An ROS generator, antimycin A, inhibits the growth of HeLa cells via apoptosis

In-cell Catalysis by Tethered Organo-Osmium Complexes Generates Selectivity for Breast Cancer Cells

Anticancer agents that exhibit catalytic mechanisms of action offer a unique multi-targeting strategy to overcome drug resistance. Nonetheless, many in-cell catalysts in development are hindered by deactivation by endogenous nucleophiles. We have synthesised a highly potent, stable Os-based 16-electron half-sandwich ('piano stool') catalyst by introducing a permanent covalent tether between the arene and chelated diamine ligand. This catalyst exhibits antiproliferative activity comparable to the clinical drug cisplatin towards triple-negative breast cancer cells and can overcome tamoxifen resistance. Speciation experiments revealed Os to be almost exclusively albumin-bound in the extracellular medium, while cellular accumulation studies identified an energy-dependent, protein-mediated Os accumulation pathway, consistent with albumin-mediated uptake. Importantly, the tethered Os complex was active for in-cell transfer hydrogenation catalysis, initiated by co-administration of a non-toxic dose of sodium formate as a source of hydride, indicating that the Os catalyst is delivered to the cytosol of cancer cells intact. The mechanism of action involves the generation of reactive oxygen species (ROS), thus exploiting the inherent redox vulnerability of cancer cells, accompanied by selectivity for cancerous cells over non-tumorigenic cells.

Potential for Drug Repositioning of Midazolam as an Inhibitor of Inflammatory Bone Resorption

Drug repositioning is a method for exploring new effects of existing drugs, the safety and pharmacokinetics of which have been confirmed in humans. Here, we demonstrate the potential drug repositioning of midazolam (MDZ), which is used for intravenous sedation, as an inhibitor of inflammatory bone resorption. We cultured a mouse macrophage-like cell line with or without MDZ and evaluated its effects on the induction of differentiation of these cells into osteoclasts. For in vivo investigations, we administered lipopolysaccharide (LPS) together with MDZ (LPS+MDZ) to the parietal region of mice and evaluated the results based on the percentage of bone resorption and calvaria volume. Furthermore, we examined the effects of MDZ on the production of reactive oxygen species (ROS) in cells and on its signaling pathway. MDZ inhibited osteoclast differentiation and bone resorption activity. In animal studies, the LPS+MDZ group showed a decreasing trend associated with the rate of bone resorption. In addition, the bone matrix volume in the LPS+MDZ group was slightly higher than in the LPS only group. MDZ inhibited osteoclast differentiation by decreasing ROS production and thereby negatively regulating the p38 mitogen-activated protein kinase pathway. Thus, we propose that MDZ could potentially be used for treating inflammatory bone resorption, for example, in periodontal disease.

Loss of Myo19 increases metastasis by enhancing microenvironmental ROS gradient and chemotaxis

Tumor metastasis involves cells migrating directionally in response to external chemical signals. Reactive oxygen species (ROS) in the form of H2O2 has been demonstrated as a chemoattractant for neutrophils but its spatial characteristics in tumor microenvironment and potential role in tumor cell dissemination remain unknown. Here we investigate the spatial ROS distribution in 3D tumor spheroids and identify a ROS concentration gradient in spheroid periphery, which projects into a H2O2 gradient in tumor microenvironment. We further reveal the role of H2O2 gradient to induce chemotaxis of tumor cells by activating Src and subsequently inhibiting RhoA. Finally, we observe that the absence of mitochondria cristae remodeling proteins including the mitochondria-localized actin motor Myosin 19 (Myo19) enhances ROS gradient and promotes tumor dissemination. Myo19 downregulation is seen in many tumors, and Myo19 expression is negatively associated with tumor metastasis in vivo. Together, our study reveals the chemoattractant role of tumor microenvironmental ROS and implies the potential impact of mitochondria cristae disorganization on tumor invasion and metastasis.

Redox processes are major regulators of leukotriene synthesis in neutrophils exposed to bacteria Salmonella typhimurium; the way to manipulate neutrophil swarming

Neutrophils play a primary role in protecting our body from pathogens. When confronted with invading bacteria, neutrophils begin to produce leukotriene B4, a potent chemoattractant that, in cooperation with the primary bacterial chemoattractant fMLP, stimulates the formation of swarms of neutrophils surrounding pathogens. Here we describe a complex redox regulation that either stimulates or inhibits fMLP-induced leukotriene synthesis in an experimental model of neutrophils interacting with Salmonella typhimurium. The scavenging of mitochondrial reactive oxygen species by mitochondria-targeted antioxidants MitoQ and SkQ1, as well as inhibition of their production by mitochondrial inhibitors, inhibit the synthesis of leukotrienes regardless of the cessation of oxidative phosphorylation. On the contrary, antioxidants N-acetylcysteine and sodium hydrosulfide promoting reductive shift in the reversible thiol-disulfide system stimulate the synthesis of leukotrienes. Diamide that oxidizes glutathione at high concentrations inhibits leukotriene synthesis, and the glutathione precursor S-adenosyl-L-methionine prevents this inhibition. Diamide-dependent inhibition is also prevented by diphenyleneiodonium, presumably through inhibition of NADPH oxidase and NADPH accumulation. Thus, during bacterial infection, maintaining the reduced state of glutathione in neutrophils plays a decisive role in the synthesis of leukotriene B4. Suppression of excess leukotriene synthesis is an effective strategy for treating various inflammatory pathologies. Our data suggest that the use of mitochondria-targeted antioxidants may be promising for this purpose, whereas known thiol-based antioxidants, such as N-acetylcysteine, may dangerously stimulate leukotriene synthesis by neutrophils during severe pathogenic infection.

A novel antimycin analogue antimycin A2c, derived from marine Streptomyces sp., suppresses HeLa cells via disrupting mitochondrial function and depleting HPV oncoproteins E6/E7

AIMS

Novel antimycin alkaloid antimycin A2c (AE) was isolated from the culture of a marine derived Streptomyces sp. THS-55. We elucidated its chemical structure by extensive spectra and clarified the specific mechanism in HPV infected-cervical cancer.

MATERIALS AND METHODS

Colony formation assay, cell cycle analysis, hoechst 33342 staining assay, et.al were used to detect the inhibitory effect of AE on cervical cancer cells. Meanwhile, flow cytometry, western blotting, immunoprecipitation, RNA interference and molecular docking were used to analyze the mechanism of AE.

KEY FINDINGS

AE exhibited potent cytotoxicity in vitro against HPV-transformed cervical cancer HeLa cell line. AE inhibited the proliferation, arrested cell cycle distribution, and triggered caspase dependent apoptosis in HeLa cells. Further studies revealed AE-induced apoptosis is mediated by the degradation of E6/E7 oncoproteins. Molecular mechanic investigation showed that AE degraded the levels of E6/E7 oncoproteins through reactive oxygen (ROS)-mediated ubiquitin-dependent proteasome system activation, and the increased ROS generation was due to the disruption of the mitochondrial function.

SIGNIFICANCE

This present work revealed that this novel marine derived antimycin alkaloid could target the mitochondria and subsequently degrade HPV E6/E7 oncoproteins, and have potential application in the design and development of lead compound for cervical cancer cells, as well as the development for tool compounds to dissect E6/E7 functions.

