Role In Reactive Oxygen Species Production Research Articles

RsRbohD1 Plays a Significant Role in ROS Production during Radish Pithiness Development.

Pithiness is one of the physiological diseases of radishes, which is accompanied by the accumulation of reactive oxygen species (ROS) during the sponging of parenchyma tissue in the fleshy roots. A respiratory burst oxidase homolog (Rboh, also known as NADPH oxidase) is a key enzyme that catalyzes the production of ROS in plants. To understand the role of Rboh genes in radish pithiness, herein, 10 RsRboh gene families were identified in the genome of Raphanus sativus using Blastp and Hmmer searching methods and were subjected to basic functional analyses such as phylogenetic tree construction, chromosomal localization, conserved structural domain analysis, and promoter element prediction. The expression profiles of RsRbohs in five stages (Pithiness grade = 0, 1, 2, 3, 4, respectively) of radish pithiness were analyzed. The results showed that 10 RsRbohs expressed different levels during the development of radish pithiness. Except for RsRbohB and RsRbohE, the expression of other members increased and reached the peak at the P2 (Pithiness grade = 2) stage, among which RsRbohD1 showed the highest transcripts. Then, the expression of 40 genes related to RsRbohD1 and pithiness were analyzed. These results can provide a theoretical basis for improving pithiness tolerance in radishes.

SARS-CoV-2 nucleocapsid protein enhances the level of mitochondrial reactive oxygen species.

Coronavirus disease 2019 (COVID-19) pathogenesis is influenced by reactive oxygen species (ROS). Nevertheless, the precise mechanisms implicated remain poorly understood. The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the main driver for this condition, is a structural protein indispensable for viral replication and assembly, and its role in ROS production has not been reported. This study shows that SARS-CoV-2 N protein expression enhances mitochondrial ROS level. Bulk RNA-sequencing suggests of aberrant redox state of the electron transport chain. Accordingly, this protein hinders ATP production but simultaneously augments the activity of complexes I and III, and most mitochondrially encoded complex I and III proteins are upregulated by it. Mechanistically, N protein of SARS-CoV-2 shows significant mitochondrial localization. It interacts with mitochondrial transcription components and stabilizes them. Moreover, it also impairs the activity of antioxidant enzymes with or without detectable interaction.

Differential effects of NOX2 and NOX4 inhibition after rodent spinal cord injury.

Reactive oxygen species (ROS) are a contributing factor to impaired function and pathology after spinal cord injury (SCI). The NADPH oxidase (NOX) enzyme is a key source of ROS; there are several NOX family members, including NOX2 and NOX4, that may play a role in ROS production after SCI. Previously, we showed that a temporary inhibition of NOX2 by intrathecal administration of gp91ds-tat immediately after injury improved recovery in a mouse SCI model. However, chronic inflammation was not affected by this single acute treatment, and other NOX family members were not assessed. Therefore, we aimed to explore the effect of genetic knockout (KO) of NOX2 or acute inhibition of NOX4 with GKT137831. A moderate SCI contusion injury was performed in 3 month old NOX2 KO and wild-type (WT) mice, who received no treatment or GKT137831/vehicle 30 minutes post-injury. Motor function was assessed using the Basso Mouse Scale (BMS), followed by evaluation of inflammation and oxidative stress markers. NOX2 KO mice, but not GKT137831 treated mice, demonstrated significantly improved BMS scores at 7, 14, and 28 days post injury (DPI) in comparison to WT mice. However, both NOX2 KO and GKT137831 significantly reduced ROS production and oxidative stress markers. Furthermore, a shift in microglial activation toward a more neuroprotective, anti-inflammatory state was observed in KO mice at 7 DPI and a reduction of microglial markers at 28 days. While acute alterations in inflammation were noted with GKT137831 administration, this was not sustained through 28 days. In vitro analysis also showed that while GKT137831 reduced ROS production by microglia, it did not translate to changes in pro-inflammatory marker expression within these cells. These data demonstrate that NOX2 and NOX4 play a role in post-injury ROS, but a single dose of NOX4 inhibitor fails to enhance long-term recovery.

Astrocytes show increased levels of Ero1α in multiple sclerosis and its experimental autoimmune encephalomyelitis animal model.

