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H Wallin

Publications and source records attributed to H Wallin.

At least 55 records · Page 3Linked to original sources
PubMed1989

Disposition and metabolism of the food mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in rats.

The disposition and metabolism of a common food mutagen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), was studied in rats. Five rats of both sexes were given a single oral dose of 14C-labeled MeIQx (3-4 mg/kg body wt). The male rats excreted 36% of the radioactivity and 15% of the mutagenic activity of the dose given in the urine collected during the first 24 h. In the females the corresponding urine contained 41% of the radioactivity and 12% of the mutagenicity. During the next 48 h only 1-3% of the radioactive dose was excreted in urine. The remaining dose was excreted in the feces except of less than 1% that was retained by the tissues after 72 h. The liver and kidney retained more radioactivity than other organs. In a separate study the metabolites of bile, urine and feces of both sexes were investigated. After a single oral dose of 20 mg 14C-labeled MeIQx/kg body wt, three major non-mutagenic metabolites were identified. These were 2-amino-4(or 5)-(beta-D-glucuronopyranosyloxy)-3,8-dimethylimidazo[4,5-f] quinoxaline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxalin-4(or 5)-yl sulfate and N-(3,8-dimethylimidazo[4,5-f]quinoxalin-2-yl) sulfamate. Another two metabolites present in bile, urine and feces were 2-(beta-D-glucuronopyranosylamino)-3,8-dimethylimidazo[4,5-f ] quinoxaline and 2-amino-8-hydroxymethyl-3-methylimidazo[4,5-f]quinoxalin-4 (or 5)yl sulfate. All metabolites were essentially non-mutagenic. Most of the mutagenicity still present in bile, urine and feces could be explained by unchanged MeIQx. Unchanged MeIQx was the most abundant form excreted in urine.

Animals↗
PubMed1989

Metabolism of the food carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in isolated rat liver cells.

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was transformed to at least 10 metabolites in suspensions of hepatocytes isolated from Aroclor 1254 treated rats. Combining biochemical data such as effects on MeIQx metabolism of metabolic modulators and incorporation of radioisotopic sulfur with UV, mass and 1H-NMR spectroscopy, we elucidated the structures of six metabolites. About 40% of the MeIQx was transformed to 2-amino-3,8-dimethylimidazo[4,5-f]quinoxalin-4(or5)-yl sulfate. Other oxygenated metabolites were 2-amino-8-hydroxymethyl-3-methylimidazo[4,5-f]quinoxalin-4(or 5)-yl sulfate and 2-amino-4(or5)-beta-D-glucuronopyranosyloxy-3,8-dimethyli midazo[4,5-f] quinoxaline. Evidence was obtained that a glutathione conjugate was formed. This metabolite, and the other oxygenated metabolites were probably formed in P-450 catalyzed reactions. Two metabolites, 2-beta-D-glucuronopyranosylamino-3,8-dimethylimidazo[4,5-f]q uinoxaline and the N-(3,8-dimethylimidazo[4,5-f]quinoxaline-2-yl) sulfamate, were direct conjugates of MeIQx.

Animals↗
PubMed1989

Genotoxicity of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP): formation of 2-hydroxamino-PhIP, a directly acting genotoxic metabolite.

Hepatocytes isolated from Aroclor 1254 (PCB) pretreated rats metabolized 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to a reactive metabolite that induced DNA damage measured by alkaline elution or as increased unscheduled DNA synthesis. PhIP induced mutations in Salmonella typhimurium TA98 and DNA strand breaks and sister chromatid exchange(s) in Chinese hamster V79 cells co-incubated with PCB-hepatocytes. No, or only minor genotoxic, effects were observed when hepatocytes from non-induced rats were used. The bacterial mutagenicity could be inhibited by alpha-naphthoflavone, indicating a role of P-450 in the activation of PhIP. At least eight different metabolites could be separated on HPLC after PhIP had been incubated with PCB-hepatocytes. All of the directly acting mutagenicity towards S.typhimurium TA98 co-eluted with one of the metabolites. The identity of this metabolite was concluded to be 2-hydroxamino-PhIP based on the following evidence: (i) it reduced ferric ion to ferrous ion as hydroxylamines do, (ii) it had an identical UV spectrum and chromatographic properties as a species formed upon reduction of 2-nitro-PhIP by NADPH P-450 reductase. This product displayed a major peak at m/z 241 during thermospray mass spectrometry in the positive-ion mode as would be expected from 2-hydroxamino-PhIP. 2-Hydroxamino-PhIP was directly genotoxic both to TA98 and V79 cells. The genotoxic activity of the medium after removing the hepatocytes remained stable for several hours. Compared to 2-amino-3,4-dimethylimidazo[4,5-f]quinolone (MeIQ), PhIP caused a much larger increase in DNA damage in V79 cells (with hepatocyte activation), whereas MeIQ was more potent with respect to DNA damage induced in hepatocytes and bacteria.

