The Underlying Pathogenic Effect Of Impaired Dnase I Activity On Rheumatoid Arthritis

Objective Aberrant formation of neutrophil extracellular traps(NETs) play important role in the pathogenesis of rheumatoid arthritis(RA) and Deoxyribonuclease I(DNase I) is capable of dispersing NETs in vivo. We aimed to investigate the underlying pathogenic effect of DNase I on RA.Methods The study was divided into two parts. ①In part one, we collected serum from 83 patients with RA and 60 healthy volunteers, Serum DNase I activity was measured by radial enzyme-diffusion method. We recorded clinical parameters during the same period when drew patients blood and analysised correlation between DNase I activity and clinical parameters of RA patients. ②In the second part, we extracted synovial fluid(SF) from 27 RA patients and 38 other inflammatory arthritis patients. SF DNase I activity was measured by radial enzyme-diffusion method and SF cfDNA level was measured with Pico Green Kit. We recorded clinical parameters during the same period when extracted SF and analysised correlation between SF cfDNA level and clinical parameters of RA patients. Comparison among groups was tested with two-sample t-test and Mann-Whitney U test and correlation between the two variables was detected using Pearson correlation and Spearman’s rank correlation test.Results ①Results of the first part can be drawn as follows: The activity of DNase I in serum was significantly lower in RA group than that in healthy control group[0.2913(0.2029,0.4064)U/ml vs 0.3980(0.2864, 0.5484)U/ml, P<0.001]. Serum DNase I activity negatively correlated with erythrocyte sedimentation rate(ESR)(r=-0.2862, P= 0.0122), neutrophil cell counts(r=-0.287, P= 0.011) and C-reactive protein(CRP)(r=-0.2790, P= 0.0184), but had no correlation with disease duration, tender joint count(TJC), swollen joint count(SJC), rheumatoid factors(RF), disease activity score-28(DAS28), anti-cyclic cirullinated peptide(anti-CCP)antibodies and X ray stage. ②Results of the second part can be drawn as follows: SF DNase I activity in RA group, ankylosing spondylitis(AS) group and gouty arthritis(GA) group were almost negative. SF cfDNA level in RA group was significantly higher than that in OA group[40.00(12.47, 163.22) ug/ml vs 9.27(4.62, 17.58) ug/ml, P=0.002], but there were no significant difference when compared to AS group [36.80(4.84, 84.82) ug/ml, P=0.428] and GA group[156.72(89.81, 257.11) ug/ml, P=0.132]. The level of SF cfDNA in RA patients did not correlate with disease duration, ESR, CRP, DAS28, neutrophil cell counts, RF-IgG, RF-IgA, RF-IgM,anti-CCP antibodies and X ray stage. In inflammatory arthritis patients, the SF cfDNA level was positively correlated to ESR(r=0.4106, P=0.0116) and CRP(r=0.5747, P=0.0002).Conclusions ①Compared to healthy controls, serum DNase I activity in RA patients was significantly lower and correlated with systemic inflammation which illustrated that serum DNase I activity in patients with higher disease activity was low and DNase I activity levels may serve as evaluation index for disease activity. ②SF cfDNA level in RA group was clearly higher when compared to OA SF cfDNA level, moreover SF DNase I activity significant decrease even deficiency. CFDNA is the major components of NETs, impairment of DNase I activity may be responsible for the enhanced NETs generation and involve in the pathogenesis of RA.