The plasma membrane of microaerophilic protists: oxidative and nitrosative stress

Fused Enzyme Glucose-6-Phosphate Dehydrogenase::6-Phosphogluconolactonase (G6PD::6PGL) as a Potential Drug Target in Giardia lamblia, Trichomonas vaginalis, and Plasmodium falciparum

Several microaerophilic parasites such as Giardia lamblia, Trichomonas vaginalis, and Plasmodium falciparum are major disease-causing organisms and are responsible for spreading infections worldwide. Despite significant progress made in understanding the metabolism and molecular biology of microaerophilic parasites, chemotherapeutic treatment to control it has seen limited progress. A current proposed strategy for drug discovery against parasitic diseases is the identification of essential key enzymes of metabolic pathways associated with the parasite's survival. In these organisms, glucose-6-phosphate dehydrogenase::6-phosphogluconolactonase (G6PD:: 6PGL), the first enzyme of the pentose phosphate pathway (PPP), is essential for its metabolism. Since G6PD:: 6PGL provides substrates for nucleotides synthesis and NADPH as a source of reducing equivalents, it could be considered an anti-parasite drug target. This review analyzes the anaerobic energy metabolism of G. lamblia, T. vaginalis, and P. falciparum, with a focus on glucose metabolism through the pentose phosphate pathway and the significance of the fused G6PD:: 6PGL enzyme as a therapeutic target in the search for new drugs.

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.

Assessment of cytotoxicity biomarkers on the microalga Chlamydomonas reinhardtii exposed to emerging and priority pollutants

Contamination of aquatic ecosystems linked to anthropogenic activity is currently a major concern; therefore, ecotoxicological studies are needed to assess its effect on organisms. The main objective of this study was to investigate the effects of different pollutants on microalgae in search of sensitive biomarkers that can promote a common cytotoxic response regardless of the contaminant. Cultures of the freshwater microalga Chlamydomonas reinhardtii were exposed for 24 h to four chemicals, three emerging pollutants (benzophenone-3, bisphenol A and oxytetracycline) and one priority substance (atrazine). A cytometric panel was carried out to assess toxicity biomarkers including cellular growth, inherent cell properties, viability, vitality, cytoplasmic membrane potential and ROS levels. Lipid peroxidation, photosynthetic efficiency and transcriptional responses of photosynthesis- and oxidative stress-related genes using RT-qPCR were also studied. Some toxicity responses showed a similar pattern; a decrease in growth rate, vitality and photosynthetic efficiency and an increase in autofluorescence and in the number of cells with depolarised cytoplasmic membrane and were found for all chemicals tested. However, ATZ and OTC provoked a decrease in cell size, whereas BP-3 and BPA caused an increase in cell size, intracellular complexity and ROS levels and a decrease in cell viability. Assayed pollutants generally promoted an overexpression of genes related to cellular antioxidant defence system and a subexpression of photosynthesis-related genes. In addition to the traditional growth endpoint, cell vitality, autofluorescence and gene expression of catalase, glutathione peroxidase and Fe-superoxide dismutase were significantly affected for all chemicals tested, showing a common cytotoxic response. Among the tested substances, BP-3 provoked the strongest cytotoxic alterations on this microalga, pointing out that some emerging contaminants could be more harmful to organisms than priority pollutants.

Effects of Bisphenol A on the microalga Chlamydomonas reinhardtii and the clam Corbicula fluminea

Bisphenol A (BPA) is used throughout the world and it could enter aquatic ecosystems causing harmful effects on humans, animals and plants. The current study relies on the investigation of the toxicity of this emerging pollutant on two freshwater species from different trophic levels: the microalga Chlamydomonas reinhardtii and the clam Corbicula fluminea. After 96 h of exposure to several concentrations of BPA, the growth of C. reinhardtii was affected, being the 96 h-EC₅₀ value for growth 30 mg L^-1. The toxicity and bioaccumulation of 30 mg L^-1 BPA in microalgae after 24 h of exposure were studied. Several cytotoxicity biomarkers such as vitality, oxidative stress and cytoplasmic membrane potential were altered in exposed cells and microalgae accumulated 0.16 pg BPA cell^-1. Regarding C. fluminea, four treatments were established: control without BPA (C); BPA in the food (microalgae pre-exposed for 24 h to 30 mg L^-1) (M); BPA in the water (7.5 mg L^-1) (W); BPA in both food and water (M + W). After one month of exposure, treated bivalves showed a significantly decrease in the filtration rate and increased lipid peroxidation levels, indicating fitness reduction and oxidative damage. Furthermore, the activities of catalase, glutathione reductase, Se-dependent and total glutathione peroxidase enzymes increased significantly in W and M + W treatments with respect to the control. Clams of the M + W treatment were the most affected, indicating that the little amount of BPA bioaccumulated by microalgae could increase the damage. Emerging contaminants may accumulate in several organisms, such as microalgae, and could have negative impacts on ecosystems.

