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Thearubigins rich black tea fraction reveals strong antioxidant activity

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Abstract

Background: Black tea contains two major polyphenols namely Theaflavins (TFs) and Thearubigins (TRs). Several reports are available on antioxidant properties of TFs. However, very little information is known about TRs. Aim: To investigate in vitro antioxidant properties of not well-known TR rich fractions in comparison with TF rich fraction. Materials and Methods: TR and TF rich fractions were checked for in vitro antioxidant activities by using standard biochemical radical scavenging assays and pulse radiolysis. These fractions were also used to evaluate the protection conferred against induced oxidative damage to biomolecules (lipids, proteins and DNA) in rat liver mitochondria. Statistical Analysis: The one-way analysis of variance test associated with the Tukey′s test was used to determine the statistical significance of the differences among experimental groups. All the statistical analyses were done using SPSS 19.0 software. Results and Conclusions: Results from this study suggest that like TF rich fraction, TR rich fraction has good antioxidant properties, which correlate to the total phenolics and flavonoids content and provide significant protection against oxidative damage to biomolecules (lipids, proteins and DNA) in rat liver mitochondria. This is the first report about the in vitro antioxidant activity of TRs rich fractions from black tea.

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... These antioxidant nutrients include vitamin C, four forms of vitamin E (α-tocopherol, β-tocopherol, γ-tocopherol, and δ-tocopherol), six carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lutein, lycopene, and zeaxanthin), 29 flavonoids (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, petunidin, (+)-catechin, (+)-gallocatechin, (−)-epicatechin, (−)-epigallocatechin, (−)-epicatechin 3-gallate, (−)-epigallocatechin 3-gallate, theaflavin, theaflavin 3-gallate, theaflavin 3′-gallate, theaflavin 3,3′-digallate, thearubigins, eriodictyol, hesperetin, naringenin, apigenin, luteolin, isorhamnetin, kaempferol, myricetin, quercetin, daidzein, genistein, and glycitein), and two PA (dimers and trimmers). As thearubigins have been reported to be as potent antioxidants as theaflavins [26], thearubigins were assigned the same antioxidant power as theaflavins. Each participant's average intake of individual antioxidants was estimated by multiplying the contents of individual antioxidants in foods by the daily consumption of each food item. ...
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The ability of curcumin, a natural antioxidant from turmeric, to inhibit radiation-induced lipid peroxidation in rat liver microsomes was examined. Curcumin was incorporated into microsomes during ultracentrifugation. The antioxidant has significant time- and concentration-dependent inhibitory effect on lipid peroxidation induced by r-radiation. Inhibition of lipid peroxidation was also observed in microsomes samples previously saturated with N2O. Curcumin also inhibited lipid peroxidation during the post-irradiation incubation.
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To investigate the protective effects of octacosanol in 6-hydroxydopamine-induced Parkinsonian rats and find whether octacosanol has effects on pro nerve growth factor (pro-NGF), NGF and the downstream effector proteins. Behavioral tests, enzymatic assay, tyrosine hydroxylase immunohistochemistry, TUNEL and Western blot were used to investigate the effects of octacosanol in this rat model of PD. Oral administration of octacosanol (35-70 mg/kg, po for 14 d) significantly improved the behavioral impairments in rats induced by 6-OHDA and dose-dependently preserved the free radical scavenging capability of the striatum. Octacosanol treatment also effectively ameliorated morphological appearances of TH-positive neuronal cells in nigrostriatal systems and decreased the apoptotic cells induced by 6-OHDA in striatum. In addition, octacosanol strikingly blocked the 6-OHDA-induced increased expression of proNGF-p75NTR-sortilin death signaling complex and its downstream effector proteins. Meantime, octacosanol prevented the decreased levels of NGF, its receptors TrkA and p-Akt which together mediated the cell survival pathway. The findings implicated that the anti-parkinsonism effects afforded by octacosanol might be mediated by its neuro-microenvironment improving potency through retrieving the ratios of proNGF:NGF and the respective receptors p75NTR:TrkA in vivo. Due to its excellent tolerability and non-toxicity, octacosanol may be a promising agent for PD treatment.
