Protection against hydrogen peroxide-induced cytotoxicity in PC12 cells by scutellarin

The present study investigated the protective actions of the antioxidant scutellarin against the cytotoxicity produced by exposure to H2O2 in PC12 cells. This was done by assaying for MTT (3,(4,5-dimethylthiazole-2-yl)2,5-diphenyl-tetrazolium bromide) reduction and lactate dehydrogenase (LDH) release. Reactive oxygen species (ROS) and Ca2+ in cells were evaluated by fluorescent microplate reader using DCFH and Fura 2-AM, respectively, as probes. Lipid peroxidation was quantified using thiobarbituric acid-reactive substances (TBARS). Mitochondrial membrane potential (MMP) was assessed by the retention of rhodamine123 (Rh123), a specific fluorescent cationic dye that is readily sequestered by active mitochondria, depending on their transmembrane potential. The DNA content and percentage of apoptosis were monitored with flow cytometry. Vitamin E, a potent antioxidant, was employed as a comparative agent. Preincubation of PC12 cells with scutellarin prevented cytotoxicity induced by H2O2. Intracellular accumulation of ROS, Ca2+ and products of lipid peroxidation, resulting from H2O2 were significantly reduced by scutellarin. Incubation of cells with H2O2 caused a marked decrease in MMP, which was significantly inhibited by scutellarin. PC12 cells treated with H2O2 underwent apoptotic death as determined by flow cytometric assay. The percentage of this H2O2-induced apoptosis in the cells was decreased in the presence of different concentrations of scutellarin. Scutellarin exhibited significantly higher potency compared to the antioxidant vitamin E. The present findings showed that scutellarin attenuated H2O2-induced cytotoxicity, intracellular accumulation of ROS and Ca2+, lipid peroxidation, and loss of MMP and DNA, which may represent the cellular mechanisms for its neuroprotective action.     

Repair of hydrogen peroxide-induced single-strand breaks in Escherichia coli deoxyribonucleic acid.

Near-ultraviolet (300 to 400 nm) irradiation of L-tryptophan yielded H2O2 (a toxic photoproduct) that was selectively lethal for rec and polA1 Escherichia coli mutants. H2O2 treatment of cells resulted in the induction of single-strand deoxyribonucleic acid breaks. These breaks were repaired to only a small extent in polA1, recA recB, and recA mutants, but were efficiently repaired in wild-type strains. We conclude that H2O2 deoxyribonucleic acid lesions require both the polA+ and recA+ pathways for repair.     

Protection of PC12 cells from hydrogen peroxide-induced cytotoxicity by salvianolic acid B, a new compound isolated from Radix Salviae miltiorrhizae

A number of studies indicate that reactive oxygen species (ROS) are involved in neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). The neuroprotective effects of salvianolic acid B (SalB) from Radix Salviae miltiorrhizae (RSM) against hydrogen peroxide (H2O2)-induced rat pheochromocytoma line PC12 injury were evaluated in the present study. Vitamin E, a potent antioxidant, was employed as a positive control agent. Following exposure of cells to H2O2 (150 microM), a marked decrease in cell survival and activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), as well as increased levels of malondialdehyde (MDA) production and lactate dehydrogenase (LDH) release were observed. In parallel, H2O2 caused significant elevation in intracellular Ca2+ level and caspase-3 activity, and induced apoptotic death as determined by flow cytometric assay. However, pretreatment of the cells with SalB (0.1-10 microM) prior to H2O2 exposure blocked these H2O2-induced cellular events noticeably. Moreover, SalB exhibited significantly higher potency as compared to Vitamin E. The present findings indicated that SalB exerts neuroprotective effects against H2O2 toxicity, which might be of importance and contribute to its clinical efficacy for the treatment of neurodegenerative diseases.     

Antimutagenic and antitumorigenic activities of nordihydroguaiaretic acid.

Nordihydroguaiaretic acid (NDGA), which occurs in the resinous exudates of many plants is used as an antioxidant in fats and oils. In this study we show that NDGA inhibited the mutagenicity of methyl methanesulfonate, benzo[a]pyrene (BP), 2-aminofluorene, and aflatoxin B1 in Salmonella typhimurium strain TA100 or TA98 in the absence and presence of rat hepatic microsomal activation system. The addition of NDGA during and after nitrosation of methylurea (MU) resulted in a dose-dependent inhibition of mutagenicity induced by nitrosation products of MU. In a two-stage skin tumorigenesis protocol using 7,12-dimethylbenz[a]anthracene (DMBA) as the initiating agent followed by twice weekly applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) as tumor promoter, pretreatment of animals with NDGA prior to DMBA application, afforded significant protection against skin tumorigenicity in female SENCAR mice. In additional studies, skin application of NDGA also inhibited the binding of topically applied [3H]BP and [3H]DMBA to epidermal DNA. When assessed in the anti-tumor promotion protocol, pretreatment of animals with NDGA before each application of TPA in DMBA-initiated mouse skin, resulted in 72% decrease in the total number of tumors when compared to non-NDGA pretreated animals. The possible mechanism(s) of the antimutagenic and anti-tumorigenic activities may be due to the multiple effects of NDGA as inhibitor of the carcinogen metabolism and DNA-adduct formation, scavenger of carcinogen free radicals, and as inhibitor of TPA-induced ornithine decarboxylase activity.     