Multiple sclerosis (MS) and its animal models are characterized by cellular inflammation within the central nervous system (CNS). The sources and consequences of this inflammation are currently not completely understood. Critical signs and mediators of CNS inflammation are reactive oxygen species (ROS) that promote inflammation. ROS originate from a variety of redox-reactive enzymes, one class of which catalyses oxidative protein folding within the endoplasmic reticulum (ER). Here, the unfolded protein response and other signalling mechanisms maintain a balance between ROS producers such as ER oxidoreductin 1α (Ero1α) and antioxidants such as glutathione peroxidase 8 (GPx8). The role of ROS production within the ER has so far not been examined in the context of MS. In this manuscript, we examined how components of the ER redox network change upon MS and experimental autoimmune encephalomyelitis (EAE). We found that unlike GPx8, Ero1α increases within both MS and EAE astrocytes, in parallel with an imbalance of other oxidases such of GPx7, and that no change was observed within neurons. This imbalance of ER redox enzymes can reduce the lifespan of astrocytes, while neurons are not affected. Therefore, Ero1α induction makes astrocytes vulnerable to oxidative stress in the MS and EAE pathologies.

Redox Signaling and Stress in Inherited Myopathies.

Significance: Reactive oxygen species (ROS) are highly reactive compounds that behave like a double-edged sword; they damage cellular structures and act as second messengers in signal transduction. Mitochondria and endoplasmic reticulum (ER) are interconnected organelles with a central role in ROS production, detoxification, and oxidative stress response. Skeletal muscle is the most abundant tissue in mammals and one of the most metabolically active ones and thus relies mainly on oxidative phosphorylation (OxPhos) to synthesize adenosine triphosphate. The impairment of OxPhos leads to myopathy and increased ROS production, thus affecting both redox poise and signaling. In addition, ROS enter the ER and trigger ER stress and its maladaptive response, which also lead to a myopathic phenotype with mitochondrial involvement. Here, we review the role of ROS signaling in myopathies due to either mitochondrial or ER dysfunction. Recent Advances: Relevant advances have been evolving over the last 10 years on the intricate ROS-dependent pathways that act as modifiers of the disease course in several myopathies. To this end, pathways related to mitochondrial biogenesis, satellite cell differentiation, and ER stress have been studied extensively in myopathies. Critical Issues: The analysis of the chemistry and the exact quantitation, as well as the localization of ROS, are still challenging due to the intrinsic labile nature of ROS and the technical limitations of their sensors. Future Directions: The mechanistic studies of the pathogenesis of mitochondrial and ER-related myopathies offer a unique possibility to discover novel ROS-dependent pathways. Antioxid. Redox Signal. 37, 301-323.

TLR4-Dependent DUOX2 Activation Triggered Oxidative Stress and Promoted HMGB1 Release in Dry Eye.

Dry eye disease (DED) is one of the most common ocular surface diseases worldwide. DED has been characterized by excessive accumulation of reactive oxygen species (ROS), following significant corneal epithelial cell death and ocular surface inflammation. However, the key regulatory factor remains unclear. In this study, we tended to explore whether DUOX2 contributed to DED development and the underlying mechanism. Human corneal epithelial (HCE) cells were treated with hyperosmolarity, C57BL/6 mice were injected of subcutaneous scopolamine to imitate DED. Expression of mRNA was investigated by RNA sequencing (RNA-seq) and quantitative real-time PCR (qPCR). Protein changes and distribution of DUOX2, high mobility group box 1 (HMGB1), Toll-like receptor 4 (TLR4), and 4-hydroxynonenal (4-HNE) were evaluated by western blot assays and immunofluorescence. Cell death was assessed by Cell Counting Kit-8 (CCK8), lactate dehydrogenase (LDH) release, and propidium iodide (PI) staining. Cellular ROS levels and mitochondrial membrane potential (MMP) were analyzed by flow cytometry. RNA-seq and western blot assay indicated a significant increase of DUOX2 dependent of TLR4 activation in DED both in vitro and in vivo. Immunofluorescence revealed significant translocation of HMGB1 within corneal epithelial cells under hyperosmolar stress. Interestingly, after ablated DUOX2 expression by siRNA, we found a remarkable decrease of ROS level and recovered MMP in HCE cells. Moreover, knockdown of DUOX2 greatly inhibited HMGB1 release, protected cell viability and abolished inflammatory activation. Taken together, our data here suggest that upregulation of DUOX2 plays a crucial role in ROS production, thereafter, induce HMGB1 release and cell death, which triggers ocular surface inflammation in DED.

