The antioxidant potential of pyruvate in the amitochondriate diplomonads Giardia intestinalis and Hexamita inflata

New Insights Into the Function of Flavohemoglobin in Mycobacterium tuberculosis: Role as a NADPH-Dependent Disulfide Reductase and D-Lactate-Dependent Mycothione Reductase

Mycobacterium tuberculosis (Mtb) produces an unconventional flavohemoglobin (MtbFHb) that carries a FAD-binding site similar to D-lactate dehydrogenases (D-LDH) and oxidizes D-lactate into pyruvate. The molecular mechanism by which MtbFHb functions in Mtb remains unknown. We discovered that the D-LDH-type FAD-binding site in MtbFHb overlaps with another FAD-binding motif similar to thioredoxin reductases and reduces DTNB in the presence of NADPH similar to trxB of Mtb. These results suggested that MtbFHb is functioning as a disulfide oxidoreductase. Interestingly, D-lactate created a conformational change in MtbFHb and attenuated its ability to oxidize NADPH. Mass spectroscopy demonstrated that MtbFHb reduces des-myo-inositol mycothiol in the presence of D-lactate unlike NADPH, indicating that D-lactate changes the specificity of MtbFHb from di-thiol to di-mycothiol. When M. smegmatis carrying deletion in the fhbII gene (encoding a homolog of MtbFHb) was complemented with the fhb gene of Mtb, it exhibited four- to fivefold reductions in lipid peroxidation and significant enhancement in the cell survival under oxidative stress. These results were corroborated by reduced lipid peroxidation and enhanced cell survival of wild-type M. smegmatis after overexpression of the fhb gene of Mtb. Since D-lactate is a by-product of lipid peroxidation and MtbFHb is a membrane-associated protein, D-lactate-mediated reduction of mycothiol disulfide by MtbFHb may uniquely equip Mtb to relieve the toxicity of D-lactate accumulation and protect the cell from oxidative damage, simultaneously balancing the redox environment under oxidative stress that may be vital for the pathogenesis of Mtb.

Oxygen levels are key to understanding "Anaerobic" protozoan pathogens with micro-aerophilic lifestyles

Publications abound on the physiology, biochemistry and molecular biology of "anaerobic" protozoal parasites as usually grown under "anaerobic" culture conditions. The media routinely used are poised at low redox potentials using techniques that remove O₂ to "undetectable" levels in sealed containers. However there is growing understanding that these culture conditions do not faithfully resemble the O₂ environments these organisms inhabit. Here we review for protists lacking oxidative energy metabolism, the oxygen cascade from atmospheric to intracellular concentrations and relevant methods of measurements of O₂, some well-studied parasitic or symbiotic protozoan lifestyles, their homeodynamic metabolic and redox balances, organism-drug-oxygen interactions, and the present and future prospects for improved drugs and treatment regimes.

Insights into VdCmr1-mediated protection against high temperature stress and UV irradiation in Verticillium dahliae

The fungus Verticillium dahliae causes vascular wilt disease on more than 200 plant species worldwide. This fungus can survive for years in soil as melanized microsclerotia. We found that VdCmr1, a transcription factor, is required for the melanin production and increased survival following UV irradiation in V. dahliae but not for microsclerotia production or virulence. Here, we provided evidence how VdCmr1 protects against high temperature (HT) and UV irradiation in V. dahliae. The results indicate that VdCmr1 mediates entry to the diapause period in V. dahliae in response to HT and contributes to the expression of proteins to minimize protein misfolding and denaturation. VdCmr1 deletion results in the misregulation of DNA repair machinery, suggestive of reduced DNA repair capacity following UV irradiation and in correlation with the low survival rate of UV-treated VdCmr1 mutants. We discovered a putative VdCmr1-dependent gene cluster associated with secondary metabolism and stress responses. We also functionally characterized two VdCmr1-responsive genes participating in HT and UV response. These results shed further light on the roles of VdCmr1 in protection from HT or UV irradiation, and the additional insights into the mechanisms of this protection may be useful to exploit for more effective disease control.

