The chondroprotective effect of diosmin on human articular chondrocytes under oxidative stress

Excessive oxidative stress, which can amplify inflammatory responses, is involved in the pathologic progression of knee osteoarthritis. Diosmin is known to possess a variety of biological functions such as antiinflammatory and antioxidant activities. We therefore demonstrated the chondroprotective potentials of diosmin on human articular chondrocytes under oxidative stress. The cytotoxicity of diosmin (5, 10, 50, and 100 μM) to chondrocytes was first evaluated. Subsequently, the cells were treated with diosmin (5 and 10 μM) after hydrogen peroxide (H₂ O₂ ) exposure. We found that the cytotoxicity of diosmin occurred in a dose-dependent manner (10, 50, and 100 μM), and low-dose diosmin (5 μM) slightly impaired cell viability. Diosmin supplementations (5 and 10 μM) did not show beneficial effects on mitochondrial activity, cytotoxicity, proliferation, and survival and the cell senescence was ameliorated in H₂ O₂ -exposed chondrocytes. On the other hand, diosmin down-regulated the mRNA levels of iNOS, COX-2, IL-1β, COL1A1, MMP-3, and MMP-9; up-regulated TIMP-1 and SOX9; and improved COL2A1 in chondrocytes under oxidative stresses. Furthermore, diosmin also regulated glutathione reductase and glutathione peroxidase of H₂ O₂ -exposed chondrocytes. In conclusion, diosmin displayed a remarkable antiinflammatory effect compared with the antioxidant capacity on human chondrocytes. Diosmin can maintain the homeostasis of extracellular matrix of articular cartilage.

Antioxidant biomarkers in Gammarus pulex to evaluate the efficiency of electrocoagulation process in landfill leachate treatment

The discharge of landfill leachate into the environment without effective treatment poses a serious threat for the aquatic ecosystems. This present study was undertaken to evaluate whether electrocoagulation process is efficient for treatment landfill leachate (LL) or not by using antioxidant biomarkers in Gammarus pulex. Glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT) activities and malondialdehyde (MDA) and glutathione (GSH) levels in G. pulex exposed to untreated, treated, and diluted rates 1/10 and 1/20 in both LL during 24 and 96 h were tested. Physiochemical characteristics of leachate (chemical oxygen demand, electrical conductivity, pH, phosphate, turbidity, NH₃, Cl^-, and color) were determined pre and post treatment. All physiochemical characteristics of LL decreased after treatment process. GSH-Px and CAT activities and GSH and MDA levels were increased in untreated groups when compared to control (p < 0.05). After treatment by electrocoagulation, MDA and GSH levels and CAT activities were returned to control values. In conclusion, the abilities of LL to stimulate oxidative stress in G. pulex have been proven. The results revealed that antioxidant parameters are useful biomarkers for determining the treatment efficiency of the electrocoagulation process.

Involvement of reactive oxygen species derived from mitochondria in neuronal injury elicited by methylmercury

Methylmercury induces oxidative stress and subsequent neuronal injury. However, the mechanism by which methylmercury elicits reactive oxygen species (ROS) production remains under debate. In this study, we investigated the involvement of mitochondrial ROS in methylmercury-induced neuronal cell injury using human neuroblastoma SH-SY5Y-derived ρ⁰ cells, which have a deletion of mitochondrial DNA and thus decreased respiratory activity. SH-SY5Y cells were cultured for 60 days in the presence of ethidium bromide to produce ρ⁰ cells. Our ρ⁰ cells showed decreases in the cytochrome c oxidase expression and activity as well as oxygen consumption compared with original SH-SY5Y cells. Methylmercury at a concentration of 1 µM induced cell death with oxidative stress in original SH-SY5Y cells, but not ρ⁰ cells, indicating that ρ⁰ cells are resistant to methylmercury-induced oxidative stress. ρ⁰ cells also showed tolerance against hydrogen peroxide and superoxide anion, suggesting that ρ⁰ cells are resistant to total ROS. These data indicate that mitochondrial ROS are clearly involved in oxidative stress and subsequent cell death induced by methylmercury. Considering that the dominant mechanism of ROS generation elicited by methylmercury is due to direct antioxidant enzyme inhibition, mitochondria might play a role in amplifying ROS in methylmercury-induced neurotoxicity.

