Treatment of CoQ10 Deficient Fibroblasts with Ubiquinone,CoQ Analogs,and Vitamin C: Time- and Compound-Dependent Effects

Background

Coenzyme Q₁₀ (CoQ₁₀) and its analogs are used therapeutically by virtue of their functions as electron carriers, antioxidant compounds, or both. However, published studies suggest that different ubiquinone analogs may produce divergent effects on oxidative phosphorylation and oxidative stress.

Methodology/Principal Findings

To test these concepts, we have evaluated the effects of CoQ₁₀, coenzyme Q₂ (CoQ₂), idebenone, and vitamin C on bioenergetics and oxidative stress in human skin fibroblasts with primary CoQ₁₀ deficiency. A final concentration of 5 µM of each compound was chosen to approximate the plasma concentration of CoQ₁₀ of patients treated with oral ubiquinone. CoQ₁₀ supplementation for one week but not for 24 hours doubled ATP levels and ATP/ADP ratio in CoQ₁₀ deficient fibroblasts therein normalizing the bioenergetics status of the cells. Other compounds did not affect cellular bioenergetics. In COQ2 mutant fibroblasts, increased superoxide anion production and oxidative stress-induced cell death were normalized by all supplements.

Conclusions/Significance

These results indicate that: 1) pharmacokinetics of CoQ₁₀ in reaching the mitochondrial respiratory chain is delayed; 2) short-tail ubiquinone analogs cannot replace CoQ₁₀ in the mitochondrial respiratory chain under conditions of CoQ₁₀ deficiency; and 3) oxidative stress and cell death can be counteracted by administration of lipophilic or hydrophilic antioxidants. The results of our in vitro experiments suggest that primary CoQ₁₀ deficiencies should be treated with CoQ₁₀ supplementation but not with short-tail ubiquinone analogs, such as idebenone or CoQ₂. Complementary administration of antioxidants with high bioavailability should be considered if oxidative stress is present.     

A water soluble CoQ10 formulation improves intracellular distribution and promotes mitochondrial respiration in cultured cells

Background

Mitochondria are both the cellular powerhouse and the major source of reactive oxygen species. Coenzyme Q₁₀ plays a key role in mitochondrial energy production and is recognized as a powerful antioxidant. For these reasons it can be argued that higher mitochondrial ubiquinone levels may enhance the energy state and protect from oxidative stress. Despite the large number of clinical studies on the effect of CoQ₁₀ supplementation, there are very few experimental data about the mitochondrial ubiquinone content and the cellular bioenergetic state after supplementation. Controversial clinical and in vitro results are mainly due to the high hydrophobicity of this compound, which reduces its bioavailability.

Principal Findings

We measured the cellular and mitochondrial ubiquinone content in two cell lines (T67 and H9c2) after supplementation with a hydrophilic CoQ₁₀ formulation (Qter®) and native CoQ₁₀. Our results show that the water soluble formulation is more efficient in increasing ubiquinone levels. We have evaluated the bioenergetics effect of ubiquinone treatment, demonstrating that intracellular CoQ₁₀ content after Qter supplementation positively correlates with an improved mitochondrial functionality (increased oxygen consumption rate, transmembrane potential, ATP synthesis) and resistance to oxidative stress.

Conclusions

The improved cellular energy metabolism related to increased CoQ₁₀ content represents a strong rationale for the clinical use of coenzyme Q₁₀ and highlights the biological effects of Qter®, that make it the eligible CoQ₁₀ formulation for the ubiquinone supplementation.     

Dictyostelium, a microbial model for brain disease

Background

Most neurodegenerative diseases are associated with mitochondrial dysfunction. In humans, mutations in mitochondrial genes result in a range of phenotypic outcomes which do not correlate well with the underlying genetic cause. Other neurodegenerative diseases are caused by mutations that affect the function and trafficking of lysosomes, endosomes and autophagosomes. Many of the complexities of these human diseases can be avoided by studying them in the simple eukaryotic model Dictyostelium discoideum.

Scope of review

This review describes research using Dictyostelium to study cytopathological pathways underlying a variety of neurodegenerative diseases including mitochondrial, lysosomal and vesicle trafficking disorders.