Role of thiocyanate, bromide and hypobromous acid in hydrogen peroxide-induced apoptosis

We have previously reported that H₂O₂-induced apoptosis in HL-60 human leukemia cells takes place in the presence of chloride, requires myeloperoxidase (MPO), and occurs through oxidative reactions involving hypochlorous acid and chloramines. We now report that when chloride is replaced by the pseudohalide thiocyanate, there is little or no H₂O₂-induced apoptosis. Furthermore, thiocyanate inhibits H₂O₂-induced apoptosis when chloride is present at physiological concentrations, and this occurs at thiocyanate concentrations that are present in human serum and saliva. In contrast, bromide can substitute for chloride in H₂O₂-induced apoptosis, but results in a lower percent of the cells induced into apoptosis. Hypobromous acid is likely a short-lived intermediate in this H₂O₂/MPO/bromide apoptosis, and reagent hypobromous acid and bromamines induce apoptosis in HL-60 cells. We conclude that the physiologic concentrations of thiocyanate found in human plasma could modulate the cytototoxicity of H₂O₂ and its resulting highly toxic MPO-generated hypochlorous acid by competing with chloride for MPO. Furthermore, the oxidative products of the reaction of thiocyanate with MPO are relatively innocuous for human leukemic cells in culture. In contrast, bromide can support H₂O₂/MPO/halide apoptosis, but is less potent than chloride and it has no effect in the presence of physiological levels of chloride.     

Suppression of heat- and polyglutamine-induced cytotoxicity by nonsteroidal anti-inflammatory drugs.

We have shown that sodium salicylate activates the heat shock promoter and induces the expression of heat shock proteins (hsps), with a concomitant increase in the thermotolerance of cells. To determine whether these effects are generally displayed by nonsteroidal anti-inflammatory drugs (NSAIDs), we examined the effects of a cyclooxygenase inhibitor, indomethacin, and a lipoxygenase inhibitor, nordihydroguaiaretic acid. Both inhibitors up-regulated the hsp promoter at 37 degrees C through the activation of heat shock factors, and increased cellular levels of hsps in mammalian cells, although the degree of the expression of hsps and thermotolerance of cells differed depending on the drugs. Furthermore, NSAIDs such as sodium salicylate and indomethacin suppressed the protein aggregation and apoptosis caused by an expanded polyglutamine tract in a cellular model of polyglutamine disease. These findings suggest that NSAIDs generally induce the expression of hsps in mammalian cells and may be used for the protection of cells against deleterious stressors and neurodegenerative diseases.     

Protective effect of vanillic acid in hydrogen peroxide-induced oxidative stress in D.Mel-2 cell line

The overproduction of reactive oxygen species (ROS) causes oxidative stress, such as Hydrogen peroxide (H₂O₂). Acute oxidative stress is one of the main reasons for cell death. In this study, the antioxidant properties of vanillic acid- a polyphenolic compound was evaluated. Therefore, this study aims to check the effectiveness of vanillic acid in H₂O₂-induced oxidative stress in D. Mel-2 cell line. The efficacy was determined by biochemical tests to check the ROS production. The cytotoxicity of H₂O₂ and vanillic acid was checked by MTT assay. The DNA fragmentation was visualized by gel electrophoresis. Protein biomarkers of oxidative stress were analyzed by western blotting. The results depict a promising antioxidant effect of vanillic acid. The IC₅₀ value of vanillic acid and H₂O₂ was found 250 μg/ml and 125 μg/ml, respectively. The catalase activity, SOF, GPx, and PC was seen less in H₂O₂ treated group compared with the control and vanillic acid treated group. However, the TBRAS activity was hight in H₂O₂ treated group. The effect of H₂O₂ on DNA fragmentation was high as compared with vanillic acid-treated cells. The protein expression of Hsp70, IL-6 and iNOS was seen significant in a vanillic acid-treated group as compared with H₂O₂ treated group. These results reinforce that at low concentration, vanillic acid could be used as an antioxidant agent in the food and pharmaceutical industries.     

