Mitochondrial depolarization following hydrogen sulfide exposure in erythrocytes from a sulfide-tolerant marine invertebrate

Difference in sulfur regulation mechanism between tube-dwelling and free-moving polychaetes sympatrically inhabiting deep-sea hydrothermal chimneys

The environment around deep sea hydrothermal vents is characterized by an abundance of sulfur compounds, including toxic hydrogen sulfide. However, numerous communities of various invertebrates are found in it. It is suggested that invertebrates in the vicinity of hydrothermal vents detoxify sulfur compounds by biosynthesis of taurine-related compounds in the body. On the other hand, the vent endemic polychaete Alvinella pompejana has spherocrystals composed of sulfur and other metals in its digestive tract. It was considered that the spherocrystals contribute to the regulation of sulfur in body fluids. Paralvinella spp. and Polynoidae. gen. sp. live sympatrically and in areas most affected by vent fluid. In this study, we focused on the digestive tract of Paralvinella spp. and Polynoidae. gen. sp. to examine whether they have spherocrystals. We also investigated the possible involvement of bacteria in the digestive tract in spherulization. Examination with a scanning electron microscope (SEM) equipped with Energy Disperse X-ray Spectroscopy (EDS) detected spherocrystals containing sulfur and iron in the digestive tract of Paralvinella spp. In contrast, such spherocrystals were not observed in that of Polynoidae. gen. sp. although sulfur is detected there by inductively coupled plasma-optical emission spectrometry (ICP-OES). Meta-16S rRNA analysis indicated that the floras of the digestive tracts of the two species were very similar, suggesting that enteric bacteria are not responsible for spherocrystal formation. Analysis of taurine-related compounds indicated that the digestive tissues of Polynoidae. gen. sp. contain a higher amount of hypotaurine and thiotaurine than those of Paralvinella spp. Therefore, the two sympatric polychaetes use different strategies for controlling sulfur, i.e., Paralvinella spp. forms spherocrystals containing elemental sulfur and iron in the digestive tract, but Polynoidae. gen. sp. accumulates taurine-related compounds instead of spherocrystals. Such differences may be related to differences in their lifestyles, i.e., burrow-dweller or free-moving, or may have been acquired phylogenetically in the evolutionary process.

Exploring Thermal Sensitivities and Adaptations of Oxidative Phosphorylation Pathways

Temperature shifts are a major challenge to animals; they drive adaptations in organisms and species, and affect all physiological functions in ectothermic organisms. Understanding the origin and mechanisms of these adaptations is critical for determining whether ectothermic organisms will be able to survive when faced with global climate change. Mitochondrial oxidative phosphorylation is thought to be an important metabolic player in this regard, since the capacity of the mitochondria to produce energy greatly varies according to temperature. However, organism survival and fitness depend not only on how much energy is produced, but, more precisely, on how oxidative phosphorylation is affected and which step of the process dictates thermal sensitivity. These questions need to be addressed from a new perspective involving a complex view of mitochondrial oxidative phosphorylation and its related pathways. In this review, we examine the effect of temperature on the commonly measured pathways, but mainly focus on the potential impact of lesser-studied pathways and related steps, including the electron-transferring flavoprotein pathway, glycerophosphate dehydrogenase, dihydroorotate dehydrogenase, choline dehydrogenase, proline dehydrogenase, and sulfide:quinone oxidoreductase. Our objective is to reveal new avenues of research that can address the impact of temperature on oxidative phosphorylation in all its complexity to better portray the limitations and the potential adaptations of aerobic metabolism.

Impact of polyethylene terephthalate microfiber length on cellular responses in the Mediterranean mussel Mytilus galloprovincialis

Many studies have investigated the toxic effects of microplastics in marine organisms, but most studied nano-sized round microplastics at high concentrations and were not environmentally relevant. To understand the cellular toxicity of polyethylene terephthalate microfibers (PET-MFs) by length (50 and 100 μm), Mediterranean mussels (Mytilus galloprovincialis) were exposed to environmental (0.5 μg/L) and high (100 mg/L) MF concentrations for four days. Short PET-MFs accumulated in the lower intestinal organs of the mussels, but long PET-MFs were only observed in the upper intestinal organs. Both sized PET-MFs affected necrosis, DNA damage, reactive oxygen species, nitric oxide, and acetylcholinesterase (AChE) activity. Significant MF length-dependent effects occurred at environmentally relevant concentrations for DNA damage (100 μm MFs) and AChE activity (50 μm MFs). However, length effects disappeared at the higher exposure concentration. The current study provides potentially sensitive indicators to detect MFs exposure and the ecotoxicological implications of MFs in marine ecosystems.

A novel transcription factor MRPS27 up-regulates the expression of sqr, a key gene of mitochondrial sulfide metabolism in echiuran worm Urechis unicinctus

Hydrogen sulfide is a natural, widely distributed, poisonous substance and sulfide: quinone oxidoreductase (SQR) is responsible for oxidizing hydrogen sulfide to less toxic sulfur compounds. The increase of SQR mRNA level is an important mechanism for organisms to adapt to hydrogen sulfide-rich environments. However, its transcriptional regulation mechanism is not very clear. In this study, a mitochondrial 28S ribosomal protein S27 (MRPS27), which has never been reported as a transcription factor, was screened by yeast one-hybrid experiment from the echiuran worm Urechis unicinctus, a benthic organism living in marine sediments. Western blotting indicated that UuMRPS27 contents increased significantly in the nuclear extract of hindgut under exposed to 150 μM sulfide. ChIP and EMSA assays demonstrated that UuMRPS27 did bind to the sqr proximal promoter, the key binding sequence was CTAGAG (+12 to +17 of the promoter) detected by DNase I footprinting assay as well as transient transfection experiments. Furthermore, UuMRPS27, as a transcription activator, exhibited the highest transcription activity compared with other reported sqr transcription factors. Our data revealed for the first time the role of MRPS27 acting as a transcription factor which expanded the understanding of sqr transcriptional regulation in sulfide metabolism mechanism.

Defense responses of sulfur dioxygenase to sulfide stress in the razor clam Sinonovacula constricta

BACKGROUND

Sulfide is a well-known toxicant widely distributed in the culture environment. As a representative burrowing benthic bivalve, the razor clam Sinonovacula constricta is highly sulfide tolerant. Mitochondrial sulfide oxidation is an important way for sulfide detoxification, where sulfur dioxygenase (SDO) is the second key enzyme.

OBJECTIVE

To investigate the mechanism of sulfide tolerance in S. constricta, the molecular characterization of its SDO (designated as ScSDO) was studied.

METHODS

The cDNA sequence of ScSDO was cloned by RACE technique. The response of ScSDO in gills and livers of S. constricta was investigated during sulfide exposure (50, 150, and 300 μM sulfide) for 0, 3, 6, 12, 24, 48, 72, and 96 h by qRT-PCR. Moreover, the temporal expression of ScSDO protein in S. constricta gills after exposure to 150 μM sulfide was detected by Western blot. The subcellular location of ScSDO was identified by TargetP 1.1 prediction and Western Blot analysis.

RESULTS

The full-length cDNA of ScSDO was 2914 bp, encoding a protein of 304 amino acids. The deduced ScSDO protein was highly conserved, containing the signature HXHXDH motif of the metallo-β-lactamase superfamily and two metal-binding sites, of which metal-binding site I is known to be the catalytically active center. Subcellular localization confirmed that ScSDO was located only in the mitochondria. Responding to the sulfide exposure, distinct time-dependent increases in ScSDO expression were detected at both mRNA and protein levels. Moreover, the gills exhibited a higher ScSDO expression level than the livers.

CONCLUSIONS

All of our results suggest that ScSDO plays an important role in mitochondrial sulfide oxidation during sulfide stress, making S. constricta highly sulfide tolerant. In addition, as a respiratory tissue, the gills play a more critical role in sulfide detoxification.

