Osteoporosis is highly prevalent in older persons. While many advances have been made in the field of osteoporosis, current treatments have been affected by unexpected side effects and limited efficacy; therefore, new approaches to identify disease mechanisms and pathways are required. This review focuses on the influence of tryptophan metabolites, particularly kynurenines and serotonin on bone. The kynurenine (KYN) pathway is associated with osteoblastogenesis and can be linked to the pathophysiology of osteoporosis. The activity of osteoblasts is reduced by 3-hydroxykynurenine (3-HKYN), a product of KYN. In addition, decreasing concentrations of 3-hydroxyanthranilic acid with aging can be one of the causes of bone loss. In contrast, picolinic acid, an end-product of the KYN pathway, acts as a bone anabolic. On the other hand, gut-derived serotonin (GDS) inhibits bone formation, whereas brain-derived serotonin enhances bone formation and decreases bone resorption. Overall, understanding the exact mechanisms of action of tryptophan metabolites on bone could have great potential to develop effective treatments for osteoporosis and other bone diseases.

骨质疏松症在老年人中非常普遍。尽管在骨质疏松症领域取得了许多进展，但目前的治疗方法受到意料不到的副作用和疗效的限制；因此，需要新的方法来确定疾病的机制和途径。这篇综述着重于色氨酸代谢产物，特别是犬尿氨酸和血清素对骨骼的影响。犬尿氨酸（KYN）途径与成骨细胞发生有关，并且可以与骨质疏松症的病理生理学联系起来。KYN的产物3-hydroxykynurenine（3-HKYN）降低了成骨细胞的活性。此外，随着年龄的增长，3-羟基邻氨基苯甲酸的浓度降低可能是造成骨质流失的原因之一。相反，吡啶甲酸（KYN途径的终产物）则起骨合成代谢的作用。另一方面，肠源性血清素（GDS）抑制骨形成，而脑源性血清素可增强骨形成并降低骨吸收。总体而言，了解色氨酸代谢产物对骨骼的确切作用机制可能具有开发有效的治疗骨质疏松症和其他骨骼疾病的潜力。