Article
Thearubigins are the most abundant group of phenolic pigments found in black tea accounting for an estimated 60% of the solids in a typical black tea infusion. Fifty years ago the term thearubigins was first introduced and up to now the chemical nature of the thearubigins remains largely unresolved if not mysterious despite many efforts clarifying their structure. This paper summarizes some of our attempts to clarify and elucidate the chemical nature of the thearubigins, presenting for 15 commercially representative teas data obtained using combustion analysis, IR spectroscopy, NMR spectroscopy, Diffusion NMR spectroscopy, UV-vis spectroscopy, Circular Dichroism spectroscopy and atomic force microscopy, MALDI-TOF-MS and ESI-FT-ICR-MS. The thearubigin fractions from these 15 teas are remarkably similar with respect to their spectroscopic fingerprint. The data obtained are consistent with the thearubigins being structures of not more than 2000Da with more than 5000 individual chemical entities detected that are susceptible to concentration-driven aggregation in aqueous solution, and that retain the chiral properties of the flavanols and theaflavins. By applying petrolomics-style data interpretation strategies and by developing novel data interpretation strategies a structural model for the thearubigins was developed.
Article
The peroxidation of rat liver microsomal lipids is stimulated in the presence of iron by the addition of NADPH or ascorbate and is inhibited by the addition of glutathione (GSH). The fate of GSH and the oxidative modification of proteins under these conditions have not been well studied. Rat liver microsomes were incubated at 37 degrees C under 95% O2:5% CO2 in the presence of 10 microM ferric chloride, 400 microM ADP, and either 450 microM ascorbic acid or 400 microM NADPH. Lipid peroxidation was assessed in the presence 0, 0.2, 0.5, 1, or 5 mM GSH by measuring thiobarbituric acid reactive substance (TBARS) and oxidative modification of proteins by measuring protein thiol and carbonyl groups. GSH inhibited TBARS and protein carbonyl group formation in both ascorbate and NADPH systems in a dose-dependent manner. Heat denaturing of microsomes or treatment with trypsin resulted in the loss of this protection. The formation of protein carbonyl groups could be duplicated by incubating microsomes with 4-hydroxynonenal. Ascorbate-dependent peroxidation caused a loss of protein thiol groups which was diminished by GSH only in fresh microsomes. Both boiling and trypsin treatment significantly decreased the basal protein thiol content of microsomes and enhanced ascorbate-stimulated lipid peroxidation. Protection against protein carbonyl group formation by GSH correlated with the inhibition of lipid peroxidation and appeared not to be due to the formation of the GSH conjugate of 4-hydroxynonenal as only trace amounts of this conjugate were detected. Ninety percent of the GSH lost after 60 min of peroxidation was recoverable as borohydride reducible material in the supernatant fraction. The remaining 10% could be accounted for as GSH-bound protein mixed disulfides. However, only 75% of the GSH lost during peroxidation appeared as glutathione disulfide, suggesting that some was converted to other soluble borohydride reducible forms. These data support a role for protein thiol groups in the GSH-mediated protection of microsomes against lipid peroxidation.
Article
Lipid peroxidation in rat uterus has been studied using NADPH- and ascorbate-induced systems. Lipid peroxidation in rat uterus is low as compared to rat liver. Uterus is more sensitive to ascorbate-induced lipid peroxidation than that induced by NADPH. Uterus contains lower amounts of phospholipids and has a lesser degree of unsaturation in lipids. Co-factor studies show that Fe2+ is more important for ascorbate-induced lipid peroxidation. Endometrium is more sensitive to ascorbate-induced lipid peroxidation than myometrium. It also contains more total lipids and phospholipids besides having a higher degree of unsaturation in the lipids as compared to myometrium. Among the subcellular fractions, mitochondria are more prone to ascorbate-induced lipid peroxidation, whereas microsomes are more sensitive to NADPH-induced lipid peroxidation. Uteri from old rats (24 months) and pregnant rats are more resistant to lipid peroxidation than those from 3-month-old control rats. Uterus of pregnant rats contains more factors which inhibit lipid peroxidation and also has a lesser degree of unsaturation in lipids compared with uterus of control rats. The possible consequences of the resistance of uterus to lipid peroxidation, especially during pregnancy and senescence, are discussed.