Increasing Pyruvate Concentration Enhances Conidial Thermotolerance in the Entomopathogenic Fungus Metarhizium robertsii

The fungal entomopathogens Metarhizium spp. have been developed as environmentally friendly mycoinsecticides. However, heat stress severely reduces the viability of Metarhizium conidia in the field, which is an important obstacle to the successful use of these mycoinsecticides. Heat treatment induces rapid accumulation of pyruvate, which timely scavenges heat-induced ROS (reactive oxygen species) in hyphal cells of M. robertsii. However, in heat-treated conidia, pyruvate accumulation occurs later than the rapid production of ROSs, which could harm the conidial cells. In the present study, a transgenic M. robertsii strain was constructed with the pyruvate kinases gene overexpressed during conidiation. Two independent transformants of the transgenic strain produced conidia under optimal conditions with elevated pyruvate concentration. This inhibits the rapid heat-induced ROS production and prevents the collapse of mitochondrial membrane potential, thereby increasing conidial tolerance to heat stress. In conclusion, the tolerance of M. robertsii conidia to heat stress was improved by increasing the conidial pyruvate concentration, which could be translated into a more effective pest control.

DNA damage induced by metronidazole in Giardia duodenalis triggers a DNA homologous recombination response

The mechanisms underlying metronidazole (MTZ) resistance in Giardia duodenalis have been associated with decreased activity of the enzymes implicated in its activation including nitroductase-1, thioredoxin reductase and pyruvate-ferredoxin oxidoreductase (PFOR). MTZ activation generates radicals that can form adducts with proteins such as thioredoxin reductase and α- and -β giardins as well as DNA damage resulting in trophozoite's death. The damage induced in DNA requires a straight forward response that may allow parasite survival. Here, we studied changes in histone H2A phosphorylation to evaluate the DNA repair response pathway after induction of double strand break (DSB) by MTZ in Giardia DNA. Our results showed that the DNA repair mechanisms after exposure of Giardia trophozoites to MTZ, involved a homologous recombination pathway. We observed a significant increase in the expression level of proteins GdDMC1B, which carries out Rad51 role in G. duodenalis, and GdMre11, after 12 h of exposure to 3.2 μM MTZ. This increase was concomitant with the generation of DSB in the DNA of trophozoites treated MTZ. Altogether, these results suggest that MTZ-induced DNA damage in Giardia triggers the DNA homologous recombination repair (DHRR) pathway, which may contribute to the parasite survival in the presence of MTZ.

Pyruvate Protects Giardia Trophozoites from Cysteine-Ascorbate Deprived Medium Induced Cytotoxicity

Giardia lamblia, an anaerobic, amitochondriate protozoan parasite causes parasitic infection giardiasis in children and young adults. It produces pyruvate, a major metabolic product for its fermentative metabolism. The current study was undertaken to explore the effects of pyruvate as a physiological antioxidant during oxidative stress in Giardia by cysteine-ascorbate deprivation and further investigation upon the hypothesis that oxidative stress due to metabolism was the reason behind the cytotoxicity. We have estimated intracellular reactive oxygen species generation due to cysteine-ascorbate deprivation in Giardia. In the present study, we have examined the effects of extracellular addition of pyruvate, during oxidative stress generated from cysteine-ascorbate deprivation in culture media on DNA damage in Giardia. The intracellular pyruvate concentrations at several time points were measured in the trophozoites during stress. Trophozoites viability under cysteine-ascorbate deprived (CAD) medium in presence and absence of extracellular pyruvate has also been measured. The exogenous addition of a physiologically relevant concentration of pyruvate to trophozoites suspension was shown to attenuate the rate of ROS generation. We have demonstrated that Giardia protects itself from destructive consequences of ROS by maintaining the intracellular pyruvate concentration. Pyruvate recovers Giardia trophozoites from oxidative stress by decreasing the number of DNA breaks that might favor DNA repair.

