Ex vivo use of cell-permeable succinate prodrug attenuates mitochondrial dysfunction in blood cells obtained from carbon monoxide-poisoned individuals

Hyperoxic exposure alters intracellular bioenergetics distribution in human pulmonary cells

AIMS

Pulmonary oxygen toxicity is caused by exposure to a high fraction of inspired oxygen, which damages multiple cell types within the lung. The cellular basis for pulmonary oxygen toxicity includes mitochondrial dysfunction. The aim of this study was to identify the effects of hyperoxic exposure on mitochondrial bioenergetic and dynamic functions in pulmonary cells.

MAIN METHODS

Mitochondrial respiration, inner membrane potential, dynamics (including motility), and distribution of mitochondrial bioenergetic capacity in two intracellular regions were quantified using cultured human lung microvascular endothelial cells, human pulmonary artery endothelial cells and A549 cells. Hyperoxic (95 % O₂) exposures lasted 24, 48 and 72 h, durations relevant to mechanical ventilation in intensive care settings.

KEY FINDINGS

Mitochondrial motility was altered following all hyperoxic exposures utilized in experiments. Inhomogeneities in inner membrane potential and respiration parameters were present in each cell type following hyperoxia. The partitioning of ATP-linked respiration was also hyperoxia-duration and cell type dependent. Hyperoxic exposure lasting 48 h or longer provoked the largest alterations in mitochondrial motility and the greatest decreases in ATP-linked respiration, with a suggestion of decreases in respiration complex protein levels.

SIGNIFICANCE

Hyperoxic exposures of different durations produce intracellular inhomogeneities in mitochondrial dynamics and bioenergetics in pulmonary cells. Oxygen therapy is utilized commonly in clinical care and can induce undesirable decrements in bioenergy function needed to maintain pulmonary cell function and viability. There may be adjunctive or prophylactic measures that can be employed during hyperoxic exposures to prevent the mitochondrial dysfunction that signals the presence of oxygen toxcity.

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.

Mitochondrial dynamics involves molecular and mechanical events in motility, fusion and fission

Mitochondria are cell organelles that play pivotal roles in maintaining cell survival, cellular metabolic homeostasis, and cell death. Mitochondria are highly dynamic entities which undergo fusion and fission, and have been shown to be very motile in vivo in neurons and in vitro in multiple cell lines. Fusion and fission are essential for maintaining mitochondrial homeostasis through control of morphology, content exchange, inheritance of mitochondria, maintenance of mitochondrial DNA, and removal of damaged mitochondria by autophagy. Mitochondrial motility occurs through mechanical and molecular mechanisms which translocate mitochondria to sites of high energy demand. Motility also plays an important role in intracellular signaling. Here, we review key features that mediate mitochondrial dynamics and explore methods to advance the study of mitochondrial motility as well as mitochondrial dynamics-related diseases and mitochondrial-targeted therapeutics.

A permeable succinate improved platelet mitochondrial respiration in paediatric acute lymphoblastic leukaemia in remission: Case report

Acute lymphoblastic leukaemia (ALL) is the most common childhood malignancy. In the last decades, the survival rate of paediatric patients diagnosed with ALL has been significantly improved due to standardised treatment protocols based on risk stratification. Platelet mitochondrial dysfunction has been recently reported to occur in most chronic diseases, including malignancies. Permeable succinate (NV118) is a novel mitochondria-targeted compound capable to alleviate disease and drug-induced mitochondrial dysfunction. It is reported here that ex vivo incubation with NV811 elicited an increase in platelet mitochondrial respiration in a paediatric patient with acute lymphoblastic leukaemia in remission.

