The role of plasma membrane in bioreduction of two tetrazolium salts, MTT, and CTC

The immunostimulatory roles of gold nanoparticles in immunization and vaccination against Brucella abortus antigens

One effective antigen carrier proposed for use in immunization and vaccination is gold nanoparticles. Prior work has shown that gold nanoparticles themselves have adjuvant properties. Currently, gold nanoparticles are used to design new diagnostic tests and vaccines against viral, bacterial, and parasitic infections. We investigated the use of gold nanoparticles as immunomodulators in immunization and vaccination with an antigen isolated from Brucella abortus. Gold nanoparticles with a diameter of 15 nm were synthesized for immunization of animals and were then conjugated to the isolated antigen. The conjugates were used to immunize white BALB/c mice. As a result, high-titer (1:10240) antibodies were produced. The respiratory and proliferative activities of immune cells were increased, as were the serum interleukin concentrations. The minimum antigen amount detected with the produced antibodies was ∼ 0.5 pg. The mice immunized with gold nanoparticles complexed with the B. abortus antigen were more resistant to B. abortus strain 82 than were the mice immunized through other schemes. This fact indicates that animal immunization with this conjugate enhances the effectiveness of the immune response. The results of this study are expected to be used in further work to examine the protective effect of gold nanoparticles complexed with the B. abortus antigen on immunized animals and to develop test systems for diagnosing brucellosis in the laboratory and in the field.

An improved MTT colorimetric method for rapid viable bacteria counting

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay has been employed in the analysis of bacterial growth. In comparison to experiments conducted on mammalian cells, the MTT bacterial assay encounters a greater number of interfering factors and obstacles that impact the accuracy of results. In this study, we have elucidated an improved MTT assay protocol and put forth an equation that establishes a correlation between colony-forming units (CFU) and the amount of formazan converted by the bacteria, drawing upon the fundamental principle of the MTT assay. This equation is represented as CFU=kF. Furthermore, we have explicated a methodology to determine the scale factor "k" by employing S. aureus and E. coli as illustrative examples. The findings indicate that S. aureus and E. coli reduce MTT by a cyclic process, from which the optimal reduction time at room temperature was determined to be approximately 30 mins. Furthermore, individual E. coli exhibits an MTT reduction capacity approximately four times greater than that of S. aureus. HPLC analysis proves to be the most accurate method for mitigating interferences during the dissolution and quantification of formazan. Additionally, this study has identified a new constraint related to the narrow linear range (0-125 μg/mL) of formazan concentration-absorbance and has presented strategies to circumvent this limitation.

Tetrazolium-based colorimetric assays underestimat the direct antitumor effects of anti-VEGF agent bevacizumab

The direct antitumor effect of bevacizumab (BEV) has long been debated. Assessment of the direct cytotoxic activities of drugs is usually conducted via in vitro experiments, of which tetrazolium-based colorimetric assays are widely employed to measure the direct antitumor activity of BEV. This study aimed to investigate whether tetrazolium-based colorimetric assays are applicable when evaluating the cytotoxicity of BEV against tumor cells. Our results showed that BEV significantly augmented tumor-cell mitochondrial metabolism. Enhanced mitochondrial metabolism caused changes in cellular oxidation-and-reduction environment and upregulated succinate dehydrogenase, which in turn promoted the reduction of tetrazolium to produce formazan. Increased formazan formation resulted in underestimation of the in vitro direct antitumor effect of BEV. Furthermore, inhibition of mitochondrial hypermetabolism partially corrected the underestimation of colorimetric assays in evaluating the direct antitumor activity of BEV. Our findings suggest that tetrazolium-based colorimetric assays are unsuitable for accurately assessing the in vitro cytotoxicity of anti-VEGF drugs and may be the methodological reason for the controversial direct antitumor effect of BEV.

In Vitro Evaluation of the Cytotoxic Potential of Thiosemicarbazide Coordinating Compounds in Hepatocyte Cell Culture

Cancer is a global medical problem and, despite research efforts in the field of tumor treatment, there is currently a shortage of specific anticancer drugs. Most anticancer drugs show significant side effects. The liver is the organ that has central functions in drug metabolism, being a major target of the harmful action of anticancer compounds. In this context, it is essential to evaluate the cytotoxic effects of potential anticancer substances. Therefore, hepatotoxicity and hepatocyte viability were determined in vitro to evaluate the action of seven new local thiosemicarbazide coordination compounds (CCT) on normal liver cells. Doxorubicin was used as a reference substance. The control group consisted of hepatocytes not exposed to CCT action. The cell viability of hepatocytes treated with CCT decreased significantly by 5-12% compared to the control, but was statistically significantly higher by 5-14% compared to doxorubicin, except after CMD-8 and CMT-67 influence, when it does not change. Thus, new local CCT had a selective effect on hepatocytes in vitro and were less hepatotoxic compared to doxorubicin, which may be the basis for further study of its potential in anticancer drugs.

Immunization of Mice with Gold Nanoparticles Conjugated to Thermostable Cancer Antigens Prevents the Development of Xenografted Tumors

Gold nanoparticles as part of vaccines greatly increase antigen stability, antigen accumulation in the lymph nodes, and antigen uptake by antigen-presenting cells. The use of such particles as part of anticancer vaccines based on heat shock proteins to increase vaccine effectiveness is timely. We prepared and characterized nanoconjugates based on 15-nm gold nanoparticles and thermostable tumor antigens isolated from MH22a murine hepatoma cells. The whole-cell lysate of MH22a cells contained the main heat shock proteins. BALB/c mice were injected with the conjugates and then received transplants of MH22a cells. The highest titer was produced in mice immunized with the complex of gold nanoparticles + antigen with complete Freund's adjuvant. The immunized mice showed no signs of tumor growth for 24 days. They also showed a decreased production of the INF-γ, IL-6, and IL-1 proinflammatory cytokines compared to the mice immunized through other schemes. This study is the first to show that it is possible in principle to use gold nanoparticles in combination with thermostable tumor antigens for antitumor vaccination. Antitumor vaccines based on thermostable tumor antigens can be largely improved by including gold nanoparticles as additional adjuvants.

Synthesis of silymarin-selenium nanoparticle conjugate and examination of its biological activity in vitro

Silymarin (Sil) was conjugated to selenium nanoparticles (SeNPs) to increase Sil bioavailability. The conjugates were monodisperse; the average diameter of the native SeNPs was ~ 20-50 ± 1.5 nm, whereas that of the conjugates was 30-50 ± 0.5 nm. The use of SeNPs to increase the bioavailability of Sil was examined with the MH-22a, EPNT-5, HeLa, Hep-2, and SPEV-2 cell lines. The EPNT-5 (glioblastoma) cells were the most sensitive to the conjugates compared to the conjugate-free control. The conjugates increased the activity of cellular dehydrogenases and promoted the penetration of Sil into the intracellular space. Possibly, SeNPs play the main part in Sil penetration of cells and Sil penetration is not associated with phagocytosis. Thus, SeNPs are promising for use as a Sil carrier and as protective antigens.