Article
Hydroxyl radicals, generated by reaction of an iron-EDTA complex with H2O2 in the presence of ascorbic acid, attack deoxyribose to form products that, upon heating with thiobarbituric acid at low pH, yield a pink chromogen. Added hydroxyl radical "scavengers" compete with deoxyribose for the hydroxyl radicals produced and diminish chromogen formation. A rate constant for reaction of the scavenger with hydroxyl radical can be deduced from the inhibition of color formation. For a wide range of compounds, rate constants obtained in this way are similar to those determined by pulse radiolysis. It is suggested that the deoxyribose assay is a simple and cheap alternative to pulse radiolysis for determination of rate constants for reaction of most biological molecules with hydroxyl radicals. Rate constants for reactions of ATP, ADP, and Good's buffers with hydroxyl radicals have been determined by this method.
Article
1. Effects of prolonged in vivo administration of the tricyclic antidepressant drug imipramine on oxidative energy metabolism in rat liver mitochondria were examined. 2. Imipramine treatment resulted in an increase in state 3 respiration rates with all the substrates tested as early as one week after treatment; this was sustained through the second week of treatment. 3. The changes in respiration rates were accompanied by a selective increase in the intramitochondrial cytochrome aa3 and c + c1 contents after both one and two weeks of treatment. 4. Administration of imipramine did not alter the total liver protein content per g tissue, the mitochondrial protein content per g tissue or the mitochondrial yield. 5. Kinetic analyses of succinoxidase activity in terms of Arrhenius plots indicated possible alterations in mitochondrial membrane lipid milieu and membrane fluidity after the drug treatment, especially in the second week.
Article
The reduction of nitro blue tetrazolium (NitroBT) with NADH mediated by phenazine methosulfate (PMS) under aerobic conditions was inhibited upon addition of superoxide dismutase. This observation indicated the involvement of superoxide aninon radical (O2−) in the reduction of NitroBT, the radical being generated in the reoxidation of reduced PMS. Similarly, the reduction of NitroBT coupled to D-amino acid oxidase-PMS system under aerobic conditions was also inhibited by superoxide dismutase. A simple method for detecting superoxide dismutase is described.
Article
Theaflavins, polyphenolic ingredients of black tea, were observed to inhibit in vitro lipid peroxidation in the erythrocyte membrane ghost and microsomal systems. Theaflavins also showed inhibition of DNA single-strand cleavage and mutagenicity, both induced by hydrogen peroxide. These results suggest that theaflavins scavenge radicals to produce antioxidative and antimutagenic effects. It was also found that the gallic acid moiety of theaflavins is essential for their potent antioxidative activities.
Article
High-density lipoprotein (HDL) has been proposed as the principal carrier of hydroperoxides in plasma, based upon data gathered with an HPLC-chemiluminescence technique. To test this hypothesis we have measured total lipid hydroperoxides in native plasma using the ferrous oxidation in Xylenol Orange (FOX) assay and then fractionated plasma into very-low-density lipoprotein (LDL) and HDL fractions. Hydroperoxides were found to accumulate principally (more than 65%) in LDL, as judged by hydroperoxide content per amount of protein or cholesterol, or expressed as a proportion of total hydroperoxide in plasma. Plasma was also incubated at 37 degrees C in the presence and absence of 2,2'-azo-bis-(2-amidinopropane) hydrochloride (AAPH), an azo-initiator of lipid peroxidation. The majority of hydroperoxides generated in plasma were recovered in the LDL fraction. Furthermore, when isolated lipoproteins were subject to oxidation initiated by AAPH, very-low-density lipoprotein and LDL showed the greatest propensity for hydroperoxide accumulation, whereas HDL seemed relatively resistant. Estimates for plasma and LDL peroxidation based upon techniques which measure total lipid hydroperoxides suggest that levels of hydroperoxides in plasma and LDL are far higher than that those estimates generated by ostensibly more selective techniques. Higher levels of hydroperoxides in LDL than those reported by HPLC-chemiluminescence also seem in greater accordance with other available data concerning LDL oxidation.
