Milk basic protein (MBP) promotes bone formation by activating osteoblasts, and decreasing bone resorption by suppressing osteoclasts

Milk contains not only bioavailable calcium source, but also other components effective for bone health. In the present study we found that milk basic protein (MBP) strongly stimulated both bone formation and bone resorption when we investigated its effect on bone metabolism in vitro and in vivo. Additionally, we also identified the active components of MBP that stimulated osteoblasts and osteoclasts. We examined the effect of daily intake of MBP on bone mineral density (BMD) and bone metabolism in a human study. The gain of BMD in the MBP group was significantly higher than that in the placebo group. The osteocalcin, a bone formation marker, increased significantly. The cross-linked N-teleopeptides of type-I collagen (NTX) excretion, a bone resorption marker, was lower in the MBP group. These results suggested that MBP promoted bone formation and suppressed bone resorption in human. In young ovariectomized (OVX) rats, the oral administration of MBP increased the contents of both bone mineral and bone proteins such as collagen. In addition, in aged OVX rats, the administration of MBP decreased bone resorption and was effective in preventing bone loss. In cell culture study, MBP increased the number of osteoblastic cells and amount of bone proteins such as collagen. There are several components that activate osteoblast. We purified and sequenced two components that had growth-promoting activity. One component was identified as a kininogen fragment 1.2 and the other was a high mobility group (HMG)-like protein. On the other hand, MBP suppressed bone resorption directly. Milk also contains several components which suppreses osteoclast. We sought to determine the active suppressive components in MBP and found that one of them was milk cystatin. These results suggest that MBP is effective for promoting bone formation by activating osteoblasts, and for decreasing in bone resorption by suppressing the action and formation of osteoclasts. Thus MBP is considered to be an effective food component.