Hydrogen peroxide responsive miR153 targets Nrf2/ARE cytoprotection in paraquat induced dopaminergic neurotoxicity

Epidemiological and animal studies suggest that environmental toxins including paraquat (PQ) increase the risk of developing Parkinson's disease (PD) by damaging nigrostriatal dopaminergic neurons. We previously showed that overexpression of a group of microRNAs (miRs) affects the antioxidant promoting factor, Nrf2 and related glutathione-redox homeostasis in SH-SY5Y dopaminergic neurons. Although, dysregulation of redox balance by PQ is well documented, the role for miRs and their impact have not been elucidated. In the current study we investigated whether PQ impairs Nrf2 and its related cytoprotective machinery by misexpression of specific fine tune miRs in SH-SY5Y neurons. Real time PCR analysis revealed that PQ significantly (p < 0.05) increased the expression of brain enriched miR153 with an associated decrease in Nrf2 and its function as revealed by decrease in 4× ARE activity and expression of GCLC and NQO1. Also, PQ and H₂O₂-induced decrease in Nrf2 3′ UTR activity was restored on miR153 site mutation suggesting a 3′ UTR interacting role. Overexpression of either anti-miR153 or Nrf2 cDNA devoid of 3′ UTR prevented PQ and H₂O₂-induced loss in Nrf2 activity confirming that PQ could cause miR153 to bind to and target Nrf2 3′ UTR thereby weakening the cellular antioxidant defense. Adenovirus mediated overexpression of cytoplasmic catalase (Ad cCAT) confirmed that PQ induced miR153 is hydrogen peroxide (H₂O₂) dependent. In addition, Ad cCAT significantly (p < 0.05) negated the PQ induced dysregulation of Nrf2 and function along with minimizing ROS, caspase 3/7 activation and neuronal death. Altogether, these results suggest a critical role for oxidant mediated miR153-Nrf2/ARE pathway interaction in paraquat neurotoxicity. This novel finding facilitates the understanding of molecular mechanisms and to develop appropriate management alternatives to counteract PQ-induced neuronal pathogenesis.     

DL0410 attenuates oxidative stress and neuroinflammation via BDNF/TrkB/ERK/CREB and Nrf2/HO-1 activation

Oxidative stress and neuroinflammation have been deeply associated with Alzheimer’s disease. DL0410 is a novel acetylcholinesterase inhibitor with potential anti-oxidative effects in AD-related animal models, while the specific mechanism has not been fully clarified. In this study, DL0410 was predicted to be related to the modification of cell apoptosis, oxidation-reduction process, inflammatory response and ERK1/ERK2 cascade by in silico target fishing and GO enrichment analysis. Then the possible protective effects of DL0410 were evaluated by hydrogen peroxide (H₂O₂)-induced oxidative stress model and lipopolysaccharides (LPS)-induced neuroinflammation model H₂O₂ decreased the viability of SH-SY5Y cells, induced malondialdehyde (MDA) accumulation, mitochondrial membrane potential (Δψm) loss and cell apoptosis, which could be reversed by DL0410 dose-dependently, indicating that DL0410 protected SH-SY5Y cells against H₂O₂-mediated oxidative stress. Western blot analysis showed that DL0410 increased the H₂O₂-triggered down-regulated TrkB, ERK and CREB phosphorylation and the expression of BDNF. In addition, TrkB inhibitor ANA-12, ERK inhibitor SCH772984 and CREB inhibitor 666-15 eliminated the inhibition of DL0410 on MDA accumulation and Δψm loss. Furthermore, DL0410 attenuates inflammatory responses and ROS production in LPS-treated BV2 cells, which is responsible for Nrf2 and HO-1 up-regulation. The present study demonstrates that DL0410 is a potential activator of the BDNF/TrkB/ERK/CREB and Nrf2/HO-1 pathway and may be a potential candidate for regulating oxidative stress and neuroinflammatory response in the brain. Together, the results showed that DL0410 is a promising drug candidate for treating AD and possibly other nervous system diseases associated with oxidative stress and neuroinflammation.     

