Cyclosporine A normalizes mitochondrial coupling, reactive oxygen species production, and inflammation and partially restores skeletal muscle maximal oxidative capacity in experimental aortic cross-clamping

Targeting Mitochondrial Dynamics during Lower-Limb Ischemia Reperfusion in Young and Old Mice: Effect of Mitochondrial Fission Inhibitor-1 (mDivi-1)

Peripheral arterial disease (PAD) strikes more than 200 million people worldwide and has a severe prognosis by potentially leading to limb amputation and/or death, particularly in older patients. Skeletal muscle mitochondrial dysfunctions and oxidative stress play major roles in this disease in relation with ischemia-reperfusion (IR) cycles. Mitochondrial dynamics through impairment of fission-fusion balance may contribute to skeletal muscle pathophysiology, but no data were reported in the setting of lower-limb IR despite the need for new therapeutic options. We, therefore, investigated the potential protective effect of mitochondrial division inhibitor-1 (mDivi-1; 50 mg/kg) in young (23 weeks) and old (83 weeks) mice submitted to two-hour ischemia followed by two-hour reperfusion on systemic lactate, muscle mitochondrial respiration and calcium retention capacity, and on transcripts specific for oxidative stress and mitochondrial dynamics. At the systemic levels, an IR-related increase in circulating lactate was still major despite mDivi-1 use (+305.9% p < 0.0001, and +269.4% p < 0.0001 in young and old mice, respectively). Further, IR-induced skeletal muscle mitochondrial dysfunctions (more severely impaired mitochondrial respiration in old mice (OXPHOS CI state, -68.2% p < 0.0001 and -84.9% p < 0.0001 in 23- and 83-week mice) and reduced calcium retention capacity (-46.1% p < 0.001 and -48.2% p = 0.09, respectively) were not corrected by mDivi-1 preconditioning, whatever the age. Further, mDivi-1 treatment did not oppose superoxide anion production (+71.4% p < 0.0001 and +37.5% p < 0.05, respectively). At the transcript level, markers of antioxidant enzymes (SOD 1, SOD 2, catalase, and GPx) and fission markers (Drp1, Fis) remained unchanged or tended to be decreased in the ischemic leg. Fusion markers such as mitofusin 1 or 2 decreased significantly after IR in both groups. In conclusion, aging enhanced the deleterious effects or IR on muscle mitochondrial respiration, and in this setting of lower-limb IR, mDivi-1 failed to protect the skeletal muscle both in young and old mice.

Peripheral Blood Mononuclear Cells Mitochondrial Respiration and Superoxide Anion after Heart Transplantation

INTRODUCTION

The mitochondrial function of circulating peripheral blood mononuclear cells (PBMCs) is an interesting new approach to cardiac diseases. Thus, PBMC's mitochondrial respiration decreases in relation to heart failure severity. However, no data are available on heart-transplanted patients (Htx).

POPULATION AND METHODS

We determined PBMCs mitochondrial respiration by high-resolution respirometry (Oroboros Instruments) and superoxide anion production using electron paramagnetic resonance (Bruker-Biospin) in 20 healthy subjects and 20 matched Htx and investigated clinical, biological, echocardiographic, coronarography and biopsy characteristics.

RESULTS

PBMCs mitochondrial respiratory chain complex II respiration was decreased in Htx (4.69 ± 0.84 vs. 7.69 ± 1.00 pmol/s/million cell in controls and Htx patients, respectively; p = 0.007) and complex IV respiration was increased (24.58 ± 2.57 vs. 15.68 ± 1.67 pmol/s/million cell; p = 0.0035). Superoxide anion production was also increased in Htx (1.47 ± 0.10 vs. 1.15 ± 0.10 µmol/min; p = 0.041). The leucocyte-to-lymphocyte ratio was increased in Htx, whom complex II correlated with leucocyte number (r = 0.51, p = 0.02) and with the left ventricular posterior wall peak early diastolic myocardial velocity (r = -0.62, p = 0.005). Complex IV was increased in the two patients with acute rejection and correlated negatively with Htx's isovolumetric relation time (r = -0.45, p = 0.045).

DISCUSSION

Although presenting with normal systolic function, Htx demonstrated abnormal PBMC's mitochondrial respiration. Unlike immunosuppressive therapies, subclinical diastolic dysfunction might be involved in these changes. Additionally, lymphopenia might reduce complex II, and acute rejection enhances complex IV respirations.

CONCLUSION

PBMC's mitochondrial respiration appears modified in Htx, potentially linked to cellular shift, mild diastolic dysfunction and/or acute rejection.

Pathophysiology of Heart Failure: A Role for Peripheral Blood Mononuclear Cells Mitochondrial Dysfunction?

Heart failure (HF) is a leading cause of hospitalization in patients aged more than 65 years and is associated with high mortality rates. A better comprehension of its physiopathology is still needed, and, in addition to neurohormonal systems and sodium glucose co-transporter 2 modulations, recent studies focus on the mitochondrial respiration of peripheral blood circulating cells (PBMCs). Thus, cardiovascular metabolic risk factors and cellular switch with an increased neutrophil/lymphocytes ratio might favor the decreased PBMC mitochondrial respiration observed in relation with HF severity. PBMCs are implicated in the immune system function and mitochondrial dysfunction of PBMC, potentially induced by their passage through a damaged heart and by circulating mitoDAMPs, which can lead to a vicious circle, thus sustaining negative cardiac remodeling during HF. This new approach of HF complex pathophysiology appears to be a promising field of research, and further studies on acute and chronic HF with reduced or preserved LVEF are warranted to better understand whether circulating PBMC mitochondrial function and mitoDAMPs follow-ups in HF patients might show diagnosis, prognosis or therapeutic usefulness.

The Role of Ca2 + in Maturation and Reprogramming of Bovine Oocytes: A System Study of Low-Calcium Model

[Ca²⁺]_i is essential for mammalian oocyte maturation and early embryonic development, as those processes are Ca²⁺ dependent. In the present study, we investigated the effect of [Ca²⁺]_i on in vitro maturation and reprogramming of oocytes in a lower calcium model of oocyte at metaphase II (MII) stage, which was established by adding cell-permeant Ca²⁺ chelator BAPTA-AM to the maturation medium. Results showed that the extrusion of the first polar body (PB1) was delayed, and oocyte cytoplasmic maturation, including mitochondrial and endoplasmic reticulum distribution, was impaired in lower calcium model. The low-calcium-model oocytes presented a poor developmental phenotype of somatic cell nuclear transfer (SCNT) embryos at the beginning of activation of zygotic genome. At the same time, oxidative stress and apoptosis were observed in the low-calcium-model oocytes; subsequently, an RNA-seq analysis of the lower-calcium-model oocytes screened 24 genes responsible for the poor oocyte reprogramming, and six genes (ID1, SOX2, DPPA3, ASF1A, MSL3, and KDM6B) were identified by quantitative PCR. Analyzing the expression of these genes is helpful to elucidate the mechanisms of [Ca²⁺]_i regulating oocyte reprogramming. The most significant difference gene in this enriched item was ID1. Our results showed that the low calcium might give rise to oxidative stress and apoptosis, resulting in impaired maturation of bovine oocytes and possibly affecting subsequent reprogramming ability through the reduction of ID1.