Proteins and polysaccharides from vegetative mycelium of medicinal basidiomycete Lentinus edodes display cytotoxicity towards human and animal cancer cell lines

Detection and study of biologically active compounds seems a promising area of research in cancer diagnostics and therapies. The glycoprotein and polysaccharide fractions showing high cytotoxicity towards several human and animal cancer cell lines: A549, Hep-2, HeLa, С6 and SPEV-2 were isolated from basidiomycete Lentinus edodes vegetative mycelium and fruiting body and further characterized. It was found that water-soluble glycoprotein fractions caused the most significant, 70-100% inhibition of metabolic activity of SPЕV-2, А549 and С6 cell lines. The effective concentrations of glycoprotein fractions reducing the viability of cancer cell lines were determined. The protein and subunit composition of fractions was studied; the highly active galactose-specific lectins were found to be present in these fractions. Comparative analysis of transcriptomes of L. edodes vegetative mycelium, fruiting body and primordium revealed the presence of carbohydrate-binding glycoproteins (lectins) specific for each stage of basidiomycete morphogenesis. Histological examination revealed some morphological indicators of immune system activation and the absence of toxic effect on gastro-intestinal mucosa of animals at peroral administration of fungal glycoprotein fractions. Fungal protein and, in particular, lectin preparations derived from L. еdodes vegetative mycelium might be considered as novel prospective tools in cancer diagnostics and therapies.

Improved Formazan Dissolution for Bacterial MTT Assay

The MTT assay, based on the enzymatic reduction of the water-soluble, yellowish tetrazolium salt 3-(4,5-dimethylthiazol)-2,5-diphenyl-tetrazolium bromide (MTT) to purple formazan, is commonly used for assessment of cell viability and proliferation. Accurate performance by the MTT assay depends on complete solubilization of cells and formazan and stability of the colored solution. Comparison of different solubilization solutions revealed that dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), buffered with ammonia buffer, pH 10, and containing 5% SDS, produced the best results. These two solvents provided rapid and complete solubilization of formazan and cells, with minimal background absorbance at 700 nm, good reproducibility (low interassay coefficient of variation), high sensitivity, and color stability for at least 24 h. A linear relationship between viable-cell number and formazan absorbance was preserved for cell densities up to ∼1 × 10⁹ cells/mL for Gram-negative and Gram-positive microorganisms. Since MTT can be reduced by medium components in the absence of cells, blanks containing all medium components but no cells should be run simultaneously. Measurements at two wavelengths, one corresponding to absorption peak of formazan (570 nm) and a background absorbance far from the peak (700 nm), are necessary to avoid artifacts due to incomplete solubilization and turbidity.

IMPORTANCE Reduction of the water-soluble tetrazolium salt 3-(4,5-dimethylthiazol)-2,5 diphenyl-tetrazolium bromide (MTT) to purple, water-insoluble formazan is commonly used for assessment of cell viability and proliferation. Spectrophotometric detection of formazan requires its solubilization. The solubilization solvent has a strong influence on data acquisition and often introduces artifacts, leading to misreading of results. This study offers a choice of solvents that minimize solubilization artifacts when the MTT test is applied to microbiological cultures.

The MTT Assay: Utility, Limitations, Pitfalls, and Interpretation in Bulk and Single-Cell Analysis

The MTT assay for cellular metabolic activity is almost ubiquitous to studies of cell toxicity; however, it is commonly applied and interpreted erroneously. We investigated the applicability and limitations of the MTT assay in representing treatment toxicity, cell viability, and metabolic activity. We evaluated the effect of potential confounding variables on the MTT assay measurements on a prostate cancer cell line (PC-3) including cell seeding number, MTT concentration, MTT incubation time, serum starvation, cell culture media composition, released intracellular contents (cell lysate and secretome), and extrusion of formazan to the extracellular space. We also assessed the confounding effect of polyethylene glycol (PEG)-coated gold nanoparticles (Au-NPs) as a tested treatment in PC-3 cells on the assay measurements. We additionally evaluated the applicability of microscopic image cytometry as a tool for measuring intracellular MTT reduction at the single-cell level. Our findings show that the assay measurements are a result of a complicated process dependant on many of the above-mentioned factors, and therefore, optimization of the assay and rational interpretation of the data is necessary to prevent misleading conclusions on variables such as cell viability, treatment toxicity, and/or cell metabolism. We conclude, with recommendations on how to apply the assay and a perspective on where the utility of the assay is a powerful tool, but likewise where it has limitations.

Unsymmetrical Trifluoromethyl Methoxyphenyl β-Diketones: Effect of the Position of Methoxy Group and Coordination at Cu(II) on Biological Activity

Copper(II) complexes with 1,1,1-trifluoro-4-(4-methoxyphenyl)butan-2,4-dione (HL1) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single crystal X-ray diffraction. The biological properties of HL1 and cis-[Cu(L1)₂(DMSO)] (3) were examined against Gram-positive and Gram-negative bacteria and opportunistic unicellular fungi. The cytotoxicity was estimated towards the HeLa and Vero cell lines. Complex 3 demonstrated antibacterial activity towards S. aureus comparable to that of streptomycin, lower antifungal activity than the ligand HL1 and moderate cytotoxicity. The bioactivity was compared with the activity of compounds of similar structures. The effect of changing the position of the methoxy group at the aromatic ring in the ligand moiety of the complexes on their antimicrobial and cytotoxic activity was explored. We propose that complex 3 has lower bioavailability and reduced bioactivity than expected due to strong intermolecular contacts. In addition, molecular docking studies provided theoretical information on the interactions of tested compounds with ribonucleotide reductase subunit R2, as well as the chaperones Hsp70 and Hsp90, which are important biomolecular targets for antitumor and antimicrobial drug search and design. The obtained results revealed that the complexes displayed enhanced affinity over organic ligands. Taken together, the copper(II) complexes with the trifluoromethyl methoxyphenyl-substituted β-diketones could be considered as promising anticancer agents with antibacterial properties.

1,5-Benzodiazepin-2(3H)-ones: In Vitro Evaluation as Antiparkinsonian Agents

A new series of twenty-three 1,5-benzodiazepin-2(3H)-ones were synthesized and evaluated in the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), ferric reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays as a new chemotype with antioxidant and good drug-like properties. All of the derivatives showed low cytotoxicity in comparison to curcumin against the human neuroblastoma SH-SY5Y and the human hepatoma HepG2 cell lines. Experimental solubility in bio-relevant media showed a good relationship with melting points in this series. Five compounds with the best antioxidant properties showed neuroprotectant activity against H₂O₂-induced oxidative stress in the SH-SY5Y cell line. From them, derivatives 4-phenyl-1H-1,5-benzodiazepin-2(3H)-one (18) and 4-(3,4,5-trimethoxyphenyl)-1H-1,5-benzodiazepin-2(3H)-one (20) yielded good neuroprotection activity in the same neuronal cell line under 6-OHD and MPP⁺ insults as in vitro models of mitochondrial dysfunction and oxidative stress in Parkinson’s disease (PD). Both compounds also demonstrated a significant reduction of intracellular Reactive Oxygen Species (ROS) and superoxide levels, in parallel with a good improvement of the Mitochondrial Membrane Potential (ΔΨm). Compared with curcumin, compound 18 better reduced lipid peroxidation levels, malondialdehyde (MDA), in SH-SY5Y cells under oxidative stress pressure and recovered intracellular glutathione synthetase (GSH) levels. Apoptosis and caspase-3 levels of SH-SY5Y under H₂O₂ pressure were also reduced after treatment with 18. Neuroprotection in neuron-like differentiated SH-SY5Y cells was also achieved with 18. In summary, this family of 1,5-benzodiazepin-2-ones with an interesting antioxidant and drug-like profile, with low cytotoxic and good neuroprotectant activity, constitutes a new promising chemical class with high potential for the development of new therapeutic agents against PD.