Differential in vivo genotoxicity of arsenic trioxide in glutathione depleted mouse bone marrow cells: expressions of Nrf2/Keap1/P62

Abstract

Generation of reactive oxygen species is one of the major contributors in arsenic-induced genotoxicity where reduced glutathione (GSH) could be an important determining factor. To understand the role of endogenous GSH, arsenic trioxide (As₂O₃) was administered in buthionine sulfoximine (BSO)- and N-acetyl-l-cysteine (NAC)-treated mice. As₂O₃-induced significant chromosome aberrations (CAs) in all treatment groups compared with the control. BSO-treated mouse bone marrow cells showed significant CAs at a dose of 2?mg As₂O₃?kg^?1 b.w. Similar induction was not evident at 4?mg As₂O₃?kg^?1 b.w. and exhibited antagonistic effect at 8?mg As₂O₃?kg^?1 b.w. To understand this differential effect, expression pattern of Nrf2 was observed. Nrf2 expression increased following As₂O₃ treatment in a dose-dependent manner up to 4?mg As₂O₃?kg^?1 b.w after which no further increase was noticed. NAC pre-treatment significantly reduced the extent of As₂O₃-induced CAs suggesting the protective role of endogenous GSH against arsenic-induced genotoxicity.     

Icaritin activates Nrf2/Keap1 signaling to protect neuronal cells from oxidative stress

Our earlier study indicated that icaritin (ICT) protected mice from cerebral ischemic injury by inhibiting oxidative stress, and this study aimed to investigate its mechanism using a H₂O₂‐treated SH‐SY5Y cells model. Cell viability was assessed by cell counting kit 8 (CCK‐8). Oxidative stress parameters were detected by flow cytometry, and signaling pathways were analyzed by immunoblotting. We found that ICT alleviated apoptosis and intracellular and mitochondrial reactive oxygen species (ROS) levels, decreased the expressions of Bax and cleaved caspase‐3, and increased the expressions of Bcl‐2 compared to H₂O₂ group. ICT increased mitochondrial membrane potential (ΔΨm) and blocked the opening of mitochondrial membrane permeability transporter (MPT), and increased the activity of glutathione peroxidase (GSH‐px), catalase (CAT), and superoxide dismutase (SOD), meanwhile, decreased the activity of malondialdehyde (MDA) compared to H₂O₂ group. Further investigation revealed that ICT significantly up‐regulated the expressions of nuclear factor erythroid 2‐related factor 2 (Nrf2), heme oxygenase 1 (HO‐1) and NAD(P)H‐quinone oxidoreductase 1 (NQO‐1). The anti‐apoptosis and antioxidative effects of ICT were blocked bay ML385, a Nrf2/Keap1 signaling pathway inhibitor. These results indicate that ICT can play a neuroprotective role against oxidative stress injury by activating Nrf2/Keap1 signaling pathway.     

Antioxidant ameliorating effects against H2O2-induced cytotoxicity in primary endometrial cells

Oxidative stress and a disrupted antioxidant system are involved in a variety of pregnancy complications. In the present study, the role of vitamin E (Vit E) and folate as radical scavengers on the GSH homeostasis in stress oxidative induced in rat endometrial cells was investigated. Primary endometrial stromal cell cultures treated with 50 and 200?µM of H₂O₂ and evaluated the cytoprotective effects of Vit E (5?µM) and folate (0.01?µM) in H₂O₂-treated cells for 24?h. Following the exposure of endometrial cells to H₂O₂ alone and in the presence of Vit E and/or folate, cell survival, glutathione peroxidase (GPx) and glutathione reductase activities and the level of reduced glutathione (GSH) were measured. Cell adhesions comprise of cell attachment and spreading on collagen were determined. Flow cytometric analysis using annexin V was used to measure apoptosis. H₂O₂ treatment showed a marked decrease in cell viability, GPx and GR activities and the level of GSH. Although Vit E or folate had some protective effect, combination therapy with Vit E and folate attenuated all the changes due to H₂O₂ toxicity. An increasing number of alive cells was showed in the cells exposed to H₂O₂ (50?µM) accompanied by co-treatment with Vit E and folic acid. The present findings indicate that co-administration of Vit E and folate before and during pregnancy may maintain a viable pregnancy and contribute to its clinical efficacy for the treatment of some idiopathic infertility.     

