scholarly journals The effect of ethanol on drug oxidations in vitro and the significance of ethanol–cytochrome P-450 interaction

1973 ◽  
Vol 134 (2) ◽  
pp. 367-375 ◽  
Author(s):  
Dominick L. Cinti ◽  
Robert Grundin ◽  
Sten Orrenius
Keyword(s):  
Microsomal Fraction ◽  
Ethanol Concentration ◽  
Inhibitory Effect ◽  
Type I ◽  
Spectral Change ◽  
High Concentration ◽  
Liver Slices ◽  
Liver Microsomal Fraction ◽  
Cytochrome P 450 ◽  
High Ethanol

The effect of ethanol on N-demethylation of aminopyrine in rat liver slices and in the microsomal fraction and on microsomal hydroxylation of pentobarbital and aniline was studied. With liver slices N-demethylation of aminopyrine was stimulated by 35–40% at low ethanol concentrations (2mm), whereas no stimulation occurred at high concentrations (100mm). With the liver microsomal fraction, an inhibitory effect was observed only at high ethanol concentrations (100mm). This was also observed with the other drugs studied. In agreement with these results, only at a high concentration did ethanol interfere with the binding of drug substrates to cytochrome P-450. Further, as previously reported, ethanol produced a reverse type I spectral change when added to the liver microsomal fraction. Evidence that this spectral change is due to removal of substrate, endogenously bound to cytochrome P-450, is reported. A dual effect of ethanol is assumed to explain the present findings; in liver slices, at a low ethanol concentration, the enhanced rate of drug oxidation is the result of an increased NADH concentration, whereas the inhibitory effect observed with the microsomal fraction at high ethanol concentration is due to the interference by ethanol with the binding of drug substrates to cytochrome P-450.

scholarly journals Loss of haem in rat liver caused by the porphyrogenic agent 2-allyl-2-isopropylacetamide

1971 ◽  
Vol 124 (4) ◽  
pp. 767-777 ◽  
Author(s):  
F. De Matteis
Keyword(s):  
Rat Liver ◽  
Microsomal Fraction ◽  
Direct Evidence ◽  
Gradual Increase ◽  
Rapid Loss ◽  
Metabolizing Enzymes ◽  
Liver Microsomal Fraction ◽  
Green Pigments ◽  
Cytochrome P 450 ◽  
Increased Activity

1. The effect of a single dose of 2-allyl-2-isopropylacetamide on the cytochrome P-450 concentration in rat liver microsomal fraction was studied. The drug caused a rapid loss of cytochrome P-450 followed by a gradual increase to above the normal concentration. 2. The loss of cytochrome P-450 was accompanied by a loss of microsomal haem and by a brown–green discoloration of the microsomal fraction suggesting that a change in the chemical constitution of the lost haem had taken place. Direct evidence for this was obtained by prelabelling the liver haems with radioactive 5-aminolaevulate: the drug caused a loss of radioactivity from the haem with an increase of radioactivity in a fraction containing certain un-identified green pigments. 3. Evidence was obtained by a dual-isotopic procedure that rapidly turning-over haem(s) may be preferentially affected. 4. The loss of cytochrome P-450 as well as the loss of microsomal haem and the discoloration of the microsomal fraction were more intense in animals pretreated with phenobarbitone and were much less evident when compound SKF 525-A (2-diethylaminoethyl 3,3-diphenylpropylacetate) was given before 2-allyl-2-isopropylacetamide, suggesting that the activity of the drug-metabolizing enzymes may be involved in these effects. 5. The relevance of the destruction of liver haem to the increased activity of 5-aminolaevulate synthetase caused by 2-allyl-2-isopropylacetamide is discussed.

scholarly journals The effect of magnesium ions on the diemthylaniline oxidation rate and electron transfer in liver microsomal fraction

1973 ◽  
Vol 136 (2) ◽  
pp. 371-379 ◽  
Author(s):  
A. I. Archakov ◽  
I. I. Karuzina ◽  
I. S. Kokareva ◽  
G. I. Bachmanova
Keyword(s):  
Electron Transfer ◽  
Fluorescence Quantum Yield ◽  
Sharp Increase ◽  
Microsomal Fraction ◽  
Magnesium Ions ◽  
Total Rate ◽  
Nadph Oxidation ◽  
Liver Microsomal Fraction ◽  
Rate Limiting ◽  
Cytochrome P 450