Silver Nanoparticles Modulate the Epithelial-to-Mesenchymal Transition in Estrogen-Dependent Breast Cancer Cells In Vitro

Silver nanoparticles (AgNPs) are frequently detected in many convenience goods, such as cosmetics, that are applied directly to the skin. AgNPs accumulated in cells can modulate a wide range of molecular pathways, causing direct changes in cells. The aim of this study is to assess the capability of AgNPs to modulate the metastasis of breast cancer cells through the induction of epithelial-to-mesenchymal transition (EMT). The effect of the AgNPs on MCF-7 cells was investigated via the sulforhodamine B method, the wound healing test, generation of reactive oxygen species (ROS), the standard cytofluorimetric method of measuring the cell cycle, and the expression of EMT marker proteins and the MTA3 protein via Western blot. To fulfill the results, calcium flux and HDAC activity were measured. Additionally, mitochondrial membrane potential was measured to assess the direct impact of AgNPs on mitochondria. The results indicated that the MCF-7 cells are resistant to the cytotoxic effect of AgNPs and have higher mobility than the control cells. Treatment with AgNPs induced a generation of ROS; however, it did not affect the cell cycle but modulated the expression of EMT marker proteins and the MTA3 protein. Mitochondrial membrane potential and calcium flux were not altered; however, the AgNPs did modulate the total HDAC activity. The presented data support our hypothesis that AgNPs modulate the metastasis of MCF-7 cells through the EMT pathway. These results suggest that AgNPs, by inducing reactive oxygen species generation, alter the metabolism of breast cancer cells and trigger several pathways related to metastasis.

Immune Response of Mice Against Babesia canis Antigens is Enhanced When Antigen is Coupled to Gold Nanoparticles

PURPOSE

The aim of this study was to isolate Babesia canis soluble antigens and to investigate the effect of their conjugates with gold nanoparticles on the immunogenicity in laboratory animals.

METHODS

A procedure was developed for isolating and purifying B. canis antigens. The isolated culture antigen of B. canis 495 was coupled to gold nanoparticles, and the conjugate was used to immunize laboratory mice.

RESULTS

Western blotting showed that the resultant antiserum specifically recognized the proteins of the B. canis strains isolated from naturally infected dogs. The antibody titer, the respiratory activity of peritoneal macrophages, the proliferative activity of splenocytes, and the production of cytokines were maximal when the animals were immunized with the antigen-nanoparticle conjugate emulsified in complete Freund's adjuvant. Without adjuvant, the babesial antigen was weakly immunogenic.

CONCLUSION

Therefore, the use of gold nanoparticles as an antigen carrier induced a broad immune response involving both cellular and humoral responses. The antibodies raised by the proposed procedure are potentially effective at immunodetection of Babesia canis infections in dogs.

The MTT assay application to measure the viability of spermatozoa: A variety of the assay protocols

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay is one of the methods used to evaluate the viability of sperm. In the assay, a tetrazolium component (MTT) is converted into MTT formazan by some specific enzymes in the viable cells. The amount of formazan product in theory is directly correlated with the percentage of viable sperms. It is quantified by measuring the absorbance using a spectrophotometer. The present article compiles the MTT assays that have been used to determine sperm viability in most animal species and humans. In each assay, other factors apart from the number of viable cells that potentially influence the accuracy and precision of results are stated, such as preparations of sperm and MTT solutions, length and conditions of incubation, and a solubilizing agent as well as the formazan detection method. Also, the strengths and shortcomings of the MTT test comparison with the others are summarized at the end of this article. This information may be useful for prospective researchers deciding to implement this colorimetric method in their experiments.

Fluorescent redox-dependent labeling of lipid droplets in cultured cells by reduced phenazine methosulfate

Natural and synthetic phenazines are widely used in biomedical sciences. In dehydrogenase histochemistry, phenazine methosulfate (PMS) is applied as a redox reagent for coupling reduced coenzymes to the reduction of tetrazolium salts into colored formazans. PMS is also currently used for cytotoxicity and viability assays of cell cultures using sulfonated tetrazoliums. Under UV (340 nm) excitation, aqueous solutions of the cationic PMS show green fluorescence (λem: 526 nm), whereas the reduced hydrophobic derivative (methyl-phenazine, MPH) shows blue fluorescence (λem: 465 nm). Under UV (365 nm) excitation, cultured cells (LM2, IGROV-1, BGC-1, and 3T3-L1 adipocytes) treated with PMS (5 μg/mL, 30 min) showed cytoplasmic granules with bright blue fluorescence, which correspond to lipid droplets labeled by the lipophilic methyl-phenazine. After formaldehyde fixation blue-fluorescing droplets could be stained with oil red O. Interestingly, PMS-treated 3T3-L1 adipocytes observed under UV excitation 24 h after labeling showed large lipid droplets with a weak green emission within a diffuse pale blue-fluorescing cytoplasm, whereas a strong green emission was observed in small lipid droplets. This fluorescence change from blue to green indicates that reoxidation of methyl-phenazine to PMS can occur. Regarding cell uptake and labeling mechanisms, QSAR models predict that the hydrophilic PMS is not significantly membrane-permeant, so most PMS reduction is expected to be extracellular and associated with a plasma membrane NAD(P)H reductase. Once formed, the lipophilic and blue-fluorescing methyl-phenazine enters live cells and mainly accumulates in lipid droplets. Overall, the results reported here indicate that PMS is an excellent fluorescent probe to investigate labeling and redox dynamics of lipid droplets in cultured cells.

Effect of growth media on the MTT colorimetric assay in bacteria

Reduction of tetrazolium salts to colored formazan products by metabolically active cells is widely used for assessment of cell viability. Among the tetrazolium compounds most commonly used is MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]. Numerous studies about sites and mechanisms of cellular reduction of MTT, performed in mammalian cell cultures, have identified various parameters that affect formazan production and can lead to overestimation/underestimation of viable cells or effects of treatment. Irrespective of lack of such data for prokaryotic cells, the MTT assay is commonly used for microbiological studies, which often leads to contradictory results or misinterpretation of data. The aim of this study was to investigate how components of growth media and conditions of growth, affect formazan formation by microbial cells. Results showed that MTT reduction depended on the amino acid composition of the medium. Several amino acids potentiated formazan production by Gram-positive and Gram-negative bacteria, with histidine having the strongest effect. Results of this study demonstrate that data obtained with the MTT test should be interpreted with caution, particularly when different growth media are used or treatments affect metabolic pathways, and that evaluation of the reliability of the MTT assay under specific conditions should be performed, to avoid erroneous results. Performing the assay with cells suspend in glucose-supplemented buffer would eliminate the effects of metabolites and will limit cell division during incubation with MTT. Another critical element to be considered is the choice of a proper solvent for dissolution of formazan crystals.

Comparative detection method of early onset cytokine-induced stress in β-cells (INS-1E)

β-Cells contain a prominent endoplasmic reticulum (ER), disrupting ER homeostasis and function, activating the unfolded protein response (UPR). Currently, no direct protocols measure the UPR initiation. Current methods to measure ER stress include the quantification of nitric oxide (NO) (indirect method), Western blotting, and qRT-PCR of downstream components. However, these methods do not account for the overlap with mitochondrial dysfunction. In this study, INS-1E cells were exposed to proinflammatory cytokines to induce ER stress, as determined using NO, thioflavin T (ThT) binding, and β-cell functionality (insulin production). ER stress was confirmed through the upregulation of CHOP. Cell viability was monitored using MTT, sulforhodamine B, and the xCELLigence system. Morphological changes were monitored using electron microscopy. IL-1β exposure-induced β-cell stress after 4 H, decreased insulin levels, and increased thioflavin binding were noted. Increased NO production was only detected after 10 H, highlighting its lack of sensitivity, and the need for a continuous, selective, rapid, convenient, and economical detection method for early onset of ER stress. Standard methods (MTT and NO) failed to detect early ER stress. The xCELLigence coupled with a functional assay such as the detection of insulin levels or ThT are better predictors of ER stress in INS-1E cells.

