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At least 361 records · Page 20Linked to original sources
PubMed2000

Acetaminophen produces cataract in DBA2 mice by Ah receptor-independent induction of CYP1A2.

The metabolic transformation of acetaminophen to N-acetyl-p-benzoquinone imine by cytochrome P450 enzymes (e.g., cytochrome P450 1A2) is a prerequisite for acetaminophen-induced cataract formation in mice. Aromatic hydrocarbons, such as beta-naphthoflavone, induce cytochrome P450 1A2 in C57BL6 mice via the mediation of the aromatic hydrocarbon receptor and render the animals susceptible to cataract formation by acetaminophen administration but not in DBA2 mice which do not respond to cytochrome P450 1A2 induction by these compounds. Polycyclic hydrocarbons, such as acenaphthylene, were recently found to induce cytochrome P450 1A2 gene expression in young DBA2 mice by aromatic hydrocarbon receptor-independent pathways. In this work, we investigated whether enhanced metabolism of acetaminophen to N-acetyl-p-benzoquinone by cytochrome P450 1A2 induction by acenaphthylene could produce cataract in young DBA2 mice. Fifteen-day-old DBA2 mice were pretreated with two intraperitoneal injections of acenaphthylene and, 24 hr later, with one injection of acetaminophen. In most mice, cataract developed 18-24 hr after acenaphthylene injection. Acenaphthylene treatment of young DBA2 mice resulted in a 2-fold increase in cytochrome P450 1A2-dependent methoxyresorufin O-demethylase activity in the liver. These results support the hypothesis that the aromatic hydrocarbon receptor-independent induction of cytochrome P450 1A2 enzyme leads to accumulation of sufficient N-acetyl-p-benzoquinone in the liver and cataract development in the eye.

Acenaphthenes↗
PubMed2003

Site-directed mutagenesis of an extradiol dioxygenase involved in tetralin biodegradation identifies residues important for activity or substrate specificity.

The sequence of the extradiol dioxygenase ThnC, involved in tetralin biodegradation, was aligned with other extradiol dioxygenases involved in biodegradation of polycyclic compounds, and a three-dimensional model of ThnC, based on the structure of the previously crystallized 2,3-dihydroxybiphenyl dioxygenase from Burkholderia fungorum LB400, was built. In order to assess the functional importance of some non-active-site residues whose relevance could not be established by structural information, a number of positions surrounding the substrate-binding site were mutated in ThnC. Ten mutant proteins were purified and their activity towards 1,2-dihydroxytetralin, 1,2-dihydroxynaphthalene and 2,3-dihydroxybiphenyl was characterized. N213H, Q198H, G206M, A282R and A282G mutants increased k(cat)/K(m) at least twofold using 1,2-dihydroxytetralin as the substrate, thus showing that activity of ThnC is not maximized for this substrate. N213H and Q198H mutants increased k(cat)/K(m) using any of the substrates tested, thus showing the relevance for activity of these two histidines, which are highly conserved in dihydroxybiphenyl dioxygenases, but not present in dihydroxynaphthalene dioxygenases. Different substitutions in position 282 had different effects on general activity or substrate specificity, thus showing the functional importance of the most C-terminal beta-sheet of the protein. A251M and G206M mutants showed increased activity specifically for a particular substrate. N213H, G206M, A282R, A282G and Y177I substitutions resulted in enzymes more tolerant to acidic pH, the most striking effect being observed in mutant Y177I, which showed maximal activity at pH 5.5. In addition, Q198D and V175D mutants, which had altered K(m), also showed altered sensitivity to substrate inhibition, thus indicating that inhibition is exerted through the same binding site. This mutational analysis, therefore, identified conserved residues important for activity or substrate specificity, and also shed some light on the mechanism of substrate inhibition exhibited by extradiol dioxygenases.

Amino Acid Sequence↗
PubMed1989

Mutagenicity arising from boiled rice on treatment with nitrous acid.

When an aqueous homogenate of boiled rice was treated with nitrous acid at pH 3, direct-acting mutagens were formed. The presence of the mutagens was demonstrated by isolating the mutagenic fractions through blue-rayon adsorption, a method used to extract polycyclic compounds, and subsequent high-performance liquid chromatography (HPLC). The mutagens were active in Salmonella typhimurium TA100 and TA98 without metabolic activation. Several different mutagens were formed, as judged from the HPLC profile.