1. Reactions of N-demethylation, p-hydroxylation and N-oxidation of one substrate, i.e. dimethylaniline, have been used to show that the activating effect of Mg2+ takes place only in the first two reactions. 2. An increase in Vmax. of N-demethylation of dimethylaniline is accompanied by an increase in Km. In the p-hydroxylation of dimethylaniline Vmax. increases whereas Km does not change. A comparison of the changes in the Km values of these reactions with the change in Ks shows that in both cases Km does not characterize the affinity of cytochrome P-450 for dimethylaniline. 3. The rate-limiting site of N-demethylation and p-hydroxylation of dimethylaniline, as well as the total rate of NADPH oxidation in the presence of dimethylaniline, is between cytochromes b5 and P-450. Addition of Mg2+ to the incubation medium changes the hydrophobic environment of phosphatidylcholine in the membrane, the process being accompanied by a sharp increase in the fluorescence quantum yield of 8-anilinonaphthalene-1-sulphonate.

scholarly journals Non-alcoholic components of Pelinkovac, a Croatian wormwood-based strong liquor, counteract the inhibitory effect of high ethanol concentration on catalase in vitro

2022 ◽  
Author(s):  
Jan Homolak ◽  
Ana Babic Perhoc ◽  
Mihovil Joja ◽  
Ivan Kodvanj ◽  
Karlo Toljan ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Free Radicals ◽  
Ethanol Concentration ◽  
Inhibitory Effect ◽  
Alcoholic Beverages ◽  
Acidic Ph ◽  
Inhibitory Effects ◽  
High Ethanol ◽  
Antioxidant Enzyme Catalase

Antioxidant enzyme catalase protects the cells against alcohol-induced oxidative stress by scavenging free radicals and metabolizing alcohol. Concentrations of ethanol present in alcoholic beverages can inhibit catalase and foster oxidative stress and alcohol-induced injury. Non-alcoholic components of pelinkovac counteract the inhibitory effects of high ethanol concentration and acidic pH on catalase in vitro.

Metabolism of Metolachlor by a Microsomal Fraction Isolated from Grain Sorghum ( Sorghum bicolor) Shoots

1990 ◽  
Vol 45 (5) ◽  
pp. 558-564 ◽  
Author(s):  
Donald E. Moreland ◽  
Frederick T. Corbin ◽  
William P. Novitzky ◽  
Carol E. Parker ◽  
Kenneth B. Tomer
Keyword(s):  
Sorghum Bicolor ◽  
Microsomal Fraction ◽  
Grain Sorghum ◽  
Side Chain ◽  
Type I ◽  
Difference Spectra ◽  
Content Type ◽  
Actinic Light ◽  
Tlc Plates ◽  
Cytochrome P 450

A microsomal fraction isolated from the shoots of 3- to 4-day-old, dark-grown, grain sorghum (Sorghum bicolor cv. Funk G 522 D R ) seedlings was characterized. The preparations had a cytochrome P-450 content that varied from approximately 90 to 150 pmol P-450/mg protein with cytochrome P-420 varying from 0 to 3% of the P-450 content. Type I difference spectra were formed with cinnamic acid and metolachlor, and a type II spectrum was formed with tetcyclacis. In short-term assays with [14C]metolachlor as substrate, the preparations produced a single time-dependent product that separated on silica gel TLC plates developed in benzene/acetone (2:1, v/v). RF values for metolachlor and the metabolite were approximately 0.70 and 0.48, respectively. The microsomal reaction required N A D P H and oxygen, and was inhibited by carbon monoxide, with the inhibition being partially reversed by actinic light. Compounds known to inhibit the activity of cytochrome P-450 monooxygenases (piperonyl butoxide, tetcyclacis, and tridiphane) also prevented formation of the metabolite. Identity of the metabolite was confirmed by TLC and positive ion thermospray LC/MS to be 2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-hydroxy-l-methylethyl)acetamide. Hence, the reaction catalyzed by the sorghum microsomes involved O-demethylation of the methoxypropyl side chain of metolachlor.

