Table 1.

Natural ROS scavengers.

ROS Scavengers	Properties and Mechanisms of Action
Enzymatic ROS scavengers
Superoxide dismutase (SOD)	Enzyme. Converts superoxide radicals into oxygen and H2O2.
Catalase (CAT)	Enzyme in the peroxisomes. Neutralizes H2O2 in water.
Glutathione peroxidase (GPx) Thioredoxin system: Thioredoxin (Trx), Peroxiredoxin (Prx), Thioredoxin reductase (TrxR)	Thiol-dependent enzymatic antioxidants. Neutralize H2O2 and are recycled by nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor.
Non-enzymatic ROS scavengers
Vitamin A (retinol) or carotenoids	Fat-soluble antioxidant. Donates electrons to neutralize free radicals.
Vitamin E (tocopherols and tocotrienols)	Fat-soluble antioxidant. Scavenges lipid peroxyl radicals.
Vitamin C (ascorbic acid)	Water-soluble antioxidant. Donates electrons to neutralize free radicals. Scavenge superoxide.
Carotenoids	Found in various fruits and vegetables. Of the ~600 types of carotenoids, some can synthesize Vitamin A. Neutralizers of ROS.
Polyphenols	Ubiquitously present in fruits and vegetables. Free-radical scavenger.
Flavonoids	Phytochemicals present in plants, fruits, and vegetables. Scavengers of ROS.
Pycnogenol (PYC)	Combination of bioflavonoids with robust capacity to scavenge free radicals.
Alliin	Found in both natural and synthetic compounds. A bioactive compound derived from garlic. Superoxide scavenger.
Allicin	Synthesized from alliin. Inhibits superoxide, nitric oxide (NO) and hydroxyl radicals.
Minerals (copper, zinc and selenium, magnesium)	Precursors to antioxidants that help regulate free radicals.
Coenzyme Q10 (CoQ10), coenzyme Q (CoQ)	Lipid antioxidant. Essential component of the ETC. Protects cells from oxidative damage.
Glutathione	Tripeptide. Detoxifies ROS. Maintains redox balance.
NADPH	NADPH, as a cofactor independently and with redoxins, plays a crucial role in ROS detoxification.
Cytochrome C	Endogenous heme protein located in mitochondria. Oxidized cytochrome C is able to scavenge superoxide radicals.