An overview of bioactivation of chemical carcinogens

2000 ◽  
Vol 28 (2) ◽  
pp. 1-6 ◽  
Author(s):  
H. R. Glatt
Keyword(s):  
High Selectivity ◽  
Cytochromes P450 ◽  
Metabolic Activation ◽  
Test System ◽  
Target Cells ◽  
Environmental Carcinogens ◽  
Metabolizing Enzymes ◽  
Enzyme Form ◽  
Test Systems

Most environmental carcinogens require metabolic activation to reactive intermediates and are mutagenic in appropriate test systems. During the last decade, the cDNAs of numerous xenobiotic-metabolizing enzymes have been cloned. The individually expressed enzymes were used to study their substrate specificities and their inhibition by other compounds. Various enzymes were expressed directly in target cells of in vitro mutagenicity tests. This is illustrated in the present study for rat and human sulphotransferases (SULTs) expressed in Salmonella typhimurium TA1538. Numerous compounds were mutagenic in the new test system. Some of these promutagens were activated by several different SULT forms, whereas many other promutagens were activated with high selectivity by a specific enzyme form, but not by genetically closely related forms from the same species (e.g. allelic variants) or orthologous enzymes from other species. Similar findings have been made using recombinant test systems for specific forms of other classes of enzymes (e.g. cytochromes P450). This high selectivity in activation (and inactivation) may explain some organotropisms as well as species and inter-individual differences in the action of carcinogens. Many carcinogen-metabolizing enzymes are induced or inhibited by other xenobiotics. Such interactions can be exploited for chemo-prevention, which however may be carcinogen-and tissue-dependent.

STEROID HORMONE METABOLISM IN RESPONSIVE TISSUES IN VITRO

1971 ◽  
Vol 68 (1_Suppl) ◽  
pp. S279-S294 ◽  
Author(s):  
Paul Robel
Keyword(s):  
Steroid Hormone ◽  
Physiological Activity ◽  
Physiological State ◽  
Target Cells ◽  
Target Tissue ◽  
Hormone Metabolism ◽  
Metabolizing Enzymes ◽  
Relationship Of

ABSTRACT Of the information available on steroid hormone metabolism in responsive tissues, only that relating hormone metabolism to physiological activity is reviewed, i. e. metabolite activity in isolated in vitro systems, binding of metabolites to target tissue receptors, specific steroid hormone metabolizing enzymes and relationship of hormone metabolism to target organ physiological state. Further, evidence is presented in the androgen field, demonstrating 5α-reduced metabolites, formed inside the target cells, as active compounds. This has led to a consideration of testosterone as a »prehormone«. The possibility that similar events take place in tissues responding to progesterone is discussed. Finally, the role of hormone metabolism in the regulation of hormone availability and/or renewal in target cells is discussed. In this context, reference is made to the potential role of plasma binding proteins and cytosol receptors.

scholarly journals Metabolic activation of clopidogrel: in vitro data provide conflicting evidence for the contributions of CYP2C19 and PON1

2011 ◽  
Vol 2 (6) ◽  
pp. 253-261 ◽  
Author(s):  
Thomas M. Polasek ◽  
Matthew P. Doogue ◽  
John O. Miners
Keyword(s):  
Metabolic Activation ◽  
Test System ◽  
In Vitro Studies ◽  
Paraoxonase 1 ◽  
In Vitro Test ◽  
Hydrolytic Cleavage ◽  
Cyp Enzymes ◽  
Conflicting Evidence ◽  
Thioester Bond

The recent report that clopidogrel efficacy may be more dependent on paraoxonase-1 (PON1) than on cytochrome P450 2C19 (CYP2C19) activity raises questions about the roles of these and other enzymes in clopidogrel activation. To provide insight into the emerging PON1 versus CYP2C19 debate, this commentary summarizes the clinical evidence on the pharmacokinetic determinants of clopidogrel efficacy. We then review the in vitro studies investigating the enzymes involved in clopidogrel activation, and comment on their strengths and limitations. There is agreement amongst in vitro studies regarding the involvement of CYP1A2 and CYP2B6 in the metabolism of clopidogrel to 2-oxo-clopidogrel. However, the evidence for other CYP enzymes in the first activation step (e.g. CYP2C19 and CYP3A4) is inconsistent and dependent on the in vitro test system and laboratory. All major drug metabolizing CYP enzymes are capable of converting 2-oxo-clopidogrel to sulfenic acid intermediates that subsequently form the active thiol metabolite. However, the extent of CYP involvement in this second step has been challenged, and new evidence suggests that CYP-independent hydrolytic cleavage of the thioester bond may be more important than oxidative metabolism.