The iron-chelating drug triapine causes pronounced mitochondrial thiol redox stress

Triapine (Tp) is an iron chelator with activity against several types of cancer. Iron-Tp [Fe(III)(Tp)₂] can be redox-cycled to generate reactive oxygen species that may contribute to its cytotoxicity. However, evidence for this mechanism in cells is limited. The cytosolic and mitochondrial thioredoxins (Trx1 and Trx2, respectively) are essential for cell survival. They are normally maintained in the reduced state, and support the function of many intracellular proteins including the peroxiredoxins (Prxs). Their redox status can indicate oxidant stress in their respective subcellular compartments. Tp treatment of human lung A549 cells caused almost complete oxidation of Trx2 and its dependent peroxiredoxin (Prx3), but there was no effect on Trx1 redox status. Significant inhibition of total TrxR activity did not occur until Tp levels were 4-fold above those needed to cause Trx2 oxidation. While Tp caused a 36-45% decline in reduced glutathione (GSH) levels, GSH accounted for >99% of the total glutathione in the absence and presence of Tp. In vitro studies demonstrated that cysteine reduces Fe(III)(Tp)₂ to Fe(II)(Tp)₂, and cysteine was faster and more efficient than reduced glutathione (GSH) in this regard. Fe(III)(Tp)₂ also mediated the oxidation of purified Trx2 in vitro. Thus, Fe(III)(Tp)₂ itself, and/or various reactive species that may result from its redox cycling, could account for Trx2 and Prx3 oxidation in Tp-treated cells. The striking difference between the effects on Trx2 and Trx1 implies a pronounced thiol redox stress that is largely directed at the mitochondria. These previously unrecognized effects of Tp could contribute to its overall cytotoxicity.     

Diphenyl diselenide induces apoptotic cell death and modulates ERK1/2 phosphorylation in human neuroblastoma SH-SY5Y cells

Diphenyl diselenide (PhSe)₂ is a synthetic organoselenium compound displaying glutathione peroxidase-like activity. Protective and antioxidant potential of (PhSe)₂ have been extensively investigated in in vivo and in vitro studies. In spite of this, there is a lack of studies addressed to the investigation of potential cytotoxic effect and signaling pathways modulated by this compound. Herein, we aimed to analyze the effects of 24-h treatment with (PhSe)₂ on cell viability and a possible modulation of signaling pathways in human neuroblastoma cell line SH-SY5Y. For this purpose, cells were incubated with (PhSe)₂ (0.3–30 μM) for 24 h and cell viability, apoptotic cell death and modulation of MAPKs (ERK1/2 and p38^MAPK), and PKC substrates phosphorylation was determined. (PhSe)₂ treatment significantly decreased cell viability and increased the number of apoptotic cells with induction of PARP cleavage. An increase in ERK1/2 phosphorylation was observed at (PhSe)₂ 3 μM. In contrast, higher concentrations of the chalcogenide inhibited ERK1/2, p38^MAPK and PKC substrate phosphorylation. Pre-treatment with ERK1/2 inhibitor, U0126, increased cell susceptibility to (PhSe)₂. Together, these data indicate a cytotoxic potential of (PhSe)₂ in a neuronal cell line, which appears to be mediated by the ERK1/2 pathway.     

Increased responsiveness to JNK1/2 mediates the enhanced H2O2-induced stimulation of Cl/HCO3 exchanger activity in immortalized renal proximal tubular epithelial cells from the SHR

We have previously demonstrated that exogenous H₂O₂ stimulates Cl⁻/HCO₃⁻ exchanger activity in immortalized renal proximal tubular epithelial (PTE) cells from both the Wistar-Kyoto (WKY) rat and the spontaneously hypertensive rat (SHR), this effect being more pronounced in SHR cells. The aim of the present study was to examine the mechanism of H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity in WKY and SHR cells. It is now reported that the SHR PTE cells were endowed with an enhanced capacity to produce H₂O₂, comparatively with WKY cells and this was accompanied by a decreased expression of SOD2, SOD3, and catalase in SHR PTE cells. The stimulatory effect of H₂O₂ on the exchanger activity was blocked by SP600125 (JNK inhibitor), but not by U0126 (MEK1/2 inhibitor) or SB203580 (p38 inhibitor) in both cell lines. Basal JNK1 and JNK2 protein expression was higher in SHR PTE cells than in WKY PTE cells. H₂O₂ had no effect on p-JNK1/2 in WKY PTE cells over time. By contrast, H₂O₂ treatment resulted in a rapid and sustained increase in JNK1/2 phosphorylation in SHR PTE cells, which was completely abolished by apocynin. Treatment of SHR PTE cells with apocynin significantly decreased the H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity. It is concluded that H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity is regulated by JNK1/2, particularly by JNK2, in SHR PTE cells. The imbalance between oxidant and antioxidant mechanisms in SHR PTE cells enhances the response of JNK1/2 to H₂O₂, which contributes to their increased sensitivity to H₂O₂.     

