Transcription, expression and tissue binding in vivo of INGAP and INGAP-related peptide in normal hamsters.

BORELLI MI; DEL ZOTTO H; FLORES LE; GARCÍA ME; BOSCHERO AC; GAGLIARDINO JJ

Helsingor, Dinamarca

Workshop; EASD Islet Study Group Symposium 2006. Beta cell replacement/regeneration in diabetes therapy; 2006

European Association for the Study of Diabetes

Aim: To screen the transcription and immunocytochemical presence of islet neogenesis-associated protein (INGAP), and measure the in vivo binding of a tyrosilated biologically active portion of INGAP pentadecapeptide (T-INGAP-PP) to different tissues from normal Syrian hamsters. Material and Methods: Immunocytochemical detection of INGAP- positive cells and INGAP transcription (RT-PCR) were performed in different normal hamster tissues. 125I-T-INGAP-PP was injected alone or with unlabeled T-INGAP-PP (0-1 mg/100 g bw); blood samples were drawn 5 to 60 min after injection. Radioactivity was measured in serum, brain, liver, kidney, small intestine and pancreas. Results were expressed as organ:serum ratio. Results: INGAP-positive cells and -mRNA were only identified in pancreatic islets and exocrine tissue. Radioactivity in serum samples increased from 0 (1,952 cpm/g serum) to 60 min (36,566 cpm/g serum). Whereas 71% of this activity was displaced by the simultaneous administration of unlabeled T-INGAP-PP at 5, 10 and 20 min, only 9% was at 60 min. Liver, pancreas and small intestine showed specific 125I-T-INGAP-PP binding. The 50% displacement of the dose-response curve from pancreatic tissue at 39.102 ng/100 gbw suggests a low binding affinity of pancreas receptor to this peptide. Conclusion: INGAP transcription/expression is probably restricted to pancreas and its effect exerted through a paracrine action. INGAP could be released and circulate bound to a serum protein and thereafter bound by liver for its inactivation. Such binding would explain the immunocytochemical presence of INGAP in small intestine, where it could play a role in epithelial cell turnover.