Leigh syndrome is a fatal pediatric neurodegenerative disease caused by mitochondrial dysfunction, which can be modeled in the Ndufs4 KO mouse with mitochondrial respiratory chain complex I (CI) deficiency. This study explores NV354, a prodrug of succinate with enhanced oral bioavailability and brain uptake, as a potential therapy to counteract this devastating condition. NV354 modulated whole-body respiration and metabolic flexibility, prevented late-stage motor dysfunction, delayed clinical ataxia scores, and improved body weight development, but had otherwise minimal effect on neurobehavior and lifespan of the animals. The succinate prodrug prevented development of the brain stem lesions pathognomonic for Leigh syndrome, attenuated neuronal loss in the brainstem, diminished activation of astrocytes, blocked hypertrophic microglial accumulation, and reduced reactive oxygen species (ROS) levels in the brain. NV354 also partially alleviated motor symptoms and metabolic decompensation in a rat model of Parkinson disease induced by the CI inhibitor rotenone. In conclusion, the succinate prodrug NV354 shows promise as a potential treatment of mitochondrial CI-related neurodegeneration.

Background and purpose:Ultra-high dose rate (UHDR) irradiation is being investigated as a strategy to widen the therapeutic window of radiotherapy, but the biological mechanisms that distinguish UHDR from conventional dose rate (CONV) irradiation remain unresolved. Because mitochondria integrate bioenergetics, redox control and stress signaling after irradiation, they represent a plausible site at which dose-rate effects could emerge. This study evaluated mitochondrial function after CONV and UHDR irradiation in a head and neck squamous cell carcinoma in vitro model. Materials and methods:LU-HNSCC4 (HN4, an oral cavity HNSCC cell line) cells and VH10 fibroblasts were treated with 0, 2, 6, 10 or 20 Gy delivered at CONV or UHDR using electron irradiation from a modified linear accelerator. High-resolution respirometry was performed immediately after irradiation and 48 h later. In the 0 and 20 Gy groups, flow cytometry was used to assess cellular reactive oxygen species (ROS), mitochondrial ROS (mtROS), mitochondrial membrane potential (MMP) and Magnesium Green fluorescence as an indirect ATP-related readout. RNA sequencing was performed in HN4 cells 48 h after 20 Gy. Results:Irradiation induced clear dose- and time-dependent increases in oxygen consumption in HN4 cells, affecting routine respiration, oxidative phosphorylation capacity and maximal electron transfer capacity. The effect was strongest at higher doses and at 48 h and involved both complex I- and complex II-linked pathways. No statistically significant differences between dose-rate modalities were detected for the principal respiratory endpoints. Flow-cytometric analyses at 20 Gy showed stress responses in both irradiation arms, with some possible differences in temporal pattern; but without a clearly distinct overall phenotype attributable to dose rate. Conclusion:The data support a model in which both CONV and UHDR engage a broadly similar post-irradiation mitochondrial adaptive program in HN4 cells. The findings are relevant to the study of radiation adaptation and support further testing of mitochondria-directed radiosensitization strategies in head and neck cancer.

Background/Objectives: Mitochondrial dysfunction is a major cause of brain injury in patients with primary mitochondrial disease. New mitochondrial therapeutics and non-invasive tools for efficacy monitoring are urgently needed. To these ends, succinate prodrug NV354 (methyl 3-[(2-acetylaminoethylthio)carbonyl]propionate) and diffuse optical techniques are promising. In this proof-of-concept study, we characterize NV354’s effects on microdialysis metrics of cerebral metabolism in a swine model of mitochondrial dysfunction and assess the associations of diffuse optical metrics with mitochondrial dysfunction and metabolic improvement. Methods: One-month-old swine received a four-hour co-infusion of rotenone with either the succinate prodrug NV354 (n = 5) or placebo (n = 5). Rotenone is a mitochondrial complex I inhibitor. Before and during co-infusion, cerebral metabolism was probed with microdialysis and diffuse optics. Microdialysis acquired interstitial lactate and pyruvate levels invasively, while diffuse optics measured changes in oxygen extraction fraction (OEF) and oxidized cytochrome-c-oxidase concentration (oxCCO). Results: Interstitial lactate continually increased in the placebo group (p < 0.01), but lactate levels plateaued in the NV354 group (p = 0.90). oxCCO also increased in the placebo group (p = 0.05), but OEF remained constant (p = 0.80). In the NV354 group, oxCCO increased (p < 0.01) while OEF decreased (p < 0.01). Conclusions: Microdialysis results suggest that NV354 treatment can increase oxygen metabolism in large animals with mitochondrial dysfunction. The optical oxCCO metric was also sensitive to metabolic changes induced by rotenone and NV354 administration.

