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At least 811 records · Page 45Linked to original sources
PubMed1990

Monoclonal antibody characterization of NADH- and NADPH-dependent hydroxylation of benzo(a)pyrene in liver microsomes from 5,6-benzoflavone-induced C57Bl/6 mice.

Monoclonal antibodies (MAb 1-7-1) directed against the isoenzymes of rat liver cytochrome P-450 induced by methylcholanthrene, inhibited benzo(a)pyrene hydroxylase less strongly at low (0.04 mM) than at high (2 mM) NADH concentration. Inhibition of NADPH dependent hydroxylation was the same irrespective of NADPH concentrations and corresponded to that observed at high NADH concentration. The same was also the h.p.l.c. pattern of the reaction products of benzo(a)pyrene hydroxylation supported by high concentration of both coenzymes. It is postulated that different cytochrome P-450 isoenzymes participate in benzo(a)pyrene hydroxylation, whereas the second one acts at high concentration of both NADH and NADPH.

Animals↗
PubMedDate not supplied

Metabolism of benzo[a]pyrene by the isolated perfused rabbit lung.

The metabolism of benzo[a]pyrene (BP) was studied in the isolated perfused rabbit lung and in rabbit pulmonary microsomes. Pretreatment of rabbits with 3-methylcholanthrene did not increase the metabolism of BP by microsomal preparations, and the pretreatment did not induce cytochrome P-448 in pulmonary microsomes. In the isolated perfused lung, BP was metabolized at a rate of about 6 nmol/min/g of lung. The intermediate arene oxides formed from BP in the isolated perfused lung were metabolized nonoxidatively by epoxide hydrase and glutathione S-transferases. The rates of the latter reactions were at least an order of magnitude less than the overall rate of metabolism. Pretreatment of the animals with 3-methylcholanthrene increased only the apparent rate of the epoxide hydrase reaction. In the isolated perfused lung, BP and some of its less polar metabolites (i.e., quinones and phenolic derivatives) were preferentially partitioned into lung tissue, precluding accurate measurement of metabolic rates by analysis of the perfusion medium alone. Covalent binding of BP-derived radioactivity to lung tissue occurred, but relatively high variability in this parameter in lungs from 3-methylcholanthrene-pretreated animals did not allow measurement of a significant difference from control lungs.

Animals↗
PubMedDate not supplied

Benzo[a]pyrene metabolism by hepatic and extrahepatic tissues in streptozotocin-diabetic rats.

The metabolism of benzo[a]pyrene (BP) by microsomes from hepatic and extrahepatic tissues of female diabetic rats was investigated. Diabetes was produced by the administration of streptozotocin, 60 mg/kg iv, and BP metabolism was studied 7 or 10 days later. BP metabolism was increased in hepatic microsomes by 75% in diabetic animals. Cytochrome P-450 levels were similarly increased. BP mono-oxygenase activity was tripled in intestinal microsomes of diabetic rats, and returned to control values on insulin treatment. The BP mono-oxygenase activity in lung microsomes from diabetic rats decreased by 40%, and was increased to control levels after insulin treatment. No significant changes in BP metabolism were observed in the kidney and adrenal tissues of diabetic animals.

Animals↗
PubMed1977

[Acceleration of the metabolism of carcinogens in the maternal body and embryos].

Outbred mice on the 19th-21st day of pregnancy were injected intravenously 3,4-benzpyrene (BP) in the dosage of 15 mg/kg or 9,10-dimethyl-1,2-benzanthracene (DMBA) in the dosage of 40 mg/Kg in control groups, and moreover preliminary injected BP (24 hours before) in experimental groups. The BP concentration of embryos and the maternal liver 15 minutes following the injection of the basic dose of the carcinogen in increased dosage of preliminary exposure first would decrease, reach the minimum, in preliminary dosage equal to 0.75 mg/Kg, and then would increase up to values observed in control experiments with the dosage of 30 mg/Kr 7.5-15 mg/Kg, and then it would fall again in the dosage of 30 mg/Kg. The preliminary injection of BP in the dosage of 0.75 mg/Kg produced a sharp fall in the carcinogen concentration in embryos and the maternal organism during the first moment of observation (after 5 minutes), but it failed to influence the rate of subsequent decrease of the substance level. An explanation of the two effects observed is suggested based on the assumption that there exist two enzymatic systems metabolizing BP: one-premanently present in the liver and the other-induced by the carcinogen. The preliminary BP injection did not influence the concentration of DMBA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

Characterization of benzo(a)pyrene hydroxylase of trout liver.

Trout liver microsomes contained as 0.40 nmole of cytochrome P-450 per mg of protein and a NADPH-cytochrome c reductase activity of 23 nmoles of cytochrome c reduced per mg of protein per min at 22 degrees. Associated with these was a high benzo(a)pyrene hydroxylase activity, which required NADPH and O2 and was inhibited by CO. With thin-layer chromatography, at least five metabolites could be identified (including dihydrodiols, phenols, and quinones of benzo(a)pyrene). Inhibitors such as 2-diethylaminoethyl-2,2-diphenylvalerate, aminopyrine, metyrapone, pyridine, n-octylamine, and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane were relatively ineffective in inhibiting trout benzo(a)pyrene hydroxylase. Typical inhibitors of 3-methylcholanthrene-induced cytochrome (P-448), such as alpha-naphthoflavone, zoxazolamine, and testosterone, were effective, however. With benzo(a)pyrene it was possible to induce type I spectral change in trout cytochrome P-450. In spite of the many enzymatic characteristics of cytochrome P-448, trout cytochrome P-450 had maximum absorbance at 450.6 nm. when in reduced form and complexed with CO. the ethyl isocyanide gave an interaction spectrum with reduced trout liver cytochrome P-450 resembling that of control rat.

Animals↗
PubMed1979

[Profiles of polycyclic aromatic hydrocarbon metabolites after treatment with various inducers of microsomal rat liver monoxygenases (author's transl)].

The microsomal oxidation of 12 frequently occurring environmental polycyclic aromatic hydrocarbons after incubation with rat-liver microsomes has been studied and their metabolites characterized by means of gas-liquid chromatography/mass spectrometry. The method enables the detection and characterisation of phenols, diols, triols, and tetrols as trimethylsilyl ethers beside the original hydrocarbons. Moreover, the induction properties of some carcinogenic and non-carcinogenic hydrocarbons (benz[a]anthracene, pyrene, chrysene, benzo[a]-pyrene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene) have been studied. Except pyrene and benzo[e]pyrene, all compounds investigated significant but different induction factors. The relevance of the induction for an estimation of the biological effect of environmental polycyclic aromatic hydrocarbons is discussed.

Animals↗