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Departments of Obstetrics and Gynecology (T.L.H., S.D., C.L., M.S., P.S.), Neurobiology (T.L.H., C.L., R.T.M., C.J.B.), Pharmacology (J.D.E., R.H.R.), Ophthalmology-Visual Science (C.J.B.), Psychiatry (D.E.R.), and Neurosurgery (D.E.R.), Yale University School of Medicine, New Haven, Connecticut 06520; Instituto Cajal (L.M.G.-S.), Consejo Superior de Investigaciones Cientificas, Madrid, Spain 28002; The Vollume Institute (M.A.C.), Oregon Health & Science University, Portland, Oregon 97006; Department of Anatomy and Histology (T.L.H., P.S.), Szent Istvan University, Faculty of Veterinary Sciences, Budapest 1078, Hungary; and The St. Kitts Biomedical Research Foundation (E.H.D., D.E.R.), St. Kitts-Nevis, West Indies
Address all correspondence and requests for reprints to: Tamas L. Horvath, Department of Obstetrics/Gynecology, Yale Medical School, 333 Cedar Street, FMB 339, New Haven, Connecticut 06520. E-mail: tamas.horvath{at}yale.edu
| Abstract |
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| Introduction |
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Mirochondrial uncoupling proteins (UCP) are protonophores that are mainly associated with peripheral energy expenditure (2, 3, 4, 5, 6, 7). The first member of these mitochondrial inner membrane proteins, UCP1, plays a well-described role in thermogenesis by the brown adipose tissue (2, 8). To date, only two other members of the family, UCP2 and UCP3, have been shown to have uncoupling activity (9). These have different tissue distributions with UCP2 expressed in a number of different brain structures (10, 11, 12). Beyond their role in regulating mitochondrial inner membrane potential, ATP levels, and local thermogenesis, these three UCPs, including UCP2, are free radical scavengers (13, 14). UCP2 is induced by neuronal stress, and it suppresses apoptotic signaling (15); coenzyme Q (CoQ10), a molecule previously found beneficial in a rodent model of PD (16), activates UCP2 (17, 18), and activation of UCP2 supports a positive energy balance (19) that is the exact opposite observed in the initial phase of PD (1). Together, these observations suggest that this mitochondrial mechanism activated by CoQ10 would not only slow or diminish neurodegeneration related to the SN dopamine cells but could also boost processes affecting energy balance. To test this hypothesis, we assessed the effect of short-term oral CoQ10 treatment on brain mitochondrial uncoupling activity in primates. Furthermore, we analyzed UCP2 expression in the SN and evaluated the effect of short-term oral CoQ10 on dopamine cell loss in monkeys treated with 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP).
| Materials and Methods |
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All experimental procedures were approved by Institutional Animal Care and Use Committees of Yale University and/or the St. Kitts Biomedical Research Foundation.
CoQ10 and MPTP treatment of nonhuman primates
Animals were fed 100 mg CoQ10 (Natrol, Inc., Chatsworth, CA) per day spread on the longitudinally cut (then reattached) surface of a banana. This resulted in doses ranging from 1522 mg/kg·d per animal. Control animals received banana only. Ten days later, a group of six CoQ10-treated and six nontreated animals received MPTP, with cumulative doses of 1.5 mg/kg MPTP/animals. Tissues were collected and processed 20 d later.
Analysis of UCP2 mRNA
Real time RT-PCR analyses was used to assess UCP2 mRNA levels in the substantia nigra of control and experimental animals. Total RNA was extracted and cDNA prepared as previously described by Horvath and colleagues (11, 15, 19, 20). Primers to amplify UCP2 were forward 5'-CTACAAGACCATTGCACGAGAGG-3' and reverse 5'-AGCTGCTCATAGGTGACAAACAT-3' and gave a 396-bp product. A 603-bp fragment of ß-actin was amplified as control. The PCR was performed as previously described by Horvath and colleagues (11, 15, 19, 20). Reactions were analyzed by gel electrophoresis, and identity of bands was confirmed by sequencing of selected samples.
Detection of UCP2 in the SN of nonhuman primates
Mesencephalic sections of monkeys were double immunostained for UCP2 and tyrosine hydroxylase using different fluorescent dyes as described elsewhere by Horvath et al. (11).
Analysis of uncoupling activity
To test the level of mitochondrial uncoupling, oxygen consumption in state-3 and state-4 respiration and respiratory control ratio (RCR: the ratio of these levels) were assessed from SN homogenates of primates as described elsewhere by Horvath and colleagues (11, 15, 19, 20). In short, dissected SN was homogenized in a medium containing 320 mM sucrose, 10 mM Tris, and 1 mM EGTA adjusted to pH 7.4 with HCl. The samples were diluted 10 times with isolation medium. The pellet was gently resuspended and stored on ice. Mitochondrial oxygen consumption was determined using a Clark-type oxygen electrode in an incubation medium containing 80 mM KCl, 50 mM HEPES (pH 7), 1 mM EGTA, 5 mM K2HPO4, 4 µM rotenone, 80 ng/ml nigericine, and 1 µg/ml oligomycin using a saturating amount of succinate as substrate at 37 C. State-3 respiration was initiated by the addition of ADP (300 µM) and subsequently state-4 and -3 respiration and RCR were assessed.
