Fatigue in rheumatoid arthritis and its relation to interleukin-6 serum level

Disease Activity Is More Associated with IL-1 Than with IL-6 in Patients with Rheumatoid Arthritis

Interleukin-1 receptor antagonist (IL-1ra) concentration reflects and is proportional to IL-1 production. Both IL-1 and IL-6 are involved in the pathogenesis of rheumatoid arthritis (RA). However, the relationship of serum levels of these two cytokines to each other in RA patients is not well-understood. In this study, our objective was to analyze the possible linear correlation between IL-1ra and IL-6 in patients with RA, and how both are related to the inflammatory activity of the disease. IL-6 and IL-1ra levels were measured in 407 patients with RA. Linear regression and partial correlations were conducted to analyze the relationship between both cytokines, and their association with RA characteristics. No correlation was found between serum levels of IL-6 and IL-1ra (Pearson's r 0.031, p = 0.61). However, disease activity and acute phase reactants were positively and significantly associated with both cytokines. Nevertheless, after controlling for covariates, disease activity scores were more strongly associated with IL-1ra compared to IL-6. Circulating IL-6 and IL-1ra do not correlate with each other in RA patients. Although both are associated with disease activity and acute phase reactants, the relationship of disease activity to IL-1ra is greater than that to IL-6.

Ultra-Sensitive and Semi-Quantitative Vertical Flow Assay for the Rapid Detection of Interleukin-6 in Inflammatory Diseases

The inflammation biomarker Interleukin 6 (IL-6) exhibits a concentration of less than 7 pg/mL in healthy serum but increases 10–100-fold when inflammation occurs. Increased serum IL-6 has been reported in chronic diseases such as rheumatoid arthritis (RA), as well as in life-threatening acute illnesses such as sepsis and cytokine release syndrome (CRS). This work seeks to meet the demand for rapid detection of serum IL-6 both for rapid monitoring of chronic diseases and for triaging patients with acute illnesses. Following the optimization of several types of gold nanoparticles, membrane pore sizes, and buffer systems, an ultra-sensitive vertical flow assay (VFA) was engineered, allowing the detection of recombinant IL-6 in spiked buffer with a limit of detection (LoD) of 10 pg/mL and a reportable range of 10–10,000 pg/mL with a 15-min assay time. The detection of IL-6 in spiked pooled healthy serum exhibited an LoD of 3.2 pg/mL and a reportable range of 10–10,000 pg/mL. The VFA’s stability was demonstrated over 1-day, two-week, four-week, and six-week storage durations at room temperature. The inter-operator CV and intra-operator CV were determined to be 14.3% and 15.2%, respectively. Three reference zones, high, low, and blank, were introduced into the cartridge to facilitate on-site semi-quantitative measurements across a 6-point semi-quantitative range. Finally, the performance of the IL-6 VFA was validated using 20 RA and 20 healthy control (HC) clinical serum samples, using ELISA as the gold standard platform. The ultra-sensitive, rapid IL-6 VFA could potentially be used to triage patients for intensive care, treatment adjustments, or for monitoring disease activity in inflammatory conditions.

Neuroendocrine and neurophysiological effects of interleukin 6 in rheumatoid arthritis

RA is a chronic, systemic, autoimmune disease characterized by inflammation and degradation of the joints, causing significant negative impact on quality of life. In addition to joint disease, symptoms and co-morbidities associated with RA-namely pain, fatigue and mood disorders-are often as debilitating as the disease itself. The pro-inflammatory cytokine IL-6 plays a critical role in RA-associated pathology. However, a greater understanding of the translational effects of IL-6 outside of the immune system is needed. This review discusses our current understanding of emerging aspects of IL-6 in RA-associated pain, fatigue and mood disorders such as depression and anxiety. This review also describes the clinical effects of IL-6 inhibition on these symptoms and co-morbidities in patients with RA.