Photocatalytic H2 Evolution Using Different Commercial TiO2 Catalysts Deposited with Finely Size-Tailored Au Nanoparticles: Critical Dependence on Au Particle Size

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO₂ photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO₂ surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO₂ composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H₂ production activities of the samples were studied in aqueous TiO₂ suspensions irradiated with near-UV light in the absence of dissolved O₂, with oxalic acid or methanol as the sacrificial agent. The H₂ evolution rates proved to be strongly dependent on Au particle size: the highest H₂ production rate was achieved when the Au particles measured ~6 nm.     

Photocatalytic H2 Production Using Pt-TiO2 in the Presence of Oxalic Acid: Influence of the Noble Metal Size and the Carrier Gas Flow Rate

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO₂ photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO₂ surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH₄. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λ_max = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H₂ evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H₂ formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H⁺/H₂ redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H₂ gas in the reaction mixture.     

Hydrogen is a preferred intermediate in the energy-conserving electron transport chain of Methanosarcina barkeri

Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F₄₂₀H₂ dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However, Methanosarcina barkeri Δfpo mutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Δfrh mutants lacking the cytoplasmic F₄₂₀-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Δfpo/Δfrh mutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless, M. barkeri does have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Δfrh mutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth of M. barkeri.     

Essential anaplerotic role for the energy-converting hydrogenase Eha in hydrogenotrophic methanogenesis

Despite decades of study, electron flow and energy conservation in methanogenic Archaea are still not thoroughly understood. For methanogens without cytochromes, flavin-based electron bifurcation has been proposed as an essential energy-conserving mechanism that couples exergonic and endergonic reactions of methanogenesis. However, an alternative hypothesis posits that the energy-converting hydrogenase Eha provides a chemiosmosis-driven electron input to the endergonic reaction. In vivo evidence for both hypotheses is incomplete. By genetically eliminating all nonessential pathways of H(2) metabolism in the model methanogen Methanococcus maripaludis and using formate as an additional electron donor, we isolate electron flow for methanogenesis from flux through Eha. We find that Eha does not function stoichiometrically for methanogenesis, implying that electron bifurcation must operate in vivo. We show that Eha is nevertheless essential, and a substoichiometric requirement for H(2) suggests that its role is anaplerotic. Indeed, H(2) via Eha stimulates methanogenesis from formate when intermediates are not otherwise replenished. These results fit the model for electron bifurcation, which renders the methanogenic pathway cyclic, and as such requires the replenishment of intermediates. Defining a role for Eha and verifying electron bifurcation provide a complete model of methanogenesis where all necessary electron inputs are accounted for.     

The Corrosion Behavior of Pure Iron under Solid Na2SO4 Deposit in Wet Oxygen Flow at 500 °C

The corrosion behavior of pure Fe under a Na₂SO₄ deposit in an atmosphere of O₂ + H₂O was investigated at 500 °C by thermo gravimetric, and electrochemical measurements, viz. potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and surface characterization methods viz. X-ray diffraction (XRD), and scanning electron microscope (SEM)/energy dispersive spectroscopy(EDS). The results showed that a synergistic effect occurred between Na₂SO₄ and O₂ + H₂O, which significantly accelerated the corrosion rate of the pure Fe. Briefly, NaFeO₂ was formed in addition to the customary Fe oxides; at the same time, H₂SO₄ gas was produced by introduction of water vapor. Subsequently, an electrochemical corrosion reaction occurred due to the existence of Na₂SO₄, NaFeO₂, and H₂O. When this coupled to the chemical corrosion reaction, the progress of the chemical corrosion reaction was promoted and eventually resulted in the acceleration of the corrosion of the pure Fe.     

Structural and dynamic aspects related to oligomerization of apo SOD1 and its mutants

The structural and dynamical properties of the metal-free form of WT human superoxide dismutase 1 (SOD1) and its familial amyotrophic lateral sclerosis (fALS)-related mutants, T54R and I113T, were characterized both in solution, through NMR, and in the crystal, through X-ray diffraction. We found that all 3 X-ray structures show significant structural disorder in 2 loop regions that are, at variance, well defined in the fully-metalated structures. Interestingly, the apo state crystallizes only at low temperatures, whereas all 3 proteins in the metalated form crystallize at any temperature, suggesting that crystallization selects one of the most stable conformations among the manifold adopted by the apo form in solution. Indeed, NMR experiments show that the protein in solution is highly disordered, sampling a large range of conformations. The large conformational variability of the apo state allows the free reduced cysteine Cys-6 to become highly solvent accessible in solution, whereas it is essentially buried in the metalated state and the crystal structures. Such solvent accessibility, together with that of Cys-111, accounts for the tendency to oligomerization of the metal-free state. The present results suggest that the investigation of the solution state coupled with that of the crystal state can provide major insights into SOD1 pathway toward oligomerization in relation to fALS.     

