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PubMedDate not supplied

Enhancement of bacterial mutagenicity of bifunctional alkylating agents by expression of mammalian glutathione S-transferase.

Recently, we inserted the plasmid vector pKK233-2 containing rat GSH S-transferase (GST) 5-5 cDNA into Salmonella typhimurium TA1535 and found that these bacteria [GST 5-5(+)] expressed the protein and produced mutations when ethylene or methylene dihalides were added [Thier, R., Taylor, J. B., Pemble, S. E., Ketterer, B., Persmark, M., Humphreys, W. G., and Guengerich, F. P. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 8576-8580]. After exposure to the known GST 5-5 substrate 1,2-epoxy-3-(4'-nitrophenoxy)propane, the GST 5-5(+) strain showed fewer mutants than the bacteria transfected with the cDNA clone in a reverse orientation [GST 5-5(-)], suggesting a protective role of GST 5-5. However, mutations were considerably enhanced in the GST 5-5(+) strain [as compared to GST 5-5(-)] when 1,2,3,4-diepoxybutane (butadiene diepoxide) or 1,2-epoxy-4-bromobutane was added. The GST 5-5(+) and GST 5-5(-) bacterial stains showed similar responses to 1,2-epoxypropane, 3,4-epoxy-1-butene, and 1,4-dibromobutane. The results suggest that some bifunctional activated butanes are transformed to mutagenic products through GSH conjugation. We also found that the GST 5-5(+) strain showed enhanced mutagenicity with 1,4-dibromo-2,3-epoxybutane, 1,2-epoxy-3-bromopropane (epibromohydrin), and (+/-)-1,4-dibromo-2,3-dihydroxybutane.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylating Agents↗
PubMed1995

Identification of N-acetylcysteine conjugates of 1,2-dibromo-3-chloropropane: evidence for cytochrome P450 and glutathione mediated bioactivation pathways.

The haloalkane 1,2-dibromo-3-chloropropane (DBCP) is a carcinogen, mutagen, nephrotoxin, and testicular toxin. The identification of N-acetylcysteine conjugates of DBCP provides information on GSH mediated and cytochrome P450 mediated bioactivation pathways in the expression of DBCP-induced toxicities. N-Acetylcysteine conjugates excreted in the urine of male Sprague-Dawley rats administered DBCP, C1D2-DBCP, C2D1-DBCP, C3D2-DBCP, or D5-DBCP (80 mg/kg) were purified by reverse-phase HPLC as their methyl ester derivatives and characterized by fast atom bombardment tandem mass spectrometry. These metabolites were also converted to tert-butyldimethylsilyl ether derivatives and analyzed by gas chromatography-mass spectrometry (GC-MS) to facilitate the identification of N-acetyl-S-(2,3-dihydroxypropyl)cysteine (Ia), an apparent regioisomer of Ia, 2-(S-(N-acetylcysteinyl))-1,3-propanediol (Ib), N-acetyl-S-(3-hydroxypropyl)cysteine (IIa), and N-acetyl-S-(3-chloro-2-hydroxypropyl)-cysteine (III). Metabolites Ia, Ib, and III displayed quantitative retention of deuterium, an observation consistent with the formation of episulfonium ion intermediate(s) in their biogenesis. Mercapturate IIa retained three atoms of deuterium from D5-DBCP, and two atoms of deuterium from the dideuterio analogs (C1D2-DBCP and C3D2-DBCP), thus invoking P450 mediated formation of 2-bromoacrolein (2-BA) as an intermediate in the biogenesis of IIa. A mechanism is proposed in which conjugate addition of GSH to 2-BA, subsequent episulfonium ion formation, and addition of GSH afford 1,2-(diglutathion-S-yl)propanal. Glutathione mediated reduction is invoked to afford S-(3-hydroxypropyl)GSH which would be excreted in the urine as IIa. The quantitative retention of deuterium from C1D2-DBCP or C3D2-DBCP was indicative of isotopically sensitive branching of P450 metabolism at either C1 or C3 to afford 2-BA. C2D1-DBCP showed a 30% retention of 1 deuterium atom in IIa; the loss of the deuterium is consistent with 2-BA formation, whereas the retention of one deuterium atom is indicative of the formation of metabolite IIa through GSH conjugation of either 2,3-dibromopropanal or 2-bromo-3-chloropropanal. These data indicate that IIa is a marker metabolite for the potent direct-acting mutagen, 2-BA, or its metabolic precursors 2,3-dibromopropanal or 2-bromo-3-chloropropanal. Therefore, evidence has been presented for bioactivation of DBCP by glutathione and cytochrome P450 mediated mechanisms.