Differential toxicity of the UV-filters BP-3 and BP-4 in Chlamydomonas reinhardtii: A flow cytometric approach

Due to the concern about the negative effects of exposure to sunlight, UV-filters are being introduced in all kind of cosmetic formulas. Wastewater treatment plants are not able to remove and/or degrade them; consequently they find their way into rivers, lakes and oceans. These chemicals are acquiring a concerning status due to their increasingly common use and the potential risk for the environment. Benzophenone-3 (BP-3) and Benzophenone-4 (BP-4) are broad-spectrum UV-filters used for the same purpose in personal care products, insecticides and plastic bags; however, after 96 h of exposure to several concentrations of these UV-filters, the growth of C. reinhardtii was more affected by BP-3 than by BP-4, being the 96 h-EC₅₀ for growth 5 mg L^-1 and 38 mg L^-1, respectively. Based on these values Chlamydomonas reinhardtii cultures were exposed during 24 h to 2.5, 5 and 10 mg L^-1 of BP-3 and 19, 38 and 76 mg L^-1 of BP-4. A cytometric panel was carried out to evaluate the effect of sublethal concentrations of these UV-filters, thus several cytotoxicity biomarkers were analysed, including chlorophyll a fluorescence, viability, metabolic activity, oxidative stress, cytoplasmic and mitochondrial membrane potentials, and intracellular pH. BP-3 and BP-4 affect C.reinhardtii cells in a different way, showing differences for three of the examined parameters. Chlorophyll a fluorescence and mitochondrial membrane potential showed a significant increase (p < 0.05) in BP-3 and a significant decrease in BP-4, whereas viability only decreased significantly in the highest concentrations of BP-3. Regarding to the other parameters analysed, a similar pattern of cytotoxicity was observed. Growth rate, vital population and metabolic activity (esterase activity) and intracellular pH decreased significantly and cytoplasmic membrane potential and ROS levels increased significantly in cultures exposed to both pollutants.

Redox Pathways as Drug Targets in Microaerophilic Parasites

The microaerophilic parasites Entamoeba histolytica, Trichomonas vaginalis, and Giardia lamblia jointly cause hundreds of millions of infections in humans every year. Other microaerophilic parasites such as Tritrichomonas foetus and Spironucleus spp. pose a relevant health problem in veterinary medicine. Unfortunately, vaccines against these pathogens are unavailable, but their microaerophilic lifestyle opens opportunities for specifically developed chemotherapeutics. In particular, their high sensitivity towards oxygen can be exploited by targeting redox enzymes. This review focusses on the redox pathways of microaerophilic parasites and on drugs, either already in use or currently in the state of development, which target these pathways.

Cytotoxic effects of the proton pump inhibitor omeprazole on the non-target marine microalga Tetraselmis suecica

Omeprazole (OMP) is one of the most commonly used drugs for the treatment of gastro-intestinal disorders. Although it is daily consumed in high quantities and commonly detected in waters worldwide, relatively little is known about its ecotoxicity. The aim of this study was to evaluate the potential acute toxicity of increasing concentrations of OMP on the marine microalga Tetraselmis suecica analysing several cytotoxicity biomarkers by flow cytometry after 24h of exposure. Results showed that OMP caused a decrease in growth and autofluorescence, an increase in cellular volume and intracellular complexity, hyperpolarization of cytoplasmic and mitochondrial membranes and intracellular acidification. In addition, large amounts of reactive oxygen species (ROS) were generated which resulted in a decrease in the percentage of the viable population. However, the viable population showed an increase in their metabolic activity as an early response to overcome the stress. In conclusion, OMP may affect proton pumps in non-target organisms such as microalgae; it disturbed pH homeostasis and provoked an early accumulation of ROS that resulted in a rapid cell death in cells exposed to the highest concentration assayed.

