Metabolic Activation of Tris(2,3-dibromopropyl)phosphate to Reactive Intermediates. I. Covalent Binding and Reactive Metabolite Formation in Vitro

1993 ◽  
Vol 118 (2) ◽  
pp. 186-195 ◽  
Author(s):  
P.G. Pearson ◽  
J.G. Omichinski ◽  
R.H. Mcclanahan ◽  
E.J. Soderlund ◽  
E. Dybing ◽  
...  
Keyword(s):  
Covalent Binding ◽  
Metabolic Activation ◽  
Reactive Intermediates ◽  
Reactive Metabolite ◽  
Metabolite Formation

Acetaminophen toxicity in fed and fasted mice

1982 ◽  
Vol 60 (3) ◽  
pp. 399-404 ◽  
Author(s):  
Robin M. Walker ◽  
Thomas E. Massey ◽  
Timothy F. McElligott ◽  
William J. Racz
Keyword(s):  
Covalent Binding ◽  
Microsomal Protein ◽  
Transferase Activity ◽  
Reactive Metabolite ◽  
Metabolite Formation ◽  
Acetaminophen Toxicity ◽  
Aryl Hydrocarbon ◽  
Significant Difference ◽  
Aryl Hydrocarbon Hydroxylase Activity ◽  
Liver Enlargement

Acetaminophen (750 mg/kg) toxicity and its modification by N-acetylcysteine (NAC, 1200 mg/kg) have been compared in fed and fasted mice. There was no significant difference between fed and fasted animals with respect to microsomal protein content, cytochrome(s) P-450 content, and aryl hydrocarbon hydroxylase activity. Glucuronyl transferase activity was significantly higher in fasted mice. Hepatotoxicity, as determined histologically and by liver enlargement was greater in fasted than fed mice. Covalent binding of [3H]acetaminophen metabolite(s) to liver proteins was also greater in fasted animals. NAC administration prevented acetaminophen-induced microscopic changes and liver enlargement and reduced the magnitude of covalent binding of acetaminophen metabolites. Fasting caused a marked fall in liver reduced sulfhydryl concentration. The incidence of acetaminophen-induced hypothermia was greater in fasted than in fed animals. NAC administration reduced hypothermia in fasted mice and abolished it in fed animals. It is concluded that enhanced acetaminophen toxicity in fasted mice compared with fed mice is unlikely to be a consequence of increased reactive metabolite formation, but rather a result of reduced inactivation of reactive metabolite(s) due to reduced hepatic glutathione stores in fasted mice.

scholarly journals Metabolic activation of acetylenic substituents to derivatives in the rat causing the loss of hepatic cytochrome P-450 and haem

1978 ◽  
Vol 174 (3) ◽  
pp. 853-861 ◽  
Author(s):  
Ian N. H. White
Keyword(s):  
Covalent Binding ◽  
Metabolic Activation ◽  
Microsomal Protein ◽  
Significant Loss ◽  
Microsomal Cytochrome ◽  
Rf Values ◽  
Green Pigments ◽  
Cytochrome P 450

1. A number of acetylenic-substituted steroidal and non-steroidal compounds, including 2,2-dipropargylacetamide, pregna-2,4-dien-20-yno[2,3-d]isoxazol-17-ol (Danazol) and acetylene gas, when administered to rats in vivo brought about a decrease in the concentrations of hepatic microsomal cytochrome P-450 and haem. Abnormal haem-breakdown products, ‘green pigments’, and porphyrins accumulated in the livers of these animals. 2. For loss of microsomal cytochrome P-450 to occur in vitro, metabolic activation of the acetylenic substituent was necessary. The enzyme system responsible required NADPH and air, and was induced by pretreatment of rats with phenobarbitone; these are characteristics typical of the microsomal mixed-function oxidases. 3. When rats were dosed with 17α-ethynyl-17β-hydroxyandrost-4-en-3-one (ethynyltestosterone, 1mmol/kg) the pattern of green pigments extracted from the liver 4h after dosing and separated by t.l.c. was quite different from that in rats given 17β-hydroxy-17α-vinylandrost-4-en-3-one (vinyltestosterone), suggesting that reduction of the unsaturated triple bond to a double bond is not normally part of the metabolic activation pathway of the acetylenic substituent. 4. The green pigments extracted from the livers of rats 4h after the administration of the acetylenic-substituted compounds (1mmol/kg) when separated by silica-gel t.l.c. had variable RF values. The number and distribution of green pigments was characteristic for each compound examined. There was little correlation between the total loss of hepatic microsomal haem and the apparent intensity of the green pigments seen on the thin-layer chromatograms. 5. After incubation of [14C]acetylene in vitro with microsomal preparations from phenobarbitone-pretreated rats and a NADPH-generating system, no significant covalent binding to microsomal protein was detected over a 30min incubation period, although under similar conditions there was a significant loss of cytochrome P-450.

scholarly journals Metabolic activation of acetylenes. Covalent binding of [1,2-14C]octyne to protein, DNA and haem in vitro and the protective effects of certain thiol compounds

1984 ◽  
Vol 220 (1) ◽  
pp. 85-94 ◽  
Author(s):  
I N H White ◽  
J B Campbell ◽  
P B Farmer ◽  
E Bailey ◽  
N H Nam ◽  
...  
Keyword(s):  
Time Course ◽  
Covalent Binding ◽  
Protoporphyrin Ix ◽  
Metabolic Activation ◽  
Protective Effects ◽  
Trans Isomers ◽  
Thiol Compounds ◽  
Microsomal Hydroxylation ◽  
Cytochrome P 450

[1,2-14C]Oct-l-yne was used to investigate metabolic activation of the ethynyl substituent in vitro. Activation of octyne by liver microsomal cytochrome P-450-dependent enzymes gave intermediate(s) that bound covalently to protein, DNA and to haem. The time course and extent of covalent binding of octyne to haem and to protein were similar. However, two different activating mechanisms are probably involved. Whereas covalent binding to protein or to DNA was inhibited by nucleophiles such as N-acetylcysteine, that to haem was little affected. When N-acetylcysteine was included in the reaction mixtures, two major octyne-N-acetylcysteine adducts were isolated and purified by high-pressure liquid chromatography. G.l.c.-mass spectrometry and n.m.r. suggest that these are the cis-trans isomers of S-3-oxo-oct-1-enyl-N-acetylcysteine. Oct-1-yn-3-one reacted non-enzymically with N-acetylcysteine at pH 7.4 and 37 degrees C with a t1/2 of about 6 s also to yield S-3-oxo-oct-l-enyl-N-acetylcysteine. The same product was formed when microsomal fractions were incubated with oct-1-yn-3-ol, N-acetylcysteine and NAD(P)+. Octyn-3-one did not appear to react with haem or protoporphyrin IX. 5. A mechanism for the metabolic activation of oct-1-yne is proposed, consisting in (a) microsomal hydroxylation of the carbon atom alpha to the acetylenic bond and (b) oxidation to yield octyn-3-one as the reactive species.

Sign in / Sign up

Export Citation Format

Share Document