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Cyclooxygenase-2 (COX-2) is thought to be an inducible enzyme, but increasing reports indicate that COX-2 is constitutively expressed in several organs. The status of COX-2 expression in bone and its physiological role remains undefined. Non-selective non-steroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors, which commonly suppress COX-2 activity, were reported to suppress osteoblast proliferation via Akt/FOXO3a/p27(Kip1) signaling, suggesting that COX-2 may be the key factor of the suppressive effects of NSAIDs on proliferation. Although Akt activation correlates with PTEN deficiency and cell viability, the role of COX-2 on PTEN/Akt regulation remains unclear. In this study, we hypothesized that COX-2 may be constitutively expressed in osteoblasts and regulate PTEN/Akt-related proliferation. We examined the localization and co-expression of COX-2 and p-Akt in normal mouse femurs and in cultured mouse (mOBs) and human osteoblasts (hOBs). Our results showed that osteoblasts adjacent to the trabeculae, periosteum and endosteum in mouse femurs constitutively expressed COX-2, while COX-2 co-expressed with p-Akt in osteoblasts sitting adjacent to trabeculae in vivo, and in mOBs and hOBs in vitro. We further used COX-2 siRNA to test the role of COX-2 in Akt signaling in hOBs; COX-2 silencing significantly inhibited PTEN phosphorylation, enhanced PTEN activity, and suppressed p-Akt level and proliferation. However, replenishment of the COX-2 enzymatic product, PGE2, failed to reverse COX-2-dependent Akt phosphorylation. Furthermore, transfection with recombinant human COX-2 (rhCOX-2) significantly reversed COX-2 siRNA-suppressed PTEN phosphorylation, but this effect was reduced when the enzymatic activity of rhCOX-2 was blocked. This finding indicated that the effect of COX-2 on PTEN/Akt signaling is not related to PGE2 but still dependent on COX-2 enzymatic activity. Conversely, COX-1 silencing did not affect PTEN/Akt signaling. Our findings provide new insight into bone physiology; namely, that COX-2 is constitutively expressed in osteoblasts in the dynamic bone growth area, which facilitates osteoblast proliferation via PTEN/Akt/p27(Kip1) signaling., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Recent studies have shown that alendronate (Aln) enhances the osteogenesis of osteoblasts and bone marrow mesenchymal stem cells. In this study, we hypothesize that Aln may act as an osteo-inductive factor to stimulate the osteogenic differentiation of human adipose-derived stem cells (hADSCs) for bone regeneration. The in vitro effect of Aln (1-10 μM) on the osteogenic ability of hADSCs was evaluated by examining mineralization and alkaline phosphatase (ALP) activity. Bone morphogenetic protein 2 (BMP2) expression was measured using a real-time polymerase chain reaction and western blot analysis. Our results indicated that 5 μM Aln was sufficient to enhance BMP2 expression, ALP activity and mineralization in hADSCs. The in vivo effect of locally administered Aln on bone repair was examined in a rat critical-sized (7-mm) calvarial defect that was implanted with a hADSC-seeded poly(lactic-co-glycolic acid) (PLGA) scaffold. Aln (5 μM/100 μl/day) was injected locally into the defect site for one week. New bone formation was evaluated by radiographic and histological analyses at 8 and 12 weeks post-implantation. The expression levels of human BMP2 (hBMP2) and hADSC localization in defect sites were examined using immunohistochemistry analysis and fluorescent in situ hybridization, respectively. Results showed that local treatment of Aln on hADSC-seeded PLGA scaffolds at week 12 had a maximal effect on bone regeneration, enhancing mineralization and bone matrix formation. In addition, hADSCs and hBMP2 were also detected at the defect sites. These results demonstrated that local delivery of Aln, a potent osteo-inductive factor, enhances hADSC osteogenesis and bone regeneration., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Tyrosinase is the first and rate limiting enzyme in the synthesis of melanin pigments for coloring hair, skin, and eyes. As reported in this study, a natural product, (-)-N-formylanonaine isolated from the leaves of Michelia alba D.C. (Magnolianceae), was found to inhibit mushroom tyrosinase with an IC50 of 74.3 microM and to have tyrosinase and melanin reducing activities in human epidermal melanocytes without apparent cytotoxicity to human cells, superior to the known tyrosinase inhibitors, such as kojic acid and 1-phenyl-2-thiourea (PTU). Based on homology modeling, the compound binds the active site by coordinating with two Cu2+ ions. In addition, the compound had antioxidation activities in tests for scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH), reducing power, and chelating metal ions. To our knowledge, this is the first study to reveal the bioactivities of (-)-N-formylanonaine from this plant species., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

People who regularly drink tea have been found to have a higher bone mineral density (BMD) and to be at less risk of hip fractures than those who do not drink it. Green tea catechins such as (-)-epigallocatechin gallate (EGCG) have been reported to increase osteogenic functioning in mesenchymal stem cells. However, its effect on osteoclastogenesis remains unclear. In this study, we investigated the effect of EGCG on RANKL-activation osteoclastogenesis and NF-kappaB in RAW 264.7, a murine preosteoclast cell line. EGCG (10-100 microM) significantly suppressed the RANKL-induced differentiation of osteoclasts and the formation of pits in murine RAW 264.7 cells and bone marrow macrophages (BMMs). EGCG appeared to target osteoclastic differentiation at an early stage but had no cytotoxic effect on osteoclast precursors. In addition, it significantly inhibited RANKL-induced NF-kappaB transcriptional activity and nuclear translocation. We conclude that EGCG inhibits osteoclastogenesis through its activation of NF-kappaB.

To establish a reliable chondrocyte culture system is valuable for investigating the phenotypic properties or the drug effects on chondrocytes. In this study, we established a chondrocyte-enriched culture system by pre-cultivating cells isolated from fetal rat articular and epiphyseal cartilage in suspension prior to cultivating in monolayer. Our results showed that the cultures with 5 days of preculture in liquid suspension produced the highest chondrocyte representative matrix of sulfated glycosaminoglycan compared to those with 1 or 3 days in suspension. We also found that PGE2 (10 and 100 nM) effects on DNA synthesis showed biphasically in 1 day-suspension chondrocyte cultures, similar to those of fibroblast cultures, while PGE2 (1-100 nM) revealed suppressive effects on DNA synthesis in 3 day-suspension chondrocyte cultures, similar to those of osteoblast cultures. However, PGE2 (0.1-100 nM) had no significant effects on the DNA synthesis of 5 days-suspension chondrocyte cultures. These results suggest that the monolayer chondrocyte culture following 5 days of suspension may be a reliable method to exclude the contaminated cells and obtain the chondrocyte-enriched cultures. In this study, we also found that 24-hour treatment of PGE1 (100-1000 nM), but not PGE2 or PGF2 alpha, revealed inhibitory effects on DNA synthesis in chondrocyte-enriched cultures. These phenomena may be as markers to check the characteristics of chondrocyte cultures derived from rat articular and epiphyseal cartilage, and also provide the information for further investigation about chondrocytic functions.