Complex oscillatory redox dynamics with signaling potential at the edge between normal and pathological mitochondrial function

The time-keeping properties bestowed by oscillatory behavior on functional rhythms represent an evolutionarily conserved trait in living systems. Mitochondrial networks function as timekeepers maximizing energetic output while tuning reactive oxygen species (ROS) within physiological levels compatible with signaling. In this work, we explore the potential for timekeeping functions dependent on mitochondrial dynamics with the validated two-compartment mitochondrial energetic-redox (ME-R) computational model, that takes into account (a) four main redox couples [NADH, NADPH, GSH, Trx(SH)2], (b) scavenging systems (glutathione, thioredoxin, SOD, catalase) distributed in matrix and extra-matrix compartments, and (c) transport of ROS species between them. Herein, we describe that the ME-R model can exhibit highly complex oscillatory dynamics in energetic/redox variables and ROS species, consisting of at least five frequencies with modulated amplitudes and period according to power spectral analysis. By stability analysis we describe that the extent of steady state—as against complex oscillatory behavior—was dependent upon the abundance of Mn and Cu, Zn SODs, and their interplay with ROS production in the respiratory chain. Large parametric regions corresponding to oscillatory dynamics of increasingly complex waveforms were obtained at low Cu, Zn SOD concentration as a function of Mn SOD. This oscillatory domain was greatly reduced at higher levels of Cu, Zn SOD. Interestingly, the realm of complex oscillations was located at the edge between normal and pathological mitochondrial energetic behavior, and was characterized by oxidative stress. We conclude that complex oscillatory dynamics could represent a frequency- and amplitude-modulated H2O2 signaling mechanism that arises under intense oxidative stress. By modulating SOD, cells could have evolved an adaptive compromise between relative constancy and the flexibility required under stressful redox/energetic conditions.Fil: Kembro, Jackelyn Melissa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Cortassa, Sonia del Carmen. University Johns Hopkins; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aon, Miguel A.. University Johns Hopkins; Estados Unido

The key role of nitric oxide in hypoxia: hypoxic vasodilation and energy supply-demand matching

Significance: a mismatch between energy supply and demand induces tissue hypoxia with the potential to cause cell death and organ failure. Whenever arterial oxygen concentration is reduced, increases in blood flow - 'hypoxic vasodilation' - occur in an attempt to restore oxygen supply. Nitric oxide is a major signalling and effector molecule mediating the body's response to hypoxia, given its unique characteristics of vasodilation (improving blood flow and oxygen supply) and modulation of energetic metabolism (reducing oxygen consumption and promoting utilization of alternative pathways). Recent advances: this review covers the role of oxygen in metabolism and responses to hypoxia, the hemodynamic and metabolic effects of nitric oxide, and mechanisms underlying the involvement of nitric oxide in hypoxic vasodilation. Recent insights into nitric oxide metabolism will be discussed, including the role for dietary intake of nitrate, endogenous nitrite reductases, and release of nitric oxide from storage pools. The processes through which nitric oxide levels are elevated during hypoxia are presented, namely (i) increased synthesis from nitric oxide synthases, increased reduction of nitrite to nitric oxide by heme- or pterin-based enzymes and increased release from nitric oxide stores, and (ii) reduced deactivation by mitochondrial cytochrome c oxidase. Critical issues: several reviews covered modulation of energetic metabolism by nitric oxide, while here we highlight the crucial role NO plays in achieving cardiocirculatory homeostasis during acute hypoxia through both vasodilation and metabolic suppression Future directions: we identify a key position for nitric oxide in the body's adaptation to an acute energy supply-demand mismatc

Following red blood cells in a pulmonary capillary

The red blood cells or erythrocytes are biconcave shaped cells and consist mostly in a membrane delimiting a cytosol with a high concentration in hemoglobin. This membrane is highly deformable and allows the cells to go through narrow passages like the capillaries which diameters can be much smaller than red blood cells one. They carry oxygen thanks to hemoglobin, a complex molecule that have very high affinity for oxygen. The capacity of erythrocytes to load and unload oxygen is thus a determinant factor in their efficacy. In this paper, we will focus on the pulmonary capillary where red blood cells capture oxygen. We propose a camera method in order to numerically study the behavior of the red blood cell along a whole capillary. Our goal is to understand how erythrocytes geometrical changes along the capillary can affect its capacity to capture oxygen. The first part of this document presents the model chosen for the red blood cells along with the numerical method used to determine and follow their shapes along the capillary. The membrane of the red blood cell is complex and has been modelled by an hyper-elastic approach coming from Mills et al (2004). This camera method is then validated and confronted with a standard ALE method. Some geometrical properties of the red blood cells observed in our simulations are then studied and discussed. The second part of this paper deals with the modeling of oxygen and hemoglobin chemistry in the geometries obtained in the first part. We have implemented a full complex hemoglobin behavior with allosteric states inspired from Czerlinski et al (1999).Comment: 17 page

