Effect of vitamin D-containing plant extracts on osteoporotic bone.

Adequate supply of vitamin D(3) is not sufficient for the prevention of post-menopausal osteoporosis, because of a tightly regulated critical step in formation of the most active vitamin D metabolite 1,25-dihydroxyvitamin D(3). Direct application of 1,25(OH)(2)D(3), however, was effective in reducing fracture rate and increasing bone mineral density as has been shown in large clinical studies. Extracts from Solanum glaucophyllum and Trisetum flavescens plants containing 1,25(OH)(2)D(3)-glycosides were characterized by their vitamin D-activity in a quail eggshell bioassay and applied in an osteoporosis model in ovariectomized rats. An extract from the grass T. flavescens and a purified extract from S. glaucophyllum were characterized by the absence of alkaloids and the analytically determined content of 1,25(OH)(2)D(3). In the ovariectomized rat model after 6 months duration, the bone metabolism relevant markers serum calcium, 1,25(OH)(2)D(3), urinary crosslinks and calcium were measured. At termination tibial mineral content was determined and as imaging procedure micro-computerized tomography was applied. The bisphosphonate alendronate was used as a positive standard. While alendronate reduced bone resorption, as seen in a reduced urinary crosslink excretion, both vitamin D metabolite-containing extracts were able to improve bone mineral density by an enhanced calcium turnover.