Prospects for the use of spherical gold nanoparticles in immunization

Recent years have seen extremely fast development of new viral nanovaccines and diagnostic agents using nanostructures prepared by biological and chemical synthesis. We used spherical gold nanoparticles (average diameter, 15 nm) as a platform for the antigen for swine transmissible gastroenteritis virus (TGEV). The literature data demonstrate that immunization of animals with the TGEV antigen coupled to gold nanoparticles (GNPs) not only activates antigen-presenting cells but also increases the proliferative activity of splenic lymphoid (antibody-forming) cells. The contents of γ-IFN, IL-1β, and IL-6 in animals immunized with GNP-antigen conjugates were found to be higher than those in intact animals or in animals given the antigen alone. The increased concentration of IL-1β in the immunized animals directly correlated with the activity of macrophages and stimulated B cells, which produce this cytokine when activated. The increased concentration of IL-6 indicates that the injected preparations are stimulatory to cellular immunity. Immunization with the TGEV antigen conjugated to GNPs as a carrier activates the respiratory activity of lymphoid cells and peritoneal macrophages, which is directly related to their transforming activity and to the activation of antibody generation. Furthermore, the use of this conjugate allows marked improvement of the structure of the animals' immune organs and restores the morphological-functional state of these organs. The microanatomical changes (increased number of follicles) indicate the activation of the B-dependent zone of the spleen and, consequently, the development of a humoral-type immunological reaction. The degradative processes observed in the animals immunized with TGEV antigen alone are evidence of weak resistance to pathogen attack. These results can be used to develop vaccines against this infection by employing TGEV antigen coupled to gold nanoparticles as a carrier.

Current methodology of MTT assay in bacteria - A review

The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium assay is a popular tool in estimating the metabolic activity of living cells. The test is based on enzymatic reduction of the lightly colored tetrazolium salt to its formazan of intense purple-blue color, which can be quantified spectrophotometrically. Under properly optimized conditions the obtained absorbance value is directly proportional to the number of living cells. Originally, the MTT assay was devised for use in eukaryotic cells lines and later applied for bacteria and fungi. As the mechanism of MTT reduction was studied in detail mostly considering eukaryotic cells, the lack of information resulted in generating a vast variety of MTT based protocols for bacterial enzymatic activity evaluation. In the presented article the main aspects of the MTT assay applicability in bacterial research were summarized, with special emphasis on sources of inaccuracies and misinterpretation of the test results.

Tetrazolium salts and formazan products in Cell Biology: Viability assessment, fluorescence imaging, and labeling perspectives

For many years various tetrazolium salts and their formazan products have been employed in histochemistry and for assessing cell viability. For the latter application, the most widely used are 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), and 5-cyano-2,3-di-(p-tolyl)-tetrazolium chloride (CTC) for viability assays of eukaryotic cells and bacteria, respectively. In these cases, the nicotinamide-adenine-dinucleotide (NAD(P)H) coenzyme and dehydrogenases from metabolically active cells reduce tetrazolium salts to strongly colored and lipophilic formazan products, which are then quantified by absorbance (MTT) or fluorescence (CTC). More recently, certain sulfonated tetrazolium, which give rise to water-soluble formazans, have also proved useful for cytotoxicity assays. We describe several aspects of the application of tetrazolium salts and formazans in biomedical cell biology research, mainly regarding formazan-based colorimetric assays, cellular reduction of MTT, and localization and fluorescence of the MTT formazan in lipidic cell structures. In addition, some pharmacological and labeling perspectives of these compounds are also described.

The Comparison of MTT and CVS Assays for the Assessment of Anticancer Agent Interactions

Multiple in vitro tests are widely applied to assess the anticancer activity of new compounds, including their combinations and interactions with other drugs. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay is one of the most commonly used assays to assess the efficacy and interactions of anticancer agents. However, it can be significantly influenced by compounds that modify cell metabolism and reaction conditions. Therefore, several assays are sometimes used to screen for potential anticancer drugs. However, the majority of drug interactions are evaluated only with this single method. The aim of our studies was to verify whether the choice of an assay has an impact on determining the type of interaction and to identify the source of discrepancies. We compared the accuracy of MTT and CVS (crystal violet staining) assays in the interaction of two compounds characterized by similar anticancer activity: isothiocyanates (ITCs) and Selol. Confocal microscopy studies were carried out to assess the influence of these compounds on the reactive oxygen species (ROS) level, mitochondrial membrane potential, dead-to-live cell ratio and MTT-tetrazolium salt reduction rate. The MTT assay was less reliable than CVS. The MTT test of Selol and 2-oxoheptyl ITC, which affected the ROS level and MTT reduction rate, gave false negative (2-oxoheptyl ITC) or false positive (Selol) results. As a consequence, the MTT assay identified an antagonistic interaction between Selol and ITC, while the metabolism-independent CVS test identified an additive or synergistic interaction. In this paper, we show for the first time that the test assay may change the interpretation of the compound interaction. Therefore, the test method should be chosen with caution, considering the mechanism of action of the compound.

Epoxy-α-lapachone has in vitro and in vivo anti-leishmania (Leishmania) amazonensis effects and inhibits serine proteinase activity in this parasite

Leishmania (Leishmania) amazonensis is a protozoan that causes infections with a broad spectrum of clinical manifestations. The currently available chemotherapeutic treatments present many problems, such as several adverse side effects and the development of resistant strains. Natural compounds have been investigated as potential antileishmanial agents, and the effects of epoxy-α-lapachone on L. (L.) amazonensis were analyzed in the present study. This compound was able to cause measurable effects on promastigote and amastigote forms of the parasite, affecting plasma membrane organization and leading to death after 3 h of exposure. This compound also had an effect in experimentally infected BALB/c mice, causing reductions in paw lesions 6 weeks after treatment with 0.44 mM epoxy-α-lapachone (mean lesion area, 24.9 ± 2.0 mm(2)), compared to untreated animals (mean lesion area, 30.8 ± 2.6 mm(2)) or animals treated with Glucantime (mean lesion area, 28.3 ± 1.5 mm(2)). In addition, the effects of this compound on the serine proteinase activities of the parasite were evaluated. Serine proteinase-enriched fractions were extracted from both promastigotes and amastigotes and were shown to act on specific serine proteinase substrates and to be sensitive to classic serine proteinase inhibitors (phenylmethylsulfonyl fluoride, aprotinin, and antipain). These fractions were also affected by epoxy-α-lapachone. Furthermore, in silico simulations indicated that epoxy-α-lapachone can bind to oligopeptidase B (OPB) of L. (L.) amazonensis, a serine proteinase, in a manner similar to that of antipain, interacting with an S1 binding site. This evidence suggests that OPB may be a potential target for epoxy-α-lapachone and, as such, may be related to the compound's effects on the parasite.

Gracilaria edulis extract induces apoptosis and inhibits tumor in Ehrlich ascites tumor cells in vivo

BACKGROUND

Marine environment is inestimable for their chemical and biological diversity and therefore is an extraordinary resource for the discovery of new anticancer drugs. Recent development in elucidation of the mechanism and therapeutic action of natural products helped to evaluate for their potential activity.