scholarly journals Studies on the mechanism of hepatic microsomal N-oxide formation. The role of cytochrome P-450 and mixed-function amine oxidase in the N-oxidation of NN-dimethylaniline

1977 ◽  
Vol 164 (3) ◽  
pp. 487-496 ◽  
Author(s):  
P Hlavica ◽  
M Kehl
Keyword(s):  
Microsomal Fraction ◽  
Amine Oxidase ◽  
The Other ◽  
Rabbit Liver ◽  
Oxide Formation ◽  
Intact Rabbit ◽  
Liver Microsomal Fraction ◽  
Nadph Dehydrogenase ◽  
Cytochrome P 450

Evidence is established for the existence of alternative metabolic routes of N-oxidation of NN-dimethylaniline in rabbit liver microsomal fraction. One pathway involves the participation of two types of cytochrome P-450 with different sensitivities towards heat. Both types may represent distinct haemoprotein species or two physical forms of a single pigment. The other pathway is represented by the mixed-function amine oxidase. The enzyme lacks NADPH dehydrogenase activity and is insensitive to treatment with 2-bromo-4'-nitroacetophenone and steapsin: it catalyses N-oxidation of imipramine, trimethylamine and NN-dimethylaniline in molar proportions considerably different from those of the cytochrome P-450-supported reactions. Cytochrome P-450 is estimated to account for the formation of at least 50-60% of the total NN-dimethylaniline N-oxide formed in the intact rabbit liver microsomal fraction, the remainder arising from the action of the mixed-function amine oxidase.

scholarly journals Mechanism of inhibition of microsomal mixed-function oxidation by the gut-contents inhibitor of the southern armyworm (Prodenia eridania)

1971 ◽  
Vol 124 (2) ◽  
pp. 427-430 ◽  
Author(s):  
S. Orrenius ◽  
M. Berggren ◽  
P. Moldéus ◽  
R. I. Krieger
Keyword(s):  
Microsomal Fraction ◽  
Gut Contents ◽  
Oxidation Reactions ◽  
Mechanism Of Inhibition ◽  
Southern Armyworm ◽  
Low Concentrations ◽  
Liver Microsomal Fraction ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

A potent inhibitor of microsomal mixed-function oxidation reactions in insects had previously been isolated and partially purified from the gut contents of Prodenia eridania and shown to be associated with proteinase activity. Incubation of rat liver microsomal fraction with low concentrations of this inhibitor led to solubilization of NADPH–cytochrome c reductase, which was paralleled by the inactivation of reduction of cytochrome P-450 by NADPH and by the inhibition of NADPH-linked benzo[3,4]pyrene hydroxylation and aminopyrine demethylation. There was little or no effect on cytochromes b5 and P-450, nor was the capacity of the latter catalyst to combine with exogenous substrates decreased. Contrary to the findings with NADPH, preincubation of microsomal fraction with the inhibitor did not cause a significant decrease in the rate of cytochrome P-450 reduction by NADH, supporting the assumption that different catalysts are involved in the electron transfer from NADH and NADPH to cytochrome P-450. The findings indicate the importance of taking the possible presence of endogenous inhibitors into consideration when evaluating low or absent mixed-function oxidation activities found in insect systems in vitro.

scholarly journals Effect of a single oral dose of methanol, ethanol and propan-2-ol on the hepatic microsomal metabolism of foreign compounds in the rat

1975 ◽  
Vol 148 (2) ◽  
pp. 269-277 ◽  
Author(s):  
G Powis
Keyword(s):  
Cytochrome C ◽  
Oral Dose ◽  
Single Oral Dose ◽  
Type I ◽  
Spectral Change ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Cytochrome P 450 ◽  
Aminopyrine Demethylation ◽  
Nadph Cytochrome C Reductase

