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Portugal CC. Ascorbate and its transporter SVCT2: The dynamic duo's integrated roles in CNS neurobiology and pathophysiology. Free Radic Biol Med 2024; 212:448-462. [PMID: 38182073 DOI: 10.1016/j.freeradbiomed.2023.12.040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 12/11/2023] [Accepted: 12/27/2023] [Indexed: 01/07/2024]
Abstract
Ascorbate is a small antioxidant molecule essential for the proper development and function of the brain. Ascorbate is transported into the brain and between brain cells via the Sodium vitamin C co-transporter 2 (SVCT2). This review provides an in-depth analysis of ascorbate's physiology, including how ascorbate is absorbed from food into the CNS, emphasizing cellular mechanisms of ascorbate recycling and release in different CNS compartments. Additionally, the review delves into the various functions of ascorbate in the CNS, including its impact on epigenetic modulation, synaptic plasticity, and neurotransmission. It also emphasizes ascorbate's role on neuromodulation and its involvement in neurodevelopmental processes and disorders. Furthermore, it analyzes the relationship between the duo ascorbate/SVCT2 in neuroinflammation, particularly its effects on microglial activation, cytokine release, and oxidative stress responses, highlighting its association with neurodegenerative diseases, such as Alzheimer's disease (AD). Overall, this review emphasizes the crucial role of the dynamic duo ascorbate/SVCT2 in CNS physiology and pathology and the need for further research to fully comprehend its significance in a neurobiological context and its potential therapeutic applications.
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Affiliation(s)
- Camila C Portugal
- I3s - Instituto de Investigação e Inovação em Saúde da Universidade do Porto and IBMC - Instituto de Biologia Molecular e Celular, Rua Alfredo Allen 208, 4200-135, Porto, Portugal.
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2
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Rashid MH, Babu D, Siraki AG. Interactions of the antioxidant enzymes NAD(P)H: Quinone oxidoreductase 1 (NQO1) and NRH: Quinone oxidoreductase 2 (NQO2) with pharmacological agents, endogenous biochemicals and environmental contaminants. Chem Biol Interact 2021; 345:109574. [PMID: 34228969 DOI: 10.1016/j.cbi.2021.109574] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 06/17/2021] [Accepted: 07/01/2021] [Indexed: 01/11/2023]
Abstract
NAD(P)H Quinone Oxidoreductase 1 (NQO1) is an antioxidant enzyme that catalyzes the two-electron reduction of several different classes of quinone-like compounds (quinones, quinone imines, nitroaromatics, and azo dyes). One-electron reduction of quinone or quinone-like metabolites is considered to generate semiquinones to initiate redox cycling that is responsible for the generation of reactive oxygen species and oxidative stress and may contribute to the initiation of adverse drug reactions and adverse health effects. On the other hand, the two-electron reduction of quinoid compounds appears important for drug activation (bioreductive activation) via chemical rearrangement or autoxidation. Two-electron reduction decreases quinone levels and opportunities for the generation of reactive species that can deplete intracellular thiol pools. Also, studies have shown that induction or depletion (knockout) of NQO1 were associated with decreased or increased susceptibilities to oxidative stress, respectively. Moreover, another member of the quinone reductase family, NRH: Quinone Oxidoreductase 2 (NQO2), has a significant functional and structural similarity with NQO1. The activity of both antioxidant enzymes, NQO1 and NQO2, becomes critically important when other detoxification pathways are exhausted. Therefore, this article summarizes the interactions of NQO1 and NQO2 with different pharmacological agents, endogenous biochemicals, and environmental contaminants that would be useful in the development of therapeutic approaches to reduce the adverse drug reactions as well as protection against quinone-induced oxidative damage. Also, future directions and areas of further study for NQO1 and NQO2 are discussed.
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Affiliation(s)
- Md Harunur Rashid
- Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada; Institute of Food and Radiation Biology, Bangladesh Atomic Energy Commission, Bangladesh
| | - Dinesh Babu
- Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada
| | - Arno G Siraki
- Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada.
