PubMed Health⌕ Search

Biomedical subjects

M Wiessler

Publications and source records attributed to M Wiessler.

At least 91 records · Page 5Linked to original sources
PubMed1987

Could N-nitrosamino phosphates be transport forms of activated N-nitrosamines?

The stability of N-nitroso-N-methylamine-N-ethyl phosphate (NMEP) and N-nitroso-N-ethylamine-N-ethyl phosphate (NEEP) was studied in rat serum and in rat liver homogenate and found to be sufficiently high for the phosphates to be transported in vivo. In liver homogenates, the cleavage was more efficient, and a higher phosphatase activity was found in liver microsomal and cytosolic fractions than in serum. The substances exert a distinct activity in the Salmonella typhimurium mutagenicity test.

Alkaline Phosphatase↗
PubMed1987

Alpha-glucuronides of N-nitrosomethylbenzylamine.

After administration of N-nitroso[14C-methyl]benzylamine to rats, a glucuronide was demonstrated in the urine, the structure of which could be assigned on the basis of synthetic marker compounds. These findings offer an explanation for the failure to detect benzylation of DNA after administration of N-nitrosomethylbenzylamine (NMBzA). The glucuronides were synthesized by a combination of enzymatic and chemical reactions.

Animals↗
PubMed1986

Tumour-promoting effect of chilli extract in BALB/c mice.

In 50% of BALB/c mice pretreated with atropine, tongue tumours were induced by fortnightly application of DMN-OAc (2 mg/kg) on the tongue. When DMN-OAc + TPA was used for the initiation-promotion protocol, tumours were observed on the tongue, the site of application, in only 10% of animals. In the same group, stomach tumours were obtained in 63% of mice, denoting that initiation-promotion could be successfully used to induce stomach tumours. Using a protocol of DMN-OAc + chilli as a promoter, we observed induction of stomach tumours. The promoter effect of chilli extract was also seen in the BHC-induced hepato-carcinogenesis system. It thus appears that, in BALB/c mice, chilli acts as a promoter in stomach and liver carcinogenesis.

Administration, Topical↗
PubMed1986

Hydroxylation of dibutylnitrosamine in the human liver and intestinal microsomal fractions.

The metabolism of the bladder carcinogen N-nitroso-di-n-butylamine (NDBA) was studied in microsomal preparations of tissues of patients of both sexes, aged 59-69 years undergoing abdominal surgery. Samples of liver, ileum, and colon were of normal histological appearance. For comparison, samples of rat liver and small intestinal mucosa microsomes were included in the study. Using 1-14C-labeled NDBA, the biotransformation to hydroxylation products retaining the nitroso group, NDBA-2-OH, NDBA-3-OH, and NDBA-4-OH, respectively, was investigated by reversed phase HPLC. In order to separate these metabolites, pooled samples were analysed by normal phase HPLC. The rate of hydroxylation of NDBA was found to be 5.5 times higher in rat liver microsomes compared to those from human liver (2.86 +/- 0.29 vs 0.52 +/- 0.03 nM X min-1 X mg-1). NDBA-3-OH proved to be the major metabolite formed (greater than 80% of total metabolites). The metabolism of NDBA was low but detectable in seven out of nine specimens of human gut, 0.1-0.5 nM X mg-1 in 1 h of incubation, and of the same order of magnitude in rat intestinal tissue (0.4-0.6 nM X mg-1).

Aged↗
PubMed1986

Influence of the carboxylesterase inhibitor bis-p-nitrophenylphosphate on the rates of hydrolysis of various alpha-esters of 1-(N-methyl-N-nitrosamino)-methanol in vitro and in vivo and on the acute toxicity and carcinogenicity of 1-(N-methyl-N-nitrosamino)-methylacetate.

