Rat Hepatic Mixed-function Oxidases Research Articles

Effect of a perfluorochemical emulsion on the rat hepatic mixed function oxidase system.

The perfluorochemical components of synthetic oxygen transporting emulsions may persist in hepatic tissue. After a single 30% blood exchange with the perfluorochemical emulsion, Fluosol-DA 20%, the effects on the microsomal metabolism of 7-methoxycoumarin and 7-ethoxycoumarin were studied over a 9-week period. Fluosol-DA treated animals were compared with controls (sham) and hetastarch-treated controls. Changes in dealkylase activities were compared with induction by phenobarbitone and 3-methylcholanthrene. The liver to body weight ratio increased by 49% in Fluosol-DA-treated rats over the controls at 1 week and the microsomal protein was increased in the Fluosol-DA-treated rats after 4 and 9 weeks. Fluosol-DA treatment induced 7-methoxycoumarin demethylase with peak differences occurring at 1 week and a Vmax 75% greater than controls. Fluosol-DA was a more potent inducer of demethylase than phenobarbitone. In addition, 7-ethoxycoumarin de-ethylase was induced by Fluosol-DA with a peak induction at 4 weeks. The Vmax at 4 weeks in Fluosol-DA-treated rats was 122% greater than control. In this case, Fluosol-DA produced less induction in de-ethylase than 3-methylcholanthrene. These studies show that Fluosol-DA induces more than one form of cytochrome P450 and the effects resemble those of phenobarbitone more than those of 3-methylcholanthrene. Hetastarch, a plasma expander, did not affect liver weights, microsomal protein content, or the cytochrome P450 system.

Induction of rat hepatic mixed-function oxidases by acetone and other physiological ketones: their role in diabetes-induced changes in cytochrome P450 proteins.

1. To evaluate the role of ketone bodies in diabetes-induced changes in hepatic cytochrome P450 composition, rats were treated with acetone, 3-hydroxybutyrate or 1,3-butanediol. 2. Treatment with acetone enhanced the rat hepatic O-dealkylations of ethoxyresorufin and methoxyresorufin, and the hydroxylation of p-nitrophenol, but had no effect on lauric acid hydroxylation and ethylmorphine N-demethylation. Neither 3-hydroxybutyrate nor 1,3-butanediol modulated the metabolism of the above substrates. 3. Immunoblot analysis of hepatic microsomal proteins revealed that treatment with acetone increased the apoprotein levels of P4501A2, P4502B1/2 and P4502E1. 4. It is concluded that acetone is responsible, at least partly, for the diabetes-induced increase in hepatic microsomal P4501A2, P4502B1/2 and P4502E1 proteins but does not mediate the increases in the P4503A1 and P4504A1 proteins. On the basis of work from our own and other laboratories a mechanism for the diabetes-induced changes in hepatic cytochrome P450 proteins is proposed.

Feprazone: An inducer of the P450 II B family of proteins in the rat

The ability of feprazone to induce the hepatic microsomal mixed-function oxidases was investigated in the rat, with emphasis being placed on the nature of the cytochrome P-450 family induced. Treatment with feprazone enhanced the p-hydroxylation of aniline and the dealkylations of benzphetamine and pentoxyresorufin but had no effect on the O-deethylation of ethoxyresorufin. The same treatment had no major effect on total cytochrome P-450 levels but increased the spectral interaction of metyrapone with reduced cytochrome P-450. Immunoblots employing monospecific polyclonal antibodies revealed that feprazone induces the apoprotein levels of the P450 II B, but not of the P450 I, family. It is concluded that feprazone is an inducer of the rat hepatic mixed-function oxidase system showing selectivity toward the P450 II B family.

In vivo and in vitro effect of phenytoin on rat hepatic mixed function oxidases

We have investigated the effect of phenytoin on the activity of aniline hydroxylase (AH*) and aminopyrine N-demethylase (APN-D) to see if early exposure to phenytoin could affect the capability of neonates to handle xenobiotics

Effect of vitamin A on rat hepatic mixed-function oxidases, glutathione transferase activity and generations of oxygen radicals.

Rat hepatic microsomal mixed-function oxidase activities were not significantly affected by vitamin A deficiency. Similarly cytosolic glutathione S-transferase and glutathione reductase activities as well as total glutathione levels were unaffected by the vitamin A status. Induction of the mixed-function oxidases by 3-methylcholanthrene or phenobarbitone was independent of the vitamin A status. No significant differences in microsomal chemiluminescence, before and following challenge with tertiary butyl hydroperoxide, were evident between the vitamin-A-deficient animals and those maintained on vitamin-A-supplemented diets. The present findings indicate that the protective action of vitamin A against chemical carcinogens is unlikely to involve modulation of the enzyme systems responsible for their metabolism.

