Potent mutagenicity of an azide, 3-azido-1,2-propanediol, in human TK6 cells

Sodium azide is a strong mutagen that has been successfully employed in mutation breeding of crop plants. In biological systems, it is metabolically converted to the proximate mutagen azidoalanine, which requires further bioactivation to a putative ultimate mutagen that remains elusive. The nature of the DNA modifications induced by azides leading to mutations is also unknown. Other mutagenic organic azido compounds seem to share the same bioactivation pathway to the ultimate mutagenic species as they induce point mutations dependent on the same DNA repair pathways. We investigated mutations induced by the representative mutagen 3-azido-1,2-propanediol (azidoglycerol, AZG) in the human TK6 cell line. Until now, azides have been considered to be non-mutagens and non-carcinogens in mammals, including humans, as judged only by the conventional clastogenicity chromosomal aberration types of bioassays. Here, we show the potent mutagenicity of AZG in cultured human cells, comparable to alkylating agents such as methyl methanesulfonate at concentrations with similar lethality. The potent ability of an organic azide to induce base substitutions in a mammalian system raises an alert with respect to human exposure to organic and inorganic azido compounds.

The Influence of Metabolic Inhibitors, Antibiotics, and Microgravity on Intact Cell MALDI-TOF Mass Spectra of the Cyanobacterium Synechococcus Sp. UPOC S4

The aim and novelty of this paper are found in assessing the influence of inhibitors and antibiotics on intact cell MALDI-TOF mass spectra of the cyanobacterium Synechococcus sp. UPOC S4 and to check the impact on reliability of identification. Defining the limits of this method is important for its use in biology and applied science. The compounds included inhibitors of respiration, glycolysis, citrate cycle, and proteosynthesis. They were used at 1–10 μM concentrations and different periods of up to 3 weeks. Cells were also grown without inhibitors in a microgravity because of expected strong effects. Mass spectra were evaluated using controls and interpreted in terms of differential peaks and their assignment to protein sequences by mass. Antibiotics, azide, and bromopyruvate had the greatest impact. The spectral patterns were markedly altered after a prolonged incubation at higher concentrations, which precluded identification in the database of reference spectra. The incubation in microgravity showed a similar effect. These differences were evident in dendrograms constructed from the spectral data. Enzyme inhibitors affected the spectra to a smaller extent. This study shows that only a long-term presence of antibiotics and strong metabolic inhibitors in the medium at 10⁻⁵ M concentrations hinders the correct identification of cyanobacteria by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF).

Assessing modulators of cytochrome c oxidase activity in Galleria mellonella larvae

Caterpillars of the greater wax moth, Galleria mellonella, are shown to be a useful invertebrate organism for examining mitochondrial toxicants (inhibitors of electron transport) and testing putative antidotes. Administration of sodium azide, sodium cyanide, or sodium (hydro)sulfide by intra-haemocoel injection (through a proleg) results in a dose-dependent paralysed state in the larvae lasting from <1 to ~40 min. The duration of paralysis is easily monitored, because if turned onto their backs, the larvae right themselves onto their prolegs once they are able to move again. The efficacy of putative antidotes to the three toxicants can routinely be assessed by observing shortened periods of paralysis with larvae given toxicant and antidote compared to larvae administered only the same dose of toxicant. The validity of the approach is demonstrated with agents previously shown to be antidotal towards cyanide intoxication in mice; namely, sodium nitrite and CoN₄[11.3.1] (cobalt(II/III) 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7)2,11,13,15-pentaenyl cation). These same compounds are shown to be antidotal towards all three toxicants in the G. mellonella caterpillars; findings that may prove important in relation to azide and sulfide poisonings, for which there are currently no effective antidotes available. The observation that sodium nitrite ameliorates cyanide toxicity in the larvae is additionally interesting because it unambiguously demonstrates that the antidotal action of nitrites does not require the involvement of methemoglobin, contributing to the resolution of an ongoing controversy.

A ratiometric Raman probe for live-cell imaging of hydrogen sulfide in mitochondria by stimulated Raman scattering

Stimulated Raman Scattering (SRS) coupled with alkyne tags has been an emerging imaging technique to visualize small-molecule species with high sensitivity and specificity. Here we describe the development of a ratiometric Raman probe for visualizing hydrogen sulfide (H2S) species in living cells as the first alkyne-based sensor for SRS microscopy. This probe uses an azide unit as a selective reactive site, and it targets mitochondria with high specificity. The SRS ratiometric images show a strong response to H2S level changes in living cells.

Knock-out of a mitochondrial sirtuin protects neurons from degeneration in Caenorhabditis elegans

Sirtuins are NAD⁺-dependent deacetylases, lipoamidases, and ADP-ribosyltransferases that link cellular metabolism to multiple intracellular pathways that influence processes as diverse as cell survival, longevity, and cancer growth. Sirtuins influence the extent of neuronal death in stroke. However, different sirtuins appear to have opposite roles in neuronal protection. In Caenorhabditis elegans, we found that knock-out of mitochondrial sirtuin sir-2.3, homologous to mammalian SIRT4, is protective in both chemical ischemia and hyperactive channel induced necrosis. Furthermore, the protective effect of sir-2.3 knock-out is enhanced by block of glycolysis and eliminated by a null mutation in daf-16/FOXO transcription factor, supporting the involvement of the insulin/IGF pathway. However, data in Caenorhabditis elegans cell culture suggest that the effects of sir-2.3 knock-out act downstream of the DAF-2/IGF-1 receptor. Analysis of ROS in sir-2.3 knock-out reveals that ROS become elevated in this mutant under ischemic conditions in dietary deprivation (DD), but to a lesser extent than in wild type, suggesting more robust activation of a ROS scavenging system in this mutant in the absence of food. This work suggests a deleterious role of SIRT4 during ischemic processes in mammals that must be further investigated and reveals a novel pathway that can be targeted for the design of therapies aimed at protecting neurons from death in ischemic conditions.

Root aquaporins contribute to whole plant water fluxes under drought stress in rice (Oryza sativa L.)

Aquaporin activity and root anatomy may affect root hydraulic properties under drought stress. To better understand the function of aquaporins in rice root water fluxes under drought, we studied the root hydraulic conductivity (Lpr) and root sap exudation rate (Sr) in the presence or absence of an aquaporin inhibitor (azide) under well-watered conditions and following drought stress in six diverse rice varieties. Varieties varied in Lpr and Sr under both conditions. The contribution of aquaporins to Lpr was generally high (up to 79% under well-watered conditions and 85% under drought stress) and differentially regulated under drought. Aquaporin contribution to Sr increased in most varieties after drought, suggesting a crucial role for aquaporins in osmotic water fluxes during drought and recovery. Furthermore, root plasma membrane aquaporin (PIP) expression and root anatomical properties were correlated with hydraulic traits. Three chromosome regions highly correlated with hydraulic traits of the OryzaSNP panel were identified, but did not co-locate with known aquaporins. These results therefore highlight the importance of aquaporins in the rice root radial water pathway, but emphasize the complex range of additional mechanisms related to root water fluxes and drought response.

