Quantifying metabolic activity of Ascaris suum L3 using resazurin reduction

BACKGROUND

Helminth infections are an important public health problem in humans and have an even greater impact on domestic animal and livestock welfare. Current readouts for anthelmintic drug screening assays are stage development, migration, or motility that can be subjective, laborious, and low in throughput. The aim of this study was to apply and optimize a fluorometric technique using resazurin for evaluating changes in the metabolic activity of Ascaris suum third-stage larvae (L3), a parasite of high economic relevance in swine.

METHODS

Ascaris suum L3 were mechanically hatched from 6- to 8-week embryonated and sucrose-gradient-enriched eggs. Resazurin dye and A. suum L3 were titrated in 96-well microtiter plates, and resazurin reduction activity was assessed by fluorometry after 24 h of incubation. Fluorescence microscopy was used to localize the resazurin reduction site within the larvae. Finally, we exposed A. suum L3 to various stress conditions including heat, methanol, and anthelmintics, and investigated their impact on larval metabolism through resazurin reduction activity.

RESULTS

We show that the non-fluorescent dye resazurin is reduced inside vital A. suum L3 to fluorescent resorufin and released into the culture media. Optimal assay parameters are 100-1000 L3 per well, a resazurin concentration of 7.5 µg/ml, and incubation at 37 °C/5% CO₂ for 24 h. An intact L2 sheath around the L3 of A. suum completely prevents the uptake of resazurin, while in unsheathed L3, the most intense fluorescence signal is observed along the larval midgut. L3 exposed to methanol or heat show a gradually decreased resazurin reduction activity. In addition, 24 h exposure to ivermectin at 0.625 µM, mebendazole at 5 µM, and thiabendazole from 10 to 100 µM significantly decreased larval metabolic activity by 55%, 73%, and 70% to 89%, respectively.

CONCLUSIONS

Together, our results show that both metabolic stressors and anthelmintic drugs significantly and reproducibly reduce the resazurin reduction activity of A. suum L3, making the proposed assay a sensitive and easy-to-use method to evaluate metabolic activity of A. suum L3 in vitro.

Characterization of Cellular Viability Using Label-Free Brightfield Live-Cell Imaging

In recent years, the assembly and annotation of chemogenomic libraries have gained interest by the phenotypic screening community. Apart from basic annotations of the compound potency and selectivity, these compound libraries benefit in particular from annotation regarding the effect of the inhibitors on cellular viability to distinguish between on-target effects of a compound and unspecific cytotoxicity. Here, we provide a protocol to determine viability as a first determinant in compound quality control, using the Incucyte live-cell imaging system. The compounds are classified according to their calculated growth rate to determine a cytotoxic, cytostatic, or healthy outcome. All compounds affecting the growth rate can be further evaluated regarding their specific effects on cell health in a high-content live-cell multiplex assay, described in Chapter 5 .

Neutral Red Uptake Assay to Assess Cytotoxicity In Vitro

The neutral red uptake (NRU) assay is a cell viability assay that can be used for the assessment of compound-induced cytotoxicity. It is based on the ability of living cells to incorporate neutral red, a weak cationic dye, in lysosomes. The quantification of xenobiotic-induced cytotoxicity is expressed as a concentration-dependent reduction of the uptake of neutral red when compared to cells exposed to corresponding vehicle controls. The NRU assay is mainly used for hazard assessment in in vitro toxicology applications. Hence, this method has been incorporated in regulatory recommendations such as the OECD test guideline TG 432, in which an in vitro 3T3-NRU-phototoxicityassay is described to assess the cytotoxicity of compounds in the presence or absence of UV light.This book chapter describes a detailed protocol to carry out the NRU assay using the human hepatoma cell line HepG2, which is frequently employed as an alternative in vitro model for human hepatocytes. As an example, the cytotoxicity of acetaminophen and acetylsalicylic acid is assessed.

