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Gilmore KM, Greer KA. Why is the dog an ideal model for aging research? Exp Gerontol 2015; 71:14-20. [PMID: 26325590 DOI: 10.1016/j.exger.2015.08.008] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Revised: 08/17/2015] [Accepted: 08/18/2015] [Indexed: 12/22/2022]
Abstract
With many caveats to the traditional vertebrate species pertaining to biogerontology investigations, it has been suggested that a most informative model is the one which: 1) examines closely related species, or various members of the same species with naturally occurring lifespan variation, 2) already has adequate medical procedures developed, 3) has a well annotated genome, 4) does not require artificial housing, and can live in its natural environment while being investigated, and 5) allows considerable information to be gathered within a relatively short period of time. The domestic dog unsurprisingly fits each criterion mentioned. The dog has already become a key model system in which to evaluate surgical techniques and novel medications because of the remarkable similarity between human and canine conditions, treatments, and response to therapy. The dog naturally serves as a disease model for study, obviating the need to construct artificial genetically modified examples of disease. Just as the dog offers a natural model for human conditions and diseases, simple observation leads to the conclusion that the canine aging phenotype also mimics that of the human. Genotype information, biochemical information pertaining to the GH/IGF-1 pathway, and some limited longitudinal investigations have begun the establishment of the domestic dog as a model of aging. Although we find that dogs indeed are a model to study aging and there are many independent pieces of canine aging data, there are many more "open" areas, ripe for investigation.
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Affiliation(s)
- Keiva M Gilmore
- Prairie View A&M University, PO Box 512, MS 2210, Prairie View, TX 77446, United States
| | - Kimberly A Greer
- Prairie View A&M University, PO Box 512, MS 2210, Prairie View, TX 77446, United States.
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Oxidative Stress and Protein Quality Control Systems in the Aged Canine Brain as a Model for Human Neurodegenerative Disorders. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2015; 2015:940131. [PMID: 26078824 PMCID: PMC4442305 DOI: 10.1155/2015/940131] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 04/29/2015] [Indexed: 12/24/2022]
Abstract
Aged dogs are considered the most suitable spontaneous animal model for studying normal aging and neurodegenerative diseases. Elderly canines naturally develop cognitive dysfunction and neuropathological hallmarks similar to those seen in humans, especially Alzheimer's disease-like pathology. Pet dogs also share similar living conditions and diets to humans. Oxidative damage accumulates in the canine brain during aging, making dogs a valid model for translational antioxidant treatment/prevention studies. Evidence suggests the presence of detective protein quality control systems, involving ubiquitin-proteasome system (UPS) and Heat Shock Proteins (HSPs), in the aged canine brain. Further studies on the canine model are needed to clarify the role of age-related changes in UPS activity and HSP expression in neurodegeneration in order to design novel treatment strategies, such as HSP-based therapies, aimed at improving chaperone defences against proteotoxic stress affecting brain during aging.
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Abstract
Aging dogs and cats show neurodegenerative features that are similar to human aging and Alzheimer disease. Neuropathologic changes with age may be linked to signs of cognitive dysfunction both in the laboratory and in a clinic setting. Less is known about cat brain aging and cognition and this represents an area for further study. Neurodegenerative diseases such as lysosomal storage diseases in dogs and cats also show similar features of human aging, suggesting some common underlying pathogenic mechanisms and also suggesting pathways that can be modified to promote healthy brain aging.
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Affiliation(s)
- Charles H Vite
- Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Section of Neurology & Neurosurgery, Department of Clinical Studies - Philadelphia, 3900 Delancey Street, Philadelphia, PA 19104, USA
| | - Elizabeth Head
- Department of Pharmacology & Nutritional Sciences, Sanders-Brown Center on Aging, University of Kentucky, 800 South Limestone Street, 203 Sanders Brown Building, Lexington, KY 40515, USA.
