Soumyakanti Adhikari

Free radical scavenging behavior of folic acid: evidence for possible antioxidant activity.

The free radical scavenging properties and possible antioxidant activity of folic acid are reported. Pulse radiolysis technique is employed to study the one-electron oxidation of folic acid in homogeneous aqueous solution. The radicals used for this study are CCl(3)O(2)(*), N(3)(*), SO(4)(*-), Br(2)(*-), *OH, and O(*-). All these radicals react with folic acid under ambient condition at an almost diffusion-controlled rate producing two types of transients. The first transient absorption maximum is around 430 nm, which decays, and a simultaneous growth at around 390 nm is observed. Considering the chemical structure of folic acid, the absorption maximum at 430 nm has been assigned to a phenoxyl radical. The latter one is proposed to be a delocalized molecular radical. A permanent product has been observed in the oxidation of folic acid with CCl(3)O(2)(*) and N(3)(*) radicals, with a broad absorption band around 370-400 nm. The bimolecular rate constants for all the radical-induced oxidation reactions of folic acid have been measured. Folic acid is seen to scavenge these radicals very efficiently. In the reaction of thiyl radicals with folic acid, it has been observed that folic acid can not only scavenge thiyl radicals but can also repair these thiols at physiological pH. While carrying out the lipid peroxidation study, in spite of the fact that folic acid is considerably soluble in water, we observed a significant inhibition property in microsomal lipid peroxidation. A suitable mechanism for oxidation of folic acid and repair of thiyl radicals by folic acid has been proposed.

Protective Activities of Some Phenolic 1,3-Diketones against Lipid Peroxidation: Possible Involvement of the 1,3-Diketone Moiety

The protective activities of four ginger‐derived phenolic 1,3‐diketones (1–4) and curcumin (5) against lipid peroxidation was studied by using different biologically relevant model systems and pulse radiolysis. The extraordinary activity of 5 vis‐à‐vis 1–4 against Fe2+‐mediated peroxidation may be attributed to the additional phenolic hydroxy group in the former, which lends it better iron‐chelating and radical‐scavenging properties. In iron‐independent peroxidation, however, the ginger constituent [6]‐dehydrogingerdione (1) showed activity comparable to that of 5; this indicates its higher affinity for the lipid peroxide radical (LOO.), due to its higher hydrophobicity. A very high rate constant for the reaction between 1 and Cl3COO., measured by pulse radiolysis, not only confirmed this, but also established the superior antioxidant efficacy of 1 in comparison to vitamins E and C. This was also evident from the results obtained from a liposomal peroxidation study with 1 and vitamin C. This study also established a synergistic effect of the latter on the antioxidant activity of 1. HPLC analysis of the products of the reaction between 1 and Cl3COO. revealed the formation of higher concentrations of ferulic acid (7), along with vanillin (6). The presence of ascorbate affected the generation of 7 more than it did that of 6. On this basis, a mechanism for the antioxidant action of 1 has been proposed, which suggests the contribution of the phenolic group as well as the active methylene group of the 1,3‐diketones.

Evaluation of Antioxidant Activity of Selected Indian Mushrooms

Cellular damage caused by reactive oxygen species (ROS) has been implicated in several diseases, and hence antioxidants have significant importance in human health. In this study, five methods were used to test and compare the antioxidant activity at different levels involving formation and scavenging of free radicals by the extracts of four mushrooms that have medicinal values. The results were expressed as Trolox equivalent antioxidant capacity (TEAC) and ascorbic acid equivalent antioxidant capacity (AEAC). In the DPPH (1,1-diphenyl 2-picryl hydrazyl) assay, the ethyl acetate extract of Phellinus rimosus showed more potent activity than the methanolic extracts of Pleurotus florida, Pleurotus sajour-caju, and Ganoderma lucidum. The ethyl acetate extract of P. rimosus at a concentration of 0.1% showed a high TEAC value (12.488). In the ABTS (2,2-azobis-3-ethylbenzthiazoline-6-sulfonic acid) spectrophotometric assay, it possessed the most effective antioxidant activity (TEAC 4.84) compared to methanolic extracts of P. florida, P. sajour-caju, and G. lucidum. The extract of P. rimosus also possessed higher activity compared to other extracts in the ferric-reducing antioxidant power (FRAP) assay. In the pulse radiolysis studies and the ORAC (oxygen radical absorbance capacity) assay also, these mushrooms showed significant activities. Results of the DPPH, ABTS, FRAP, and ORAC assays indicate that all the four mushrooms examined showed significant antioxidant activities. Among these, P. rimosus extract seems to be the more effective antioxidant.