Human peripheral blood mononuclear cells (PBMCs) can be easily sampled from healthy individuals and patients. Density gradient isolation from human blood or leukocyte concentrates yields a mononuclear cell population of mainly lymphocytes, monocytes, and natural killer (NK) cells. PBMCs are vital circulating cells of the immune system and rely on oxidative phosphorylation (OXPHOS) for their energy production. OXPHOS capacity can be assessed using oxygraphy in intact and permeabilized PBMCs and has been used to investigate disorders of the immune system, but also, similarly to platelets, employed as a bioenergetic biomarker, that is, a “liquid biopsy” of disease conditions unrelated to immune dysregulation. Here, we present some key aspects of mitochondrial respiration in PBMCs isolated from leukocyte concentrates and whole blood using the Oroboros O2k oxygraph. We assessed the limits of sample amount and the impact of storage time and temperature and explored critical aspects of digitonin permeabilization. Furthermore, we provide respiratory rates and internal ratios from healthy controls using simple and comprehensive protocols for intact and permeabilized PBMCs, respectively. We conclude that detailed information on OXPHOS capacity in PBMCs can be reproducibly assessed ex vivo, but that great care must be taken during permeabilization to achieve correct measures of respiratory rates.

Investigating respiratory fluxes is decisive for understanding the complex interplay between metabolic processes. Studies of cells and tissues with limited sample availability and low respiratory rates may benefit from small experimental volumes. We examined if the 0.5-mL chamber yields results consistent with the 2.0-mL chamber at identical sample concentrations used in high-resolution respirometry with the Oroboros. The background O2 flux was 4-fold higher in 0.5-mL than 2.0-mL chambers at air saturation but was reproducible, allowing for accurate background correction. The optimal stirring speed was between 550 rotations per minute (rpm) and 750 rpm in the 0.5-mL chamber. Respiratory fluxes in living cells, permeabilized cells, and isolated mitochondria were measured in parallel in the 0.5-mL and 2.0-mL chambers, using Substrate-Uncoupler-Inhibitor Titration protocols with 14 to 20 titrations. O2 fluxes in the different chamber types were identical within the limits of detection. The 0.5-mL chamber, requiring close to four times less sample than the 2.0-mL chamber, offers a significant advantage for studies with limited amounts of sample or low respiratory capacities.

Axonal injuries commonly contribute to poor functional outcomes following traumatic brain injury (TBI). To assess cerebral blood flow (CBF) and energy metabolic disturbances in a TBI model of widespread axonal injury, we exposed 105 adult mice to the central (midline) fluid percussion injury (cFPI) diffuse TBI model, or sham injury, and used 9.4 T magnetic resonance (MR) arterial spin labeling (ASL), cortical and hippocampal mitochondrial respiration, and hippocampal MR spectroscopy at 1- and 7-days post-injury (dpi). Widespread, bilateral CBF reductions were observed at day 1 dpi, changes that were normalized by 7 dpi. However, cortical and hippocampal mitochondrial respiration and reactive oxygen species (ROS) production was not significantly altered at 1 and 7 dpi. Moreover, hippocampal volumes, evaluated by MRI, were not altered by cFPI, and by immunohistochemistry only a few apoptotic hippocampal cells were observed. By MRS, evidence of delayed (7 dpi) membrane disruption (phosphocholine and glycerophosphocholine) and glutamate/glutamine increase were observed. While widespread traumatic axonal pathology associated with functional impairments is observed in this TBI model, early CBF alterations were transient and did not translate into significant energy metabolic disturbances. Instead, the delayed hippocampal metabolite changes observed by MRS may contribute to the functional impairment observed in this diffuse TBI model.

