People who take insulin to treat their diabetes may one day bolster their treatment with another naturally occurring substance, a study in rats suggests. Roughly 16 million Americans have diabetes, which is characterized by high blood sugar levels resulting from the body’s failure either to use or produce the hormone insulin.

In humans, the body produces insulin from part of a large protein formed by two chains connected by a small amino-acid chain called C-peptide. The new findings regarding C-peptide surprised the Missouri and Indiana investigators, as researchers previously disregarded it, believing the amino-acid chain did little, if anything, other than participate in the formation of insulin.

In the study, investigators led by Dr. Y. Ido, of the Washington School of Medicine in St. Louis, found that giving human C-peptide to diabetic rats prevented or decreased diabetic damage to nerve cells and blood vessels.

While the investigators still do not know how human C-peptide slowed the damage, they hope that additional studies will lead to better treatment for people with diabetes, according to findings published Friday in the journal Science.

Although human C-peptide may prove useful in treating diabetes, this treatment “should not be considered an alternative to insulin or other blood [sugar]-lowering agents,” the researchers cautioned.

Instead, it could be used in combination with other therapies to improve the quality of life for diabetics, they wrote. Diabetes can lead to serious and life-threatening complications, including blindness, kidney disease and nerve damage. Each year, the results in 54,000 leg and foot amputations.

The “tantalizing possibilities” of human C-peptide complementing insulin therapy deserves further study, Dr. Donald F. Steiner, senior investigator at the Howard Hughes Medical Institute in Chicago and a professor of biochemistry and molecular biology at the University of Chicago, wrote in an accompanying editorial.

The findings offer tremendous possibilities for advancing the treatment of diabetes, said Dr. Gerald Bernstein, president-elect of the American Diabetes Association and an associate clinical professor at the Albert Einstein College of Medicine in New York.

“It could help virtually all tissues” by greatly reducing the complications of Type 1 diabetes, he speculated. In Type 1 diabetes, the body lacks human C-peptide. However, it remains unclear why in Type 2 diabetes, in which human C-peptide is present, normal levels of the amino acid chain do not help prevent tissue damage.

But increasing levels of C-peptide in Type 2 diabetics above normal may, in fact, reduce complications in these patients, according to study co-author Dr. J. R. Williamson, a professor of pathology at Washington University School of Medicine. He added that small, short-term clinical studies conducted by Swedish researchers have demonstrated promise in humans.

Science (1997;277:563-6)

New York Times: July 25, 1997