Utilization of Different Omic Approaches to Unravel Stress Response Mechanisms in the Parasite Entamoeba histolytica

During its life cycle, the unicellular parasite Entamoeba histolytica is challenged by a wide variety of environmental stresses, such as fluctuation in glucose concentration, changes in gut microbiota composition, and the release of oxidative and nitrosative species from neutrophils and macrophages. The best mode of survival for this parasite is to continuously adapt itself to the dynamic environment of the host. Our ability to study the stress-induced responses and adaptive mechanisms of this parasite has been transformed through the development of genomics, proteomics or metabolomics (omics sciences). These studies provide insights into different facets of the parasite's behavior in the host. However, there is a dire need for multi-omics data integration to better understand its pathogenic nature, ultimately paving the way to identify new chemotherapeutic targets against amebiasis. This review provides an integration of the most relevant omics information on the mechanisms that are used by E. histolytica to resist environmental stresses.

Pyruvate Accumulation Is the First Line of Cell Defense against Heat Stress in a Fungus

Heat tolerance is well known to be key to fungal survival in many habitats, but our mechanistic understanding of how organisms adapt to heat stress is still incomplete. Using Metarhizium robertsii, an emerging model organism for assessing evolutionary processes, we report that pyruvate is in the vanguard of molecules that scavenge heat-induced reactive oxygen species (ROS). We show that, as well as inducing a rapid burst of ROS production, heat stress also downregulates genes for pyruvate consumption. The accumulating pyruvate is the fastest acting of several M. robertsii ROS scavengers, efficiently reducing protein carbonylation, stabilizing mitochondrial membrane potential, and promoting fungal growth. The acetate produced from pyruvate-ROS reactions itself causes acid stress, tolerance to which is regulated by Hog1 mitogen-activated protein kinase. Heat stress also induces pyruvate accumulation in several other fungi, suggesting that scavenging of heat-induced ROS by pyruvate is widespread.

Heat is a dangerous challenge for most organisms, as it denatures proteins and induces the production of ROS that inactivate proteins, lipid membranes, and DNA. How organisms respond to this stress is not fully understood. Using the experimentally tractable insect pathogen Metarhizium robertsii as a model organism, we show for the first time that heat stress induces pyruvate production and that this functions as the first line of defense against heat-induced ROS. Heat stress also induces rapid pyruvate accumulation in other fungi, suggesting that pyruvate is a common but unappreciated defense against stress.

Transcriptomics Indicates Active and Passive Metronidazole Resistance Mechanisms in Three Seminal Giardia Lines