The MTT Assay: A Method for Error Minimization and Interpretation in Measuring Cytotoxicity and Estimating Cell Viability

The MTT assay is extensively used, most often to infer a measure of cytotoxicity of treatments to cells. As with any assay though, there are a number of limitations. The method described here is designed with consideration of how the MTT assay fundamentally works to account for, or at least identify, confounding factors in measurements. It also provides a decision-making framework to best interpret and complement the MTT assay to apply it as either a measure of metabolic activity or cell viability.

Phototoxicity of BODIPY in long-term imaging can be reduced by intramolecular motion

For long-term live-cell fluorescence imaging and biosensing, it is crucial to work with a dye that has high fluorescence quantum yield and photostability without being detrimental to the cells. In this paper, we demonstrate that neutral boron-dipyrromethene (BODIPY)-based molecular rotors have great properties for high-light-dosage demanding live-cell fluorescence imaging applications that require repetitive illuminations. In molecular rotors, an intramolecular rotation (IMR) allows an alternative route for the decay of the singlet excited state (S₁) via the formation of an intramolecular charge transfer state (CT). The occurrence of IMR reduces the probability of the formation of a triplet state (T₁) which could further react with molecular oxygen (³O₂) to form cytotoxic reactive oxygen species, e.g., singlet oxygen (¹O₂). We demonstrate that the oxygen-related nature of the phototoxicity for BODIPY derivatives can be significantly reduced if a neutral molecular rotor is used as a probe. The studied neutral molecular rotor probe shows remarkably lower phototoxicity when compared with both the non-rotating BODIPY derivative and the cationic BODIPY-based molecular rotor in different light dosages and dye concentrations. It is also evident that the charge and localization of the fluorescent probe are as significant as the IMR in terms of the phototoxicity in a long-term live-cell imaging.

A Simple Bioluminescent Assay for the Screening of Cytotoxic Molecules Against the Intracellular Form of Leishmania infantum

This chapter describes a viability assay for the intracellular (amastigote) and clinically relevant form of Leishmania infantum that is based on the detection of bioluminescence (BL) signal. The assay uses a reporter cell line of L. infantum that expresses constitutively a redshifted luciferase from Photinus pyralis and murine macrophages (cell line J774.A1) as host cells for infection. The host cell line was selected because it is a differentiated cell line, easy to manipulate in vitro, and advantageous for ethical reasons. This chapter introduces an assay designed for the screening of bioactive compounds/molecules employing a 96-well microplate and a 24 h treatment. The assay setup shows excellent balance between simplicity (cell culture manipulation/infection and timing) and quality parameters, as well as potential to detect drug-like molecules acting in a fast and cytotoxic manner.

Development of genistein-loaded gold nanoparticles and their antitumor potential against prostate cancer cell lines

Soy isoflavone genistein (Gen) exerts beneficial effects against prostate cancer cells in vitro and in vivo. However, its use as a chemoprevention/therapeutic agent is largely limited due to its low bioavailability. In this study we synthesized two variants of a new delivery system, genistein-gold nanoparticles conjugates Gen@AuNPs1 and Gen@AuNPs2, by an environmentally friendly method, using a dual role of Gen to reduce Au³⁺ and stabilize the formed AuNPs, with no additional component. The formation of Gen@AuNPs was confirmed via UV-Vis spectroscopy, FTIR, and Raman spectra measurements. The spherical shape and uniform size of Gen@AuNPs1 and Gen@AuNPs2 (10 ± 2 and 23 ± 3 nm, respectively), were determined by transmission electron microscopy. The nano-conjugates also varied in hydrodynamic diameter (65.0 ± 1.7 and 153.0 ± 2.2 nm) but had similar negative zeta potential (-35.0 ± 2.5 and -37.0 ± 1.6 mV), as measured by dynamic light scattering. The Gen loading was estimated to be 46 and 48%, for Gen@AuNPs1 and Gen@AuNPs2, respectively. The antiproliferative activities of GenAuNPs were confirmed by MTT test in vitro on three malignant prostate carcinoma cell lines (PC3, DU 145, and LNCaP), while selectivity toward malignant phenotype was confirmed using non-cancerous MRC-5 cells. Flow cytometric analysis showed that the inhibition on cell proliferation of more potent Gen@AuNPs1 nano-conjugate is comparable with the effects of free Gen. In conclusion, the obtained results, including physicochemical characterization of newly synthesized AuNPs loaded with Gen, cytotoxicity, and IC₅₀ assessments, indicate their stability and bioactivity as an antioxidant and anti-prostate cancer agent, with low toxicity against human primary cells.

