Markers of oxidative and nitrosative stress in systemic lupus erythematosus: correlation with disease activity

Abstract

Objective: Free radical-mediated reactions have been implicated as contributors in a number of autoimmune diseases, including systemic lupus erythematosus (SLE). However, the potential for oxidative/nitrosative stress to elicit an autoimmune response or to contribute to disease pathogenesis, and thus be useful when determining a prognosis, remains largely unexplored in humans. This study was undertaken to investigate the status and contribution of oxidative/nitrosative stress in patients with SLE.

Methods: Sera from 72 SLE patients with varying levels of disease activity according to the SLE Disease Activity Index (SLEDAI) and 36 age- and sex-matched healthy controls were evaluated for serum levels of oxidative/nitrosative stress markers, including antibodies to malondialdehyde (anti-MDA) protein adducts and to 4-hydroxynonenal (anti-HNE) protein adducts, MDA/HNE protein adducts, superoxide dismutase (SOD), nitrotyrosine (NT), and inducible nitric oxide synthase (iNOS).

Results: Serum analysis showed significantly higher levels of both anti-MDA/anti-HNE protein adduct antibodies and MDA/HNE protein adducts in SLE patients compared with healthy controls. Interestingly, not only was there an increased number of subjects positive for anti-MDA or anti-HNE antibodies, but also the levels of both of these antibodies were statistically significantly higher among SLE patients whose SLEDAI scores were > or = 6 as compared with SLE patients with lower SLEDAI scores (SLEDAI score <6). In addition, a significant correlation was observed between the levels of anti-MDA or anti-HNE antibodies and the SLEDAI score (r = 0.734 and r = 0.647, respectively), suggesting a possible causal relationship between these antibodies and SLE. Furthermore, sera from SLE patients had lower levels of SOD and higher levels of iNOS and NT compared with healthy control sera.

Conclusion: These findings support an association between oxidative/nitrosative stress and SLE. The stronger response observed in serum samples from patients with higher SLEDAI scores suggests that markers of oxidative/nitrosative stress may be useful in evaluating the progression of SLE and in elucidating the mechanisms of disease pathogenesis.

Figure 1

(A) Anti-MDA- and anti-HNE-protein adduct antibodies in the sera of SLE patients (n=72) and control subjects (n=36). The antibodies were determined by specific ELISAs. (B) Serum anti-MDA- and anti-HNE-protein adduct antibodies in SLE patients with SLEDAI < 6 (n=28) and SLEDAI ≥ 6 (n=44) vs. controls (n=36). The results are means ± SD. * p < 0.05 vs. controls; # p < 0.05 vs. SLEDAI < 6.

Figure 2

Correlation of serum anti-MDA-protein antibodies (A) or anti-HNE-protein antibodies (B) with SLEDAI. The correlation was established by calculating correlation coefficients between anti-MDA-protein antibodies or anti-HNE-protein antibodies and SLEDAI.

Figure 3

MDA-protein adducts and HNE-protein adducts in the sera of SLE patients with SLEDAI < 6 (n=28) and SLEDAI ≥ 6 (n=44) vs. controls (n=36). The results are means ± SD. * p < 0.05 vs. controls; # p < 0.05 vs. SLEDAI < 6.

Figure 4

CuZn SOD (A), nitrotyrosine (B) and iNOS (C) levels in the sera of SLE patients with SLEDAI < 6 (n=28) and SLEDAI ≥ 6 (n=44) vs. controls (n=36). Values are means ± SD. * p < 0.05 vs. controls; # p < 0.05 vs. SLEDAI < 6.