, cardioprotective role. However, upon progression of HF, FA oxidation and mitochondrial oxidative activity are decreased, resulting in a significant drop in cardiac ATP levels. In HF, as a compensatory response to decreased oxidative metabolism, glucose uptake and glycolysis are upregulated, but this upregulation is not sufficient to compensate for a drop in ATP production. Elevated mitochondrial ROS generation and ROS-mediated damage, when they overwhelm the cellular antioxidant defense system, induce heart injury and contribute to the progression of HF. Mitochondrial uncoupling proteins (UCPs), which promote proton leak across the inner mitochondrial membrane, have emerged as essential regulators of mitochondrial membrane potential, respiratory activity and ROS generation. Although the physiological role of UCP2 and UCP3, expressed in the heart, has not been clearly established, increasing evidence suggests that these proteins by promoting mild uncoupling could reduce mitochondrial ROS generation and cardiomyocyte apoptosis and ameliorate thereby myocardial function. Further investigation on the alterations in cardiac UCP activity and regulation will advance our understanding of their physiological roles in the healthy and diseased heart and also may facilitate the development of novel and more efficient therapies.

Unbreak my heart: targeting mitochondrial autophagy in diabetic cardiomyopathy

SIGNIFICANCE

Diabetes is strongly associated with increased incidence of heart disease and mortality due to development of diabetic cardiomyopathy. Even in the absence of cardiovascular disease, cardiomyopathy frequently arises in diabetic patients. Current treatment options for cardiomyopathy in diabetic patients are the same as for nondiabetic patients and do not address the causes underlying the loss of contractility.

RECENT ADVANCES

Although there are numerous distinctions between Type 1 and Type 2 diabetes, recent evidence suggests that the two disease states converge on mitochondria as an epicenter for cardiomyocyte damage.

CRITICAL ISSUES

Accumulation of dysfunctional mitochondria contributes to cardiac tissue injury in both acute and chronic conditions. Removal of damaged mitochondria by macroautophagy, termed "mitophagy," is critical for maintaining cardiomyocyte health and contractility both under normal conditions and during stress. However, very little is known about the involvement of mitophagy in the pathogenesis of diabetic cardiomyopathy. A growing interest in this topic has given rise to a wave of publications that aim at deciphering the status of autophagy and mitophagy in Type 1 and Type 2 diabetes.

FUTURE DIRECTIONS

This review summarizes these recent studies with the goal of drawing conclusions about the activation or suppression of autophagy and mitophagy in the diabetic heart. A better understanding of how autophagy and mitophagy are affected in the diabetic myocardium is still needed, as well as whether they can be targeted therapeutically.

Sorbitol dehydrogenase inhibitor protects the liver from ischemia/reperfusion-induced injury via elevated glycolytic flux and enhanced sirtuin 1 activity

Sorbitol dehydrogenase (SDH), a key enzyme of the polyol pathway, has recently been demonstrated to have an important role in mediating tissue ischemia/reperfusion (I/R) injury. The present study investigated how this enzyme may affect the ischemic liver and the mechanism underlying its effect. Firstly, C57BL/6 mice were subjected to oral administration of CP-470,711 (5 mg/kg body weight/day for five days) and 70% hepatic I/R. Next the present study further investigated the changes in liver function, histology, inflammation, apoptosis and necrosis; the cytosolic adenosine triphosphate (ATP) and nictotinamide adenine dinucleotide [NAD(H)] contents and the protein level of caspase 3 and sirtuin 1 (SIRT1). The data demonstrated that sorbitol dehydrogenase inhibitor (SDI)-administration significantly alleviated I/R-induced liver injury, palliated histological changes and lowered the level of hepatocyte apoptosis and necrosis. In addition, SDI-pretreatment in ischemic liver markedly maintained the cytosolic ATP and NAD(H) proportion, enhanced SIRT1 and suppressed the activation of caspase 3 at the protein level. The findings in the present study revealed that the flux through SDH may render the liver more vulnerable to I/R-induced injury and interventions targeting this enzyme may provide a novel adjunctive approach to protect from severe tissue injury following liver ischemia.

