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PubMed1996

Growth hormone-responsive DT-diaphorase-mediated bioreduction of tetrazolium salts.

Microculture tetrazolium assays (MTAs) rely upon the bioreduction of tetrazolium salts to their intensely coloured formazans. Although these assays are being extensively used, the intracellular mechanisms responsible for the formazan production are not known. MTAs currently provide the basis for uniquely precise in vitro bioassays for human growth hormone (hGH) which use the Nb2 cells. We have compared two contrasting tetrazolium salts, namely 3-(4,5-dimethyl-thiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) and 5-(3-carboxymethoxyphenyl)-2-(4,5-dimethylthiazolyl)-3-(4-++ +sulfophenyl) tetrazolium, inner salt (MTS), in this system. An intermediate electron acceptor (IEA) is obligatory for the MTS- but not the MTT-bioassay. We report that inhibitors of DT-diaphorase abolished MTS- but not MTT-formazan production. We conclude that substitution of MTT with MTS/menadione resulted in formazan production via a different electron transfer pathway which is exclusively mediated by DT-diaphorase.

Animals↗
PubMed1993

Use of an aqueous soluble tetrazolium/formazan assay to measure viability and proliferation of lymphokine-dependent cell lines.

A new tetrazolium compound, MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt), has recently been described which in the presence of phenazine methosulfate (PMS) is reduced by living cells to yield a formazan product that can be assayed colorimetrically. An important advantage of MTS/PMS over other tetrazolium dyes (e.g., MTT) is the aqueous solubility of the reduced formazan product which eliminates the need for detergent solubilization or organic solvent extraction steps. Its advantages over XTT/PMS, another tetrazolium which yields a water-soluble formazan product, include the absorbance range of color produced (515-580 nm as opposed to 450 nm), the rapidity of color development, and the storage stability of the MTS/PMS reagent solution. In the present study, MTS/PMS was used to assay viability and proliferation of the IL-2-dependent HT-2 and CTLL-2 cell lines and the IL-3-dependent FDC-P1 and FL5.12 cell lines. With each cell line, the amount of formazan product was time-dependent and proportional to the number of viable cells. Furthermore, with both HT-2 and CTLL-2 cells it was found that cultures could be simultaneously labeled with MTS/PMS and [3H]thymidine, with relatively little effect of the dye on uptake of the latter. This feature was further capitalized upon in studies with FDC-P1 cells, in which the co-addition of MTS/PMS and [3H]thymidine was used to distinguish between cell viability and proliferation.

Animals↗
PubMed2006

The formation of bioactive amyloid species by prion proteins in vitro and in cells.

Amyloid proteins are a group of proteins that can polymerize into cross beta-sheeted amyloid species. We have found that enhancing cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) formazan exocytosis is a common property of bioactive amyloid species formed from all of the amyloid proteins tested to date. In this report, we show that the infectious amyloid species of the prion protein HET-s of the filamentous fungus Podospora anserina, like other amyloidogenic proteins, also enhances MTT formazan exocytosis. More strikingly, cellular MTT formazan exocytosis revealed the formation of bioactive amyloid species in prion-infected mouse N2a neuroblastoma cells. These findings suggest that cellular MTT formazan exocytosis can be useful for studying the roles of bioactive amyloid species in prion infectivity and prion-induced neurodegeneration.

Amyloid beta-Peptides↗
PubMed1990

Flow cytometric evaluation of nitro blue tetrazolium (NBT) reduction in human polymorphonuclear leukocytes.

