Beena Mishra

Quantitative cellular uptake, localization and cytotoxicity of curcumin in normal and tumor cells.

Using absorption and fluorescence spectroscopic methods, quantitative cellular uptake of curcumin, an antioxidant and anti-tumor agent from Curcuma longa, was calculated in two types of normal cells: spleen lymphocytes, and NIH3T3 and two tumor cell lines: EL4 and MCF7. Both the uptake and fluorescence intensity of curcumin were significantly higher in tumor cells compared to the normal cells. A linear dependency on the uptake was observed with treatment concentration of curcumin. Using laser confocal microscopy, intracellular localization of curcumin was monitored and the results indicated that curcumin is located both in the cell membrane and the nucleus. Sub-cellular fractionation of curcumin-loaded MCF7 cells supported the differential distribution of curcumin in membrane, cytoplasm and nuclear compartments of cell with maximum localization in the membrane. Cytotoxicity studies in different cell lines indicated that the toxicity of curcumin increased with increasing uptake.

Fluorescence spectroscopic studies on binding of a flavonoid antioxidant quercetin to serum albumins

Binding of quercetin to human serum albumin (HSA) was studied and the binding constant measured by following the red-shifted absorption spectrum of quercetin in the presence of HSA and the quenching of the intrinsic protein fluorescence in the presence of different concentrations of quercetin. Fluorescence lifetime measurements of HSA showed decrease in the average lifetimes indicating binding at a location, near the tryptophan moiety, and the possibility of fluorescence energy transfer between excited tryptophan and quercetin. Critical transfer distance (Ro) was determined, from which the mean distance between tryptophan-214 in HSA and quercetin was calculated. The above studies were also carried out with bovine serum albumin (BSA).

Reactions of superoxide radicals with curcumin: probable mechanisms by optical spectroscopy and EPR.

Reactions of superoxide-crown ether complex with curcumin have been studied in acetonitrile. Optical absorption spectra showed that curcumin on reaction with superoxide forms a blue color intermediate absorbing at 560 nm, which subsequently decayed in a few hours with the development of the absorption band corresponding to the parent curcumin. The regeneration was 100% at low superoxide concentrations (1:1, or 1:2 or 1:3 of curcumin:superoxide) but reduced to 60% at high superoxide concentration (>1:5). The regeneration of curcumin is confirmed by HPLC analysis. Stopped-flow studies in acetonitrile following either the decay of parent curcumin at 420 nm or formation of 560 nm absorption have been used to determine the rate constant for the reaction of superoxide with curcumin. EPR studies confirmed the disappearance of characteristic superoxide signal in presence of curcumin with the formation of new featureless signal with g=2.0067. Based on these studies it is concluded that at low superoxide concentrations curcumin effectively causes superoxide dismutation without itself undergoing any chemical change. At higher concentrations of superoxide, curcumin inhibits superoxide activity by reacting with it.

Pulse radiolysis studies on reactions of hydroxyl radicals with selenocystine derivatives.

Reactions of hydroxyl radicals (*OH) with selenocystine (SeCys) and two of its analogues, diselenodipropionic acid (SeP) and selenocystamine (SeA), have been studied in aqueous solutions at pHs of 1, 7, and 10 using the pulse radiolysis technique coupled with absorption detection. All of these diselenides react with *OH radicals with rate constants of approximately 10(10) M(-1) s(-1), producing diselenide radical cations ( approximately 1-5 micros after the pulse), with an absorption maximum at 560 nm, by elimination of H(2)O or OH(-) from hydroxyl radical adducts. Assignment of the 560 nm band to the diselenide radical cation was made by comparing the transient spectra with those produced upon reaction of diselenides with specific one-electron oxidants, Cl(2)(*-) (pH 1) and Br(2)(*-) radicals (pHs of 7 and 10). SeP having a carboxylic acid functionality showed quantitative conversion of hydroxyl radical adducts to radical cations. The compounds SeCys and SeA, having an amino functional group, in addition to the radical cations, produced a new transient with lambda(max) at 460 nm, at later time scales ( approximately 20-40 micros after the pulse). The rate and yield of formation of the 460 nm band increased with increasing concentrations of either SeCys or SeA. In analogy with similar studies reported for analogous disulfides, the 460 nm transient absorption band has been assigned to a triselenide radical adduct. The one-electron reduction potentials of the compounds were estimated to be 0.96, 1.3, and 1.6 V versus NHE, respectively, for SeP, SeCys, and SeA at pH 7. From these studies, it has been concluded that the electron-donating carboxylic acid group decreases the reduction potential and facilitates quantitative conversion of hydroxyl radical adducts to radical cations, while the electron-withdrawing NH(3)(+) group not only increases the reduction potential but also leads to fragmentation of the hydroxyl radical adduct to selenyl radicals, which are converted to triselenide radical adducts.

