Nature's Pharmacy: Ancient Knowledge, Modern Medicine
Pacific Yew (Taxus brevifolia)
Yew
Name, Habitat and Appearance
The Pacific yew is a dark green, single-needle evergreen that is distinguished from other evergreens by its red berry-like fruit and its lack of cones. Yew grows slowly in very shady areas. A 30 to 50 centimeter trunk will be approximately 140 to 245 years old. The oldest known yew is 500 years old. The trunk is usually twisted in appearance. Branches are sprawling and have lacy foliage. The wood is tough, heavy, resistant to decay and coarse-grained. Yew wood makes excellent bows. The bark of the tree is about 2 mm thick and consists of papery scales. Yew grows throughout northern temperate zones and is more often found in cultivation than in the wild. It prefers a soil rich in lime. The slow-growing evergreen tree often reaches 80 ft. in height with rust-red bark and flat, dark green, needlelike leaves.
Legends and Folklore
A yew planted at the southwest corner of a house was thought to protect the dwelling from evil. The third witch in Macbeth Act IV.I.22-34 lists these ingredients in the witches brew.
Scale of dragon, tooth of wolf,
Witches' mummy, maw and gulf
Of the ravin'd salt-sea shark,
Root of hemlock digg'd i' th' dark,
Liver of blaspheming Jew,
Gall of goat, and slips of yew,
Silver'd in the moon's eclipse,
Nose of Turk and Tartar's lips,
Finger of birth-strangle babe
Ditch-deliver'd by a drab,
Make the gruel thick and slab.
Add thereto a tiger's chaudron,
For th' ingredients of our cauldron.
History
The yew tree was sacred to the Druids, who, it is thought, considered it an emblem of immortality. They planted the tree in holy sites, a practice that continued with the advent of Christianity. As a result, many medieval churchyards contain ancient yews, some thought to be over 1,000 years old. Although yew has been used in small doses to treat rheumatic and urinary problems, its extreme toxicity makes it an unsafe medicinal plant. One of its constituents is taxol, which inhibits cell division and has been extensively researched for its potential as an anticancer drug. Taxol is most commonly found in the Pacific yew.
Taxol was initially extracted from the bark of the Pacific yew in the 1960's. Since that time its use as an anti-cancer drug has become well established. Taxol is now also being used in a wide variety of non-cancer related medical applications. The Pacific yew and the taxol derived from it are compelling examples of the unknown values in forests throughout the world. Although ethnobotanical records have shown that some of the medicinal properties of yew have been known for centuries it wasn't until 1966 that Pacific yew was included in a massive screening of 35,000 species by the United States National Cancer Institute. Monroe Wall, a chemist from North Carolina, discovered taxol extracted from the bark of Pacific yew as the one outstanding compound having anticancer activity.
By 1971 Wall had described the molecular structure of taxol and reported that it was the most promising suppressor of tumor cells he had ever seen. Without the support of the National Cancer Institute, Wall gave up without patenting taxol. In 1977 Wall's findings were confirmed and by 1979 taxol's unique mode of action was worked out by a team of New York pharmacologists. Its publication was noted by the National Cancer Institute.
Human trials started in 1983 and continued until 1989. Great promise was shown for women with previously incurable ovarian cancer. This led the National Cancer Institute to issue a contract with Bristol Myers-Squibb, a pharmaceutical company based in the United States, for the clinical development of taxol.
Warning
Yew is extremely toxic and should be taken only under the supervision of a physician. It is poisonous!
Modern Medicinal Uses
One of the more promising new drugs for treating advanced and recurrent ovarian cancer is taxol, originally extracted from the Pacific yew but now manufactured in the laboratory. New chemotherapeutic agents, new biological agents designed to stimulate the immune system, and new methods of delivering treatment with fewer adverse effects are under study.
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