Lack of hepatic microsomal metabolism of deoxynivalenol and its metabolite, DOM-1

Rat hepatic microsomal preparations were used to study the metabolism of deoxynivalenol (DON) and its metabolite 3α,7α,15-trihydroxytrichothec-9,12-dien-8-one (DOM-1). The N-demethylation of ethylmorphine was monitored to assess the viability of the mixed-function oxidase. DON was incubated with microsomes and an NADPH-generating system. Samples were removed from the incubation system and analysed for DON using an HPLC equipped with a UV detector. After incubation for 30 min, there was no evidence of disappearance of DON or of the presence of new metabolites; neither was microsomal NADPH oxidation altered by the addition of DON. Rat and pig hepatic microsomal preparations were used to assess DON glucuronidation, using p-nitrophenol disappearance to check the viability of the microsomal glucuronidating system. When DON was incubated with microsomes and 14C-labelled uridine 5′-diphosphoglucuronic acid, no radioactivity was detected in the TLC zone where the glucuronide was expected. Three rats and one pig were dosed orally with 2 mg DON/kg and samples of their urine and faeces were extracted and incubated with β-glucuronidase or with buffer only. No differences in DON or DOM-1 concentrations were detected between samples incubated with or without β-glucuronidase. These results suggest that DON was neither bioactivated to a more toxic product nor oxidized to a less toxic compound by the rat hepatic mixed-function oxidase system. Likewise, DOM-1 was not reactivated or metabolized by this system. Neither DON nor DOM-1 glucuronides were formed either in in vitro liver systems or in vivo.

Induction of rat hepatic mixed function oxidases by aromatic amines and its relationship to their bioactivation to mutagens

Hepatic microsomal mixed-function oxidase activities were determined in rats pretreated with the aromatic amines 2-aminoanthracene, 2-naphthylamine or 4-aminobiphenyl. All three amines stimulated the O-deethylation of ethoxyresorufin (cytochromes P-448) but none had any effect on the p-hydroxylation of analine. 2-Aminoanthracene and 4-aminobiphenyl also stimulated the NADPH-dependent reduction of cytochrome c and 2-naphthylamine inhibited the N-demethylation of benzphetamine. Hepatic preparations from animals pretreated with 2-aminoanthracene were more efficient in converting this carcinogen to mutagens while in contrast pretreatment with Aroclor 1254 caused a marked decrease in mutagenicity. 4-Aminobiphenyl also enhanced its own activation but Aroclor-pretreated preparations were the most effective. The latter preparations were also more efficient than controls in activating 2-naphthylamine to mutagens. It is concluded that 4-aminobiphenyl and 2-aminoanthracene enhance their own activation at least partly, by inducing the synthesis of cytochromes P-448.

Effect of 2-aminoanthracene and 4-aminobipheny I administration on their activation to mutagens and on rat hepatic mixed-function oxidases

Conference Article| February 01 1986 Effect of 2-aminoanthracene and 4-aminobipheny I administration on their activation to mutagens and on rat hepatic mixed-function oxidases CHRISTINE M. STEELE; CHRISTINE M. STEELE 1Department of Biochemistry, University of Surrey, Guildford GU2 5XH, Surrey, U.K. Search for other works by this author on: This Site PubMed Google Scholar COSTAS IOANNIDES COSTAS IOANNIDES 1Department of Biochemistry, University of Surrey, Guildford GU2 5XH, Surrey, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1986) 14 (1): 99–100. https://doi.org/10.1042/bst0140099 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation CHRISTINE M. STEELE, COSTAS IOANNIDES; Effect of 2-aminoanthracene and 4-aminobipheny I administration on their activation to mutagens and on rat hepatic mixed-function oxidases. Biochem Soc Trans 1 February 1986; 14 (1): 99–100. doi: https://doi.org/10.1042/bst0140099 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1986 Biochemical Society1986 Article PDF first page preview Close Modal You do not currently have access to this content.

Specificity of medicarpin and related isoflavonoids in inhibition of rat hepatic mixed function oxidase activity.

