Methylene blue attenuates acute liver injury induced by paraquat in rats.

Paraquat (PQ) poisoning often leads to severe oxidative liver injury. Recent studies have reported that methylene blue (MB) can prevent oxidative stress-induced diseases. This study tested the hypothesis that MB treatment reduced acute liver injury induced by PQ in rats. Adult male Sprague-Dawley (SD) rats were randomly divided into four groups: (1) normal group, (2) MB group (2mg/kg i.p.), (3) PQ group (35 mg/kg i.p.) and (4) PQ+MB group (MB 2mg/kg i.p. administrated 2h after PQ). We evaluated the changes of liver histopathology, serum liver enzymatic activities, oxidative stress, heme oxygenase-1 expression, and mitochondrial permeability transition. The rats were injected with PQ produced liver injury, evidenced by histological changes and elevated serum alkaline phosphatase and alanine transaminase levels; PQ also led to oxidative stress, an increase of malondialdehyde content and mitochondrial permeability transition pore opening. Pathological damage and all of the above mentioned markers were reversed in the animals treated with MB than in those who received PQ alone. Meanwhile, MB significantly increased the contents of superoxide dismutase, adenosine triphosphate and the expression of heme oxygenase-1. In conclusion, MB had a protective effect against PQ-induced hepatic damage in rats. The mechanisms of the protection seem to be the inhibition of mitochondrial permeability transition opening and the increase of heme oxygenase-1 expression.