Acetylcysteine↗
PubMed2000

Lignin peroxidase initiates O2-dependent self-propagating chemical reactions which accelerate the consumption of 1-(3',4'-dimethoxyphenyl)propene.

Lignin peroxidase (LiP) has been used to study the C(alpha)-C(beta) cleavage of the propylene side chain in 1-(3',4'-dimethoxyphenyl)propene (DMPP) to 3,4-dimethoxybenzaldehyde (veratraldehyde, VAD). Under an air atmosphere, LiP oxidized DMPP to VAD (27.8%) and 1-(3',4'-dimethoxyphenyl)propan-2-one (DMPA, 8.7%), after 10 min of incubation. Dissolved O(2) was rapidly consumed during DMPP conversion, of which one-third was converted into superoxide. The remaining two-thirds of the consumed O(2) was involved in C(alpha)-C(beta) cleavage of DMPP to VAD and in self-propagating chemical reactions stimulating the consumption of DMPP. The involvement of peroxyl radicals, in the chemical consumption of DMPP, was confirmed by using the well-known peroxyl radical reductant Mn(2+). This metal ion severely inhibited the DMPP consumption rate under air, but did not affect the lower enzymic DMPP consumption rate under N(2). The substoichiometric requirement of LiP for H(2)O(2) during DMPP oxidation could be explained in part by dismutation of superoxide, but more importantly by direct chemical reactions of DMPP-derived peroxyl radicals with fresh DMPP. Another VAD-producing route was found by incubating the DMPP oxidation product, DMPA, with LiP. Under air the molar yield of VAD was 29.7%. In the absence of O(2), the C(alpha)-C(beta) cleavage of DMPA to VAD was strongly inhibited and side-chain coupling products (dimers) were formed instead. As a whole, the results suggest two new roles of O(2) in LiP-mediated oxidation of aromatic substrates. First, O(2) is responsible for the formation of reactive peroxyl intermediates, which can directly react with other substrate molecules and thereby accelerate consumption rates. Secondly, O(2) can prevent coupling reactions by lowering the pool of carbon-centred radicals accumulating during LiP catalysis.

Air↗
PubMed2001

Analysis of stable low molecular weight (LMW) RNA profiles of hydrocarbon metabolizing bacteria by staircase electrophoresis.

Staircase electrophoresis (SCE) in polyacrilamide gels was used to analyze the stable low-molecular weight (LMW) RNA profiles of several propane and butane oxidizing bacteria belonging to different species and genera. Differences in the number and distribution of the RNA bands in these profiles allowed us to differentiate among them. Congruent results were found between the established classification of these bacteria and results obtained by LMW RNA profiling and moreover, some misclassified strains can be assigned to the correct genus and species using this technique. LMW RNA profiling by staircase electrophoresis, which makes possible the analysis of a large number of strains in a short time, permits rapid identification of hydrocarbon metabolizing species when compared with LMW RNA profiles of reference strains.

Bacteria↗
PubMed1997

Denitrification of the genotoxicant 2-nitropropane: relationship to its mechanism of toxicity.