Methanol and ethanol administered to rats as a single oral dose increased aniline hydroxylation by the hepatic microsomal fraction by a maximum of 169 and 66% respectively, whereas aminopyrine demethylation was inhibited by 51 and 61%. The concentration of microsomal cytochrome P-450, and the activities of NADPH-cytochrome c reductase and NADPH-cytochrome P-450 reductase were unchanged. Propan-2-ol, administered as a single oral dose, increased microsomal aniline hydroxylation by 165% and increased aminopyrine demethylation by 83%. The concentration of cytochrome P-450 was unchanged whereas NADPH-cytochrome c reductase and NADPH-cytochrome P-450 reductase were both increased by 38%. Methanol, ethanol and propan-2-ol administration resulted in a decreased type I spectral change but had no effect on the reverse type I spectral change. Methanol administration decreased the type II spectral change whereas ethanol and propan-2-ol had no effect. Cycloheximide blocked the increases in aniline hydroxylation and aminopyrine demethylation but could not completely prevent the decreases in aminopyrine demethylation. The increases in aniline hydroxylation were due to an increase in V, but Km was unchanged. The ability of acetone to enhance and compound SKF 525A to inhibit microsomal aniline hydroxylation was decreased by the administration of all three alcohols. The decrease in the metabolism of aminopyrine may result from a decrease in the binding to the type I site with a consequent failure of aminopyrine to stimulate the reduction of cytochrome P-450. Methanol administration may lead to an increase in aniline hydroxylation because of a failure of aniline to inhibit cytochrome P-450 reduction.

scholarly journals A requirement for dietary lipids for induction of cytochrome P-450 by phenobarbitone in rat liver microsomal fraction

1971 ◽  
Vol 122 (4) ◽  
pp. 569-573 ◽  
Author(s):  
W. J. Marshall ◽  
A. E. M. McLean
Keyword(s):  
Enzyme Activity ◽  
Linoleic Acid ◽  
Dietary Protein ◽  
Microsomal Fraction ◽  
Coconut Oil ◽  
Dietary Lipids ◽  
Liver Microsomal Fraction ◽  
The Difference ◽  
Microsomal Hydroxylation ◽  
Cytochrome P 450

1. Rats fed on purified synthetic diets have a markedly lower cytochrome P-450 concentration and hydroxylating enzyme activity in liver microsomal fraction than rats fed on stock pellets. 2. When both groups are treated with phenobarbitone the difference is even greater, the purified diet allowing only 50% of the cytochrome P-450 concentrations of controls. 3. Addition of herring oil, linoleic acid or 0.1% oxidized sitosterol to the diets allows induction of cytochrome P-450 to take place. 4. Addition of coconut oil to the diet does not permit induction of cytochrome P-450. 5. The interactions between dietary protein and the lipid substances are explored. 6. The mechanism of induction of microsomal hydroxylation enzymes by drugs is discussed in the light of these requirements.

scholarly journals Relationship between the reduction of oxygen, artificial acceptors and cytochrome P-450 by NADPH-cytochrome c reductase

1977 ◽  
Vol 168 (2) ◽  
pp. 133-139 ◽  
Author(s):  
V Lyakhovich ◽  
V Mishin ◽  
A Pokrovsky
Keyword(s):  
Cytochrome C ◽  
Microsomal Fraction ◽  
Metabolic Inhibitor ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Cytochrome C Reduction ◽  
Km Value ◽  
Liver Microsomal Fraction ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

The interaction of NADPH—cytochrome c reductase with oxygen, artificial acceptors and cytochrome P-450 was studied. The generation of superoxide anion radicals (O2-.) from the oxidation of adrenaline to adrenochrome catalysed by NADPH—cytochrome c reductase proceeds independently of the interaction of the enzyme with the artificial anaerobic acceptors cytochrome c or 2,6-dichlorophenol-indophenol. Propyl 3,4,5-trihydroxybenzoate inhibited competitively the adrenaline oxidation by isolated NADPH—cytochrome c reductase (Ki 3.2—4.7 micrometer) and inhibited non-competitively the cytochrome c reduction (Ki 92—109 micrometer). In contrast with the process of electron transfer to cytochrome c, the rate of reduction of cytochrome P-450 and the rate of oxidation of adrenaline in liver microsomal fraction are correlated. Hexobarbital increases the Vmax. of adrenaline oxidation without affecting the Km value, whereas metyrapone, a metabolic inhibitor decreases Vmax. without affecting the Km. From the results obtained, some conclusions about NADPH—cytochrome c reductase function were made.

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