The effect of an in vivo treatment with the carboxylesterase inhibitor bis-p-nitrophenylphosphate (BNPP) on the hydrolysis of 1-(N-methyl-N-nitrosamino)-methylacetate (NNMA), 1-(N-methyl-N-nitrosamino)-methylbutyrate (NNMB), 1-(N-methyl-N-nitrosamino)-methylbenzoate (NNMBz) and 1-(N-methyl-N-nitrosamino)-methylpivaloate (NMMP) in rat tissue homogenates was studied. The rates of hydrolysis were specific for each compound and different in every organ tested; the extent of inhibition of the hydrolysis by BNPP was also substrate and organ specific. In some cases no inhibition at all was observed. The rate of elimination of NNMA, NNMB, and NNMP from blood was not influenced by BNPP pretreatment. The LD50 of NNMA after i.v. application showed a rise of 85% with a BNPP pretreatment. BNPP also influenced the carcinogenicity of NNMA, whereby the total carcinogenic potency was not altered, but the organotropism had changed slightly.

Animals↗
PubMed1986

Use of diethyldithiocarbamate as a probe to detect stable intermediates during the decomposition of several mutagenic and nonmutagenic N-nitroso compounds.

By showing that methyldiethyldithiocarbamate is formed from the reaction of methylnitrosourea and disulfiram, we demonstrated in previous experiments that one of the anticarcinogenic/antimutagenic mechanisms of disulfiram is the scavenging of reactive species. We propose that this reaction may be employed additionally as a model for elucidating the following: (a) possible reactions between alkylating species and nucleophilic sites within the cell, and (b) the existence of stable intermediates during the metabolism of N-nitroso compounds. With structurally related pairs of nitrosoureas (n-propyl/isopropyl; cyclopropyl/allyl; 2-phenylethyl/l-phenylethyl), for which each alkylating group of the first compound can spontaneously rearrange to form the alkylating group of the second isomer, we investigated whether the alkylation proceeds via a monomolecular (sn1) or a bimolecular substitution (sn2). For this, we comparatively determined the relative mutagenic activities of each isomer in Salmonella typhimurium TA 1535, as well as their reactivities towards diethyldithiocarbamate (DDTC) by identifying the reaction products. These studies were aimed at revealing the possible formation of a free carbonium ion in the decomposition of several nitrosoureas in the rat liver supernatant fraction. Our system showed that DDTC reacts by two competing mechanisms: attack at the diazonium ion and at the free carbonium ion. Therefore the striking differences which were observed in the mutagenic potency of cyclopropylnitrosourea and N-nitrosoallylurea as well as of N-nitroso-2-phenylethylurea and N-nitroso-1-phenylethylurea cannot be explained only by the different electrophilic reactivities of the respective intermediates.

Animals↗
PubMed1986

Determination of DNA single strand breaks and selective DNA amplification by N-nitrodimethylamine and analogs, and estimation of the indicator cells' metabolic capacities.

N-nitrodimethylamine is metabolized oxidatively to N-nitrohydroxymethylmethylamine, which decomposes to yield formaldehyde and N-nitromethylamine. All four compounds and N-nitromethylamine were tested for their ability to induce DNA single strand breaks in hepatocytes and in SV 40-transformed Chinese hamster embryo cell lines. Only the two monoalkylnitramines were positive. They induced single strand breaks in hepatocytes, but were not effective in the other cells. Formaldehyde and N-nitrohydroxymethylmethylamine were toxic to the cells. None of the compounds tested was able to induce selective DNA amplification in the two transformed cell lines. Enzymes involved in drug metabolism were assayed in the hamster cell lines. The activity of UDP-glucuronosyltransferase and cytosolic epoxide hydrolase were not detectable. N-nitrodimethylamine demethylation was low. The content of reduced glutathione and the activities of glutathione transferase and membrane bound epoxide hydrolase were comparable to values obtained in the rat liver.

Animals↗
PubMed1986

DNA adducts by N-nitroso compounds.

Some unsolved problems in DNA alkylation by N-nitroso compounds are discussed in this overview. Does O6 alkylation of guanine represent the initiating event exclusively or are O4 alkylation of thymidine and phosphate triester formation also involved in the initiating process? Does the formation of rearranged DNA alkylation products by longer chained alkylnitroso compounds have any significance for the carcinogenic effects of these compounds? The concept of hard and soft acids and bases (HSAB principle) as a qualitative model can predict the changes in the DNA alkylation pattern by branched carbenium ions.