Involvement of Mitochondrial Mechanisms in the Cytostatic Effect of Desethylamiodarone in B16F10 Melanoma Cells

Previously, we showed that desethylamiodarone (DEA), a major metabolite of the widely used antiarrhythmic drug amiodarone, has direct mitochondrial effects. We hypothesized that these effects account for its observed cytotoxic properties and ability to limit in vivo metastasis. Accordingly, we examined DEA’s rapid (3–12 h) cytotoxicity and its early (3–6 h) effects on various mitochondrial processes in B16F10 melanoma cells. DEA did not affect cellular oxygen radical formation, as determined using two fluorescent dyes. However, it did decrease the mitochondrial transmembrane potential, as assessed by JC-1 dye and fluorescence microscopy. It also induced mitochondrial fragmentation, as visualized by confocal fluorescence microscopy. DEA decreased maximal respiration, ATP production, coupling efficiency, glycolysis, and non-mitochondrial oxygen consumption measured by a Seahorse cellular energy metabolism analyzer. In addition, it induced a cyclosporine A–independent mitochondrial permeability transition, as determined by Co²⁺-mediated calcein fluorescence quenching measured using a high-content imaging system. DEA also caused outer mitochondrial membrane permeabilization, as assessed by the immunoblot analysis of cytochrome C, apoptosis inducing factor, Akt, phospho-Akt, Bad, and phospho-Bad. All of these data supported our initial hypothesis.

Mitochondrial Mechanisms Underlying Tolerance to Fluctuating Oxygen Conditions: Lessons from Hypoxia-Tolerant Organisms

Oxygen (O2) is essential for most metazoan life due to its central role in mitochondrial oxidative phosphorylation (OXPHOS), which generates >90% of the cellular adenosine triphosphate. O2 fluctuations are an ultimate mitochondrial stressor resulting in mitochondrial damage, energy deficiency, and cell death. This work provides an overview of the known and putative mechanisms involved in mitochondrial tolerance to fluctuating O2 conditions in hypoxia-tolerant organisms including aquatic and terrestrial vertebrates and invertebrates. Mechanisms of regulation of the mitochondrial OXPHOS and electron transport system (ETS) (including alternative oxidases), sulphide tolerance, regulation of redox status and mitochondrial quality control, and the potential role of hypoxia-inducible factor (HIF) in mitochondrial tolerance to hypoxia are discussed. Mitochondrial phenotypes of distantly related animal species reveal common features including conservation and/or anticipatory upregulation of ETS capacity, suppression of reactive oxygen species (ROS)-producing electron flux through ubiquinone, reversible suppression of OXPHOS activity, and investment into the mitochondrial quality control mechanisms. Despite the putative importance of oxidative stress in adaptations to hypoxia, establishing the link between hypoxia tolerance and mitochondrial redox mechanisms is complicated by the difficulties of establishing the species-specific concentration thresholds above which the damaging effects of ROS outweigh their potentially adaptive signaling function. The key gaps in our knowledge about the potential mechanisms of mitochondrial tolerance to hypoxia include regulation of mitochondrial biogenesis and fusion/fission dynamics, and HIF-dependent metabolic regulation that require further investigation in hypoxia-tolerant species. Future physiological, molecular and genetic studies of mitochondrial responses to hypoxia, and reoxygenation in phylogenetically diverse hypoxia-tolerant species could reveal novel solutions to the ubiquitous and metabolically severe problem of O2 deficiency and would have important implications for understanding the evolution of hypoxia tolerance and the potential mitigation of pathological states caused by O2 fluctuations.

Evaluation of microplastic toxicity in accordance with different sizes and exposure times in the marine copepod Tigriopus japonicus

The indiscriminate use of plastic has greatly increased microplastic contamination risk in the marine environment. Microplastics can affect all marine life via the food web, from primary producers (e.g., microalgae) to final consumers (e.g., carnivorous fish). Thus, several studies have attempted to evaluate microplastic toxicity, but information about the underlying mechanisms of their effect is limited. Therefore, in this study, we examined multiple factors that could contribute to microplastic-induced toxicity. We investigated the potential molecular effects of microplastic size and exposure time. We exposed the marine copepod Tigriopus japonicus to 50 nm and 10 μm polystyrene microbeads. We found that both size and exposure time increased intracellular levels of reactive oxygen species. In addition, antioxidant-related gene expression was modulated and antioxidant enzyme activities were changed significantly. The results of this study provide important insights into the molecular mechanisms of microplastic-induced toxicity in a marine organism.

Toxicological effects of irregularly shaped and spherical microplastics in a marine teleost, the sheepshead minnow (Cyprinodon variegatus)

The increasing global contamination of plastics in marine environments is raising public concerns about the potential hazards of microplastics to environmental and human health. Microplastics formed by the breakdown of larger plastics are typically irregular in shape. The objective of this study was to compare the effects of spherical or irregular shapes of microplastics on changes in organ distribution, swimming behaviors, gene expression, and enzyme activities in sheepshead minnow (Cyprinodon variegatus). Both types of microplastics accumulated in the digestive system, causing intestinal distention. However, when compared to spherical microplastics, irregular microplastics decreased swimming behavior (i.e., total distance travelled and maximum velocity) of sheepshead minnow. Both microplastics generated cellular reactive oxygen species (ROS), while ROS-related molecular changes (i.e., transcriptional and enzymatic characteristics) differed. This study provides toxicological insights into the impacts of environmentally relevant (fragmented) microplastics on fish and improves our understanding of the environmental effects of microplastics in the ecosystem.

Soluble Uric Acid Activates the NLRP3 Inflammasome

Uric acid is a damage-associated molecular pattern (DAMP), released from ischemic tissues and dying cells which, when crystalized, is able to activate the NLRP3 inflammasome. Soluble uric acid (sUA) is found in high concentrations in the serum of great apes, and even higher in some diseases, before the appearance of crystals. In the present study, we sought to investigate whether uric acid, in the soluble form, could also activate the NLRP3 inflammasome and induce the production of IL-1β. We monitored ROS, mitochondrial area and respiratory parameters from macrophages following sUA stimulus. We observed that sUA is released in a hypoxic environment and is able to induce IL-1β release. This process is followed by production of mitochondrial ROS, ASC speck formation and caspase-1 activation. Nlrp3^-/- macrophages presented a protected redox state, increased maximum and reserve oxygen consumption ratio (OCR) and higher VDAC protein levels when compared to WT and Myd88^-/- cells. Using a disease model characterized by increased sUA levels, we observed a correlation between sUA, inflammasome activation and fibrosis. These findings suggest sUA activates the NLRP3 inflammasome. We propose that future therapeutic strategies for renal fibrosis should include strategies that block sUA or inhibit its recognition by phagocytes.

Non-Thermal Atmospheric Pressure Plasma Efficiently Promotes the Proliferation of Adipose Tissue-Derived Stem Cells by Activating NO-Response Pathways

Non-thermal atmospheric pressure plasma (NTAPP) is defined as a partially ionized gas with electrically charged particles at atmospheric pressure. Our study showed that exposure to NTAPP generated in a helium-based dielectric barrier discharge (DBD) device increased the proliferation of adipose tissue-derived stem cells (ASCs) by 1.57-fold on an average, compared with untreated cells at 72 h after initial NTAPP exposure. NTAPP-exposed ASCs maintained their stemness, capability to differentiate into adipocytes but did not show cellular senescence. Therefore, we suggested that NTAPP can be used to increase the proliferation of ASCs without affecting their stem cell properties. When ASCs were exposed to NTAPP in the presence of a nitric oxide (NO) scavenger, the proliferation-enhancing effect of NTAPP was not obvious. Meanwhile, the proliferation of NTAPP-exposed ASCs was not much changed in the presence of scavengers for reactive oxygen species (ROS). Also, Akt, ERK1/2, and NF-κB were activated in ASCs after NTAPP exposure. These results demonstrated that NO rather than ROS is responsible for the enhanced proliferation of ASCs following NTAPP exposure. Taken together, this study suggests that NTAPP would be an efficient tool for use in the medical application of ASCs both in vitro and in vivo.

