Computational Modeling Analysis of Generation of Reactive Oxygen Species by Mitochondrial Assembled and Disintegrated Complex II

Mitochondrial Glutathione in Cellular Redox Homeostasis and Disease Manifestation

Mitochondria are critical for providing energy to maintain cell viability. Oxidative phosphorylation involves the transfer of electrons from energy substrates to oxygen to produce adenosine triphosphate. Mitochondria also regulate cell proliferation, metastasis, and deterioration. The flow of electrons in the mitochondrial respiratory chain generates reactive oxygen species (ROS), which are harmful to cells at high levels. Oxidative stress caused by ROS accumulation has been associated with an increased risk of cancer, and cardiovascular and liver diseases. Glutathione (GSH) is an abundant cellular antioxidant that is primarily synthesized in the cytoplasm and delivered to the mitochondria. Mitochondrial glutathione (mGSH) metabolizes hydrogen peroxide within the mitochondria. A long-term imbalance in the ratio of mitochondrial ROS to mGSH can cause cell dysfunction, apoptosis, necroptosis, and ferroptosis, which may lead to disease. This study aimed to review the physiological functions, anabolism, variations in organ tissue accumulation, and delivery of GSH to the mitochondria and the relationships between mGSH levels, the GSH/GSH disulfide (GSSG) ratio, programmed cell death, and ferroptosis. We also discuss diseases caused by mGSH deficiency and related therapeutics.

Computational Modeling Analysis of Kinetics of Fumarate Reductase Activity and ROS Production during Reverse Electron Transfer in Mitochondrial Respiratory Complex II

Reverse electron transfer in mitochondrial complex II (CII) plays an important role in hypoxia/anoxia, in particular, in ischemia, when the blood supply to an organ is disrupted and oxygen is not available. A computational model of CII was developed in this work to facilitate the quantitative analysis of the kinetics of quinol-fumarate reduction as well as ROS production during reverse electron transfer in CII. The model consists of 20 ordinary differential equations and 7 moiety conservation equations. The parameter values were determined at which the kinetics of electron transfer in CII in both forward and reverse directions would be explained simultaneously. The possibility of the existence of the "tunnel diode" behavior in the reverse electron transfer in CII, where the driving force is QH₂, was tested. It was found that any high concentrations of QH₂ and fumarate are insufficient for the appearance of a tunnel effect. The results of computer modeling show that the maximum rate of succinate production cannot provide a high concentration of succinate in ischemia. Furthermore, computational modeling results predict a very low rate of ROS production, about 50 pmol/min/mg mitochondrial protein, which is considerably less than 1000 pmol/min/mg protein observed in CII in forward direction.

Kinetic Mathematical Modeling of Oxidative Phosphorylation in Cardiomyocyte Mitochondria

Oxidative phosphorylation (OXPHOS) is an oxygen-dependent process that consumes catabolized nutrients to produce adenosine triphosphate (ATP) to drive energy-dependent biological processes such as excitation-contraction coupling in cardiomyocytes. In addition to in vivo and in vitro experiments, in silico models are valuable for investigating the underlying mechanisms of OXPHOS and predicting its consequences in both physiological and pathological conditions. Here, we compare several prominent kinetic models of OXPHOS in cardiomyocytes. We examine how their mathematical expressions were derived, how their parameters were obtained, the conditions of their experimental counterparts, and the predictions they generated. We aim to explore the general landscape of energy production mechanisms in cardiomyocytes for future in silico models.

