Hepatic Microsomal Mixed Function Oxidase Research Articles

Suppression of the hepatic microsomal cytochrome P-450 dependent mixed function oxidase. Activities in golden hamster during Leishmania donovani infection

Experimental infection of golden hamsters with Leishmania donovani caused significant alterations in the hepatic microsomal mixed function oxidase system. Gross examination of liver indicated hepatomegaly. Microsomal protein contents were only marginally elevated. Cytochrome P-450 as well as haem contents were significantly decreased and it directly correlated with the degree of infection. Cytochrome b 5 exhibited elevation at lower degrees of infection which came down to control levels at the peak infection. Concomitant suppression was also noticed in cytochrome P-450 dependent monooxygenase activities, viz. aniline hydroxylase, benzo[ a]pyrene hydroxylase and aminopyrine N-demethylase. No significant change was observed in NADH-cytochrome b 5 reductase and NADPH-cytochrome c reductase. The results indicate suppression of hepatic microsomal MFO activities during visceral leishmaniasis.

The effects of cadmium, mercury and lead in vitro on hepatic microsomal mixed function oxidase and lipid peroxidation.

In this study, the authors investigated the effect of cadmium, mercury and lead in vitro on hepatic microsomal mixed function oxidase and lipid peroxidation. The results showed that these metals could inhibit the activity of hepatic microsomal aniline hydroxylase, decrease the concentration of hepatic microsomal cytochrome P-450 and increase the concentration of the inactive form of hemoprotein, P-420. Besides, they could enhance hepatic microsomal lipid peroxidation. There were marked concentration-dependent responses in these microsomal reactions. Thus, it may be suggested that cadmium, mercury and lead are capable of impairing hepatic microsomal mixed function oxidase in vitro by stimulating membrane lipid peroxidation.

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-demeth-ylase and aniline hydroxylase.

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.

Induction of the rat hepatic microsomal mixed-function oxidases by two aza-arenes: A comparison with their non-heterocyclic analogues

The ability of the aza-aromatic polycyclic aromatic hydrocarbons 10-azobenz( a)pyrene and benz( a) acridine to induce the rat hepatic microsomal mixed-function oxidases was compared to that of their non-heterocyclic analogues benz( a) pyrene and benz( a) anthracene respectively. All four hydro-carbons markedly increased the O-deethylations of ethoxyresorufln and ethoxycoumarin, the non-heterocyclic analogues being the more potent. A more modest increase was seen in the O-dealkylation of pentoxyresorufin. All four hydrocarbons induced proteins recognised by antibodies to cytochrome P-450aIAI but no increase was seen when antibodies to cytochrome P-450IIB1 were employed. The metabolic activation of benz( a)pyrene and Glu-P-1 to mutagenic intermediates in the Ames test was enhanced by all pretreatments. It is concluded that the aza-aromatic polycyclic hydrocarbons, like their non-heterocyclic analogues, selectively induce the cytochrome P-450I family of proteins.

Induction of hepatic mixed-function oxidases by permethrin and cypermethrin in chicks fed vitamin A-deficient diet

The effect of permethrin and cypermethrin on the induction of hepatic mixed-function oxidases was studied in chicks fed a vitamin A-deficient diet. Oral administration of permethrin at 10, 50, 100, and 200 mg/kg for 6 consecutive days induced microsomal protein, cytochrome P-450, and NADPH-cytochrome c reductase in dose-dependent manner. Treatment with cypermethrin at a dose of 200 mg/kg body weight induced NADPH-cytochrome c reductase and cytochrome b 5. However both insecticides had no effect on the glutathione S-transferase activity. Permethrin and cypermethrin appear to be weak inducers of hepatic microsomal mixed-function oxidases in chicks fed vitamin A-deficient diet.