METHODS

We evaluated Gracilaria edulis J. Ag (Brown algae), for its antitumor potential against the Ehrlich ascites tumor (EAT) in vivo and in vitro. Cytotoxicity evaluation of Ethanol Extract of Gracilaria edulis (EEGE) using EAT cells showed significant activity. In vitro studies indicated that EEGE cytotoxicity to EAT cells is mediated through its ability to produce reactive oxygen species (ROS) and therefore decreasing intracellular glutathione (GSH) levels may be attributed to oxidative stress.

RESULTS

Apoptotic parameters including Annexin-V positive cells, increased levels of DNA fragmentation and increased caspase-2, caspase-3 and caspase-9 activities indicated the mechanism might be by inducing apoptosis. Intraperitoneally administration of EEGE to EAT-bearing mice helped to increase the lifespan of the animals significantly inhibited tumor growth and increased survival of mice. Extensive hematology, biochemistry and histopathological analysis of liver and kidney indicated that daily doses of EEGE up to 300 mg/kg for 35 days are well tolerated and did not cause hematotoxicity nor renal or hepatotoxicity.

CONCLUSION

Comprehensive antitumor analysis in animal model and in Ehrlich Ascites Tumor cells was done including biochemical, and pathological evaluations indicate antitumor activity of the extract and non toxic in vivo. It was evident that the mechanism explains the apoptotic activity of the algae extract.

A novel staining protocol for multiparameter assessment of cell heterogeneity in Phormidium populations (cyanobacteria) employing fluorescent dyes

Bacterial populations display high heterogeneity in viability and physiological activity at the single-cell level, especially under stressful conditions. We demonstrate a novel staining protocol for multiparameter assessment of individual cells in physiologically heterogeneous populations of cyanobacteria. The protocol employs fluorescent probes, i.e., redox dye 5-cyano-2,3-ditolyl tetrazolium chloride, ‘dead cell’ nucleic acid stain SYTOX Green, and DNA-specific fluorochrome 4′,6-diamidino-2-phenylindole, combined with microscopy image analysis. Our method allows simultaneous estimates of cellular respiration activity, membrane and nucleoid integrity, and allows the detection of photosynthetic pigments fluorescence along with morphological observations. The staining protocol has been adjusted for, both, laboratory and natural populations of the genus Phormidium (Oscillatoriales), and tested on 4 field-collected samples and 12 laboratory strains of cyanobacteria. Based on the mentioned cellular functions we suggest classification of cells in cyanobacterial populations into four categories: (i) active and intact; (ii) injured but active; (iii) metabolically inactive but intact; (iv) inactive and injured, or dead.

MTT assay for cell viability: Intracellular localization of the formazan product is in lipid droplets

Although MTT is widely used to assess cytotoxicity and cell viability, the precise localization of its reduced formazan product is still unclear. In the present study the localization of MTT formazan was studied by direct microscopic observation of living HeLa cells and by colocalization analysis with organelle-selective fluorescent probes. MTT formazan granules did not colocalize with mitochondria as revealed by rhodamine 123 labeling or autofluorescence. Likewise, no colocalization was observed between MTT formazan granules and lysosomes labeled by neutral red. Taking into account the lipophilic character and lipid solubility of MTT formazan, an evaluation of the MTT reaction was performed after treatment of cells with sunflower oil emulsions to induce a massive occurrence of lipid droplets. Under this condition, lipid droplets revealed a large amount of MTT formazan deposits. Kinetic studies on the viability of MTT-treated cells showed no harmful effects at short times. Quantitative structure-activity relations (QSAR) models were used to predict and explain the localization of both the MTT tetrazolium salt and its formazan product. These predictions were in agreement with experimental observations on the accumulation of MTT formazan product in lipid droplets.

Cytotoxicity of all-trans-retinal increases upon photodegradation

All-trans-retinal (AtRal) can accumulate in the retina as a result of excessive exposure to light. The purpose of this study was to compare cytotoxicity of AtRal and photodegraded AtRal (dAtRal) on cultured human retinal pigment epithelial cells in dark and upon exposure to visible light. AtRal was degraded by exposure to visible light. Cytotoxicity was monitored by imaging of cell morphology, propidium iodide staining of cells with permeable plasma membrane and measurements of reductive activity of cells. Generation of singlet oxygen photosensitized by AtRal and dAtRal was monitored by time-resolved measurements of characteristic singlet oxygen phosphorescence. Photodegradation of AtRal resulted in a decrease in absorption of visible light and accumulation of the degradation products with absorption maximum at ∼330 nm. Toxicity of dAtRal was concentration-dependent and was greater during irradiation with visible light than in dark. DAtRal was more cytotoxic than AtRal both in dark and during exposure to visible light. Photochemical properties of dAtRal indicate that it may be responsible for the maximum in the action spectra of retinal photodamage recorded in animals. In conclusion, photodegradation products of AtRal may impose a significant threat to the retina and therefore their roles in retinal pathology need to be explored.

Immunostimulatory effect of gold nanoparticles conjugated with transmissible gastroenteritis virus

Animals were immunized with transmissible gastroenteritis virus conjugated with gold nanoparticles. The resultant antibodies had a higher titer than antibodies produced in response to native virus. Immunization with the antigen-colloidal gold complex led to a significant increase of the peritoneal macrophages respiratory activity and of plasma IFN-γ level in immunized animals.

Vital dye reaction and granule localization in periplasm of Escherichia coli

Background

Tetrazolium salts are widely used in biology as indicators of metabolic activity – hence termed vital dyes – but their reduction site is still debated despite decades of intensive research. The prototype, 2,3,5- triphenyl tetrazolium chloride, which was first synthesized a century ago, often generates a single formazan granule at the old pole of Escherichia coli cells after reduction. So far, no explanation for their pole localization has been proposed.

Method/Principal Findings

Here we provide evidence that the granules form in the periplasm of bacterial cells. A source of reducing power is deduced to be thiol groups destined to become disulfides, since deletion of dsbA, coding for thiol-oxidase, enhances the formation of reduced formazan. However, pervasive reduction did not result in a random distribution of formazan aggregates. In filamentous cells, large granules appear at regular intervals of about four normal cell-lengths, consistent with a diffusion-to-capture model. Computer simulations of a minimal biophysical model showed that the pole localization of granules is a spontaneous process, i.e. small granules in a normal size bacterium have lower energy at the poles. This biased their diffusion to the poles. They kept growing there and eventually became fixed.

Conclusions

We observed that formazan granules formed in the periplasm after reduction of tetrazolium, which calls for re-evaluation of previous studies using cell-free systems that liberate inaccessible intracellular reductant and potentially generate artifacts. The localization of formazan granules in E. coli cells can now be understood. In living bacteria, the seeds formed at or migrated to the new pole would become visible only when that new pole already became an old pole, because of the relatively slow growth rate of granules relative to cell division.