[A pathophysiological role of cytochrome p450 involved in production of reactive oxygen species]

Dysregulation of the production of reactive oxygen species (ROS) determines cellular function. Cytochrome P450s (CYPs) regulates ROS production and contributes to the process of cell death. This review summarizes our recent findings, focusing on the involvement of CYPs in pathophysiology induced by ROS. 1. Quinone toxicity in hepatocytes: CYPs require electrons supplied from NADPH-cytochrome P450 reductase (NPR) during the process of metabolism. NPR also provides electrons to quinone compounds, which compete with CYPs over electrons. Inhibition of CYPs shifts NPR's electron flow more to quinones, which accelerates the redox cycle to enhance ROS production and quinone toxicity. 2. Myocardial ischemia-reperfusion injury: Reperfusion of blood flow after coronary artery occlusion induces cell damage, as evident by the extension of myocardial infarct size and caspase-independent cell apoptosis. CYP2C6 appears to be a source for ROS production, since sulfaphenazole, a selective inhibitor of CYP2C6, reduces this damage. ROS produced by CYP2C6 during the reperfusion causes translational activation of Noxa and BimEL, as well as the suppression of caspase activation, resulting in caspase-independent apoptosis. 3. Primary hepatocyte apoptosis: Inhibition of catalase and glutathione peroxidase increases intracellular ROS and elicits caspase-independent hepatocyte apoptosis. SKF-525A, a pan-CYP inhibitor, suppresses these ROS increases and hepatocyte apoptosis. Increased ROS activates ERK and AP-1 by inhibition of tyrosine phosphatase, and inhibits BimEL degradation by proteasome. These results in the accumulation of mitochondrial BimEL, which then induces the release of cytochrome c and endonuclease G (EndoG). Increased ROS also keeps caspases inactivated. As a result, EndoG executes nucleosomal DNA fragmentation.

Tributyltin induces oxidative stress and neuronal injury by inhibiting glutathione S-transferase in rat organotypic hippocampal slice cultures

Tributyltin (TBT) has been used as a heat stabilizer, agricultural pesticide and antifouling agents on ships, boats and fish-farming nets; however, the neurotoxicity of TBT has recently become a concern. TBT is suggested to stimulate the generation of reactive oxygen species (ROS) inside cells. The aim of this study was to determine the mechanism of neuronal oxidative injury induced by TBT using rat organotypic hippocampal slice cultures. The treatment of rat hippocampal slices with TBT induced ROS production, lipid peroxidation and cell death. Pretreatment with antioxidants such as superoxide dismutase, catalase or trolox, suppressed the above phenomena induced by TBT, indicating that TBT elicits oxidative stress in hippocampal slices, which causes neuronal cell death. TBT dose-dependently inhibited glutathione S-transferase (GST), but not glutathione peroxidase or glutathione reductase in the cytosol of rat hippocampus. The treatment of hippocampal slices with TBT decreased the GST activity. Pretreatment with reduced glutathione attenuated the reduction of GST activity and cell death induced by TBT, indicating that the decrease in GST activity by TBT is involved in hippocampal cell death. When hippocampal slices were treated with sulforaphane, the expression and activity of GST were increased. Notably, TBT-induced oxidative stress and cell death were significantly suppressed by pretreatment with sulforaphane. These results indicate that GST inhibition could contribute, at least in part, to the neuronal cell death induced by TBT in hippocampal slices. This study is the first report to show the link between neuronal oxidative injury and the GST inhibition elicited by TBT.

Antioxidant properties of rare sugar D-allose: Effects on mitochondrial reactive oxygen species production in Neuro2A cells

The anti-oxidative activity of the rare sugar D-allose has recently been reported, but the mechanism is largely unclear. In this study, we evaluated the reactive oxygen species (ROS) scavenging activities of D-allose and then examined the effects of D-allose on ROS production in mitochondria to clarify the antioxidant properties of D-allose. While D-allose did not scavenge hydrogen peroxide and superoxide anions, it eliminated hydroxyl radicals to the same extent as D-glucose. Rotenone, an uncoupler of mitochondrial respiratory complex I, induces ROS production in mouse neuroblastoma Neuro2A cells in the presence of D-glucose. However, in the presence of D-allose, there was no change in the ROS levels in Neuro2A cells following rotenone treatment. Furthermore, treatment with D-allose attenuated the D-glucose-dependent ROS generation induced by rotenone. Whereas treatment with D-glucose enhanced ATP synthesis in Neuro2A cells, D-allose was less effective in producing intracellular ATP than D-glucose. Treatment with D-allose inhibited the ATP synthesis stimulated by D-glucose. These results suggest that D-allose suppresses ROS production in the mitochondria due to competition with D-glucose at the cellular level.