Flow cytometric assay to assess short-term effects of personal care products on the marine microalga Tetraselmis suecica

Large quantities of personal care products (PCPs) are used daily and many of their chemical ingredients are subsequently released into marine environments. Cultures of the marine microalga Tetraselmis suecica were exposed for 24 h to three emerging compounds included in the main classes of PCPs: the UV filter benzophenone-3 (BP-3), the disinfectant triclosan (TCS) and the fragrance tonalide (AHTN). Concentrations tested, expressed as cellular quota (pg cell^-1), ranged from 5 to 40 for BP-3, from 2 to 16 for TCS and from 1.2 to 2.4 for AHTN. A small cytometric panel was carried out to evaluate key cytotoxicity biomarkers including inherent cell properties, growth and metabolic activity and cytoplasmic membrane properties. BP-3 caused a significant increase in growth rate, metabolic activity and chlorophyll a fluorescence from 10 pg cell^-1. However, growth and esterase activity decreased in cells exposed to all TCS and AHTN concentrations, except the lowest ones. Also these two compounds provoked a significant swelling of cells, more pronounced in the case of TCS-exposed cells. Although all treated cells remained viable, changes in membrane potential were observed. BP-3 and AHTN caused a significant depolarization of cells from 10 to 1.6 pg cell^-1, respectively; however all TCS concentrations assayed caused a noticeable hyperpolarization of cells. Metabolic activity and cytoplasmic membrane potential were the most sensitive parameters. It can be concluded that the toxicological model used and the toxicological parameters evaluated are suitable to assess the toxicity of these emerging contaminants.

The past, present and future of fluorescent protein tags in anaerobic protozoan parasites

The world health organization currently recognizes diarrhoeal diseases as a significant cause of death in children globally. Protozoan parasites such as Giardia and Entamoeba that thrive in the oxygen-deprived environment of the human gut are common etiological agents of diarrhoea. In the urogenital tract of humans, the anaerobic protozoan parasite Trichomonas vaginalis is notorious as the most common non-viral, sexually transmitted pathogen. Even with high medical impact, our understanding of anaerobic parasite physiology is scarce and as a result, treatment choices are limited. Fluorescent proteins (FPs) are invaluable tools as genetically encoded protein tags for advancing knowledge of cellular function. These FP tags emit fluorescent colours and once attached to a protein of interest, allow tracking of parasite proteins in the dynamic cellular space. Application of green FPs-like FPs in anaerobic protozoans is hindered by their oxygen dependency. In this review, we examine aspects of anaerobic parasite biology that clash with physio-chemical properties of FPs and limit their use as live-parasite protein tags. We expose novel FPs, such as miniSOG that do not require oxygen for signal production. The potential use of novel FPs has the opportunity to leverage the anaerobe parasitologist toolkit to that of aerobe parasitologist.

Chlamydomonas reinhardtii cells adjust the metabolism to maintain viability in response to atrazine stress

Chlamydomonas reinhardtii cells were exposed to a sublethal concentration of the widespread herbicide atrazine for 3 and 24h. Physiological parameters related to cellular energy status, such as cellular activity and mitochondrial and cytoplasmic membrane potentials, monitored by flow cytometry, were altered in microalgal cells exposed to 0.25μM of atrazine. Transcriptomic analyses, carried out by RNA-Seq technique, displayed 12 differentially expressed genes between control cultures and atrazine-exposed cultures at both tested times. Many cellular processes were affected, but the most significant changes were observed in genes implicated in amino acid catabolism and respiratory cellular process. Obtained results suggest that photosynthesis inhibition by atrazine leads cells to get energy through a heterotrophic metabolism to maintain their viability.

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.