Effects of azide on electron transport of exoelectrogens in air-cathode microbial fuel cells

The effects of azide on electron transport of exoelectrogens were investigated using air-cathode MFCs. These MFCs enriched with azide at the concentration higher than 0.5mM generated lower current and coulomb efficiency (CE) than the control reactors, but at the concentration lower than 0.2mM MFCs generated higher current and CE. Power density curves showed overshoot at higher azide concentrations, with power and current density decreasing simultaneously. Electrochemical impedance spectroscopy (EIS) showed that azide at high concentration increased the charge transfer resistance. These analyses might reflect that a part of electrons were consumed by the anode microbial population rather than transferred to the anode. Bacterial population analyses showed azide-enriched anodes were dominated by Deltaproteobacteria compared with the controls. Based on these results it is hypothesized that azide can eliminate the growth of aerobic respiratory bacteria, and at the same time is used as an electron acceptor/sink.

Differential resistance of drinking water bacterial populations to monochloramine disinfection

The impact of monochloramine disinfection on the complex bacterial community structure in drinking water systems was investigated using culture-dependent and culture-independent methods. Changes in viable bacterial diversity were monitored using culture-independent methods that distinguish between live and dead cells based on membrane integrity, providing a highly conservative measure of viability. Samples were collected from lab-scale and full-scale drinking water filters exposed to monochloramine for a range of contact times. Culture-independent detection of live cells was based on propidium monoazide (PMA) treatment to selectively remove DNA from membrane-compromised cells. Quantitative PCR (qPCR) and pyrosequencing of 16S rRNA genes was used to quantify the DNA of live bacteria and characterize the bacterial communities, respectively. The inactivation rate determined by the culture-independent PMA-qPCR method (1.5-log removal at 664 mg·min/L) was lower than the inactivation rate measured by the culture-based methods (4-log removal at 66 mg·min/L). Moreover, drastic changes in the live bacterial community structure were detected during monochloramine disinfection using PMA-pyrosequencing, while the community structure appeared to remain stable when pyrosequencing was performed on samples that were not subject to PMA treatment. Genera that increased in relative abundance during monochloramine treatment include Legionella, Escherichia, and Geobacter in the lab-scale system and Mycobacterium, Sphingomonas, and Coxiella in the full-scale system. These results demonstrate that bacterial populations in drinking water exhibit differential resistance to monochloramine, and that the disinfection process selects for resistant bacterial populations.

Drp1 dephosphorylation in ATP depletion-induced mitochondrial injury and tubular cell apoptosis

Recent studies revealed a striking morphological change of mitochondria during apoptosis. Mitochondria become fragmented and notably, the fragmentation contributes to mitochondrial outer membrane permeabilization and consequent release of apoptotic factors. In renal tubular cells, mitochondrial fragmentation involves the activation of Drp1, a key mitochondrial fission protein. However, it is unclear how Drp1 is regulated during tubular cell apoptosis. In this study, we examined Drp1 regulation during tubular cell apoptosis following ATP depletion. Rat kidney proximal tubular cells (RPTC) were subjected to azide treatment or severe hypoxia in glucose-free medium to induce ATP depletion. During ATP depletion, Drp1 was shown to be dephosphorylated at serine-637. Drp1 dephosphorylation could be suppressed by cyclosporine A and FK506, two calcineurin inhibitors. Importantly, cyclosporine A and FK506 could also prevent mitochondrial fragmentation, Bax accumulation, cytochrome c release, and apoptosis following ATP depletion in RPTC. The results suggest that calcineurin-mediated serine-637 dephosphorylation is involved in Drp1 activation during ATP depletion in renal tubular cells. Upon activation, Drp1 contributes to mitochondrial fragmentation and outer membrane permeabilization, resulting in the release of apoptogenic factors and apoptosis.

Light-Activated Destruction of Cancer Cell Nuclei by Platinum Diazide Complexes

A possible way to avoid dose-limiting side effects of platinum anticancer drugs is to employ light to cause photochemical changes in nontoxic platinum prodrugs that release active antitumor agents. This strategy could be used in the treatment of localized cancers accessible to irradiation (e.g., bladder, lung, esophagus, and skin). We report here that nontoxic photolabile diam(m)ino platinum(IV) diazido complexes inhibit the growth of human bladder cancer cells upon irradiation with light, and are non-crossresistant to cisplatin. Their rate of photolysis closely parallels that of DNA platination, indicating that the photolysis products interact directly, and rapidly, with DNA. Photoactivation results in a dramatic shrinking of the cancer cells, loss of adhesion, packing of nuclear material, and eventual disintegration of their nuclei, indicating a different mechanism of action from cisplatin.

Severe cytochrome c oxidase inhibition in vivo does not induce a pyrimidine deficiency; neuroprotective action of oral uridine prodrug PN401 requires supraphysiological levels of uridine

It has been hypothesized that mitochondrial respiratory chain dysfunction leads to a pyrimidine deficiency since the pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase is coupled to the electron transport chain. The uridine prodrug triacetyluridine (PN401) is neuroprotective in several models of neurodegenerative disease involving respiratory chain toxins. Therefore, the therapeutic effects of PN401 might involve the correction of a pyrimidine deficiency secondary to respiratory chain impairment. We infused mice with the cytochrome c oxidase inhibitor azide, which inhibited brain complex IV activity. Chronic infusion of azide for 2 or 14 days induced significant toxicity and mortality but did not cause a pyrimidine deficit in the brain. In contrast, the pyrimidine synthesis inhibitor N-phosphonoacetyl-l-aspartate (PALA) produced a pyrimidine deficit with minimal mortality. Treatment with 6% PN401 decreased mortality and cerebrocortical apoptosis caused by azide. Previously, we found that optimal neuroprotection against mitochondrial complex II inhibition required 4-6% PN401. PN401 at 1, 3, 6 and 10% in chow induced nonlinear increases in plasma uridine with 6% PN401 elevating plasma uridine up to 80 muM, and these higher micromolar uridine levels were also required for neuroprotection in chemical hypoxia models in vitro. Our results indicate that severe complex IV inhibition in vivo does not lead to a pyrimidine deficiency, and therefore the protective effect of PN401 in the azide toxin model is not mediated through the correction of a pyrimidine deficiency. Furthermore, supraphysiological levels of uridine are required to produce optimal protective effects in disorders involving impairment of mitochondrial respiratory complex II or IV.

Hemolysis of human erythrocytes by hypochlorous acid is modulated by amino acids, antioxidants, oxidants, membrane-perforating agents and by divalent metals

The optimal conditions under which hypochlorous acid (NaOCl) either hemolyzes human RBC or kills monkey kidney epithelial cells (BGM) in culture had been investigated. While in Hank's balanced salt solution (HBSS), micromolar amounts of NaOCl caused full hemolysis and also killed BGM cells, in D-MEM or RPMI media rich in amino acids, 25-40 mM of hypochlorite were needed to induce cell injury. Cells exposed to high amounts of NaOCl became highly refractory to strong detergents. Hemolysis by NaOCl was strongly inhibited by a large variety of antioxidants. RBC treated by subtoxic concentrations either of peroxide, peroxyl radical, NO, cholesterol, PLA2, PLC as well as by N2, argon or by mixture of CO2 (10%) and O2 (90%) became much more susceptible to lysis by NaOCl. On the other hand, while RBC treated by Fe2+, Co2+, and V2+ and to a lesser extent with Cu2+ became highly resistant to NaOCl hemolysis presumably due to NaOCl decomposition, no such effect was found either with Co2+ or by Mn2+. RBC treated by azide to destroy catalase and then incubated with peroxide and with NaOCl failed to undergo hemolysis due to the ability of peroxide to decompose NaOCl. The inhibitory effects of the divalent metals on NaOCl-induced hemolysis were also substantiated by measuring the decrease in pH and by cyclic voltammetry. The findings that like peroxide, NaOCl also synergizes with membrane-perforating agents and with a protease to kill epithelial cells further implicate such "cocktails" in cell injury in inflammatory conditions. Taken together, because of the capacity of many agents to scavenge NaOCl, tissue damage by NaOCl-generated neutrophils can take place primarily if activated neutrophils closely adhere to target cells to avoid the scavenging effects of amino acids and of antioxidants. Therefore, the significance of the data which had tested the cytotoxic effects of NaOCl using cells suspended only in salt solutions, should be reconsidered.

