Kidney Tubular-Cell Secretion of Osteoblast Growth Factor Is Increased by Kaempferol： A Scientific Basis for ＂The Kidney Controlling the Bone＂ Theory of Chinese Medicine

Objective： To study, at the cytological level, the basic concept of Chinese medicine that “the Kidney （Shen） controls the bone”. Methods： Kaempferol was isolated form Rhizoma Drynariae （Gu Sui Bu, GSB） and at several concentrations was incubated with opossum kidney （OK） cells, osteoblasts （MC3T3 El） and human fibroblasts （HF） at cell concentrations of 2 x 104/mL. Opossum kidney cell-conditioned culture media with kaempferol at 70 nmol/L （70kaθOKM） and without kaempferol （oOKM） were used to stimulate MC3T3 E1 and HF proliferation. The bone morphological protein receptors I and Ⅱ （BMPR I and Ⅱ） in OK cells were identified by immune-fluorescence staining and Western blot analysis. Results： Kaempferol was found to increase OK cell growth （P〈0.05）, but alone did not promote MC3T3 E1 or HF cell proliferation. However, although OKM by itself increased MC3T3 E1 growth by 198% （P〈0.01）, the 70kaθOKM further increased the growth of these cells by an additional 127% （P〈0.01）. It indicates that the kidney cell generates a previously unknown osteoblast growth factor （OGF） and kaempferol increases kidney cell secretion of OGF. Neither of these media had any significant effect on HF growth. Kaempferol also was found to increase the level of the BMPR Ⅱ in OK cells. Conclusions： This lends strong support to the original idea that the Kidney has a significant influence over bone-formation, as suggested by some long-standing Chinese medical beliefs, kaempferol may also serve to stimulate kidney repair and indirectly stimulate bone formation.