Neuropeptide Y Y1 receptor antagonism increases bone mass in mice

The neuropeptide Y system has emerged as one of the major neural signalling pathways regulating bone homeostasis. Absence of Y1 receptor signalling from bone forming osteoblasts is responsible for an enhancement on bone mass in mice, suggesting that pharmacological blockade of Y1 receptors may offer a novel anabolic treatment option for improving bone mass. Here we show that oral administration of the selective Y1 receptor antagonist BIBO3304 for 8 weeks dose-dependently increases bone mass in mice. Histomorphometric analysis revealed a significant 1.5-fold increase in cancellous bone volume in the femora of mice treated with BIBO3304. Furthermore, bone microarchitecture was improved, with greater trabecular number and trabecular thickness. This increase in bone mass was associated with a significant increase in bone anabolic activity of osteoblasts and, interestingly, was evident despite a coincident increase in bone resorption, as evidenced by an increase in the number of the osteolytic osteoclasts. Changes were also evident in cortical bone, with a significant increase in periosteal mineral apposition rate. Importantly, no adverse extra-skeletal side effects were observed through Y1 receptor antagonism over the 8-week treatment period, with no effects of even the higher BIBO3304 dose on body weight, adiposity, energy metabolism or circulating corticosterone levels. Taken together, this work describes the first NPY-based anabolic treatment for improving bone mass, and highlights the therapeutic potential of blocking Y1 receptor signalling for the prevention of, or recovery from, degenerative skeletal diseases.