Free radical reactions of a naturally occurring flavone baicalein and possible mechanisms towards its membrane protective properties.

Baicalein (5, 6, 7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one), a naturally occurring flavone present in some of the medicinal plants is known for its potential therapeutic effects, such as cardioprotective, anticancer and anti-inflammatory properties. However, detailed role and mechanisms behind its protective properties against different generators for oxidative stress have not been examined. In the present study, we investigated the possible protective ability of baicalein against the membrane damage caused by reactive oxygen species (ROS) and reactive nitrogen species (RNS) and the mechanisms involved using pulse radiolysis technique. Baicalein offered efficient protection even at a concentration of 10 microM towards membrane damage caused by lipid peroxidation induced by the gamma-radiation, peroxyl radicals, ascorbate-Fe2+ and peroxynitrite in rat liver mitochondria and heart homogenate. To elucidate its reaction mechanisms with biologically relevant radicals, transient absorption spectroscopy employing pulse radiolysis technique was used. Baicalein showed fairly high rate constants (3.7 x 10(9), 1.3 x 10(9) and 8.0 x 10(8) dm3 mol(-1) s(-1) for hydroxyl, azidyl and alkylchloroperoxyl radicals, respectively), suggesting that baicalein can act as an effective scavenger of these radicals. In each case, the phenoxyl radical of baicalein was generated. Thus, it was evident that the phenolic moiety of baicalein was responsible for the free radical scavenging process. Baicalein also reacts with linoleic acid peroxyl radical (LOO*), indicating its ability to act as a chain breaking antioxidant. Peroxynitrite-mediated radicals were shown to be reactive towards baicalein and the bimolecular rate constants were 2.5 x 10(7) and 3 x 10(8) dm3 mol(-1) s(-1) for *NO2 and CO3*(-) radicals, respectively. In conclusion, our results revealed the potential of baicalein in protecting mitochondrial membrane against oxidative damage induced by the four different agents. We propose that the protective effect is mediated via scavenging of primary and secondary radicals generated during oxidative stress.

A study of antioxidant properties of some varieties of grapes (Vitis vinifera L.).

Grapes (Vitis vinifera L.) are a major fruit crop in the world. Grapes seem to confer health benefits due to their antioxidant activity. We have evaluated the antioxidant potential of 11 grapes varieties from India and nearby Asian countries. The assays employed involve different levels of antioxidant action like ferric reducing antioxidant power, radical scavenging by 1,1-diphenyl-2-picrylhydrazyl, ferrylmyoglobin/2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid, oxygen radical absorbance capacity (ORAC), and inhibition of lipid peroxidation. The total phenolic and flavonoids contents were also estimated. Our study indicates that cv. Mango is the most potent followed by Sharad Seedless. Ethanolic extracts were found to be more effective than aqueous extracts. Cv. Sharad Seedless, Mango, and Manikchaman also had high ORAC values. Their HPLC analysis showed the presence of various antioxidant polyphenols. In conclusion our studies identified some varieties of grapes with high antioxidant activities and showed that their high antioxidant potential may be due to their phenolic and flavonoid contents.

Evaluation of the antioxidant activity of wheatgrass (Triticum aestivum L.) as a function of growth under different conditions.

The antioxidant activity of wheatgrass, which is consumed as a dietary supplement, was estimated at different levels. The methods employed include FRAP (ferric reducing antioxidant power), ABTS (2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid) and DPPH (1,1'-diphenyl-2-picrylhydrazyl) assays. Aqueous and ethanol extracts of wheatgrass grown under different conditions over a period of 6, 7, 8, 10 and 15 days were used. Lipid peroxidation and oxygen radical absorbance capacity (ORAC) were determined and utilized to check the potency of a few selected extracts. Different conditions used for growth were (1) tap water, (2) tap water with nutrients, (3) soil and tap water, and (4) soil with nutrients. For comparison, a commercially available wheatgrass tablet was analysed. To explain the reasons behind the observed differences, the total phenolic and flavonoid contents of the extracts were measured. These contents increased with growth under all the conditions. The ethanol extracts were found to have a higher phenolic and flavonoid content than the aqueous extracts. The highest FRAP values occurred on day 15 of growth under condition 4, the values being 0.463 and 0.573 mmol of ascorbic acid and Trolox equivalents/100 g fresh wheatgrass for aqueous and ethanol extracts, respectively. In the aqueous extracts no specific trend was observed with the DPPH assay for the different conditions nor for the growth period. In the case of ethanol extracts, however, it increased with the growth period and the wheatgrass grown in condition 4 was found to be the most effective. These extracts were also found to inhibit significantly ascorbate-Fe2+ induced lipid peroxidation in rat liver mitochondria. The ORAC values of aqueous and ethanol extracts of day 10 with condition 4 were found to be 39.9 and 48.2, respectively, being higher than those reported for many natural extracts or vegetables.