Structural role of an unsaturated lactone in acute toxicity of rubratoxin B isolated from Penicillium rubrum

AbstractRubratoxin B is a substituted higher homolog of byssochlamic acid in which the ethyl group is replaced by a six‐membered ring containing an unsaturated lactone. Hydrogenation of the unsaturated lactone greatly reduces the acute toxixity of the compound. The acute median lethal doses of rubratoxin B and hydrogenated rubratoxin in male mice were 5.6 and 31 mg/kg, respectively. Pretreatment with phenobarbital (60 rag/kg × 4 days) or with SKF 525A (40 mg/kg) failed to significantly alter the toxicity of either compound. Histopathological examination of mice treated with rubratoxin B (3.5 mg/kg) revealed areas of hepatic zonal necrosis and marked necrosis of kidney tubules. No necrosis was observed in mice treated with hydrogenated rubratoxin (20 mg/kg). Hepatic microsomal mixed function oxidase activity was significantly reduced in mice pretreated with rubratoxin B (0.5 mg/kg × 4 days), while pretreatment with hydrogenated rubratoxin (2.5 mg/kg × 4 days) failed to depress microsomal activity. Our studies document the requirement of an alpha, beta unsaturated lactone ring for rubratoxin B toxicity. Based on the results from these studies the mechanism for rubratoxin B induced toxicity is postulated to be due to its electrophilic properties and subsequent alkylating activity.

Effects of bile duct obstruction and decompression on hepatic microsomal mixed function oxidase system in rats

The effects of biliary obstruction and drainage on the hepatic microsomal mixed function oxidase system were studied in rats. Bile duct obstruction produced a significant reduction in the hepatic cytochrome P-450 dependent mixed function oxidase system. After release of the bile duct obstruction, the reduction in microsomal enzymes was practically reversible; however, the process of recovery was slow and differed with the microsomal enzymes in question. Increases in cytochrome b 5 content and NADH-cytochrome b 5 reductase activity were slower than increases in cytochrome P-450 content and NADPH-cytochrome c reductase activity. Aniline hydroxylase activity increased more rapidly and corresponded to cytochrome P-450 contents more so than did the aminopyrine demethylase activity. After the release of bile duct obstruction, however, the bile acids which had accumulated in the liver during cholestasis were reduced rapidly, to a normal range. These results suggest that there is a discrepancy between reductions in hepatic bile acids and those in the hepatic microsomal mixed function oxidase system after biliary decompression.

Effect of caffeine on the hepatic microsomal mixed function oxidase system during phenobarbital and benzo[ a] pyrene treatment in rats

Simultaneous administration of caffeine (100 mg/kg, i.p., 3 days) and phenobarbital (80 mg/kg, i.p., 3 days) to adult male rats resulted in a significant decrease in hepatic cytochrome P-450 and acetanilide hydroxylase activity, compared to phenobarbital administration alone. While simultaneous administration of caffeine and benzo[ a]pyrene (20 mg/kg, i.p., 2 days) increased acetanilide hydroxylase, compared to benzo[ a]pyrene administration, no change was seen in the cytochrome P-450 concentration. In vitro addition of 2.5 mM caffeine to microsomal incubations from untreated, phenobarbital- and benzo[ a]pyrene-treated rats inhibited aminopyrine N-demethylase activity. No significant difference was seen in the extent of aminopyrine N-demethylase inhibition due to the in vitro addition of caffeine to microsomes from untreated or phenobarbital-treated rats, whereas inhibition in microsomes from benzo[ a]pyrene-treated rats was greater.

Environmental implications of incineration of municipal solid waste and ash disposal

Owing to unsightliness and the threat of groundwater pollution, landfilling of municipal solid waste (MSW) is giving way to incineration in many communities. Environmental contamination from particulate and gaseous emissions containing heavy metals, polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF), polycyclic aromatics (PCA), acids and other compounds from such incinerators, as well as safe ash disposal, are of great concern. Concentration ranges of elements and organic toxicants in incinerator ashes, emissions and cooling waters are given. The literature is reviewed concerning the effects of incinerator operating parameters on emissions. Incinerators equipped with modern pollution control devices (electrostatic precipitators, fabric filters, dry scrubbers, spray towers) and operated at optimum temperature with sufficient oxygen, turbulence (mixing) and residence time for complete combustion appear to minimize ash, elemental, gaseous and organic emissions. Environmental aspects of MSW incineration are considered and reviewed. The presence of metals and organics in incinerator quench water and in leachates from ash disposed in landfills are reviewed, as well as their toxicity to fish. The behavior and effects of atmospheric emissions in soils and plants are discussed. Research on the effect of ash-derived PCDD and PCDF on hepatic microsomal mixed function oxidase activity and the immune system in laboratory animals is cited. The presence of metals, organics and mutagens in the incinerator workplace air and the possible effects of air-borne contaminants on inhabitants nearby is reviewed. Several studies dealing with human risk assessment of MSW incineration are cited.

