Antioxidant activity of Smoke Shield in-vitro and in-vivo

Smoke Shield is a proprietory formulation containing extract of turmeric (Curcuma longa), obtained by supercritical carbon dioxide gas extraction and post-supercritical hydroethanolic extraction, together with extracts of green tea and other spices whose presence synergistically increases the activity of turmeric. This study evaluates the antioxidant potentials of Smoke Shield in-vitro and in experimental animals, as well as in human models. Smoke Shield was found to scavenge superoxide radicals generated by photoreduction of riboflavin (50% inhibitory concentration = 91 microg mL(-1)) and hydroxyl radicals generated by Fenton reaction (50% inhibitory concentration = 95 microg mL(-1)) and reduced lipid peroxidation. Administration of Smoke Shield to mice was found to elevate antioxidant enzymes such as catalase and superoxide dismutase in blood as well as in liver and kidney. Glutathione-S-transferase activity was found to be significantly elevated in liver and kidney of animals treated with Smoke Shield. Glutathione levels were also significantly elevated in blood. Glutathione reductase was significantly elevated in kidney. Administration of Smoke Shield decreased the lipid peroxidation in serum, liver and kidney, as well as reduced the levels of conjugated dienes and hydroperoxides. Administration of Smoke Shield to smokers was found to increase the superoxide dismutase and glutathione in blood and decrease glutathione peroxidase. Smoke Shield inhibited phase I enzymes as represented by aniline-hydroxylase and aminopyrenedemethylase in-vitro. These results indicate that Smoke Shield has potent antioxidant activity, could inhibit phase I enzymes and increase detoxifying enzymes, which makes it an effective chemoprotective herbal formulation.

Antitumour and anticarcinogenic activity of Phyllanthus amarus extract

Aqueous extract of Phyllanthus amarus (P. amarus) treatment exhibited potent anticarcinogenic activity against 20-methylcholanthrene (20-MC) induced sarcoma development and increased the survival of tumour harboring mice. The extract administration (p.o) was also found to prolong the life span of Dalton's Lymphoma Ascites (DLA) and Ehrlich Ascites Carcinoma (EAC) bearing mice and reduced the volume of transplanted solid tumours. The extract inhibited aniline hydroxylase, a P-450 enzyme. The concentration required for 50% inhibition (IC(50)) was found to be 540 microg/ml. The extract was found to inhibit DNA topoisomerase II of Saccharomyces cerevisiae mutant cell cultures and inhibited cell cycle regulatory enzyme cdc25 tyrosine phosphatase (IC(50-25) microg/ml). Antitumour and anticancer activity of P. amarus may be related with the inhibition of metabolic activation of carcinogen as well as the inhibition of cell cycle regulators and DNA repair.

Effect of Picrorrhiza kurroa extract on transplanted tumours and chemical carcinogenesis in mice

Anti-tumour and anti-carcinogenic activity of Picrorrhiza kurroa extract were studied in mice. Administration of 20-methylcholanthrene (20 MC) produced 100% induction of sarcoma in control mice, whereas the tumour incidence and tumour related deaths were significantly inhibited by the oral administration of P. kurroa extract 150 and 750 mg/kg body weight, respectively. The extract was also found to reduce the volume of transplanted solid tumours induced by Dalton's lymphoma ascites (DLA) tumour cell lines and increased the life span of ascites tumour bearing mice. P. kurroa extract inhibited yeast topoisomerase I and II enzyme activity when tested on Saccharomyces cerevisiae mutant cell cultures. The extract did not inhibit the enzyme involved in the activation of carcinogen and the cell cycle regulatory enzyme cdc2 kinase.

Effect of vitamin E on lipid peroxidation and liver monooxigenase activity in experimental influenza virus infection

Influenza virus infection was associated with development of oxidative stress in liver of mice, viz. increase in amount of lipid peroxidation products, decrease in cytochrome P-450 and NADP. H-cytochrome c-reductase activity, and inhibition of liver monooxygenases (aniline hydroxylase, ethylmorphine-N-demethylase, amidopyrine-N-demethylase and analgin-N-demethylase). These effects were most pronounced on the 7th day after virus inoculation as compared to the 5th one. Supplementation of mice with vitamin E before virus inoculation leads to liver protection against oxidative stress and toxicosis. A marked decrease of lipid peroxidation products and an increase of cytochrome P-450 and activities of monooxygenases was established. The stabilizing effect of vitamin E was dose-dependent and was most pronounced on the 5th day after virus inoculation as compared to the 7th one.

Studies on the cytochrome P450 (CYP)-mediated metabolic properties of miocamycin: evaluation of the possibility of a metabolic intermediate complex formation with CYP, and identification of the human CYP isoforms

Some macrolide antibiotics cause clinical drug interactions, resulting in altered metabolism of concomitantly administered drugs, via the formation of a metabolic intermediate (MI) complex with cytochrome P450 (CYP), or competitive inhibition of CYP. In this study, the possibility of MI complex formation by miocamycin (MOM) was assessed first. CYP contents and activities in rat liver microsomes were not affected and there were no detectable MI complexes after administration of MOM for either 3 or 10 days to rats. Furthermore, MOM did not form MI complexes in vitro even with microsomes from humans or dexamethasone-pretreated rats. Second, in vitro studies were conducted to identify the human CYP isoforms involved in four 14-hydroxylation reactions in the MOM metabolic pathway. The results showed that it was most likely CYP3A4 involved in the hydroxylations: 1) each hydroxylation in human liver microsomes from 10 different donors strongly correlated with testosterone 6 beta-hydroxylation; 2) each hydroxylation was essentially inhibited by ketoconazole and troleandomycin; 3) only cDNA-expressed CYP3A4 and CYP3A5 catalyzed the hydroxylations, and the activities of CYP3A5 were below 5% of those of CYP3A4; and 4) the apparent K(M) values obtained with native human liver microsomes were comparable with those obtained with cDNA-expressed CYP3A4. In conclusion, MOM is not an inhibitor of CYP via the formation of an MI complex. Moreover, CYP3A4 is mainly responsible for catalyzing the hydroxylation of MOM metabolites. Because CYP3A4 is the most abundant form of CYP in the liver and intestine, this isoform probably accounts for the majority of drug-MOM interactions observed in clinical practice.

Antimutagenic and anticarcinogenic potentials of some Thai vegetables

Fifteen kinds of commonly consumed Thai vegetables were sequentially extracted with hexane, chloroform and methanol, and then tested for antimutagenic activities against direct-acting (AF-2 and NaN3) and indirect-acting (AFB1 and B(a)P) mutagens using Ames' Salmonella mutagenicity test with Salmonella typhimurium TA100 as tester strain. It was found that only the methanol extract of neem leaves contain weak antimutagen inhibiting the mutagenicities of both direct-acting mutagens. Interestingly, all vegetables studied were found to contain chemical compounds, mainly nonpolar ones, capable of inhibiting the mutagenicity of AFB1, while only some vegetables contain chemical compounds capable of inhibiting the mutagenicity of B(a)P, which is also an indirect-acting mutagen. Studies on anticarcinogenic potentials demonstrated that Thai bitter gourd fruits, but not sweet basil leaves, at the concentration of 6.25% and 12.5% in the diet, partially inhibited DMBA-induced mammary gland carcinogenesis in female Sprague-Dawley rats when fed to the animals 2 weeks prior to DMBA. Results in the present study therefore demonstrated that most Thai vegetables contain antimutagens inhibiting the mutagenicity of some indirect-acting mutagen, particularly AFB1. The mechanism of their antimutagenicity may probably be the inhibition of the activity of metabolic-activating enzymes in rat liver homogenates. Very interestingly, our results clearly reveal that Thai bitter gourd fruits, which possess Phase II enzymes inducing property, as well as the ability to reduce Phase I enzyme activities in rat liver, contain some anticarcinogens or chemopreventive agents. However, sweet basil leaves that possess both Phase I and Phase II enzyme-inducing properties may not contain any anticarcinogen, at least against DMBA-induced mammary gland carcinogenesis.

