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Journal of Thai Traditional & Alternative Medicine Vol. 6 No. 2 May-August (Supplement) 2008 ˜˘

OR-39

Comparative antioxidant activities of curcumin and its hydrogenated

metabolites

1 2 1 3
Poorichaya Somparn , Chada Phisalapong , Somjai Nakornchai , Supeenun Unchern ,
3
Noppawan Phumala Morales
1
Department of Pharmacology, Faculty of Pharmacy, Mahidol University; Bangkok 10400
2
Government Pharmaceutical Organization, Rama 6 Rd, Rajatevee, Bangkok 10400
3
Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok 10400

Rational: Oxidative stress plays a major role in the pathogenesis of various diseases including neurodegenerative
diseases, myocardial ischemia-reperfusion injury and cancer. Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-
heptadiene-3,5,-dione], the principal yellow pigment isolated from turmeric (Curcuma longa L.), is known as a
potent antioxidant comparable to α-tocopherol. Its antioxidant activities have been studied in several in vitro
models. Despite its poor bioavailability, the therapeutic benefits of curcumin in animals have been demonstrated in
several oxidative stress models, such as Alzheimerûs disease, ethanol-induced oxidative injury in brain, liver, heart
and kidney, and myocardial ischemic damage. It is possible that the metabolites of curcumin could mediate major
antioxidant activities in vivo. In human and rat hepatocytes, curcumin is metabolized into curcumin glucuronide,
curcumin sulfate, tetrahydrocurcumin (THC), hexahydrocurcumin (HHC) and octahydrocurcumin (OHC). However,
to date, there has been no comparative study on the antioxidant activities of curcumin and its hydrogenated
metabolites.

Objective: The aim of this study is to compare the antioxidant activities of curcumin and hydrogenated deriva-
tives (THC, HHC and OHC).

Methodology: The antioxidant activities of curcumin and its hydrogenated metabolites were comparatively studied

using 2,2-diphenyl-1-picrylhydrazyl (DDPH) radical, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH)-induced
linoleic oxidation and AAPH-induced red blood cell hemolysis assays.

Results: Hydrogenated derivatives of curcumin exhibited stronger DPPH scavenging activity compared to curcumin
and a reference antioxidant, trolox. The scavenging activity significantly decreased in the order
THC>HHC=OHC>trolox>curcumin. Stronger antioxidant activities toward lipid peroxidation and red blood cell
hemolysis were also demonstrated in the hydrogenated derivatives. By the model of AAPH-induced linoleic

oxidation, the stoichiometric number of peroxyl radical that can be trapped per molecule (n) of hydrogenated
derivatives were 3.4, 3.8 and 3.1 for THC, HHC and OHC, respectively. The number (n) of curcumin was 2.7
which are comparable to trolox. The inhibition of AAPH-induced red blood cell hemolysis significantly decreased

in the order OHC>THC>HHC>trolox>curcumin.
Conclusion: Results in all models demonstrated the ortho-methoxyphenolic groups of curcumin are involved in

antioxidant activities. On the other hand, hydrogenation at conjugated double bonds of the central seven carbon
chain and β diketone of curcumin to THC, HHC and OHC remarkably enhance antioxidant activity.