2,4-Dinitrophenol (DNP) is a potent mitochondrial uncoupler briefly marketed in the 1930s as a weight-reducing agent before being banned by the FDA after reports of severe toxicity. Since the early 2000s, DNP has reemerged as an illicit “fat-burner”, causing characteristic metabolic disturbances with a high risk of fatal outcome. We describe two Swedish cases of DNP poisoning: one fatal after suicidal ingestion and one non-fatal after use for weight reduction. Clinical data, mitochondrial respirometry, and analysis of gas exchange and ventilatory dynamics were used to characterize the metabolic disturbances under intensive care. The fatal case progressed within hours to respiratory acidosis, hyperthermia, severe hyperkalemia, and peri-mortem rigidity consistent with catastrophic ATP depletion. The non-fatal case showed similar but reversible toxicity, with sustained yet manageable hypermetabolism lasting more than a week. Serial platelet respirometry demonstrated a marked initial increase in uncoupled respiration, followed by a progressive decline with a functional half-life of 4.9 days. Together, these cases suggest a self-amplifying feedback loop central to DNP toxicity, in which excessive CO₂ production from mitochondrial uncoupling causes local acidosis that enhances mitochondrial DNP uptake. Glucose supplementation and hyperkalemia management are essential supportive measures, whereas active cooling and high minute ventilation may blunt this self-reinforcing metabolic acceleration. Severe poisoning may result in a state of “runaway uncoupling,” a term we propose for the catastrophic progression to death observed in numerous DNP poisonings. This feedback loop illustrates the unpredictable toxicokinetics of DNP and reinforces the FDA’s early conclusion: DNP is “unfit for human consumption”.

Incubation temperature affects both growth and energy metabolism in birds after hatching. Changes in cellular mechanisms, including mitochondrial function, are a likely but unexplored explanation for these effects. To test whether temperature-dependent changes to mitochondria may link embryonic development to the post-natal phenotype, we incubated Japanese quail eggs at constant low (36.0°C), medium (37.5°C) or high (39.0°C) temperature and studied mitochondrial function and growth during embryogenesis and at hatching. Embryos grew faster and had higher mitochondrial metabolism at the high incubation temperature. Low incubation temperature slowed embryonic development and decreased phosphorylating respiration but was associated with higher adenosine triphosphate production efficiency. These respiration changes were mirrored by differences in mitochondrial content, which was the lowest in cold embryos. Neither treatment affected reactive oxygen species production. Hence, improved coupling efficiency in cold embryos may have partially compensated for lower adenosine triphosphate production without increasing oxidative stress. Size differences had disappeared by hatching. However, cold-incubated chicks had a higher mitochondrial content compared with the other groups. Our study suggests that thermal suppression of embryonic metabolism may be compensated by a combination of increased coupling, longer developmental time and late-occurring upregulation of mitochondrial content. The long-term implications of these results should be studied further.

Research on birds suggests that extreme weather events during development may have long-lasting consequences on form and function. The underlying cellular mechanisms mediating such phenotypic effects are poorly studied. We raised Japanese quail in warm (30°C) or cold (10°C) temperatures from hatching until adulthood and then measured mitochondrial metabolism in intact blood cells at representative normothermic body temperature (41°C) and a hyperthermic temperature (45°C), that quail commonly attain when heat stressed. To investigate whether any postnatal developmental effects were reversible, half of the cold- and warm-acclimated birds were assigned to a common garden (20°C) three weeks before the measurements. Across groups, hyperthermia was associated with increased proton leak but decreased phosphorylating respiration (where ATP is produced) and maximal working capacity of the mitochondria. Cold-reared birds were more strongly affected by heat stress: the increase in proton leak was 1.6-fold higher compared with warm-acclimated birds. This did not reflect developmental programming, as the difference did not remain in the common-garden birds. Our study describes the cellular consequences of overheating and suggests that cold acclimation during postnatal development is traded off against heat tolerance at the level of cellular metabolism. These findings have potential implications for understanding avian responses to climate change.

Background/Objectives: Sepsis is a life-threatening condition characterized by organ dysfunction due to a dysregulated host response to infection. Mitochondrial dysfunction is considered a key contributor to the pathogenesis of sepsis, but its molecular mechanisms remain unclear. Methods: In this study, we used a cecal ligation and puncture (CLP) model to induce sepsis in wild-type (WT) and cyclophilin D knockout (CypD KO) mice. Liver tissues were collected at 0, 6, and 18 h post-CLP and analyzed using liquid chromatography–tandem mass spectrometry (LC-MS/MS). Results: Metabolomic profiling revealed that lactate levels significantly increased in the WT mice but remained stable in the KO mice. While AMP levels were preserved in the KO mice, these mice had significantly higher glutathione disulfide (GSSG) and spermidine concentrations than the WT mice at 18 h (p < 0.05). The levels of malondialdehyde (MDA), a marker of oxidative stress, were also significantly lower in the KO mice at 18 h (p < 0.05). These findings suggest that CypD deficiency preserves mitochondrial function, enhances resistance to oxidative stress, and mitigates septic liver injury. Conclusions: Our results highlight the potential of targeting mitochondrial permeability transition as a therapeutic strategy for sepsis.

