Background: The redox imbalance between nitric oxide and superoxide generated in the endothelium is thought to play a pivotal role in the development of endothelial dysfunction. A third reactive oxygen species (ROS), H2O2, is known to have both beneficial and detrimental effects on the vasculature. Nonetheless, the influence of the hydroxyl radical, a byproduct of H2O2 decay, is unclear, and there is no direct evidence that the hydroxyl radical impairs endothelial function in conduit arteries. Molecular hydrogen (H2) neutralizes detrimental ROS, especially the hydroxyl radical.
Objectives: To assess the influence of the hydroxyl radical on the endothelium and to confirm that a gaseous antioxidant, H2, can be a useful modulator of blood vessel function.
Methods: The efficacy of water containing a high concentration of H2 was tested by measuring flow-mediated dilation (FMD) of the brachial artery (BA). The subjects were randomly divided into two groups: the high-H2 group, who drank high-H2 water containing 7 ppm H2 (3.5 mg H2 in 500 mL water); and the placebo group. Endothelial function was evaluated by measuring the FMD of the BA. After measurement of diameter of the BA and FMD at baseline, volunteers drank the high-H2 water or placebo water immediately and with a 30-minute interval; FMD was compared to baseline.
Results: FMD increased in the high-H2 group (eight males; eight females) from 6.80%±1.96% to 7.64%±1.68% (mean ± standard deviation) and decreased from 8.07%±2.41% to 6.87%±2.94% in the placebo group (ten males; eight females). The ratio to the baseline in the changes of FMD showed significant improvement (P<0.05) in the high-H2 group compared to the placebo group.
Conclusion: H2 may protect the vasculature from shear stress-derived detrimental ROS, such as the hydroxyl radical, by maintaining the nitric oxide-mediated vasomotor response.
Keywords: 5–7 ppm; flow-mediated dilation; hydroxyl radical; molecular hydrogen; peroxynitrite; reactive oxygen species.