依达拉奉对H2O2致星形胶质细胞损伤的保护作用

目的:观察依达拉奉(EDA)对H2O2损伤后的星形胶质细胞活力的影响及其细胞内谷胱甘肽(GSH)含量、诱导型一氧化氮合酶(iNOS)表达的影响.方法:应用MTT法检测星形胶质细胞活力;Tietze法检测细胞内GSH含量;Western-blot法检测细胞内iNOS的表达.结果:H2O2作用24 h后可呈浓度依赖性地抑制星形胶质活力;EDA可逆转H2O2导致的星形胶质细胞活力的下降,胞内GSH含量的降低以及iNOS表达的增加.结论:EDA可改善H2O2所致的星形胶质细胞的氧化损伤.     

Kinetics of Microcystin-LR Removal in a Real Lake Water by UV/H2O2 Treatment and Analysis of Specific Energy Consumption

The hepatotoxin microcystin-LR (MC-LR) represents one of the most toxic cyanotoxins for human health. Considering its harmful effect, the World Health Organization recommended a limit in drinking water (DW) of 1 µg L⁻¹. Due to the ineffectiveness of conventional treatments present in DW treatment plants against MC-LR, advanced oxidation processes (AOPs) are gaining interest due to the high redox potential of the OH^• radicals. In this work UV/H₂O₂ was applied to a real lake water to remove MC-LR. The kinetics of the UV/H₂O₂ were compared with those of UV and H₂O₂ showing the following result: UV/H₂O₂ > UV > H₂O₂. Within the range of H₂O₂ tested (0–0.9 mM), the results showed that H₂O₂ concentration and the removal kinetics followed an increasing quadratic relation. By increasing the initial concentration of H₂O₂, the consumption of oxidant also increased but, in terms of MC-LR degraded for H₂O₂ dosed, the removal efficiency decreased. As the initial MC-LR initial concentration increased, the removal kinetics increased up to a limit concentration (80 µg L⁻¹) in which the presence of high amounts of the toxin slowed down the process. Operating with UV fluence lower than 950 mJ cm⁻², UV alone minimized the specific energy consumption required. UV/H₂O₂ (0.3 mM) and UV/H₂O₂ (0.9 mM) were the most advantageous combination when operating with UV fluence of 950–1400 mJ cm⁻² and higher than 1400 mJ cm⁻², respectively.     

Primaquine-mediated oxidative metabolism in the human red cell: Lack of dependence on oxyhemoglobin,H2O2 formation,or glutathione turnover

Stimulation of the hexose monophosphate shunt by primaquine results from the oxidation of NADPH by primaquine. This conclusion was based on the observations that primaquine lowered cellular NADPH but not GSH and that, in red cells in which the GSH was unavailable for reaction, primaquine still stimulated the rate of the hexose monophosphate shunt. In a non-cellular system, primaquine interacted with NADPH, but not GSH, to produce H₂O₂. Stimulation of the hexose monophosphate shunt by primaquine does not primarily involve H₂O₂ accumulation since stimulation of the pathway by primaquine was also observed in red cells containing methemoglobin, a red cell preparation in which no H₂O₂ accumulates. Methemoglobin prevented the formation and/or accumulation of H₂O₂ in intact red cells incubated with primaquine as well as in a non-cellular system containing primaquine plus Fe²⁺-EDTA as an H₂O₂ source. Methemoglobin probably acts by scavenging reactive intermediates since oxyhemoglobin was formed from methemoglobin in the non-cellular experiments. In the red cell, primaquine stimulated glucose-dependent conversion of methemoglobin to oxyhemoglobin.     