Major conclusions

Generalised mitochondrial respiratory deficiencies in Dictyostelium produce a consistent pattern of defective phenotypes that are caused by chronic activation of a cellular energy sensor AMPK (AMP-activated protein kinase) and not ATP deficiency per se. Surprisingly, when individual subunits of Complex I are knocked out, both AMPK-dependent and AMPK-independent, subunit-specific phenotypes are observed. Many nonmitochondrial proteins associated with neurological disorders have homologues in Dictyostelium and are associated with the function and trafficking of lysosomes and endosomes. Conversely, some genes associated with neurodegenerative disorders do not have homologues in Dictyostelium and this provides a unique avenue for studying these mutated proteins in the absence of endogeneous protein.

General significance

Using the Dictyostelium model we have gained insights into the sublethal cytopathological pathways whose dysregulation contributes to phenotypic outcomes in neurodegenerative disease. This work is beginning to distinguish correlation, cause and effect in the complex network of cross talk between the various organelles involved. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research     

TMEM126A is a mitochondrial located mRNA (MLR) protein of the mitochondrial inner membrane

Background

Hereditary optic neuropathies (HONs) are a heterogeneous group of disorders that affect retinal ganglion cells (RGCs) and axons that form the optic nerve. Leber's Hereditary Optic Neuropathy and the autosomal dominant optic atrophy related to OPA1 mutations are the most common forms. Nonsyndromic autosomal recessive optic neuropathies are rare and their existence has been long debated. We recently identified the first gene responsible for these conditions, TMEM126A. This gene is highly expressed in retinal cellular compartments enriched in mitochondria and supposed to encode a mitochondrial transmembrane protein of unknown function.

Methods

A specific polyclonal antibody targeting the TMEM126A protein has been generated. Quantitative fluorescent in situ hybridization, cellular fractionation, mitochondrial membrane association study, mitochondrial sub compartmentalization analysis by both proteolysis assays and transmission electron microscopy, and expression analysis of truncated TMEM126A constructs by immunofluorescence confocal microscopy were carried out.

Results

TMEM126A mRNAs are strongly enriched in the vicinity of mitochondria and encode an inner mitochondrial membrane associated cristae protein. Moreover, the second transmembrane domain of TMEM126A is required for its mitochondrial localization.

Conclusions

TMEM126A is a mitochondrial located mRNA (MLR) that may be translated in the mitochondrial surface and the protein is subsequently imported to the inner membrane. These data constitute the first step toward a better understanding of the mechanism of action of TMEM126A in RGCs and support the importance of mitochondrial dysfunction in the pathogenesis of HON.

General significance

Local translation of nuclearly encoded mitochondrial mRNAs might be a mechanism for rapid onsite supply of mitochondrial membrane proteins.     

Pyruvate therapy for Leigh syndrome due to cytochrome c oxidase deficiency

Background

Recently we proposed the therapeutic potential of pyruvate therapy for mitochondrial diseases. Leigh syndrome is a progressive neurodegenerative disorder ascribed to either mitochondrial or nuclear DNA mutations.

Methods

In an attempt to circumvent the mitochondrial dysfunction, we orally applied sodium pyruvate and analyzed its effect on an 11-year-old female with Leigh syndrome due to cytochrome c oxidase deficiency accompanied by cardiomyopathy. The patient was administered sodium pyruvate at a maintenance dose of 0.5 g/kg/day and followed up for 1 year.

Results

The exercise intolerance was remarkably improved so that she became capable of running. Echocardiography indicated improvements both in the left ventricle ejection fraction and in the fractional shortening. Electrocardiography demonstrated amelioration of the inverted T waves. When the pyruvate administration was interrupted because of a gastrointestinal infection, the serum lactate level became elevated and the serum pyruvate level, decreased, suggesting that the pyruvate administration was effective in decreasing the lactate-to-pyruvate ratio.

Conclusions

These data indicate that pyruvate therapy was effective in improving exercise intolerance at least in a patient with cytochrome c oxidase deficiency.

General significance

Administration of sodium pyruvate may prove effective for other patients with cytochrome c oxidase deficiency due to mitochondrial or nuclear DNA mutations.     

