Nitrite-mediated protection against hypochlorous acid-induced chondrocyte toxicity: a novel cytoprotective role of nitric oxide in the inflamed joint?
OBJECTIVE
To examine the potential consequences of overproduction of nitric oxide (NO) and nitrite (NO(2) (-)) in the inflamed rheumatoid joint.


METHODS
Human articular chondrocytes in culture were exposed to HOCl (hypochlorous acid, a physiologic oxidant formed in increased amounts at sites of chronic inflammation), and assays of cell viability, intracellular ATP and glutathione (GSH), and lactate dehydrogenase (LDH) were performed. HOCl-induced lipid peroxidation and activation of the MAP kinases ERK-1/2, JNK-1/2, and p38 were also measured. The modulatory effects of NO-derived nitrite (NO(2) (-)) and nitrate (NO(3) (-)) on HOCl-mediated chondrocyte toxicity were investigated.


RESULTS
Exposure of human articular chondrocytes to HOCl resulted in a concentration- and time-dependent loss of viability, decrease in ATP and GSH levels, LDH leakage, and cell death. HOCl induced significant lipid peroxidation as well as activation of the MAP kinases ERK-1/2 and p38 but not JNK-1/2. However, the presence of NO(2) (-) but not NO(3) (-) substantially decreased HOCl-dependent cellular toxicity even when NO(2) (-) was added at low (microM) concentrations. In sharp contrast, NO(2) (-) (1 mM) did not inhibit superoxide-, hydroxyl radical-, H(2)O(2)-, or peroxynitrite-mediated cytotoxicity. Furthermore, culture media from cells treated with interleukin-1beta (to generate NO and NO(2) (-)) offered significantly more protection against HOCl-mediated cytotoxicity than culture media from untreated cells.


CONCLUSIONS
These data suggest that NO(2) (-) accumulation at chronically inflamed sites where both HOCl and NO are overproduced may be cytoprotective against damage induced by HOCl. Accumulation of NO(2) (-) could represent a novel cytoprotective role of NO in inflamed joints. A mechanism for this is suggested.
Whiteman
Matthew
M
National University of Singapore, Republic of Singapore. bchwml@nus.edu.sg
Rose
Peter
P
Siau
Jia Ling
JL
Halliwell
Barry
B
D000255:Adenosine Triphosphate / Q000378:metabolism; D002358:Cartilage, Articular; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D019610:Cytoprotection / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D006997:Hypochlorous Acid / Q000633:toxicity*; D007375:Interleukin-1 / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology; D009573:Nitrites / Q000378:metabolism / Q000494:pharmacology*; D016877:Oxidants / Q000633:toxicity*
D017077:Culture Media, Conditioned; D007375:Interleukin-1; D009566:Nitrates; D009573:Nitrites; D016877:Oxidants; D006997:Hypochlorous Acid; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D020928:Mitogen-Activated Protein Kinases; D005978:Glutathione