Abstract
The effect of β‐cryptoxanthin, a kind of carotenoid, on cell differentiation and mineralization in osteoblastic MC3T3‐E1 cells was investigated. Cells were cultured for 72 h in a minimum essential medium containing 10% fetal bovine serum (FBS), and the cells with subconfluency were changed to a medium containing either vehicle or β‐cryptoxanthin (10^−8^ to 10^−6^ M) without FBS. Cells were cultured for 3 to 21 days. Gene expression in osteoblastic cells was determined using reverse transcription‐polymerase chain reaction (RT‐PCR). Culture with β‐cryptoxanthin (10^−7^ or 10^−6^ M) for 3 days caused a significant increase in Runx2 type 1, Runx2 type 2, α1 (I) collagen, and alkaline phosphatase mRNA levels in osteoblastic cells. These increases were completely blocked in the presence of cycloheximide, an inhibitor of protein synthesis, or 5,6‐dichloro‐1‐β‐D‐ribofuranosylbenzimidazole (DRB), an inhibitor of transcriptional activity. Meanwhile, vitamin A (10^−6^ M) did not have a significant effect on Runx2 type 1 mRNA expression in the cells. The effect of β‐cryptoxanthin (10^−6^ M) in stimulating Runx2 type 1 and α1 (I) collagen mRNA levels, protein content, and alkaline phosphatase activity in the cells was also seen in the presence of vitamin A (10^−6^ M), suggesting that the mode of β‐cryptoxanthin action differs from that of vitamin A. Prolonged culture with β‐cryptoxanthin (10^−6^ M) for 3 to 21 days caused a significant increase in cell number, deoxyribonucleic acid (DNA) content, protein content, and alkaline phosphatase activity in osteoblastic cells, suggesting that β‐cryptoxanthin stimulates cell proliferation and differentiation. Moreover, culture with β‐cryptoxanthin (10^−7^ or 10^−6^ M) for 5 to 21 days caused a remarkable increase in mineralization. This study demonstrates that β‐cryptoxanthin has a stimulatory effect on cell differentiation and mineralization due to enhancing gene expression of proteins, which involve in bone formation in osteoblastic MC3T3‐E1 cells. © 2005 Wiley‐Liss, Inc.