Hepatic Microsomal Mixed Function Oxidase Research Articles

Microsomal enzyme induction, egg production, and reproduction in three lines of Japanese quail fed polybrominated biphenyls.

The sensitivity of three genetic lines of Japanese quail to polybrominated biphenyls (PBBs) was evaluated using criteria of egg production, reproduction, and induction of the hepatic microsomal mixed-function oxidase (MFO) system. Two genetic lines of quail, developed to diverge in their plasma cholesterol response to exogenous adrenocorticotropin (ACTH) (a "Low" line and a "High" line), were compared to a random-bred line ("Random"). ACTH administration caused increases in plasma cholesterol in the Low line that were 15 and 39% below the Random-line values in males and females, respectively, while High-line values were 31% higher in males and 36% higher in females when compared to the respective Random-line values. Hepatic activities of aryl hydrocarbon hydroxylase (AHH) and hexobarbital hydroxylase (HxH) were not significantly influenced by ACTH administration or by genetic line in either sex. PBBs fed at 40 or 80 mg/kg diet for 5 wk resulted in significant increases in hepatic AHH and aminopyrine N-demethylase (APND) activities and cytochrome P-450 concentrations. The induction of AHH, APND, and cytochrome P-450 was significantly less in Low-line males in comparison to Random- and High-line males, while the induction of AHH was less in Low-line females when compared to females from the other two lines, based on covariance analysis. In terms of reproductive parameters, there was a greater adverse effect on egg production at 80 ppm PBBs in Low-line females when compared to the Random and High lines. These data indicate an example in which the biological toxicity of a compound and the induction of a 3-methylcholanthrene-type hepatic enzyme are not directly correlated.

Development of basal and induced aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity in the chicken embryo in ovo.

The development of the hepatic microsomal mixed-function oxidase system was studied to determine the basal level of embryonic enzyme activity and the inducibility of this system throughout growth and differentiation. Chicken embryo livers were assayed for basal and inducible hepatic aryl hydrocarbon hydroxylase (AHHase; designated elsewhere as AHH) activity from the first appearance of the liver as a discrete organ at 5 days of incubation (DI) through day 10 after hatching. In addition, whole-embryo and viscera preparations were assayed at 3 and 4 DI. Basal AHHase activity was equal to or greater than adult levels from 3 DI through hatching in all preparations (approximately 0.3-0.5 nmol/min per mg). A 3-fold increase in basal activity above adult values occurred at hatching. The onset of inducibility in chicken embryo liver between 5 and 6 DI was concomitant with hepatocyte differentiation. A developmental profile of 24-hr 3,4,3', 4'-tetrachlorobiphenyl-induced AHHase activity showed 15- to 30-fold induction over controls from 7 DI through day 10 after hatching, with a maximum of 15 nmol/min per mg at 14 DI and day 1 after hatching, a specific activity greater than 50% greater than maximal induction in the adult. Embryonic AHHase activity was also induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin, 3-methylcholanthrene, beta-naphthoflavone, and sodium phenobarbital. Induction kinetics throughout embryonic development were similar to those reported for the adult chicken and other animals. These findings demonstrate development of a mixed-function oxidase system in very early embryogenesis and then in the liver as it differentiates. Liver AHHase activity is inducible throughout development and perinatally but such activity is under strict developmental regulation. The chicken embryo has adult levels of AHHase activity which would be sufficient to achieve metabolic activation of promutagens/carcinogens before and after hepatocyte differentiation.

Effects of polybrominated biphenyls on the concentration and clearance of steroids from blood.

Hepatic microsomal mixed-function oxidases have been stimulated when cattle were experimentally fed polybrominated biphenyls (PBB; fireMaster BP-6). These changes provide mechanisms for alteration of the metabolism and clearance of steroid hormones that might then affect reproductive function. This study was conducted to examine the effects of PBB on the clearance of radiolabel from injected estradiol-17 beta and progesterone along with daily determinations of concentrations of endogenous estradiol-17 beta and progestins in blood plasma. Toxicity was induced by dosing two Holstein cows with 25 g of fireMaster BP-6/d for 39 or 50 d. Single iv injections of 35 microCi [4-14C] progesterone and 400 microCi [2,4,6,7-3H] estradiol-17 beta were given on d -5, 10, 30 and 38 or 48 relative to dosing. Last injections were given when severe toxic symptoms were observed in each animal. Clinical signs, blood constituents, and necropsy findings confirmed the toxic syndrome. Clearance of 14C from progesterone was described by a biexponential function of time, while 3H from estradiol was cleared more slowly with a triexponential function. The total clearance rate for radiolabel from progesterone was approximately four times greater than estradiol throughout the experiments. The total clearance rates were similar for both steroids before and 10 d after dosing with PBB. A toxic syndrome was well developed by d 30 of PBB dosing and the total clearance rate of both steroids decreased approximately 50% with precipitous decreases when animals were terminally toxic. Despite the developing toxic syndrome, plasma concentrations of estradiol-17 beta and total progestins were normal and the periodicity of estrous cycles was maintained.

