beta-Cryptoxanthin stimulates bone formation and inhibits bone resorption in tissue culture in vitro

The effect of beta-cryptoxanthin, which is greatly present in fruits, has not been clarified so far on bone metabolism. The effect of beta-cryptoxanthin on bone formation and bone resorption was investigated in tissue culture in vitro. Rat femoral-diaphyseal (cortical bone) and -metaphyseal (trabecular bone) tissues were cultured for 48 h in Dulbecco's modified Eagle's medium (high glucose, 4.5%) supplemented with antibiotics and bovine serum albumin. The experimental cultures contained 10(-8)-10(-5) M beta-cryptoxanthin. The presence of beta-cryptoxanthin (10(-6) or 10(-5) M) caused a significant increase in calcium content, alkaline phosphatase activity and deoxyribonucleic acid (DNA) content in the diaphyseal and metaphyseal tissues. These increases were completely prevented in the presence of cycloheximide (10(-6) M), an inhibitor of protein synthesis. beta-Carotene (10(-6) or 10(-5) M) or xantine (10(-6) or 10(-5) M) had no effect on the diaphyseal and metaphyseal calcium contents. The bone-resorbing factors parathyroid hormone (1-34) (PTH; 10(-7) M) or prostaglandin E2 (PGE2; 10(-5) M) caused a significant decrease in calcium content in the diaphyseal and metaphyseal tissues. The decrease in bone calcium content induced by PTH or PGE2 was completely inhibited by beta-cryptoxanthin (10(-8)-10(-6) M). In addition, beta-cryptoxanthin (10(-8)-10(-6) M) completely inhibited the PTH (10(-7) M)- or PGE, (10(-5) M)-induced increase in medium glucose consumption and lactic acid production by diaphyseal and metaphyseal tissues. The inhibitory effect of beta-cryptoxanthin (10(-7) M) on PTH (10(-7) M)- or PGE2 (10(-5) M)-stimulated decrease in the diaphyseal calcium content was significantly prevented in the presence of 10(-3) M vanadate, an inhibitor of protein tyrosine phosphatase. Vanadate (10(-3) M) did not have a significant effect on calcium content and lactic acid production in control bone tissues. The present study demonstrates that beta-cryptoxanthin has a direct stimulatory effect on bone formation and an inhibitory effect on bone resorption in tissue culture in vitro.