‘Lick it better’ is good medical advice

Press, 11 September 1980, Page 15

‘Lick it better’ is good medical advice

By

RICHARD KNOX,

Globe”

For centuries, humans have observed that animals lick their wounds. Now a group of scientists

has discovered why: they are applying nature’s healing balm, a substance made in large amounts by the salivary glands. The discovery’s implications are potentially large. It hints at'. the possible development of a woundhealing drug invaluable for treating trauma and post-surgery patients. It opens new avenues for research into the mysterious way the body regulates cell growth — the central riddle in cancer, a disease of unregulated growth. Mammals apparently have “known” instinctively about the wound-healing substance for millenia. In fact, since human saliva also contains the restorative chemical in high concentrations, it is possible that we obey some ancient self-medicating impulse when we automatically put a finger in our mouths after it has been cut. The self-medication turns out to be a substance called nerve growth factor (N.G.F.), a mysterious protein discovered nearly 30 years ago in cancer cells and later found to be secreted by nearly every type of body cell. N.G.F. was one of the earliest known of a rapidly expanding class of cell proteins that regulate the

growth of specific types of target cells. Another member of the class is an elusive substance called angiogenesis factor (A.F.) that stimulates blood vessels to grow towards the cells that secrete it. The fact that many cancerous tumours secrete A.F. has touched off a worldwide effort to purify it and devise. ways of blocking it — thereby halting the cancer in its tracks. N.G.F. was named in the early 1950 s for its capacity to call forth the dramatic growth of nerve cells in chick embryos and test-tube cultures. However, its übiquitousness within the body and. its newly found ability to stimulate healing signifies that it plays a much broader role than previously recognised. In recent experiments, scientists found that when N.G.F., if applied to an open wound, either experimentally by the scientists or by a hurt animal or its companions, through licking, it accelerates wound-healing four-to-five fold. “We believe it is the first time anyone has found a naturally occurring product that can drastically increase the

healing of superficial wounds,” says Dr Michael Young, of the University of Florida medical school, leader of a scientific team that includes researchers at the Massachusetts General Hospital and the Shriners Burns Institute in Boston.

The finding, published recently in the Proceedings of the National Academy of Sciences, was made by Dr Young, who was formerly at Massachusetts General, and a Harvard-associated team

of Arthur K. C. Li, Mary J. Koroly, Marinus E. Schattenkerk, and Ronald A. Malt.

; Several years ago, the Massachusetts Hospital team hypothesised N.G.F.’s role in wound-healing after discovering the substance in cells called fibroblasts that are precursors to skin and scar tissue. That discovery was made in experiments with mice. However, many other mammals, up to and including humans, are known to have high concentrations of N.G.F. in their saliva. Dr Young cautiously suggests that it may eventually be possible to use N.G.F. to make a wound-healing medication that would be especially useful after surgery and in cases of severe burns and other trauma. Such an elixir would be especially valuable for patients whose woundhealing capacity is compromised by, . illness or; age. Another hope, derived from N.G.F.'s originally recognised nerve-stimu-lating properties, is that the. natural substance, or an artificially engineered cousin, might one day be used to reverse the devastating effects of spinal

cord injury, muscular dystrophy, and other diseases that destroy nerve cells. There is now no way to make the cells of the central nervous system — the brain, the spinal cord — regrow after they have been severed. Peripheral nerves (those outside the spinal cord that enervate muscles of the body) can often be induced to regenerate, but only if the ends of the severed nerve are sutured together.

The healing property of N.G.F, is expected to stimulate a new line of research into the mysteries of healing and the way that cells tell one another to start growing or to stop. “We need to find out what cell N.G.F. is ‘talking to’ on the other end of the telephone line,” as Dr Young puts it.

Researchers in Melbourne reported last year that mice that were wounded experimentally in a place where they could not lick the wound, and isolated from other mice, healed much more slowly than others whose wounds were licked.

Taking this another step, the researchers showed, through a series of mouse experiments, that it is the N.G.F., not some other component of saliva,z that is responsible for accelerating healing. First, they removed the salivery glands responsible for making N.G.F. (only one of three type of salivery glands make it) and allowed cage-mates, which also had their N.G.F.-pro-ducing glands removed, to lick the wound. The wound did not heal as fast.' Then they took rats without ‘ N.G.F.-producing salivary glands and dripped pure N.G.F. on the wounds several times in a concentration similar to that found in normal mouse saliva. The N.G.F.treated animals healed much faster than others deprived of the substance. Because one of N.G.F.’s properties is to stimulate the chain reaction which breaks down blood clots, the experimenters thought this might be the way it promoted wound-healing. However, other. enzymes known to start the clotdestroying action had no

effect when applied to the mouse wounds, so N.G.F. apparently works in a different way.

One of the next items on the researchers’ agenda is to purify human N.G.F., a step that Dr Young ex--pects may take another year. Once this is done, it will be possible to devise a sensitive test for the presence of N.G.F. in tissues, a development that will open the way for dozens of intriguing experiments. For instance, there is a disease of “over-healing” in which monstrous scars, called keloid scars, form. The researchers would like to know if the disease, primarily affecting blacks, is related to a defect in N.G.F. production. Another field in which , N.G.F., might turn out to be crucial is embryology. Science has no real idea how foetus cells communicate in, the intricate orchestration of development Scientists also believe it is significant that N.G.F. is present in many cancer cells in amounts 10-fold higher than in normal ceils.