Fatty acids in synovial fluid (SF) and inflammatory markers in SF and serum from patients with inflammatory joint diseases. With focus on correlation of n-6 and n-3 polyunsaturated fatty acids to SF cytokines interleukin (IL)-6 and IL-12 and serum Creactive protein
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Little attention has been brought on the lipid content and fatty acid composition directly in synovial fluid (SF) from joints of patients with inflammatory joint diseases. Studies indicate that excessive SF lipids and fatty acids found in patients with rheumatoid arthritis are mainly derived from blood. Several studies have demonstrated a relationship between n-6 and n-3 polyunsaturated fatty acids (PUFA) in blood and inflammation. Generally, a high content of n-6 PUFA, and an increased ratio between the n-6 to n-3 PUFA increases tissue formation of more potent pro-inflammatory eicosanoids and cytokines, whereas an increased content of n-3 long chain PUFA (LCPUFA), may have anti-inflammatory effects. Little is known about these fatty acids with respect to effects in the actual site of inflammation and joint destruction. We have performed a cross-sectional study of synovial fluid (SF) from 86 patients with various inflammatory joint diseases, including rheumatoid arthritis (RA), psoriatic arthritis (PsA), reactive arthritis (ReA), and ankylosing spondylitis (AS). The three latter diseases are all included in the main group of diseases, the spondyloarthropaties (SpA). The SF n-6 and n- 3 PUFA levels, and the ratios between them, were correlated to the specific inflammatory markers, i.e C-reactive protein (CRP) in serum, and interleukin (IL)-6 and IL-12 in SF. There were found significant correlations of n-6 and n-3 PUFA levels, and ratios between them, to levels of inflammatory markers in SF, which included the patient groups with chronic inflammatory joint diseases, i.e the RA, PsA and AS groups. The correlations included most frequently positive correlation of n-6 arachadonic acid (AA) precursors, including linoleic acid (LA) and dihomo-l-linolenic acid (DGLA), to levels of IL-6. The levels of inflammatory markers (serum CRP, SF IL-6 and IL-12) and the correlation between them, and the genereal SF fatty acid composition were also studied in the same patients. There were significantly higher levels of serum CRP in RA patients and AS compared with the PsA group. No differences were found concerning the levels of IL-6 in SF between groups, which represented the most abundant cytokine in SF. As for levels of IL-12, there were found significantly higher levels of the cytokine in SF from RA patients as compared with PsA group and the SpA main group. From the correlation of inflammatory markers, a significant weakly negative correlation between SF IL-12 and IL-6 in RA patients was found. Further, significant weakly positive correlations between serum CRP and SF IL-6 in all patients and the SpA group were found. Approximately half of the fatty acid composition in SF of all patients constitutes of PUFA, mostly n-6, whereas the other half is divided nearly equally between saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA). Significantly differences were only found between the RA and AS subgroup or more frequently SpA main group. All statistically significant differences were seen between the n-6 and n-3 PUFA levels. The RA group had generally higher content of n-3 fatty acids contributing to a lower n-6 to n-3 ratio.
PublisherThe University of Bergen
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