Chromatography, High Pressure Liquid↗
PubMed1994

Probabilistic health risk assessment for exposures to estuary sediments and biota contaminated with polychlorinated biphenyls, polychlorinated terphenyls and other toxic substances.

A Latin Hypercube probabilistic risk assessment methodology was employed in the assessment of health risks associated with exposures to contaminated sediment and biota in an estuary in the Tidewater region of Virginia. The primary contaminants were polychlorinated biphenyls (PCBs), polychlorinated terphenyls (PCTs), polynuclear aromatic hydrocarbons (PAHs), and metals released into the estuary from a storm sewer system. The exposure pathways associated with the highest contaminant intake and risks were dermal contact with contaminated sediment and ingestion of contaminated aquatic and terrestrial biota from the contaminated area. As expected, all of the output probability distributions of risk were highly skewed, and the ratios of the expected value (mean) to median risk estimates ranged from 1.4 to 14.8 for the various exposed populations. The 99th percentile risk estimates were as much as two orders of magnitude above the mean risk estimates. For the sediment exposure pathways, the stability of the median risk estimates was found to be much greater than the stability of the expected value risk estimates. The interrun variability in the median risk estimate was found to be +/- 1.9% at 3000 iterations. The interrun stability of the mean risk estimates was found to be approximately equal to that of the 95th percentile estimates at any number of iterations. The variation in neither contaminant concentrations nor any other single input variable contributed disproportionately to the overall simulation variance. The inclusion or exclusion of spatial correlations among contaminant concentrations in the simulation model did not significantly effect either the magnitude or the variance of the simulation risk estimates for sediment exposures.

Adult↗
PubMed1991

Antiviral activity of the photoactive plant pigment hypericin.

The polycyclic compound hypericin, a known photodynamic agent, was investigated for antiviral activity in the presence and absence of light. The three viruses tested: murine cytomegalovirus; Sindbis virus; and human immunodeficiency virus type 1, were all susceptible to hypericin; but these antiviral activities were considerably enhanced, in a dose-dependent manner, by exposure to light.

Animals↗
PubMed1985

Fungal metabolism of tert-butylphenyl diphenyl phosphate.

The fungal metabolism of tert-butylphenyl diphenyl phosphate (BPDP) was studied. Cunninghamella elegans was incubated with BPDP for 7 days, and the metabolites formed were separated by thin-layer, gas-liquid, or high-pressure liquid chromatography and identified by 1H nuclear magnetic resonance and mass spectral techniques. C. elegans metabolized BPDP predominantly at the tert-butyl moiety to form the carboxylic acid 4-(2-carboxy-2-propyl)triphenyl phosphate. In addition, 4-hydroxy-4'-(2-carboxy-2-propyl)triphenyl phosphate, triphenyl phosphate, diphenyl phosphate, 4-(2-carboxy-2-propyl)diphenyl phosphate, 2-(4-hydroxyphenyl)-2-methyl propionic acid, and phenol were detected. Similar metabolites were found in the 28 fungal cultures which were examined for their ability to metabolize BPDP. Experiments with [14C]BPDP indicated that C. elegans metabolized 70% of the BPDP after 7 days and that the ratio of organic-soluble metabolites to water-soluble metabolites was 8:2. The results indicate that fungi preferentially oxidize BPDP at the alkyl side chain and at the aromatic rings to form hydroxylated derivatives. The trace levels of mono- and diaryl metabolites and the low level of phosphotriesterase activity measured in C. elegans indicate that phosphatase cleavage is a minor pathway for fungal metabolism of BPDP.

Biodegradation, Environmental↗
PubMed1991

Reduction of nitrosubstituted aromatic compounds by the halophilic anaerobic eubacteria Haloanaerobium praevalens and Sporohalobacter marismortui.