Oxidative metabolic burst of activated human polymorphonuclear leukocytes (PMN) is most commonly investigated in clinical practice by evaluating nitroblue tetrazolium (NBT) reduction at the single cell level. Reduced NBT precipitates where the redox reaction has taken place and can be visualized as PMN-associated dark blue granules of formazan in light microscopy. Although widely used and not technically demanding, this method remains subjective and labor intensive, especially when large numbers of samples need to be investigated. We developed a new flow cytometry technique in which PMN membrane was rendered fluorescent by a short incubation with fluorescein-conjugated Concanavalin A. PMN were then incubated with NBT and increasing doses of a suitable stimulus, such as phorbol myristate acetate (PMA). Formazan has a distinct peak of absorption at 520 nm that represents the peak of emission of fluorescein. As a consequence, formazan quenches the PMN-associated fluorescence. Data show that a dose-dependent reduction of fluorescence can be obtained using graded amounts of PMA in normal PMN cultures. PMN-associated fluorescence remains unchanged in control patients with chronic granulomatous (CGD) disease, a disorder characterized by a selective impairment of PMN oxidative metabolism. Electronic cell size increases upon PMA incubation in normal PMN, irrespective of the presence of NBT. Conversely, forward light scatter intensity decreases in the presence, but not in the absence, of NBT indicating that the phenomenon is due to the capacity of formazan to absorb/scatter the incident light. The present method for easily detecting NBT reducing activity at single cell level by flow cytometry makes use of commonly available, inexpensive reagents and standard instrumentation. It could become a useful test for clinical purposes.

Concanavalin A↗
PubMed1983

Studies on the phenazine methosulphate-tetrazolium salt capture reaction in NAD(P)+-dependent dehydrogenase cytochemistry. I. Localization artefacts caused by the escape of reduced co-enzyme during cytochemical reactions for NAD(P)+-dependent dehydrogenases.

The correct localization of oxidative enzymes using cytochemical tetrazolium methods, in which low molecular weight electron carriers such as NAD(P)H and reduced phenazine methosulphate (PMSH) are used, can be endangered by the escape of the reduced intermediates before they react to form the insoluble formazan at the true enzyme-containing sites. To investigate this phenomenon, the glucose-6-phosphate dehydrogenase reaction was studied in fixed erythrocytes which, because of their microscopic dimensions, are well-suited for studying the loss of intermediates. A mixture of active and heat-inactivated fixed erythrocytes was incubated in a PMS-supplemented medium for glucose-6-phosphate dehydrogenase. The cytophotometric histograms showed that the final formazan precipitate was equally distributed over both active and inactivated cells. When bovine serum albumin was added to the medium, all the formazan was found to be bound to this protein and the erythrocytes remained essentially unstained. The false localization in this system could be explained by an unfavourable balance between the capture of electrons carried by NADPH within the erythrocyte and the diffusion of NADPH out of the erythrocyte. The rate constant of NADPH oxidation was determined, as was also the diffusion constant of NADPH in a protein matrix. Substituting the data obtained into formulae derived from the enzyme cytochemical localization theory of Holt & O'Sullivan (1958), it was calculated that the capture reaction was highly deficient and, theoretically, less than 1% of the total amount of formazan produced was localized within the erythrocyte which explains the false localization observed. The importance of these findings for the cytochemical demonstration of NAD(P)+-dependent dehydrogenases in cells and electropherograms is briefly discussed.

Coenzymes↗
PubMed1990

A quantitative colorimetric method to evaluate the functional state of human polymorphonuclear leukocytes.

The colorimetric assay previously described by Mosmann for the measurement of cell viability and proliferation has been modified for the assessment of the functional state of human polymorphnuclear cells (PMNs). The ability of PMNs to reduce the tetrazolium salt MTT to formazan reflects directly the degree of stimulation induced by various agents. The underlying mechanism of MTT-reduction to formazan seems to be similar to that of nitroblue tetrazolium (NBT)-reduction. In contrast to the NBT-reduction assay, the formazan produced from MTT can easily be measured by an ELISA reader. Parallel experiments revealed a qualitative correlation between the concentration of formazan produced from MTT and the concentration of cytochrome C reduced by PMNs. Although oxidative burst may not be the actual lytic mechanism in cellular cytotoxicity of PMN, we also observed an association between MTT-reduction capacity and the cytotoxic activity of PMNs from normal donors in antibody dependent cellular cytotoxicity. Our results indicate that the MTT-reduction assay can be employed to estimate the functional state of polymorphnuclear granulocytes.

Cell Division↗
PubMed1997

Free radicals generated by electrolysis reduces nitro blue tetrazolium in isolated rat heart.