Long-Lasting Binding of IT-066 to Human Histamine H2 Receptor

Based on animal models, IT-066, a histamine H₂-receptor antagonist, is reported to possess potent and long-lasting antagonisms on histamine H₂ receptor (H₂R) -mediated effects. However, no reports have been published concerning its interaction with the human H₂R. The aim of this study is to characterize its interaction with human H₂R. Chinese hamster ovary cell lines stably expressing human H₂Rs were obtained. The effects of IT-066, famotidine, and ranitidine on tiotidine binding and histamine-stimulated cAMP production were analyzed. IT-066 inhibited [³H]tiotidine binding and histamine-stimulated cAMP production more potently than famotidine or ranitidine. In addition, preincubation with 10^–5 M IT-066, but not with 10^–5 M famotidine or 10^–4 M ranitidine, had marked inhibitory effects long after extensive washing. Paraformaldehyde fixation of the cells blunted inhibition of [³H]tiotidine binding induced by preincubation with IT-066, but not that by preincubation with famotidine or ranitidine. IT-066 has potent and long-lasting antagonisms on human H₂R. At least one of the IT-066 binding sites is not shared by famotidine, ranitidine, or tiotidine and is affected by paraformaldehyde fixation.     

Inhibition of apoptosis in acute promyelocytic leukemia cells leads to increases in levels of oxidized protein and LMP2 immunoproteasome

On reaching maturity, animal organs cease to increase in size because of inhibition of cell replication activities. It follows that maintenance of optimal organ function depends on the elimination of oxidatively damaged cells and their replacement with new cells. To examine the effects of oxidative stress and apoptosis on the accumulation of oxidized proteins, we exposed acute promyelocytic leukemia cells to arsenic trioxide (As(2)O(3)) in the presence and absence of a general caspase inhibitor (benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone), which is known to inhibit caspase-induced apoptosis. We confirm that treatment of cells with As(2)O(3) induces apoptosis and leads to the accumulation of oxidized proteins. Furthermore, inhibition of caspase activities prevented As(2)O(3)-induced apoptosis and led to a substantial increase in accumulation of oxidized proteins. Moreover, inhibition of caspase activity in the absence of As(2)O(3) led to elevated levels of the LMP2 immunoproteasome protein. We also show that caspase inhibition leads to increases in the levels of oxidized proteins obtained by treatments with hydrogen peroxide plus ferrous iron. Collectively, these results suggest the possibility that an age-related loss in capacity to carry out apoptosis might contribute to the observed accumulation of oxidized proteins during aging and in age-related diseases.     

The hydrogen sulfide signaling system: changes during aging and the benefits of caloric restriction

Hydrogen sulfide gas (H₂S) is a putative signaling molecule that causes diverse effects in mammalian tissues including relaxation of blood vessels and regulation of perfusion in the liver, but the effects of aging on H₂S signaling are unknown. Aging has negative impacts on the cardiovascular system. However, the liver is more resilient with age. Caloric restriction (CR) attenuates affects of age in many tissues. We hypothesized that the H₂S signaling system is negatively affected by age in the vasculature but not in the liver, which is typically more resilient to age, and that a CR diet minimizes the age affect in the vasculature. To investigate this, we determined protein and mRNA expression of the H₂S-producing enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), H₂S production rates in the aorta and liver, and the contractile response of aortic rings to exogenous H₂S. Tissue was collected from Fisher 344 × Brown Norway rats from 8–38 months of age, which had been maintained on an ad libitum (AL) or CR diet. The results demonstrate that age and diet have differential effects on the H₂S signaling system in aorta and liver. The aorta showed a sizeable effect of both age and diet, whereas the liver only showed a sizeable effect of diet. Aortic rings showed increased contractile sensitivity to H₂S and increased protein expression of CSE and CBS with age, consistent with a decrease in H₂S concentration with age. CR appears to benefit CSE and CBS protein in both aorta and liver, potentially by reducing oxidative stress and ameliorating the negative effect of age on H₂S concentration. Therefore, CR may help maintain the H₂S signaling system during aging.     

