In vitro metabolic activation of ethidium bromide and other phenanthridinium compounds: mutagenic activity in Salmonella typhimurium

Decomposition of DNA staining agent ethidium bromide by gamma irradiation: Conditions, kinetics, by-products, biological activity, and removal from wastewater

Ethidium Bromide (Eth-Br) is an intercalating agent commonly used in medical and biological laboratories as a DNA staining dye. Despite its popular use, aqueous solutions containing Eth-Br showed high toxicity, mutagenic capacity, and deactivate DNA transcription. In this study, the removal of Eth-Br from aqueous solutions by gamma irradiation has been fully investigated. Gamma irradiation was capable of achieving a near complete removal of Eth-Br in neutral and non-buffered aqueous solutions at an absorbed dose of 15 kGy. Various experimental conditions were studied and showed that the removal efficiency is not diminished. The addition of hydrogen peroxide (2 %) to the irradiated solutions reduced the D₅₀ and D₉₀ by 50 %. Modeling Eth-Br decomposition showed that the reaction followed pseudo first-order kinetics and reaches at least 90 % removal under all experimental conditions. TOC and HPLC measurements confirmed that Eth-Br is fully mineralized when the absorbed dose reaches 15 kGy. The biological activity of Eth-Br after irradiation treatment was investigated with synthetic DNA and natural DNA. The biological activity of Eth-Br was deactivated at an absorbed dose as low as 5 kGy. Toxicity measurement with E-coli bacteria also confirmed that the absorbed dose of 5 kGy was sufficient to remove Eth-Br toxicity.

Adsorption of ethidium bromide from aqueous solution onto nutraceutical industrial fennel seed spent: Kinetics and thermodynamics modeling studies

Dye pollutants from research laboratories are one of the major sources for environmental contamination. In the present study, a nutraceutical industrial fennel seed spent (NIFSS) was explored as potential adsorbent for removal of ethidium bromide (EtBr) from aqueous solution. The adsorbent was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Through batch experiments, the operating variables like initial dye concentration, adsorbent dosage, temperature, contact time, and pH were optimized. Equilibrium data were analyzed using three number of two-parameter and six number of three-parameter isotherm models. The adsorption kinetics was studied using pseudo-first order and pseudo-second order. The diffusion effects were studied by film diffusion, Webber-Morris, and Dumwald-Wagner diffusion models. The thermodynamic parameters; change in enthalpy (ΔHº), entropy (ΔSº), and Gibbs free energy (ΔGº) of adsorption system were also determined and evaluated.

Isolation and Quantification of DNA

Purifying DNA is the key to successful cloning. The cleaner the final preparation of DNA, the more efficient will be the enzymatic reactions that use the DNA as a template or a substrate. In the 1930s and 1940s, the scientific literature began to accumulate methods to release DNA from cells and to remove cellular constituents that inhibit or act as competitors on enzymatically catalyzed reactions. Since then, thousands of protocols for purification of DNA from a wide variety of organisms, tissues, and bodily fluids have been published. This introduction provides an overview of methods for isolation and quantification of DNA.

Magnetic Activated-ATP@Fe3O4 Nanocomposite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of Ethidium Bromide

Magnetic attapulgite-Fe₃O₄ nanocomposites (ATP-Fe₃O₄) were prepared by coprecipitation of Fe₃O₄ on ATP. The composites were characterized by scanning electron microscopey, X-ray diffractometry, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, energy dispersive spectrometer and transmission electron microscopy. Surface characterization showed that Fe₃O₄ particles with an average size of approximately 15 nm were successfully embedded in matrix of ATP. The capacity of the Fe₃O₄-activated ATP (A-ATP@Fe₃O₄) composites for catalytic degradation of ethidium bromide (EtBr, 80 mg/L) at different pH values, hydrogen peroxide (H₂O₂) concentrations, temperatures, and catalyst dosages was investigated. EtBr degradation kinetics studies indicated that the pseudo-first-order kinetic constant was 2.445 min⁻¹ at T = 323 K and pH 2.0 with 30 mM H₂O₂, and 1.5 g/L of A-ATP@Fe₃O₄. Moreover, a regeneration study suggested that A-ATP@Fe₃O₄ maintained over 80% of its maximal EtBr degradation ability after five successive cycles. The effects of the iron concentrations and free radical scavengers on EtBr degradation were studied to reveal possible catalytic mechanisms of the A-ATP@Fe₃O₄ nanocomposites. Electron Paramagnetic Resonance revealed both hydroxyl (∙OH) and superoxide anion (∙O₂⁻) radicals were involved in EtBr degradation. Radical scavenging experiment suggested EtBr degradation was mainly ascribed to ∙OH radicals, which was generated by reaction between Fe²⁺ and H₂O₂ on the surface of A-ATP@Fe₃O₄.

