Frequency of Teriparatide Administration Affects the Histological Pattern of Bone Formation in Young Adult Male Mice

Evidence supports that daily and once-weekly administration of teriparatide, human (h) PTH(1-34), enhance bone mass in osteoporotic patients. However, it is uncertain whether different frequencies of hPTH(1-34) administration would induce bone formation similarly in terms of quantity and quality. To investigate that issue, mice were subjected to different frequencies of PTH administration, and their bones were histologically examined. Frequencies of administration were 1 time/2 days, 1 time a day, and 2 and 4 times a day. Mice were allocated to either to control or to 3 different dosing regimens: 80 mu g/kg of hPTH(1-34) per injection (80 mu g/kg per dose), 80 mu g/kg of hPTH(1-34) per day (80 mu g/kg.d), or 20 mu g/kg of hPTH(1-34) per day (20 mu g/kg.d). With the regimens of 80 mu g/kg per dose and 80 mu g/kg.d, high-frequency hPTH(1-34) administration increased metaphyseal trabecular number. However, 4 doses per day induced the formation of thin trabeculae, whereas the daily PTH regimen resulted in thicker trabeculae. A similar pattern was observed with the lower daily hPTH(1-34) dose (20 mu g/kg.d): more frequent PTH administration led to the formation of thin trabeculae, showing a thick preosteoblastic cell layer, several osteoclasts, and scalloped cement lines that indicated accelerated bone remodeling. On the other hand, low-frequency PTH administration induced new bone with mature osteoblasts lying on mildly convex surfaces representative of arrest lines, which suggests mini-modeling-based bone formation. Thus, high-frequency PTH administration seems to increase bone mass rapidly by forming thin trabeculae through accelerated bone remodeling. Alternatively, low-frequency PTH administration leads to the formation of thicker trabeculae through bone remodeling and minimodeling.