Free radical scavenging ability and antioxidant efficiency of curcumin and its substituted analogue

Free radical reactions of curcumin and its ethoxy substituted derivative (C1) 1,7-bis-(4-hydroxy-3-ethoxy phenyl)-1,6-heptadiene-3,5-dione have been studied using a pulse radiolysis technique in homogeneous aqueous-organic solutions like acetonitrile-water and isopropanol-water mixtures, as well as in neutral TX-100 and cationic CTAB micellar solutions. The phenoxyl radicals of curcumin or C1 were generated by one-electron transfer to several oxidants like N(3)(.), Br(2)(-.), CCl(3)O(2)(.), glutathione radicals which exhibit absorption from a 300-600-nm wavelength region with the maximum at 490-500 nm. Other important properties of the phenoxyl radicals such as extinction coefficient, radical lifetime and their formation and decay rate constants were also determined in these systems. The antioxidant property of curcumin and C1 were estimated in terms of their ability to inhibit the lipid peroxidation in liposomes and also in terms of trolox equivalent antioxidant capacity (TEAC). The results were compared with alpha-tocopherol.     

Application of Marcus theory of electron transfer for the reactions between HRP compound I and II and 2,4-disubstituted phenols

Reactions between horseradish peroxidase (HRP) compound I and II and some natural phenolic antioxidants were studied at pH 7. The bimolecular rate constants for these reactions were determined using a sequential mixing stopped-flow spectrometer. The rate constants for the reactions of compound I were found to be two orders of magnitude higher than those for compound II. The phenols under study showed a significant difference in their one-electron reduction potential values. As the rate constants also changed systematically with their one-electron potentials, the Marcus theory of electron transfer was applied to the above determined rate constants and the thermodynamic driving force (deltaG(o)), from which the reorganization energy (lambda) for the electron transfer from phenols to both compound I and II was estimated.     

Antibacterial and ulcer healing effects of organoselenium compounds in naproxen induced and Helicobacter pylori infected Wistar rat model

Aim of the present study was to evaluate in vitro toxicity and in vivo antibacterial, anti-inflammatory, antiulcer, and antioxidant activities of two organoselenium compounds, selenocystine (SeCys) and ebselen (Ebs). The study was conducted in experimentally induced ulcers in rodent model infected with Helicobacter pylori (H. pylori). In vitro toxicological studies on normal spleenic lymphocytes revealed that SeCys and Ebs were non-toxic to the cells even at 100 μM concentration. Antibacterial activity was observed at 500 μg/mL concentration of either of the compounds against H. pylori. In vivo studies after treatment with SeCys and Ebs (500 μg/kg/day) resulted in significant reduction in ROS production and inhibition of lipid peroxidation in gastric tissue. The antioxidant and anti-inflammatory activities of both the compounds were also confirmed by their ability to lower GSH reduction, to induce the expression of antioxidant genes such as GPx-4, and MnSOD and to suppress inflammatory genes namely COX-2, TNF-α and TGF-β. In addition, the immunomodulatory activity of both the compounds was evident by enhance of the CD4 levels and maintenance of the IgG, IL-6 and IL-10 levels. Persistent treatment (500 μg/kg, for 28 days) with both the compounds showed considerable (p < 0.05) ulcer healing property supporting its role in gastro protection. In conclusion, the results of our study suggest that both SeCys and Ebs possess broad spectrum of activities without any potential toxicity.     

Delayed activation of PKCdelta and NFkappaB and higher radioprotection in splenic lymphocytes by copper (II)-Curcumin (1:1) complex as compared to curcumin

A mononuclear 1:1 copper complex of curcumin had been found to be superior to curcumin in its anti-oxidant properties. This paper describes the radio-protective effects of the complex in splenic lymphocytes from swiss mice. The complex was found to be very effective in protecting the cells against radiation-induced suppression of glutathione peroxidase, catalase and superoxide dismutase (SOD) activities. Both curcumin and the complex protected radiation-induced protein carbonylation and lipid peroxidation in lymphocytes with the complex showing better protection than curcumin. It also showed better overall protection by decreasing the radiation-induced apoptosis. The kinetics of activation of PKCdelta and NFkappaB after irradiation in presence or absence of these compounds was looked at to identify the molecular mechanism involved. The modulation of irradiation-induced activation of PKCdelta and NFkappaB by curcumin and the complex was found different at later time periods although the initial response was similar. The early responses could be mere stress responses and the activation of crucial signaling factors at later time periods may be the determinants of the fate of the cell. In this study this delayed effect was observed in case of complex but not in case of curcumin. The delayed effect of the complex along with the fact that it is a better free radical scavenger must be the reason for its better efficacy. The complex was also found to be less cytotoxic then curcumin at similar concentration.     