Giardia duodenalis is an intestinal parasite that causes 200-300 million episodes of diarrhoea annually. Metronidazole (Mtz) is a front-line anti-giardial, but treatment failure is common and clinical resistance has been demonstrated. Mtz is thought to be activated within the parasite by oxidoreductase enzymes, and to kill by causing oxidative damage. In G. duodenalis, Mtz resistance involves active and passive mechanisms. Relatively low activity of iron-sulfur binding proteins, namely pyruvate:ferredoxin oxidoreductase (PFOR), ferredoxins, and nitroreductase-1, enable resistant cells to passively avoid Mtz activation. Additionally, low expression of oxygen-detoxification enzymes can allow passive (non-enzymatic) Mtz detoxification via futile redox cycling. In contrast, active resistance mechanisms include complete enzymatic detoxification of the pro-drug by nitroreductase-2 and enhanced repair of oxidized biomolecules via thioredoxin-dependent antioxidant enzymes. Molecular resistance mechanisms may be largely founded on reversible transcriptional changes, as some resistant lines revert to drug sensitivity during drug-free culture in vitro, or passage through the life cycle. To comprehensively characterize these changes, we undertook strand-specific RNA sequencing of three laboratory-derived Mtz-resistant lines, 106-2ID10, 713-M3, and WB-M3, and compared transcription relative to their susceptible parents. Common up-regulated genes encoded variant-specific surface proteins (VSPs), a high cysteine membrane protein, calcium and zinc channels, a Mad-2 cell cycle regulator and a putative fatty acid α-oxidase. Down-regulated genes included nitroreductase-1, putative chromate and quinone reductases, and numerous genes that act proximal to PFOR. Transcriptional changes in 106-2ID10 diverged from those in 713-r and WB-r (r ≤ 0.2), which were more similar to each other (r = 0.47). In 106-2ID10, a nonsense mutation in nitroreductase-1 transcripts could enhance passive resistance whereas increased transcription of nitroreductase-2, and a MATE transmembrane pump system, suggest active drug detoxification and efflux, respectively. By contrast, transcriptional changes in 713-M3 and WB-M3 indicated a higher oxidative stress load, attributed to Mtz- and oxygen-derived radicals, respectively. Quantitative comparisons of orthologous gene transcription between Mtz-resistant G. duodenalis and Trichomonas vaginalis, a closely related parasite, revealed changes in transcripts encoding peroxidases, heat shock proteins, and FMN-binding oxidoreductases, as prominent correlates of resistance. This work provides deep insight into Mtz-resistant G. duodenalis, and illuminates resistance-associated features across parasitic species.

Drug resistance in Giardia duodenalis

Giardia duodenalis is a microaerophilic parasite of the human gastrointestinal tract and a major contributor to diarrheal and post-infectious chronic gastrointestinal disease world-wide. Treatment of G. duodenalis infection currently relies on a small number of drug classes. Nitroheterocyclics, in particular metronidazole, have represented the front line treatment for the last 40 years. Nitroheterocyclic-resistant G. duodenalis have been isolated from patients and created in vitro, prompting considerable research into the biomolecular mechanisms of resistance. These compounds are redox-active and are believed to damage proteins and DNA after being activated by oxidoreductase enzymes in metabolically active cells. In this review, we explore the molecular phenotypes of nitroheterocyclic-resistant G. duodenalis described to date in the context of the protist's unusual glycolytic and antioxidant systems. We propose that resistance mechanisms are likely to extend well beyond currently described resistance-associated enzymes (i.e., pyruvate ferredoxin oxidoreductases and nitroreductases), to include NAD(P)H- and flavin-generating pathways, and possibly redox-sensitive epigenetic regulation. Mechanisms that allow G. duodenalis to tolerate oxidative stress may lead to resistance against both oxygen and nitroheterocyclics, with implications for clinical control. The present review highlights the potential for systems biology tools and advanced bioinformatics to further investigate the multifaceted mechanisms of nitroheterocyclic resistance in this important pathogen.

Giardia intestinalis escapes oxidative stress by colonizing the small intestine: A molecular hypothesis

Giardia intestinalis is the microaerophilic protozoon causing giardiasis, a common infectious intestinal disease. Giardia possesses an O(2) -scavenging activity likely essential for survival in the host. We report that Giardia trophozoites express the O(2) -detoxifying flavodiiron protein (FDP), detected by immunoblotting, and are able to reduce O(2) to H(2) O rapidly (∼3 μM O(2) × min × 10(6) cells at 37 °C) and with high affinity (C(50) = 3.4 ± 0.7 μM O(2)). Following a short-term (minutes) exposure to H(2) O(2) ≥ 100 μM, the O(2) consumption by the parasites is irreversibly impaired, and the FDP undergoes a degradation, prevented by the proteasome-inhibitor MG132. Instead, H(2) O(2) does not cause degradation or inactivation of the isolated FDP. On the basis of the elevated susceptibility of Giardia to oxidative stress, we hypothesize that the parasite preferentially colonizes the small intestine since, compared with colon, it is characterized by a greater capacity for redox buffering and a lower propensity to oxidative stress.