Increased expression of c-Fos by extracellular signal-regulated kinase activation under sustained oxidative stress elicits BimEL upregulation and hepatocyte apoptosis

We previously reported that the inhibition of catalase and glutathione peroxidase activities by treatment with 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid evoked sustained increases in the levels of reactive oxygen species and apoptosis in rat primary hepatocytes. Apoptosis was accompanied by increased expression of BimEL, following activation of extracellular signal-regulated kinase. The aim of this study was to characterize the mechanism underlying hepatocyte apoptosis by identifying the transcription factor that induces BimEL expression. The bim promoter region was cloned into a promoterless-luc vector, and promoter activity was monitored by a luciferase assay. The luciferase activity increased in the presence of ATZ + mercaptosuccinic acid. Pretreatment with a MEK inhibitor, U0126, or an antioxidant, vitamin C, suppressed the promoter activity. Furthermore, ATZ + mercaptosuccinic acid-induced luciferase activity was attenuated by mutation of the activator protein-1 binding site in the bim promoter region. The amounts of total and phosphorylated c-Fos increased over time in the presence of ATZ + mercaptosuccinic acid, whereas the amounts of total and phosphorylated c-Jun remained unchanged. Chromatin immunoprecipitation revealed that both c-Fos and c-Jun localized to the activator protein-1-binding site in the bim promoter region. BimEL expression and hepatocyte apoptosis were suppressed by knockdown of c-Fos and c-Jun, respectively. These results indicate that increases in c-Fos following extracellular signal-regulated kinase activation are critical for BimEL upregulation and apoptosis.

Crucial role of cytochrome P450 in hepatotoxicity induced by 2,3-dimethoxy-1,4-naphthoquinone in rats

Quinone toxicity is induced by two principal mechanisms: arylation/alkylation and a redox cycle. We have previously shown that increases in intracellular levels of superoxide anion and cell death induced by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), a redox cycling quinone, are enhanced by pretreatment of rat primary hepatocytes with cytochrome P450 inhibitors. This indicates a novel interaction of quinones with cytochrome P450, and is thus worthy of further investigation using an in vivo model. The aim of this study was to examine the effects of cytochrome P450 inhibitors on DMNQ-induced hepatotoxicity in rats. When DMNQ was administered intraperitoneally, the activities of serum alanine aminotransferase and aspartate aminotransferase were found to increase in a dose-dependent manner, indicating that hepatotoxicity was induced by treatment with DMNQ. Pretreatment with the cytochrome P450 inhibitors SKF-525A (SKF), cimetidine and ketoconazole potentiated the DMNQ-induced hepatotoxicity. The blood concentration of DMNQ was not affected by administration of SKF. Pretreatment with the antioxidant α-tocopherol almost completely attenuated the hepatotoxicity induced by DMNQ and by the combination of DMNQ with SKF. Levels of reduced glutathione in the liver were decreased and levels of oxidized glutathione were increased by treatment with DMNQ. These effects were potentiated by pretreatment with SKF. DMNQ-induced lipid peroxidation in the liver was also enhanced by pretreatment with SKF. Taken together, these results indicate that DMNQ-induced hepatotoxicity is augmented by inhibition of cytochrome P450 and that this augmentation is due to the enhancement of oxidative stress.

Sustained contraction and endothelial dysfunction induced by reactive oxygen species in porcine coronary artery

A combination of purine and xanthine oxidase (XOD) dose-dependently elicited sustained contraction of porcine coronary arterial rings and resulted in increased concentrations of superoxide anions and hydrogen peroxide. These contractile responses appeared, with a delay, after the application of purine and XOD, used as a reactive oxygen species (ROS)-generating system. Coronary arteries precontracted with prostaglandin F(2alpha) failed to relax in response to substance P after exposing the arterial preparation to this ROS-generating system. The contractile response of the coronary artery to the ROS-generating system was almost completely inhibited by catalase (130 U/ml), and was partially inhibited by superoxide dismutase (60 U/ml), or mannitol (30 mM). A voltage-dependent L-type Ca(2+) channel antagonist, nicardipine, had no effect on contraction. Dysfunction of endothelial cells was completely prevented by catalase, but not by superoxide dismutase or mannitol. These results suggest that superoxide anions, hydrogen peroxide and hydroxyl radicals might be involved in eliciting sustained, delayed-onset coronary artery contraction, which is not related to L-type Ca(2+) channels. They also suggest that hydrogen peroxide might play a major role in endothelial dysfunction of the porcine coronary artery.