淫羊藿苷对H2O2诱导的软骨细胞氧化损伤的保护作用及其机制

目的 探究淫羊藿苷（icariin，ICA）对H₂O₂诱导的软骨细胞氧化损伤的保护作用及相关机制。方法 分离SD新生大鼠软骨细胞，随机分为对照组、H₂O₂模型组、ICA低剂量组、ICA中剂量组、ICA高剂量组；采用CCK8法检测各组细胞增殖能力的变化；采用ELISA试剂盒检测各组细胞中活性氧（reactive oxygen，ROS）、超氧化物歧化酶（superoxide dismutase，SOD）、丙二醛（malondialdehyde，MDA）、过氧化氢酶（catalase，CAT）以及谷胱甘肽过氧化物酶（glutathione peroxidase，GSH-Px）的表达情况；流式细胞术检测各组细胞周期情况，并计算增殖指数（proliferation index，PI）；Hoechst染色观察各组细胞核凋亡情况；分别采用荧光定量PCR （qRT-PCR）和Western blotting检测凋亡相关因子及Nrf2/HO-1通路的表达情况。结果 与对照组相比，H₂O₂模型组细胞增殖能力降低，ROS、MDA含量升高，SOD、CAT及GSH-Px含量下降，细胞凋亡情况加重；经ICA干预后，软骨细胞的增殖能力上升，ROS、MDA含量下降，SOD、CAT及GSH-Px含量增加，并且ICA能够有效抑制软骨细胞凋亡，上调Nrf2和HO-1蛋白的表达。结论 ICA对H₂O₂诱导的软骨细胞氧化损伤具有保护作用，能够抑制软骨细胞凋亡，其机制跟Nrf2/HO-1信号通路有关。     

H2O2 production,modification of the glutathione status and methemoglobin formation in red blood cells exposed to diethyldithiocarbamate in vitro

Human red blood cells treated with the CuZn superoxide dismutase inhibitor diethyldithio-carbamate (DDC) undergo metabolic modifications in addition to the superoxide dismutase inhibition: oxidation of the reduced glutathione (GSH) to oxidized glutathione (GSSG), methemoglobin formation, and increased hexose monophosphate shunt activity were observed. The magnitudes of these changes are dependent on the DDC concentration. Under nitrogen, only superoxide dismutase inhibition occurs. After removal of the GSH with N-ethylmaleimide, production of H₂O₂ can be detected by measuring the red cell catalase inhibition in the presence of 3-amino-1,2,4-triazole. H₂O₂ production is not altered by conversion of oxyhemoglobin to methemoglobin by sodium nitrite prior to incubation. GSH oxidation and methemoglobin formation are stopped when DDC is eliminated from the incubation medium after completion of the superoxide dismutase inhibition. These data indicate that methemoglobin formation and modification of the GSH status in red cells treated by DDC are not a direct consequence of the CuZn Superoxide dismutase inhibition but are due rather to a DDC-dependent production of H₂O₂.     

Luteolin inhibits H2O2-induced cellular senescence via modulation of SIRT1 and p53

Luteolin, a sort of flavonoid, has been reported to be involved in neuroprotective function via suppression of neuroinflammation. In this study, we investigated the protective effect of luteolin against oxidative stress-induced cellular senescence and its molecular mechanism using hydrogen peroxide (H₂O₂)-induced cellular senescence model in House Ear Institute-Organ of Corti 1 cells (HEI-OC1). Our results showed that luteolin attenuated senescent phenotypes including alterations of morphology, cell proliferation, senescence-associated β-galactosidase expression, DNA damage, as well as related molecules expression such as p53 and p21 in the oxidant challenged model. Interestingly, we found that luteolin induces expression of sirtuin 1 in dose- and time-dependent manners and it has protective role against H₂O₂-induced cellular senescence by upregulation of sirtuin 1 (SIRT1). In contrast, the inhibitory effect of luteolin on cellular senescence under oxidative stress was abolished by silencing of SIRT1. This study indicates that luteolin effectively protects against oxidative stress-induced cellular senescence through p53 and SIRT1. These results suggest that luteolin possesses therapeutic potentials against age-related hearing loss that are induced by oxidative stress.     