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.

Effects of dietary protein level on hepatic microsomal mixed-function oxidase systems during aging in two generations of Syrian hamsters

Syrian hamsters were fed one of three levels of lactalbumin (10, 20, or 40%) from 4 weeks of age. Parents (F 0 generation) and their offspring (F 1 generation) remained for life on the parental diet. Randomly selected hamsters from both generations were killed at 0, 6, 18, 30, and 60 weeks to evaluate hepatic microsomal drug metabolism systems. Microsomal protein content rose with increased dietary protein in both generations of females at 30 and 60 weeks and in both generations of males at 18 weeks. Microsomal protein rose during life, but the timing and magnitude of the increase varied with sex, diet, and generation. Cytochrome P-450 content increased with elevation in dietary protein at most measurement times in females and at all measurement times in F 1 generation males. Hepatic aryl hydrocarbon hydroxylase (AHH) and aniline hydroxylase (ANH) activities were influenced by dietary protein, primarily at 6, 18, and 30 weeks, and these values tended to decline between maturity and senescence. AHH generally increased as dietary protein rose, except at 30 weeks, at which time the group fed the medium protein level usually had the highest activity. ANH activity was either elevated in groups fed the 20 or 40% lactalbumin levels or depressed in these groups at 6 and 18 weeks when these values were influenced by dietary protein. The effects depended upon sex and generation. Age effects on hepatic microsomal metabolism in hamsters varied by sex and dietary protein and were somewhat different than those reported for other rodents.

Different responsiveness of hepatic and pulmonary microsomal mixed function oxidases to phenobarbital-type and 3-methylcholanthrene-type polychlorinated biphenyls in rats.

Inductive effects of pretreatments with a phenobarbital(PB)-type 2, 4, 5, 2', 4', 5'-hexachlorobiphenyl(HCB), a 3-methylcholantrene(MC)-type 3, 4, 5, 3', 4'-pentachlorbiphenyl(PenCB) and a mixed type polychlorinated biphenyl(PCB) mixture, Kanechlor(KC-)400 as well as PB and MC on the hepatic and pulmonary microsomal mixed function oxidases(MFOs) were examined and compared using male Wistar rats. Hepatic cytochrome P-450(448) content was increased 2- to 4-fold by pretreatment with all inducers tested, whereas the pulmonary content was slightly elevated only by the MC-type(MC and PenCB) and mixed type inducers. Benzphetamine(BZ) N-demethylase activity in the liver was strongly enhanced by the PB-type(PB and HCB) and mixed type inducers, but not affected by MC and suppressed by PenCB. Pulmonary BZ N-demethylation was not affected by pretreatments with the MC-type and mixed type inducers while both PB-type inducers decreased the activity. The PB-type inducers, showing a weak inducibility for aryl hydrocarbon hydroxylase(AHH) in the liver, also diminished the activity in the lung. In contrast, a marked enhancement of AHH activity in both organs was caused by pretreatment with the MC-type and mixed type inducers. AHH activity in both organs from PenCB-treated rats was highly sensitive to alpha-naphthoflavone but almost insensitive to SKF 525-A. These results strongly suggest that the pulmonary MFO in rats in inducible only with MC-type but not with PB-type PCB unlike the hepatic MFO.

Endotoxin and low protein diet induced depression of the rat hepatic drug metabolism.

