Abstract
Protein nitration is a prominent feature of inflammatory processes in the joint. We have developed immunoassays specific for a peptide of the α-helical region of type II collagen
108HRGYPGLDG
116 (Coll 2-1) and its nitrated form
108HRGY(NO
2)PGLDG
116 (Coll 2-1 NO
2) in biological fluids.
Coll 2-1 and Coll 2-1 NO
2 peptides were injected into rabbits. Two antisera (D3 and D37) were selected for their specificity and affinity and used to develop specific immunoassays. Coll 2-1 and Coll 2-1 NO
2 were measured in sera of 242 healthy subjects (N), 67 patients with primary knee osteoarthritis (OA) and 19 patients with rheumatoid arthritis (RA).
In healthy subjects, Coll 2-1 and Coll 2-1 NO
2 concentrations were 125.13
±
3.71
nM and 0.16
±
0.08
nM, respectively. In OA and RA, Coll 2-1 and Coll 2-1 NO
2 serum levels were found to be significantly increased compared to controls of the same range of age (Coll 2-1: OA: 200.80
±
8.98
nM, RA: 172.30
±
19.05
nM, normal: 126.60
±
6.70
nM and Coll 2-1 NO
2: OA: 0.26
±
0.02, RA: 0.38
±
0.05, normal: 0.12
±
0.01
nM). Coll 2-1 NO
2 levels were significantly more elevated in RA than in OA patients (
P
<
0.05). As a consequence, the ratio Coll 2-1 NO
2/Coll 2-1 was 1.6 times higher in RA than in OA subjects. No relationship was found between the radiological OA severity and the levels of Coll 2-1 and Coll 2-1 NO
2 in serum. Coll 2-1 NO
2, but not Coll 2-1, was correlated with C-reactive protein in the sera of OA and RA patients.
The determination of both Coll 2-1 and Coll 2-1 NO
2 in serum of arthritic patients seems to be a promising useful tool for the detection of oxidative-related cartilage degradation episode. Further, these markers could be helpful for monitoring the effects of anti-inflammatory or antioxidant drugs on cartilage degradation.