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Formazans can be lost from tissue sections when the incubation medium is removed at the end of a dehydrogenase reaction. The loss is not uniform and will clearly affect the interpretation of results. This suggests that both the qualitative evaluation of the reaction and the measurement of enzyme activity should be made at the time of incubation.
A rapid, enzyme-linked colorimetric assay, for the sequential determination of nanomole quantities of glucose and fructose in the same sample, has been developed for the measurement of fructosyl transferase activity in plant extracts. The assay extends the conventional dehydrogenase-linked assay for these sugars by utilizing the intermediary electron carrier, phenazine methosulfate, to couple NADP reduction to the production of a formazan dye from the tetrazolium salt, thiazolyl blue, in a form suitable for measurement using a microtiter plate reader. When the microtiter plate assay was used to measure the activities of yeast invertase and sucrose:sucrose fructosyl transferase from Lolium temulentum, results obtained were very similar to results obtained using the conventional procedure. The rapidity, small scale, and ease of execution of the method offers considerable advantages over the conventional hexose assay and is particularly suitable for screening of large numbers of small samples, exploiting both the speed of the microtiter plate reader and the facility of for microcomputer processing of data. The potential of this method for use with other enzyme systems and other metabolites is discussed.
A new microplate assay for the determination of activity in vitro against Giardia intestinalis has been developed in which viability is measured by soluble formazan production from a tetrazolium reagent. Metabolic reduction of the latter gives rise to a coloured product which may be determined directly by optical density measurement. Using this method the anti-giardial activities of more than 20 anti-microbial compounds have been assessed. The results obtained with a number of known anti-giardial agents, including metronidazole (50% inhibitory concentration [IC50] = 2.98 microM) and furazolidone (IC50 = 4.14 microM), compare well with previously published data; mepacrine, however, was found to produce a biphasic dose-response curve from which two IC50 values (0.816 and 6.83 microM) were obtained. This method provides a convenient means by which the search for new anti-giardial agents may be facilitated.
The discovery of small molecule inhibitors of cytotoxicity induced by amyloid-beta (Abeta) oligomers, either applied extracellularly or accumulated intraneuronally, is an important goal of drug development for Alzheimer's disease (AD), but has been limited by the lack of efficient screening methods. Here we describe our approach using two cell-based methods. The first method takes advantage of the unique ability of extracellularly applied Abeta oligomers to rapidly induce the exocytosis of formazan formed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). We employed a short protocol to quantify this toxicity, and quickly identified two novel inhibitors, code-named CP2 and A5, from two compound libraries. A second independent screen of the same libraries using our previously published MC65 protection assay, which identifies inhibitors of toxicity related to intracellular Abeta oligomers, also selected the same two leads, suggesting that both assays select for the same anti-Abeta oligomer properties displayed by these compounds. We further demonstrated that A5 attenuated the progressive aggregation of existing Abeta oligomers, reduced the level of intracellular Abeta oligomers, and prevented the Abeta oligomer-induced death of primary cortical neurons, effects similar to those demonstrated by CP2. Our results suggest that, when combined, the two methods would generate fewer false results and give a high likelihood of identifying leads that show promises in ameliorating Abeta oligomer-induced toxicities within both intraneuronal and extracellular sites. Both assays are simple, suitable for rapid screening of a large number of medicinal libraries, and amenable for automation.
It has recently been reported that methyl-beta-cyclodextrin-solubilized cholesterol protects PC12 cells from amyloid beta protein (Abeta) toxicity. To ask if this is the case in brain neurons, we investigated its effect in primary cultured rat hippocampal neurons. In basal culture conditions with no addition of Abeta, methyl-beta-cyclodextrin-solubilized cholesterol at concentrations of 30-100 microM was toxic to neurons, but at concentrations of 1-10 microM promoted neuronal survival. Methyl-beta-cyclodextrin-solubilized cholesterol at 1-10 microM was also effective in protecting neurons from toxicity of 20 microM Abeta. However, these effects were all mimicked by methyl-beta-cyclodextrin alone, but not by cholesterol solubilized by dimethylsulfoxide or ethanol. The effects of methyl-beta-cyclodextrin-solubilized cholesterol on neuronal survival and Abeta toxicity are probably attributed to the action of methyl-beta-cyclodextrin, but not cholesterol. Alternatively, we found that methyl-beta-cyclodextrin-solubilized cholesterol at lower concentrations ( > 10 nM) inhibited cellular reduction of 3-(4,5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) by promoting the exocytosis of MTT formazan. This effect was shared by dimethylsulfoxide- or ethanol-solubilized cholesterol, but not by methyl-beta-cyclodextrin, supporting that it is attributed to the action of cholesterol. These results suggest that cholesterol does not protect neurons from Abeta toxicity, or rather inhibits cellular MTT reduction in a similar manner to Abeta.
BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PD) deficiency has increased prevalence rates in tropical Africa, tropical and subtropical Asia and some parts of the Mediterranean. Earlier studies on G6PD deficiency in the Philippines have shown prevalence rates of 4.5% to 25.7%. METHODS: In the present study, 3278 male newborns were screened for G6PD deficiency using the modified formazan method, a simple screening procedure affordable in the setting of a developing country. Subjects with positive screening results were recalled for confirmatory testing using a commercial assay kit for quantitative enzyme determination. RESULTS: Of the 3278 boys studied, 186 revealed positive screening results. Of the 186, 65 boys had confirmatory testing. Of these 65 boys, 45 were confirmed to have G6PD deficiency and 20 had normal results. This study reveals an incidence of G6PD deficiency of 3.9% among male Filipinos. CONCLUSIONS: This study recommends the inclusion of G6PD deficiency in the panel of disorders for newborn screening among Filipino newborns.
Formazan cells were less numerous in the peripheral blood of vervet monkeys (Cercopithecus aethiops) receiving a "O" protein-low calorie diet than in animals fed a full or a protein but not calorie deficient diet.
We have developed an effective and optimally safe microculture method for rapid and convenient assay of the in vitro cytopathic effects of human immunodeficiency virus (HIV-1) on human lymphoblastoid or other suitable host cells. The assay procedure is applicable to the evaluation of drug effects on in vitro infections induced directly in cultured host cells by cell-free HIV-1 or by coculture with H9 cells chronically infected with HIV-1. The assay uses a newly developed tetrazolium reagent that is metabolically reduced by viable cells to yield a soluble, colored formazan product measurable by conventional colorimetric techniques. This simple microassay minimizes the number of plate manipulations typically required with other assay methods and, coupled with computerized data collection and analysis, facilitates large-scale screening of agents for potential antiviral activity. To support and enhance the discovery of new anti-HIV-1 agents, the National Cancer Institute is offering investigators worldwide the opportunity to submit new candidate agents for anti-HIV-1 screening with this method.
Various new substituted formazans were synthesized and characterized by elemental analyses, IR and mass spectral data. The compounds were evaluated for their ability to protect against inflammation by carrageenin-induced paw edema in albino rats of either sex. The active derivatives of the present series were also tested for their analgesic activity against aconitine-induced writhing in albino mice and ulcerogenic activity in albino rats. The toxicity of the compounds was assessed by determination of their approximate LD50 on albino mice. An attempt has also been made to establish a structure-activity relationship.
Several screening tests for glucose 6 phosphate dehydrogenase (G6PD) deficiency have been reported thus far, and a standardized method of testing was proposed by the International Council for Standardization in Hematology (ICSH). The screening test used in any particular laboratory depends upon a number of factors such as cost, time required, temperature, humidity, and availability of reagents. In this study, a direct comparison between three different G6PD screening methods has been undertaken. In 71 cases (50 hematologically normal volunteers, 9 hemizygous G6PD-deficient males, and 12 heterozygous deficient females), the blue formazan spot test (BFST) was compared with the conventional methemoglobin reduction test (HiRT) and the ICSH-recommended fluorescent spot test (FST-ICSH). In all cases, the results obtained with the three screening tests were correlated with the enzyme activity assayed spectrophotometrically. In hemizygous G6PD-deficient males, all cases were equally detected with the three methods: BFST (4.7-6.64, controls: 11.1-13.4), BMRT (score +3 in all 9 cases), and FST (no fluorescence in 9 cases). In heterozygous G6PD-deficient females, two methods detected 7 out of 12 cases (BFST: 8.71-11.75, controls: 11.1-13.4; and BMRT: score +3 in 7 cases), whereas the FST-ICSH missed all 12 cases that presented a variable degree of fluorescence. Although the sensitivity for G6PD-deficient carrier detection is the same for the BMRT and the BFST, the latter has the advantage of being semiquantitative and not merely qualitative. Unfortunately, none of the three screening tests compared here allowed the detection of the 100% heterozygote carrier state of G6PD deficiency.