Zinc ethylene-bis-dithiocarbamate (Zineb)-mediated inhibition of monooxygenases and lipid peroxidation in bovine liver microsomes

Hepatic bovine microsomes were incubated with Zineb concentrations ranging from 2.5 mM to 2.5 microM. Only the higher concentrations of the fungicide (2.5 and 0.25 mM) elicited a sharp decline in cytochrome P450, cytochrome b5 and total sulphydryl groups content as well as in the activities of NADPH cytochrome c reductase, aminopyrine N-demethylase and aniline 4-hydroxylase. The loss of cytochrome P450 was matched by a concomitant increase in the amount of cytochrome P420, which represents a catalytically inactive form of cytochrome P450. The same concentrations of the fungicide, either alone or in the presence of NADPH 1 mM, failed to increase the amount of thiobarbituric reactive substances with respect to control incubations, thereby excluding the possibility of lipid peroxidation as a contributing factor in the loss of cytochrome P450 and in the inhibition of cytochrome P450-mediated metabolism. It is concluded that Zineb can depress monooxygenase activity in bovine hepatic microsomes mainly through the denaturation of cytochrome P450 and the impaired transfer of reducing equivalents to the complex cytochrome P450-substrate. These mechanisms might also account for the inhibition in lipid peroxidation brought about by the fungicide.

Effects of an immunosuppressive agent, tacrolimus (FK-506), on the activities of cytochrome P-450-linked monooxygenase systems in rat liver microsomes

The effects of an immunosuppressive agent, tacrolimus (FK-506), on the activities of cytochrome P-450-linked monooxygenase systems with respect to three cytochrome P-450 isozymes in rat liver microsomes were investigated. FK-506 non-competitively inhibited the aniline p-hydroxylase, p-nitroanisole O-demethylase and lidocaine N-deethylase activities of cytochrome P-450-linked monooxygenase systems, these activities being mainly catalyzed by cytochromes P-450 CYP2E1, CYP2C11 and CYP3A4, respectively, and the Ki values of the activities for FK-506 were determined to be 605, 491 and 97 microM, respectively. The inhibition of cytochrome P-450-linked monooxygenase systems by FK-506 seemed to involve the direct inhibition of cytochromes P-450 because the NADPH-cytochrome c reductase and NADPH-ferricyanide reductase activities of NADPH-cytochrome P-450 reductase were not affected by the presence of 1 mM FK-506 at all. A spectrophotometric study showed that a reverse type I spectral change was induced on the addition of FK-506 to rat liver microsomes, and the Ks value was apparently 125 microM. On the other hand, the EPR spectra of cytochromes P-450 in rat liver microsomes were not affected by 1 mM FK-506. These results suggest direct interaction between FK-506 and cytochrome P-450 apoproteins, except for the heme iron regions of cytochromes P-450, resulting in inhibition of the drug-metabolism activities catalyzed by cytochromes P-450.

Subanesthetic concentrations of drugs inhibit cytochrome P450-mediated metabolism of aniline

We reported previously that 18 compounds varying in general anesthetic potency by up to 66 000-fold inhibited, at anesthetic concentrations, the metabolism of arachidonic acid and aminopyrine by cytochrome P450 monooxygenases in rat liver microsomes. Now, we report that P450-mediated para-hydroxylation of aniline is more sensitive to the anesthetics. The Ki values for enzyme inhibition for seven compounds were close to and for seven compounds 5-40 times less than their respective anesthetic potencies. Endogenous substrates with an aniline-like binding mode to P450 include histamine and related imidazoles. Acetone and each of the halogenated compounds, halothane, enflurane, and chloroform, stimulated aniline hydroxylase activity at concentrations well below and above their EC50 values. These potent actions on the universal P450 isoenzymes may contribute to pharmacological effects of the anesthetics associated with levels of drug well below concentrations that effect general anesthesia.

Characterization of the independent and combined effects of two inhibitors on oxidative drug metabolism in rat liver microsomes

To evaluate how two inhibitors influence oxidative drug metabolism, this study investigated the inhibitory effects of mexiletine with cimetidine and mexiletine with lidocaine, both individually and in combination, on the oxidative metabolism of two probe substrates, aminopyrine and aniline in rat liver microsomes. Mexiletine was a competitive inhibitor of aminopyrine N-demethylation, whereas cimetidine was a mixed type of inhibitor (Ki = 2.00 +/- 0.04 and 0.20 +/- 0.02 mM, respectively). For aniline hydroxylation, mexiletine exhibited a mixed type of inhibition, whereas lidocaine was a noncompetitive inhibitor (Ki = 0.60 +/- 0.07 and 8.50 +/- 0.12 mM, respectively). The combined inhibition of either mexiletine with cimetidine or mexiletine with lidocaine on aminopyrine and aniline metabolism was close to the fully additive effects of the individual compounds when their individual concentrations were below a 2-fold Ki concentration, regardless of the apparent kinetic inhibition type. The combined inhibition was less than fully additive when the individual concentrations were twice the Ki or above. These results demonstrate that, when two inhibitors of oxidative drug metabolism are combined, both the Ki values and the concentrations of inhibitors play important roles in determining the extent of additive inhibition of enzyme activity.

Tellurite specifically affects squalene epoxidase: investigations examining the mechanism of tellurium-induced neuropathy

A peripheral neuropathy characterized by a transient demyelinating/remyelinating sequence results when young rats are fed a tellurium-containing diet. The neuropathy occurs secondary to a systemic block in cholesterol synthesis. Squalene accumulation suggested the lesion was at the level of squalene expoxidase, a microsomal monooxygenase that uses NADPH cytochrome P450 reductase to receive its necessary reducing equivalents from NADPH. We have now demonstrated directly specificity for squalene epoxidase; our in vitro studies show that squalene epoxidase is inhibited 50% in the presence of 5 microM tellurite, the presumptive in vivo active metabolite. Under these conditions, the activities of other monooxygenases, aniline hydroxylase and benzo(a)pyrene hydroxylase, were inhibited less than 5%. We also present data suggesting that tellurite inhibits squalene epoxidation by interacting with highly susceptible -SH groups present on this monooxygenase. In vivo studies of specificity were based on the compensatory response to feeding of tellurium. Following tellurium intoxication, there was up-regulation of squalene epoxidase activity both in liver (11-fold) and sciatic nerve (fivefold). This induction was a specific response, as demonstrated in liver by the lack of up-regulation following exposure to the nonspecific microsomal enzyme inducer, phenobarbital. As a control, we also measured the microsomal monooxygenase activities of aniline hydroxylase and benzo(a)pyrene hydroxylase. Although they were induced following phenobarbital exposure, activities of these monooxygenases were not affected following tellurium intoxication, providing further evidence of specificity of tellurium intoxication for squalene epoxidase.