Animals↗
PubMed1989

4-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate--a major metabolite of the food mutagen 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP) in the rat.

Isolated rat hepatocytes (4 X 10(6) cells/ml metabolized the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP) (100 microM) to at least eight different metabolites in a 4 h duration. The major metabolite formed was 4-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate (4'-PhIP sulfate). Its rate of formation was increased in hepatocytes from PCB pretreated animals in comparison to hepatocytes from untreated animals. One of the other metabolites was the unconjugated derivative of the sulfate (4'-OH-PhIP). This metabolite was also found after in-vitro incubations of rat liver microsomes from PCB or beta-naphthoflavone pretreated animals. The evidence for the proposed structure of the major metabolite is based on [1H]NMR and UV spectroscopy, incorporation of radiolabelled sulfate and arylsulfatase-lability. The formation of 4'-PhIP sulfate was inhibited by the P-450 inhibitors alpha-naphthoflavone and metyrapone and when incubated in sulfate-free medium added the sulfotransferase inhibitor pentachlorophenol. 4'-PhIP sulfate was also the major metabolite of PhIP in the urine of exposed rat.

Animals↗
PubMed1988

A model system for studying covalent binding of food carcinogens MeIQx, MeIQ and IQ to DNA and protein.

We have studied the covalent binding of carcinogenic aminoimidazoazaarene compounds to macromolecules in a microsomal model system. The 14C-labelled compounds were incubated with rat-liver microsomes, and binding to macromolecules was measured after their precipitation on glass filters, which were washed several times in organic solvents. The amount of radioactivity was determined by liquid scintillation counting. Covalent binding was dependent on the addition of NADPH, with an optimal concentration of about 1 mM. The binding appeared to follow saturation kinetics when carcinogen concentrations were lower than 200 microM, with Km values of less than 20 microM. At 50 microM, 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline (MeIQ) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) bound more effectively than 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). When DNA was included in the incubations, binding to this macromolecule was ten-fold less per milligram than binding to proteins. In comparison with microsomes from untreated animals, those from rats treated with beta-naphthoflavone caused up to nine-fold more binding of MeIQx, six-fold more of IQ and three times as much of MeIQ. Induction by Aroclor 1254 caused up to 17-fold more binding, whereas induction by phenobarbital caused up to three-fold more binding. The effects of the inducers were greatest for MeIQx and IQ, while smaller effects were seen for MeIQ. The results are most consistent with cytochrome P450-dependent metabolic activation of the carcinogens to hydroxylamine metabolites, for which an isoenzyme(s) inducible by polyaromatic and polychlorinated hydrocarbons is most effective. To our knowledge, this is the first report that MeIQx is metabolized to reactive species capable of covalent binding to macromolecules.

Animals↗
PubMed1987

Investigation of benzo[a]pyrene-globin adducts.

The nature of the adducts formed between benzo[a]pyrene (BP) and globin were investigated in animals treated with [3H]BP. Modification levels on globin were determined by radioactivity measurements. Since BP tetraols can be released from benzo[a]pyrene diol epoxide modified protein and DNA by acid treatment, globin samples were treated with acid, released tetraols separated by HPLC and quantitated by scintillation counting. In addition, acid released material was measured in a competitive enzyme linked immunosorbent assay (ELISA) using antibodies which recognize BP tetraols. Both measurements indicate that only 2% of bound radioactivity could be released as free BP tetraols. These studies indicate that benzo[a]pyrene diol epoxide may not be the major metabolite of BP involved in globin binding.

Animals↗
PubMed1985

Evidence that covalent binding of metabolically activated phenol to microsomal proteins is caused by oxidised products of hydroquinone and catechol.

The metabolic activation of [14C]phenol resulting in covalent binding to proteins has been studied in rat liver microsomes. The covalent binding was dependent on microsomal enzymes and NADPH and showed saturation kinetics for phenol with a Km-value of 0.04 mM. The metabolites hydroquinone and catechol were formed at rates which were 10 or 0.7 times that of the binding rate of metabolically activated phenol. The effects of cytochrome P-450 inhibitors and cytochrome P-450 inducers on the metabolism and binding of phenol to microsomal proteins, suggest that cytochrome P-450 isoenzyme(s) other than P-450 PB-B or P-450 beta NF-B catalyses the metabolic activation of phenol. Furthermore, reconstituted mixed-function oxidase systems containing cytochrome P-450 PB-B and P-450 beta NF-B were (on basis of cytochrome P-450 content) 6 and 11 times less active in catalysing the formation of hydroquinone than microsomes. The isolated metabolites hydroquinone and catechol bound more extensively to microsomal proteins than phenol and the binding of these was not stimulated by NADPH. The binding occurring during the metabolism of phenol could be predicted by the rates of formation of hydroquinone and catechol and the rates by which the isolated metabolites were bound to proteins.

Animals↗
PubMed1984

Covalent binding of benzo[a]pyrene to cytochrome P-450 beta NF-B2 and other proteins in reconstituted mixed-function oxidase systems.

