Mitochondrial respiratory chain complex I dysfunction induced by N-methyl carbamate ex vivo can be alleviated with a cell-permeable succinate prodrug

Targeting the lactic acid metabolic pathway for antitumor therapy

Lactic acid is one of the most abundant products of cellular metabolism and has historically been considered a cell-damaging metabolic product. However, as research has deepened, the beneficial effects of lactic acid on tumor cells and the tumor microenvironment have received increasing attention from the oncology community. Lactic acid can not only provide tumor cells with energy but also act as a messenger molecule that promotes tumor growth and progression and protects tumor cells from immune cells and killing by radiation and chemotherapy. Thus, the inhibition of tumor cell lactic acid metabolism has emerged as a novel antitumor treatment strategy that can also effectively enhance the efficacy of conventional antitumor therapies. In this review, we classify the currently available therapies targeting lactic acid metabolism and examine their prospects for clinical application.

Cell-Free DNA as a Biomarker in a Rodent Model of Chlorpyrifos Poisoning Causing Mitochondrial Dysfunction

INTRODUCTION

Organophosphates (OPs) are a major public health problem worldwide due to ease of access and high toxicity lacking effective biomarkers and treatment. Cholinergic agents such as OPs and carbamates are responsible for many pesticide-related deaths. While the inhibition of AChE is thought to be the main mechanism of injury, there are other important pathways that contribute to the overall toxicity of OPs such as mitochondrial dysfunction. An existing gap in OP poisoning are biomarkers to gauge severity and prognosis. Cell-free DNA (cfDNA) are novel biomarkers that have gained increased attention as a sensitive biomarker of disease with novel use in acute poisoning. This study investigates alterations in cerebral mitochondrial function in a rodent model of chlorpyrifos poisoning with the use of cfDNA as a potential biomarker.

METHODS

Twenty rodents were divided into two groups: Control (n = 10) and Chlorpyrifos (n = 10). Chlorpyrifos was administered through the venous femoral line with a Harvard Apparatus 11 Elite Syringe pump (Holliston, MA, USA) at 2 mg/kg. Animals were randomized to receive chlorpyrifos versus the vehicle (10% DMSO) for 60 min which would realistically present an acute exposure with continued absorption. At the end of the exposure (60 min), isolated mitochondria were measured for mitochondrial respiration along with measures of acetylcholinesterase activity, cfDNA, cytokines and western blot.

RESULTS

The Chlorpyrifos group showed a significant decrease in heart rate but no change in the blood pressure. There was a significant increase in bulk cfDNA concentrations and overall decrease in mitochondrial respiration from brain tissue obtained from animals in the Chlorpyrifos group when compared to the Control group with no difference in acetylcholinesterase activity. In addition, there was a significant increase in both IL-2 and IL-12 in the Chlorpyrifos group.

CONCLUSIONS

In our study, we found that the total cfDNA concentration may serve as a more accurate biomarker of OP exposure compared to acetylcholinesterase activity. In addition, there was an overall decrease in cerebral mitochondrial function in the Chlorpyrifos group when compared to the Control group.

Alteration in Cerebral Metabolism in a Rodent Model of Acute Sub-lethal Cyanide Poisoning

INTRODUCTION

Cyanide exposure can occur in various settings such as industry and metallurgy. The primary mechanism of injury is cellular hypoxia from Complex IV (CIV) inhibition. This leads to decreased ATP production and increased reactive oxygen species production. The brain and the heart are the organs most affected due to their high metabolic demand. While the cardiac effects of cyanide are well known, the cerebral effects on cellular function are less well described. We investigated cerebral metabolism with a combination of brain respirometry, microdialysis, and western blotting using a rodent model of sub-lethal cyanide poisoning.

METHODS

Twenty rodents were divided into two groups: control (n = 10) and sub-lethal cyanide (n = 10). Cerebral microdialysis was performed during a 2 mg/kg/h cyanide exposure to obtain real-time measurements of cerebral metabolic status. At the end of the exposure (90 min), brain-isolated mitochondria were measured for mitochondrial respiration. Brain tissue ATP concentrations, acyl-Coenzyme A thioesters, and mitochondrial content were also measured.

RESULTS

The cyanide group showed significantly increased lactate and decreased hypotension with decreased cerebral CIV-linked mitochondrial respiration. There was also a significant decrease in cerebral ATP concentration in the cyanide group and a significantly higher cerebral lactate-to-pyruvate ratio (LPR). In addition, we also found decreased expression of Complex III and IV protein expression in brain tissue from the cyanide group. Finally, there was no change in acyl-coenzyme A thioesters between the two groups.

