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PubMed2000

The atomic-resolution structure of a novel bacterial esterase.

BACKGROUND: A novel bacterial esterase that cleaves esters on halogenated cyclic compounds has been isolated from an Alcaligenes species. This esterase 713 is encoded by a 1062 base pair gene. The presence of a leader sequence of 27 amino acids suggests that this enzyme is exported from the cytosol. Esterase 713 has been over-expressed in Agrobacterium without this leader sequence. Its amino acid sequence shows no significant homology to any known protein sequence. RESULTS: The crystal structure of esterase 713 has been determined by multiple isomorphous replacement and refined to 1. 1 A resolution. The subunits of this dimeric enzyme comprise a single domain with an alpha/beta hydrolase fold. The catalytic triad has been identified as Ser206-His298-Glu230. The acidic residue of the catalytic triad (Glu230) is located on the beta6 strand of the alpha/beta hydrolase fold, whereas most other alpha/beta hydrolase enzymes have the acidic residue located on the beta7 strand. The oxyanion hole is formed by the mainchain nitrogens of Cys71 and Gln207 as identified by the binding of a substrate analogue, (S)-7-iodo-2,3,4,5-tetrahydro-4-methyl-3-oxo-1H-1, 4-benzodiazepine-2-acetic acid. Cys71 forms a disulphide bond with the neighbouring Cys72. CONCLUSIONS: Despite negligible sequence homology, esterase 713 has structural similarities to a number of other esterases and lipases. Residues of the oxyanion hole were confirmed by structural comparison with Rhizomucor miehei lipase. It is proposed that completion of a functional active site requires the formation of the disulphide bond between adjacent residues Cys71 and Cys72 on export of the esterase into the oxidising environment of the periplasmic space.

Alcaligenes↗
PubMed1997

[Radiotherapy of glioblastoma].

Glioblastoma cells appear to be inherently radioresistant and to present a significant fraction of hypoxic cells. The most significant prognostic factors to compare results achieved in several series of patients are the age, performance status and quality of surgical resection. Several randomized trials have provided evidence supporting the efficacy of radiation therapy in the treatment of glioblastoma. Prescription of a 60-Gy dose delivered according to a conventional dose-fractionation scheme (single daily fractions of 1.7 to 2 Gy five times per week) in a target volume with a 2-3 cm margin of tissue surrounding the perimeter of the contrast enhancing lesion on computerized tomography and magnetic resonance imaging is derived from observations made in several retrospective and prospective studies. Evidence of improvement in survival was observed neither in patients receiving hyperfractioned and accelerated radiotherapy, nor in patients for whom radiation sensitizers such as nitroimidazole compounds or halogenated pyrimidine analogs were associated to radiation therapy. The addition of nitrosourea to radiotherapy increases the 2-year survival rate by about 10%. Combination of full-dose external beam radiotherapy and brachytherapy or radiosurgery boost in selected patients with glioblastoma leads to an increase in the median survival, while external beam radiation alone in patients with similar prognosis does not.

Age Factors↗
PubMed1998

Mutagenicity of three disinfection by-products: di- and trichloroacetic acid and chloral hydrate in L5178Y/TK +/- (-)3.7.2C mouse lymphoma cells.

The disinfection of water, required to make it safe for human consumption, leads to the presence of halogenated organic compounds. Three of these carcinogenic 'disinfection by-products', dichloroacetic acid (DCA), trichloroacetic acid (TCA) and chloral hydrate (CH) have been widely evaluated for their potential toxicity. The mechanism(s) by which they exert their activity and the steps in the etiology of the cancers that they induce are important pieces of information that are required to develop valid biologically-based quantitative models for risk assessment. Determining whether these chemicals induce tumors by genotoxic or nongenotoxic mechanisms (or a combination of both) is key to this evaluation. We evaluated these three chemicals for their potential to induce micronuclei and aberrations as well as mutations in L5178Y/TK +/- (-)3.7.2C mouse lymphoma cells. TCA was mutagenic (only with S9 activation) and is one of the least potent mutagens that we have evaluated. Likewise, CH was a very weak mutagen. DCA was weakly mutagenic, with a potency (no. of induced mutants/microgram of chemical) similar to (but less than) ethylmethanesulfonate (EMS), a classic mutagen. When our information is combined with that from other studies, it seems reasonable to postulate that mutational events are involved in the etiology of the observed mouse liver tumors induced by DCA at drinking water doses of 0.5 to 3.5 g/l, and perhaps chloral hydrate at a drinking water dose of 1 g/l. The weight-of-evidence for TCA suggest that it is less likely to be a mutagenic carcinogen. However, given the fact that DCA is a weak mutagen in the present and all of the published studies, it seems unlikely that it would be mutagenic (or possibly carcinogenic) at the levels seen in finished drinking water.

