Human and experimental toxicology.
Explore the source record for details and available documents.
Adenoma↗
Biomedical subjects
H Greim
Publications and source records attributed to H Greim.
Compartmental transfer of mercury released from amalgam.
The number of amalgam-covered surfaces and the occlusal area of the fillings, the concentrations of total mercury in plasma, erythrocytes and urine, the urinary excretion rate, and the absorbed daily doses estimated by two separate methods from intra-oral Hg emission were determined in 29 volunteers with a low amalgam load. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated by multiple correlations between these variables. In addition, the combination of variables most representative of the entire compartmental transfer of amalgam Hg was determined. Urinary excretion (1), Hg concentration in plasma (2) and absorbed dose (3) were most closely correlated to each other, followed by correlations with the variables of the fillings (4). Correlation coefficients were 0.75 for variables 1 vs 2 and 2 vs 3, and 0.49 for variables 3 vs 4. It was concluded that variables 1-3 best reflected the transfer of mercury from amalgam fillings throughout the organism and that they were relatively insensitive to dietary mercury. The determination of total mercury in plasma and of its urinary excretion rate appears, under practical aspects, most suitable for the investigation of Hg uptake from amalgam.
Adult↗
Stable expression of human inducible nitric oxide synthase in V79 Chinese hamster cells.
A recombinant expression vector containing the full-length cDNA for human inducible nitric oxide (NO) synthase was constructed for constitutive expression in V79 Chinese hamster cells. Expression was followed by Western analyses using three different NO synthase antisera. Activity remained stable during 4 months of continued cultivation. Activities were 25 pmol min-1 mg-1 cytosolic protein with L-arginine and 47 pmol min-1 mg-1 cytosolic protein with NG-hydroxy-L-arginine as substrates. Activity was concentration-dependently inhibited by inhibitors such as NG-methyl-L-arginine, NG-nitro-L-arginine, NG-nitro-L-arginine methyl ester, aminoguanidine, and S-methyl-isothiourea. The rank order of inhibitor potencies was different from published results obtained with rodent inducible NOS. Parental V79 cells do not express and cannot be induced for NO synthase activity. Therefore, the genetically engineered V79 cell line is defined for the cDNA-encoded human inducible NO synthase. The new cell line may serve as a useful tool to study human inducible NO synthase.
Animals↗
Stable expression of human cytochrome P450 3A4 in conjunction with human NADPH-cytochrome P450 oxidoreductase in V79 Chinese hamster cells.
V79 Chinese hamster cells were constructed for stable expression of human cytochrome P450 3A4 with and without coexpression of human NADPH-cytochrome P450 oxidoreductase. Expression of the cDNAs was shown by Northern and Western analyses. Activity was tested by 6 beta-hydroxylation of testosterone for cytochrome P450 3A4 and by cytochrome c reduction for NADPH-cytochrome P450 reductase. Five V79 cell lines were obtained expressing cytochrome P450 3A4, human NADPH-cytochrome P450 oxidoreductase, and both. Cytochrome P450 3A4 activity depended highly on cytochrome P450 reductase activity, with lowest activity when only the parental Chinese hamster cytochrome P450 reductase was present, 5- and 10-fold higher when coexpressed with the human NADPH-cytochrome P450 reductase. Correspondingly, cytotoxic and genotoxic potency of aflatoxin B1 was increased by orders of magnitudes when human cytochrome P450 3A4 was coexpressed with the human NADPH-cytochrome P450 reductase. The effect of NADPH-cytochrome P450 reductase coexpression on cytochrome P450 3A4 activity was also tested by nifedipine oxidation and midazolam hydroxylation. Nifedipine oxidation was increased about 10-fold, 1-hydroxylation of midazolam and 4-hydroxylation of midazolam were increased 15-fold.
Aflatoxin B1↗
The German toxicology curriculum: establishing a postgraduate training program for experts in toxicology.
