oxidants and antioxidants in biology - Oxygen Club of California

Comparison of Antioxidant and Scavenging Activity of
Aloe-emodin, Emodin and Rhein on Free Radical and ROS
FRANKLIN VARGAS *, YRENE H. DÍAZ 1 AND
KARLA M. CARBONELL 1
Laboratorio de Fotoquímica, Centro de Química, Instituto Venezolano de
Investigaciones Científicas I.V.I.C., Caracas. 1 Escuela de Química, Universidad
Central de Venezuela, Caracas, Venezuela.
Anthraquinones and dianthrones (1,8-dihydroxyanthra-quinones,
DHAs) are present in several plants mainly as glycosides.
These compounds have both therapeutic and cytotoxic properties
related with diverse types of human affections. For example, aloeemodin
(1,8-dihydroxy-3-hydroxy-methylanthraquinone) is a compound
present in Aloe vera leaves, which exhibits antifungal,
mutagenic, and tumorigenic properties, although in a recent report
aloe-emodin was postulated as a new lead antitumor drug; emodin
(1,3,8-trihydroxy-6-methylanthraquinone) possesses anticancer,
diuretic, antibacterial, vasorelaxant and anti-inflammatory effects,
and rhein (1,8-dihydroxyanthraquinone-3-carboxilic acid) is the
active metabolite of diacerein, a drug for the treatment of patients
with osteoarthritis. In this work we investigated the ability of
emodin (1), aloe-emodin (2) and rhein (3) to inhibit free radical or
reactive oxygen species ( . OH, 1 O 2 , H 2 O 2 ) generated in cell-free
systems using isoluminol and luminol-enhanced chemiluminescence
and electronic absorption spectra. In the presence of 1, 2 and
3 a dose-dependent inhibition period was seen in this system as assayed
by isoluminol-enhanced chemiluminescence (ILCL) with
horseradish peroxidase (HRP), as also luminol-enhanced chemiluminescence
(LCL) with H 2 O 2 or ferrous iron. On the other hand,
these hydroxyanthraquinone were capable to quenching the absorbance
of ethanolic solutions of galvanoxyl radical. In a separate experiment
we observed the trapping of singlet oxygen ( 1 O 2 ) generated
by rose bengal, by the presence of 1, 2 or 3. These results
suggest that emodin, aloe-emodin and rhein scavenges reactive
oxygen and free radicals species in the following decreasing order:
emodin > rhein > aloe-emodin.
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