Physico-Chemical Studies on the Evaluation of the Antioxidant Activity of Herbal Extracts and Active Principles of Some Indian Medicinal Plants

Understanding of the efficacy and mechanism for the reaction of the biologically important radicals with natural and/or synthetic antioxidants is the first step towards the development of future therapeutic agents. The kinetic parameters e.g., formation and decay rate constants predict the efficacy of an antioxidant and its fate after reaction. These parameters also dictate the ease with which competing reactions would occur in a bio-environment. The spectroscopic parameters provide the clue to the site of free radical attack to these antioxidants. Here, in this article an attempt has been made to show the use of physico-chemical methods in the evaluation of antioxidant activity of some important medicinal plants commonly used in India and the subcontinent. The systems chosen here for discussions are herbal extracts as such, curcumin from turmeric, methoxy phenols from Indian spices, dehydrogingerdione from ginger and bakuchiol from Psoralea corylifolia. All the examples shown in this article illustrate the potential of the pulse radiolysis coupled with kinetic spectroscopy and other physicochemical techniques for the study of antioxidants either in the form of mixture as in herbal extract or as an isolated compound.

Antioxidant activity and free radical scavenging reactions of gentisic acid: in-vitro and pulse radiolysis studies.

Abstract Antioxidant activity of gentisic acid has been studied using fast chemical kinetics and two in vitro models, namely the isolated rat liver mitochondria (RLM) and the human erythrocytes. The presence of gentisic acid (GA) during irradiation significantly reduced the levels of gamma radiation induced damages to lipids and proteins in RLM. Further, GA imparted protection to the human erythrocytes against exposure to gamma radiation. Molecular mechanism of free radical scavenging reactions has been evaluated with the help of rate constants and transients obtained from gentisic acid using pulse radiolysis technique. GA efficiently scavenged hydroxyl radical (k = 1.1 × 1010 dm3mol−1s−1) to produce reducing adduct radical (∼76%) and oxidizing phenoxyl radical (∼24%). GA has also scavenged organohaloperoxyl radical (k = 9.3 × 107 dm3 mol−1s−1). Ascorbate has been found to repair phenoxyl radical of GA (k = 1.0 × 107 dm3mol−1s−1). Redox potential value of GA•/GA couple (0.774 V vs NHE) obtained by cyclic voltammetry is less than those of physiologically important oxidants, which supports the observed antioxidant capacity of GA. We, therefore, propose that the antioxidant and radioprotective properties of GA are exerted by its phenoxyl group.

Evaluation of free radical scavenging activity of morel mushroom, Morchella esculenta mycelia: a potential source of therapeutically useful antioxidants.

Cellular damage caused by reactive oxygen species (ROS) has been implicated in several diseases and antioxidants are known to protect the body from this damage. Antioxidants thus, have gained significant importance in human health. The search for effective, non-toxic natural compounds with antioxidant activity has intensified in recent years. Mycelia of a number mushrooms have recently been successfully used for the development of novel pharmaceutical products. We examined the aqueous-ethanol extract of cultured mycelia of the morel mushroom, Morchella esculenta (L.) Pers. (Morchellaceae) for its ability to scavenge super oxide, hydroxyl, nitric oxide, 2,2′-diphenyl-1-picrylhydrazyl (DPPH), and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radicals as well as for inhibition of lipid peroxidation. The extract efficiently scavenged all these radicals and also inhibited lipid peroxidation. Ferric reducing antioxidant power (FRAP) assay indicated the hydrogen donating capacity of the extract. The pulse radiolysis studies using ABTS and carbonate radical (CO3•-) showed that the extract significantly carried out the decay of these radicals in a concentration-dependent manner. In conclusion, the investigation showed that the morel mushroom mycelium is an excellent source of antioxidants which are capable of imparting protection at different levels. The findings suggest the potential therapeutic use of morel mushroom, M. esculenta mycelia as an efficient antioxidant.