Oxygen free radicals (OFR) are highly cytotoxic when produced in the myocardium under certain pathological conditions. In isolated rat hearts perfused retrogradely, OFR were generated by electrolysis of the Krebs-Henseleit buffer (two platinum electrodes, DC current, 10 mA, 1 min). In order to find evidence that OFR are produced, we used nitro blue tetrazolium (NBT) a soluble compound which yields a dark blue formazan pigment in the presence of reducing agents. Hearts were subdivided into: control, electrolysed, NBT (3.3 mg/ml) perfusion during electrolysis in the presence or absence of scavengers. The xanthine-xanthine oxidase (XXO) system known to produce superoxide radical was used as a reference. Specimens were fixed with formaldehyde and stained with eosine or Kernechtrot in preparation for light microscopical examination. Several areas of acute necrosis expressed by hyalinisation and loss of striation were observed in electrolysed hearts which present a pattern of wavy disrupted myofibers and an increase in interstitial spaces. A very faint deposition of formazan was observed in some rare areas of NBT perfused heart. Only the electrolysed group perfused with NBT and the one perfused with XXO plus NBT presented an extensive formazan deposition, mostly in the areas of fibre necrosis. Formazan was barely detectable when superoxide dismutase plus catalase were perfused in the XXO system, while it was still apparent when perfused in electrolysed hearts. These results support the hypothesis that electrolysis can be used to generate different species of OFR and to evaluate the protective action of scavenger and antioxidants against OFR-induced myocardial damage.

Animals↗
PubMed2003

An improved, simple screening method for detection of glucose-6-phosphate dehydrogenase deficiency.

We established a new, simple and rapid screening method for detection of glucose-6-phosphate dehydrogenase (G6PD)-deficiency by using a new formazan substrate, 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H tetrazolium monosodium salt (WST-8) with a hydrogen carrier of 1-methoxyphenazine methosulfate (1-methoxy PMS), instead of a combination of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) and phenazine methosulfate (PMS), as used in many previous formazan methods. WST-8 does not react with haemoglobin, and the formed formazan is highly water-soluble, differing from MTT. Thus, the whole procedure can be performed in aqueous solution in a tube or well without any special equipment other than micropipettes. Within 1 h at room temperature, the strong orange colour of the WST-8 formazan formed in normal blood samples could be distinguished, by naked eye, from G6PD-deficient blood samples with less than 50% residual activity. We also found that reagents in the WST-8/1-methoxy PMS method were more resistant against exposure to sunlight than those in an MTT/PMS method. As the new method is both qualitative and quantitative, it is possible to express G6PD activity as increase of NADPH concentration by reading absorbance at 460 nm after incubation for 30 or 60 min.

Blood Specimen Collection↗
PubMed2005

Improved localization of glucose-6-phosphate dehydrogenase activity in cells with 5-cyano-2,3-ditolyl-tetrazolium chloride as fluorescent redox dye reveals its cell cycle-dependent regulation.

Since the introduction of cyano-ditolyl-tetrazolium chloride (CTC), a tetrazolium salt that gives rise to a fluorescent formazan after reduction, it has been applied to quantify activity of dehydrogenases in individual cells using flow cytometry. Confocal laser scanning microscopy (CLSM) showed that the fluorescent formazan was exclusively localized at the surface of individual cells and not at intracellular sites of enzyme activity. In the present study, the technique has been optimized to localize activity of glucose-6-phosphate dehydrogenase (G6PD) intracellularly in individual cells. Activity was demonstrated in cultured fibrosarcoma cells in different stages of the cell cycle. Cells were incubated for the detection of G6PD activity using a medium containing 6% (w/v) polyvinyl alcohol, 5 mM CTC, magnesium chloride, sodium azide, the electron carrier methoxyphenazine methosulphate, NADP, and glucose-6-phosphate. Before incubation, cells were permeabilized with 0.025% glutaraldehyde. Fluorescent formazan was localized exclusively in the cytoplasm of fibrosarcoma cells. The amount of fluorescent formazan in cells increased linearly with incubation time when measured with flow cytometry and CLSM. When combining the Hoechst staining for DNA with the CTC method for the demonstration of G6PD activity, flow cytometry showed that G6PD activity of cells in S phase and G2/M phase is 27 +/- 4% and 43 +/- 4% higher, respectively, than that of cells in G1 phase. CLSM revealed that cells in all phases of mitosis as well as during apoptosis contained considerably lower G6PD activity than cells in interphase. It is concluded that posttranslational regulation of G6PD is responsible for this cell cycle-dependent activity.

