Endocrine Abstracts

The gastro-entero-pancreatic hormones are involved in the regulation of postprandial nutrient homeostasis. Food intake or fasting triggers the release of these hormones. A direct connection between food intake and bone turnover, assessed by biochemical markers of bone resorption and formation, has been demonstrated in animals and humans.

The aim was to study the expression of receptors for the gut hormones, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 and 2 (GLP-1, GLP-2), ghrelin (GHR) and the obestatin receptor, (GPR39) and effects in vitro of GIP and GLP-1 in three osteoblastic cell lines, SaOS-2, Te-85 and Mg-63, which represent different stages of osteoblastic differentiation.

Quantitative real time PCR was performed using an iCycler (iQ Bio-Rad). cDNA samples were analysed for the genes of interest and normalised using beta-actin. Cell cultures were treated for 5 days with varying concentrations of GIP and GLP-1 and parathyroid hormone (PTH) was used as a control (1–1000 pM). After treatment, supernatants were harvested and alkaline phosphatase (ALP) was measured as a marker of osteoblast cell function. Tewnty-four hours after exposure to the peptides a fluorescence assay for cell viability was performed, in which the signal is proportional to the number of living cells.

Receptors for all five of the gut hormones were expressed in the three osteoblastic cell lines. The expression of GLP-1, GLP-2, ghrelin and obestatin receptors was higher in less differentiated cell lines (Te-85 and Mg-63) whereas the GIP receptor was expressed at a higher level in the most mature cell line SaOS-2.

To date, only the SaOS-2 cell line demonstrated functional responses to GIP with concentrations from 10 to 1000 pM stimulating ALP production. Viability was greater when Te85 and Mg63 were stimulated with GLP-1.

Our results indicate that osteoblast function may be directly influenced in the postprandial and post-absorptive states by the release of gut hormones in response to changes in dietary intake.