Effects of deflected droplet electrostatic cell sorting on the viability and exoproteolytic activity of bacterial cultures and marine bacterioplankton

The cell-sorting capability of flow cytometers makes it possible to isolate specific populations of cells with pre-defined cytometric characteristics. A better knowledge of the biological effects of the sorting process is necessary for the future cell sorting applications. In this paper we report the effects of flow cytometric sorting on bacterial viability and exoproteolytic activity (EPA) of bacterial cultures and marine bacterioplankton. Sorting bacterial cultures and bacterioplankton samples reduce viability as assessed by plate counts and produce variations in the exoproteolytic activity. These effects indicate that deflected electrostatic sorting may significantly alter the biological properties of the sorted bacteria.

Mutagenicity of sodium azide and its metabolite azidoalanine in Drosophila melanogaster

The mutagenic and toxic activities of sodium azide (NaN(3) ) and its organic metabolite L-azidoalanine [N(3)-CH(2)-CH(NH)(2)-COOH] were examined in the different stages of spermatogenesis in Drosophila melanogaster. Both azide and azidoalanine were toxic to the injected males, but azidoalanine was significantly less toxic than sodium azide. Following the injection with 0.2 microl of these compounds in the hemocoel of young adult wild-type males, the minimum concentrations of these compounds with complete toxic effects (zero survival) were 40 mM sodium azide and 160 mM azidoalanine. Sex-linked recessive lethals were scored by the Muller-5 method in three successive broods, representing sperms (brood A), spermatids (brood B), and a compiled group of meiotic and premeiotic germ cell stages (brood C). The results provide strong experimental evidence that azidoalanine is significantly (p<0.01) mutagenic to all stages of spermatogenesis in Drosophila melanogaster. Sodium azide, however, was not significantly (p>0.05) mutagenic and did not increase the rate of sex-linked recessive lethals over those produced by the control group injected with 0.45% NaCl. These results indicate the requirement of metabolic activation of azide in Drosophila as a prerequisite for its mutagenic effects.

Increased Ro15-4513-induced seizures following multiple ethanol withdrawals

Clinical research into the etiology of ethanol withdrawal seizures has shown an increase in the number and severity of seizures with increasing numbers of withdrawal episodes. The aim of the present study was to determine the effects of multiple ethanol withdrawals on the seizure sensitivity to the GABA(A) receptor inverse agonist Ro15-4513. In this study, three groups of laboratory rats received varying amounts of either continuous or intermittent ethanol exposure. A fourth group (Naive) received no ethanol exposure. Eight hours following the last withdrawal from chronic ethanol exposure, animals were tested for sensitivity to Ro15-4513-induced motor convulsions. Seizure sensitivity was significantly increased in all ethanol-treated groups compared to ethanol-naive controls, which did not exhibit any convulsive responses to this dose of Ro15-4513. Furthermore, rats exposed to multiple ethanol withdrawals exhibited significantly higher sensitivity to drug-induced seizures than did animals experiencing only a single ethanol withdrawal. Although the specific mechanism of this enhanced convulsant effect of Ro15-4513 following multiple ethanol withdrawals remains to be determined, these results suggest an involvement of GABA(A)-benzodiazepine receptors in this multiple withdrawal phenomenon.

Allium cepa anaphase-telophase root tip chromosome aberration assay on N-methyl-N-nitrosourea, maleic hydrazide, sodium azide, and ethyl methanesulfonate

The Allium anaphase-telophase assay was used to show genotoxicity of N-methyl-N-nitrosourea (MNU), maleic hydrazide (MH), sodium azide (NaN3) and ethyl methanesulfonate (EMS). All agents induced chromosome aberrations at statistically significant levels. The rank of the lowest doses with positive effect was as follows: NaN3 0.3 mg/l < MH 1 mg/l < MNU 41 mg/l < EMS 100 mg/l. The results were compared with results from other plant assays (Arabidopsis, Vicia, Tradescantia) and for MH and MNU the values were found to be within the same range, whereas the results in the Allium test for NaN3 and EMS were in a lower range than that found for the other plant assays. EMS and MMS (methyl methanesulfonate), two chemicals used as positive controls in mutagenicity testing, were compared in the Allium test, and MMS was found to be about ten times more potent in inducing chromosome aberrations than EMS. Recording of micronuclei in interphase cells showed that this endpoint does not give more information of clastogenicity than recording of chromosome aberrations in anaphase-telophase cells.

Mutation induction and mutation spectra of S. typhimurium TA100 after exposure to isohistidines

L-Isohistidine and D,L-isohistidine, but not D-isohistidine, caused an increase of the number of mutant colonies in S. typhimurium strain TA100. Spontaneous and also sodium azide or 2-aminoanthracene induced mutant numbers were enhanced by L-isohistidine and by an isomeric mixture of D,L- and L-isohistidine. These effects could not be attributed to a growth-enhancing property. The colony probe hybridization procedure was used to investigate the effects of the histidines on the spontaneous and azide-induced spectra of the hisG46 allele in strain TA100. D,L-Isohistidine, but not the D-isomer, caused and increase of transitions (CCC-->CTC) and transversions (CCC-->CAC) in the spontaneous spectrum. Sodium azide alone induced a strong increase of CCC-->CTC transitions; combination with the D,L-isohistidine led to a further enhancement of this type of base substitutions, whereas with the L-isomer, no such effect was observed. This supports the hypothesis that the activity of D,L-isohistidine is probably not due to DNA-damaging properties, but rather to indirect mechanisms, such as enhancement of the infidelity of DNA replication and/or interference with DNA-repair or proofreading functions.

Synergistic/comutagenic action in the Ames test as an indication of irrelevant positive findings

A number of structurally very diverse compounds which cause weak positive effects in the Ames test by evident or suspect irrelevant mechanisms is discussed. As a unifying observation we describe synergistic effects in combination with known mutagens in the responsive strains and comutagenic effects in initially unresponsive strains. We argue that the compounds enhance the formation of spontaneous (or mutagen-induced) revertant colonies by test-specific mechanisms likely to be of no relevance to multicellular eukaryotic organisms rather than possessing intrinsic genotoxic (i.e. DNa-damaging) properties in the Ames test.

