Correlation of mitochondrial respiration in platelets, peripheral blood mononuclear cells and muscle fibers

There is a growing interest for the possibility of using peripheral blood cells (including platelets) as markers for mitochondrial function in less accessible tissues. Only a few studies have examined the correlation between respiration in blood and muscle tissue, with small sample sizes and conflicting results. This study investigated the correlation of mitochondrial respiration within and across tissues. Additional analyses were performed to elucidate which blood cell type would be most useful for assessing systemic mitochondrial function. There was a significant but weak within tissue correlation between platelets and peripheral blood mononuclear cells (PBMCs). Neither PBMCs nor platelet respiration correlated significantly with muscle respiration. Muscle fibers from a group of athletes had higher mass-specific respiration, due to higher mitochondrial content than non-athlete controls, but this finding was not replicated in either of the blood cell types. In a group of patients with primary mitochondrial diseases, there were significant differences in blood cell respiration compared to healthy controls, particularly in platelets. Platelet respiration generally correlated better with the citrate synthase activity of each sample, in comparison to PBMCs. In conclusion, this study does not support the theory that blood cells can be used as accurate biomarkers to detect minor alterations in muscle respiration. However, in some instances, pronounced mitochondrial abnormalities might be reflected across tissues and detectable in blood cells, with more promising findings for platelets than PBMCs.

Cyclosporine as Therapy for Traumatic Brain Injury

Drug development in traumatic brain injury (TBI) has been impeded by the complexity and heterogeneity of the disease pathology, as well as limited understanding of the secondary injury cascade that follows the initial trauma. As a result, patients with TBI have an unmet need for effective pharmacological therapies. One promising drug candidate is cyclosporine, a polypeptide traditionally used to achieve immunosuppression in transplant recipients. Cyclosporine inhibits mitochondrial permeability transition, thereby reducing secondary brain injury, and has shown neuroprotective effects in multiple preclinical models of TBI. Moreover, the cyclosporine formulation NeuroSTAT® displayed positive effects on injury biomarker levels in patients with severe TBI enrolled in the Phase Ib/IIa Copenhagen Head Injury Ciclosporin trial (NCT01825044). Future research on neuroprotective compounds such as cyclosporine should take advantage of recent advances in fluid-based biomarkers and neuroimaging to select patients with similar disease pathologies for clinical trials. This would increase statistical power and allow for more accurate assessment of long-term outcomes.

Succinate prodrugs as treatment for acute metabolic crisis during fluoroacetate intoxication in the rat

Sodium fluoroacetate (FA) is a metabolic poison that systemically inhibits the tricarboxylic acid (TCA) cycle, causing energy deficiency and ultimately multi-organ failure. It poses a significant threat to society because of its high toxicity, potential use as a chemical weapon and lack of effective antidotal therapy. In this study, we investigated cell-permeable succinate prodrugs as potential treatment for acute FA intoxication. We hypothesized that succinate prodrugs would bypass FA-induced mitochondrial dysfunction, provide metabolic support, and prevent metabolic crisis during acute FA intoxication. To test this hypothesis, rats were exposed to FA (0.75 mg/kg) and treated with the succinate prodrug candidate NV354. Treatment efficacy was evaluated based on cardiac and cerebral mitochondrial respiration, mitochondrial content, metabolic profiles and tissue pathology. In the heart, FA increased concentrations of the TCA metabolite citrate (+ 4.2-fold, p < 0.01) and lowered ATP levels (- 1.9-fold, p < 0.001), confirming the inhibition of the TCA cycle by FA. High-resolution respirometry of cardiac mitochondria further revealed an impairment of mitochondrial complex V (CV)-linked metabolism, as evident by a reduced phosphorylation system control ratio (- 41%, p < 0.05). The inhibition of CV-linked metabolism is a novel mechanism of FA cardiac toxicity, which has implications for drug development and which NV354 was unable to counteract at the given dose. In the brain, FA induced the accumulation of β-hydroxybutyrate (+ 1.4-fold, p < 0.05) and the reduction of mitochondrial complex I (CI)-linked oxidative phosphorylation (OXPHOSCI) (- 20%, p < 0.01), the latter of which was successfully alleviated by NV354. This promising effect of NV354 warrants further investigations to determine its potential neuroprotective effects.

Succinate prodrugs in combination with atropine and pralidoxime protect cerebral mitochondrial function in a rodent model of acute organophosphate poisoning

Pesticides account for hundreds of millions of cases of acute poisoning worldwide each year, with organophosphates (OPs) being responsible for the majority of all pesticide-related deaths. OPs inhibit the enzyme acetylcholinesterase (AChE), which leads to impairment of the central- and peripheral nervous system. Current standard of care (SOC) alleviates acute neurologic-, cardiovascular- and respiratory symptoms and reduces short term mortality. However, survivors often demonstrate significant neurologic sequelae. This highlights the critical need for further development of adjunctive therapies with novel targets. While the inhibition of AChE is thought to be the main mechanism of injury, mitochondrial dysfunction and resulting metabolic crisis may contribute to the overall toxicity of these agents. We hypothesized that the mitochondrially targeted succinate prodrug NV354 would support mitochondrial function and reduce brain injury during acute intoxication with the OP diisopropylfluorophosphate (DFP). To this end, we developed a rat model of acute DFP intoxication and evaluated the efficacy of NV354 as adjunctive therapy to SOC treatment with atropine and pralidoxime. We demonstrate that NV354, in combination with atropine and pralidoxime therapy, significantly improved cerebral mitochondrial complex IV-linked respiration and reduced signs of brain injury in a rodent model of acute DFP exposure.

Effect of Cyclosporine on Cytokine Production in Elective Coronary Artery Bypass Grafting: A Sub-Analysis of the CiPRICS (Cyclosporine to Protect Renal Function in Cardiac Surgery) Study

OBJECTIVES

The augmented inflammatory response to cardiac surgery is a recognized cause of postoperative acute kidney injury. The present study aimed to investigate the effects of preoperative cyclosporine treatment on cytokine production and delineate factors associated with postoperative kidney impairment.

DESIGN

A randomized, double-blind, placebo-controlled, single-center study.

SETTING

At a tertiary care, university hospital.

PARTICIPANTS

Patients eligible for elective coronary artery bypass grafting surgery; 67 patients were enrolled.

INTERVENTIONS

Patients were randomized to receive 2.5 mg/kg cyclosporine or placebo before surgery. Cytokine levels were measured after the induction of anesthesia and 4 hours after the end of cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Tissue-aggressive (interleukin [IL]-1β, macrophage inflammatory protein [MIP]-1β, granulocyte colony-stimulating factor [G-CSF], IL-6, IL-8, IL-17, MCP-1), as well tissue-lenient (IL-4) cytokines, were significantly elevated in response to surgery. Changes in cytokine levels were not affected by cyclosporine pretreatment.

CONCLUSIONS

Elective coronary artery bypass grafting surgery with cardiopulmonary bypass triggers cytokine activation. This activation was not impacted by preoperative cyclosporine treatment.

Evaluation of Diffusion Tensor Imaging and Fluid Based Biomarkers in a Large Animal Trial of Cyclosporine in Focal Traumatic Brain Injury

All phase III trials evaluating medical treatments for traumatic brain injury (TBI), performed to date, have failed. To facilitate future success there is a need for novel outcome metrics that can bridge pre-clinical studies to clinical proof of concept trials. Our objective was to assess diffusion tensor imaging (DTI) and biofluid-based biomarkers as efficacy outcome metrics in a large animal study evaluating the efficacy of cyclosporine in TBI. This work builds on our previously published study that demonstrated a reduced volume of injury by 35% with cyclosporine treatment based on magnetic resonance imaging (MRI) results. A focal contusion injury was induced in piglets using a controlled cortical impact (CCI) device. Cyclosporine in a novel Cremophor/Kolliphor EL-free lipid emulsion, NeuroSTAT, was administered by continuous intravenous infusion for 5 days. The animals underwent DTI on day 5. Glial fibrillary acidic protein (GFAP), as a measure of astroglia injury, and neurofilament light (NF-L), as a measure of axonal injury, were measured in blood on days 1, 2, and 5, and in cerebrospinal fluid (CSF) on day 5 post-injury. Normalized fractional anisotropy (FA) was significantly (p = 0.027) higher in in the treatment group, indicating preserved tissue integrity with treatment. For the biomarkers, we observed a statistical trend of a decreased level of NF-L in CSF (p = 0.051), in the treatment group relative to placebo, indicating less axonal injury. Our findings suggest that DTI, and possibly CSF NF-L, may be feasible as translational end-points assessing neuroprotective drugs in TBI.