Reactive Oxygen Species: A Promising Therapeutic Target for SDHx-Mutated Pheochromocytoma and Paraganglioma.

Simple SummaryPheochromocytoma and paraganglioma are rare neuroendocrine tumors that arise from chromaffin cells of the adrenal medulla or their neural crest progenitors located outside the adrenal gland, respectively. About 10–15% of patients develop metastatic disease for whom treatment options and availability are extremely limited. The risk of developing metastatic disease is increased for patients with mutations in succinate dehydrogenase subunit B, which leads to metabolic reprogramming and redox imbalance. From this perspective, we focus on redox imbalance caused by this mutation and explore potential opportunities to therapeutically target reactive oxygen species production in these rare tumors.Pheochromocytoma (PHEO) and paraganglioma (PGL) are rare neuroendocrine tumors derived from neural crest cells. Germline variants in approximately 20 PHEO/PGL susceptibility genes are found in about 40% of patients, half of which are found in the genes that encode succinate dehydrogenase (SDH). Patients with SDH subunit B (SDHB)-mutated PHEO/PGL exhibit a higher likelihood of developing metastatic disease, which can be partially explained by the metabolic cell reprogramming and redox imbalance caused by the mutation. Reactive oxygen species (ROS) are highly reactive molecules involved in a multitude of important signaling pathways. A moderate level of ROS production can help regulate cellular physiology; however, an excessive level of oxidative stress can lead to tumorigenic processes including stimulation of growth factor-dependent pathways and the induction of genetic instability. Tumor cells effectively exploit antioxidant enzymes in order to protect themselves against harmful intracellular ROS accumulation, which highlights the essential balance between ROS production and scavenging. Exploiting ROS accumulation can be used as a possible therapeutic strategy in ROS-scavenging tumor cells. Here, we focus on the role of ROS production in PHEO and PGL, predominantly in SDHB-mutated cases. We discuss potential strategies and approaches to anticancer therapies by enhancing ROS production in these difficult-to-treat tumors.

Oxidative Stress-Derived Mitochondrial Dysfunction in Chronic Obstructive Pulmonary Disease: A Concise Review.

Chronic obstructive pulmonary disease (COPD) is a progressive and disabling disorder marked by airflow limitation and extensive destruction of lung parenchyma. Cigarette smoke is the major risk factor for COPD development and has been associated with increased oxidant burden on multiple cell types in the lungs. Elevated levels of reactive oxygen species (ROS) may significantly affect expression of biological molecules, signaling pathways, and function of antioxidant defenses. Although inflammatory cells, such as neutrophils and macrophages, contribute to the release of large quantities of ROS, mitochondrial dysfunction plays a critical role in ROS production due to oxidative phosphorylation. Although mitochondria are dynamic organelles, excess oxidative stress is able to alter mitochondrial function, morphology, and RNA and protein content. Indeed, mitochondria may change their shape by undergoing fusion (regulated by mitofusin 1, mitofusin 2, and optic atrophy 1 proteins) and fission (regulated by dynamin-related protein 1), which are essential processes to maintain a healthy and functional mitochondrial network. Cigarette smoke can induce mitochondrial hyperfusion, thus reducing mitochondrial quality control and cellular stress resistance. Furthermore, diminished levels of enzymes involved in the mitophagy process, such as Parkin (a ubiquitin ligase E3) and the PTEN-induced putative kinase 1 (PINK1), are commonly observed in COPD and correlate directly with faulty removal of dysfunctional mitochondria and consequent cell senescence in this disorder. In this review, we highlight the main mechanisms for the regulation of mitochondrial quality and how they are affected by oxidative stress during COPD development and progression.

Targeting Redox Metabolism in Pancreatic Cancer.