A Second Life for Seafood Waste: Therapeutical Promises of Polyhydroxynapthoquinones Extracted from Sea Urchin by-Products

Coping with a zero-waste, more sustainable economy represents the biggest challenge for food market nowadays. We have previously demonstrated that by applying smart multidisciplinary waste management strategies to purple sea urchin (Paracentrotus lividus) food waste, it is possible to obtain both a high biocompatible collagen to produce novel skin substitutes and potent antioxidant pigments, namely polyhydroxynapthoquinones (PHNQs). Herein, we have analyzed the biological activities of the PHNQs extract, composed of Spinochrome A and B, on human skin fibroblast cells to explore their future applicability in the treatment of non-healing skin wounds with the objective of overcoming the excessive oxidative stress that hinders wound tissue regeneration. Our results clearly demonstrate that the antioxidant activity of PHNQs is not restricted to their ability to scavenge reactive oxygen species; rather, it can be traced back to an upregulating effect on the expression of superoxide dismutase 1, one of the major components of the endogenous antioxidant enzymes defense system. In addition, the PHNQs extract, in combination with Antimycin A, displayed a synergistic pro-apoptotic effect, envisaging its possible employment against chemoresistance in cancer treatments. Overall, this study highlights the validity of a zero-waste approach in the seafood chain to obtain high-value products, which, in turn, may be exploited for different biomedical applications.

Antioxidant and chemoprotective potential of Streptomyces levis strain isolated from human gut

In the current study, Streptomyces levis strain HFM-2 has been isolated from healthy human gut. Streptomyces sp. HFM-2 was identified based on the polyphasic approach that included cultural, morphological, chemotaxonomical, phylogenetic, physiological, and biochemical characteristics. 16S rRNA gene sequence of strain HFM-2 exhibited 100% similarity with Streptomyces levis strain 15423 (T). The EtOAc extract of Streptomyces levis strain HFM-2 showed potential antioxidant activity, along with 69.53 ± 0.19%, 64.76 ± 0.13%, and 84.82 ± 0.21% of scavenging activity for ABTS, DPPH, and superoxide radicals, respectively at 600 µg/mL. The IC50 values i.e. 50% scavenging activity for DPPH, ABTS, and superoxide radicals were achieved at 497.19, 388.13, and 268.79 (µg/mL), respectively. The extract's reducing power and total antioxidant capacity were determined to be 856.83 ± 0.76 and 860.06 ± 0.01 µg AAE/mg of dry extract, respectively. In addition, the EtOAc extract showed protection against DNA damage from oxidative stress caused by Fenton's reagent, and cytotoxic activity against HeLa cervical cancer, Skin (431) cancer, Ehrlich-Lettre Ascites-E (EAC) carcinoma, and L929 normal cell lines. The IC50 values against HeLa, 431 skin, and EAC carcinoma cell lines were found to be 50.69, 84.07, and 164.91 µg/mL, respectively. The EtOAc extract showed no toxicity  towards L929 normal cells. In addition, flow cytometric analysis exhibited reduced mitochondrial membrane potential (MMP), and enhanced levels of reactive oxygen species (ROS). The EtOAc extract was chemically analyzed using GCMS to determine the components executing its bioactivities.

Endogenous PP2A inhibitor CIP2A degradation by chaperone-mediated autophagy contributes to the antitumor effect of mitochondrial complex I inhibition

Combined inhibition of oxidative phosphorylation (OXPHOS) and glycolysis has been shown to activate a PP2A-dependent signaling pathway, leading to tumor cell death. Here, we analyze highly selective mitochondrial complex I or III inhibitors in vitro and in vivo to elucidate the molecular mechanisms leading to cell death following OXPHOS inhibition. We show that IACS-010759 treatment (complex I inhibitor) induces a reactive oxygen species (ROS)-dependent dissociation of CIP2A from PP2A, leading to its destabilization and degradation through chaperone-mediated autophagy. Mitochondrial complex III inhibition has analogous effects. We establish that activation of the PP2A holoenzyme containing B56δ regulatory subunit selectively mediates tumor cell death, while the arrest in proliferation that is observed upon IACS-010759 treatment does not depend on the PP2A-B56δ complex. These studies provide a molecular characterization of the events subsequent to the alteration of critical bioenergetic pathways and help to refine clinical studies aimed to exploit metabolic vulnerabilities of tumor cells.

OXPHOS inhibitors, metabolism and targeted therapies in cancer

More and more studies highlight the complex metabolic characteristics and plasticity of cancer cells. To address these specificities and explore the associated vulnerabilities, new metabolism-targeting therapeutic strategies are being developed. It is more and more accepted that cancer cells do not produce their energy only from aerobic glycolysis, as some subtypes strongly rely on mitochondrial respiration (OXPHOS). This review focuses on classical and promising OXPHOS inhibitors (OXPHOSi), unravelling their interest and modes of actions in cancer, particularly in combination with other strategies. Indeed, in monotherapy, OXPHOSi display limited efficiency as they mostly trigger cell death in cancer cell subtypes that strongly depend on mitochondrial respiration and are not able to shift to other metabolic pathways to produce energy. Nevertheless, they remain very interesting in combination with conventional therapeutic strategies such as chemotherapy and radiotherapy, increasing their anti-tumoral actions. In addition, OXPHOSi can be included in even more innovative strategies such as combinations with other metabolic drugs or immunotherapies.

Renin-angiotensin-system increases phosphorylated tau and Reactive Oxygen Species in human cortical neuron cell line

Alzheimer's Disease (AD) is the most common cause of dementia. AD patients had increased extracellular amyloid β plaques and intracellular hyperphosphorylated tau (p-tau) in neurons. Recent studies have shown an association between the Renin-Angiotensin System (RAS) and AD. The involvement of RAS has been mediated through Angiotensin II (AngII), which is overexpressed in aging brains. However, the exact mechanism of how AngII contributes to AD is unknown. Thus, we hypothesize that AngII increases p-tau by activating its kinases, CDK5 and MAPK. In the human cortical neuron cell line, HCN2, treatment with AngII upregulated the gene expression of CDK5 (2.9 folds, p < 0.0001) and MAPTK (1.9 folds, p < 0.001). The AT1R antagonist, Losartan, blocked the changes in tau kinases. Also, AngII-induced the MAPK activation, increasing its phosphorylation by 400% (p < 0.0001), an increase that was also blocked by Losartan. An increase in p-tau by AngII was observed using fluorescent microscopy. We then quantified Reactive Oxygen Species (ROS) production, and it was significantly increased by AngII (p < 0.01), and treatment with Losartan blunted their production (p < 0.05). The data obtained demonstrated that AngII might contribute to the pathogenesis of AD.

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Angiotensin II increases CDK5 and MAPK gene expression in human cortical neuron cell line.

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Angiotensin II increases tau phosphorylation in human cortical neuron cell line.

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Angiotensin II increases Reactive Oxygen Species production in human cortical neuron cell line.

Marine Natural Product Antimycin A Suppresses Wheat Blast Disease Caused by Magnaporthe oryzae Triticum

The application of chemical pesticides to protect agricultural crops from pests and diseases is discouraged due to their harmful effects on humans and the environment. Therefore, alternative approaches for crop protection through microbial or microbe-originated pesticides have been gaining momentum. Wheat blast is a destructive fungal disease caused by the Magnaporthe oryzae Triticum (MoT) pathotype, which poses a serious threat to global food security. Screening of secondary metabolites against MoT revealed that antimycin A isolated from a marine Streptomyces sp. had a significant inhibitory effect on mycelial growth in vitro. This study aimed to investigate the inhibitory effects of antimycin A on some critical life stages of MoT and evaluate the efficacy of wheat blast disease control using this natural product. A bioassay indicated that antimycin A suppressed mycelial growth (62.90%), conidiogenesis (100%), germination of conidia (42%), and the formation of appressoria in the germinated conidia (100%) of MoT at a 10 µg/mL concentration. Antimycin A suppressed MoT in a dose-dependent manner with a minimum inhibitory concentration of 0.005 μg/disk. If germinated, antimycin A induced abnormal germ tubes (4.8%) and suppressed the formation of appressoria. Interestingly, the application of antimycin A significantly suppressed wheat blast disease in both the seedling (100%) and heading stages (76.33%) of wheat at a 10 µg/mL concentration, supporting the results from in vitro study. This is the first report on the inhibition of mycelial growth, conidiogenesis, conidia germination, and detrimental morphological alterations in germinated conidia, and the suppression of wheat blast disease caused by a Triticum pathotype of M. Oryzae by antimycin A. Further study is required to unravel the precise mode of action of this promising natural compound for considering it as a biopesticide to combat wheat blast.