Heat shock protein 90 as a potential drug target against surra

Trypanosomiasis is caused by Trypanosoma species which affect both human and animal populations and pose a major threat to developing countries. The incidence of animal trypanosomiasis is on the rise. Surra is a type of animal trypanosomiasis, caused by Trypanosoma evansi, and has been included in priority list B of significant diseases by the World Organization of Animal Health (OIE). Control of surra has been a challenge due to the lack of effective drugs and vaccines and emergence of resistance towards existing drugs. Our laboratory has previously implicated Heat shock protein 90 (Hsp90) from protozoan parasites as a potential drug target and successfully demonstrated efficacy of an Hsp90 inhibitor in cell culture as well as a pre-clinical mouse model of trypanosomiasis. This article explores the role of Hsp90 in the Trypanosoma life cycle and its potential as a drug target. It appears plausible that the repertoire of Hsp90 inhibitors available in academia and industry may have value for treatment of surra and other animal trypanosomiasis.

Trypanosoma evansi and surra: a review and perspectives on transmission, epidemiology and control, impact, and zoonotic aspects

This paper reviews the transmission modes of Trypanosoma evansi. Its worldwide distribution is attributed to mechanical transmission. While the role of tabanids is clear, we raise questions on the relative role of Haematobia sp. and the possible role of Stomoxys sp. in delayed transmission. A review of the available trypanocidal drugs and their efficacy in various host species is useful for understanding how they interact in disease epidemiology, which is complex. Although there are similarities with other mechanically transmitted trypanosomes, T. evansi has a more complex epidemiology due to the diversity of its hosts and vectors. The impact of clinical and subclinical disease is difficult to establish. A model was developed for buffaloes in the Philippines, which could be transferred to other places and livestock systems. Since Trypanosoma evansi was reported in humans, further research is required to investigate its zoonotic potential. Surra remains a potentially emerging disease that is a threat to Australia, Spain, and France. A number of questions about the disease have yet to be resolved. This brief review of the basic knowledge of T. evansi suggests that there is renewed interest in the parasite, which is spreading and has a major economic impact.

Tuning the cellular uptake and cytotoxicity properties of oligonucleotide intercalator-functionalized mesoporous silica nanoparticles with human cervical cancer cells HeLa

A series of organically functionalized, MCM-41 type mesoporous silica nanoparticle materials (PAP-LP-MSN and AP-PAP-MSN) with different pore sizes (5.7 nm and 2.5 nm, respectively) were synthesized and characterized. We selectively decorated the exterior particle surface of PAP-LP-MSN and the interior pore surface of AP-PAP-MSN with an oligonucleotide intercalating phenanthridinium functionality. While phenanthridinium itself is a cell membrane impermeable molecule, we demonstrated that both phenanthridinium-immobilized PAP-LP-MSN and AP-PAP-MSN materials could indeed be internalized by live human cervical cancer cells (HeLa). We discovered that the PAP-LP-MSN nanoparticles with the phenanthridium groups located on the exterior surface were able to bind to cytoplasmic oligonucleotides, such as messenger RNAs, of HeLa cells resulting in severe cell growth inhibition. In contrast, the cytotoxicity of AP-PAP-MSN, where the same oligonucleotide intercalating molecules were anchored inside the pores, was significantly lowered upon the endocytosis by HeLa cells. We envision that this approach of combining the selective functionalization of the two different surfaces (exterior particle and interior pore surfaces) with morphology control of mesoporous silica nanoparticles would lead to a new generation of nanodevices with tunable biocompatibility and cell membrane trafficking properties for many biomedical applications.