Trophic structure of amoeba communities near roots of Medicago sativa after contamination with fuel oil no. 6

Root exudation increases microbial activity, selecting bacterial and fungal communities that metabolize organic matter such as hydrocarbons. However, a strong contamination pulse of hydrocarbons around plant roots may reorganize the soil's microbial trophic structure toward amoebae feeding on bacteria. We conducted a microcosm experiment to elucidate the effect of Medicago sativa on the trophic structure of naked amoebae after a strong pulse of pollution (50,000 ppm of fuel oil no. 6, which is a mixture of long chains ranging from C10 to C28). Plants were seeded 24 h after contamination and species of amoebae in the microcosms were identified at 1, 30, and 60 days after pollution. Several species from three trophic groups of naked amoeba were still alive 24 h after the hydrocarbon pulse. Non-planted microcosms harbored three trophic groups after 60 days, while planted ones nourished four groups. The bacterivore group was the most diverse in all microcosms, followed by protist-eaters and omnivores. The quantity of amoebae was significantly higher (3.4×10(3) organisms/g soil) in the planted pots than in the non-planted ones (1.3×10(3) organisms/g soil after 30 days of pollution (P ≤ 0.01). The shortest hydrocarbon chains (C10-C14) disappeared or diminished in all microcosms, and the longest ones increased in the planted ones. M. sativa thus exerted a positive effect on species richness, quantity, and the composition of amoebae trophic groups in contaminated soil. This indirect effect on bacterial predators is another key factor underlying hydrocarbon assimilation by living organisms during phytoremediation.

Impact of ciprofloxacin and chloramphenicol on the lipid bilayer of Staphylococcus aureus: changes in membrane potential

The present study was undertaken to explore the interaction of ciprofloxacin and chloramphenicol with bacterial membranes in a sensitive and in a resistant strains of Staphylococcus aureus by using 1-anilino-8-naphthalene sulfonate (ANS). The binding of this probe to the cell membrane depends on the surface potential, which modulates the binding constant to the membrane. We observed that these antibiotics interacted with the bilayer, thus affecting the electrostatic surface potential. Alterations caused by antibiotics on the surface of the bacteria were accompanied by a reduction in the number of binding sites and an increase in the ANS dissociation constant in the sensitive strain, whereas in the ciprofloxacin-resistant strain no significant changes were detected. The changes seen in the electrostatic surface potential generated in the membrane of S. aureus by the antibiotics provide new aspects concerning their action on the bacterial cell.

Screening acute cytotoxicity biomarkers using a microalga as test organism

The present study checked the suitability of the integration of flow cytometry (FCM) as technique and a freshwater microalga (Chlamydomonas moewusii) as cell system model for ecotoxicological studies, looking for sensitive biomarkers of acute cytotoxicity of potential contaminants in aquatic systems. The detection of the potential acute toxicity of a pollutant is of interest because pulse discharges of contaminants to natural waters could lead to high concentrations of these substances that are only present for short periods of time but can affect aquatic organisms such as microalgae. Physiological alterations in C. moewusii cells were analysed after 1h of exposure to different concentrations of the herbicide paraquat. Cell viability was not affected, but the acute toxicity of paraquat was evident at other levels of cell physiology. Herbicide-treated cells showed lower autofluorescence and higher size and internal complexity, lower esterase activity and lower mitochondrial membrane potential. Paraquat induced the depolarisation of the plasma membrane and the increase of intracellular free calcium level and cytosolic pH in a concentration-dependent percentage of cells. All these effects can be related to the oxidative stress induced by the herbicide, as revealed the significantly increased intracellular levels of reactive oxygen species in cultures exposed to paraquat concentrations which induced the physiological alterations mentioned above. Excluding cell viability and mitochondrial membrane potential, these cytotoxicity endpoints could be considered sensitive biomarkers for the short-term exposure to pollutants such as herbicides.

Flow cytometric analysis to evaluate physiological alterations in herbicide-exposed Chlamydomonas moewusii cells

Investigation of herbicide toxicology in non-target aquatic primary producers such as microalgae is of great importance from an ecological point of view. In order to study the toxicity of the widely used herbicide paraquat on freshwater green microalga Chlamydomonas moewusii, physiological changes associated with 96 h-exposures to this pollutant were monitored using flow cytometry (FCM) technique. Intracellular reactive oxygen species concentration, cytoplasmic membrane potential, metabolic activity and cell protein content were monitored to evaluate the toxicological impact of paraquat on algal physiology. Results showed that herbicide paraquat induced oxidative stress in C. moewusii cells, as it indicated the increase of both superoxide anion and hydrogen peroxide levels observed in non-chlorotic cells of cultures exposed to increasing herbicide concentrations. Furthermore, a progressive increase in the percentage of depolarised cells and a decrease in the metabolic activity level were observed in response to paraquat when non-chlorotic cells were analysed. Chlorotic cells were probably non-viable cells, based on the cytoplasmic membrane depolarisation, its metabolically non-active state and its drastically reduced protein content. In view of the obtained results, we have concluded that a range of significant physiological alterations, detected by flow cytometry, occur when C. moewusii, an ubiquitous microalga in freshwater environments, is challenged with environmentally relevant concentrations of the herbicide paraquat.