Respiration triggers heme transfer from cytochrome c peroxidase to catalase in yeast mitochondria

In exponentially growing yeast, the heme enzyme, cytochrome c peroxidase (Ccp1) is targeted to the mitochondrial intermembrane space. When the fermentable source (glucose) is depleted, cells switch to respiration and mitochondrial H₂O₂ levels rise. It has long been assumed that CCP activity detoxifies mitochondrial H₂O₂ because of the efficiency of this activity in vitro. However, we find that a large pool of Ccp1 exits the mitochondria of respiring cells. We detect no extramitochondrial CCP activity because Ccp1 crosses the outer mitochondrial membrane as the heme-free protein. In parallel with apoCcp1 export, cells exhibit increased activity of catalase A (Cta1), the mitochondrial and peroxisomal catalase isoform in yeast. This identifies Cta1 as a likely recipient of Ccp1 heme, which is supported by low Cta1 activity in ccp1Δ cells and the accumulation of holoCcp1 in cta1Δ mitochondria. We hypothesized that Ccp1’s heme is labilized by hyperoxidation of the protein during the burst in H₂O₂ production as cells begin to respire. To test this hypothesis, recombinant Ccp1 was hyperoxidized with excess H₂O₂ in vitro, which accelerated heme transfer to apomyoglobin added as a surrogate heme acceptor. Furthermore, the proximal heme Fe ligand, His175, was found to be ∼85% oxidized to oxo-histidine in extramitochondrial Ccp1 isolated from 7-d cells, indicating that heme labilization results from oxidation of this ligand. We conclude that Ccp1 responds to respiration-derived H₂O₂ via a previously unidentified mechanism involving H₂O₂-activated heme transfer to apoCta1. Subsequently, the catalase activity of Cta1, not CCP activity, contributes to mitochondrial H₂O₂ detoxification.Cytochrome c peroxidase (Ccp1) is a monomeric nuclear encoded protein with a 68-residue N-terminal mitochondrial targeting sequence (1). This presequence crosses the inner mitochondrial membrane and is cleaved by matrix proteases (2, 3). Mature heme-loaded Ccp1 is found in the mitochondrial intermembrane space (IMS) in exponentially growing yeast (2, 3) but the point of insertion of its single b-type heme is unknown. Under strict anaerobic conditions, Ccp1 is present in mitochondria as the heme-free form or apoform (4). Once cells are exposed to O₂ and heme biosynthesis is turned on, apoCcp1 converts rapidly to the mature holoenzyme by noncovalently binding heme (5).It is well established that mature Ccp1 functions as an efficient H₂O₂ scavenger in vitro (6). Its catalytic cycle involves the reaction of ferric Ccp1 with H₂O₂ (Eq. 1) to form compound I (CpdI) with a ferryl (Fe^IV) heme and a cationic indole radical localized on Trp191 (W191^+•). CpdI is one-electron reduced by the ferrous heme of cytochrome c (Cyc1) to compound II (CpdII) with ferryl heme (Eq. 2), and electron donation by a second ferrous Cyc1 returns CpdII to the resting Ccp1^III form (Eq. 3):Ccp1^III + H₂O₂ → CpdI(Fe^IV, W191^+?) + H₂O[1]CpdI(Fe^IV, W191^+?) + Cyc1^II → CpdII(Fe^IV) + Cyc1^III[2]CpdII(Fe^IV) + Cyc1^II → Ccp1^III + Cyc1^III + H₂O.