[Toxicologic evaluation of barbiturate poisonings in relation to histologic liver findings].
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Barbiturates↗
Biomedical subjects
A Schmoldt
Publications and source records attributed to A Schmoldt.
[Postmortem evaluation of barbiturate poisonings].
The evaluation of barbiturate intoxication as the cause of death is often difficult when the concentration in body fluids and organs is not extremely high. The problem arises because of the great capacity of barbiturates to produce tolerance after chronic use, a property that is often unknown. Therefore, the most abused barbiturates were studied to assess whether chronic intake causes morphological liver changes or not. It was found that the chronic abuse of drugs containing seco-, cyclo-, brallo-, and/or pentobarbital produces hypertrophy of the smooth endoplasmic reticulum of hepatocytes corresponding to that of phenobarbital. Neither acute barbiturate overdose (without a history of abuse) nor chronic abuse of opiates causes similar liver changes. In conclusion, barbiturate tolerance can be evaluated postmortem by light microscopic examination of the liver.
Animals↗
[Metabolism of digitalis glycosides].
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Biotransformation↗
Induction of specific monooxygenases by isosteric heterocyclic compounds of benz[a]anthracene, benzo[c]phenanthrene and chrysene.
Benzo[c]phenanthrene and a series of heterocyclic compounds (benzo[b]naphtho(1,2-d)thiophene; benzo[b]naphtho(2,1-d)thiophene; benz[a]acridine and benz[c]acridine) were tested to their capacity of inducing monooxygenase activity in rat liver by means of recording the metabolite profile of benz[a]anthracene formed in rat liver microsomal incubations. Although all compounds tested were found to be weak monooxygenase inducers the pretreatment of rats with them resulted in significant changes of the microsomal metabolite profile of benz[a]anthracene. The thiophenes equally gave rise to oxidation at the 5,6- and the 8,9-positions, whereas the benzacridines being isosteric to benz[a]anthracene favoured the K-region oxidation (5,6-oxidation). A structure-dependent effect of monooxygenase inducers on the metabolite profile of benz[a]anthracene is discussed.
Animals↗
Benzo[e]pyrene metabolism in rat liver microsomes: dependence of the metabolite profile on the pretreatment of rats with various monooxygenase inducers.
Benzo[r]pyrene (B[e]P) is metabolized by liver microsomes of untreated rats to trans-4,5-dihydroxy-4,5-dihydrobenzo(e)pyrene and 1- as well as 3-hydroxybenzo[e]pyrene as shown by g.l.c. and mass spectrometry of their trimethylsilyl ethers. After pretreatment of the rats with various monooxygenase inducers oxidation at the 9/10-position was also observed. In addition, secondary oxidation to dihydrodiolepoxides and the formation of a tetrol, tentatively identified as 4,5,9,10-tetrahydroxy-4,5,9,10-tetrahydrobenzo[e]pyrene was detected after incubation of B[e]P with liver microsomes of rats treated with polycyclic aromatic hydrocarbons. However, no formation of the supposed ultimate carcinogen, the 9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydrobenzo[e]pyrene could be observed after any of the pretreatments.
Animals↗
On the substrate specificity of the digitoxigenin monodigitoxoside conjugating UDP-glucuronyltransferase in rat liver.
The aim of the present study was to investigate the specificity of the UDP-glucuronosyltransferase (EC 2.4.1.17) involved in the conjugation of digitoxigenin monodigitoxoside. By in vitro assays with detergent activated liver microsomes it was found that (1) digitoxigenin monodigitoxoside is by far the best substrate of all cardenolides and cardenolide digitoxosides tested. (2) In the presence of saturating UDP-glucuronate concentrations an apparent Km of 5.8 microM was obtained from linear Lineweaver-Burk plots together with a Vmax of about 150 pmoles/mg microsomal protein/min (3) Neither phenobarbital nor polycyclic aromatic hydrocarbons caused a considerable induction of the enzyme without change of the apparent Km, but spironolactone did. (4) The conjugation of the substrate (4 microM) could only be inhibited by the 3'-epi-digitoxoside of digitoxigenin. (5) 25-50 microM substrate inhibited only the conjugation of the 3'-epimer and that of digoxigenin monodigitoxoside. It is suggested that there is a form of glucuronyltransferase which specifically conjugates digitoxigenin monodigitoxoside.