Cell-Permeable Succinate Rescues Mitochondrial Respiration in Cellular Models of Statin Toxicity

Statins are the cornerstone of lipid-lowering therapy. Although generally well tolerated, statin-associated muscle symptoms (SAMS) represent the main reason for treatment discontinuation. Mitochondrial dysfunction of complex I has been implicated in the pathophysiology of SAMS. The present study proposed to assess the concentration-dependent ex vivo effects of three statins on mitochondrial respiration in viable human platelets and to investigate whether a cell-permeable prodrug of succinate (complex II substrate) can compensate for statin-induced mitochondrial dysfunction. Mitochondrial respiration was assessed by high-resolution respirometry in human platelets, acutely exposed to statins in the presence/absence of the prodrug NV118. Statins concentration-dependently inhibited mitochondrial respiration in both intact and permeabilized cells. Further, statins caused an increase in non-ATP generating oxygen consumption (uncoupling), severely limiting the OXPHOS coupling efficiency, a measure of the ATP generating capacity. Cerivastatin (commercially withdrawn due to muscle toxicity) displayed a similar inhibitory capacity compared with the widely prescribed and tolerable atorvastatin, but did not elicit direct complex I inhibition. NV118 increased succinate-supported mitochondrial oxygen consumption in atorvastatin/cerivastatin-exposed platelets leading to normalization of coupled (ATP generating) respiration. The results acquired in isolated human platelets were validated in a limited set of experiments using atorvastatin in HepG2 cells, reinforcing the generalizability of the findings.

Cell-permeable succinate prodrugs rescue mitochondrial respiration in cellular models of acute acetaminophen overdose

Acetaminophen is one of the most common over-the-counter pain medications used worldwide and is considered safe at therapeutic dose. However, intentional and unintentional overdose accounts for up to 70% of acute liver failure cases in the western world. Extensive research has demonstrated that the induction of oxidative stress and mitochondrial dysfunction are central to the development of acetaminophen-induced liver injury. Despite the insight gained on the mechanism of acetaminophen toxicity, there still is only one clinically approved pharmacological treatment option, N-acetylcysteine. N-acetylcysteine increases the cell’s antioxidant defense and protects liver cells from further acetaminophen-induced oxidative damage. Because it primarily protects healthy liver cells rather than rescuing the already injured cells alternative treatment strategies that target the latter cell population are warranted. In this study, we investigated mitochondria as therapeutic target for the development of novel treatment strategies for acetaminophen-induced liver injury. Characterization of the mitochondrial toxicity due to acute acetaminophen overdose in vitro in human cells using detailed respirometric analysis revealed that complex I-linked (NADH-dependent) but not complex II-linked (succinate-dependent) mitochondrial respiration is inhibited by acetaminophen. Treatment with a novel cell-permeable succinate prodrug rescues acetaminophen-induced impaired mitochondrial respiration. This suggests cell-permeable succinate prodrugs as a potential alternative treatment strategy to counteract acetaminophen-induced liver injury.

Copenhagen Head Injury Ciclosporin Study: A Phase IIa Safety, Pharmacokinetics, and Biomarker Study of Ciclosporin in Severe Traumatic Brain Injury Patients

Traumatic brain injury (TBI) contributes to almost one third of all trauma-related deaths, and those that survive often suffer from long-term physical and cognitive deficits. Ciclosporin (cyclosporine, cyclosporin A) has shown promising neuroprotective properties in pre-clinical TBI models. The Copenhagen Head Injury Ciclosporin (CHIC) study was initiated to establish the safety profile and pharmacokinetics of ciclosporin in patients with severe TBI, using a novel parenteral lipid emulsion formulation. Exploratory pharmacodynamic study measures included microdialysis in brain parenchyma and protein biomarkers of brain injury in the cerebrospinal fluid (CSF). Sixteen adult patients with severe TBI (Glasgow Coma Scale 4–8) were included, and all patients received an initial loading dose of 2.5 mg/kg followed by a continuous infusion for 5 days. The first 10 patients received an infusion dosage of 5 mg/kg/day whereas the subsequent 6 patients received 10 mg/kg/day. No mortality was registered within the study duration, and the distribution of adverse events was similar between the two treatment groups. Pharmacokinetic analysis of CSF confirmed dose-dependent brain exposure. Between- and within-patient variability in blood concentrations was limited, whereas CSF concentrations were more variable. The four biomarkers, glial fibrillary acidic protein, neurofilament light, tau, and ubiquitin carboxy-terminal hydrolase L1, showed consistent trends to decrease during the 5-day treatment period, whereas the samples taken on the days after the treatment period showed higher values in the majority of patients. In conclusion, ciclosporin, as administered in this study, is safe and well tolerated. The study confirmed that ciclosporin is able to pass the blood–brain barrier in a TBI population and provided an initial biomarker-based signal of efficacy.

Bioenergetic bypass using cell-permeable succinate, but not methylene blue, attenuates metformin-induced lactate production

BACKGROUND

Metformin is the most common pharmacological treatment for type 2 diabetes. It is considered safe but has been associated with the development of lactic acidosis under circumstances where plasma concentrations exceed therapeutic levels. Metformin-induced lactic acidosis has been linked to the drug's toxic effect on mitochondrial function. Current treatment strategies aim to remove the drug and correct for the acidosis. With a mortality of 20%, complementary treatment strategies are needed. In this study, it was investigated whether targeting mitochondria with pharmacological agents that bypass metformin-induced mitochondrial dysfunction can counteract the energetic deficit linked to toxic doses of metformin.

METHODS

The redox agent methylene blue and the cell-permeable succinate prodrug NV118 were evaluated by measuring mitochondrial respiration and lactate production of human platelets exposed to metformin and co-treated with either of the two pharmacological bypass agents.

RESULTS

The cell-permeable succinate prodrug NV118 increased mitochondrial respiration which was linked to phosphorylation by the ATP-synthase and alleviated the increase in lactate production induced by toxic doses of metformin. The redox agent methylene blue, in contrast, failed to mitigate the metformin-induced changes in mitochondrial respiration and lactate generation.

CONCLUSIONS

The cell-permeable succinate prodrug NV118 bypassed the mitochondrial dysfunction and counteracted the energy deficit associated with toxic doses of metformin. If similar effects of NV118 prove translatable to an in vivo effect, this pharmacological strategy presents as a promising complementary treatment for patients with metformin-induced lactic acidosis.

Neuroprotective Effects of Cyclosporine in a Porcine Pre-Clinical Trial of Focal Traumatic Brain Injury

Mitochondrial dysfunction is thought to be a hallmark of traumatic brain injury (TBI) and plays a pivotal role in the resulting cellular injury. Cyclophilin D-mediated activation of the mitochondrial permeability transition pore has been suggested to contribute to this secondary injury cascade. Cyclosporine possesses neuroprotective properties that have been attributed to the desensitization of mitochondrial permeability transition pore activation. In vivo animal experiments have demonstrated neuroprotective effects of cyclosporine in more than 20 independent experimental studies in a multitude of different experimental models. However, the majority of these studies have been carried out in rodents. The aim of the present study was to evaluate the efficacy of a novel and cremophor/kolliphor EL-free lipid emulsion formulation of cyclosporine in a translational large animal model of TBI. A mild-to-moderate focal contusion injury was induced in piglets using a controlled cortical impact device. After initial step-wise analyses of pharmacokinetics and comparing with exposure of cyclosporine in clinical TBI trials, a 5-day dosing regimen with continuous intravenous cyclosporine infusion (20 mg/kg/day) was evaluated in a randomized and blinded placebo-controlled setting. Cyclosporine reduced the volume of parenchymal injury by 35%, as well as improved markers of neuronal injury, as measured with magnetic resonance spectroscopic imaging. Further, a consistent trend toward positive improvements in brain metabolism and mitochondrial function was observed in the pericontusional tissue. In this study, we have demonstrated efficacy using a novel cyclosporine formulation in clinically relevant and translatable outcome metrics in a large animal model of focal TBI.