The cytochromes P-450 of the mixed function oxidase system metabolize a wide variety of endogenous compounds to either nontoxic products or toxic metabolites. A number of natural products, such as flavonoids, influence this metabolism. Exposure to these compounds may therefore be a factor in animal and human responsiveness to cytochrome P-450 substrates. We have examined the effect of the pterocarpan medicarpin on the cytochrome P-450-dependent aryl hydrocarbon hydroxylase (AHH) and ethoxycoumarin deethylase (ECD) activities of rat liver microsomes. Medicarpin and maackiain and two of their biosynthetic precursors inhibit the constitutive and phenobarbital (PB)-induced types of AHH, but have little effect on the 3-methylcholanthrene (MC)-induced type of AHH. This is in contrast to the effect of the commonly used cytochrome P-450 inhibitor 7,8-benzoflavone, which inhibits the hepatic AHH of MC-treated rats and has no effects on the AHH of control or PB-treated rats. However, medicarpin inhibited the constitutive as well as the PB- and MC-induced ECD. The specific modulatory effect as well as its relative availability suggests the utility of medicarpin as a probe for different forms of cytochrome P-450 in animal tissues.

Inhibition of rat hepatic mixed function oxidases by antimalarial drugs: Selectivity for cytochromes P-450 and P-448

Intraperitoneal administration of chloroquine, primaquine and quinacrine to rats resulted in inhibition of the hepatic microsomal mixed-function oxidases. The N-demethylation of benzphetamine (cytochrome P-450) was inhibited by chloroquine only while the O-deethylation of ethoxyresorufin (cytochrome P-448) was inhibited by primaquine and quinacrine. When incubated with hepatic microsomes from phenobarbital-pretreated rats, chloroquine and primaquine, but not quinacrine, caused a concentration-dependent inhibition of benzphetamine N-demethylase activity. Incubation of hepatic microsomes from β-naphthoflavone rats with primaquine and quinacrine, but not chloroquine, resulted in a concentration-dependent inhibition of the O-deethylation of ethoxyresorufin. These observations demonstrate that chloroquine and quinacrine are specific inhibitors of cytochromes P-450 and P-448, respectively.

Effect of aging on response to induction and metabolizing activity of the hepatic mixed-function oxidase system of male Sprague-Dawley rats.

The composition and activity of the rat hepatic mixed-function oxidase system were investigated, in male rats 17 to 127 weeks old, with respect to content of its various components and their response to induction by phenobarbital and beta-naphthoflavone. There were decreases in many of the components of this enzyme system in older rats which could not be fully compensated by phenobarbital induction. However, there appeared to be no age-related loss of response to induction by beta-naphthoflavone. Decreases in mixed-function oxidase enzymes with age did not occur at the same rate or to the same extent. Metabolic studies with ethylmorphine and aniline demonstrated some age-associated changes which did not necessarily parallel reductions in the enzyme system. For example, there was a reduction in apparent Km as a function of age for the hydroxylation of aniline in rats treated with beta-naphthoflavone, even though they showed no apparent change in the amount of cytochrome P-450. There was also a trend to altered Km for the demethylation of ethylmorphine in saline or corn oil treated rats in older animals. We feel that these changes are a reflection of differential reductions in the various isoenzymes of cytochromes P-450. Further studies are planned to confirm this hypothesis.

Effect of stannous fluoride and sodium fluoride on hepatic mixed-function oxidase activities in the rat

Alterations in rat hepatic mixed-function oxidase activities were measured in vivo and in vitro 20 hr after pretreatment with a single dose of stannous fluoride or sodium fluoride. SnF 2 pretreatment significantly decreased the N-demethylation of aminopyrine and O-demethylation of p-nitroanisole; whereas, NaF in an equimolar dose did not affect N-demethylation but did decrease O-demethylation. Hexobarbital sleeping time was significantly prolonged by SnF 2 but not by NaF. Furthermore, the elimination half-life of antipyrine was increased by SnF 2 but not by NaF. These results demonstrate that the inhibition by SnF 2 of hepatic mixed-function oxidase activities in the rat is primarily due to the stannous ion and that fluoride ion has very little affect on these enzyme activities.

Changes in the rat hepatic mixed function oxidase system associated with chronic ethanol vapor inhalation

Chronic ethanol vapor inhalation by rats increased hepatic microsomal aniline hydroxylase activity, increasing the turnover number and decreasing the K m. Activity of ethanol-induced microsomes toward other substrates was also examined. The increase in aniline hydroxylase activity as a result of ethanol treatment is attributed to an increase in a form of cytochrome P-450 with a high specific activity toward aniline. Since the ethanol effect on aniline hydroxylation had disappeared 24 hr after treatment was discontinued, a high rate of turnover of this enzyme was deduced. Dimethylsulfoxide (56 mM) produced a reverse type I spectral change in ethanol-induced, but not in control, microsomes. This was interpreted as being due to a change in the spin state of the cytochrome P-450 in these microsomes. Acetone added to the incubation produced an increased rate of aniline hydroxylation by microsomes from control and ethanol-induced rats. The difference between the rate of aniline hydroxylation by control microsomes and the rate by ethanol-induced microsomes was, however, abolished at higher acetone concentrations.