Analysis of nordihydroguaiaretic acid in Larrea divaricata Cav. extracts by micellar electrokinetic chromatography

Introduction – Larrea divaricata Cav. is a common shrub used in folk medicine to treat a variety of diseases. The main product extracted from this bush is nordihydroguaiaretic acid (NDG), which is a potent antioxidant. Objective – In this paper we propose a novel method for the quantification of NDG in different extracts of Larrea divaricata. The concentration of NDG in two different aqueous extracts (I and D) and an ethanolic extract (Eet) was analysed, in order to evaluate the safe use of the extracts for pharmacological purposes. Methodology – Micellar electrokinetic chromatography (MEKC) was performed under the following conditions: the background electrolyte used consisted of 20 mm phosphate buffer (pH 7.5), 10 mm sodium dodecyl sulphate and 10% acetonitrile. Results – The limits of detection and quantitation of NDG were 4.54 × 10^?4 and 10.6 × 10^?4 mg/mL, respectively. The concentration of this acid in both aqueous extracts was within the safe levels. However, the decoction must be used carefully because the concentration of the acid was almost over the recommended limit. In the case of ethanolic extracts, the amount of NDG was above the safe concentration, which is in agreement with the solubility of the active compound in ethanol. Conclusions – The conclusions of this study demonstrate that most of these plant extracts should be used with care, especially those which are used with medicinal purposes. This is the first research on the quantification of NDG using MEKC in jarilla extracts. Copyright © 2010 John Wiley & Sons, Ltd.     

Methylated polyphenols are poor "chemical" antioxidants but can still effectively protect cells from hydrogen peroxide-induced cytotoxicity

Several polyphenolic compounds, including flavonoids and phenolic acids, were compared with their per-methylated forms in both chemical and cell-based assays for antioxidant capacity. Methylation largely eliminated "chemical" antioxidant capacity, according to ferric reducing antioxidant power and oxygen radical absorbance capacity assays. Methylation, however, only moderately reduced protection of human Jurkat cells in culture, from hydrogen peroxide-mediated cytotoxicity, at physiologically relevant concentrations. Neither methylated nor un-methylated compounds were detectably metabolized by the cells. It appears that the protective mechanism of polyphenolic antioxidants against high concentrations of hydrogen peroxide in human cells may be largely unrelated to chemical antioxidant capacity.     

Suppression of clonogenicity by mammalian Dnmt1 mediated by the PCNA-binding domain.

Overexpression of the major DNA methyltransferase Dnmt1 is cytotoxic and has been hypothesized to result in aberrant hypermethylation of genes required for cell survival. Indeed, overexpression of mouse or human Dnmt1 in murine and human cell lines decreased clonogenicity. By frame-shift and deletion constructs, this effect of mouse Dnmt1 was localized at the N-terminal 124 amino acid domain, which mediates interaction with proliferating cell nuclear antigen (PCNA). Mutation of the PCNA-binding site restored normal cloning efficiencies. Overexpression of Dnmt3A or Dnmt3B, which do not interact with PCNA, yielded weaker effects on clonogenicity. Following introduction of the toxic domain, no significant effects on apoptosis, replication, or overall DNA methylation were observed for up to 3 d. Suppression of clonogenicity by Dnmt1 was also observed in cell lines lacking wild-type p53, p21(CIP1), or p16(INK4A). Suppression of clonogenicity by Dnmt1 overexpression may act as a fail-safe mechanism against carcinogenicity of sustained Dnmt1 overexpression.     

Parallel inhibition of neutrophil arachidonic acid metabolism and lysosomal enzyme secretion by nordihydroguaiaretic acid

Arachidonic acid at concentrations from 0.2 to 2.0 × 10?⁶M induces the secretion of lysosomal enzymes from cytochalasin B-treated rabbit neutrophils. These concentrations of arachidonic acid are metabolized primarily to hydroxyeicosatetraenic acids rather than to cyclooxygenase products. A good correlation is observed between the extent of arachidonic acid metabolism and the secretion of lysosomal enzymes. Nordihydroguaiaretic acid (1?10μM) inhibits both lysosomal enzyme secretion and the production of lipoxygenase products by neutrophils.     

Bruton's tyrosine kinase is essential for hydrogen peroxide-induced calcium signaling.