Article
The antioxidant properties of theaflavins and their gallate esters were studied by investigating their abilities to scavenge free radicals in the aqueous and lipophilic phases. The total relative antioxidant activities in the aqueous phase were assessed by measuring their direct ABTS.+ radical scavenging abilities, and by their efficacies in inhibiting the degradation of deoxyribose induced by iron. The propensities for enhancing the resistance of LDL to oxidation mediated by Cu2+ were also measured. The results show that the hierarchy of reactivity of these compounds as antioxidants is: theaflavin digallate > 3'-monogallate = 3-monogallate > theaflavin. Spectroscopic studies show that all the compounds chelate iron and copper; enhanced absorbance in the visible region is observed in the case of the iron-digallate complex, but not with copper.
Article
Studies in experimental animals have shown that compounds in tea can inhibit the process of carcinogenesis, with the beneficial effects accruing to both green and black teas. Herein epidemiologic studies around the world are reviewed to assess the rates and risks of cancer among black tea drinkers. Ecologic data suggest at most a modest benefit on total cancer, as there is considerable international variation in black tea consumption but generally small differences in overall cancer rates. Cohort studies of tea drinkers and case control studies of specific cancers show mixed results. Consistent dose-related patterns have yet to emerge, although detailed data from these studies on cancer risks according to amount and duration of black tea intake are often limited. Several investigations point to the possibility of somewhat lowered risks of digestive tract cancers among tea drinkers, but the evidence is inconclusive. Further research, especially involving populations with wide ranges of tea consumption, is needed to clarify black tea's impact on cancer risk.
Article
Most nonenzymatic antioxidant activity (scavenging of free radicals, inhibition of lipid peroxidation, etc.) is mediated by redox reactions. The antioxidant (AO) activity of polyphenols (PPs), as ferric-reducing power, was determined for the first time using a modified FRAP (ferric reducing/antioxidant power) assay. Reaction was followed for 30 min, and both Fe(II) standards and samples were dissolved in the same solvent to allow comparison. Selected representative PPs included flavonoids (quercetin, rutin, and catechin), resveratrol, tannic acid, and phenolic acids (gallic, caffeic, and ferulic). Carotenoids (beta-carotene and zeaxanthine), ascorbic acid, Trolox, and BHA were included for comparison. Equivalent concentration 1 (EC(1)), as the concentration of AO with a reducing effect equivalent to 1 mmol/L Fe(II), was used to compare AO efficiency. PPs had lower EC(1) values, and therefore higher reducing power, than ascorbic acid and Trolox. Tannic acid and quercetin had the highest AO capacity followed by gallic and caffeic acids. Resveratrol showed the lowest reducing effect. Carotenoids had no ferric reducing ability. Polyphenol's AO efficiency seemed to depend on the extent of hydroxylation and conjugation.
Article
Fractionation of a methanolic extract of the leaves of Anthurium versicolor has resulted in the isolation of two main fractions, I and II. Both the extract and the fractions were assayed for their radical-scavenging activity by means of an in vitro test (bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical) and showed a significant radical-scavenging effect. Subsequent chromatographic fractionation of the most active fraction, II, has led to the isolation and characterization, as major constituents, of four new flavone glycosides, acacetin 6-C-[alpha-L-rhamnopyranosyl-(1-->3)-beta-D-glucopyranoside] (1), acacetin 6-C-[beta-D-xylopyranosyl-(1-->6)-beta-D-glucopyranoside] (2), acacetin 6-C-[beta-D-apiofuranosyl-(1-->3)-beta-D-glucopyranoside] (3), and acacetin 8-C-[alpha-L-rhamnopyranosyl-(1-->3)-beta-D-glucopyranoside] (4), as well as vitexin (apigenin-8-C-beta-D-glucopyranoside) and rosmarinic acid. The structures of 1-4 were determined using spectroscopic methods.
Article
Recent studies have implicated the signaling factor Sonic hedgehog (Shh) as a negative regulator of pancreatic development, but as a positive regulator of pancreas function in amniotes [1-4]. Here, using genetic analysis, we show that specification of the pancreas in the teleost embryo requires the activity of Hh proteins. Zebrafish embryos compromised in Hh signaling exhibit disruption in the expression of the pancreas-specifying homeobox gene pdx-1 and concomitantly show almost complete absence of the endocrine pancreas. Reciprocally, ubiquitous activation of the Hh pathway in wild-type embryos causes ectopic induction of endodermal pdx-1 expression and the differentiation of supernumerary endocrine cells. Our results suggest that Hh proteins influence pancreas specification via inductive interactions from the axial midline rather than through their localized expression in the endodermal cells themselves.