Impairment of calcium ATPases by high glucose and potential pharmacological protection

The review deals with impairment of Ca(2+)-ATPases by high glucose or its derivatives in vitro, as well as in human diabetes and experimental animal models. Acute increases in glucose level strongly correlate with oxidative stress. Dysfunction of Ca(2+)-ATPases in diabetic and in some cases even in nondiabetic conditions may result in nitration of and in irreversible modification of cysteine-674. Nonenyzmatic protein glycation might lead to alteration of Ca(2+)-ATPase structure and function contributing to Ca(2+) imbalance and thus may be involved in development of chronic complications of diabetes. The susceptibility to glycation is probably due to the relatively high percentage of lysine and arginine residues at the ATP binding and phosphorylation domains. Reversible glycation may develop into irreversible modifications (advanced glycation end products, AGEs). Sites of SERCA AGEs are depicted in this review. Finally, several mechanisms of prevention of Ca(2+)-pump glycation, and their advantages and disadvantages are discussed.

Inhibition of sorbitol dehydrogenase by nucleosides and nucleotides

Sorbitol dehydrogenase inhibitors have been found to prevent, or alleviate, various secondary complications of diabetes mellitus. In the present study, the effects of nucleosides and nucleotides on the rate of sorbitol oxidation catalyzed by the sheep liver enzyme were studied by steady-state kinetics at pH 7.4. Various such compounds, including ATP and the 2'-deoxy-analogues of ATP, ADP and AMP, reversibly inhibit enzyme activity by formation of enzyme-coenzyme-inhibitor ternary complexes. In each case, no deviations from linearity were seen in the double-reciprocal plots using sorbitol or NAD(+) as the varied substrate and there was a linear relationship between inhibitor concentration and the observed inhibitory effects. Sorbitol was docked into a model of the sheep SDH-NAD(+) complex based upon the structure of the human SDH-NAD(+) holoenzyme. The resulting structure of the ternary complex of sheep SDH, NAD(+) and sorbitol (PMDB ID code PM 0078068) shows that the reactive C-2 hydroxyl group of sorbitol is oriented toward the 4'-position of the nicotinamide moiety of the coenzyme, and that the adjacent primary hydroxyl group of sorbitol interacts with the catalytic zinc. The results indicate that the ribose moiety of the inhibitor structures is an important determinant for the observed effects. Specifically, the 2'-position of the ribose ring exerts an effect with respect to inhibitor potency.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

Fasudil protects the heart against ischemia-reperfusion injury by attenuating endoplasmic reticulum stress and modulating SERCA activity: the differential role for PI3K/Akt and JAK2/STAT3 signaling pathways

Disordered calcium homeostasis can lead to endoplasmic reticulum (ER) stress. Our previous data showed that time course activation of ER stress contributes to time-related increase in ischemia-reperfusion (I/R) injury. However, it has not been tested whether PI3K/Akt and JAK2/STAT3 pathways play differential roles in reducing ER stress to protect the heart. In the present study, using fasudil which is a specific inhibitor of ROCK, we aimed to investigate whether improved SERCA expression and activity accounts for reduced ER stress by ROCK inhibition, specifically whether PI3K/Akt and JAK2/STAT3 pathways are differentially involved in modulating SERCA activity to reduce ER stress and hence I/R injury. The results showed that during the reperfusion period following 45 min of coronary ligation the infarct size (IS) increased from 3 h of reperfusion (45.4±5.57%) to 24 h reperfusion (64.21±5.43, P<0.05), which was associated with ER stress dependent apoptosis signaling activation including CHOP, Caspase-12 and JNK (P<0.05, respectively).The dynamic ER stress activation was also related to impaired SERCA activity at 24 h of reperfusion. Administration of fasudil at 10 mg/Kg significantly attenuated ROCK activation during reperfusion and resulted in an improved SERCA activity which was closely associated with decreases in temporal activation of ER stress and IS changes. Interestingly, while both PI3K/Akt and JAK2/STAT3 signaling pathways played equal role in the protection offered by ROCK inhibition at 3 h of reperfusion, the rescued SERCA expression and activity at 24 h of reperfusion by fasudil was mainly due to JAK2/STAT3 activation, in which PI3K/Akt signaling shared much less roles.

