Raloxifene and Vitamin K₂ Combine to Improve the Femoral Neck Strength of Ovariectomized Rats

We evaluated the skeletal effects of two osteoporosis therapies in an ovariectomized rat model, raloxifene and vitamin K₂, as well as the vitamin K₂ plus raloxifene (K + Ral) combination. In two studies, 6-month-old rats were ovariectomized, except for sham-ovariectomy controls (Sham), and dosed orally with vehicle, 30 mg/kg vitamin K₂, 1 mg/kg raloxifene, or the combination of K + Ral for 6 weeks following surgery. Vitamin K₂ had no effect on serum estrogen, low-density lipoprotein cholesterol (LDL-C), or urinary deoxypyridinoline levels, but slightly increased osteocalcin levels compared to Ovx. Raloxifene lowered total cholesterol, LDL-C, osteocalcin, and urinary deoxypyridinoline levels to below Ovx levels, while having no effect on estrogen levels. Raloxifene, but not vitamin K₂, prevented ovariectomy-induced loss of bone in the distal femoral metaphysis and proximal tibial metaphysis, as did the K + Ral combination. Raloxifene, but not vitamin K₂, partially prevented, loss of vertebral bone mineral density (BMD), whereas K + Ral had BMD greater than that of Ovx. Vitamin K₂ increased bone formation rate to above Ovx, whereas raloxifene and K + Ral reduced bone formation rate to Sham levels. Vitamin K₂ had no effect on eroded surface compared to Ovx, while raloxifene and K + Ral reduced eroded surface to Sham levels. Groups were not different in the BMD of femoral midshaft; however vitamin K₂ was observed to increase periosteal mineralizing surface of the tibial shaft to above Ovx, while raloxifene reduced periosteal mineralizing surface toward Sham levels. Femoral neck strength was not different between groups, indicating no significant beneficial effect of either raloxifene or vitamin K₂ at this site. However, K + Ral had reproducibly greater femoral neck strength than Ovx or Sham. Raloxifene, but not vitamin K₂, partially prevented loss of lumbar vertebra strength; but K + Ral was not different from Sham or Ovx. Therefore, raloxifene and vitamin K₂ had complementary effects on bone resorption and formation activities, respectively, resulting in a reproducible, significant improvement of femoral neck strength. These rat data suggest interesting therapeutic possibilities that may require clinical verification.