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PubMed2005

Gap junction channels reconstituted in two closely apposed lipid bilayers.

Intercellular communication mediated by gap junction channels plays an important role in many cellular processes. In contrast to other channels, gap junction channels span two plasma membranes resulting in an intracellular location for both ends of the junctional pore and the regulatory sites for channel gating. This configuration presents unique challenges for detailed experimental studies of junctional channel physiology and ligand-activation in situ. Availability of an appropriate model system would significantly facilitate future studies of gap junction channel function and structure. Here we show that the double-membrane channel can be reconstituted in pairs of closely apposed lipid bilayers, as experienced in cells. We have trapped the calcium-sensitive dye, arsenazo III (AIII), partially calcium-saturated (AIII-Ca), in one population of connexin32 reconstituted-liposomes, and EGTA in a second one. In such mixtures, the interaction of EGTA with AIII-Ca was measured by a large color shift from blue to red (decreased absorbance at 652 nm). The exchange of these compounds through gap junctions was proportional to these decrements. Results indicate that these connexon-mediated interliposomal channels are functional and are inhibited by the addition of alpha-glycyrrhetinic acid and by flufenamic acid, two gap junction communication inhibitors. Future use of this model system has the potential to improve our understanding of the permeability and modulation of junctional channels in its native intercellular assembly.

Arsenicals↗
PubMed1997

Lung cancer mortality in a cohort of workers employed at a cadmium recovery plant in the United States: an analysis with detailed job histories.

OBJECTIVES: To identify and measure any relations between occupational exposure to cadmium compounds (oxide, sulphide, and sulphate) and the risk of mortality from lung cancer. METHODS: The mortality experience of 571 male production workers from a cadmium recovery facility in the United States was investigated for the period 1940-82. All study subjects were first employed in the period 1926-69; they had all been employed for at least six months between 1 January 1940 and 31 December 1969. Newly abstracted detailed job histories for the period 1926-76 were combined with assessments of exposures to cadmium over time to develop individual estimates of cumulative exposure to cadmium (total exposure and exposures received both in the presence and absence of "high" exposures to arsenic trioxide). Poisson regression was used to investigate risks of mortality from lung cancer in relation to four concentrations of cumulative exposure to cadmium (< 400, 400-999, 1000-1999, > 2000 mg.m-3.days). RESULTS: After adjustment for age attained, year of hire, and Hispanic ethnicity, there was a significant positive trend (P < 0.05) between cumulative exposure to cadmium and risks of mortality from lung cancer. Relative to a risk of unity for the lowest exposure category (first level), risks were 2.30 (95% confidence interval (95% CI) 0.72 to 7.36), 2.83 (95% CI 0.75 to 10.72), and 3.88 (95% CI 1.04 to 14.46) for the second, third, and fourth categories, respectively. Similar findings were obtained after adjustment for age only. Trends were more pronounced when employment histories were lagged first by 10 years and then by 20 years. A separate analysis examined the independent effects of exposure to cadmium received in the presence of high exposures to arsenic trioxide (mainly cadmium oxide) and exposures to cadmium received without such exposure to arsenic (mainly cadmium sulphide and cadmium sulphate). A significant trend for a risk of lung cancer was found only for exposures to cadmium received in the presence of arsenic trioxide. CONCLUSIONS: Hypotheses which are consistent with the study findings include: (a) cadmium oxide in the presence of arsenic trioxide is a human lung carcinogen, (b) cadmium oxide and arsenic trioxide are human lung carcinogens and cadmium sulphate and cadmium sulphide are not (or they are less potent carcinogens), or (c) arsenic trioxide is a human lung carcinogen and cadmium oxide, cadmium sulphate, and cadmium sulphide are not. There were only 21 deaths from lung cancer available for this analysis and it is impossible to gauge which, if any, of these hypotheses are correct.

Arsenic Trioxide↗
PubMed2005

Electrochemical alkaline Fe(VI) water purification and remediation.

Fe(VI) is an unusual and strongly oxidizing form of iron, which provides a potentially less hazardous water-purifying agent than chlorine. A novel on-line electrochemical Fe(VI) water purification methodology is introduced. Fe(VI) addition had been a barrier to its effective use in water remediation, because solid Fe(VI) salts require complex (costly) syntheses steps and solutions of Fe(VI) decompose. Online electrochemical Fe(VI) water purification avoids these limitations, in which Fe(VI) is directly prepared in solution from an iron anode as the FeO42- ion, and is added to the contaminant stream. Added FeO42- decomposes, by oxidizing a wide range of water contaminants including sulfides (demonstrated in this study) and other sulfur-containing compounds, cyanides (demonstrated in this study), arsenic (demonstrated in this study), ammonia and other nitrogen-containing compounds (previously demonstrated), a wide range of organics (phenol demonstrated in this study), algae, and viruses (each previously demonstrated).

