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| Antioxidant | Chemical structures | Potential functions |
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Vitamin E
(α-tocopherol) |  | A powerful, lipid-soluble chain-breaking antioxidant found in lipid membranes, circulating lipoproteins and low-density lipoprotein (LDL) particles [70] and has been shown to decrease Free-radical-mediated damage caused by toxic chain reactions in neuronal cells and helps to inhibit dementia pathogenesis in mammalian cells. |
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| Vitamin C |  | A water-soluble antioxidant, and an inhibitor of lipid peroxidation, acts as a major defense against free radicals in whole blood and plasma. |
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| β-carotene |  | A lipid-soluble antioxidant which may reduce lipid peroxidation, improve antioxidant status [80], and quench singlet oxygen rapidly [81]. |
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| Vitamin B12 |  | An antioxidant that increases choline acetyltransferase activity in cholinergic neurons in cats [88] and improves cognitive functions in AD patients. |
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| LA(α-lipoic acid) |  | A coenzyme of mitochondrial pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, can recycle other antioxidants such as vitamin C and E and glutathione and increase the production of acetylcholine or as a chelator of redox-active metals to combat the accumulation of lipid peroxidation products [94]. |
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| CoQ10 (ubiquinone) |  | A cofactor of the electron transport chain and it preserves mitochondrial membrane potential during oxidative stress and protects neuronal cells through attenuating Aβ overproduction and intracellular Aβ plaque deposits. |
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| Selenium | | A cofactor of glutathione peroxidase, and Se-glutathione peroxidase can also act as an antioxidant. |
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| MitoQ | | An antioxidant targeted to mitochondria and is produced by conjugation of the lipophilic triphenylphosphonium (TPP+) cation to coenzyme Q [100]. |
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| Szeto Schiller (SS) peptide 31 | | A mitochondria-targeted antioxidants (MTAs) concentrate in the inner mitochondrial membrane and decrease mitochondrial toxicity [103], they can prevent the neurotoxin 1-methyl-4-phenylpyridium (MPP+-) induced inhibition of oxygen consumption and ATP production and mitochondrial swelling [106]. |
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| Caffeine |  | An antioxidant that can inhibit amyloidosis and Aβ production and reduce brain Aβ levels in transgenic mouse models for early-onset familial AD. |
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| Curcumin |   | An antioxidant that has antioxidant, antiinflammatory, and antiamyloid pathology activity in an Alzheimer transgenic mouse models, and it inhibits enzymes lipoxygenase and cyclooxygenase 2 that are responsible for the synthesis of the proinflammatory leukotrienes, prostaglandins, and thromboxanes [108]. |
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| Berberine |  | an antioxidant that exhibits anti-AD effects through both ChEs and Aβ pathways, and can also inhibit ROS and RNS [23]. |
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| Palmatine |  | An antioxidant that exhibits anti-AD effects through both ChEs and Aβ pathways and can also inhibit ROS and RNS [23]. |
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| Silibinin (silybin) |  | A flavonoid derived from the herb milk thistle (Silybum marianum), it prevents memory impairment and oxidative damage induced by Aβ in mice. |
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| Ginkgo biloba | | A natural plant that contains a variety of compounds such as flavonoids and terpenoids which have free radical scavenging ability, and it can reduce amyloid precursor protein [112] and inhibit Aβ aggregation in vitro. |
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| Melatonin |  | A mammalian hormone synthesized mainly in the pineal gland, and it scavenges oxygen and nitrogen-based reactants generated in mitochondria by stimulating the expression and activity of glutathione peroxidase, superoxide dismutase, and NO synthetase [116], and it also contributes to the reduction of oxidative damage in cells [79]. |
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| Selegiline (L-deprenyl) |  | A selective monoamine oxidase-B inhibitor which can generate potent vasodilator nitric oxide particularly in cerebral blood vessels rapidly [127] and protect the vascular endothelium from the toxic effects of Aβ peptide and enhance the function of nigral neurons or enhance their survival by inhibiting oxidative deamination [73, 115]. |
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| Estrogen |   | An antioxidant which protects neurons from the toxicity of Aβ. |
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| Estrogen |  | An antioxidant which protects neurons from the tacitly of Aβ. |
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