Plagiochin E,an antifungal bis(bibenzyl), exerts its antifungal activity through mitochondrial dysfunction-induced reactive oxygen species accumulation in Candida albicans

Background

Plagiochin E (PLE) is an antifungal macrocyclic bis(bibenzyl) isolated from liverwort Marchantia polymorpha L. Its antifungal mechanism is unknown. To elucidate the mechanism of action, its effect on mitochondria function in Candida albicans was studied.

Methods

We assayed the mitochondrial membrane potential (mtΔψ) using rhodamine 123, measured ATP level in mitochondria by HPLC, and detected the activities of mitochondrial F₀F₁-ATPase and dehydrogenases. Besides, the mitochondrial dysfunction-induced reactive oxygen species (ROS) production was determined by a fluorometric assay, and the effects of antioxidant L-cysteine on PLE-induced ROS production and the antifungal effect of PLE on C. albicans were also investigated.

Results

Exposure to PLE resulted in an elevation of mtΔψ, and a decrease of ATP level in mitochondria. The ATP depletion owed to PLE-induced enhancement of mitochondrial F₀F₁-ATPase and inhibition of the mitochondrial dehydrogenases. These dysfunctions of mitochondria caused ROS accumulation in C. albicans, and this increase in the level of ROS production and PLE-induced decrease in cell viability were prevented by addition of L-cysteine, indicating that ROS was an important mediator of the antifungal action of PLE.

Conclusions

PLE exerts its antifungal activity through mitochondrial dysfunction-induced ROS accumulation in C. albicans.

General significance

The effect of PLE on the mitochondria function in C. albicans was assayed for the first time. These results would conduce to elucidate its underlying antifungal mechanism.     

Certain Strongylocentrotus purpuratus sperm mitochondrial proteins co-purify with low density detergent-insoluble membranes and are PKA or PKC-substrates possibly involved in sperm motility regulation

Background

Sea urchin sperm motility is regulated by Speract, a sperm-activating peptide (SAP) secreted from the outer egg coat. Upon binding to its receptor in the sperm flagellum, Speract induces a series of ionic and metabolic changes in Strongylocentrotus purpuratus spermatozoa that regulate their motility. Among these events, protein phosphorylation is one of the most relevant and evidence indicates that some proteins of the Speract signaling cascade localize in low density detergent-insoluble membranes (LD-DIM).

Methods

LD-DIM-derived proteins from immotile, motile or Speract-stimulated S. purpuratus sperm were resolved in 2-D gels and the PKA and PKC substrates detected with specific antibodies were identified by LC–MS/MS.

Results

Differential PKA and PKC substrate phosphorylation levels among the LD-DIM isolated from sperm in different motility conditions were found and identified by mass spectrometry as: ATP synthase, creatine kinase, NADH dehydrogenase (ubiquinone) flavoprotein 2, succinyl-CoA ligase and the voltage-dependent anion channel 2 (VDAC2), which are mitochondrial proteins, as well as, the cAMP-dependent protein kinase type II regulatory (PKA RII) subunit, Tubulin β chain and Actin Cy I changed their phosphorylation state.

Conclusions

Some mitochondrial proteins regulated by PKA or PKC may influence sea urchin sperm motility.

General significance

The fact that a high percentage (66%) of the PKA or PKC substrates identified in LD-DIM are mitochondrial proteins suggests that the phosphorylation of these proteins modulates sea urchin sperm motility via Speract stimulation by providing sufficient energy to sperm physiology. Those mitochondrial proteins are indeed PKA- or PKC-substrates in the sea urchin spermatozoa.     

3D NMR structure of a complex between the amyloid beta peptide (1–40) and the polyphenol ε-viniferin glucoside: Implications in Alzheimer's disease

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. There is a consensus that Aβ is a pathologic agent and that its toxic effects, which are at present incompletely understood, may occur through several potential mechanisms. Polyphenols are known to have wide-ranging properties with regard to health and for helping to prevent various diseases like neurodegenerative disorders. Thus inhibiting the formation of toxic Aβ assemblies is a reasonable hypothesis to prevent and perhaps treat AD

Methods

Solution NMR and molecular modeling were used to obtain more information about the interaction between the Aβ_1–40 and the polyphenol ε-viniferin glucoside (EVG) and particularly the Aβ residues involved in the complex.

