Medicinal plants and Alzheimer's disease: from ethnobotany to phytotherapy

The use of complementary medicines, such as plant extracts, in dementia the rapy varies according to the different cultural traditions. In orthodox Wes tern medicine, contrasting with that in China and the Far East for example, pharmacological properties of traditional cognitive- or memory-enhancing p lants have not been widely investigated in the context of current models of Alzheimer's disease. An exception is Gingko biloba in which the gingkolide s have antoxidant, neuroprotective and cholinergic activities relevant to A lzheimer's disease mechanisms. The therapeutic efficacy of Ginkgo extracts in Alzheimer's disease in placebo controlled clinical trials is reportedly similar to currently prescribed drugs such as tacrine or donepezil and, imp ortantly, undesirable side effects of Gingko are minimal. Old European refe rence books, such as those on medicinal herbs, document a variety of other plants such as Salvia officinalis (sage) and Melissa officinalis (balm) wit h memory-improving properties, and cholinergic activities have recently bee n identified in extracts of these plants. Precedents for modern discovery o f clinically relevant pharmacological activity in plants with long-establis hed medicinal use include, for example, the interaction of alkaloid opioids in Papaver somniferum (opium poppy) with endogenous opiate receptors in th e brain. With recent major advances in understanding the neurobiology of Al zheimer's disease, and as yet limited efficacy of so-called rationally desi gned therapies, it, may be timely to re-explore historical archives for new directions in drug development. This article considers not only the value of an integrative traditional and modern scientific approach to developing new treatments for dementia, but also in the understanding of disease mecha nisms. Long before the current biologically-based hypothesis of cholinergic derangement in Alzheimer's disease emerged, plants now known to contain ch olinergic antagonists were recorded for their amnesia- and dementia-inducin g properties.