Using Btk-deficient DT40 cells and the transfectants expressing wild-type Btk or Btk mutants in either kinase (Arg(525) to Gln), Src homology 2 (SH2, Arg(307) to Ala), or pleckstrin homology (PH, Arg(28) to Cys) domains, we investigated the roles and structure-function relationships of Btk in hydrogen peroxide-induced calcium mobilization. Our genetic evidence showed that Btk deficiency resulted in a significant reduction in hydrogen peroxide-induced calcium response. This impaired calcium signaling is correlated with the complete elimination of IP3 production and the significantly reduced tyrosine phosphorylation of PLCgamma2 in Btk-deficient DT40 cells. All of these defects were fully restored by the expression of wild-type Btk in Btk-deficient DT40 cells. The data from the point mutation study revealed that a defect at any one of the three functional domains would prevent a full recovery of Btk-mediated hydrogen peroxide-induced intracellular calcium mobilization. However, mutation at either the SH2 or PH domain did not affect the hydrogen peroxide-induced activation of Btk. Mutation at the SH2 domain abrogates both IP3 generation and calcium release, while the mutant with the nonfunctional PH domain can partially activate PLCgamma2 and catalyze IP3 production but fails to produce significant calcium mobilization. Thus, these observations suggest that Btk-dependent tyrosine phosphorylation of PLCgamma2 is required but not sufficient for hydrogen peroxide-induced calcium mobilization. Furthermore, hydrogen peroxide stimulates a Syk-, but not Btk-, dependent tyrosine phosphorylation of B cell linker protein BLNK. The overall results, together with those reported earlier [Qin et al. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 7118], are consistent with the notion that functional SH2 and PH domains are required for Btk to form a complex with PLCgamma2 through BLNK in order to position the Btk, PLCgamma2, and phosphatidylinositol 4,5-bisphosphate in close proximity for efficient activation of PLCgamma2 and to maximize its catalytic efficiency for IP3 production.     

Protection of cultured endothelial cells from hydrogen peroxide-induced injury by antibody-conjugated catalase

The cytoprotective features of catalase-antibody conjugate prepared by covalent conjugation of catalase to rabbit antibody against mouse IgG is described. The bifunctional cross-linking agent m-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS) was used for conjugation. Functionally active conjugate binds specifically to the plastic-adsorbed mouse IgG and to the surface of live human endothelial cells treated with mouse antiserum against human endothelial cells. Up to 4 units of catalase activity can bind to 1 cm2 of the endothelial monolayer. The targeted catalase protects endothelial cells from cytotoxic action of hydrogen peroxide: the minimal cytotoxic concentration of H2O2 for protected cells is 80-times higher than for intact cells. This effect is attributed partly to local reduction of H2O2 concentration in the cell microenvironment. Targeted catalase was estimated to reduce H2O2 concentration 8-fold near the cell surface with respect to average total concentration.     

Suppression of cell-mediated tumor cell lysis and complement-induced cytotoxicity by trypan blue.

Different forms of cell-mediated cytotoxicity were suppressed in the presence of trypan blue. The systems affected included lysis of antibody-coated tumor cells by normal and C. parvum-stimulated mouse peritoneal cells and lysis of allogeneic targets by immune effector cells. The inhibition, measured in a 4-hr 51Cr release assay, was reversible and did not occur in the presence of 30% fetal calf serum or albumin. Binding between effector and target cells through Fc receptors was not affected, and lysis of allogeneic cells was inhibited at the lytic step rather than at the binding step. In contrast, lysis of sensitized erythrocytes was not inhibited by trypan blue, suggesting that lysis of these targets may not involve the steps required in tumor cell lysis. Trypan blue blocked the function of antibody before binding to target cells and also suppressed complement-induced cytolysis. Most individual complement components were susceptible to the inhibitory action of trypan blue. These results reveal an affinity of trypan blue for proteins in general that may be responsible for many of its biologic actions.     

Effect of ethanol on hydrogen peroxide-induced AMPK phosphorylation

AMP-activated protein kinase (AMPK) responds to oxidative stress. Previous work has shown that ethanol treatment of cultured hepatoma cells and of mice inhibited the activity of AMPK and reduced the amount of AMPK protein. Ethanol generates oxidative stress in the liver. Since AMPK is activated by reactive oxygen species, it seems paradoxical that ethanol would inhibit AMPK in the hepatoma cells. In an attempt to understand the mechanism whereby ethanol inhibits AMPK, we studied the effect of ethanol on AMPK activation by exogenous hydrogen peroxide. The effects of ethanol, hydrogen peroxide, and inhibitors of protein phosphatase 2A (PP2A) [either okadaic acid or PP2A small interference RNA (siRNA)] on AMPK phosphorylation and activity were examined in rat hepatoma cells (H4IIEC3) and HeLa cells. In H4IIEC3 cells, hydrogen peroxide (H(2)O(2), 1 mM) transiently increased the level of phospho-AMPK to 1.5-fold over control (P < 0.05). Similar findings were observed in HeLa cells, which do not express the upstream AMPK kinase, LKB1. H(2)O(2) markedly increased the phosphorylation of LKB1 in H4IIEC3 cells. Ethanol significantly inhibited the phosphorylation of PKC-zeta, LKB1, and AMPK caused by exposure to H(2)O(2). This inhibitory effect of ethanol required its metabolism. More importantly, the inhibitory effects of ethanol on H(2)O(2)-induced AMPK phosphorylation were attenuated by the presence of the PP2A inhibitor, okadaic acid, or PP2A siRNA. The inhibitory effect of ethanol on AMPK phosphorylation is exerted through the inhibition of PKC-zeta and LKB1 phosphorylation and the activation of PP2A.