CONCLUSIONS

The key finding demonstrates mitochondrial dysfunction in brain tissue that corresponds with a decrease in mitochondrial function, ATP concentrations, and an elevated LPR indicating brain dysfunction at a sub-lethal dose of cyanide.

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 function and cellular energy maintenance during aging in a Drosophila melanogaster model of Parkinson Disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by movement disorders as well as loss of dopaminergic neurons. Moreover, genes affecting mitochondrial function, such as SNCA, Parkin, PINK1, DJ-1 and LRRK2, were demonstrated to be associated with PD and other neurodegenerative disease. Additionally, mitochondrial dysfunction and cellular energy imbalance are common markers found in PD. In this study, we used the pink1 null mutants of Drosophila melanogaster as a Parkinson's disease model to investigate how the energetic pathways and mitochondrial functions change during aging in a PD model. In our study, the loss of the pink1 gene decreased the survival percent and the decreased climbing index during aging in pink1^-/- flies. Furthermore, there was an impairment in mitochondrial function demonstrated by a decrease in OXPHOS CI&CII-Linked and ETS CI&CII-Linked in pink1^-/- flies at 3, 15 and 30 days of life. Interestingly, OXPHOS CII-Linked and ETS CII-Linked presented decreases only at 15 days of life in pink1^-/- flies. Moreover, there was an increase in peroxide (H₂O₂) levels in pink1^-/- flies at 15 and 30 days of life. Loss of the pink1 gene also decreased the activity of citrate synthase (CS) and increased the activity of lactate dehydrogenase (LDH) in pink1^-/- flies head. Our results demonstrate a metabolic shift in ATP production in pink1^-/- flies, which changed from oxidative to glycolytic pathways from 15 days of age, and is apparently more pronounced in the central nervous system.

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 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.

Leigh Syndrome: A Tale of Two Genomes

Leigh syndrome is a rare, complex, and incurable early onset (typically infant or early childhood) mitochondrial disorder with both phenotypic and genetic heterogeneity. The heterogeneous nature of this disorder, based in part on the complexity of mitochondrial genetics, and the significant interactions between the nuclear and mitochondrial genomes has made it particularly challenging to research and develop therapies. This review article discusses some of the advances that have been made in the field to date. While the prognosis is poor with no current substantial treatment options, multiple studies are underway to understand the etiology, pathogenesis, and pathophysiology of Leigh syndrome. With advances in available research tools leading to a better understanding of the mitochondria in health and disease, there is hope for novel treatment options in the future.

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.

Carbofuran cytotoxicity, DNA damage, oxidative stress, and cell death in human umbilical vein endothelial cells: Evidence of vascular toxicity

Carbofuran is a broad-spectrum carbamate insecticide, which principally inhibits the acetylcholinesterase (AChE) enzyme in the nervous system. Nonetheless, their selective action is not restricted to a single species and expanded to humans. No studies are available on the toxicological effects of carbofuran in the endothelial cells (ECs), which first confronts the toxicants in blood vessels. Hence, we have exposed the human umbilical vein ECs (HUVECs) with carbofuran for 24 h, which significantly reduced the cell survival to 25.16% and 33.48% at 500 and 1,000 μM analyzed by MTT assay. In the neutral red uptake (NRU) assay, 16.68%, 30.99%, and 58.11% survival decline was found at 250, 500, and 1,000 μM of carbofuran. HUVECs exposed to carbofuran showed significant increase in the intracellular reactive oxygen species (ROS), indicating oxidative stress at low concentrations. In parallel, HUVECs showed hyperpolarization effects in the mitochondrial membrane potential (ΔΨm) upon carbofuran exposure. Carbofuran induced DNA damage in HUVECs measured as 8.80, 11.82, 35.56, and 79.69 Olive tail moment (OTM) in 100-, 250-, 500-, and 1,000-μM exposure groups. Flow cytometric analysis showed apoptotic peak (SubG1) and G2M arrest in the HUVECs exposed to carbofuran. Overall, our novel data confirm that carbofuran is toxic for the EC cells, especially at the higher concentrations, which may affect the vascular functions and possibly angiogenesis. Hence, carbofuran should be applied judiciously, and detailed vascular studies are warranted to gain an in-depth information focusing the transcriptomic and translation changes employing suitable in vivo and in vitro test models.

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.