Oxygen consumption in platelets as an adjunct diagnostic method for pediatric mitochondrial disease

BackgroundDiagnosing mitochondrial disease (MD) is a challenge. In addition to genetic analyses, clinical practice is to perform invasive procedures such as muscle biopsy for biochemical and histochemical analyses. Blood cell respirometry is rapid and noninvasive. Our aim was to explore its possible role in diagnosing MD.MethodsBlood samples were collected from 113 pediatric patients, for whom MD was a differential diagnosis. A respiratory analysis model based on ratios (independent of mitochondrial specific content) was derived from a group of healthy controls and tested on the patients. The diagnostic accuracy of platelet respirometry was evaluated against routine diagnostic investigation.ResultsMD prevalence in the cohort was 16%. A ratio based on the respiratory response to adenosine diphosphate in the presence of complex I substrates had 96% specificity for disease and a positive likelihood ratio of 5.3. None of the individual ratios had sensitivity above 50%, but a combined model had 72% sensitivity.ConclusionNormal findings of platelet respirometry are not able to rule out MD, but pathological results make the diagnosis more likely and could strengthen the clinical decision to perform further invasive analyses. Our results encourage further study into the role of blood respirometry as an adjunct diagnostic tool for MD.

The radiation dose to overweighted patients undergoing myocardial perfusion SPECT can be significantly reduced: validation of a linear weight-adjusted activity administration protocol

BACKGROUND

Large body size can cause a higher proportion of emitted photons being attenuated within the patient. Therefore, clinical myocardial perfusion SPECT (MPS) protocols often include unproportionally higher radioisotope activity to obese patients. The aim was to evaluate if a linear weight-adjusted low-dose protocol can be applied to obese patients and thereby decrease radiation exposure.

METHODS AND RESULT

Two hundred patients (>110 kg, BMI 18-41, [n = 69], ≤ 110 kg, BMI 31-58, [n = 131]) underwent 99mTc-tetrofosmin stress examination on a Cadmium Zinc Telluride or a conventional gamma camera using new generations of reconstruction algorithm (Resolution Recovery). Patients <110 kg were administered 2.5 MBq/kg, patients between 110 and 120 kg received 430 MBq and patients >120 kg received 570 MBq according to clinical routine. Patients >110 kg had 130% total number of counts in the images compared to patients <110 kg. Recalculating the counts to correspond to an administered activity of 2.5 MBq/kg resulted in similar number of counts across the groups. Image analyses in a subgroup with images corresponding to high activity and 2.5 MBq/kg showed no difference in image quality or ischemia quantification.

CONCLUSION

Linear low-dose weight-adjusted protocol of 2.5 MBq/kg in MPS can be applied over a large weight span without loss of counts or image quality, resulting in a significant reduction in radiation exposure to obese patients.

Ciclosporin to Protect Renal function In Cardiac Surgery (CiPRICS): a study protocol for a double-blind, randomised, placebo-controlled, proof-of-concept study

INTRODUCTION

Acute kidney injury (AKI) after cardiac surgery is common and results in increased morbidity and mortality. One possible mechanism for AKI is ischaemia-reperfusion injury caused by the extracorporeal circulation (ECC), resulting in an opening of the mitochondrial permeability transition pore (mPTP) in the kidneys, which can lead to cell injury or cell death. Ciclosporin may block the opening of mPTP if administered before the ischaemia-reperfusion injury. We hypothesised that ciclosporin given before the start of ECC in cardiac surgery can decrease the degree of AKI.

METHODS AND ANALYSIS

Ciclosporin to Protect Renal function In Cardiac Surgery (CiPRICS) study is an investigator-initiated double-blind, randomised, placebo-controlled, parallel design, single-centre study performed at a tertiary university hospital. The primary objective is to assess the safety and efficacy of ciclosporin to limit the degree of AKI in patients undergoing coronary artery bypass grafting surgery. We aim to evaluate 150 patients with a preoperative estimated glomerular filtration rate of 15-90 mL/min/1.73 m². Study patients are randomised in a 1:1 ratio to receive study drug 2.5 mg/kg ciclosporin or placebo as an intravenous injection after anaesthesia induction but before start of surgery. The primary end point consists of relative P-cystatin C changes from the preoperative day to postoperative day 3. The primary variable will be tested using an analysis of covariance method. Secondary end points include evaluation of P-creatinine and biomarkers of kidney, heart and brain injury.

ETHICS AND DISSEMINATION

The trial is conducted in compliance with the current version of the Declaration of Helsinki and the International Council for Harmonisation (ICH) Good Clinical Practice guidelines E6 (R1) and was approved by the Regional Ethical Review Board, Lund and the Swedish Medical Products Agency (MPA). Written and oral informed consent is obtained before enrolment into the study.

TRIAL REGISTRATION NUMBER

NCT02397213; Pre-results.

Cell-permeable succinate prodrugs bypass mitochondrial complex I deficiency

Mitochondrial complex I (CI) deficiency is the most prevalent defect in the respiratory chain in paediatric mitochondrial disease. This heterogeneous group of diseases includes serious or fatal neurological presentations such as Leigh syndrome and there are very limited evidence-based treatment options available. Here we describe that cell membrane-permeable prodrugs of the complex II substrate succinate increase ATP-linked mitochondrial respiration in CI-deficient human blood cells, fibroblasts and heart fibres. Lactate accumulation in platelets due to rotenone-induced CI inhibition is reversed and rotenone-induced increase in lactate:pyruvate ratio in white blood cells is alleviated. Metabolomic analyses demonstrate delivery and metabolism of [(13)C]succinate. In Leigh syndrome patient fibroblasts, with a recessive NDUFS2 mutation, respiration and spare respiratory capacity are increased by prodrug administration. We conclude that prodrug-delivered succinate bypasses CI and supports electron transport, membrane potential and ATP production. This strategy offers a potential future therapy for metabolic decompensation due to mitochondrial CI dysfunction.

Mitochondrial Respiratory Function in Peripheral Blood Cells from Huntington's Disease Patients

Background

Patients with Huntington's disease display symptoms from both the central nervous system and peripheral tissues. Mitochondrial dysfunction has been implicated as part of the pathogenesis of the disease and has been reported in brain tissue and extracerebral tissues, such as muscle and blood cells, but the results are inconsistent. Therefore, the authors performed a refined evaluation of mitochondrial function in 2 types of peripheral blood cells from 14 patients with Huntington's disease and 21 control subjects. Several hypotheses were predefined, including impaired mitochondrial complex II function (primary), complex I function (secondary), and maximum oxidative phosphorylation capacity (secondary) in patient cells.

Methods

High-resolution respirometry was applied to viable platelets and mononuclear cells. Data were normalized to cell counts, citrate synthase activity, and mitochondrial DNA copy numbers.

Results

Normalized to citrate synthase activity, platelets from patients with Huntington's disease displayed respiratory dysfunction linked to complex I, complex II, and lower maximum oxidative phosphorylation capacity. No difference was seen in mononuclear cells or when platelet data were normalized to cell counts or mitochondrial DNA. The ratio of complex I respiration through maximum oxidative phosphorylation was significantly decreased in patients compared with controls. The corresponding ratio for complex II was unaffected.

Conclusions

The data indicate decreased function of mitochondrial complex I in peripheral blood cells from patients with Huntington's disease, although this could not be uniformly confirmed. The results do not confirm a systemic complex II dysfunction and do not currently support the use of mitochondrial function in blood cells as a biomarker for the disease.

Mitochondrial response in a toddler-aged swine model following diffuse non-impact traumatic brain injury

Traumatic brain injury (TBI) is an important health problem, and a leading cause of death in children worldwide. Mitochondrial dysfunction is a critical component of the secondary TBI cascades. Mitochondrial response in the pediatric brain has limited investigation, despite evidence that the developing brain's response differs from that of the adult, especially in diffuse non-impact TBI. We performed a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a swine model of diffuse TBI (rapid non-impact rotational injury: RNR), and examined the cortex and hippocampus. A substrate-uncoupler-inhibitor-titration protocol examined the role of the individual complexes as well as the uncoupled maximal respiration. Respiration per mg of tissue was also related to citrate synthase activity (CS) as an attempt to control for variability in mitochondrial content following injury. Diffuse RNR stimulated increased complex II-driven respiration relative to mitochondrial content in the hippocampus compared to shams. LEAK (State 4o) respiration increased in both regions, with decreased respiratory ratios of convergent oxidative phosphorylation through complex I and II, compared to sham animals, indicating uncoupling of oxidative phosphorylation at 24h. The study suggests that proportionately, complex I contribution to convergent mitochondrial respiration was reduced in the hippocampus after RNR, with a simultaneous increase in complex-II driven respiration. Mitochondrial respiration 24h after diffuse TBI varies by location within the brain. We concluded that significant uncoupling of oxidative phosphorylation and alterations in convergent respiration through complex I- and complex II-driven respiration reveals therapeutic opportunities for the injured at-risk pediatric brain.