Effects of N-n-butyl haloperidol iodide on the rat myocardial sarcoplasmic reticulum Ca(2+)-ATPase during ischemia/reperfusion

We have previously shown that N-n-butyl haloperidol iodide (F(2)), a newly synthesized compound, reduces ischemia/reperfusion (I/R) injury by preventing intracellular Ca(2+) overload through inhibiting L-type calcium channels and outward current of Na(+)/Ca(2+) exchanger. This study was to investigate the effects of F(2) on activity and protein expression of the rat myocardial sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) during I/R to discover other molecular mechanisms by which F(2) maintains intracellular Ca(2+) homeostasis. In an in vivo rat model of myocardial I/R achieved by occluding coronary artery for 30-60 min followed by 0-120 min reperfusion, treatment with F(2) (0.25, 0.5, 1, 2 and 4 mg/kg, respectively) dose-dependently inhibited the I/R-induced decrease in SERCA activity. However, neither different durations of I/R nor different doses of F(2) altered the expression levels of myocardial SERCA2a protein. These results indicate that F(2) exerts cardioprotective effects against I/R injury by inhibiting I/R-mediated decrease in SERCA activity by a mechanism independent of SERCA2a protein levels modulation.

Exercise tames the wild side of the Myc network: a hypothesis

We propose that the well-documented therapeutic actions of repeated physical activities over human lifespan are mediated by the rapidly turning over proto-oncogenic Myc (myelocytomatosis) network of transcription factors. This transcription factor network is unique in utilizing promoter and epigenomic (acetylation/deacetylation, methylation/demethylation) mechanisms for controlling genes that include those encoding intermediary metabolism (the primary source of acetyl groups), mitochondrial functions and biogenesis, and coupling their expression with regulation of cell growth and proliferation. We further propose that remote functioning of the network occurs because there are two arms of this network, which consists of driver cells (e.g., working myocytes) that metabolize carbohydrates, fats, proteins, and oxygen and produce redox-modulating metabolites such as H₂O₂, NAD⁺, and lactate. The exercise-induced products represent autocrine, paracrine, or endocrine signals for target recipient cells (e.g., aortic endothelium, hepatocytes, and pancreatic β-cells) in which the metabolic signals are coupled with genomic networks and interorgan signaling is activated. And finally, we propose that lactate, the major metabolite released from working muscles and transported into recipient cells, links the two arms of the signaling pathway. Recently discovered contributions of the Myc network in stem cell development and maintenance further suggest that regular physical activity may prevent age-related diseases such as cardiovascular pathologies, cancers, diabetes, and neurological functions through prevention of stem cell dysfunctions and depletion with aging. Hence, regular physical activities may attenuate the various deleterious effects of the Myc network on health, the wild side of the Myc-network, through modulating transcription of genes associated with glucose and energy metabolism and maintain a healthy human status.

Aldose reductase, oxidative stress, and diabetic mellitus

Diabetes mellitus (DM) is a complex metabolic disorder arising from lack of insulin production or insulin resistance (Diagnosis and classification of diabetes mellitus, 2007). DM is a leading cause of morbidity and mortality in the developed world, particularly from vascular complications such as atherothrombosis in the coronary vessels. Aldose reductase (AR; ALR2; EC 1.1.1.21), a key enzyme in the polyol pathway, catalyzes nicotinamide adenosine dinucleotide phosphate-dependent reduction of glucose to sorbitol, leading to excessive accumulation of intracellular reactive oxygen species (ROS) in various tissues of DM including the heart, vasculature, neurons, eyes, and kidneys. As an example, hyperglycemia through such polyol pathway induced oxidative stress, may have dual heart actions, on coronary blood vessel (atherothrombosis) and myocardium (heart failure) leading to severe morbidity and mortality (reviewed in Heather and Clarke, 2011). In cells cultured under high glucose conditions, many studies have demonstrated similar AR-dependent increases in ROS production, confirming AR as an important factor for the pathogenesis of many diabetic complications. Moreover, recent studies have shown that AR inhibitors may be able to prevent or delay the onset of cardiovascular complications such as ischemia/reperfusion injury, atherosclerosis, and atherothrombosis. In this review, we will focus on describing pivotal roles of AR in the pathogenesis of cardiovascular diseases as well as other diabetic complications, and the potential use of AR inhibitors as an emerging therapeutic strategy in preventing DM complications.