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Ravasz D, Kacso G, Fodor V, Horvath K, Adam-Vizi V, Chinopoulos C. Reduction of 2-methoxy-1,4-naphtoquinone by mitochondrially-localized Nqo1 yielding NAD + supports substrate-level phosphorylation during respiratory inhibition. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:909-924. [PMID: 29746824 DOI: 10.1016/j.bbabio.2018.05.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 04/26/2018] [Accepted: 05/03/2018] [Indexed: 01/07/2023]
Abstract
Provision of NAD+ for oxidative decarboxylation of alpha-ketoglutarate to succinyl-CoA by the ketoglutarate dehydrogenase complex (KGDHC) is critical for maintained operation of succinyl-CoA ligase yielding high-energy phosphates, a process known as mitochondrial substrate-level phosphorylation (mSLP). We have shown previously that when NADH oxidation by complex I is inhibited by rotenone or anoxia, mitochondrial diaphorases yield NAD+, provided that suitable quinones are present (Kiss G et al., FASEB J 2014, 28:1682). This allows for KGDHC reaction to proceed and as an extension of this, mSLP. NAD(P)H quinone oxidoreductase 1 (NQO1) is an enzyme exhibiting diaphorase activity. Here, by using Nqo1-/- and WT littermate mice we show that in rotenone-treated, isolated liver mitochondria 2-methoxy-1,4-naphtoquinone (MNQ) is preferentially reduced by matrix Nqo1 yielding NAD+ to KGDHC, supporting mSLP. This process was sensitive to inhibition by specific diaphorase inhibitors. Reduction of idebenone and its analogues MRQ-20 and MRQ-56, menadione, mitoquinone and duroquinone were unaffected by genetic disruption of the Nqo1 gene. The results allow for the conclusions that i) MNQ is a Nqo1-preferred substrate, and ii) in the presence of suitable quinones, mitochondrially-localized diaphorases other than Nqo1 support NADH oxidation when complex I is inhibited. Our work confirms that complex I bypass can occur by quinones reduced by intramitochondrial diaphorases oxidizing NADH, ultimately supporting mSLP. Finally, it may help to elucidate structure-activity relationships of redox-active quinones with diaphorase enzymes.
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Affiliation(s)
- Dora Ravasz
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary
| | - Gergely Kacso
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary
| | - Viktoria Fodor
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary
| | - Kata Horvath
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary
| | - Vera Adam-Vizi
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary
| | - Christos Chinopoulos
- Department of Medical Biochemistry, Semmelweis University, Budapest 1094, Hungary.
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Yu-Wai-Man P, Soiferman D, Moore DG, Burté F, Saada A. Evaluating the therapeutic potential of idebenone and related quinone analogues in Leber hereditary optic neuropathy. Mitochondrion 2017; 36:36-42. [PMID: 28093355 PMCID: PMC5644719 DOI: 10.1016/j.mito.2017.01.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 12/29/2016] [Accepted: 01/12/2017] [Indexed: 01/09/2023]
Abstract
Leber hereditary optic neuropathy (LHON) is an important cause of mitochondrial blindness among young adults. In this study, we investigated the potential of four quinone analogues (CoQ1, CoQ10, decylubiquinone and idebenone) in compensating for the deleterious effect of the m.11778G>A mitochondrial DNA mutation. The LHON fibroblast cell lines tested exhibited reduced cell growth, impaired mitochondrial bioenergetics and elevated levels of reactive oxygen species (ROS). Idebenone increased ATP production and reduced ROS levels, but the effect was partial and cell-specific. The remaining quinone analogues had variable effects and a negative impact on certain mitochondrial parameters was observed in some cell lines.
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Affiliation(s)
- Patrick Yu-Wai-Man
- Wellcome Trust Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK; Newcastle Eye Centre, Royal Victoria Infirmary, Newcastle upon Tyne, UK; NIHR Biomedical Research Centre at Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, UK; Department of Clinical Neurosciences, School of Clinical Medicine, University of Cambridge, Cambridge, UK.
| | - Devorah Soiferman
- Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel; Department of Genetics and Metabolic Diseases, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - David G Moore
- Wellcome Trust Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Florence Burté
- Wellcome Trust Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Ann Saada
- Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel; Department of Genetics and Metabolic Diseases, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
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Old Things New View: Ascorbic Acid Protects the Brain in Neurodegenerative Disorders. Int J Mol Sci 2015; 16:28194-217. [PMID: 26633354 PMCID: PMC4691042 DOI: 10.3390/ijms161226095] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Revised: 09/23/2015] [Accepted: 10/14/2015] [Indexed: 12/13/2022] Open
Abstract
Ascorbic acid is a key antioxidant of the Central Nervous System (CNS). Under brain activity, ascorbic acid is released from glial reservoirs to the synaptic cleft, where it is taken up by neurons. In neurons, ascorbic acid scavenges reactive oxygen species (ROS) generated during synaptic activity and neuronal metabolism where it is then oxidized to dehydroascorbic acid and released into the extracellular space, where it can be recycled by astrocytes. Other intrinsic properties of ascorbic acid, beyond acting as an antioxidant, are important in its role as a key molecule of the CNS. Ascorbic acid can switch neuronal metabolism from glucose consumption to uptake and use of lactate as a metabolic substrate to sustain synaptic activity. Multiple evidence links oxidative stress with neurodegeneration, positioning redox imbalance and ROS as a cause of neurodegeneration. In this review, we focus on ascorbic acid homeostasis, its functions, how it is used by neurons and recycled to ensure antioxidant supply during synaptic activity and how this antioxidant is dysregulated in neurodegenerative disorders.