1. The stabilities of the industrial chemical and constituent of cigarette smoke 2-nitropropane (2-NP) and its aci tautomer propane 2-nitronate (P2N) towards hepatic enzymes and proteins such as serum proteins and oxyhaemoglobin were investigated in vitro in biological (hepatocytes and subcellular liver fractions) and model systems (serum proteins, oxyhaemoglobin, methylene blue). 2. Denitrification of 2-NP, P2N and 2-deutero 2-nitropropane (2H-NP) occurred in murine hepatocytes significantly faster than in rat cells. For 2-NP the rates were 1271 +/- 167 versus 820 +/- 125 pmol nitrite x min-1 x 10(6) cells-1. 3. A similar observation was made in microsomes, where 2-NP denitrification was 1460 +/- 110 (mouse) versus 480 +/- 80 pmol nitrite x min-1 x mg protein-1 (rat). 4. The major NO2(-)-forming activity was found to be localized in the microsomal fraction. 5. Conversion of 2-NP into P2N, either chemically or enzymatically, was a prerequisite for rapid denitrification. 6. Serum proteins and oxyhaemoglobin proved to be capable of denitrifying P2N (198 +/- 24 pmol nitrite x min-1 x mg protein-1 and 7.1 +/- 1.0 nmol nitrite x min-1 x nmol HbO2(-1) respectively), but were much less active towards 2-NP (24 +/- 2 pmol nitrite x min-1 x mg protein-1 and none respectively). 7. Methylene blue decomposed 2-NP and P2N at rates of 11 +/- 3 and 192 +/- 4 pmol nitrite x min-1 x nmol, methylene blue-1 respectively. The dye also enhanced NO2- formation from P2N and 2-NP in the presence of hepatocytes or serum proteins, with a concomitant enhancement of both 2-NP and P2N toxicity. 8. The results presented report species differences in the denitrification rate of 2-NP and highlight the crucial nitro-aci tautomerism of 2-NP as a pivotal determinant of 2-NP toxicity.

Acetone↗
PubMed1984

Glutathione-mediated binding of dibromoalkanes to DNA: specificity of rat glutathione-S-transferases and dibromoalkane structure.

1,2-Dibromo-[1,2-14C]ethane was bound irreversibly to DNA when glutathione S-transferase or rat liver cytosolic components were added to incubations of calf thymus DNA and glutathione at 37 degrees C. There was no DNA binding of 1,2-dibromoethane when glutathione was absent or in incubations of DNA with microsomal proteins with or without NADPH, thus supporting the proposal that the major route of DNA binding by 1,2-dibromoethane occurs via conjugation to glutathione. In vitro binding of 1,2-dibromoethane occurred most effectively when the YaYc (or 'B') isozyme of glutathione S-transferase was included in incubations of DNA with 1,2-dibromoethane and glutathione. Other dihaloalkanes were incubated with DNA in the presence of glutathione S-transferase and [35S]glutathione. Of these, only 1,2-dibromo-3-chloropropane and tris-(2,3-dibromopropyl)-phosphate led to significant DNA binding of [35S]glutathione. 1,2-Dibromo-3-chloro-[1,3-14C]propane was bound to DNA when glutathione and glutathione S-transferase were present. However, even higher 1,2-dibromo-3-chloropropane binding to DNA occurred when cytosol or microsomes were included in incubations without glutathione. When glutathione was added to incubations containing cytosol and 1,2-dibromo-3-chloropropane, total DNA binding was decreased. Thus, the actual amount of DNA binding by dihaloethanes in vivo may be the result of a complicated balance among the opposing roles of glutathione conjugation in detoxicating and activating processes.

Animals↗
PubMed1997

Sudden death due to butane inhalation.

Sudden death due to the inhalation of halogenated hydrocarbons is a well-documented phenomenon in the scientific and medical literature. Recently, there has been sporadic information suggesting that nonhalogenated hydrocarbons may cause potentially fatal cardiac arrhythmias. This report documents five sudden deaths due to inhalation of nonhalogenated hydrocarbons: n-butane, isobutane and propane. The hydrocarbons were identified by headspace gas chromatography in blood, brain, and lung tissue. Case histories, toxicological findings and analytical procedures are discussed.

Administration, Inhalation↗
PubMed2000

A novel nitrate ester reverses the cognitive impairment caused by scopolamine in the Morris water maze.

