Medicinal plants, phytochemicals and Alzheimer's disease.

Natural, plant-derived products have been used by humans for a number of millennia as medical treatments, including for CNS disorders such as cognitive decline. Plants are an important source of pharmacologically active chemical entities. Over the last 25 years a sizeable minority of new, registered drugs have been derived from, or mimic, phytochemicals. These include galantamine, an alkaloid used for the treatment of cognitive declines associated with Alzheimer's disease (AD). The active components of plant based products are generally secondary metabolites, with the majority falling into the chemical structural groups of alkaloids, terpenoids and phenolics. Members of these chemical classes play differing roles in the ecological life of plants, and subsequently exert differing profiles of costs/benefits in terms of efficacy and tolerability in humans. Potential, novel plant based treatments for the symptoms or causes of AD that are reviewed here include the alkaloid-huperzine A, a number of extracts with terpenoid bioactives-including Gingko biloba, Salvia officinalis/lavandulaefolia, Melissa officinalis and Bacopa monniera, and a range of phenolics, including the single molecule polyphenols-resveratrol, curcumin and epigallocatechin gallate. This latter group, which are edible components of everyday foods, are particularly promising and have garnered substantial basic research. However, their potential beneficial properties require confirmation in human trials.Taken as a whole, the extant evidence regarding potential plant based treatments for AD suggests that extracts containing multiple terpenoids, and multiple or single phenolics that are found in common foodstuffs may have roles to play in treating or slowing the onset of AD.