CYP2E1-mediated mechanism of anti-genotoxicity of the broccoli constituent sulforaphane

The broccoli constituent sulforaphane (1-isothiocyanate-4-methylsulfinylbutane) has previously been shown to protect rats against 9,10-dimethyl-1,2-benz[a]anthracene tumorigenesis, thought to be due, at least in part, to induction of phase II detoxification. We investigated the ability of sulforaphane to also inhibit the phase I enzyme cytochrome P450 isoenzyme 2E1 (CYP2E1), which is responsible for activation of several carcinogens, including dialkylnitrosamines. Using the p-nitrophenol hydroxylation assay in microsomes from livers of acetone-treated Sprague-Dawley rats, sulforaphane was shown to be a potent competitive inhibitor of CYP2E1 with a Ki of 37.0 +/- 4.5 microM. In view of this result, we studied the capacity of sulforaphane to inhibit the genotoxicity of N-nitrosodimethylamine (NDMA). Sulforaphane at concentrations of > 0.8 microM inhibited the mutagenicity of NDMA (4.4 mg/plate) in Salmonella typhimurium strain TA100 after pre-incubation for 45 min with cytosol extract from livers of Balb/c mice pre-treated with acetone. Unscheduled DNA synthesis induced by NDMA (33.5 microM) in mouse hepatocytes was inhibited in a dose-dependent manner by sulforaphane at 0.064-20 microM. Sulforaphane was unable to inhibit mutagenicity of sodium azide (5 micrograms/plate), a direct acting mutagen, in the Salmonella assay. It was not itself genotoxic in hepatocytes, as measured by unscheduled DNA synthesis, or mutagenic in the strain of Salmonella employed and cytotoxic only at high concentrations (> or = 0.5 mM). These findings suggest that inhibition of CYP2E1 by sulforaphane may offer chemoprotection against carcinogenic substrates of this enzyme.

Generation of reactive oxygen species by Co(II) from H2O2 in the presence of chelators in relation to DNA damage and 2'-deoxyguanosine hydroxylation

The generation of reactive oxygen species by Co(II) from H2O2 in the presence of chelators and related DNA damage was investigated by electron spin resonance (ESR), electrophoretic assays, and high-performance liquid chromatography (HPLC). Incubation of Co(II) with beta-alanyl-3-methyl-L-histidine (anserine) and H2O2 generated .OH radicals. Omission of any one component sharply reduced the amount of .OH radicals generated, indicating that anserine modulated the oxidation potential of Co(II) to enhance its capability to generate .OH radicals from H2O2. Formate only moderately decreased the .OH radical generation, while ethanol had no observable effect, indicating that the generation of .OH radical is site specific. The metal ion chelator 1,10-phenanthroline reduced the .OH radical generation, and deferoxamine suppressed it with the formation of deferoxamine nitroxide radical. Electrophoretic assays using both lambda Hind III linear DNA and PM2 supercoiled DNA showed that .OH radicals generated from a mixture of Co(II), H2O2, and anserine caused DNA strand breaks. A mixture of Co(II), H2O2, and 1,10-phenanthroline also caused DNA strand breaks, which were inhibited by sodium azide, indicating that 1O2 was involved in DNA damage. HPLC measurements showed that .OH radicals and 1O2 generated by Co(II) reactions caused 2'-deoxyguanosine hydroxylation to form 8-hydroxy-2'-deoxyguanosine. ESR spin trapping measurements provided evidence for 1O2 generation by Co(II) from H2O2 in the presence of 1,10-phenanthroline. The results indicate that the oxidation potential of Co(II) can be modulated by chelators to facilitate its generation of reactive oxygen species from H2O2. These species may be involved in Co(II)-induced cellular damage.

Mutagenicity of alkyl azides

Alkyl azides showed mutagenicity for S. typhimurium TA100 strain with S9 mix. However, no significant activity was observed for TA98 either with or without S9 mix or for TA100 without S9 mix. On the other hand, 3-azido-1,2-propanediol showed the enantioselective activity regardless of S9 mix. Two aryl azides tested were not mutagenic, and trimethylsilyl azide exhibited potent activity for TA100. Their structure-activity relationships are discussed.

Regional brain effects of sodium azide treatment on cytochrome oxidase activity: a quantitative histochemical study

The objective of the present study was to determine if regional variation in brain cytochrome oxidase activity was observed following systemic administration of sodium azide. An image analysis system calibrated with internal standards of known cytochrome oxidase activity was used to quantify cytochrome oxidase in histochemically stained brain sections. Rats receiving chronic infusion of sodium azide (400 micrograms/hr), which were sacrificed after two weeks, showed a substantial decrease in brain cytochrome oxidase activity over those infused with saline. All of the 22 regions sampled from telencephalic, diencephalic, and mesencephalic levels, showed a significant activity reduction which ranged between 26% and 37%. The regions that appeared significantly more vulnerable to the sodium azide effects were the mesencephalic reticular formation and the central amygdala, which displayed the largest decrease in activity. In addition, interregional correlations of activity showed a deeply modified pattern of correlative metabolic activity between hippocampal, amygdaloid and cortical areas after azide treatment. The regional effects found were consistent with azide-induced learning and memory dysfunctions.

Mutagenicity and anti-mutagenicity of selected spices

Using Salmonella typhimurium strains TA 100 and TA 1535, the mutagenicity and anti-mutagenicity of extracts of several spices were checked. Spices like pepper, pippali, ginger and mustard increased the number of revertants indicating their mutagenic potential. Garlic extract on the other hand was found to inhibit the mutagenicity produced by direct acting mutagens such as N-methyl N'-nitro-N-nitrosoguanidine and sodium azide. Asafoetida and turmetic extract were found to inhibit microsomal activation dependent mutagenicity of 2-acetamidofluorene. Similar results were also obtained using curcumin and eugenol which are phenolics present in turmeric and clove respectively. These results indicated that some of the spices may ameliorate the effect of environmental mutagens especially present in the food.

Influence of salinity on copper and azide toxicity to larval topsmelt Atherinops affinis (Ayres)

Performance of a 7-d growth and survival toxicity test protocol using larval topsmelt, Atherinops affinis (Ayres), was evaluated for copper chloride and sodium azide at representative estuarine salinities. Results showed that topsmelt are amenable to toxicity testing at estuarine salinities ranging from 5 to 34/1000 since control survival was 100% in all toxicity tests. Sensitivity to both toxicants increased at lower salinities, with the LC50s for copper ranging from 205 micrograms/L at 34/1000 to 44 micrograms/L at 10/1000, and those for sodium azide ranging from 54 mg/L at 34/1000 to 7 mg/L at 5/1000. Larval tissue osmolality decreased with increasing copper concentration relative to control fish. Copper uptake was not affected by changes in salinity. This suggests that increased sensitivity to copper was due, in part, to the increasing physiological challenge of osmoregulation. It is also possible that cupric ion concentration increased at lower salinities, resulting in reduced larval survival. It is hypothesized that increased sensitivity to azide at lower salinity was due to the interaction between azide toxicity and increasing osmotic challenge. A second experiment with azide showed that larval acclimation time did not affect the interaction between salinity and azide toxicity.