The effects of the combination of low protein diet feeding and endotoxin (E. coli, serotype 026 B6) upon rat hepatic microsomal mixed function oxidase (MFO) enzymes were investigated. Short-term (7 days) feeding of low protein (8%) diet and acute (single dose) exposure to endotoxin resulted in an additive decrease in MFO enzymes. However, chronic (7 days) endotoxin exposure did not depress liver microsomal MFO enzyme activities except for aniline hydroxylase. Long-term (105 days) feeding of the low protein diet and acute endotoxin exposure further decreased aminopyrine N-demethylase and benzo(a)pyrene hydroxylase activities compared to individual treatments. These results suggest that, under these experimental conditions, the two host-related environmental factors interact and potentiate a decrease in rat hepatic microsomal drug metabolizing enzymes. These observations may be of clinical relevance to explain altered drug reactions in patients with gram-negative infections and endotoxemia under the conditions of malnutrition.

Effect of the degradation of cytochrome P-450 heme by secobarbital on polychlorinated biphenyls (PCB)-induced hepatic vitamin A reduction and lipid peroxide formation in rats.

The present studies were conducted to characterize the relevance of a microsomal mixed function oxidase system to the polychlorinated biphenyls (PCB)-induced vitamin A reduction and endogenous lipid peroxide formation in the liver of rats. And also, this study dealt with an influence of scavengers on the hepatic lipid peroxide formation stimulated by PCB. Rats were given a 0.01% PCB diet supplemented with adequate nutrients, for 14 days. In an experiment, secobarbital was injected subcutaneously for the degradation of hepatic microsomal cytochrome P-450 heme. A marked liver enlargement and a significant increase of total liver lipid content were observed in the PCB group. The secobarbital enhanced the PCB-induced liver enlargement but no effect of secobarbital on the lipid content was recognized. PCB significantly induced hepatic microsomal cytochrome P-450, but not both cytochrome b5 and NADPH-cytochrome c reductase. The secobarbital suppressed the induction of cytochrome P-450 caused by PCB to approximately one-half. The hepatic vitamin A content significantly decreased on PCB administration and the secobarbital slightly enhanced the PCB-induced vitamin A reduction. However, the vitamin A content in the secobarbital-injected control group decreased to nearly the same levels as in the PCB groups. Therefore, it was presumed that the hepatic microsomal mixed function oxidase system, especially the cytochrome P-450, was possibly not directly involved in the PCB-induced hepatic vitamin A reduction or that a metabolic system related to mixed function oxidase system was involved in the reduction. On the other hand, the hepatic lipid peroxide content tended to increase on PCB administration though no significant difference was recognized. In contrast, the hepatic lipid peroxide content significantly increased in the secobarbital-injected PCB group as compared with the secobarbital-injected control group. However, there was no difference in the lipid peroxide contents between the control groups with and without the injection of secobarbital, and also between the PCB groups. The hepatic vitamin E contents lowered in the secobarbital-injected groups but no effect was observed on PCB administration. The glutathione peroxidase activity decreased significantly on PCB administration and the secobarbital further decreased the activity. Therefore, it was suggested that the significant increase and tendency of increase in hepatic lipid peroxide contents in the PCB groups with and without injection of secobarbital were ascribed to an insufficiency of lipid peroxide scavengers in the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative toxicology of mirex, photomirex and chlordecone after oral administration to the mouse

AbstractThe toxicities of chlordecone (CD), mirex (M) and photomirex (PM) were compared in the male mouse after daily oral administration of 10 mg/kg in corn oil vehicle (10 ml/kg). Mortality occurred starting day 10 with M, and day 16 with PM and CD, and LT50 values were 132, 265 and 254 mg/kg, respectively. However the LT50 values of M, PM or CD were not different (range, 100–125 mg/kg) when animals were intubated with the compounds daily at 25 or 50 mg/kg. Food and water consumption and body weight were decreased after M, but PM and CD increased these parameters. Other symptoms of toxicity included severe diarrhea with M, whereas a moderate diarrhea occurred with PM and little or no diarrhea with CD. The effects of M, PM or CD on the hepatic microsomal mixed function oxidase system were compared 4 d after the administration of 10 mg/kg/d of these compounds. M and PM were equipotent, whereas CD was found to be approximately half as effective in inducing cytochrome P‐450 and associated enzyme activities. CD and M caused a decrease in blood glucose levels due to enhanced oxidation, since liver glycogen levels were also reduced. CD‐induced tremors could not be prevented by restoring the blood glucose level. CD levels in liver, muscle, whole brain and plasma were several‐fold higher than for either M or PM. These results suggest that although structurally similar, these three analogs differ significantly in their biological effects.