Article
The chemistry underlying the changes which occur during tea leaf fermentation is reviewed and used as a basis for proposals for the structure of thearubigins, the major pigments of black teas.
Article
In the current study, we have focused on isolation and detection of major radical oxidation products from theaflavin in order to better understand antioxidation mechanisms of this compound. Theanaphthoquinone was identified as a major oxidation product of theaflavin from two different oxidant model systems: DPPH and peroxidase/hydrogen peroxide. This result indicated that the benzotropolone moiety in theaflavin may play an important role in its antioxidant properties. The stability of theaflavin was studied in varying pH solutions: simulated gastric juice and buffer solutions of pH 5.5, pH 7.4, and pH 8.5. The results indicated that theaflavin is unstable in alkaline conditions, while it was stable in acidic conditions. Theanaphthoquinone was identified as an autoxidation product of theaflavin during its stability study in alkaline conditions.
Article
Black tea accounts for nearly 80% of total World tea production. It contains dimeric flavanols and polymeric polyphenols known as theaflavins (TF) and thearubigins (TR). TR is exclusively present in black tea. On the basis of our previous potent antimutagenic and anticlastogenic effects of TF and TR in vitro in bacterial system and in vivo in mouse bone marrow cells, we have decided to extend our study in human cells in vitro. This study investigated the anticlastogenic effects of black tea polyphenols TF and TR as measured by chromosomal aberrations (CA) and micronuclei formation (MN) against two known mutagens/carcinogens i.e. benzo[a]pyerne (B[a]P) and aflatoxin B1(AFB1) with S9 activation. A significant decrease in both CA and MN were observed in the human lymphocyte cultures treated with either TF or TR pretreated with either B[a]P or AFB1 (250, 500, 1000 microg/ml) when compared with B[a]P or AFB1 treated cultures alone. TF shows more protective effects than TR in this in vitro system. These results indicate that both TF and TR have significant anticlastogenic effects in vitro in human lymphocytes.
Article
Fenugreek (Trigonella foenum-graecum) is used as a spice, vegetable and a medicinal plant. Since antioxidant properties have been linked to health benefits of natural products, such properties were studied in germinated fenugreek seeds which are considered to be more beneficial than dried seeds. Different fractions of the germinated seeds were used to determine their antioxidant potential at different levels. The assays employed were ferric reducing antioxidant power, radical scavenging by 1,1-diphenyl-2-picrylhydrazyl, ferrylmyoglobin/2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid, pulse radiolysis, oxygen radical absorbance capacity and inhibition of lipid peroxidation in mitochondrial preparations from rat liver. An aqueous fraction of fenugreek exhibited the highest antioxidant activity compared with other fractions. As the quantity of phenolic and flavonoid compounds can be related to antioxidant activity, the contents from these extracts were measured. HPLC analysis was carried out to detect polyphenols, flavonoids and other components. This study reveals significant antioxidant activity in germinated fenugreek seeds which may be due partly to the presence of flavonoids and polyphenols.