Alkylation↗
PubMed1986

Identification and mutagenicity of metabolites of aristolochic acid formed by rat liver.

The rat liver 9000 g supernatant mediated metabolism of the carcinogenic aristolochic acid, which consists of aristolochic acid I (AAI) and aristolochic acid II (AAII), was investigated. Under anaerobic conditions the major metabolites were the corresponding aristolactams for both AAI and AAII. In contrast under aerobic conditions AAII was not detectably metabolized and the only metabolite found for AAI was the O-demethylated derivative aristolochic acid Ia (AAIa). The metabolites were identified by their u.v., mass and n.m.r. spectra and by comparison with reference standards. The mutagenic activities of the three metabolites were determined in Salmonella typhimurium strains TA1537 and TA 100. The aristolactams were mutagenic in both strains when a metabolizing system was present. These results indicate that AAI or AAII and their aristolactams exert their effect via a common reactive intermediate, probably the corresponding hydroxylamine. AAIa was only very weakly mutagenic and this metabolite may therefore not be regarded as a major mutagenic metabolite of AAI. These findings suggest that the acids are preferentially metabolized by two totally different pathways in vitro, namely an oxidative pathway for AAI and a reductive pathway for AAII.

Animals↗
PubMed1986

N-nitroso-hydroxyalkyl-alkylamine phosphate esters--a new class of N-nitroso compounds.

A new class of phosphate-esterified alpha-hydroxyalkyl-alkyl-nitrosamines is described. Here we report the synthesis of these compounds. The mechanism of their formation from the corresponding alpha-acetoxy compounds, and starting from alpha-hydroperoxy compounds is studied by monitoring the reactions in the u.v.-spectrophotometer, by reaction with alkaline phosphatase and by determination of aldehydes generated during degradation of the N-nitrosoacetylesters. Their stability in aqueous solution and their phosphatase-induced degradation was determined. It was found that alpha-phosphate-nitrosamines are more stable in aqueous solution than the alpha-acetates or the parent alpha-hydroxy compounds. Therefore their role as intermediates in nitrosamine metabolism is discussed.

Alkaline Phosphatase↗
PubMed1986

Metabolic nitrite formation from N-nitrosamines: are there other pathways than reductive denitrosation by cytochrome P-450?

To demonstrate whether there are any pathways of nitrite formation from N-nitrosamines other than reductive denitrosation by cytochrome P-450 we performed the following experiments. An esterified alpha-hydroxylated nitrosamine was incubated in a microsomal system to test if nitrite generation is coupled with or linked to the oxidative bioactivation pathway. Simultaneously, inhibitors of microsomal esterases were added to test if the intact molecule or a metabolite from the oxidative metabolism was responsible for nitrite formation. To check if the superoxide radical anion could be related to the mechanism of nitrite generation, nitrosamines were incubated with a xanthine oxidase/hypoxanthine system. To test if the OH radical was involved in nitrite formation, nitrosamines were incubated with an artificial hydroxy-radical generating system (xanthine oxidase/hypoxanthine system supplemented with Fe2+/EDTA). Measurable amounts of nitrite were detected after incubation of the esterified-hydroxylated N-nitrosamine when the hydrolysis by microsomal esterases was inhibited by diisopropylfluorophosphate or paraoxon and when the N-nitrosamines were incubated with the artificial hydroxy-radical generating system. Nitrite formation could not be detected in the O2(-)-generating system (xanthine oxidase/hypoxanthine) or when the esterified alpha-hydroxylated N-nitrosamine was incubated without inhibition of the microsomal esterases. These results demonstrate that besides reductive denitrosation by cytochrome P-450, nitrite generation from N-nitrosamines can also be caused by hydroxy-radicals. The importance of this possible pathway for the in vivo situation of nitrosamine metabolism is discussed.

Animals↗
PubMed1986

Inhibition of the metabolism of N-nitrosoacetoxymethylmethylamine in the rat by disulfiram.

