Biology Reference
In-Depth Information
17.4
Discussion
In general, reactive oxygen species (ROS) are highly reactive molecules or intermediates
that are continuously produced by all aerobic organisms, primarily as a consequence of
aerobic respiration. Accumulation of ROS results in oxidative damage to important mol-
ecules such as protein, lipids, and DNA, which may result in cellular dysfunction and
mutation, thus promoting the development of disease (Halliwell and Aruoma
1991
) .
On the other hand, taurine and its metabolic precursor, hypotaurine, have been
proposed to participate in the cellular mechanisms involved in the protection against
oxidative damage such as inhibition of lipid peroxidation. Especially hypotaurine
has an excellent ability to scavenge hydroxyl radical, the most potent oxidant that
can be formed from oxygen considered, the likely initiator of lipid peroxidation
(Huxtable
1992
). By contrast, the molecular mechanisms of taurine have still to be
defined as this amino acid reacts poorly with superoxide, hydrogen peroxide, and
hydroxyl radicals (Aruoma et al.
1988
). Therefore, the objective of the present study
was to examine the in vitro antioxidant properties of taurine against several reactive
species such as DPPH, hydroxyl, superoxide, and alkyl radical at various concentra-
tions using a spin-trapping electron method.
In the present study, DPPH radical scavenging activity of taurine at various con-
centrations, from 0.0625 to 1 mg/mL, was elevated with a decrease of ESR signals in
a dose-dependent manner compared to the control. These results indicated that the
taurine possessed strong scavenging activity against DPPH radicals, and that the abil-
ity of the taurine may be attributed to its hydrogen donating ability. The hydroxyl radi-
cal is one of the most reactive radicals generated from biologic molecules and can
damage living cells (Bergamini et al.
2004
). In our present study, the taurine exhibited
stronger scavenging activity against hydroxyl radical, and the radical scavenging
activity occurred in a dose-dependent manner. Recently, it was reported that taurine
acts as a good in vitro scavenger of reactive oxygen such as peroxyl radical and anion
superoxide and nitrogen species including nitric oxide and peroxynitrate (Oliveira
et al.
2010
) . However, Navneet et al. (
2008
) reported that taurine did not in fl uence the
level of hydroxyl radical production caused by 1-methyl-4-phenylpyridinium (MPP
+
),
which is the oxidized metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine
(MPTP) in mitochondria in mice. In contrast, it has been reported that the intraperito-
neal injection of 200 mg/kg taurine is sufficient to prevent hypoxia-induced lactate
accumulation and lipid peroxidation in rat brain (Mankovskaya et al.
2000
) . Other
previous studies reported that taurine deficiency increased malondialdehyde (MDA)
levels, which is a relatively stable end product of lipid peroxidation that decreased in
taurine-supplemented animals (Kaplan et al.
1993
; Öz et al.
1999
) . These previous
results showed that taurine has been considered a potent free radical scavenger and
antioxidant. In general, free radical generator, AAPH, is an azo compound that under-
goes thermal decomposition to produce molecular nitrogen and two carbon radicals,
which rapidly react with oxygen to give peroxyl radicals (Krasowska et al.
2000
) . Our
present study showed that taurine exhibited stronger scavenging activity against alkyl
radical. It has been well known that superoxide radical can cause cellular damage by
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