Effects of Magnetic Infrared Laser Irradiation on Formalin-Induced Chronic Paw Inflammation of Mice

[Purpose] The purpose of the present study was to investigate the effect of magnetic infrared laser (MIL) irradiation on formalin-induced chronic inflammation. [Subjects] Male ICR mice. [Methods] Mice were subaponeurotically injected in the left hind paw with 0.02 ml of 3.75% formalin, then subjected to 1.33, 2.66 and 6.65 J/cm2 of MIL irradiation, once a day for 10 days during which then the hind-paw thickness and volume were measured daily. The paw wet-weight, histological profiles, histomorphometrical analyses and paw tumor necrosis factor (TNF)-α contents were conducted at termination and compared with those of dexamethasone, 15 mg/kg, intraperitoneally injected mice. [Results] After two formalin treatments, a marked increase in the paw thickness and volume was detected in the formalin-injected control as compared with the vehicle control. Also at the time of sacrifice the paw wet-weights, and paw TNF-α contents were also dramatically increased and confirmed by histopathological observations. However, these formalin-induced chronic inflammatory changes were significantly and dose-dependently decreased by MIL irradiation. [Conclusion] MIL radiation has favorable effects on formalin-induced chronic inflammation mediated by TNF-α suppression, and MIL therapy may represent an alternative approach for the treatment of chronic inflammatory diseases.