The stability of N-nitrosoacetoxymethylmethylamine (NAMM) in rat serum in vitro, the half-life in blood in vivo and the exhalation rate of 14CO2 after the application of 14C-labelled NAMM were studied with and without disulfiram (DSF) pre-treatment. It was found that the metabolism of NAMM is inhibited by DSF in vitro as well as in vivo. The influence is thought to be due to inhibition of esterase activity, as shown by comparing the kinetics of the degradation of NAMM with those of p-nitrophenylacetate. In contrast to this result the exhalation of 14CO2 does not seem to be influenced by the esterase inhibiting effect of DSF.

Animals↗
PubMed1986

Intestinal metabolism of nitrosamines. 1. Transport and metabolism of six nitrosamines in isolated perfused rat small intestinal segments.

Possible relationships between structure and metabolism of nitrosamines have been investigated in the rat small intestine. Isolated segments of jejunum and ileum were perfused from the luminal side for 2 h with a Tyrode solution containing one of four symmetrical dialkylnitrosamines with 2-5 carbon atoms per side chain, all 14C-labeled at the alpha position, or one of two unsymmetrical nitrosamines, N-nitroso-tert-butylmethylamine and N-nitrosomethylbenzylamine, 14C-labeled in the methyl group. Besides measurement of 14CO2 production and covalent binding of 14C to intestinal tissue, the absorbed fluid (absorbate) as well as the perfusion medium and tissue homogenates were analysed by h.p.l.c. for the presence of polar metabolites to assess the intestinal metabolism of nitrosamines. Neither N-nitrosodiethylamine nor the two unsymmetrical nitrosamines were metabolized to any significant extent. With increasing chain length of symmetrical dialkylnitrosamines small intestinal metabolism increased dramatically. At a concentration of 1 microM up to 60% and 30% of N-nitrosodipropylamine (NDPA) in jejunal and ileal segments, respectively, and greater than 90% of N-nitrosodibutylamine (NDBA) and N-nitrosodipentylamine (NDAA) in both intestinal segments were metabolized during absorption. Metabolites were found also in perfusate and tissue homogenate but generally at lower percentages as compared with the absorbate. With increasing concentrations the percentage of metabolites decreased, the decrease being more pronounced in ileal as compared with jejunal segments. CO2 production and covalent binding were negligible in ileal segments but amounted up to 5-8% and 0.1-0.4% of the dose in jejunal segments perfused with NDPA, NDBA or NDAA. With NDBA and NDAA no concentration-dependent decrease could be observed, the highest amounts of 14CO2 and bound 14C being found at intermediate concentrations. At concentrations below 10 microM metabolic pathways other than alpha-hydroxylation seem to be of greater importance. The toxicological evaluation of the high intestinal first-pass metabolism of NDPA, NDBA and NDAA must await the identification and quantitation of the metabolites formed.

Animals↗
PubMed1985

Embryotoxicity induced by alkylating agents: left-sided preponderance of paw malformations induced by acetoxymethyl-methylnitrosamine in mice.

The alkylating agent acetoxymethyl-methylnitrosamine (DMN-OAc) triggers preferential left-sided paw defects in mice following IP administration on either day 11 or 12 of pregnancy. Predominantly, ectrodactyly and hypoplasia of the left paws were found. In an organ culture system, using limb buds of 11-day-old mouse embryos, differentiation is severely impaired following addition of 2 microM DMN-OAc to the culture medium. Left and right limbs are equally affected. In contrast, when DMN-OAc is administered in vivo to the dams with subsequent culturing of the limb buds, growth and differentiation of the left limb buds is more affected when compared to the right. Furthermore, DNA alkylation experiments were performed: in vitro, following addition of (14C)-DMN-OAc (2.3 microM) to the culture medium, the DNA alkylation rate of the limb bud DNA is determined. In vivo, following IP administration of 10 mg/kg DMN-OAc to the dams on day 11 of pregnancy, the extent of DNA alkylation of whole-embryo DNA is similar. However, the DNA alkylation rate of separately pooled left and right limb buds exhibits a two-fold difference according to the different teratogenic susceptibility. The results obtained with both in vivo and in vitro systems are consistent with the thesis that a certain amount of DNA alkylation in the tissue of the embryos is the initial step of alkylating agent-induced teratogenicity.

