Maintenance of trabecular structure and bone volume by vitamin K-2 in mature rats with long-term tail suspension

Bone volume loss is one of the major health problems during long-term spaceflight. We examined the effects of vitamin K-2 on bone abnormalities in tail-suspended mature male Sprague-Dawley rats (13 weeks old). In this model, increased bone resorption and sustained suppression of bone formation resulted in progressive bone loss in 4 weeks, which simulates bone changes in humans during spaceflight. A significant decrease in bone mineral density (BMD), as well as a decreased mineral apposition rate (MAR), increased number of osteoclasts per bone perimeter (N.Oc/B.Pm), and increased osteoclast surface per bone surface (Oc.S/BS) in the suspended group was effectively prevented by vitamin K-2 given orally (menatetrenone, 22mg/kg body weight). Microfocus computed tomography (CT) and node-strut analyses revealed that the volume and structure of trabecular bone were maintained near normal by the vitamin K-2 treatment. A recent report has suggested the abnormal metabolism or action of vitamin K in a microgravity environment, and our data therefore suggest that vitamin K-2 may be useful for the prevention of bone loss and for the maintenance of normal trabecular structure during spaceflight.