Effect of Molecular Interactions on Electron-Transfer and Antioxidant Activity of Bis(alkanol)selenides: A Radiation Chemical Study.

Understanding electron-transfer processes is crucial for developing organoselenium compounds as antioxidants and anti-inflammatory agents. To find new redox-active selenium antioxidants, we have investigated one-electron-transfer reactions between hydroxyl ((.) OH) radical and three bis(alkanol)selenides (SeROH) of varying alkyl chain length, using nanosecond pulse radiolysis. (.) OH radical reacts with SeROH to form radical adduct, which is converted primarily into a dimer radical cation (>Se∴Se<)(+) and α-{bis(hydroxyl alkyl)}-selenomethine radical along with a minor quantity of an intramolecularly stabilized radical cation. Some of these radicals have been subsequently converted to their corresponding selenoxide, and formaldehyde. Estimated yield of these products showed alkyl chain length dependency and correlated well with their antioxidant ability. Quantum chemical calculations suggested that compounds that formed more stable (>Se∴Se<)(+) , produced higher selenoxide and lower formaldehyde. Comparing these results with those for sulfur analogues confirmed for the first time the distinctive role of selenium in making such compounds better antioxidants.

Contrasting reactions of hydrated electron and formate radical with 2-thio analogues of cytosine and uracil.

2-Thiocytosine (TC) and 2-thiouracil (TU) were subjected to hydrated electron (eaq-), formate radical (CO2˙-) and 2-hydroxypropan-2-yl radical ((CH3)2˙COH) reactions in aqueous medium. Transients were characterized by absorption spectroscopy and the experimental findings were rationalized by DFT calculations at LC-ωPBE and M06-2X levels using a 6-311+G(d,p) basis set and SMD solvation. In eaq- reactions, a ring N-atom protonated radical of TC and an exocyclic O-atom protonated radical of TU were observed via addition of eaq- and subsequent protonation by solvent molecules. However, two competing but simultaneous mechanisms are operative in CO2˙- reactions with TC and TU. The first one corresponds to formations of N(O)-atom protonated radicals (similar to eaq- reactions); the second mechanism led to 2 center-3 electron, sulfur-sulfur bonded neutral dimer radicals, TCdim˙ and TUdim˙. DFT calculations demonstrated that H-abstraction by CO2˙- from TC(TU) results in S-centered radical which upon combination with TC(TU) provide the dimer radical. In some cases, DFT energy profiles were further validated by CBS-QB3//M06-2X calculations. This is the first time report for a contradictory behavior in the mechanisms of eaq- and CO2˙- reactions with any pyrimidines or their thio analogues.

Fatty acid conjugates of water-soluble (±)-trans-Selenolane-3,4-diol: effects of alkyl chain length on the antioxidant capacity.

Fatty acid monoesters of the title compound (DHS(red) ), of variable carbon chain length (propionate, laurate, myristate, palmitate, and stearate), were synthesized, and their antioxidant capacities were evaluated by means of a lipid peroxidation assay with lecithin/cholesterol liposomes. The selenides with long alkyl chains exhibited significant antioxidant activity (IC50 =9-34 µM) against accumulation of lipid hydroperoxide. Incorporation of the myristate into the liposome was ≈50 % by EPMA analysis. Intermediacy of the selenoxide was examined by NMR. In addition, enhancement of interfacial redox catalytic activity was observed for the myristate, but not for PhSeSePh and edaravone, in a PhCl/H2 O biphasic peroxidation assay. These results suggested that a combination of a hydrophilic selenide moiety as a redox center with a long alkyl chain is an effective approach to selenium antioxidants with interfacial glutathione-peroxidase-like (GPx-like) activity. The activity can be controlled by the alkyl chain length.

Stable selones in glutathione-peroxidase-like catalytic cycle of selenonicotinamide derivative.

