Metabolic and antioxidant system alterations in an astrocytoma cell line challenged with mitochondrial DNA deletion

Phenethyl isothiocyanate induces oxidative cell death in osteosarcoma cells with regulation on mitochondrial network, function and metabolism

Phenethyl isothiocyanate (PEITC), a kind of isothiocyanate available in cruciferous vegetables, exhibits inhibitory effects on cancers. PEITC has been extensively recorded for its effect on regulation of redox status in cancer cells. Our previous studies revealed that PEITC induced ROS-dependent cell death in osteosarcoma. Mitochondria are the main sites for ROS generation and play significant role in deciding cell fate. To dissect the mechanism of PEITC's action on osteosarcoma cells, we detected changes on mitochondrial network, function and metabolism in K7M2 and 143B cells. Here, PEITC induced cytosolic, lipid and mitochondrial ROS production in osteosarcoma cells. It changed mitochondrial morphology from elongated to punctate network and decreased mitochondrial mass. Meantime, PEITC increased mitochondrial transmembrane potential in short time, decreased it with time prolonged, and later collapsed it in K7M2 cells, and reduced it in 143B cells. PEITC inhibited proliferation potential of osteosarcoma cells with damage on mitochondrial respiratory chain complexes. Further, PEITC-treated osteosarcoma cells experienced a sudden increase in ATP level, and later its content was decreased. Moreover, PEITC downregulated the expressions of mitochondrial respiratory chain complexes including COX IV, UQCR, SDHA and NDUFA9 in 143B cells and COX IV in K7M2 cells. At last, by using Rho 0 cells derived from K7M2 and 143B cells, we found that osteosarcoma cells that depleted mtDNA were less sensitive to PEITC-induced changes on cellular morphology, cytoskeleton filament, mitochondrial transmembrane potential and ROS generation. In conclusion, our study demonstrated that mitochondria may play important role in PEITC-induced oxidative cell death in osteosarcoma cells.

A glyphosate-based herbicide disrupted hematopoiesis and induced organ toxicities, ameliorated by vitamin B12 in a mouse model

Glyphosate-based herbicides (GBH) are widely used worldwide. Their negative impact on human health is a matter of debate by regulatory bodies and the public. The present study sought to determine the impact of a GBH on the vital organs; and the potential protective effects of vitamin B12 (cyanocobalamin) supplementation. Sixty white Swiss mice were randomly assigned to five treatment groups, each containing twelve mice. Group one represented the normal control; Group two mice were treated with 375 mg/kg of GBH for 56 days; Group three mice received 10 mg/kg of cyanocobalamin for 56 days; Group four mice were administered with 375 mg/kg of GBH and 10 mg/kg cyanocobalamin for 56 days and Group five received 10 mg/kg cyanocobalamin first for 7 days, then continued thereafter co-administered together with 375 mg/kg of GBH for 56 days). Oral administration of GBH induced severe anemia in mice, which was attenuated by cyanocobalamin. Moreover, GBH resulted in a very significant alteration of platelets, WBCs, and its sub-types. Once again, cyanocobalamin stabilized the levels of platelets and WBCs in the presence of GBH. GBH-induced elevation of triglycerides and HDL was nullified by the administration of cyanocobalamin. Further studies showed evidence for GBH-induced inflammation represented by an imbalance in serum levels of the TNF-α: IL-10 and IFN-γ ratios. The GBH severely depleted GSH levels in the liver. A GBH-induced rise in GSH in the kidney, lungs and brain was noted; and is an indicator of antioxidant capacity enhancement in response to a GBH-induced oxidant challenge. Moreover, cyanocobalamin supplementation abrogated GBH-induced oxidative stress as depicted by stabilized GSH levels in the liver, kidney, lungs, and brain. In the presence of cyanocobalamin, the GBH-induced liver injury depicted by elevation of AST, ALT, and bilirubin, was attenuated. From the results, we conclude that the capacity of cyanocobalamin to assuage GBH-induced inflammatory responses, hepatotoxicity, and hematological alteration as well as oxidative stress may be attributable to its antioxidant and anti-inflammatory properties. The current findings provide a solid foundation for further scrutiny of this phenomenon, with vital implications in GBH exposure and the role of potent antioxidant supplementation in the management of GBH-induced toxicity.

Suppression of methylmercury-induced IL-6 and MCP-1 expressions by N-acetylcysteine in U-87MG human astrocytoma cells

AIMS

The aim of this study was to clarify the involvement of oxidative stress in methylmercury (MeHg)-induced pro-inflammatory cytokine expressions and the suppressive effects of N-acetylcysteine (NAC) in MeHg-induced cytokine expression.

MATERIALS AND METHODS

Using U-87-MG human astrocytoma cell line, interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1 expressions induced by 4 μM MeHg were measured at mRNA and protein levels. Hydrogen peroxide (H2O2) and superoxide anion (O2(-)) were quantified by flow-cytometry analysis. To examine the suppressive effects of NAC on the cytokine expressions among different timing of NAC treatment, cells were treated with 0.5 or 5mM NAC before, simultaneously, or after MeHg administration.