Excretory/secretory proteome of the adult stage of Echinostoma caproni

The excretory/secretory proteome of Echinostoma caproni (Trematoda: Echinostomatidae) adults collected from experimentally infected mice was investigated using a proteomic approach. We performed a shot-gun liquid chromatography/tandem mass spectrometry for the separation and identification of tryptic peptides from the excretory/secretory products of E. caproni adult worms. Database search was performed using MASCOT search engine (Matrix-Science) and ProteinPilot software v2.0 (Applied Biosystems). A total of 39 parasite proteins were accurately identified. Strikingly, metabolic enzymes, and particularly glycolytic enzymes, constituted the largest protein family in the excretory/secretory proteome of E. caproni adult worms. Moreover, representative proteins involved in parasite structure, response against stress, chaperones, calcium-binding, and signal transduction were also identified. This work extends our knowledge of host-parasite relationships in the E. caproni-rodent model that is extensively used to analyze the factors determining the intestinal helminth rejection. Consequently, information on many proteins may be useful to better understand the molecular basis that determines the survival of this parasite in the definitive host.

Sustained release nanoparticulate formulation containing antioxidant-ellagic acid as potential prophylaxis system for oral administration

The aim of the present work was to develop ellagic acid (EA) loaded poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles for oral administration. PLGA nanoparticles were prepared by a method based on the concept of emulsion-diffusion-evaporation by using polyethylene glycol (PEG) 400 as a cosolvent for solubilizing the drug. While developing this method, didodecyldimethylammomium bromide (DMAB) and polyvinyl alcohol (PVA), alone and in combination with chitosan (CS) were employed. DMAB stabilized particles were the smallest of all the formulations with a particle size of 148.5 nm. PVA alone gave particles of 269.7 nm but a blend with CS (80:20) resulted in an increase in particle size (359.6 +/- 23.6 nm). Initial release of EA from nanoparticles in pH 7.4 phosphate buffer was rapid, followed by a slower sustained release. Release rates followed the order PVA > PVA-CS > DMAB. Release rate from the PLGA-DMAB particles was slowest, which is attributed to higher hydrophobicity of DMAB as compared to PVA, preventing diffusion of drug out of polymeric matrix. Insolubility of CS at alkaline pH could have retarded the release in case of PVA-CS system. In situ intestinal permeability study of pure drug and the drug encapsulated in nanoparticles prepared using PVA, PVA-CS blend and DMAB as stabilizer in rats showed 66, 75, 73 and 87% permeation, respectively. EA showed good free radical scavenging effect in a yeast cell culture model as well as in a cell free system.

Stress response pathways in protozoan parasites

Diseases caused by protozoan parasites have a dramatic impact on world health. Emerging drug resistance and a general lack of experimental understanding has created a void in the medicine cabinet used to treat these widespread infections. A novel therapeutic idea that is receiving more attention is centred on targeting the microbe's response to the multitude of environmental stresses it encounters. Protozoan pathogens have complex life cycles, often having to transition from one host to another, or survive in a cyst form in the environment until a new host arrives. The need to respond to environmental cues and stress, and endure in less than optimal conditions, is paramount to their viability and successful progression through their life cycle. This review summarizes the research on parasitic stress responses for Apicomplexa, kinetoplastids and anaerobic protozoa, with an eye towards how these processes may be exploited therapeutically.

Ethyl pyruvate decreased early nuclear factor-kappaB levels but worsened survival in lipopolysaccharide-challenged mice

BACKGROUND

Ethyl pyruvate (EP) treatment inhibits nuclear factor (NF)-kappaB-mediated inflammation and has been considered for sepsis. However, NF-kappaB is also protective, and its inhibition may have adverse effects.

METHODS

We studied EP in lipopolysaccharide-challenged mice and systematically analyzed its efficacy in published sepsis models.