Animals↗
PubMed2004

Theoretical studies on vibrational spectra of some halides of Group IIB elements.

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.

Cadmium Compounds↗
PubMed2000

Isolation and characterization of a tetrachloroethylene dechlorinating bacterium, Clostridium bifermentans DPH-1.

A tetrachloroethylene (PCE)-degrading gram-positive, endospore forming, anaerobic bacterium, strain DPH-1, was isolated from a contaminated site. The organism was identified as Clostridium bifermentans by 16S rRNA gene sequence analysis and based on its physiological characteristics. Strain DPH-1 could dechlorinate high concentrations of PCE (0.9 mM), via trichloroethylene (TCE) to cis-1,2-dichloroethylene (cDCE) at a rate of 0.43 micromol/h.mg protein, as well as a number of other halogenated aliphatic compounds.

Journal Article↗
PubMed2005

Altered drug influx/efflux and enhanced metabolic activity in triclabendazole-resistant liver flukes.

Triclabendazole (TCBZ) is a halogenated benzimidazole compound that possesses high activity against immature and adult stages of the liver fluke, Fasciola hepatica. The intensive use of TCBZ in endemic areas of fascioliasis has resulted in the development of liver flukes resistant to this compound. TCBZ sulphoxide (TCBZSO) and TCBZ sulphone (TCBZSO2) are the main molecules recovered in the bloodstream of TCBZ-treated animals. In order to gain some insight into the possible mechanisms of resistance to TCBZ, the goals of the work described here were: to compare the ex vivo transtegumental diffusion of TCBZ parent drug and its sulpho-metabolites (TCBZSO and TCBZSO2) into TCBZ-susceptible and -resistant liver flukes; and to assess the comparative pattern of TCBZ biotransformation by TCBZ-susceptible and -resistant F. hepatica. For the tegumental diffusion studies, TCBZ-susceptible (Cullompton) and -resistant (Sligo) adult flukes collected from untreated infected sheep were incubated (15-180 min) in KRT buffer containing either TCBZ, TCBZSO or TCBZSO2 (5 nmol.ml-1). For the metabolism studies, microsomal fractions obtained from TCBZ-susceptible and -resistant flukes were incubated for 60 min with TCBZ (40 microM), and the amount of the formed metabolic product (TCBZSO) was measured. Drug/metabolite concentrations were quantified by HPLC. All the assayed TCBZ-related molecules penetrated through the tegument of both TCBZ-susceptible and -resistant flukes. However, significantly lower (approximately 50%) concentrations of TCBZ and TCBZSO were recovered within the TCBZ-resistant flukes compared to the TCBZ-susceptible ones over the 180 min incubation period. The rate of TCBZ sulphoxidative metabolism into TCBZSO was significantly higher (39%) in TCBZ-resistant flukes. The flavin-monooxigenase (FMO) enzyme system appears to be the main metabolic pathway involved in the formation of TCBZSO in both TCBZ-susceptible and -resistant flukes. The altered drug influx/efflux and enhanced metabolic capacity identified in TCBZ-resistant liver flukes may account for the development of resistance to TCBZ.

Animals↗
PubMed2002

Photochemical mass balance of 2,3,7,8-TeCDD in aqueous solution under UV light shows formation of chlorinated dihydroxybiphenyls, phenoxyphenols, and dechlorination products.