Induction of the rat hepatic microsomal mixed-function oxidases by 3 imidazole-containing antifungal agents: selectivity for the cytochrome P-450IIB and P-450III families of cytochromes P-450

Administration of the imidazole antifungal agents ketoconazole, miconazole and clotrimazole gave rise to increases in the microsomal cytochrome P-450 levels and the NADPH-dependent reduction of cytochrome c. Clotrimazole, and to a much lesser extent miconazole and ketoconazole, stimulated the dealkylation of pentoxyresorufin. All 3 agents gave rise to small, but significant increases in the O-deethylations of ethoxycoumarin and ethoxyresorufin. The antifungal-induced O-deethylation of ethoxycoumarin was much more sensitive to inhibition by metyrapone rather than by α-naphthoflavone. The binding of metyrapone to reduced microsomes was enhanced by treatment of animals with the 3 antifungal agents, clotrimazole being clearly the most potent. Immunoquantitation of cytochrome P-450 proteins using an ELISA procedure and employing anti-cytochrome P-450c ( P-450IA1, P-448 low spin) and P-450b ( P-450IIB1) antisera revealed that clotrimazole and miconazole, but not ketoconazole, induced the levels of phenobarbital-induced cytochromes P-450, while none of the antifungal agents increased the levels of cytochrome of P-448 proteins. Similar results were obtained using Western blots employing the above antibodies. On SDS-polyacrylamide gel electrophoresis microsomes derived from animals pretreated with clotrimazole showed intensification of a band at 51 kDa which was identified by Western blotting as the PCN-inducible form of cytochrome P-450 (cytochrome P-450p, P-450III family). Similar, but less pronounced intensification was seen with microsomes from animals pretreated with miconazole and ketoconazole. Furthermore, microsomes from clotrimazole- and ketoconazole-treated animals interacted with erythromycin to yield type I spectra. It is concluded that the imidazole-containing agents clotrimazole and miconazole, and to a much lesser extent ketoconazole, are potent inducers of the rat hepatic microsomal mixed-function oxidases, displaying selectivity towards the P-450IIB (phenobarbital-inducible) and P-450III (PCN-inducible) families of cytochrome P-450 proteins.

Clonidine effects on disposition of xenobiotics in rats: inhibited elimination of flow-limited but not extraction-limited agents.

1. The alpha 2-adrenoceptor agonist, clonidine, reduces the hepatobiliary clearance of the anionic dye, sulphobromophthalein (BSP) in rodents. We now compare the effects of clonidine on BSP elimination with its effects on disposition of compounds which are metabolized by hepatic microsomal mixed function oxidases. 2. BSP, 100 mg kg-1 was administered i.v. to rats at 4 h after s.c. saline or clonidine, 0.2 mg kg-1. Thirty min later, plasma BSP levels were 121.4 +/- 2.25 micrograms ml-1 in saline-treated rats, while in clonidine-treated rats they were 631.5 +/- 141.0 micrograms ml-1. Clonidine raised hepatic BSP levels from 256.0 +/- 28.9 micrograms g-1 tissue to 568.5 +/- 86.5 micrograms g-1. 3. Acute administration of clonidine (0.2 mg kg-1 s.c.) or repeated clonidine dosing (0.2 mg kg-1, s.c. twice daily for 10 days) did not affect the disposition of intravenously administered [14C]-antipyrine (15 mg kg-1). 4. Activities of the P450 mixed function oxidase enzymes, aniline hydroxylase and aminopyrine N-demethylase, were identical in liver microsomes from saline-treated rats and in microsomes from rats given single or multiple s.c. doses of clonidine (0.2 mg kg-1). 5. Addition of clonidine or other 2-substituted imidazoles at concentrations up to 2 microM did not affect the activities of aniline hydroxylase or of aminopyrine N-demethylase in suspensions of rat liver microsomes. Other substituted imidazoles, including cimetidine, clotrimazole and metronidazole, at concentrations of 0.2 microM or higher, inhibited the activities of these microsomal enzymes. 6. Clonidine slowed BSP elimination, which is probably hepatic blood flow-limited, but not the extraction-limited elimination of antipyrine, which is metabolized by hepatic microsomal enzymes.

