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February 2002
Vol. 5, No. 2, p 16.
news in brief

Head lice: Pawpaws’ prey

opening artThe pawpaw tree, grown for its exotic banana-like fruit, also contains components called annonaceous acetogenins (AAs), which kill head lice (Pediculus capitis) with 100% efficiency, according to medicinal chemist Jerry McLaughlin, who has studied the bark of pawpaw trees for 25 years at Purdue University (West Lafayette, IN).

In a yet-unpublished study of schoolchildren and their families conducted in the Sussex-Wantage Regional School District in New Jersey, two head washings using pawpaw extract performed eight days apart killed all head lice in children and adults. Some families who participated in the study had struggled with controlling resistant head lice for more than a year.

The impressive substance has already reached the market in the form of a lice-killing shampoo sold by Nature’s Sunshine Products (Provo, UT), of which McLaughlin now serves as chief scientific officer. It will be particularly helpful for the many cases of head lice that have grown resistant to the myriad treatments currently in use. “This is the first truly innovative new product for head lice to be marketed in 50 years,” says McLaughlin.

AAs are derivatives of long-chain fatty acids. By a complex mechanism of action, they block energy production in mitochondria, and pests “run out of energy and die,” according to McLaughlin. Safety studies show that no irritation or signs of toxicity occur when the compounds are applied topically to humans. If AAs are accidentally swallowed, they naturally induce vomiting to prevent poisoning. When fed to mice, which lack a vomit reflex, AAs must compose at least 5% of the diet before toxicity occurs.

Pawpaw trees grow in 26 eastern and southern states, yet ensuring an adequate supply for commercialization is a challenge. In 2000, McLaughlin purchased 18,000 lb of pawpaw twigs. Bark on smaller twigs contains the highest concentration of AAs, but it must be collected during the month of May. The biological activity of AAs peaks during this time, says McLaughlin, because “the plants pump up production to protect themselves against pests.” Other trees in the same plant family produce AAs, but they all grow in tropical regions, making procurement impractical. Some synthetic work is ongoing, but sorting out which AA structures are important and how they act synergistically is a long-term project, so McLaughlin and lice sufferers will have to rely on the pawpaw for now.


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