Background/Objectives: In recent years, it has been suggested that sedatives may cause brain damage. One possible mechanism is interference with oxidative phosphorylation of brain mitochondria, but much remains unknown. In this study, we focused on dexmedetomidine, midazolam, and propofol, essential sedatives in anesthesia and intensive care, and aimed to understand the effects of these drugs on mouse brain mitochondria. Methods: We measured changes in mitochondrial respiratory capacity and swelling rate upon exposure to these sedatives in a wide concentration range. For the sedative that demonstrated impaired mitochondrial function we explored the possible involvement of mitochondrial permeability transition pore opening using brain mitochondria from cyclophilin D knockout (CypD KO) mice and detected cytochrome c (cyt c) release by Western blot. Results: Of the three sedatives, only high concentrations of propofol exhibited reduced respiratory capacity and mitochondrial swelling, toxicity which was not prevented by CypD KO. Furthermore, propofol did not induce cyt c release. Conclusions: These results suggest that propofol-induced brain mitochondrial dysfunction is a mechanism independent of mPTP opening.

Succinate prodrug NV354 is a promising therapy for mitochondrial dysfunction. We used diffuse optical and microdialysis techniques to characterize its effects on cerebral oxygen metabolism during rotenone poisoning. One-month-old swine received a four-hour co-infusion of rotenone with either the succinate prodrug NV354 (n = 5) or placebo (n = 5). Cerebral interstitial lactate continually increased in the placebo group (p < 0.01), but lactate levels plateaued in the NV354 group (p = 0.90), which is consistent with NV354’s ability to increase oxygen metabolism in large animals. The study presents first in vivo optical measurements of changes in cytochrome-c-oxidase redox state induced by primary mitochondrial dysfunction and mitochondrial-targeted drugs.

Antibiotics are crucial in treating infectious diseases, particularly in intensive care unit patients, but they can lead to side effects such as ototoxicity. A mechanism for this is antibiotics targeting mitochondrial components in eucaryotic cells, due to their resemblance of those in bacteria. Here we investigate how five classes of antibiotics (carbapenems, fluoroquinolones, aminoglycosides, glycopeptides, and oxazolidinones) affect mitochondrial respiratory function, ATP levels, mitochondrial membrane potential and levels of reactive oxygen species in an inner-ear derived epithelial cell line (HEI-OC1) and human primary blood cells (PBMCs) at clinically relevant concentrations.Mitochondrial respiration in intact HEI-OC1 cells was suppressed in response to the majority of the tested antibiotics. This effect was lost when the HEI-OC1 cells were permeabilized and substrate supply controlled. Further in these cells, ROS levels were increased and ATP levels reduced. In contrast, no measure of mitochondrial function of PBMCs was affected by any antibiotics at the same concentration. We show that HEI-OC1 cells are sensitive to a broad range of antibiotics, and that the mechanism of toxicity to mitochondrial respiration is upstream of the mitochondrial respiratory chain, with downstream effects on mitochondrial respiration, ATP levels and ROS levels.

Over the past two decades there has been increased interest in orphan drug development for rare diseases. However, hurdles to clinical trial design for these disorders remain. This phase 1a/1b study addressed several challenges, while evaluating the safety and tolerability of the novel oral molecule KL1333 in healthy volunteers and subjects with primary mitochondrial disease. KL1333 aims to normalize the NAD+:NADH ratio that is critical for ATP production. The trial incorporated innovative design elements with potential translatability to other rare diseases including patient involvement, adaptive design and exploratory objectives, all of which have subsequently informed the protocol of an ongoing phase 2, pivotal efficacy study of KL1333. Results indicate KL1333 is safe and well tolerated, with dose-dependent gastrointestinal side effects, and validate potential novel outcome measures in primary mitochondrial disease including the 30-s Sit to Stand, and the patient-reported fatigue scales. Importantly, the data from the trial support efficacy of KL1333 based on improvements in fatigue and functional strength and endurance. Furthermore, the study highlights the value in using phase 1 studies to capture data that helps optimize later phase efficacy trial design.

