Hepatic Microsomal Aminopyrine N-demethylase Research Articles

Study on the relation between lupus anticoagulant and pregnancy-induced hypertension

The possible maternal hepatic and reproductive effects of 1,2,4-trichlorobenzene (TCB) were assessed in rats given 0, 36, 120, 360, and 1200 mg/kg/day of TCB on Days 9–13 of gestation. The animals were sacrificed on Day 14 of pregnancy. Maternal deaths (29 rats, 66 rats) were recorded in the 360 and 1200 mg/kg/day treatment groups and body weight gain was significantly decreased in the 360 mg/kg/day TCB group. Maternal liver weight, liver/body weight ratio, and hepatic microsomal protein content were unaffected by TCB treatment. Although Day 14 NADPH-cytochrome c reductase activity was affected only at 360 mg/kg/day TCB, the maternal hepatic microsomal cytochrome P-450 content was significantly increased by administration of both 120 and 360 mg/kg/day of TCB. Hepatic microsomal aminopyrine N-demethylase, ethoxyresorufin O-deethylase, and UDP-glucuronyl transferase activity towards p-nitrophenol were also increased at 120 and 360 mg/kg TCB. Glutathione S-transferase activity to 1-chloro-2,4-dinitrobenzene and 1,2 dichloro-4-nitrobenzene were both increased by pretreatment with TCB. Although pretreatment with 360 mg/kg/day TCB did not increase resorptions, embryolethality, or teratogenicity, embryonic development was significantly retarded by all four growth criteria used (head length, crown-rump length, somite number, and protein content).

Acute toxicity, percutaneous absorption and effects on hepatic mixed function oxidase activities of 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) and its chlorinated derivatives.

Acute toxicity of 2,4,4'-trichloro-2'-hydroxydiphenyl ether (Irgasan DP300) (I) and its three chlorinated derivatives, 2',3,4,4'-tetrachloro-2-hydroxydiphenyl ether (II), 2',4,4',5-tetrachloro-2-hydroxydiphenyl ether (III) and 2',3,4,4',5-pentachloro-2-hydroxydiphenyl ether (IV), in mice were examined by intraperitoneal injection. The LD50 values of Irgasan DP300, II, III and IV were 1,090, 710, 650 and 430 mg/kg, respectively. The percutaneous absorptions of these tritiated compounds were also examined by the application on the backs of mice. The radioactivities in most tissues reached to the maximal levels at 12 h or 18 h after dosing, which corresponded to 11-76% of the maximal levels given by the oral administration (Kanetoshi et al. 1988a). These results show the high percutaneous absorbability of Irgasan DP300 and its chlorinated derivatives. The intraperitoneal administrations of III and IV to rats induced hepatic microsomal aminopyrine N-demethylase and aniline 4-hydroxylase activities similarly to phenobarbital. These chlorinated derivatives also increased cytochrome P-450 content, and the activities of aminopyrine N-demethylase and N-methylaniline N-demethylase in hepatic microsomes from mice. The extents of the increases were similar to those by phenobarbital and 3-methylcholanthrene.

Biochemical Changes and Morphological Alterations of the Liver in Guinea‐Pigs after Administration of Simvastatin (HMG CoA Reductase‐Inhibitor)

Simvastatin is a potent competitive inhibitor of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) which is the rate-limiting enzyme of cholesterol synthesis. In guinea-pigs, administration of a high oral dose of simvastatin (125 mg/kg/day at the beginning of the study) during 18 days had a major hepatotoxic effect whereas a lower oral dose (30 mg/kg/day) did not seem to cause any liver damage. A significant reduction in microsomal Cyt P 450 content was only observed on a high dose of simvastatin whereas HMG CoA reductase activity was reduced in the group with the low simvastatin dose. The hepatic microsomal aminopyrine N-demethylase activity remained unchanged in all groups. The liver lesion was hepatocellular necrosis accompanied in some animals by a biliary duct proliferation. It was associated with a 10-fold elevation in serum aspartate and alanine aminotransferase activities, as well as a great reduction in daily food intake and body weight (28%). The hepatotoxicity of simvastatin could result from the low basal content of HMG-CoA reductase in guinea-pig liver, the prolonged inhibition of mevalonate synthesis and probably, from the absence of HMG-CoA reductase enzyme de novo synthesis.

