Abstract
The effect of β‐cryptoxanthin, a kind of carotenoid, on osteoclastic cells in mouse marrow culture system in vitro was investigated. The macrophage colony‐stimulating factor (M‐CSF)‐dependent bone marrow macrophages were cultured in the presence of M‐CSF (10 ng/ml) and receptor activator of NF‐κB ligand (RANKL; 25 ng/ml) for 4 days. The osteoclastic cells formed were further cultured in medium containing either vehicle or β‐cryptoxanthin (10^−8^–10^−6^ M) with or without M‐CSF (10 ng/ml) and RANKL (50 ng/ml) for 24–72 h. Osteoclastic cells were significantly decreased with culture of β‐cryptoxanthin (10^−7^ or 10^−6^ M) with or without M‐CSF and RANKL for 24, 48, or 72 h. β‐Cryptoxanthin (10^−8^ M)‐induced decrease in osteoclastic cells were significantly inhibited in the presence of caspase‐3 inhibitor (10^−8^ or 10^−7^ M). Agarose gel electrophoresis showed the presence of low‐molecular‐weight deoxyribonucleic acid (DNA) fragments of adherent cells cultured with β‐cryptoxanthin (10^−7^ or 10^−6^ M) for 24 or 48 h, indicating that the carotenoid induces apoptotic cell death. Apoptosis‐related gene expression was determined using reverse transcription‐polymerase chain reaction (RT‐PCR). Culture with β‐cryptoxanthin (10^−7^ or 10^−6^ M) for 24 or 48 h caused a significant increase in caspase‐3 mRNA expression in the presence or absence of M‐CSF and RANKL, while Bcl‐2 and Apaf‐2 mRNA expressions were significantly increased with culture of β‐cryptoxanthin (10^−7^ or 10^−6^ M) without M‐CSF and RANKL for 24 or 48 h. Akt‐1 mRNA expression was not significantly changed with culture of the carotenoid (10^−7^ or 10^−6^ M) for 24 or 48 h. Moreover, tartrate‐resistant acid phosphatase (TRACP) activity, or TRACP and cathepsin K mRNA expressions were significantly decreased with culture of β‐cryptoxanthin (10^−6^ M) in the presence or absence of M‐CSF and RANKL for 48 h. This study demonstrates that β‐cryptoxanthin has stimulatory effects on apoptotic cell death and suppressive effects on osteoclastic cell function. J. Cell. Biochem. 98: 1185–1195, 2006. © 2006 Wiley‐Liss, Inc.