Results

The study demonstrates the formation of a complex between two EVG molecules and Aβ_1–40 in peptide characteristic regions that could be in agreement with the inhibition of aggregation. Indeed, in previous studies, we reported that EVG strongly inhibited in vitro the fibril formation of the full length peptides Aβ_1–40 and Aβ_1–42, and had a strong protective effect against PC12 cell death induced by these peptides.

Conclusion

For the full length peptide Aβ_1–40, the binding sites observed could explain the EVG inhibitory effect on fibrillization and thus prevent amyloidogenic neurotoxicity.

General significance

Even though this interaction might be important at the biological level to explain the protective effect of polyphenols in neurodegenerative diseases, caution is required when extrapolating this in vitro model to human physiology.     

COQ4 Mutations Cause a Broad Spectrum of Mitochondrial Disorders Associated with CoQ10 Deficiency

Primary coenzyme Q10 (CoQ₁₀) deficiencies are rare, clinically heterogeneous disorders caused by mutations in several genes encoding proteins involved in CoQ₁₀ biosynthesis. CoQ₁₀ is an essential component of the electron transport chain (ETC), where it shuttles electrons from complex I or II to complex III. By whole-exome sequencing, we identified five individuals carrying biallelic mutations in COQ4. The precise function of human COQ4 is not known, but it seems to play a structural role in stabilizing a multiheteromeric complex that contains most of the CoQ₁₀ biosynthetic enzymes. The clinical phenotypes of the five subjects varied widely, but four had a prenatal or perinatal onset with early fatal outcome. Two unrelated individuals presented with severe hypotonia, bradycardia, respiratory insufficiency, and heart failure; two sisters showed antenatal cerebellar hypoplasia, neonatal respiratory-distress syndrome, and epileptic encephalopathy. The fifth subject had an early-onset but slowly progressive clinical course dominated by neurological deterioration with hardly any involvement of other organs. All available specimens from affected subjects showed reduced amounts of CoQ₁₀ and often displayed a decrease in CoQ₁₀-dependent ETC complex activities. The pathogenic role of all identified mutations was experimentally validated in a recombinant yeast model; oxidative growth, strongly impaired in strains lacking COQ4, was corrected by expression of human wild-type COQ4 cDNA but failed to be corrected by expression of COQ4 cDNAs with any of the mutations identified in affected subjects. COQ4 mutations are responsible for early-onset mitochondrial diseases with heterogeneous clinical presentations and associated with CoQ10 deficiency.     

Modelling biochemical features of mitochondrial neuropathology

Background

The neuropathology of mitochondrial disease is well characterised. However, pathophysiological mechanisms at the level of biochemistry and cell biology are less clear. Progress in this area has been hampered by the limited accessibility of neurologically relevant material for analysis.

Scope of review

Here we discuss the recent development of a variety of model systems that have greatly extended our capacity to understand the biochemical features associated with mitochondrial neuropathology. These include animal and cell based models, with mutations in both nuclear and mitochondrial DNA encoded genes, which aim to recapitulate the neuropathology and cellular biochemistry of mitochondrial diseases.

Major conclusions

Analysis of neurological tissue and cells from these models suggests that although there is no unifying mode of pathogenesis, dysfunction of the oxidative phosphorylation (OXPHOS) system is often central. This can be associated with altered reactive oxygen species (ROS) generation, disruption of the mitochondrial membrane potential (ΔΨ_m) and inadequate ATP synthesis. Thus, other cellular processes such as calcium (Ca^2 +) homeostasis, cellular signaling and mitochondrial morphology could be altered, ultimately compromising viability of neuronal cells.

General significance

Mechanisms of neuronal dysfunction in mitochondrial disease are only just beginning to be characterised, are system dependent and complex, and not merely driven by energy deficiency. The diversity of pathogenic mechanisms emphasises the need for characterisation in a wide range of models, as different therapeutic strategies are likely to be needed for different diseases.This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.     

