Epigenetic regulation of 15-lipoxygenase-1 expression in human chondrocytes by promoter methylation

OBJECTIVE AND DESIGN

15-Lipoxygenase-1 (15-LOX-1) catalyzes the biosynthesis of many anti-inflammatory and immunomodulatory lipid mediators and was reported to have protective properties in several inflammatory conditions, including osteoarthritis (OA). This study was designed to evaluate the expression of 15-LOX-1 in cartilage from normal donors and patients with OA, and to determine whether it is regulated by DNA methylation.

METHODS

Cartilage samples were obtained at autopsy from normal knee joints and from OA-affected joints at the time of total knee joint replacement surgery. The expression of 15-LOX-1 was evaluated using real-time polymerase chain reaction (PCR). The role of DNA methylation in 15-LOX-1 expression was assessed using the DNA methyltransferase inhibitor 5-Aza-2'-desoxycytidine (5-Aza-dC). The effect of CpG methylation on 15-LOX-1 promoter activity was evaluated using a CpG-free luciferase vector. The DNA methylation status of the 15-LOX-1 promoter was determined by pyrosequencing.

RESULTS

Expression of 15-LOX-1 was upregulated in OA compared to normal cartilage. Treatment with 5-Aza-dC increased 15-LOX-1 mRNA levels in chondrocytes, and in vitro methylation decreased 15-LOX-1 promoter activity. There was no difference in the methylation status of the 15-LOX-1 gene promoter between normal and OA cartilage.

CONCLUSION

The expression level of 15-LOX-1 was elevated in OA cartilage, which may be part of a repair process. The upregulation of 15-LOX-1 in OA cartilage was not associated with the methylation status of its promoter, suggesting that other mechanisms are involved in its upregulation.

Abietic acid attenuates IL-1β-induced inflammation in human osteoarthritis chondrocytes

Abietic acid has been reported to have anti-inflammatory activity. However, whether abietic acid has anti-inflammatory effects against osteoarthritis (OA) remains unclear. The present study aimed to measure the anti-inflammatory effects of abietic acid on OA in vitro. Human osteoarthritis chondrocytes were pretreated with abietic acid 1 h before IL-1β treatment. The results showed that treatment of abietic acid significantly inhibited IL-1β-induced TNF-α, NO, PGE2 production, and COX-2 expression. Abietic acid also concentration-dependently suppressed MMP1, MMP3, and MMP13 production induced by IL-1β. Moreover, the increased phosphorylation levels of NF-κB p65 and IκBα were inhibited by the treatment of abietic acid. We also found that the expression of PPAR-γ was increased by abietic acid. The inhibition of abietic acid on TNF-α, NO, and PGE2 production were reversed by GW9662, the inhibitor of PPAR-γ. In conclusion, the study elucidated abietic acid suppressed IL-1β-induced inflammation in human osteoarthritis chondrocytes by activating PPAR-γ.

Effects of platycodin D on IL-1β-induced inflammatory response in human osteoarthritis chondrocytes

Platycodin D (PYD), a major saponin derived and isolated from the roots of Platycodon grandiflorum, has been reported to have anti-inflammatory and anti-tumor effects. The present study aimed to investigate the effects of PYD on IL-1β-stimulated human osteoarthritis chondrocytes. Chondrocytes were treated with PYD 1h before IL-1β treatment. The levels of MMP1, MMP13, IL-8, RANTES, PGE2, and NO were measured in this study. The expression of LXRα, NF-κB, and IκBα were detected by western blot analysis. The results showed that PYD significantly inhibited IL-1β-induced MMP1, MMP13, IL-8, RANTES, PGE2, and NO production. PYD also suppressed IL-1β-induced NF-κB activation. Furthermore, the expression of LXRα was up-regulated by PYD in a dose-dependent manner. In addition, LXRα siRNA inhibited the effects of PYD on MMP1, MMP13, PGE2, and NO production in human osteoarthritis chondrocytes. In conclusion, these results suggested that PYD attenuated IL-1β-induced inflammatory response in osteoarthritis chondrocyte by activating LXRα.

Schisantherin A suppresses interleukin-1β-induced inflammation in human chondrocytes via inhibition of NF-κB and MAPKs activation

Osteoarthritis is a degenerative joint disease that is characterized by the inflammation of synovium. Schisantherin A (SchA), a dibenzocyclooctadiene lignan isolated from the fruit of Schisandra sphenanthera, has been shown to have anti-inflammatory activity. The aim of this study was to investigate the anti-inflammatory effects of SchA on interleukin-1β (IL-1β)-stimulated human osteoarthritis chondrocytes. Human osteoarthritis chondrocytes were pretreated with SchA 1h before IL-1β treatment. The effects of SchA on NO, PGE2, iNOS, COX-2, and TNF-α production were detected in this study. The production of MMP-1, MMP3, MMP13 were measured by ELISA. The expression of NF-κB and MAPKs were detected by western blotting. Our results showed that SchA inhibited IL-1β-induced NO, PGE2, and TNF-α production in a dose-dependent manner. Moreover, IL-1β-induced MMP1, MMP3, and MMP13 expression were significantly inhibited by treatment of SchA. In addition, SchA significantly inhibited IL-1β-induced NF-κB and MAPKs activation. Taken together, these results suggest that SchA exhibits anti-inflammatory effects against IL-1β-stimulated chondrocytes by blocking NF-κB and MAPKs signaling pathways.

Taraxasterol inhibits IL-1β-induced inflammatory response in human osteoarthritic chondrocytes

Osteoarthritis (OA), a chronic degenerative joint disease, is a leading cause of disability among elderly patients. Taraxasterol, a pentacyclic-triterpene isolated from Taraxacum officinale, has been shown to have anti-inflammatory effects. However, the protective effect of taraxasterol on OA remains unclear. In order to provide a scientific basis for the applicability of taraxasterol in OA, the anti-inflammatory effects of taraxasterol on IL-1β-stimulated osteoarthritic chondrocytes were investigated. Chondrocytes were pretreated with taraxasterol 1h before IL-1β treatment. The productions of MMP-1, MMP3, MMP13, PGE2 and NO were measured by ELISA and Griess reaction. The expression of COX-2, iNOS, and NF-κB was detected by western blot analysis. Our results demonstrated that taraxasterol dose-dependently suppressed MMP-1, MMP3, MMP13, PGE2 and NO production induced by IL-1β. The expression of COX-2 and iNOS was also inhibited by taraxasterol. Western blot analysis showed that taraxasterol suppressed IL-1β-induced NF-κB activation in a dose-dependent manner. Taken together, we found that taraxasterol protected human chondrocytes by inhibiting MMPs, NO and PGE2 production. Taraxasterol may be a useful agent for prevention and treatment of OA.