Cell metabolism is reprogrammed in cancer cells to meet their high bioenergetics and biosynthetic demands. This metabolic reprogramming is accompanied by alterations in redox metabolism, characterized by accumulation of reactive oxygen species (ROS). Elevated production of ROS, mostly by mitochondrial respiration, is counteracted by higher production of antioxidant defenses (mainly glutathione and antioxidant enzymes). Cancer cells are adapted to a high concentration of ROS, which contributes to tumorigenesis, metastasis formation, resistance to therapy and relapse. Frequent genetic alterations observed in pancreatic ductal adenocarcinoma (PDAC) affect KRAS and p53 proteins, which have a role in ROS production and control, respectively. These observations led to the proposal of the use of antioxidants to prevent PDAC development and relapse. In this review, we focus on the therapeutic strategies to further increase ROS level to induce PDAC cell death. Combining the promotion of ROS production and inhibition of antioxidant capacity is a promising avenue for pancreatic cancer therapy in the clinic.

Vasodilation of Tea Polyphenols Ex Vivo Is Mediated by Hydrogen Peroxide Under Rapid Compound Decay.

Improvement of endothelial function represents a major health effect of tea in humans. Ex vivo, tea and tea polyphenols stimulate nitric oxide (NO)-dependent vasodilation in isolated blood vessels. However, it was reported that polyphenols can generate reactive oxygen species (ROS) in vitro. We therefore aimed to elucidate the role of ROS production in tea polyphenol-induced vasodilation in explanted aortic rings. Vasorelaxation of rat aortic rings was assessed in an organ chamber model with low concentrations of epigallocatechin-3-gallate (EGCG), theaflavin-3,3’-digallate (TF3), and with green and black tea, with or without pretreatment with catalase or superoxide dismutase (SOD). The stability of EGCG and TF3 was measured by HPLC, and the levels of hydrogen peroxide (H2O2) were determined. EGCG and green tea-induced vasorelaxation was completely prevented by catalase and slightly increased by SOD. TF3 and black tea yielded similar results. Both EGCG and TF3 were rapidly degraded. This was associated with increasing H2O2 levels over time. Hydrogen peroxide concentrations produced in a time range compatible with tea polyphenol decay induced NO-dependent vasodilation in aortic rings. In conclusion, tea polyphenol-induced vasodilation in vitro is mediated by low levels of H2O2 generated during compound decay. The results could explain the apparent lack of vasodilatory effects of isolated tea polyphenols in humans.

Involvement of Reactive Oxygen Species (ROS) in BCR Signaling as a Second Messenger.

Reactive oxygen species (ROS) are not only toxic substances inducing oxidative stress but also play a role in receptor signaling as a second messenger, which augments signaling through various receptors by oxidizing ROS-sensitive signaling molecules. Among ROS, H2O2 is suggested to be an important second messenger because of its relative stability. H2O2 is generated by superoxide dismutase (SOD)-mediated conversion of superoxide produced by membrane-localized NADPH oxidases (NOXes). Superoxide and H2O2 are also produced as a by-product of mitochondrial respiratory chain and various other metabolic reactions. BCR ligation induces ROS production in two phases. ROS production starts immediately after BCR ligation and ceases in 1h, then re-starts 2h after BCR ligation and lasts 4-6h. ROS production in the early phase is mediated by NOX2, a NOX isoform, but does not regulate BCR signaling. In contrast, ROS production at the late phase augments BCR signaling. Although the involvement of mitochondrial respiration was previously suggested in prolonged BCR ligation-induced ROS production, we recently demonstrated that NOX3, another NOX isoform, plays a central role in ROS production at the late phase. NOXes are shown to be a component of ROS-generating signaling endosome called redoxosome together with endocytosed receptors and receptor-associated signaling molecules. In redoxosome, ROS generated by NOXes augment signaling through the endocytosed receptor. The role of NOXes and redoxosome in BCR signaling needs to be further elucidated.

Cationic Liposomes Cause ROS Generation and Release of Neutrophil Extracellular Traps