Mechanism of cell detachment from temperature-modulated, hydrophilic-hydrophobic polymer surfaces

Poly(N-isopropylacrylamide) (PIPAAm), exhibiting a lower critical solution temperature (LCST) at 25 degrees C in physiological phosphate buffered saline solution (pH 7.4) and at 32 degrees C in pure water, was grafted onto the surfaces of commercial polystyrene cell culture dishes. This PIPAAm-grafted surface exhibited hydrophobic surface properties at temperatures over the LCST and hydrophilic surface properties below the LCST. Endothelial cells and hepatocytes attached and proliferated on PIPAAm-grafted surfaces at 37 degrees C, above the LCST. The cultured cells were readily detached from these surfaces by lowering the incubation temperature without the usual damage associated with trypsinization. In this case, the optimum temperature for cell detachment was 10 degrees C for hepatocytes and 20 degrees C for endothelial cells. Cell detachment was partially inhibited by sodium azide treatment, suggesting that cell metabolism directly affects cell detachment. Morphological changes of the adherent cells during cell detachment experiments indicated further involvement of active cellular metabolic processes. Cells detached from hydrophobic-hydrophilic PIPAAm surfaces not only via reduced cell-surface interactions caused by the spontaneous hydration of grafted PIPAAm chains, but also by active cell morphological changes which were a function of cell metabolism.

Arabidopsis assay for mutagenicity

Four laboratories, two in the Czech Republic (Brno and Prague) and two in the CIS (Moscow and Duschanbe), participated in the International Programme on Chemical Safety's (IPCS) collaborative study to evaluate the utility of the most commonly used plant test systems, including the Arabidopsis thaliana assay, for assessing the mutagenic potential of environmental agents. Out of the five compounds evaluated in the Arabidopsis assay, three compounds, i.e., ethyl methanesulfonate, N-methyl-N-nitrosourea, and azidoglycerol, were reported to be mutagenic by all four participating laboratories. Sodium azide (NaN3) demonstrated a negative response in all four laboratories, whereas maleic hydrazide was reported to be weakly mutagenic by one laboratory and nonmutagenic by the other three laboratories.

Tradescantia stamen hair mutation bioassay

The Tradescantia stamen hair mutation (Trad-SH) assay (clone 4430) was evaluated for its efficiency and reliability as a screen for mutagens in an IPCS collaborative study on plant systems. Four coded chemicals, i.e. azidoglycerol (AG, 3-azido-1,2-propanediol), N-methyl-N-nitrosourea (MNU), sodium azide (NaN3) and maleic hydrazide (MH) were distributed by the Radian Corporation to the five laboratories in five different countries for testing mutagenicity. Pink mutations were scored between the 7th and 14th day according to a standard protocol. Test results from the five individual laboratories were analyzed and compared after decoding. One out of the two laboratories that conducted tests on AG demonstrated that AG is a mutagen with genetically effective doses ranging from 50 to 100 micrograms/ml. MH yielded positive responses in all laboratories but no linear dose-response pattern was observed. The effective dose range for MH was between 1 and 45 micrograms/ml. The mutagenicity of MNU was reported by five laboratories in the dose range between 10 and 80 micrograms/ml. NaN3, which exhibited a relatively high degree of toxicity, elicited a positive mutagenic response in three of the five laboratories in which it was tested. As with MNU the effective dose for NaN3 ranged between 3 and 80 micrograms/ml. The results from the current study substantiate the Trad-SH assay as a reliable system for screening chemicals for their potential mutagenic effects. Although the study was carried out exclusively under laboratory conditions, a survey of the current literature would indicate that the Trad-SH assay could be an effective in situ monitor of gaseous, liquid, and radioactive pollutants as well.

Tradescantia micronucleus bioassay

Four coded chemicals, azidoglycerol (AG), N-methyl-N-nitrosourea (MNU), sodium azide (NaN3), and maleic hydrazide (MH), were tested with the Tradescantia micronucleus (Trad-MCN) bioassay by five independent laboratories from five different countries. The purpose of this international collaborative study was to evaluate four plant bioassays, of which the Trad-MCN assay was one, for their sensitivity, efficiency and reliability. The study was carried out under the sponsorship of the International Programme on Chemical Safety. All laboratories adhered to a standard Trad-MCN protocol which suggested that three replicate tests be conducted with each chemical. The results reported by all laboratories, although not equal, showed good agreement among the laboratories. In fact, all five laboratories obtained positive results with MH and MNU, while four of the five laboratories achieved positive results with NaN3. AG was tested in only three laboratories. Two reported negative results, while one reported positive results but only at a single high dose. The data from this study suggest that under normal conditions, the Trad-MCN bioassay is an efficient and reliable short-term bioassay for clastogens. It is suitable for the rapid screening of chemicals, and also is specially qualified for in situ monitoring of ambient pollutants.

Comparative mutagenicity of chemicals selected for test in the International Program on Chemical Safety's collaborative study on plant systems for the detection of environmental mutagens

A review has been made for the four compounds (maleic hydrazide, methyl nitrosourea, sodium azide, azidoglycerol) tested in the International Program on Chemical Safety's collaborative study on plant systems. Maleic hydrazide (MH) is a weak cytotoxic/mutagenic chemical in mammalian tissues and is classified as a class 4 chemical. In contrast, with few exceptions such as Arabidopsis, MH is a potent mutagen/clastogen in plant systems. The difference in its response between plant and animal tissue is likely due to differences in the way MH is metabolized. MH appears to be noncarcinogenic and has been given a negative NCI/NTP carcinogen rating. Methyl nitrosourea (MNU) is a toxic, mutagenic, radiomimetic, carcinogenic, and teratogenic chemical. It has been shown to be a mutagen in bacteria, fungi, Drosophila, higher plants, and animal cells both in vitro and in vivo. MNU is a clastogen in both animal and human cell cultures, plant root tips and cell cultures inducing both chromosome and chromatid aberrations as well as sister-chromatid exchanges. Carcinogenicity has been confirmed in numerous studies and involves the nervous system, intestine, kidney, stomach, bladder and uterus, in the rat, mouse, and hamster. MNU produces stage-specific teratogenic effects and also interferes with embryonic development. The experimental evidence that strongly indicates the mutagenic effects of MNU underlines the possible hazard of this compound to human beings. The experimental evidence for the stringent handling of this compound is clear. Sodium azide (NaN3) is cytotoxic in several animal and plant systems and functions by inhibiting protein synthesis and replicative DNA synthesis at low dosages. It is mutagenic in bacteria, higher plants and human cells and has been used as a positive control in some systems. In general, tests for clastogenicity have been negative or weakly positive. No evidence of carcinogenicity has been reported in a 2-year study seeking carcinogenic activity in male and female rats. Its advantages in comparison to other efficient mutagens are claimed to be a high production of gene mutations accompanied by a low frequency of chromosomal rearrangements and safer handling because of its nonclastogenic and noncarcinogenic action on humans. Azidoglycerol (AG) is a very potent mutagen in bacteria, yeast and higher plants including Arabidopsis and Tradescantia; however, it only slightly enhances the frequencies of recessive lethals in Drosophila. AG is at best a weak clastogen and is without effect in inducing chromosomal aberrations and SCEs in human peripheral lymphocytes in vitro. In microbial and plant systems, AG is considerably more potent than sodium azide in the maximal frequencies of mutation induced. In particular, in Saccharomyces cerevisae, AG is 3000-fold more mutagenic than sodium azide. Its carcinogenic and teratogenic properties are unknown.