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Jaber S, Polster BM. Idebenone and neuroprotection: antioxidant, pro-oxidant, or electron carrier? J Bioenerg Biomembr 2014; 47:111-8. [PMID: 25262284 DOI: 10.1007/s10863-014-9571-y] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 08/15/2014] [Indexed: 12/30/2022]
Abstract
UNLABELLED Ubiquinone, commonly called coenzyme Q10 (CoQ), is a lipophilic electron carrier and endogenous antioxidant found in all cellular membranes. In the mitochondrial inner membrane it transfers electrons to complex III of the electron transport chain. The short chain CoQ analogue idebenone is in clinical trials for a number of diseases that exhibit a mitochondrial etiology. Nevertheless, evidence that idebenone ameliorates neurological symptoms in human disease is inconsistent. Although championed as an antioxidant, idebenone can also act as a pro-oxidant by forming an unstable semiquinone at complex I. The antioxidant function of idebenone is critically dependent on two-electron reduction to idebenol without the creation of unstable intermediates. Recently, cytoplasmic NAD(P)H quinone oxidoreductase 1 (NQO1) was identified as a major enzyme catalyzing idebenone reduction. While reduction allows idebenone to act as an antioxidant, evidence also suggests that NQO1 enables idebenone to shuttle reducing equivalents from cytoplasmic NAD(P)H to mitochondrial complex III, bypassing any upstream damage to the electron transport chain. In this mini-review we discuss how idebenone can influence mitochondrial function within the context of cytoprotection. Importantly, in the brain NQO1 is expressed primarily by glia rather than neurons. As NQO1 is an inducible enzyme regulated by oxidative stress and the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway, optimizing NQO1 expression in appropriate cell types within a specific disease context may be key to delivering on idebenone's therapeutic potential.
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Affiliation(s)
- Sausan Jaber
- Department of Anesthesiology, Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore St., MSTF 5-34, Baltimore, MD, 21201, USA
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Erb M, Hoffmann-Enger B, Deppe H, Soeberdt M, Haefeli RH, Rummey C, Feurer A, Gueven N. Features of idebenone and related short-chain quinones that rescue ATP levels under conditions of impaired mitochondrial complex I. PLoS One 2012; 7:e36153. [PMID: 22558363 PMCID: PMC3338594 DOI: 10.1371/journal.pone.0036153] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 03/27/2012] [Indexed: 12/14/2022] Open
Abstract
Short-chain quinones have been investigated as therapeutic molecules due to their ability to modulate cellular redox reactions, mitochondrial electron transfer and oxidative stress, which are pathologically altered in many mitochondrial and neuromuscular disorders. Recently, we and others described that certain short-chain quinones are able to bypass a deficiency in complex I by shuttling electrons directly from the cytoplasm to complex III of the mitochondrial respiratory chain to produce ATP. Although this energy rescue activity is highly interesting for the therapy of disorders associated with complex I dysfunction, no structure-activity-relationship has been reported for short-chain quinones so far. Using a panel of 70 quinones, we observed that the capacity for this cellular energy rescue as well as their effect on lipid peroxidation was influenced more by the physicochemical properties (in particular logD) of the whole molecule than the quinone moiety itself. Thus, the observed correlations allow us to explain the differential biological activities and therapeutic potential of short-chain quinones for the therapy of disorders associated with mitochondrial complex I dysfunction and/or oxidative stress.
