ARTIFICIAL SPIT
MAKING ARTIFICIAL SPIT SOUNDS like a strange research objective only if you have plenty of
spit of your own. People who take antidepressants, undergo radiation therapy, or suffer from
Sjogren's syndrome--which is characterized by a shortfall of all body fluids-- do not have plenty
of spit, and it is more than an annoyance. "Saliva protects and lubricates tooth surfaces and kills
different types of microbes," explains Michael Levine, an oral biologist at the State University of
New York at Buffalo. "Some of the consequences of dry mouth are increased fungal infections
and certain types of dental decay and gum disease."
The artificial spit Levine and his colleagues are working on would not only make the mouth feel
wetter and more comfortable but would also be able to protect it from bacteria and fungi that can
destroy teeth and gums. Recently the researchers passed a milestone. They cloned two of the
major proteins found in saliva histatins and cystatins.
Histatins are small proteins that keep the fungus Candida albicans in check. "The histatins punch
holes in the fungus's cell membrane, and then things that are essential for the fungus to survive
leak out," explains Levine. Cystatins are larger molecules that protect the mouth from a variety of
microorganisms, including viruses and some bacteria. They do this by interfering with the action
of enzymes called thiol proteases. These protein-cutters are thought to be involved in microbe
replication, and when microbes release them in the mouth, they also seem to destroy gum tissue.
Now that Levine and his colleagues have cloned these two types of protein and can make them in
their lab, they can tinker with the proteins' structure and try to improve on nature's design. And
although the researchers are still a long way from a complete artificial saliva--at the moment, for
instance, they're trying to clone two other proteins that make spit a good lubricant--Levine
predicts that histatins and cystatins will be available for fighting ordinary tooth decay before the
decade is out. Packaging them is still a problem, however. "Most proteins, to be biologically
active, have to maintain a certain shape," says Levine. "If you put them in a mouthwash or a
paste, you don't know if they're going to maintain that shape."
Source: Discover, Jul93, Vol. 14 Issue 7, p12, 2p