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 Linn), is known as a potent antioxidant comparable to a-tocopherol. Its antioxidant activities have been studied in several in vitro models. 1) Despite its poor bioavailability, 2-4) the therapeutic benefits of curcumin in animals have been demonstrated in several oxidative stress models such as Alzheimer's disease, 5) ethanol induced oxidative injury in brain, liver, heart and kidney, 6,7) and myocardial ischemic damage.8) It is possible that the metabolites of curcumin could mediate major antioxidant activities in vivo.In mouse, curcumin is first biotransformed to dihydrocurcumin (DHC) and tetrahydrocurcumin (THC) and these compounds are subsequently converted to monoglucuronide conjugates including curcumin-glucuronide, dihydrocurcuminglucuronide and tetrahydrocurcumin-glucuronide. 9) In human and rat hepatocytes, curcumin is metabolized into curcumin glucuronide, curcumin sulfate, THC, hexahydrocurcumin (HHC) and octahydrocurcumin (OHC). 10,11) Antioxidant activities of THC have already been studied both in vitro and in vivo. Venkatesan et al. 12) reported that THC had higher activity than curcumin in protecting the nitrite induced oxidation of haemoglobin and lysis of erythrocytes. THC has also been demonstrated to be more potent than curcumin in protection against ferric nitrilotriacetate (Fe-NTA) induced oxidative renal damage in mice. 13) THC produces this protective effect to cells against oxidative stress by scavenging of free radicals, 14) inhibition of lipid peroxidation and formation of hydroperoxides. 15) To the best of our knowledge, the antioxidant activities of HHC and OHC have not been reported.We are also interested in the antioxidant activities of natural demethoxyl derivatives of curcumin, demethoxycurcumin (Dmc) and bisdemethoxycurcumin (Bdmc), which are always found together with curcumin in tumeric extracts and in commercial preparation of curcumin. Antioxidant activities of Dmc and Bdmc have been reported in the model systems of hydroxyl radical induced DNA damage, 16) DPPH radical scavenging activity 17) and recently in lipid peroxidation. 18)However, to date, there has been no comparative study on the antioxidant activities of curcumin with its natural demethoxy derivatives and metabolite hydrogenated derivatives. In particular, the ability to provide protection against lipid and cell membrane damage of all of those derivatives has not yet been reported. The aim of this study is to compare the antioxidant activities of curcumin, its demethoxy derivatives (Dmc and Bdmc), and hydrogenated derivatives (THC, HHC and OHC) using three in vitro models: radical scavenging activity by DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, AAPH [2,2Ј-azobis(2-amidinopropane)dihydrochloride] induced linole...
Hibiscus sabdariffa LINN. (roselle) is widely cultivated in tropical areas and its red persistent calyx is the major component possessing a sour taste that is used as beverage and food colorants. It contains many chemical constituents including alkaloids, L-ascorbic acid, anisaldehyde, anthocyanin, bcarotene, b-sitosterol, citric acid, cyanidin-3-rutinoside, delphinidin, galactose, gossypetin, hibiscetin, mucopolysaccharide, pectin, protocatechuic acid, polysaccharide, quercetin, stearic acid and wax. As a traditional medicine, it is claimed to be effective against kidney stones and urinary bladder stones.1,2) It is also used for its antibacterial, antifungal, hypocholesterolemic, antispasmodic and antihypertensive actions. [3][4][5][6] Numerous studies have linked the elevation of plasma low-density lipoprotein (LDL)-cholesterol (LDL-C) level with the increased incidence of atherosclerotic events. LDL particles undergo extensive lipid peroxidation, resulting in generation of oxidized LDL and formation of atherosclerotic lesions. [7][8][9][10][11] Predictably, antioxidants such as a-tocopherol and probucol have been found to reduce LDL oxidation. [12][13][14][15] Various antioxidant constituents have been found in the calyx of Hibiscus sabdariffa LINN., including hibiscus anthocyanin, quercetin, L-ascorbic acid and protocatechuic acid (PCA). Antioxidant effects of roselle extracts have been investigated in many experimental models, [16][17][18][19] however the antioxidant effects of Hibiscus sabdariffa LINN. on LDL oxidation have so far not been fully determined. The present study was designed to quantitatively investigate the antioxidant effect of roselle on the oxidative modification of LDL induced by CuSO 4 in vitro by monitoring the formation of conjugated dienes and the formation of thiobarbituric acid reactive substances (TBARs). MATERIALS AND MATHODS Plant Material and ExtractsThe dried calyxes of roselle were blended to a fine powder and one kilogram of powders was extracted with 1 l of water and filtered through filter paper by suction. The filtrates were pooled and dried at 50°C in a rotary evaporator. The average yield of the extract was 45.0%. The extracts were stored in a dark, moisture-free container at 4°C. The antioxidant effect of PCA, a polyphenolic compound, has been investigated and found to exhibit potent action in primary cultures of rat hepatocytes induced by tert-butylhydroperoxide (t-BHP).18) Therefore, in the present experiment, PCA content in the calyx of roselle was used for the standardization of batches; 25 mg of dried calyx extracts contained 10.98 mg of PCA. For this experiment, 150 mg of the crude extracts were dissolved in 1 ml of distilled water.Reagents Disodium ethylene diamine was purchased from Mallinckrodt Inc. (St. Louis, MO, U.S.A.) and sodium chloride, sodium carbonate and sodium hydroxide from Merck (Haar, Germany). Diethylether was purchased from BDH laboratory supplies (Poole, England). Thiobarbituric acid, potassium bromide, disodium phosphate, sodium phosphate, sod...
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