Interactions of monoamine oxidase inhibitors, N-acetylenic analogues of tryptamine, with rat liver microsomal cytochrome P450

Interactions between some novel and potent monoamine oxidase inhibitors (MAOIs), acetylenic analogues of tryptamine, and rat liver microsomal cytochrome P450 (P450) as evidenced by visible spectra analysis were analysed. Compounds with a secondary aliphatic amine moiety throughout induced type II difference spectra and exhibited the highest affinity for P450, whereas tertiary amines induced type I spectral changes and showed diminished affinity. P450 dependent aniline hydroxylase activity was inhibited by all compounds in an irreversible time-dependent manner. Only tertiary aliphatic amines constituted the substrate for P450-dependent N-demethylase activity, with comparable kinetic parameters. The N-demethylated metabolites were identified by thin-layer chromatography and mass-spectrometric analyses. These findings describe the role of P450-dependent microsomal mono-oxygenase systems in the metabolism of some MAOI acetylenic tryptamine derivatives and the possible hepatic contribution to adverse interactions between MAOIs, endobiotics and sympathomimetic compounds.

Antimutagenic and mutagenic potentials of Chinese radish

The edible part of fresh Chinese radish was chopped into small pieces, lyophilized, and then extracted sequentially with hexane, chloroform, and methanol. The solvent in each fraction was removed by evaporation under reduced pressure at 50-55 degrees C, and the residue was dissolved in dimethylsufoxide just before being tested for antimutagenicity as well as mutagenicity using the Salmonella/mammalian microsome mutagenicity test. We found that none of the three fractions exhibited any mutagenicity toward S. typhimurium strains TA98 and TA100 when tested either in the presence or absence of S-9 mix. Interestingly, however, hexane and chloroform extracts could strongly inhibit the mutagenicities of both direct mutagens (e.g., 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide and sodium azide) and indirect mutagens (e.g., aflatoxin B1). In contrast, however, these two fractions did not inhibit the mutagenicity of benzo[a]pyrene, which is also an indirect mutagen. Both hexane and chloroform extracts could also markedly inhibit the activities of rat liver aniline hydroxylase and aminopyrine demethylase. The methanol fraction could inhibit neither the mutagenicities of direct or indirect mutagens tested nor the activities of those two rat liver enzymes. Results of the present study demonstrate that Chinese radish may not contain any mutagenic compound but does contain some nonpolar compounds with antimutagenic activity toward both direct and indirect mutagens. In addition, the antimutagenic activity toward aflatoxin B1 may be partly due to the inhibition of enzymes necessary for activation of this mutagen.

The responses of hepatic monooxygenases of guinea pig to cadmium and nickel

When Cd (3.58 mg CdCl2.H2O/kg, ip) was administered to male guinea pigs 72 h prior to sacrifice, the metal significantly inhibited the aniline 4-hydroxylase (AH) (16%), ethylmorphone N-demethylase (EMND) (26%), and aminopyrine N-demethylase (AMND) (18%) activities and cytochrome P-450 (12%) and cytochrome b5 (10%) levels. Cd did not alter the hepatic microsomal heme level. Cd, however, significantly increased the hepatic microsomal p-nitroanisole O-demethylase (p-NAOD) (53%) activity. When Ni (59.5 mg NiCl2 x 6H2O/kg, sc) was administered to the guinea pigs 16 h prior to sacrifice, the metal significantly depressed AH (49%), p-NAOD (66%), EMND (47%), and AMND (37%) activities, and cytochrome P-450 (15%), cytochrome b5 (24%), and microsomal heme (28%) levels. For the combined treatment, animals received the single dose of Ni 56 h after the single dose of Cd and then were killed 16 h later. In these animals, significant inhibitions were noted in AH (51%), EMND (47%), and AMND (30%) activities, and cytochrome P-450 (15%), cytochrome b5 (26%), and microsomal heme (30%) compared to those of controls. In the case of p-NAOD activity, the influence was in favor of Ni, i.e., the inhibition was about 61% by the combined treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of delta-9-tetrahydrocannabinol and theophylline on hepatic microsomal drug metabolizing enzymes

Theophylline (Th) under in vitro conditions stimulated the activities of rat liver microsomal aniline hydroxylase, N-demethylase and O-demethylase, while delta-9-tetrahydrocannabinol (delta-9-THC) inhibited the activities of these hepatic microsomal drug metabolizing enzymes under similar conditions. delta-9-THC-induced inhibition of hepatic microsomal drug metabolizing enzymes was significantly reduced in the presence of Th. Analysis of Lineweaver-Burk plots showed that Th-induced stimulation of hepatic microsomal drug metabolizing enzymes occurs due to an increase in substrate affinity (1/Km) and of Vmax. delta-9-THC-induced inhibition of N-demethylase and O-demethylase is probably due to competition of the drug with the substrates for a common intermediate in the microsomal electron transport chain. Non-competitive and mixed-type inhibition caused by delta-9-THC on aniline hydroxylation appears to be associated with a non-specific action of delta-9-THC. Blocking of delta-9-THC-induced inhibition or reduction of Th-induced stimulation of hepatic drug metabolizing enzymes with Th or delta-9-THC was due to an increase or decrease in either Vmax, substrate affinity (1/Km) or both with respect to the corresponding Km and Vmax observed with delta-9-THC or Th alone.

Stimulatory and inhibitory effects of dimethyl sulfoxide on microsomal aniline hydroxylase activity

Dimethyl sulfoxide (DMSO) at a single dose of 3 ml/kg body wt, administered i.p. to male rats, caused a significant increase in the hepatic microsomal aniline hydroxylase activity. However, the level of cytochrome P-450, the activities of NADPH-cytochrome c reductase, benzphetamine N-demethylase and aminopyrine N-demethylase were unchanged at 24 h post-treatment. DMSO interacted with control rat liver microsomes in vitro and produced a type II spectral change (peak at 420 nm and trough at 392 nm). On the other hand, liver microsomes from DMSO-treated rats gave qualitatively similar spectra, but with a higher magnitude of binding. Liver microsomes from DMSO-treated rats showed a 3.4-fold increase in Vmax for aniline hydroxylase, while Km was found to be the same when compared with control rat liver microsomes. In vitro addition of 6 mM DMSO to microsomal incubations from control and DMSO-treated rats caused a 9-fold and a 25-fold increase in Km, respectively, while Vmax values for aniline hydroxylase were unchanged. When DMSO (6 mM) was incubated with rat liver microsomes in the presence of NADPH, there was formation of formaldehyde. The results suggest an interaction of DMSO with microsomal cytochrome P-450.