Vicia faba chromosomal aberration assay

A collaborative study involving laboratories in six countries was initiated under the sponsorship of the International Programme on Chemical Safety (IPCS) to determine the sensitivity, efficiency and reliability of the Vicia faba root tip meristem chromosomal aberration assay using a standardized protocol. The six laboratories that participated in this study were located in the Slovak Republic, India, Japan, Poland, Sweden and the USA. All laboratories adhered to a standardized protocol for the Vicia faba chromosomal aberration assay. Four coded chemicals, azidoglycerol (AG), N-methyl-N-nitrosourea (MNU), sodium azide (NaN3) and maleic hydrazide (MH) were tested with the Vicia faba chromosomal aberration assay. Of the four chemicals, three (MH, AG and MNU) were found to be clastogenic and gave a concentration related response. However, the results of NaN3 were equivocal which might be explained by the stability of NaN3. The conclusions from this study suggest that the Vicia faba chromosomal aberration bioassay is an efficient and reliable short-term bioassay for the rapid screening of chemicals for clastogenicity.

Systemic or local administration of azide produces striatal lesions by an energy impairment-induced excitotoxic mechanism

Sodium azide is an inhibitor of cytochrome oxidase which produces selective striatal lesions in both rodents and primates. In the present study we investigated the neurochemical and histologic effects of both intrastriatal and systemic administration of sodium azide, as well as the age dependence and mechanism of the lesions. Intrastriatal administration of sodium azide produced dose-dependent lesions. Neurochemical and histologic evaluation showed that markers of both spiny projection neurons (GABA, substance P) and aspiny interneurons (somatostatin, neuropeptide Y, NADPH-diaphorase) were equally affected. Subacute systemic administration of sodium azide resulted in lesions with a similar neurochemical profile; however, in contrast to intrastriatal injections there was sparing of dopaminergic striatal afferents. Prior decortication significantly attenuated lesions produced by intrastriatal administration of sodium azide, consistent with an excitotoxic process. Chronic administration of sodium azide for 1 month lead to striatal neuropathological changes. Lesions produced by intrastriatal administration of sodium azide in 1-, 4-, and 12-month-old animals showed age dependence. Both freeze-clamp measurements and chemical-shift magnetic resonance spectroscopy confirmed that sodium azide impairs oxidative phosphorylation in the striatum following either intrastriatal or systemic administration. These results show that the striatum is particularly vulnerable to oxidative stress produced by sodium azide, and that it produces striatal lesions by a secondary excitotoxic mechanism.

Characteristics of low molecular weight substances regulating plasma superoxide dismutase activity

Low molecular weight peptides which inhibit both plasma and red cell superoxide dismutase (SOD) activity have been isolated from human plasma. Several fractions of the substance were isolated chromatographically. The most active peptides have molecular weight about 1000 and 5000 D. The peptide lowering the SOD activity accelerates the hemoglobin oxidation reaction by NaNO2 and diminishes the laboratory animals' period of life in the process of intoxication by NaNO2. Another peptide was also isolated from human plasma and increased the SOD activity. The work is in progress on purification of this substance and investigation of its physical properties.

Mutation spectrum of a binary mixture of mutagens (methapyrilene and sodium azide) in strain TA1535 of Salmonella

Methapyrilene (MP) is a rat-liver carcinogen and cocarcinogen that exhibits a narrow spectrum of mutagenic activity in Salmonella typhimurium, inducing only a 2-fold increase in revertants only in the base-substitution strain TA1535; it also enhances the mutagenic activity of sodium azide (NaN3) in the same strain. To examine the effects of MP at the molecular level, we used the colony probe hybridization procedure developed by Cebula and Koch (Mutation Res., 229 (1990) 79-87) to identify the base substitutions in approximately 800 background, MP-, NaN3-, and MP + NaN3-induced revertants of the hisG46 allele of strain TA1535. The predominant mutation in all 4 mutation spectra was a CCC-->CTC transition. The results suggest a mechanism by which MP enhances the infidelity of the DNA replication complex or inhibits a DNA repair or proofreading function, resulting in the production of more of the same error that occurs normally and that is also induced by NaN3. Such a mechanism might be the basis for the carcinogenic and cocarcinogenic activities of MP. To our knowledge, this is the first report of the molecular analysis of mutants produced by exposure of cells to a binary mixture of mutagens.

Toxicology of selected nitric oxide-donating xenobiotics, with particular reference to azide

Nitric oxide (NO) has been discovered recently to be a ubiquitous, endogenous mediator, which is responsible for a variety of normal physiological functions. However, NO also has been implicated in several pathophysiological processes. For example, the pulmonary toxicity of various nitrogen oxides, including NO, found in photochemical smog has been studied for decades; endogenous NO also is associated with bleomycin-induced lung damage, as well as other adverse effects. Recently, a variety of xenobiotics have been shown to owe their biological activity in vivo to their biotransformation to NO. Thus, the therapeutic vasodilatation produced by drugs such as nitroglycerin and sodium nitroprusside is now believed to result from their release of NO, which then mimics the effects of endogenously synthesized NO. The toxic effects of NO prodrugs are, therefore, a matter of concern, especially the extent to which, if any, NO contributes to their toxicity. As reviewed here, NO does not appear to contribute importantly to the toxicity of the NO donors nitrite, hydroxylamine, or nitroprusside. However, it is by no means clear whether or not the NO generated in vivo from sodium azide contributes in a major way to its toxicity. Azide is almost as acutely toxic as cyanide, with which it shares a number of biological effects; yet, azide also has certain cardiovascular actions in common with nitrite. Unlike either cyanide or nitrite, some evidence suggests a tendency for azide to produce low-grade cumulative toxicity. In laboratory animals, azide frequently produces nonasphyxial convulsions, whereas most human deaths appear to be the result of cardiovascular collapse. Neither of these azide-induced syndromes appears to be due to the inhibition of cytochrome c oxidase. Azide is widely used as a preservative in aqueous laboratory reagents and as the propellant in automobile air bags and aircraft escape chutes. Both of these inflable systems are generally safe, and will prevent untold numbers of injuries and deaths. However, to protect workers who handle these devices and others who may come into contact with the sodium azide propellant in these systems, our rudimentary knowledge of azide toxicity needs to be expanded.

Mutagenicity of 3-azido-1,2-propanediol and 9-(3-azido-2-hydroxypropyl)-adenine in repair deficient strains of Escherichia coli

The mutagenicity of two non-aromatic organic azido compounds, 3-azido-1,2-propanediol (AG) and 9-(3-azido-2-hydroxypropyl)-adenine (AHPA), was studied in E. coli repair deficient strains uvrA6, uvrA6 + umuC36, uvrA6+ umuC122::Tn5, polA1, tagA1+ alkA1, ada and dam3. The mutagenicity of both agents was markedly enhanced by defects of UvrABC excinuclease (uvrA6) and was independent of umuC function of the SOS error-prone pathway. Neither azido compound promoted umuDC operon expression. The mutagenicity of AG in tag A1, alkA1 and ada mutants does not differ from that found in the wild-type strain. The expression of both ada and alkA genes was not elevated by AG. Experiments on polA1 and dam3 mutants suggest that DNA polymerase I as well as the mutHLS mismatch repair pathway does not contribute to the removal of putative DNA lesions induced by AG.