Animals↗
Influence of monooxygenase inducers on the metabolic profile of phenanthrene in rat liver microsomes.
The oxidation of phenanthrene by rat liver microsomes significantly depends on the pretreatment of the animals as shown by means of gas chromatography/mass spectrometry. Whereas untreated animals convert phenanthrene exclusively into the 9,10-dihydrodiol (K-region), pretreatment with various polycyclic aromatic hydrocarbons and related compounds resulted in different rates of additional oxidation at the 1,2- and 3,4-position. Moreover, secondary metabolism to dihydrodiol epoxides, detected as triols, was observed. Despite considerable concentration of the proximate carcinogen of phenanthrene (1,2-dihydrodiol) only low concentrations of the ultimate carcinogen were detected which may explain the carcinogenic inefficiency of this hydrocarbon.
Animals↗
On the metabolic activation of benz[a]acridine and benz[c]acridine by rat liver and lung microsomes.
The metabolism of benz[a]- and benz[c]acridine by liver and lung microsomes from untreated, phenobarbital (PB)-treated and benzo[k]fluoranthene (BkF)-treated rats has been studied by gas chromatography/mass spectrometry (GC/MS). Epoxidation and hydrolysis of the epoxides to dihydrodiols were found to be the predominant pathways for all substrates. N-Oxidation is likely to occur in the case of benz[c]acridine. However, no unequivocal evidence could be obtained for the formation of the ultimate carcinogens--the t-3,4-dihydrodiol-1,2-epoxides--in case of both benz[a]- and benz[c]acridine. K-Region oxidation was induced by phenobarbital, whereas the formation of non-K-region metabolites increased after BkF treatment in the case of benz[c]acridine.
Acridines↗
The metabolism of pyrene by rat liver microsomes and the influence of various mono-oxygenase inducers.
1. Pyrene metabolite g.l.c. profiles were recorded and metabolites identified by mass spectrometry. 2. Pyrene is metabolized by liver microsomes of untreated rats to 1-hydroxypyrene, 4,5-dihydroxy-4,5-dihydropyrene, two different diphenols and a triol, tentatively identified as 1,4,5-trihydroxy-4,5-dihydropyrene. 3. Pretreatment with phenobarbital or polychlorinated biphenyls favours oxidation at the K-region, whereas cytochrome P-448 inducers stimulate oxidation at the non-K-region of pyrene. 4. 1-Hydroxypyrene does not inhibit pyrene oxidation. 5. Pyrene diphenols are formed by secondary oxidation of 1-hydroxypyrene. 6. Triols are formed from dihydrodiols by secondary oxidation.
Animals↗
On the glucuronidation of digitalis compounds in different species.
Experiments were undertaken to evaluate for various species the activity and specificity of the glucuronyltransferase(s) which are responsible for the conjugation of digitoxin or its metabolites formed by oxidative cleavage of the sugar chain. As shown for rats the glucuronide of digitoxigenin monodigitoxoside is the main polar digitoxin metabolite in vivo. However, it cannot be decided whether this digitoxoside or another metabolite is the best substrate for the glucuronyltransferase. Therefore, in vitro measurements were made with possible cleavage products of digitoxin using detergent activated liver microsomes. Digitoxigenin monodigitoxoside is by far the best substrate for the microsomal glucuronyltransferase of rats (120 pmoles/mg/min). Ten-fold lower values were found with digitoxigenin bisdigitoxoside and only traces of glucuronides were formed with digitoxin, digitoxigenin or its 3-epimer. With liver microsomes of other species the glucuronidation rates for digitoxigenin monodigitoxoside decreased in the following order: rat greater than rabbit greater than guinea-pig greater than cat (1:0.3:0.2:0.05). For rabbit liver microsomes, however, the best substrate was the 3-epi-digitoxigenin instead of the monodigitoxoside (145 pmoles/mg/min). Experiments with tissue slices of liver and small intestine revealed further differences between rats and rabbits. Whereas rat intestine was nearly inactive the activity of rabbit intestine attained about 50% of that found in the liver. It can be concluded that various species show remarkable differences in the activity, stereospecificity and organ distribution of the glucuronyltransferase(s) conjugating cardenolide derivatives.
