Murine cytochrome P4503A is induced by 2-methyl-3-buten-2-ol, 3-methyl-1-pentyn-3-ol(meparfynol), and tert-amyl alcohol

1. Colupulone, a constituent of hops, was shown to be a potent inducer of hepatic P4503A in mouse. The olefin, 2-methyl-3-buten-2-ol (RC = CH2), is formed from lupulones when hops are exposed to atmospheric hydroxyl radicals. This suggested the possibility that the same reaction may occur in vivo. The credibility of this hypothesis was enhanced when RC = CH2 was shown to induce P4503A in mouse. Ethylmorphine (EM) N-demethylation, a functional marker for P4503A, was also induced by RC = CH2. 2. 3-Methyl-1-pentyn-3-ol (RC identical to meparfynol), a sedative and close structural analogue of RC = CH2, also induced P4503A and EM N-demeythylation. Tert-amyl alcohol (RC-CH3), the saturated analogue of RC = CH2, was included in t he study with the expectation that it would serve as a negative control for the anticipated induction of P4503A by the other two alcohols. This proved not to be the case; RC-CH3 was about as active an inducer of P4503A as RC = CH2 and RC identical to CH. The possibility is considered that, like valproic acid, RC-CH3 is metabolized to an olefin by P450. 3. Hydroxylation of aniline and benzo[a]pyrene by hepatic microsomes from mice treated with the three alcohols were used as functional markers for the induction of P4502E and P4501A respectively. RC = CH2 at the two lowest levels of administration suppressed aniline hydroxylation but had no effect at the highest level. RC identical to CH was ineffective and RC-CH3 was moderately inductive at all three levels. Each of the three compounds were weak to moderate inducers of benzo[a]pyrene hydroxylation.

Effects of colupulone, a component of hops and brewers yeast, and chromium on glucose tolerance and hepatic cytochrome P450 in nondiabetic and spontaneously diabetic mice

Brewers yeast contains factors that increase and decrease glucose tolerance. Hop components (lupulones) that adhere to yeast during the brewing process elicit a variety of biological effects including the induction of hepatic cytochrome P4503A. Colupulone was tested for its effects on glucose tolerance and cytochrome P450. Serum glucose levels 30 min after the injection of glucose were lowered by colupulone in nondiabetic Swiss-Webster mice, elevated in diabetic C57B1/KSJ-db/db mice, and unaffected in nondiabetic C57B1/KSJ+m/+m mice. Colupulone lowered hemoglobin glycation slightly in +m/+m mice but not in db/db mice. The cytochrome P450 system was highly induced by colupulone in both db/db and +m/+m mice. Chromium, which acts in concert with the factor in yeast that enhances glucose tolerance, had little or no effect on the plasma glucose level or the cytochrome P450 system in either +m/+m or db/db mice.

Interferon induces sleep and other CNS responses in mice recovering from hexobarbital anesthesia

Immediately after recovery from hexobarbital anesthesia, mice were injected intraperitoneally with one of the following interferons: natural mouse alpha/beta, recombinant mouse (rmouse gamma IFN-A) or human alpha A, alpha D, alpha AD interferon (rHu alpha IFN-A, rHu alpha IFN-D, rHu alpha IFN-AD). All of these interferons, except rHu alpha IFN-A induced unconsciousness ("sleep"); all produced stimulatory effects that mimicked those produced by morphine in the mouse. Quantification of the duration of sleep, induced by rmouse gamma IFN, was investigated and found to be dose-related. Only 3 of the 5 interferons (mouse alpha/beta IFN; rmouse gamma IFN, rHu alpha IFN-AD) possesses antiviral activity and depresses the cytochrome P-450 system in the mouse, yet all 5 of the interferons produced CNS effects. This partition of effects, together with the very short latency of the interferon-induced CNS effects, shows that the CNS effects were mechanistically independent of the anti-viral and anti-cytochrome P-450 effects. This disparity of the actions of the interferons suggests the possibility that selected morphine antagonists could be used to counter some of the dose-limiting CNS effects of the large doses of interferons used in clinical situations.