Ca2+-mediated coupling between neuromuscular junction and mitochondria in skeletal muscle

The volitional movement of skeletal is controlled by the motor neuron at the site of neuromuscular junction (NMJ) where the retrograde signals are also passed back from muscle to the motor neuron. As the normal function of muscle largely depends on mitochondria that determine the fate of a skeletal muscle myofiber, there must exist a fine-controlled functional coupling between NMJ and mitochondria in myofibers. This mini-review discusses recent publications that reveal how spatiotemporal profiles of intracellular free Ca²⁺ could couple mitochondrial function with the activity of NMJ in skeletal muscle myofibers.

Skeletal Muscle Mitochondrial Dysfunction and Oxidative Stress in Peripheral Arterial Disease: A Unifying Mechanism and Therapeutic Target

Peripheral artery disease (PAD) is caused by atherosclerosis in the lower extremities, which leads to a spectrum of life-altering symptomatology, including claudication, ischemic rest pain, and gangrene requiring limb amputation. Current treatments for PAD are focused primarily on re-establishing blood flow to the ischemic tissue, implying that blood flow is the decisive factor that determines whether or not the tissue survives. Unfortunately, failure rates of endovascular and revascularization procedures remain unacceptably high and numerous cell- and gene-based vascular therapies have failed to demonstrate efficacy in clinical trials. The low success of vascular-focused therapies implies that non-vascular tissues, such as skeletal muscle and oxidative stress, may substantially contribute to PAD pathobiology. Clues toward the importance of skeletal muscle in PAD pathobiology stem from clinical observations that muscle function is a strong predictor of mortality. Mitochondrial impairments in muscle have been documented in PAD patients, although its potential role in clinical pathology is incompletely understood. In this review, we discuss the underlying mechanisms causing mitochondrial dysfunction in ischemic skeletal muscle, including causal evidence in rodent studies, and highlight emerging mitochondrial-targeted therapies that have potential to improve PAD outcomes. Particularly, we will analyze literature data on reactive oxygen species production and potential counteracting endogenous and exogenous antioxidants.

Physiological Ca2+ Transients Versus Pathological Steady-State Ca2+ Elevation, Who Flips the ROS Coin in Skeletal Muscle Mitochondria

Mitochondria are both the primary provider of ATP and the pivotal regulator of cell death, which are essential for physiological muscle activities. Ca²⁺ plays a multifaceted role in mitochondrial function. During muscle contraction, Ca²⁺ influx into mitochondria activates multiple enzymes related to tricarboxylic acid (TCA) cycle and oxidative phosphorylation, resulting in increased ATP synthesis to meet the energy demand. Pathophysiological conditions such as skeletal muscle denervation or unloading also lead to elevated Ca²⁺ levels inside mitochondria. However, the outcomes of this steady-state elevation of mitochondrial Ca²⁺ level include exacerbated reactive oxygen species (ROS) generation, sensitized opening of mitochondrial permeability transition pore (mPTP), induction of programmed cell death, and ultimately muscle atrophy. Previously, both acute and long-term endurance exercises have been reported to activate certain signaling pathways to counteract ROS production. Meanwhile, electrical stimulation is known to help prevent apoptosis and alleviate muscle atrophy in denervated animal models and patients with motor impairment. There are various mechanistic studies that focus on the excitation-transcription coupling framework to understand the beneficial role of exercise and electrical stimulation. Interestingly, a recent study has revealed an unexpected role of rapid mitochondrial Ca²⁺ transients in keeping mPTP at a closed state with reduced mitochondrial ROS production. This discovery motivated us to contribute this review article to inspire further discussion about the potential mechanisms underlying differential outcomes of physiological mitochondrial Ca²⁺ transients and pathological mitochondrial Ca²⁺ elevation in skeletal muscle ROS production.

Reactive species-induced microvascular dysfunction in ischemia/reperfusion

Vascular endothelial cells line the inner surface of the entire cardiovascular system as a single layer and are involved in an impressive array of functions, ranging from the regulation of vascular tone in resistance arteries and arterioles, modulation of microvascular barrier function in capillaries and postcapillary venules, and control of proinflammatory and prothrombotic processes, which occur in all segments of the vascular tree but can be especially prominent in postcapillary venules. When tissues are subjected to ischemia/reperfusion (I/R), the endothelium of resistance arteries and arterioles, capillaries, and postcapillary venules become dysfunctional, resulting in impaired endothelium-dependent vasodilator and enhanced endothelium-dependent vasoconstrictor responses along with increased vulnerability to thrombus formation, enhanced fluid filtration and protein extravasation, and increased blood-to-interstitium trafficking of leukocytes in these functionally distinct segments of the microcirculation. The number of capillaries open to flow upon reperfusion also declines as a result of I/R, which impairs nutritive perfusion. All of these pathologic microvascular events involve the formation of reactive species (RS) derived from molecular oxygen and/or nitric oxide. In addition to these effects, I/R-induced RS activate NLRP3 inflammasomes, alter connexin/pannexin signaling, provoke mitochondrial fission, and cause release of microvesicles in endothelial cells, resulting in deranged function in arterioles, capillaries, and venules. It is now apparent that this microvascular dysfunction is an important determinant of the severity of injury sustained by parenchymal cells in ischemic tissues, as well as being predictive of clinical outcome after reperfusion therapy. On the other hand, RS production at signaling levels promotes ischemic angiogenesis, mediates flow-induced dilation in patients with coronary artery disease, and instigates the activation of cell survival programs by conditioning stimuli that render tissues resistant to the deleterious effects of prolonged I/R. These topics will be reviewed in this article.