[3]Because Ccp1 production is not under O₂/heme control (4, 5), CCP activity is assumed to be the frontline defense in the mitochondria, a major source of reactive oxygen species (ROS) in respiring cells (7). Contrary to the time-honored assumption that Ccp1 catalytically consumes the H₂O₂ produced during aerobic respiration (8), recent studies in our group reveal that the peroxidase behaves more like a mitochondrial H₂O₂ sensor than a catalytic H₂O₂ detoxifier (9–11). Notably, Ccp1 competes with complex IV for reducing equivalents from Cyc1, which shuttles electrons from complex III (ubiquinol cytochrome c reductase) to complex IV (cytochrome c oxidase) in the electron transport chain (12).Because CCP activity in the IMS siphons electrons from energy production, an H₂O₂ sensor role for Ccp1 should be energetically more favorable for the cell. Key evidence for a noncatalytic role for Ccp1 in H₂O₂ removal is that the isogenic strain producing the catalytically inactive Ccp1^W191F protein accumulates less H₂O₂ than wild-type cells (10). In fact, this mutant strain exhibits approximately threefold higher catalase A (Cta1) activity than wild-type cells (10) whereas CCP1 deletion results in a strain (ccp1Δ) with negligible Cta1 activity and high H₂O₂ levels (5). Unlike Cta1, which is the peroxisomal and mitochondrial catalase isoform in yeast (13), the cytosolic catalase Ctt1 (14) exhibits comparable activity in the wild-type, Ccp1^W191F, and ccp1Δ strains (10). Given that both Ccp1 and Cta1 are targeted to mitochondria, we hypothesized that Ccp1 may transfer its heme to apoCta1 in respiring cells.Cta1 is nuclear encoded with embedded mitochondrial and peroxisomal targeting sequences (15). Like Ccp1, each monomer noncovalently binds a b-type heme and mature Cta1 is active as a homotetramer. Synthesis of the Cta1 monomer is under O₂/heme control such that the apoenzyme begins to accumulate only during the logarithmic phase of aerobic growth (16). Hence, its O₂/heme independent production (4, 5) allows apoCcp1 to acquire heme while cells are synthesizing apoCta1. This, combined with our observation that Cta1 activity increases in respiring cells producing Ccp1 or Ccp1^W191F but not in ccp1Δ cells (10), led us to speculate that respiration-derived H₂O₂ triggers heme donation from Ccp1 to apoCta1 within mitochondria.What experimental evidence would support heme donation by Ccp1? It has been demonstrated that mutation of the proximal heme Fe ligand, His175, to a residue with weak or no Fe-coordinating ability produces Ccp1 variants (H175P, H175L, H175R, and H175M) that undergo mitochondrial processing but do not accumulate in isolated yeast mitochondria (17). Presumably, reduced heme affinity allows the Ccp1 variants to unfold and cross the outer mitochondrial membrane (17). Hence, we argued that if wild-type Ccp1 donated its heme, the apoprotein would likewise exit mitochondria. Consequently, we examine here age-dependent Ccp1–green fluorescent protein (Ccp1-GFP) localization in live cells chromosomally expressing Ccp1 C-terminally fused to GFP as well as the distribution of wild-type Ccp1 between subcellular fractions. Because weakening or removal of the proximal Fe ligand on His175 mutation reduces heme affinity (17), His175 oxidation in wild-type Ccp1 should have a similar effect, which we investigate here. We further speculated that in the absence of apoCta1 as an acceptor for its heme, more Ccp1 would remain trapped in the IMS so we compare mitochondrial Ccp1 levels in wild-type and cta1∆ cells. Our combined results support triggering of heme donation from Ccp1 to apoCta1 by respiration-derived H₂O₂. Such H₂O₂-activated heme transfer between proteins has not been reported to date and its implications in H₂O₂ signaling are discussed.     