Mathematical Modeling of ROS Production and Diode-like Behavior in the SDHA/SDHB Subcomplex of Succinate Dehydrogenases in Reverse Quinol-Fumarate Reductase Direction

Succinate dehydrogenase (SDH) plays an important role in reverse electron transfer during hypoxia/anoxia, in particular, in ischemia, when blood supply to an organ is disrupted, and oxygen is not available. It was detected in the voltammetry studies about three decades ago that the SDHA/SDHB subcomplex of SDH can have such a strong nonlinear property as a "tunnel-diode" behavior in reverse quinol-fumarate reductase direction. The molecular and kinetic mechanisms of this phenomenon, that is, a strong drop in the rate of fumarate reduction as the driving force is increased, are still unclear. In order to account for this property of SDH, we developed and analyzed a mechanistic computational model of reverse electron transfer in the SDHA/SDHB subcomplex of SDH. It was shown that a decrease in the rate of succinate release from the active center during fumarate reduction quantitatively explains the experimentally observed tunnel-diode behavior in SDH and threshold values of the electrode potential of about -80 mV. Computational analysis of ROS production in the SDHA/SDHB subcomplex of SDH during reverse electron transfer predicts that the rate of ROS production decreases when the tunnel-diode behavior appears. These results predict a low rate of ROS production by the SDHA/SDHB subcomplex of SDH during ischemia.

A Comprehensive Overview of the Complex Role of Oxidative Stress in Aging, The Contributing Environmental Stressors and Emerging Antioxidant Therapeutic Interventions

Introduction

Aging is a normal, inevitable, irreversible, and progressive process which is driven by internal and external factors. Oxidative stress, that is the imbalance between prooxidant and antioxidant molecules favoring the first, plays a key role in the pathophysiology of aging and comprises one of the molecular mechanisms underlying age-related diseases. However, the oxidative stress theory of aging has not been successfully proven in all animal models studying lifespan, meaning that altering oxidative stress/antioxidant defense systems did not always lead to a prolonged lifespan, as expected. On the other hand, animal models of age-related pathological phenotypes showed a well-correlated relationship with the levels of prooxidant molecules. Therefore, it seems that oxidative stress plays a more complicated role than the one once believed and this role might be affected by the environment of each organism. Environmental factors such as UV radiation, air pollution, and an unbalanced diet, have also been implicated in the pathophysiology of aging and seem to initiate this process more rapidly and even at younger ages.

Aim

The purpose of this review is to elucidate the role of oxidative stress in the physiology of aging and the effect of certain environmental factors in initiating and sustaining this process. Understanding the pathophysiology of aging will contribute to the development of strategies to postpone this phenomenon. In addition, recent studies investigating ways to alter the antioxidant defense mechanisms in order to prevent aging will be presented.

Conclusions

Careful exposure to harmful environmental factors and the use of antioxidant supplements could potentially affect the biological processes driving aging and slow down the development of age-related diseases. Maybe a prolonged lifespan could not be achieved by this strategy alone, but a longer healthspan could also be a favorable target.

Calpain-mediated protein targets in cardiac mitochondria following ischemia-reperfusion

Calpain 1 and 2 (CPN1/2) are calcium-dependent cysteine proteases that exist in cytosol and mitochondria. Pharmacologic inhibition of CPN1/2 decreases cardiac injury during ischemia (ISC)-reperfusion (REP) by improving mitochondrial function. However, the protein targets of CPN1/2 activation during ISC-REP are unclear. CPN1/2 include a large subunit and a small regulatory subunit 1 (CPNS1). Genetic deletion of CPNS1 eliminates the activities of both CPN1 and CPN2. Conditional cardiomyocyte specific CPNS1 deletion mice were used in the present study to clarify the role of CPN1/2 activation in mitochondrial damage during ISC-REP with an emphasis on identifying the potential protein targets of CPN1/2. Isolated hearts from wild type (WT) or CPNS1 deletion mice underwent 25 min in vitro global ISC and 30 min REP. Deletion of CPNS1 led to decreased cytosolic and mitochondrial calpain 1 activation compared to WT. Cardiac injury was decreased in CPNS1 deletion mice following ISC-REP as shown by the decreased infarct size compared to WT. Compared to WT, mitochondrial function was improved in CPNS1 deletion mice following ischemia-reperfusion as shown by the improved oxidative phosphorylation and decreased susceptibility to mitochondrial permeability transition pore opening. H2O2 generation was also decreased in mitochondria from deletion mice following ISC-REP compared to WT. Deletion of CPNS1 also resulted in less cytochrome c and truncated apoptosis inducing factor (tAIF) release from mitochondria. Proteomic analysis of the isolated mitochondria showed that deletion of CPNS1 increased the content of proteins functioning in regulation of mitochondrial calcium homeostasis (paraplegin and sarcalumenin) and complex III activity. These results suggest that activation of CPN1 increases cardiac injury during ischemia-reperfusion by impairing mitochondrial function and triggering cytochrome c and tAIF release from mitochondria into cytosol.