Selenonicotinamide, 2,2'-diselenobis[3-amidopyridine] (NictSeSeNict) exhibits glutathione-peroxidase (GPx)-like activity, catalyzing the reduction of hydrogen peroxide (H2O2) by glutathione (GSH). Estimated reactivity parameters for the reaction of selenium species, according to the Dalziel kinetic model, towards GSH (ϕGSH) and H2O2 (ϕH2O2), indicated that the rate constant for the reaction of NictSeSeNict with GSH is higher as compared to that with H2O2, indicating that the activity is initiated by reduction. (77)Se NMR spectroscopy, HPLC analysis, mass spectrometry (MS) and absorption spectroscopy were employed to understand the nature of selenium intermediates responsible for the activity. The (77)Se NMR resonance at 525 ppm due to NictSeSeNict disappeared in the presence of GSH with the initial appearance of signals at δ 364 and 600 ppm, assigned to selone (NictC=Se) and selenenyl sulfide (NictSeSG), respectively. Reaction of H2O2 with NictSeSeNict produced a mixture of selenenic acid (NictSeOH) and seleninic acid (NictSeO2H) with (77)Se NMR resonances appearing at 1069 and 1165 ppm, respectively. Addition of three equivalents of GSH to this mixture produced a characteristic (77)Se NMR signal of NictSeSG. HPLC analysis of the product formed by the reaction of NictSeSeNict with GSH confirmed the formation of NictC=Se absorbing at 375 nm. Stopped-flow kinetic studies with global analysis revealed a bimolecular rate constant of 4.8 ± 0.5 × 10(3) M(-1) s(-1) and 1.7 ± 0.6 × 10(2) M(-1) s(-1) for the formation of NictC=Se produced in two consecutive reactions of NictSeSeNict and NictSeSG with GSH, respectively. Similarly the rate constant for the reaction of NictC=Se with H2O2 was estimated to be 18 ± 1.8 M(-1) s(-1). These studies clearly indicated that the GPx activity of NictSeSeNict is initiated by reduction to form NictSeSG and a stable selone, which is responsible for its efficient GPx activity.

Pulse radiolysis studies of 3,5-dimethyl pyrazole derivatives of selenoethers.

One electron redox reaction of two asymmetric 3,5-dimethyl pyrazole derivatives of selenoethers attached to ethanoic acid (DPSeEA) and propionic acid (DPSePA) were studied by pulse radiolysis technique using transient absorption detection. The reaction of the hydroxyl ((•)OH) radical with DPSeEA or DPSePA at pH 7 produced transients absorbing at 500 nm and at 300 nm, respectively. The absorbance at 500 nm increased with increasing parent concentration indicating formation of dimer radical cations. From the absorbance changes, the equilibrium constants for the formation of dimer radical cation of DPSeEA and DPSePA were estimated as 2020 and 1608 M(-1), respectively. The rate constants at pH 7 for the reaction of the (•)OH radical with DPSeEA and DPSePA were determined to be 9.6 × 10(9) and 1.4 × 10(10) M(-1) s(-1), respectively. The dimer radical cation of DPSeEA and DPSePA decayed by first order kinetics with a rate constant of 2.8 × 10(4) and 5.5 × 10(3) s(-1), respectively. The yield of radical cations of DPSeEA and DPSePA were estimated from the secondary electron transfer reaction, which corresponds to 38% and 48% of (•)OH radical yield, respectively. Some fraction of monomer radical cation undergoes decarboxylation reaction, and the yield of decarboxylation was 25% and 20% for DPSeEA and DPSePA, respectively. These results have implication in understanding their antioxidant activity. The reaction of trichloromethyl peroxyl radical, glutathione, and ascorbic acid further support their antioxidant behavior.

Radical cations of aromatic selenium compounds: role of Se···X nonbonding interactions.

Selenium centered radical cations in aliphatic selenium compounds are stabilized by formation of two-center-three electron (2c-3e) hemi bonds either with nearby heteroatoms forming monomer radicals or with selenium atoms of the parent molecules forming dimer radicals. Such radicals in aromatic selenium compounds would generally be stabilized as monomers by the delocalization of the spin density along the aromatic ring. To test the assumption if aromatic selenides having Se···X nonbonding interactions can show different types of radical cations, we have performed pulse radiolysis studies of three structurally related aromatic selenium compounds and the results have been substantiated with cyclic voltammetry and quantum chemical calculations. The three aromatic selenium compounds have functional groups like -CH2N(CH3)2 (1), -CH2OH (2), and -CH3 (3) at ortho position to the -SeCH3 moiety. The energy of Se···X nonbonding interactions (E(nb)) for these compounds is in the order 1 (Se···N) > 2 (Se···O) > 3 (Se···H). Radical cations, 1(•+), 2(•+) and 3(•+) were produced by the one-electron oxidation of 1, 2 and 3 by radiolytically generated (•)OH and Br2(•-) radicals. Results on transient spectra, lifetime, and secondary reactions of 1(•+), 2(•+), and 3(•+) indicated that 1(•+) shows a significantly different absorption spectrum, longer lifetime, and less oxidizing power compared to those of 2(•+) or 3(•+). Quantum chemical calculations suggested that 1(•+) is stabilized by the formation of a 2c-3e bond between Se and N atoms, whereas 2(•+) and 3(•+) acquire stability through the delocalization of the spin density on the aromatic ring. These results provide evidence for the first time that stronger nonbonding interactions between Se···N in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds.