A Fluorescent Probe Strategy for the Detection and Discrimination of Hydrogen Peroxide and Peroxynitrite in Cells

Aryl boronate fluorescent probes allow the non-invasive study of dynamic cellular processes involving the reactive species, hydrogen peroxide (H2O2) and peroxynitrite (ONOO-). However, the ability of these probes to differentiate...

Oxidative Stress Enhances Autophagy-Mediated Death Of Stem Cells Through Erk1/2 Signaling Pathway - Implications For Neurotransplantations

Stem cell therapies are becoming increasingly popular solutions for neurological disorders. However, there is a lower survival rate of these cells after transplantation. Oxidative stress is linked to brain damage, and it may also impact transplanted stem cells. To better understand how transplanted cells respond to oxidative stress, the current study used H₂O₂. We briefly illustrated that exogenous H₂O₂ treatment exaggerated oxidative stress in the human dental pulp and mesenchymal stem cells. 2',7'-Dichlorofluorescin diacetate (DCFDA), MitoSOX confirms the reactive oxygen species (ROS) involvement, which was remarkably subsided by the ROS inhibitors. The findings showed that H₂O₂ activates autophagy by enhancing pro-autophagic proteins, Beclin1 and Atg7. Increased LC3II/I expression (which co-localized with lysosomal proteins, LAMP1 and Cathepsin B) showed that H₂O₂ treatment promoted autophagolysosome formation. In the results, both Beclin1 and Atg7 were observed co-localized in mitochondria, indicating their involvement in mitophagy. The evaluation of Erk1/2 in the presence and absence of Na-Pyruvate, PEG-Catalase, and PD98059 established ROS-Erk1/2 participation in autophagy regulation. Further, these findings showed a link between apoptosis and autophagy. The results conclude that H₂O₂ acts as a stressor, promoting autophagy and mitophagy in stem cells under oxidative stress. The current study may help understand better cell survival and death approaches for transplanted cells in various neurological diseases. The current study uses human Dental Pulp and Mesenchymal Stem cells to demonstrate the importance of H₂O₂-driven autophagy in deciding the fate of these cells in an oxidative microenvironment. To summarise, we discovered that exogenous H₂O₂ treatment causes oxidative stress. Exogenous H₂O₂  treatment also increased ROS production, especially intracellular H₂O₂. H₂O₂ stimulated the ErK1/2 signaling pathway and autophagy. Erk1/2 was found to cause autophagy. Further, the function of mitophagy appeared to be an important factor in the H₂O₂-induced regulation of these two human stem cell types. In a nutshell, by engaging in autophagy nucleation, maturation, and terminal phase proteins, we elucidated the participation of autophagy in cell dysfunction and death.

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

Simple Summary

Pheochromocytoma 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.

Abstract

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.

Parkinson's disease-associated VPS35 mutant reduces mitochondrial membrane potential and impairs PINK1/Parkin-mediated mitophagy

Background

Mitochondrial dysfunction plays a prominent role in the pathogenesis of Parkinson’s disease (PD), and several genes linked to familial PD, including PINK1 (encoding PTEN-induced putative kinase 1 [PINK1]) and PARK2 (encoding the E3 ubiquitin ligase Parkin), are directly involved in processes such as mitophagy that maintain mitochondrial health. The dominant p.D620N variant of vacuolar protein sorting 35 ortholog (VPS35) gene is also associated with familial PD but has not been functionally connected to PINK1 and PARK2.

Methods

To better mimic and study the patient situation, we used CRISPR-Cas9 to generate heterozygous human SH-SY5Y cells carrying the PD-associated D620N variant of VPS35. These cells were treated with a protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to induce the PINK1/Parkin-mediated mitophagy, which was assessed using biochemical and microscopy approaches.

Results

Mitochondria in the VPS35-D620N cells exhibited reduced mitochondrial membrane potential and appeared to already be damaged at steady state. As a result, the mitochondria of these cells were desensitized to the CCCP-induced collapse in mitochondrial potential, as they displayed altered fragmentation and were unable to accumulate PINK1 at their surface upon this insult. Consequently, Parkin recruitment to the cell surface was inhibited and initiation of the PINK1/Parkin-dependent mitophagy was impaired.

Conclusion

Our findings extend the pool of evidence that the p.D620N mutation of VPS35 causes mitochondrial dysfunction and suggest a converging pathogenic mechanism among VPS35, PINK1 and Parkin in PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00243-4.

Dimeric lipo-α/sulfono-γ-AA hybrid peptides as broad-spectrum antibiotic agents

There is an urgent need to develop novel antibiotic agents that can combat emerging drug resistance. Herein, we report the design and investigation of a class of short dimeric antimicrobial lipo-α/sulfono-γ-AA hybrid peptides. Some of these peptides exhibit potent and broad-spectrum antimicrobial activity toward both clinically related Gram-positive and Gram-negative bacteria. The TEM study suggests that these hybrid peptides can compromise bacterial membranes and lead to bacterial death. Membrane depolarization and fluorescence microscopy studies also indicate that the mechanism of action is analogous to host-defense peptides (HDPs). Furthermore, the lead compound shows the ability to effectively inhibit biofilms formed from MRSA and E. coli. Further development of the short dimeric lipo-α/sulfono-γ-AA hybrid peptides may lead to a new generation of antimicrobial biomaterials to combat drug resistance.

Characterizing effects of excess copper levels in a human astrocytic cell line with focus on oxidative stress markers

BACKGROUND

Being an essential trace element, copper is involved in diverse physiological processes. However, excess levels might lead to adverse effects. Disrupted copper homeostasis, particularly in the brain, has been associated with human diseases including the neurodegenerative disorders Wilson and Alzheimer's disease. In this context, astrocytes play an important role in the regulation of the copper homeostasis in the brain and likely in the prevention against neuronal toxicity, consequently pointing them out as a potential target for the neurotoxicity of copper. Major toxic mechanisms are discussed to be directed against mitochondria probably via oxidative stress. However, the toxic potential and mode of action of copper in astrocytes is poorly understood, so far.

METHODS

In this study, excess copper levels affecting human astrocytic cell model and their involvement in the neurotoxic mode of action of copper, as well as, effects on the homeostasis of other trace elements (Mn, Fe, Ca and Mg) were investigated.

RESULTS

Copper induced substantial cytotoxic effects in the human astrocytic cell line following 48 h incubation (EC₃₀: 250 μM) and affected mitochondrial function, as observed via reduction of mitochondrial membrane potential and increased ROS production, likely originating from mitochondria. Moreover, cellular GSH metabolism was altered as well. Interestingly, not only cellular copper levels were affected, but also the homeostasis of other elements (Ca, Fe and Mn) were disrupted.