Acrylamide as an inducer of metabolic activation system (S9) in rats

The S9 fraction was prepared from rats i.p. injected with a single dose of 75 mg/kg acrylamide. The efficiency of the acrylamide induction procedure was verified on Salmonella mutagenicity testing (TA98 and TA100) using a number of known mutagens. These mutagens are aflatoxin B1, benzo[alpha]pyrene, 2-acetylaminofluorene and sodium azide. The activity of the mutagen is measured in terms of histidine revertant numbers which were found to be almost proportional to the concentration of acrylamide-induced S9. The maximum activation of the mutagens (except sodium azide) was recorded using around 50 microliters of S9 per plate. The efficiency of our prepared S9 fraction as a metabolic activator for some known mutagens is comparable to that of standard S9. On the basis of our results, acrylamide-induced S9 demonstrated considerable increase in the activation of the tested compounds. Accordingly, acrylamide could be used as an additional procedure for the induction of rat hepatic enzymes (S9).

The lack of L-azidoalanine interaction with DNA. In vitro studies

A Bacillus subtilis transformation system was used to investigate the possible direct effect of L-azidoalanine on DNA in vitro. A B. subtilis (trp-) deletion and repair deficient (uvr-) strain was constructed and used as a recipient for treated DNA. The data obtained indicate that L-azidoalanine, at the described conditions, does not interact with DNA in vitro. Thus, L-azidoalanine failed to produce any DNA damage even in the absence of an excision repair mechanism.

Studies on antimutagenic effects of guava (Psidium guajava) in Salmonella typhimurium

The water and chloroform extracts of guava were tested for their antimutagenicity. The water extract was effective in inactivating the mutagenicity of direct-acting mutagens, e.g., 4-nitro-o-phenylenediamine, sodium azide, and the S9-dependent mutagen, 2-aminofluorene, in the tester strains of Salmonella typhimurium. The chloroform extract was inactive. Autoclaving of the water extract for 15 min did not reduced its activity appreciably. The enhanced inhibitory activity of the extracts on pre-incubation suggests the possibility of desmutagens in the extracts. Besides ascorbic acid and citric acid, the major constituents of the extracts, the role of other antimutagenic factors in the extracts cannot be ruled out.

Reactivity and genotoxicity of arylnitrenium ions in bacterial and mammalian cells

Electrophilic arylnitrenium ions are considered to be the ultimate reactive intermediates formed by metabolism of mutagenic and carcinogenic arylamines and nitroarenes; they can produce DNA damage by reaction with specific sites on DNA bases. We studied their formation, reactivity and the genotoxic sequelae of their reactions with cellular DNA to understand the mutagenic and carcinogenic activities of arylamines and nitroarenes as a function of their chemical structure. Arylnitrenium ions were generated by the convenient non-metabolic procedure, photolysis of arylazides, to study the reactivity of these ultimate intermediates with DNA, by means of 32P-postlabelling, and the induction of histidine reversions in Salmonella, HPRT mutations and sister chromatid exchange in mammalian (Chinese hamster V79) cells. Good correlations were observed between the DNA-binding potencies and the mutagenic and SCE-inducing potencies of the arylnitrenium ions, among these the nitrenium ions derived from the heterocyclic food mutagens/carcinogens MeIQ, IQ, and MeIQx. This suggests that the reactivity of the arylnitrenium ions and the quantity of adducts formed with DNA are the principal determinants of the final quantity of genetic alterations in Salmonella and in V79 cells. Conversely, the quality of the adducts, that is, the structure of the arylamine residue bound, appears to be of less significance.

In vivo response of the rat's retinal pigment epithelium to azide: changes induced by light damage

Functional changes in retinal pigment epithelium (RPE) associated with light-induced retinal damage were studied by measuring transocular potential changes evoked by injections of azide and thiocyanate (SCN-). The retinal damage by light in the rat is classified into two types: Type 1, rod cell death associated with RPE deterioration; Type 2, the loss of rod cells without RPE deterioration. To study the type 1 damage, littermate pairs of long-term dark-adapted adult albino rats were tested at 1 h and 10 d after the exposure to green light of 1,200 lx for 1/2 to 24 h. Time course of the damage progress was also followed for 12 h. We found that 1) RPE was affected rapidly by the damaging light, 2) the exposure length determined the ultimate degree of RPE damage, 3) damaging effects on RPE proceeded slower and weaker after exposure than during continuous light, 4) progress of the damage in RPE was two-phasic; during the first phase, the SCN- response was enhanced and the azide response was reduced; both responses were decreased rapidly in the second phase. The first phase was assumed to indicate a depolarization of the basolateral membrane of RPE, and the second phase to manifest the structural deterioration of RPE. The type 2 damage was studied in young rats with exposure to weak light for 28 d. At 30 d after the exposure, a-wave of the ERG and number of rod cells were substantially reduced but azide and SCN- responses were affected slightly.

Electrical responses of the rat's retinal pigment epithelium to azide and thiocyanate

In the rat under urethane anesthesia, a fast intravenous injection of a bolus of sodium azide elicited a transient cornea-positive change in transocular potential (azide response). A bolus injection of sodium thiocyanate (NaSCN) produced a cornea-negative response (SCN- response) with a similar rising phase as the azide response, but with a faster return from the peak. The peak amplitude depended on bolus volume, concentration, animal strain, and age. For more than 24 h, the azide and SCN- responses could be recorded repeatedly from a single rat with little variation in peak amplitudes. Following an administration of iodate, known to degenerate the retinal pigment epithelium (RPE), the transocular d.c. potential decreased; the azide response became smaller and then was inverted in polarity, whereas the SCN- response became larger. Azide and SCN- are assumed to depolarize and hyperpolarize the basal membrane of RPE, respectively. The equilibrium potential of ions passing through the putative azide-sensitive channels is assumed less negative than resting potential of RPE cells. The SCN- response probably represents a diffusion potential of SCN- permeating through anionic channels at a higher rate than Cl-. Results demonstrate the feasibility of in vivo electrophysiological measurement of the functional state and the structural integrity of RPE under pathological conditions.

On the induction of umu gene expression in Salmonella typhimurium strain TA1535/pSK1002 by some nitrofurans

Several nitrofurans were found to induce umu gene expression in Salmonella typhimurium TA1535/pSK1002 as defined on the basis of at least a 2-fold increase of beta-galactosidase activity over the background level. beta-Galactosidase activity increased with increasing concentrations of the chemical, attained a maximum at a concentration which was different for different nitrofurans used, and then gradually decreased with a further increase of the nitrofuran concentration. The umu gene expression test revealed that the genotoxic activity was highest for furazolidone and lowest for 5-nitro-2-furaldehyde.