Cross-disciplinary approaches for measuring parasitic helminth viability and phenotype

Parasitic worms (helminths) within the Phyla Nematoda and Platyhelminthes are responsible for some of the most debilitating and chronic infectious diseases of human and animal populations across the globe. As no subunit vaccine for any parasitic helminth is close to being developed, the frontline strategy for intervention is administration of therapeutic, anthelmintic drugs. Worryingly, and unsurprising due to co-evolutionary mechanisms, many of these worms are developing resistance to the limited compound classes currently being used. This unfortunate reality has led to a renaissance in next generation anthelmintic discovery within both academic and industrial sectors. However, a major bottleneck in this process is the lack of quantitative methods for screening large numbers of small molecules for their effects on the whole organism. Development of methodologies that can objectively and rapidly distinguish helminth viability or phenotype would be an invaluable tool in the anthelmintic discovery pipeline. Towards this end, we describe how several basic techniques currently used to assess single cell eukaryote viability have been successfully applied to parasitic helminths. We additionally demonstrate how some of these methodologies have been adopted for high-throughput use and further modified for assessing worm phenotype. Continued development in this area is aimed at increasing the rate by which novel anthelmintics are identified and subsequently translated into everyday, practical applications.

Effects of Salvia miltorrhiza in neural differentiation of rat mesenchymal stem cells with optimized protocol

AIM OF THE STUDY

The present study was aimed to explore the effects of Salvia miltorrhiza in inducing rMSCs to differentiate into functional neurons.

MATERIALS AND METHODS

rMSCs were isolated and cultured in vitro, then Salvia miltorrhiza was added to induce rMSCs to differentiate repeatedly for 5 times with an optimized protocol, and neurophysiological functions such as action potential, endocytosis and exocytosis of the induced cells were investigated.

RESULTS

About 98% of rMSCs expressed markers related to neural stem cells after treatment with preinduction medium, but they remained fibroform, the classical morphological state of MSCs, after exposure to induction medium for 2h, and the induced cells showed a neural shape. Next, fetal bovine serum (FBS) was added into the induction medium, transforming the neuron-like cells into fibroform cells. Finally, after exposure to induction medium, the cells could be transformed into neuron-like cells again. After the procedure was repeated 5 times, the induced cells displayed a classical neural shape and more than 95% of them expressed neural markers, including TUJ-1, NF and synaptophysin. Furthermore, the induced cells displayed neurophysiological functions, as characterized by action potential, endocytosis and exocytosis in response to a solution with a high concentration of potassium (K(+)).

CONCLUSION

Salvia miltorrhiza can induce rMSCs to differentiate into neurons with neurophysiological functions efficiently by an optimized protocol.

Functional attenuation of human sperm by novel, non-surfactant spermicides: precise targeting of membrane physiology without affecting structure

BACKGROUND

We have attempted to identify structural, physiological and other targets on human sperm vulnerable to the spermicidal action of two novel series of non-detergent molecules, reported to irreversibly immobilize human sperm in <30 s, apparently without disrupting plasma membrane.

METHODS

Three sperm samples were studied. Scanning and transmission electron microscopy were used to assess structural aberrations of sperm membrane; plasma membrane potential and intracellular pH measurements (fluorometric) were used to detect changes in sperm physiology; reactive oxygen species (ROS, fluorometric) and superoxide dismutase activity (colorimetric) were indicators of oxidative stress; and sperm dynein ATPase activity demonstrated alterations in motor energy potential, in response to spermicide treatment. Post-ejaculation tyrosine phosphorylation of human sperm proteins (immunoblotting) was a marker for functional integrity.