Ugonin U stimulates NLRP3 inflammasome activation and enhances inflammasome-mediated pathogen clearance

The NOD-like receptor pyrin domain 3 (NLRP3) inflammasome contains Nod-like receptors, a subclass of pattern recognition receptors, suggesting that this complex has a prominent role in host defenses. Various structurally diverse stimulators activate the NLRP3 inflammasome through different signaling pathways. We previously reported that ugonin U (UgU), a natural flavonoid isolated from Helminthostachys zeylanica (L) Hook, directly stimulates phospholipase C (PLC) and triggers superoxide release in human neutrophils. In the present study, we showed that UgU induced NLRP3 inflammasome assembly and subsequent caspase-1 and interleukin (IL)-1β processing in lipopolysaccharide-primed human monocytes. Moreover, UgU elicited mitochondrial superoxide generation in a dose-dependent manner, and a specific scavenger of mitochondrial reactive oxygen species (ROS) diminished UgU-induced IL-1β and caspase-1 activation. UgU induced Ca²⁺ mobilization, which was inhibited by treatment with inhibitors of PLC or inositol triphosphate receptor (IP₃R). Blocking Ca²⁺ mobilization, PLC, or IP₃R diminished UgU-induced IL-1β release, caspase-1 activation, and mitochondrial ROS generation. These data demonstrated that UgU activated the NLPR3 inflammasome activation through Ca²⁺ mobilization and the production of mitochondrial ROS. We also demonstrated that UgU-dependent NLRP3 inflammasome activation enhanced the bactericidal function of human monocytes. The ability of UgU to stimulate human neutrophils and monocytes, both of which are professional phagocytes, and its capacity to activate the NLRP3 inflammasome, which is a promising molecular target for developing anti-infective medicine, indicate that UgU treatment should be considered as a possible novel therapy for treating infectious diseases.

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The immuno-stimulatory effects UgU in human monocytes were evaluated.

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UgU induces Ca²⁺ mobilization and eventually activates the NLRP3 inflammasome.

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UgU facilitates the bactericidal function of human monocytes.

Garlic oil polysulfides: H2S- and O2-independent prooxidants in buffer and antioxidants in cells

The health benefits of garlic and other organosulfur-containing foods are well recognized and have been attributed to both prooxidant and antioxidant activities. The effects of garlic are surprisingly similar to those of hydrogen sulfide (H2S), which is also known to be released from garlic under certain conditions. However, recent evidence suggests that polysulfides, not H2S, may be the actual mediator of physiological signaling. In this study, we monitored formation of H2S and polysulfides from garlic oil in buffer and in human embryonic kidney (HEK) 293 cells with fluorescent dyes, 7-azido-4-methylcoumarin and SSP4, respectively and redox activity with two redox indicators redox-sensitive green fluorescent protein (roGFP) and DCF. Our results show that H2S release from garlic oil in buffer requires other low-molecular-weight thiols, such as cysteine (Cys) or glutathione (GSH), whereas polysulfides are readily detected in garlic oil alone. Administration of garlic oil to cells rapidly increases intracellular polysulfide but has minimal effects on H2S unless Cys or GSH are also present in the extracellular medium. We also observed that garlic oil and diallyltrisulfide (DATS) potently oxidized roGFP in buffer but did not affect DCF. This appears to be a direct polysulfide-mediated oxidation that does not require a reactive oxygen species intermediate. Conversely, when applied to cells, garlic oil became a significant intracellular reductant independent of extracellular Cys or GSH. This suggests that intracellular metabolism and further processing of the sulfur moieties are necessary to confer antioxidant properties to garlic oil in vivo.

A case of mistaken identity: are reactive oxygen species actually reactive sulfide species?

Stepwise one-electron reduction of oxygen to water produces reactive oxygen species (ROS) that are chemically and biochemically similar to reactive sulfide species (RSS) derived from one-electron oxidations of hydrogen sulfide to elemental sulfur. Both ROS and RSS are endogenously generated and signal via protein thiols. Given the similarities between ROS and RSS, we wondered whether extant methods for measuring the former would also detect the latter. Here, we compared ROS to RSS sensitivity of five common ROS methods: redox-sensitive green fluorescent protein (roGFP), 2', 7'-dihydrodichlorofluorescein, MitoSox Red, Amplex Red, and amperometric electrodes. All methods detected RSS and were as, or more, sensitive to RSS than to ROS. roGFP, arguably the "gold standard" for ROS measurement, was more than 200-fold more sensitive to the mixed polysulfide H2Sn(n = 1-8) than to H2O2 These findings suggest that RSS may be far more prevalent in intracellular signaling than previously appreciated and that the contribution of ROS may be overestimated. This conclusion is further supported by the observation that estimated daily sulfur metabolism and ROS production are approximately equal and the fact that both RSS and antioxidant mechanisms have been present since the origin of life, nearly 4 billion years ago, long before the rise in environmental oxygen 600 million years ago. Although ROS are assumed to be the most biologically relevant oxidants, our results question this paradigm. We also anticipate our findings will direct attention toward development of novel and clinically relevant anti-(RSS)-oxidants.

The amino acid sensor GCN2 controls gut inflammation by inhibiting inflammasome activation

The integrated stress response (ISR) is a homeostatic mechanism by which eukaryotic cells sense and respond to stress-inducing signals, such as amino acid starvation. General controlled non-repressed (GCN2) kinase is a key orchestrator of the ISR, and modulates protein synthesis in response to amino acid starvation. Here we demonstrate in mice that GCN2 controls intestinal inflammation by suppressing inflammasome activation. Enhanced activation of ISR was observed in intestinal antigen presenting cells (APCs) and epithelial cells during amino acid starvation, or intestinal inflammation. Genetic deletion of Gcn2 (also known as Eif2ka4) in CD11c(+) APCs or intestinal epithelial cells resulted in enhanced intestinal inflammation and T helper 17 cell (TH17) responses, owing to enhanced inflammasome activation and interleukin (IL)-1β production. This was caused by reduced autophagy in Gcn2(-/-) intestinal APCs and epithelial cells, leading to increased reactive oxygen species (ROS), a potent activator of inflammasomes. Thus, conditional ablation of Atg5 or Atg7 in intestinal APCs resulted in enhanced ROS and TH17 responses. Furthermore, in vivo blockade of ROS and IL-1β resulted in inhibition of TH17 responses and reduced inflammation in Gcn2(-/-) mice. Importantly, acute amino acid starvation suppressed intestinal inflammation via a mechanism dependent on GCN2. These results reveal a mechanism that couples amino acid sensing with control of intestinal inflammation via GCN2.

Spatial compartmentalization of free radical formation and mitochondrial heterogeneity in bivalve gills revealed by live-imaging techniques

BACKGROUND

Reactive oxygen (ROS) and nitrogen (RNS) species are produced during normal unstressed metabolic activity in aerobic tissues. Most analytical work uses tissue homogenates, and lacks spatial information on the tissue specific sites of actual ROS formation. Live-imaging techniques (LIT) utilize target-specific fluorescent dyes to visualize biochemical processes at cellular level.