Electrochemistry↗
PubMed2001

Fragmentation pathways of organoarsenical compounds by electrospray ion trap multiple mass spectrometry (MS6).

With its detection limit well below 30 pg microl(-1) LC-MS-MS has become a sensitive and thus popular analytical technique for organoarsenical compounds. Collision induced dissociation (CID) is a valuable tool for speciation and facilitates a positive identification of the species detected. However, it is not straightforward to understand the fragmentation pathways of organoarsenical compounds when only CID-MS-MS data is available. In the present paper we have investigated multiple mass spectrometry (MSn, n=1, 2, 3, 4, 5, 6) with electrospray CID fragmentation for a number of organoarsenical compounds likely to occur in the environment. The investigated compounds were tetramethylarsonium, trimethylarsinoxide, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, and dimethylarsinoylethanol. By CID of (protonated) organoarsenical cations mostly even-electron fragments are produced after neutral loss processes such as elimination of H2, H2O, CH4, C2H2, C2H4, C2H6, HCHO, CH3OH, C2H5OH, C2H4O, and CH2CO. However, abundant odd-electron fragments are also formed after elimination of radical species. Evidence for reduction of As(V) to As(III) as a driving force in the odd-electron ion formation is obtained.

Arsenicals↗
PubMed2003

Photochemical oxidation of As(III) in ferrioxalate solutions.

Photochemical reactions involving aqueous Fe(III) complexes are known to generate free radical species such as OH* that are capable of oxidizing numerous inorganic and organic compounds. Recent work has shown that As(III) can be oxidized to As(V) via photochemical reactions in ferric-citrate solutions; however, the mechanisms of As(III) oxidation and the potential importance of photochemical oxidation in natural waters are poorly understood. Consequently, the objectives of this study were to evaluate oxidation rates of As(III) in irradiated ferrioxalate solutions as a function of pH, identify mechanisms of photochemical As(III) oxidation, and evaluate the oxidation of As(III) in a representative natural water containing dissolved organic C (DOC). The oxidation of As(III) was studied in irradiated ferrioxalate solutions as a function of pH (3-7), As(III), Fe(III), and 2-propanol concentration. Rates of As(III) oxidation (0.5-254 microM h(-1)) were first-order in As(III) and Fe(III) concentration and increased with decreasing pH. Experiments conducted at pH 5.0 using 2-propanol as an OH* scavenger in light and dark reactions suggested that OH* is the important free radical responsible for As(III) oxidation. Significant rates of As(III) oxidation (4-6 microM h(-1)) were also observed in a natural water sample containing DOC, indicating that photochemical oxidation of As(III) may contribute to arsenic (As) cycling in natural waters.

Arsenic↗
PubMed2006

Clinically tolerable concentrations of arsenic trioxide induce p53-independent cell death and repress NF-kappa B activation in Ewing sarcoma cells.

Ewing sarcoma (ES), a highly malignant pediatric tumor, is consistently associated with translocations that fuse the EWS gene with a member of the ETS family gene, most commonly FLI-1. Despite significant advances with multiagent chemotherapy, surgery and radiotherapy, about 40% of ES patients still die from the disease. It is therefore necessary to explore novel agents for possible treatment of this tumor. Here the authors investigated the sensitivity of ES cells to clinically tolerable concentrations of arsenic trioxide (As2O3), a compound known to induce differentiation and apoptosis of other types of malignant cells. The authors report that As2O3 uniformly induced death of 6 ES-derived cell lines irrespective of their p53 status. As2O3 resulted in an apoptotic phenotype which was inhibited by the broad-spectrum caspase inhibitor ZVAD-fmk. These effects correlated with prolonged c-jun N-terminal kinase activation, which is a signal for apoptosis in ES cells. As2O3 also decreased basal and cytokine-induced NF-kappa B activity. Since the authors previously demonstrated that NF-kappa B exerts an antiapoptotic action in ES cells, As2O3 treatment may also result in a sensitization of these cells to other drugs used in combination therapy. These effects, combined with its antiangiogenic action, define As2O3 as a good candidate for future protocols to improve treatments of Ewing sarcomas, irrespective of the p53 status of the tumor.