A postgraduate training program in toxicology has been established in Germany. Theoretical training in toxicology is offered on a modular basis to candidates aiming at certification as an "Expert in Toxicology, DGPT." The certificate is awarded by the German Society of Experimental and Clinical Pharmacology and Toxicology [Deutsche Gesellschaft für Experimentelle und Klinische Pharmakologie und Toxikologie (DGPT)]. The precondition for entering the training program is a university degree in medicine, chemistry, biochemistry, biology, or a related subject. To be eligible to take the final examination for Expert in Toxicology, DGPT candidates must have at least 5 years of full-time practical experience in toxicology. They must have gained comprehensive knowledge in at least 1 relevant field, broad knowledge in another 2 fields, and basic knowledge in all 15 relevant fields of toxicology. Candidates must submit at least three independent peer-reviewed papers or professional assessments in toxicology or pharmacology. The course program for providing theoretical training is a joint venture of the German toxicological institutions involved in education. More than a dozen courses, covering the spectrum of fields in toxicology, are held each year at toxicological institutes of universities and research centers throughout Germany specializing in the respective fields. The courses provide candidates with instruction from Germany's leading authorities at research facilities in various fields of toxicology. They provide the best possible education in the spectrum of toxicological subdisciplines.
Accreditation↗
Chlorinated dibenzodioxins and dibenzofurans (PCDD/F) in blood and human milk of non occupationally exposed persons living in the vicinity of a municipal waste incinerator.
The concentrations of chlorinated dibenzodioxins and dibenzofurans (PCDD/F) in human blood and in milk from non-occupationally exposed persons living in the vicinity of a municipal waste incinerator were determined. As compared to background levels in the general population in Germany the results give no indication of an enhanced body burden of PCDD/F. This is in agreement with earlier investigations in the same area, showing normal background concentrations in soil, fruit and vegetables. In conclusion, no direct health hazard related to PCDD/F-emissions from a local municipal waste incinerator may be expected.
Adolescent↗
Stable expression and coexpression of human cytochrome P450 oxidoreductase and cytochrome P450 1A2 in V79 Chinese hamster cells: sensitivity to quinones and biotransformation of 7-alkoxyresorufins and triazines.
V79 Chinese hamster cell lines were genetically engineered for the stable expression of human NADPH-cytochrome P450 oxidoreductase (CYPOR) alone or for the combined expression of CYPOR and human cytochrome P450 1A2 (CYP1A2). As determined by immunoblotting, the expression level of CYP1A2 in the latter cell line was found to be the same as in a previously constructed V79 cell line expressing CYP1A2 only. The heterologous expression of CYPOR in V79 cells resulted in increased sensitivity to quinone-type cytotoxins, e.g. duroquinone and menadione, that exert their toxicity primarily through the production of reactive oxygen species during redox cycling. The metabolic properties of the cell line expressing both CYPOR and CYP1A2 were characterized regarding dealkylation and deethylation of 7-alkoxyresorufins and sulfoxidation of the triazine derivatives ametryne and terbutryne, in comparison with the cell line expressing only CYP1A2. Increased CYPOR activity impaired the CYP1A2-dependent fluorometric resorufin assay, presumably by conversion of the 7-alkoxyresorufins and resorufin to their one-electron-reduced semiquinoneimine forms. The CYP1A2-dependent metabolism of the triazine derivatives ametryne and terbutryne was moderately enhanced by increased CYPOR activity. Interestingly, with CYPOR overexpression sulfoxidation was increased 2-3-fold, compared with N-deethylation, with a 1.3-1.9-fold increase. Thus, the level of CYPOR not only had an influence on CYP1A2 activity rates but also affected the relative proportions of metabolites in CYP1A2-specific metabolite profiles.
Animals↗
Stable expression of human cytochrome P450 2E1 in V79 Chinese hamster cells.
A V79 Chinese hamster cell line was constructed for stable expression of human cytochrome P450 2E1 (CYP2E1) by integration of a SV40 Early promoter recombinant CYP2E1 cDNA into the chromosomal DNA. The cDNA encoded CYP2E1 was effectively expressed and enzymatically active, as shown by hydroxylation of chlorzoxazone and of p-nitrophenol, at rates of about 70 pmol x mg-1 total protein x min-1. CYP2E1 content and activity was increased upon cultivation in the presence of ethanol indicating a substrate mediated stabilization effect. A similar stabilizing effect was also observed for inhibitors of CYP2E1, e.g. imidazole, 4-methylpyrazole, and isoniazid. The feasibility of the newly established cell line V79MZh2E1 for toxicological studies was shown by CYP2E1-mediated activation of N-nitrosodimethylamine and p-nitrophenol and a dose-dependent cytotoxic and mutagenic effect.