Persistently Altered Brain Mitochondrial Bioenergetics After Apparently Successful Resuscitation From Cardiac Arrest

BACKGROUND

Although advances in cardiopulmonary resuscitation have improved survival from cardiac arrest (CA), neurologic injury persists and impaired mitochondrial bioenergetics may be critical for targeted neuroresuscitation. The authors sought to determine if excellent cardiopulmonary resuscitation and postresuscitation care and good traditional survival rates result in persistently disordered cerebral mitochondrial bioenergetics in a porcine pediatric model of asphyxia-associated ventricular fibrillation CA.

METHODS AND RESULTS

After 7 minutes of asphyxia, followed by ventricular fibrillation, 5 female 1-month-old swine (4 sham) received blood pressure-targeted care: titration of compression depth to systolic blood pressure of 90 mm Hg and vasopressor administration to a coronary perfusion pressure >20 mm Hg. All animals received protocol-based vasopressor support after return of spontaneous circulation for 4 hours before they were killed. The primary outcome was integrated mitochondrial electron transport system (ETS) function. CA animals displayed significantly decreased maximal, coupled oxidative phosphorylating respiration (OXPHOSCI + CII) in cortex (P<0.02) and hippocampus (P<0.02), as well as decreased phosphorylation and coupling efficiency (cortex, P<0.05; hippocampus, P<0.05). Complex I- and complex II-driven respiration were both significantly decreased after CA (cortex: OXPHOSCI P<0.01, ETSCII P<0.05; hippocampus: OXPHOSCI P<0.03, ETSCII P<0.01). In the hippocampus, there was a significant decrease in maximal uncoupled, nonphosphorylating respiration (ETSCI + CII), as well as a 30% reduction in citrate synthase activity (P<0.04).

CONCLUSIONS

Mitochondria in both the cortex and hippocampus displayed significant alterations in respiratory function after CA despite excellent cardiopulmonary resuscitation and postresuscitation care in asphyxia-associated ventricular fibrillation CA. Analysis of integrated ETS function identifies mitochondrial bioenergetic failure as a target for goal-directed neuroresuscitation after CA. IACUC Protocol: IAC 13-001023.

Cyclosporine before PCI in Patients with Acute Myocardial Infarction

BACKGROUND

Experimental and clinical evidence suggests that cyclosporine may attenuate reperfusion injury and reduce myocardial infarct size. We aimed to test whether cyclosporine would improve clinical outcomes and prevent adverse left ventricular remodeling.

METHODS

In a multicenter, double-blind, randomized trial, we assigned 970 patients with an acute anterior ST-segment elevation myocardial infarction (STEMI) who were undergoing percutaneous coronary intervention (PCI) within 12 hours after symptom onset and who had complete occlusion of the culprit coronary artery to receive a bolus injection of cyclosporine (administered intravenously at a dose of 2.5 mg per kilogram of body weight) or matching placebo before coronary recanalization. The primary outcome was a composite of death from any cause, worsening of heart failure during the initial hospitalization, rehospitalization for heart failure, or adverse left ventricular remodeling at 1 year. Adverse left ventricular remodeling was defined as an increase of 15% or more in the left ventricular end-diastolic volume.

RESULTS

A total of 395 patients in the cyclosporine group and 396 in the placebo group received the assigned study drug and had data that could be evaluated for the primary outcome at 1 year. The rate of the primary outcome was 59.0% in the cyclosporine group and 58.1% in the control group (odds ratio, 1.04; 95% confidence interval [CI], 0.78 to 1.39; P=0.77). Cyclosporine did not reduce the incidence of the separate clinical components of the primary outcome or other events, including recurrent infarction, unstable angina, and stroke. No significant difference in the safety profile was observed between the two treatment groups.

CONCLUSIONS

In patients with anterior STEMI who had been referred for primary PCI, intravenous cyclosporine did not result in better clinical outcomes than those with placebo and did not prevent adverse left ventricular remodeling at 1 year. (Funded by the French Ministry of Health and NeuroVive Pharmaceutical; CIRCUS ClinicalTrials.gov number, NCT01502774; EudraCT number, 2009-013713-99.).

Mitochondrial bioenergetic alterations after focal traumatic brain injury in the immature brain

Traumatic brain injury (TBI) is one of the leading causes of death in children worldwide. Emerging evidence suggests that alterations in mitochondrial function are critical components of secondary injury cascade initiated by TBI that propogates neurodegeneration and limits neuroregeneration. Unfortunately, there is very little known about the cerebral mitochondrial bioenergetic response from the immature brain triggered by traumatic biomechanical forces. Therefore, the objective of this study was to perform a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a high-fidelity large animal model of focal controlled cortical impact injury (CCI) 24h post-injury. This novel approach is directed at analyzing dysfunction in electron transport, ADP phosphorylation and leak respiration to provide insight into potential mechanisms and possible interventions for mitochondrial dysfunction in the immature brain in focal TBI by delineating targets within the electron transport system (ETS). Development and application of these methodologies have several advantages, and adds to the interpretation of previously reported techniques, by having the added benefit that any toxins or neurometabolites present in the ex-vivo samples are not removed during the mitochondrial isolation process, and simulates the in situ tricarboxylic acid (TCA) cycle by maximizing key substrates for convergent flow of electrons through both complexes I and II. To investigate alterations in mitochondrial function after CCI, ipsilateral tissue near the focal impact site and tissue from the corresponding contralateral side were examined. Respiration per mg of tissue was also related to citrate synthase activity (CS) and calculated flux control ratios (FCR), as an attempt to control for variability in mitochondrial content. Our biochemical analysis of complex interdependent pathways of electron flow through the electron transport system, by most measures, reveals a bilateral decrease in complex I-driven respiration and an increase in complex II-driven respiration 24h after focal TBI. These alterations in convergent electron flow though both complex I and II-driven respiration resulted in significantly lower maximal coupled and uncoupled respiration in the ipsilateral tissue compared to the contralateral side, for all measures. Surprisingly, increases in complex II and complex IV activities were most pronounced in the contralateral side of the brain from the focal injury, and where oxidative phosphorylation was increased significantly compared to sham values. We conclude that 24h after focal TBI in the immature brain, there are significant alterations in cerebral mitochondrial bioenergetics, with pronounced increases in complex II and complex IV respiration in the contralateral hemisphere. These alterations in mitochondrial bioenergetics present multiple targets for therapeutic intervention to limit secondary brain injury and support recovery.

The E3 ligase synoviolin controls body weight and mitochondrial biogenesis through negative regulation of PGC-1β

Obesity is a major global public health problem, and understanding its pathogenesis is critical for identifying a cure. In this study, a gene knockout strategy was used in post-neonatal mice to delete synoviolin (Syvn)1/Hrd1/Der3, an ER-resident E3 ubiquitin ligase with known roles in homeostasis maintenance. Syvn1 deficiency resulted in weight loss and lower accumulation of white adipose tissue in otherwise wild-type animals as well as in genetically obese (ob/ob and db/db) and adipose tissue-specific knockout mice as compared to control animals. SYVN1 interacted with and ubiquitinated the thermogenic coactivator peroxisome proliferator-activated receptor coactivator (PGC)-1β, and Syvn1 mutants showed upregulation of PGC-1β target genes and increase in mitochondrion number, respiration, and basal energy expenditure in adipose tissue relative to control animals. Moreover, the selective SYVN1 inhibitor LS-102 abolished the negative regulation of PGC-1β by SYVN1 and prevented weight gain in mice. Thus, SYVN1 is a novel post-translational regulator of PGC-1β and a potential therapeutic target in obesity treatment.

Importance of correct patient positioning in myocardial perfusion SPECT when using a CZT camera

INTRODUCTION

Myocardial perfusion single photon emission computed tomography (MPS) is one of the most widely used diagnostic methods in patients with suspected ischemic heart disease (IHD). Recently, a novel technique based on cadmium-zinc-telluride (CZT) detectors, pinhole collimators, and a stationary gantry was introduced for MPS. The aim of this work was to investigate how patient positioning affects the reconstructed MPS images using this novel technique.

MATERIALS AND METHODS

Eighteen patients referred for a clinical MPS due to suspected IHD were included in the study. All patients underwent MPS imaging on a GE Discovery NM 530c CZT camera. After image acquisition with the heart positioned in the center of the quality field of view (QFOV), the patients were re-imaged in different positions 5-20 mm off-center. The heart was still positioned within the limits of the QFOV during the off-center scans. The summed stress score and/or the summed rest score (SSS and/or SRS) for the acquisition performed in the center was compared to the same parameter for the acquisitions performed off-center.

RESULTS

There was a statistically significant increase in SSS and/or SRS when imaging was performed with the heart 5-20 mm outside the center of the QFOV compared to optimal positioning (7.7 ± 1.3 vs 6.6 ± 1.3, P = .006). The SSS and/or SRS increased with ≥2 U in 35% (14/40) of the off-center examinations.

