Truncated (des-[27-31]) C-peptide is not a major secretory product of human islets.
OBJECTIVE
It has been suggested that C-peptide is bioactive and that such bioactivity is lost when the last five amino acids are removed. In rats, C-peptide is truncated in beta-cell granules leading to the loss of these last five residues and secretion of des-[27-31]-C-peptide. The aim of this study was to determine whether this truncated form of C-peptide was also a secretory product of human islets.


METHODS
Plasma from healthy subjects, patients with Type II (non-insulin-dependent) diabetes mellitus or insulinoma and cord blood was analysed by HPLC and ELISA. This method allows for separation and quantification of intact C-peptide and des-[27-31]-C-peptide. Human islets were pulse-chased and secretion stimulated by a mixture of secretagogues. Radioactive products secreted to the medium were analysed by HPLC and the relative amount of intact and truncated C-peptide measured.


RESULTS
The proportion of total C-peptide immunoreactivity comprised of des-[27-31]-C-peptide was 1.5% or less in all plasma samples, except for that from one patient with insulinoma where it was 4.2%. The proportion of radiolabelled des-[27-31]-C-peptide released from isolated islets was less than 1%.


CONCLUSIONS
In contrast to the situation in rats, des-[27-31]-C-peptide is not a major secretory product of human islets and its contribution to total circulating C-peptide is not increased in Type II diabetes or in patients with insulinoma.
Paoletta
M
M
Louis Jeantet Research Laboratories, University of Geneva Medical Centre, Geneva, Switzerland.
Kahn
S E
SE
Halban
P A
PA
D000328:Adult; D002096:C-Peptide / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D003924:Diabetes Mellitus, Type 2 / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay; D005312:Fetal Blood / Q000737:chemistry*; D006801:Humans; D007231:Infant, Newborn; D007340:Insulinoma / Q000097:blood*; D007515:Islets of Langerhans / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000097:blood*; D010446:Peptide Fragments / Q000097:blood*; D012016:Reference Values
D002096:C-Peptide; C102310:C-peptide, des-(27-31)-; D010446:Peptide Fragments