Mouth to mouth: saliva transfer can help animals communicate, medicate, or even kill. Evolution has given rise to a variety of salivary mixtures that are being mined for ways to help save human lives

Natural History, Nov, 2004 by Lawrence A. Tabak, Robert Kuska

Nature's efforts to tinker with saliva are also attracting medical investigators. In 1995, for instance, workers in Venezuela isolated, (from the saliva of the common vampire bat (Desmodus rotundus), an unusual compound that blocks blood clotting in a highly specific way. Memorably, they dubbed it Draculin. The substance is now under study in the United States as a possible new treatment to fight the onset of stroke.

Last year one pharmaceutical firm, Eli Lilly and Co., based in Indianapolis, Indiana, and its collaborators reported hope fill results from a clinical trial of a drug extracted from the saliva of the Gila monster [see "Venomous Lizards of the Desert," by Daniel 1.). Beck, July/August 2004], The animal eats as few as three big meals a year, and its salivary proteins help maintain steady levels of blood sugar for long periods. The rationale behind the study, and the drug that is the focus of the clinical trial, is that this property of Gila monster spit could also help control blood-sugar levels in humans, and thus treat people with type 2 diabetes.

What about our own saliva? The National Institute of Dental and Craniofacial Research (NIDCR), in Bethesda, Maryland, has launched a new initiative to create the first comprehensive catalog of every salivary protein, Such a catalog would serve as a "molecular parts list" for future research. The institute is also exploring how and in what contexts saliva might replace blood for testing the presence of alcohol, illegal drugs, and blood-borne proteins, such as HIV antibodies.

It is a fact--albeit a little-known one--that salivary glands secrete proteins into the circulatory system as well as into the digestive tract. Building on this fact, one NIDCR biologist, Bruce J. Baum, is leading a research team that has begun to transfer specific genes into salivary glands. With minimal coaxing, the cells of those glands should be able to act as natural protein factories, pumping the proteins encoded by the transferred genes into the bloodstream at steady levels. Thus it could come to pass that an injection made directly into the salivary gland might be able to treat diseases that result from mutations in single genes, among them type 1 diabetes, growth-hormone deficiency, and hypoparathyroidism.

Do its potential therapeutic benefits make spit seem just a bit less unpalatable? We hope so. And we certainly won't be surprised if-a fluid that people turn away from today comes to be appreciated for what it is: one of nature's favorite genetics laboratories, and a source of lifesaving medical advances.