On the electronic structure of ethidium

The electronic structure of the common intercalating agent ethidium bromide (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide) is dominated by an interplay of electron donating and withdrawing effects mediated by its nitrogen atoms. X-ray crystallography, UV/Vis and IR absorption, fluorescence emission, and NMR spectroscopy are used to probe the electronic properties of the phenanthridinium "core" of ethidium as well as its exocyclic amines and 6-phenyl groups. Interestingly, despite its positive charge, most of ethidium's aromatic carbon and hydrogen atoms have high electron densities (compared to both 6-phenylphenanthridine and benzene). The data suggest that electron donation by ethidium's exocyclic amines dominates over the electron withdrawing effects of its endocyclic iminium in their combined influence on the electron densities of these atoms. Ethidium's nitrogen atoms are, conversely, electron deficient where the 5-position is the most electropositive, followed by the 3-amino, and lastly the 8-amino group. These results have been used to generate an empirically-based pi-electron density map of ethidium that may prove useful to understanding its nucleic acid binding specificity.

Synthesis, photophysical properties, and nucleic acid binding of phenanthridinium derivatives based on ethidium

A series of substituted phenanthridine derivatives has been synthesized by converting the amines at the 3- and 8-positions of ethidium bromide into guanidine, pyrrole, urea, and various substituted ureas. The resulting derivatives exhibit unique spectral properties that change upon binding nucleic acids. The compounds were analyzed for their ability to inhibit the HIV-1 Rev-Rev Response Element (RRE) interaction, as well as for their affinity to calf thymus DNA. One derivative (3,8-bis-urea-ethylenediamine-5-ethyl-6-phenylphenanthridinium trifuroracetate) has an enhanced affinity and specificity for HIV-1 RRE as compared to ethidium bromide. These results indicate that the nucleic acid affinity and specificity of an intercalating agent can be tuned by synthetic modification of its exocyclic amines.

The effect of inducing agents on the metabolism of ethidium bromide by isolated rat hepatocytes

The metabolism of ethidium bromide by isolated rat hepatocytes is significantly enhanced by pre-treatment of animals with phenobarbitone (PB) and 3-methylcholanthrene (3-MC). Pre-treatment with PB and 3-MC results in a 2.5- and 1.5-fold increase, respectively in the amount of the principal metabolite, ethidium 8-N-glucuronide, compared with that formed by hepatocytes from untreated rats. The formation of ethidium 3-N-glucuronide is not enhanced by pre-treatment with either PB or 3-MC. Two new metabolites, hydroxyethidium glucuronide and a transient unidentified species, have been detected by HPLC and are formed only by hepatocytes from animals pre-treated with 3-MC.

Bioavailability, pharmacokinetics, and tissue distribution of 14C homidium after parenteral administration to Boran cattle

The absorption, distribution and elimination characteristics of 14C homidium have been described in non-infected and Trypanosoma congolense-infected cattle treated with 14C homidium chloride by either intramuscular (i.m.) or intravenous (i.v.) injection at a dose level of 1 mg/kg body weight. Results show that the mean (+/-SD) elimination of the drug from plasma followed a biexponential process, with half-lives of 0.084 +/- 0.006 h and 97.66 +/- 16.28 h for the distribution and elimination phases after intravenous injection, respectively. Bioavailability of the intramuscular dose was 62.5% and 57.8% in non-infected and trypanosome-infected cattle, respectively. Absorption was rapid, with a tmax of 15 min and a mean Cmax (+/-SD) of 268.4 +/- 4.09 ng/mL following the intramuscular dose in non-infected cattle. The major route of excretion was via faeces. Approximately 90% of the total dose given to non-infected i.m.-treated cattle was excreted within 14 days. Following intramuscular administration of the drug, residues remained high in the major excretory organs, with the liver having concentrations of 1411 and 1199 ng/g after 14 and 28 days, respectively. Over the same period, the values in the kidneys were 649 and 448 ng/g. Concentrations in the liver 14 and 21 days following i.v. treatment were 2195 and 2454 ng/g, respectively. These results show that there was no significant difference in liver drug residues between 14 and 21 days, or 28 days depending on the treatment given, suggesting that once the drug is in this organ, it is released back into the circulation at an extremely slow rate.