Cadmium deposition and hepatic microsomal activity in mice fed swiss chard grown on municipal incinerator refuse ash

Incineration of municipal solid waste results in the production of millions of tons of ash that may be typically high in heavy metals such as cadmium. Disposal of such ash in landfills capped with soil could lead to absorption of such metals by plants and deposition in foraging animal tissues. In this study, weanling, male mice were fed swiss chard that was grown on soil amended with 10% w/w municipal incinerator refuse ash. Cadmium was taken up by the swiss chard (8.15 ppm, dry wt). The mice fed diets containing 25% of ash-grown chard showed mean kidney and liver concentrations of cadmium (ppm, dry wt), respectively, of 2.80 ± 0.30 and 0.45 ± 0.03. Control mice fed soil-grown chard showed significantly lower kidney and liver concentrations of cadmium, i.e. 0.39 ± 0.02 and 0.05 ± 0.00 ppm. Since refuse incinerator ashes may contain various organic toxicants that can be hepatic microsomal inducers, the relative liver weights and hepatic microsomal aminopyrine N-demethylase and p-nitroanisole O-demethylase activities of mice fed control or ash-grown chard were measured. No consistent increases in these latter parameters were found in the ash-grown chard fed mice as compared with the control animals.

Attenuation of low dose phenobarbital induction of hepatic microsomal aminopyrine N-demethylase activity in rats by cimetidine

Cimetidine, a substituted imidazole, is an inhibitor of hepatic cytochrome P-450-mediated drug metabolism in rats and humans. We investigated the effect of cimetidine on phenobarbital induction of hepatic microsomal aminopyrine N-demethylase activity in the rat. Phenobarbital induction of aminopyrine N-demethylase was log-linear in the range of 1–6 mg/kg/day and the ED 50 was approximately 3 mg/kg/day. Cimetidine 75 mg/kg (four times a day) attenuated the induction of aminopyrine N-demethylase activity by 58% in low dose (3 mg/kg/day) but not in high dose (40 mg/kg/day) phenobarbital treated rats. This result could not be explained by residual inhibition of enzyme activity by cimetidine and suggests that cimetidine affects the induction of hepatic cytochrome P-450 by low dose phenobarbital.

Effect of cimetidine on hepatic biochemical changes, liver toxicity and major urinary metabolite excretion of trichloroethylene in rats.

The effects of cimetidine (CIM) (an inhibitor of the hepatic microsomal monooxygenase system) on the metabolism and hepatotoxicity of trichloroethylene (TRI) were studied in male Sprague-Dawley rats. Rats were given three doses of 120 mg/kg i.p. (low-dose regimen) of CIM at 0, 6 and 11 h for 1 day, or ten doses of 200 mg/kg (high-dose regimen) at 8, 11, 14 and 17 h for 2 days and 8 and 11 h on 3rd day. Trichloroethylene (0.5 or 0.65 ml/kg) was administered i.p. 1 h after 2nd dose (low-dose regimen) or 9th dose (high-dose regimen) of CIM. In the low-dose regimen study, the activity of hepatic microsomal aminopyrine N-demethylase was decreased 1 and 5 h after the second dose and 7 h after the third dose of CIM, but became normal 20 h after the last dose. The cytochrome P-450 content and the activities of aniline hydroxylase and epoxide hydratase remained unchanged. Trichloroethylene at both dose levels produced liver toxicity, as verified by increase in activities of SDH and SGPT as well as by liver histology. Cimetidine alone had no such effect. An apparent reduction in TRI toxicity by CIM (at both dose regimens) could be observed histologically. The biochemical tests (SDH and SGPT) corroborated the histological changes only when TRI was given at a dose of 0.5 ml/kg combined with a high-dose regimen of CIM. Cimetidine at both dose regimens had a tendency to decrease the in vivo metabolism of TRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of psoralen and angelicin on hepatic drug-metabolizing enzyme activities

The effects of psoralen and angelicin on hepatic microsomal drug-metabolizing enzyme (DME) activities were investigated to elucidate the mode of the interaction of furanocoumarins with DME system. A single administration (30mg/kg, i.p.) of both coumarins to mice caused a significant prolongation of hexobarbital-induced hypnosis as well as an increase in strychnine toxicity. The inhibitory potencies of both coumarins as measured by rat hepatic microsomal aminopyrine N-demethylase and hexobarbital hydroxylase activitiesin vitro were considerably weaker than those of other furanocoumarins which possess a side chain moiety. Both coumarins were found to have significant inducing effects on DME system, with repeated treatments of them. The activities of an angular coumarin were stronger than those of a linear coumarin.

