Background and objectives Hyaluronan (HA) is a glucosaminoglycane, mainly known for its lubricating and shock absorbing properties in joints, present in almost every tissue in the body. An association was recently reported between the concentration of HA and back stiffness in patients with ankylosing spondylitis (AS). Depending on the molecular size, HA also has different inflammatory properties. The aim of this study was to analyse plasma levels of HA in ASpatients and a reference population to evaluate any difference between the groups regarding HA concentration and/or molecular weight of HA molecules. We also compared the results in the patient group with variables reflecting inflammation and stiffness as measured by BASFI.
Materials and methods In a cohort of 66 patients with AS and a matched reference population of 30 controls, HA concentration was determined using enzyme-linked immunosorbent assay (ELISA). In subgroups consisting of in all 30 patients and eleven controls, respectively, selected with respect to inflammatory and stiffness status, HA molecular weight was analysed using gasphase electrophoretic molecular mobility analysis (GEMMA). In the patient group, the results were compared with laboratory and other parameters available.
Results No difference was found between the groups regarding HA total concentration (p = 0.77). However, when assessing the molecular weight with GEMMA, a relative increase of high molecular weight (HMW) HA compared to low molecular weight (LMW) HA was discovered. HMW HA (GEMMA peak 4) increased with a fold change of 2.4 (p < 0.02). The levels of a group of cytokines, TNF-α, IL-6, IL-17 and IFN-γ, correlated in the AS patients, where the levels of TNF-α and IL-6 also correlated to the relative increase of HMW HA (peak 4), compared to LMW HA.
There were no significant correlations between HA and the stiffness status of the patients.
Conclusions The correlation of the levels of inflammatory factors to changes in the HA metabolism may indicate an association of HA to the development of AS. Furthermore, HA showed a link to inflammatory processes via TNF. The significant correlation found among the patients between the concentrations of HA of a certain molecular weight and TNF-α is interesting, since TNF-α inhibitors are used successfully in the treatment of AS. However, the patients’ estimation of their stiffness could not be related to the molecular analyses.