Verapamil stereoisomers induce antiproliferative effects in vascular smooth muscle cells via autophagy

Calcium channel blockers (CCBs) are important in the management of hypertension and limit restenosis. Although CCB efficacy could derive from decreased blood pressure, other mechanisms independent of CCB activity also can contribute to antiproliferative action. To understand mechanisms of CCB-mediated antiproliferation, we studied two structurally dissimilar CCBs, diltiazem and verapamil, in cultured rat vascular smooth muscle cells (VSMC). To elucidate CCB-independent effects, pure stereoisomers of verapamil (R-verapamil, inactive VR; S-verapamil, active, VS) were used. The effects of CCB exposure on cell viability (MTT reduction), cell proliferation ((3)H-thymidine incorporation), VSMC morphology by light and transmission electron microscopy (TEM) and autophagy (LC3I/II, ATG5) were measured. In general, verapamil, VR or VS treatment alone (80 μM) appreciably enhanced MTT absorbance although higher concentrations (VR or VS) slightly decreased MTT absorbance. Diltiazem (140 μM) markedly decreased MTT absorbance (40%) at 120 h. VR or VS treatment inhibited (3)H-thymidine incorporation (24h) and induced cytological alterations (i.e., karyokinesis, enhanced perinuclear MTT deposition, accumulated perinuclear "vacuoles"). TEM revealed perinuclear "vacuoles" to be aggregates of highly laminated and electron-dense vesicles resembling autophagosomes and lysosomes, respectively. Increased autophagosome activity was confirmed by a concentration-dependent increase in LC3-II formation by Western blotting and by increased perinuclear LC3-GFP(+) puncta in verapamil-treated VSMC. Verapamil stereoisomers appeared to decrease perinuclear mitochondrial density. These observations indicate that antiproliferative effects of verapamil stereoisomers are produced by enhanced mitochondrial damage and upregulated autophagy in VSMC. These effects are independent of CCB activity indicating a distinct mechanism of action that could be targeted for more efficacious anti-atherosclerotic and anti-restenosis therapy.

The control of root growth by reactive oxygen species in Salix nigra Marsh. seedlings

The production of reactive oxygen species (ROS) in specific regions of Salix seedlings roots seems essential for the normal growth of this organ. We examined the role of different ROS in the control of root development in Salix nigra seedlings, and explored possible mechanisms involved in the regulation of ROS generation and action. Root growth was not significantly affected by OH quenchers, while it was either partially or completely inhibited in the presence of H₂O₂ or O₂·⁻ scavengers, respectively. O₂·⁻ production was elevated in the root apex, particularly in the subapical meristem and protodermal zones. Apical O₂·⁻ generation activity was correlated to a high level of either Cu/Zn superoxide dismutase protein as well as carbonylated proteins. While NADPH-oxidase (NOX) was probably the main source of O₂·⁻ generation, the existence of other sources should not be discarded. O₂·⁻ production was also high in root hairs during budding, but it markedly decreased when the hair began to actively elongate. Root hair formation increased in the presence of H₂O₂ scavengers, and was suppressed when H₂O₂ or peroxidase inhibitors were supplied. The negative effect of H₂O₂ was partially counteracted by a MAPKK inhibitor. Possible mechanisms of action of the different ROS in comparison with other plant model systems are discussed.

Reactive oxygen species are involved in pollen tube initiation in kiwifruit

The role of reactive oxygen species (ROS) during pollen tube growth has been well established, but its involvement in the early germination stage is poorly understood. ROS production has been reported in germinating tobacco pollen, but evidence for a clear correlation between ROS and germination success remains elusive. Here, we show that ROS are involved in germination and pollen tube formation in kiwifruit. Using labelling with dihydrofluorescein diacetate (H(2) FDA) and nitroblue tetrazolium (NBT), endogenous ROS were detected immediately following pollen rehydration and during the lag phase preceding pollen tube emergence. Furthermore, extracellular H(2) O(2) was found to accumulate, beginning a few minutes after pollen suspension in liquid medium. ROS production was essential for kiwifruit pollen performance, since in the presence of compounds acting as superoxide dismutase/catalase mimic (Mn-5,10,15,20-tetrakis(1-methyl-4-pyridyl)21H,23H-porphin, Mn-TMPP) or as NADPH oxidase inhibitor (diphenyleneiodonium chloride, DPI), ROS levels were reduced and pollen tube emergence was severely or completely inhibited. Moreover, ROS production was substantially decreased in the absence of calcium, and by chromium and bisphenol A, which inhibit germination in kiwifruit. Peroxidase activity was cytochemically revealed after rehydration and during germination. In parallel, superoxide dismutase enzymes, particularly the Cu/Zn-dependent subtype - which function as superoxide radical scavengers - were detected by immunoblotting and by an in-gel activity assay in kiwifruit pollen, suggesting that ROS levels may be tightly regulated. Timing of ROS appearance, early localisation at the germination aperture and strict requirement for germination clearly suggest an important role for ROS in pollen grain activation and pollen tube initiation.

Assay of the multiple energy-producing pathways of mammalian cells

BACKGROUND

To elucidate metabolic changes that occur in diabetes, obesity, and cancer, it is important to understand cellular energy metabolism pathways and their alterations in various cells.

METHODOLOGY AND PRINCIPAL FINDINGS

Here we describe a technology for simultaneous assessment of cellular energy metabolism pathways. The technology employs a redox dye chemistry specifically coupled to catabolic energy-producing pathways. Using this colorimetric assay, we show that human cancer cell lines from different organ tissues produce distinct profiles of metabolic activity. Further, we show that murine white and brown adipocyte cell lines produce profiles that are distinct from each other as well as from precursor cells undergoing differentiation.

CONCLUSIONS

This technology can be employed as a fundamental tool in genotype-phenotype studies to determine changes in cells from shared lineages due to differentiation or mutation.

Beauvericin from the Endophytic Fungus, Fusarium redolens, Isolated from Dioscorea zingiberensis and Its Antibacterial Activity

From the fungal endophyte, Fusarium redolens Dzf2, isolated from rhizomes of the Chinese medicinal plant Dioscorea zingiberensis, beauvericin was obtained by TLC in combination with bioautographic antibacterial assay. The compound was identified by spectroscopic and physicochemical means. The median effective inhibitory concentration (IC50) values of beauvericin against six test bacteria ( Bacillus subtilis, Staphylococcus haemolyticus, Pseudomonas lachrymans, Agrobacterium tumefaciens, Escherichia coli and Xanthomonas vesicatoria) were between 18.4 and 70.7 μg/mL. The beauvericin content of F. redolens Dzf2 mycelia was 9.60 mg/g dw, and beauvericin yield 62.4 mg/L. The obtained results show the potential use of the endophytic fungus for its biological role in providing its host plant with protection, as well as the possible development of beauvericin as an antibacterial.

Growth inhibition and pro-apoptotic activity of violacein in Ehrlich ascites tumor

The continuing threat to biodiversity lends urgency to the need of identification of sustainable source of natural products. This is not so much trouble if there is a microbial source of the compound. Herein, violacein, a natural indolic pigment extracted from Chromobacterium violaceum, was evaluated for its antitumoral potential against the Ehrlich ascites tumor (EAT) in vivo and in vitro. Evaluation of violacein cytotoxicity using different endpoints indicated that EAT cells were twofold (IC(50)=5.0 microM) more sensitive to the compound than normal human peripheral blood lymphocytes. In vitro studies indicated that violacein cytotoxicity to EAT cells is mediated by a rapid (8-12h) production of reactive oxygen species (ROS) and a decrease in intracellular GSH levels, probably due to oxidative stress. Additionally, apoptosis was primarily induced, as demonstrated by an increase in Annexin-V positive cells, concurrently with increased levels of DNA fragmentation and increased caspase-2, caspase-9 and caspase-3 activities up to 4.5-, 6.0- and 5.5-fold, respectively, after 72 h of treatment. Moreover, doses of 0.1 and 1.0 microg kg(-1) violacein, administered intraperitoneally (i.p.) to EAT-bearing mice throughout the lifespan of the animals significantly inhibited tumor growth and increased survival of mice. In view of these results, a 35-day toxicity study was conducted in vivo. Complete hematology, biochemistry (ALT, AST and creatinine levels) and histopathological analysis of liver and kidney indicated that daily doses of violacein up to 1000 microg kg(-1) for 35 days are well tolerated and did not cause hematotoxicity nor renal or hepatotoxicity when administered i.p. to mice. Altogether, these results indicate that violacein causes oxidative stress and an imbalance in the antioxidant defense machinery of cells culminating in apoptotic cell death. Furthermore, this is the first report of its antitumor activity in vivo, which occurs in the absence of toxicity to major organs.