Inhibition of microsomal lipid peroxidation and cytochrome P-450-catalyzed reactions by nitrofuran compounds

(5-Nitro-2-furfurylidene)amino compounds bearing triazol-4-yl, benzimidazol-1-yl, pyrazol-1-yl, triazin-4-yl or related groups (a) stimulated superoxide anion radical generated by rat liver microsomes in the presence of NADPH and oxygen; (b) inhibited the NADPH-dependent, iron-catalyzed microsomal lipid peroxidation; (c) prevented the NADPH-dependent destruction of cytochrome P-450; (d) inhibited the NADPH-dependent microsomal aniline 4-hydroxylase activity; (e) failed to inhibit either the cumenyl hydroperoxide-dependent lipid peroxidation or the aniline-4-hydroxylase activity, except for the benzimidazol-1-yl and the substituted triazol-4-yl derivatives, which produced minor inhibitions. Reducing equivalents enhanced the benzimidazol-1-yl derivative inhibition of the cumenyl hydroperoxide-induced lipid peroxidation. The ESR spectrum of the benzimidazol-1-yl derivative, reduced anaerobically by NADPH-supplemented microsomes, showed characteristic spin couplings. Compounds bearing unsaturated nitrogen heterocycles were always more active than those bearing other groups, such as nifurtimox or nitrofurazone. The energy level of the lowest unoccupied molecular orbital was in fair agreement with the capability of nitrofurans for redox-cycling and related actions. It is concluded that nitrofuran inhibition of microsomal lipid peroxidation and cytochrome P-450-catalyzed reactions was mostly due to diversion of reducing equivalents from NADPH to dioxygen. Trapping of free radicals involved in propagating lipid peroxidation might contribute to the overall effect of the benzimidazol-1-yl and substituted triazol-4-yl derivatives.

Effects of cimetidine on drug metabolism in rat pups

The effects of cimetidine on drug metabolism were studied in male and female rat pups and compared to similar effects in adult rats. As in adult rats, cimetidine 50 mg/kg/day i.p. for 7 days in the 2nd, 3rd, 4th or 5th weeks of life resulted in prolonged pentobarbitone sleeping times (diminished pentobarbitone hydroxylase activities), particularly when administered during the 3rd week. These effects of cimetidine were reversible since they continued only up to 2 weeks in males and 4 weeks in females, but by the 6th week were no longer observed. Pretreatment with cimetidine 15, 25 and 50 mg/kg/day i.p. for 7 days, resulted in a dose-dependent inhibition of aminopyrine N-demethylase and aniline hydroxylase as well as a prolongation of pentobarbitone sleeping time in both pups and adults, aniline hydroxylase being the least affected. In general, female pups were more adversely affected than male pups and adults. The therapeutic and toxicological relevance of these results in man are discussed.

Inhibition of rat liver monooxygenase activities by 2-methyl-1,4-naphthoquinone (menadione)

In rat liver microsomes, 2-methyl-1,4-naphthoquinone (menadione) inhibits cytochrome P450 (cyt P450)-mediated aniline-p-hydroxylation and aminopyrine-N-demethylation with Ki values of 12 and 14.5 microM, respectively. The inhibitions of aniline-p-hydroxylation and aminopyrine-N-demethylation are mixed uncompetitive-noncompetitive and mixed competitive-noncompetitive, respectively. NADP antagonizes the inhibitory effect of menadione on aniline-p-hydroxylase activity but not that on aminopyrine-N-demethylase activity. Menadione does not give rise to any spectral change of cyt P450, but modifies the type I binding spectrum induced by aminopyrine. In contrast, menadione does not change the type II binding spectrum induced by aniline. These results indicate that menadione may inhibit aniline-p-hydroxylase activity by acting as a substrate for NADPH-cyt P450 reductase in the place of cyt P450 and inhibit aminopyrine-N-demethylase activity by impairing the binding of aminopyrine to cyt P450.

[The state of the microsomal oxidative system in the rat liver during fecal peritonitis]

Content and activity of cytochrome P-450, activity of main microsomal enzymes as well as content of glycogen, lactic and pyruvic acids were studied in liver tissue of rats within 24, 48 and 72 hrs after simulation of acute fecal peritonitis. Inhibition of the enzymatic activity of microsomal oxidative system correlated with hypoxia which developed in liver tissue within all the periods of acute fecal peritonitis studied. At the same time, catalytic activity of cytochrome P-450 was increased towards substrates of the I and II types. Endotoxemia and hypoxia of liver tissue, resulting in activation of phospholipases, appear to be mainly responsible for inhibition of microsomal enzymes activity in liver tissue under conditions of acute peritonitis.

Mutagenicity and antimutagenicity of Thai medicinal plants

Crude extracts and partially purified as well as purified fractions were prepared from three Thai medicinal plants, namely, Acanthus ebracteatus Vahl, Plumbago indica Linn, and Rhinacanthus nasuthus Kurz, and then tested for their mutagenic and antimutagenic potentials using the Salmonella/microsome mutagenicity test. All fractions tested were not mutagenic toward either strain TA98 or TA100 whether tested in the presence or absence of S-9 mix. Interestingly, however, various fractions--especially those extracted by organic solvents such as petroleum ether, hexane, and chloroform, as well as some purified compounds from these plants--could strongly inhibit the mutagenicity of aflatoxin B1 (AFB1), an indirect mutagen, when tested in the presence of S-9 mix but not that of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), which does not require metabolic activation for its mutagenicity. Furthermore, these fractions could markedly inhibit the activity of rat liver aniline hydroxylase, which is one of the cytochrome-P450-mediated reactions. These results therefore suggest that these Thai medicinal plants contain an antimutagen(s) which inhibits chemical mutagenesis by inhibiting the enzyme activities necessary for activation of indirect mutagens/carcinogens. Identification as well as anticarcinogenicity of purified compounds of these plants are being investigated in our laboratory.

The role of hydrophobicity and electronic factors in regulating alcohol inhibition of cytochrome P-450-mediated aniline hydroxylation

The role of hydrophobicity and electronic factors in regulating alcohol inhibition of cytochrome P-450-mediated aniline p-hydroxylation has been investigated by the formulation of quantitative structure-activity relationships. The activity of linear primary alcohols and unhindered linear secondary alcohols shows a linear dependence on log P, where P is the octanol-water partition coefficient. Hindered primary and secondary alcohols are less active than this relationship predicts. An equation describing the activity of both hindered and unhindered primary and secondary alcohols shows that alcohol inhibition of aniline hydroxylation is regulated by hydrophobicity and steric effects. No role for electronic factors can be discerned. Similarities are found between alcohol inhibition and the binding of alkyl amines to cytochrome P-450, suggesting that alcohols may bind to the amine binding site.

In vitro inhibition of mouse hepatic mixed-function oxidase enzymes by helenalin and alantolactone

