Inhibitory effect of genistein on bone resorption in tissue culture.

The effect of genistein on bone resorption in vitro was investigated. Femoral-metaphyseal tissues obtained from elderly female rats were cultured for 48 hr in Dulbecco's modified Eagle's medium (high glucose, 4.5%) supplemented with antibiotics and bovine serum albumin. The experimental cultures contained 10(-7) to 10(-3) M genistein. The bone-resorbing factors parathyroid hormone (1-34) (PTH; 10(-7) M), prostaglandin E2 (PGE2; 10(-5) M), and lipopolysaccharide ( 10 microg/mL) caused a significant decrease in bone calcium content. The decrease in bone calcium content induced by bone-resorbing factors was inhibited completely by genistein (10(-7) to 10(-5) M). In addition, this isoflavonoid (10(-5) M) completely inhibited the PTH (10(-7) M)- or PGE2 (10(-5) M)-induced increase in medium glucose consumption and lactic acid production by bone tissues. Moreover, genistein (10(-5) M) blocked both PTH (10(-7) M)-increased acid phosphatase and -decreased alkaline phosphatase activities of bone tissues. The inhibitory effect of genistein (10(-5) M) on PTH (10(-7) M)-stimulated bone resorption was clearly prevented by the presence of 10(-6) M tamoxifen, an anti-estrogen reagent. Genistein (10(-5) M) did not further enhance the inhibitory effect of estrogen (10(-9) M) on PTH-stimulated bone resorption. These findings indicate that genistein has a direct inhibitory effect on bone resorption in tissue culture in vitro.