Luminescence-Based, Low- and Medium-Throughput Assays for Drug Screening in Schistosoma mansoni Larval Stage

Schistosomiasis is one of the major parasitic diseases with more than  200 million people infected worldwide every year. Praziquantel is the drug of choice against the schistosomiasis although the use of a single drug to treat such a large amount of infected people appears particularly worrisome. For this reason, the search of new schistosomicidal compounds is viewed as an urgent goal and a number of screening campaigns have been carried out in the past years. The larval stage of Schistosoma (schistosomula) has been widely used in order to identify new compounds against the parasite. Here we describe detailed practical procedures for a luminescence-based assay proven to be highly effective for the selection of schistosomicidal compounds on small and medium-high scale. The assay is based on the quantitation of the parasite ATP, a good indicator of metabolically active cells, as measure of schistosomula viability. This assay is fast and reproducible, and it is suitable either for manual or for semiautomated screenings.

Handling deviating control values in concentration-response curves

In cell biology, pharmacology and toxicology dose-response and concentration-response curves are frequently fitted to data with statistical methods. Such fits are used to derive quantitative measures (e.g. EC\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{20}$$\end{document}20 values) describing the relationship between the concentration of a compound or the strength of an intervention applied to cells and its effect on viability or function of these cells. Often, a reference, called negative control (or solvent control), is used to normalize the data. The negative control data sometimes deviate from the values measured for low (ineffective) test compound concentrations. In such cases, normalization of the data with respect to control values leads to biased estimates of the parameters of the concentration-response curve. Low quality estimates of effective concentrations can be the consequence. In a literature study, we found that this problem occurs in a large percentage of toxicological publications. We propose different strategies to tackle the problem, including complete omission of the controls. Data from a controlled simulation study indicate the best-suited problem solution for different data structure scenarios. This was further exemplified by a real concentration-response study. We provide the following recommendations how to handle deviating controls: (1) The log-logistic 4pLL model is a good default option. (2) When there are at least two concentrations in the no-effect range, low variances of the replicate measurements, and deviating controls, control values should be omitted before fitting the model. (3) When data are missing in the no-effect range, the Brain-Cousens model sometimes leads to better results than the default model.

In vitro effects of glyphosate-based herbicides and related adjuvants on primary culture of hemocytes from Haliotis tuberculata

Glyphosate-based herbicides are among the most produced and widely-used herbicides. Studies have shown that commercial formulations and adjuvants may be more toxic to non-target organisms than the active ingredients alone, but the mechanisms of action of these chemicals remain unclear. The aim of this study was to investigate the in vitro effects of glyphosate, a commercial formulation and adjuvant alone using primary culture of hemocytes from the European abalone Haliotis tuberculata, a commonly farmed shellfish. Glyphosate was found to have negligible effects on viability, phagocytic activities and lysosome stability even with very high doses (i.e. 100 mg L-1). By contrast, greater effects on viability were observed for the commercial formulation and adjuvant alone, with EC50 values of 41.42 mg L-1 and 1.85 mg L-1, respectively. These results demonstrate that the toxic sublethal effects (i.e. phagocytic activity and destabilization of lysosomal membranes) of formulated glyphosate came from adjuvants and suggest they may be related to cell and organelle membrane destabilization.

Human platelet lysate efficiency, stability, and optimal heparin concentration required in culture of mammalian cells

Background

Fetal bovine serum (FBS) has been used to support the growth and proliferation of mammalian cells for decades. Owing to several risk factors associated with FBS, several trials have been conducted to evaluate substitutes to FBS with the same efficiency and the lower risk issues.