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4
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Head E. A canine model of human aging and Alzheimer's disease. Biochim Biophys Acta Mol Basis Dis 2013; 1832:1384-9. [PMID: 23528711 DOI: 10.1016/j.bbadis.2013.03.016] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 03/15/2013] [Accepted: 03/17/2013] [Indexed: 12/22/2022]
Abstract
The aged dog naturally develops cognitive decline in many different domains (including learning and memory) but also exhibits human-like individual variability in the aging process. The neurobiological basis for cognitive dysfunction may be related to structural changes that reflect neurodegeneration. Molecular cascades that contribute to degeneration in the aging dog brain include the progressive accumulation of beta-amyloid (Aβ) in diffuse plaques and in the cerebral vasculature. In addition, neuronal dysfunction occurs as a consequence of mitochondrial dysfunction and cumulative oxidative damage. In combination, the aged dog captures key features of human aging, making them particularly useful for the development of preventive or therapeutic interventions to improve aged brain function. These interventions can then be translated into human clinical trials. This article is part of a Special Issue entitled: Animal Models of Disease.
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Affiliation(s)
- Elizabeth Head
- Department of Molecular and Biomedical Pharmacology, University of Kentucky, Lexington, KY 40536, USA.
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Dowling ALS, Head E. Antioxidants in the canine model of human aging. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1822:685-9. [PMID: 22005070 PMCID: PMC3291812 DOI: 10.1016/j.bbadis.2011.09.020] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Revised: 09/29/2011] [Accepted: 09/30/2011] [Indexed: 01/15/2023]
Abstract
Oxidative damage can lead to neuronal dysfunction in the brain due to modifications to proteins, lipids and DNA/RNA. In both human and canine brain, oxidative damage progressively increases with age. In the Alzheimer's disease (AD) brain, oxidative damage is further exacerbated, possibly due to increased deposition of beta-amyloid (Aβ) peptide in senile plaques. These observations have led to the hypothesis that antioxidants may be beneficial for brain aging and AD. Aged dogs naturally develop AD-like neuropathology (Aβ) and cognitive dysfunction and are a useful animal model in which to test antioxidants. In a longitudinal study of aging beagles, a diet rich in antioxidants improved cognition, maintained cognition and reduced oxidative damage and Aβ pathology in treated animals. These data suggest that antioxidants may be beneficial for human brain aging and for AD, particularly as a preventative intervention. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.
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Affiliation(s)
- Amy L S Dowling
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY 40536, USA
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Head E. Neurobiology of the aging dog. AGE (DORDRECHT, NETHERLANDS) 2011; 33:485-496. [PMID: 20845082 PMCID: PMC3168593 DOI: 10.1007/s11357-010-9183-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Accepted: 09/02/2010] [Indexed: 05/29/2023]
Abstract
Aged canines naturally accumulate several types of neuropathology that may have links to cognitive decline. On a gross level, significant cortical atrophy occurs with age along with an increase in ventricular volume based on magnetic resonance imaging studies. Microscopically, there is evidence of select neuron loss and reduced neurogenesis in the hippocampus of aged dogs, an area critical for intact learning and memory. The cause of neuronal loss and dysfunction may be related to the progressive accumulation of toxic proteins, oxidative damage, cerebrovascular pathology, and changes in gene expression. For example, aged dogs naturally accumulate human-type beta-amyloid peptide, a protein critically involved with the development of Alzheimer's disease in humans. Further, oxidative damage to proteins, DNA/RNA and lipids occurs with age in dogs. Although less well explored in the aged canine brain, neuron loss, and cerebrovascular pathology observed with age are similar to human brain aging and may also be linked to cognitive decline. Interestingly, the prefrontal cortex appears to be particularly vulnerable early in the aging process in dogs and this may be reflected in dysfunction in specific cognitive domains with age.
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Affiliation(s)
- Elizabeth Head
- Sanders-Brown Center on Aging, Department of Molecular and Biomedical Pharmacology, University of Kentucky, 800 South Limestone Street, Lexington, KY 40536, USA.