Effect of the Phosphodiesterase 5 Inhibitor Sildenafil on Ischemia-Reperfusion-Induced Muscle Mitochondrial Dysfunction and Oxidative Stress

Lower-limb ischemia-reperfusion (IR) is frequent and associated with significant morbidity and mortality. Phosphodiesterase 5 inhibitors demonstrated antioxidant and beneficial effects in several organs submitted to IR, but their effects on muscle mitochondrial functions after lower-limb IR are unknown. Unilateral hindlimb IR (2 h tourniquet followed by 2 h reperfusion) without or with sildenafil (1mg/kg ip 30 minutes before ischemia) was performed in 18 mice. Maximal oxidative capacity (V_Max), relative contribution of the mitochondrial respiratory chain complexes, calcium retention capacity (CRC)—a marker of apoptosis—and reactive oxygen species (ROS) production were determined using high-resolution respirometry, spectrofluorometry, and electron paramagnetic resonance in gastrocnemius muscles from both hindlimbs. IR significantly reduced mitochondrial V_Max (from 11.79 ± 1.74 to 4.65 ± 1.11 pmol/s*mg wet weight (ww), p < 0.05, −50.2 ± 16.3%) and CRC (from 2.33 ± 0.41 to 0.84 ± 0.18 µmol/mg dry weight (dw), p < 0.05; −61.1 ± 6.8%). ROS tended to increase in the ischemic limb (+64.3 ± 31.9%, p = 0.08). Although tending to reduce IR-related ROS production (−42.4%), sildenafil failed to reduce muscle mitochondrial dysfunctions (−63.3 ± 9.2%, p < 0.001 and −55.2 ± 7.6% p < 0.01 for V_Max, and CRC, respectively). In conclusion, lower limb IR impaired skeletal muscle mitochondrial function, but, despite tending to reduce ROS production, pharmacological preconditioning with sildenafil did not show protective effects.

Cyclophilin D deficiency protects against the development of mitochondrial ROS and cellular inflammation in aorta

INTRODUCTION

Inflammation and oxidative stress are closely correlated in the pathology of cardiovascular disease. Mitochondrial cyclophilin D (CypD), the important modulator for mPTP opening, is increasingly recognized as a key regulator of cellular ROS generation. Besides, its association with cell inflammation is also being discovered. However, the effects of CypD in modulating vascular inflammatory response is unknown. We sought to investigate whether CypD deficiency attenutes vascular inflammation under physical conditions.

METHODS AND RESULTS

We adopted CypD KO mouse and their littermate controls to observe the effects of CypD deficiency on aortic mitochondrial functions and vascular inflammation. As we found in our study, we confirmed that under physical conditions, CypD deficiency enhanced mouse whole body metabolic status, increased aortic mitochondrial complex III activity and decreased mitochondrial ROS generation. Functionally, CypD deficiency also attenuated inflammatory molecules expression, including VCAM-1, IL-6 and TNF-α in mouse aorta.

CONCLUSIONS

Our results review that mitochondrial CypD is involved in the regulation of inflammation in aorta and provide insights that blocking mitochondrial CypD enhances vascular resistance to inflammatory injuries.

Hypoxic Preconditioning Attenuates Reoxygenation-Induced Skeletal Muscle Dysfunction in Aged Pulmonary TNF-α Overexpressing Mice

Aim: Skeletal muscle subjected to hypoxia followed by reoxygenation is susceptible to injury and subsequent muscle function decline. This phenomenon can be observed in the diaphragm during strenuous exercise or in pulmonary diseases such as chronic obstructive pulmonary diseases (COPD). Previous studies have shown that PO₂ cycling or hypoxic preconditioning (HPC), as it can also be referred to as, protects muscle function via mechanisms involving reactive oxygen species (ROS). However, this HPC protection has not been fully elucidated in aged pulmonary TNF-α overexpressing (Tg⁺) mice (a COPD-like model). We hypothesize that HPC can exert protection on the diaphragms of Tg⁺ mice during reoxygenation through pathways involving ROS/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/extracellular signal regulated kinase (ERK), as well as the downstream activation of mitochondrial ATP-sensitive potassium channel (mitoK_ATP) and inhibition of mitochondrial permeability transition pore (mPTP).

Methods: Isolated Tg⁺ diaphragm muscle strips were pre-treated with inhibitors for ROS, PI3K, Akt, ERK, or a combination of mitoK_ATP inhibitor and mPTP opener, respectively, prior to HPC. Another two groups of muscles were treated with either mitoK_ATP activator or mPTP inhibitor without HPC. Muscles were treated with 30-min hypoxia, followed by 15-min reoxygenation. Data were analyzed by multi-way ANOVA and expressed as means ± SE.

Results: Muscle treated with HPC showed improved muscle function during reoxygenation (n = 5, p < 0.01). Inhibition of ROS, PI3K, Akt, or ERK abolished the protective effect of HPC. Simultaneous inhibition of mitoK_ATP and activation of mPTP also diminished HPC effects. By contrast, either the opening of mitoK_ATP channel or the closure of mPTP provided a similar protective effect to HPC by alleviating muscle function decline, suggesting that mitochondria play a role in HPC initiation (n = 5; p < 0.05).

Conclusion: Hypoxic preconditioning may protect respiratory skeletal muscle function in Tg⁺ mice during reoxygenation through redox-sensitive signaling cascades and regulations of mitochondrial channels.

Cyclophilin D, Somehow a Master Regulator of Mitochondrial Function

Cyclophilin D (CyPD) is an important mitochondrial chaperone protein whose mechanism of action remains a mystery. It is well known for regulating mitochondrial function and coupling of the electron transport chain and ATP synthesis by controlling the mitochondrial permeability transition pore (PTP), but more recent evidence suggests that it may regulate electron transport chain activity. Given its identification as a peptidyl-prolyl, cis-trans isomerase (PPIase), CyPD, is thought to be involved in mitochondrial protein folding, but very few reports demonstrate the presence of this activity. By contrast, CyPD may also perform a scaffolding function, as it binds to a number of important proteins in the mitochondrial matrix and inner mitochondrial membrane. From a clinical perspective, inhibiting CyPD to inhibit PTP opening protects against ischemia⁻reperfusion injury, making modulation of CyPD activity a potentially important therapeutic goal, but the lack of knowledge about the mechanisms of CyPD's actions remains problematic for such therapies. Thus, the important yet enigmatic nature of CyPD somehow makes it a master regulator, yet a troublemaker, for mitochondrial function.

