Proinsulin C-peptide--biological activity?

Patients with diabetes can lead relatively normal lives when treated with the hormone insulin, although they eventually exhibit vascular and neural complications. Now a report in this week9s issue by Ido et al. (p. 563) suggests that these complications might be alleviated by the simultaneous administration of C-peptide, a protein fragment cleaved from insulin during its synthesis. In his Perspective, Steiner describes how C-peptide, previously thought to be biologically inactive, may correct the vascular and neural dysfunctions of diabetes.