RESULTS

After lipopolysaccharide, compared with placebo (n = 68), each of six doses of EP (0.01-100 mg/kg, n = 204) increased the hazards ratio of death. Although these increases were individually not significant (p = .13 to .37), when combined, they were (log mean +/- SEM, 0.26 +/- 0.13; p = .01). At 3 and 9 hrs after challenge, lipopolysaccharide increased lung NF-kappaB and 12 serum cytokines (p < or = .05 vs. phosphate-buffered saline challenge, except for interleukin-4 at 9 hrs). With lipopolysaccharide, although EP (100 mg/kg) decreased NF-kappaB and 11 of 12 cytokines at 3 hrs, it increased NF-kappaB and 11 of 12 cytokines at 9 hrs in patterns that differed (p < or = .05) across time points. In 14 published comparisons, EP's effects on the odds ratio of death varied (I2 = 85% [95% confidence interval, 74-91%], p < .0001), decreasing it significantly in five of the studies but not the other nine. In three of the latter, it increased time to death.

CONCLUSION

Although EP has had promising effects in some preclinical sepsis models, it has not in others, and in the present model, it worsened outcome. Based on the complex role NF-kappaB has regulating both maladaptive and protective host responses, further defining factors that influence EP's effects is important if this agent is considered for patients with or at risk of sepsis.

Excretory-secretory proteome of larval Schistosoma mansoni and Echinostoma caproni, two parasites of Biomphalaria glabrata

Schistosoma mansoni and Echinostoma caproni are two trematode species that use different strategies (mimicry and immunosuppression, respectively) to interfere with the snail innate immune system. Parasites excretory-secretory (ES) products have been shown to play a key role in these host-parasite immune interactions. However, they remain largely uncharacterized in larval trematodes. We developed a global proteomic approach to characterize the ES proteome of S. mansoni and E. caproni primary sporocysts. In ES products of both parasites, we found proteins involved in reactive oxygen species scavenging, glycolysis, signalling or calcium binding (superoxide dismutase Cu/Zn; glutathione S-transferase; aldo-keto-reductase; triose-phosphate isomerase; glyceraldehyde-3-phosphate dehydrogenase; aldolase, enolase, MICAL-like, calreticulin). According to their predicted functions, we propose a model in which these proteins (i) are involved in antioxidant activity, (ii) prevent hemocyte encapsulation process or (iii) favor invasion and migration of sporocysts in host tissues. These results suggest that S. mansoni and E. caproni sporocysts develope a strong immune protection during the first hours of infection giving them enough time to build up a long lasting immune evasion strategy relying on molecular mimicry or immunosuppression, respectively.

The overexpression of NADPH-producing enzymes counters the oxidative stress evoked by gallium, an iron mimetic

Gallium (Ga), an iron (Fe) mimetic promoted an oxidative environment and elicited an antioxidative response in Pseudomonas fluorescens. Ga-stressed P. fluorescens was characterized by higher amounts of oxidized lipids and proteins compared to control cells. The oxidative environment provoked by Ga was nullified by increased synthesis of NADPH. The activity and expression glucose 6-phosphate dehydrogenase (G6PDH) and isocitrate dehydrogenase-NADP (ICDH) were stimulated in Ga-cultures. The induction of isoenzymes of these dehydrogenases was also evident in the Ga-stressed cells. Although superoxide dismutase (SOD) activity was significantly enhanced in Ga-stressed cultures, catalase activity experienced a marked diminution. Fe metabolism appeared to be severely impeded by Ga toxicity. This is the first demonstration of the oxidative stress evoked by Ga to be neutralized by a reductive environment generated via the overexpression of NADPH-producing enzymes.