RESULTS

Disulfide esters of carbothioic acid (DSE compounds) caused complete sperm attenuation at > or =0.002% concentration with hyper-polarization of sperm membrane potential (P < 0.001), intracellular alkalinization (P < 0.01), ROS generation (P < 0.05) and no apparent effect on sperm (n = 150) membrane structure. Isoxazolecarbaldehyde compounds required > or =0.03% for spermicidal action and caused disrupted outer acrosomal membrane structure, depolarization of membrane potential (P < 0.001), intracellular acidification (P < 0.01) and ROS generation (P < 0.01). Detergent [nonoxynol-9 (N-9)] action was sustainable at > or =0.05% and involved complete breakdown of structural and physiological membrane integrity with ROS generation (P < 0.001). All spermicides caused functional attenuation of sperm without inhibiting motor energetics. Unlike N-9, DSE-37 (vaginal dose, 200 microg) completely inhibited pregnancy in rats and vaginal epithelium was unchanged (24 h,10 mg).

CONCLUSIONS

The study reveals a unique mechanism of action for DSE spermicides. DSE-37 holds promise as a safe vaginal contraceptive. CDRI Communication No. 7545.

Methodological aspects of measuring absolute values of membrane potential in human cells by flow cytometry

The bis-barbituric acid oxonol, DiBAC(4)(3) is used as a standard potentiometric probe in human cells. However, its fluorescence depends not only on membrane potential but also varies with nonpotential related changes in the amount of intracellular free and bound dye. This study demonstrates the influence of different experimental conditions on this nonspecific fluorescence proportion. IGR1 melanoma cells as a model were specifically altered in cell volume and protein content by depolarizing treatments or cell cycle synchronization. Flow cytometry was performed over a wide range of extracellular DiBAC(4)(3) concentrations. Fixation and increase in protein content led to a nonspecifically enhanced fluorescence, while changes in the amount of free intracellular dye as a result of altered cell volume proved to be negligible. To establish a calibration curve using totally depolarized cells, the pore-forming action of gramicidin should be preferred to fixation. Below 100 nM DiBAC(4)(3), the logarithmic relation between cell fluorescence and dye concentration turned into a virtually linear function intersecting with zero. Consequently, calibration can then be confined to determination of the fluorescence of depolarized cells stained with the same concentration as used for the actual measurement of membrane potential. Unexpectedly, quenching of fluorescence occurred in totally depolarized cells at concentrations higher than 6,250 nM. Linearity and quenching could be confirmed by additional experiments on Chinese hamster ovary CHO-K1 and B lymphoblastoid LCL-HO cells.

A novel Giardia lamblia nitroreductase, GlNR1, interacts with nitazoxanide and other thiazolides

The nitrothiazole analogue nitazoxanide [NTZ; 2-acetolyloxy-N-(5-nitro-2-thiazolyl)benzamide] represents the parent compound of a class of drugs referred to as thiazolides and exhibits a broad spectrum of activities against a wide variety of helminths, protozoa, and enteric bacteria infecting animals and humans. NTZ and other thiazolides are active against a wide range of other intracellular and extracellular protozoan parasites in vitro and in vivo, but their mode of action and respective subcellular target(s) have only recently been investigated. In order to identify potential targets of NTZ and other thiazolides in Giardia lamblia trophozoites, we have developed an affinity chromatography system using the deacetylated derivative of NTZ, tizoxanide (TIZ), as a ligand. Affinity chromatography on TIZ-agarose using cell extracts of G. lamblia trophozoites resulted in the isolation of an approximately 35-kDa polypeptide, which was identified by mass spectrometry as a nitroreductase (NR) homologue (EAA43030.1). NR was overexpressed as a six-histidine-tagged recombinant protein in Escherichia coli, purified, and then characterized using an assay for oxygen-insensitive NRs with dinitrotoluene as a substrate. This demonstrated that the NR was functionally active, and the protein was designated GlNR1. In this assay system, NR activity was severely inhibited by NTZ and other thiazolides, demonstrating that the antigiardial activity of these drugs could be, at least partially, mediated through inhibition of GlNR1.

