Anti-inflammatory effects of low-dose rate ionizing radiation on cell lines derived from osteoarthritis patients

The efficacy of low-dose rate ionizing radiation (LDRIR) for anti-inflammatory treatment has been confirmed in various clinical studies. However, the radiobiological mechanisms involved in the anti-inflammatory action of LDRIR have not been completely elucidated. This study investigated whether LDRIR at 0.5 or 1 Gy affected the regulation of cytokine messenger RNA expression and protein levels in inflamed synoviocytes and chondrocytes induced by lipopolysaccharide. Intercellular adhesion molecule-1, interleukin-6, interleukin-8, and growth-regulated alpha protein expression were analyzed in synoviocytes and chondrocytes at 24 h after lipopolysaccharide treatment using reverse transcription polymerase chain reaction, immunostaining, Western blotting, and enzyme-linked immunosorbent assays. The messenger RNA expression levels of interleukin-6, interleukin-8, and growth-regulated alpha protein were lower in synoviocytes cotreated with lipopolysaccharide and 0.5 or 1 Gy radiation than in those treated with lipopolysaccharide alone. The immunostaining results showed that all target cytokines were downregulated after 0.5 and 1 Gy of radiation in inflamed synoviocytes and chondrocytes. In chondrocytes, all four cytokines were significantly downregulated at a dose rate of 0.053 Gy/min, and the extent of regulation was similar to that at 4.02 Gy/min. Our findings indicate that LDRIR may regulate pro-inflammatory cytokine expression in both synoviocytes and chondrocytes, regardless of the dose rate. Therefore, LDRIR can alleviate concerns of carcinogenesis and may be useful in clinical settings.