Hydrogen peroxide detoxification is a key mechanism for growth of ammonia-oxidizing archaea

Ammonia-oxidizing archaea (AOA), that is, members of the Thaumarchaeota phylum, occur ubiquitously in the environment and are of major significance for global nitrogen cycling. However, controls on cell growth and organic carbon assimilation by AOA are poorly understood. We isolated an ammonia-oxidizing archaeon (designated strain DDS1) from seawater and used this organism to study the physiology of ammonia oxidation. These findings were confirmed using four additional Thaumarchaeota strains from both marine and terrestrial habitats. Ammonia oxidation by strain DDS1 was enhanced in coculture with other bacteria, as well as in artificial seawater media supplemented with α-keto acids (e.g., pyruvate, oxaloacetate). α-Keto acid-enhanced activity of AOA has previously been interpreted as evidence of mixotrophy. However, assays for heterotrophic growth indicated that incorporation of pyruvate into archaeal membrane lipids was negligible. Lipid carbon atoms were, instead, derived from dissolved inorganic carbon, indicating strict autotrophic growth. α-Keto acids spontaneously detoxify H₂O₂ via a nonenzymatic decarboxylation reaction, suggesting a role of α-keto acids as H₂O₂ scavengers. Indeed, agents that also scavenge H₂O₂, such as dimethylthiourea and catalase, replaced the α-keto acid requirement, enhancing growth of strain DDS1. In fact, in the absence of α-keto acids, strain DDS1 and other AOA isolates were shown to endogenously produce H₂O₂ (up to ∼4.5 μM), which was inhibitory to growth. Genomic analyses indicated catalase genes are largely absent in the AOA. Our results indicate that AOA broadly feature strict autotrophic nutrition and implicate H₂O₂ as an important factor determining the activity, evolution, and community ecology of AOA ecotypes.Refining knowledge about the intricacies of the global nitrogen cycle is critical for improving efforts to manage the biosphere (1, 2). Nitrogenous compounds are ubiquitous in aquatic and terrestrial habitats, occurring in both living and deceased biomass (e.g., as amino acids) and in inorganic pools (e.g., ammonia, nitrite, nitrate). They are the naturally occurring microbial communities native to soils and waters that catalyze the cascade of biochemical transformations that constitute the global N cycle [e.g., ammonification, nitrification, denitrification, anaerobic ammonia oxidation, dissimilatory nitrate reduction to ammonia, nitrogen fixation; Canfield et al. (1)].Ammonia is a key nitrogen-containing compound that occurs in waters and soils. Physiologically, ammonia can act directly as a plant nutrient and is also an energy-rich substrate that is oxidized by naturally occurring chemoautotrophic microorganisms [a physiological group that derives ATP from oxidation of an inorganic compound (in this case, ammonia) and derives cellular carbon from carbon dioxide] that carry out nitrification, a two-step process that oxidizes ammonia to nitrate. Recently, however, Bacteria that are capable of complete nitrification (ammonia to nitrate in one step; comammox) were cultivated from an oil exploration well and an anammox reactor (3, 4). The powerful greenhouse gas nitrous oxide (N₂O) is produced as a byproduct of nitrification via intermediary metabolites that include hydroxylamine (NH₂OH), nitroxyl hydride (HNO), and nitrite (NO₂⁻) [for details, see Hu et al. (5)].Traditionally, Bacteria have been considered the key agents in ammonia oxidation in terrestrial and aquatic habitats (6, 7). This view has been drastically altered in the last decade with the discovery that Archaea are often far more abundant and more active in performing ammonia oxidation (8–11). Understanding the physiological foundations of ammonia oxidation and N-cycle biogeochemistry is essential for making predictions about when and in which habitats the process will occur. The traditional view about ammonia oxidation is that it is catalyzed by chemoautotrophs. Originally, AOA were also presumed to be chemolithoautotrophs, similar to their long-characterized bacterial counterparts (12). However, recent reports have suggested that some AOA may use (or even require) organic carbon substrates to achieve ammonia oxidation (13, 14). Mussmann et al. (15) reported the lack of CO₂ fixation by a clade of Thaumarchaeota abundant in refinery nitrifying sludges. The controversy surrounding chemoautotrophic versus mixotrophic (autotrophy and heterotrophy combined) paradigms for ammonia oxidation needs to be resolved.Here we advance fundamental knowledge about the physiology of AOA. We isolated the thaumarchaeotal ammonia-oxidizing strains and show that their growth is stimulated by α-keto organic acids such as pyruvate. Surprisingly, however, pyruvate was not assimilated as a carbon source during ammonia oxidation. Instead, we found that α-keto organic acids served to nonenzymatically detoxify H₂O₂. Our results reveal that previously reported “nutritional requirements” by marine microorganisms for α-keto acids have likely been misinterpreted as indicating “mixotrophic growth.” Acceleration of ammonia oxidation by catalase and catalase-positive cocultures grown with strain DDS1 supports the principle that the in situ metabolic activities of many biogeochemically critical microbial populations (involved in the cycling of C and N and other elements) may be regulated by fellow adjacent populations that produce enzymes able to detoxify toxic reactive oxygen species in ocean water, particularly H₂O₂.     

Comparison of PPIs and H2-receptor antagonists plus prokinetics for dysmotility-like dyspepsia

AIM: To compare efficacy of proton pump inhibitors (PPIs) with H₂-receptor antagonists (H₂RAs) plus prokinetics (Proks) for dysmotility-like symptoms in functional dyspepsia (FD).METHODS: Subjects were randomized to receive open-label treatment with either rabeprazole 10 mg od (n = 57) or famotidine 10 mg bid plus mosapride 5 mg tid (n = 57) for 4 wk. The primary efficacy endpoint was change (%) from baseline in total dysmotility-like dyspepsia symptom score. The secondary efficacy endpoint was patient satisfaction with treatment.RESULTS: The improvement in dysmotility-like dyspepsia symptom score on day 28 was significantly greater in the rabeprazole group (22.5% ± 29.2% of baseline) than the famotidine + mosapride group (53.2% ± 58.6% of baseline, P < 0.0001). The superior benefit of rabeprazole treatment after 28 d was consistent regardless of Helicobacter pylori status. Significantly more subjects in the rabeprazole group were satisfied or very satisfied with treatment on day 28 than in the famotidine + mosapride group (87.7% vs 59.6%, P = 0.0012). Rabeprazole therapy was the only significant predictor of treatment response (P < 0.0001), defined as a total symptom score improvement ≥ 50%.CONCLUSION: PPI monotherapy improves dysmotility-like symptoms significantly better than H₂RAs plus Proks, and should be the treatment of first choice for Japanese FD.     