Deficiency in frataxin homologue YFH1 in the yeast Pichia guilliermondii leads to missregulation of iron acquisition and riboflavin biosynthesis and affects sulfate assimilation

Pichia guilliermondii is a representative of yeast species that overproduce riboflavin (vitamin B2) in response to iron deprivation. P. guilliermondii YFH1 gene coding for frataxin homologue, eukaryotic mitochondrial protein involved in iron trafficking and storage, was identified and deleted. Constructed P. guilliermondii Δyfh1 mutant grew very poorly in a sucrose-containing synthetic medium supplemented with sulfate or sulfite as a sole sulfur source. Addition of sodium sulfide, glutathione, cysteine, methionine, N-acetyl-L-cysteine partially restored growth rate of the mutant suggesting that it is impaired in sulfate assimilation. Cellular iron content in Δyfh1 mutant was ~3-3.5 times higher as compared to the parental strain. It produced 50-70 times more riboflavin in iron sufficient synthetic media relative to the parental wildtype strain. Biomass yield of the mutant in the synthetic glutathione containing medium supplemented with glycerol as a sole carbon source was 1.4- and 2.6-fold increased as compared to sucrose and succinate containing media, respectively. Oxygen uptake of the Δyfh1 mutant on sucrose, glycerol or succinate, when compared to the parental strain, was decreased 5.5-, 1.7- and 1.5-fold, respectively. Substitution of sucrose or glycerol in the synthetic iron sufficient medium with succinate completely abolished riboflavin overproduction by the mutants. Deletion of the YFH1 gene caused hypersensitivity to hydrogen peroxide and exogenously added riboflavin and led to alterations in superoxide dismutase activities. Thus, deletion of the gene coding for yeast frataxin homologue has pleiotropic effect on metabolism in P. guilliermondii.

Experimental conditions affect the site of tetrazolium violet reduction in the electron transport chain of Lactococcus lactis

The reduction of tetrazolium salts to coloured formazans is often used as an indicator of cell metabolism during microbiology studies, although the reduction mechanisms have never clearly been established in bacteria. The objective of the present study was to identify the reduction mechanisms of tetrazolium violet (TV) in Lactococcus lactis using a mutagenesis approach, under two experimental conditions generally applied in microbiology: a plate test with growing cells, and a liquid test with non-growing (resting) cells. The results showed that in both tests, TV reduction resulted from electron transfer from an intracellular donor (mainly NADH) to TV via the electron transport chain (ETC), but the reduction sites in the ETC depended on experimental conditions. Using the plate test, menaquinones were essential for TV reduction and membrane NADH dehydrogenases (NoxA and/or NoxB) were partly involved in electron transfer to menaquinones. In this case, TV reduction mainly occurred outside the cells and in the outer part of the plasma membrane. During the liquid test, TV was directly reduced by NoxA and/or NoxB, probably in the inner part of the membrane, where NoxA and NoxB are localized. In this case, reduction was directly related to the intracellular NADH pool. Based on these findings, new applications for TV tests are proposed, such as NADH pool determination with the liquid test and the screening of mutants affected in menaquinone biosynthesis with the plate test. Preliminary results using other tetrazolium salts in the plate test showed that the reduction sites depended on the salt, suggesting that similar studies should be carried out with other tetrazolium salts so that the outcome of each test can be interpreted correctly.

Analytical methods to assess nanoparticle toxicity

During the past 20 years, improvements in nanoscale materials synthesis and characterization have given scientists great control over the fabrication of materials with features between 1 and 100 nm, unlocking many unique size-dependent properties and, thus, promising many new and/or improved technologies. Recent years have found the integration of such materials into commercial goods; a current estimate suggests there are over 800 nanoparticle-containing consumer products (The Project on Emerging Nanotechnologies Consumer Products Inventory, , accessed Oct. 2008), accounting for 147 billion USD in products in 2007 (Nanomaterials state of the market Q3 2008: stealth success, broad impact, Lux Research Inc., New York, NY, 2008). Despite this increase in the prevalence of engineered nanomaterials, there is little known about their potential impacts on environmental health and safety. The field of nanotoxicology has formed in response to this lack of information and resulted in a flurry of research studies. Nanotoxicology relies on many analytical methods for the characterization of nanomaterials as well as their impacts on in vitro and in vivo function. This review provides a critical overview of these techniques from the perspective of an analytical chemist, and is intended to be used as a reference for scientists interested in conducting nanotoxicological research as well as those interested in nanotoxicological assay development.

Interferon-gamma sensitizes hepatitis B virus-expressing hepatocarcinoma cells to 5-fluorouracil through inhibition of hepatitis B virus-mediated nuclear factor-kappaB activation

Nuclear factor (NF)-kappaB is important for immune responses and cell survival; however, abnormal activation of NF-kappaB is linked with many types of diseases, including hepatocellular carcinoma (HCC). Our previous report indicated that hepatitis B virus (HBV) induces NF-kappaB activation through NF-kappaB-inducing kinase (NIK), and this can be blocked specifically by interferon (IFN)-gamma. In the present study, we report that HBV expression in HCC cell lines induces drug resistance against 5-fluorouracil (5-FU). This drug resistance was abolished by inhibition of NF-kappaB activation through small interfering RNA-mediated NIK 'knockdown' and IFN-gamma treatment. In addition to the reduced NF-kappaB activation and drug resistance, the upregulated growth arrest- and DNA damage-inducible protein 45beta (Gadd45beta) in HBV-expressing HCC cell lines was downregulated by the small interfering RNA-mediated NIK knockdown and IFN-gamma treatment. The overexpression of Gadd45beta in HCC cell lines also induces drug resistance against 5-FU. Based on our data, we suggest that IFN-gamma treatment might be helpful for chemotherapy in HBV-integrated HCC through inhibition of the NIK-mediated NF-kappaB activation and downregulation of the NF-kappaB target gene Gadd45beta.

NADPH oxidase-dependent reactive oxygen species formation required for root hair growth depends on ROP GTPase

Reactive oxygen species (ROS) production by an NADPH oxidase (NOX) encoded by AtrbohC/RHD2 is required for root hair growth in Arabidopsis thaliana. ROP (RHO of plants) GTPases are also required for normal root hair growth and have been proposed to regulate ROS production in plants. Therefore, the role of ROP GTPase in NOX-dependent ROS formation by root hairs was investigated. Plants overexpressing wild-type ROP2 (ROP2 OX), constitutively active (CA-rop2), or dominant negative (DN-rop2) rop2 mutant proteins were used. Superoxide formation by root hairs was detected by superoxide dismutase-sensitive nitroblue tetrazolium reduction, and ROS production in the root hair differentiation zone was detected by dihydrofluorescein diacetate oxidation. Both probes showed that ROS production was increased in ROP2 OX and CA-rop2 plants, and decreased in DN-rop2 plants, relative to wild-type plants. When CA-rop2 was expressed in the NOX loss-of-function rhd2-1 mutant, ROS formation and root hair growth were impaired, suggesting that RHD2 is required for this ROP2-dependent ROS formation.