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Affiliation(s)
- Michael Erb
- Santhera Pharmaceuticals, Liestal, Switzerland
| | | | | | | | - Roman H. Haefeli
- Santhera Pharmaceuticals, Liestal, Switzerland
- Biozentrum, University of Basel, Basel, Switzerland
| | | | | | - Nuri Gueven
- Santhera Pharmaceuticals, Liestal, Switzerland
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Bongard RD, Myers CR, Lindemer BJ, Baumgardt S, Gonzalez FJ, Merker MP. Coenzyme Q(1) as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type and Nqo1-null mouse lung. Am J Physiol Lung Cell Mol Physiol 2012; 302:L949-58. [PMID: 22268123 DOI: 10.1152/ajplung.00251.2011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies showed that coenzyme Q(1) (CoQ(1)) reduction on passage through the rat pulmonary circulation was catalyzed by NAD(P)H:quinone oxidoreductase 1 (NQO1) and mitochondrial complex I, but that NQO1 genotype was not a factor in CoQ(1) reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ(1) reduction in the isolated perfused wild-type (NQO1(+/+)) and Nqo1-null (NQO1(-)/(-)) mouse lung. CoQ(1) reduction was measured as the steady-state pulmonary venous CoQ(1) hydroquinone (CoQ(1)H(2)) efflux rate during infusion of CoQ(1) into the pulmonary arterial inflow. CoQ(1)H(2) efflux rates during infusion of 50 μM CoQ(1) were not significantly different for NQO1(+/+) and NQO1(-/-) lungs (0.80 ± 0.03 and 0.68 ± 0.07 μmol·min(-1)·g lung dry wt(-1), respectively, P > 0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ(1)H(2) efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min(-1)·g lung dry wt(-1) for NQO1(+/+) and NQO1(-/-), respectively, P < 0.05). Exposure of mice to 100% O(2) for 48 h also depressed CoQ(1)H(2) efflux rates in NQO1(+/+) and NQO1(-/-) lungs (0.43 ± 0.03 and 0.11 ± 0.04 μmol·min(-1)·g lung dry wt(-1), respectively, P < 0.05 by ANOVA). The impact of rotenone or hyperoxia on CoQ(1) redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ(1) recoveries, the latter measured by spectrophotometry or mass spectrometry. Complex I activity in mitochondria-enriched lung fractions was depressed in hyperoxia-exposed lungs for both genotypes. This study provides new evidence for the potential utility of CoQ(1) as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.
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Affiliation(s)
- Robert D Bongard
- Medical College of Wisconsin, Zablocki VAMC, Milwaukee, WI 53295, USA
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Haefeli RH, Erb M, Gemperli AC, Robay D, Courdier Fruh I, Anklin C, Dallmann R, Gueven N. NQO1-dependent redox cycling of idebenone: effects on cellular redox potential and energy levels. PLoS One 2011; 6:e17963. [PMID: 21483849 PMCID: PMC3069029 DOI: 10.1371/journal.pone.0017963] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Accepted: 02/21/2011] [Indexed: 11/25/2022] Open
Abstract
Short-chain quinones are described as potent antioxidants and in the case of idebenone have already been under clinical investigation for the treatment of neuromuscular disorders. Due to their analogy to coenzyme Q10 (CoQ10), a long-chain quinone, they are widely regarded as a substitute for CoQ10. However, apart from their antioxidant function, this provides no clear rationale for their use in disorders with normal CoQ10 levels. Using recombinant NAD(P)H:quinone oxidoreductase (NQO) enzymes, we observed that contrary to CoQ10 short-chain quinones such as idebenone are good substrates for both NQO1 and NQO2. Furthermore, the reduction of short-chain quinones by NQOs enabled an antimycin A-sensitive transfer of electrons from cytosolic NAD(P)H to the mitochondrial respiratory chain in both human hepatoma cells (HepG2) and freshly isolated mouse hepatocytes. Consistent with the substrate selectivity of NQOs, both idebenone and CoQ1, but not CoQ10, partially restored cellular ATP levels under conditions of impaired complex I function. The observed cytosolic-mitochondrial shuttling of idebenone and CoQ1 was also associated with reduced lactate production by cybrid cells from mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) patients. Thus, the observed activities separate the effectiveness of short-chain quinones from the related long-chain CoQ10 and provide the rationale for the use of short-chain quinones such as idebenone for the treatment of mitochondrial disorders.
