Table 2. Roles and efficacy of herbal and other food-derived nootropic agents.
| Natural Nootropic | Subject | Putative/Confirmed Roles and Mechanisms | References | |||
|---|---|---|---|---|---|---|
| Ginkgo biloba | Human (Clinical trial), rodent | Ginkgolides, bilobalide and proanthocyanidins are potent free radical scavengers/antioxidants which confer neuroprotection. Enhanced monoaminergic transmission. Increased cerebral blood flow via nitric oxide. Reduced amyloid neurotoxicity. | [111, 112] | |||
| Panax quinquefolius | Rodent | Increased choline uptake in synaptosomal preparations. Other putative mechanisms including hypoglycaemic action and effect of ginsenoside Rb1. | [113] | |||
| Panax ginseng | Human (Clinical trial), | Ginsenosides minimise inhibition of cholinergic transmission by amyloid-β protein in Alzheimer disease. Ginsenoside Rb1 increases cell survival in the hippocampus cornus ammonis 3 and dentate gyrus. |
[114, 115, 116] | |||
|
Bacopa
monnieri |
Rodent | Acetylcholinesterase inhibition, choline acetyltransferase activation, β-amyloid reduction, increased cerebral blood flow, monoamine potentiation and antioxidant neuroprotection. |
[117] | |||
| Nicotiana tabacum | Human (case study), rodent | Nicotine enhances efficacy of the cholinergic system, facilitating memory consolidation. Restoration of normal dendritic connections and the balance between hippocampal excitatory/inhibitory signals. |
[118, 119] | |||
| Nicotiana rustica | - | Nicotine content may facilitate memory during short-term use, as above. | - | |||
| Rhodiola rosea | - | Acts as an adaptogen due to the glycoside salidroside. | [120] | |||
| Gotu kola (Centella asiatica) | Rodent | Asiatic acid, asiaticoside, caffeoylquinic acids an madecassoside have neurotropic effects, including increased dendritic arborisation and synaptogenesis; probably due to modulations of signal transduction pathways. | [121] | |||
| Lion's mane (Hericium erinaceus) | Rodent | In mouse hippocampal slices, it causes an increase in spontaneous/evoked excitatory synaptic current in mossy fibre-Cornus ammonis-3synapse. Hericenones and erinacines increase levels of Nerve Growth Factor (NGF) in the brain, leading to increased neurite outgrowth and differentiation. | [122] | |||
| Kapikacchu (Mucuna pruriens) | Rodent | Contains L-Dopa which is a precursor of brain monoamines and neuromelanins. May contain other compounds with neuroprotective effects. | [123] | |||
| Ashwagandha (Withania somnifera) |
Guinea-pig, Rodent | Contains withanolides A to Y, dehydrowithanolide R, withasomniferin A, withasomidienone, withasomniferols A to C, withaferin A, and withanone. Also contains sitoindosides and beta-sitosterol. Restores levels of BDNF and regulates synaptic plasticity. Can trigger pathways for neural cell survival and plasticity. | [ 124. 125] | |||
| Montmorency cherry | Rodent | Reduced age-associated inflammatory (GFAP, NOX-2, COX-2)/autophagy (phosphorylated mTOR, Beclin 1, and p62/SQSTM) markers; and promotion of protein/cellular homeostasis in the hippocampus. | [126] | |||
| Huperzine A (Huperzia serrata) | Maacaques | Huperzine-A is a reversible acetylcholinesterase (AChE) inhibitor, and probable modulator of glutamatergic transmission. Also regulates brain cell mitochondria energetics and works as an antioxidant. | [127] | |||
| Vinpocetine | Rodent | Inhibits phosphodiesterase (PDE) enzyme to enhance second messenger-mediated signalling in pathways involved in learning and memory. Inhibits κB kinase (IKK)/Nuclear Factor-kappa B (NF-κB), and extracellular signal-regulated kinase (ERK) 1/2 to reduce inflammation. Enhances the structural dynamics of dendritic spines. | [128] | |||
| L-theanine | Human (Clinical trial), Rodent |
Improved cognitive function possibly via a decrease in NMDA-dependent CA1 long-term potentiation (LTP) and increase in NMDA-independent CA1-LTP. Antioxidant effect. Enhanced hippocampl neurogenesis. | [129, 130] | |||
| L-tyrosine | Rodent | Enhanced central catecholamine synthesis in rodents. | [131] | |||
| Taurine (l-taurine) | Rodent | Restores AChE and ChAT balance which are critical for the regulation of acetylcholine. Can decrease the insoluble fraction of amyloid beta in Alzheimer disease. | [132, 133] | |||
| Acetyl-l-carnitine | Rodent | Enhancement of high-affinity choline uptake, acetylcholine (ACh) synthesis, and depolarisation-evoked ACh release. Increased excitatory postsynaptic potential slope and population spike size in rat hippocampal slices. | [134] | |||