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Short-term supplementation with acetyl-L-carnitine and lipoic acid alters plasma protein carbonyl levels but does not improve cognition in aged beagles. Exp Gerontol 2009; 44:752-9. [PMID: 19735717 DOI: 10.1016/j.exger.2009.08.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Revised: 07/31/2009] [Accepted: 08/31/2009] [Indexed: 01/15/2023]
Abstract
Previous work has shown that a diet enriched with antioxidants and mitochondrial co-factors improves cognition in aged dogs, which is accompanied by a reduction in oxidative damage in the brain. The objective of the present study was to assess the effects of supplementation with mitochondrial co-factors on cognition and plasma protein carbonyl levels in aged dogs. Specifically, we aimed to test whether the individual or combined action of lipoic acid (LA) and acetyl-l-carnitine (ALCAR) could account for the beneficial effects of the enriched diet that contained both plus antioxidants. Dogs were given LA or ALCAR, alone and then in combination and cognition was assessed using a spatial learning task and two discrimination and reversal paradigms. Dogs receiving the ALCAR supplement showed an increase in protein carbonyl levels that was associated with increased error scores on the spatial task, and which was reduced upon additional supplementation with LA. We did not observe significant positive effects on cognition. The present findings suggest that short-term supplementation with LA and ALCAR is insufficient to improve cognition in aged dogs, and that the beneficial effects of the full spectrum diet arose from either the cellular antioxidants alone or their interaction with LA and ALCAR.
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Christie LA, Opii WO, Head E. Strategies for improving cognition with aging: insights from a longitudinal study of antioxidant and behavioral enrichment in canines. AGE (DORDRECHT, NETHERLANDS) 2009; 31:211-220. [PMID: 19714491 PMCID: PMC2734239 DOI: 10.1007/s11357-008-9063-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Accepted: 05/17/2008] [Indexed: 05/28/2023]
Abstract
Studies in humans suggest that lifestyle factors can have a beneficial impact on the risk for developing cognitive decline and dementia with age. There is growing evidence that maintaining a physically and intellectually active lifestyle can positively impact cognitive ability in older individuals. Dietary factors, such as the intake of antioxidants, may also prevent age-related cognitive decline. However, studies in humans are challenging; many variables cannot be controlled, making it difficult for researchers to determine the exact types and quantities of enrichment and dietary factors necessary for positive effects on cognition. Studies in animal models of human aging allow researchers to precisely control such variables, and can be used to assess the mechanisms and molecular pathways underlying any positive effects. Here we review the results of an intervention study using a canine model of human aging. The study was unique in that it compared the effects of dietary antioxidant supplementation alone and in combination with behavioral enrichment. We found that both interventions lead to improvements in cognitive ability in aged dogs; however, combining the treatments preserved cognition to a greater extent than either treatment alone. Overall, the results suggest that antioxidant supplementation and behavioral enrichment target separate yet complementary molecular pathways to improve cognition, and support the idea that combinations of treatments to improve cognition and slow brain aging will produce greater benefits than single interventions.
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Affiliation(s)
- Lori-Ann Christie
- Institute for Brain Aging & Dementia, University of California, 1259 Gillespie NRF, Irvine, CA 92697-4540 USA
| | - Wycliffe O. Opii
- Institute for Brain Aging & Dementia, University of California, 1259 Gillespie NRF, Irvine, CA 92697-4540 USA
| | - Elizabeth Head
- Institute for Brain Aging & Dementia, University of California, 1259 Gillespie NRF, Irvine, CA 92697-4540 USA
- Department of Neurology, University of California, 1259 Gillespie NRF, Irvine, CA 92697-4540 USA
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Head E, Nukala VN, Fenoglio KA, Muggenburg BA, Cotman CW, Sullivan PG. Effects of age, dietary, and behavioral enrichment on brain mitochondria in a canine model of human aging. Exp Neurol 2009; 220:171-6. [PMID: 19703441 DOI: 10.1016/j.expneurol.2009.08.014] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Revised: 08/04/2009] [Accepted: 08/15/2009] [Indexed: 11/19/2022]
Abstract
Dogs develop cognitive decline and a progressive accumulation of oxidative damage. In a previous longitudinal study, we demonstrated that aged dogs treated with either an antioxidant diet or with behavioral enrichment show cognitive improvement. The antioxidant diet included cellular antioxidants (vitamins E and C, fruits and vegetables) and mitochondrial cofactors (lipoic acid and carnitine). Behavioral enrichment consisted of physical exercise, social enrichment, and cognitive training. We hypothesized that the antioxidant treatment improved neuronal function through increased mitochondrial function. Thus, we measured reactive oxygen species (ROS) production and bioenergetics in mitochondria isolated from young, aged, and treated aged animals. Aged canine brain mitochondria show significant increases in ROS production and a reduction in NADH-linked respiration. Mitochondrial function (ROS and NADH-linked respiration) was improved selectively in aged dogs treated with an antioxidant diet. In contrast, behavioral enrichment had no effect on any mitochondrial parameters. These results suggest that an antioxidant diet improves cognition by maintaining mitochondrial homeostasis, which may be an independent molecular pathway not engaged by behavioral enrichment.