Cationic liposomes are used as nanocarriers of drugs in chemotherapy, antibacterial therapy, and gene therapy. Positively charged stearylamine is commonly used in cationic liposome production. It has been shown that cationic liposomes, when applied intravenously, impact the functions and viability of blood cells, including neutrophils (innate immunity cells). In this work we studied the influence of phosphatidylcholine cationic liposomes containing stearylamine (SA liposomes) on the activity of human neutrophils–their ability of the formation of extracellular traps (NETs) and of the production of reactive oxygen species (ROS). The ratio of phosphatidylcholine to stearylamine in the liposomes was 9 : 1. Phosphatidylcholine liposomes (PC liposomes) were used as control. Liposomes were 140 ± 49 nm in diameter and differed in zeta-potential: PC liposomes had –1.74 ± 0.31 mV, while SA-liposomes had 11.40 ± 0.44 mV. NETs were visualized by light and fluorescent microscopy. It was found that the cells remained intact after a 90-min incubation with PC liposomes (control experiment), while incubation with SA liposomes caused an extrusion of thin DNA fibers into the extracellular space, i.e., the formation of NETs. ROS generation by neutrophils incubated with the liposomes and stimulated either with 0.5 mg/mL of zymozan, or with 40 nM of phorbol-12-miristate-13 acetate, or without stimulation was assessed by luminol-dependent chemiluminescence. It was shown that PC liposomes did not exert any significant effect on chemiluminescence of unstimulated and zymozan-stimulated neutrophils. PMA in the presence of liposomes did not exert any effect on the cells. SA liposomes had a complex impact on the activity of neutrophils: they inhibited the effects of zymozan and caused a prominent respiratory burst independently of the presence of the additional stimulation. The time before the maximal intensity of chemiluminescence peak after incubation with SA-liposomes ranged from 1 to 3 h and significantly differed from the time before the maximal intensity of chemoluminescence peak after incubation with zymozan or PMA (30–40 min). Apocynin, a NADPH-oxidase inhibitor, suppressed the respiratory burst induced by SA liposomes, indicating that NADPH oxidase has a role in ROS production caused by SA liposomes. To assess characteristics of the respiratory burst, lucigenin-dependent chemiluminescence sensitive to superoxide anion radical ( $${\text{O}}_{2}^{{ \bullet -}}$$ ) was registered, and it was found that $${\text{O}}_{2}^{{ \bullet -}}$$ is not produced after stimulation of neutrophils by SA liposomes. On the basis of these findings we conclude that SA liposomes are a polyfunctional factor that can affect the formation of NETs, suppress the action of zymozan, and stimulate ROS production by neutrophils.

Functional characterization of a reactive oxygen species modulator 1 gene in Litopenaeus vannamei

Reactive oxygen species (ROS) imparts a dual effect on multicellular organisms, wherein high levels are usually harmful, and low levels could facilitate in combating pathogenic microorganisms; therefore, the regulation of ROS production is critical. Previous studies have suggested that ROS contributes to resistance to the white spot syndrome virus (WSSV) or Vibrio alginolyticus in Litopenaeus vannamei. However, the regulation of ROS metabolism in L. vannamei remains elusive. In the present study, we proved that the overexpression of L. vannamei reactive oxygen species modulator 1 (LvROMO1) increases ROS production in Drosophila Schneider 2 (S2) cells. Real-time RT-PCR analysis indicated that LvROMO1 is induced by WSSV or V. alginolyticus infection and β-glucan or microcystin (MC-LR) injection. Further investigation showed that LvROMO1 responding to MC-LR, thereby inducing hemocytes to undergo apoptosis, and ultimately resulting in hepatopancreatic damage. And LvROMO1 downregulation induced an increase in the cumulative mortality of WSSV-infected shrimp by reducing ROS production and suppressing the expression of antimicrobial peptides genes. The findings of present study suggest that LvROMO1 plays an important role in ROS production in L. vannamei and is involved in innate immunity.

Unconventional role of voltage-gated proton channels (VSOP/Hv1) in regulation of microglial ROS production.

It has been established that voltage-gated proton channels (VSOP/Hv1), encoded by Hvcn1, support reactive oxygen species (ROS) production in phagocytic activities of neutrophils (El Chemaly etal. ) and antibody production in B lymphocytes (Capasso etal. ). VSOP/Hv1 is a potential therapeutic target for brain ischemia, since Hvcn1 deficiency reduces microglial ROS production and protects brain from neuronal damage (Wu etal. ). In the present study, we report that VSOP/Hv1 has paradoxical suppressive role in ROS production in microglia. Extracellular ROS production was lower in neutrophils of Hvcn1-/- mice than WT mice as reported. In contrast, it was drastically enhanced in isolated Hvcn1-/- microglia as compared with cells from WT mice. Actin dynamics was altered in Hvcn1-/- microglia and intracellular distribution of cytosolic NADPH oxidase subunit, p67, was changed. When expression levels of oxidative stress responsive antioxidant genes were compared between WT and Hvcn1-/- in cerebral cortex at different ages of animals, they were slightly decreased in Hvcn1-/- mice at younger stage (1day, 5days, 3weeks old), but drastically increased at aged stage (6months old), suggesting that the regulation of microglial ROS production by VSOP/Hv1 is age-dependent. We also performed brain ischemic stroke experiments and found that the neuroprotective effect of VSOP/Hv1deficiency on infarct volume depended on the age of animals. Taken together, regulation of ROS production by VSOP/Hv1 is more complex than previously thought and significance of VSOP/Hv1 in microglial ROS production depends on age.