Hydrogen sulphide pathway contributes to the enhanced human platelet aggregation in hyperhomocysteinemia

Homocysteine is metabolized to methionine by the action of 5,10 methylenetetrahydrofolate reductase (MTHFR). Alternatively, by the transulfuration pathway, homocysteine is transformed to hydrogen sulphide (H₂S), through multiple steps involving cystathionine β-synthase and cystathionine γ-lyase. Here we have evaluated the involvement of H₂S in the thrombotic events associated with hyperhomocysteinemia. To this purpose we have used platelets harvested from healthy volunteers or patients newly diagnosed with hyperhomocysteinemia with a C677T polymorphism of the MTHFR gene (MTHFR++). NaHS (0.1–100 µM) or l-cysteine (0.1–100 µM) significantly increased platelet aggregation harvested from healthy volunteers induced by thrombin receptor activator peptide–6 amide (2 µM) in a concentration-dependent manner. This increase was significantly potentiated in platelets harvested from MTHFR++ carriers, and it was reversed by the inhibition of either cystathionine β-synthase or cystathionine γ-lyase. Similarly, in MTHFR++ carriers, the content of H₂S was significantly higher in either platelets or plasma compared with healthy volunteers. Interestingly, thromboxane A₂ production was markedly increased in response to both NaHS or l-cysteine in platelets of healthy volunteers. The inhibition of phospholipase A₂, cyclooxygenase, or blockade of the thromboxane receptor markedly reduced the effects of H₂S. Finally, phosphorylated–phospholipase A₂ expression was significantly higher in MTHFR++ carriers compared with healthy volunteers. In conclusion, the H₂S pathway is involved in the prothrombotic events occurring in hyperhomocysteinemic patients.Hyperhomocysteinemia (HHcy) is a risk factor for neurovascular and cardiovascular disease associated with endothelial dysfunction and accelerated atherosclerosis (1–3). Many clinical and epidemiological studies have demonstrated a positive correlation between homocysteine (Hcy) plasma levels and cardiovascular disorders (4, 5), leading to the general conclusion that Hcy is a prothrombotic factor (6–8). However, the mechanism(s) through which elevated circulating levels of Hcy promote vascular disease and thrombosis is still unclear (9). Hcy has two primary fates: conversion through a reaction catalyzed by 5,10 methylenetetrahydrofolate reductase (MTHFR) into l-methionine or conversion to l-cysteine (l-Cys) via a transulfuration pathway (10, 11). The transulfuration pathway relies upon cystathionine β-synthase (CBS) to transform Hcy in cysthathionine, which is converted by cystathionine γ-lyase (CSE) into l-Cys. Thereafter, both enzymes convert l-Cys to generate hydrogen sulphide (H₂S) (12, 13). H₂S has been recognized as the third member of the family of gaseous transmitters (14), and it is present in human blood at micromolar concentrations (10–100 μM) (15). It rapidly travels through cell membranes without using any specific receptor/transporter or intracellular signaling proteins. CBS and CSE are differentially expressed in cardiovascular as well as in several other body districts (13). The physiological functions of H₂S are mediated by a variety of molecular targets, including ion channels and signaling proteins (16–18). Alterations in H₂S metabolism contribute to an array of cardiovascular disorders such as hypertension, atherosclerosis, heart failure, and diabetes (19). Nevertheless, the influence of H₂S on platelet function and, in turn, on blood clotting has been poorly explored. We hypothesized that H₂S could be involved in the thrombotic events associated with HHcy. To address this issue, we used human platelets harvested either from healthy volunteers or from patients with a C677T polymorphism of the MTHFR gene (MTHFR++) that is linked to HHcy (20–22).     

Direct Electrochemistry and Electrocatalysis of Horseradish Peroxidase Immobilized in a DNA/Chitosan-Fe3O4 Magnetic Nanoparticle Bio-Complex Film