KEY FINDINGS

MeHg exposure at 4 μM, a non-cytotoxic concentration, significantly induced MCP-1 and IL-6 expressions at both mRNA and protein levels. A significant increase of H2O2 production but not O2(-) was observed. MeHg-induced expression of MCP-1 and IL-6 mRNA was reduced by 10-20% in the presence of 5mM NAC (co-treatment experiment) compared to cells treated with MeHg only. Pre-treatment of cells with 0.5 or 5mM NAC at 0.5 or 1h and its subsequent washout before MeHg addition suppressed MCP-1 and IL-6 cytokine expressions. Post-treatment of cells with NAC after MeHg addition also suppressed the cytokine induction, but the magnitude of suppression was evidently lower than in co-treated cells even though the H2O2 generation was almost completely suppressed by NAC.

SIGNIFICANCE

NAC may effectively suppress the MeHg-induced cytokine production through both, inhibition of reactive oxygen species as well as extracellular chelation of MeHg in astrocytes.

Anthocyanin-rich açaí (Euterpe oleracea Mart.) extract attenuates manganese-induced oxidative stress in rat primary astrocyte cultures

Manganese (Mn) is an essential element for human health. However, at high concentrations Mn may be neurotoxic. Mn accumulates in astrocytes, affecting their redox status. In view of the high antioxidant and anti-inflammatory properties of the exotic Brazilian fruit açaí (Euterpe oleracea Mart.), its methanolic extract was obtained by solid-phase extraction (SPE). This açaí extract showed considerable anthocyanins content and direct antioxidant capacity. The açaí extract scavenged 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH•) with an EC₅₀ of 19.1 ppm, showing higher antioxidant activity compared to butylated hydroxytoluene (BHT), but lower than ascorbic acid and quercetin. This obtained açaí extract also attenuated Mn-induced oxidative stress in primary cultured astrocytes. Specifically, the açaí extract at an optimal and nutritionally relevant concentration of 0.1 μg/ml prevented Mn-induced oxidative stress by (1) restoring GSH/GSSG ratio and net glutamate uptake, (2) protecting astrocytic membranes from lipid peroxidation, and (3) decreasing Mn-induced expression of erythroid 2-related factor (Nrf2) protein. A larger quantity of açaí extract exacerbated the effects of Mn on these parameters except with respect to lipid peroxidation assessed by means of F₂-isoprostanes. These studies indicate that at nutritionally relevant concentration, anthocyanins obtained from açaí protect astrocytes against Mn neurotoxicity, but at high concentrations, the "pro-oxidant" effects of its constituents likely prevail. Future studies may be profitably directed at potential protective effects of açaí anthocyanins in nutraceutical formulations.

Neuroprotection against neuroblastoma cell death induced by depletion of mitochondrial glutathione

Mitochondrial glutathione pool is vital in protecting cells against oxidative stress as the majority of the cellular reactive oxygen species are generated in mitochondria. Oxidative stress is implicated as a causative factor in neuronal death in neurodegenerative disorders. We hypothesized that depletion of mitochondrial glutathione leads to mitochondrial dysfunction and apoptotic death of SK-N-SH (human neuroblastoma) cells and investigated the neuroprotective strategies against GSH depletion. SK-N-SH cells were treated with two distinct inhibitors of glutathione metabolism: L-buthionine-(S, R)-sulfoximine (BSO) and ethacrynic acid (EA). EA treatment caused depletion of both the total and mitochondrial glutathione (while BSO had no effect on mitochondrial glutathione), enhanced rotenone-induced ROS production, and reduced the viability of SK-N-SH cells. Glutathione depletion by BSO or EA demonstrated positive features of mitochondria-mediated apoptosis in neuroblastoma cell death. Prevention of apoptosis by Bcl2 overexpression or use of antioxidant ebselen did not confer neuroprotection. Co-culture with U-87 (human glioblastoma) cells protected SK-N-SH cells from the cell death. Our data suggest that depletion of mitochondrial glutathione leads to mitochondrial dysfunction and apoptosis. The study indicates that preventing mitochondrial glutathione depletion could become a novel strategy for the development of neuroprotective therapeutics in neurodegenerative disorders.