This paper presents a synthesis about some hydrazones, formazans and copper's complexes combinations. The structure of the new compounds was confirmed by the results of the quantitative elementary and IR spectral analysis. The antimicrobial and antiinflammatory activities were investigated.
This paper presents the synthesis of some tetrazolium salts and metal complexes combinations, which are derived from aromatic and heterocyclic formazans. Elemental quantitative analyses and spectral data confirmed the structure of the new synthesized compounds. The new synthesized compounds were submitted to microbiological tests.
Alkaline phosphatase-conjugated secondary antibodies on blotting membranes were visualized by means of a modified formazan staining method (Hodson & Skillen 1988). It is based on the standard 5-bromo-4-chloro-3-indolyl phosphate/Nitroblue tetrazolium method, but employs different buffer conditions and thiazolyl blue instead of Nitroblue. It gave a sensitivity of 1 ng albumin in a 12 mm2 dot and less background staining on dot blots than the standard method. The new protocol provides an advantage with regard to ease of staining and preparation of reagents while it equals the former method with respect to sensitivity.
Two methods have been used to determine the isobestic (equiconcentration) wavelength of formazans derived from nitroblue tetrazolium-succinate dehydrogenase (EC 1.3.99.1) activity in cryostat sections of the rat superior cervical ganglion prior to microdensitometric measurements. Both methods indicate that maximal absorbance of the final reaction product is at a wavelength of 540-550 nm. This wavelength differs by 35-45 nm from that used to measure the same reaction product in sections of other rat tissues such as liver and implies that it may be unwise to adopt a "standard" wavelength for a particular reaction product when making microdensitometric measurements in relation to quantitative enzyme histochemistry.
Fifteen 1-aryl-3-(3'-nitro-4'-methoxyphenyl)-5-phenyl formazans and five 3-aryl-5-(3'-nitro-4'-methoxy phenyl)-2-phenyl tetrazolium bromides have been tested against Escherichia coli and Pseudomonas aeruginosa for their antibacterial and against Aspergillus flavus and Helminthosporium gramineum for their antifungal activities. Most of the compounds have shown promising antibacterial and antifungal action. These compounds were also found to exhibit significant antiviral activity against sunnhemp rosette virus in Cyamopsis tetragonoloba plants in vivo as well as in vivo.
The tetrazolium salt, 3-(4,5-dimethyl-thiazolyl-2)-2,5-diphenyl tetrazolium bromide (MTT) has recently been established as a substitute for Nitro-blue tetrazolium (NBT) in stain mixtures using antibody-conjugated alkaline phosphatase for the location of proteins on Western blots (Heegaard, 1990). Experiments reported here show that MTT is as sensitive as NBT in digoxigenin-labeled probe localization (on nucleic acid blots) utilizing alkaline-phosphatase-labelled, anti-digoxigenin antibodies. Moreover, as the formazan from MTT is soluble in ethanol, it is shown that spectrophotometric quantitation can be used to estimate the amount of target DNA on dot and Southern blots. For dot blotting, pBR328 was used as the probe and pBR322 as target. For Southern blots, human rDNA was used as the probe and total genomic calf DNA as the target. Staining response was linear over at least six twofold DNA dilutions in both types of blot.
A colorimetric method for measuring the viability of Leishmania promastigotes is described that is based on the reduction of the tetrazolium salt, XTT, to a water-soluble formazan. Values obtained by the XTT method correlated well with parasite number (r=0.965) and with methods that rely upon the reduction of MTT or MTS (r=0.96 and 0.97, respectively). The IC(50) values obtained by XTT method with amphotericin-B, miltefosine and ketoconazole were similar to those previously reported by other methods. The XTT method proved to be a reliable and convenient method for the screening of methanolic extracts from 1059 plants and was used for the bioassay-guided fractionation of the alkaloid aegeline from Sarcorhachis naranjoana.
Formazans react with boron triacetate to produce boratatetrazines, which can be reduced to yield borataverdazyl radical anions--the first boron containing verdazyl radicals.