Table 1 Cited Properties of H₂ as a Medical Gas with Suggested Chemical/Biological Mechanisms.

radical scavenging antioxidant

• selectively reduces hydroxyl radicals (•OH) and reactive nitrogen oxide species (NO₂ and N₂O₃) but did not eliminate O₂^- or H₂O₂ when tested in in vitro [40].

• does not decrease the steady-state levels of nitric oxide (NO) [40] which may be beneficial as endogenous NO signaling pathways modulate pulmonary vascular tone and leukocyte/endothelial interactions [64].

• increases antioxidant enzymes such as catalase, superoxide dismutase or heme oxygenase-1 [39, 44].

• diminished lipid peroxidation as indicated by MDA levels when compared to air-treated grafts [65].

• drinking hydrogen-containing water with concentrations as low as 0.04 mM, significantly reduced the loss of dopaminergic neurons, decreased accumulation of DNA damage, and lipid peroxidation in mice with Parkinson's disease induced by oral administration of MPTP [66].

anti-apoptotic

• postulated to inhibit caspase-3 activation [67].

anti-inflammatory

• down-regulation of pro-inflammatory cytokines, such as interleukin (IL)-1 β, IL-6, chemokine (CC motif) ligand 2 and tumor necrosis factor-α (TNF-α) [68, 69].