Menadione kills trophozoites and cysts of Giardia intestinalis

Production of reactive oxygen species by redox cycling in the presence of low levels of oxygen has been studied as a possible approach to anti-protozoal chemotherapeutic strategy. Incubation of the diplomonad flagellate Giardia intestinalis with 2-methy-1,4-naphthoquinone (menadione), under anaerobic conditions, gave UV absorption changes characteristic of reduction to menadiol; partial reversal was observed on admitting O(2). Under microaerobic conditions, similar to those on the surface of the jejunal mucosa, trophozoites consumed O(2) rapidly in the presence of menadione; reaction products included singlet O(2) (monitored by single photon counting of O(2)-dependent low-level chemiluminescence) and H(2)O(2) (measured by the formation of Complex I of microperoxidase). Trophozoites became swollen and incapable of regulatory volume control; these irreversible responses led to loss of motility, cessation of flagellar activity and cell death. Comparison of the sensitivities of trophozoites to metronidazole and menadione gave LC(50) values ( microg x ml(-1)) of 1.2 and 0.7, respectively; corresponding values for cysts (measured by in vitro excystation capacities) were >50 and 1.3. Menadione (LD(50) in mice, 0.5 g kg(-1)) is therefore a potentially more useful and general anti-giardial agent than metronidazole, as it is active against cysts as well as trophozoites.

The plasma membrane of microaerophilic protists: oxidative and nitrosative stress

The trans-plasma-membrane electrochemical potential of microaerophilic protists was monitored by the use of voltage-sensitive charged lipophilic fluorophores; of the many available probes, the anionic oxonol dye bis(1,3-dibarbituric acid)-trimethine oxonol [DiBAC4(3)] is an example of one which has been successfully employed using fluorescence microscopy, confocal laser-scanning microscopy and flow cytometry. Several microaerophilic protists have been investigated with this dye; these were Giardia intestinalis, Trichomonas vaginalis, Tritrichomonas foetus, Hexamita inflata and Mastigamoeba punctachora. Under conditions where they exhibit normal vitality, these organisms exclude DiBAC4(3) by virtue of their maintenance of a plasma-membrane potential (negative inside). Uptake of the fluorophore is indicative of disturbance to this membrane (i.e. by inhibition of pump/leak balance, blockage of channels or generation of ionic leaks), and is indicative of metabolic perturbation or environmental stress. Here, it is shown that oxidative or nitrosative stress depolarizes the plasma membranes of the aforementioned O2-sensitive organisms and allows DiBAC4(3) influx. Oxonol uptake thereby provides a sensitive and early indication of plasma-membrane perturbation by agents that may lead to cytotoxicity and eventually to cell death by necrotic or apoptotic pathways.

Cytochrome P-450 metabolites but not NO, PGI2, and H2O2 contribute to ACh-induced hyperpolarization of pressurized canine coronary microvessels

The endothelium-dependent hyperpolarization of cells has a crucial role in regulating vascular tone, especially in microvessels. Nitric oxide (NO) and prostacyclin (PGI2), in addition to endothelium-derived hyperpolarizing factor (EDHF), have been reported to hyperpolarize vascular smooth muscle in several organs. Studies have reported the hyperpolarizing effects of these factors are increased by a stretch in large coronary arteries. EDHF has not yet been identified and cytochrome P-450 metabolites and H2O2 are candidates for EDHF. With the use of the membrane potential-sensitive fluorescent dye bis-(1,3-dibutylbarbituric acid)trimethione oxonol [DiBAC4(3)], we examined whether NO, PGI2, cytochrome P-450 metabolites, and H2O2 contribute to ACh-induced hyperpolarization in pressurized coronary microvessels. Canine coronary arterial microvessels (60-356 mum internal diameter) were cannulated and pressurized at 60 cmH2O in a vessel chamber perfused with physiological salt solution containing DiBAC4(3). Fluorescence intensity and diameter were measured on a computer. There was a linear correlation between changes in the fluorescence intensity and membrane potential. ACh significantly decreased the fluorescence intensity (hyperpolarization) of the microvessels without any inhibitors. Endothelial damage caused by air perfusion abolished the ACh-induced decrease in fluorescence intensity. The inhibitors of NO synthase and cyclooxygenase did not affect the ACh-induced decreases in the fluorescence intensity. The addition of 17-octadecynoic acid, a cytochrome P-450 monooxygenase inhibitor, to those inhibitors significantly attenuated the ACh-induced decreases in fluorescence intensity, whereas catalase, an enzyme that dismutates H2O2 to form water and oxygen, did not. Furthermore, catalase did not affect the vasodilation produced by ACh. These results indicate that NO and PGI2 do not contribute to the ACh-induced hyperpolarization and that the cytochrome P-450 metabolites but not H2O2 are involved in EDHF-mediated hyperpolarization in canine coronary arterial microvessels.