COMPARATIVE TOXICOLOGY OF MIREX, PHOTOMIREX AND CHLORDECONE AFTER ORAL ADMINISTRATION TO THE MOUSE

The toxicities of chlordecone (CD), mirex (M) and photomirex (PM) were compared in the male mouse after daily oral administration of 10 mg/kg in corn oil vehicle (10 ml/kg). Mortality occurred starting day 10 with M, and day 16 with PM and CD, and LT50 values were 132, 265 and 254 mg/kg, respectively. However the LT50 values of M, PM or CD were not different (range, 100–125 mg/kg) when animals were intubated with the compounds daily at 25 or 50 mg/kg. Food and water consumption and body weight were decreased after M, but PM and CD increased these parameters. Other symptoms of toxicity included severe diarrhea with M, whereas a moderate diarrhea occurred with PM and little or no diarrhea with CD. The effects of M, PM or CD on the hepatic microsomal mixed function oxidase system were compared 4 d after the administration of 10 mg/kg/d of these compounds. M and PM were equipotent, whereas CD was found to be approximately half as effective in inducing cytochrome P-450 and associated enzyme activities. CD and M caused a decrease in blood glucose levels due to enhanced oxidation, since liver glycogen levels were also reduced. CD-induced tremors could not be prevented by restoring the blood glucose level. CD levels in liver, muscle, whole brain and plasma were several-fold higher than for either M or PM. These results suggest that although structurally similar, these three analogs differ significantly in their biological effects.

Effect of carbon tetrachloride--alcohol-induced liver fibrosis on microsomal mixed-function oxidases and the cytosolic glutathione-conjugating system in rat liver.

1. Subchronic treatment of male and female rats with CCl4 (0.2 ml/kg orally twice weekly) and drinking water containing 5% ethanol for four weeks led to a 20 to 40-fold increase in serum sorbitol dehydrogenase activity and to an augmentation of the liver triglyceride and hydroxyproline contents, indicating steatosis and fibrosis, respectively. Liver fibrosis was less pronounced in females than in male rats. 2. As a consequence of these alterations the hepatic microsomal mixed-function oxidase activity as measured by aminopyrine demethylation was decreased with concomitant loss of cytochrome P-450 in both sexes. Aniline hydroxylation as well as the activity of the NADPH-cytochrome c reductase showed no significant alterations. 3. While the hepatic glutathione content remained unchanged, the cytosolic glutathione S-transferase activities towards both an aryl and an epoxide substrate were markedly decreased following the development of liver fibrosis both in male and female rats.

Endocrine control of daily variations in hepatic mixed function oxidase activity in the adult male rat

Abstract The hormonal control of rhythmic fluctuations in hepatic microsomal mixed function oxidase activity was examined by incubating microsomes prepared from intact control, sham‐operated, pinealectomized (PX), adrenalectomized (AX), and pinealectomized‐adrenalectomized (PXAX) adult male rats with aminopyrine (AP) and [4‐C14]3ß‐hydroxy‐5‐androsten‐17‐one (DHA). The animals were kept on a 12:12 light‐dark cycle for 15 days prior to killingatl, 4, 6 and 10 hafter light and at 1, 4, 6 and 10 h after dark. The rate of both the N‐demethylation of AP and the 7α‐hydroxy lation of DHA varies diurnally with maximal and minimal activities in the dark and light periods, respectively. The fluctuation in both reactions fits a symmetric sine curve for all endocrine treatment groups except for the 7α‐hydroxylation in PX animals. PXAX was the only treatment resulting in a significant increase in 7α‐hydroxylase activity. The data suggest that the pineal may be involved in mediating the effects of environmental light on liver 7α‐hydroxylase activity.

Toxicologic studies with swine fed corn grown on municipal sewage sludge-amended soil.