Evaluation of Antioxidant Activity and Characterization of Phenolic Constituents of Phyllanthus amarus Root

The antioxidant property of the 70% aqueous ethanol extract of Phyllanthus amarus roots and its ether-soluble, ethyl acetate-soluble, and aqueous fractions were investigated by various in vitro assays. The root extracts showed higher DPPH, hydroxyl, superoxide, and nitric oxide radical scavenging and reducing power activity. Among all the samples, the ethyl acetate-soluble fraction demonstrated highest radical scavenging activity and total phenolics content. Twenty-eight different phenolic compounds were identified by LCMS/MS analysis of the ethyl acetate-soluble fraction. The majority of the compounds were found to exist as their glycosides, and many of these were gallic acid derivatives. Free epicatechin and gallic acid were also identified in the ethyl acetate-soluble fraction. The present investigation suggested that P. amarus root is a potent antioxidant and can be used for the prevention of diseases related to oxidative stress.

Ganoderma lucidum total triterpenes prevent radiation-induced DNA damage and apoptosis in splenic lymphocytes in vitro.

The development of radioprotective agents has been the subject of intense research, especially in the field of radiotherapy. In this study, we examined the radioprotective activity of the total triterpenes isolated from Ganoderma lucidum (Fr.) P. Karst in mouse splenic lymphocytes in vitro. Using the MTT assay, Ganoderma triterpenes were found to have no effect on cell viability, indicating that they are non-toxic to splenic lymphocytes. The effect of the total triterpenes on DNA damage and apoptosis induced by radiation was analyzed using the comet assay, DNA ladder assay and flow cytometric analysis. Total triterpenes were found to be highly effective in preventing DNA laddering, even at low concentrations (25μg/ml). The comet assay demonstrated that the G. triterpenes effectively prevented DNA damage, and flow cytometry revealed a reduction in apoptotic cells. The effect of the total triterpenes on intracellular reactive oxygen species (ROS) level and endogenous antioxidant enzyme activity in splenic lymphocytes were determined to elucidate possible radioprotective mechanisms. Total triterpenes successfully reduced the formation of intracellular ROS and enhanced endogenous antioxidant enzyme activity in splenic lymphocytes following irradiation. Thus, these findings indicate that the total triterpenes isolated from G. lucidum have a remarkable ability to protect normal cells from radiation-induced damage, which suggests therapeutic potential.

Thiyl radical induced isomerization of unsaturated fatty acids: determination of equilibrium constants

Thiyl radical-induced isomerization of polyunsaturated fatty acids (PUFAs) have been studied in homogeneous solution and in liposomes. Four one-trans isomers of arachidonic acid have been assigned with the help of 13C NMR spectroscopy. At a dose of 132 Gy, the trans fraction amounts to 9.2 ± 1.2% in each of the four isomers. Therefore, all the four double bonds are equally susceptible to isomerization, which can be achieved by means of gamma radiolysis or chemolysis (AAPH) using both lipophilic and hydrophilic thiols. The equilibrium is characterised by a cis/trans ratio of 19 : 81, far away from the composition of the natural fatty acids (cis fraction 100%). However, compared to the linoleate isomerization in the homogeneous solution, we observed a preferential formation of trans-trans isomers if linoleate is incorporated in the bilayer of liposomes. This difference might be explained by the better fitting of the all-trans isomer into the parallel-aligned acyl chains. The isomerization step takes place within an adduct of the thiyl radical to an olefinic bond. Using a competition method, the numerical value of the equilibrium constant for the adduct formation was determined by pulse radiolysis to be (15 ± 5) dm3 mol-1. This value does not depend on the number of double bonds and holds for all fatty acids under investigation.

Transformation of phospholipid membranes by thiyl radicals via cis-trans isomerization of fatty acid residues.

Thiyl radical-mediated transformation of unsaturated fatty acid residues are reported. Beside the initiation of lipid peroxidation, thiyl radicals can efficiently cause isomerization of fatty acid residues in a catalytic manner. The latter process is observed in homogeneous solutions as well as in organized assemblies, leading to a denaturation of the natural all-cis-isomers of fatty acid residues of lipid bilayers. The degree of denaturation goes parallel with an increase in the number of double bonds and in the hydrophobicity of thiols. For arachidonic acid methyl ester, a decay of the all-cis-isomer to approximately 30% after a gamma irradiation dose of 1.8 kGy in micelles is observed. The reversibility of the isomerization reaction is demonstrated in liposomes by the fact that the cis/trans-equilibrium is independent of configuration of the starting compound.