Understanding the Gut-Bone Signaling Axis

L. R. Bielke, B. M. Hargis, J. D. Latorre

Intestinal barrier leakage and/or altered gut microbial composition has been shown to markedly impact both osteoblast and osteoclast activities, systemically through circulation of gut immune cells and cytokines and locally by causing inflammation of extraintestinal organs such as the liver and bone marrow. Mild cases of heightened intestinal inflammation can cause bone loss in male mice in the absence of any overt nutritional deficiencies or weight loss, which has also been shown in chickens that have been infected with Salmonella. For poultry, ingredients selected for feed formulation have also a significant impact on gut health, intestinal microbiota, bone quality, and performance parameters. Consumption of diets with a high content of soluble non-starch polysaccharides (NSP) can affect bone quality parameters by reducing the amount of conjugated bile acids in the intestine, therefore diminishing the absorption of fat-soluble vitamins such as vitamin D and minerals like calcium and phosphorus. Recent enteric inflammation studies have shown that high NSP-containing diets have effects on intestinal viscosity, bone mineral content, and breaking strength, along with increased fluorescein isothiocyanate-dextran (FITC-d) leakage. Other skeletal diseases, such as bacterial chondronecrosis with osteomyelitis and enterococcal spondylitis, have a microbial component that is associated with increased mucosal permeability of the gut. Probiotics targeted toward control of enteric inflammation, either created through infectious disease or poor diet, may serve as a strategy for control of predisposing factors that lead to bone disorders.