RESULTS

Together with oxidative stress measurements, here we report application of LIT to bivalve gills for ex-vivo analysis of gill physiology and mapping of ROS and RNS formation in the living tissue. Our results indicate that a) mitochondria located in the basal parts of the epithelial cells close to the blood vessels are hyperpolarized with high Δψm, whereas b) the peripheral mitochondria close to the cilia have low (depolarized) Δψm. These mitochondria are densely packed (mitotracker Deep Red 633 staining), have acidic pH (Ageladine-A) and collocate with high formation of nitric oxide (DAF-2DA staining). NO formation is also observed in the endothelial cells surrounding the filament blood sinus. ROS (namely H2O2, HOO(•) and ONOO(-) radicals, assessed through C-H2DFFDA staining) are mainly formed within the blood sinus of the filaments and are likely to be produced by hemocytes as defense against invading pathogens. On the ventral bend of the gills, subepithelial mucus glands contain large mucous vacuoles showing higher fluorescence intensities for O2 (•-) than the rest of the tissue. Whether this O2 (•-) production is instrumental to mucus formation or serves antimicrobial protection of the gill surface is unknown. Cells of the ventral bends contain the superoxide forming mucocytes and show significantly higher protein carbonyl formation than the rest of the gill tissue.

CONCLUSIONS

In summary, ROS and RNS formation is highly compartmentalized in bivalve gills under unstressed conditions. The main mechanisms are the differentiation of mitochondria membrane potential and basal ROS formation in inner and outer filament layers, as well as potentially antimicrobial ROS formation in the central blood vessel. Our results provide new insight into this subject and highlight the fact that studying ROS formation in tissue homogenates may not be adequate to understand the underlying mechanism in complex tissues.

Sulfide exposure results in enhanced sqr transcription through upregulating the expression and activation of HSF1 in echiuran worm Urechis unicinctus

Sulfide is a natural, widely distributed, poisonous substance. Sulfide: quinone oxidoreductase (SQR) is responsible for the initial oxidation of sulfide in mitochondria. To study transcriptional regulation of sqr after sulfide exposure, a 2.6-kb sqr upstream sequence from echiuran worm Urechis unicinctus was cloned by genome walking. Bioinformatics analysis showed 3 heat shock elements (HSEs) in proximal promoter region of the sqr upstream sequence. Moreover, an Hsf1 cDNA in U. unicinctus (UuHsf1) was isolated with a full-length sequence of 2334 bp and its polyclonal antibody was prepared using U. unicinctus HSF1 (UuHSF1) expressed prokaryotically with whole sequence of its open reading frame (ORF). In vivo ChIP and in vitro EMSA assays revealed UuHSF1 could interact with the sqr proximal promoter region. Transient transfection and mutation assays indicated that UuHSF1 bound specifically to HSE (-155bp to -143bp) and enhanced the transcription of sqr. Furthermore, sulfide treatment experiments demonstrated that sulfide could increase the expression of HSF1 protein, and induce trimerization of the protein which binds to HSEs and then activate sqr transcription. Quantitative real-time PCR analysis revealed sqr mRNA level increased significantly after U. unicinctus was exposed to sulfide for 6h, which corresponded to content changes of both trimeric HSF1 and HSF1-HSE complex. We concluded that UuHSF1 is a transcription factor of sqr and sulfide could induce sqr transcription by upregulating the expression and activation of HSF1 in U. unicinctus exposed to sulfide.

Transcriptional response to sulfide in the Echiuran Worm Urechis unicinctus by digital gene expression analysis

Background

Urechis unicinctus, an echiuran worm inhabiting the U-shaped burrows in the coastal mud flats, is an important commercial and ecological invertebrate in Northeast Asian countries, which has potential applications in the study of animal evolution, coastal sediment improvement and marine drug development. Furthermore, the worm can tolerate and utilize well-known toxicant-sulfide. However, knowledge is limited on the molecular mechanism of U. unicinctus responding to sulfide due to deficiency of its genetic information.

Methods

In this study, we performed Illumina sequencing to obtain the first Urechis unicinctus transcriptome data. Sequenced reads were assembled and then annotated using blast searches against Nr, Nt, Swiss-Prot, KEGG and COG. The clean tags from four digital gene expression (DGE) libraries were mapped to the U. unicinctus transcriptome. DGE analysis and functional annotation were then performed to reveal its response to sulfide. The expressions of 12 candidate genes were validated using quantitative real-time PCR. The results of qRT-PCR were regressed against the DGE analysis, with a correlation coefficient and p-value reported for each of them.

Results

Here we first present a draft of U. unicinctus transcriptome using the Illumina HiSeq^TM 2000 platform and 52,093 unique sequences were assembled with the average length of 738 bp and N50 of 1131 bp. About 51.6 % of the transcriptome were functionally annotated based on the databases of Nr, Nt, Swiss-Prot, KEGG and COG. Then based on the transcriptome, the digital gene expression analysis was conducted to examine the transcriptional response to sulfide during 6, 24 and 48 h exposure, and finally 1705, 1181 and 1494 tag-mapped genes were identified as differentially expressed genes in the 6-h, 24-h and 48-h libraries, then were further subjected to pathway analyses.

Conclusions

In the DGE database of U. unicinctus, the alterations in certain known sulfide-related pathways indicate similar changes in response to sulfide. For more than 80 % of the identified pathway members, this is the first report on their association with sulfide stress, among which glycolysis pathway and PIDD involving pathways were unique and discussed in details, and were thought to play important roles in the sulfide tolerance of U. unicinctus. All the results are helpful to explain the mechanism of sulfide tolerance and detoxification.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2094-z) contains supplementary material, which is available to authorized users.

Light-dependent sulfide oxidation in the anoxic zone of the Chesapeake Bay can be explained by small populations of phototrophic bacteria

Microbial sulfide oxidation in aquatic environments is an important ecosystem process, as sulfide is potently toxic to aerobic organisms. Sulfide oxidation in anoxic waters can prevent the efflux of sulfide to aerobic water masses, thus mitigating toxicity. The contribution of phototrophic sulfide-oxidizing bacteria to anaerobic sulfide oxidation in the Chesapeake Bay and the redox chemistry of the stratified water column were investigated in the summers of 2011 to 2014. In 2011 and 2013, phototrophic sulfide-oxidizing bacteria closely related to Prosthecochloris species of the phylum Chlorobi were cultivated from waters sampled at and below the oxic-anoxic interface, where measured light penetration was sufficient to support populations of low-light-adapted photosynthetic bacteria. In 2012, 2013, and 2014, light-dependent sulfide loss was observed in freshly collected water column samples. In these samples, extremely low light levels caused 2- to 10-fold increases in the sulfide uptake rate over the sulfide uptake rate under dark conditions. An enrichment, CB11, dominated by Prosthecochloris species, oxidized sulfide with a Ks value of 11 μM and a Vmax value of 51 μM min(-1) (mg protein(-1)). Using these kinetic values with in situ sulfide concentrations and light fluxes, we calculated that a small population of Chlorobi similar to those in enrichment CB11 can account for the observed anaerobic light-dependent sulfide consumption activity in natural water samples. We conclude that Chlorobi play a far larger role in the Chesapeake Bay than currently appreciated. This result has potential implications for coastal anoxic waters and expanding oxygen-minimum zones as they begin to impinge on the photic zone.

