Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 23 Vitamins
nature, reactions involving oxidized lipoic acid involve electrophilic
mechanisms owing to the oxidized state of the two
sulfurs in lipoic acids.
Reduction of oxidative stress by LA supplementation
has been demonstrated in animal models ( Fuchs and
Zimmer, 1997 ). To determine how normal development
or pathological conditions are affected by genetic alterations
in the ability of mammalian cells to synthesize LA
and whether dietary LA can circumvent its endogenous
absence, mice deficient in lipoic acid synthase (Lias) have
been generated. Mice heterozygous for disruption of the
Lias gene develop normally, and their plasma levels of
thiobarbituric acid-reactive substances do not differ from
those of wild-type mice. However, the heterozygotes have
significantly reduced erythrocyte glutathione levels, indicating
that their endogenous antioxidant capacity is lower
than those of wild-type mice. Homozygous embryos die
by day 8 to 12 of gestation. Of nutritional interest, supplementing
the diet of heterozygous mothers with LA (1.65 g/
kg of body weight) during pregnancy fails to prevent the
prenatal deaths of homozygous embryos. Apparently, an
endogenous LA synthesis is essential for developmental
survival and cannot be replaced by LA in maternal tissues
and blood via the diet ( Fuchs and Zimmer, 1997 ).
5 . Pyrroloquinoline Quinone
Pyrroloquinoline quinone (PQQ) is a cofactor that was
originally isolated from methylotrophic bacteria. PQQ is
utilized in bacteria as a redox cycling cofactor. It has been
shown to be present in mammalian tissue; however, its primary
function is still not clear, although recent evidence
suggests that gestational deficiency affects mitochondriogenesis
( Steinberg et al., 1994, 2003 ; Stites et al., 2000a,
2000b, 2006 ). PQQ is a growth stimulant in mammals fed
chemically defined diets, particularly in mice. If there is a
requirement for PQQ, however, it is yet to be established.
The growth response in neonates is most obvious in offspring
from dams that have been nutritionally deprived of
PQQ throughout their adult lives.
VI . CONCLUDING REMARKS
Vitamins evolved to serve unique and complex roles: as
cofactors, as signaling agents in cells, as regulators of
gene expression, and as redox and free-radical quenching
agents. All natural vitamins are organic food substances
found only in living things. With few exceptions, the body
cannot manufacture or synthesize vitamins. They must be
supplied in the diet. As is the case for any substance that
is essential to a given function, all vitamins at some point
in development can be viewed as limiting nutrients, the
absence of which results in specific deficiency signs and
symptoms.
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