Nox4 Plays a Role in TGF-β-Dependent Lens Epithelial to Mesenchymal Transition.

PurposeTransforming growth factor-β induces an epithelial to mesenchymal transition (EMT) in the lens, presented as an aberrant growth and differentiation of lens epithelial cells. Studies in other models of EMT have shown that TGF-β–driven EMT is dependent on the expression of the reactive oxygen species (ROS)–producing enzyme nicotinamide adenine dinucleotide phosphate (NADPH)–oxidase-4 (Nox4). We investigate the role of this enzyme in TGF-β–induced lens EMT and determine whether it is required for this pathologic process.MethodsRat lens epithelial explants were used to investigate the role of Nox4 in TGF-β–driven lens EMT. Nox1–4 expression and localization was determined by immunolabeling and/or RT-PCR. NADPH–oxidase–produced ROS were visualized microscopically using the fluorescent probe, dihydroethidium (DHE). VAS2870, a pan-NADPH oxidase inhibitor, was used to determine the specificity of Nox4 expression and its role in ROS production, and subsequently TGF-β–driven EMT.ResultsWe demonstrate, for the first time to our knowledge, in rat lens epithelial explants that TGF-β treatment induces Nox4 (but not Nox1–3) expression and activity. Increased Nox4 expression was first detected at 6 to 8 hours following TGF-β treatment and was maintained in explants up to 48 hours. At 8 hours after TGF-β treatment, Nox4 was observed in cell nuclei, while at later stages in the EMT process (at 48 hours), Nox4 was predominately colocalized with α-smooth muscle actin. The inhibition of Nox4 expression and activity using VAS2870 inhibited EMT progression.ConclusionsTransforming growth factor-β drives the expression of the ROS-producing enzyme Nox4 in rat lens epithelial cells and Nox4 inhibition can impede the EMT process.

New insights into reactive oxygen species and nitric oxide signalling under low oxygen in plants.

Plants produce reactive oxygen species (ROS) when exposed to low oxygen (O2 ). Much experimental evidence has demonstrated the existence of an oxidative burst when there is an O2 shortage. This originates at various subcellular sites. The activation of NADPH oxidase(s), in complex with other proteins, is responsible for ROS production at the plasma membrane. Another source of low O2 -dependent ROS is the mitochondrial electron transport chain, which misfunctions when low O2 limits its activity. Arabidopsis mutants impaired in proteins playing a role in ROS production display an intolerant phenotype to anoxia and submergence, suggesting a role in acclimation to stress. In rice, the presence of the submergence 1A (SUB1A) gene for submergence tolerance is associated with a higher capacity to scavenge ROS. Additionally, the destabilization of group VII ethylene responsive factors, which are involved in the direct O2 sensing mechanism, requires nitric oxide (NO). All this evidence suggests the existence of a ROS and NO - low O2 mechanism interplay which likely includes sensing, anaerobic metabolism and acclimation to stress. In this review, we summarize the most recent findings on this topic, formulating hypotheses on the basis of the latest advances.

The Pim Kinase Inhibitor AZD1208 Enhances Topoisomerase-2 Inhibitor Induction of Apoptosis of Acute Myeloid Leukemia Cells with FLT3-ITD through Increased Oxidative Stress