Polychlorinated dibenzo-p-dioxins (PCDDs) are a class of halogenated diaryl compounds that are environmentally important because of their high toxicity and bioaccumulatory properties. There is an incomplete understanding of their photochemistry because the majority of photoproducts, as indicated by incomplete mass balances, have not been identified. We studied the photochemical transformation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) in aqueous solution using 302 nm light. Our results allow for the first photochemical mass balance (92-99%) for this compound and confirm the operation of a novel photochemical pathway, which gives rise to 2,2'-dihydroxy-4,4',5,5'-tetrachlorobiphenyl (4,4',5,5'-TeCDHBP) at >50% conversion from the starting material. Rearrangement from 2,3,7,8-TeCDD to 4,4',5,5'-TeCDHBP takes place following preferential homolytic C-O bond cleavage via a proposed mechanism analogous to the parent dibenzo-p-dioxin system. Photochemical conversion from the starting material to dechlorinated PCDDs or chlorinated phenoxyphenols are minor pathways, although the exact contribution of the strictly dechlorination pathways remains uncertain because of the complexity of the system. The results suggest that the photochemical conversion of PCDDs to chlorinated dihydroxybiphenyls, which are also polychlorinated biphenyl (PCB) metabolites, may be an important part of their environmental fate.

Biphenyl Compounds↗
PubMed2005

Polybrominated diphenyl ethers and hydroxylated and methoxylated brominated and chlorinated analogues in the plasma of fish from the Detroit River.

Novel classes and congeners of contaminant residues that are structurally analogous to polybrominated diphenyl ether (PBDE) flame retardants were assessed in the plasma of seven benthic- and six pelagic-feeding fish species from the highly contaminated Detroit River corridor, namely, hydroxylated-PBDEs (OH-PBDEs), methoxylated-PBDEs (MeO-PBDEs), and the antimicrobial OH-trichlorodiphenyl ether, triclosan, and its methylated (MeO) triclosan analogue. In all samples sigmaPBDE concentrations were comprised mainly of BDE47, BDE99, and BDE100 (>85%) and ranged from 155 pg/g wet weight (ww) to 21 069 pg/g ww. Of the 14 OH-PBDE congeners assessed, as many as 10 congeners were identified, although profiles were generally dominated by 6-OH-BDE47 with lesser amounts of 2'-OH-BDE68, 4'-OH-BDE49, and 4-OH-BDE42. sigmaOH-PBDE concentrations ranged from 2.7 to 198 pg/g ww, with sigmaPBDE to sigmaOH-PBDE concentration ratios ranging from 0.0005 to 0.02. OH-PBDEs are likely derived in these freshwater species as metabolites of precursor PBDEs and are subsequently retained in the blood, for example, 6-OH-BDE47, 4'-OH-BDE49, and 4-OH-BDE42 could be derived from BDE47. Portions of concentrations of the OH-PBDEs may also be of alternate origins and are accumulated and retained in these fish. In all samples, the 14 MeO-PBDEs monitored were below detection (<0.01 pg/g ww). Anthropogenic triclosan concentrations ranged from 750 to >10 000 pg/g ww and is clearly a bioaccumulative halogenated phenolic compound in these fish. MeO-triclosan concentrations were considerably lower. In addition to emerging classes of brominated contaminant such as PBDEs, whether of metabolic or anthropogenic origin, fish collected from the Detroit River are exposed to a complex profile of PBDE-like organohalogens.

Animals↗
PubMed2005

Degradation of drinking water disinfection byproducts by synthetic goethite and magnetite.

Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface. Fe(II), a potent reductant when associated with iron oxide surfaces, can mediate the reduction of halogenated organic compounds. Batch experiments were performed to investigate the kinetics and pathways of the degradation of selected chlorinated disinfection byproducts (OBPs) by Fe(II) in the presence of synthetic goethite and magnetite. Trichloronitromethane was degraded via reduction, while trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldyde hydrate were transformed via both hydrolysis and reduction. Chloroform and trichloroacetic acid were unreactive. Observed pseudo-first-order reductive dehalogenation rates were influenced by DBP chemical structure and identity of the reductant. Fe(II) bound to iron minerals had greater reactivity than either aqueous Fe(II) or structural Fe(II) present in magnetite. For DBPs of structure Cl3C-R, reductive dehalogenation rate constants normalized by the surface density of Fe(II) on both goethite and magnetite correlated with the electronegativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1-trichloropropanone.

Disinfectants↗
PubMed1992

Hydantoin bioisosteres. In vivo active spiro hydroxy acetic acid aldose reductase inhibitors.

The hypothesis that clinical side effects of the aldose reductase inhibitor (ARI) sorbinil were related to its hydantoin ring led to a bioisosteric analysis and replacement of the hydantoin by a spiro hydroxy acetic acid moiety as in 40. These hydroxy acids, compared to hydantoins, showed a similar potency increase on chroman 2-methyl substitution, a similar orthogonal relationship of acidic to aromatic moieties, and similar ARI enantioselectivity. In this series the six-membered spiro hydroxy acetic acid anion array is a bioisostere for a spiro hydantoin anion and leads to ARIs with excellent in vivo activity. In vitro and in vivo activity was improved over 40 by chroman cis 2-methylation as in 4 and by aromatic 6,7-halogen substitution. Compounds with the best acute in vivo activity in rats were compared for chronic in vivo activity. The highest tissue levels and best chronic in vivo activities were found in the racemic 6,7-dichloro and 6-fluoro-7-chloro analogues 18 and 23. ARI activity was enantioselective for 58 and 60, the 2R,4R-enantiomers of 18 and 23. 7-Chloro-6-fluoro-cis-4-hydroxy-2(R)-methyl-chroman-4-acetic acid (60) was selected for phase 1 clinical trials and did not exhibit sorbinil-like hypersensitivity side effects.

Aldehyde Reductase↗
PubMed2006

Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles.

In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disk-like structures as compared to other halide ions. The study also suggests that the presence of Cl- ions during the synthesis promotes the growth of nanotriangles, whereas the presence of I- ions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.

Anisotropy↗
PubMed2000

Mechanistic aspects of the metabolism of 1,3-dichloropropene in rats and mice.

1,3-Dichloropropene (DCP) is used in agriculture for the control of nematodes in a variety of food crops. The major routes of metabolism for this halogenated aliphatic compound involve conjugation with glutathione and oxidation to carbon dioxide. An additional, minor route of metabolism proposed for this compound involves epoxidation to the corresponding 1,3-dichloropropene oxide (DCPO). Recent in vivo studies have provided evidence for the formation of DCPO in mice following intraperitoneal (ip) administration of 350-700 mg of DCP/kg, which is equal to, or exceeds, the reported oral LD(50) for this compound in mice [Schneider, M., et al. (1998) Chem. Res. Toxicol. 11, 1137-1144]. The potential for epoxidation of DCP in rats and mice at lower doses administered orally was therefore examined. Following oral administration of 100 mg of DCP/kg of body weight to F344 rats and B(6)C(3)F(1) mice, no DCPO was found in the liver or blood 0-90 min postdosing at a relatively low detection limit (10 ng/g of tissue). Only very low levels of DCPO were seen following ip administration of 100 mg of DCP/kg of body weight in blood of B(6)C(3)F(1) mice. Substantial levels of DCPO were only seen as a metabolite of DCP following ip administration of 700 mg of DCP/kg to B(6)C(3)F(1) or Swiss-Webster mice. Significant nonlinearity of DCP epoxidation was evident following ip administration, with approximately 130-fold less DCPO in mice given 100 vs 700 mg/kg. The time course of DCPO formation could only be followed for 76 min, due to 100% mortality in Swiss-Webster mice at the 700 mg/kg dose level. The formation of measurable DCPO in mice was also accompanied by acute hepatic damage following ip administration of 100 or 700 mg of DCP/kg to mice. In contrast, no evidence of acute toxicity was noted in mice treated with 100 mg/kg via oral gavage. These data suggest that measurable epoxidation of DCP to DCPO, in the rodent, occurs only at relatively high dose levels which result in acute hepatic injury or death. It was concluded that findings of DCPO formation at lethal doses administered via bolus internal injections do not reflect DCPO formation at lower doses administered via the natural portal of entry.

