Plants Used in Traditional Chinese Medicine
The practice of TCM has been documented for thousands of years, and the medicinal preparations used include various substances of animal, fungal and plant origin. TCM has also influenced the traditional medicine practiced in neighbouring regions, such as Japan, Korea and Vietnam.
Evodia rutaecarpa (Juss.) Benth.
The plant described in the Pharmacopoeia of the People’s Republic of China (2005) as Evodia rutaecarpa (Juss.) Benth. (Rutaceae) is used in TCM for its reputed cardiotonic, restorative and analgesic effects. Extracts and alkaloids isolated from this plant have been investigated for activities that might help to explain the reputed restorative effects. An ethanol extract of this plant and four compounds present, dehydroevodiamine, evodiamine, rutaecarpine and synephrine, have been shown to be anti-inflammatory in vitro, an action that has been implicated as potential therapy in some cognitive disorders.
The alkaloid rutaecarpine is also reported to inhibit COX-2 activity in vitro and to be anti-inflammatory in vivo, although another study showed evodiamine to inhibit COX-2 induction and NF-kB activation, whilst rutaecarpine did not show these effects. Evodiamine has also been shown to inhibit both constitutive and induced NF-kB activation and NF-kB -regulated gene expression. Dehydroevodiamine increases cerebral blood flow in vivo, an action that might also improve cognitive function, and it may have a neuroprotective action, since it inhibited glutamate uptake and release in vitro. Dehydroevodiamine (hydrochloride) also prevents impairment of learning and memory and neuronal loss and is not considered to be associated with any serious adverse effects. E. rutaecarpa extract and dehydroevodiamine both inhibited acetylcholinesterase in vitro and reversed scopolamine-induced memory impairment in rats. In addition to reversing scopolamine-induced amnesia, dehydroevodiamine is reported to be even more effective in the reversal of beta-amyloid-peptide-induced amnesia in vivo, indicating that it may improve cognitive ability by influencing cholinergic function and by other mechanisms.
Since the alkaloids rutaecarpine and dehydroevodiamine are inhibitors of cholinesterase, their chemical structures have been used as a basis for the development of new cholinesterase inhibitors, including synthetic compounds which combine the structural features of these alkaloids with tacrine.
Ginkgo biloba
Huperzia serrata
Magnolia officinalis Rehder & E.H.Wilson
In traditional Chinese medicine (TCM), the bark of the root and stem of Magnolia officinalis Rehder & E.H.Wilson (Magnoliaceae) has been used as a remedy for alleviating anxiety and nervous disturbances. Many of the more recent studies investigating any basis for the CNS effects of Magnolia officinalis have focused on the biphenolic lignans isolated from Magnolia officinalis, honokiol and magnolol, and although a variety of in vitro tests and some in vivo studies have been undertaken that may explain the reputed effects, there is a lack of clinical evidence for efficacy.
Modulation of cholinergic function could explain any favourable effects of this remedy on memory, as both honokiol and magnolol increase choline acetyltransferase activity, they inhibit acetylcholinesterase activity in vitro and they increase hippocampal acetylcholine release in vivo. Other activities that may preserve cognitive function have also been associated with Magnolia officinalis and the component lignans. An extract, magnolol and honokiol showed antioxidant activity, and magnolol was neuroprotective in vitro. In another study, both magnolol and honokiol, the latter being the most potent, were neuroprotective against glutamate-, NMDA-and H202-induced mitochondrial dysfunction in vitro, effects associated with an antioxidant action and antagonism of excitatory amino-acid-induced toxicity; these two compounds are suggested to differ in some mechanisms by which they are neuroprotective. The anti-inflammatory activity of magnolol both in vitro and in vivo could be explained by its ability to inhibit cyclo-oxygenase and 5-lipoxygenase or by regulating the NF-kB pathway. Modulation of the NF-kB pathway has also been shown to occur with honokiol and it protected against cerebral ischemia-reperfusion injury in rodents, which was attributed to its antioxidant, anti-inflammatory and antiplatelet aggregation properties. Also from the bark of Magnolia officinalis are the (+)- and (-)-enantiomers of syringaresinol and a mixture of their glucosides; these compounds promoted dose-dependent neuritogenesis in vitro. These potential neurotrophins and the lignans honokiol and magnolol appear to show some activities that could be relevant in disorders in which cognition is impaired, but more in-depth studies, particularly those assessing their clinical relevance and safety, are needed.