The objective of this study was to test the hypothesis that activation of soluble guanylyl cyclase and increased cGMP formation in the brain would improve task acquisition in cognitively impaired animals. We evaluated the effects of a novel nitrate ester, GT 715 (2,3-dinitrooxy-(2,3-bis-nitrooxypropyldisulfanyl)-propane), in scopolamine-induced impairment of task acquisition in the Morris water maze. GT 715 improved task acquisition in scopolamine-pretreated animals in a time- and dose-dependent manner, whereas the prototypical nitrate ester, glyceryl trinitrate (GTN), was ineffective. GT 715 also was more effective and more potent than GTN for activation of hippocampal guanylyl cyclase. The results of this study therefore suggest that stimulation of cerebral soluble guanylyl cyclase activity may be an effective strategy to improve learning and memory performance in individuals in whom cognitive abilities are impaired by injury, disease, or ageing.

Animals↗
PubMed2003

Acute massive rhabdomyolysis due to prolonged inhalation of liquid gas.

A very rare case of non-fatal acute massive rhabdomyolysis caused by unintentional prolonged inhalation of liquid gas (consisting of butane and propane) in a previously healthy adult is presented. The immediate diagnosis and intensive symptomatic therapy prevented any other severe complications of rhabdomyolysis, and the patient made a complete recovery without any sequelae.

Accidents, Home↗
PubMed1978

The direct measurement of temperature changes within freeze-fracture specimens during rapid quenching in liquid coolants.

We have evaluated the cooling rates of specimens mounted in a variety of freeze-fracture holders when plunged into a series of liquid coolants. these rates were measured using miniature thermocouples placed within the mounted specimens. The most rapid cooling rates were obtained using propane at 83 K as the coolant. When mounted on a newly devised 'copper sandwich' holder, specimen cooling rates in excess of 4500 K/s have been recorded. A simple guillotine-like device for quenching freeze-fracture specimens under reproducible conditions is presented.

Chlorofluorocarbons, Methane↗
PubMed1982

Optimum conditions for cryoquenching of small tissue blocks in liquid coolants.

Three approaches were taken with the aim of defining the optimum conditions of rapid cryopreservation in liquid quenchants. In a theoretical approach, two mathematical models were used. The first is of value in defining the absolute maximum rates of cooling which could be achieved at various depths in the tissues. The second highlights the poor thermal properties of liquid coolants and therefore emphasizes the essential requirement for vigorous quenchant mixing and rapid specimen entry. Experimental work with thermocouples showed that fastest cooling rates occur at the leading edge of the object entering coolant. Of five quenchants investigated, cooling rates were in the order, propane greater than Freon 22 greater than Freon 12 greater than liquid nitrogen slush greater than liquid nitrogen. Other considerations, however, may affect the choice of quenchant. For a given quenchant, cooling rate is maximal near the equilibrium freezing point. The consequences of quenching in the presence of thermal gradients either within the coolant or in the gas layer above it are shown. Cooling rate was found to be approximately proportional to entry velocity at least up to approximately 2 m s-1 in our system. Stereological analysis of rapidly quenched, freeze-substituted tissue samples, of geometry which imposed an approximately unidirectional heat flow, revealed four zones: (i) a narrow surface layer (approximately 10 micrometers) of low image contrast and apparent of ice crystals; (ii) a zone of enhanced contrast with ice crystals whose size increased rapidly with depth from the surface (the 'slope'); (iii) a sharply defined zone (the 'ridge') of maximum ice crystal size beyond which there is (iv) an extensive 'plateau' with smaller ice crystals and no marked increase in size with depth. The 'ridge' of maximal ice-crystal damage was consistently found but varied considerably in depth from the surface (approximately 25-120 micrometers) between samples. The existence of the deeper plateau region of relatively uniform ice-crystal-size may be of significance in X-ray microanalytical studies of physiological processes at some depth from the sample surface. In terms of our present understanding of the quenching process, the conditions for optimal cryofixation of small tissue samples are listed.

Chlorofluorocarbons, Methane↗
PubMed1982

The relative efficiency of various fluids in the rapid freezing of protozoa.

