Recent studies on anti-inflammatory effects of radon inhalation in mice

Radon therapy, which has been performed in Misasa (Japan) and Badgastein (Austria), was found to have a beneficial effect on pain-related diseases. Although several clinical studies of the curative effects on pain related diseases have been reported, the mechanism remains to be incompletely elucidated. In order to further clarify the mechanism, we developed radon exposure systems for small animals. In the present paper, we review several studies on the anti-inflammatory effects of radon inhalation in mice. We first examined whether radon inhalation inhibits carrageenan-induced inflammatory paw in mice. Radon concentration in mouse cage was approximately 2000 Bq/m 3 , which is similar to the level of radon therapy at Misasa Medical Center, Okayama University Hospital. Although carrageenan administration into right hind paw of mice induced paw edema, radon inhalation inhibited the edema. Antioxidants such as superoxide dismutase (SOD) and catalase were significantly higher in the radon-treated mice than in the sham-treated mice. Since the development of carrageenan-induced inflammation is mediated by reactive oxygen species (ROS), the inhibition of paw edema by radon inhalation is probably due to activation of antioxidant functions. We next examined the effects of radon inhalation on dextran sulfate sodium (DSS)-induced colitis in mice. Results showed that radon inhalation suppressed the damage caused by DSS-induced colitis. In addition, the mediators of inflammatory response such as tumor necrosis factor-alpha (TNF-α) were inhibited, and antioxidants such as SOD were increased by radon inhalation. Next, we examined the effects of radon inhalation on formalin-induced inflammatory pain in mice. Results showed that radon inhalation inhibited the licking response time. TNF-α, activated by formalin-induced inflammation, was lower in the radon-treated mice than in the sham-treated mice. Antioxidant activities such as SOD activity were increased in the mice that inhaled radon. These findings suggested that radon inhalation inhibits several types of inflammation in mice due to activation of antioxidant functions.