Animals↗
Studies on the mechanism of stimulation of microsomal H2O2 formation and benzo(a)pyrene hydroxylation by substrates and flavone.
The addition of activators like flavone and hexobarbital to hepatic microsomes markedly stimulates H2O2 formation. The similar increase observed with flavone of microsomal hydroxylation of benzo(a)pyrene and its inhibition by catalase and methanol suggests but does not prove a necessary interaction of microsomal H2O2 production with benzo(a)pyrene hydroxylation. Hexobarbital and flavone-stimulated H2O2 formation is optimal at a stoichiometric relationship of these activators and NADPH. This implies either their direct participation as electron donors or their indirect involvement in electron transport by facilitation of stoichiometric substrate cytochrome P-450/NADPH flavoprotein interactions. Steady state kinetics data are consistent with a scheme in which the formation in microsomes of a complex of 1 mole of NADPH with NADPH-cytochrome P-450 reductase and 1 mole hexobarbital with cytochrome P-450 regulates H2O2 formation.
Animals↗
Dose-dependent induction of rat liver microsomal aryl hydrocarbon monooxygenase by benzo[k]fluoranthene.
The environmentally widespread polycyclic aromatic hydrocarbon (PAH) benzo[k]fluoranthene is a potent AHH inducer. This has been proven by recording the benz[a]anthracene metabolite profile in the rat liver by means of gas chromatography/mass spectrometry (GC/MS) technique. Even a total dose of 3 times 50 micrograms/kg body wt increases the metabolism of benz[a]anthracene by a factor of 2. The formation of the 8,9- as well as the 5,6-dihydrodiol is stimulated to about the same extent, whereas the formation of the 10,11-dihydrodiol is suppressed. After comparatively low doses of the inducer, a metabolite is formed which corresponds in all parameters with the postulated ultimate carcinogen 3,4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenz[a]anthracene. This metabolite and a number of other primary and secondary oxidation products could be identified after incubation with induced but not with normal microsomes. Therefore, it should be emphasised that metabolite profiles have to be recorded instead of measuring brutto conversions of PAH substrates to evaluate inducing effects.
Animals↗
The influence of polycyclic aromatic hydrocarbons as inducers of monooxygenases on the metabolite profile of benz[a]anthracene in rat liver microsomes.
Microsomal oxidation of benz[a]anthracene (BaA) in rat liver has been shown to occur at various positions (1,2-, 3,4-, 5,6-, 8,9- and 10,11-position) by means of gas chromatography/mass spectrometry (GC/MS) and comparison with synthetic reference substances. In normal rats trans-5,6-, 8,9- and, mainly, 10,11-dihydrodiols have been detected as primary metabolites. The induction of monooxygenases by polycyclic aromatic hydrocarbon (PAH) results in a considerable change in the metabolite profile, since the 5,6- and 8,9-isomers become the main metabolites while the amount of 10,11-isomer is not increased. Simultaneously, the secondary metabolism to form triols and tetrols is induced. Phenobarbital as well as 'moderately inducing' PAH (pyrene, benzo[ghi]perylene, benzo[e]pyrene) induced the oxidation at 5,6- and 8,9-position, whereas almost all other compounds investigated, especially the benzofluoranthenes, additionally induced the oxidation at the 3,4-position forming the precursor of the ultimate carcinogen of BaA, 3,4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenz[a]anthracene, which was detected as its isomerisation product, the 2,3,4-triol.
Animals↗
Time course of oxidative benz[a]anthracene metabolism by liver microsomes of normal and PCB-treated rats.