CONCLUSION

It is important to carefully position the patient's heart within the center of the QFOV when performing MPS with the Discovery NM 530c CZT camera to avoid positioning-related image artifacts that could affect the diagnostic accuracy.

Cytokine and nitric oxide levels in patients with sepsis--temporal evolvement and relation to platelet mitochondrial respiratory function

BACKGROUND

The levels of nitric oxide (NO) and various cytokines are known to be increased during sepsis. These signaling molecules could potentially act as regulators and underlie the enhancement of mitochondrial function described in the later phase of sepsis. Therefore, we investigated the correlation between observed changes in platelet mitochondrial respiration and a set of pro- and anti-inflammatory cytokines as well as NO plasma levels in patients with sepsis.

METHODS AND RESULTS

Platelet mitochondrial respiration and levels of TNFα, MCP-1 (monocyte chemotactic protein-1), INFγ (interferon-γ), IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10 and IL-17 and NO were analyzed in 38 patients with severe sepsis or septic shock at three time points during one week following admission to the ICU. Citrate synthase, mitochondrial DNA and cytochrome c were measured as markers of cellular mitochondrial content. All mitochondrial respiratory states increased over the week analyzed (p<0.001). IL-8 levels correlated with maximal mitochondrial respiration on day 6-7 (p = 0.02, r2 = 0.22) and was also higher in non-survivors compared to survivors on day 3-4 and day 6-7 (p = 0.03 respectively). Neither NO nor any of the other cytokines measured correlated with respiration or mortality. Cytochrome c levels were decreased at day 1-2 by 24 ± 5% (p = 0.03) and returned towards values of the controls at the last two time points. Citrate synthase activity and mitochondrial DNA levels were similar to controls and remained constant throughout the week.

CONCLUSIONS

Out of ten analyzed cytokines and nitric oxide, IL-8 correlated with the observed increase in mitochondrial respiration. This suggests that cytokines as well as NO do not play a prominent role in the regulation of platelet mitochondrial respiration in sepsis. Further, the respiratory increase was not accompanied by an increase in markers of mitochondrial content, suggesting a possible role for post-translational enhancement of mitochondrial respiration rather than augmented mitochondrial mass.

Cytokine and nitric oxide levels in patients with sepsis--temporal evolvement and relation to platelet mitochondrial respiratory function

Background

The levels of nitric oxide (NO) and various cytokines are known to be increased during sepsis. These signaling molecules could potentially act as regulators and underlie the enhancement of mitochondrial function described in the later phase of sepsis. Therefore, we investigated the correlation between observed changes in platelet mitochondrial respiration and a set of pro- and anti-inflammatory cytokines as well as NO plasma levels in patients with sepsis.

Methods and Results

Platelet mitochondrial respiration and levels of TNFα, MCP-1 (monocyte chemotactic protein-1), INFγ (interferon-γ), IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10 and IL-17 and NO were analyzed in 38 patients with severe sepsis or septic shock at three time points during one week following admission to the ICU. Citrate synthase, mitochondrial DNA and cytochrome c were measured as markers of cellular mitochondrial content. All mitochondrial respiratory states increased over the week analyzed (p<0.001). IL-8 levels correlated with maximal mitochondrial respiration on day 6–7 (p = 0.02, r² = 0.22) and was also higher in non-survivors compared to survivors on day 3–4 and day 6–7 (p = 0.03 respectively). Neither NO nor any of the other cytokines measured correlated with respiration or mortality. Cytochrome c levels were decreased at day 1–2 by 24±5% (p = 0.03) and returned towards values of the controls at the last two time points. Citrate synthase activity and mitochondrial DNA levels were similar to controls and remained constant throughout the week.

Conclusions

Out of ten analyzed cytokines and nitric oxide, IL-8 correlated with the observed increase in mitochondrial respiration. This suggests that cytokines as well as NO do not play a prominent role in the regulation of platelet mitochondrial respiration in sepsis. Further, the respiratory increase was not accompanied by an increase in markers of mitochondrial content, suggesting a possible role for post-translational enhancement of mitochondrial respiration rather than augmented mitochondrial mass.

Respiratory uncoupling by increased H(+) or K(+) flux is beneficial for heart mitochondrial turnover of reactive oxygen species but not for permeability transition

Background

Ischemic preconditioning has been proposed to involve changes in mitochondrial H⁺ and K⁺ fluxes, in particular through activation of uncoupling proteins and ATP-sensitive K⁺ channels (MitoK_ATP). The objectives of the present study were to explore how increased H⁺ and K⁺ fluxes influence heart mitochondrial physiology with regard to production and scavenging of reactive oxygen species (ROS), volume changes and resistance to calcium-induced mitochondrial permeability transition (mPT).

Results

Isolated rat heart mitochondria were exposed to a wide concentration range of the protonophore CCCP or the potassium ionophore valinomycin to induce increased H⁺ and K⁺ conductance, respectively. Simultaneous monitoring of mitochondrial respiration and calcium retention capacity (CRC) demonstrated that the relative increase in respiration caused by valinomycin or CCCP correlated with a decrease in CRC, and that no level of respiratory uncoupling was associated with enhanced resistance to mPT. Mitochondria suspended in hyperosmolar buffer demonstrated a dose-dependent reduction in CRC with increasing osmolarity. However, mitochondria in hypoosmolar buffer to increase matrix volume did not display increased CRC. ROS generation was reduced by both K⁺- and H⁺-mediated respiratory uncoupling. The ability of heart mitochondria to detoxify H₂O₂ was substantially greater than the production rate. The H₂O₂ detoxification was dependent on respiratory substrates and was dramatically decreased following calcium-induced mPT, but was unaffected by uncoupling via increased K⁺ and H⁺ conductance.

Conclusion

It is concluded that respiratory uncoupling is not directly beneficial to rat heart mitochondrial resistance to calcium overload irrespective of whether H⁺ or K⁺ conductance is increased. The negative effects of respiratory uncoupling thus probably outweigh the reduction in ROS generation and a potential positive effect by increased matrix volume, resulting in a net sensitization of heart mitochondria to mPT activation.

Patients with sepsis exhibit increased mitochondrial respiratory capacity in peripheral blood immune cells

Introduction

In sepsis, mitochondria have been associated with both initial dysfunction and subsequent upregulation (biogenesis). However, the evolvement of mitochondrial function in sepsis over time is largely unknown, and we therefore investigated mitochondrial respiration in peripheral blood immune cells (PBICs) in sepsis patients during the first week after admission to the intensive care unit (ICU).

Methods

PBICs from 20 patients with severe sepsis or septic shock were analyzed with high-resolution respirometry 3 times after admission to the ICU (within 48 hours, days 3 to 4 and days 6 to 7). Mitochondrial DNA (mtDNA), cytochrome c (Cyt c), and citrate synthase (CS) were measured as indicators of cellular mitochondrial content.

Results

In intact PBICs with endogenous substrates, a gradual increase in cellular respiration reached 173% of controls after 1 week (P = 0.001). In permeabilized cells, respiration using substrates of complex I, II, and IV were significantly increased days 1 to 2, reaching 137%, 130%, and 173% of controls, respectively. In parallel, higher levels of CS activity, mtDNA, and Cyt c content in PBICs (211%, 243%, and 331% of controls for the respective indicators were found at days 6 to 7; P < 0.0001). No differences in respiratory capacities were noted between survivors and nonsurvivors at any of the time points measured.

Conclusions

PBICs from patients with sepsis displayed higher mitochondrial respiratory capacities compared with controls, due to an increased mitochondrial content, as indicated by increased mitochondrial DNA, protein content, and enzyme activity. The results argue against mitochondrial respiratory dysfunction in this type of cells in sepsis.

Functional and pharmacological characteristics of permeability transition in isolated human heart mitochondria

The objective of the present study was to validate the presence and explore the characteristics of mitochondrial permeability transition (mPT) in isolated mitochondria from human heart tissue in order to investigate if previous findings in animal models of cardiac disorders are translatable to human disease. Mitochondria were rapidly isolated from fresh atrial tissue samples obtained from 14 patients undergoing Maze surgery due to atrial fibrillation. Human heart mitochondria exhibited typical mPT characteristics upon calcium overload such as swelling, evaluated by changes in light scattering, inhibition of respiration and loss of respiratory coupling. Swelling was a morphologically reversible event following transient calcium challenge. Calcium retention capacity (CRC), a quantitative measure of mPT sensitivity assayed by following extramitochondrial [Ca(2+)] and changes in respiration during a continuous calcium infusion, was significantly increased by cyclophilin D (CypD) inhibitors. The thiol-reactive oxidant phenylarsine oxide sensitized mitochondria to calcium-induced mPT. Release of the pro-apoptotic intermembrane protein cytochrome c was increased after, but not before, calcium discharge and respiratory inhibition in the CRC assay. From the present study, we conclude that adult viable heart mitochondria have a CypD- and oxidant-regulated mPT. The findings support that inhibition of mPT may be a relevant pharmacological target in human cardiac disease and may underlie the beneficial effect of cyclosporin A in reperfusion injury.