Selenium-containing amino acids are targets for myeloperoxidase-derived hypothiocyanous acid: determination of absolute rate constants and implications for biological damage.

Elevated MPO (myeloperoxidase) levels are associated with multiple human inflammatory pathologies. MPO catalyses the oxidation of Cl-, Br- and SCN- by H2O2 to generate the powerful oxidants hypochlorous acid (HOCl), hypobromous acid (HOBr) and hypothiocyanous acid (HOSCN) respectively. These species are antibacterial agents, but misplaced or excessive production is implicated in tissue damage at sites of inflammation. Unlike HOCl and HOBr, which react with multiple targets, HOSCN targets cysteine residues with considerable selectivity. In the light of this reactivity, we hypothesized that Sec (selenocysteine) residues should also be rapidly oxidized by HOSCN, as selenium atoms are better nucleophiles than sulfur. Such oxidation might inactivate critical Sec-containing cellular protective enzymes such as GPx (glutathione peroxidase) and TrxR (thioredoxin reductase). Stopped-flow kinetic studies indicate that seleno-compounds react rapidly with HOSCN with rate constants, k, in the range 2.8×10(3)-5.8×10(6) M-1·s-1 (for selenomethionine and selenocystamine respectively). These values are ~6000-fold higher than the corresponding values for H2O2, and are also considerably larger than for the reaction of HOSCN with thiols (16-fold for cysteine and 80-fold for selenocystamine). Enzyme studies indicate that GPx and TrxR, but not glutathione reductase, are inactivated by HOSCN in a concentration-dependent manner; k for GPx has been determined as ~5×105 M-1·s-1. Decomposed HOSCN did not induce inactivation. These data indicate that selenocysteine residues are oxidized rapidly by HOSCN, with this resulting in the inhibition of the critical intracellular Sec-dependent protective enzymes GPx and TrxR.

3,3'-Diselenodipropionic acid (DSePA): A redox active multifunctional molecule of biological relevance.

BACKGROUND: Extensive research is being carried out globally to design and develop new selenium compounds for various biological applications such as antioxidants, radio-protectors, anti-carcinogenic agents, biocides, etc. In this pursuit, 3,3'-diselenodipropionic acid (DSePA), a synthetic organoselenium compound, has received considerable attention for its biological activities. SCOPE OF REVIEW: This review intends to give a comprehensive account of research on DSePA so as to facilitate further research activities on this organoselenium compound and to realize its full potential in different areas of biological and pharmacological sciences. MAJOR CONCLUSIONS: It is an interesting diselenide structurally related to selenocystine. It shows moderate glutathione peroxidase (GPx)-like activity and is an excellent scavenger of reactive oxygen species (ROS). Exposure to radiation, as envisaged during radiation therapy, has been associated with normal tissue side effects and also with the decrease in selenium levels in the body. In vitro and in vivo evaluation of DSePA has confirmed its ability to reduce radiation induced side effects into normal tissues. Administration of DSePA through intraperitoneal (IP) or oral route to mice in a dose range of 2 to 2.5 mg/kg body weight has shown survival advantage against whole body irradiation and a significant protection to lung tissue against thoracic irradiation. Pharmacokinetic profiling of DSePA suggests its maximum absorption in the lung. GENERAL SIGNIFICANCE: Research work on DSePA reported in fifteen years or so indicates that it is a promising multifunctional organoselenium compound exhibiting many important activities of biological relevance apart from radioprotection.

Anti-unlcer and antimicrobial activities of sodium selenite against Helicobacter pylori: in vitro and in vivo evaluation.