Triggering apoptotic death of human epidermal keratinocytes by malic Acid: involvement of endoplasmic reticulum stress- and mitochondria-dependent signaling pathways

Malic acid (MA) has been commonly used in cosmetic products, but the safety reports in skin are sparse. To investigate the biological effects of MA in human skin keratinocytes, we investigated the potential cytotoxicity and apoptotic effects of MA in human keratinocyte cell lines (HaCaT). The data showed that MA induced apoptosis based on the observations of DAPI staining, DNA fragmentation, and sub-G1 phase in HaCaT cells and normal human epidermal keratinocytes (NHEKs). Flow cytometric assays also showed that MA increased the production of mitochondrial superoxide (mito-SOX) but decreased the mitochondrial membrane potential. Analysis of bioenergetics function with the XF 24 analyzer Seahorse extracellular flux analyzer demonstrated that oxygen consumption rate (OCR) was significantly decreased whereas extracellular acidification rate (ECAR) was increased in MA-treated keratinocytes. The occurrence of apoptosis was proved by the increased expressions of FasL, Fas, Bax, Bid, caspases-3, -8, -9, cytochrome c, and the declined expressions of Bcl-2, PARP. MA also induced endoplasmic reticulum stress associated protein expression such as GRP78, GADD153, and ATF6α. We demonstrated that MA had anti-proliferative effect in HaCaT cell through the inhibition of cell cycle progression at G0/G1, and the induction of programmed cell death through endoplasmic reticulum stress- and mitochondria-dependent pathways.

Characteristics and function of sulfur dioxygenase in Echiuran worm Urechis unicinctus

Background

Sulfide is a common toxin to animals and is abundant in coastal and aquatic sediments. Sulfur dioxygenase (SDO) is thought to be the key enzyme involved in sulfide oxidation in some organisms. The echiuran worm, Urechis unicinctus, inhabits coastal sediment and tolerates high concentrations of sulfide. The SDO is presumably important for sulfide tolerance in U. unicinctus.

Results

The full-length cDNA of SDO from the echiuran worm U. unicinctus, proven to be located in the mitochondria, was cloned and the analysis of its sequence suggests that it belongs to the metallo-β-lactamase superfamily. The enzyme was produced using an E. coli expression system and the measured activity is approximately 0.80 U mg protein⁻¹. Furthermore, the expression of four sub-segments of the U. unicinctus SDO was accomplished leading to preliminary identification of functional domains of the enzyme. The identification of the conserved metal I (H113, H115, H169 and D188), metal II (D117, H118, H169 and H229) as well as the potential glutathione (GSH) (R197, Y231, M279 and I283) binding sites was determined by enzyme activity and GSH affinity measurements. The key residues responsible for SDO activity were identified by analysis of simultaneous mutations of residues D117 and H118 located close to the metal II binding site.

Conclusion

The recombinant SDO from U. unicinctus was produced, purified and characterized. The metal binding sites in the SDO were identified and Y231 recognized as the mostly important amino acid residue for GSH binding. Our results show that SDO is located in the mitochondria where it plays an important role in sulfide detoxification of U. unicinctus.

Hydrogen sulfide-mediated myocardial pre- and post-conditioning

Coronary artery disease is a major cause of morbidity and mortality in the Western world. Acute myocardial infarction, resulting from coronary artery atherosclerosis, is a serious and often fatal consequence of coronary artery disease, resulting in cell death in the myocardium. Pre- and post-conditioning of the myocardium are two treatment strategies that reduce the amount of cell death significantly. Hydrogen sulfide has recently been identified as a potent cardioprotective signaling molecule, which is a highly effective pre- and post-conditioning agent. The cardioprotective signaling pathways involved in hydrogen sulfide-based pre- and post-conditioning will be explored in this article.

Screening of genes related to sulfide metabolism in Urechis unicinctus (Echiura, Urechidae) using suppression subtractive hybridization and cDNA microarray analysis

Exogenous sulfide can generally induce metabolic injuries in most organisms and even cause death. However, organisms inhabiting intertidal zones, hydrothermal vents, and cold seeps, can tolerate, metabolize, and utilize sulfide. In this study, both suppression subtractive hybridization and cDNA microarray analysis were employed to screen sulfide metabolism-related genes from the body wall in echiuran worm Urechis unicinctus, a marine sediment species. A total of 3456 monoclones were isolated and 82 were identified as differentially expressed genes in worms exposed to 50 μM sulfide for 24 h, compared to controls. The identified genes encoded proteins with multiple processes, including metabolism, cellular process, biological regulation, response to stimulus, multicellular organismal process, localization, development, and cellular component organization. Eight genes, serase, vacuolar protein, src tyrosine kinase, sulfide oxidase-like oxidoreductase, aprataxin, SN-RNP, aminopeptidase, and predicted protein, were selected to verify expression in the worm using qRT-PCR. The agreement of gene expression evaluation was 62.5% between the results of microarray analysis and qRT-PCR. These new data will provide clues for further probing of the molecular mechanism of sulfide metabolism.

Response of sulfide:quinone oxidoreductase to sulfide exposure in the echiuran worm Urechis unicinctus

Sulfide is a natural, widely distributed, poisonous substance, and sulfide:quinone oxidoreductase (SQR) is responsible for the initial oxidation of sulfide in mitochondria. In this study, we examined the response of SQR to sulfide exposure (25, 50, and 150 μM) at mRNA, protein, and enzyme activity levels in the body wall and hindgut of the echiuran worm Urechis unicinctus, a benthic organism living in marine sediments. The results revealed SQR mRNA expression during sulfide exposure in the body wall and hindgut increased in a time- and concentration-dependent manner that increased significantly at 12 h and continuously increased with time. At the protein level, SQR expression in the two tissues showed a time-dependent relationship that increased significantly at 12 h in 50 μM sulfide and 6 h in 150 μM, and then continued to increase with time while no significant increase appeared after 25 μM sulfide exposure. SQR enzyme activity in both tissues increased significantly in a time-dependent manner after 50 μM sulfide exposure. We concluded that SQR expression could be induced by sulfide exposure and that the two tissues studied have dissimilar sulfide metabolic patterns. A U. unicinctus sulfide-induced detoxification mechanism was also discussed.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

2',5'-Dihydroxychalcone-induced glutathione is mediated by oxidative stress and kinase signaling pathways

Hydroxychalcones are naturally occurring compounds that continue to attract considerable interest because of their anti-inflammatory and antiangiogenic properties. They have been reported to inhibit the synthesis of the inducible nitric oxide synthase and to induce the expression of heme oxygenase-1. This study examines the mechanisms by which 2',5'-dihydroxychalcone (2',5'-DHC) induces an increase in cellular glutathione (GSH) levels using a cell line stably expressing a luciferase reporter gene driven by antioxidant-response elements (MCF-7/AREc32). The 2',5'-DHC-induced increase in cellular GSH levels was partially inhibited by the catalytic antioxidant MnTDE-1,3-IP(5+), suggesting that reactive oxygen species (ROS) mediate the antioxidant adaptive response. 2',5'-DHC treatment induced phosphorylation of the c-Jun N-terminal kinase (JNK) pathway, which was also inhibited by MnTDE-1,3-IP(5+). These findings suggest a ROS-dependent activation of the AP-1 transcriptional response. However, whereas 2',5'-DHC triggered the NF-E2-related factor 2 (Nrf2) transcriptional response, cotreatment with MnTDE-1,3-IP(5+) did not decrease 2',5'-DHC-induced Nrf2/ARE activity, showing that this pathway is not dependent on ROS. Moreover, pharmacological inhibitors of mitogen-activated protein kinase (MAPK) pathways showed a role for JNK and p38MAPK in mediating the 2',5'-DHC-induced Nrf2 response. These findings suggest that the 2',5'-DHC-induced increase in GSH levels results from a combination of ROS-dependent and ROS-independent pathways.

