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| Plant extracts/phytochemicals (plant source)/natural products/substances | Study model | Neuroprotective activities | References |
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| Turmeric (powdered rhizome of Curcuma longa Linn (5% curcumin) | Case studies of 3 patients with progressive dementia | (i) Improvement in the behavioral symptoms and quality of life | [256] |
|
| Coconut oil enriched Mediterranean diet | 44 patients with Alzheimer’s disease | (i) improved the cognitive functions | [257] |
|
| Germinated brown rice (Malaysian mixed varieties; MR219 and MR220) | Aβ (1–42)-induced toxicity in SH-SY5Y cells | (i) Reduced intracellular ROS generation | [258] |
| (ii) Attenuated Aβ (1–42)-induced cell death |
|
| Huperzine A isolated from Huperzia serrata | Hypoxic-ischemic and glutamate-induced brain injury and cytotoxicity | (i) Reduce Aβ (1–42)-induced neuronal cell death | [259] |
| (ii) Decrease oxidative damage |
| (iii) Protects neurons from cytotoxic and apoptosis |
| (iv) Inhibited the glutamate toxicity |
|
| Huperzine A isolated from Huperzia serrata | 50 patients with Alzheimer’s disease | (i) Improvement in memory, cognitive, and behavior functions | [260] |
|
| Methanolic extract of Lactuca capensis thunb. leaves | Aβ (1–42)-induced neurotoxicity in rats | (i) Ameliorated cognitive impairment and memory deficits | [261] |
| (ii) Decreased acetylcholinesterase activity |
| (iii) Restored the level of GSH and the activities of antioxidant enzymes (superoxide dismutase and glutathione peroxidase) |
| (iv) Decreased the lipid peroxidation and protein oxidation level |
| (v) Attenuated hippocampal apoptosis by lowering the enrichment factor of apoptosis level |
| (v) Increased BDNF mRNA copy number |
| (vi) Decreased IL-1β mRNA copy number |
|
| Osmotin, a plant protein extracted from Nicotiana tabacum | Aβ (1–42)-treated mouse and Aβ (1–42)-induced neurotoxicity in HT22 cells | (i) Reversed synaptic deficits | [262] |
| (ii) Attenuated Aβ accumulation and BACE-1 expression |
| (iii) Increased spontaneous alternation behavior |
| (iv) Ameliorated memory impairment in a Y-maze test |
| (v) Alleviated the hyperphosphorylation of the tau protein at serine 413 through the regulation of the aberrant phosphorylation of p-PI3K, p-Akt (serine 473), and p-GSK3β (serine 9) |
| (vi) Prevented Aβ (1–42)-induced apoptosis and neurodegeneration in the Aβ (1–42)-treated mouse |
| (vii) Attenuated Aβ (1–42)-induced neurotoxicity in vitro of neuronal HT22 cells and primary cultures of hippocampal neurons |
|
| Safflower yellow (natural safflower aqueous extract) | Aβ (1–42)-induced rats | (i) Improved short- and long-term memory of rats | [263] |
| (ii) Decreased inflammatory markers (iNOS, IL-1β, IL-6, and TNF-α levels) |
| (iii) Reduced neuronal cell loss in the hippocampus and cortex |
| (iv) Inhibited the activation of glial cells |
| (v) Downregulated M1 microglial markers (iNOS and CD86) |
| (vi) Upregulated M2 microglial markers (arginase-1, CD2066, and YM-1) |
|
| Tabernaemontana divaricata root extract | Aβ (25–35)-induced mouse | (i) Prevented memory loss | [264] |
| (ii) Decreased lipid peroxidation |
| (iii) Increased neuronal density in the hippocampus |
|
| Yacon (Smallanthus sonchifolius (poepp. and endl.) H. Robinson) leaf extract | Aβ (25–35)-induced rats | (i) Decreased oxidative stress in the hippocampus | [265] |
| (ii) Prevented memory deficits |
| (iii) Attenuated the hippocampal damage |
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