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Affiliation(s)
- Roman H. Haefeli
- Santhera Pharmaceuticals, Liestal, Switzerland
- Biozentrum, University of Basel, Basel, Switzerland
| | - Michael Erb
- Santhera Pharmaceuticals, Liestal, Switzerland
| | | | | | | | | | - Robert Dallmann
- Institute of Pharmacology and Toxicology, University of Zürich, Zürich, Switzerland
| | - Nuri Gueven
- Santhera Pharmaceuticals, Liestal, Switzerland
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Kim E, Liu Y, Baker CJ, Owens R, Xiao S, Bentley WE, Payne GF. Redox-Cycling and H2O2 Generation by Fabricated Catecholic Films in the Absence of Enzymes. Biomacromolecules 2011; 12:880-8. [DOI: 10.1021/bm101499a] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
| | | | - C. Jacyn Baker
- Beltsville Agricultural Research Center, United States Department of Agriculture, Beltsville, Maryland 20705, United States
| | - Robert Owens
- Beltsville Agricultural Research Center, United States Department of Agriculture, Beltsville, Maryland 20705, United States
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López-Lluch G, Rodríguez-Aguilera JC, Santos-Ocaña C, Navas P. Is coenzyme Q a key factor in aging? Mech Ageing Dev 2010; 131:225-35. [PMID: 20193705 DOI: 10.1016/j.mad.2010.02.003] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Revised: 01/19/2010] [Accepted: 02/20/2010] [Indexed: 01/28/2023]
Abstract
Coenzyme Q (Q) is a key component for bioenergetics and antioxidant protection in the cell. During the last years, research on diseases linked to Q-deficiency has highlighted the essential role of this lipid in cell physiology. Q levels are also affected during aging and neurodegenerative diseases. Therefore, therapies based on dietary supplementation with Q must be considered in cases of Q deficiency such as in aging. However, the low bioavailability of dietary Q for muscle and brain obligates to design new mechanisms to increase the uptake of this compound in these tissues. In the present review we show a complete picture of the different functions of Q in cell physiology and their relationship to age and age-related diseases. Furthermore, we describe the problems associated with dietary Q uptake and the mechanisms currently used to increase its uptake or even its biosynthesis in cells. Strategies to increase Q levels in tissues are indicated.
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Affiliation(s)
- Guillermo López-Lluch
- Centro Andaluz de Biología del Desarrollo (CABD), Universidad Pablo de Olavide, CIBERER-Instituto de Salud Carlos III, Carretera de Utrera, Km 1, 41013 Sevilla, Spain
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12
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Audi SH, Merker MP, Krenz GS, Ahuja T, Roerig DL, Bongard RD. Coenzyme Q1 redox metabolism during passage through the rat pulmonary circulation and the effect of hyperoxia. J Appl Physiol (1985) 2008; 105:1114-26. [PMID: 18703762 DOI: 10.1152/japplphysiol.00177.2008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The objective was to evaluate the pulmonary disposition of the ubiquinone homolog coenzyme Q(1) (CoQ(1)) on passage through lungs of normoxic (exposed to room air) and hyperoxic (exposed to 85% O(2) for 48 h) rats. CoQ(1) or its hydroquinone (CoQ(1)H(2)) was infused into the arterial inflow of isolated, perfused lungs, and the venous efflux rates of CoQ(1)H(2) and CoQ(1) were measured. CoQ(1)H(2) appeared in the venous effluent when CoQ(1) was infused, and CoQ(1) appeared when CoQ(1)H(2) was infused. In normoxic lungs, CoQ(1)H(2) efflux rates when CoQ(1) was infused decreased by 58 and 33% in the presence of rotenone (mitochondrial complex I inhibitor) and dicumarol [NAD(P)H-quinone oxidoreductase 1 (NQO1) inhibitor], respectively. Inhibitor studies also revealed that lung CoQ(1)H(2) oxidation was via mitochondrial complex III. In hyperoxic lungs, CoQ(1)H(2) efflux rates when CoQ(1) was infused decreased by 23% compared with normoxic lungs. Based on inhibitor effects and a kinetic model, the effect of hyperoxia could be attributed predominantly to 47% decrease in the capacity of complex I-mediated CoQ(1) reduction, with no change in the other redox processes. Complex I activity in lung homogenates was also lower for hyperoxic than for normoxic lungs. These studies reveal that lung complexes I and III and NQO1 play a dominant role in determining the vascular concentration and redox status of CoQ(1) during passage through the pulmonary circulation, and that exposure to hyperoxia decreases the overall capacity of the lung to reduce CoQ(1) to CoQ(1)H(2) due to a depression in complex I activity.
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Affiliation(s)
- Said H Audi
- Research Service 151, Zablocki VAMC, 5000 W. National Avenue, Milwaukee, WI 53295, USA.
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