Physiological regulation of cardiac contractility by endogenous reactive oxygen species

Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of congestive heart failure. However, emerging evidence suggests the involvement of ROS in the regulation of various physiological cellular processes in the myocardium. In this review, we summarize the latest findings regarding the role of ROS in the acute regulation of cardiac contractility. We discuss ROS-dependent modulation of the inotropic responses to G protein-coupled receptor agonists (e.g. β-adrenergic receptor agonists and endothelin-1), the potential cellular sources of ROS (e.g. NAD(P)H oxidases and mitochondria) and the proposed end-targets and signalling pathways by which ROS affect contractility. Accumulating new data supports the fundamental role of endogenously generated ROS to regulate cardiac function under physiological conditions.

Ablation of junctin or triadin is associated with increased cardiac injury following ischaemia/reperfusion

AIMS

Junctin and triadin are calsequestrin-binding proteins that regulate sarcoplasmic reticulum (SR) Ca(2+) release by interacting with the ryanodine receptor. The levels of these proteins are significantly down-regulated in failing human hearts. However, the significance of such decreases is currently unknown. Here, we addressed the functional role of these accessory proteins in the heart's responses to ischaemia/reperfusion (I/R) injury.

METHODS AND RESULTS

Isolated mouse hearts were subjected to global I/R, and contractile parameters were assessed in wild-type (WT), junctin-knockout (JKO), and triadin-knockout (TKO) hearts. Both JKO and TKO were associated with significantly depressed post-I/R contractile recovery. However, ablation of triadin resulted in the most severe post-I/R phenotype. The additional contractile impairment of TKO hearts was not related to a mitochondrial death pathway, but attributed to endoplasmic reticulum (ER) stress-mediated apoptosis. Activation of the X-box-binding protein-1 and transcriptional up-regulation of C/EBP-homologous protein (CHOP) provided a molecular mechanism of caspase-12-dependent apoptosis in myocytes. In addition, elevation of cytosolic Ca(2+) during reperfusion was associated with the activation of calpain proteases and troponin I breakdown. Accordingly, treatment with the calpain inhibitor MDL-28170 significantly ameliorated post-I/R impairment of contractile recovery in intact hearts.

CONCLUSION

These findings indicate that deficiency of either junctin or triadin impairs the contractile recovery in post-ischaemic hearts, which appears to be primarily attributed to increased ER stress and activation of calpain.

A potential therapeutic role for aldose reductase inhibitors in the treatment of endotoxin-related inflammatory diseases

INTRODUCTION

Aldose reductase (AR) was initially thought to be involved in the secondary diabetic complications because of its glucose-reducing potential. However, evidence from recent studies indicates that AR is an excellent reducer of a number of lipid peroxidation-derived aldehydes as well as their glutathione conjugates, which regulate inflammatory signals initiated by oxidants such as cytokines, growth factors and bacterial endotoxins, and revealed the potential use of AR inhibition as an approach to prevent inflammatory complications.

AREAS COVERED

An extensive Internet and Medline search was performed to retrieve information on understanding the role of AR inhibition in the pathophysiology of endotoxin-mediated inflammatory disorders. Overall, inhibition of AR appears to be a promising strategy for the treatment of endotoxemia, sepsis and other related inflammatory diseases.

EXPERT OPINION

Current knowledge provides enough evidence to indicate that AR inhibition is a logical therapeutic strategy for the treatment of endotoxin-related inflammatory diseases. Since AR inhibitors have already gone to Phase III clinical studies for diabetic complications and found to be safe for human use, their use in endotoxin-related inflammatory diseases could be expedited. However, one of the major challenges will be the discovery of AR-regulated clinically relevant biomarkers to identify susceptible individuals at risk of developing inflammatory diseases, thereby warranting future research in this area.