The sesquiterpene lactones (STL) helenalin and alantolactone were effective in vitro inhibitors of the mouse hepatic microsomal mixed-function oxidase (MFO) enzymes, aminopyrine demethylase (APD), aniline hydroxylase (ANH) and 7-ethoxyresorufin deethylase (ERD). Helenalin and alantolactone concentrations of 0.5 mM produced a 50-60% inhibition of APD and ERD, and a 20-30% inhibition of ANH. An increase in substrate (aminopyrine) concentration from 0.5 to 25 mM decreased STL inhibition of APD by 12-32%. APD was also inhibited at low aminopyrine concentrations (0.5 mM) by the helenalin derivative 2,3,11,13-tetrahydrohelenalin (tetrahydrohelenalin). The STL produced type I binding spectra with oxidized microsomes; Ks values for helenalin and alantolactone were 161 and 9 microM respectively. These results suggest that STL inhibition of the MFO system results, in part, from STL binding to the substrate-binding site of cytochrome P-450. It has been reported that the irreversible alkylation of protein cysteinyl residues is responsible for STL inhibition of several different enzymes, and second-order rate constants for the reaction of helenalin and alantolactone with glutathione were 25.1 and 1.80 mM-1.hr-1 respectively. Tetrahydrohelenalin did not react with glutathione. However, the subsequent addition of 3.0 mM thiols, i.e. L-cysteine, N-acetylcysteine or glutathione, to STL-treated (0.5 mM) microsomes reversed helenalin and alantolactone inhibition of APD and ERD by 50-80%. The ability of thiols to reverse STL inhibition of APD was decreased 20-43% by the coincubation of STL and microsomes with an NADPH-generating system. In addition, established effects of sulfhydryl-reactive compounds on the MFO system, i.e. inhibition of NADPH-cytochrome c reductase and conversion of cytochrome P-450 to cytochrome P-420, were not observed after addition of helenalin (1.0 mM) or alantolactone (0.5 mM) to mouse hepatic microsomes. These results suggest that STL inhibition of MFO enzymes may not be dependent upon the reactivity of the STL towards sulfhydryl groups. Instead, we suggest that STL binding to the substrate-binding site of cytochrome P-450 and subsequent metabolism of the STL may contribute to inhibition of the MFO system.

Effect of sizofilan, an immunomodulator, on hepatic microsomal mixed-function oxidase activities in rats

Mixed-function oxidase activities of hepatic microsomal preparations from rats were examined after intraperitoneal administration of sizofilan (SPG), an immunomodulator. Repeated doses of SPG (3 mg/kg/12 hr, 4 times) depressed the hepatic cytochrome P-450 content and the activities of aminopyrine N-demethylase and aniline hydroxylase.

Effects in vitro of copper and zinc on hepatic cytochrome P-450 activities

1. In previous studies we have shown that hepatic copper and zinc increases and liver microsomal cytochrome P-450 activities greatly decreases in adjuvant arthritic rats. 2. In the present paper we study if the changes in copper and zinc could be related to depression of drug microsomal activity. Thus, the effect of in vitro addition of copper or zinc to microsomal fraction upon aminopyrine N-demethylase (AND) and aniline p-hydroxylase (APH) activity was measured. 3. Both metals produced an inhibition of enzyme activity. The reduction of AND and APH activities produced by copper (ID25 = 4.7 x 10(-5)M to AND; 1.05 x 10(-5)M to APH) was greater than that obtained with zinc (ID25 = 2.26 x 10(-4)M to AND; 3.3 x 10(-4)M to APH).

Pyrazole is different from acetone and ethanol as an inducer of the polysubstrate monooxygenase system in mice: evidence that pyrazole-inducible P450Coh is distinct from acetone-inducible P450ac

The induction of liver microsomal monooxygenase activities elicited by pyrazole, ethanol, and acetone, all shown to be inducers of rat P450j and rabbit P450LM3a, has been compared in inbred strains of DBA/2N, AKR/J, and Balb/c mouse. Pyrazole strongly increases coumarin 7-hydroxylase (COH) activity in DBA/2N but much less in other strains. The effect of pyrazole on aniline p-hydroxylase and ethanol oxidase activities is also strain dependent: an increase was seen only in the DBA/2N strain. Ethanol and acetone were unable to induce COH, whereas aniline p-hydroxylase and ethanol oxidase were elevated about 1.4- to 3.3-fold in all strains. No strain difference could be detected in aniline p-hydroxylase or ethanol oxidase inducibility. There was a strong correlation between aniline p-hydroxylase and ethanol oxidase activities in every strain, whereas no positive correlation could be found between COH and aniline p-hydroxylase activities. Immunoinhibition experiments showed that a polyclonal antibody against purified pyrazole-inducible COH (P450Coh) blocked about 90% of COH activity, but only about 10% of aniline p-hydroxylase or ethanol oxidase in mouse liver microsomes. Monoclonal antibody 1-91-3 (raised against rat acetone-inducible P450ac) did not inhibit COH, whereas aniline p-hydroxylase was blocked 46-76% and ethanol oxidase 25-70%, depending on the source of microsomes. In immunoblots, anti-P450Coh recognized only its own antigen but not the P450ac, whereas monoclonal antibody 1-98-1 against P450ac detected P450ac and a corresponding form in the D2 mouse liver, but not the P450Coh. The purified P450ac and P450Coh had molecular masses of 52 and 50 kDa, respectively, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These antigens were expressed differentially in response to pyrazole, ethanol, and acetone: P450Coh was increased only after pyrazole treatment, but 1-98-1-detectable protein was elevated in D2 mouse liver microsomes by ethanol and acetone, but not by pyrazole. We conclude that mouse P450Coh and rat P450ac are not corresponding forms of the same isozyme, and that a P450ac-like protein, responsible for most of aniline p-hydroxylation and ethanol oxidation, is present in the D2 mouse liver. These two P450 isozymes are also dissimilarly expressed in the mouse liver in response to inducer administration.

Inhibition of hepatic microsomal drug metabolism by the steroid hydroxylase inhibitor SU-10'603

SU-10'603 is a pyridine derivative that has been widely used as a steroid 17-hydroxylase inhibitor. Studies were done to compare the effects of SU-10'603 with those of the structurally related compound, metyrapone, on hepatic microsomal drug metabolism in vitro in rats and guinea pigs. In rat liver microsomes, SU-10'603 produced a concentration-dependent (0.01 to 1.0 mM) inhibition of ethylmorphine demethylation, aniline hydroxylation, and benzo[a]pyrene hydroxylation. A concentration of 0.1 to 0.2 mM decreased the metabolism of all three substrates by approximately 50%. SU-10'603 was a more potent inhibitor of ethylmorphine metabolism than metyrapone, and its relative potency was even greater with respect to aniline and benzo[a]pyrene metabolism. Similar results were obtained with guinea pig liver microsomes. SU-10'603 and metyrapone produced type II spectral changes in hepatic microsomes, but the apparent affinity of SU-10'603 for cytochrome(s) P-450 was greater than that of metyrapone. Both compounds inhibited the binding of type I substrates to microsomal cytochromes P-450; SU-10'603 was the more potent inhibitor. The results indicate that SU-10'603 is a potent inhibitor of hepatic microsomal monooxygenases whose mechanism of action is similar to that of metyrapone.

Inhibitory effects of ketoconazole and miconazole on cytochrome P-450-mediated oxidative metabolism of testosterone and xenobiotics in mouse hepatic microsomes--comparative study with cimetidine

The inhibitory effects of ketoconazole (KCZ) and miconazole (MCZ), imidazole containing antimycotics, on the hydroxylations of testosterone as a model for endogenous steroids, and the N-demethylation of aminopyrine and the hydroxylation of aniline as models for xenobiotics were compared with those of cimetidine in mouse hepatic microsomes. In vitro, both KCZ and MCZ inhibited these enzyme activities in a dose-dependent manner. The inhibitory potencies of KCZ and MCZ for testosterone hydroxylations and aminopyrine N-demethylation were much greater, with 50% inhibition concentration (IC50) values 2-3 orders of magnitude lower than those of cimetidine, while the potencies of these antimycotics for aniline hydroxylation were similar to that of cimetidine. Although KCZ, MCZ and cimetidine produced type II difference spectra, the difference between the antimycotics (405 nm) and cimetidine (392-405 nm) was found in the trough position of the difference spectra. Spectral dissociation constants (Ks) of these antimycotics (2.2 x 10(-7) - 5.4 x 10(-6) M) were also 1-2 orders of magnitude lower than those of cimetidine (1.3 x 10(-5) - 1.6 x 10(-4) M), and both KCZ and cimetidine had two kinds of Ks, while MCZ had a single Ks. Pentobarbital sleeping time was prolonged in a dose-dependent manner by the i.p. administration of 10-50 mg/kg of KCZ, MCZ or cimetidine, and the potencies for the prolongation of sleeping time decreased in the order of MCZ greater than KCZ greater than cimetidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of liver microsomal monooxygenases and substrate competition with aniline hydroxylase from rats chronically fed low-fat and high-fat-containing alcohol diets