ABSTRACT Although mitochondrial respiration is believed to explain a substantial part of the variation in resting metabolic rate (RMR), few studies have empirically studied the relationship between organismal and cellular metabolism. We therefore investigated the relationship between RMR and mitochondrial respiration of permeabilized blood cells in wild great tits (Parus major L.). We also studied the correlation between mitochondrial respiration traits and blood cell count, as normalizing mitochondrial respiration by the cell count is a method commonly used to study blood metabolism. In contrast to previous studies, our results show that there was no relationship between RMR and mitochondrial respiration in intact blood cells (i.e. with the ROUTINE respiration). However, when cells were permeabilized and interrelation re-assessed under saturating substrate availability, we found that RMR was positively related to phosphorylating respiration rates through complexes I and II (i.e. OXPHOS respiration) and to the mitochondrial efficiency to produce energy (i.e. net phosphorylation efficiency), though variation explained by the models was low (i.e. linear model: R2=0.14 to 0.21). However, unlike studies in mammals, LEAK respiration without [i.e. L(n)] and with [i.e. L(Omy)] adenylates was not significantly related to RMR. These results suggest that phosphorylating respiration in blood cells can potentially be used to predict RMR in wild birds, but that this relationship may have to be addressed in standardized conditions (permeabilized cells) and that the prediction risks being imprecise. We also showed that, in our conditions, there was no relationship between any mitochondrial respiration trait and blood cell count. Hence, we caution against normalising respiration rates using this parameter as is sometimes done. Future work should address the functional explanations for the observed relationships, and determine why these appear labile across space, time, taxon, and physiological state.

Mitochondrial dysfunction is considered a hallmark of aging. Up to now, a gradual decline of mitochondrial respiration with advancing age has mainly been demonstrated in human muscle tissue. A handful of studies have examined age-related mitochondrial dysfunction in human blood cells, and only with small sample sizes and mainly in platelets. In this study, we analyzed mitochondrial respiration in peripheral blood mononuclear cells (PBMCs) and platelets from 308 individuals across the human lifespan (0–86 years). In regression analyses, with adjustment for false discovery rate (FDR), we found age-related changes in respiratory measurements to be either small or absent. The main significant changes were an age-related relative decline in complex I-linked respiration and a corresponding rise of complex II-linked respiration in PBMCs. These results add to the understanding of mitochondrial dysfunction in aging and to its possible role in immune cell and platelet senescence.

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.

IntroductionHead and neck squamous cell carcinoma (HNSCC) constitutes a heterogeneous group of cancers. Human papilloma virus (HPV) is associated with a subtype of HNSCC with a better response to treatment and more favorable prognosis. Mitochondrial function and metabolism vary depending on cancer type and can be related to tumor aggressiveness. This study aims to characterize the metabolism of HPV-positive and HPV-negative HNSCC cell lines.MethodsOxidative phosphorylation (OXPHOS) and glycolysis were assessed in intact cells, in four HNSCC cell lines using Seahorse XF Analyzer. OXPHOS was further studied in permeabilized cells using high-resolution respirometry in an Oroboros O2K. Metabolomic analysis was performed using mass spectroscopy.ResultsThe HPV-negative cell lines were found to display a higher OXPHOS capacity and were also able to upregulate glycolysis when needed. The HPV-positive cell line had a higher basal glycolytic rate but lower spare OXPHOS capacity. These cells were also unable to increase respiration in response to succinate, unlike the HPV-negative cells. In the metabolomic analysis, the HPV-positive cells showed a higher kynurenine/tryptophan ratio.DiscussionHPV-positive HNSCC preferred glycolysis to compensate for lower OXPHOS reserves, while the HPV-negative HNSCC displayed a more versatile metabolism, which might be related to increased tumor aggressiveness. The higher kynurenine/tryptophan ratio of HPV-positive HNSCC might be related to increased indoleamine 2,3-dioxygenase activity due to the carcinoma’s viral origin. This study highlights important metabolic differences between HPV-positive and HPV-negative cancers and suggests that future metabolic targets for cancer treatment should be individualized based on specific tumor metabolism.

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.