Activation of diverse eicosanoid pathways in osteoarthritic cartilage: a lipidomic and genomic analysis.

Objective: Non-steroidal anti-inflammatory drugs (NSAIDs) that are prescribed for treatment of osteoarthritis (OA) symptoms including pain and inflammation target the production eicosanoids which exhibit numerous functions in various cell types. In these studies, we have (a) identified the diverse eicosanoid pathways that are activated in human chondrocytes of normal and OA cartilage, (b) delineated the modulation of eicosanoids in the presence of NSAIDS and selective COX-2 inhibitors, and (c) characterized eicosanoid products and various transcripts modulated by various inhibitors of eicosanoids in human OA cartilage by gene expression arrays.

Methods: Immunoassay analysis of culture supernatants were utilized to determine the spectrum of eicosanoids derived from both the cyclooxygenase (COX) and lipoxygenase (LOX) pathways of normal and human OA cartilage in ex-vivo conditions. Human OA cartilage was incubated in ex-vivo conditions to examine spontaneous or IL-1 induced production of eicosanoids in the presence of various COX inhibitors. Gene expression analysis was performed to analyze the expression of mRNA in the presence and absence of COX-2 inhibitors in OA cartilage in ex-vivo conditions.

Results: Normal and OA human cartilage explants produced multiple eicosanoids of the COX and LOX pathways. PGF1α, PGF2α, PGE2 > TXB2, PGD2, and LTB4 were spontaneously generated by normal and OA cartilage. Among these, elevated levels of PGE2 and LTB4 were generated in OA as compared to normal cartilage. IL-1 treatment further enhanced these eicosanoids production. Treatment of OA cartilage explants with cyclooxygenase inhibitors (celecoxib & indomethacin) augmented LTB4 accumulation by 2- to 4-fold. A follow-up pharmacogenomic analysis identified approximately 90 cytokine and growth factor related transcripts that were modulated following selective COX-2 inhibition.

Conclusion: These studies for the first time demonstrate that normal and OA cartilage generates multiple and differential eicosanoid products. Inhibition of the COX- pathway in human OA cartilage caused accumulation of end products (LTB4) of the 5LO pathway. Furthermore, celecoxib, a selective COX-2 inhibitor, regulated numerous genes in cartilage, which are linked to the NFkB and AP-1 pathways at the mRNA level. In conclusion, these experiments demonstrate the complex and pleotropic role of eicosanoids in human cartilage homeostasis and pathophysiology of OA.