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

Amiodarone is a potent antiarrhythmic drug and displays substantial liver toxicity in humans. It has previously been demonstrated that amiodarone and its metabolite (desethylamiodarone, DEA) can inhibit mitochondrial function, particularly complexes I (CI) and II (CII) of the electron transport system in various animal tissues and cell types. The present study, performed in human peripheral blood cells, and one liver-derived human cell line, is primarily aimed at assessing the concentration-dependent effects of these drugs on mitochondrial function (respiration and cellular ATP levels). Furthermore, we explore the efficacy of a novel cell-permeable succinate prodrug in alleviating the drug-induced acute mitochondrial dysfunction. Amiodarone and DEA elicit a concentration-dependent impairment of mitochondrial respiration in both intact and permeabilized platelets via the inhibition of both CI- and CII-supported respiration. The inhibitory effect seen in human platelets is also confirmed in mononuclear cells (PBMCs) and HepG2 cells. Additionally, amiodarone elicits a severe concentration-dependent ATP depletion in PBMCs, which cannot be explained solely by mitochondrial inhibition. The succinate prodrug NV118 alleviates the respiratory deficit in platelets and HepG2 cells acutely exposed to amiodarone. In conclusion, amiodarone severely inhibits metabolism in primary human mitochondria, which can be counteracted by increasing mitochondrial function using intracellular delivery of succinate.

Cell-Permeable Succinate Increases Mitochondrial Membrane Potential and Glycolysis in Leigh Syndrome Patient Fibroblasts

Mitochondrial disorders represent a large group of severe genetic disorders mainly impacting organ systems with high energy requirements. Leigh syndrome (LS) is a classic example of a mitochondrial disorder resulting from pathogenic mutations that disrupt oxidative phosphorylation capacities. Currently, evidence-based therapy directed towards treating LS is sparse. Recently, the cell-permeant substrates responsible for regulating the electron transport chain have gained attention as therapeutic agents for mitochondrial diseases. We explored the therapeutic effects of introducing tricarboxylic acid cycle (TCA) intermediate substrate, succinate, as a cell-permeable prodrug NV118, to alleviate some of the mitochondrial dysfunction in LS. The results suggest that a 24-hour treatment with prodrug NV118 elicited an upregulation of glycolysis and mitochondrial membrane potential while inhibiting intracellular reactive oxygen species in LS cells. The results from this study suggest an important role for TCA intermediates for treating mitochondrial dysfunction in LS. We show, here, that NV118 could serve as a therapeutic agent for LS resulting from mutations in mtDNA in complex I and complex V dysfunctions.

Emerging cellular-based therapies in carbon monoxide poisoning

Carbon monoxide (CO) is an odorless and colorless gas with multiple sources that include engine exhaust, faulty furnaces, and other sources of incomplete combustion of carbon compounds such as house fires. The most serious complications for survivors of consequential CO exposure are persistent neurological sequelae occurring in up to 50% of patients. CO inhibits mitochondrial respiration by specifically binding to the heme a₃ in the active site of CIV-like hydrogen sulfide, cyanide, and phosphides. Although hyperbaric oxygen remains the cornerstone for treatment, it has variable efficacy requiring new approaches to treatment. There is a paucity of cellular-based therapies in the area of CO poisoning, and there have been recent advancements that include antioxidants and a mitochondrial substrate prodrug. The succinate prodrugs derived from chemical modification of succinate are endeavored to enhance delivery of succinate to cells, increasing uptake of succinate into the mitochondria, and providing metabolic support for cells. The therapeutic intervention of succinate prodrugs is thus potentially applicable to patients with CO poisoning via metabolic support for fuel oxidation and possibly improving efficacy of HBO therapy.

Hyperbaric oxygen alters intracellular bioenergetics distribution in human dermal fibroblasts

AIMS

Hyperbaric oxygen therapy (HBOT), used to promote wound healing, has limited efficacy in many clinical conditions. Wound healing exerts bioenergetic demands on cells that can exceed their intrinsic bioenergetic capacity to proliferate and migrate. The aim of this investigation was to quantify the effects of HBOT on mitochondrial dynamics and bioenergetics functions in cells relevant to wound healing.

MAIN METHODS

High-resolution respirometry and fluorescence microscopy were used to quantify mitochondrial respiration, intermembrane potential, dynamics, including motility, and the intracellular distribution of mitochondrial bioenergetic capacity partitioned into perinuclear and cell peripheral regions in cultured human dermal fibroblasts. Cells were subjected to a range of gas mixtures and hyperbaric pressures, including conditions utilized in clinical care.