Reactions of reactive oxygen species (ROS) with curcumin analogues: Structure-activity relationship

Three curcumin analogues viz., bisdemethoxy curcumin, monodemethoxy curcumin, and dimethoxycurcumin that differ at the phenolic substitution were synthesized. These compounds have been subjected for free radical reactions with DPPH radicals, superoxide radicals (O(2)(?-)), singlet oxygen ((1)O(2)) and peroxyl radicals (CCl(3)O(2)(?)) and the bimolecular rate constants were determined. The DPPH radical reactions were followed by stopped-flow spectrometer, (1)O(2) reactions by transient luminescence spectrometer, and CCl(3)O(2)(?) reactions using pulse radiolysis technique. The rate constants indicate that the presence of o-methoxy phenolic OH increases its reactivity with DPPH and CCl(3)O(2)(?), while for molecules lacking phenolic OH, this reaction is very sluggish. Reaction of O(2)(?-) and (1)O(2) with curcumin analogues takes place preferably at β-diketone moiety. The studies thus suggested that both phenolic OH and the β-diketone moiety of curcumin are involved in neutralizing the free radicals and their relative scavenging ability depends on the nature of the free radicals.     

Antioxidant and antiproliferative activity of curcumin semicarbazone

A new semicarbazone derivative of curcumin (CRSC) was synthesized and examined for its antioxidant, antiproliferative, and antiradical activity and compared with those of curcumin (CR). The antioxidant activity was tested by their ability to inhibit radiation induced lipid peroxidation in rat liver microsomes. The antiproliferative activity was tested by studying the in vitro activity of CRSC against estrogen dependant breast cancer cell line MCF-7. Kinetics of reaction of (2,2'-diphenyl-1-picrylhydrazide) DPPH, a stable hydrogen abstracting free radical was studied to measure the antiradical activity using stopped-flow spectrophotometer. Finally one-electron oxidized radicals of CRSC were generated and characterized by pulse radiolysis. The results suggest that the probable site of attack for CRSC is both the phenolic OH and the imine carbonyl position. CRSC shows efficient antioxidant and antiproliferative activity although its antiradical activity is less than that of CR.     

Evaluation of a new copper(II)-curcumin complex as superoxide dismutase mimic and its free radical reactions

A mononuclear (1:1) copper complex of curcumin, a phytochemical from turmeric, was synthesized and examined for its superoxide dismutase (SOD) activity. The complex was characterized by elemental analysis, IR, NMR, UV-VIS, EPR, mass spectroscopic methods and TG-DTA, from which it was found that a copper atom is coordinated through the keto-enol group of curcumin along with one acetate group and one water molecule. Cyclic voltammetric studies of the complex showed a reversible Cu(2+)/Cu(+) couple with a potential of 0.402 V vs NHE. The Cu(II)-curcumin complex is soluble in lipids and DMSO, and insoluble in water. It scavenges superoxide radicals with a rate constant of 1.97 x 10(5) M(-1) s(-1) in DMSO determined by stopped-flow spectrometer. Subsequent to the reaction with superoxide radicals, the complex was found to be regenerated completely, indicating catalytic activity in neutralizing superoxide radicals. Complete regeneration of the complex was observed, even when the stoichiometry of superoxide radicals was 10 times more than that of the complex. This was further confirmed by EPR monitoring of superoxide radicals. The SOD mimicking activity of the complex was determined by xanthine/xanthine oxidase assay, from which it has been found that 5 microg of the complex is equivalent to 1 unit of SOD. The complex inhibits radiation-induced lipid peroxidation and shows radical-scavenging ability. It reacts with DPPH radicals with rate constant 10 times less than that of curcumin. Pulse radiolysis-induced one-electron oxidation of the complex by azide radicals in TX-100 micellar solutions produced strongly absorbing ( approximately 500 nm) phenoxyl radicals, indicating that the phenolic moiety of curcumin remained intact on complexation with copper. The results confirm that the new Cu(II)-curcumin complex possesses SOD activity, free radical neutralizing ability, and antioxidant potential. Quantum chemical calculations with density functional theory have been performed to support the experimental observations.     