Animals↗
Assessment of structurally related chemicals: toxicity and ecotoxicity of acrylic acid and acrylic acid alkyl esters (acrylates), methacrylic acid and methacrylic acid alkyl esters (methacrylates).
BUA compiled the available data on toxicity and ecotoxicity for several acrylic and methacrylic acid esters and their corresponding acids. A comparison of these data revealed a qualitative similarity in the toxicological and ecotoxicological properties of the compounds considered. The data indicate that methacrylates are less reactive than the corresponding acrylates.
Acrylates↗
Genetically engineered mammalian cells and applications.
In general, cells genetically engineered for stable and defined expression of xenobiotic-metabolizing enzymes are useful tools whenever a metabolism-related problem in toxicology and pharmacology is to be solved. It is the genetic and phenotypic nature of a given cell that determines its applicability. Mammalian cells have useful characteristics not given in bacterial, yeast or insect cells, which also may express xenobiotic-metabolizing enzymes. It is the problem to be solved and the question to be answered which determine the optimal choice for the best-suited expression system. There may even be subtle differences between mammalian cells of different species and organ origin, which might play a role in choosing a mammalian expression system. Thus, the level and specificity of the xenobiotic-metabolizing enzyme, the experimental testing conditions, and the biological endpoints present in a chosen cell are the most important criteria to be observed in the application of the mammalian expression systems.
Animals↗
Cytochrome P450 mediated reactions studied in genetically engineered V79 Chinese hamster cells.
V79 Chinese hamster cells genetically engineered for stable expression of rat and human CYP have been shown to serve as analytical tools for studying metabolism related problems in toxicology and pharmacology. Here, the application of rat and human CYP1A1 and CYP1A2 is demonstrated for comparative studies on the oxidation of polycyclic aromatic hydrocarbons, such as phenanthrene, benz[a]anthracene, and benzo[a]pyrene. Live cells were cultivated for 2 days in the presence of these chemicals. Thereafter, the supernatant medium was checked for metabolites by gas chromatography and mass spectrometry. Marked cytochromes P450 and species dependent differences in the metabolite profiles were observed. Most important was the finding, that human cytochrome P450 1A1 almost exclusively oxidized benzo[a]pyrene in the 7,8,9,10-position, yielding the ultimate carcinogen 7,8-dihydroxy-9,10-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene whereas the rat cytochrome P450 1A1 oxidized benzo[]pyrene in the 4,5-position and 7,8,9,10-position. The importance of this finding is underlined by results from cytotoxicity studies. Benzo[a]pyrene was twice as cytotoxic in the human cytochrome P450 1A1 than in the rat cytochrome P450 1A1 expressing V79 cells. Species and cytochrome P450 specific metabolite profiles were also observed for phenanthrene and benz[a]anthracene.
Animals↗
Biomarkers as tools in human health risk assessment.
Evaluation of occupational or environmental risk due to exposure to chemicals requires sufficient information on the toxic profiles, mechanisms of action, toxicokinetics, dose-response relation, exposure, and the target dose. Usually exposure is estimated by measuring concentrations of the agent in air, food, water, soil, dust, or other media with which a population or an individual is in contact. However, this external exposure is only a rough estimate for the internal exposure (agent dose or its metabolite at the critical target in the organism). Factors of influence are bioavailability of the chemicals, variations in concentrations and routes of exposure, physical activity, and individual variation in rates of metabolism, distribution, and excretion. All these affect the concentration of the toxic agent at the critical target, which is the most precise information for risk assessment. Thus, internal exposure is best measured by determining the concentration of the toxicant or its ultimate metabolite at the critical site in the target organ or by determining adducts with cellular macromolecules such as proteins, amino acids, DNA, or its bases. The latter are easily available in experimental toxicology from animal experiments but only occasionally from humans. For health surveillance such data usually are not available, because they require invasive procedures such as biopsies. Therefore, more accessible body fluids or tissue are used, such as blood, urine, or adipose tissue, or adducts with macromolecules such as albumin or hemoglobin in the blood, DNA adducts in peripheral lymphocytes, or altered DNA bases in urine such as 8-hydroxyguanine. All of these are indicators for exposure, whereas risk can only be estimated if the correlation between their deviations from normal and the dose-response at the critical target is known.