Animals↗
PubMed2000

Trimethyltin reduces ATP levels and MTT reduction in the LRM55 rat astrocytoma cell line.

The LRM55 rat astrocytoma cell line was used to study the time and concentration effects of trimethyltin (TMT) exposure on intracellular adenosine triphosphate (ATP) levels, formazan production from (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), and lactate dehydrogenase (LDH) release. TMT concentrations of > or =50 microM produced a delayed increase in extracellular LDH from approximately 20% at 24 h to almost 70%, at 72 h. Twenty-four hours before cell lysis was detectable ATP levels decreased to less than 30% and formazan production declined to 70% (50 microM), 31% (100 microM), and 21% (200 microM) of control values. Concentrations of TMT (5 and 10 microM) that produced little or no LDH release also decreased ATP levels (62 and 49% of control, respectively) and formazan production (63 and 52% of control, respectively) by 48 h. These data support the hypothesis that TMT exposure interferes with energy production and that this event likely contributes to the delayed cell death seen in this cell line. Moreover, the declines in ATP and formazan production can occur at subtoxic concentrations in LRM55 cells.

Adenosine Triphosphate↗
PubMed2002

[Study on tetrazolium salt colorimetric assay for growth and survival of bacteria].

To establish a tetrazolium salt(MTT) colorimetric assay for bacteria growth and survival, living or boiling killed bacteria S. aureus and E. coli were incubated with MTT in microdilution plate for 36-37 degrees C at different time. DMSO was added as formazan dissolvent and the mixtures were measured for optical density(A) or absorbence at 510 nm wave length. Living bacteria were incubated with different amount of MTT for different time. The formazan were dissolved with different amount of DMSO and the A value were measured at different wave length. The results showed that yellow MTT could be reduced into blue formazan by living bacteria S. aureus and E. coli and the A value was directly proportional to concentration of the bacteria. A values of bacteria decreased with increasing of boiling time. To some extents, absorbence of living bacteria was direct proportion to MTT concentration and incubation time in the range of 0-2 hours. DMSO was good dissolvent for bacteria formazan and the highest absorbence could be reached in wave length range of 510-530 nm. It was suggested that MTT colorimetric assay could be used for measurement of bacteria growth and survival, and its optimal parameters were as follows: MTT concentration is 0.3 mg/ml. MTT incubation time was 2 hours. DMSO amount as dissoventis was 2-fold volume of bacteria suspension. Measurement wave length was 510-530 nm.

Colony Count, Microbial↗
PubMedDate not supplied

[Quantitative method of determining the activity of zinc- and copper-dependent superoxide dismutase in biological material].

The activity of superhydroxide dismutase was estimated by following rate of inhibition of non-enzymatic reduction of tetrazolium salt in reaction with superhydroxide ions, which were continuously generated in a photochemical system. The quantitative estimations were achieved by using para-nitrotetrazolium chloride, which was reduced to formazanes soluble in acetone. Formation of formazanes by the photochemical system (riboflavin + tetramethylethylene diamine + O2 + para-nitrotetrazolium chloride + light) in presence of biological material and cyanide was compared with formation of formazanes in absence of cyanide for specific estimation of Zn, Cu-dependent forms of superhydroxide dismutase. The rate of enzymatic cyanide sensitive inhibition of the photochemical formation of formazanes from paranitrotetrazolium chloride was determined by the activity of Zn, Cu-dependent superhydroxide dismutase in biological material and might be expressed in units of the activity -- un. ac. = 10/(0,026.% inhibition--1,3).

Animals↗
PubMed1984

[Improved demonstration of topochemical dehydrogenase in the CNS with a nitro-monotetrazolium salt].

