Enzyme-linked immunosorbent assay for screening dioxin soil contamination by uncontrolled combustion during informal recycling in slums

Uncontrolled combustion due to garbage recycling is a widespread activity among slum dwellers in distressed economy countries and has been indicated as a major source of dioxin contamination. However, because of the high cost and complexity of gas chromatography/high-resolution mass spectrometry (GC-HRMS) analysis, the magnitude of the problem remains largely unknown. The present study describes a first approach toward the use of a dioxin antibody-based enzyme-linked immunosorbent assay (ELISA) as the basis for a sustainable, simple, and low-cost monitoring program to assess the toxicological impact of uncontrolled combustion in slums. A panel of 16 samples was analyzed by GC-HRMS and ELISA on split extracts. Close to 20% of the analyzed samples showed dioxin concentrations up to almost twice the guidance level for residential soil in several countries, pointing out the need for performing a large-scale monitoring program. Despite the potential for variations in dioxin congener distribution due to the mixed nature of the incinerated material, there was a good correlation between the toxic equivalents as determined by GC-HRMS and ELISA. Furthermore, an interlaboratory ELISA validation showed that the capacity to perform the dioxin ELISA was successfully transferred between laboratories. It was concluded that the ELISA method performed very well as a screening tool to prioritize samples for instrumental analysis, which allows cutting down costs significantly.

Pathogenesis of aryl hydrocarbon receptor-mediated development of lymphoma is associated with increased cyclooxygenase-2 expression

Epidemiological studies indicate that exposure to environmental pollutants such as pesticides and dioxins leads to the pathogenesis of lymphoma and leukemia. Here, we show that activation of the aryl hydrocarbon receptor (AhR) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in loss of the programmed cell death (apoptosis) response in three different lymphoma cell lines, which plays a key role in the development of cancer, especially lymphoma and leukemia. The AhR-mediated inhibition of apoptosis in vitro was associated with a clear increase of cyclooxygenase-2 (COX-2) and deregulation of genes of the B-cell lymphoma-2 (Bcl-2) family involved in apoptosis including Bcl-xl and Mcl-1 in several lymphoma cell lines. Treatment with the COX-2 inhibitor NS-398 and the AhR antagonist 3'-methoxy-4'-nitroflavone abolished the TCDD-induced resistance of apoptosis in vitro. Furthermore, using micropositron emission tomography imaging, in vivo findings demonstrated that exposure to TCDD promotes the development of lymphoma in superficial lymph nodes of C57BL/10J mice, which was associated with a marked increase of COX-2 expression in the affected lymph nodes. The results indicate that AhR activation and COX-2 overexpression likely represent a mechanism of resistance to apoptosis in lymphoma cell lines that might be relevant for the development of lymphoma in vivo.

Interaction of diuron and related substituted phenylureas with the Ah receptor pathway

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of structurally diverse chemicals, including the ubiquitous environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin. Here, we have examined the ability of diuron, a widely used herbicide, and several structurally related substituted phenylureas to bind to and activate/inhibit the AhR and AhR signal transduction. Diuron induced CYP1A1 mRNA levels in mouse hepatoma (Hepa1c1c7) cells and AhR-dependent luciferase reporter gene expression in stably transfected mouse, rat, guinea pig, and human cell lines. In addition, ligand binding and gel retardation analysis demonstrated the ability of diuron to competitively bind to and stimulate AhR transformation and DNA binding in vitro and in intact cells. Several structurally related substituted phenylureas competitively bound to the guinea pig hepatic cytosolic AhR, inhibited 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced AhR-dependent luciferase reporter gene expression in a species-specific manner and stimulated AhR transformation and DNA binding, consistent with their role as partial AhR agonists. These results demonstrate not only that diuron and related substituted phenylureas are AhR ligands but also that exposure to these chemicals could induce/inhibit AhR-dependent biological effects.

Drosophila pro-apoptotic Bcl-2/Bax homologue reveals evolutionary conservation of cell death mechanisms

Genetic analysis of programmed cell death in Drosophila reveals many similarities with mammals. Heretofore, a missing link in the fly has been the absence of any Bcl-2/Bax family members, proteins that function in mammals as regulators of mitochondrial cytochrome c release. A Drosophila homologue of the human killer protein Bok (DBok) was identified. The predicted structure of DBok is similar to pore-forming Bcl-2/Bax family members. DBok induces apoptosis in insect and human cells, which is suppressible by anti-apoptotic human Bcl-2 family proteins. A caspase inhibitor suppressed DBok-induced apoptosis but did not prevent DBok-induced cell death. Moreover, DBok targets mitochondria and triggers cytochrome c release through a caspase-independent mechanism. These characteristics of DBok reveal evolutionary conservation of cell death mechanisms in flies and humans.

Methyl and phenyl esters and thioesters of carboxylic acids as surrogate substrates for microassay of proteinase K esterase activity

The development of a microassay for proteinase K esterase activity with carboxylic acid esters is reported using novel substrates of the general formula R-C(O)-XR'. Highest rates of hydrolysis have been obtained with the O-phenyl esters CH(3)(CH(2))(n = 1 - 2)-S-(CH(2))(n = 1 - 2) C(O)-O-phenyl and their thioester analogs in studies where R, X and R' have been varied. The phenol release has been measured with 4-aminoantipyrine and potassium ferricyanide to determine the rates of O-phenyl ester hydrolyses. Thioester hydrolyses have been monitored continuously with 5,5'-dithio-bis (2-nitrobenzoic acid).

Reactive naphthalene metabolite binding to hemoglobin and albumin

Earlier work has shown that the murine Clara cell cytotoxicant, naphthalene, is metabolized to reactive metabolites which deplete glutathione or, in the absence of sufficient glutathione, become bound covalently to tissue macromolecules. Correlations between bound metabolite levels in the lung with injury suggests an association between reactive metabolite binding and toxicity. In this study we examine the formation of covalent naphthalene adducts with hemoglobin and albumin in mice to determine whether these serve as useful indices of exposure and metabolism for a chemical which shows a glutathione threshold. Covalent binding of radioactivity from [3H]naphthalene to both albumin and hemoglobin was dose dependent and a glutathione threshold was observed. At early times after naphthalene administration, the formation of albumin adducts was 10- to 30-fold higher than that of hemoglobin adducts. Hemoglobin and albumin adduct levels decreased by apparent first-order processes with half-lives of 11.5 and 1.8 days, respectively. These half-lives are consistent with the turnover of these blood proteins in the mouse. Pretreatment with buthionine sulfoximine resulted in higher levels of albumin adduct but in no alteration of hemoglobin adduct levels in comparison with control. In contrast, diethylmaleate pretreatment increased the level of hemoglobin adduct but not albumin adduct. The antibody to naphthalene mercapturates recognized the hemoglobin adduct(s) but not the albumin adduct(s). Comparison of the data from ELISA (standardized using hydroxymercaptodihydronaphthalene) and radiochemical analysis yielded curves with identical slopes; the absolute levels of adduct found by ELISA were approximately half those measured with radiochemical techniques.(ABSTRACT TRUNCATED AT 250 WORDS)