The Effect of Dietary Protein Depletion and Repletion on Rat Hepatic Mixed Function Oxidase Activities

The Effect of Dietary Protein Depletion and Repletion on Rat Hepatic Mixed Function Oxidase Activities

Effect of alteration of rat hepatic mixed-function oxidase (MFO) activity on the toxicity of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD)

The effect of alteration of the activity of the hepatic mixed-function oxidase (MFO) enzyme systems on the toxicity of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in rats has been examined. These experiments have indicated the naturally occurring age and sex-related differences in hepatic MFO activity in rats are inversely correlated with the 20-day LD50 of TCDD in these animals. The effect of administering inducers and inhibitors of the hepatic MFO enzyme systems on the 20-day LD50 of TCDD in rats has also been examined. In all cases there was an inverse relationship between the activity of the hepatic MFO system at the time of TCDD administration and the toxicity of TCDD as determined by the 20-day LD50.

Effect of morestan and other substituted quinoxalines on the activities of various rat hepatic mixed-function oxidases

Morestan (6-methyl-2,3-quinoxalinedithiol cyclic-S,S carbonate) and two of its metabolites: methyl-2,3-quinoxalinedithiol and 6-methyl-2,3-quinoxalinedihydroxy were administered to male and female rats by intraperitoneal route for 4 consecutive days (50 mg/kg/daily). Morestan was also administered by esophageal intubation for 4 days at the dose of 75 mg/kg/daily. After evaluating the pentobarbital sleeping time in the animals on the 5th day, aminopyrine N-demethylase, p-nitroanisole O-demethylase and aromatic aniline hyroxylase activities and levels of cytochrome P450, proteins and RNA were measured in the microsomal hepatic fraction. Protein and nucleic acid levels were also measured in whole liver. The 3 substances studied caused considerable decreases in activity of certain microsomal enzymes: morestan inhibits some hepatic mixed-function oxidase systems; in females it is more active by peroral administration, and in males by intraperitoneal route. However, 6-methyl-2,3-quinoxalinedithiol is an even more powerful inhibitor of monooxygenase activities both in males and females. 6-methyl-2,3-quinoxalinedihydroxy also decreases activity by microsomal enzymes, but its action is inferior to that of the other two products investigated.

Effect of mirex on the activities of various rat hepatic mixed-function oxidases.

Mirex (dodecachlorooctahydro-1,3,4-metheno-2H-cyclobuta[cd]pentalene) was orally administered to male and female rats at daily dosages of 5, 10, 25, and 50 mg/kg for 5 days and its effects on aniline hydroxylas,p-nitroanisoleO-demethylase, ethyl morphine-N-demethylase, and UDP-glucruonyltransferase activities in the liver were studied. Liver-to-body weight ratios show significant increases at all of the doses tested, reaching maximum of 206 and 230 per cent of controls at a dose of 25 mg/kg for males and females, respectively. Metabolism of each of the substrates is altered by each dose of mirex fed. Aniline hydroxylase activity is decreased at all levels tested and the reduction is progressive with the dose. The Mirex content of rat liver microsomes is, by analysis, 9.69, 14.75, and 36.73 µg per 0.2gram-equivalents of liver microsomes from male rats treated at 10, 25, and 50 mg/kg, respectively. Aniline hydroxylase activity is not affected by addition of up to 400 µg of mirex to the reaction mixtures, using liver preparations from untreated animals.p-Nitroanisole demethylation activity is induced to a maximum in animals treated at 5 mg/kg. Ethyl morphine demethylase is induced to a maximum by 10 mg/kg in male and 25 mg/kg in female rats. Higher doses manifest a reversal ofp-nitroanisole-and ethyl morphine demethylase activities in both the sexes. Although the UDP-glucuronyl transferase specific activity is unaffected by mirex pretreatment, total activity in the liver increases to a maximum of 173 and 149 percent of controls at 25 mg/kg in males and females, respectively. Thus, it appears that chronic low doses of mirex seriously alter hepatic mixed-function oxidase systems of exposed animals, although mirex is not a substrate for any of these enzymes.