The time course for the oxidative metabolism of benz[a]anthracene by liver microsomes of normal, 3,3',4,4'-tetrachlorobiphenyl-(TCBP) and polychlorinated biphenyl-(PCB) treated rats has been investigated. These are shown not to be linear in all cases. In normal microsomes the 10,11-dihydrodiol is the main metabolite, followed by the 5,6- and 8,9-dihydrodiols. Secondary metabolism, i.e. formation of dihydrodiol epoxides, is observed only after 5 min. In contrast, TCBP microsomes produced predominantly the 5,6-dihydrodiol followed by the 8,9-dihydrodiol, whereas the formation of the 10,11-dihydrodiol is suppressed. Metabolism deriving from oxidation of the 5,6-position is increased 15-20 fold; again secondary metabolites occur between the 5th and 10th min of incubation. Gas chromatography and mass spectra data suggests the formation of the ultimate carcinogen, 3,4-dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenz[a]anthracene, as concluded from detection of its rearrangement product, the 2,3,4-triol. In PCB-treated rats secondary metabolism is observed within 2.5 min. 5,6-Oxidation is increased 27 fold, 8,9-oxidation 10 fold, but 10,11-oxidation is completely suppressed. The above-mentioned ultimate carcinogen is also formed. Moreover, a series of tetrols is detected. Optimum incubation times dependent on the problem under study are discussed.
Animals↗
Glass-capillary-gas chromatography/mass spectrometry data of mono- and polyhydroxylated benz[a]anthracene. Comparison with benz[a]anthracene metabolites from rat liver microsomes.
By means of glass-capillary-gas chromatography all possible benz[a]anthracene metabolites formed by rat liver microsomes (phenols, dihydrodiols, dihydrodiol enols and tetrahydrotetrols) can be separated. Mass spectra of their trimethylsilyl ethers show intense molecule ions and, in most cases, characteristic fragments. K-Region diols and their secondary oxidation products can be recognized by the ratio (m/e 147) (m/e 191) greater than 1, whereas the ratio is inverse in all other dihydrodiol trimethylsilyl ethers investigated. With the exception of 1,2-dihydrobenz[a]anthracene-1,2,3-triol all vicinal dihydrodiol enols investigated exhibit an intense elimination of the fragment CH = CH-OSiMe3 according to m/e 379. The conformation of vicinal tetrahydrobenz[a]anthracenetetrols possibly can be distinguished by the intensity of m/e 380 (M - 240) since only in those possessing two or more subsequent Me3SiO groups in the same conformation intense elimination of Me3Si-O-CH = CH-O-SiMe3 is observed. Retention times and mass spectrometric data of a series of synthetic benz[a]anthracene derivatives are presented as a base for the identification of benz[a]anthracene metabolites in biological systems.
Animals↗
Cleavage of digoxigenin digitoxosides by rat liver microsomes.
Microsomal monoxygenases can oxidize the axial hydroxyl of the terminal digitoxosyl of digoxin (dg-3), digoxigenin bis-, and digoxigenin mono-digitoxoside (dg-2 and dg-1, respectively) to an oxo-group. The corresponding metabolites (15'-dehydro-dg-3, 9'-dehydro-dg-2, and 3'-dehydro-1, respectively) have been identified by chromatographic and chemical methods. Only after this oxibation the terminal sugar can be split off, presumably by beta-elimination. Therefore, for the degradation of dg-3 three successive cytochrome P450 catalyzed oxidations are necessary before digoxigenin (dg-0) can be obtained. The highest oxibation rate was observed with dg-1 (120-150 pmoles/mg microsomal protein/min) and by far the lowest with dg-2 (6-7 pmoles/min) as the substrate (concentration was 30/microM). The latter may contribute to the effect that dg-2 is the main dg-3 metabolite in vivo. Pretreatment of rats with canrenoate enhanced the microsomal oxidation of dg-3, dg-2, and dg-1 by a factor of 3.2, 2.3 and 1.3, respectively. In contrast, there was no increase after pretreatment with phenobarbital.
Animals↗
Effects of inducers and inhibitors of rat liver mono-oxygenases on digitoxin metabolism.
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Animals↗
On the metabolism of various polycyclic aromatic hydrocarbons (PAH) by liver microsomes of variously pretreated rats.
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Animals↗