Over a 3-yr period 336 MT/ha of dried sewage sludge, from a municipal waste treatment plant, was applied in liquid form to land subsequently used to grow corn. The sludge contained 115 mg Cd, 4,200 mg Zn and 538 mg Ni/kg dry matter and comprised the solids remaining after treatment of the waste waters of approximately 260 industries as well as domestic users. Corn grain harvested from the plot amended with sewage sludge (SA corn) or corn grown on a plot without sludge addition (control corn) was fed to a total of 56 pigs to determine the effect on growth performance and parameters indicative of toxicity. Each treatment consisted of seven pens of four pigs each with an average initial weight of 17.6 kg. The growth trial was terminated when pigs weighed approximately 90 kg. No differences were observed between treatment groups for average daily gain, feed: gain ratio or daily feed intake. Higher (P less than .01) concentrations of Cd, Ni and Zn were found in SA corn compared with the control corn. This resulted in higher (P less than .01) concentrations of Cd in kidney and liver and Ni in kidney of pigs fed SA corn as compared with pigs fed control corn. No significant differences were observed in Cd or Ni concentrations in muscle or in hepatic microsomal mixed-function oxidase (MFO) activity and liver:body weight ratios, which is indicative of the absence or low levels of organic toxicants in SA corn. In addition, no significant treatment effects were observed when corn, feces and urine samples were evaluated for the presence of mutagenic substances. Histopathologic analysis of various tissues for lesions demonstrated that pigs fed SA corn were not adversely affected.

Aflatoxin: Toxicity to Dairy Cattle and Occurrence in Milk and Milk Products - A Review

Aflatoxins are toxic and carcinogenic secondary metabolites produced by some common aspergilli during growth on feeds, foods or laboratory media. Aflatoxin B1 (AFB1) is a decaketide (C20-polyketide) which is synthesized by the mold from acetate units via the polyketide pathway. Methionine contributes the methoxy-methyl group. Six known intermediate compounds in the biosynthesis of AFB1 include norsolorinic acid, averantin, averufin, versiconal hemiacetal acetate, versicolorin A and sterigmatocystin. Other aflatoxins (B2, B2a, G1, G2 and G2a) appear to be conversion products of AFB1. When aflatoxins, and in particular AFB1, occur in feed and are consumed by dairy cattle, a variety of symptoms can occur, which includes unthriftiness, anorexia and decreased milk production. Changes in amounts of enzymes and other blood constituents also result from ingestion of AFB1. The hepatic microsomal mixed-function oxidase system of the cow converts some of the ingested AFB1 into aflatoxin M1 (AFM1), which is excreted in milk. AFM1 retains the toxicity of, but is less carcinogenic than AFB1. Certain heat treatments associated with milk processing appear to inactivate a portion of the AFM1 in milk. If raw milk contains AFM1, products (fluid products, nonfat dried milk, cultured milks, natural cheese, process cheese, butter) made from such milk also will contain AFM1. AFM1 appears to be associated with the casein fraction of milk, hence concentrating the casein in the manufacture of products (e.g. cheese, nonfat dry milk) is accompanied by concentrating of the AFM1. Methods involving thin-layer or high-performance liquid chromatography are commonly used to detect and quantify AFM1 in milk and milk products.

Polychlorinated biphenyls (Aroclors 1016 and 1242): effect on hepatic microsomal mixed function oxidases in mink and ferrets.

A comparison was made of the induction responses of two PCBs (Aroclors 1016 and 1242) on the hepatic microsomal mixed function oxidase (MFO) system in two genetically similar species, mink and European ferrets, previously shown to differ significantly in sensitivity to these same Aroclors. Feeding Aroclors for 28 days at a subtoxic level (20 ppm) resulted in weak induction of the MFO system. Aroclor 1242 was a more potent inducer than Aroclor 1016. Using a dosing regime which resulted in toxic effects in mink but not in ferrets, greater induction was noted in ferrets compared to mink. Furthermore, only 3-methyl-cholanthrene (MC)-type induction was observed. Phenobarbital (PB) inducible enzymes were either not affected or were inhibited by Aroclor treatment. The results suggest an inverse relationship between extent of MC-type induction and toxicity in these species.

Influence of ozone and nitrogen dioxide on hepatic microsomal enzymes in mice.

Since ambient concentrations of ozone and nitrogen dioxide increase drug-induced sleeping time in female mice, potential mechanisms were sought by investigating the effects of these gases on hepatic microsomal mixed-function oxidases in female CD-1 mice. A 3-h exposure to 9800 microgram O3/m3 (5 ppm) or 9400 microgram NO2/m3 (5 ppm) did not change the concentration of cytochrome P-450 significantly. Aniline hydroxylase, but not aminopyrine N-demethylase or p-nitroanisole O-demethylase, activities were increased following a 3-h exposure to 9400 microgram O3/m3 (5 ppm). Aniline hydroxylase activity was also increased after a 2-d (5 h/d) exposure to 1960 microgram O3/m3 (1 ppm). None of these enzyme activities were affected by a 3-h exposure to 9400 microgram NO2/m3 (5 ppm). In these studies, O3 sometimes increased wet liver weight, and thus additional experiments were conducted. A 5-h exposure to 1960 microgram O3/m3 (1 ppm) caused a lesser decrease in body weight than the decrease observed after a similar air exposure. Liver wet weights were elevated after O3 exposure. However, there were no significant changes in liver dry weight, liver dry-to-wet-weight ratio, or ratios of liver (wet or dry) weight to body weight. From these data, it is concluded that mechanisms other than those investigated are responsible for the effect of O3 and NO2 on drug-induced sleeping time. However, the activity of one mixed-function oxidase was slightly increased by O3, indicating a hitherto unrecognized systemic effect of O3 exposure.