Effects of interferon, polyriboinosinic acid--polyribocytidilic acid and steroids on the cytochrome P450 system of cultured primary mouse hepatocytes

An earlier study from this laboratory showed that the hepatic murine cytochrome P450 (P450) system was depressed by interferon in vivo but induced in cultured primary hepatocytes. The current investigation attempted to resolve this contradiction. The P450 content of the cells used in the earlier study fell precipitously during the first 24 hr of culture and remained at the same low level throughout another 48 hr of incubation. This failure to maintain the P450 level suggested that the cells may not have been sufficiently viable to support the mechanisms involved in the depressant activity of interferon. Accordingly, a chemically defined medium containing hydrocortisone was devised which supported an acceptable level and function of the P450 system throughout a 72 hr incubation period. Functionality of the P450 system was evaluated by measuring aminopyrine N-demethylase and benzo[a]pyrene hydroxylase activities. When this steroid supplemented medium was used, interferon depressed both activities by about 25%; however, neither activity was affected significantly by poly IC. On the other hand, benzo[a]pyrene hydroxylase activity was depressed by both poly IC and interferon in hepatocytes induced with dexamethasone or with dexamethasone plus 3-methylcholanthrene. These studies emphasize the necessity of maintaining an acceptable level of homeostasis in cultured hepatocytes if one is to derive meaningful interpretations of certain biological events.

Lipid peroxidation-cytochrome P450 interactions. Use of linoleic acid hydroperoxide in the characterization of the spin-state of membrane-bound P450

1. A procedure (linolenic acid hydroperoxide (LAHP) deletion method) is described in which LAHP is added to the reference cuvette of a pair of spectrally balanced cuvettes containing hepatic microsomes to produce a composite high spin (HS)-low spin (LS)-spectrum of P450. 2. The LAHP deletion method was used to determine the spin state of P450 in rat hepatic microsomes with and without the addition of type I compounds. 3. Advantage was taken of the temperature dependency of the spin state of P450 to determine the overall enthalpic and entropic changes for the spin equilibrium to generate computer-derived spectra of HS and LS forms of P450, and to construct a nomogram that allows direct estimation of the percentage of HS and LS spin forms of P450 in intact microsomes at temperatures compatible with biochemical functions. 4. The h.p.l.c. deletion method was used to demonstrate that HS-P450 comprised 57% of the P450 in hepatic microsomes; addition of type I substrates to these microsomes raised the level of HS-P450 to 97%. 5. The percentage of HS-P450 generated by the addition of type I compounds to microsomes declined with increasing deletions of P450 until at the extrapolated 100% level of deletion there was no HS-P450 above that of the original 57% observed in the absence of added compounds. This can be explained if LAHP destroys part of the LS-P450 while altering the remaining LS-P450 such that it retains its LS spectral characteristics but loses its capacity to form HS P450 when type I substrates are added. 6. These studies support the concept that about 50% of hepatic microsomal P450 is functionally in the HS state due to binding with high affinity endogenous substrates or other membrane components; the remaining P450 is LS-P450 that can bind to exogenous substrates to form HS-P450. 7. Applications of the LAHP deletion method for assessment of catalytic properties of membrane-bound P450 at ambient temperatures are discussed.

Identification of the antibiotic hops component, colupulone, as an inducer of hepatic cytochrome P-4503A in the mouse

A higher level of cytochrome P-450 (P450)-dependent ethylmorphine (EM) N-demethylase activity was observed in hepatic microsomes from mice fed a natural-ingredient diet ("crude diet") than in those from mice fed a semi-purified diet ("purified diet"). This led to the testing of individual ingredients of the crude diet as inducers of the P-450 system. Brewers yeast proved to be the most significant inductive component of the crude diet. Further investigation revealed that hop components (lupulones) absorbed on yeast during the brewing process were responsible for the induction of the P-450 system. The induction of P-450 and several P-450-dependent monooxygenase activities (EM N-demethylation, aniline hydroxylation, benzo[a]pyrene hydroxylation) by colupulone with respect to dose and time course were investigated. The very large increase in EM N-demethylase activity elicited by colupulone suggested that P-4503A had been induced. Western blot technology verified this speculation. Western blot analysis of microsomal protein from mice fed hops, brewers yeast, or the residue of a hexane extract of hops supported the conclusion that all of these substances induced P-4503A. These substances were also relatively good inducers of P-4502B, but not as inductive of this isozyme as the crude diet. This is interpreted to mean that not all of the inductive properties of the crude diet are due to hop components. These studies question the use of crude commercial diets in studies of P-450 systems. They may also challenge some current definitions of "constitutive" and "induced" P-450s.