Animals↗
Inhibition of cytochromes P4501A by nitric oxide.
Inflammatory stimulation of the liver leads to the induction of nitric oxide (NO) biosynthesis. Because NO binds to the catalytic heme moiety of cytochromes P450 (CYPs), we investigated whether NO interferes with specific CYP-dependent metabolic pathways. In a first experimental approach V79 Chinese hamster cells genetically engineered for stable expression of rat and human CYP1A1 and -1A2 were used. Incubation with the NO donors sodium nitroprusside and S-nitrosylacetylpenicillamine led to a concentration-dependent inhibition of all four CYP enzymes. CYP1A1 was more sensitive to the inhibitory effect of NO than CYP1A2. In the second part of the study, endogenous NO synthesis was induced in rat hepatocytes by incubation with a mixture of cytokines and endotoxin. Concurrently, as NO production in hepatocytes increased within 24 hr, a decrease in CYP1A1-dependent benzo[a]pyrene turnover was observed to almost undetectable levels. The competitive inhibitor of NO synthesis, NG-monomethyl-L-arginine, was able to significantly restore CYP1A1 activity in the presence of cytokines and endotoxin. Inhibition of hepatocellular CYP activity by NO was predominantly due to a direct effect on the enzymes. However, NO-dependent inhibition of CYP expression at a transcriptional level was also demonstrated. Our results indicate that inhibition of NO biosynthesis in patients suffering from systemic inflammatory response syndromes may help to restore biotransformation capacity of the liver.
Animals↗
New scientific arguments for regulation of ethylene oxide residues in skin-care products.
Ethylene oxide (EO) occurs as a contaminant of skin-care products because current commercial preparations of polyglycol ethers may contain ethylene oxide monomer residues, up to the order of 1 ppm. Using current regulatory worst-case assumptions, the presence of EO in skin-care products might lead to a maximal human daily external ethylene oxide dose of about 2.8 micrograms, and a consecutive maximal daily absorbed dose of 0.39 microgram. Two methods of toxicokinetic analysis have been used to compare this possible EO load by use of skin-care products with the inevitable load of EO which is produced endogenously in the organism. On the basis of a previous assessment of the endogenous production of ethylene and ethylene oxide (Filser et al. 1992) it is inferred that the absorbed EO dose of 0.39 microgram is about 1/30 of the unavoidable human endogenous load by endogenous EO. Alternatively, for a second calculation molecular dosimetry data have been used which were based on experimental quantification of the hydroxyethyl adduct of EO to the N-terminal valine of hemoglobin (HOEtVal) in rats. If the worst-case assumptions for human EO absorption from skin-care products are transferred to the rat species, the associated internal EO doses are about 1/110 of the internal EO doses which were calculated from the background HOEtVal concentrations observed in untreated animals. The divergence between both lines of calculation is mainly due to differences in HOEtVal background concentrations between man and rat.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Inhibition of intercellular communication of rat hepatocytes by nafenopin: involvement of protein kinase C.