Mitochondrial transporter ATP binding cassette mitochondrial erythroid is a novel gene required for cardiac recovery after ischemia/reperfusion

BACKGROUND

Oxidative stress and mitochondrial dysfunction are central mediators of cardiac dysfunction after ischemia/reperfusion. ATP binding cassette mitochondrial erythroid (ABC-me; ABCB10; mABC2) is a mitochondrial transporter highly induced during erythroid differentiation and predominantly expressed in bone marrow, liver, and heart. Until now, ABC-me function in heart was unknown. Several lines of evidence demonstrate that the yeast ortholog of ABC-me protects against increased oxidative stress. Therefore, ABC-me is a potential modulator of the outcome of ischemia/reperfusion in the heart.

METHODS AND RESULTS

Mice harboring 1 functional allele of ABC-me (ABC-me(+/-)) were generated by replacing ABC-me exons 2 and 3 with a neomycin resistance cassette. Cardiac function was assessed with Langendorff perfusion and echocardiography. Under basal conditions, ABC-me(+/-) mice had normal heart structure, hemodynamic function, mitochondrial respiration, and oxidative status. However, after ischemia/reperfusion, the recovery of hemodynamic function was reduced by 50% in ABC-me(+/-) hearts as a result of impairments in both systolic and diastolic function. This reduction was associated with impaired mitochondrial bioenergetic function and with oxidative damage to both mitochondrial lipids and sarcoplasmic reticulum calcium ATPase after reperfusion. Treatment of ABC-me(+/-) hearts with the superoxide dismutase/catalase mimetic EUK-207 prevented oxidative damage to mitochondria and sarcoplasmic reticulum calcium ATPase and restored mitochondrial and cardiac function to wild-type levels after reperfusion.

CONCLUSIONS

Inactivation of 1 allele of ABC-me increases the susceptibility to oxidative stress induced by ischemia/reperfusion, leading to increased oxidative damage to mitochondria and sarcoplasmic reticulum calcium ATPase and to impaired functional recovery. Thus, ABC-me is a novel gene that determines the ability to tolerate cardiac ischemia/reperfusion.

Hypoxia. 4. Hypoxia and ion channel function

The ability to sense and respond to oxygen deprivation is required for survival; thus, understanding the mechanisms by which changes in oxygen are linked to cell viability and function is of great importance. Ion channels play a critical role in regulating cell function in a wide variety of biological processes, including neuronal transmission, control of ventilation, cardiac contractility, and control of vasomotor tone. Since the 1988 discovery of oxygen-sensitive potassium channels in chemoreceptors, the effect of hypoxia on an assortment of ion channels has been studied in an array of cell types. In this review, we describe the effects of both acute and sustained hypoxia (continuous and intermittent) on mammalian ion channels in several tissues, the mode of action, and their contribution to diverse cellular processes.

Redox signaling in cardiac myocytes

The heart has complex mechanisms that facilitate the maintenance of an oxygen supply-demand balance necessary for its contractile function in response to physiological fluctuations in workload as well as in response to chronic stresses such as hypoxia, ischemia, and overload. Redox-sensitive signaling pathways are centrally involved in many of these homeostatic and stress-response mechanisms. Here, we review the main redox-regulated pathways that are involved in cardiac myocyte excitation-contraction coupling, differentiation, hypertrophy, and stress responses. We discuss specific sources of endogenously generated reactive oxygen species (e.g., mitochondria and NADPH oxidases of the Nox family), the particular pathways and processes that they affect, the role of modulators such as thioredoxin, and the specific molecular mechanisms that are involved-where this knowledge is available. A better understanding of this complex regulatory system may allow the development of more specific therapeutic strategies for heart diseases.