Microchannel acoustophoresis does not impact survival or function of microglia, leukocytes or tumor cells

BACKGROUND

The use of acoustic forces to manipulate particles or cells at the microfluidic scale (i.e. acoustophoresis), enables non-contact, label-free separation based on intrinsic cell properties such as size, density and compressibility. Acoustophoresis holds great promise as a cell separation technique in several research and clinical areas. However, it has been suggested that the force acting upon cells undergoing acoustophoresis may impact cell viability, proliferation or cell function via subtle phenotypic changes. If this were the case, it would suggest that the acoustophoresis method would be a less useful tool for many cell analysis applications as well as for cell therapy.

METHODS

We investigate, for the first time, several key aspects of cellular changes following acoustophoretic processing. We used two settings of ultrasonic actuation, one that is used for cell sorting (10 Vpp operating voltage) and one that is close to the maximum of what the system can generate (20 Vpp). We used microglial cells and assessed cell viability and proliferation, as well as the inflammatory response that is indicative of more subtle changes in cellular phenotype. Furthermore, we adapted a similar methodology to monitor the response of human prostate cancer cells to acoustophoretic processing. Lastly, we analyzed the respiratory properties of human leukocytes and thrombocytes to explore if acoustophoretic processing has adverse effects.

RESULTS

BV2 microglia were unaltered after acoustophoretic processing as measured by apoptosis and cell turnover assays as well as inflammatory cytokine response up to 48 h following acoustophoresis. Similarly, we found that acoustophoretic processing neither affected the cell viability of prostate cancer cells nor altered their prostate-specific antigen secretion following androgen receptor activation. Finally, human thrombocytes and leukocytes displayed unaltered mitochondrial respiratory function and integrity after acoustophoretic processing.

CONCLUSION

We conclude that microchannel acoustophoresis can be used for effective continuous flow-based cell separation without affecting cell viability, proliferation, mitochondrial respiration or inflammatory status.

Cyclophilin-D inhibition in neuroprotection: dawn of a new era of mitochondrial medicine

Traumatic brain injury and ischemia can result in marked neuronal degeneration and residual impairment of cerebral function. However, no effective pharmacological treatment directed at tissues of the central nervous system (CNS) for acute intervention has been developed. The detailed pathophysiological cascade leading to -neurodegeneration in these conditions has not been elucidated, but cellular calcium overload and mitochondrial dysfunction have been implicated in a wide range of animal models involving degeneration of the CNS. In particular, activation of the calcium-induced mitochondrial permeability transition (mPT) is considered to be a major cause of cell death inferred by the broad and potent neuroprotective effects of -pharmacological inhibitors of mPT, especially modulators of cyclophilin activity and, more specifically, genetic inactivation of the mitochondrial cyclophilin, cyclophilin D. Reviewed are evidence and challenges that could bring on the dawning of mitochondrial medicine aimed at safeguarding energy supply following acute injury to the CNS.

Mitochondrial respiration in human viable platelets--methodology and influence of gender, age and storage

Studying whole cell preparations with intact mitochondria and respiratory complexes has a clear benefit compared to isolated or disrupted mitochondria due to the dynamic interplay between mitochondria and other cellular compartments. Platelet mitochondria have a potential to serve as a source of human viable mitochondria when studying mitochondrial physiology and pathogenic mechanisms, as well as for the diagnostics of mitochondrial diseases. The objective of the present study was to perform a detailed evaluation of platelet mitochondrial respiration using high-resolution respirometry. Further, we aimed to explore the limits of sample size and the impact of storage as well as to establish a wide range of reference data from different pediatric and adult cohorts. Our results indicate that platelet mitochondria are well suited for ex-vivo analysis with the need for minute sample amounts and excellent reproducibility and stability.

Brain mitochondrial function in a murine model of cerebral malaria and the therapeutic effects of rhEPO

Cerebral malaria (CM) is a life-threatening complication of Plasmodium falciparum infection. The pathogenesis of CM is complex. Cerebral metabolic dysfunction is implicated in CM, which may be caused by both an impaired cerebral microcirculation and a dysregulated inflammatory response affecting cellular respiration of mitochondria. Recombinant human erythropoietin (rhEPO) is a promising new therapy that has been shown to reduce mortality in a mouse model of CM. In order to further elucidate the metabolic dysfunction in CM the objective of the present study was to assess brain mitochondrial respiratory function in CM with and without rhEPO treatment. The P. berghei ANKA - C57BL/6 murine model of CM was used. Mitochondrial respiration was analyzed in brain homogenates using high-resolution respirometry and a multiple substrate and inhibitor protocol. The animals were divided into four groups; infected injected with saline or with rhEPO, non-infected injected with saline or with rhEPO. Infected mice developed CM and treatment with rhEPO attenuated clinical signs of disease. There were no differences in respiratory parameters of brain mitochondria between infected and non-infected mice and no connection between disease severity and mitochondrial respiratory function. Treatment with rhEPO similarly had no effect on respiratory function. Thus cerebral metabolic dysfunction in CM does not seem to be directly linked to altered mitochondrial respiratory capacity as analyzed in brain homogenates ex vivo. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Cyclophilin D-sensitive mitochondrial permeability transition in adult human brain and liver mitochondria

The mitochondrial permeability transition (mPT) is considered to be a major cause of cell death under a variety of pathophysiological conditions of the central nervous system (CNS) and other organs. Pharmacological inhibition or genetic knockout of the matrix protein cyclophilin D (CypD) prevents mPT and cell degeneration in several models of brain injury. If these findings in animal models are translatable to human disease, pharmacological inhibition of mPT offers a promising therapeutic target. The objective of this study was to validate the presence of a CypD-sensitive mPT in adult human brain and liver mitochondria. In order to perform functional characterization of human mitochondria, fresh tissue samples were obtained during hemorrhage or tumor surgery and mitochondria were rapidly isolated. Mitochondrial calcium retention capacity, a quantitative assay for mPT, was significantly increased by the CypD inhibitor cyclosporin A in both human brain and liver mitochondria, whereas thiol-reactive compounds and oxidants sensitized mitochondria to calcium-induced mPT. Brain mitochondria underwent swelling upon calcium overload, which was reversible upon calcium removal. To further explore mPT of human mitochondria, liver mitochondria were demonstrated to exhibit several classical features of the mPT phenomenon, such as calcium-induced loss of membrane potential and respiratory coupling, as well as release of the pro-apoptotic protein cytochrome c. We concluded that adult viable human brain and liver mitochondria possess an active CypD-sensitive mPT. Our findings support the rationale of CypD and mPT inhibition as pharmacological targets in acute and chronic neurodegeneration.

Temporal increase of platelet mitochondrial respiration is negatively associated with clinical outcome in patients with sepsis

Introduction

Mitochondrial dysfunction has been suggested as a contributing factor to the pathogenesis of sepsis-induced multiple organ failure. Also, restoration of mitochondrial function, known as mitochondrial biogenesis, has been implicated as a key factor for the recovery of organ function in patients with sepsis. Here we investigated temporal changes in platelet mitochondrial respiratory function in patients with sepsis during the first week after disease onset.

Methods

Platelets were isolated from blood samples taken from 18 patients with severe sepsis or septic shock within 48 hours of their admission to the intensive care unit. Subsequent samples were taken on Day 3 to 4 and Day 6 to 7. Eighteen healthy blood donors served as controls. Platelet mitochondrial function was analyzed by high-resolution respirometry. Endogenous respiration of viable, intact platelets suspended in their own plasma or phosphate-buffered saline (PBS) glucose was determined. Further, in order to investigate the role of different dehydrogenases and respiratory complexes as well as to evaluate maximal respiratory activity of the mitochondria, platelets were permeabilized and stimulated with complex-specific substrates and inhibitors.