Peroxisome proliferators (PPs) have been shown to cause tumours in rodent liver. The mechanism of action of these chemicals is only poorly understood. Current evidence, however, suggests that they may cause tumours through a tumour promoting activity. In the present study we therefore evaluated the effect of three peroxisome proliferators on gap junctional intercellular communication (IC) of cultured hepatocytes. Interference with IC is thought to be one of the mechanisms involved in tumour promotion. IC was detected by dye coupling of hepatocytes using microinjection of Lucifer Yellow CH. Five hours after plating, coupling of the cells amounted to approximately 90%. Incubation of hepatocytes with the PPs mono(2-ethylhexyl)phthalate (MEHP), nafenopin and [4-chloro-6-(2,3- xylidino)-2-pyrimidylthio]acetic acid (Wy-14,643) decreased dye coupling of the hepatocytes. Half maximal effects were obtained at approximately 50 microM nafenopin, 150 microM Wy-14,643 and 200 microM MEHP. Addition of the specific inhibitor of Ca(2+)-dependent protein kinase C isoenzymes, Gö 6976 (2 microM), prevented inhibition of IC by nafenopin, but not by the two other peroxisome proliferators. Further studies suggest significant differences in the mechanisms underlying inhibition of dye coupling between hepatocytes by nafenopin and by phenobarbital, a known tumour promoter in the liver. The results show that the PPs nafenopin, MEHP and Wy-14,643 decrease IC between cultured hepatocytes. Inhibition of IC by nafenopin, but not by MEHP and Wy-14,643, is most likely mediated by Ca(2+)-dependent protein kinase C isoenzymes.
Animals↗
Genetically engineered in vitro systems for biotransformation studies.
In order to understand cytochrome P450-mediated metabolism of xenobiotics such as drugs and pollutants, several cell systems are genetically engineered for metabolic competence by cloning cDNAs encoding cytochrome P450 and other enzymes and by heterologous expression in bacterial, yeast, and mammalian cells. Genetically engineered cell systems are defined for the cDNA enzyme function. In conjunction with cell intrinsic properties, these genetically engineered cell systems can be used for the assessment of metabolism-dependent pharmacological and/or toxicological effects.
Animals↗
Stable expression of human cytochrome P450 1A1 cDNA in V79 Chinese hamster cells and metabolic activation of benzo[a]pyrene.
A V79 Chinese hamster cell line stably expressing human cytochrome P450 1A1 (CYP1A1) was obtained by chromosomal integration of the human CYP1A1 cDNA under the control of the SV40 early promoter. Chromosomal integration was verified by Southern analysis, and effective transcription of the human CYP1A1 cDNA was demonstrated by Northern analysis. The CYP1A1 cDNA-encoded protein was characterized by Western analysis using anti-rat CYP1A1. Intracellular association of CYP1A1 with the endoplasmic reticulum could be visualized by in situ immunofluorescence. Crude cell lysates of the V79 derived cell line was able to catalyze 7-ethoxyresorufin-O-deethylation (EROD) with an activity of about 50 pmol min-1 mg-1 total protein, and an aryl hydrocarbon hydroxylase activity (AHH) of 25 pmol min-1 mg-1. CYP1A1 dependent cytotoxicity, measured by neutral red uptake, and genotoxicity, determined by the frequency of micronucleus formation, of benzo[a]pyrene (B[a]P) and trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-diol) could be demonstrated at substrate concentrations as low as 10 nM. Thus, this cell line presents a sensitive tool for studying CYP1A1 mediated metabolism of polycyclic aromatic hydrocarbons (PAH). B[a]P and the purified (+)- and (-)-enantiomers of B[a]P-7,8-diol were compared for their mutagenicity. The (-)-enantiomer was found to be 3-5-fold more mutagenic than the (+)-enantiomer.
Animals↗
Relative potency of chlorinated dibenzo-p-dioxins (CDDs) in acute, subchronic and chronic (carcinogenicity) toxicity studies: implications for risk assessment of chemical mixtures.
This paper shows that the relative toxic potency of four chlorinated dibenzo-p-dioxins (CDDs) is similar in two species with different sensitivities (guinea pig, Sprague-Dawley rat). More importantly, it also demonstrates that the relative toxic potencies of these homologues are very similar for acute, subchronic and chronic dosing in the same species (rat). Furthermore, examination of different endpoints of toxicity (mortality, porphyria, carcinogenicity) suggests that the dose-responses for these diverse end-points after acute, subchronic, and chronic administration are very similar if not identical for tetra-CDD. Based on toxicokinetic and toxicodynamic considerations, a new, possibly generalizable rule (average tissue concentration x time = toxicity) is derived for CDDs. Implicit in the relative potency arguments of CDDs is the requirement of a practical threshold dose for all endpoints of toxicity including cancer.
Administration, Oral↗