N-n-butyl haloperidol iodide preserves cardiomyocyte calcium homeostasis during hypoxia/ischemia

AIMS

N-n-Butyl haloperidol iodide (F(2)) is a novel compound derived from haloperidol. In our previous work, F(2) was found to be an L-type calcium channel blocker which played a protective role in rat heart ischemic-reperfusion injury in a dose-dependent manner. In the current study, we aimed to investigate the effects and some possible mechanisms of F(2) on calcium transients in hypoxic/ischemic rat cardiac myocytes.

METHODS AND RESULTS

Calcium transients' images of rat cardiac myocytes were recorded during simulated hypoxia, using a confocal calcium imaging system. The amplitude, rising time from 25% to 75% (RT25-75), decay time from 75% to 25% (DT75-25) of calcium transients, and resting [Ca(2+)](i) were extracted from the images by self-coding programs. In this study, hypoxia produced a substantial increase in diastolic [Ca(2+)](i) and reduced the amplitude of calcium transients. Both RT25-75 and DT75-25 of Ca(2+) transients were significantly prolonged. And F(2) could reduce the increase in resting [Ca(2+)](i)and the prolongation of RT25-75 and DT75-25 of Ca(2+) transients during hypoxia. F(2) also inhibited the reduction in amplitude of calcium transients which was caused by 30-min hypoxia. The activity of SERCA2a (sarcoplasmic reticulum Ca(2+)-ATPase, determined by test kits) decreased after 30-min ischemia, and intravenous F(2) in rats could ameliorate the decreased activity of SERCA2a. The inward and outward currents of NCX (recorded by whole-cell patch-clamp analysis) were reduced during 10-min hypoxia, and F(2) further inhibited the outward currents of NCX during 10-min hypoxia. All these data of SERCA2a and NCX might be responsible for the changes in calcium transients during hypoxia.

CONCLUSION

Our data suggest that F(2) reduced changes in calcium transients that caused by hypoxia/ischemia, which was regarded to be a protective role in calcium homeostasis of ventricular myocytes, probably via changing the function of SERCA2a.

Evaluation of the aldose reductase inhibitor fidarestat on ischemia-reperfusion injury in rat retina

This study evaluated the effects of retinal ischemia-reperfusion (IR) injury and pre-treatment with the potent and specific aldose reductase inhibitor fidarestat on apoptosis, aldose reductase and sorbitol dehydrogenase expression, sorbitol pathway intermediate concentrations, and oxidative-nitrosative stress. Female Wistar rats were pre-treated with either vehicle (N-methyl-D-glucamine) or fidarestat, 32 mg kg(-1) d(-1) for both, in the right jugular vein, for 3 consecutive days. A group of vehicle- and fidarestat-treated rats were subjected to 45-min retinal ischemia followed by 24-h reperfusion. Ischemia was induced 30 min after the last vehicle or fidarestat administration. Retinal IR resulted in a remarkable increase in retinal cell death. The number of TUNEL-positive nuclei increased 48-fold in the IR group compared with non-ischemic controls (p<0.01), and this increase was partially prevented by fidarestat. AR expression (Western blot analysis) increased by 19% in the IR group (p<0.05), and this increase was prevented by fidarestat. Sorbitol dehydrogenase and nitrated protein expressions were similar among all experimental groups. Retinal sorbitol concentrations tended to increase in the IR group but the difference with non-ischemic controls did not achieve statistical significance (p=0.08). Retinal fructose concentrations were 2.2-fold greater in the IR group than in the non-ischemic controls (p<0.05). Fidarestat pre-treatment of rats subjected to IR reduced retinal sorbitol concentration to the levels in non-ischemic controls. Retinal fructose concentrations were reduced by 41% in fidarestat-pre-treated IR group vs. untreated ischemic controls (p=0.0517), but remained 30% higher than in the non-ischemic control group. In conclusion, IR injury to rat retina is associated with a dramatic increase in cell death, elevated AR expression and sorbitol pathway intermediate accumulation. These changes were prevented or alleviated by the AR inhibitor fidarestat. The results identify AR as an important therapeutic target for diseases involving IR injury, and provide the rationale for development of fidarestat and other AR inhibitors.