Abstract We examined sodium selenite, an inorganic selenium supplement, for its ulcer healing properties and antimicrobial activity against gastric pathogen Helicobacter pylori. Minimum inhibitory concentrations (MIC) were determined using disk diffusion and flow cytometry. The studies were performed over a concentration range of 1 microg/ml to 500 microg/ml sodium selenite. Mild activity was seen at 10 microg/ml and 50 microg/ml, a moderate response at 100 microg/ml and strong response at 500 microg/ml with a MIC value of 10 microg/ml. The compound was found to be active at low pH without any resistance after 10 passages. Flow cytometry data showed a characteristic shift of the viability peak in comparison with the control, thereby confirming the bactericidal effects of sodium selenite. Sodium selenite administered in Wistar rats, pre-ulcerated with naproxen and infected with H. pylori, showed ulcer healing and anti-H. pylori activity at a concentration range of 10-50 microg/rat; however concentrations of 100 microg/rat and 500 microg/rat were found to be toxic in the in vivo studies. In conclusion, sodium selenite shows both ulcer healing and anti-H. pylori activity at a low concentration (10 microg/rat) without toxicity.

One-electron redox processes in a cyclic selenide and a selenoxide: a pulse radiolysis study.

One-electron redox reactions of cyclic selenium compounds, DL-trans-3,4-dihydroxy-1-selenolane (DHS(red)), and DL-trans-3,4-dihydroxy-1-selenolane oxide (DHS(ox)) were carried out in aqueous solutions using nanosecond pulse radiolysis, and the resultant transients were detected by absorption spectroscopy. Both *OH radical and specific one-electron oxidant, Br(2)(*-) radical reacted with DHS(red) to form similar transients absorbing at 480 nm, which has been identified as a dimer radical cation (DHS(red))(2)(*+). Secondary electron transfer reactions of the (DHS(red))(2)(*+) were studied with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS(2-)) and superoxide (O(2)(*-)) radicals. The bimolecular rate constants for the electron transfer reaction between (DHS(red))(2)(*+) with ABTS(2-) was determined as 2.4 +/- 0.4 x 10(9) M(-1) s(-1). From this reaction, the yield of (DHS(red))(2)(*+) formed on reaction with *OH radical was estimated in the presence of varying phosphate concentrations. (DHS(red))(2)(*+) reacted with O(2)(*-) radical with a bimolecular rate constant of 2.7 +/- 0.1 x 10(9) M(-1) s(-1) at pH 7. From the same reaction, the positive charge on (DHS(red))(2)(*+) was confirmed by the kinetic salt effect. HPLC analysis of the products formed in the reaction of (DHS(red))(2)(*+) with O(2)(*-) radicals showed formation of the selenoxide, DHS(ox). In order to know if a similar mechanism operated during the reduction of DHS(ox), its reactions with e(aq)(-) were studied at pH 7. The rate constant for this reaction was determined as 5.6 +/- 0.9 x 10(9) M(-1) s(-1), and no transient absorption could be observed in the wavelength region from 280 to 700 nm. It is proposed that the radical anion (DHS(ox))(*-) formed by a one-electron reduction would get protonated to form a hydroxyl radical adduct, which in presence of proton donors, would undergo dehydration to form DHS(*+). Evidence for this mechanism was obtained by converting DHS(*+) to (DHS(red))(2)(*+) with the addition of DHS(red) to the same system. Quantum chemical calculations provided supporting evidence for some of the redox reactions.

Reactions of hydroxyl radical with bergenin, a natural poly phenol studied by pulse radiolysis.

