Inactivation of xanthine oxidoreductase is associated with increased joint swelling and nitrotyrosine formation in acute antigen-induced arthritis.
OBJECTIVE
Arthritis is associated with increased articular formation of nitrotyrosine, which may contribute to injury. Nitrotyrosine is formed by nitration of tyrosine by reactive nitrogen species such as peroxynitrite, the formation of which may be enhanced by xanthine oxidoreductase (XOR), since it can generate nitric oxide from nitrite/nitrate, and superoxide during xanthine metabolism. We hypothesized that inactivation of XOR would protect against antigen-induced arthritis (AIA) and decrease nitrotyrosine formation.


METHODS
AIA was induced with methylated bovine serum albumin (mBSA) in three groups of Wistar rats: animals fed on (1) tungsten-enriched chow (0.7 g/kg) (TG), which inactivates XOR, (2) standard chow (SG), and (3) rats treated with allopurinol (50 mg/kg/day; p.o.) (AG). Nitrotyrosine in patella-synovium was quantified by mass spectrometry three weeks after intra-articular (i.a.) antigen injection.


RESULTS
Treatment with tungsten, but not allopurinol, suppressed plasma and articular XOR activity at < or = 0.9% of normal levels. XOR inactivation was associated with increased knee swelling 24-48 hrs post i.a. mBSA, compared with controls (mean increase +/- SEM of knee diameter from baseline of 3.3 +/- 0.5, 2.0 +/- 0.3 and 1.9 +/- 0.2 mm in TG, SG and AG (n = 14 each group), respectively; p < 0.05, TG vs SG, ANOVA). Mean ratio of articular nitrotyrosine-tyrosine (+/- SEM) was increased in the XOR-inactivated group, compared with controls: 12.3 +/- 0.7, 9.6 +/- 0.8 and 10.4 +/- 0.5 pg/microg in TG, SG and AG, respectively; p < 0.05, TG vs SG.


CONCLUSIONS
Contrary to expectation, XOR inactivation was associated with increased joint swelling and articular tyrosine nitration in acute AIA, suggesting a novel, protective role for XOR in inflammatory arthritis.
Klocke
R
R
Department of Pharmacy & Pharmacology/Schoolfor Health, University of Bath, UK. Rainer.Klocke@dgoh.nhs.uk
Mani
A R
AR
Moore
K P
KP
Blake
D R
DR
Mapp
P I
PI
D000493:Allopurinol / Q000627:therapeutic use; D000818:Animals; D001169:Arthritis, Experimental / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D002417:Cattle; D004791:Enzyme Inhibitors / Q000627:therapeutic use; D007596:Joints / Q000201:enzymology* / Q000473:pathology; D008297:Male; D011859:Radiography; D051381:Rats; D017208:Rats, Wistar; D012710:Serum Albumin, Bovine / Q000008:administration & dosage; D013264:Stifle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology; D013583:Synovial Membrane / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D014414:Tungsten / Q000627:therapeutic use; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism*; D014968:Xanthine Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism
D004791:Enzyme Inhibitors; D012710:Serum Albumin, Bovine; C002744:3-nitrotyrosine; D014443:Tyrosine; D000493:Allopurinol; D014968:Xanthine Dehydrogenase; D014414:Tungsten