Assessment of the Skin Irritancy Potential of Synthetic Detergents (Syndets)

1984 ◽  
Vol 12 (1) ◽  
pp. 25-32
Author(s):  
P.J. Dykes ◽  
D.L. Williams ◽  
L.A. Jenner ◽  
R. Marks
Keyword(s):  
Rank Order ◽  
Viable Cell ◽  
Skin Surface ◽  
Test System ◽  
Human Skin Fibroblasts ◽  
Test Systems ◽  
Viable Cells ◽  
Cell Layers

Summary Among the factors which determine the degree of damage to the skin are (a) the resistance of the stratum corneum to the solubilisation of its components, (b) the intrinsic toxicity of the compound, and (c) the susceptibility of the viable cell layers to damage. In this study of the toxicity of syndets we have attempted to compare their properties in vivo and in vitro and relate these to cutaneous irritancy studies in normal volunteers. The “solubilising” effect of a series of syndets has been studied using the forced desquamation technique. Although no differences could be determined in terms of the corneocytes released from the skin surface, the protein solubilised did differ according to the syndet used and a rank order could be obtained. The susceptibility of viable cells to lysis by syndets has been studied in vitro, using human skin fibroblasts. This test system was able to discriminate between the different syndets and gave the same rank order as the in vivo human test. Comparison with the standard cutaneous irritancy test indicated some correlation between the two test systems and the irritancy test. However, the rank order correlation did show some discrepancy, and the use of such test systems as predictors of cutaneous irritancy is still being investigated.

Overview and Status of in vitro Transformation

1979 ◽  
Vol 62 (4) ◽  
pp. 889-899
Author(s):  
Andrew Sivak
Keyword(s):  
Cell Culture ◽  
Syrian Hamster ◽  
Animal Studies ◽  
Leukemia Virus ◽  
Metabolic Activation ◽  
Diploid Cell ◽  
Target Cells ◽  
Hamster Embryo Cells ◽  
Embryo Cells

Abstract The development of standardized assay procedures has permitted the exploitation of cell culture systems as bioassay tools for the detection of chemical carcinogens. These systems fall generally into 3 classes: diploid cell strains, Syrian hamster embryo cells; cell lines, mouse BALB/c-3T3 and mouse C3H-10½; and cells + virus, Fischer rat cells infected with Rauscher leukemia virus and Syrian hamster embryo cells infected with adenovirus. The results accumu-lated to date show a good correlation between transformation response in cell culture and carcinogenicity of chemicals in whole animal studies. The major advantages of these systems are their relative brevity (10 days–6 weeks) and resultant low costs, their agreement with whole animal bioassays, and their direct biological relevance to the carcinogenic process. The present major disadvantages are the uncertain nature of the metabolic capabilities of the target cells and the lack of a metabolic activation system that is reliable and adaptable for routine bioassays. The development of epithelial cell systems such as breast, liver, lung, and skin may solve the problem of carcinogen metabolism as well as provide target cells that are representative of major organ sites for cancer in man. The rational use of cell culture bioassays for neoplastic transformation is a valuable component of the toxicological armamentarium to assess risk to humans from exposure to chemicals.

The Antiproliferative Agents trans-Bis(resorcylaldoximato) copper(II) and trans-Bis(2,3,4- trihydroxybenzaldoximato)copper(II) and Cytopathic Effects of HIV

2004 ◽  
Vol 59 (7-8) ◽  
pp. 609-611 ◽  
Author(s):  
Hannu Elo
Keyword(s):  
Antiviral Agents ◽  
Leukemia Cell ◽  
Test System ◽  
Leukemia Cell Line ◽  
Target Cells ◽  
Tetrazolium Salt ◽  
Human Leukemia ◽  
Vitro Assay ◽  
Cytopathic Effects

Abstracttrans-Bis(resorcylaldoximato)copper(II) and trans-bis- (2,3,4-trihydroxybenzaldoximato)copper(II) (CuRES2 and CuTRI2, respectively) have been tested for antiviral properties against HIV, using an in vitro assay that measures the ability of the test compounds to prevent the killing of susceptible human cells by HIV. In the case of CuTRI2, T4 lymphocytes (CEM-V and CEM-Z cell lines) were exposed to HIV at a virus to cell ratio approx. 0.05 in microtiter plates. In the case of CuRES2, a human leukemia cell line (MT-2) was used instead. The tetrazolium salt XTT was added to all wells, and the cultures were incubated and analyzed spectrophotometrically to quantitate formazan production and viewed microscopically for detection of viable cells. In spite of their antiproliferative properties, neither agent had any detectable ability to prevent the cytopathic effects of HIV in cultures of the target cells used. Because the test system employed was constructed in such a way as to detect antiviral agents acting at any stage of the virus reproductive cycle, the results obtained strongly suggest that neither studied agent has any value as the direct prevention of the cell destruction caused by HIV is concerned.

scholarly journals IN VITRO ALLERGY DIAGNOSIS: A COMPARATIVE ANALYSIS OF IgE SPECIFIC TO THE INHALANT ALLERGENS, OBTAINED BY IMMULITE AND PHADIA ASSAY SYSTEMS

2019 ◽  
Vol 21 (5) ◽  
pp. 997-1004
Author(s):  
E. V. Zueva ◽  
I. V. Khamitova ◽  
A. M. Melichkina ◽  
L. L. Lazarenko ◽  
L A. Bakanina ◽  
...  
Keyword(s):  
Skin Test ◽  
Method Comparison ◽  
Birch Pollen ◽  
Test System ◽  
Skin Tests ◽  
Laboratory Research ◽  
Test Results ◽  
Test Systems ◽  
Specificity And Sensitivity

