Locally Delivered Metabolite Derivative Promotes Bone Regeneration in Aged Mice.

Repair of large bone defects is still a major challenge, especially for the aged population. One alternative to address this issue is using the biomaterial-mediated bone morphogenetic protein 2 (BMP2) delivery technique, although high-dose BMP2 can cause serious concerns. α-Ketoglutarate (AKG) is a key intermediate in the tricarboxylic acid cycle and emerging as an intriguing antiaging molecule to extend the life/health span in different organisms. While one recent study indicates that the dietary AKG could significantly reduce bone loss and improve bone anabolism in aged mice, the therapeutic potential of AKG for bone regeneration has not been studied so far. Moreover, the poor cell permeability, large dose requirement, and long-term systemic administration of AKG hinder its applications in clinics and cellular mechanism studies. Dimethyl α-ketoglutarate (DMAKG) is a cell-permeable derivative of AKG with promising potential, although its role in osteogenesis is still elusive. Therefore, we aim to study the potential roles of DMAKG for bone regeneration using both in vitro cell culture and in vivo aged mouse models. Compared to AKG, our data indicated that DMAKG could more effectively improve osteoblastic differentiation. In addition, DMAKG significantly reduced adipogenic differentiation and improved osteogenic differentiation of a mouse multipotential mesenchymal stem cell line. Importantly, our result indicated that DMAKG significantly promoted BMP2-induced osteoblastic differentiation and mineralization in vitro. Moreover, DMAKG could not only significantly mitigate lipopolysaccharide (LPS)-stimulated inflammation in macrophages but also largely rescue LPS-inhibited osteoblastic differentiation. Consistently, our in vivo study demonstrated that gelatin scaffold-mediated local release of DMAKG significantly promoted BMP2-induced bone regeneration in aged mice, which is compromised by chronic inflammation and high adipogenesis. Overall, we, for the first time, report that locally delivered metabolite derivative, DMAKG, could improve BMP2-induced bone regeneration in aged mice. Our study suggests DMAKG has a promising therapeutic potential for bone regeneration through modulating local inflammation and stem cell differentiation.