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Affiliation(s)
- E Head
- Institute for Brain Aging & Dementia, Department of Neurology, University of California, Irvine, CA, USA.
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Head E. Oxidative damage and cognitive dysfunction: antioxidant treatments to promote healthy brain aging. Neurochem Res 2008; 34:670-8. [PMID: 18683046 DOI: 10.1007/s11064-008-9808-4] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2008] [Accepted: 07/08/2008] [Indexed: 11/26/2022]
Abstract
Oxidative damage in the brain may lead to cognitive impairments in aged humans. Further, in age-associated neurodegenerative disease, oxidative damage may be exacerbated and associated with additional neuropathology. Epidemiological studies in humans show both positive and negative effects of the use of antioxidant supplements on healthy cognitive aging and on the risk of developing Alzheimer disease (AD). This contrasts with consistent behavioral improvements in aged rodent models. In a higher mammalian model system that naturally accumulates human-type pathology and cognitive decline (aged dogs), an antioxidant enriched diet leads to rapid learning improvements, memory improvements after prolonged treatment and cognitive maintenance. Cognitive benefits can be further enhanced by the addition of behavioral enrichment. In the brains of aged treated dogs, oxidative damage is reduced and there is some evidence of reduced AD-like neuropathology. In combination, antioxidants may be beneficial for promoting healthy brain aging and reducing the risk of neurodegenerative disease.
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Affiliation(s)
- Elizabeth Head
- Department of Neurology, Institute for Brain Aging & Dementia, University of California, 1259 Gillespie Neuroscience Research Facility, Irvine, CA 92697-4540, USA.
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Head E, Rofina J, Zicker S. Oxidative stress, aging, and central nervous system disease in the canine model of human brain aging. Vet Clin North Am Small Anim Pract 2008; 38:167-78, vi. [PMID: 18249248 PMCID: PMC2390776 DOI: 10.1016/j.cvsm.2007.10.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Decline in cognitive functions that accompany aging in dogs may have a biologic basis, and many of the disorders associated with aging in dogs may be mitigated through dietary modifications that incorporate specific nutraceuticals. Based on previous research and the results of laboratory and clinical studies, antioxidants may be one class of nutraceutical that provides benefits to aged dogs. Brains of aged dogs accumulate oxidative damage to proteins and lipids, which may lead to dysfunction of neuronal cells. The production of free radicals and lack of increase in compensatory antioxidant enzymes may lead to detrimental modifications to important macromolecules within neurons. Reducing oxidative damage through food ingredients rich in a broad spectrum of antioxidants significantly improves, or slows the decline of, learning and memory in aged dogs.
