杏吧原创

IN SHAKESPEARE鈥檚 day, apothecaries treated memory loss in the elderly with
sage and lemon balm, while 2500 years ago the Greek physician Hippocrates
recommended wormwood. They may have been on to something鈥攁ll these herbs
have similar effects to drugs used to treat Alzheimer鈥檚 disease. And two of them
are already undergoing clinical trials.

The brains of Alzheimer鈥檚 patients lose nicotinic receptors, one of the two
types of receptor for the neurotransmitter acetylcholine. Increasing the levels
of acetylcholine in the brain can help alleviate cognitive problems. Several
drugs companies are now testing drugs that stimulate nicotinic receptors, which
not only simulates a boost in acetylcholine levels but can also lead to the
production of new receptors.

Elaine Perry of the University of Newcastle wondered if the herbal remedies
exploited the same mechanism. She and her colleagues made ethanol extracts of
various species of sage, the related herb lemon balm (Melissa
officinalis) and wormwood (Artemisia absinthium). They tested the
extracts to see if they contained compounds that bound to acetylcholine
receptors in the human brain.

Wormwood contained chemicals that bound strongly to both types of
acetylcholine receptors, the nicotinic and the muscarinic. Lemon balm bound to
either or both, depending on the variety. Pineapple sage (Salvia
elegans) bound strongly to the muscarinic receptors. Only common sage (
S. officinalis) did not bind strongly to either receptor. The strength of
the binding depended on the concentration of the extract, but some samples bound
as strongly as carbamylcholine, a powerful drug that resembles
acetylcholine.

鈥淭he results are intriguing,鈥� says Alzheimer鈥檚 expert Gareth Roberts, who
heads Proteon, a biotechnology company in Cambridge. 鈥淢ost of our
pharmaceuticals were derived from plants.鈥� But he warns that licensing herbs for
treatment can be difficult, as plants contain varying quantities of active
ingredients.

Perry suspects plants make the compounds to poison plant-eating insects,
whose nervous systems have similar receptors. Even before the results of Perry鈥檚
work were known, varieties of sage and lemon balm were in the first stage of
clinical trials at Newcastle. Lemon balm is being administered to volunteers as
aromatherapy. 鈥淭he active compounds are volatile, so that is an effective way to
deliver the drug,鈥� says Perry.

But she cautions against trying to protect your mental faculties by drinking
absinthe, an especially potent spirit whose main flavouring is wormwood and
which also contains lemon balm. It was banned in much of Europe in the 19th
century, but has recently become available again. 鈥淎bsinthe contains lots of
toxic substances,鈥� says Perry. 鈥淚t鈥檚 not the best way to get your wormwood.鈥