Bilirubin as a potent antioxidant suppresses experimental autoimmune encephalomyelitis: implications for the role of oxidative stress in the development of multiple sclerosis.

Increasing evidence shows that oxidative stress plays an important role in the pathogenesis of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). In recent years, bilirubin has been demonstrated to be a potent antioxidant in vitro. In this study, we administered bilirubin to rats with acute and chronic EAE. Bilirubin prevented both acute and chronic EAE effectively. More significantly, bilirubin suppressed ongoing clinical EAE and halted EAE progression when given after disease onset. Subsequent histological examination showed that if administered to rats before the onset of EAE, bilirubin interfered with the invasion of inflammatory cells into the central nervous system (CNS) because it protected the blood-brain barrier (BBB) from free radical-induced permeability changes. However, in some cases, inflammation still occurred even when no clinical illness was observed. In rats with treatment initiated after the onset of EAE, despite the clinical improvements, treatment with bilirubin did not reduce the degree of CNS inflammation, or change cytokine expression in CNS lesions, indicating a lack of immunosuppressive effect of this treatment. By contrast, bilirubin treatment significantly alleviated oxidative damage in the spinal cord, and the clinical signs of EAE correlated well with the degree of oxidative injury in the lesions. Our results suggest that free radicals play an important role in the final effector stages of EAE, and that antioxidant therapies may have potential for the treatment of MS.