Succinate dehydrogenase (SDH) and glutamate dehydrogenase (GDH) were determined parallel to the tetrazolium salts p-DNTT, NBT and TNBT under different conditions using sagittal brain sections of newborn and 3 till 100-day-old rats. Under conventional incubation conditions for SDH (37 degrees C, 30 min), the tetrazolium salts p-DNTT stained more intensely than NBT or TNBT. Decrease of the final concentration of tetrazolium salts from 1.2 mmol/l to 0.6 mM effected a considerable increase of p-DNTT formazan development. Using NBT or TNBT, the formazan formation was significantly smaller. In contrast to SDH the demonstration of GDH activity under incubations conditions mentioned is unsatisfactory at any rate. Preservation of mitochondria during the preparation and incubation procedure improved evidently the quality of the GDH-demonstration, especially by use of p-DNTT. The formazan of p-DNTT was formed to be amorphous and was confined exclusively to enzyme containing compartments, whereas formazanes of the NBT and TNBT spread out more diffusely.

Animals↗
PubMedDate not supplied

In vitro chemosensitivity testing of leukemic cells: development of a semiautomated colorimetric assay.

A rapid chemosensitivity assay was developed, employing the human continuous leukemic cell lines HL 60, K 562, FLG 29.1. This automated colorimetric assay is based on the characteristic of viable, metabolically active cells to cleave p-iodonitrotetrazolium violet (INT) into a red formazan derivative, whose optical density is readable at 492 nm by an automated microtiter-plate reader photometer. A linear relationship was found between the viable cell number and the optical density of INT cleaved by the cellular samples. Dead cells did not reduce INT and did not interfere with the formazan derivative generation and the photometric reading. Leukemic cell lines were also tested for INT formazan derivative generation after exposure to antileukemic drugs at various concentrations, representative of plasma levels obtainable in vivo. A dose-dependent inhibition was detected, with different sensitivity patterns, related both to the drugs and to the different cell lines. A significant correlation between the viable cell number and the amount of tetrazolium salt cleaved was also demonstrated after drug exposure. INT assay allows the processing of a great number of samples and gives the opportunity to screen several drugs, saving time and yielding fully reliable results.

Autoanalysis↗
PubMed1992

In situ detection of oxidative stress in rat hepatocytes.

In rat hepatocytes in primary culture incubated with nitro blue tetrazolium, formazan content was increased by addition of t-butyl hydroperoxide, a potent oxidant, in a dose-related manner, but not by addition of valinomycin, which kills hepatocytes through mitochondrial damage. This increment after t-butyl hydroperoxide addition was not seen in hepatocytes preincubated with deferoxamine mesylate, a ferric iron chelator which inhibits radical formation. Liver perfusion with nitro blue tetrazolium and t-butyl hydroperoxide in rats produced formazan deposition faintly on the surface of hepatocytes throughout the liver and prominently in the cytoplasm of some hepatocytes, which was attenuated when performed following deferoxamine mesylate perfusion. When liver perfusion with nitro blue tetrazolium was performed in carbon tetrachloride-intoxicated rats, formazan deposition appeared diffusely in hepatocytes in the centrilobular areas. Similar deposition was also observed on the surface and in the cytoplasm of hepatocytes in the periportal and mid-zonal areas in rats undergoing post-ischaemic reperfusion. Liver perfusion with nitro blue tetrazolium can detect in situ oxidative stress in hepatocytes and may be a useful tool for studying the role of lipid peroxidation in rat liver injury.

Animals↗
PubMed2001

A cell-based method for the detection of nanomolar concentrations of bioactive amyloid.

A cell-based method for the detection of nanomolar concentrations of bioactive amyloid peptide is described. The method is based upon the observation that fibrillogenic amyloid peptides specifically and dramatically enhance the exocytosis of the intracellular vesicles that are involved in transporting the reduced tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT formazan), with the formation of unique formazan crystals on the cell surface. It is found that the ability of amyloid peptides to induce MTT formazan exocytosis is closely associated with both their neurotoxicity and their ability to activate glia cells, two biological activities of amyloid peptides that are believed to cause neurodegeneration. This simple assay for bioactive amyloid species can be of great value in the screening of anti-amyloid drugs and in the study of amyloid fibrillogenesis with a cell-based model.

