Glucose-dependent insulinotropic polypeptide (GIP) induces calcitonin gene-related peptide (CGRP)-I and procalcitonin (Pro-CT) production in human adipocytes.

CONTEXT

Increased plasma levels of glucose-dependent insulinotropic polypeptide (GIP), calcitonin CT gene-related peptide (CGRP)-I, and procalcitonin (Pro-CT) are associated with obesity. Adipocytes express functional GIP receptors and the CT peptides Pro-CT and CGRP-I. However, a link between GIP and CT peptides has not been studied yet.

OBJECTIVE

The objective of the study was the assessment of the GIP effect on the expression and secretion of CGRP-I and Pro-CT in human adipocytes, CGRP-I and CT gene expression in adipose tissue (AT) from obese vs. lean subjects, and plasma levels of CGRP-I and Pro-CT after a high-fat meal in obese patients.

DESIGN AND PARTICIPANTS

Human preadipocyte-derived adipocytes, differentiated in vitro, were treated with GIP. mRNA expression and protein secretion of CGRP-I and Pro-CT were measured. Human CGRP-I and CT mRNA expression in AT and CGRP-I and Pro-CT plasma concentrations were assessed.

RESULTS

Treatment with 1 nm GIP induced CGRP-I mRNA expression 6.9 ± 1.0-fold (P < 0.001 vs. control) after 2 h and CT gene expression 14.0 ± 1.7-fold (P < 0.001 vs. control) after 6 h. GIP stimulated CGRP-I secretion 1.7 ± 0.2-fold (P < 0.05 vs. control) after 1 h. In AT samples of obese subjects, CGRP-I mRNA expression was higher in sc AT (P < 0.05 vs. lean subjects), whereas CT expression was higher in visceral AT (P < 0.05 vs. lean subjects). CGRP-I plasma levels increased after a high-fat meal in obese patients.

CONCLUSION

GIP induces CGRP-I and CT expression in human adipocytes. Therefore, elevated Pro-CT and CGRP-I levels in obesity might result from GIP-induced Pro-CT and CGRP-I release in AT and might be triggered by a high-fat diet. How these findings relate to the metabolic complications of obesity warrants further investigations.