Methods

In this study, human platelet lysate (HPL) derived from activated human platelets was evaluated as an alternative to FBS due to the associated risk factors. To evaluate the efficiency of the preparation process, platelet count was performed before and after activation. The concentrations of several growth factors and proteins were measured to investigate HPL efficiency. HPL stability was studied at regular intervals, and optimal heparin concentration required to prevent gel formation in various media was determined. The biological activity of HPL and FBS was compared by evaluating the growth performance of Vero and Hep-2 cell lines.

Results

Result of platelet count assay revealed the efficiency of HPL preparation process. Growth factor concentrations in HPL were significantly higher than those in FBS, while the protein content of HPL was lower than that of FBS. Stability study data showed that the prepared HPL was stable for up to 15 months at -20℃. Ideal heparin concentration to be used in different media was dependent on calcium concentration. Results of cell viability assay showed that HPL was superior to FBS in supporting the growth and proliferation of Vero and Hep-2 cells.

Conclusion

The HPL prepared by the mechanical activation of platelets may serve as an efficient alternative to FBS in cell culture process.

Nanotoxicity Assessment Using Embryonic Zebrafish

The emergence of nanomaterials in industrial processing and consumer products has generated an increased presence of nano-enabled products in the environment and now pose an increased risk of exposure to living organisms. However, assessing the risks of nanomaterials is a challenging task because of a large variety and great variability in their properties. Here, we describe a methodology for assessing toxicity and evaluate potential risks posed by nanomaterials using zebrafish embryos as a model organism. Zebrafish are a well-established organism that has a number of advantages over other biological models. These include optical transparency, similar structure and arrangement of organs, and conserved genetic pathways compared to other vertebrates. Their rapid development and high numbers of embryos enables high throughput screening to study toxicity of a large number of nanomaterials. The method described in this chapter can be used as a universal screening approach to assess toxicity of any type of nanomaterials, determine both lethal and sublethal effects, measure LD50 doses, evaluate morphological and organ defects, cell apoptosis, and production of reactive species.

Evaluation of Demodex mite viability using motility and scattered light intensity

Demodex mites have been suggested to have a role in various cutaneous and ocular disorders pathogenesis, such as rosacea or blepharitis. Evaluation of potential treatments with anti-Demodex effects is difficult because the viability of living mites needs to be evaluated during their exposure to the agent being tested. Mite viability is currently based solely on their observed movement. However, this method of assessing viability has significant limitations as mites may be resting, immobile or paralysed at any given observation point giving the observer a false impression of the organism's death. To overcome this limitation we evaluated a new quantitative method of evaluating the viability of Demodex mites by using scattered light intensity (SLI). We demonstrated that when combined with observation of mite motility, SLI provided increased accuracy of the evaluation of viability of mites being studied. This new viability assay will help address the technical challenges of mite viability experiments. Accurate evaluation of mite viability will enhance mite biology research and allow for more accurate in vitro toxicity assays of proposed anti-mite agents.

Variable Dose Analysis: A Novel High-throughput RNAi Screening Method for Drosophila Cells

Genetic screens are a powerful approach to identify previously uncharacterized genes involved in specific biological processes. Several technologies have been developed for high-throughput screens using reagents such as RNAi or CRISPR, and each approach is associated with specific advantages and disadvantages. Variable Dose Analysis (VDA), is an RNAi-based method developed in Drosophila cells that improves signal-to-noise ratio compared to previous methods. VDA assays are performed by co-transfecting cells with a plasmid expressing shRNA, (a type of RNAi that can be easily expressed from a DNA plasmid) against a gene of interest and a second plasmid expressing a fluorescent reporter protein. Fluorescent protein expression, can be used as an indirect readout of shRNA expression and therefore target gene knockdown efficiency. Using this approach, we can measure phenotypes over a range of knockdown efficiencies in a single sample. When applied to genetic interaction screens, VDA results in improved consistency between screens and reliable detection of known interactions. Furthermore, because phenotypes are analyzed over a range of target gene knockdown efficiencies, VDA allows the detection of phenotypes and genetic interactions involving essential genes at sub-lethal knockdown efficiency. This therefore represents a powerful approach to high-throughput screening applicable to a wide range of biological questions.

