Fibronectin fragments elevate nitric oxide (NO) and inducible NO synthetase (iNOS) levels in bovine cartilage and iNOS inhibitors block fibronectin fragment mediated damage and promote repair.
OBJECTIVE
To determine whether fibronectin fragments (Fn-f) upregulate nitric oxide (NO) and inducible NO synthetase (iNOS) levels in explants and whether iNOS inhibitors block Fn-f mediated cartilage damage or promote repair.


METHODS
Bovine cartilage explants were studied.


METHODS
Explants were cultured with Fn-f and involvement of NO pathway investigated.


METHODS
Induction of iNOS was tested by RT-PCR. Upregulation of iNOS protein was visualized by Western blotting. Proteoglycan (PG) content of cartilage treated with iNOS inhibitors was tested by dye binding assays of cartilage digests.


RESULTS
Fn-fs elevated NO release in explants and upregulated iNOS protein and mRNA while native Fn had only weak activity. Three different iNOS inhibitors blocked Fn-f mediated PG depletion from explants and facilitated restoration of PG in pre-damaged cartilage.


CONCLUSIONS
The Fn-f cartilage damaging pathway involves upregulation of iNOS. Interestingly, iNOS inhibitors not only blocked damage but repaired damaged cartilage. This may be the first report of reparative activities of iNOS inhibitors.
Department of Biochemistry, Rush Medical College at Rush-Presbyterian-St. Luke's Medical Center, 1653 West Congress Parkway, Chicago, IL 60612-3864, USA.
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Pichika
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Homandberg
D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D002417:Cattle; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005353:Fibronectins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D010446:Peptide Fragments / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology; D011509:Proteoglycans / Q000378:metabolism; D046509:Tissue Culture Techniques; D014945:Wound Healing / Q000187:drug effects*
D004791:Enzyme Inhibitors; D005353:Fibronectins; D010446:Peptide Fragments; D011509:Proteoglycans; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II