Statistics Results are expressed as mean SEM. Statistical analyses were performed by using GraphPad Instat 3. 0. Two groups were analyzed by selleck inhibitor using paired or unpaired t tests. For three groups and more, statistical analyses were per formed by using the one way ANOVA Bonferroni multiple comparison test or Inhibitors,Modulators,Libraries the repeated measures ANOVA, followed by Tukey multiple comparison test. Signifi cance was set at P 0. 05. Results Human osteoblasts internalize MSU OBs are known to ingest MSU microcrystals in vitro with some efficacy. These observations, together with the pathologic findings of MSU included in bone matrix and a scarce presence of OB close to tophaceous bone lesions, suggest that Inhibitors,Modulators,Libraries OBs are unable to destroy these crystals. Thus, MSU could remain intact inside OBs and deregulate specialized functions of OBs.

To evaluate the fate of MSU in the presence of OBs, live confluent primary human OBs were cultured Inhibitors,Modulators,Libraries with graded concentrations of MSU during 7 days. OBs that phagocytized MSU showed, after 48 hours of incubation, consistent morphologic changes, as studied with con focal microscopy. OBs dose dependently internalized MSU from 0. 1 to 1 mg 106 cells with an optimal effect at 0. 5 mg 106 cells, followed by a plateau. More than 90% of OBs had MSU internalized in large and fluid filled vacuoles, each containing a single microcrystal. Volume and shape of vacuoles depend on crystal size. Inhibitors,Modulators,Libraries Vacuoles were individualized with light microscopy after, at least, 24 hours of incuba tion. Numbers of vacuoles with MSU averaged 30 per OB.

Most of MSU were completely internalized in cells, but some crystals remained partially engulfed or along side the membrane. After 7 days of culture, phagocytosis of 0. 5 mg MSU 106 OBs was associated with unchanged vacuoles. These data suggest a pro longed process that could partly detoxify the cells by retaining Inhibitors,Modulators,Libraries MSU microcrystals in permanent phagosomes with a final noncapacity of OB to eliminate MSU containing vacuoles. MSU affects OB proliferation but not viability Because MSU can modulate cellular apoptosis and proliferation, the impact of MSU on OB sur vival and proliferation was evaluated before studying specialized OB functions. MSU at concentrations up to 1 mg 106 cells for 72 hours of culture did not modify the incorporation of propidium iodide by OBs, and an average of 80% PI negative OBs was rou tinely obtained in control conditions, as well as in the presence of MSU.

In contrast, the prolif eration rate of MSU treated OBs dose dependently decreased from 0. 1 to 1 mg MSU 106 cells. The significant threshold reduction promotion was observed at 0. 3 mg MSU, with a plateau of reduction attained at 0. 8 mg MSU. The respective proliferation rates were re duced from 30% to 55% of the OB proliferation rate in control conditions.