Metabolic activation of dimethylnitrosamine to mutagens: Role of cytochromes P-450 and P-448

Pretreatment of hamsters with phenobarbitone, 3-methylcholanthrene and Arochlor 1254 induced the hepatic microsomal mixed function oxidases, yet decreased the efficiency of activation of dimethyl-nitrosamine (DMN) to intermediates mutagenic to the Salmonella typhimurium strain TA-100. Furthermore, no correlation was obtained between cytochrome P-450 content, microsomal demethylation of DMN and its activation to mutagens. These results indicate that the demethylation of DMN by the mixed-function oxidases is not the rate-limiting step in the metabolic activation of the carcinogen to mutagen(s), and that other microsomal or soluble enzymes may be involved.

Stimulation of drug and carcinogen metabolism by prolonged oral tobacco consumption

Oral administration of tobacco to rats for 21 days caused remarkable stimulation of the metabolism of phenacetin, aniline and benzo[ a]pyrene, a carcinogen, by hepatic microsomal mixed function oxidases (MFO). Such treatment for 6 days resulted in a small increase in the activities of phenacetin O-dealkylase and aromatic hydrocarbon hydroxylase (AHH) without affecting aniline hydroxylase activity. Nicotine given orally was found to be a relatively weak inducer of phenacetin O-dealkylase and aniline hydroxylase, and elicited a maximum increase in their activities within 6 days which remained unchanged even after 21 days of continuous administration. However, these two enzyme systems were not affected following only one or two doses of tobacco and nicotine. Both tobacco and nicotine inhibited these biotransformations in vitro.

Hepatic microsomes from freshwater fish—II. Reduction of benzo(a)pyrene metabolism by the fish anesthetics quinaldine sulfate and tricaine

1. A single in vivo exposure of brook trout ( Salvelinus fontinalis) to a 30.0 mg/l solution of quinaldine sulfate or a 112.5 mg/l solution of tricaine for 5 min significantly reduced the in vitro hydroxylation of benzo(a)pyrene. 2. Since quinaldine sulfate and tricaine formed type I and II binding spectra, respectively, with brook trout hepatic cytochrome P-450, these chemicals probably reduced benzo(a)pyrene hydroxylase enzyme activity by altering the form(s) of cytochrome P-450 responsible for this activity. 3. Hepatic microsomal cytochrome P-450 from brook trout treated with tricaine for 5 min and then placed into fresh water 24 hr had returned to control levels. 4. Caution should be exercised in the use of quinaldine sulfate or tricaine to anesthetize fish prior to analysis of hepatic microsomal mixed function oxidases.

The mutagenicity of 9-hydroxyellipticine and its induction of cytochrome P-448 activity in rat liver microsomes

Administration of a single dose of the inhibitor of the hepatic mixed function oxidases, 9-hydroxyellipticine (9-OHE), resulted in a marked increase in the cytochrome P-448 catalysed activities of ethoxyresorufin O-deethylase, biphenyl 2-hydroxylase and activation of benzo[a]pyrene to mutagens. In contrast there was no effect on the cytochrome P-450 catalysed benzphetamine N-demethylase activity. The inductive effect was prevented by simultaneous administration of the protein synthesis inhibitors cycloheximide and actinomycin D. It is concluded that 9-OHE may also act as an inducer of the hepatic microsomal mixed function oxidases, selectively inducing the synthesis of cytochrome P-448. Therefore, 9-OHE, like other inhibitors of this enzyme system, exhibits a biphasic effect, its inhibitory phase being followed by one of enzyme induction. 9-OHE was a direct mutagen in the Salmonella typhimurium strains TA 98 and TA 100.