Effect of four-day treatment with carbamazepine at different dose levels on microsomal enzyme induction, drug metabolism and drug toxicity.

The effect of intraperitoneal injections of 0, 30, 60 and 100 mg/kg of carbamazepine (CBZ), twice a day for 4 days, was studied in 4 groups of 6 male Sprague-Dawley rats per group to evaluate its hepatic enzymatic induction, toxicity and metabolism. Rats were sacrificed on the fifth day and the urines of the last 24 hours were collected. While the activities of hepatic microsomal aminopyrine N-demethylase and epoxide hydratase tended to increase with the dose of CBZ, the cytochrome P-450 content and the activity of aniline hydroxylase however reached a maximum at 60 mg/kg. The percentage of the administered daily dose of CBZ excreted as unchanged CBZ in the urine increased considerably with the dose, while that of metabolites such as carbamazepine-10,11-epoxide (CBZ-E), trans-10,11-dihydrodihydroxycarbamazepine (TDC), and thioethers (T) did not markedly change. These data not only corroborate a maximum in enzyme induction but also suggest a saturation of the induced hepatic enzymes. Urinary T and TDC, representing more than 50% and less than 10%, respectively of the total amount recovered, tend to demonstrate that the glutathione conjugation with the intermediates of CBZ leading to the formation of higher mercapturates could be more important than the epoxide-diol pathway for the metabolism of CBZ under conditions of repeated dosing.

Response of Japanese quail fed seed meal from sunflowers grown on a municipal sludge-amended soil: elevation of cadmium in tissues.

Sunflowers were grown on soil amended with 224 metric tons/ha of municipal sewage sludge from Syracuse, N.Y. The yield of sunflower seeds was reduced by 47.2% by the sludge addition. The harvested seeds contained 1.71 ppm dry weight of cadmium. Deoiled seed meal was incorporated as 25 and 50% of semipurified diet and fed to male and female Japanese quail. The concentrations of cadmium were higher in kidney, liver, muscle, and eggs of birds fed the sludge-grown seed meal as compared to control quail. Tissue concentrations of cadmium increased with increasing dietary levels of sludge-grown seed meal. No significant differences (p greater than 0.05) were observed between dietary treatments in the activity of hepatic microsomal p-nitroanisole O-demethylase or aminopyrine N-demethylase in the male birds. Additionally, no mutagenic activity, either direct or with metabolic activation, was found in quail eggs. No observable changes in tissue ultrastructure were observed under electron microscopy in any of the treatment groups. There were no significant (p greater than 0.05) differences among the dietary treatment groups in feed intake, growth rate, egg production, or egg hatchability.

Role of 3,5-dichlorophenyl methyl sulfone, a metabolite of m-dichlorobenzene, in the induction of hepatic microsomal drug-metabolizing enzymes by m-dichlorobenzene in rats

The increases in the hepatic microsomal aminopyrine N-demethylase activity and in the content of cytochrome P-450 produced by m-dichlorobenzene ( m-DCB) occurred after increases in the hepatic concentration of 3,5-dichlorophenyl methyl sulfone, a minor metabolite. The extent of increases in aminopyrine N-demethylase activity and in the content of cytochrome P-450 at 48 hr after po administration of 200 mg/kg (1.36 mmol/kg) of m-DCB was almost equal to that 72 hr after the ip administration of 25 μmol/kg of the sulfone (Kimura et al., 1983). m-DCB in liver was not detectable at that time, and the concentration of sulfone was 63 to 70% of that 48 to 72 hr after the ip administration of 50 μmol/kg of sulfone. Administration of m-DCB (200 mg/kg) produced a significant reduction in hexobarbital sleeping time, but this reduction was less than that produced by administration of the sulfone (50 μmol/kg). The protein band patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the microsomes from rats treated with the sulfone and m-DCB were similar to those of phenobarbital-treated rats but were different from those of 3-methylcholanthrene-treated rats. The sulfone showed type I interaction with the cytochrome P-450 ( K s, 0.17 m m). The sulfone was formed from the sulfide but reduction of the sulfone was not observed when it was incubated in a hepatic microsomal preparation. The pattern of induction by the sulfone and m-DCB was similar to that by phenobarbital and differed from that by 3-methylcholanthrene. From these results, 3,5-dichlorophenyl methyl sulfone is considered to be a major contributing factor of the inducing activity of m-DCB and to be a potent phenobarbital-like inducer.