Effects of energy and/or protein restriction on hepatic microsomal mixed function oxidase in male broiler chicks

1. 1. Effect of energy and/or protein intake on a mixed function oxidase system (MFO) in hepatic microsomes was studied in male broiler chicks. 2. 2. Contents of cytochrome P-450 and b5 in 72 hr starvation were larger than those in 12 and 36 hr starvations. 3. 3. Reduction of energy and protein intake did not change the MFO, except cytochrome P-450. 4. 4. Reduction of energy intake under the same protein intake increased the cytochrome P-450 content and aminopyrine N-demethylase activity. An increase in protein intake under the same energy intake also increased the cytochrome P-450 content.

Effect of diisopropyl 1,3-dithiolan-2-ylidenemalonate(NKK-100) on the components of hepatic microsomal mixed function oxidase in male broiler chicks.

Effect of oral administration of diisopropyl 1, 3-dithiolan-2-ylidenemalonate (NKK-100) on the components of mixed function oxidase system in hepatic microsomes was investigated in male broiler chicks. Feeding NKK-100 increased relative liver weight and microsomal protein content of the liver. Contents of cytochrome P 450 and b 5 per mg microsomal protein and g liver increased with NKK-100 levels. The activities of NADPH-cytochrome c reductase and NADH-cytochrome b 5 reductase per g liver were enhanced by feeding NKK-100, while those activities per mg microsomal protein remained unchanged. Pretreatment with clopidol (an anticoccidial agent) and colistin (an antibiotic) did not affect the components of MFO. These results suggests that NKK-100 has a property to activate the hepatic microsomal MFO and the effect of NKK-100 are more prominent in the increases in specific activities of cytochrome P 450 and b 5 rather than in those of NADPH-cytochrome c reductase or NADH-cytochrome b 5 reductase.

Streptozotocin-induced diabetes modulates the metabolic activation of chemical carcinogens

The effect of chemically-induced diabetes on the hepatic microsomal mixed-function oxidase system and the activation of chemical carcinogens was investigated in animals treated with streptozotocin (STZ). In order to distinguish between the effects of the diabetogenic chemical per se and that of the diabetic state, groups of STZ-treated animals received either nicotinamide simultaneously with STZ to prevent the onset of diabetes, or daily treatment with insulin in order to reverse the effects of diabetes. STZ-treated animals exhibited higher pentoxyresorufin O-dealkylase, ethoxyresorufin O-deethylase, ethoxycoumarin O-deethylase, aniline p-hydroxylase and NADPH-cytochrome c reductase activities; similarly, increases were seen in cytochrome p-450 and b 5 levels. All of these effects were prevented by nicotinamide and, at least partly, antagonised by insulin therapy. Treatment of animals with STZ markedly increased the activation, by liver microsomes in vitro, of Trp-P-1 and Trp-P-2 to mutagens, the effect being totally preventable by nicotinamide and successfully antagonised with insulin therapy. The diabetic animals were similarly more efficient in activating MeIQ but the effect was not preventable by nicotinamide or reversed by insulin. In contrast no changes were seen in the activation of IQ and only a modest increase in the case of MeIQx. It is concluded that diabetes may modulate the metabolic activation of some chemical carcinogens, presumably by changing the ratio of the various cytochrome p-450 isoezymes.

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.

In vivo protection by protein A of hepatic microsomal mixed function oxidase system of CCl 4-administered rats

The in vivo protection by protein A of hepatic mixed function oxidase system of carbon tetrachloride (CCl 4) administered rats, has been investigated in the present communication. Aryl hydrocarbon hydroxylase activity was decreased by 63% in CCl 4 administered rats while in protein A + CCl 4 administered rats the decrease was in the range of 22–25% (group IV–V). The aryl hydrocarbon hydroxylase activity in protein A + CCl 4 administered rats showed significant increase in group IV (P < 0.005) and group V (P < 0.001) in comparison to CCl 4 alone (group II). Similarly, aniline hydroxylase and aminopyrene N-demethylase were decreased, by 75 and 84% respectively in CCl 4 administered rats and 31% and 54–64%, respectively in protein A + CCl 4 administered rats (groups IV and V). The aniline hydroxylase activity was also found enhanced in protein A + CCl 4 administered group IV and V (P < 0.001). In addition the aminopyrene N-demethylase also showed significant increase in its activity in group IV (P < 0.001) and group V (P < 0.001) in comparison to CCl 4 alone. In accordance with these data, serum glutamic oxaloacetic transaminase and glutamic pyruvic transaminase exhibited significantly less increase in their activity in animals receiving protein A and CCl 4 than those treated with CCl 4 alone. Protein A alone was found to have no effect on any of these enzymes. Our results indicate that protein A protects CCl 4 induced injury as judged by the biochemical alterations and suggests that it may be useful in providing an excellent system for the investigation on the regeneration of the hepatic enzyme activity following toxic insult of CCl 4.