Ethyl pyruvate: a novel anti-inflammatory agent

Pyruvate plays a central role in intermediary metabolism. Pyruvate, however, is also a potent antioxidant and free radical scavenger, and numerous studies have shown that treatment with this compound can be salutary in numerous pathologic conditions that are thought to be mediated, at least in part, by redox-dependent phenomena. Unfortunately, aqueous solutions of pyruvate rapidly undergo an aldol-like condensation reaction to form 2-hydroxy-2-methyl-4-ketoglutarate (parapyruvate), a compound that is a potent inhibitor of a critical step in the mitochondrial tricarboxylic acid cycle. To circumvent this issue, our laboratory formulated a derivative of pyruvic acid, ethyl pyruvate, in a calcium- and potassium-containing balanced salt solution. We showed that treatment with this fluid could ameliorate much of the structural and functional damage to the intestinal mucosa caused by mesenteric ischemia and reperfusion in rats. In subsequent studies, we showed that treatment with ethyl pyruvate solution could improve survival in rodent models of hemorrhagic shock and resuscitation and also down-regulate a number of proinflammatory genes. Recently, ethyl pyruvate was also shown to improve survival in murine models of acute endotoxemia and bacterial peritonitis. Although the biochemical basis for the anti-inflammatory actions of pyruvate remain to be elucidated, this simple compound warrants further evaluation as a treatment for a number of conditions commonly encountered in the practice of critical care medicine.

Ethyl pyruvate ameliorates intestinal epithelial barrier dysfunction in endotoxemic mice and immunostimulated caco-2 enterocytic monolayers

Ethyl pyruvate (EP) solution ameliorates ileal mucosal hyperpermeability and decreases the expression of several proinflammatory genes in ileal and/or colonic mucosa when it is used instead of Ringer's lactate solution (RLS) to resuscitate mice from hemorrhagic shock. To test the hypothesis that EP can ameliorate gut barrier dysfunction induced by other forms of inflammation, we incubated Caco-2 monolayers for 24 to 48 h with cytomix (a mixture of interferon-gamma, tumor necrosis factor-alpha, and interleukin-1beta) in the presence or absence of graded concentrations of EP or sodium pyruvate. Cytomix increased the permeability of Caco-2 monolayers to fluorescein isothiocyanate-labeled dextran (FD4; average molecular mass 4 kDa), but this effect was inhibited by adding 0.1 to 10 mM EP (but not similar concentrations of sodium pyruvate) to the culture medium. EP inhibited several other cytomix-induced phenomena, including nuclear factor-kappaB activation, inducible nitric oxide synthase mRNA expression, and nitric oxide production. Cytomix altered the expression and localization of the tight junctional proteins, ZO-1 and occludin, but this effect was prevented by EP. Delayed treatment with EP solution instead of RLS ameliorated ileal mucosal hyperpermeability to FD4 and bacterial translocation to mesenteric lymph nodes in mice challenged with lipopolysaccharide (LPS). These data support the view that EP ameliorates cytokine- and/or LPS-induced derangements in intestinal epithelial barrier function.