Bioactivity-guided fractionation of Coronopus didymus: A free radical scavenging perspective

The whole plant aqueous extract of Coronopus didymus Linn. was fractionated on the basis of polarity and resulting fractions were evaluated for free radical scavenging ability. The most non-polar fraction (CDF1) was found to be more active than other fractions in scavenging DPPH, ABTS(-), nitric oxide and hydroxyl radicals in steady-state conditions. Stop-flow spectrometric studies showed 58.13% inhibition of 100 microM DPPH at a concentration of 150 microg/ml of CDF1 in 1000 s and 32.31% scavenging of 960 microM ABTS(-) at a concentration of 300 microg/ml of CDF1 in 100 s. The reaction of CDF1 with hydroxyl radicals produced by pulse radiolysis showed a transient spectrum with absorption peaks at 320, 390 and 400 nm, indicating the presence of flavonoids/related components. Competition kinetics with potassium thiocyanate against scavenging of hydroxyl radicals showed a reactivity of 0.1326 against thiocyanate. CDF1 also protected against Fenton reagent-induced calf thymus DNA damage at a concentration of 400 mg/ml indicating it to be the most potent fraction.     

In vitro radioprotection studies of organoselenium compounds: differences between mono- and diselenides

Organoselenium compounds belonging to the class of monoselenides, such as selenomethionine (SeM) and methylselenocysteine (MSeCys) and diselenides including selenocystine (SeCys) and selenopropionic acid (SePA), were examined for their comparative radioprotective effects using in vitro models. Effects of these compounds on the inhibition of γ-radiation induced lipid peroxidation in liposomes, protein carbonylation in bovine serum albumin (BSA) and strand breaks in pBR322 plasmid DNA, assessed, respectively, by the formation of thiobarbituric acid reactive substances, formation of 2,2′-dinitrophenyl hydrazine (DNPH) carbonyl complex and horizontal gel electrophoresis, were used to compare their radioprotective ability. The IC₅₀ values for SeCys, SePA, SeM and MSeCys for lipid peroxidation were 27 ± 1, 33 ± 2, 200 ± 8 and 163 ± 4 μM, respectively, and the values for inhibition of protein carbonylation were >200, 300 ± 6, 464 ± 8 and 436 ± 3 μM, respectively. Inhibition of DNA strand break formation was tested at 200 μM for all the compounds and SePA and SeCys exhibited a protective effect on DNA, while SeM and MSeCys did not lead to any protection. The in vitro cytotoxicity studies in normal and tumor cells revealed that MSeCys and SeM were not cytotoxic to lymphocytes and EL4 tumor cells at the concentrations employed. In contrast, SeCys was toxic, with a higher effect on tumor cells than lymphocytes. Our studies suggest that the non-toxic diselenides like SePA should be explored as protective agents against γ-irradiation induced damage.     

Synthesis, pulse radiolysis, and in vitro radioprotection studies of melatoninolipoamide, a novel conjugate of melatonin and alpha-lipoic acid

A novel conjugate of melatonin 2 and alpha-lipoic acid 4 has been prepared using DCC mediated coupling. The conjugate named melatoninolipoamide has been assigned its structure 1 on the basis of spectral analysis (UV, IR, NMR, and EI-MS). Pulse radiolysis studies of the conjugate were carried out in aqueous solutions with both oxidizing and reducing radicals. The results indicate that the melatonin moiety of the conjugate reacts preferably with oxidizing radicals and the lipoic acid moiety exhibits preferential reaction with reducing radicals. The in vitro radioprotection ability of 1 was examined by gamma-radiation induced lipid peroxidation in liposomes and hemolysis of erythrocytes, and compared the results with those of melatonin and alpha-lipoic acid. The studies suggest that the conjugate can be explored as a probable radioprotector.