Metabolic Therapy of Heart Failure: Is There a Future for B Vitamins?

Heart failure (HF) is a plague of the aging population in industrialized countries that continues to cause many deaths despite intensive research into more effective treatments. Although the therapeutic arsenal to face heart failure has been expanding, the relatively short life expectancy of HF patients is pushing towards novel therapeutic strategies. Heart failure is associated with drastic metabolic disorders, including severe myocardial mitochondrial dysfunction and systemic nutrient deprivation secondary to severe cardiac dysfunction. To date, no effective therapy has been developed to restore the cardiac energy metabolism of the failing myocardium, mainly due to the metabolic complexity and intertwining of the involved processes. Recent years have witnessed a growing scientific interest in natural molecules that play a pivotal role in energy metabolism with promising therapeutic effects against heart failure. Among these molecules, B vitamins are a class of water soluble vitamins that are directly involved in energy metabolism and are of particular interest since they are intimately linked to energy metabolism and HF patients are often B vitamin deficient. This review aims at assessing the value of B vitamin supplementation in the treatment of heart failure.

Critical requirement of SOS1 RAS-GEF function for mitochondrial dynamics, metabolism, and redox homeostasis

SOS1 ablation causes specific defective phenotypes in MEFs including increased levels of intracellular ROS. We showed that the mitochondria-targeted antioxidant MitoTEMPO restores normal endogenous ROS levels, suggesting predominant involvement of mitochondria in generation of this defective SOS1-dependent phenotype. The absence of SOS1 caused specific alterations of mitochondrial shape, mass, and dynamics accompanied by higher percentage of dysfunctional mitochondria and lower rates of electron transport in comparison to WT or SOS2-KO counterparts. SOS1-deficient MEFs also exhibited specific alterations of respiratory complexes and their assembly into mitochondrial supercomplexes and consistently reduced rates of respiration, glycolysis, and ATP production, together with distinctive patterns of substrate preference for oxidative energy metabolism and dependence on glucose for survival. RASless cells showed defective respiratory/metabolic phenotypes reminiscent of those of SOS1-deficient MEFs, suggesting that the mitochondrial defects of these cells are mechanistically linked to the absence of SOS1-GEF activity on cellular RAS targets. Our observations provide a direct mechanistic link between SOS1 and control of cellular oxidative stress and suggest that SOS1-mediated RAS activation is required for correct mitochondrial dynamics and function.

Preventing Myocardial Injury Following Non-Cardiac Surgery: A Potential Role for Preoperative Antioxidant Therapy with Ubiquinone

Over 240 million non-cardiac operations occur each year and are associated with a 15-20% incidence of adverse perioperative cardiovascular events. Unfortunately, preoperative therapies that have been useful for chronic ischemic heart diseases, such as coronary artery revascularization, antiplatelet agents, and beta-blockers have failed to improve outcomes. In a pre-clinical swine model of ischemic heart disease, we showed that daily administration of ubiquinone (coenzyme Q₁₀, CoQ₁₀) enhances the antioxidant status of mitochondria within chronically ischemic heart tissue, potentially via a PGC1α-dependent mechanism. In a randomized controlled trial, among high-risk patients undergoing elective vascular surgery, we showed that NT Pro-BNP levels are an important means of risk-stratification during the perioperative period and can be lowered with administration of CoQ₁₀ (400 mg/day) for 3 days prior to surgery. The review provides background information for the role of oxidant stress and inflammation during high-risk operations and the potential novel application of ubiquinone as a preoperative antioxidant therapy that might reduce perioperative adverse cardiovascular outcomes.