Antioxidant
An antioxidant is a molecule that neutralises reactive oxygen species or limits the damage they cause, usually by giving up electrons. Some come from food; others, such as glutathione, cells make for themselves.
Also called antioxidant defence.
Cells run layered defences. Small molecules such as glutathione, the most abundant small thiol that cells make, reduce oxidants directly (Forman 2009). Enzymes do much of the rest: the peroxiredoxins remove hydrogen peroxide (Bolduc 2019), as does catalase, and glutathione-dependent enzymes such as GPX4 protect membrane fats.
Many of these defences are switched on together by Nrf2, which was lower in cartilage cells from older and osteoarthritic donors than in cells from younger donors (Taylor 2023). Under oxidative stress, human cartilage cells lost activity in two recycling enzymes, glutathione reductase and thioredoxin reductase, while catalase held steady (Del Carlo 2003).
Some antioxidants work by helping the cell's own systems. Lipoic acid, once reduced to dihydrolipoic acid, raised cells' own glutathione in several cell types in the lab by helping them take up cysteine (Han 1997).
Sources
- Forman HJ, Zhang H, Rinna A. Glutathione: overview of its protective roles, measurement, and biosynthesis. Mol Aspects Med 2009.
- Bolduc JA, Collins JA, Loeser RF. Reactive oxygen species, aging and articular cartilage homeostasis. Free Radic Biol Med 2019.
- Taylor EL, Collins JA, Gopalakrishnan P et al. Age and oxidative stress regulate Nrf2 homeostasis in human articular chondrocytes. Osteoarthritis Cartilage 2023.
- Carlo MD Jr, Loeser RF. Increased oxidative stress with aging reduces chondrocyte survival: correlation with intracellular glutathione levels. Arthritis Rheum 2003.
- Han D, Handelman G, Marcocci L et al. Lipoic acid increases de novo synthesis of cellular glutathione by improving cystine utilization. Biofactors 1997.
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