Abnormalities, Drug-Induced↗
PubMed1985

Influence of a prolonged treatment with disulfiram and D(-)penicillamine on nitrosodiethylamine-induced biological and biochemical effects in rats. I. Investigations on the drug metabolizing system.

The influence of a prolonged treatment with disulfiram (DSF) and D(-)penicillamine (PA) on biological and biochemical effects induced by nitrosodiethylamine (NDEA) was studied in rats. The combination of NDEA and DSF led to a massive and early development of esophageal tumors, which were fatal to the animals. No liver tumors were observed in this group, whereas PA in combination with NDEA led to an increased development of liver tumors compared with NDEA alone. In the last two groups, only incidental tumors of the esophagus were observed. Nasal cavity tumors also appeared earlier in the animals treated with DSF and NDEA than in animals treated with NDEA alone or with NDEA plus PA. At a biochemical level, DSF led to a significant inhibition of hepatic anilinehydroxylase and nitroso-dimethylaminedemethylase in contrast to PA, which had no influence on these enzymes. The reduced activities of these drug-metabolizing enzymes did not appear to be related to gross cytochrome P450 content. Highly significant increases in glutathione content and glutathione-S-transferase activity (GSH/GST) were induced by DSF but not by PA. Because N-nitrosodiethylamine requires enzymatic activation to form the ultimate carcinogen, it is suggested that the observed inhibition of nitrosamine-transforming enzymes in the liver during DSF treatment leads to an increased amount of intact nitrosamines in other organs, e.g., in the esophagus, where it could be transformed to the ultimate carcinogen. DSF treatment alone or in combination with NDEA leads to an accumulation of trace elements in the liver, whereas PA eliminated copper and cobalt. The possible influence of these elements on tumor development is discussed in part II of this study.

Animals↗
PubMed1985

Influence of a prolonged treatment with disulfiram and D-penicillamine on nitrosodiethylamine-induced biological and biochemical effects. II. Investigations on trace elements in the liver.

The influence of a 28-week treatment with disulfiram (DSF), D-penicillamine (PA), and nitrosodiethylamine (NDEA), as well as with a combination of DSF or PA with NDEA on the concentrations of eight essential trace elements in the whole liver tissue of rats was measured by means of neutron activation analysis. While NDEA treatment lowered the Zn content of the liver, DSF alone or in combination with NDEA enhanced the Zn and Se concentration by 50%-80%. Co, Cu, and Cd levels were increased by factors of 10, 60, and 110, respectively. The Mo concentration was decreased by 50% after DSF administration. PA reduced Cu, Co, and Zn in the liver. PA/NDEA treatment also lowered Cu, Co, and Zn content, but there was no strengthening effect of PA on the decrease in Zn observed with NDEA. The change of trace element concentrations, especially of Cu, is discussed with regard to the observed tumor induction in the liver, which tended to be increased by a combined NDEA/PA administration compared with NDEA treatment alone, whereas a protective action of DSF against NDEA induced liver tumors could not be established.

Animals↗
PubMed1985

Reduced glutathione inhibits the alkylation by N-nitrosodimethylamine of liver DNA in vivo and microsomal fraction in vitro.

The transfer of radioactivity from N-nitroso-[14C]dimethylamine to trichloroacetic acid precipitable macromolecules in the microsomal fraction of rat liver was investigated. This transfer was found to depend on N-nitrosodimethylamine being metabolized. Cytosolic fraction and cytosol enriched with reduced glutathione inhibited the binding of radioactivity to acid insoluble proteins. Depletion of glutathione in rat liver with diethylmaleate prior to i.v. administration of 10 mg N-nitroso-[14C]dimethylamine/kg led to an increase in O6-methylguanine and N-7-methylguanine in DNA. If rats were fed disulfiram for 6 days (2 g/kg feed), glutathione and glutathione S-transferase were enhanced, and the degree of methylation of guanine by N-nitrosodimethylamine was greatly reduced, as was the metabolism of N-nitrosodimethylamine in the intact animal. Fasting rats for 24 h did not change the N-nitrosodimethylamine-demethylase activity in vitro but greatly enhanced the methylation of guanine in vivo, while the glutathione content and glutathione S-transferase activity were not changed compared to fed animals.

Alkylation↗