Bone resorption is decreased postprandially by intestinal factors and glucagon-like peptide-2 is a possible candidate.

OBJECTIVE: Food intake inhibits bone resorption by a mechanism thought to involve gut hormones, and the intestinotrophic glucagon-like peptide 2 (GLP-2) is a candidate because exogenous GLP-2 inhibits bone resorption in humans. The purpose of the study was to investigate patients with short-bowel syndrome (SBS) or total gastrectomy in order to elucidate whether the signal for the meal-induced reduction of bone resorption is initiated from the stomach or the intestine. MATERIAL AND METHODS: Bone resorption was assessed from the serum concentration of collagen type I C-telopeptide cross-links (s-CTX) and compared with the plasma concentrations of GLP-2. Bone formation was assessed from serum osteocalcin concentrations. Seven SBS patients with a preserved colon and 7 with SBS and colectomy and 7 healthy controls were given a breakfast test meal (936 kcal). Eight patients who had undergone total gastrectomy had an oral glucose load (75 g in 150 ml). RESULTS: The SBS patients without a colon showed no reduction in bone resorption (s-CTX) to a meal, whereas SBS patients with a colon had an intermediate response with a 27% (p<0.05) reduction of s-CTX from baseline after 120 min as compared with 66% (p<0.001) for normal controls. A significant reduction of 53% (p<0.001) was seen in gastrectomized patients after receiving oral glucose, which is comparable with the published data for the oral glucose tolerance test (OGGT) in healthy subjects (50% reduction over 120 min). Bone formation was unchanged for both SBS and gastrectomy patients. GLP-2 concentrations increased significantly in all groups with the exception of the SBS plus colectomy group. CONCLUSIONS: An intestinal factor is responsible for the postprandial reduction in bone resorption, and our findings are compatible with such a function for GLP-2.

Characterization of osteoclasts derived from CD14+ monocytes isolated from peripheral blood.

Bone resorption is solely mediated by osteoclasts. Therefore, a pure osteoclast population is of high interest for the investigation of biological aspects of the osteoclasts, such as the direct effect of growth factors and hormones, as well as for testing and characterizing inhibitors of bone resorption. We have established a pure, stable, and reproducible system for purification of human osteoclasts from peripheral blood. We isolated CD14-positive (CD14+) monocytes using anti-CD14-coated beads. After isolation, the monocytes are differentiated into mature osteoclasts by stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappaB ligand (RANKL). Osteoclast formation was only observed in the CD14+ population, not in the CD14- population, and only in the presence of both M-CSF and RANKL, confirming that the CD14+ system is a pure population of osteoclast precursors. No expression of osteoclast markers was observed in the absence of RANKL, whereas RANKL dose-dependently induced the expression of cathepsin K, tartrate-resistant acid phosphatase (TRACP), and matrix metallo proteinase (MMP)-9. Furthermore, morphological characterization of the cells demonstrated that actin rings were only formed in the presence of RANKL. Moreover, the osteoclasts were capable of forming acidic resorption lacunae, and inhibitors of lysosomal acidification attenuated this process. Finally, we measured the response to known bone resorption inhibitors, and found that the osteoclasts were sensitive to these and thereby provided a robust and valid method for interpretation of the effect of antiresorptive compounds. In conclusion, we have established a robust assay for developing osteoclasts that can be used to study several biological aspects of the osteoclasts and which in combination with the resorption marker CTX-I provides a useful tool for evaluating osteoclast function in vitro.