Depression of Hepatic Microsomal Enzyme Systems by Lentinan in Mice

Studies were performed to determine the effects of an immunopotentiating agent, lentinan, on the hepatic drug-metabolizing enzymes in mice. Lentinan was injected twice a day for two days, and the enzyme activities were determined 12 hr after the last injection of lentinan. A lentinan dose of over 0.25 mg/kg was required to cause a significant decrease (20–40%) in the hepatic microsomal aminopyrine N-demethylase and aniline hydroxylase activities. The loss of drug-metabolizing activity by the treatment with lentinan agreed with the loss of cytochrome P-450 content in many cases. Strain and substrate differences concerning the effect of lentinan on the metabolism of drug were also observed. That is to say, the loss of cytochrome P-450 content by the treatment with lentinan was observed in the ddY, C57BL/6 and BDF1 strain mice, but was not observed in the DBA/2, C3H/He and C57BL/10 strain mice. The decrease in the activities of 7-ethoxycoumarin O-deethylase and biphenyl 2-hydroxylase by the treatment with lentinan was considerably less than that of aminopyrine N-demethylase and aniline hydroxylase in ddY mice.

Toxicity of trichlorotoluene isomers: a 28-day feeding study in the rat.

Groups of 10 male and 10 female rats were fed alpha,alpha,alpha-, alpha,2,6- or 2,3,6- trichlorotoluene (TCT) in their diet at 0, 0.5, 5.0, 50 or 500 ppm for 28 days. Growth rate and food consumption were not affected by treatment. No deaths occurred. Significant increases in liver weights were observed in male rats fed 5.0 and 500 ppm 2,3,6-TCT. Mild serum biochemical changes occurred in male rats. These included increased SDH activities in the groups fed 5.0 and 50 ppm alpha, alpha, alpha-TCT, and 5.0 ppm 2,3,6-TCT. Alpha, alpha, alpha-TCT at 500 ppm caused elevated LDH activities in male rats. Hepatic microsomal aminopyrine N-demethylase activities were increased in male rats fed 500 ppm alpha,2,6-TCT. Hematological parameters were not affected by treatment. Mild histological changes were seen in the liver, kidney and thyroid of treated rats. Data presented here suggest that alpha, alpha, alpha-, alpha,2,6- and 2,3,6-TCT possess a low order of oral toxicity in the rat.

Effect of 1.1.1 trifluoro-N-(2-methyl-4-phenyl sulfonyl) methane sulfonamide (Destun 50WP) on rat hepatic microsomal enzymes, aniline hydroxylase and amino-pyrine N-demethylase.

Investigations have been carried out to determine the effects of the herbicide 1.1.1 trifluoro-N-(2-methyl-4-phenyl sulfonyl) methane sulfonamide (Destun) on some hepatic microsomal drug metabolizing enzymes in rat. Administration of 100 mg herbicide/kg rat (i.p. or oral) resulted in a stimulation of aniline hydroxylase and p-aminopyrene N-demethylase activities by 1.3 fold and 1.6 fold respectively. A dose-related increase in enzyme activities was observed with a maximum effect at about 100 mg Destun/kg rat. The increased microsomal protein content, liver weight: body weight ratio and decreased sleeping time in the herbicide-treated animals indicated the possibility of Destun being an "inducer". Results of investigations on the kinetic properties of aniline hydroxylase and p-aminopyrene-N-demethylase on administration of Destun suggests that in addition to its inducer effect, the herbicide could stimulate the enzyme activities by decreasing the affinity of these enzymes for their respective substrates.

