Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder, which severely impacts on the global economic development and healthcare system. Though AD has been studied for more than 100 years since 1906, the exact cause(s) and pathogenic mechanism(s) remain to be clarified. Also, the efficient disease-modifying treatment and ideal diagnostic method for AD are unavailable. Perturbed cerebral glucose metabolism, an invariant pathophysiological feature of AD, may be a critical contributor to the pathogenesis of this disease. In this review, we firstly discussed the features of cerebral glucose metabolism in physiological and pathological conditions. Then, we further reviewed the contribution of glucose transportation abnormality and intracellular glucose catabolism dysfunction in AD pathophysiology, and proposed a hypothesis that multiple pathogenic cascades induced by impaired cerebral glucose metabolism could result in neuronal degeneration and consequently cognitive deficits in AD patients. Among these pathogenic processes, altered functional status of thiamine metabolism and brain insulin resistance are highly emphasized and characterized as major pathogenic mechanisms. Finally, considering the fact that AD patients exhibit cerebral glucose hypometabolism possibly due to impairments of insulin signaling and altered thiamine metabolism, we also discuss some potential possibilities to uncover diagnostic biomarkers for AD from abnormal glucose metabolism and to develop drugs targeting at repairing insulin signaling impairment and correcting thiamine metabolism abnormality. We conclude that glucose metabolism abnormality plays a critical role in AD pathophysiological alterations through the induction of multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, and so forth. To clarify the causes, pathogeneses and consequences of cerebral hypometabolism in AD will help break the bottleneck of current AD study in finding ideal diagnostic biomarker and disease-modifying therapy.
Oxidative stress plays a significant role in the pathogenesis of Alzheimer's disease (AD), a devastating disease of the elderly. The brain is more vulnerable than other organs to oxidative stress, and most of the components of neurons (lipids, proteins, and nucleic acids) can be oxidized in AD due to mitochondrial dysfunction, increased metal levels, infl ammation, and β-amyloid (Aβ) peptides. Oxidative stress participates in the development of AD by promoting Aβ deposition, tau hyperphosphorylation, and the subsequent loss of synapses and neurons. The relationship between oxidative stress and AD suggests that oxidative stress is an essential part of the pathological process, and antioxidants may be useful for AD treatment.Keywords: Alzheimer's disease; oxidative stress; β-amyloid; tau; metals; antioxidants ·Review· IntroductionThe human brain, although it constitutes only 2% of the body weight, consumes ~20% of the oxygen supplied by the respiratory system [1] . The high energy-consumption of the brain means that it is more susceptible to oxidative stress than any other organ. As the basic functional unit of the brain, the neuron is particularly vulnerable to oxidative damage because it has a higher metabolic rate than other cells [2] . The oxidation of lipids, proteins, and nucleic acids in neurons is a common pathological feature of Alzheimer's disease (AD) [3] . Neurons contain a large amount of polyunsaturated fatty acids (PUFAs) that can interact with reactive oxygen species (ROS), leading to a selfpropagating cascade of lipid peroxidation and molecular destruction [4] . Furthermore, neurons contain low levels of glutathione, an essential antioxidant for eliminating free radicals [5] . Therefore, neurons are highly susceptible to oxidative stress.An increased oxidative burden has been reported in the brains of non-demented elderly and/or sporadic AD patients [6,7] . Increased levels of oxidative stress biomarkers in the blood reflect such stress in the brain [8,9] . Currently, many blood markers of oxidative stress have been identified in AD patients or related animal models, including protein carbonyls and 3-nitrotyrosine [10,11] , , malondialdehyde (MDA) [12] , 4-hydroxynonenal (4-HNE), and F2-isoprostanes (F2-IsoPs) [13][14][15][16] . Apart from the intracellular accumulation of free radicals, changes in the activities or expressions of antioxidant enzymes, such as superoxide dismutase (SOD) and catalase, have also been described in both the central nervous system and peripheral tissues of AD patients [14,17] . Thus, oxidative stress is an important pathological feature in AD.However, how and where the oxidative stress originates in AD are open questions. Research has suggested that mitochondrial dysfunction [12,18,19] , metal accumulation [12,20,21] , hyperphosphorylated tau [22,23] , inflammation [24,25] , and β-amyloid (Aβ) accumulation [12,19] are the basic mechanisms underlying the induction of oxidative stress. Deficiency or destruction of components of the antioxidant system such as SOD in the mi...
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