The cooling efficiencies of various fluids at low temperature were compared by measuring the temperature decay in 3 microliter water samples plunged into them. A simple model of cooling was used in order to discuss the results. Liquid ethane was found to produce a cooling rate of 660 KS-1, about twice that of liquid propane, while ethanol was almost as effective as ethane between 273 to 223 K. The heat-transfer coefficient of liquid ethane was estimated to be between 1500 and 5000 W m-2 K-1, depending on the physical state assumed for the water sample. Samples of flagellated organisms, after being frozen rapidly in the above way, were freeze-substituted by the method of Barlow & Sleigh (1979). Although this fixation did not give good definition of the microtubules of the flagellar axoneme, it exhibited reasonable tissue preservation in thin sections of the cell body. The fixation method resulted in preserved flagellar wave shapes, which were observed under the light microscope and in critical-point dried cells examined by scanning and conventional electron microscopy. It was concluded (a) that methods for preserving the wave shape of the flagellum and for preserving its internal structure may not be compatible, and (b) that although the present cooling method (with ethane) approaches the speed required to arrest a flagellar wave, further improvements in the speed of the method are desirable.

Animals↗
PubMed1985

An inexpensive device for freeze drying and plastic embedding tissues at low temperatures.

The preparation of biological tissues for electron microscopy by rapid freezing retains the original localization of ions and molecules. A reproducible freezing regime was established by quenching tissues in liquid propane according to the method of Elder et al. (1981). Tissue was thereafter freeze dried in a custom built freeze drying device with a liquid nitrogen cooled stage to prevent ice recrystallization during drying. The device was also designed to allow the vacuum embedding of tissue in low temperature resin such as Lowicryl and polymerization in situ. This paper describes the design of the device and an example of its use in the freeze drying of cartilage. The results show that minimal ice damage occurs to the chondrocytes and that intracellular organelles are clearly visible. The regime described may prove a useful and pragmatic alternative to cutting tissue in the frozen state. Translocation of elements is unlikely except perhaps in the case of very labile elements such as Na and K, but this remains to be fully elucidated.

Animals↗
PubMed1991

Study of potassium deficiency in cardiac muscle: quantitative X-ray microanalysis and cryotechniques.

An imbalance of potassium in cardiac muscle causes an alteration of heart function. The distribution and concentration of potassium in rat papillary heart muscle was studied using cryofixation and X-ray microanalysis. Freeze-dried cryosections and sections of freeze-dried, embedded tissue were analysed. Bulk frozen specimens were freeze-dried either in a vacuum or by a new technique using liquid propane as a cryodehydration medium. These two methods of freeze-drying were tested for elemental retention in other specimens, with comparable results. A potassium concentration of 120 mmol/l was measured in normal myocytes of cardiac papillary muscle compared to 80 mmol/l in myocytes of animals stressed by a temperature of 45 degrees C for 1 h. The presumed physiological significance of the findings is discussed.

Animals↗
PubMed1991

Validation of convection-limited cooling of samples for freeze-fracture electron microscopy.

Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. A simple heat transfer model is experimentally validated to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples [Biot modulus, (hd/k) less than 1] by measuring cooling rates in a variety of samples, materials, and cryogens. In comparison to the commonly accepted conduction-limited model, the convection-limited model predicts, and our experiments show, that cooling rates are proportional to the surface area to volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. We show that almost any material can be frozen at similar rates if the sample thickness, the cryogen, and the method and velocity of contact with cryogen are similar. Liquid ethane or propane cooled to liquid nitrogen temperature are shown to give the best results.

Ethane↗
PubMedDate not supplied

Argon/propane ionization-chamber dosimetry for mixed x-ray/neutron fields.

The photoneutrons produced by high-energy x-ray machines can diffuse through the mazes usually employed at the treatment-room entrance and readily penetrate the lead-lined doors used for x-ray shielding. The measurement of these neutrons in the presence of x-rays and the determination of dose equivalent poses a problem for which there is currently no standard method of solution. In order to separate x-ray dose from neutron dose, the author employed an ionization chamber alternately filled with argon or propane. The response characteristics of this chamber to x-ray and neutrons are described. Quality factors were determined from a calculated neutron spectrum. As a result of these measurements, a 10-in. polyethylene door was added to the entranceway of a 25-MV linear accelerator.

Argon↗