Efficient isolation and observation of the most complex human commensal, Demodex spp

Demodex spp. mites are an often neglected member of the human skin microbiome. Mostly they are commensals, although their pathophysiological role in rosacea, spinulosis folliculorum, and other skin diseases is recognized. Little is known about their life cycle, biology, and physiology. Demodex mites cannot be cultivated in vitro, thereby complicating research immensely. The manual extraction from human sebum is laborious and death can only be detected by surrogate markers like ceased movement or loss of fluorescence. Here we present a new approach for the extraction of larger mite numbers and the hitherto most precise way to detect death. The extraction of mites from sebum and debris by hand can be accelerated by a factor 10 using sucrose gradient centrifugation, which is well tolerated by the mites. Staining with propidium iodide allows for easy identification of dead mites, excluding frail mites that stopped moving, and has no negative effect on overall mite survival. We anticipate our methods to be a starting point for more sophisticated research and ultimately in vitro cultivation of Demodex spp. mites.

Mechanisms of oxidative stress caused by CuO nanoparticles to membranes of the bacterium Streptomyces coelicolor M145

Toxic effects of widely used CuO nanoparticles (NPs) on the genus Streptomyces has been seldom studied. This work investigated toxicities of several sizes of CuO nanoparticles (NPs) to Streptomyces coelicolor M145 (S. coelicolor M145). Compared with NPs, toxicity of micrometer-sized CuO on M145 was trivial. In 0.9% NaCl, when the concentration of CuO NPs was 100 mg/L, survival of bacteria increased from 18.3% in 20 nm particles to 31.1% in 100 nm particles. With increasing concentrations of CuO, the level of ROS gradually increased and there were significant differences (p ＜ 0.05) in ROS exposed to 20, 40 and 100 nm (80 nm) CuO NPs. In TSBY medium, toxicity of CuO NPs was less and mainly attributed to release of Cu²⁺, analysis by confocal laser scanning microscope (CLSM) showed that size of the mycelium did not change although some individual bacteria died. This was likely due to Cu²⁺ released from NPs entering cells through the membrane, while in 0.9% NaCl, lesions on membranes was caused by NPs outside the bacteria. This research indicated that toxicity of CuO NPs to S. coelicolor, is related to both size of NPs and is dependent on characteristics of the medium.

CAPSULE

This is the first time to measure the toxicity of nano materials to Streptomyces, and toxic CuO NPs to Streptomyces have been shown to differ depending on medium.

Transformation Products of Carbamazepine (CBZ) After Ozonation and their Toxicity Evaluation Using Pseudomonas sp. Strain KSH-1 in Aqueous Matrices

Carbamazepine (CBZ) is an anti-epileptic and anti-convulsant drug widely used for the treatment of epilepsy and other bipolar disorders. Ozone as an advanced oxidation process has been widely used for the degradation of CBZ resulting in the formation of transformation products (ozonides). The present research aims to isolate and identify potential microorganism, capable of degradation of CBZ and its transformation products. The cell viability and cytotoxicity of pure CBZ and their ozone transformation products were evaluated using the cells of Pseudomonas sp. strain KSH-1 through cell viability assay tests. The cells metabolic activity was assessed at varying CBZ concentrations (~ 10-25 ppm, pure CBZ) and cumulatively for ozone transformation products. For pure CBZ, % cell viability decreases as CBZ concentration increases, while, in case of post-ozonated CBZ transformation products, the viability decreases initially and then increases upon exposure of ozone with a maximum cell viability of 97 ± 2.8% evaluated for 2 h post-ozonated samples.

Basic Colorimetric Proliferation Assays: MTT, WST, and Resazurin

This chapter describes selected assays for the evaluation of cellular viability and proliferation of cell cultures. The underlying principle of these assays is the measurement of a biochemical marker to evaluate the cell's metabolic activity. The formation of the omnipresent reducing agents NADH and NADPH is used as a marker for metabolic activity in the following assays. Using NADH and NADPH as electron sources, specific dyes are biochemically reduced which results in a color change that can be determined with basic photometrical methods. The assays selected for this chapter include MTT, WST, and resazurin. They are applicable for adherent or suspended cell lines, easy to perform, and comparably economical. Detailed protocols and notes for easier handling and avoiding pitfalls are enclosed to each assay.