Influence of iron on modulation of the antioxidant system in rat brains exposed to lead

The objective of this study was to evaluate markers of oxidative stress in the brains of rats exposed to lead acetate (Pb(C₂H₃O₂)₂), either associated or not associated with ferrous sulfate (FeSO₄). A total of 36 weaning rats (Rattus norvegicus) were divided into 6 groups of six animals and exposed to lead acetate for six weeks. In the control group (control), the animals received deionized water. The Pb260 and Pb260 + Fe received 260 µM lead acetate, and the Pb1050 and Pb1050 + Fe received 1050 µM lead acetate. The Pb260 + Fe and Pb1050 + Fe were supplemented with 20 mg of ferrous sulfate/Kg body weight every 2 days. Group Fe received deionized water and ferrous sulfate. The rat brains were collected to analyze the enzymatic activity of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and the concentration of reduced glutathione (GSH), lipid peroxidation (TBARS), and total antioxidant substance (TAS) (DPPH^? technique). The activity of SOD and GPx in the experimental groups decreased compared to the control, together with the concentration of GSH (p < 0.05). For CAT analysis, SOD tended to increase in concentration in the experimental groups without a concomitant exposure to FeSO₄, whereas GPx showed a slight tendency to increase in activity compared to the control. For TAS‐DPPH^?, there was a decrease in the experimental groups (p < 0.05). According to the results, SOD, GPx, and GSH were affected by lead acetate and exposure to ferrous sulfate changed this dynamic. However, further studies are needed to verify whether ferrous sulfate acts as a protectant against the toxic effects of lead. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 813–822, 2017.     

Inhibition of curcumin on influenza A virus infection and influenzal pneumonia via oxidative stress,TLR2/4, p38/JNK MAPK and NF-κB pathways

Oxidative stress, Nrf2-HO-1 and TLR-MAPK/NF-κB signaling pathways have been proved to be involved in influenza A virus (IAV) replication and influenzal pneumonia. In the previous studies, we have performed several high-throughput drug screenings based on the TLR pathways. In the present study, through plaque inhibition test, luciferase reporter assay, TCID₅₀, qRT-PCR, western blotting, ELISA and siRNA assays, we investigated the effect and mechanism of action of curcumin against IAV infection in vitro and in vivo. The results showed that curcumin could directly inactivate IAV, blocked IAV adsorption and inhibited IAV proliferation. As for the underlying mechanisms, we found that curcumin could significantly inhibit IAV-induced oxidative stress, increased Nrf2, HO-1, NQO1, GSTA3 and IFN-β production, and suppressed IAV-induced activation of TLR2/4/7, Akt, p38/JNK MAPK and NF-κB pathways. Suppression of Nrf2 via siRNA significantly abolished the stimulatory effect of curcumin on HO-1, NQO1, GSTA3 and IFN-β production and meanwhile blocked the inhibitory effect of curcumin on IAV M2 production. Oxidant H₂O₂ and TLR2/4, p38/JNK and NF-κB agonists could significantly antagonize the anti-IAV activity of curcumin in vitro. Additionally, curcumin significantly increased the survival rate of mice, reduced lung index, inflammatory cytokines and lung IAV titer, and finally improved pulmonary histopathological changes after IAV infection. In conclusion, curcumin can directly inactivate IAV, inhibits IAV adsorption and replication; and its inhibition on IAV replication may be via activating Nrf2 signal and inhibiting IAV-induced activation of TLR2/4, p38/JNK MAPK and NF-κB pathways.     

Adriamycin stimulates NADPH-dependent lipid peroxidation in liver microsomes not only by enhancing the production of O2∸ and H2O2, but also by potentiating the catalytic activity of ferrous ions

The antitumor drug, adriamycin, enhances NADPH-dependent lipid peroxidation in liver microsomes via the formation of Superoxide anion radicals (O₂^?) and hydrogen peroxide (H₂O₂). In the presence of metal ions additional reactive species are generated, causing stimulation of lipid peroxidation.However, in this study it was found that the stimulation of NADPH-dependent lipid peroxidation by adriamycin was not only affected by the production of O₂^? and H₂O₂. Adriamycin also enhances the catalysis by metal ions of the formation of those reactive oxygen species which initiate peroxidation. This was inferred from the fact that adriamycin stimulated malondialdehyde production at low ferrous ion concentrations, whereas at high ferrous ion concentrations no stimulation was found. Additional evidence was found in experiments in which the enzymic redox cycle of adriamycin in microsomes was abolished by heat-inactivation of the microsomes, and O₂^? and H₂O₂ were only produced with xanthine and xanthine oxidase. In this case in the presence of ferrous ions, adriamycin stimulated lipid peroxidation.