Treatment of human astrocytoma U87 cells with silicon dioxide nanoparticles lowers their survival and alters their expression of mitochondrial and cell signaling proteins

Recent evidence suggests silicon dioxide micro- and nanoparticles induce cytotoxic effects on lung cells. Thus, there is an increasing concern regarding their potential health hazard. Nevertheless, the putative toxicity of nanoparticles in mammalian cells has not yet been systematically investigated. We previously noted that several metallic oxide nanoparticles exert differential cytotoxic effects on human neural and nonneural cells. Therefore, we hypothesized that silicon dioxide nanoparticles induce cytotoxicity in U87 cells by lowering their survival by decreasing cell survival signaling and disturbing mitochondrial function. To investigate this hypothesis, we determined the activities of the key mitochondrial enzymes, citrate synthase and malate dehydrogenase, in astrocytoma U87 cells treated with silicon dioxide nanoparticles. In addition, we studied the expression of the mitochondrial DNA-encoded proteins, cytochrome C oxidase II and nicotinamide adenine dinucleotide (NADPH) dehydrogenase subunit 6, and cell signaling pathway protein extracellular signal-regulated kinase (ERK) and phosphorylated ERK in treated U87 cells. The activated form of ERK controls cell growth, differentiation, and proliferation. In parallel, we determined survival of U87 cells after treating them with various concentrations of silicon dioxide nanoparticles. Our results indicated that treatment with silicon dioxide nanoparticles induced decreases in U87 cell survival in a dose-related manner. The activities of citrate synthase and malate dehydrogenase in treated U87 cells were increased, possibly due to an energetic compensation in surviving cells. However, the expression of mitochondrial DNA-encoded cytochrome C oxidase subunit II and NADH dehydrogenase subunit 6 and the cell signaling protein ERK and phosphorylated ERK were altered in the treated U87 cells, suggesting that silicon dioxide nanoparticles induced disruption of mitochondrial DNA-encoded protein expression, leading to decreased mitochondrial energy production and decreased cell survival/proliferation signaling. Thus, our results strongly suggest that the cytotoxicity of silicon dioxide nanoparticles in human neural cells implicates altered mitochondrial function and cell survival/proliferation signaling.

Reduced glutathione regenerating enzymes undergo developmental decline and sexual dimorphism in the rat cerebral cortex

Oxidative stress during development may predispose humans to neurodegenerative disorders in old age. Moreover, numerous ailments of brain disproportionately affect one of the genders. We therefore hypothesized that, activities of enzymes regenerating and utilizing glutathione (GSH) show sexual dimorphism and developmental differences in rat brain. To test this hypothesis, we collected cortex tissue from male and female Sprague-Dawley rats at post-natal day (PN) 5, PN 10, PN 20, PN 30, and PN 60. We measured tissue levels of NADP-linked isocitrate dehydrogenase (NADP-ICDH), glucose-6-phosphate dehydrogenase (G6PDH), and, glutathione reductase (GR) by UV spectrophotometry and determined glutathione peroxidase (GPx) expression therein by western blotting. Our results showed that sexual maturation had an impact on activities of enzymes that regenerate and utilize GSH and rat female cortex had more anti-oxidant capacity. Moreover, age-related decline in the activities of these key enzymes were observed. Reduced glutathione and NADPH protects the brain from oxidative stress. Thus, our results may have implications for neurodegenerative disorders like Parkinson's disease and developmental disorders of brain like autism in which oxidative stress plays a key role.

Consequences of cytoplasmic irradiation: studies from microbeam

The prevailing dogma for radiation biology is that genotoxic effects of ionizing radiation such as mutations and carcinogenesis are attributed mainly to direct damage to the nucleus. However, with the development of microbeam that can target precise positions inside the cells, accumulating evidences have shown that energy deposit by radiation in nuclear DNA is not required to trigger the damage, extra-nuclear or extra-cellular radiation could induce the similar biological effects as well. This review will summarize the biological responses after cytoplasm irradiated by microbeam, and the possible mechanisms involved in cytoplasmic irradiation.

Mitochondrial function and nuclear factor-kappaB-mediated signaling in radiation-induced bystander effects

Although radiation-induced bystander effects have been well described over the past decade, the mechanisms of the signaling processes involved in the bystander phenomenon remain unclear. In the present study, using the Columbia University charged particle microbeam, we found that mitochondrial DNA-depleted human skin fibroblasts (rho(o)) showed a higher bystander mutagenic response in confluent monolayers when a fraction of the same population were irradiated with lethal doses compared with their parental mitochondrial-functional cells (rho(+)). However, using mixed cultures of rho(o) and rho(+) cells and targeting only one population of cells with a lethal dose of alpha-particles, a decreased bystander mutagenesis was uniformly found in nonirradiated bystander cells of both cell types, indicating that signals from one cell type can modulate expression of bystander response in another cell type. In addition, we found that Bay 11-7082, a pharmacologic inhibitor of nuclear factor-kappaB (NF-kappaB) activation, and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a scavenger of nitric oxide (NO), significantly decreased the mutation frequency in both bystander rho(o) and rho(+) cells. Furthermore, we found that NF-kappaB activity and its dependent proteins, cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS), were lower in bystander rho(o) cells when compared with their rho(+) counterparts. Our results indicated that mitochondria play an important role in the regulation of radiation-induced bystander effects and that mitochondria-dependent NF-kappaB/iNOS/NO and NF-kappaB/COX-2/prostaglandin E2 signaling pathways are important to the process.