Reactions of pulse radiolytically generated hydroxyl (()OH) radicals and one-electron specific oxidants, Br(2)(-) radicals with bergenin, a polyphenolic tannin derivative, were studied and the transients detected by absorption spectrometry. The transient absorption spectrum produced during the reaction of ()OH radicals with bergenin was broad, and pH dependent. Different modes of reactions of ()OH radicals with bergenin, viz., addition to the aromatic ring adduct and hydrogen abstraction was established by time resolved (5-400micros) transient absorption studies and also by the reaction of Br(2)(-) radicals. Comparing the transient spectra with ()OH radicals and Br(2)(-) radicals at pH 4.5 and 8.5, the absorption maximum of the phenoxyl radical was found to be at 440nm at pH 4.5 and 480nm at pH 8.5. Phenoxyl radicals are produced during ()OH radical reaction through the formation of ()OH radical adduct followed by water/OH(-) elimination. While the phenoxyl radicals of bergenin are oxidizing in nature, the hydroxyl radical adducts and the radicals produced from hydrogen abstraction are of reducing nature. The yield of the oxidizing radicals produced from the ()OH radical reaction with bergenin was determined to be 26.2% by secondary electron transfer reaction from TMPD. On the other hand the yield of reducing radicals produced from the ()OH radical reaction with bergenin was determined to be 74.1% by secondary electron transfer reaction to MV(2+). ()OH radical reactions with bergenin under oxygenated conditions and reaction with trichloro methyl peroxyl radicals with bergenin produced a new transient absorbing at 400nm, which is attributed to peroxyl type of radicals. The one-electron reduction potential for the formation of phenoxyl radical from bergenin was determined to be 0.938V versus NHE at pH 7, by electron transfer equilibrium between bergenin and chlorpromazine. The above results confirmed that reaction of ()OH radicals with bergenin, mainly produced radical adducts and one-electron oxidation accounts to only a minor process. The radical adducts may be converted to peroxyl radicals in presence of oxygen. Based on these results it can be concluded that although bergenin is a polyphenol, it may not act as a potent antioxidant, but may be act as pro-oxidant.

Differential free radical scavenging activity and radioprotection of caesalpinia digyna extracts and its active constituent.

Two extracts E1and E2 were prepared from the dried root of the plant Caesalpinia digyna by extracting with solvents of different polarity. The extracts were standardized with respect to a polyphenol, bergenin, by LC- MS analysis and they were subjected to free radical scavenging activity and in vitro radioprotection studies. Free radical reactions were carried out with superoxide, hydroxyl, and peroxyl radicals and DPPH. In vitro radioprotecting activity was studied by following their effect on gamma-radiation induced lipid peroxidation, protein carbonylation and DNA damage. The results indicated that E1 with higher free radical scavenging ability is also a more potent inhibitor of radiation induced damage to proteins, DNA and liposomes than E2. Comparing the results with those for bergenin indicated that bergenin alone is not responsible for the free radical scavenging ability and in vitro radioprotection. The studies also confirmed that the extracts enriched with bergenin are more effective than the isolated polyphenol, bergenin.

pH-Labile Magnetic Nanocarriers for Intracellular Drug Delivery to Tumor Cells.

We report the development of pH-labile ascorbic acid-coated magnetic nanocarriers (AMNCs) for effective delivery of the anticancer drug doxorubicin hydrochloride (DOX) to tumor cells. The uniqueness of this drug delivery system lies in the covalent conjugation of DOX through carbamate and hydrazone bonds, resulting in a slow and sustained drug release profile at different environmental acidities. X-ray diffraction and transmission electron microscopy analyses reveal the formation of crystalline single-phase Fe3O4 nanoparticles with an average size of 10 nm. The changes in the interfacial characteristics of the nanocarriers and the presence of organic coatings are probed by infrared spectroscopy, dynamic light scattering, zeta potential, and thermogravimetric measurements. AMNCs show high colloidal stability in aqueous and cell culture media and possess good magnetic field responsivity and protein resistance characteristics. The drug-loaded nanocarriers exhibited sustained pH-triggered release of drug molecules in acidic mediums, substantial cellular internalization, and significant toxicity toward the proliferation of mouse skin fibrosarcoma (WEHI-164), human breast cancer (MCF-7), and human lung cancer (A549) cells. However, it showed significantly lower toxicity in human normal lung (WI26VA) cells. Overall, these results suggest a pH-sensitive drug release of nanoformulations, which showed selective toxicity to tumor than normal cells.

Mechanism of radioprotection by dihydroxy-1-selenolane (DHS): Effect of fatty acid conjugation and role of glutathione peroxidase (GPx).