CONCLUSION

One potential toxic mode of action of copper seems to be effects on the mitochondria along with induction of oxidative stress in the human astrocytic cell model. Moreover, excess copper levels seem to interact with the homeostasis of other essential elements such as Ca, Fe and Mn. Disrupted element homeostasis might also contribute to the induction of oxidative stress, likely involved in the onset and progression of neurodegenerative disorders. These insights in the toxic mechanisms will help to develop ideas and approaches for therapeutic strategies against copper-mediated diseases.

Antimycin A shows selective antiproliferation to oral cancer cells by oxidative stress-mediated apoptosis and DNA damage

The antibiotic antimycin A (AMA) is commonly used as an inhibitor for the electron transport chain but its application in anticancer studies is rare. Recently, the repurposing use of AMA in antiproliferation of several cancer cell types has been reported. However, it is rarely investigated in oral cancer cells. The purpose of this study is to investigate the selective antiproliferation ability of AMA treatment on oral cancer cells. Cell viability, flow cytometry, and western blotting were applied to explore its possible anticancer mechanism in terms of both concentration- and exposure time-effects. AMA shows the higher antiproliferation to two oral cancer CAL 27 and Ca9-22 cell lines than normal oral HGF-1 cell lines. Moreover, AMA induces the production of higher reactive oxygen species (ROS) levels and pan-caspase activation in oral cancer CAL 27 and Ca9-22 cells than in normal oral HGF-1 cells, providing the possible mechanism for its selective antiproliferation effect of AMA. In addition to ROS, AMA induces mitochondrial superoxide (MitoSOX) generation and depletes mitochondrial membrane potential (MitoMP). This further supports the AMA-induced oxidative stress changes in oral cancer CAL 27 and Ca9-22 cells. AMA also shows high expressions of annexin V in CAL 27 and Ca9-22 cells and cleaved forms of poly (ADP-ribose) polymerase (PARP), caspase 9, and caspase 3 in CAL 27 cells, supporting the apoptosis-inducing ability of AMA. Furthermore, AMA induces DNA damage (γH2AX and 8-oxo-2'-deoxyguanosine [8-oxodG]) in CAL 27 and Ca9-22 cells. Notably, the AMA-induced selective antiproliferation, oxidative stress, and DNA damage were partly prevented from N-acetylcysteine (NAC) pretreatments. Taken together, AMA selectively kills oral cancer cells in an oxidative stress-dependent mechanism involving apoptosis and DNA damage.

Why All the Fuss about Oxidative Phosphorylation (OXPHOS)?

Certain subtypes of cancer cells require oxidative phosphorylation (OXPHOS) to survive. Increased OXPHOS dependency is frequently a hallmark of cancer stem cells and cells resistant to chemotherapy and targeted therapies. Suppressing the OXPHOS function might also influence the tumor microenvironment by alleviating hypoxia and improving the antitumor immune response. Thus, targeting OXPHOS is a promising strategy to treat various cancers. A growing arsenal of therapeutic agents is under development to inhibit this biological process. This Perspective provides an overview of the structure and function of OXPHOS complexes, their biological functions in cancer, relevant research tools and models, as well as the limitations of OXPHOS as drug targets. We also focus on the current development status of OXPHOS inhibitors and potential therapeutic strategies to strengthen their clinical applications.

[The mechanisms of taxodione-induced apoptosis in BCR-ABL-positive leukemia cells]

Chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL) are caused by a fusion protein, BCR-ABL, which induces cellular transformation by activating the signaling molecules, STAT5 and Akt. The specific BCR-ABL inhibitors including imatinib, nilotinib, and dasatinib, are clinically utilized in the treatment with CML and ALL patients. Although these BCR-ABL inhibitors are initially successful in the treatment of leukemia, many patients develop drug resistance due to the appearance of the gatekeeper mutation of BCR-ABL, T315I. Recently, we found that taxodione, a quinone methide diterpene isolated from a conifer, Taxodium distichum, significantly induced apoptosis in human myelogenous leukemia-derived K562 cells, which is positive for the bcr-abl gene. Taxodione reduced the activities of mitochondrial respiratory chain complex III, leading to the production of reactive oxygen species (ROS). An antioxidant agent, N-acetylcysteine (NAC), canceled taxodione-induced ROS production and apoptotic cell death, suggesting that taxodione induced apoptosis through ROS accumulation. Furthermore, in K562 cells treated with taxodione, BCR-ABL, STAT5 and Akt were sequestered in mitochondrial fraction, and their localization changes decrease their abilities to stimulate cell proliferation. Strikingly, NAC canceled these taxodione-caused inhibition of BCR-ABL, STAT5 and Akt. In addition, taxodione significantly induced apoptosis in transformed Ba/F3 cells by not only BCR-ABL but also T315I-mutated BCR-ABL through the generation of ROS, suggesting that taxodione has potential as anti-tumor drug with high efficacy to overcome BCR-ABL T315I mutation-mediated resistance in leukemia cells. It's also expected that these knowledge becomes an important clue in the development of anti-cancer drugs against the broad range of tumors.

Self-Assembled Nanomedicines for Anticancer and Antibacterial Applications

Self-assembly strategies have been widely applied in the nanomedicine field, which provide a convenient approach for building various structures for delivery carriers. When cooperating with biomolecules, self-assembly systems have significant influence on the cell activity and life process and could be used for regulating nanodrug activity. In this review, self-assembled nanomedicines are introduced, including materials, encapsulation, and releasing strategies, where self-assembly strategies are involved. Furthermore, as a promising and emerging area for nanomedicine, in situ self-assembly of anticancer drugs and supramolecular antibiotic switches is also discussed about how to regulate drug activity. Selective pericellular assembly can block mass transformation of cancer cells inducing cell apoptosis, and the intracellular assembly can either cause cell death or effectively avoid drug elimination from cytosol of cancer cells because of the assembly-induced retention (AIR) effect. Host-guest interactions of drug and competitive molecules offer reversible regulations of antibiotic activity, which can reduce drug-resistance and inhibit the generation of drug-resistant bacteria. Finally, the challenges and development trend in the field are discussed.

Detection of hydrogen peroxide production in the isolated rat lung using Amplex red

The objectives of this study were to develop a robust protocol to measure the rate of hydrogen peroxide (H₂O₂) production in isolated perfused rat lungs, as an index of oxidative stress, and to determine the cellular sources of the measured H₂O₂ using the extracellular probe Amplex red (AR). AR was added to the recirculating perfusate in an isolated perfused rat lung. AR's highly fluorescent oxidation product resorufin was measured in the perfusate. Experiments were carried out without and with rotenone (complex I inhibitor), thenoyltrifluoroacetone (complex II inhibitor), antimycin A (complex III inhibitor), potassium cyanide (complex IV inhibitor), or diohenylene iodonium (inhibitor of flavin-containing enzymes, e.g. NAD(P)H oxidase or NOX) added to the perfusate. We also evaluated the effect of acute changes in oxygen (O₂) concentration of ventilation gas on lung rate of H₂O₂ release into the perfusate. Baseline lung rate of H₂O₂ release was 8.45 ± 0.31 (SEM) nmol/min/g dry wt. Inhibiting mitochondrial complex II reduced this rate by 76%, and inhibiting flavin-containing enzymes reduced it by another 23%. Inhibiting complex I had a small (13%) effect on the rate, whereas inhibiting complex III had no effect. Inhibiting complex IV increased this rate by 310%. Increasing %O₂ in the ventilation gas mixture from 15 to 95% had a small (27%) effect on this rate, and this O₂-dependent increase was mostly nonmitochondrial. Results suggest complex II as a potentially important source and/or regulator of mitochondrial H₂O₂, and that most of acute hyperoxia-enhanced lung rate of H₂O₂ release is from nonmitochondrial rather than mitochondrial sources.