The receptor tyrosine kinase fms-like tyrosine kinase-3 (FLT3) is expressed on acute myeloid leukemia (AML) cells in most patients, and is mutated most commonly by internal tandem duplication (ITD), in approximately 30% of patients, resulting in constitutive activation and growth signaling. Initial treatment for AML consists of combination chemotherapy including cytarabine (AraC) and a topoisomerase-2 (TOP-2) inhibitor, most commonly daunorubicin (DNR). Other TOP-2 inhibitors, including mitoxantrone (Mitox) and etoposide (VP-16) are also active in AML. AML patients with FLT3-ITD achieve remission, but have high relapse rates and short disease-free survival. FLT3 inhibitors are in clinical trials, but so far with limited and transient activity. Hence new therapeutic approaches targeting additional signaling molecules are needed. Pim-1 kinase, a pro-survival oncogene, is transcriptionally upregulated downstream of FLT3-ITD and promotes its signaling in a positive feedback loop. We have shown that the Pim kinase inhibitor AZD1208 enhances apoptosis induction of FLT3-ITD cells by FLT3 inhibitors, both in vitro and in vivo. We hypothesized that Pim-1 kinase inhibition might also enhance apoptosis induction by chemotherapy drugs. Ba/F3 cells transfected with FLT3-ITD (Ba/F3-ITD) were treated with DNR, Mitox, VP-16 or AraC at their approximate IC50 concentrations with and without 1µM AZD1208, and viable cells were counted. While growth of Ba/F3-ITD was reduced by DNR, Mitox, VP-16 or AraC, it was abrogated by co-treatment with AZD1208 and DNR, Mitox or VP-16, but not AraC. Ba/F3 cells transfected with wild type (WT) FLT3 (Ba/F3-WT) were less sensitive to this effect. To determine whether the effect on growth was cytostatic or cytotoxic, we studied cell cycle by flow cytometric analysis of propidium iodide (PI) staining. A significant increase in Ba/F3-ITD cells in sub-G1 phase was seen following treatment with AZD1208 and TOP-2 inhibitors, compared to TOP-2 inhibitors alone, consistent with enhanced apoptosis. Significant (P<0.0001) increase in apoptosis in multiple FLT3-ITD cell lines, including transfected Ba/F3-ITD and 32D-ITD cells and human AML cells MV4-11 and MOLM-14, co-treated with AZD1208 and TOP-2 inhibitors was confirmed using Annexin V/PI staining. Minimal or no effect was seen with combination treatment in Ba/F3-WT or 32D-WT cells. Further, treatment of Ba/F3-ITD cells with AZD1208 and TOP-2 inhibitors, in relation to TOP-2 inhibitors alone, accelerated loss of mitochondrial membrane potential (MMP) and increased cytochrome c release, caspase-3 activation and PARP cleavage. Enhanced induction of apoptosis (P<0.001) was also seen in FLT3-ITD AML patient samples co-treated with AZD1208 and TOP-2 inhibitors, in relation to TOP-2 inhibitors alone, but was not seen in FLT3-WT AML patient samples, nor in AML remission bone marrow samples, with the latter observation supporting a favorable therapeutic index. Consistent with the effects on cell growth, co-treatment with AZD1208 did not sensitize Ba/F3-ITD cells to apoptosis induction by AraC, and AZD1208 actually modestly decreased AraC-induced apoptosis in Ba/F3-ITD (P<0.0001) and 32D-ITD (P<0.01) cells. Additionally co-treatment with AZD1208 and AraC decreased AraC-induced loss of MMP, release of cytochrome c and caspase-3 activation in Ba/F3-ITD cells (P<0.001). Mechanistically, when compared to TOP-2 inhibitors alone, co-treatment with AZD1208 and TOP-2 inhibitors increased oxidative stress in Ba/F3-ITD cells, as evidenced by more than two-fold increased generation of reactive oxygen species (ROS). Further, treatment with the ROS scavenger N-acetyl cysteine markedly attenuated the increase in apoptosis produced by AZD1208 and TOP-2 inhibitors, consistent with a causative role of ROS production in apoptosis induction, through increased DNA damage. Finally, consistent with the lack of increase in apoptosis, co-treatment with AZD1208 and AraC did not increase ROS generation. We conclude that Pim kinase inhibition enhances induction of apoptosis of AML cells with FLT3-ITD by TOP-2 inhibitors, but not AraC, through increased oxidative stress. The selective effect in FLT3-ITD cells may be due to high baseline ROS levels and/or Pim-1 kinase overexpression. Our work supports potential clinical applicability of combining a Pim kinase inhibitor with TOP-2 inhibitors, but not AraC, to treat AML with FLT3-ITD. Disclosures Huszar: Astra Zeneca: Employment.

MicroRNA-21 regulates cell proliferation and apoptosis in H₂O₂-stimulated rat spinal cord neurons.