KEY FINDINGS

Motility was reduced immediately following all HBOT exposures utilized in experiments. Inhomogeneities in intermembrane potential and respiration parameters were produced by different HBOT conditions. The partitioning of ATP-linked respiration was also HBOT-condition dependent. Application of HBOT at common clinical pressure and oxygen conditions resulted in the largest immediate decrement in mitochondrial motility and reductions in ATP-linked respiration in both the cell periphery and perinuclear zones. Aberrations in motility and respiration were also present 6 h after exposure.

SIGNIFICANCE

HBOT produces intracellular distinctions and inhomogeneities in mitochondrial dynamics and bioenergetics. HBOT as is commonly applied in clinical medicine induced undesirable and persistent alterations in bioenergy function needed to support cell migration and/or proliferation. There may be alternative HBOT parameters that more effectively engender maintenance and adequacy of intracellular bioenergy supply to promote wound healing.

Alterations in cerebral and cardiac mitochondrial function in a porcine model of acute carbon monoxide poisoning

OBJECTIVES

The purpose of this study is the development of a porcine model of carbon monoxide (CO) poisoning to investigate alterations in brain and heart mitochondrial function.

DESIGN

Two group large animal model of CO poisoning.

SETTING

Laboratory.

SUBJECTS

Ten swine were divided into two groups: Control (n = 4) and CO (n = 6).

INTERVENTIONS

Administration of a low dose of CO at 200 ppm to the CO group over 90 min followed by 30 min of re-oxygenation at room air. The Control group received room air for 120 min.

MEASUREMENTS

Non-invasive optical monitoring was used to measure cerebral blood flow and oxygenation. Cerebral microdialysis was performed to obtain semi real time measurements of cerebral metabolic status. At the end of the exposure, both fresh brain (cortical and hippocampal tissue) and heart (apical tissue) were immediately harvested to measure mitochondrial respiration and reactive oxygen species (ROS) generation and blood was collected to assess plasma cytokine concentrations.

MAIN RESULTS

Animals in the CO group showed significantly decreased Complex IV-linked mitochondrial respiration in hippocampal and apical heart tissue but not cortical tissue. There also was a significant increase in mitochondrial ROS generation across all measured tissue types. The CO group showed a significantly higher cerebral lactate-to-pyruvate ratio. Both IL-8 and TNFα were significantly increased in the CO group compared with the Control group obtained from plasma. While not significant there was a trend to an increase in optically measured cerebral blood flow and hemoglobin concentration in the CO group.

CONCLUSIONS

Low-dose CO poisoning is associated with early mitochondrial disruption prior to an observable phenotype highlighting the important role of mitochondrial function in the pathology of CO poisoning. This may represent an important intervenable pathway for therapy and intervention.

In vitro comparison of hydroxocobalamin (B12a) and the mitochondrial directed therapy by a succinate prodrug in a cellular model of cyanide poisoning

The objective of this study was to compare the use of hydroxocobalamin (B12a) and a succinate prodrug to evaluate for improvement in mitochondrial function in an in vitro model of cyanide poisoning. Peripheral blood mononuclear cells (PBMC) and human aortic smooth muscle cells (HASMC) incubated with 50 mM of sodium cyanide (CN) for five minutes serving as the CN group compared to controls. We investigated the following: (1) Mitochondrial respiration; (2) Superoxide and mitochondrial membrane potential with microscopy; (3) Citrate synthase protein expression. All experiments were performed with a cell concentration of 2-3 × 106 cells/ml for both PBMC and HASMC. There were four conditions: (1) Control (no exposure); (2) Cyanide (exposure only); (3) B12a (cyanide exposure followed by B12a treatment); (4) NV118 (cyanide followed by NV118 treatment). In this study the key findings include: (1) Improvement in key mitochondrial respiratory states with the succinate prodrug (NV118) but not B12a; (2) Attenuation of superoxide production with treatment of NV118 but not with B12a treatment; (3) The changes in respiration were not secondary to increased mitochondrial content as measured by citrate synthase; (4) The use of easily accessible human blood cells showed similar mitochondrial response to both cyanide and treatment to HASMC. The use of a succinate prodrug to circumvent partial CIV inhibition by cyanide with clear reversal of cellular respiration and superoxide production that was not attributed to changes in mitochondrial content not seen by the use of B12a.