Impaired myogenic development, differentiation and function in hESC-derived SMA myoblasts and myotubes

Spinal muscular atrophy (SMA) is a severe genetic disorder that manifests in progressive neuromuscular degeneration. SMA originates from loss-of-function mutations of the SMN1 (Survival of Motor Neuron 1) gene. Recent evidence has implicated peripheral deficits, especially in skeletal muscle, as key contributors to disease progression in SMA. In this study we generated myogenic cells from two SMA-affected human embryonic stem cell (hESC) lines with deletion of SMN1 bearing two copies of the SMN2 gene and recapitulating the molecular phenotype of Type 1 SMA. We characterized myoblasts and myotubes by comparing them to two unaffected, control hESC lines and demonstrate that SMA myoblasts and myotubes showed altered expression of various myogenic markers, which translated into an impaired in vitro myogenic maturation and development process. Additionally, we provide evidence that these SMN1 deficient cells display functional deficits in cholinergic calcium signaling response, glycolysis and oxidative phosphorylation. Our data describe a novel human myogenic SMA model that might be used for interrogating the effect of SMN depletion during skeletal muscle development, and as model to investigate biological mechanisms targeting myogenic differentiation, mitochondrial respiration and calcium signaling processes in SMA muscle cells.

N-Acetyl Cysteine Restores Limb Function, Improves Mitochondrial Respiration, and Reduces Oxidative Stress in a Murine Model of Critical Limb Ischaemia

OBJECTIVE/BACKGROUND

The aim of this study was to investigate whether antioxidant therapy might decrease oxidative stress related deleterious effects in the setting of critical limb ischaemia (CLI).

METHODS

Twenty Swiss mice were submitted to sequential right femoral and iliac ligatures; the left limb served as control. The mice were assigned to two groups: in the first group (no-treatment group, n = 10) no treatment was administered; in the second group (N-acetyl cysteine [NAC] group, n = 10) NAC was administered by dissolution in drinking water for 4 weeks, starting on day 7, when CLI was effective. Clinical and functional scores were assessed by two blinded investigators. Mice were killed on day 40 and mitochondrial respiratory chain complex activities, calcium retention capacity, oxidative stress, and histological analysis were analysed.

RESULTS

Ischaemic muscles in the no-treatment group showed significantly impaired mitochondrial respiration and calcium retention capacity, with increased production of reactive oxygen species; but no statistical difference was noticed when comparing ischaemic muscles in the NAC group (n = 10) to contralateral muscles (n = 10) and to control muscles in the no-treatment group (n = 10). Ischaemic muscles in the no-treatment group exhibited myopathic features such as wider range in fibre size, rounded shape, centrally located nuclei, and smaller cross sectional areas, but none of these features were observed in contralateral muscles or in NAC-group muscles (ischaemic or controls).

CONCLUSION

Targeting inhibition of oxidative stress may be a potential therapeutic strategy for muscle protection in CLI and might be considered as potential adjunctive therapy to revascularisation procedures.

Diabetes Worsens Skeletal Muscle Mitochondrial Function, Oxidative Stress, and Apoptosis After Lower-Limb Ischemia-Reperfusion: Implication of the RISK and SAFE Pathways?

Objectives: Diabetic patients respond poorly to revascularization for peripheral arterial disease (PAD) but the underlying mechanisms are not well understood. We aimed to determine whether diabetes worsens ischemia-reperfusion (IR)-induced muscle dysfunction and the involvement of endogenous protective kinases in this process.

Materials and Methods: Streptozotocin-induced diabetic and non-diabetic rats were randomized to control or to IR injury (3 h of aortic cross-clamping and 2 h of reperfusion). Mitochondrial respiration, reactive oxygen species (ROS) production, protein levels of superoxide dismutase (SOD2) and endogenous protective kinases (RISK and SAFE pathways) were investigated in rat gastrocnemius, together with upstream (GSK-3β) and downstream (cleaved caspase-3) effectors of apoptosis.

Results: Although already impaired when compared to non-diabetic controls at baseline, the decline in mitochondrial respiration after IR was more severe in diabetic rats. In diabetic animals, IR-triggered oxidative stress (increased ROS production and reduced SOD2 levels) and effectors of apoptosis (reduced GSK-3β inactivation and higher cleaved caspase-3 levels) were increased to a higher level than in the non-diabetics. IR had no effect on the RISK pathway in non-diabetics and diabetic rats, but increased STAT 3 only in the latter.

Conclusion: Type 1 diabetes worsens IR-induced skeletal muscle injury, endogenous protective pathways not being efficiently stimulated.

Moderate Exercise Allows for shorter Recovery Time in Critical Limb Ischemia

Whether and how moderate exercise might allow for accelerated limb recovery in chronic critical limb ischemia (CLI) remains to be determined. Chronic CLI was surgically induced in mice, and the effect of moderate exercise (training five times per week over a 3-week period) was investigated. Tissue damages and functional scores were assessed on the 4th, 6th, 10th, 20th, and 30th day after surgery. Mice were sacrificed 48 h after the last exercise session in order to assess muscle structure, mitochondrial respiration, calcium retention capacity, oxidative stress and transcript levels of genes encoding proteins controlling mitochondrial functions (PGC1α, PGC1β, NRF1) and anti-oxidant defenses markers (SOD1, SOD2, catalase). CLI resulted in tissue damages and impaired functional scores. Mitochondrial respiration and calcium retention capacity were decreased in the ischemic limb of the non-exercised group (V_max = 7.11 ± 1.14 vs. 9.86 ± 0.86 mmol 02/min/g dw, p < 0.001; CRC = 7.01 ± 0.97 vs. 11.96 ± 0.92 microM/mg dw, p < 0.001, respectively). Moderate exercise reduced tissue damages, improved functional scores, and restored mitochondrial respiration and calcium retention capacity in the ischemic limb (V_max = 9.75 ± 1.00 vs. 9.82 ± 0.68 mmol 02/min/g dw; CRC = 11.36 ± 1.33 vs. 12.01 ± 1.24 microM/mg dw, respectively). Exercise also enhanced the transcript levels of PGC1α, PGC1β, NRF1, as well as SOD1, SOD2, and catalase. Moderate exercise restores mitochondrial respiration and calcium retention capacity, and it has beneficial functional effects in chronic CLI, likely by stimulating reactive oxygen species-induced biogenesis and anti-oxidant defenses. These data support further development of exercise therapy even in advanced peripheral arterial disease.

