Synthesis and release of human cartilage matrix proteoglycans are differently regulated by nitric oxide and prostaglandin-E2.
OBJECTIVE
Recent studies showed beneficial effects of COX-2 inhibition on proteoglycan turnover of both IL-1beta/tumour necrosis factor alpha (TNFalpha) damaged cartilage and of osteoarthritic cartilage. Although proteoglycan release and content were normalised, proteoglycan synthesis was only partially influenced. Prostaglandin-E2 is the main product formed by COX-2. We therefore evaluate the role of prostaglandin-E2 in relation to nitric oxide in disturbing cartilage proteoglycan turnover.


METHODS
Human healthy cartilage, alone or in the presence of IL-1beta+TNFalpha, was cultured for 7 days with or without prostaglandin-E2 or the selective COX-2 inhibitor (celecoxib 10 microM). Changes in cartilage matrix proteoglycan turnover, levels of prostaglandin-E2 and nitric oxide were determined.


RESULTS
Proteoglycan synthesis and release of the cartilage were not affected by prostaglandin-E2 alone. Addition of IL-1beta+TNFalpha to healthy cartilage resulted in inhibition of proteoglycan synthesis and increase in proteoglycan release. When prostaglandin-E2 was added, in addition to IL-1beta+TNFalpha, proteoglycan release increased further, but proteoglycan synthesis was not influenced further. Addition of a selective COX-2 inhibitor to the IL-1beta+TNFalpha treated cartilage inhibited the enhanced prostaglandin-E2 production and almost completely normalised proteoglycan release, whereas synthesis remained unaffected. Also, the enhanced NO-levels remained elevated. Prostaglandin-E2 levels correlated significantly with proteoglycan release, whereas NO levels correlated significantly with proteoglycan synthesis.


CONCLUSIONS
The present results suggest involvement of prostaglandin-E2 in enhanced cartilage proteoglycan release but not synthesis, although healthy cartilage has to be sensitised by IL-1beta+tumour necrosis factor alpha (TNFalpha). IL-1beta+TNFalpha induced NO seems to be involved in inhibition of proteoglycan synthesis, independent of prostaglandin-E2, and thus seems insensitive to regulation by (selective) COX-2 inhibitors.
Mastbergen
S C
SC
Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, The Netherlands. s.mastbergen@umcutrecht.nl
Bijlsma
J W J
JW
Lafeber
F P J G
FP
D000368:Aged; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D000068579:Celecoxib; D051546:Cyclooxygenase 2 / Q000378:metabolism; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000378:metabolism*; D005260:Female; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism*; D010007:Osteochondritis / Q000378:metabolism; D011509:Proteoglycans / Q000032:analysis / Q000096:biosynthesis* / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D018709:Statistics, Nonparametric; D013449:Sulfonamides / Q000494:pharmacology; D046509:Tissue Culture Techniques; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D052246:Cyclooxygenase 2 Inhibitors; D007375:Interleukin-1; D011509:Proteoglycans; D011720:Pyrazoles; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D000068579:Celecoxib; D015232:Dinoprostone