Thermodynamics and kinetics of sulfide oxidation by oxygen: a look at inorganically controlled reactions and biologically mediated processes in the environment

The thermodynamics for the first electron transfer step for sulfide and oxygen indicates that the reaction is unfavorable as unstable superoxide and bisulfide radical ions would need to be produced. However, a two-electron transfer is favorable as stable S(0) and peroxide would be formed, but the partially filled orbitals in oxygen that accept electrons prevent rapid kinetics. Abiotic sulfide oxidation kinetics improve when reduced iron and/or manganese are oxidized by oxygen to form oxidized metals which in turn oxidize sulfide. Biological sulfur oxidation relies on enzymes that have evolved to overcome these kinetic constraints to affect rapid sulfide oxidation. Here we review the available thermodynamic and kinetic data for H(2)S and HS• as well as O(2), reactive oxygen species, nitrate, nitrite, and NO(x) species. We also present new kinetic data for abiotic sulfide oxidation with oxygen in trace metal clean solutions that constrain abiotic rates of sulfide oxidation in metal free solution and agree with the kinetic and thermodynamic calculations. Moreover, we present experimental data that give insight on rates of chemolithotrophic and photolithotrophic sulfide oxidation in the environment. We demonstrate that both anaerobic photolithotrophic and aerobic chemolithotrophic sulfide oxidation rates are three or more orders of magnitude higher than abiotic rates suggesting that in most environments biotic sulfide oxidation rates will far exceed abiotic rates due to the thermodynamic and kinetic constraints discussed in the first section of the paper. Such data reshape our thinking about the biotic and abiotic contributions to sulfide oxidation in the environment.

Sulfide:quinone oxidoreductase from echiuran worm Urechis unicinctus

Sulfide is a natural, widely distributed, poisonous substance, and sulfide:quinone oxidoreductase (SQR) has been identified to be responsible for the initial oxidation of sulfide in mitochondria. In this study, full-length SQR cDNA was cloned from the echiuran worm Urechis unicinctus, a benthic organism living in marine sediments. The protein consisted of 451 amino acids with a theoretical pI of 8.98 and molecular weight of 50.5 kDa. Subsequently, the SQR mRNA expression in different tissues was assessed by real-time reverse transcription and polymerase chain reaction and showed that the highest expression was in midgut, followed by anal sacs and coelomic fluid cells, and then body wall and hindgut. Furthermore, activated SQR was obtained by dilution refolding of recombinant SQR expression in E. coli, and the refolded product showed optimal activity at 37 °C and pH 8.5 and K (m) for ubiquinone and sulfide at 15.6 µM and 40.3 µM, respectively. EDTA and GSH had an activating effect on refolded SQR, while Zn(2+) caused decreased activity. Western blot showed that SQR in vivo was located in mitochondria and was ∼ 10 kDa heavier than the recombinant protein. In addition, SQR, detected by immunohistochemistry, was mainly located in the epithelium of all tissues examined. Ultrastructural observations of these tissues' epithelium by transmission electron microscopy provided indirect cytological evidence for its mitochondrial location. Interesting aspects of the U. unicinctus SQR amino acid sequence, its catalytic mechanism, and the different roles of these tissues in sulfide metabolic adaptation are also discussed.

Development of hydrogen sulfide-based therapeutics for cardiovascular disease

The physiological role of the gaseous signaling molecule hydrogen sulfide (H(2)S) was first realized in the mid-1990s with the work of Abe and Kimura. Since then, it has become evident that this endogenous gas is extremely important in the homeostasis of the cardiovascular system and the pathogenesis of cardiovascular disease. Several biotechnology companies have developed and are developing H(2)S-based therapeutic compounds, and there are ongoing clinical trials investigating the therapeutic potential of H(2)S. Several organic and chemical compounds that are known H(2)S donors have the potential to be developed into effective H(2)S-based therapeutic agents. This review will provide a historical and current perspective on the role(s) of H(2)S in the cardiovascular system and the current state of development and future outlook of H(2)S-based therapies for cardiovascular disease.

Hydrogen sulfide induces oxidative damage to RNA and DNA in a sulfide-tolerant marine invertebrate

Hydrogen sulfide acts as an environmental toxin across a range of concentrations and as a cellular signaling molecule at very low concentrations. Despite its toxicity, many animals, including the mudflat polychaete Glycera dibranchiata, are periodically or continuously exposed to sulfide in their environment. We tested the hypothesis that a broad range of ecologically relevant sulfide concentrations induces oxidative stress and oxidative damage to RNA and DNA in G. dibranchiata. Coelomocytes exposed in vitro to sulfide (0-3 mmol L(-1) for 1 h) showed dose-dependent increases in oxidative stress (as 2',7'-dichlorofluorescein fluorescence) and superoxide production (as dihydroethidine fluorescence). Coelomocytes exposed in vitro to sulfide (up to 0.73 mmol L(-1) for 2 h) also acquired increased oxidative damage to RNA (detected as 8-oxo-7,8-dihydroguanosine) and DNA (detected as 8-oxo-7,8-dihydro-2'-deoxyguanosine). Worms exposed in vivo to sulfide (0-10 mmol L(-1) for 24 h) acquired elevated oxidative damage to RNA and DNA in both coelomocytes and body wall tissue. While the consequences of RNA and DNA oxidative damage are poorly understood, oxidatively damaged deoxyguanosine bases preferentially bind thymine, causing G-T transversions and potentially causing heritable point mutations. This suggests that sulfide can be an environmental mutagen in sulfide-tolerant invertebrates.

The relevance of oxidative stress and cytotoxic DNA lesions for spontaneous mutagenesis in non-replicating yeast cells

Mutations arising during times of cell cycle-arrest may considerably contribute to aging and cancerogenesis. Endogenous oxidative stress could be one of the major triggers for these mutations. We used Saccharomyces cerevisiae cells, arrested by starvation for the essential amino acid lysine, to study the occurrence of reactive oxygen species (ROS), abasic (AP) sites and double strand breaks (DSBs). Furthermore, we analyzed the mutation frequencies in resting wild type cells and in cells deficient for Apn1 (with an impaired base excision repair) or Dnl4 (with an inactivated non-homologous end joining (NHEJ) DSB repair pathway) by monitoring reversions of an auxotrophy-causing frameshift in the LYS2 gene. By fluorescence methods, we observed a distinct increase of ROS-affected cells in the course of starvation-induced cell cycle-arrest. In addition, we could reveal that AP sites and DSBs accumulated under these conditions. The frequency of spontaneous frameshift mutations in wild type cells was decreased to 50% upon addition of 6mM N-acetyl cysteine. However, this radical scavenger had no effect in Dnl4-deficient cells. Our results support the hypothesis that (via an active NHEJ DSB repair pathway) the incidence of spontaneous frameshift mutations in a cell cycle-arrested state is considerably governed by oxidative stress.

Casiopeína IIgly-induced oxidative stress and mitochondrial dysfunction in human lung cancer A549 and H157 cells

Casiopeínas are a series of mixed chelate copper complexes that are being evaluated as anticancer agents. Their effects in the cell include oxidative damage and mitochondrial dysfunction, yet the molecular mechanisms leading to such effects remain unclear. We tested whether [Cu(4,7-dimethyl-phenanthroline)(glycinate)]NO(3) (Casiopeína IIgly or Cas IIgly) could alter cellular glutathione (GSH) levels by redox cycling with GSH to generate ROS and cellular oxidative stress. Cas IIgly induced a dramatic drop in intracellular levels of GSH in human lung cancer H157 and A549 cells, and is able to use GSH as source of electrons to catalyze the Fenton reaction. In both cell lines, the toxicity of Cas IIgly (2.5-5 microM) was potentiated by the GSH synthesis inhibitor l-buthionine sulfoximine (BSO) and diminished by the catalytic antioxidant manganese(III) meso-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin (MnTDE-1,3-IP(5+)), thus supporting an important role for oxidative stress. Cas IIgly also caused an over-production of reactive oxygen species (ROS) in the mitochondria and a depolarization of the mitochondrial membrane. Moreover, Cas IIgly produced mitochondrial DNA damage that resulted in an imbalance of the expression of the apoproteins of the mitochondrial respiratory chain, which also can contribute to increased ROS production. These results suggest that Cas IIgly initiates multiple possible sources of ROS over-production leading to mitochondrial dysfunction and cell death.