Anti-Leukemic Properties of Histamine in Monocytic Leukemia: The Role of NOX2

In patients with acute myeloid leukemia (AML), treatment with histamine dihydrochloride (HDC) and low-dose IL-2 (HDC/IL-2) in the post-chemotherapy phase has been shown to reduce the incidence of leukemic relapse. The clinical benefit of HDC/IL-2 is pronounced in monocytic forms of AML, where the leukemic cells express histamine type 2 receptors (H2R) and the NAPDH oxidase-2 (NOX2). HDC ligates to H2Rs to inhibit NOX2-derived formation of reactive oxygen species, but details regarding the anti-leukemic actions of HDC remain to be elucidated. Here, we report that human NOX2+ myelomonocytic/monocytic AML cell lines showed increased expression of maturation markers along with reduced leukemic cell proliferation after exposure to HDC in vitro. These effects of HDC were absent in corresponding leukemic cells genetically depleted of NOX2 (NOX2-/-). We also observed that exposure to HDC altered the expression of genes involved in differentiation and cell cycle progression in AML cells and that these effects required the presence of NOX2. HDC promoted the differentiation also of primary monocytic, but not non-monocytic, AML cells in vitro. In a xenograft model, immunodeficient NOG mice were inoculated with wild-type or NOX2-/- human monocytic AML cells and treated with HDC in vivo. The administration of HDC reduced the in vivo expansion of NOX2+/+, but not of NOX2-/- human monocytic AML cells. We propose that NOX2 may be a conceivable target in the treatment of monocytic AML.

Marine Streptomyces sp. derived antimycin analogues suppress HeLa cells via depletion HPV E6/E7 mediated by ROS-dependent ubiquitin-proteasome system

Four new antimycin alkaloids (1–4) and six related known analogs (5–10) were isolated from the culture of a marine derived Streptomyces sp. THS-55, and their structures were elucidated by extensive spectroscopic analysis. All of the compounds exhibited potent cytotoxicity in vitro against HPV-transformed HeLa cell line. Among them, compounds 6–7 were derived as natural products for the first time, and compound 5 (NADA) showed the highest potency. NADA inhibited the proliferation, arrested cell cycle distribution, and triggered apoptosis in HeLa cancer cells. Our molecular mechanic studies revealed NADA degraded the levels of E6/E7 oncoproteins through ROS-mediated ubiquitin-dependent proteasome system activation. This is the first report that demonstrates antimycin alkaloids analogue induces the degradation of high-risk HPV E6/E7 oncoproteins and finally induces apoptosis in cervical cancer cells. The present work suggested that these analogues could serve as lead compounds for the development of HPV-infected cervical cancer therapeutic agents, as well as research tools for the study of E6/E7 functions.

Effects of Benzo(e)pyrene on Reactive Oxygen/Nitrogen Species and Inflammatory Cytokines Induction in Human RPE Cells and Attenuation by Mitochondrial-involved Mechanism

Purpose:

To identify inhibitors that could effectively lower reactive oxygen/nitrogen species (ROS/RNS), complement and inflammatory cytokine levels induced by Benzo(e)pyrene [B(e)p], an element of cigarette smoke, in human retinal pigment epithelial cells (ARPE-19) in vitro.

Methods:

ARPE-19 cells were treated for 24 hours with 200 μM, 100 μM, and 50 μM B(e)p or DMSO (dimethyl sulfoxide)-equivalent concentrations. Some cultures were pre-treated with ROS/RNS inhibitors (NG nitro-L-arginine, inhibits nitric oxide synthase; Apocynin, inhibits NADPH oxidase; Rotenone, inhibits mitochondrial complex I; Antimycin A, inhibits mitochondria complex III) and ROS/RNS levels were measured with a fluorescent H₂ DCFDA assay. Multiplex bead arrays were used to measure levels of Interleukin-6 (IL-6), Interleukin-8 (IL-8), Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF), Transforming Growth Factor alpha (TGF-α) and Vascular Endothelial Growth Factor (VEGF). IL-6 levels were also measured by an enzyme-linked immunosorbent assay. Real-time qPCR analyses were performed with primers for C3 (component 3), CFH (inhibits complement activation), CD59 (inhibitor of the complement membrane attack complex (MAC)) and CD55/DAF (accelerates decay of target complement target proteins).

Results:

The ARPE-19 cultures treated with B(e)p showed significantly increased ROS/RNS levels (P < 0.001), which were then partially reversed by 6 μM Antimycin A (19%, P = 0.03), but not affected by the other ROS/RNS inhibitors. The B(e)p treated cultures demonstrated increased levels of IL-6 (33%; P = 0.016) and GM-CSF (29%; P = 0.0001) compared to DMSO-equivalent controls, while the expression levels for components of the complement pathway (C3, CFH, CD59 and CD55/DAF) were not changed.

Conclusion:

The cytotoxic effects of B(e)p include elevated ROS/RNS levels along with pro-inflammatory IL-6 and GM-CSF proteins. Blocking the Qi site of cytochrome c reductase (complex III) with Antimycin A led to partial reduction in B(e)p induced ROS production. Our findings suggest that inhibitors for multiple pathways would be necessary to protect the retinal cells from B(e)p induced toxicity.

TUFM downregulation induces epithelial-mesenchymal transition and invasion in lung cancer cells via a mechanism involving AMPK-GSK3β signaling

Mitochondrial dysfunction and epithelial-to-mesenchymal transition (EMT) play important roles in cancer development and metastasis. However, very little is known about the connection between mitochondrial dysfunction and EMT. Tu translation elongation factor, mitochondrial (TUFM), a key factor in the translational expression of mitochondrial DNA, plays an important role in the control of mitochondrial function. Here, we show that TUFM is downregulated in human cancer tissues. TUFM expression level was positively correlated with that of E-cadherin and decreased significantly during the progression of human lung cancer. TUFM knockdown induced EMT, reduced mitochondrial respiratory chain activity, and increased glycolytic function and the production of reactive oxygen species (ROS). Mechanistically, TUFM knockdown activated AMPK and phosphorylated GSK3β and increased the nuclear accumulation of β-catenin, leading to the induction of EMT and increased migration and metastasis of A549 lung cancer cells. Although TUFM knockdown also induced EMT of MCF7 breast cancer cells, the underlying mechanism appeared somewhat different from that in lung cancer cells. Our work identifies TUFM as a novel regulator of EMT and suggests a molecular link between mitochondrial dysfunction and EMT induction.

Antimycin-type depsipeptides: discovery, biosynthesis, chemical synthesis, and bioactivities

This review discusses the isolation, structural variation, biosynthesis, chemical synthesis, and biological activities of antimycin-type depsipeptides.