Dihydroxy-1-selenolane (DHS) previously reported to exhibit radioprotective activity was investigated to understand its mechanism of action in CHO cells of epithelial origin. DHS pre-treatment at 25 µM for 16 h significantly protected CHO cells from radiation (4-11 Gy)-induced delayed mitotic cell death. Further to examine, how increased cellular uptake can influence this mechanism, studies have been performed with DHS-C6, a lipophilic conjugate of DHS. Accordingly CHO cells pre-treated with DHS-C6, showed increased survival against radiation exposure. Notably treatment with both DHS and DHS-C6 significantly increased glutathione peroxidase (GPx) activity in cells by âˆ¼ 2.5 fold. Additionally, the compound DHS or DHS-C6 led to faster repair of DNA in irradiated cells and subsequently inhibited the G2/M arrest. Anticipating the role of GPx in radioprotection, our investigations revealed that addition of mercaptosuccinic acid, a pharmacological inhibitor of GPx reversed all the above effects of DHS or DHS-C6. Further inhibitors of check point kinase 1 (CHK1) and DNA-protein kinase (DNA-PK) although abrogated the radioprotective effect of DHS or DHS-C6 separately, did not show additive effect in combination with GPx inhibitor, suggesting their cross talk. In contrast to these results, both DHS and DHS-C6 treatment did not protect spleen lymphocytes from the radiation-induced apoptosis. Thus results confirmed that both DHS and DHS-C6 protected cells from radiation-induced mitotic death by augmenting DNA repair in a GPx dependant manner.

Toxicity and Antigenotoxic Effect of Hispolon Derivatives: Role of Structure in Modulating Cellular Redox State and Thioredoxin Reductase.

Hispolon (HS), a bioactive polyphenol, and its derivatives such as hispolon monomethyl ether (HME), hispolon pyrazole (HP), and hispolon monomethyl ether pyrazole (HMEP) were evaluated for comparative toxicity and antigenotoxic effects. The stability of HS derivatives in biological matrices followed the order HS < HP ≈ HME < HMEP. The cytotoxicity analysis of HS derivatives indicated that HP and HMEP were less toxic than HS and HME, respectively, in both normal and tumor cell types. The mechanisms of toxicity of HS and HME involved inhibition of thioredoxin reductase (TrxR) and/or induction of reductive stress. From the enzyme kinetic and docking studies, it was established that HS and HME interacted with the NADPH-binding domain of TrxR through electrostatic and hydrophobic bonds, resulting in inhibition of the catalytic activity. Subsequently, treatment with HS, HP, and HMEP at a nontoxic concentration of 10 µM in Chinese Hamster Ovary (CHO) cells showed significant protection against radiation (4 Gy)-induced DNA damage as assessed by micronuclei and γ-H2AX assays. In conclusion, the above results suggested the importance of phenolic and diketo groups in controlling the stability and toxicity of HS derivatives. The pyrazole derivatives, HP and HMEP, may gain significance in the development of functional foods.

Transport of liposomal and albumin loaded curcumin to living cells: an absorption and fluorescence spectroscopic study.

Curcumin, a lipid soluble antioxidant, exhibits solvent and medium sensitive absorption and fluorescence properties. Using such changes, the average binding constants of curcumin to phosphatidylcholine (PC) liposomes and human serum albumin (HSA) were estimated to be 2.5 x 10(4) M(-1) and 6.1 x 10(4) M(-1) respectively. From the studies on temperature dependent fluorescence anisotropy of liposomal curcumin and its fluorescence quenching by acrylamide and iodide, it was concluded that curcumin is located in the gel phase of the liposomes. Similarly from the studies on quenching of tryptophan fluorescence in HSA by curcumin, it was found to be in the same domain as that of tryptophan. Both liposomal and HSA vehicles were examined for the transfer of curcumin to spleen lymphocyte cells, EL4 lymphoma cell line and compared with aqueous DMSO vehicles. From these studies it was found that liposomal vehicle is capable of loading more curcumin in to cells than HSA or aqueous-DMSO, and lymphoma cells show preferential uptake of curcumin to lymphocytes. The fluorescence of curcumin in EL4 lymphoma cells was found to be significantly higher as compared to the lymphocytes. The present study demonstrates a simple and quantitative method of estimation of curcumin delivered to cells by different vehicles using absorption and fluorescence spectroscopy.

Cellular evaluation of diselenonicotinamide (DSNA) as a radioprotector against cell death and DNA damage.