Inhibition of carbamazepine and phenytoin metabolism by nafimidone, a new antiepileptic drug.

When nafimidone (NFM), a new antiepileptic drug, was given to six patients already taking carbamazepine (CBZ) and phenytoin (PHT) as part of a late phase I pilot efficacy trial, it reduced CBZ elimination by 76-87% and reduced PHT elimination by 38-77%. CBZ and PHT levels rose within 24 h after NFM was started, and began to decline within 12 h after NFM was stopped. The inhibitory effect on CBZ metabolism persisted throughout the course of 1 year of long-term follow-up in all five patients who continued with the drug after completion of the pilot study. Inhibition of PHT elimination persisted in three of the patients, but PHT elimination returned to baseline rates in the other two patients during long-term follow-up. The inhibition of CBZ and PHT metabolism is probably due to binding of cytochrome P-450 by NFM or a metabolite and thus inhibition of the hepatic microsomal mixed-function oxidase system.

Effects of various pretreatments on the acute nephrotoxic potential of styrene in fischer-344 rats

The effects of various inducers and inhibitors of hepatic microsomal mixed-function oxidase (MFO) system and diethylmaleate treatment on styrene-induced acute nephrotoxicity in male Fischer-344 rats were studied. Groups of rats were pretreated with either 3-methylcholanthrene (15 mg/kg, i.p., 3 days), or phenobartial (80 mg/kg, i.p., 3 days), or SKF525-A (50 mg/kg, i.p., 1 h), or piperonyl butoxide (300 mg/kg, i.p., 2 h), or diethylmaleate (400 mg/kg, i.p., 90 min) prior to an i.p. administration of styrene (0, 0.6 and 0.9 g/kg) in corn oil. The uptake of p- aminohippurate (PAH) by renal cortical slices, the morphology of renal cortices, as well as urinary excretion of N- acetyl-β- D-glucosaminidase (NAG) and γ-glutamyl transpeptidase (γ-GT) of control and pretreated rats were examined 24 h after styrene. The inducers and inhibitors of MFO system failed to modify further the acute nephrotoxicity of styrene. On the other hand, diethylmaleate pretreatment not only reduced further the uptake of PAH, but also produced further significant increase in the urinary excretion of NAG and γ-GT observed at the higher dose of styrene. Similarly, ultrastructural studies showed a moderate increase in the severity of kidney damage induced at the higher dose of styrene due to pretreatment with diethylmaleate. These data suggest that tissue glutathione concentrations and hence, corresponding conjugating activity might be important determinants of styrene nephrotoxicity The results further indicate that a metabolic activation system not involving certain cytochrome P-450 might be responsible in styrene-induced nephrotoxicity.

Effect of Plasmodium yoelli nigeriensis infection and chloroquine on the hepatic mixed function oxidase system of mice

Plasmodium yoelli nigeriensis infection in albino mice significantly altered the hepatic microsomal mixed function oxidase system. Cytochrome P-450 (the terminal monooxygenase) and other monooxygenases, viz. aniline hydroxylase, aminopyrine- N-demethylase and benzo(a)pyrene hydroxylase were significantly lowered while microsomal heme showed 4-fold increase at 80% parasitaemia. Noticeable impairment in the other components like NADH:cytochrome b 5 reductase, NADPH:cytochrome c reductase, cytochrome b 5 and glucose-6-phosphatase was also observed. Oral treatment of normal and P. y. nigeriensis infected mice with chloroquine (64 mg per kg body weight for 4 days) caused lowering of mixed function oxidase activitied which however showed a recovering trend, a week after cessation of treatment.