Antimycin A induces death of the human pulmonary fibroblast cells via ROS increase and GSH depletion

Antimycin A (AMA) inhibits the growth of various cells via stimulating oxidative stress-mediated death. However, little is known about the anti-growth effect of AMA on normal primary lung cells. Here, we investigated the effects of AMA on cell growth inhibition and death in human pulmonary fibroblast (HPF) cells in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. AMA inhibited the growth of HPF cells with an IC50 of ~150 µM at 24 h. AMA induced a G1 phase arrest of the cell cycle and it also triggered apoptosis accompanied by the loss of mitochondrial membrane potential (MMP; ∆Ψm). AMA increased ROS levels including O2᛫- in HPF cells from the early time point of 25 min. It induced GSH depletion in HPF cells in a dose-dependent manner. Z-VAD (a pan-caspase inhibitor) did not significantly prevent cell death and MMP (∆Ψm) loss induced by AMA. N-acetylcysteine (NAC; an antioxidant) attenuated cell growth inhibition, death and MMP (∆Ψm) loss in AMA-treated HPF cells and NAC generally decreased the ROS level in these cells as well. Vitamin C enhanced cell growth inhibition, death, GSH depletion and O2᛫- levels in 100 µM AMA-treated HPF cells whereas this agent strongly attenuated these effects in 200 µM AMA-treated cells. In conclusion, AMA inhibited the growth of HPF cells via apoptosis as well as a G1 phase arrest of the cell cycle. AMA-induced HPF cell death was related to increased ROS levels and GSH depletion.

Posttranslational Regulation of Human DNA Polymerase ι

Human DNA polymerases (pols) η and ι are Y-family DNA polymerase paralogs that facilitate translesion synthesis past damaged DNA. Both polη and polι can be monoubiquitinated in vivo. Polη has been shown to be ubiquitinated at one primary site. When this site is unavailable, three nearby lysines may become ubiquitinated. In contrast, mass spectrometry analysis of monoubiquitinated polι revealed that it is ubiquitinated at over 27 unique sites. Many of these sites are localized in different functional domains of the protein, including the catalytic polymerase domain, the proliferating cell nuclear antigen-interacting region, the Rev1-interacting region, and its ubiquitin binding motifs UBM1 and UBM2. Polι monoubiquitination remains unchanged after cells are exposed to DNA-damaging agents such as UV light (generating UV photoproducts), ethyl methanesulfonate (generating alkylation damage), mitomycin C (generating interstrand cross-links), or potassium bromate (generating direct oxidative DNA damage). However, when exposed to naphthoquinones, such as menadione and plumbagin, which cause indirect oxidative damage through mitochondrial dysfunction, polι becomes transiently polyubiquitinated via Lys¹¹- and Lys⁴⁸-linked chains of ubiquitin and subsequently targeted for degradation. Polyubiquitination does not occur as a direct result of the perturbation of the redox cycle as no polyubiquitination was observed after treatment with rotenone or antimycin A, which both inhibit mitochondrial electron transport. Interestingly, polyubiquitination was observed after the inhibition of the lysine acetyltransferase KATB3/p300. We hypothesize that the formation of polyubiquitination chains attached to polι occurs via the interplay between lysine acetylation and ubiquitination of ubiquitin itself at Lys¹¹ and Lys⁴⁸ rather than oxidative damage per se.

Immunomodulatory effect of melatonin in SK-LU-1 human lung adenocarcinoma cells co-cultured with peripheral blood mononuclear cells

OBJECTIVES

The anti-cancer potential of melatonin has been examined using a variety of experimental approaches. Melatonin immunomodulatory action was evaluated against the lung cancer cell line SK-LU-1, in co-culture with human peripheral blood mononuclear cells (PBMC).

MATERIALS AND METHODS

Melatonin was tested on the cell line only after 24 h incubation (direct effect), and on the co-culture system of SK-LU-1 and PBMC to investigate any indirect effect. Apoptotic induction of the cancer cells was assessed using annexin V/PI staining with flow cytometric analysis for membrane alteration. Intracellular superoxide anion (O2 (•-) ) and hydrogen peroxide (H2 O2 ) for intracellular oxidative stress and glutathione (GSH) for intracellular anti-oxidation were measured with specific fluorescence probes. DNA fractions were measured employing propidium iodide (PI) fluorescence staining.

RESULTS

High doses of melatonin were directly toxic to SK-LU-1 cells, while PBMC-mediated indirect effect occurred after moderate doses (1 μm). Under co-culture conditions, increases in apoptotic cell death, increase in oxidative stress by reduction of GSH and cell cycle arrest in G0 /G1 in SK-LU-1 cells, were observed as the immunomodulatory effect of melatonin.

CONCLUSION

Melatonin had indirect effects on lung cancer cells by enhancement of immunomodulatory effects, but further studies of mechanism(s) involved are needed.

NF-κB plays a key role in microcystin-RR-induced HeLa cell proliferation and apoptosis

Microcystins (MCs) are well-known cyanobacterial toxins produced in eutrophic waters and can act as potential carcinogens and have caused serious risk to human health. However, pleiotropic even paradoxical actions of cells exposure to MCs have been reported, and the mechanisms of MC-induced tumorigenesis and apoptosis are still unknown. In this study, we performed the first comprehensive in vitro investigation on carcinogenesis associated with nuclear factor kappa B (NF-κB) and its downstream genes in HeLa cells (Human cervix adenocarcinoma cell line from epithelial cells) exposure to MC-RR. HeLa cells were treated with 0, 20, 40, 60, and 80 µg/mL MC-RR for 4, 8, 12, and 24 h. HeLa cells presented dualistic responses to different doses of MCs. CCK8 assay showed that MC-RR exposure evidently enhanced cell viability of HeLa cells at lower MCs doses. Cell cycle and apoptosis analysis revealed that lower MCs doses promoted G1/S transition and cell proliferation while higher doses of MCs induced apoptosis, with a dose-dependent manner. Electrophoretic mobility shift assay (EMSA) revealed that MC-RR could increase/decrease NF-κB activity at lower/higher MC-RR doses, respectively. Furthermore, the expression of NF-κB downstream target genes including c-FLIP, cyclinD1, c-myc, and c-IAP2 showed the same variation trend as NF-κB activity both at mRNA and protein levels, which were induced by lower doses of MC-RR and suppressed by higher doses. Our data verified for the first time that NF-κB pathway may mediate MC-induced cell proliferation and apoptosis and provided a better understanding of the molecular mechanism for potential carcinogenicity of MC-RR.

Oxidative stress promotes D-GalN/LPS-induced acute hepatotoxicity by increasing glycogen synthase kinase 3β activity

OBJECTIVE

Our previous studies have demonstrated that glycogen synthase kinase 3β (GSK3β) activity is increased in the progression of acute liver failure (ALF), which aggravates liver injury, while its regulatory mechanism remains elusive. This study is designated to address whether oxidative stress activates GSK3β to promote ALF.

METHODS

In a murine model induced by D-galactosamine (D-GalN) (700 mg/kg) and LPS (10 μg/kg), N-acetylcysteine (300 mg/kg) or SB216763 (25 mg/kg) was used to inhibit oxidative stress or GSK3β activity, respectively. Serum alanine aminotransferase and aspartate aminotransferase levels were assessed. The parameters of oxidative stress were evaluated in liver tissue. Whether GSK3β inhibition protects hepatocytes from oxidative stress-induced cell apoptosis was investigated in vitro. Moreover, the activity of GSK3β was measured in the liver of chronic hepatitis B (CHB) patients and ALF patients.

RESULTS

In vivo, N-acetylcysteine ameliorated the D-GalN/LPS-induced hepatotoxicity and reduced GSK3β activity; GSK3β inhibition increased hepatic superoxide dismutase activity and the glutathione content, decreased malondialdehyde production in the liver tissues; while GSK3β inhibition suppressed the JNK activation in the liver and decreased cytochrome c release from mitochondria. In vitro, GSK3β inhibition lessened hepatocytes apoptosis induced by H2O2 or Antimycin A, as demonstrated by decreased LDH activity, and reduced cleavage of caspase-3 expression. Furthermore, GSK3β activity in the CHB patients was increased in the phase of ALF.