A modified, economic, sensitive method for measuring total antioxidant capacities of human plasma and natural compounds using Indian saffron (Crocus sativus).

BACKGROUND: Free radicals are involved in various human diseases that can possibly be prevented by antioxidants. There are many but rather expensive methods to determine total antioxidant capacity of human plasma (for endogenous antioxidant levels) or plant extracts/natural compounds (for antioxidant potential in terms of radical inhibiting or scavenging properties). We describe a simple, fast and economical 'crocin assay' using the Indian spice saffron. METHODS: In crocin assay, the extent of bleaching of crocin, a carotenoid from saffron, by peroxyl radicals generated by thermal decomposition of azo-initiator was measured. We examined its applicability to clinical samples and plant extracts. RESULTS: The cost of Indian saffron is almost 38 times less per unit dry weight compared to the 'Sigma' saffron. Yet, it gives 26 times better yield of crocin than that from 'Sigma' saffron. It was also shown that Indian saffron is rich in crocin. The total antioxidant capacity (TAC) values of human plasma from normal, healthy individuals, using Sigma as well as Indian crocin, expressed in terms of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) equivalent antioxidant capacity (TEAC), were comparable. We have also demonstrated that crocin assay can be used for clinical samples such as plasmas from healthy and diabetic individuals. The antioxidant potentials, TEAC, of plant extracts and pure natural compounds by Indian and Sigma crocin assays were similar. Addition of uric acid to plasma induced a concentration-dependent response. The assay was compared to standard radical scavenging 1,1'-diphenyl-2-picrylhydrazyl (DPPH) assay and was found to match well, showing better sensitivity and hence validates this assay for natural compounds and clinical samples. CONCLUSIONS: Development of crocin assay using the Indian saffron is economical and sensitive method for measurement of total antioxidant capacities from human plasma as well as natural compounds and plant extracts.

Antioxidant availability of turmeric in relation to its medicinal and culinary uses.

Turmeric (Curcuma longa) has been used in Indian cooking, and in herbal remedies. Its possible mechanism of action was examined in terms of antioxidant availability during actual cooking conditions and in therapeutic applications using standardized extracts. The assays involve different levels of antioxidant action such as oxygen radical absorbance capacity (ORAC), radical scavenging abilities using 1,1-diphenyl-2-picryl hydrazyl (DPPH), 2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS), ferric reducing antioxidant power (FRAP) and protection of membranes examined by inhibition of lipid peroxidation besides the content of phenols and total flavonoids. The aqueous and ethanol extracts of two major preparations of turmeric, corresponding to its use in cooking and medicine, showed significant antioxidant abilities. In conclusion, the studies reveal that the ability of turmeric to scavenge radicals, reduce iron complex and inhibit peroxidation may explain the possible mechanisms by which turmeric exhibits its beneficial effects in relation to its use in cooking and medicine.

Antioxidant properties of Plumbago zeylanica, an Indian medicinal plant and its active ingredient, plumbagin.

Plumbago zeylanica (known as "Chitrak") is a useful Indian medicinal plant. The root of the plant and its constituents are credited with potential therapeutic properties including anti-atherogenic, cardiotonic, hepatoprotective and neuroprotective properties. To examine possible mechanisms of action of P. zeylanica (Chitrak), in relation to its reported beneficial properties, antioxidant effects of the aqueous/alcoholic extracts of root, corresponding to medicinal preparations, and the active ingredient, plumbagin, were studied. Methods used included: ferric reducing/antioxidant power (FRAP), radical scavenging of 1,1-diphenyl-2-picryl hydrazyl (DPPH) and 2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS), lipid peroxidation in rat liver mitochondria induced by different agents, and estimating phenolic and flavonoid content. In FRAP/DPPH assays, boiled ethanolic extracts were the most effective, while in the ABTS assay boiled aqueous extracts were the most efficient. These extracts also significantly inhibited lipid peroxidation induced by cumene hydroperoxide, ascorbate-Fe(2+) and peroxynitrite and contained high amounts of polyphenols and flavonoids. To examine the mechanisms of action in detail, antioxidant and pulse radiolysis studies with plumbagin were conducted. The hydroxyl (.OH), alkyl peroxyl (CCl(3)OO.), linoleic acid peroxyl (LOO.), and glutathiyl (GS.) radicals generate a phenoxyl radical upon reaction with plumbagin. The bimolecular rate constants were: .OH, 2.03 x 10(9) dm(3)mol(-1)s(-1); CCl(3)OO., 1.1 x 10(9) dm(3)mol(-1)s(-1); LOO., 6.7 x 10(7) dm(3)mol(-1)s(-1); and GS., 8.8 x 10(8) dm(3)mol(-1)s(-1). In conclusion, our studies reveal that extracts of P. zeylanica and its active ingredient plumbagin have significant antioxidant abilities that may possibly explain some of the reported therapeutic effects.