Non-invasive, electro-orientation-based viability assay using optically transparent electrodes for individual fission yeast cells

A non-invasive assay of cylindrical yeast cell viability based on electro-orientation (EO) in an alternating electric field was developed, in which cell viability can be determined by each cell's EO direction without the need for reagents. A cell suspension of a few microliters was sandwiched between a pair of optically transparent indium-tin-oxide (ITO) plate electrodes. Observation under a light microscope enabled easy identification of EO based on cell shape, e.g., cells were standing upright and appeared perfectly circular when oriented parallel to the electric field direction (standing position), and they were lying flat and had an elongated shape when oriented perpendicular to the field (lain-down position). The alternative EO positions of living or dead cells were dependent on the applied frequency: opposite EO positions were obtained by applying an AC voltage of 1.5V at 10MHz; at which point, only living cells rapidly attained a standing position, whereas dead cells were lain-down within 10s. All the cell's EO positions agreed well with a viability assay by florescence staining. Therefore, at the single-cell level and fluorescently label-free, it was possible to simply and accurately determine whether individual cells were alive or dead based on their shape.

Anti-proliferative and anti-migratory effects of hyperforin in 2D and 3D artificial constructs of human dermal fibroblasts - A new option for hypertrophic scar treatment?

Hyperforin (HYP), one of the main bioactive compounds in extracts of Hypericum perforatum, is a potential drug candidate for the treatment of skin diseases. Since extracts have proven to support wound healing, in the present study effects of HYP on human dermal fibroblasts (HDF) were evaluated in 2D and 3D in vitro dermal constructs. Viability and cytotoxicity assays as well as a live-dead cell staining were performed to test at which concentration HYP reduces viability and/or shows cytotoxicity. Furthermore a differentiation between cytotoxic, anti-proliferative and anti-migratory effects was done. For the latter purpose a 2D migration assay was performed. HDF-induced contraction of a 3D artificial dermal (AD) construct was determined at given HYP concentration. Induction of apoptosis was examined by determination of caspase 3/7 activities. HYP reduced viability of HDF down to 70% at concentrations of 5-10µM. This decrease was not due to cytotoxicity but to a reduction in proliferation as shown from both the proliferation assay and the cytotoxicity assay as well as from live-dead cell staining. The 2D migration assay showed that HYP reduced migration activity of HDF cells at a concentration of 10µM. At this concentration HYP also reduced the HDF-induced contraction of collagen gels as 3D AD constructs. Apoptotic effects of HYP were excluded performing a caspase 3/7 activity detecting assay. The results show for the first time that HYP may be rather a potential candidate for treatment of hypertrophic scars than promoting effects which are understood as important in wound healing.

Assaying Cellular Viability Using the Neutral Red Uptake Assay

The neutral red uptake assay is a cell viability assay that allows in vitro quantification of xenobiotic-induced cytotoxicity. The assay relies on the ability of living cells to incorporate and bind neutral red, a weak cationic dye, in lysosomes. As such, cytotoxicity is expressed as a concentration-dependent reduction of the uptake of neutral red after exposure to the xenobiotic under investigation. The neutral red uptake assay is mainly used for hazard assessment in in vitro toxicology applications. This method has also been introduced in regulatory recommendations as part of 3T3-NRU-phototoxicity-assay, which was regulatory accepted in all EU member states in 2000 and in the OECD member states in 2004 as a test guideline (TG 432). The present protocol describes the neutral red uptake assay using the human hepatoma cell line HepG2, which is often employed as an alternative in vitro model for human hepatocytes. As an example, the cytotoxicity of acetaminophen and acetyl salicylic acid is assessed.