Male Sprague-Dawley rats fed ethanol (EtOH) 36% of total calories for four weeks in a liquid diet containing either 34% (HF) or 12% (LF) of calories as fat were studied with respect to induction of microsomal monooxygenases (MFO) and substrate competition with EtOH-inducible aniline hydroxylase. The specific activity and turnover of aniline hydroxylase were induced to similar extents by HF-EtOH and LF-EtOH diets. Whereas, both LF-EtOH and HF-EtOH caused a decrease in the turnover of arylhydrocarbon (benzo[a]pyrene) hydroxylase (AHH) and aldrin epoxidase compared to pair-fed (PF) controls, LF-EtOH but not HF-EtOH increased the turnover of ethoxycoumarin and ethoxyresorufin O-deethylase (ECOD and EROD). The increase in ECOD and EROD and the decrease in AHH by EtOH is contrary to the parallel induction of these activities by 3-methylcholanthrene (3-MC) and Aroclor 1254 (Aroclor). Benzo(a)pyrene (BaP) stimulated aniline hydroxylase in the HF-EtOH and PF systems, whereas with LF diet, stimulation was seen only in the EtOH group. Ethoxycoumarin (EC) inhibited aniline hydroxylase by microsomes from EtOH- and pyrazole-treated rats, whereas it stimulated aniline hydroxylase by control microsomes, suggesting that the EC effects were associated with EtOH-inducible cytochrome P-450. Ethoxyresorufin (ER) inhibited aniline hydroxylase in EtOH and PF groups, thus the differential effects of EC were not nonspecific O-deethylase effects. The effects of EtOH feeding on ECOD, EROD, and AHH (ie, substrates for 3-MC-inducible cytochrome P-450) displayed a greater differential between the experimental and control group with the LF- than with the HF-containing diet. The findings suggest that the alteration of certain MFO activities by chronic EtOH ingestion can be modified by the content of dietary fat. Moreover, the competition dynamics of MFO substrates toward EtOH-inducible aniline hydroxylase are altered by EtOH feeding and, in turn, modified by dietary fat.

[Functional state of the hepatocyte cytoplasmic network in rats with thermal burns]

Intensity of xenobiotic biotransformation estimated by means of "hexenal" test as well as enzymatic activity in liver microsomes were studied in rats with burns corresponding to impairment of 3%, 10% and 20% of body surface within 1 hr, 1, 3, 6 and 15 days. Soporific effect of hexenal was distinctly increased in the burns, which correlated to the severity of thermic impairment. Activities of amidopyrine-N-demethylase and aniline hydroxylase as well as content of protein, cytochromes P450 and b5 were decreased in liver microsomes. At the same time, lipid peroxidation was activated in microsomes, content of diene conjugates and diene ketones was increased in blood serum and in liver postmitochondrial fraction of experimental animals. Disfunction of hepatocyte cytoplasmic structures appears to be among the factors responsible for a body intoxication in burns.

New heterocyclic modifiers of oxidative drug metabolism--II. Steric factors in the interaction of isomeric 2-(naphthyl)methylbenzimidazoles with rat hepatic microsomal cytochrome P-450 and monooxygenase activities

The inhibitory potency of the two isomeric 2-(naphthyl)methylbenzimidazoles towards three monooxygenase activities (aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and aniline p-hydroxylase) was assessed in hepatic microsomal fractions from untreated, phenobarbitone-induced and beta-naphthoflavone-induced rats. The isomers were essentially equipotent with each other as inhibitors of the phenobarbitone-induced monooxygenases (the ratio of the I50s of the isomers was about 1.0 in each case) but differences between the isomers were noted in the inhibition potencies against three monooxygenase activities from beta-naphthoflavone-induced liver. The isomer 2-(1'-naphthyl)methylbenzimidazole was approximately twice as potent as the 2'-naphthyl isomer against 7-ethoxyresorufin O-deethylase activity, whereas the opposite was observed with respect to 7-ethoxycoumarin O-deethylase inhibition; aniline p-hydroxylase was poorly inhibited by both isomers. The binding affinity and extent of binding, assessed from double-reciprocal plots of spectral binding studies, of the 1'-isomer was much greater than that of the 2'-isomer in beta-naphthoflavone-induced microsomes. Inhibition data in untreated hepatic microsomes were more complex and the finding of principal interest was that the 1'-isomer was poorly inhibitory towards aniline p-hydroxylase activity whereas the 2'-isomer enhanced this activity. These studies suggest that the steric conformations of the isomeric naphthylmethylbenzimidazoles at the cytochrome P-450 active centre determines the extent to which the inhibitors modulate a specific monooxygenase activity, and that multiple binding sites with the capacity to interact to different extents with benzimidazole derivatives are present in P-450 in beta-naphthoflavone-induced hepatic microsomes. The apparent importance of steric conformation as a determinant of inhibition and enhancement of aniline p-hydroxylase in untreated microsomal fractions may well reflect specific interactions with multiple binding sites.

Interaction of miconazole, ketoconazole and itraconazole with rat-liver microsomes

The interaction of the antimycotics miconazole, ketoconazole and itraconazole with liver microsomes from untreated rats or from rats pretreated with phenobarbital or 3-methylcholanthrene, gave rise to type II difference spectra. The interactions of the antimycotics with control, phenobarbital-induced or 3-methylcholanthrene-induced microsomes were biphasic, except for the monophasic binding of ketoconazole to phenobarbital-induced microsomes. The N-demethylation of N,N-dimethylaniline, the O-demethylation of p-nitroanisole and the hydroxylation of aniline in microsomes from untreated and inducer-treated rats were lowered by miconazole and ketoconazole, the former being the more potent inhibitor. Control microsomes were less sensitive than induced microsomes. Itraconazole was almost devoid of inhibitory properties. The three antimycotics were non-competitive (mixed) inhibitors of enzyme activities in phenobarbital-induced microsomes. The Ki values were of the same order of magnitude as the Ks values, except for itraconazole. For the latter drug, Ki values were much greater than could be expected from the spectral studies. It is concluded that the antimycotics affect microsomal enzyme activities via a direct interaction of an azole-nitrogen with the haem group of cytochrome P-450. The interaction with mammalian cytochrome P-450 decreases from miconazole greater than ketoconazole much greater than itraconazole and is much weaker than the interaction of the antimycotics with yeast cytochrome P-450.