Maternal hepatic and embryonic effects of 1,2,4-trichlorobenzene in the rat

The possible maternal hepatic and reproductive effects of 1,2,4-trichlorobenzene (TCB) were assessed in rats given 0, 36, 120, 360, and 1200 mg/kg/day of TCB on Days 9–13 of gestation. The animals were sacrificed on Day 14 of pregnancy. Maternal deaths ( 2 9 rats, 6 6 rats) were recorded in the 360 and 1200 mg/kg/day treatment groups and body weight gain was significantly decreased in the 360 mg/kg/day TCB group. Maternal liver weight, liver/body weight ratio, and hepatic microsomal protein content were unaffected by TCB treatment. Although Day 14 NADPH-cytochrome c reductase activity was affected only at 360 mg/kg/day TCB, the maternal hepatic microsomal cytochrome P-450 content was significantly increased by administration of both 120 and 360 mg/kg/day of TCB. Hepatic microsomal aminopyrine N-demethylase, ethoxyresorufin O-deethylase, and UDP-glucuronyl transferase activity towards p-nitrophenol were also increased at 120 and 360 mg/kg TCB. Glutathione S-transferase activity to 1-chloro-2,4-dinitrobenzene and 1,2 dichloro-4-nitrobenzene were both increased by pretreatment with TCB. Although pretreatment with 360 mg/kg/day TCB did not increase resorptions, embryolethality, or teratogenicity, embryonic development was significantly retarded by all four growth criteria used (head length, crown-rump length, somite number, and protein content).

Effect of phenobarbital on toxicity of pyrrolizidine (Senecio) alkaloids in sheep.

The effect of prolonged phenobarbital (PB) administration on the toxicity of Senecio jacobaea (SJ) was studied in sheep. Hepatic microsomal mixed function oxidase (MFO) activity was monitored. Pentobarbital sleeping times were decreased after 17 d of treatment, indicating initial induction of MFO. At 105 d of treatment, hepatic microsomal aminopyrine N-demethylase activity and cytochrome P-450 levels were increased (P less than .05) as a result of PB administration. No differences (P greater than .05) were observed in activity of microsomal epoxide hydrolase, glutathione S-transferase or liver glutathione as a result of SJ and (or) PB. Epoxide hydrolase activity in control sheep was about fivefold higher than values previously reported for rats. Liver Cu concentration was increased (P less than .05) in sheep receiving PB and SJ when compared with controls, but no differences (P greater than .05) were observed in the hepatic intracellular distribution of Cu as a result of PB and(or) SJ. Histopathological examination of liver revealed greater incidence and severity of lesions in animals receiving SJ, but PB did not appear to potentiate SJ intoxication. The results suggest that MFO induction by PB does not increase the susceptibility of sheep to SJ intoxication. Sheep possess a high activity of hepatic microsomal epoxide hydrolase which could account for their resistance to SJ intoxication.

Partial inhibition of hepatic microsomal aminopyrine N-demethylase by caffeine in partially purified cytochrome P450

Cytochrome P-450 substrate interactions were studied with cytochrome P-450 partially purified from livers of untreated, phenobarbital-treated, benzo[ a]pyrene-treated and caffeine-treated rats. Partial inhibition of aminopyrine N-demethylase in presence of in vitro caffeine observed with intact microsomes was further investigated in a reconstituted system composed of partially purified cytochrome c reductase. Caffeine addition (in vitro) to partially purified cytochrome P-450 altered the hexobarbital, aniline and ethylisocyanide induced spectral change, and decreased NADPH oxidation in presence of substrates aminopyrine and acetanilide. NADPH oxidation was found to be increased in presence of aminopyrine and unaltered in presence of acetanilide in reconstituted system having partially purified cytochrome P-450 from caffeine-treated rats. Our studies suggest that caffeine acts as a true modifier of cytochrome P-450 and is possibly responsible for the formation of abortive complexes with aminopyrine.

Inhibition of rat hepatic microsomal aminopyrine N-demethylase activity by benzimidazole derivatives. Quantitative structure-activity relationships.