Allergen-specific diagnostics is carried out on the basis of the data collection from the patient’s family and personal history, skin test results, provocative tests and laboratory research methods. Methods for determining specific IgE antibodies (sIgE) play a key role in confirming the diagnosis and identifying the pathogenetic mechanism of an immediate-type hypersensitivity to an allergen. The purpose of the study was to evaluate the results of determining sIgE for allergens of cat epithelium, house dust mite D. farinae and birch pollen in the blood serum of patients suffering from respiratory allergy, by comparing two methods of ImmunoCAP Phadia and 3gAllergy Immulite, as well as determining whether the results of these test systems are in concordance with the results of skin tests in the patients. The serum samples were obtained from patients of St. Petersburg adult outpatient clinics, who suffered from respiratory allergies (n = 50). The samples were analyzed in parallel in two laboratories, with each of the laboratories using single test systems. The retrospective skin test results were obtained from twenty six of the fifty selected patients. The inter-method comparison was conducted by determining the concordance of positive and negative results, correlation and regression analysis of sIgE results for each allergen and ROC-analysis to compare the diagnostic specificity and sensitivity of test systems in relation to the results of skin tests. This study showed that, in terms of agreement and contingency of the results, the Immulite test system had a close relationship with the Phadia test system. Both analysis of classes and quantitative sIgE analysis showed a good positive correlation from 0.79 to 0.99 (p < 0.0001) between the two test systems for all three allergens. High accuracy of coincidence in terms of sensitivity, area under the ROC curves (AUC) and cut-off threshold in both test systems was obtained for the D. farinae allergen. For allergens of cat epithelium and birch pollen, some differences between test systems were observed, i.e., sensitivity and AUC values were significantly higher in Immulite than in Phadia assay for both allergens.Thus, the inter-method comparison gave almost equivalent binary and quantitative results of the determination of sIgE antibodies to cat, tick and birch allergens. Comparison of in vitro test results, and their correlation with skin tests showed that the cat and birch in vitro antibody testing with Immulite assay was more closely connected with skin test results, than Phadia assay system.

scholarly journals In vitro mutagenicity of selected environmental carcinogens and their metabolites in MutaMouse FE1 lung epithelial cells

Mutagenesis ◽  
2021 ◽  
Author(s):  
Lisa Hölzl-Armstrong ◽  
Andrea Nævisdal ◽  
Julie A Cox ◽  
Alexandra S Long ◽  
Nikolai L Chepelev ◽  
...  
Keyword(s):  
Metabolic Activation ◽  
Fold Increase ◽  
Lung Epithelial Cells ◽  
Environmental Carcinogens ◽  
Treatment Conditions ◽  
Mouse Lymphoma Assay ◽  
Mutagenicity Assay ◽  
Genotoxic Carcinogens ◽  
Cyp Isozymes

Abstract Chemicals in commerce or under development must be assessed for genotoxicity; assessment is generally conducted using validated assays (e.g. Tk mouse lymphoma assay) as part of a regulatory process. Currently, the MutaMouse FE1 cell mutagenicity assay is undergoing validation for eventual use as a standard in vitro mammalian mutagenicity assay. FE1 cells have been shown to be metabolically competent with respect to some cytochrome P450 (CYP) isozymes; for instance, they can convert the human carcinogen benzo[a]pyrene into its proximate mutagenic metabolite. However, some contradictory results have been noted for other genotoxic carcinogens that require two-step metabolic activation (e.g. 2-acetylaminofluorene and 2-amino-3-methylimidazo[4,5-f]quinoxaline). Here, we examined three known or suspected human carcinogens, namely acrylamide, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 4-aminobiphenyl (4-ABP), together with their proximate metabolites (i.e. glycidamide, N-OH-PhIP and N-OH-4-ABP), to aid in the validation of the FE1 cell mutagenicity assay. Assessments of the parent compounds were conducted both in the presence and absence of an exogenous metabolic activation mixture S9; assessments of the metabolites were in the absence of S9. The most potent compound was N-OH-PhIP -S9, which elicited a mutant frequency (MF) level 5.3-fold over background at 5 µM. There was a 4.3-fold increase for PhIP +S9 at 5 µM, a 1.7-fold increase for glycidamide −S9 at 3.5 mM and a 1.5-fold increase for acrylamide +S9 at 4 mM. Acrylamide −S9 elicited a marginal 1.4-fold MF increase at 8 mM. Treatment with PhIP −S9, 4-ABP ±S9 and N-OH-4-ABP −S9 failed to elicit significant increases in lacZ MF with any of the treatment conditions tested. Gene expression of key CYP isozymes was quantified by RT-qPCR. Cyp1a1, 1a2 and 1b1 are required to metabolise PhIP and 4-ABP. Results showed that treatment with both compounds induced expression of Cyp1a1 and Cyp1b1 but not Cyp1a2. Cyp2e1, which catalyses the bioactivation of acrylamide to glycidamide, was not induced after acrylamide treatment. Overall, our results confirm that the FE1 cell mutagenicity assay has the potential for use alongside other, more traditional in vitro mutagenicity assays.

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