Somatic mutations in mitochondrial genome and their potential roles in the progression of human gastric cancer

Background

Somatic mutation in mitochondrial DNA (mtDNA) has been proposed to contribute to initiation and progression of human cancer. In our previous study, high frequency of somatic mutations was found in the D-loop region of mtDNA of gastric cancers. However, it is unclear whether somatic mutations occur in the coding region of mtDNA of gastric cancers.

Methods

Using DNA sequencing, we studied 31 gastric cancer specimens and corresponding non-cancerous stomach tissues. Moreover, a human gastric cancer SC-M1 cell line was treated with oligomycin to induce mitochondrial dysfunction. Cisplatin sensitivity and cell migration were analyzed.

Results

We identified eight somatic mutations in the coding region of mtDNAs of seven gastric cancer samples (7/31, 22.6%). Patients with somatic mutations in the entire mtDNA of gastric cancers did not show significant association with their clinicopathologic features. Among the eight somatic mutations, five point mutations (G3697A, G4996A, G9986A, C12405T and T13015C) are homoplasmic and three mutations (5895delC, 7472insC and 12418insA) are heteroplasmic. Four (4/8, 50%) of these somatic mutations result in amino acid substitutions in the highly conserved regions of mtDNA, which potentially lead to mitochondrial dysfunction. In addition, in vitro experiments in SC-M1 cells revealed that oligomycin-induced mitochondrial dysfunction promoted resistance to cisplatin and enhanced cell migration. N-acetyl cysteine was effective in the prevention of the oligomycin-enhanced migration, which suggests that reactive oxygen species generated by defective mitochondria may be involved in the enhanced migration of SC-M1 cells.

General Significance

Our results suggest that somatic mtDNA mutations and mitochondrial dysfunction may play an important role in the malignant progression of gastric cancer.     

Rapid uptake of lipophilic triphenylphosphonium cations by mitochondria in vivo following intravenous injection: Implications for mitochondria-specific therapies and probes

Background

Mitochondrial dysfunction contributes to a range of pathologies, consequently there is a need to monitor mitochondrial function and to intervene pharmacologically to prevent mitochondrial damage. One approach to this is to deliver antioxidants, probes and pharmacophores to mitochondria by conjugation to the lipophilic triphenylphosphonium (TPP) cation that is taken up selectively by mitochondria driven by the membrane potential.

Conclusions

Oral administration of TPP-conjugated antioxidants protects against mitochondrial damage in vivo. However, there is also a need to deliver molecules rapidly to mitochondria to respond quickly to pathologies and for the real-time assessment of mitochondrial function.

Methods

To see if this was possible we investigated how rapidly TPP cations were taken up by mitochondria in vivo following intravenous (iv) administration.

Results

AlkylTPP cations were accumulated selectively by mitochondria within mice within 5 min of iv injection. The extent of uptake was enhanced 10–30-fold relative to simple alkylTPP cations by attaching functional groups to the TPP cation via long, hydrophobic alkyl chains. Conclusions: Mitochondria-targeted antioxidants, probes and pharmacophores can be delivered into mitochondria within minutes of iv administration.

General significance

These findings greatly extend the utility of mitochondria-targeted lipophilic cations as therapies and probes.     

Methyl pyruvate rescues mitochondrial damage caused by SIGMAR1 mutation related to amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a disease caused by motor neuron degeneration. Recently, a novel SIGMAR1 gene variant (p.E102Q) was discovered in some familial ALS patients.

Methods

We address mechanisms underlying neurodegeneration caused by the mutation using Neuro2A cells overexpressing σ₁R^E102Q, a protein of a SIGMAR1 gene variant (p.E102Q) and evaluate potential amelioration by ATP production via methyl pyruvate (MP) treatment.

Results

σ₁R^E102Q overexpression promoted dissociation of the protein from the endoplasmic reticulum (ER) membrane and cytoplasmic aggregation, which in turn impaired mitochondrial ATP production and proteasome activity. Under ER stress conditions, overexpression of wild-type σ₁R suppressed ER stress-induced mitochondrial injury, whereas σ₁R^E102Q overexpression aggravated mitochondrial damage and induced autophagic cell death. Moreover, σ₁R^E102Q-overexpressing cells showed aberrant extra-nuclear localization of the TAR DNA-binding protein (TDP-43), a condition exacerbated by ER stress. Treatment of cells with the mitochondrial Ca^2 + transporter inhibitor Ru360 mimicked the effects of σ₁R^E102Q overexpression, indicating that aberrant σ₁R-mediated mitochondrial Ca^2 + transport likely underlies TDP-43 extra-nuclear localization, segregation in inclusion bodies, and ubiquitination. Finally, enhanced ATP production promoted by methyl pyruvate (MP) treatment rescued proteasome impairment and TDP-43 extra-nuclear localization caused by σ₁R^E102Q overexpression.

