metabolic syndrome

# Introduction Eye diseases like glaucoma, diabetic retinopathy and age-related macular degeneration share a common culprit: **oxidative stress** from harmful reactive oxygen species (ROS). Excess ROS can damage DNA, lipids and proteins in the retina and optic nerve, driving vision loss ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC4878665/#:~:text=Hydrogen%20can%20exert%20antioxidant%20and,indicate%20that%20the%20application%20of)) ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC10674431/#:~:text=Molecular%20hydrogen%20%28H_,can%20prevent%20a%20reduction%20in)). **Molecular hydrogen (H₂)** has emerged as a unique antioxidant therapy. H₂ is a tiny, tasteless gas that easily penetrates cell membranes and ocular barriers ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC10674431/#:~:text=Molecular%20hydrogen%20%28H_,can%20prevent%20a%20reduction%20in)). It selectively neutralizes only the most toxic ROS (like hydroxyl radicals •OH and peroxynitrite ONOO⁻) while leaving normal signaling ROS intact ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC4878665/#:~:text=Hydrogen%20can%20exert%20antioxidant%20and,indicate%20that%20the%20application%20of)). In doing so, H₂ restores cellular **redox balance** without blocking beneficial biochemical signals. In addition, H₂ can trigger protective pathways – for example, it upregulates antioxidant enzymes (superoxide dismutase, catalase, glutathione systems) via Nrf2 signaling and suppresses pro-inflammatory factors ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC4878665/#:~:text=Hydrogen%20can%20exert%20antioxidant%20and,indicate%20that%20the%20application%20of)) ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC10674431/#:~:text=RGCs,2%7D%20may)). These properties suggest H₂ could guard retinal neurons (and the optic nerve) by modulating **redox signaling** in ophthalmic tissues. # Mechanisms of H₂ Action in Ocular Tissues The therapeutic appeal of H₂ lies in its physical properties. As the smallest molecule, it diffuses rapidly through tissues and bio-barriers ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC10674431/#:~:text=Molecular%20hydrogen%20%28H_,can%20prevent%20a%20reduction%20in)). For example, inhaled H₂ or hydrogen-saturated water (HRW) quickly elevates H₂ levels in the blood and eyes. Once inside cells, H₂ “soaks up” highly reactive radicals. Unlike general antioxidants, H₂ does not indiscriminately scavenge all ROS – it reacts preferentially with the strongest oxidants ([pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC4878665/#:~:text=Hydrogen%20can%20exert%20antioxidant%20and,indicate%20that%20the%20application%20of)). This means normal ROS signaling (needed for cell function) is preserved while damaging radicals are detoxified. In practice, studies show H₂ lowers oxidative biomarkers (like 4-hydroxynonenal and malondialdehyde) and inflammatory me

Molecular Hydrogen and Redox Signaling in Ocular Neuroprotection

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