Oxidative stress can alter the expression level of microRNAs (miRNAs) and has a role in oxidative damage generated by reactive oxygen species (ROS). While previous studies have demonstrated that miR‑146a, miR‑21 and miR‑150 are essential for ROS production in heart disease, the role of these miRNAs in spinal cord injuries has not yet been examined. The present study focused on examining the role of miR‑146a, miR‑21 and miR‑150 during H2O2 stimulation in rat neuronal spinal cord (RN‑sc) cells. RN‑sc cells were treated with H2O2, and cells were harvested for reverse transcription quantitative polymerase chain reaction (RT‑qPCR) to detect the expression levels of miR‑146a, miR‑21 and miR‑150. The results demonstrated that miR‑146a, miR‑21 and miR‑150 expression was upregulated during H2O2 treatment. T-cell death and apoptosis were investigated using an MTT assay and flow cytometric analysis, respectively. Following miR‑21 silencing, H2O2‑induced cell death and apoptosis were reduced in RN‑sc cells, while miR‑150 silencing had no effect. Furthermore, Smad7 was identified as a direct target of miR‑21 using a Luciferase reporter assay, RT-qPCR and western blot analysis. In addition, while H2O2 downregulated Smad7 protein expression, this was reversed by inhibiting miR‑21 expression. Based on previous studies, it was predicted that miR‑21 has a role in ROS production through regulating Smad7 in rat spinal cord neurons.

Succinate dehydrogenase (mitochondrial complex II) is a source of reactive oxygen species in plants and regulates development and stress responses.

Reactive oxygen species (ROS) are signaling molecules that regulate plant development and responses to stresses. Mitochondria are the source of most ROS in heterotrophic cells, and mitochondrial complex I and complex III are regarded as the main sites of ROS production in plant mitochondria. Recent studies have demonstrated that succinate dehydrogenase (SDH) also contributes to mitochondrial ROS production. However, the ability of SDH to generate ROS in plants is unclear. The aim of this study was to evaluate the role of SDH in mitochondrial ROS production. Our results demonstrated that SDH is a direct source of ROS in Arabidopsis thaliana and Oryza sativa, and the induction of ROS production by specific SDH inhibitors impaired plant growth. In addition, this effect was accompanied by the down-regulation of cell cycle genes and the up-regulation of stress-related genes. However, the partial inhibition of SDH by a competitive inhibitor decreased ROS production, which was associated with increased shoot and root growth, and prevented the down-regulation of cell cycle genes and the induction of stress-related genes by noncompetitive inhibitors. In conclusion, SDH plays an important role in ROS production, being a direct source of ROS in plant mitochondria and regulating plant development and stress responses.

Abstract 272: Chronic Hyperlipidemia Alters the Population of Endothelial Progenitor Cells in Bone Marrow and Peripheral Circulation via Both ROS-dependent and Independent Mechanisms

Background/Aims: Bone marrow (BM)-derived endothelial progenitor cells (EPCs) make significant contribution to the function and integrity of vasculature. The number of EPCs is significantly decreased in hyperlipidemic patients. Reactive oxygen species (ROS) and oxidative stress were considered an important mechanism for the development of atherosclerosis in hyperlipidemia. The present study was to determine the role of ROS production in the changes of EPC population in chronic hyperlipidemia. Methods and Results: EPC numbers and ROS formation in BM and blood were determined in wild-type (WT) male C57BL/6 mice and hyperlipidemic LDL receptor knockout (LDLR-/-) mice with high fat diet for 4 months. Intracellular blood, extracellular BM and blood ROS production was significantly increased in hyperlipidemic LDLR-/- mice that was effectively blocked with N-acetylcysteine treatment. Hyperlipidemia produced complex changes in EPC populations in BM and blood. The c-Kit+/CD31+ cell number was significantly decreased in BM and blood, and the numbers of CD34+/CD133+ cells and Sca-1+/Flk-1+ cells were significantly decreased in blood without change in BM, which were not affected by inhibition of ROS production. Interestingly, blood CD34+/Flk-1+ cell number was significantly increased in hyperlipidemic mice that was prevented when ROS formation was inhibited. Conclusions: Chronic hyperlipidemia produced significant and complex changes in EPC populations in both BM and circulation through both ROS-dependent and ROS-independent mechanisms in mice.