Bioenergetics dysfunction, mitochondrial permeability transition pore opening and lipid peroxidation induced by hydrogen sulfide as relevant pathomechanisms underlying the neurological dysfunction characteristic of ethylmalonic encephalopathy

Hydrogen sulfide (sulfide) accumulates at high levels in brain of patients with ethylmalonic encephalopathy (EE). In the present study, we evaluated whether sulfide could disturb energy and redox homeostasis, and induce mitochondrial permeability transition (mPT) pore opening in rat brain aiming to better clarify the neuropathophysiology of EE. Sulfide decreased the activities of citrate synthase and aconitase in rat cerebral cortex mitochondria, and of creatine kinase (CK) in rat cerebral cortex, striatum and hippocampus supernatants. Glutathione prevented sulfide-induced CK activity decrease in the cerebral cortex. Sulfide also diminished mitochondrial respiration in cerebral cortex homogenates, and dissipated mitochondrial membrane potential (ΔΨm) and induced swelling in the presence of calcium in brain mitochondria. Alterations in ΔΨm and swelling caused by sulfide were prevented by the combination of ADP and cyclosporine A, and by ruthenium red, indicating the involvement of mPT in these effects. Furthermore, sulfide increased the levels of malondialdehyde in cerebral cortex supernatants, which was prevented by resveratrol and attenuated by glutathione, and of thiol groups in a medium devoid of brain samples. Finally, we verified that sulfide did not alter cell viability and DCFH oxidation in cerebral cortex slices, primary cortical astrocyte cultures and SH-SY5Y cells. Our data provide evidence that bioenergetics disturbance and lipid peroxidation along with mPT pore opening are involved in the pathophysiology of brain damage observed in EE.

Mevalonolactone disrupts mitochondrial functions and induces permeability transition pore opening in rat brain mitochondria: Implications for the pathogenesis of mevalonic aciduria

Mevalonic aciduria (MVA) is caused by severe deficiency of mevalonic kinase activity leading to tissue accumulation and high urinary excretion of mevalonic acid (MA) and mevalonolactone (ML). Patients usually present severe neurologic symptoms whose pathophysiology is poorly known. Here, we tested the hypothesis that the major accumulating metabolites are toxic by investigating the in vitro effects of MA and ML on important mitochondrial functions in rat brain and liver mitochondria. ML, but not MA, markedly decreased mitochondrial membrane potential (ΔΨm), NAD(P)H content and the capacity to retain Ca²⁺ in the brain, besides inducing mitochondrial swelling. These biochemical alterations were totally prevented by the classical inhibitors of mitochondrial permeability transition (MPT) cyclosporine A and ADP, as well as by ruthenium red in Ca²⁺-loaded mitochondria, indicating the involvement of MPT and an important role for mitochondrial Ca²⁺ in these effects. ML also induced lipid peroxidation and markedly inhibited aconitase activity, an enzyme that is highly susceptible to free radical attack, in brain mitochondrial fractions, indicating that lipid and protein oxidative damage may underlie some of ML-induced deleterious effects including MTP induction. In contrast, ML and MA did not compromise oxidative phosphorylation in the brain and all mitochondrial functions evaluated in the liver, evidencing a selective toxicity of ML towards the central nervous system. Our present study provides for the first time evidence that ML impairs essential brain mitochondrial functions with the involvement of MPT pore opening. It is therefore presumed that disturbance of brain mitochondrial homeostasis possibly contributes to the neurologic symptoms in MVA.

Muscles Susceptibility to Ischemia-Reperfusion Injuries Depends on Fiber Type Specific Antioxidant Level

Muscle injury resulting from ischemia-reperfusion largely aggravates patient prognosis but whether and how muscle phenotype modulates ischemia-reperfusion-induced mitochondrial dysfunction remains to be investigated. We challenged the hypothesis that glycolytic muscles are more prone to ischemia-reperfusion-induced injury than oxidative skeletal muscles. We therefore determined simultaneously the effect of 3 h of ischemia induced by aortic clamping followed by 2 h of reperfusion (IR, n = 11) on both gastrocnemius and soleus muscles, as compared to control animals (C, n = 11). Further, we investigated whether tempol, an antioxidant mimicking superoxide dismutase, might compensate a reduced defense system, likely characterizing glycolytic muscles (IR-Tempol, n = 7). In the glycolytic gastrocnemius muscle, as compared to control, ischemia-reperfusion significantly decreased mitochondrial respiration (-30.28 ± 6.16%, p = 0.003), increased reactive oxygen species production (+79.15 ± 28.72%, p = 0.04), and decreased reduced glutathione (-28.19 ± 6.80%, p = 0.011). Less deleterious effects were observed in the oxidative soleus muscle (-6.44 ± 6.30%, +4.32 ± 16.84%, and -8.07 ± 10.84%, respectively), characterized by enhanced antioxidant defenses (0.63 ± 0.05 in gastrocnemius vs. 1.24 ± 0.08 μmol L^-1 g^-1 in soleus). Further, when previously treated with tempol, glycolytic muscle was largely protected against the deleterious effects of ischemia-reperfusion. Thus, oxidative skeletal muscles are more protected than glycolytic ones against ischemia-reperfusion, thanks to their antioxidant pool. Such pivotal data support that susceptibility to ischemia-reperfusion-induced injury differs between organs, depending on their metabolic phenotypes. This suggests a need to adapt therapeutic strategies to the specific antioxidant power of the target organ to be protected.

Left Ventricular Transmural Gradient in Mitochondrial Respiration Is Associated with Increased Sub-Endocardium Nitric Oxide and Reactive Oxygen Species Productions

OBJECTIVE

Left ventricle (LV) transmural gradient in mitochondrial respiration has been recently reported. However, to date, the physiological mechanisms involved in the lower endocardium mitochondrial respiration chain capacity still remain to be determined. Since, nitric oxide (NO) synthase expression in the heart has spatial heterogeneity and might impair mitochondrial function, we investigated a potential association between LV transmural NO and mitochondrial function gradient.

METHODS

Maximal oxidative capacity (VMax) and relative contributions of the respiratory chain complexes II, III, IV (VSucc) and IV (VTMPD), mitochondrial content (citrate synthase activity), coupling, NO (electron paramagnetic resonance), and reactive oxygen species (ROS) production (H2O2 and dihydroethidium (DHE) staining) were determined in rat sub-endocardium (Endo) and sub-epicardium (Epi). Further, the effect of a direct NO donor (MAHMA NONOate) on maximal mitochondrial respiratory rates (Vmax) was determined.

