Hey everyone,
I often read that the words "Antioxidants" and "ROS-Scavengers" are used as synoyms and without regard of the experimental or biological context. Therefore I tried clarify these two words in chemical and biological terms.
In general, substances, which have a preference to give electrons are reducing components (reductants) and substances, which have a preference of taking electrons are oxidzing components (also called oxidants). Not all but many radicals are oxidizing compounds (because they are lacking one or more electrons and want to fill that gap to become stable). Of course there, are also strong oxidants that are not radicals.
A cell, as a stable biological system, wants to avoid a lot of radialcs (or strong oxidizing or reducing subtances) going around, because they react with biomolecules and therefore damage the cell. "Antioxidant" is a general term for all chemical substances, which can reduce an oxidizing substance (not only in the cell).
Reactive oxygen species (ROS) are just one example of oxidizing substances in biological systems. In this group you have to distinguish between radicals (Superoxide anion, Hydroxyl radical, Peroxyradical) and non-radicals (Hydrogen peroxide, hypocchloride, singelt oxygen, ozone). Please see for a detailed description this new review:
Sies H, Jones DP. Reactive oxygen species (ROS) as pleiotropic physiological signalling agents [published online ahead of print, 2020 Mar 30]. Nat Rev Mol Cell Biol. 2020;10.1038/s41580-020-0230-3. doi:10.1038/s41580-020-0230-3
If a substance you add to your cell can react with at least one of these substances (it does not matter if radical or not) this substance is a "ROS-Scavenger". How the substance is doing the job depends on its chemistry and the ROS subspecies it reacts with. NAC for example can directly exepct eletrons from radicals. It also refills the gluthathion pool of cells, which is necessary to decompose hydrogen peroxide. So NAC can (directly and indirectly) "scavenge" different types of ROS (not only radicals). From the cellular point of view it is a ROS-Scavenger, from the chemical point of view it reduces a oxidizing component, so it is an antioxidant.
I am looking forward to additions in this definition especially from chemists, who are experts in this field.
All the bestand stay healthy :)
Marc
Not every antioxidant compound can be considered as ROS-Scavenger ... because there are other oxidant compounds of various types such as reactive nitrogen species as well as rractive sulfur species and others ... Thus when mentioning the word antioxidants it includes all oxidant compounds of various types and cannot be specialized Only for ROS-Scavenger.
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Thank you for launching this interesting discussion.
As Luay A. Al-Helaly said not every antioxidant can be considered as ROS scavenger as there are antioxidants able to scavenge both ROS and RNS like ascorbate while other antioxidants are not as much as efficient against RNS such as some carotenoids compounds..
Moreover, we must distinguich between scavenging, chemical quenching and physical quenching as mechanisms of ROS detoxification from physico-chemical point of view..
Here he is not talking about the removal mechanism for oxidant compounds, but only on the use of the term " Antioxidant ".
Well done
Mohamad Issaoui
Thank you Dr. luay,
Normally, the term "scavenger" reflects also the mechanism of action as from terminologic point of view some researchers note difference between scavenger and quencher.
In my opinion, the term "scavenger" is generally referred to the "sacrificial" nucleophilic antioxidants such as the powerful glutathione and ascorbate that donate their electrons to reduce ROS (H2O2 and radicals) while it is better to say that singlet oxygen 1O2 is "quenched" by tocopherol or carotenoïds antioxidants that are directly involved in energy dissipation process.
Regards,
I share the opinion of Mohammad Issawi that the term "quenching" is more suited for lowering energy states. In the field of photosynthesis and its involved molecules, the term is also used, when the electrons of photoreceptor molecules are reduced to ground state, but the released energy is not used.
Thank you you all for this very interesting discussion. From my point, as a biologist, I am very happy that people with more knowledge of chemistry and physics give comments. Biologists go often wild with chemical terms and use them without differentiation.
In context of this topic, I would like to bring to your attention a recent review of our group, "Functions of ROS in macrophages and antimicrobial immunity". In this review, we give an introduction to ROS and their sources in macrophages, summarize the versatile roles of ROS in direct and indirect antimicrobial immune defense and provide an overview of commonly used ROS probes, ROS source inhibitors and ROS scavengers (also the difference between ROS scavengers and antioxidants, which are not synonymous, is explained). If you like, please have a look at: Functions of ROS in Macrophages and Antimicrobial Immunity February 2021, Antioxidants 10(2):313 DOI: https://doi.org/10.3390/antiox10020313
For all who do not want to read the whole review here the passage about ROS scavengers from Article Functions of ROS in Macrophages and Antimicrobial Immunity
The term “ROS scavenger” broadly describes any chemical or biological molecule, which is capable of detoxifying one or more ROS subspecies by different mechanisms defined by the chemistry of the ROS scavenger and the ROS subspecies [367]. Therefore a ROS scavenger not only scavenges radicals (like ●OH and O2●−), but can also scavenge nonradicals (like H2O2) or more than one ROS subspecies in dependency of the chemical structure of the scavenger. Moreover, this should not be mistaken with the term “Antioxidant”, which chemically defines molecules or atoms that can in general reduce an oxidizing substance and are not limited to ROS [66,368]. By this definition, antioxidants can include ROS scavengers, but also other chemicals that reduce for example RNS. Therefore, an antioxidant is not automatically a ROS scavenger and these two terms should not be mixed up.
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