ANTIOXIDANT / OXIDANT BALANCE:
Antioxidant /
Oxidant Balance:
Health = Oxidant / Antioxidant Balance - Meet Dr. ROS Jeckyll and Mr. ROS Hyde
Reactive Oxygen Species (ROS) - Life's
Oxygen ParadoxMeet
Dr. ROS Jeckyll and
Mr. ROS Hyde
ROS are mostly free radicalsSo exactly what is a
Free Radical? Free radicals
have become a subject of great interest due to their implication in numerous diseases,
including rheumatoid arthritis, Alzheimer's disease, high blood pressure, atherosclerosis,
liver cell injury and cancer.
- A
free radical (also called just a
radical)
is a small ion or molecule with one or more unpaired
electron in its outer orbital(s) making it highly reactive and likely to take
part in chemical reactions with your body's proteins, lipids, carbohydrates and
DNA. Electrons within atoms and
molecules occupy orbital spaces, in which each orbit holds a maximum of two
electrons oxidize
another atom). A radical can
have more than one unpaired electron .
- A
free radical
is formed by:
• The loss or addition
of an electron from a stable molecule
• A normal molecule
splitting into two fragments - each retaining one of a previous pair of electrons.
This is not common in the body, since it needs high energy input E.g. UV, ionizing
radiation.
- A newly
formed free radical
quickly "steals" an
electron(s)
from a nearby molecule.
This satisfies
its need for a pair (or pairs) of them in its outer orbital(s), thereby turning
its "victim"into a free radical . A chain
reaction is thus proliferated, resulting in the disruption of a living cell.
- Free radicals
can have positive, negative or neutral charge. Identity as a
radical only concerns the arrangement of its
electrons in its outer orbital(s). Charge is
determined by the difference between the number of protons and
electrons . E.g. A neutral molecule could have gained or lost an
electron. A non-neutral molecule could become
neutral with the addition or loss of an electron .
Free radicals are frequently
denoted by a dot placed immediately to the upper right of the atomic symbol or molecular
formula. Example free radicals include:
• Cl•
•
Hydroxyl Radical (OH • )
•
Nitric Oxide (NO• )
• Peroxynitrite (OONO• )
• Alkoxyl Radical
(LO • )
The most important
free radicals
in the body are derivatives of
oxygen. However,
radicals can also be non-oxygen -centered:
• Carbon-centered
radicals . E.g. CCI3 • arises from the attack of an
oxidizing
radical on an organic molecule;
• Hydrogen centered
radicals. Result from attack of the H atom (H•);
• Sulfur-centered
radicals. Produced in the oxidation of glutathione resulting in thiyl
radical (R-S•);
• Nitrogen-centered
radicals. E.g.phenyl diazine radical.
Reactive Oxygen Species (ROS) "Activatable" Oxygen Molecule
3 O2
The oxygen
molecule found in the air we breathe is chemically written as
3 O2 .
3 O2
two oxygen
atoms which make up an
oxygen
molecule. The "3" refers to it being
in the triplet or ground state ,
meaning its outer (valence) electrons are
spinning in parallel, i.e. in the same direction, in separate orbitals.
The
3 2
molecule found in the air, is not very reactive because it
is a
di-radical .
So named because it has two electrons in different
orbitals without a "mate", making it "hungry" for two
electrons ( e- ). In fact, the oxygen molecule has TWO unpaired
electrons WITH PARALLEL SPINS . This makes 3 O 2 3 O2 to be an oxidant in the rare case that the reductant
(the molecule supplying the electrons) also has two unpaired electrons, with parallel
spins opposite to that of oxygen).
This keeps us from spontaneously combusting in
our oxygen atmosphere!
The usefulness of the
3 2
oxygen molecule, with its two unpaired
electrons,
to produce more reactive molecules than
itself . These are called Reactive
Oxygen Species (ROS).
E.g. the very reactive
Singlet oxygen (1 O2 *
) oxygen's
electrons does a spin flip and jumps to a higher
orbital following absorption of
energy ,
ooxygen
can be activated by receiving single
electrons by chemical transfer , as in metabolism.
ROS have
the utmost significance for our healthROS are absolutely necessary
for day-to-day functions in the body. E.g.
ROS are
part of the process of digesting food, necessary for generating of
ATP (cellular energy); Immune system macrophages
and neutrophils use
ROS
ROS can be toxic
to cells. Proteins, membrane lipids, carbohydrates
and nucleic acids (DNA, RNA) are subject to cellular damage by
ROS,
and are implicated in many chronic diseases.
- ROS
can be the direct cause of a disease
state (e.g. atherosclerosis, by irritating/damaging vascular lining).
- In
other cases such as rheumatoid arthritis, ROS
mediate and perpetuate cellular damage
- Various
stimuli, such as radiation, inflammation, aging and high concentrations of
oxygen
greatly increase the rate of formation of
ROS .
ROS
are removed by protective enzymes and
antioxidants
Meet Some of the Oxygen Family's "Active" Offspring
(
ROS or "Active"
Oxygen)
(derived from Oxygen, not
all are free radicals)
O2 -
Superoxide radical (anion)
OH•
Hydroxyl radical
OH-
Hydroxyl anion (not a radical)
LOO•
Peroxyl radical
LO•
Alkoxyl Radical
H2 O2
Hydrogen peroxide
(not a radical)
1 O 2
Singlet oxygen
(not a radical)
O3
Ozone (not a radical)
NO •
Nitric oxide
ONOO-
Peroxynitrite (anion) (not a radical)
HOCl
Hypochlorous acid
LOOH
Peroxide
Other notes on ROS
ROS include
radicals,
ions and peroxides
ROS should not be
thought of as "bad". Even though most
ROS are free radicals, ROS are formed as necessary intermediates in a variety
of normal biochemical reactions in the body.
Although some non-radical
ROS
are not particularly reactive themselves, they can
produce extremely reactive
radicals - E.g.
Hydrogen peroxide
can produce the
hydroxyl radical ( OH• ) .
The radicals
of most concern to the body are the
hydroxyl radical (OH • ),
alkoxy radical
(LO • )
and
Superoxide radical
(O2 •- )
ROMs. Reactive
oxygen molecular
products, such as H2O2 , ROOH, ROOR,
singlet oxygen ,
epoxides, endoperoxides and dioxetanes react with some metal ions to produce
hydroxyl
and alkoxyl radicals, and so may be considered as active
ROS
Perhydroxyl radical (OOH • ).
A powerful oxidant, but its biological relevance is probably minor
because of its low concentration at physiological pH.
(Cl2 = 1.0)
Fluorine 2.23
Hydroxyl Radical (OH) 2.06
Atomic Oxygen (singlet) 1.78
Ozone 1.50
Hydrogen Peroxide 1.31
Perhydroxyl Radical (OOH) 1.25
Potassium Permanganate 1.24
Chlorine Dioxide 1.15
Bromine 0.80
Chart of
ROS and their
Metabolites in the Body
ROS Chart