RESULTS

Mitochondrial respiratory chain activities were reduced in the Endo compared with the Epi (-16.92%; P = 0.04 for Vmax and -18.73%; P = 0.02, for Vsucc, respectively). NO production was two-fold higher in the Endo compared with the Epi (P = 0.002) and interestingly, increasing NO concentration reduced Vmax. Mitochondrial H2O2 and LV ROS productions were significantly increased in Endo compared to Epi, citrate synthase activity and mitochondrial coupling being similar in the two layers.

CONCLUSIONS

LV mitochondrial respiration transmural gradient is likely related to NO and possibly ROS increased production in the sub-endocardium.

Chronology of mitochondrial and cellular events during skeletal muscle ischemia-reperfusion

Peripheral artery disease (PAD) is a common circulatory disorder of the lower limb arteries that reduces functional capacity and quality of life of patients. Despite relatively effective available treatments, PAD is a serious public health issue associated with significant morbidity and mortality. Ischemia-reperfusion (I/R) cycles during PAD are responsible for insufficient oxygen supply, mitochondriopathy, free radical production, and inflammation and lead to events that contribute to myocyte death and remote organ failure. However, the chronology of mitochondrial and cellular events during the ischemic period and at the moment of reperfusion in skeletal muscle fibers has been poorly reviewed. Thus, after a review of the basal myocyte state and normal mitochondrial biology, we discuss the physiopathology of ischemia and reperfusion at the mitochondrial and cellular levels. First we describe the chronology of the deleterious biochemical and mitochondrial mechanisms activated by I/R. Then we discuss skeletal muscle I/R injury in the muscle environment, mitochondrial dynamics, and inflammation. A better understanding of the chronology of the events underlying I/R will allow us to identify key factors in the development of this pathology and point to suitable new therapies. Emerging data on mitochondrial dynamics should help identify new molecular and therapeutic targets and develop protective strategies against PAD.

Skeletal muscle ischemia-reperfusion injury and cyclosporine A in the aging rat

Old patients exhibit muscle impairments and increased perioperative risk during vascular surgery procedures. Although aging generally impairs protective mechanisms, data are lacking concerning skeletal muscle in elderly. We tested whether cyclosporine A (CsA), which protects skeletal muscle from ischemia-reperfusion (IR) in young rats, might reduce skeletal muscle mitochondrial dysfunction and oxidative stress in aging rats submitted to hindlimb IR. Wistar rats aged 71-73 weeks were randomized to IR (3 h unilateral tourniquet application and 2 h reperfusion) or IR + CsA (10 mg/kg cyclosporine IV before reperfusion). Maximal oxidative capacity (VM ax ), acceptor control ratio (ACR), and relative contribution of the mitochondrial respiratory chain complexes II, III, IV (VS ucc ), and IV (VTMPD /Asc ), together with calcium retention capacity (CRC) a marker of apoptosis, and tissue reactive oxygen species (ROS) production were determined in gastrocnemius muscles from both hindlimbs. Compared to the nonischemic hindlimb, IR significantly reduced mitochondrial coupling, VMax (from 7.34 ± 1.50 to 2.87 ± 1.22 μMO2 /min/g; P < 0.05; -70%), and VS ucc (from 6.14 ± 1.07 to 3.82 ± 0.83 μMO2 /min/g; P < 0.05; -42%) but not VTMPD /Asc . IR also decreased the CRC from 15.58 ± 3.85 to 6.19 ± 0.86 μMCa(2+) /min/g; P < 0.05; -42%). These alterations were not corrected by CsA (-77%, -49%, and -32% after IR for VM ax, VS ucc , and CRC, respectively). Further, CsA significantly increased ROS production in both hindlimbs (P < 0.05; +73%). In old rats, hindlimb IR impairs skeletal muscle mitochondrial function and increases oxidative stress. Cyclosporine A did not show protective effects.

2-Methylcitric acid impairs glutamate metabolism and induces permeability transition in brain mitochondria

Accumulation of 2-methylcitric acid (2MCA) is observed in methylmalonic and propionic acidemias, which are clinically characterized by severe neurological symptoms. The exact pathogenetic mechanisms of brain abnormalities in these diseases are poorly established and very little has been reported on the role of 2MCA. In the present work we found that 2MCA markedly inhibited ADP-stimulated and uncoupled respiration in mitochondria supported by glutamate, with a less significant inhibition in pyruvate plus malate respiring mitochondria. However, no alterations occurred when α-ketoglutarate or succinate was used as respiratory substrates, suggesting a defect on glutamate oxidative metabolism. It was also observed that 2MCA decreased ATP formation in glutamate plus malate or pyruvate plus malate-supported mitochondria. Furthermore, 2MCA inhibited glutamate dehydrogenase activity at concentrations as low as 0.5 mM. Kinetic studies revealed that this inhibitory effect was competitive in relation to glutamate. In contrast, assays of osmotic swelling in non-respiring mitochondria suggested that 2MCA did not significantly impair mitochondrial glutamate transport. Finally, 2MCA provoked a significant decrease in mitochondrial membrane potential and induced swelling in Ca(2+)-loaded mitochondria supported by different substrates. These effects were totally prevented by cyclosporine A plus ADP or ruthenium red, indicating induction of mitochondrial permeability transition. Taken together, our data strongly indicate that 2MCA behaves as a potent inhibitor of glutamate oxidation by inhibiting glutamate dehydrogenase activity and as a permeability transition inducer, disturbing mitochondrial energy homeostasis. We presume that 2MCA-induced mitochondrial deleterious effects may contribute to the pathogenesis of brain damage in patients affected by methylmalonic and propionic acidemias. We propose that brain glutamate oxidation is disturbed by 2-methylcitric acid (2MCA), which accumulates in tissues from patients with propionic and methylmalonic acidemias because of a competitive inhibition of glutamate dehydrogenase (GDH) activity. 2MCA also induced mitochondrial permeability transition (PT) and decreased ATP generation in brain mitochondria. We believe that these pathomechanisms may be involved in the neurological dysfunction of these diseases.

