Enzyme and protein studies of demyelination in diabetes

Neuropathological evidence of demyelination was found in the brain and sciatic nerve of diabetic patients at autopsy. The activity of acid proteinase was somewhat increased in the white matter but decreased in the gray matter of diabetic patients. No increase was observed in the activity of neutral proteinase in diabetic white and gray matter. The activities of beta-glucuronidase and 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP) were of the same level as those of the controls. The activities of all 4 enzymes appeared to be increased in the diabetic nerve, with the possible exception of CNP which was measured from only 1 nerve. Furthermore, the amount of total protein was markedly decreased in diabetic peripheral myelin. The encephalitogenic basic protein of diabetic brain myelin was normal in the disc gel electrophoretic patterns of brain myelin proteins. However, the basic proteins of peripheral myelin were reduced in a number of diabetic patients. The present biochemical findings for diabetic white and gray matter were largely normal. Instead, the increased activities of at least the proteinases and beta-glucuronidase in diabetic peripheral nerve, together with the loss of basic proteins, indicate extensive biochemical damage of the peripheral nervous system in diabetes. They suggest that demyelination and other phenomena observed in diabetic peripheral nerve are not caused only by angiopathy and impaired circulation.