CONCLUSIONS

Results indicate that GSK3β activation contributes to liver injury by participating in oxidative stress response in ALF and is, therefore, a potential therapeutic target for ALF.

MARCH5-mediated quality control on acetylated Mfn1 facilitates mitochondrial homeostasis and cell survival

Mitochondrial dynamics and quality control have a central role in the maintenance of cellular integrity. Mitochondrial ubiquitin ligase membrane-associated RING-CH (MARCH5) regulates mitochondrial dynamics. Here, we show that mitochondrial adaptation to stress is driven by MARCH5-dependent quality control on acetylated Mfn1. Under mitochondrial stress conditions, levels of Mfn1 were elevated twofold and depletion of Mfn1 sensitized these cells to apoptotic death. Interestingly, overexpression of Mfn1 also promoted cell death in these cells, indicating that a fine tuning of Mfn1 levels is necessary for cell survival. MARCH5 binds Mfn1 and the MARCH5-dependent Mfn1 ubiquitylation was significantly elevated under mitochondrial stress conditions along with an increase in acetylated Mfn1. The acetylation-deficient K491R mutant of Mfn1 showed weak interaction with MARCH5 as well as reduced ubiquitylation. Neither was observed in the acetylation mimetic K491Q mutant. In addition, MARCH5-knockout mouse embryonic fibroblast and MARCH5(H43W)-expressing HeLa cells lacking ubiquitin ligase activity experienced rapid cell death upon mitochondrial stress. Taken together, a fine balance of Mfn1 levels is maintained by MARCH5-mediated quality control on acetylated Mfn1, which is crucial for cell survival under mitochondria stress conditions.

Effect of HA14-1 on apoptosis-regulating proteins in HeLa cells

Overexpression of Bcl-2 has been recognized in various malignancies. Recently, HA14-1, a Bcl-2 antagonist, has been identified for its anti-apoptotic effect. However, mode of action of HA14-1 still remains to be elucidated. In this study, we examined HA14-1 binding efficiency with receptor proteins through molecular docking. Cell viability using HeLa cells was evaluated through MTT assay after exposure to different concentration of HA14-1. Moreover, after HA14-1 exposure, expressions of tumor suppressor protein (p53), BH3-only protein (Puma) and apoptosis-associated proteins were analyzed by Western blotting. From the results, it was found that HA14-1 occupied all three domains; BH1, BH2, and BH3 within the hydrophobic pocket of Bcl-2. However, HA14-1 occupied only BH1 and BH3 of Bcl-xl, conversely, no such stable bond was observed for Bax and Bak. ARG107 and TYR101 were the amino acids involved in the binding of HA14-1 to Bcl-2 and Bcl-xl, respectively. Additionally, decrease in Bcl-2 and Bcl-xl expression along with increase in p53 and Puma expression after exposure to HA14-1 was observed. The results suggested p53 pathway to be the probable mechanism of action for the induction of apoptosis in HeLa cell by downregulating the effect of anti-apoptotic proteins suggesting that HA14-1 may provide therapeutic potential for the treatment of human cervical cancer.

Discovery of potent broad spectrum antivirals derived from marine actinobacteria

Natural products provide a vast array of chemical structures to explore in the discovery of new medicines. Although secondary metabolites produced by microbes have been developed to treat a variety of diseases, including bacterial and fungal infections, to date there has been limited investigation of natural products with antiviral activity. In this report, we used a phenotypic cell-based replicon assay coupled with an iterative biochemical fractionation process to identify, purify, and characterize antiviral compounds produced by marine microbes. We isolated a compound from Streptomyces kaviengensis, a novel actinomycetes isolated from marine sediments obtained off the coast of New Ireland, Papua New Guinea, which we identified as antimycin A1a. This compound displays potent activity against western equine encephalitis virus in cultured cells with half-maximal inhibitory concentrations of less than 4 nM and a selectivity index of greater than 550. Our efforts also revealed that several antimycin A analogues display antiviral activity, and mechanism of action studies confirmed that these Streptomyces-derived secondary metabolites function by inhibiting the cellular mitochondrial electron transport chain, thereby suppressing de novo pyrimidine synthesis. Furthermore, we found that antimycin A functions as a broad spectrum agent with activity against a wide range of RNA viruses in cultured cells, including members of the Togaviridae, Flaviviridae, Bunyaviridae, Picornaviridae, and Paramyxoviridae families. Finally, we demonstrate that antimycin A reduces central nervous system viral titers, improves clinical disease severity, and enhances survival in mice given a lethal challenge with western equine encephalitis virus. Our results provide conclusive validation for using natural product resources derived from marine microbes as source material for antiviral drug discovery, and they indicate that host mitochondrial electron transport is a viable target for the continued development of broadly active antiviral compounds.

Neuroprotective effect of leukemia inhibitory factor on antimycin A-induced oxidative injury in differentiated PC12 cells

As a neurotrophic cytokine, leukemia inhibitory factor (LIF) has neuroendocrine effects and exerts neuroprotective effects on various neuron injuries both in vitro and in vivo. The aim of the present study was to investigate whether LIF can protect PC12 cells from antimycin A (AMA)-induced oxidative stress. LIF (0.5 and 1 ng/ml) increased PC12 cell viability and significantly attenuated AMA-induced cell death as demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Results from Hoechst 33342 staining and flow cytometry assay showed that AMA induced apoptosis significantly in PC12 cells, while pretreatment with LIF (0.5 and 1 ng/ml) can attenuate this injury. The presence of LIF partly prevented AMA-induced elevated reactive oxygen species level and decreased superoxide dismutase level, which indicated the antioxidative effects of LIF on the neuron oxidative injury. In conclusion, LIF might protect PC12 cells from the injury induced by AMA through the downregulation of oxidative stress, which may provide basic information of using LIF as a potential targeted therapy for oxidative injury in neurons.

Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity

Autophagy is a cellular self-digestion process that mediates protein quality control and serves to protect against neurodegenerative disorders, infections, inflammatory diseases and cancer. Current evidence suggests that autophagy can selectively remove damaged organelles such as the mitochondria. Mitochondria-induced oxidative stress has been shown to play a major role in a wide range of pathologies in several organs, including the heart. Few studies have investigated whether enhanced autophagy can offer protection against mitochondrially-generated oxidative stress. We induced mitochondrial stress in cardiomyocytes using antimycin A (AMA), which increased mitochondrial superoxide generation, decreased mitochondrial membrane potential and depressed cellular respiration. In addition, AMA augmented nuclear DNA oxidation and cell death in cardiomyocytes. Interestingly, although oxidative stress has been proposed to induce autophagy, treatment with AMA did not result in stimulation of autophagy or mitophagy in cardiomyocytes. Our results showed that the MTOR inhibitor rapamycin induced autophagy, promoted mitochondrial clearance and protected cardiomyocytes from the cytotoxic effects of AMA, as assessed by apoptotic marker activation and viability assays in both mouse atrial HL-1 cardiomyocytes and human ventricular AC16 cells. Importantly, rapamycin improved mitochondrial function, as determined by cellular respiration, mitochondrial membrane potential and morphology analysis. Furthermore, autophagy induction by rapamycin suppressed the accumulation of ubiquitinylated proteins induced by AMA. Inhibition of rapamycin-induced autophagy by pharmacological or genetic interventions attenuated the cytoprotective effects of rapamycin against AMA. We propose that rapamycin offers cytoprotection against oxidative stress by a combined approach of removing dysfunctional mitochondria as well as by degrading damaged, ubiquitinated proteins. We conclude that autophagy induction by rapamycin could be utilized as a potential therapeutic strategy against oxidative stress-mediated damage in cardiomyocytes.