Hypotaurine and sulfhydryl-containing antioxidants reduce H2S toxicity in erythrocytes from a marine invertebrate

Hypotaurine (HT) has been proposed to reduce sulfide toxicity in some deep-sea invertebrates by scavenging free radicals produced from sulfide oxidation or by scavenging sulfide via the reaction of HT with sulfide, forming thiotaurine (ThT). We tested whether HT or several antioxidants could reduce the total dissolved sulfide concentration in buffered seawater exposed to H2S, and whether HT, ThT or antioxidants could increase the viability of Glycera dibranchiataerythrocytes exposed to H2S in vitro. We found that 5 and 50 mmol l–1 HT reduced the dissolved sulfide in cell-free buffer exposed to H2S by up to 80% whereas the antioxidants glutathione ethyl ester (GEE), N-acetylcysteine (NAC), l-ascorbic acid (ASC), Tempol and Trolox had no consistent effect. Exposure of erythrocytes to 0.10%–3.2% H2S (producing 0.18–4.8 mmol l–1 sulfide) decreased the fraction of viable cells, as evidenced by loss of plasma membrane integrity, with virtually no cells remaining viable at 1.0% or more H2S. Addition of HT (0.5–50 mmol l–1) significantly increased the fraction of viable cells (e.g. from 0.01 to 0.84 at 0.32% H2S) whereas ThT (0.5 and 5 mmol l–1) decreased cell viability. GEE (0.03–3 mmol l–1) and NAC (0.001–1 mmol l–1), which contain sulfhydryl groups, increased cell viability during H2S exposure but to a lesser extent than HT whereas ASC, Tempol and Trolox, which do not contain sulfhydryl groups, decreased viability or had no effect. These data show that HT can protect cells from sulfide in vitro and suggest that sulfide scavenging, rather than free radical scavenging, is the most important mechanism of protection.

Analysis of calcium ion homeostasis and mitochondrial function in cerebellar granule cells of adult CaV 2.1 calcium ion channel mutant mice

CaV 2.1 voltage-gated calcium channels (VGCC) are highly expressed by cerebellar neurons, and their dysfunction is linked to human disorders including familial hemiplegic migraine, episodic ataxia type 2 and spinocerebellar ataxia type 6. Altered calcium homeostasis, due to dysfunctional Ca(V 2.1 VGCC can severely affect mitochondrial function, eventually leading to neuronal cell death. We study leaner and tottering mice, which carry autosomal recessive mutations in the gene coding for the alpha 1A pore-forming subunit of CaV 2.1 VGCC. Both leaner and tottering mice exhibit cerebellar ataxia and epilepsy. Excessive leaner cerebellar granule cell (CGC) death starts soon after postnatal day 10, but it is not known whether the degree of CGC cell death observed in adult leaner mice is significantly different from wild type mice. We used Fluoro-Jade and TUNEL staining to quantify apoptotic cell death in leaner and wild type CGC. We investigated calcium homeostasis, mitochondrial function and generation of reactive oxygen species (ROS) in isolated CGC, using indicator dyes Fura-2AM, TMRM and CMH2DCFDA, respectively. We observed a small but significant increase in number of apoptotic adult leaner CGC. Calcium homeostasis and mitochondrial function also were altered in leaner CGC. However, no significant differences in ROS levels were observed. It is possible that CGC death in leaner mice may be related to mitochondrial dysfunction but may not be directly related to decreased basal intracellular calcium.

Nitric oxide and mitochondrial status in noise-induced hearing loss

The study investigated the distribution of nitric oxide (NO) within isolated outer hair cells (OHCs) from the cochlea, its relationship to mitochondria and its modulation of mitochondrial function. Using two fluorescent dyes--4,5-diamino-fluorescein diacetate (DAF-2DA), which detects NO, and tetramethyl rhodamine methyl ester (TMRM+), a mitochondrial membrane potential dye--it was found that a relatively greater amount of the DAF fluorescence in OHCs co-localized with mitochondria in comparison to DAF fluorescence in the cytosole. This study also observed reduced mitochondrial membrane potential of OHCs and increased DAF fluorescence following exposure of the cells to noise (120 dB SPL for 4 h) and to an exogenous NO donor, NOC-7 (>350 mm). Antibody label for nitrotyrosine was also increased, indicating NO-related formation of peroxynitrite in both mitochondria and the cytosol. The results suggest that NO may play an important physiological role in regulating OHC energy status and act as a potential agent in OHC pathology.

Single-walled carbon nanotube interactions with HeLa cells

This work concerns exposing cultured human epithelial-like HeLa cells to single-walled carbon nanotubes (SWNTs) dispersed in cell culture media supplemented with serum. First, the as-received CoMoCAT SWNT-containing powder was characterized using scanning electron microscopy and thermal gravimetric analyses. Characterizations of the purified dispersions, termed DM-SWNTs, involved atomic force microscopy, inductively coupled plasma - mass spectrometry, and absorption and Raman spectroscopies. Confocal microRaman spectroscopy was used to demonstrate that DM-SWNTs were taken up by HeLa cells in a time- and temperature-dependent fashion. Transmission electron microscopy revealed SWNT-like material in intracellular vacuoles. The morphologies and growth rates of HeLa cells exposed to DM-SWNTs were statistically similar to control cells over the course of 4 d. Finally, flow cytometry was used to show that the fluorescence from MitoSOXtrade mark Red, a selective indicator of superoxide in mitochondria, was statistically similar in both control cells and cells incubated in DM-SWNTs. The combined results indicate that under our sample preparation protocols and assay conditions, CoMoCAT DM-SWNT dispersions are not inherently cytotoxic to HeLa cells. We conclude with recommendations for improving the accuracy and comparability of carbon nanotube (CNT) cytotoxicity reports.

Identification of proteins involved in the functioning of Riftia pachyptila symbiosis by Subtractive Suppression Hybridization

Background

Since its discovery around deep sea hydrothermal vents of the Galapagos Rift about 30 years ago, the chemoautotrophic symbiosis between the vestimentiferan tubeworm Riftia pachyptila and its symbiotic sulfide-oxidizing γ-proteobacteria has been extensively studied. However, studies on the tubeworm host were essentially targeted, biochemical approaches. We decided to use a global molecular approach to identify new proteins involved in metabolite exchanges and assimilation by the host. We used a Subtractive Suppression Hybridization approach (SSH) in an unusual way, by comparing pairs of tissues from a single individual. We chose to identify the sequences preferentially expressed in the branchial plume tissue (the only organ in contact with the sea water) and in the trophosome (the organ housing the symbiotic bacteria) using the body wall as a reference tissue because it is supposedly not involved in metabolite exchanges in this species.

Results

We produced four cDNA libraries: i) body wall-subtracted branchial plume library (BR-BW), ii) and its reverse library, branchial plume-subtracted body wall library (BW-BR), iii) body wall-subtracted trophosome library (TR-BW), iv) and its reverse library, trophosome-subtracted body wall library (BW-TR). For each library, we sequenced about 200 clones resulting in 45 different sequences on average in each library (58 and 59 cDNAs for BR-BW and TR-BW libraries respectively). Overall, half of the contigs matched records found in the databases with good E-values. After quantitative PCR analysis, it resulted that 16S, Major Vault Protein, carbonic anhydrase (RpCAbr), cathepsin and chitinase precursor transcripts were highly represented in the branchial plume tissue compared to the trophosome and the body wall tissues, whereas carbonic anhydrase (RpCAtr), myohemerythrin, a putative T-Cell receptor and one non identified transcript were highly specific of the trophosome tissue.

