Fusion of parathyroid hormone (1–34) to an albumin-binding domain improves osteogenesis

Osteoporosis is a common severe orthopedic disease that can lead to bone fractures and significantly reduce a patient's quality of life. Teriparatide (parathyroid hormone, PTH (1–34)) has been approved for the treatment of osteoporosis. However, PTH (1–34) needs to be injected once daily due to its short half-life of 1 h. To improve the pharmacokinetic and pharmacodynamic profiles of PTH (1–34), a G148-ABD3 (GA3) domain, which can bind to albumin non-covalently, was employed to modify PTH (1–34). The resultant PTH34-GA3-GS1 and PTH34-GA3-GS3 fusion proteins were constructed by fusing PTH (1–34) to the N-terminus of GA3 via (G4S)1 and (G4S)3 linkers, respectively. The fusion proteins were highly expressed in Escherichia coli. In vitro results showed that both PTH34-GA3-GS1 and PTH34-GA3-GS3 could bind to human serum albumin (HSA) with high affinity. The fusion proteins significantly increased the proliferation and differentiation of osteoblastic MC3T3-E1 cells, thereby promoting osteogenesis. PTH34-GA3-GS3 increased intracellular and serum calcium levels more than PTH34-GA3-GS1 did. The half-lives of PTH34-GA3-GS1 and PTH34-GA3-GS3 were 8.4 h and 9.1 h, respectively, which are significantly longer than that of PTH (1–34). Injection of PTH34-GA3-GS3 every three days increased bone mineral density and improved trabecular structure in ovariectomized mice, indicating that PTH34-GA3-GS3 has the potential to alleviate osteoporosis in humans. In conclusion, the fusion proteins maintained the biological activity of native PTH (1–34) and were not affected by the GA3 moiety, which extended the half-life of PTH (1–34). Long-acting GA3-fusion PTH (1–34) proteins have therapeutic effects on osteoporosis by improving osteogenesis and by enhancing the proliferation and differentiation of osteoblasts.