Objective: It is to characterize the underlying molecular mechanisms of the anti-atherosclerotic effects of hydrogen (dihydrogen; H(2)), a novel antioxidant. In particular, to examine the effects of hydrogen on athero-susceptibility in lipoproteins and aorta of apolipoprotein E knockout (apoE-/-) mice.
Methods and results: Plasma analysis by enzymatic method and spectrophotometric measurement showed that eight weeks intraperitoneally injection of hydrogen-saturated saline remarkably decreased plasma total and non-high-density lipoprotein (non-HDL) cholesterol, and malondialdehyde in apoE-/- mice fed either chow or high fat diet. Western blot analysis showed hydrogen treatment reduced the contents of apolipoprotein B (apoB), a major protein constituent of non-HDL in either plasma or hepatic tissues. Moreover, ELISA assay revealed that the production of tumor necrosis factor-α and interleukin-6 were significantly suppressed by hydrogen in RAW264.7 macrophages, after stimulation with the isolated non-HDL from treated or untreated mice. Immunohistochemistry of aortic valve sections revealed that hydrogen suppressed the expression of several proinflammatory factors and decreased vessel wall infiltration of macrophages. Besides, real-time PCR and Western blot analysis disclosed that hepatic scavenger receptor class B type I (SR-BI), ATP-binding cassette (ABC) transporters ABCG8, ABCB4, ABCB11, and macrophage SR-BI, were all induced by hydrogen treatment. Finally arterial wall lipid disposition displayed by oil red O staining was reduced significantly in aortic root and whole aorta en face in hydrogen administrated mice. In addition, hydrogen significantly improved HDL functionality in C57BL/6J mice assessed in two independent ways, namely (i) stimulation of cholesterol efflux from macrophage foam cells by measuring HDL-induced [(3)H]cholesterol efflux, and (ii) protection against LDL oxidation as a measure of Cu(2+)-induced TBARS formation.
Conclusion: These results reveal that administration of hydrogen-saturated saline decreases athero-susceptibility in apoB-containing lipoprotein and aortic atherosclerosis in apoE-/- mice and improves HDL functionality in C57BL/6J mice.
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