Extracellular mitochondrial DNA and oxidatively damaged DNA in synovial fluid of patients with rheumatoid arthritis

Abstract

We investigated whether plasma and synovial fluid (SF) samples from patients with rheumatoid arthritis (RA) contained extracellular mitochondrial DNA (mtDNA) or the oxidatively damaged DNA adduct 8-hydroxy-2′-deoxyguanosine (8-oxodG). Moreover, we correlated the laboratory findings of the patients with RA with their levels of mtDNA and 8-oxodG. SF and plasma samples from 54 patients with RA, SF from 30 non-arthritic control subjects, and plasma from 22 healthy volunteers were collected. The samples were subjected to polymerase chain reaction (PCR) using mitochondrial genomic primers, and the products were analyzed by SDS-polyacrylamide-gel electrophoresis. The intensities of the PCR-amplified bands were quantified and normalized to a reference sample. Furthermore, the SF samples were assayed by enzyme-linked immunosorbent assay for 8-oxodG. Extracellular PCR-amplifiable mtDNA was detected in the SF of 38 of 54 (70%) patients with RA, but not in any of the SF controls. PCR-amplifiable mtDNA was detected in the plasma of 30 of 54 (56%) of patients with RA and in 6 of 22 (27%) of the healthy volunteers. The levels of mtDNA in the plasma and SF samples of patients with RA were significantly higher (P < 0.0001) than in the respective control samples. The presence of both mtDNA and 8-oxodG in SF was significantly correlated with the presence of rheumatoid factor in the patients with RA. Extracellular mtDNA and oxidized DNA were detected in the SF of the great majority of patients with RA, but were absent or present at low levels in the control SF. These findings indicate that endogenous nucleic acid compounds might participate in joint inflammation by activating immune cells in the joints to produce pro-inflammatory cytokines.

Oxidative modification enhances the immunostimulatory effects of extracellular mitochondrial DNA on plasmacytoid dendritic cells

“…Furthermore, a significant correlation was observed between the levels of 8-oxodG and rheumatoid factor positivity. Higher concentrations of 8-oxodG (>1.5 ng/ml) in the synovial fluid were also associated with more severe clinical manifestations, but the correlations were found not to be statistically significant [42]. It is worth mentioning that source of the elevated oxidatively damaged DNA adducts (mitochondrial DNA or nuclear DNA) was not identified in that study.…”

“…In a prior study extracellular mtDNA and 23 oxidized DNA (8-oxo-7,8-dihydro-2'-deoxyguanosine, 8-oxodG) were detected in the synovial fluid samples of the great majority of patients with rheumatoid arthritis, but were absent or present at low levels in the samples of healthy controls [42]. Furthermore, a significant correlation was observed between the levels of 8-oxodG and rheumatoid factor positivity.…”

“…Mitochondria contain enzymes whose function is to remove these lesions, thus reversing the effects of oxidative insult and preventing mutations [40,41]. However, when oxidative damage to DNA is excessive and mtDNA is released before repair, e.g., under inflammatory processes, it may contain high level of 8-oxoG [42]. In this study we investigated the immunomodulating potential of this 8-oxoG-enriched mtDNA on both human and murine pDCs.…”

Oxidative Stress and the Use of Antioxidants for the Treatment of Rheumatoid Arthritis

“…These increased mitochondrial ROS levels showed a statistically significant correlation with plasma TNF-α levels in RA patients. Another study [115] analyzed plasma and SF from 54 RA patients to see if either contained mitochondrial DNA (mtDNA) or the oxidatively damaged DNA adduct, 8-hydroxy-2'-deoxyguanosine. Elevated mtDNA was identified in both the SF and plasma from RA patients versus healthy controls, and the presence of mtDNA and the oxidized DNA adduct in SF was significantly correlated with the presence of RF in these RA patients There has been a growing awareness that a variety of cell types, including macrophages, neutrophils, mast cells, B cells and T cells contribute to the etiology of RA particularly in the SF [5] .…”

The Impact of Circulating Mitochondrial DNA on Cardiomyocyte Apoptosis and Myocardial Injury After TLR4 Activation in Experimental Autoimmune Myocarditis

“…MtDNA functions an important role in the development of different kinds of inflammatory diseases, such as RA, sterile SIRS, diabetes mellitus, Parkinson’s disease and heart diseases [11, 13, 17, 50, 51]. Mitochondrial damage characteristic with membrane permeability transition, ROS production and insufficient mitophagy corporately leads to mtDNA secretion, which exerts potent activation effect on inflammation response [12, 47, 52].…”