The effects of cyclosporin A (CsA) on hepatic microsomal drug metabolism in the rat

The effects of cyclosporin A (CsA), a powerful immunosuppressant, on the hepatic microsomal mixed function oxidase (MFO) system was studied in male rats. Difference spectroscopy studies indicated that CsA binds to cytochrome P-450 producing a type I spectral change. To investigate potential interactions with the MFO system, CsA was administered orally at doses of either 25 mg/kg or 50 mg/kg once daily for 9 days. Various metabolic parameters were examined, including: levels of microsomal protein, cytochrome P-450, and cytochrome b5, NADPH-cytochrome c reductase activity, N-demethylation of ethylmorphine (ETM), and p-hydroxylation of aniline (ANL). Rats treated with 50 mg/kg showed a 25% or greater decrease over controls in all parameters examined except microsomal protein and cytochrome b5 levels. Rats treated with 25 mg/kg showed a 28% or greater decrease in all parameters except microsomal protein, cytochrome b5, and cytochrome P-450. Kinetic studies of ETM-N-demethylase and ANL-hydroxylase activities were conducted either with microsomes prepared from CsA-treated animals (50 mg/kg/day for 5 days) or with pooled microsomes prepared from untreated animals to which CsA was added directly. Enzyme reaction velocities were measured and apparent KM and apparent Vmax were determined. Studies with CsA-treated animals revealed a 57% decrease in both KM and Vmax for ETM-N-demethylase, and a 46% decrease in KM and a 32% decrease in Vmax for ANL-hydroxylase. Studies involving direct addition of CsA to microsomes at final concentrations of 0.01 mM and 0.10 mM revealed no significant changes in apparent KM or Vmax for either enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Triphenyl tin hepatotoxicity in rats

Hepatic microsomal aniline hydroxylase and aminopyrine N-demethylase in vitro activities and the biliary excretion of sulfobromophthalein (BSP) were significantly reduced in rats treated with triphenyl tin (TPT) in daily doses of 1 mg/kg i.p. for 3 days. Bile flow, liver weight, serum enzyme activities, and hepatic sulfhydryl groups and thiobarbituric reactant levels were unaffected in TPT-treated animals. Moreover, TPT failed to induce any appreciable change in the biliary excretion of both the organic base procainamide ethobromide and the organic acid amaranth which is excreted into the bile in the unmetabolized form. TPT has been shown to be an effective inhibitor of rat liver glutathione-S-transferase activity. Reduced conjugation with glutathione may play a role as a factor determining the low rate of biliary BSP excretion in the TPT-treated rats.

In vivo and in vitro inhibition of hepatic microsomal drug metabolism by ketoconazole

Ketoconazole (KC), a broad spectrum antifungal drug, has been recognized recently as a cause of hepatic injury. The mechanism of the adverse reaction remains unclear: a metabolic idiosincrasy has been suggested. However as a substituted imidazole, KC might be expected to interfere with the hepatic microsomal mixed function oxidases. Ethylmorphine N-demethylase (E-DM) and aniline hydroxylase (A-OH) activities were determined in rat liver microsomes in the presence of increasing amounts of KC. Both were inhibited in an exponential fashion. The E-DM inhibition was almost complete at concentrations greater than 250 microM and was of the mixed type. A much weaker effect was observed for A-OH. A significant inhibition of E-DM was also observed when KC was administered in vivo to rats either orally for 7 days at the dose of 100 mg/kg/day (P less than 0.02) or intraperitoneally for 4 days at the dose of 50 or 100 mg/kg day (P less than 0.01 or P less than 0.001 respectively). A-OH activity was significantly reduced (P less than 0.01) only after ip administration of 100 mg/kg/day of the drug for 4 days. Neither the amount of cytochrome P-450 nor NADPH cytochrome c reductase activity were affected at the doses considered. These data show that KC interferes with hepatic oxidative drug metabolism and suggest that this mechanism might be involved in the unwanted side effects of therapy with KC.

The mechanism of inhibition by 2,2'-pyridylisatogen tosylate of NADPH-linked enzyme activities in microsomes isolated from rat liver

Microsomal preparations isolated from rat liver were used to study the action of 2.2'-pyridylisatogen tosylate (PIT) on aniline hydroxylation, cytochrome c reduction and NADPH oxidation. PIT was found to inhibit both the NADPH-dependent (5-100 microM, PIT) and the NADPH-independent (0.05-2.5 mM, PIT) hydroxylation of aniline, but had no significant effect on either the NADPH-dependent oxidation of hexobarbital, or the NADPH-independent hydrolysis of glucose-6-phosphatase. PIT was also found to inhibit cytochrome c reductase competitively (Ki = 35 microM) and to stimulate NADPH oxidation (ED50 = 6.5 microM) PIT and aniline were both found to bind to the microsomal haemoprotein cytochrome P-450 and produce Type II spectral changes. It is proposed that PITs ability to bind to the haemoprotein and its ability to accept electrons from the microsomal NADPH-cytochrome c reductase system leads to the inhibition of aniline hydroxylase activity.

Effects of the interferon inducing agents tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC) on the hepatic monooxygenase systems of the developing neonatal rat

This paper describes the effects of the interferon inducing agents tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC) on the postnatal development of hepatic cytochrome P-450-linked monooxygenase systems of male rats from birth through early adolescence. The administration of tilorone to rats on days 1 and 2 postpartum modified the changes in the activities of hepatic monooxygenase systems that occur normally during the first four days postpartum. Thus, aniline hydroxylase activity, which develops very rapidly during the first 2 days postpartum, was depressed markedly by tilorone, ethylmorphine N-demethylase activity was depressed moderately, and benzo[a] pyrene hydroxylase, normally the slowest of the three monooxygenase activities to develop, was induced. These changes in monooxygenase activities occurred without a significant change in the cytochrome P-450 content. These observations suggest that not all species of neonatal cytochrome P-450 are affected equally by tilorone administration. By day 7 postpartum, the cytochrome P-450 content and all three monooxygenase activities were depressed in rats that had received tilorone on days 1 and 2 postpartum. All three monooxygenase systems were depressed by the administration of a single dose of poly IC (10 mg/kg) in 1-, 2-, 21-, 28- and 56-day-old rats. The length of the period between maximal depression and complete recovery of cytochrome P-450 systems was shown to be a function of the age of the rat; it increased from about 6 hr in 1-day-old rats to 48 hr in 56-day-old rats. Protein is synthesized more rapidly and degraded more slowly in neonate than in adult animals; this may account for the more rapid recovery of poly IC-induced depression of monooxygenase systems in neonates.

Effect of prostacyclin on the mixed function microsomal oxigenase system in the rat liver

The microsomal fraction of the liver was studied for protein and cytochrome P450 contents as well as for aminopyrine-N-demethylase and aniline-hydroxylase activity and for its BIC spectrum under the effect of PG-I2 treatment. A significant increase was found in the cytochrome P450 content after short term treatment, while continuation of PG-I2 administration caused a significant and long lasting decrease of cytochrome P450. After prolonged application of PG-I2 the aniline-hydroxylase content decreased significantly, while the aminopyrine-N-demethylase enzyme showed no change. The BIC spectrum after 80 days PG-I2 treatment significantly decreased in the 431-432 nm region, corresponding to the decrease of cytochrome P450. Long term PG-I2 application caused no detectable ultrastructural changes in the liver.