Prophage induction by DNA topoisomerase II poisons and reactive-oxygen species: role of DNA breaks

Various compounds were evaluated for their ability to induce prophage lambda in the Escherichia coli WP2s(lambda) microscreen assay. The inability of a DNA gyrase subunit B inhibitor (novobiocin) to induce prophage indicated that inhibition of the gyrase's ATPase was insufficient to elicit the SOS response. In contrast, poisons of DNA gyrase subunit A (nalidixic acid and oxolinic acid) were the most potent inducers of prophage among the agents examined here. This suggested that inhibition of the ligation function of subunit A, which also has a DNA nicking activity, likely resulted in DNA breaks that were available (as single-stranded DNA) to act as strong SOS-inducing signals, leading to prophage induction. Agents that both intercalated and produced reactive-oxygen species (the mammalian DNA topoisomerase II poisons, adriamycin, ellipticine, and m-AMSA) were the next most potent inducers of prophage. Agents that produced reactive-oxygen species only (hydrogen peroxide and paraquat) were less potent than adriamycin and ellipticine but more potent than m-AMSA. Agents that intercalated but did not generate reactive-oxygen species (actinomycin D) or that did neither (teniposide) were unable to induce prophage, suggesting that intercalation alone may be insufficient to induce prophage. These results illustrate the variety of mechanisms (and the relative effectiveness of these mechanisms) by which agents can induce prophage. Nonetheless, these agents may induce prophage by producing essentially the same type of DNA damage, i.e., DNA strand breaks. The potent genotoxicity of the DNA gyrase subunit A poisons illustrates the genotoxic consequences of perturbing an important DNA-protein complex such as that formed by DNA and DNA topoisomerase.

Quantitative structure-activity relationships of mutagenic aromatic and heteroaromatic azides and amines

Photolysis of arylazides with long-wavelength UV light in an aqueous medium produces short-lived reactive species that bind to DNA and induce mutations in Salmonella typhimurium TA98. Nitrenes are known reactive products of azide photolysis, so that the DNA-binding and mutagenic species is either a nitrene or nitrene derivative. In the present study we presupposed that the nitrenium ion is the key intermediate. The electronic properties of 19 nitrenium ions with different chemical structures were calculated by the semi-empirical method AM1 and the resulting values plotted against the logarithm of the mutagenicity (log MUT) by means of linear regression analysis. Log MUT correlates with the stability of the nitrenium ion, the energy level of the LUMO and the charges on the exocyclic nitrogen with r = -0.804, 0.865 and -0.874 respectively. Thus, the mutagenicity of the azides is directly proportional to the stability of the nitrenium ions and inversely proportional to the electrophilicity of the exocyclic nitrogen. Furthermore, the mutagenicity of the azides correlates with the mutagenicity of the corresponding arylamines with r = 0.91 (n = 13). These correlations support the key role of the nitrenium ions and demonstrate the value of their electronic structure for the prediction of the mutagenicity of arylazides and arylamines.

Mutagenic activity of arylnitrenium ions from arylazides--induction of sister chromatid exchange in mammalian (V79 Chinese hamster) cells

Photolysis of arylazides produces short-lived reactive species, very likely arylnitrenium ions which bind to nucleotides and DNA and produce mutations in Salmonella. The present report shows that arylazides can be photo-activated in mammalian (V79 Chinese hamster) cells and that sister chromatid exchange can thus be induced. Arylazides studied are (in order of decreasing SCE-inducing potency) azido-isoIQ, azido-MeIQ, azido-IQ, azido-MeIQx, azido-PhIP, 6-azido-chrysene, 2-azidofluorene, 4-azidofluorene, 2-azido-naphthalene, 4-azidobi-phenyl, 2-azidobiphenyl, 2,4,6-trimethylphenylazide, phenylazide (inactive). The structure-activity relationships emerging from the data are the same as those found previously in Salmonella. In line with this, a clearcut positive linear correlation was seen between the logarithm of the SCE-inducing potency in V79 cells and the logarithm of the mutagenic potency in Salmonella (r = 0.955). Therefore, the ultimate reactive species derived from IQ and related heterocyclic aromatic amines are extremely potent genotoxins, not only in a bacterial but also in a mammalian cell. Previous findings of only weak genotoxic activity of IQ and related food mutagens in certain cultured mammalian cells must therefore be reinterpreted as the result of an insufficient activation of these amines in the cells used, possibly because of insufficient acetylation competence.

Antimutagenicity of propionic acid bacteria

The antimutagenic effect of dialysed cell extracts of 4 strains of propionic acid bacteria was examined against the mutagenicity of sodium azide in the TA1535 tester strain of Salmonella typhimurium using the Ames test. It was noted that dialysates of 2 strains of Propionibacterium shermanii, P. pentosaceum and P. acnes, significantly reduced sodium azide-induced revertants. The dialysate of propionic acid cocci did not show an antimutagenic effect. The inhibitory activity was enhanced if the mutagen and extract were coincubated for 20 min prior to performing the mutagenicity assay. Antimutagenicity of dialysates from P. shermanii VKM-103 against MNNG and 9-aminoacridine was shown in S. typhimurium strains TA1535 and TA97. The antimutagenic activity was found in the protein fraction of the cell extract of P. shermanii. The proteins of the dialysate of P. shermanii were separated using a Toyopearl gel column into 3 main peaks according to their molecular weights. The antimutagenic activity towards sodium azide was found in the second and the third peaks. We suggest that dialysates of the cells of propionic acid bacteria contain several kinds of antimutagenic substances with different molecular weights.

A microplate version of the SOS/umu-test for rapid detection of genotoxins and genotoxic potentials of environmental samples

The umu-microtest is a miniaturized automated short-term test version proposed for screening of umuC-dependent mutagenic potentials of chemicals relevant to environmental pollution, river water and industrial waste water. The test is based on the SOS/umu-test and has been modified in order to allow extensive testing of environmental samples. Genetically engineered Salmonella typhimurium (TA1535/pSK1002) are incubated on a microplate rotor in a sloping position for 2 h with the test samples, followed by addition of fresh culture medium to reach a 10-fold dilution of the incubation medium. 2 h later, the activity of the beta-galactosidase, which reflects umuC induction, is determined colorimetrically. The incubation of the bacteria in the presence of the test compounds as well as the assessment of beta-galactosidase activity takes place in 96-well microplates, thus enabling simultaneous screening of large numbers of samples. Data of the genotoxic potentials are available within 8 h. Computer-controlled automation is possible by using a laboratory workstation.

Mutagenic activity of 6-azido deoxyhexoses and azido alcohols in Salmonella typhimurium and its inhibition by a structure-similar carbon source in the medium

6-Azido-6-deoxy (AZd) derivatives of D-glucose, D-mannose, D-altrose, D-allose, L-idose, D-galactose, D-galactonic acid and D-galactitol, 3-azido-1,2-propanediol (azidoglycerol), 3,1-diazido-2-propanol (diazidoglycerol) and (at much higher doses) 2-azidoethanol were mutagenic in Salmonella typhimurium strains TA100 and TA1535. The mutagenic response was similar to that induced by sodium azide, i.e., the azido compounds failed to induce mutations in strain TA98, and mutagenesis was independent of plasmid pKM101, and independent of external activation. The specific mutagenicity (his+ rev/mmole) of AZd-glucose and AZd-galactose was decreased with increasing concentrations of D-glucose or D-galactose in the minimal agar medium and enhanced 100-fold or more when 0.2% citrate rather than 0.2% glucose served as the carbon source in the medium. Similarly, the mutagenic efficiency of azidoglycerol was inhibited by glycerol but not by D-glucose or D-galactose; however, the mutagenicity of sodium azide was not influenced by any of these carbon sources in the medium. The inhibition of the mutagenic action of azido hexoses and azido alcohols by non-azido structural analogs is assumed to reside in competition in transmembrane transport or for the metabolic pathways.