Suppression Effect of Astaxanthin on Osteoclast Formation In Vitro and Bone Loss In Vivo

Osteoporosis is characterized by a reduction of the bone mineral density (BMD) and microarchitectural deterioration of the bone, which lead to bone fragility and susceptibility to fracture. Astaxanthin (AST) has a variety of biological activities, such as a protective effect against asthma or neuroinflammation, antioxidant effect, and decrease of the osteoclast number in the right mandibles in the periodontitis model. Although treatment with AST is known to have an effect on inflammation, no studies on the effect of AST exposure on bone loss have been performed. Thus, in the present study, we examined the antiosteoporotic effect of AST on bone mass in ovariectomized (OVX) mice and its possible mechanism of action. The administration of AST (5, 10 mg/kg) for 6 weeks suppressed the enhancement of serum calcium, inorganic phosphorus, alkaline phosphatase, total cholesterol, and tartrate-resistant acid phosphatase (TRAP) activity. The bone mineral density (BMD) and bone microarchitecture of the trabecular bone in the tibia and femur were recovered by AST exposure. Moreover, in the in vitro experiment, we demonstrated that AST inhibits osteoclast formation through the expression of the nuclear factor of activated T cells (NFAT) c1, dendritic cell-specific transmembrane protein (DC-STAMP), TRAP, and cathepsin K without any cytotoxic effects on bone marrow-derived macrophages (BMMs). Therefore, we suggest that AST may have therapeutic potential for the treatment of postmenopausal osteoporosis.