Inhibition of Osteoarthritis-Related Molecules by Isomucronulatol 7-O-β-d-glucoside and Ecliptasaponin A in IL-1β-Stimulated Chondrosarcoma Cell Model

Osteoarthritis (OA) is the common form of arthritis and is characterized by disability and cartilage degradation. Although natural product extracts have been reported to have anti-osteoarthritic effects, the potential bioactivity of Ryupunghwan (RPH), a traditional Korean medicinal botanical formula that contains Astragalus membranaceus, Turnera diffusa, Achyranthes bidentata, Angelica gigas, Eclipta prostrata, Eucommia ulmoides, and Ilex paraguariensis, is not known well. Therefore, the inhibitory effects of single compounds isolated from RPH on the OA-related molecules were investigated using IL-1β-stimulated chondrosarcoma SW1353 (SW1353) cell model. Two bioactive compounds, isomucronulatol 7-O-β-d-glucoside (IMG) and ecliptasaponin A (ES) were isolated and purified from RPH using column chromatography, and then the structures were analyzed using ESI-MS, ¹H-NMR, and ¹³C-NMR spectrum. The expression or amount of matrix metalloproteinase 13 (MMP13), COX1/2, TNF-α, IL-1β or p65 was determined by RT-PCR, Western blot, and enzyme-linked immunosorbent assay (ELISA). RPH pretreatment reduced the expression and amounts of MMP13, and the expression of collagen II, COX1/2, TNF-α, IL-1β or p65, which were increased in IL-1β-stimulated SW1353 cells. IMG reduced the expression of all OA-related molecules, but the observed inhibitory effect was less than that of RPH extract. The other single compound ES showed the reduced expression of all OA-related molecules, and the effect was stronger than that in IMG (approximately 100 fold). Combination pretreatment of both single components remarkably reduced the expression of MMP13, compared to each single component. These synergic effects may provide potential molecular modes of action for the anti-osteoarthritic effects of RPH observed in clinical and animal studies.

ATR signaling controls the bystander responses of human chondrosarcoma cells by promoting RAD51-dependent DNA repair

PURPOSE

Radiation-induced bystander effect (RIBE) frequently is seen as DNA damage in unirradiated bystander cells, but the repair processes initiated in response to that DNA damage are not well understood. RIBE-mediated formation of micronuclei (MN), a biomarker of persistent DNA damage, was previously observed in bystander normal fibroblast (AG01522) cells, but not in bystander human chondrosarcoma (HTB94) cells. The molecular mechanisms causing this disparity are not clear. Herein, we investigate the role of DNA repair in the bystander responses of the two cell lines.

METHODS

Cells were irradiated with X-rays and immediately co-cultured with un-irradiated cells using a trans-well insert system in which they share the same medium. The activation of DNA damage response (DDR) proteins was detected by immunofluorescence staining or Western blotting. MN formation was examined by the cytokinesis-block MN assay, which is a robust method to detect persistent DNA damage.

RESULTS

Immunofluorescent foci of γH2AX and 53BP1, biomarkers of DNA damage and repair, revealed a greater capacity for DNA repair in HTB94 cells than in AG01522 cells in both irradiated and bystander populations. Autophosphorylation of ATR at the threonine 1989 site was expressed at a greater level in HTB94 cells compared to AG01522 cells at the baseline and in response to hydroxyurea treatment or exposure to 1 Gy of X-rays. An inhibitor of ATR, but not of ATM, promoted MN formation in bystander HTB94 cells. In contrast, no effect of either inhibitor was observed in bystander AG01522 cells, indicating that ATR signaling might be a pivotal pathway to preventing the MN formation in bystander HTB94 cells. Supporting this idea, we found an ATR-dependent increase in the fractions of bystander HTB94 cells with pRPA2 S33 and RAD51 foci. A blocker of RAD51 facilitated MN formation in bystander HTB94 cells.

CONCLUSION

Our results indicate that HTB94 cells were likely more efficient in DNA repair than AG01522 cells, specifically via ATR signaling, which inhibited the bystander signal-induced MN formation. This study highlights the significance of DNA repair efficiency in bystander cell responses.