Deregulation of mitochondrial functions provoked by long-chain fatty acid accumulating in long-chain 3-hydroxyacyl-CoA dehydrogenase and mitochondrial permeability transition deficiencies in rat heart--mitochondrial permeability transition pore opening as a potential contributing pathomechanism of cardiac alterations in these disorders

Mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies are fatty acid oxidation disorders biochemically characterized by tissue accumulation of long-chain fatty acids and derivatives, including the monocarboxylic long-chain 3-hydroxy fatty acids (LCHFAs) 3-hydroxytetradecanoic acid (3HTA) and 3-hydroxypalmitic acid (3HPA). Patients commonly present severe cardiomyopathy for which the pathogenesis is still poorly established. We investigated the effects of 3HTA and 3HPA, the major metabolites accumulating in these disorders, on important parameters of mitochondrial homeostasis in Ca(2+) -loaded heart mitochondria. 3HTA and 3HPA significantly decreased mitochondrial membrane potential, the matrix NAD(P)H pool and Ca(2+) retention capacity, and also induced mitochondrial swelling. These fatty acids also provoked a marked decrease of ATP production reflecting severe energy dysfunction. Furthermore, 3HTA-induced mitochondrial alterations were completely prevented by the classical mitochondrial permeability transition (mPT) inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca(2+) uptake blocker, indicating that LCHFAs induced Ca(2+)-dependent mPT pore opening. Milder effects only achieved at higher doses of LCHFAs were observed in brain mitochondria, implying a higher vulnerability of heart to these fatty acids. By contrast, 3HTA and docosanoic acids did not change mitochondrial homeostasis, indicating selective effects for monocarboxylic LCHFAs. The present data indicate that the major LCHFAs accumulating in mitochondrial trifunctional protein and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies induce mPT pore opening, compromising Ca(2+) homeostasis and oxidative phosphorylation more intensely in the heart. It is proposed that these pathomechanisms may contribute at least in part to the severe cardiac alterations characteristic of patients affected by these diseases.

A new murine model of sustainable and durable chronic critical limb ischemia fairly mimicking human pathology

OBJECTIVE

To establish a chronic mouse model of critical limb ischemia (CLI) with in vivo and ex vivo validation, closely mimicking human pathology.

METHODS

Swiss mice (n = 28) were submitted to sequential unilateral femoral (day 0) and iliac (day 4) ligatures. Ischemia was confirmed by clinical scores (tissue and functional damages) and methoxyisobutylisonitrile (MIBI) scintigraphies at days 0, 4, 6, 10, 20, and 30. At days 10, 20, and 30, muscle mitochondrial respiration, calcium retention capacity (CRC), and production of reactive oxygen species (ROS) were investigated, together with transcripts of mitochondrial biogenesis and antioxidant enzymes. Histological analysis was also performed.

RESULTS

Clinical and functional damage confirmed CLI. MIBI scintigraphies showed hypoperfusion of the ischemic limb, which remained stable until day 30. Mitochondrial respiration was impaired in ischemic muscles compared with controls (Vmax = 7.93 ± 0.99 vs. 10.09 ± 2.87 mmol/L O2/minute/mg dry weight [dw]; p = .01), together with impaired CRC (7.4 ± 1.6 mmol/L minute/mg dw vs. 11.9 ± 0.9 mmol/L minute/mg dw; p < .001) and biogenesis (41% decrease in peroxisome proliferator-activated receptor gamma coactivator [PGC]-1α, 49% decrease in PGC-1β, and 41% decrease in nuclear respiratory factor-1). Ischemic muscles also demonstrated increased production of ROS under electron paramagnetic resonance (0.084 ± 0.029 vs. 0.051 ± 0.031 mmol/L minute/mg dw; p = .03) and with dihydroethidium staining (3622 ± 604 arbitrary units of fluorescence vs. 1224 ± 324; p < .01), decreased antioxidant enzymes (32% decrease in superoxide dismutase [SOD]1, 41% decrease in SOD2, and 49% decrease in catalase), and myopathic features (wider range in fiber size, rounded shape, centrally located nuclei, and smaller cross-sectional areas). All defects were stable over time.

CONCLUSION

Sequential femoral and iliac ligatures closely mimic human functional, clinical, scintigraphic, and skeletal muscle mitochondrial characteristics, and could prove useful for testing therapeutic approaches.

Autumnalamide, a prenylated cyclic peptide from the cyanobacterium Phormidium autumnale, acts on SH-SY5Y cells at the mitochondrial level

Filamentous cyanobacteria of the genus Phormidium have been rarely studied for their chemical diversity. For the first time, the cultivable Phormidium autumnale was shown to produce a prenylated cyclic peptide named autumnalamide (1). The structure of this peptide was fully determined after a deep exploration of the spectroscopic data, including NMR and HRMS. Interestingly, a prenyl moiety was located on the guanidine end of the arginine amino acid. The absolute configurations of most amino acids were assessed using enantioselective GC/MS analysis, with (13)C NMR modeling being used for the determination of d-arginine and d-proline. The effects of 1 on sodium and calcium fluxes were studied in SH-SY5Y and hNav 1.6 HEK cells. When the Ca(2+) influx was stimulated by thapsigargin, strong inhibition was observed in the presence of 1. As a consequence, this compound may act by disrupting the normal calcium uptake of this organelle, inducing the opening of the mitochondrial permeability transition pore, which results in the indirect blockade of store-operated channels.

Remote effects of lower limb ischemia-reperfusion: impaired lung, unchanged liver, and stimulated kidney oxidative capacities

Remote organ impairments are frequent and increase patient morbidity and mortality after lower limb ischemia-reperfusion (IR). We challenged the hypothesis that lower limb IR might also impair lung, renal, and liver mitochondrial respiration. Two-hour tourniquet-induced ischemia was performed on both hindlimbs, followed by a two-hour reperfusion period in C57BL6 mice. Lungs, liver and kidneys maximal mitochondrial respiration (V(max)), complexes II, III, and IV activity (V(succ)), and complex IV activity (V(TMPD)) were analyzed on isolated mitochondria. Lower limb IR decreased significantly lung V(max) (29.4 ± 3.3 versus 24 ± 3.7 μmol O2/min/g dry weight, resp.; P = 0.042) and tended to reduce V(succ) and V(TMPD). IR did not modify liver but increased kidneys mitochondrial respiration (79.5 ± 19.9 versus 108.6 ± 21.4, P = 0.035, and 126 ± 13.4 versus 142.4 ± 10.4 μmol O2/min/g dry weight for V(max) and V(succ), resp.). Kidneys mitochondrial coupling was increased after IR (6.5 ± 1.3 versus 8.8 ± 1.1, P = 0.008). There were no histological changes in liver and kidneys. Thus, lung mitochondrial dysfunction appears as a new early marker of hindlimb IR injuries in mice. Further studies will be useful to determine whether enhanced kidneys mitochondrial function allows postponing kidney impairment in lower limb IR setting.

