NUTRITION
duced by plants and algae, as well as several bacteria
and fungi. Compounds are deeply coloured yellow,
orange or red. Carotenoids from the diet are stored
in the fatty tissues of animals, and carnivorous ani-
mals obtain the compounds from animal fat. There
are over 600 known carotenoids; they are split into
two classes, xanthophylls (which contain oxygen)
and carotenes (which are purely hydrocarbons, and
contain no oxygen). Humans and animals are mostly
incapable of synthesising carotenoids, and must ob-
tain them through their diet. Dogs absorb beta-caro-
tene differently from humans, cleaving it and leaving
very little intact beta-carotene. In part, the beneficial
effects of carotenoids are thought to be due to their
role as antioxidants. beta-carotene may have added
benefits due its ability to be converted to vitamin A.
SAMe
S-adenosylmethionine (SAMe) is a precursor of glu-
tathione, a major antioxidant molecule in the body.
Oral supplementation can assist to replenish glu-
tathione stores. In addition SAMe also has anti-in-
flammatory properties.
Glutathione (GSH)
Glutathione is an important antioxidant in animals
and is capable of preventing damage to impor-
tant cellular components caused by reactive oxygen
species such as free radicals, peroxides, lipid perox-
ides and heavy metals.
Glutathione reduces disulfide bonds by serving
as an electron donor. In the process, glutathione
is converted to its oxidized form, glutathione di-
sulfide (GSSG). Once oxidized, glutathione can be
reduced back by glutathione reductase, using NA-
DPH as an electron donor. (Note: a very important
antioxidant in haemoglobin - especially feline hae-
moglobin, due to the increased number of sulphide
bonds in this species.)
Glutathione exists in both reduced (GSH) and oxi-
dized (GSSG) states. In the reduced state, the thiol
group of cysteine is able to donate a reducing equiv-
alent (H+ and e − ) to other molecules, such as reac-
tive oxygen species to neutralise them. After donat-
ing an electron, glutathione itself becomes reactive
and readily reacts with another reactive glutathione
to form glutathione disulfide (GSSG). Such a reac-
tion is probable due to the relatively high concentra-
tion of glutathione in cells. GSH can be regenerated
from GSSG by the enzyme glutathione reductase. In
healthy cells and tissue, more than 90% of the total
glutathione pool is in the reduced form (GSH) and
less than 10% exists in the disulfide form (GSSG).
The ratio of reduced glutathione to oxidized glu-
tathione within cells is often used as a measure of
cellular oxidative stress.
vet360
Issue 06 | DECEMBER 2017 | 42
Melatonin
Melatonin is a strong antioxidant which easily crosses
cell membranes and the blood–brain barrier. Unlike
other antioxidants, melatonin does not undergo redox
cycling, which is the ability of a molecule to undergo
repeated reduction and oxidation. Once oxidized, it
cannot be reduced to its former state, and had there-
fore been referred to as a terminal (or suicidal) antiox-
idant.
MITOCHONDRIAL CO-FACTORS
Recent research has shown that some molecules
classified as mitochondrial co-factors (lipoic acid,
L-carnitine) may also act to enhance function of aged
mitochondrion such that there are less ROS produced
during aerobic respiration. Supplementation of foods
with these co-factors increases their concentration
within cells, restores mitochondrial efficiency and re-
duces oxidative damage to RNA.
L-Carnitine
L-Carnitine is an amino acid synthesised in the liver
and kidney from lysine and methionine in the pres-
ence of ascorbate. L-carnitine facilitates the transpor-
tation of long chain fatty acids into the mitochondria
where they undergo beta–oxidation which produces a
large amount of energy (ATP).The main dietary sourc-
es of carnitine are red meat, fish and dairy products.
White meat is less rich in L-carnitine and vegetables
contain none. Because L-carnitine can be synthesised
de novo - it is not considered an essential nutrient.
Co-enzyme Q10
Co-enzyme Q10 is a co-factor required for ener-
gy production and has antioxidant properties. It is a
fat-soluble substance, which resembles a vitamin and
is present primarily in the mitochondria. It is a compo-
nent of the electron transport chain and participates
in aerobic cellular respiration, which generates energy
in the form of ATP. Ninety-five percent of the human
body’s energy is generated this way. Therefore, those
organs with the highest energy requirements, such as
the heart, liver, and kidney, have the highest Co-en-
zyme Q10 concentrations.
The take home message here is that nutraceutical
supplementation of antioxidants is a very INEXACT sci-
ence. One cannot just buy a single supplement from
a health shop and start supplementing and expect re-
sults. There seems to be an important interaction be-
tween the different types of antioxidants for maximum
effect. More publications assessing the oxidative stress
of various disease processes in animals and the results
of interventions are coming out in the literature in re-
cent years.
References: Available online: www.vet360.vetlink.co.za