The influence of proteins on silver staining of nucleic acids following polyacrylamide gel electrophoresis

The influence, on silver staining, of proteins and restriction enzymes in polymerase chain reaction (PCR) products was studied in 12-20% polyacrylamide gels. For small DNA fragments (74, 41 and 33 bp) best results were achieved using 20% polyacrylamide gels. In 12% gels, restriction enzymes and also proteins used for PCR (bovine serum albumin, Taq-DNA polymerase) interfere with silver staining of nucleic acids.

Evaluation of the efficacy of a slow release device containing homidium bromide in rabbits infected with Trypanosoma congolense

The subcutaneous implantation of a slow release device (SRD) containing 1 mg kg-1 homidium bromide (Ethidium) protected 95% of the rabbits for at least 3 months against reinfection with different stocks of Trypanosoma congolense. Only 30.8% of the animals, which received the classical intramuscular injection of 1 mg kg-1 homidium bromide, were protected for more than 1 month. The advantages of an SRD against injection of homidium bromide are a longer protection period, less variation in the percentage of protected animals and the possibility to recover the implants at slaughter. The possible effects on the development of resistance have to be examined further.

Cellulose bearing covalently linked copper phthalocyanine trisulphonate as an adsorbent selective for polycyclic compounds and its use in studies of environmental mutagens and carcinogens

A method useful as a preconcentration technique for isolating mutagens and carcinogens is described. Cotton bearing covalently linked copper phthalocyanine trisulphonate as ligand (blue cotton) can adsorb selectively compounds having three or more fused rings. The adsorption takes place in aqueous media, involving 1:1 complex formation between the ligand and the polycyclic compound. The desorption can be done by elution with organic solvents, most effectively with methanol containing ammonia. As many important environmental mutagens and carcinogens are polycyclics, this adsorption is useful as a means of extracting this class of materials from crude samples such as food, urine and river waters. The use of copper phthalocyanine as a ligand for chromatographic supports has recently been initiated, yielding promising results for the effective separation of polycyclic aromatic compounds from each other.

Destruction of ethidium bromide in solution by ozonolysis

Ethidium bromide can be rapidly destroyed in aqueous solutions or in isoamyl alcohol by ozonolysis in the presence of H2O2 to give a mixture of organic acids. In a variety of buffers commonly used in recombinant DNA technology destruction of ethidium bromide was more than 99.9%. The yellow reaction mixture after ozonolysis was shown to be nonmutagenic. This method may be used in laboratories for the disposal of ethidium bromide wastes.

Ethidium bromide resistance in a rat liver epithelial cell line: association with enhanced drug efflux

Ethidium bromide-resistant cell strains were obtained by continuous selection of an adult rat liver-derived cell line (ARL6T) grown in the continuous presence of 200 ng/ml ethidium bromide. Comparison of resistant strains and parental (sensitive) cells was made for uptake and binding of ethidium bromide, visualized as fluorescent ethidium bromide-nucleic acid complexes. Although uptake of ethidium bromide was similar in parental and resistant cells, efflux kinetics were markedly different. Over a three-hour period, parental (sensitive) cells maintained fluorescence following a short ethidium bromide pulse (100 micrograms/ml ethidium bromide). In contrast, ethidium bromide-resistant cell lines eliminated photographically detectable fluorescent complexes within three hours following pulse exposure to ethidium bromide. The rapid elimination of ethidium bromide-fluorescent complexes in all (5) resistant cell strains examined supports an efflux mechanism as contributing to the resistance of ethidium bromide cytotoxicity in these cells.

Ethidium bromide: destruction and decontamination of solutions

Ethidium bromide in water, TBE buffer, Mops buffer, and cesium chloride solution may be completely degraded by reaction with sodium nitrite and hypophosphorous acid. Only non-mutagenic reaction mixtures were produced. Destruction was greater than 99.8% in all cases; the limit of detection was 0.5 micrograms ethidium bromide per milliliter of solution. Ethidium bromide also may be removed completely from the above solutions by using Amberlite XAD-16 resin. The limit of detection was 0.05 micrograms ethidium bromide per milliliter of solution (0.27 micrograms/ml when cesium chloride solution was used).