Results

Platelets suspended in their own septic plasma exhibited increased basal non-phosphorylating respiration (state 4) compared to controls and to platelets suspended in PBS glucose. In parallel, there was a substantial increase in respiratory capacity of the electron transfer system from Day 1 to 2 to Day 6 to 7 as well as compared to controls in both intact and permeabilized platelets oxidizing Complex I and/or II-linked substrates. No inhibition of respiratory complexes was detected in septic patients compared to controls. Non-survivors, at 90 days, had a more elevated respiratory capacity at Day 6 to 7 as compared to survivors. Cytochrome c increased over the time interval studied but no change in mitochondrial DNA was detected.

Conclusions

The results indicate the presence of a soluble plasma factor in the initial stage of sepsis inducing uncoupling of platelet mitochondria without inhibition of the electron transfer system. The mitochondrial uncoupling was paralleled by a gradual and substantial increase in respiratory capacity. This may reflect a compensatory response to severe sepsis or septic shock, that was most pronounced in non-survivors, likely correlating to the severity of the septic insult.

Increased potassium conductance of brain mitochondria induces resistance to permeability transition by enhancing matrix volume

Modulation of K(+) conductance of the inner mitochondrial membrane has been proposed to mediate preconditioning in ischemia-reperfusion injury. The mechanism is not entirely understood, but it has been linked to a decreased activation of mitochondrial permeability transition (mPT). In the present study K(+) channel activity was mimicked by picomolar concentrations of valinomycin. Isolated brain mitochondria were exposed to continuous infusions of calcium. Monitoring of extramitochondrial Ca(2+) and mitochondrial respiration provided a quantitative assay for mPT sensitivity by determining calcium retention capacity (CRC). Valinomycin and cyclophilin D inhibition separately and additively increased CRC. Comparable degrees of respiratory uncoupling induced by increased K(+) or H(+) conductance had opposite effects on mPT sensitivity. Protonophores dose-dependently decreased CRC, demonstrating that so-called mild uncoupling was not beneficial per se. The putative mitoK(ATP) channel opener diazoxide did not mimic the effect of valinomycin. An alkaline matrix pH was required for mitochondria to retain calcium, but increased K(+) conductance did not result in augmented DeltapH. The beneficial effect of valinomycin on CRC was not mediated by H(2)O(2)-induced protein kinase Cepsilon activation. Rather, increased K(+) conductance reduced H(2)O(2) generation during calcium infusion. Lowering the osmolarity of the buffer induced an increase in mitochondrial volume and improved CRC similar to valinomycin without inducing uncoupling or otherwise affecting respiration. We propose that increased potassium conductance in brain mitochondria may cause a direct physiological effect on matrix volume inducing resistance to pathological calcium challenges.

Evaluation of putative inhibitors of mitochondrial permeability transition for brain disorders--specificity vs. toxicity

Inhibition of mitochondrial permeability transition (mPT) has emerged as a promising approach for neuroprotection and development of well-tolerated mPT inhibitors with favorable blood-brain barrier penetration is highly warranted. In a recent study, 28 clinically available drugs with a common heterocyclic structure were identified as mPT inhibitors e.g. trifluoperazine, promethazine and nortriptyline. In addition, neuroprotection by structurally unrelated drugs e.g. neurosteroids, 4-hydroxy-tamoxifen and trimetazidine has been attributed to direct inhibition of mPT. The regulation of mPT is complex and highly dependent on the prevailing experimental conditions. Several features of mPT, such as swelling, depolarization or NADH oxidation, can also occur independently of the mPT phenomenon. Here, in isolated rodent brain-derived and human liver mitochondria, we re-evaluate drugs promoted as potent mPT inhibitors. We address the definition of an mPT inhibitor and present strategies to reliably detect mPT inhibition in vitro. Surprisingly, none of the 12 compounds tested displayed convincing mPT inhibition or effects comparable to cyclophilin D inhibition by the non-immunosuppressive cyclophilin inhibitor D-MeAla(3)-EtVal(4)-Cyclosporin (Debio 025). Propofol and 2-aminoethoxydiphenyl borate (2-APB) inhibited swelling in de-energized mitochondria but did not increase calcium retention capacity (CRC). Progesterone, trifluoperazine, allopregnanolone and 4-hydroxy-tamoxifen dose-dependently reduced CRC and respiratory control and were thus toxic rather than beneficial to mitochondrial function. Interestingly, topiramate increased CRC at high concentrations likely by a mechanism separate from direct mPT inhibition. We conclude that a clinically relevant mPT inhibitor should have a mitochondrial target and increase mitochondrial calcium retention at concentrations which can be translated to human use.

Probing the molecular mechanisms of neuronal degeneration: importance of mitochondrial dysfunction and calcineurin activation

Cerebral injury is a critical aspect of the management of patients in intensive care. Pathological conditions induced by cerebral ischemia, hypoxia, head trauma, and seizure activity can result in marked residual impairment of cerebral function. We have investigated the potential mechanisms leading to neuronal cell death in pathological conditions, with the aim of discovering therapeutic targets and methods to minimize neuronal damage resulting from insults directed at the central nervous system (CNS). Over the years, deeper understanding of the mechanisms of neuronal cell death has indeed evolved, enabling clinical critical care management to salvage neurons that are at the brink of degeneration and to support recovery of brain function. However, no substantial breakthrough has been achieved in the quest to develop effective pharmacological neuroprotective therapy directed at tissues of the CNS. The current situation is unacceptable, and preservation of function and protection of the brain from terminal impairment will be a vital medical issue in the twenty-first century. To achieve this goal, it is critical to clarify the key mechanisms leading to neuronal cell death. Here, we discuss the importance of the calcineurin/immunophilin signal transduction pathway and mitochondrial involvement in the detrimental chain of events leading to neuronal degeneration.

Calcium-induced generation of reactive oxygen species in brain mitochondria is mediated by permeability transition

Mitochondrial uptake of calcium in excitotoxicity is associated with subsequent increase in reactive oxygen species (ROS) generation and delayed cellular calcium deregulation in ischemic and neurodegenerative insults. The mechanisms linking mitochondrial calcium uptake and ROS production remain unknown but activation of the mitochondrial permeability transition (mPT) may be one such mechanism. In the present study, calcium increased ROS generation in isolated rodent brain and human liver mitochondria undergoing mPT despite an associated loss of membrane potential, NADH and respiration. Unspecific permeabilization of the inner mitochondrial membrane by alamethicin likewise increased ROS independently of calcium, and the ROS increase was further potentiated if NAD(H) was added to the system. Importantly, calcium per se did not induce a ROS increase unless mPT was triggered. Twenty-one cyclosporin A analogs were evaluated for inhibition of calcium-induced ROS and their efficacy clearly paralleled their potency of inhibiting mPT-mediated mitochondrial swelling. We conclude that while intact respiring mitochondria possess powerful antioxidant capability, mPT induces a dysregulated oxidative state with loss of GSH- and NADPH-dependent ROS detoxification. We propose that mPT is a significant cause of pathological ROS generation in excitotoxic cell death.

Spinal cord mitochondria display lower calcium retention capacity compared with brain mitochondria without inherent differences in sensitivity to cyclophilin D inhibition

The mitochondrial permeability transition (mPT) is a potential pathogenic mechanism in neurodegeneration. Varying sensitivity to calcium-induced mPT has been demonstrated for regions within the CNS possibly correlating with vulnerability following insults. The spinal cord is selectively vulnerable in e.g. amyotrophic lateral sclerosis and increased mPT sensitivity of mitochondria derived from the spinal cord has previously been demonstrated. In this study, we introduce whole-body hypothermia prior to removal of CNS tissue to minimize the effects of differential tissue extraction prior to isolation of spinal cord and cortical brain mitochondria. Spinal cord mitochondria were able to retain considerably less calcium when administered as continuous infusion, which was not related to a general increased sensitivity of the mPT to calcium, its desensitization to calcium by the cyclophilin D inhibitor cyclosporin-A, or to differences in respiratory parameters. Spinal cord mitochondria maintained a higher concentration of extramitochondrial calcium during infusion than brain mitochondria possibly related to an increased set-point concentration for calcium uptake. A hampered transport and retention capacity of calcium may translate into an increased susceptibility of the spinal cord to neurodegenerative processes involving calcium-mediated damage.

Re-evaluation of mitochondrial permeability transition as a primary neuroprotective target of minocycline

Minocycline has been shown to be neuroprotective in ischemic and neurodegenerative disease models and could potentially be relevant for clinical use. We revisited the hypothesis that minocycline acts through direct inhibition of calcium-induced mitochondrial permeability transition (mPT) resulting in reduced release of cytochrome c (cyt c). Minocycline, at high dosage, was found to prevent calcium-induced mitochondrial swelling under energized conditions similarly to the mPT inhibitor cyclosporin A (CsA) in rodent mitochondria derived from the CNS. In contrast to CsA, minocycline dose-dependently reduced mitochondrial calcium retention capacity (CRC) and respiratory control ratios and was ineffective in the de-energized mPT assay. Further, minocycline did not inhibit calcium- or tBid-induced cyt c release. We conclude that the neuroprotective mechanism of minocycline is likely not related to direct inhibition of mPT and propose that the mitochondrial effects of minocycline may contribute to toxicity rather than tissue protection at high dosing in animals and humans.