The interaction of arylalkybenzimidazoles and related compounds with microsomal oxidation

A series of 2-arylalkyl- and 2-(4'-alkyl)phenoxymethylbenzimidazoles was synthesized and evaluated as inhibitors of mixed-function oxidase activity in phenobarbitone- and beta-naphthoflavone-induced rat liver microsomes. Higher homologues of the 2-arylalkyl series were more potent inhibitors than lower homologues against all mono-oxygenase activities except aniline p-hydroxylation. Smaller 2-substituents were associated with relatively low-affinity reverse type I spectral binding behaviour, whereas larger substituents were associated with type I binding of high affinity.

[Comparative inhibitory analysis of aniline hydroxylation by cytochrome P-450 in NADPH-, hydroperoxide cumyl- and H2O2-dependent systems]

The p-hydroxylation of aniline in the presence of liver microsomes and isolated cytochrome P-450 in NADPH-, H2O2- and cumyl hydroperoxide (CHP)-dependent systems was investigated. A comparative inhibitory analysis of these reactions was carried out. It was shown that the mechanism of the H2O2-dependent hydroxylation reactions is similar to that of the NADPH-dependent monooxygenase reactions and, consequently, this model system should be preferably used for the study of the mechanisms of aniline hydroxylation reactions instead of the CHP-dependent system. Since the kcat value for the H2O2-dependent system is much higher than that for the NADPH- or CHP-systems, it may be assumed that when H2O2 is used as a cosubstrate for this reaction, the true value of the degradation constant for the cytochrome P-450--O2(2-)--aniline peroxycomplex can be measured.

Inhibition of hepatic azo-reductase and aromatic hydroxylase by radiopharmaceuticals containing tin

Mice given single i.v. doses of some radiopharmaceuticals containing stannous chloride as a reducing agent, showed significant inhibition of hepatic azo-reductase and aromatic hydroxylase activity at dose levels which contained as little as 0.2 mg/kg of stannous chloride. Cytochrome P-450 content was also reduced significantly. Some of the above radiopharmaceuticals would have to be injected at approx. 10 times the maximum recommended human dose to reach a 0.2 mg/kg dose level of stannous chloride in man, provided other sources of stannous ion were excluded.

Inhibitory effect of phenelzine on oxidative microsomal enzyme systems of rat liver

The inhibitory effects of phenelzine on the hepatic microsomal demethylation of aminopyrine, N,N-dimethylaniline, and p-nitroanisole on the hydroxylation of aniline and on the pharmacokinetics of antipyrine were investigated in the rat. Phenelzine produced a competitive and noncompetitive inhibition of the demethylation of p-nitroanisole and N,N-dimethylaniline, respectively, but was a mixed-type inhibitor of the aminopyrine N-demethylase and aniline hydroxylase. The inhibition constant, Ki, varied between 0.06 to 0.25 mM depending on the substrate used. Preincubation of phenelzine for 30 min with the microsomal homogenate prior to substrate addition doubled its inhibitory effect. Phenelzine induced a type II spectral change when combined with oxidized cytochrome P-450 with a Ks value of 0.4 mM. The administration of one dose of 50 mg X kg-1 of phenelzine sulfate concomitantly with 50 mg X kg-1 of antipyrine resulted in a significant decrease of the serum elimination of antipyrine. The serum half-life, apparent volume of distribution, and total body clearance of antipyrine were modified to 3.6 h, 294.1 mL X kg-1, and 56.8 mL X h-1 X kg-1, respectively, from 1.5 h, 666.7 mL X kg-1, and 312.5 mL X h-1 X kg-1 when antipyrine was administered alone. It is concluded that the inhibitory effect of phenelzine on the microsomal oxidative reactions of rat liver is related to its interaction with cytochrome P-450.

Inhibition of hepatic drug metabolism in the rat after Corynebacterium parvum treatment

Drug-metabolizing enzyme activities, cytochrome concentration, and protein content of hepatic microsomal preparations from adult, female Sprague-Dawley rats were examined at 1-, 3-, 6-, 10-, 14- and 17-day intervals after administration of a single intravenous injection of Corynebacterium parvum (C. parvum) at a dose of 10 mg/m2. Aniline hydroxylase (AH) activity, aminopyrine demethylase (APD) activity, and cytochrome P-450 concentration were reduced 20-50% on days 3-6 and, thereafter, gradually recovered to control levels by day 17. Cytochrome c reductase activity and cytochrome b5 concentration were reduced significantly (24%) only on day 10. Microsomal protein concentration was unchanged. C. parvum added in vitro had no effect on AH or APD activity. Although livers of treated rats were only slightly (less than 20%) enlarged, gross splenomegaly was apparent, reaching a maximum on day 6. A marked inverse correlation existed between the temporal variation in the size of the spleen and APD activity. In rats killed 6 days after administration of C. parvum at 0.67 to 10.00 mg/m2, a direct relationship was apparent between the adjuvant dose and the magnitude of reduction of APD activity. A similar relationship was apparent between splenomegaly and APD activity. Histopathologic examination of liver sections from treated rats revealed numerous granulomas throughout the parenchyma. The magnitude of enzyme inhibition generally paralleled the severity of the hepatic lesions.

Effect of chloramphenicol on hepatic mitochondrial and microsomal functions in protein-energy malnourishment

In both protein-energy malnourished (PEM) and normal rats, chloramphenicol (7.5 mg/kg) competitively inhibits the activities of aniline hydroxylase and p-aminopyrine N-demethylase. The decrease in enzyme activities was very much less in PEM rats. In both groups of animals, chloramphenicol also lowered the respiratory control ratio (RCR) of mitochondria. However, as with the microsomal function, the decrease in mitochondrial RCR in PEM rats (18.2%) was much less than that (45.8%) in normal rats. These results suggest that the toxic effects of chloramphenicol could be less in PEM conditions.

Inhibition of microsomal drug metabolism by mitochondria and cytochrome c oxidation of extramitochondrial NADPH

Microsomal aniline p-hydroxylase and aminopyrine N-demethylase activities were inhibited by mitochondria. The magnitude of the inhibition increased in parallel with the amount of added mitochondria. The inhibition was reverted by 0.2 mM KCN. Marked inhibition of these microsomal enzyme activities was observed also in the presence of cytochrome c and low amounts of mitochondria causing negligible inhibition in themselves. The inhibition increased with the concentration of cytochrome c and it was reverted by KCN. Microsome-free mitochondria did not oxidize NADPH even in the presence of cytochrome c, although NADH oxidation has been demonstrated under these circumstances [Sottocasa et al., J. cell Biol. 32, 415, (1967)]. However, completion of the system by addition of microsomes resulted in the oxidation of NADPH, which was inhibited by KCN. These findings may indicate the cooperation of the microsomal and mitochondrial compartments in the regulation of drug metabolism.

Evoked effects of oestradiol on hepatic cholesterol 7 alpha-hydroxylase and drug oxidase in castrated rats

1. Oestradiol administration in castrated rats resulted in an increased activity of the cholesterol 7 alpha-hydroxylase and a decreased activity of the drug oxidase enzyme systems. 2. Aqueous solutions of oestradiol (up to 25.10(-6)M) incubated in vitro with microsomes, binds into the microsomal membrane framework reducing the activity of both enzyme systems. 3. The specific activity of cholesterol 7 alpha-hydroxylase, drops after 3 hr preincubation with oestradiol to at least 70% of its original value. 4. Actinomycin D and cycloheximide administration reduced the oestradiol-induced and control cholesterol 7 alpha-hydroxylase activity to the same level, 6 hr after the injections.