The Salmonella typhimurium/mammalian microsomal assay. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The Salmonella assay has been in use for almost 15 years and can be defined as a routine test for mutagenicity and for predicting potential carcinogenicity. It detects the majority of animal carcinogens and consequently plays an important role in safety assessment. The test is also routinely used as the frontline screen for environmental samples (complex mixtures) isolated from air, water and food. This role will continue to remain an area of growth as or because sample volumes associated with these testing areas are generally very limited and more extensive testing is generally impossible. While this test, like all others, has some limitations, it is recommended that it be regularly included in all genetic testing batteries.

Structure-function characterization of phenanthridinium compounds as mutagens in Salmonella

The mutagenic activity of some phenanthridinium compounds was examined by using Salmonella typhimurium strain TA98. Microsomal enzyme activation of the compounds was necessary for the detection of frameshift mutagenesis. Amino and/or azido functions at both R3 and R8 were structural requisites for significant mutagenic activity, although mutagenicity was severely reduced for the diazido analog. When an azido or amino group was substituted by hydrogen at either R3 or R8, mutagenic activities were minimal, and the deaminated compound (3,8-dihydro derivative) was not mutagenic. Propidium was only slightly more mutagenic than the monoamino and monoazido analogs. Relationships between mutagenic activity and chemical structure of phenanthridinium compounds are discussed.

Human fibroblast strains showing increased sensitivity or resistance to ethidium bromide

The sensitivity of a number of human fibroblast cell strains towards the DNA intercalating and mutagenic agent ethidium bromide has been examined. Among the cell strains investigated, 3 were of fetal origin, 6 from clinically normal adult persons, 2 from Lesch-Nyhan individuals and 1 each from persons with 3 genetic disorders, xeroderma pigmentosum, Fanconi anemia and Bloom syndrome, which are known to predispose to cancer. Results of our studies show that cells derived from 2 otherwise normal individuals exhibits a marked sensitivity towards ethidium bromide as compared to the rest of the group. At the same time all 3 cell strains of fetal origin were found to be highly resistant to killing by this agent. These results are discussed in relation to the toxic/mutagenic effects of ethidium bromide.

Mutagenic responses of five independent genetic loci in CHO cells to a variety of mutagens. Development and characteristics of a mutagen screening system based on selection for multiple drug-resistant markers

With the aim of developing a sensitive mutagen screening system, the responses of 15 different chemical mutagens at 5 independent genetic loci in Chinese hamster ovary (CHO) cells have been determined. The genetic markers which have been employed include resistance to thioguanine (Thgr), ouabain (OuaR), the protein synthesis inhibitor emetine (Emtr), the polyamine synthesis inhibitor methylglyoxal bisguanylhydrazone (Mbgr) and the nucleoside analog 5,6-dichlororibofuranosyl benzimidazole (DrbR). The optimal selection conditions for all of these genetic markers in CHO cells have been described. The chemicals whose response was investigated in these studies include direct-acting alkylating agents (ethyl methane-sulfonate, methyl methanesulfonate, beta-propiolactone, ethyleneimine, N-nitrosomethylurea and 4-nitroquinoline-N-oxide), DNA intercalating and cross-linking agents (ICR-170, acridine orange, ethidium bromide, mitomycin C and actinomycin D), polycyclic hydrocarbons (benzo[a]pyrene (B(a)P) and 7,12-dimethylbenz[a]anthracene (DMBA)) and aromatic amines (benzidine and beta-naphthylamine). Simultaneous examination of the response of the set of genetic markers to these chemicals revealed that although all of these chemicals caused a dose-dependent increase in the frequency of mutations at many of the above genetic loci, the magnitude of the mutagenic response at different genetic loci varied greatly depending upon the chemical. Of the genetic loci examined, no one single locus showed higher response to all of the above chemicals, instead, depending upon the chemical, specific loci were found to be more responsive than others. The polycyclic hydrocarbons and aromatic amines were weakly mutagenic in this system at several genetic loci even without any exogenous microsomal activation, although in the presence of a rat liver S9 fraction similar toxic and mutagenic effects of B(a)P and DMBA were observed at 5-20-fold lower concentrations. These results indicate that CHO cells may possess significant capacity for the metabolic activation of many procarcinogens, and also underscore the merits of measuring the mutagenic response at multiple genetic loci in mutagen screening studies.