Histological analyses
We analyzed dopamine cell numbers in the SN of control and experimental monkeys using unbiased stereology. The unbiased stereological methods for cell number assessment used a systematic random sampling method and met the statistical requirements necessary to ensure an unbiased estimate of the feature of interest. We chose to sample every 10th section (30 µm thick) to assess cell number; the starting point of the series for each animal was randomly selected from the first 10 sections. Because an F test analysis of cell counts in different experimental and control groups revealed a significant nonhomogeneity of variances between groups, the Kruskal-Wallis one-way nonparametric ANOVA test was selected for statistical comparisons. A level of confidence of P < 0.05 was adopted.
| Results |
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State-3 and -4 respirations and RCR in control and CoQ10-treated monkeys
To assess whether short-term (30 d) oral CoQ10 affects the brain, we analyzed state-3 and -4 respirations and RCR = state-3/state-4 in the SN of control (n = 6) and CoQ10-treated monkeys. Oxygen consumption in state-3 respiration (phosphorylation) was elevated in CoQ10-treated animals (Fig. 1C
). However, RCR values of CoQ10-treated SN did not change because state-4 respiration (oxygen consumption related to mitochondrial proton leak regulated by UCP2) was also enhanced (Fig. 1C
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Nigral dopamine cell counts in control, CoQ10-, MPTP-, and CoQ10 + MPTP-treated monkeys
We analyzed dopamine cell numbers in the SN of control and experimental monkeys using unbiased stereology. We found that in intact and CoQ10-treated animals, the numbers of SN dopamine cells/mm3 were 7480.33 ± 1492.04 SEM and 6734.5 ± 951.41 SEM, respectively. MPTP treatment induced a 70% loss of dopamine cells in the SN (1958.8 ± 140.97 cells/mm3; P < 0.01). Pretreatment of MPTP monkeys with CoQ10 resulted in dopamine cell counts (5891.66 ± 621.57) statistically not different from intact and CoQ10 values (Fig. 1
, D and E).
| Discussion |
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State-4 respiration is enhanced by oral CoQ10, most likely due to the activation of UCP2, which was found to be constitutively expressed in the SN dopamine cells in nonhuman primates. In fact, a controlled reduction of mitochondrial membrane potential (i.e. increased state-4 respiration) by UCP2 has been shown to be neuroprotective and has been proposed to be a self-defense mechanism that may be up-regulated in some neurodegenerative disorders (15). However, the mechanism responsible for the beneficial effects of oral CoQ10 in PD may be the consequence of the enhancement of other mitochondrial mechanisms as well.
To date, only limited information is available on the regulation of UCP2 mRNA expression and translation, and the function of the protein in the brain. UCP2 activity as a protonophore, similar to UCP1, requires fatty acids and is nucleotide dependent (3, 9, 17, 18, 21, 22). There are in vitro and in vivo data available on peripheral UCP2 expression that show varying levels of regulation of UCP2 by different hormones, including leptin and thyroid hormone (23, 24, 25). It appears, however, that the regulation of UCP2 by these hormones is tissue specific and most likely involves indirect mechanisms of action. Other biologically active substances were also shown to affect transcription, translation, and/or activity of UCP2. These include retinoic acid (26, 27), lipopolysaccharides (28), superoxides (9, 21, 22), and CoQ10 (17, 18). In particular, after the revelations that superoxides regulate UCP2 transcriptionally and postranslationally (21), Klingenberg and his colleagues (17, 18) showed that the functionality of UCP2 as a mitochondrial uncoupler requires CoQ10 as mandatory cofactor.
CoQ10 has been shown to reduce the effects of MPTP on striatal dopamine concentrations in mice but is unable to protect SN dopamine neurons from cell death (16). Our observations of a robust effect of CoQ10 in the protection of SN dopamine neurons in primates demonstrate the importance of species differences in the PD models and suggest that the potent effects of CoQ10 may result from activation of UCP2. Because CoQ10 was shown to be safe and well tolerated in humans (29, 30), and to slow the progression of symptom development in PD patients (31), our data implicating UCPs in this process offer an alternative mechanism of action of oral CoQ10 in neuroprotection. Furthermore, these observations highlight the potential that other substances and metabolic and endocrine conditions that favor mitochondrial uncoupling may exhibit neuroprotective properties that will be useful in slowing the progression of PD.
| Footnotes |
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Abbreviations: CoQ10, Coenzyme Q; MPTP, 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine; PD, Parkinsons disease; RCR, respiratory control ratio; SN, substantia nigra; UCP, uncoupling proteins.
Received February 3, 2003.
Accepted for publication March 13, 2003.
| References |
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-dependent mechanism. Biochem Biophys Res Commun 251:313319[CrossRef][Medline]
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