Amyloid↗
PubMed1977

Histochemistry of 3beta-hydroxysteroid dehydrogenase in rat ovary. I. Amethodological study.

By recording the incubation time needed for initial appearance of the red and blue formazans the reliability of the histochemical method for 3beta-HSD was investigated: 1. Prefixation of small tissue blocks with 1% W/V methanol-free formaldehyde (pH=7.2) for up to 30 min preserved morphological integrity as well as maximal enzyme activity. Moreover, the substantivity of formazans and lipids was enhanced. 2. Commercial available glutaraldehyde (pH=7.2) induced SH groups in the tissue (even at 0.1% W/V for 5 min) thereby enhancing the Nothing dehydrogenase reaction. 3. Preextraction of lipids with acetone for 20 min at -30 degree C caused no loss of activity and was an inevitable step if a reliable activity pattern had to be achieved (e.g. in interstitial cells). 4. No diffusion of enzyme was noticed within 30 min of preincubation in phosphate buffer (0.2 M, pH=7.2) at 20 degree C. 5. By using the double-section incubation method no diffusion of 3beta-HSD or rediffusion of NADH or PMSH could be noticed withn 45 min of incubation, provided that low concentrations of NAD (0.1 mg/ml) and PMS (0.003 mg/ml) were balanced against the concentration of Nitro BT (0.5 mg/ml) or Tetranitro BT (1.0mg/ml). 6. The utlity of different inhibitors of alkaline phosphomonoesterase was tested and discussed. 7. By inhibiting alkaline phosphomonoesterase with 0.1 mM of L-p-bromotetramisole or 16 mM of beta-glycerophosphate, 3beta-HSD was shown to be exclusively NAD-linked. 8. Levamisole was a potent inhibitor of NADH-tetrazolium reductase as well as 3 beta-HSD, but not of NADPH-tetrazolium reductase. 9. 3beta-HSD possess SH groups requisite for the activity as this enzyme was totally inhibited by N-ethyl maleimide. 10. Whether alcohol dehydrogenases may use steroids as substrate is discussed; It is concluded that preextraction (by acetone) and/or the use of an inhibitor of alcohol dehydrogenase (1,10-phenanthroline) has to be performed. 11. Propylene glycol was a poor solvent for all substrates and was itself an excellent substrate for alcohol dehydrogenase. 12. Specifications for the ideal solvent of steroid substrates in the histochemical practice are proposed. DMSO showed to be promising as a steroid solvent (e.g. extraction of formazans was considerably lower as compared to DMF). 13. The utilization of substrates was descending in the following order (using 1 mM and 0.1 ml/ml of either DMF or DMSO): epiandrosterone, methandriol, dehydroepiandrosterone and pregnenolone. 14. If DMSO was used as solvent for pregnenolone (but not for the other substrates tested) an evident increase of activity was recorded as compared to DMF.

Alcohol Oxidoreductases↗
PubMed1990

Potential of a soluble tetrazolium/formazan assay for the evaluation of filarial viability.

Using female Acanthocheilonema viteae we have investigated the bioreduction of the tetrazolium reagent XTT (2,3-bis(2-methoxy-4-nitro-sulphonyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide). Unlike the formazan formed by other tetrazolium salts, that derived from XTT readily diffuses out of A. viteae in vitro. Formazan formation can therefore be quantified by direct absorbance reading of the incubation medium, eliminating the need for a DMSO solubilization step. Optimum assay conditions involved a 4 h incubation, in the presence of the electron coupling agent phenazine methosulphate (PMS). Repeat 4 h incubations with XTT-PMS were well tolerated by worms for 5 consecutive days. This confirmed the low toxicity of XTT formazan and its usefulness in the semi-continuous assessment of filarial viability. In comparison to our previously reported MTT (3-(4, 5 dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide)-reduction assay XTT-PMS reduction showed comparable drug sensitivity and accuracy, however XTT-PMS appears to be at least 10-15 times less efficiently reduced by A. viteae females. A possible application of the XTT assay using female Onchocerca volvulus is discussed.

Animals↗