A DNA/chitosan-Fe₃O₄ magnetic nanoparticle bio-complex film was constructed for the immobilization of horseradish peroxidase (HRP) on a glassy carbon electrode. HRP was simply mixed with DNA, chitosan and Fe₃O₄ nanoparticles, and then applied to the electrode surface to form an enzyme-incorporated polyion complex film. Scanning electron microscopy (SEM) was used to study the surface features of DNA/chitosan/Fe₃O₄/HRP layer. The results of electrochemical impedance spectroscopy (EIS) show that Fe₃O₄ and enzyme were successfully immobilized on the electrode surface by the DNA/chitosan bio-polyion complex membrane. Direct electron transfer (DET) and bioelectrocatalysis of HRP in the DNA/chitosan/Fe₃O₄ film were investigated by cyclic voltammetry (CV) and constant potential amperometry. The HRP-immobilized electrode was found to undergo DET and exhibited a fast electron transfer rate constant of 3.7 s⁻¹. The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP(Fe^(III)) and HRP(Fe^(II)). The obtained electrode also displayed an electrocatalytic reduction behavior towards H₂O₂. The resulting DNA/chitosan/Fe₃O₄/HRP/glassy carbon electrode (GCE) shows a high sensitivity (20.8 A·cm⁻²·M⁻¹) toward H₂O₂. A linear response to H₂O₂ measurement was obtained over the range from 2 μM to 100 μM (R² = 0.99) and an amperometric detection limit of 1 μM (S/N = 3). The apparent Michaelis-Menten constant of HRP immobilized on the electrode was 0.28 mM. Furthermore, the electrode exhibits both good operational stability and storage stability.     

Stimulation by nizatidine, a histamine H(2)-receptor antagonist, of duodenal HCO(3)(-)secretion in rats:relation to anti-cholinesterase activity

AIM:To examine whether nizatidine stimulates duodenal HCO(3)(-) secretion in rats by inhibiting AChE activity.METHODS:Under pentobarbital anesthesia, a proximal duodenal loop was perfused with saline, and the HCO(3)(-) secretion was measured at pH 7.0 using a pH-stat method and by adding 10mM HCl. Nizatidine, neostigmine, carbachol or famotidine was administered i.v. as a single injection.RESULTS:Intravenous administration of nizatidine (3-30mg/kg) dose-dependently increased duodenal HCO(3)(-) secretion, and the effect at 10mg/kg was equivalent to that obtained by carbachol at 0.01mg/kg. This nizatidine action was observed at the same dose range that inhibited acid secretion and enhanced gastric motility, mimicked by i.v. injection of neostigmine(0.03mg/kg), and significantly attenuated by bilateral vagotomy and prior s.c. administration of atropine but not by indomethacin, a cyclooxygenase inhibitor, or NG-nitro-L-arginine methyl ester, a NO synthase inhibitor. The HCO(3)(-) secretory response to acetylcholine (0.001mg/kg) was significantly potentiated by the concurrent administration of nizatidine (3mg/kg,i.v.). The IC(50) of nizatidine for AChE of rat erythrocytes was 1.4·10(-6) M, about 12 times higher than that of neostigmine. Neither famotidine (> 10(-3) M, 30mg/kg, i.v.) nor cisapride (> 10(-3) M,3mg/kg, i.v.) had any influence on AChE activity or duodenal HCO(3)(-) secretion. Duodenal damage induced by acid perfusion (100mM HCl for 4h) in the presence of indomethacin was significantly prevented by nizatidine and neostigmine, at the doses that increased the HCO(3)(-)secretion.CONCLUSION:Nizatidine stimulates duodenal HCO(3)(-) secretion, in both vagal dependent and atropine sensitive manners, and the action is associated with the anti-AChE activity of this agent.     

Effect of Bimetallic-Activated Carbon Impregnation on Adsorption–Desorption Performance for Hydrogen Sulfide (H2S) Capture

This study reports on the impregnation of bi-metallic adsorbents based on commercial coconut activated carbon (CAC), surface-modified with metal acetate (ZnAc₂), metal oxide (ZnO and TiO₂), and the basic compound potassium hydroxide (KOH). The morphology of the adsorbents was then characterized with SEM-EDX, the microporosity was determined using Brunauer–Emmett–Teller (BET) analysis, the thermal stability was investigated via thermogravity analysis (TGA), and functional group analysis was undertaken with Fourier-transform infrared (FTIR) spectroscopy. These modified adsorbents were subjected to a real adsorption test for H₂S capture using a 1 L adsorber with 5000 ppm H₂S balanced for N₂, with temperature and pressure maintained at an ambient condition. Adsorption–desorption was carried out in three cycles with the blower temperature varied from 50 °C to 150 °C as the desorption condition. Characterization results revealed that the impregnated solution homogeneously covered the adsorbent surface, effecting the morphology and properties. Based on this study, it was found that ZnAc₂/TiO₂/CAC_DCM showed a significant increase in adsorption capacity with the different temperatures applied for the desorption in the second cycle: 1.67 mg H₂S/g at 50 °C, 1.84 mg H₂S/g at 100 °C, and 1.96 mg H₂S/g at 150 °C. ZnAc₂/ZnO/CAC_DCM seemed to produce the lowest percentage of degradation in the three cycles for all the temperatures used in the adsorption–desorption process. Therefore, ZnAc₂/ZnO/CAC_DCM has the potential to be used and commercialized for biogas purification for H₂S removal.     