Conclusions

Our observations suggest that neurodegeneration seen in some forms of ALS are due in part to aberrant mitochondrial ATP production and proteasome activity as well as TDP-43 mislocalization resulting from the SIGMAR1 mutation.

General significance

ATP supplementation by MP represents a potential therapeutic strategy to treat ALS caused by SIGMAR1 mutation.     

The ins and outs of the intermembrane space: Diverse mechanisms and evolutionary rewiring of mitochondrial protein import routes

Background

Mitochondrial biogenesis is an essential process in all eukaryotes. Import of proteins from the cytosol into mitochondria is a key step in organelle biogenesis. Recent evidence suggests that a given mitochondrial protein does not take the same import route in all organisms, suggesting that pathways of mitochondrial protein import can be rewired through evolution. Examples of this process so far involve proteins destined to the mitochondrial intermembrane space (IMS).

Scope of review

Here we review the components, substrates and energy sources of the known mechanisms of protein import into the IMS. We discuss evolutionary rewiring of the IMS import routes, focusing on the example of the lactate utilisation enzyme cytochrome b₂ (Cyb2) in the model yeast Saccharomyces cerevisiae and the human fungal pathogen Candida albicans.

Major conclusions

There are multiple import pathways used for protein entry into the IMS and they form a network capable of importing a diverse range of substrates. These pathways have been rewired, possibly in response to environmental pressures, such as those found in the niches in the human body inhabited by C. albicans.

General significance

We propose that evolutionary rewiring of mitochondrial import pathways can adjust the metabolic fitness of a given species to their environmental niche. This article is part of a Special Issue entitled Frontiers of Mitochondrial.     

LRRK2, but not pathogenic mutants,protects against H2O2 stress depending on mitochondrial function and endocytosis in a yeast model

Background

Mutations in LRRK2 are the most common genetic cause of Parkinson's disease (PD). Studies in the yeast Saccharomyces cerevisiae have provided valuable insights into the mechanisms of cellular dysfunction associated with the expression of faulty PD genes.

Methods

We developed a yeast model for full-length LRRK2 studies. We expressed wild-type (wt) LRRK2 and mutations and evaluated their role during oxidative stress conditions. The involvement of mitochondria was assessed by using rho-zero mutants and by evaluating reactive oxygen species (ROS) production and mitochondrial membrane potential by flow cytometry. The involvement of endocytosis was also studied by testing several endocytic mutants and by following the vacuolar delivery of the probe FM4-64.

Results

Expression of LRRK2 in yeast was associated to increased hydrogen peroxide resistance. This phenotype, which was dependent on mitochondrial function, was not observed for PD-mutants G2019S and R1441C or in the absence of the kinase activity and the WD40 repeat domain. Expression of the pathogenic mutants stimulated ROS production and increased mitochondrial membrane potential. For the PD-mutants, but not for wild-type LRRK2, endocytic defects were also observed. Additionally, several endocytic proteins were required for LRRK2-mediated protection against hydrogen peroxide.

Conclusions

Our results indicate that LRRK2 confers cellular protection during oxidative stress depending on mitochondrial function and endocytosis.

General significance

Both the loss of capacity of LRRK2 pathogenic mutants to protect against oxidative stress and their enhancement of dysfunction may be important for the development of PD during the aging process.     