Apoptosis↗
PubMed1972

Antigen recognition and the immune response. Structural requirements in the side chain of tyrosine for immuno-genicity of L-tyrosine-azobenzenearsonate.

The low molecular weight compound L-tyrosine-azobenzenearsonate (RAT) induces a cellular immune response in guinea pigs. The contribution of the side chain of tyrosine to the immunogenicity of RAT and the structural requirements at that position for immunogenicity were assessed by synthesizing a series of analogs of RAT containing modifications in the side chain of tyrosine and employing them as immunogens. Removal of either the carboxyl or amino group did not markedly affect immunogenicity, measured by the induction of delayed cutaneous sensitivity, whereas deletion of both completely abolished it. However, a charged group was not required since side chains containing a polar hydroxyl group could substitute for chains bearing an amino or carboxyl group. The size of the side chain exerted a pronounced influence; the charged or polar substituent had to be extended from the phenolic ring by at least two carbon atoms in order to confer immunogenicity.

Animals↗
PubMed1972

Antigen recognition and the immune response. "Self-help" with symmetrical bifunctional antigen molecules.

L-Tyrosine-p-azobenzenearsonate (RAT) induces cellular immunity without humoral antibody in guinea pigs. Asymmetric bifunctional antigens composed of one RAT moiety and one dinitrophenyl (DNP) group separated by flexible spacers induce anti-RAT cellular immunity and an anti-DNP humoral response. Symmetrical bifunctional antigens of similar design but comprised of two RAT determinants induce cellular immunity without demonstrable anti-RAT antibody. However, when the flexible spacer is replaced by a rigid decaproline chain, humoral anti-RAT responses are provoked. Since RAT contains both electropositive (azo) and electronegative (arsonate) centers, the failure of bifunctional RAT compounds with flexible spacers to induce humoral immunity might be ascribed either to intramolecular stacking, which compromises their bifunctional character, or to interaction of both determinants with receptors on the same cell surface, which would fail to satisfy the requirement for cooperation. In order to distinguish between these alternatives, symmetrical bifunctional antigens composed of two L-tyrosine-p-azophenyltrimethylammonium (TAT) determinants separated by flexible or rigid spacers were synthesized. TAT is immunogenic and does not cross-react with RAT. Furthermore, it contains only electropositive centers and consequently bifunctional molecules do not undergo intramolecular stacking. Immunization with either flexibly or rigidly spaced bifunctional TAT antigens raised anti-TAT antibody. These results conclusively demonstrate that "self-help," cooperation between bone marrow-derived and thymus-derived lymphocytes of identical or similar specificity, can occur, provided the determinants on the antigen are prevented from associating with each other.

Animals↗
PubMed1984

Proportion of lung cancers due to occupational exposure.

The proportions of male lung cancers due to occupational exposure and, respectively, to cigarette smoking in a highly industrialized area of Northern Italy were estimated in a population-based case-control study in 1976-9. Two hundred and four out of the 211 lung cancer cases and 351 controls sampled from the source population were questioned about their occupational and smoking histories. On the basis of the occupational history each subject was classified as probably exposed (+), possibly exposed (?), or unexposed (-) to one or more of the chemicals known to be carcinogenic for the human lung, namely asbestos, polycyclic aromatic hydrocarbons, arsenic, nickel and chromium compounds, BCME, CMME and vinyl chloride. Upon stratification by cigarette smoking, contrasting the occupationally exposed subjects, whether certainly or uncertainly defined, with the unexposed ones, the RR for lung cancer was 2.1 and the occupational etiologic fraction was 0.33 (95% confidence interval 0.19-0.47). The tobacco etiologic fraction was 0.81, while the two exposures together accounted for 89% of the total burden of incident cases. If 33% of all male lung cancers were of occupational aetiology, then this alone would represent 5% of all cancer deaths.

Aged↗
PubMed1976

Atoxyl-induced damage to the sensory cells in the organ of Corti in the guinea pig cochlea.

Atoxyl-induced damage to the inner and the outer hair cells in the guinea pig cochlea starts in the apical coil and spreads successively downward toward the round window. Vesicular degeneration of both the inner and the outer hair cells and the cell organelles occurs. The degeneration is probably caused by an alteration in ionic composition of the endolymph resulting from primary changes of the stria vascularis (vesiculation and rejection of degenerated marginal and intermediate cells) as reported by Anniko and Wersäll (1975). However, a direct action of atoxyl on the sensory cells of the organ of Corti cannot be excluded.

Aniline Compounds↗