Obtention and Characterization of Ferrous Chloride FeCl2·4H2O from Water Pickling Liquors

As a hazardous waste, water pickling liquors must be properly treated. An alternative consists of promoting the formation of ferrous salts from this residue due to their higher ferrous content. Since FeCl₂·4H₂O is widely used in several applications, obtaining pure crystals of this material appears to be an interesting prospect. However, this compound has scarcely been investigated. In the present work, FeCl₂·4H₂O crystals were obtained from water pickling liquors. Their structural and morphological characteristics were investigated by X-ray diffraction, scanning electron microscopy as well as Mössbauer spectroscopy. In addition, the photoluminescence study of the obtained samples was also assessed. It was observed that after some aging time, the obtained crystals changed in colour from green to more yellowish. As such, the aged sample was also evaluated, and their structural characteristics were compared with the original crystals. Despite this, the obtained crystals exhibit a FeCl₂·4H₂O structure, which is not modified with the aging of the sample.     

Inhibition of hydrogen sulfide generation contributes to gastric injury caused by anti-inflammatory nonsteroidal drugs

BACKGROUND & AIMS: Hydrogen sulfide (H(2)S), an endogenous gaseous mediator that causes vasodilation, is generated in mammalian tissues by cystathionine beta-synthase (CBS) and cystathionine-gamma-lyase (CSE). Here, we have investigated the role of H(2)S in a rodent model of nonsteroidal anti-inflammatory drug (NSAID) gastropathy. METHODS: Rats were given acetyl salycilic acid (ASA) or an NSAID alone or in combination with NaHS, an H(2)S donor, and killed 3 hours later. Gastric blood flow was measured by laser-Doppler flowmetry, whereas intravital microscopy was used to quantify adhesion of leukocytes to mesenteric postcapillary endothelium. RESULTS: At a dose of 100 micromol/kg, NaHS attenuated by 60%-70% the gastric mucosal injury, and tumor necrosis factor (TNF)-alpha, intercellular adhesion molecule (ICAM)-1, and lymphocyte function-associated antigen (LFA)-1 mRNA up-regulation induced by NSAIDs (P < .05) NaHS administration prevented the associated reduction of gastric mucosal blood flow (P < .05) and reduced ASA-induced leukocyte adherence in mesenteric venules. NaHS did not affect suppression of prostaglandin E(2) (PGE(2)) synthesis by NSAIDs. Glibenclamide, a K(ATP) channel inhibitor, and DL-propargylglycine, a CSE inhibitor, exacerbated, whereas pinacidil, a K(ATP) opener, attenuated gastric injury caused by ASA. Exposure to NSAIDs reduced H(2)S formation and CSE expression (mRNA and protein) and activity by 60%-70%. By promoter deletion and mutation analysis, an Sp1 consensus site was identified in the CSE promoter. Exposure to NSAIDs inhibits Sp1 binding to its promoter and abrogates CSE expression in HEK-293 cells transfected with a vector containing the core CSE promoter. Exposure to NSAIDs inhibits Sp1 and ERK phosphorylation. CONCLUSIONS: These data establish a physiologic role for H(2)S in regulating the gastric microcirculation and identify CSE as a novel target for ASA/NSAIDs.     

The Fate of Asymptomatic Recurrences of Duodenal Ulcer

Thirty-six patients in whom an asymptomatic duodenal ulcer had been detected endoscopically were followed up clinically and endoscopically during the following months. Ten of the patients were receiving either no treatment or placebo, and 26 patients were receiving maintenance treatment with either 150 mg ranitidine or 400 mg Cimetidine at night. Treatment remained unchanged during the follow-up period. The cumulative annual rate of spontaneous healing was approximately one quarter, whether or not patients were receiving active maintenance therapy. However, the likelihood of developing symptoms during the year after detection of the asymptomatic ulcer was significantly greater in those patients receiving no treatment or placebo (77%) than in those receiving active maintenance therapy (27%). One patient, receiving no treatment, bled from his ulcer during the follow-up period. We conclude that routine endoscopic reexamination, to detect asymptomatic ulcer recurrences in patients receiving maintenance treatment for duodenal ulceration, is probably unnecessary, since the recurrences rarely cause clinical problems, despite prolonged failure to heal.