Administration, Oral↗
PubMedDate not supplied

A new structure-activity model for Ah receptor binding. Polychlorinated dibenzo-p-dioxins and dibenzofurans.

A new structure-affinity model for the aromatic hydrocarbon (Ah) receptor is reported. The proposed mathematical model completely eliminates multiple regression analysis in its formulation and overcomes the cross-class comparison inherent to classical quantitative structure-activity relationships. Taking the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) as model xenobiotics, the binding affinity of a PCDD relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is shown to be analytically related to the electron affinities, entropies, and lipophilicities of PCDD and TCDD. From the calculated dissociation constants of PCDD-Ah receptor complexes, the corresponding equilibrium constants of PCDF-Ah complexes could be computed, in agreement with the experimental observation that the trend in the binding affinities of PCDDs and PCDFs to the Ah receptor are similar. The reported model is capable of quantitatively explaining the quantitatively estimating the in vitro binding affinities of PCDDs, PCDFs, and related xenobiotics to the Ah receptor. Therefore, a halogenated aromatic compound is expected to have a higher affinity for the cytosolic protein than TCDD if it is less lipophilic and has a higher electron affinity and lower entropy. Furthermore, the affinities of structurally related polychlorinated aromatic xenobiotics for the Ah receptor could be computed from their entropies and electron affinities.

Chemical Phenomena↗
PubMed2002

[Shampoo].

The diversity of qualities demanded from a shampoo by today's consumer go beyond the sole function of cleansing the hair and scalp. A cosmetic benefit is expected, and the shampoo formulation has to be tailored to all the possible variations associated with hair quality (dry, greasy, permed, bleached, dyed), age (baby shampoo), care habit (frequency of shampooing) and specific problems relating to the superficial condition of the scalp (dandruff, seborrhea). The standard graduate medical training programs devote limited attention to the subject of shampoos, and much of the readily available information concerning shampoos is supplied by the industry. We should be increasingly aware that our patients look to us to supply information on what can be expected from a shampoo to enable them to make more informed choices at the consumer level. Moreover, selected ingredients of shampoos that have been popular with the consumer are currently under attack because of potential risks associated with their use, e.g. halogenated organic compounds, formaldehyde, nitromusc, and crude coal tar. Their critical appraisal also has to follow strict scientific criteria.

Consumer Behavior↗
PubMed2002

Chloracne: histopathologic findings in one case.

BACKGROUND: Chloracne is an acneiform eruption due to poisoning by halogenated aromatic compounds having a specific molecular shape. This condition is always a symptom of systemic poisoning by chemical chloracnegens and not just a cutaneous disorder. METHODS: We have studied a patient with severe chloracne who showed cutaneous lesions involving mostly the face and the axillae. RESULTS: Histopathologic study of the facial lesions demonstrated that almost every vellus hair follicle was involved, showing a dilated infundibulum filled by a keratotic plug. This keratotic material was mostly composed of orthokeratotic basket-weave basophilic corneocytes, namely infundibular keratin, although there were also some dilated infundibula containing eosinophilic laminated or granular sebum at their center. Small infundibular cysts were more numerous than comedones. Mature and well-developed sebaceous glands were seen at the base of many of the dilated infundibula and no squamous metaplasia of the sebaceous glands or ducts could be demonstrated. Hyperpigmentation of the lesions resulted from hyperproduction of melanin by a normal number of melanocytes along the basal layer of the epidermis and infundibular epithelium. Abundant melanin granules also impregnated the corneocytes of the infundibular plugs. CONCLUSIONS: Our findings support the notion that tiny infundibular cysts rather than comedones represent the basic lesions of chloracne.

Acneiform Eruptions↗