Updated 6:57 PM ET November 10, 1999
By Penny Stern, MD
NEW YORK, Nov 10 (Reuters Health) -- By injecting an insulin-like protein into rats, scientists have apparently reversed some diabetes-related nerve damage, according to an American Journal of Pathology report released this week.
The finding suggests that the protein may be a treatment for some of the nerve complications of diabetes in humans.
"We have found that a distinctive type of structural change develops in diabetic rats -- and man, which is visible as large swellings involving the sites... where nerve cells communicate," lead author Dr. Robert E. Schmidt explained to Reuters Health, adding that the study shows that 2 months of treatment with the protein, insulin-like growth factor-I, can reverse these swellings in rats.
Insulin-like growth factor-I (IGF-I), a protein that bears a chemical resemblance to insulin, appears to affect nerve function, including nerve impulse conduction and axonal regrowth, Schmidt said. "We know that circulating blood levels of IGF-I are decreased in diabetic humans, particularly in patients with neuropathy, and animals," he added.
Neuropathy is the general term applied to a number of disturbances in nerve function. Diabetics often develop a range of neuropathies as a complication of the disease because nerve cells and their axons -- the branch-like cell structure involved in transmitting impulses -- are exquisitely sensitive to the high levels of blood sugar that characterize the disease. The damage sustained by these cells may result in loss of sensation, particularly in the feet and hands, and with involuntary nerve functions that control certain basic reflexes.
Schmidt, a researcher at Washington University School of Medicine in St. Louis, Missouri, used diabetic rats to investigate IGF-I's impact on nerve damage. "We did not expect that a short course of IGF-I... would prove capable of nearly normalizing the structural changes (seen in these experimental animals)," he said.
Of note was that Schmidt and colleagues "made no attempt to control (the animals') blood sugar and indeed, sought not to affect this value," he told Reuters Health. Conventional medical wisdom holds that control of blood sugar levels in diabetics is crucial to the limiting complications of the disease though, as Schmidt pointed out, "precise control of blood sugar values in most human diabetics has been difficult to achieve." He stressed, however, that IGF-I does not represent "a replacement for the close control of blood sugar levels in the human diabetic."
But IGF-I is not without its potential problems, Schmidt noted. When used at high doses, the substance appears to cause side effects. Moreover, "epidemiological studies have suggested that... IGF-I (may be associated) with certain neoplasms (abnormal growths)," he said.
Nevertheless, IGF-I may someday be a treatment for diabetic neuropathy, and perhaps for other nerve diseases. According to Schmidt, the protein has been studied in amyotrophic lateral sclerosis (Lou Gehrig's disease), although no definitive conclusions have been reached regarding IGF-I's therapeutic efficacy in that disorder. "It has (also) been considered for use in diseases as different as multiple sclerosis, stroke, and brain trauma," Schmidt continued. He acknowledged, however, that further work will be required "to determine if such optimism is warranted."
SOURCE: American Journal of Pathology 1999;155:1651-1660.