Nitazoxanide, a broad-spectrum thiazolide anti-infective agent for the treatment of gastrointestinal infections

Colonisation of the gastrointestinal tract by anaerobic bacteria, protozoa, trematodes, cestodes and/or nematodes and other infectious pathogens, including viruses, represents a major cause of morbidity and mortality in Africa, South America and southeast Asia, as well as other parts of the world. Nitazoxanide is a member of the thiazolide class of drugs with a documented broad spectrum of activity against parasites and anaerobic bacteria. Moreover, the drug has recently been reported to have a profound activity against hepatitis C virus infection. In addition, nitazoxanide exhibits anti-inflammatory properties, which have prompted clinical investigations for its use in Crohn's disease. Studies with nitazoxanide derivatives have determined that there must be significantly different mechanisms of action acting on intracellular versus extracellular pathogens. An impressive number of clinical studies have shown that the drug has an excellent bioavailability in the gastrointestinal tract, is fast acting and highly effective against gastrointestinal bacteria, protozoa and helminthes. A recent Phase II study has demonstrated viral response (hepatitis C) to monotherapy, with a low toxicity and an excellent safety profile over 24 weeks of treatment. Pre-clinical studies have indicated that there is a potential for application of this drug against other diseases, not primarily affecting the liver or the gastrointestinal tract.

Cytotoxic effect of curcumin on Giardia lamblia trophozoites

Giardia lamblia is one of the most important worldwide causes of intestinal infections produced by protozoa. Thus, the search for new alternative therapeutic approaches for this parasitic disease is very important. Common drugs used to control and eradicate this infection, frequently exhibit side effects that force patients to abandon treatment. The present work evaluates the anti-protozoan activity of curcumin, the main constituent of turmeric. Axenic G. lamblia (Portland 1 strain) cultures were exposed to different concentrations of curcumin. Its effects were evaluated on parasite growth, adhesion capacity and parasite morphology. We also evaluated the capacity of curcumin to induce an apoptosis-like effect. All curcumin concentrations inhibited trophozoite growth and adhesion in more than 50% in dose and time dependent manner. Morphological changes were described as protrusions formed under the cytoplasmic membrane, deformation due to swelling and cell agglutination. Curcumin induced apoptosis-like nuclear staining in dose and time dependent manner. In conclusion, curcumin exhibited a cytotoxic effect in G. lamblia inhibiting the parasite growth and adherent capacity, induced morphological alterations, provoked apoptosis-like changes. Future in vitro and in vivo experiments are endowed to elucidate the effect of curcumin in an experimental model of G. lamblia infection, analyze the involvement of ion channels in the swelling effect of curcumin during an apparent osmotic deregulation in G. lamblia trophozoites. This will lead to the proposal of the action mechanism of curcumin as well as the description of mechanism involved during the activation process for the apoptotic-like effect.

In vitro effects of thiazolides on Giardia lamblia WB clone C6 cultured axenically and in coculture with Caco2 cells

The thiazolides represent a novel class of anti-infective drugs, with the nitrothiazole nitazoxanide [2-acetolyloxy-N-(5-nitro 2-thiazolyl) benzamide] (NTZ) as the parent compound. NTZ exhibits a broad spectrum of activities against a wide variety of helminths, protozoa, and enteric bacteria infecting animals and humans. In vivo, NTZ is rapidly deacetylated to tizoxanide (TIZ), which exhibits similar activities. We have here comparatively investigated the in vitro effects of NTZ, TIZ, a number of other modified thiazolides, and metronidazole (MTZ) on Giardia lamblia trophozoites grown under axenic culture conditions and in coculture with the human cancer colon cell line Caco2. The modifications of the thiazolides included, on one hand, the replacement of the nitro group on the thiazole ring with a bromide, and, on the other hand, the differential positioning of methyl groups on the benzene ring. Of seven compounds with a bromo instead of a nitro group, only one, RM4820, showed moderate inhibition of Giardia proliferation in axenic culture, but not in coculture with Caco2 cells, with a 50% inhibitory concentration (IC50) of 18.8 microM; in comparison, NTZ and tizoxanide had IC50s of 2.4 microM, and MTZ had an IC50 of 7.8 microM. Moreover, the methylation or carboxylation of the benzene ring at position 3 resulted in a significant decrease of activity, and methylation at position 5 completely abrogated the antiparasitic effect of the nitrothiazole compound. Trophozoites treated with NTZ showed distinct lesions on the ventral disk as soon as 2 to 3 h after treatment, whereas treatment with metronidazole resulted in severe damage to the dorsal surface membrane at later time points.