Natural bioactive compounds in estrogen deficiency-induced osteoporosis: Classification and an integrated gut microbiota-metabolite-immune-bone framework

Figure 2 Direct and microbiota-mediated mechanisms of natural bioactive compounds in postmenopausal osteoporosis. Natural bioactive compounds may influence bone remodeling through direct effects on osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells, microbial biotransformation, and the gut barrier-immune-inflammatory network. Solid arrows indicate principal pathways supported mainly by preclinical evidence. Bidirectional arrows indicate proposed, associative or feedback relationships. LPS: Lipopolysaccharide; ER: Estrogen receptor; SCFAs: Short-chain fatty acids.