Conclusion

Quantitative PCR analyses were congruent with our libraries results thereby confirming the existence of tissue-specific transcripts identified by SSH. We focused our study on the transcripts we identified as the most interesting ones based on the BLAST results. Some of the keys to understanding metabolite exchanges may remain in the sequences we could not identify (hypothetical proteins and no similarity found). These sequences will have to be better studied by a longer -or complete- sequencing to check their identity, and then by verifying the expression level of the transcripts in different parts of the worm.

Hydrogen sulfide induces direct radical-associated DNA damage

Hydrogen sulfide (H(2)S) is produced by indigenous sulfate-reducing bacteria in the large intestine and represents an environmental insult to the colonic epithelium. Clinical studies have linked the presence of either sulfate-reducing bacteria or H(2)S in the colon with chronic disorders such as ulcerative colitis and colorectal cancer, although at this point, the evidence is circumstantial and underlying mechanisms remain undefined. We showed previously that sulfide at concentrations similar to those found in the human colon induced genomic DNA damage in mammalian cells. The present study addressed the nature of the DNA damage by determining if sulfide is directly genotoxic or if genotoxicity requires cellular metabolism. We also questioned if sulfide genotoxicity is mediated by free radicals and if DNA base oxidation is involved. Naked nuclei from untreated Chinese hamster ovary cells were treated with sulfide; DNA damage was induced by concentrations as low as 1 micromol/L. This damage was effectively quenched by cotreatment with butylhydroxyanisole. Furthermore, sulfide treatment increased the number of oxidized bases recognized by formamidopyrimidine [fapy]-DNA glycosylase. These results confirm the genotoxicity of sulfide and strongly implicate that this genotoxicity is mediated by free radicals. These observations highlight the possible role of sulfide as an environmental insult that, given a predisposing genetic background, may lead to genomic instability or the cumulative mutations characteristic of colorectal cancer.

Hepatitis C virus core protein increases mitochondrial ROS production by stimulation of Ca2+ uniporter activity

Many viruses have evolved mechanisms to alter mitochondrial function. The hepatitis C virus (HCV) produces a viral core protein that targets to mitochondria and increases Ca2+-dependent ROS production. The aim of this study was to determine whether core's effects are mediated by changes in mitochondrial Ca2+ uptake. Core expression caused enhanced mitochondrial Ca2+ uptake in response to ER Ca2+ release induced by thapsigargin or ATP. It also increased mitochondrial superoxide production and mitochondrial permeability transition (MPT). Incubating mouse liver mitochondria with an HCV core (100 ng/mg) in vitro increased Ca2+ entry rate by approximately 2-fold. Entry was entirely inhibited by the mitochondrial Ca2+ uniporter inhibitor, Ru-360, but not influenced by an Na+/Ca2+ exchanger inhibitor or ROS scavengers. These results indicate that core directly increases mitochondrial Ca2+ uptake via a primary effect on the uniporter. This enhanced the ability of mitochondria to sequester Ca2+ in response to ER Ca2+ release, and increased mitochondrial ROS production and MPT. Thus, the mitochondrial Ca2+ uniporter is a newly identified target for viral modification of cell function.

Increased expression of stress proteins in the surf clam Donax variabilis following hydrogen sulfide exposure

Endogenous free radical production and resulting oxidative damage may result from exposure to hypoxia, hyperoxia, or hydrogen sulfide. Previous investigations of sulfide-induced oxidative damage have produced conflicting results, perhaps because these studies utilized species presumably adapted to sulfide. We examined the effects of sulfide, hypoxia and hyperoxia on the surf clam Donax variabilis to test whether these stressors induce a cellular response to oxidative stress. These clams inhabit high-energy sandy beaches and are unlikely to have specific adaptations to these stressors. In duplicate flow-through experiments performed in fall and spring, clams were exposed to normoxia (22 kPa P(O(2))), hypoxia (10 kPa), hyperoxia (37 kPa), or sulfide with normoxia ( approximately 100 mumol L(-1), 22 kPa respectively) for 24 h. We quantified whole-animal expression of three antioxidants (Cu/Zn and Mn superoxide dismutases, glutathione peroxidase), a lipid peroxidation marker (4-hydroxy-2E-nonenol-adducted protein), a DNA repair enzyme (OGG1-m), four heat shock proteins (small Hsp, Hsp60, Hsp70, and mitochondrial Hsp70), ubiquitin, and actin. Clams exposed to sulfide showed upregulation of the greatest number of stress proteins and the pattern was consistent with a cellular response to oxidative stress. Furthermore, there was a marked seasonality, with greater stress protein expression in clams from the spring.

Comparison of the abilities of ambient and manufactured nanoparticles to induce cellular toxicity according to an oxidative stress paradigm

Nanomaterial properties differ from those bulk materials of the same composition, allowing them to execute novel activities. A possible downside of these capabilities is harmful interactions with biological systems, with the potential to generate toxicity. An approach to assess the safety of nanomaterials is urgently required. We compared the cellular effects of ambient ultrafine particles with manufactured titanium dioxide (TiO2), carbon black, fullerol, and polystyrene (PS) nanoparticles (NPs). The study was conducted in a phagocytic cell line (RAW 264.7) that is representative of a lung target for NPs. Physicochemical characterization of the NPs showed a dramatic change in their state of aggregation, dispersibility, and charge during transfer from a buffered aqueous solution to cell culture medium. Particles differed with respect to cellular uptake, subcellular localization, and ability to catalyze the production of reactive oxygen species (ROS) under biotic and abiotic conditions. Spontaneous ROS production was compared by using an ROS quencher (furfuryl alcohol) as well as an NADPH peroxidase bioelectrode platform. Among the particles tested, ambient ultrafine particles (UFPs) and cationic PS nanospheres were capable of inducing cellular ROS production, GSH depletion, and toxic oxidative stress. This toxicity involves mitochondrial injury through increased calcium uptake and structural organellar damage. Although active under abiotic conditions, TiO2 and fullerol did not induce toxic oxidative stress. While increased TNF-alpha production could be seen to accompany UFP-induced oxidant injury, cationic PS nanospheres induced mitochondrial damage and cell death without inflammation. In summary, we demonstrate that ROS generation and oxidative stress are a valid test paradigm to compare NP toxicity. Although not all materials have electronic configurations or surface properties to allow spontaneous ROS generation, particle interactions with cellular components are capable of generating oxidative stress.

Mitochondrial oxidative stress in the lungs of cystic fibrosis transmembrane conductance regulator protein mutant mice

Cystic fibrosis is a fatal genetic disorder involving dysfunction of the cystic fibrosis transmembrane regulator protein (CFTR) resulting in progressive respiratory failure. Previous studies indicate that CFTR regulates cellular glutathione (GSH) transport and that dysfunctional CFTR is associated with chronic pulmonary oxidative stress. The cause and the source of this oxidative stress remain unknown. The current study examines the role of the mitochondria in CFTR-mediated pulmonary oxidative stress. Mitochondrial GSH levels and markers of DNA and protein oxidation were assessed in the lung mitochondria from CFTR-knockout mice. In addition, in vitro models using human CFTR-sufficient and -deficient lung epithelial cells were also employed. Mitochondrial GSH levels were found to be decreased up to 85% in CFTR-knockout mice, and 43% in human lung epithelial cells deficient in CFTR. A concomitant 29% increase in the oxidation of mitochondrial DNA, and a 30% loss of aconitase activity confirmed the existence of a mitochondrial oxidative stress. Flow cytometry revealed significantly elevated levels of cellular reactive oxygen species (ROS) in CFTR-deficient human lung cells. These studies suggest that dysfunctional CFTR leads to an increase in the level of ROS and mitochondrial oxidative stress. This oxidative stress, however, appears to be a consequence of lower mitochondrial GSH levels and not increased oxidation of GSH. Further studies are needed to determine how CFTR deficiency contributes to mitochondrial oxidative stress and the role this plays in CFTR-mediated lung pathophysiology.