Frameshift mutagenesis of 9-aminoacridine derivatives in Salmonella typhimurium

It has been noted that 9-aminoacridine reverts a his C frameshift but not one in his D in the Salmonella strains used in the Ames test, without metabolic activation. The 2 sites differ in the arrangement of G and C residues present. We show here that a series of 9-aminoacridine derivatives exhibits the same selectivity as 9-aminoacridine provided there is at least one exocyclic amino hydrogen at the central ring position in acridines, or the analogous site in aminoquinolines. The results are consistent with a model derived from NMR experiments on 9-aminoacridine binding to dinucleoside phosphates, in which the N-H group is situated in the duplex so as to participate in a hydrogen bond with one base while excluding its complementary partner, thereby provoking mismatching. We also report a strong difference in the dose-response behavior of 9-aminoacridine, quinacrine and a bifunctional derivative of quinacrine.

Proflavin: an unusual mutagen

In the Salmonella typhimurium mutagenicity assay, proflavin (PF), in the dark, was shown to possess some direct-acting frameshift mutagenic activity for strains TA1537 and TA98. In the presence of microsomal enzymes from mouse, hamster and rat livers, frameshift mutagenic activity for strain TA1538 and enhanced mutagenicity for strain TA1537 was observed. Exposure of bacteria to PF in the presence of visible light resulted in base substitution (strain TA1535) as well as frameshift (TA1537, TA1538, TA98) genetic activities. The findings are taken to indicate that PF possesses direct-acting frameshift activity (TA1537 and TA98) by virtue of its ability to intercalate between DNA base-pairs. The frameshift activity (TA1538, TA98 and enhanced TA1537) seen following metabolic or photo-activation may be due to the formation of chemical adducts between the cellular DNA and oxidation products of PF (a base-displacement effect). The light-induced base-substitution activity probably results from the generation of singlet oxygen which reacts with the guanine moiety of DNA. The mutagenic photoproduct of PF appears to be stable.

The development of a "Microtitre" fluctuation test for the detection of indirect mutagens, and its use in the evaluation of mixed enzyme induction of the liver

The "Microtitre" Fluctuation test recently introduced for the detection of direct mutagens has been adapted for the detection of indirect mutagens through the incorporation of an "S9-mix" metabolic system. It compares favourably with Greens' original method for the detection of a range of chemical mutagens. The technique has been employed in the evaluation of mixed enzyme induction using phenobarbitone and beta-naphthoflavone (benzoflavone), as a safe substitute for Aroclor-1254. The post-mitchondrial preparations from rats induced with the combined inducers had a similar "metabolic competence" to those derived from Aroclor induced animals. Such a combination would therefore provide a useful alternative to Aroclor-1254 for routine screening. It was found that the level of "S9" present in the metabolic system greatly affected the quantitative mutagenic response. This varied considerably from chemical to chemical and underlined the need for such preliminary investigations in routine screening.

The relation of repair phenomena to mutation induction in bacteria

The relation of various processes to mutation induction by radiation and chemicals is discussed for for various species of bacteria. A variety of repair processes have been identified at the molecular level that can eliminate many kinds of potentially mutagenic lesions before they can be converted to final mutation. Fixation often but not always occurs at replication. A number of mutagens, including UV light, ionizing radiation, and a number of chemicals, induce an error-prone process, perhaps a modification of the proof-reading system, that allows bacteria to survive after potentially lethal damage at the expense of making errors. Some mutagens, notably monofunctional alkylating agents and base analogues, produce mutations by other processes. Even in these cases, repair processes play an important role. There is some evidence that error-free as well as error-prone repair processes can be induced. A brief discussion is given of the relation of these findings to the practical problems of hazards estimations.