Binding mitochondria to cryogel monoliths allows detection of proteins specifically released following permeability transition

Following proapoptotic signals such as calcium-induced mitochondrial permeability transition or translocation of proapoptotic proteins, mitochondria induce cell death through release of apoptogenic proteins. The mechanism of release and the identity of the released proteins are currently debated. Earlier attempts at identification of the apoptogenic proteins have been hampered by a high nonspecific background. Our aim was to develop a novel method where background release was eliminated, allowing proteins specifically released from mitochondria following proapoptotic stimulation to be identified. Liver mitochondria were immobilized and washed on cryogel monoliths prior to induction of protein release (calcium or Bid/Bax). Immobilized mitochondria exhibited normal morphology and swelling response and retained respiratory activity. The released proteins were collected, concentrated, separated on polyacrylamide gels which were cut into pieces, trypsin-digested, and analyzed using liquid chromatography-tandem mass spectrometry. Control samples contained no protein, and stimulation with calcium and Bid/Bax resulted in identification of 68 and 82 proteins, respectively. We conclude that, in combination with the robust proteomic approach, immobilization on cryogel monoliths is a fruitful approach for studying specific protein release from isolated mitochondria. We propose that this method is a powerful tool to further characterize the role of mitochondria in cell death induction.

The temperature dependence and involvement of mitochondria permeability transition and caspase activation in damage to organotypic hippocampal slices following in vitro ischemia

The aggravating effect of hyperglycemia on ischemic brain injury can be mimicked in a model of in vitro ischemia (IVI) using murine hippocampal slice cultures. Using this model, we found that the damage in the CA1 region following IVI in the absence or presence of 40 mm glucose (hyperglycemia) is highly temperature dependent. Decreasing the temperature from 35 to 31 degrees C during IVI prevented cell death, whereas increasing the temperature by 2 degrees C markedly aggravated damage. As blockade of the mitochondrial permeability transition (MPT) is equally effective as hypothermia in preventing ischemic cell death in vivo, we investigated whether inhibition of MPT or of caspases was protective following IVI. In the absence of glucose, the MPT blockers cyclosporin A and MeIle4-CsA but not the immunosuppressive compound FK506 diminished cell death. In contrast, following hyperglycemic IVI, MPT blockade was ineffective. Also, the pan-caspase inhibitor Boc-Asp(OMe)fluoromethyl ketone did not decrease cell death in the CA1 region following IVI or hyperglycemic IVI. We conclude that cell death in the CA1 region of organotypic murine hippocampal slices following IVI is highly temperature dependent and involves MPT. In contrast, cell death following hyperglycemic IVI, although completely prevented by hypothermia, is not mediated by mechanisms that involve MPT or caspase activation.

The Nonimmunosuppressive Cyclosporin Analogs NIM811 and UNIL025 Display Nanomolar Potencies on Permeability Transition in Brain-Derived Mitochondria

Cyclosporin A (CsA) is highly neuroprotective in several animal models of acute neurological damage and neurodegenerative disease with inhibition of the mitochondrial permeability transition (mPT) having emerged as a possible mechanism for the observed neuroprotection. In the present study, we have evaluated two new nonimmunosuppressive cyclosporin analogs NIM811 (Novartis) and UNIL025 (Debiopharm) for their ability to inhibit mPT in rat brain-derived mitochondria. Both NIM811 and UNIL025 were found to be powerful inhibitors of calcium-induced mitochondrial swelling under energized and deenergized conditions, and the maximal effects were identical to those of native CsA. The potencies of mPT inhibition by NIM811 and UNIL025 were stronger, with almost one order of magnitude higher potency for UNIL025 compared to CsA, correlating to their respective inhibitory action of cyclophilin activity. These compounds will be instrumental in the evaluation of mPT as a central target for neuroprotection in vivo.

Life span extension and reduced neuronal death after weekly intraventricular cyclosporin injections in the G93A transgenic mouse model of amyotrophic lateral sclerosis

Object. The authors investigated whether cyclosporin A (CsA), a cyclophilin ligand with mitochondrial permeability transition pore-blocking and calcineurin-inhibiting properties, affects motor function, neuronal death, and life span in the G93A transgenic mouse model of familial amyotrophic lateral sclerosis (FALS).

Methods. The G93A mice received weekly intracerebroventricular injections of CsA (20 µg/mouse/week) starting at the age of 65 days, and physical performance on an exercise wheel was monitored beginning at 84 days of age. Mice were allowed to survive for clinical observation of body weight, hindlimb weakness, and life span or until a defined end stage or were killed at 110 days of age for histological analysis.

Conclusions. Treatment with CsA significantly delayed the onset of hindlimb weakness and also extended the time from its onset to paralysis. The overall life span of CsA-treated G93A mice was significantly extended, by 12% compared with vehicle-treated transgenic littermates. The CsA also prolonged physical performance on the exercise wheel and delayed weight loss. Histologically, there was significant preservation of both cervical and lumbar spine motor neurons and also tyrosine hydroxylase—positive dopaminergic substantia nigra neurons in 110-day-old CsA-treated mice compared with their transgenic littermates. The local administration of CsA directly into the brain ventricles is an effective means of central nervous system drug delivery (because CsA does not readily cross the blood—brain barrier), which in this study ameliorated clinical and neuropathological features of FALS in G93A mice. The remarkably low intrathecal CsA dose required for neuroprotection reduces potential adverse effects of systemic immunosuppression or nephrotoxicity seen with chronic systemic delivery of the drug.

Brain-derived respiring mitochondria exhibit homogeneous, complete and cyclosporin-sensitive permeability transition

The mitochondrial permeability transition (mPT) is increasingly implicated in neuronal cell death. In the present study, isolated respiring brain mitochondria were examined for their ability to undergo calcium-induced mPT and their sensitivity to mPT inhibition by cyclosporin A (CsA). Previous studies have suggested a heterogeneous response to calcium, a limitation of CsA inhibition, and a relative resistance in the ability of respiring brain mitochondria to undergo mPT. Using fluorometric and electron microscopic analyses, we found that virtually the whole population of respiring brain mitochondria readily undergo mPT and swell upon calcium exposure. Further, brain mitochondria were highly sensitive to CsA which potentiated morphological recovery after transient swelling as well as completely blocked mPT induction in the presence of a low concentration of ADP. Using flow cytometry, which allows analysis of individual mitochondria, we demonstrate that both brain and liver mitochondria display homogeneous responses to calcium-induced mPT. We conclude that the mPT is one likely target for the broad in vivo neuroprotective effects displayed by CsA when allowed to penetrate the blood-brain barrier, and that development of compounds inhibiting mPT may prove beneficial for the treatment of severe brain disease.

Powerful cyclosporin inhibition of calcium-induced permeability transition in brain mitochondria

The mitochondrial permeability transition (mPT) is considered to be an important mediator of apoptosis and necrosis, and is specifically blocked by cyclosporin A (CsA). CsA has been shown to exert a potent neuroprotective action in vivo when allowed to cross the blood-brain barrier in various animal models of acute neurological insults and neurodegenerative disease. The neuroprotective effect of CsA is considered to be mediated through specific inhibition of the mitochondrial permeability transition pore (mPTP) and through inhibition of neuronal calcineurin activity. Characterization of mPT has mainly been performed in liver and heart mitochondria, and some brain studies have reported a decreased inhibitory effect of CsA and questioned the importance of mPT in brain-derived mitochondria. We have used the de-energized model of swelling to examine the mPT in brain-derived non-synaptosomal mitochondria. Ca(2+)-induced swelling was evaluated by electron microscopy and by measurement of spectrophotometric alterations in light scattering. Permeability transition was readily induced in a majority of the mitochondria at a wide range of Ca(2+) levels and was powerfully inhibited by CsA with a half-maximal effect at approximately 23 nM CsA. The swelling kinetics and CsA effects were comparable to previous findings in de-energized liver and heart mitochondria. Careful characterization of mPT and CsA effects in brain-derived mitochondria is the first step in evaluating newly developed CsA analogues capable of crossing the blood-brain barrier and preferentially entering the brain. The importance of CsA causing a shift of the mitochondrial sensitivity to Ca(2+) in neurological disorders is discussed.