Reactive oxygen species produced by NADPH oxidase are involved in pollen tube growth

Tip-localized reactive oxygen species (ROS) were detected in growing pollen tubes by chloromethyl dichlorodihydrofluorescein diacetate oxidation, while tip-localized extracellular superoxide production was detected by nitroblue tetrazolium (NBT) reduction. To investigate the origin of the ROS we cloned a fragment of pollen specific tobacco NADPH oxidase (NOX) closely related to a pollen specific NOX from Arabidopsis. Transfection of tobacco pollen tubes with NOX-specific antisense oligodeoxynucleotides (ODNs) resulted in decreased amount of NtNOX mRNA, lower NOX activity and pollen tube growth inhibition. The ROS scavengers and the NOX inhibitor diphenylene iodonium chloride (DPI) inhibited growth and ROS formation in tobacco pollen tube cultures. Exogenous hydrogen peroxide (H2O2) rescued the growth inhibition caused by NOX antisense ODNs. Exogenous CaCl2 increased NBT reduction at the pollen tube tip, suggesting that Ca2+ increases the activity of pollen NOX in vivo. The results show that tip-localized ROS produced by a NOX enzyme is needed to sustain the normal rate of pollen tube growth and that this is likely to be a general mechanism in the control of tip growth of polarized plant cells.

Microtransponders, the miniature RFID electronic chips, as platforms for cell growth in cytotoxicity assays

BACKGROUND

An electronic radio frequency (RF) microchip, the microtransponder (MTP), has been developed as a platform for assays in the fields of genomics and proteomics. Upon activation by light, each MTP provides a unique RF identification (ID) signal that matches a chip to the specific biological material attached to it. The MTP is powered by a photocell and has an antenna that transmits the signal. The aim of the present study was to explore utility of MTPs as a platform for cell growth in cytotoxicity assays.

METHODS

The MCF-7, MCF-116, A549, or T-24 cells growing on MTPs placed in petri dishes or slide chambers were cultured untreated or exposed to antitumor drugs topotecan, mitoxantrone, or onconase for up to 4 days. Their attachment to- and growth on- MTPs was assessed by fluorescence microscopy and laser scanning cytometry (LSC) and compared with growth on the dish surface in the MTP neighborhood. The MTPs were fixed in ethanol, stained with propidium iodide (PI), and interrogated in flow in the instrument capable to rapidly (up to 103 MTPs/s) identify their ID signal and measure fluorescence.

RESULTS

The cells plated on MTPs exhibited similar attachment properties to those plated in culture dishes. When measured by LSC, they had similar mitotic activity, growth rate, and cell cycle distributions as the cells adhering to the culture dish in the neighborhood of MTPs. The fluorescence intensity of MTPs provided information about the cell number per MTP, which made it possible to assess cell growth rate and monitor the cytostatic/cytotoxic effects of the tested drugs.

CONCLUSIONS

The MTP-based system holds promise for the multiplexed cell assays in which numerous different cell lines can be screened for their growth rate or sensitivity while exposed to particular agents in the same vessel. Other advantages of the system are the rapidity of the screening and a very large number of ID codes. Because many cell lines/types can be assayed in a single dish, the system also offers cost savings on tissue culture reagents.

Recovery after short-term bilirubin exposure in human NT2-N neurons

We used human NT2-N neurons to investigate delayed effects of short-term exposure to unconjugated bilirubin (UCB). Cell viability was evaluated with MTT reduction assays and nuclear morphology. A 6-h exposure to 1, 5, or 25 microM UCB and serum deprivation (SED) significantly diminished MTT reduction. 96 h after rescue of neurons with removal of UCB and re-incubation in the original serum-containing medium, delayed effects were evident as recovery (1 microM UCB), intermediate cell death (5 microM UCB), or near complete cell death (25 microM UCB). The impact of 6 h of SED alone appeared to be modest in rescued neurons. In this model, co-treatment with the specific caspase-3 inhibitor, zDEVD.FMK (100 microM), or the pancaspase inhibitor zVAD.FMK (100 microM) did not improve viability in rescued neurons exposed to 5 microM UCB, while treatment with the NMDA receptor antagonist MK-801 (1 microM) enhanced the number of undamaged nuclei (86 +/- 14% versus 50 +/- 12%, P = 0.001). MK-801 had, however, no impact on MTT reduction. In a different model with a 102-h continuous exposure to UCB and SED, we found a significant additional toxic impact of serum deprivation. Separate experiments suggested that this was a result of late caspase-mediated toxicity. We conclude that UCB-mediated effects may be reversible in this model. Blockade of excitotoxic mechanisms, but not caspase activity may prevent delayed cell death.

Celecoxib can induce cell death independently of cyclooxygenase-2, p53, Mdm2, c-Abl and reactive oxygen species

Cell lines that do not overexpress functional cyclooxygenase-2 are resistant to the normal plasma levels of celecoxib achieved following oral ingestion. Cell growth inhibition was demonstrated after 24 h exposure to 80 micromol/l celecoxib while significant death was not detected at concentrations below 120 micromol/l following 24 h exposure. This growth inhibition and death induction was identified to be independent of p53 and Hdm2 in these cells, despite wild-type p53 stabilization and Hdm2 diminution in some lines. Cell death induced by celecoxib was preceded by the generation of reactive oxygen species within 4 h of drug exposure. The precise mechanism of elicitation of reactive oxygen species in these cells remains to be elucidated, although it was found to be independent of p53 and c-Abl, while in vitro, celecoxib enhanced superoxide radical production by xanthine oxidase. Importantly, the failure of anti-oxidants to protect from death indicates that celecoxib induces death independently of reactive oxygen species and that reactive oxygen species generation may be an insufficient trigger of death in p53-deficient cells.

Parameters for cellular viability and membrane function in chenopodium cells show a specific response of extracellular pH to heat shock with extreme Q10

The effect of brief heat shock on Chenopodium cells was investigated by measuring biochemical parameters for cellular vitality, membrane function and integrity: extracellular pH, release of osmotic compounds, phosphatase, protein and betalain, and cellular reduction of DCPIP and MTT. A threshold temperature was found at 45 degrees C, where release of osmotic compounds, protein and betalain, and reduction of DCPIP and MTT indicate loss of vitality. Extracellular pH and an alkaline phosphatase responded 10-20 degrees C below this threshold, suggesting that extracellular alkalinization, and probably the release of a phosphatase, are part of a specific cellular response to abiotic stress induced by heat shock. The extracellular proton concentration did not increase above 45 degrees C: this may indicate equilibration of gradients driving this process or an inactivation of cellular mechanisms responsible for extracellular alkalinization. The response of extracellular pH to heat shock in Chenopodium cell suspensions was fast, i.e., up to +1 pH in 5 min. Addition of the K+/H+ antiporter nigericin to Chenopodium cells caused an extracellular alkalinization similar to heat shock. The heat shock-induced extracellular alkalinization was characterized by Q10 values for distinct ranges of temperature (Q10 of 56 for 24-31 degrees C, 2.3 for 31-42 degrees C, and 1.0 for 42-50 degrees C). To the author's knowledge, the Q10 of 56 is the highest found up to now. These results suggest that extracellular protons are involved in temperature sensing and signalling in plant cells, probably via a channel-mediated pathway.