Antimicrobial activity of new green-functionalized oxazoline-based oligomers against clinical isolates

Background

The search for new antimicrobial compounds able to overcome the global issue of microbial resistance to antibiotics is a priority worldwide. Moreover, several commensal microorganisms have been increasingly associated to opportunistic microbial infections. Having previously disclosed the green synthesis and preliminary characterization of the oligomers [linear oligo(ethylenimine) hydrochloride and oligo(2-methyl-2-oxazoline) quaternized with N,N-dimethyldodecylamine] we herein report on the screening of these oligomers against a battery of 69 clinical isolates of Aerococcus spp., Candida spp., Staphylococcus spp. and Streptococcus spp.

Findings

The isolates’ susceptibility to both oligomers was evaluated by determining their minimal inhibitory concentration (MIC) and the biocidal effectiveness of each compound was further confirmed through spectrophotometric measurements and fluorescence microscopy. The MIC values of the 69 isolates were highly variable, yet favourably comparable with those of other antimicrobial polymers. The viability assays resulted in 100% of microbial killing rate after only 5 min, highlighting the promising antimicrobial action of these oligomers.

Conclusions

Though further studies are required, evidence suggests that a strong effort should be done in order to confirm these compounds as valid alternatives for several clinical applications. This is reinforced by their well described biocompatibility with human tissues and by their proposed mechanism of action which difficult the development of microbial resistance to these compounds.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-015-1166-5) contains supplementary material, which is available to authorized users.

Development of a new oxygen consumption rate assay in cultures of Acanthamoeba (Protozoa: Lobosea) and its application to evaluate viability and amoebicidal activity in vitro

A new fluorometric method has been developed for measuring the oxygen consumption rate (OCR) of Acanthamoeba cultures in microplates and for screening molecules with amoebicidal activity against this microorganism. The use of a biofunctional matrix (containing an oxygen-sensitive fluorogenic probe) attached to the microplate wells allowed continuous measurement of OCR in the medium, hence assessment of amoebic growth. The new OCR method applied to cell viability yielded a linear relationship and monitoring was much quicker than with indirect viability assays previously used. In addition, two drugs were tested in a cytotoxicity assay monitored by the new OCR viability test. With this procedure, the standard amoebicidal drug chlorhexidine digluconate showed an IC50 of 3.53 + 1.3 mg/l against Acanthamoeba polyphaga and 3.19 + 1.2 mg/l against Acanthamoeba castellanii, whereas a cationic dendrimer [G1Si(NMe3+)4] showed an IC50 of 6.42 + 1.3 mg/l against A. polyphaga. These data agree with previous studies conducted in our laboratory. Therefore, the new OCR method has proven powerful and quick for amoebicidal drug screening and is likely to be applied in biochemical studies concerning protozoa respiration and metabolism.

In vitro efficacy of ethanolic extract of Artemisia absinthium (Asteraceae) against Leishmania major L. using cell sensitivity and flow cytometry assays

Leishmaniasis is one of the most neglected human diseases with an estimated global burden ranking second in mortality and fourth in morbidity among the tropical infections. Chemotherapy involving the use of drugs like glucantime is the mainstay treatment in endemic areas of Iran. Drug resistance is increasingly prevalent, so search for alternative therapy is gathering pace. Medicinal herbs, like wormwood Artemisia, have chemical compounds effective against a number of pathogens. In this study, the efficacy of ethanol extract from Artemisia absinthium (Asteraceae) against Leishmania major L. was investigated in vitro. The outcome of different effective doses (1-40 mg/ml) of ethanol extracts from this medicinal herb, A. absinthium, on a standard Iranian parasite strain of L. major was examined. The L. major promastigote cell sensitivity and mortality or viability effects due to the addition of herbal extract were measured using the MTT assay and the flow cytometry technique, respectively. There was complete agreement between the two assays. The lethal concentration (LC50) was measured as 101 mg/ml. Some contrasting relationships between the medicinal herb concentrations and the viability of parasites were observed; so that there was an increased multiplication of the parasite at low concentrations of the drug, but an anti-parasitic apoptotic effect was seen at high concentrations of A. absinthium. It was concluded that there might be one or more chemical constituents within the herbal extract of wormwood which at high concentration controlled cell division and affected the relevant activity within the only one giant mitochondrion in this flagellate parasite. At low doses, however, it showed the opposite effect of leading to mitotic cell divisions.