Thermodynamically-Constrained Computational Modeling of Lung Tissue Bioenergetics and the Effect of Hyperoxia-Induced Acute Lung Injury

Altered lung tissue bioenergetics is an important and early step in the pathogenesis of acute lung injury (ALI), one of the most common causes of admission to medical ICUs. A wealth of information exists regarding the effect of ALI on specific mitochondrial and cytosolic processes in isolated mitochondria, cultured endothelial cell, and intact lungs. However, the interdependence of lung cellular processes makes it difficult to quantify the impact of a change in a single or multiple cellular process(es) on overall lung tissue bioenergetics. Integrating bioenergetics data from isolated mitochondria and intact lung is necessary for determining the functional significance of targeting a specific cellular process for prognostic and/or therapeutic purposes. Thus, the main objective of my dissertation was to develop and validate comprehensive, thermodynamically-constrained models of mitochondrial and lung tissue bioenergetics, and to use these models to predict the impact of ALI-induced changes in mitochondrial and cytosolic processes on lung tissue bioenergetics. For Aim 1, I developed an integrated model of the bioenergetics of mitochondria isolated from rat lungs, which incorporates the major biochemical reactions and transport processes in lung mitochondria. The model was validated by assessing its ability to predict experimental data not used for parameter estimation. The model provides important insights into the bioenergetics of lung mitochondria and how they differ from those of mitochondria from other organs. For Aim 2, I developed and validated an integrated computational model of lung tissue bioenergetics. The model expanded the computational model developed under Aim 1 by accounting for glucose uptake and phosphorylation, glycolysis, and the pentose phosphate pathway. The model was then used to gain novel insights into how lung tissue glycolytic rate is regulated by exogenous substrates, and assess differences in the bioenergetics of isolated mitochondria isolated from lung tissue and those of mitochondria in intact lungs. For Aim 3, the models developed under Aims 1 and 2 were used to quantify the impact of previously measured changes in specific mitochondrial processes in a rat model of clinical ALI on lung mitochondrial and tissue bioenergetics. To the best of our knowledge, the two computational models are the first for lung mitochondrial and tissue bioenergetics. These models provide a mechanistic and quantitative framework for integrating available lung tissue bioenergetics data, for testing novel hypotheses regarding the role of different cytosolic and mitochondrial processes in lung tissue bioenergetics and the pathogenesis of ALI, and for identifying potential therapeutic targets for ALI

Itaconate modulates tricarboxylic acid and redox metabolism to mitigate reperfusion injury.

ObjectivesCerebral ischemia/reperfusion (IR) drives oxidative stress and injurious metabolic processes that lead to redox imbalance, inflammation, and tissue damage. However, the key mediators of reperfusion injury remain unclear, and therefore, there is considerable interest in therapeutically targeting metabolism and the cellular response to oxidative stress.MethodsThe objective of this study was to investigate the molecular, metabolic, and physiological impact of itaconate treatment to mitigate reperfusion injuries in in vitro and in vivo model systems. We conducted metabolic flux and bioenergetic studies in response to exogenous itaconate treatment in cultures of primary rat cortical neurons and astrocytes. In addition, we administered itaconate to mouse models of cerebral reperfusion injury with ischemia or traumatic brain injury followed by hemorrhagic shock resuscitation. We quantitatively characterized the metabolite levels, neurological behavior, markers of redox stress, leukocyte adhesion, arterial blood flow, and arteriolar diameter in the brains of the treated/untreated mice.ResultsWe demonstrate that the "immunometabolite" itaconate slowed tricarboxylic acid (TCA) cycle metabolism and buffered redox imbalance via succinate dehydrogenase (SDH) inhibition and induction of anti-oxidative stress response in primary cultures of astrocytes and neurons. The addition of itaconate to reperfusion fluids after mouse cerebral IR injury increased glutathione levels and reduced reactive oxygen/nitrogen species (ROS/RNS) to improve neurological function. Plasma organic acids increased post-reperfusion injury, while administration of itaconate normalized these metabolites. In mouse cranial window models, itaconate significantly improved hemodynamics while reducing leukocyte adhesion. Further, itaconate supplementation increased survival in mice experiencing traumatic brain injury (TBI) and hemorrhagic shock.ConclusionsWe hypothesize that itaconate transiently inhibits SDH to gradually "awaken" mitochondrial function upon reperfusion that minimizes ROS and tissue damage. Collectively, our data indicate that itaconate acts as a mitochondrial regulator that controls redox metabolism to improve physiological outcomes associated with IR injury

Modeling of Oxygen Transport and Cellular Energetics Explains Observations on In Vivo Cardiac Energy Metabolism

