Comparison of the Effect of Vitamin K2 and Risedronate on Trabecular Bone in Glucocorticoid-Treated Rats: A Bone Histomorphometry Study

PURPOSE To compare the effect of vitamin K(2) and risedronate on trabecular bone in glucocorticoid (GC)-treated rats. MATERIALS AND METHODS Forty-eight Sprague-Dawley female rats, 3 months of age, were randomized by the stratified weight method into 5 groups according to the following treatment schedule: age-matched control, GC administration, and GC administration with concomitant administration of vitamin K(2), risedronate, or vitamin K(2) + risedronate. GC (methylprednisolone sodium succinate, 5.0 mg/kg) and risedronate (10 microg/kg) were administered subcutaneously three and five times a week, respectively. Vitamin K(2) (menatetrenone, 30 mg/kg) was administered orally three times a week. At the end of the 8-week experiment, bone histomorphometric analysis was performed on trabecular bone of the tibial proximal metaphysis. RESULTS GC administration decreased trabecular bone mass compared with age-matched controls because of decreased bone formation (mineralizing surface, mineral apposition rate, and bone formation rate) and increased bone erosion. Vitamin K(2) attenuated GC-induced trabecular bone loss by preventing GC-induced decrease in bone formation (mineralizing surface) and subsequently reducing GC-induced increase in bone erosion. Risedronate prevented GC-induced trabecular bone loss by preventing GC-induced increase in bone erosion although it also suppressed bone formation (mineralizing surface, mineral apposition rate, and bone formation rate). Vitamin K(2) mildly attenuated suppression of bone formation (mineralizing surface) and bone erosion caused by risedronate without affecting trabecular bone mass when administered in combination. CONCLUSION The present study showed differential effect of vitamin K(2) and risedronate on trabecular bone in GC-treated rats.