Article
Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The "two-faced" character of ROS is substantiated by growing body of evidence that ROS within cells act as secondary messengers in intracellular signalling cascades, which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. The cumulative production of ROS/RNS through either endogenous or exogenous insults is termed oxidative stress and is common for many types of cancer cell that are linked with altered redox regulation of cellular signalling pathways. Oxidative stress induces a cellular redox imbalance which has been found to be present in various cancer cells compared with normal cells; the redox imbalance thus may be related to oncogenic stimulation. DNA mutation is a critical step in carcinogenesis and elevated levels of oxidative DNA lesions (8-OH-G) have been noted in various tumours, strongly implicating such damage in the etiology of cancer. It appears that the DNA damage is predominantly linked with the initiation process. This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process. Attention is focused on structural, chemical and biochemical aspects of free radicals, the endogenous and exogenous sources of their generation, the metal (iron, copper, chromium, cobalt, vanadium, cadmium, arsenic, nickel)-mediated formation of free radicals (e.g. Fenton chemistry), the DNA damage (both mitochondrial and nuclear), the damage to lipids and proteins by free radicals, the phenomenon of oxidative stress, cancer and the redox environment of a cell, the mechanisms of carcinogenesis and the role of signalling cascades by ROS; in particular, ROS activation of AP-1 (activator protein) and NF-kappaB (nuclear factor kappa B) signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. The role of enzymatic (superoxide dismutase (Cu, Zn-SOD, Mn-SOD), catalase, glutathione peroxidase) and non-enzymatic antioxidants (Vitamin C, Vitamin E, carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), flavonoids, selenium and others) in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors, including Ref-1, NF-kappaB, AP-1 are also reviewed.
Article
The objective of this study was to investigate how 6 commonly used solvent systems affected the yields of phenolic substances and the antioxidant capacity of extracts from 8 major classes of food legumes. Several antioxidant-related phytochemical compositions, namely, total phenolic content (TPC), total flavonoids content (TFC), and condensed tannins content (CTC), were investigated. In addition, antioxidant activities were tested using 2,2-diphenyl-1-picryhydrazyl (DPPH) free radical scavenging, ferric-reducing antioxidant power (FRAP), and the oxygen radical absorbance capacity (ORAC). The results showed that the 50% acetone extracts exhibited the highest TPC for yellow pea, green pea, chickpea, and yellow soybean. Acidic 70% acetone (+0.5% acetic acid) extracts exhibited the highest TPC, TFC, and FRAP values for black bean, lentil, black soybean, and red kidney bean. The 80% acetone extracts exhibited the highest TFC, CTC, and DPPH-free radical scavenging activity for yellow pea, green pea, chickpea, and yellow soybean. The 70% ethanol extracts exhibited the greatest ORAC value for all selected legumes. These results indicated that solvents with different polarity had significant effects on total phenolic contents, extracted components, and antioxidant activities. High correlations between phenolic compositions and antioxidant activities of legume extracts were observed. The information is of interest to the nutraceutical food/ingredient industries since legumes are a rich source of antioxidants.
Article
The antioxidant properties of theaflavins and their gallate esters, namely theaflavin (TF1), theaflavin-3(3')-gallate (TF2) and theaflavin-3,3'-digallate (TF3) were investigated by comparing with epigallocatechin gallate (EGCG). The order of hydroxyl radicals-scavenging ability was TF3>TF2>TF1>EGCG. The order of 2,2-diphenyl-1-picrylhydrazyl scavenging ability was TF3>TF2>EGCG>TF1. TF1, TF2, and TF3 showed more effective effects than EGCG in protection against H2O2-mediated damage in HPF-1 cells. TF2 was the most potent accelerant of HPF-1 cell proliferation. TF1, TF2 and TF3 suppressed the accumulation of intracellular reactive species in H2O2-mediated damage HPF-1 cells. Pre-treated for 2h and eliminated from the cells, TF1 and TF3 still showed protective effects against H2O2-mediated damage in HPF-1 cells. This suggests that the protective effects of TF1 and TF3 on oxidative damage HPF-1 cells may be responsible for other mechanisms, rather than only scavenging the already formed reactive species. It remains to be determined whether TF1 and TF3 improved the normal HPF-1 cell resistive abilities toward radical-damage in pre-treatment. Further studies of the effects of theaflavins on some enzymes or signal transduction in the normal HPF-1 cells are underway.
Research Project was fully sponsored by (UGC-CAS Conflict of Interest: None declared. of radiation induced lipid peroxidation by curcumin
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Source of Support: Research Project was fully sponsored by (UGC-CAS, University of Pune), Conflict of Interest: None declared. of radiation induced lipid peroxidation by curcumin. Int J Pharm 1997;151:127‑30.
Research on antioxidant activity of flavonoids from natural materials
  • J Zhinshen
  • T Mengcheng
  • W Jianming
Zhinshen J, Mengcheng T, Jianming W. Research on antioxidant activity of flavonoids from natural materials. Food Chem 1998;64:555-9.