Biology Reference
In-Depth Information
Total contents of ARs determined by gas
chromatography and the colorimetric
method based in Fast Blue B were highly
correlated (Landberg
et al
., 2009). In our
laboratory we are currently comparing the
accurancy of total levels of ARs deter-
mined by the new colorimetric method
based on Fast Blue RR with those meas-
ured by GC-MS.
Electron impact mass spectra of ARs
have a base fragment at
m
/
z
124, due to
McLafferty rearrangement of the phenolic
ring, and other minor fragments at
m
/
z
123 due to the dihydroxytropylium ion
formed by direct b-cleavage,
m
/
z
137 due to
g-cleavage and
m
/
z
166 of unknown origin
(Fig. 10.6). The
m
/
z
abundance ratio of
123/124 is about 1:5 in accordance with
meta
-dihydroxy substitution in the ben-
zene ring.
High-performance liquid chromato-
graphy (HPLC) has also been used for the
analysis of ARs. Prior to HPLC analysis,
extracts may be filtered or purified by
solid-phase extraction on silica, C8 or C18
and chromatography is achieved using
reversed-phase columns. Detection cou-
pled to HPLC has been performed with
either UV or diode array detectors set at
275-280 nm. Absorption at these wave-
lengths was attributed to the resorcinolic
ring (Ross
et al.
, 2004a). Nevertheless,
current GC methods are superior to HPLC
in their ability to separate different AR
homologues. HPLC analysis offers possi-
bilities for purification more than quanti-
tative measurement and may be more
appropriate for analysis of the more water-
soluble
10.7.1
Effects on nucleic acids
ARs can affect the structure and metabolism
of nucleic acids. They are able to inhibit
both DNA and RNA synthesis (Gianetti
et al.
,
1978), as well as to induce DNA strand scis-
sion (Scanell
et al
., 1988). This process
occurs in the presence of both copper and
ARs (Singh
et al.,
1995). A hydroxylation of
the 5-AR substrate dependent on Cu
2+
and
O
2
would generate 6-alkyl-1,2,4-trihydroxy-
benzenes. The catechol moiety of these
molecules would be oxidized by Cu
2+
, gen-
erating a quinone derivative with subse-
quent formation of reactive oxygen species
and alkylation of the DNA strand. It was
shown that DNA binding is mediated by the
alkyl substituent of ARs and becomes more
efficient as the length of the chain increases.
Formation of H
2
O
2
and - OH seem to be
needed for DNA scission and DNA cleavage
is not sequence specific. Further reseach
indicated that ARs can inhibit a DNA-repair
enzyme, DNA polymerase b, at fairly low
concentrarions (IC
50
= 14 mM), and bis-ARs
are more efficient in DNA cleavage and
inhibition of the mentioned enzyme than
5-ARs (Starck
et al.
, 2000). DNA polymerase
b is believed to repair the damage caused by
agents employed as anti-tumour agents,
such as bleomycin and cisplatin. Preventing
DNA reparation, ARs and their derivatives
offer the possibility of increasing the effec-
tiveness of these anti-tumour agents. Other
reports also showed ARs as being active
competitive inhibitors of the reverse tran-
scriptase (He, 1990).
ARs are also able to reduce the muta-
genic activity of some indirect mutagens,
whereas they are less active on direct muta-
gens. Compared with anthocyanins, ARs
were potent inhibitors of the rate and fre-
quency of induced mutations in cultured
lymphocytes. Later, the anticancer effects
of ARs were attributed to the capability of
these compounds to increase apoptosis in
genotoxically damaged cells (Gasiorowsky
et al
., 2001). Although anti-mutagenic and
anti-tumoural bioactivites of ARs seem
promising, more research is needed to
determine the real impact of these mol-
ecules
in vivo
.
AR
metabolites
in
biological
fluids.
10.7 Bioactivity in Organisms and
Potential Roles for Resorcinolic
Lipids in Plant Physiology
The amphiphilic character of 5-n-ARs has
been repeatedly invoked as a key feature
in the explanation of the biological acti-
vities of these lipid phenolics. Possible
effects of ARs on living organisms are as
follows.
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