A reconstituted mixed-function oxidase system, containing the major beta-naphthoflavone-induced isozyme of rat liver cytochrome P-450 bound benzo[a]pyrene covalently in the presence of NADPH. NADPH-cytochrome P-450 reductase was required for binding and a maximum rate of adduct formation was obtained at 8 units of reductase per nmol cytochrome P-450. Phosphatidylcholine inhibited this reaction. Benzo[a]pyrene was bound to the cytochrome, but not to the reductase, as shown by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Approximately 6 molecules of benzo[a]pyrene bound to each molecule cytochrome P-450 during prolonged incubations. No binding occurred when the beta-naphthoflavone-induced isozyme of cytochrome P-450 was replaced by the major isozyme induced by phenobarbital, but both cytochromes incorporated benzo[a]pyrene to approximately the same extent when they were incubated together in the presence of the reductase and NADPH. Metabolically activated benzo[a]pyrene also bound covalently to purified epoxide hydrolase, when this enzyme was added to the reconstituted mixed-function oxidase system.

Animals↗
PubMed1984

Enzyme immunoassay of benzo[a]pyrene conjugated to DNA, RNA and microsomal proteins using a monoclonal antibody.

An enzyme immunoassay for the detection of benzo[a]pyrene covalently conjugated to macromolecules has been developed. The monoclonal antibody, raised through in vitro immunization reacted with benzo[a]pyrene metabolites bound to DNA, RNA and proteins. The lower detection limit for the assay was 1 pmol for benzo[a]pyrene bound to DNA or RNA, and 5 pmol when bound to protein.

Animals↗
PubMed1981

A rapid and sensitive method for determination of covalent binding of benzo[a]pyrene to proteins.

A method is presented for the quantitative determination of covalent binding of metabolically activated benzo[a]pyrene to microsomal proteins. After incubation of radiolabelled benzo[a]pyrene with microsomes and NADPH, the mixture is applied to filter paper discs. These are immersed in ethanol to precipitate the proteins. Unbound radiolabel is removed by repeated washes of the filters in organic solvents before scintillation counting. The method is simple, rapid, sensitive and accurate, and works both with 14C- and 3H-labelled compounds. The method is suitable for measuring the incorporation of other radiolabelled xenobiotics to proteins of both microsomes and other subcellular fractions and for the analysis of binding to isolated proteins.

Animals↗
PubMed1975

Effect of quinidine on maintaining sinus rhythm after conversion of atrial fibrillation or flutter. A multicentre study from Stockholm.

In a controlled study comprising 176 patients, quinidine in the form of Kinidin Durules was found to reduced significantly the recurrence of the atrial fibrillation during a 1-year follow-up period after successful electric shock conversion. After one year, 51 per cent (52/101) of the patients in the quinidine group, and 28 per cent (21/75) in the control group remained in sinus rhythm (P smaller than 0.001). No less than 43 per cent of the patients converted to sinus rhythm during treatment with maintenance doses of quinidine sulphate before intended DC conversion. Gastrointestinal side-effects were not uncommon, and caused interruption of quinidine treatment in some cases.

Adult↗
PubMedDate not supplied

Gravimetric determination of ash in foods: NMKL collaborative study.

A gravimetric method for the determination of ash was collaboratively studied in 14 laboratories. The food is ashed at 550 degrees C to constant weight and the ash is determined by weighing. Seven samples of various food commodities with estimated ash contents varying between low and high (0.07-8.0 g/100 g) were included in the study. The relative standard deviations for reproducibility varied, ranging from 1.0 and 1.3 for ash contents of 7.2 and 8.0 g/100 g, to 11 +/- 1% for low ash contents of 0.07 and 0.27 g/100 g.

Food Analysis↗
PubMedDate not supplied

Phenobarbital, drug metabolism, and human cancer.

To investigate the possible influence of anticonvulsant treatment on cancer risk, a nested case-control study of 104 lung cancers, 18 bladder cancers, and 322 cancer-free controls was conducted. The background for the study was previous observations among 8004 epileptics in Denmark with a significantly high risk for lung cancer and a significantly low risk for bladder cancer. Cigarette smoking appears to explain the lung cancer excess but not the low risk for bladder cancer, another tobacco-related disease. Information was abstracted on 94 and 95% of the cases and controls, respectively. Lung cancer was not associated with any anticonvulsant drug, but bladder cancer was inversely related to use of phenobarbital (PB). The apparent protective effect of PB was further evaluated in a study of rats given 4-aminobiphenyl (ABP), a bladder carcinogen. The levels of 4-aminobiphenyl adducts in hemoglobin and in bladder and liver DNA were significantly lower in rats given PB prior to 4-aminobiphenyl, compared to controls. These studies suggest that PB may induce drug-metabolizing enzymes of the liver that deactivate bladder carcinogens found in cigarette smoke and provide clues to the role of activation and detoxification of carcinogens in humans.

Animals↗