COX5B regulates MAVS-mediated antiviral signaling through interaction with ATG5 and repressing ROS production

Innate antiviral immunity is the first line of the host defense system that rapidly detects invading viruses. Mitochondria function as platforms for innate antiviral signal transduction in mammals through the adaptor protein, MAVS. Excessive activation of MAVS-mediated antiviral signaling leads to dysfunction of mitochondria and cell apoptosis that likely causes the pathogenesis of autoimmunity. However, the mechanism of how MAVS is regulated at mitochondria remains unknown. Here we show that the Cytochrome c Oxidase (CcO) complex subunit COX5B physically interacts with MAVS and negatively regulates the MAVS-mediated antiviral pathway. Mechanistically, we find that while activation of MAVS leads to increased ROS production and COX5B expression, COX5B down-regulated MAVS signaling by repressing ROS production. Importantly, our study reveals that COX5B coordinates with the autophagy pathway to control MAVS aggregation, thereby balancing the antiviral signaling activity. Thus, our study provides novel insights into the link between mitochondrial electron transport system and the autophagy pathway in regulating innate antiviral immunity.

Pattern recognition receptors are vital to innate immunity. In the antiviral innate immunity, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), such as RIG-I and MDA5, sense viral RNAs through their C-terminal helicase domains, then initiate the antiviral response through interaction with the essential adaptor protein MAVS, which is located in mitochondrial outer membrane. Although cumulative studies have showed that mitochondria-associated MAVS plays an important role in antiviral signaling, much remains unknown about the mechanism of MAVS activity related to mitochondrial membrane localization. In this article we demonstrate that the CcO complex subunit COX5B negatively regulates the MAVS-mediated antiviral pathway through interaction with MAVS. At the mechanistic level, we show that COX5B inhibits MAVS-mediated antiviral pathway by suppressing ROS production, and coordinating with the autophagy pathway to control MAVS aggregation. Our data support a notion that mitochondrial electron transport system coordinates with the autophagy pathway to regulate MAVS-mediated signaling for a tight control of innate antiviral immunity.

Glutathionylation state of uncoupling protein-2 and the control of glucose-stimulated insulin secretion

The role of reactive oxygen species (ROS) in glucose-stimulated insulin release remains controversial because ROS have been shown to both amplify and impede insulin release. In regard to preventing insulin release, ROS activates uncoupling protein-2 (UCP2), a mitochondrial inner membrane protein that negatively regulates glucose-stimulated insulin secretion (GSIS) by uncoupling oxidative phosphorylation. With our recent discovery that the UCP2-mediated proton leak is modulated by reversible glutathionylation, a process responsive to small changes in ROS levels, we resolved to determine whether glutathionylation is required for UCP2 regulation of GSIS. Using Min6 cells and pancreatic islets, we demonstrate that induction of glutathionylation not only deactivates UCP2-mediated proton leak but also enhances GSIS. Conversely, an increase in mitochondrial matrix ROS was found to deglutathionylate and activate UCP2 leak and impede GSIS. Glucose metabolism also decreased the total amount of cellular glutathionylated proteins and increased the cellular glutathione redox ratio (GSH/GSSG). Intriguingly, the provision of extracellular ROS (H(2)O(2), 10 μM) amplified GSIS and also activated UCP2. Collectively, our findings indicate that the glutathionylation status of UCP2 contributes to the regulation of GSIS, and different cellular sites and inducers of ROS can have opposing effects on GSIS, perhaps explaining some of the controversy surrounding the role of ROS in GSIS.

Effect of resveratrol on oxygen consumption by Philasterides dicentrarchi, a scuticociliate parasite of turbot

The phytoalexin resveratrol (RESV) displays antiparasitic activity against Philasterides dicentrarchi, a scuticociliate pathogen of turbot, and causes oxidative stress, inhibition of antioxidant enzyme activity and morphological alterations in the parasite mitochondria. In this study, we analysed the mitochondrial biology of P. dicentrarchi and assessed the effect of RESV on mitochondrial metabolism. We found that RESV caused dose-dependent inhibition of mitochondrial electron transport and O₂ consumption in ciliates permeabilized with digitonin. Although the RESV molecule has a high capacity for antiradical and antioxidant activity, it induced a high level of pro-oxidant activity against the ciliate, thus causing a significant increase in intracellular ROS production. The increased ROS production was accompanied by mitochondrial collapse and dysfunction of mitochondrial membrane potential (ΔΨm) and by a significant increase in intracellular Ca⁺² levels. RESV inhibited parasite growth in a similar way to antimycin A, an inhibitor of mitochondrial electron transport and ROS generator. The findings confirm the mitochondria as a target in the potential development of effective antiparasitic treatments.

Tiron protects against UVB-induced senescence-like characteristics in human dermal fibroblasts by the inhibition of superoxide anion production and glutathione depletion

BACKGROUND/OBJECTIVES

  Free radicals and reactive oxygen species (ROS), which are generated by UV irradiation, may induce an irreversible growth arrest similar to senescence. Tiron, 4,5-dihydroxy-1,3-benzene disulfonic acid, is a widely used antioxidant to rescue ROS-evoked cell death. The aim of the article was to explore the effects of tiron on skin photoaging and associated mechanisms.

METHODS

  The effects of tiron on cell proliferation were determined using 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide. Senescent cells were determined by morphology and senescence-associated β-galactosidase activity analysis. Intracellular hydrogen peroxide, superoxide anion and glutathione concentration were analysed by a fluorescent probe. The concomitant changes of protein expression were analysed with Western blot.

RESULTS

  Human dermal fibroblasts were induced to premature senescence by sub-cytotoxic doses of irradiated UVB. Strong senescence-associated β-galactosidase activity and increased intracellular superoxide anion were observed in human dermal fibroblasts irradiated by UVB. Tiron blocks UVB-induced glutathione depletion and increase of superoxide anion and protects against UVB-induced senescence-like characteristics in human dermal fibroblasts. Compared with normal fibroblasts, UVB-irradiated human dermal fibroblasts showed a higher ratio of active (hypophosphorylated) to inactive (phosphorylated) forms of Rb and p38, upregulation of p53 or p16 and c-Myc and insulin-like growth factor 1 (IGF-1) downregulation. After treatment with tiron, p53, p16 c-Myc and IGF-1 as well as phosphorylation Rb and p38 could partially recover.

CONCLUSION

  These results indicate that tiron protects against UVB-induced senescence-like characteristics in human dermal fibroblasts via the inhibition of production of superoxide anion and glutathione depletion, and modulation of related senescence proteins.

Role of oxidative stress in diabetes-mediated vascular dysfunction: unifying hypothesis of diabetes revisited

Oxidative stress is recognized as a key participant in the development of diabetic complications in the vasculature. One of the seminal studies advancing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress-mediated diversion of glycolytic intermediates into pathological pathways was a key underlying element in the development of diabetic complications. It is widely recognized that flux through glycolysis slows during diabetes. However, several bottlenecks develop in the glycolytic pathway, including glucose transport, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase. Of these limiting steps in glycolysis, glyceraldehyde-3-phosphate dehydrogenase is most sensitive to oxidative stress, leading to the hypothesis that glyceraldehyde-3-phosphate inactivation by ribosylation underlies the diversion of glycolytic intermediates into pathological pathways. However, recent studies question the mechanism underlying the effect of reactive oxygen species on key enzymes of the glycolytic pathway. The present review critiques the major premises of the hypothesis and concludes that further study of the role of oxidative stress in the development of diabetes-mediated vasculature dysfunction is warranted.