The moderately halophilic, obligately anaerobic eubacteria Haloanaerobium praevalens DSM 2228 and Sporohalobacter marismortui ATCC 35420 are able to reduce a variety of nitrosubstituted aromatic compounds at a high rate to the corresponding amines. Compounds degraded included nitrobenzene, o-nitrophenol, m-nitrophenol, p-nitrophenol, nitroanilines, 2,4-dinitrophenol, and 2,4-dinitroaniline. Most of these compounds, when added at concentrations of 50 to 100 mg/liter, were completely transformed within 24 h, but at the highest concentrations growth rates were somewhat lowered. Growth of H. praevalens in the presence of 14C-labeled p-nitrophenol showed that the compound was not incorporated by the cells or degraded to acid-volatile compounds.

Anaerobiosis↗
PubMed1999

Cloning and characterization of a tetracycline resistance determinant present in Agrobacterium tumefaciens C58.

Agrobacterium tumefaciens C58 and its derivatives give rise to spontaneous mutants resistant to tetracycline at a high frequency. We observed that a mutation affecting a tRNA processing function significantly affected the emergence of such mutants, suggesting that C58 contained a positively acting gene conferring resistance to tetracycline. A cosmid clone conferring resistance to tetracycline in Escherichia coli and Agrobacterium was isolated from a genomic bank of one such mutant. Subcloning, transposon mutagenesis, and DNA sequence analysis revealed that this DNA fragment contained two divergently transcribed genes, tetA and tetR, encoding products that were very similar to proteins of the Tet(A) class of tetracycline resistance systems. In the clone from this mutant, tetR was disrupted by an IS426. The homologous region from wild-type NT1 contained an intact tetR gene and did not confer resistance to tetracycline. Hybridization analysis showed that of 22 members of the genus Agrobacterium surveyed, only strains C58 and T37 contained the tet determinant. Moreover, only these two strains mutated to resistance to this antibiotic. Unlike other Tet(A) systems, neither tetracycline nor a series of its derivatives induced the expression of this tet gene unit. Other polycyclic compounds, including many of plant origin, also did not induce this tet gene system. The divergent promoter region of this tet system contained a single inverted repeat element identical to one such operator repeat in the promoter region of the tet determinant from the IncP1alpha R plasmid RP4. TetR repressor proteins from the Agrobacterium tet system and from RP4 interacted with the heterologous operators. While the repressive effect of the TetR protein from strain C58 (TetRC58) on the tetA gene from strain RP4 (tetARP4) was not relieved by tetracycline, repression of tetAC58 by TetRRP4 was lifted by this antibiotic.

Agrobacterium tumefaciens↗
PubMed1994

Urban air pollution by carcinogenic and genotoxic polyaromatic hydrocarbons in the former USSR.

The content of major carcinogenic and genotoxic polyaromatic hydrocarbons (PAH) in urban air, vehicle, and industrial emissions is assessed. A sensitive, specific, and selective method for PAH and nitro-PAH quantitation was developed on the basis of low-temperature luminescence-spectra of frozen polycrystalline solutions. Polyarene contents in urban air and urban industrial emissions, as well as vehicle exhausts, are compared to the Russian Ministry of Health standard of maximal permissible concentration for benzo[a]pyrene in the ambient air. Special attention was paid to the study of PAH profiles and characteristics of different sources. The feasibility of using benzo[a]pyrene to assess PAH content in industrial and vehicle emissions was explored. PAH profiles in the ambient air and local emissions are compared. In addition, genotoxicity of the emissions of coke plant and diesel engine exhausts are compared to their polyarene content.

Air Pollution↗
PubMed1983

Effect of gossypol on the motility and metabolism of human spermatozoa.

Gossypol, a polycyclic compound isolated from cotton seeds, had a dose-dependent inhibitory effect on human sperm motility. The drug also inhibited powerfully fructolysis and glycolysis by human spermatozoa. Both lactate and CO2 formation from the 14C-labelled sugars was inhibited, and the prevention of CO2 formation from [1-14C]pyruvate and [2-14C]pyruvate by gossypol indicated a direct effect on the tricarboxylic acid cycle. Repeated washing of the sperm cells after gossypol pretreatment failed to abolish the inhibitory effect on CO2 production. The profound disturbances of the sperm energy metabolism induced by gossypol were also reflected by a striking fall of the sperm ATP content. Gossypol had little effect on glucose utilization by minces of human vaginal mucosa, indicating the specificity of gossypol.

Adenosine Triphosphate↗