Background and objectives Rheumatoid arthritis (RA) is a chronic inflammatory disease of the joints. For RA treatment, primarily drugs are used. However additional pain relieve is achieved when RA patients are treated either locally with low doses of sparsely ionising photons or by exposure to Radon. Main contributors to the inflammatory state in RA are adipokines, mainly produced by adipose tissue. To assess the effect of low radiation doses, we measured levels of adipokines in serum of patients with musculoskeletal diseases during Radon treatment. In additional in vitro experiments, we examined whether irradiation modifies the effects of recombinant adipokines on the expression of inflammatory and bone destructive factors in synovial fibroblasts (SF), key players in RA.
Material and methods Serum samples were collected from patients before and after treatment with radon baths. Adipokine levels were measured by ELISA. Human SF from RA patients (RASF) and healthy donors (NSF) were pretreated with adipokines for 24h prior to irradiation with X-rays, and cell supernatants were collected after 24h to measure inflammatory factors known to contribute to the inflammatory process in RA (IL-6, IL-8, MMP-1).
Results In the serum of patients, a significant decrease of the level of the adipokine visfatin was observed after therapy. The level of adiponectin was either reduced or unchanged, and no marked difference was observed for leptin. The results obtained in vitro using primary SF confirm the induction of proinflammatory factors by stimulation with adipokines. Irradiation of SF after treatment with adipokines, in turn, significantly reduces the expression of inflammatory factors.
Conclusion Our data show for the first time a reduction of adipokine levels in serum of Radon treated patients. Since it is known that an elevated visfatin level positively correlates with serum levels of inflammatory factors IL-6 and CRP in RA patients, we hypothesise, that the decrease in serum visfatin level after low-dose irradiation affects the inflammatory process in the joint. Our in vitro results suggest the release of inflammatory factors after adipokine stimulation in both NSF and RASF can be reduced by low-dose X-ray irradiation, therefore potentially inhibiting inflammation in the joint of RA patients.