Correlating the GPx Activity of Selenocystine Derivatives with One-Electron Redox Reactions

With an aim to develop water soluble, less toxic glutathione peroxidase (GPx) mimics, three selenocystine (SeCys) derivatives, viz., selenocystamine (SeA), diselenodipropionic acid (SeP), and methyl ester of diselenodipropionic acid (MeSeP) have been synthesized and examined for GPx activity along with SeCys. The GPx activity of the compounds was found to be in the order SeCys ≅ SeA > MeSeP > SeP. The relative affinity of these GPx mimics towards the substrates thiol and hydroperoxide were determined by Lineweaver-Burk (L-B) plots. Since the enzyme activity involves several steps of reduction and oxidation reactions, attempts have been made to understand the role of such processes in deciding the efficacy of diselenides as GPx mimics. For this, one-electron redox chemistry of these compounds was studied in aqueous solutions at pH 7 using nanosecond pulse radiolysis technique. From these studies, it was concluded that SeCys and SeA, which can undergo easy one-electron reduction, exhibit high GPx activity.

Tuning intermicellar potentials through adsorbed molecules: van der Waals and Coulombic contributions

A micellar system with salicylic acid (SA) adsorbed on Triton X-100 is investigated with cloud-point measurements and small-angle neutron scattering. The novel feature of SA being in two forms, charged and uncharged, on the micellar surface is exploited to tune the van der Waals and the Coulombic contributions to the intermicellar potentials. A quantitative method of analysing the data, capable of being applied to similar systems, is described.

Pulse radiolysis studies on reaction of ˙OH radical with N-acetyl methionine in aqueous solution

In neutral aqueous solutions, hydroxyl radicals were observed to react with N-acetyl methionine (N-AM) to form transient absorption bands at 290, 360 and 490 nm. The absorbance at 290 and 360 nm bands decreased, whereas the absorbance at 490 nm band increased with solute concentration. The bands at 290 and 360 nm were observed to be quenched by oxygen, whereas the band at 490 nm was not affected. These bands were assigned to α-thio radical, OH-adduct and dimer radical cation, respectively. In acidic solutions, dimer radical cation was the only transient species formed on hydroxyl radical reaction. Cl˙−2 was able to react with N-AM and formed a dimer radical cation absorbing at 490 nm. Redox studies revealed that the one-electron oxidation potential of N-AM is between 1.3 and 2.1 V vs. NHE.

Direct energy transfer in charged micellar systems : a model

Abstract In the present paper, the non-radiative energy transfer between the donor coumarin 102 and the acceptor rhodamine 6G was studied in order to investitage Forsters mechanism when the donor is locked inside the micelle of cetyl trimethyl ammonium bromide and the acceptor is distributed in the electrical double layer. The Forster radius and the micellar charge are evaluated.

Formation of Dimer Radical Cations of Selenourea on Oxidation: Pulse Radiolysis Studies

Abstract Reactions of oxidizing radicals like hydroxyl (·OH) radical, specific electron transfer agents like N 3 ·, and I 2 −. radicals were studied with selenourea (SeU) and compared with thiourea (ThU) using pulse radiolysis technique in microsecond time scales. Both the compounds efficiently react with ·OH radicals, however, SeU undergoes easier oxidation by secondary oxidants as compared to ThU. The results were supported by cyclic voltammetry studies. The radical cations of both SeU and ThU formed on oxidation undergo dimerization with the parent molecule to form two-centered three-electron-hemi bonded radical cations absorbing at 410 and 400 nm respectively with the stabilization energies of 21.1 and 20.5 kcal/mol for SeU and ThU, respectively. Preliminary studies indicated that at low concentration of SeU, the dimerization is prevented and the oxidation reaction produced metallic Se nanoparticles.