Diselenonicotinamide (DSNA), a synthetic organoselenium compound, was evaluated for its radioprotective effect in cellular models. A clonogenic assay in Chinese Hamster Ovary (CHO) cells and an apoptosis assay in murine splenic lymphocytes indicated that pre-treatment with DSNA at a concentration of 25 µM significantly protected them from radiation-induced cell death. Upon irradiation (1-12 Gy), dose-response studies were carried out under similar treatment conditions, and its dose modification factor (DMF) was estimated to be 1.26. Furthermore, DSNA showed its radioprotective effect, even when administered after exposure to radiation. Mechanistic investigation revealed that DSNA increased the intracellular levels of GPx and GSH in irradiated cells. In line with this observation, the addition of a pharmacological inhibitor of GPx cycle, abrogated the activity of DSNA. The radioprotective effect of DSNA was also complemented by its ability to prevent radiation-induced DNA damage as monitored by micronucleus and γ-H2AX assays. Furthermore, treatment with DSNA did not show much change in the expressions of Nrf2 dependent genes (γ-GCL and HO-1), but the presence of a pharmacological inhibitor of Nrf2 abrogated the radioprotective activity of DSNA against cell death and DNA damage. Additionally, ATRA treatment also inhibited the DSNA-mediated up-regulation of a repair gene RAD51, suggesting possible involvement of basal Nrf2 in the anti-genotoxic effect of DSNA. In conclusion, the present study demonstrates radioprotection by a synthetic organoselenium compound containing nutritionally important moieties like selenium and nicotinamide.

Dihydroxyselenolane (DHS) supplementation improves survival following whole-body irradiation (WBI) by suppressing tissue-specific inflammatory responses.

Dihydroxyselenolane (DHS), a simple water-soluble organoselenium compound, was evaluated for radioprotection in BALB/c mice after whole-body irradiation (WBI) (8Gy (60)Co, 1Gy/min), by monitoring 30-d post-irradiation survival and biochemical/histological changes in radiosensitive organs. Intraperitoneal administration of DHS at 2mg/kg for five consecutive days before irradiation and three times per week during the post-irradiation period showed maximum benefit (40% improvement in 30 d post-irradiation survival). DHS treatment, despite inducing expression of glutathione peroxidases (GPx1, GPx2, and GPx4) in spleen and intestine, did not protect against radiation-induced acute (10-day) haematopoietic and gastrointestinal toxicities. DHS treatment significantly reduced radiation-induced DNA damage in peripheral leukocytes and inflammatory responses in intestine, lung, and circulation. The anti-inflammatory effect of DHS was associated with reductions in lipid peroxidation, expression of pro-inflammatory genes such as Icam-1, Ccl-2, and iNos-2, and subsequent infiltration of inflammatory cells. Irradiated mice treated with DHS survived until day 30 post-irradiation and showed restoration of spleen cellularity and intestinal villi, but had moderately increased systemic and tissue-specific inflammatory responses. Another organoselenium compound, selenomethionine, evaluated in parallel with DHS at the same dose and treatment schedule, showed comparable radioprotective effects. The mechanism of radioprotection by DHS is mainly via suppression of inflammatory responses.

Free radical reactions of isoxazole and pyrazole derivatives of hispolon: kinetics correlated with molecular descriptors.

Hispolon (HS), a natural polyphenol found in medicinal mushrooms, and its isoxazole (HI) and pyrazole (HP) derivatives have been examined for free radical reactions and in vitro antioxidant activity. Reaction of these compounds with one-electron oxidant, azide radicals ([Formula: see text]) and trichloromethyl peroxyl radicals ([Formula: see text]), model peroxyl radicals, studied by nanosecond pulse radiolysis technique, indicated formation of phenoxyl radicals absorbing at 420 nm with half life of few hundred microseconds (µs). The formation of phenoxyl radicals confirmed that the phenolic OH is the active centre for free radical reactions. Rate constant for the reaction of these radicals with these compounds were in the order kHI ≅ kHP > kHS. Further the compounds were examined for their ability to inhibit lipid peroxidation in model membranes and also for the scavenging of 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical and superoxide ([Formula: see text]) radicals. The results suggested that HP and HI are less efficient than HS towards these radical reactions. Quantum chemical calculations were performed on these compounds to understand the mechanism of reaction with different radicals. Lower values of adiabatic ionization potential (AIP) and elevated highest occupied molecular orbital (HOMO) for HI and HP compared with HS controlled their activity towards [Formula: see text] and [Formula: see text] radicals, whereas the contribution of overall anion concentration was responsible for higher activity of HS for DPPH, [Formula: see text], and lipid peroxyl radical. The results confirm the role of different structural moieties on the antioxidant activity of hispolon derivatives.