Attenuation of skeletal muscle and renal injury to the lower limb following ischemia-reperfusion using mPTP inhibitor NIM-811

Introduction

Operation on the infrarenal aorta and large arteries of the lower extremities may cause rhabdomyolysis of the skeletal muscle, which in turn may induce remote kidney injury. NIM-811 (N-metyl-4-isoleucine-cyclosporine) is a mitochondria specific drug, which can prevent ischemic-reperfusion (IR) injury, by inhibiting mitochondrial permeability transition pores (mPTP).

Objectives

Our aim was to reduce damages in the skeletal muscle and the kidney after IR of the lower limb with NIM-811.

Materials and methods

Wistar rats underwent 180 minutes of bilateral lower limb ischemia and 240 minutes of reperfusion. Four animal groups were formed called Sham (receiving vehicle and sham surgery), NIM-Sham (receiving NIM-811 and sham surgery), IR (receiving vehicle and surgery), and NIM-IR (receiving NIM-811 and surgery). Serum, urine and histological samples were taken at the end of reperfusion. NADH-tetrazolium staining, muscle Wet/Dry (W/D) ratio calculations, laser Doppler-flowmetry (LDF) and mean arterial pressure (MAP) monitoring were performed. Renal peroxynitrite concentration, serum TNF-α and IL-6 levels were measured.

Results

Less significant histopathological changes were observable in the NIM-IR group as compared with the IR group. Serum K⁺ and necroenzyme levels were significantly lower in the NIM-IR group than in the IR group (LDH: p<0.001; CK: p<0.001; K⁺: p = 0.017). Muscle mitochondrial viability proved to be significantly higher (p = 0.001) and renal function parameters were significantly better (creatinine: p = 0.016; FENa: p<0.001) in the NIM-IR group in comparison to the IR group. Serum TNF-α and IL-6 levels were significantly lower (TNF-α: p = 0.003, IL-6: p = 0.040) as well as W/D ratio and peroxynitrite concentration were significantly lower (p = 0.014; p<0.001) in the NIM-IR group than in the IR group.

Conclusion

NIM-811 could have the potential of reducing rhabdomyolysis and impairment of the kidney after lower limb IR injury.

Mitochondrial bioenergetics deregulation caused by long-chain 3-hydroxy fatty acids accumulating in LCHAD and MTP deficiencies in rat brain: a possible role of mPTP opening as a pathomechanism in these disorders?

Long-chain 3-hydroxylated fatty acids (LCHFA) accumulate in long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies. Affected patients usually present severe neonatal symptoms involving cardiac and hepatic functions, although long-term neurological abnormalities are also commonly observed. Since the underlying mechanisms of brain damage are practically unknown and have not been properly investigated, we studied the effects of LCHFA on important parameters of mitochondrial homeostasis in isolated mitochondria from cerebral cortex of developing rats. 3-Hydroxytetradecanoic acid (3 HTA) reduced mitochondrial membrane potential, NAD(P)H levels, Ca(2+) retention capacity and ATP content, besides inducing swelling, cytochrome c release and H2O2 production in Ca(2+)-loaded mitochondrial preparations. We also found that cyclosporine A plus ADP, as well as ruthenium red, a Ca(2+) uptake blocker, prevented these effects, suggesting the involvement of the mitochondrial permeability transition pore (mPTP) and an important role for Ca(2+), respectively. 3-Hydroxydodecanoic and 3-hydroxypalmitic acids, that also accumulate in LCHAD and MTP deficiencies, similarly induced mitochondrial swelling and decreased ATP content, but to a variable degree pending on the size of their carbon chain. It is proposed that mPTP opening induced by LCHFA disrupts brain bioenergetics and may contribute at least partly to explain the neurologic dysfunction observed in patients affected by LCHAD and MTP deficiencies.

Sulfite disrupts brain mitochondrial energy homeostasis and induces mitochondrial permeability transition pore opening via thiol group modification

Sulfite oxidase (SO) deficiency is biochemically characterized by the accumulation of sulfite, thiosulfate and S-sulfocysteine in tissues and biological fluids of the affected patients. The main clinical symptoms include severe neurological dysfunction and brain abnormalities, whose pathophysiology is still unknown. The present study investigated the in vitro effects of sulfite and thiosulfate on mitochondrial homeostasis in rat brain mitochondria. It was verified that sulfite per se, but not thiosulfate, decreased state 3, CCCP-stimulated state and respiratory control ratio in mitochondria respiring with glutamate plus malate. In line with this, we found that sulfite inhibited the activities of glutamate and malate (MDH) dehydrogenases. In addition, sulfite decreased the activity of a commercial solution of MDH, that was prevented by antioxidants and dithiothreitol. Sulfite also induced mitochondrial swelling and reduced mitochondrial membrane potential, Ca(2+) retention capacity, NAD(P)H pool and cytochrome c immunocontent when Ca(2+) was present in the medium. These alterations were prevented by ruthenium red, cyclosporine A (CsA) and ADP, supporting the involvement of mitochondrial permeability transition (MPT) in these effects. We further observed that N-ethylmaleimide prevented the sulfite-elicited swelling and that sulfite decreased free thiol group content in brain mitochondria. These findings indicate that sulfite acts directly on MPT pore containing thiol groups. Finally, we verified that sulfite reduced cell viability in cerebral cortex slices and that this effect was prevented by CsA. Therefore, it may be presumed that disturbance of mitochondrial energy homeostasis and MPT induced by sulfite could be involved in the neuronal damage characteristic of SO deficiency.

Free radicals and sprint exercise in humans

Sprint exercise ability has been critical for survival. The remarkably high-power output levels attained during sprint exercise are achieved through strong activation of anaerobic, and to a lesser extent, aerobic energy supplying metabolic reactions, which generate reactive oxygen and nitrogen species (RONS). Sprint exercise may cause oxidative stress leading to muscle damage, particularly when performed in severe acute hypoxia. However, with training oxidative stress is reduced. Paradoxically, total plasma antioxidant capacity increases during the subsequent 2 h after a short sprint due to the increase in plasma urate concentration. The RONS produced during and immediately after sprint exercise play a capital role in signaling the adaptive response to sprint. Antioxidant supplementation blunts the normal AMPKα and CaMKII phosphorylation in response to sprint exercise. However, under conditions of increased glycolytic energy turnover and muscle acidification, as during sprint exercise in severe acute hypoxia, AMPKα phosphorylation is also blunted. This indicates that an optimal level of RONS-mediated stimulation is required for the normal signaling response to sprint exercise. Although RONS are implicated in fatigue, most studies convey that antioxidants do not enhance sprint performance in humans. Although currently controversial, it has been reported that antioxidant ingestion during training may jeopardize some of the beneficial adaptations to sprint training.