Stimulation of insulin release from pancreatic islets by quinones

Coenzyme Q (CoQ₀) and other quinones were shown to be potent insulin secretagogues in the isolated pancreatic islet. The order of potency was CoQ₀benzoquinonehydroquinonemenadione. CoQ₆ and CoQ₁₀ (ubiquinone), duroquinone and durohydroquinone did not stimulate insulin release. CoQ₀'s insulinotropism was enhanced in calcium-free medium and CoQ₀ appeared to stimulate only the second phase of insulin release. CoQ₀ inhibited inositol mono-, bis- and trisphosphate formation. Inhibitors of mitochondrial respiration (rotenone, antimycin A, FCCP and cyanide) and the calcium channel blocker verapamil, did not inhibit CoQ₀-induced insulin release. Dicumarol, an inhibitor of quinone reductase, did not inhibit CoQ₀-induced insulin release, but it did inhibit glucose-induced insulin release suggesting that the enzyme and quinones play a role in glucose-induced insulin release. Quinones may stimulate insulin release by mimicking physiologically-occuring quinones, such as CoQ₁₀, by acting on the plasma membrane or in the cytosol. Exogenous quinones may bypass the quinone reductase reaction, as well as many reactions important for exocytosis.     

Redox status and pharmacokinetics of coenzyme Q10 in rat plasma after its single intravenous administration

The pharmacokinetics of the total pool of coenzyme Q₁₀ (CoQ₁₀), its oxidized (ubiquinone) and reduced (ubiquinol, CoQ₁₀H₂) forms have been investigated in rats plasma during 48 h after a single intravenous injection of a solution of solubilized CoQ₁₀ (10 mg/kg) to rats. Plasma levels of CoQ₁₀ were determined by HPLC with spectrophotometric and coulometric detection. In plasma samples taken during the first minutes after the CoQ₁₀ intravenous injection, the total pool of coenzyme Q₁₀ and proportion of CoQ₁₀H₂ remained unchanged during two weeks of storage at ?20°C. The kinetic curve of the total pool of coenzyme Q₁₀ corresponds to a one-compartment model (R ₂ = 0.9932), while the corresponding curve of its oxidized form fits to the two-compartment model. During the first minutes after the injection a significant portion of plasma ubiquinone undergoes reduction, and after 7 h the concentration of ubiquinol predominates. The decrease in total plasma coenzyme Q₁₀ content was accompanied by the gradual increase in plasma ubiquinol, which represented about 90% of total plasma CoQ₁₀ by the end of the first day. The results of this study demonstrate the ability of the organism to transform high concentrations of the oxidized form of CoQ₁₀ into the effective antioxidant (reduced) form and justify prospects of the development of parenteral dosage forms of CoQ₁₀ for the use in the treatment of acute pathological conditions.     

Roles of mitochondrial fragmentation and reactive oxygen species in mitochondrial dysfunction and myocardial insulin resistance

Purpose

Evidence suggests an association between aberrant mitochondrial dynamics and cardiac diseases. Because myocardial metabolic deficiency caused by insulin resistance plays a crucial role in heart disease, we investigated the role of dynamin-related protein-1 (DRP1; a mitochondrial fission protein) in the pathogenesis of myocardial insulin resistance.

Methods and Results

DRP1-expressing H9c2 myocytes, which had fragmented mitochondria with mitochondrial membrane potential (ΔΨ_m) depolarization, exhibited attenuated insulin signaling and 2-deoxy-d-glucose (2-DG) uptake, indicating insulin resistance. Treatment of the DRP1-expressing myocytes with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP) significantly improved insulin resistance and mitochondrial dysfunction. When myocytes were exposed to hydrogen peroxide (H₂O₂), they increased DRP1 expression and mitochondrial fragmentation, resulting in ΔΨ_m depolarization and insulin resistance. When DRP1 was suppressed by siRNA, H₂O₂-induced mitochondrial dysfunction and insulin resistance were restored. Our results suggest that a mutual enhancement between DRP1 and reactive oxygen species could induce mitochondrial dysfunction and myocardial insulin resistance. In palmitate-induced insulin-resistant myocytes, neither DRP1-suppression nor TMPyP restored the ΔΨ_m depolarization and impaired 2-DG uptake, however they improved insulin signaling.

Conclusions

A mutual enhancement between DRP1 and ROS could promote mitochondrial dysfunction and inhibition of insulin signal transduction. However, other mechanisms, including lipid metabolite-induced mitochondrial dysfunction, may be involved in palmitate-induced insulin resistance.