Observations on the relationship between cardiac work rate and the levels of energy metabolites adenosine triphosphate (ATP), adenosine diphosphate (ADP), and phosphocreatine (CrP) have not been satisfactorily explained by theoretical models of cardiac energy metabolism. Specifically, the in vivo stability of ATP, ADP, and CrP levels in response to changes in work and respiratory rate has eluded explanation. Here a previously developed model of mitochondrial oxidative phosphorylation, which was developed based on data obtained from isolated cardiac mitochondria, is integrated with a spatially distributed model of oxygen transport in the myocardium to analyze data obtained from several laboratories over the past two decades. The model includes the components of the respiratory chain, the F(0)F(1)-ATPase, adenine nucleotide translocase, and the mitochondrial phosphate transporter at the mitochondrial level; adenylate kinase, creatine kinase, and ATP consumption in the cytoplasm; and oxygen transport between capillaries, interstitial fluid, and cardiomyocytes. The integrated model is able to reproduce experimental observations on ATP, ADP, CrP, and inorganic phosphate levels in canine hearts over a range of workload and during coronary hypoperfusion and predicts that cytoplasmic inorganic phosphate level is a key regulator of the rate of mitochondrial respiration at workloads for which the rate of cardiac oxygen consumption is less than or equal to approximately 12 μmol per minute per gram of tissue. At work rates corresponding to oxygen consumption higher than 12 μmol min(−1) g(−1), model predictions deviate from the experimental data, indicating that at high work rates, additional regulatory mechanisms that are not currently incorporated into the model may be important. Nevertheless, the integrated model explains metabolite levels observed at low to moderate workloads and the changes in metabolite levels and tissue oxygenation observed during graded hypoperfusion. These findings suggest that the observed stability of energy metabolites emerges as a property of a properly constructed model of cardiac substrate transport and mitochondrial metabolism. In addition, the validated model provides quantitative predictions of changes in phosphate metabolites during cardiac ischemia

Design of instrumentation for metabolic monitoring of the Adélie penguin : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University

The motivating question for the work described in this thesis was "How does the Adélie penguin cope with cold?" It was reasoned that the time-scale of temperature changes in Antarctica precluded all but metabolic and physiological responses. To determine these, a system capable of measuring and recording these biological variables in the penguins natural environment, was designed. A device, based on the principles of near infrared spectroscopy, was developed that could measure the relative oxygen saturation of haemoglobin and the reduction state of cytochrome oxidase as well as heart rate and blood volume. The completed device was housed in a black, waterproof, plastic container, measuring 65mm x 92mm x 25mm and weighing 132.7g. Co-ordination of measurements was achieved with operating system-like control software implemented in Motorola HC11 assembly code. Synchronous detection was used for signal acquisition and a pulse algorithm, implemented in assembly code, allowed real time pulse measurement from the input signals. Programs were written in Matlab and C++ to investigate the characteristics and limits of these techniques. Preliminary testing of the device on human subjects successfully showed changes in metabolic state as a result of physical activity. The results of field testing on Adélie penguins were unable to answer the original question due to a number of physical factors. However, the success of human trials suggests that, with modification and improvement, the device has potential as a valuable research instrument, applicable to a variety of other species

A COMPUTATIONAL MODEL RELATING TISSUE OXYGEN CONSUMPTION TO OXYGEN DELIVERY IN A KROGH CYLINDER MODEL OF SKELETAL MUSCLE

Oxygen transport from a capillary to skeletal muscle tissue is a complex process that involves convective and diffusive mechanisms to deliver adequate oxygen to meet tissue metabolic activities. Typically, oxygen uptake in tissue is set by oxygen demand, which is set by metabolic activity. The relationship between the oxygen consumption (VO2) of an isolated perfused tissue and the rate of delivery of oxygen (QO2) to the tissue has been a subject of interest to many investigators over the past century. Experiments have shown that there is a critical value of QO2 below which tissue VO2 begins to decline. The Michaelis-Menten kinetics model for oxygen-dependent oxygen consumption is investigated as a modeling assumption in a computational study of oxygen transport from capillaries to skeletal muscle tissue using the Krogh cylinder model. The work presented in this thesis extends Schumacker and Samsel’s computational model to include the more accurate Michaelis-Menten kinetic description of the oxygen tension (PO2) dependence of VO2, using the parameter km, the PO2 for half-maximal VO2. This study aims to predict the relationship between oxygen consumption and oxygen delivery by considering the oxygen transport processes at the microvascular level. The dependence of oxygen consumption on oxygen delivery, critical oxygen extraction, critical oxygen delivery, and tissue oxygen tension profiles were examined as a function of km. The critical oxygen delivery was found to depend on km, increasing nonlinearly as km increases. The fractional oxygen extraction at the critical QO2 varied inversely with km. The venous oxygen partial pressure (PvO2) also varied with km. Finally, the predicted radial profile of tissue oxygen tension at the critical QO2 depended on km. At lower critical oxygen delivery and at lower km, the critical radial distance at which tissue oxygen partial pressure was found to be km occurred closer to the end of the capillary. The present results suggest that the value of km influences the relationship between tissue oxygen consumption and oxygen supply as the oxygen delivery is reduced to the critical point. Ultimately, km becomes the fundamental parameter that specifies how oxygen consumption depends on oxygen tension instead of the critical mitochondrial oxygen tension