Eight-two benzimidazole derivatives have been prepared and tested for the ability to inhibit cytochrome P-450 mediated enzyme activity (aminopyrine N-demethylase) from phenobarbitone-induced rat hepatic microsomes. Using physicochemical parameters and multiple regression analysis, we derived a quantitative structure-activity relationship (QSAR) that describes up to 87% of the data variance in terms of hydrophobic and electronic effects and the molar refractivity of the substituent in the 2-position of the benzimidazole ring.

Differential effects of chronic ethanol feeding on cytochrome P-448- and P-450-mediated drug metabolism in the rat

The effects of chronic ethanol feeding on cytochrome P-448- and P-450-mediated drug metabolism have been studied both in vivo and in vitro in the rat, using caffeine, phenacetin, antipyrine and aminopyrine as test substrates. N-Demethylation of aminopyrine (P-450 mediated) was increased both in vivo and in vitro in rats after chronic ethanol feeding (P < 0.05) whereas in vivo N-demethylation of caffeine and O-dealkylation of phenacetin (P-448 mediated) were unchanged in the same animals. N- rmDemethylation of antipyrine was increased by both phenobarbital and 3-methylcholanthrene pretreatment and by chronic ethanol feeding (P < 0.05), possibly due to cytochrome P-450 induction. Furthermore, the Michaelis affinity constants. K m , for hepatic microsomal aminopyrine N-demethylase and antipyrine N-demethylase were lower in chronic ethanol-fed animals (P < 0.05), suggesting a qualitative change in the enzymes resulting in greater substrate affinity. These findings suggest a differential effect of chronic ethanol feeding on the induction of cytochrome P-450- and cytochrome P-448-mediated drug metabolism, with a greater effect on the former microsomal system.

Effect of hexachlorophene, tribromsalan, trichlorcarban and cloflucarban on hexobarbital sleeping time and hepatic drug-metabolizing enzyme activity in vitro in the rat

Oral administration of the antibactenals hexachlorophene, tribromsalan and trichlorcarban at doses of 50, 10 and 40 mg/kg, respectively, caused significant increases in hexobarbital sleeping time in male Wistar rats, while an oral dose of 40 mg/kg of cloflucarban gave only a slight increase. The four halogenated antibacterials inhibited hepatic microsomal aminopyrine N-demethylase and aniline hydroxylase activities in vitro but had no effect on hepatic microsomal NADPH-cytochrome c reductase activity. The addition of each of the antibacterials to hepatic microsomes produced a type I difference spectrum. The spectral binding constants for interaction of hexachlorophene, tribromsalan, trichlorcarban and cloflucarban with hepatic microsomal cytochrome P450 were 33, 62, 66 and 40 μM respectively. The per cent of in vitro inhibition of hepatic microsomal mixed-function oxidase activity by these agents increased with increasing incubation times. The addition of bovine serum albumin to the incubation mixtures partially reversed the inhibition of microsomal drug metabolism caused by the halogenated antibacterial agents in vitro.

Trans-Stilbene oxide: An inducer of rat hepatic microsomal and nuclear epoxide hydrase and mixed-function oxidase activities

The administration of trans-stilbene oxide to rats resulted in increased hepatic microsomal and nuclear epoxide hydrase (with styrene oxide (SO), benzo[ a]pyrene 4,5-oxide (4,5-BP) as substrates) and aryl hydrocarbon hydroxylase (AHH) activities. Hepatic microsomal aminopyrine N-demethylase, benzphetamine N-demethylase, and ethylmorphine N-demethylase activities were also increased. These increases in microsomal enzyme activity were dose- and time-dependent (about 100% at 200 mg/kg body weight, administered for 2 consecutive days). However, only marginal increases in hepatic microsomal NADPH-cytochrome c reductase activity and cytochrome P-450 content were observed. No apparent proliferation of hepatic endoplasmic reticulum occurred in trans-stilbene oxide pretreated rats. The administration of trans-stilbene oxide has no effect on hepatic glutathione S-transferase activities (with SO or 4,5-BPO as substrates). None of the parameters were affected in pulmonary microsomes from treated rats. The in vitro addition of trans-stilbene oxide (10 −6–10 −2 M) did not affect hepatic epoxide hydrase or glutathione S-transferase activities.