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Affiliation(s)
- Elizabeth Head
- Institute for Brain Aging and Dementia, Department of Neurology, University of California at Irvine, 1259 Gillespie Neuroscience Research Facility, Irvine, CA 92697-4540, USA
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Head E. Combining an Antioxidant-Fortified Diet with Behavioral Enrichment Leads to Cognitive Improvement and Reduced Brain Pathology in Aging Canines: Strategies for Healthy Aging. Ann N Y Acad Sci 2007; 1114:398-406. [PMID: 17717087 DOI: 10.1196/annals.1396.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The number of elderly individuals in our population is rapidly rising and age-associated neurodegenerative disease is becoming more prevalent. Thus, identifying ways by which we can promote healthy aging are becoming more critical. Lifestyle factors, such as engaging in physical, intellectual, and social activities, are protective against dementia in aged individuals. Similarly, there is some evidence to suggest that antioxidants are beneficial. Observational studies in humans have been confirmed and extended in rodent model systems. We present additional evidence that, in a canine model of aging, combining an antioxidant-enriched diet and behavioral enrichment (including social, physical, and cognitive components) can lead to substantial improvements in cognition and reduced brain pathology. These results suggest that modifying lifestyle factors can have a beneficial impact on the aging process, even in aged individuals with existing cognitive decline and brain pathology.
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Affiliation(s)
- Elizabeth Head
- Institute for Brain Aging & Dementia, Department of Neurology, University of California at Irvine, 1259 Gillespie NRF, Irvine, CA 92697-4540, USA.
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Roudebush P, Zicker SC, Cotman CW, Milgram NW, Muggenburg BA, Head E. Nutritional management of brain aging in dogs. J Am Vet Med Assoc 2005; 227:722-8. [PMID: 16178393 DOI: 10.2460/javma.2005.227.722] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Philip Roudebush
- Technical Information Services, Hill's Pet Nutrition Inc, PO Box 148, Topeka, KS 66601, USA
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Abstract
Decline in cognitive function that accompanies aging in dogs might have a biological basis, and many of the disorders associated with aging in canines might be preventable through dietary modifications that incorporate specific nutraceuticals. Based on previous research and the results of laboratory and clinical studies, antioxidants might be one class of nutraceutical that benefits aged dogs. Brains of aged dogs accumulate oxidative damage to proteins and lipids, which can lead to dysfunction of neuronal cells. The production of free radicals and lack of increase in compensatory antioxidant enzymes might lead to detrimental modifications to important macromolecules within neurons. Reducing oxidative damage through food ingredients rich in a broad spectrum of antioxidants significantly improves, or slows the decline of, learning and memory in aged dogs; however, determining which compounds, combinations, dosage ranges, when to initiate intervention, and long-term effects constitute critical gaps in knowledge about this subject.
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Affiliation(s)
- Elizabeth Head
- Institute for Brain Aging and Dementia, University of California at Irvine, 1259 Gillespie NRF, Irvine, CA 92697-4540, USA.
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Head E, Liu J, Hagen TM, Muggenburg BA, Milgram NW, Ames BN, Cotman CW. Oxidative damage increases with age in a canine model of human brain aging. J Neurochem 2002; 82:375-81. [PMID: 12124438 DOI: 10.1046/j.1471-4159.2002.00969.x] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We assayed levels of lipid peroxidation, protein carbonyl formation, glutamine synthetase (GS) activity and both oxidized and reduced glutathione to study the link between oxidative damage, aging and beta-amyloid (Abeta) in the canine brain. The aged canine brain, a model of human brain aging, naturally develops extensive diffuse deposits of human-type Abeta. Abeta was measured in immunostained prefrontal cortex from 19 beagle dogs (4-15 years). Increased malondialdehyde (MDA), which indicates increased lipid peroxidation, was observed in the prefrontal cortex and serum but not in cerebrospinal fluid (CSF). Oxidative damage to proteins (carbonyl formation) also increased in brain. An age-dependent decline in GS activity, an enzyme vulnerable to oxidative damage, and in the level of glutathione (GSH) was observed in the prefrontal cortex. MDA level in serum correlated with MDA accumulation in the prefrontal cortex. Although 11/19 animals exhibited Abeta, the extent of deposition did not correlate with any of the oxidative damage measures, suggesting that each form of neuropathology accumulates in parallel with age. This evidence of widespread oxidative damage and Abeta deposition is further justification for using the canine model for studying human brain aging and neurodegenerative diseases.
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Affiliation(s)
- E Head
- Institute for Brain Aging and Dementia, University of California, Irvine, California 92697-4540, USA.
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