In vitro translational activity of messenger-RNA isolated from mice treated with the interferon inducer, polyriboinosinic acid.polyribocytidylic acid

Treatment of mice with interferon and interferon inducers causes down regulation of a number of hepatic proteins. In a previous publication it was demonstrated that these treatments depress hepatic protein synthesis and increase protein degradation, particularly of the endoplasmic reticulum Gooderham NJ and Mannering GJ, Arch Biochem Biophys 250: 418-425, 1986. In the present study the effects of polyriboinosinic acid.polyribocytidylic acid (poly IC) treatment on mouse hepatic RNA levels and the translation of this RNA in a cell-free system were examined. Poly IC treatment of mice increased hepatic poly (A+) RNA levels. The translation of isolated poly(A+)RNA was evaluated at various intervals after the administration of poly IC. Translation was marginally increased at 3-6 hr after treatment and depressed after 12-18 hr. Antibodies were employed to examine the effects of poly IC treatment on specific polypeptides in order to evaluate the in vitro translation of mRNAs for tyrosine aminotransferase and albumin; translation of these proteins was biphasic with pronounced depression. These studies indicate that in vivo interferon may regulate gene expression by altering levels of hepatic proteins via increased transcription and decreased translation.

Role of xanthine oxidase in the interferon-mediated depression of the hepatic cytochrome P-450 system in mice

Interferon, interferon inducers, and a variety of other immunomodulators are known to depress the hepatic cytochrome P-450 drug-metabolizing system. Two concepts have been proposed to explain this phenomenon. (a) The steady-state of cytochrome P-450 is altered through decreased synthesis and increased degradation of cytochrome P-450 apoprotein. (b) Interferon induces xanthine oxidase; superoxide generated by interferon-induced xanthine oxidase destroys cytochrome P-450. The current study investigated the second concept. Administered polyribonucleotides [polyriboinosinic acid.polyribocytidylic acid (poly IC), polyriboinosinic acid.polycytidylic acid, polylysine and carboxymethylcellulose, mismatched poly IC], recombinant murine gamma-interferon, and a natural murine alpha/beta-interferon were shown to depress hepatic cytochrome P-450 and selected microsomal cytochrome P-450-dependent monooxygenase reactions and to induce hepatic xanthine oxidase activity. The feeding of tungstate in the drinking water largely depleted xanthine oxidase in mice; cytochrome P-450 levels and monooxygenase activities were not affected by tungstate treatment. Tungstate rendered the level of xanthine oxidase much below that in mice that had not received tungstate regardless of whether or not they had received poly IC or interferon; nevertheless, poly IC and interferon produced losses of cytochrome P-450 and monooxygenase activities in these tungstate-treated mice equivalent to those observed in mice that had not received tungstate. The administration of N-acetylcysteine did not prevent the loss of cytochrome P-450 induced by poly IC, as has been reported, nor did the incubation of microsomal cytochrome P-450 with buttermilk xanthine oxidase and hypoxanthine cause a loss of cytochrome P-450, which has also been reported. It is concluded from these studies that the induction of xanthine oxidase and the loss of cytochrome P-450 generated by interferon are coincidental rather than causally related phenomena.

NADPH- and linoleic acid hydroperoxide-induced lipid peroxidation and destruction of cytochrome P-450 in hepatic microsomes

Temporal aspects of the effects of inhibitors on hepatic cytochrome P-450 destruction and lipid peroxidation induced by NADPH and linoleic acid hydroperoxide (LAHP) were compared. In the absence of added Fe2+, NADPH-induced lipid peroxidation in hepatic microsomes exhibited a slow phase followed by a fast phase. The addition of Fe2+ eliminated the slow phase, thus demonstrating that iron is a rate-limiting component in the reaction. EDTA, which complexes iron, and p-chloromercurobenzoate (pCMB), which inhibits NADPH-cytochrome P-450 reductase, inhibited both phases of the reaction. Catalase as well as scavengers of hydroxyl radical, inhibited NADPH-induced lipid peroxidation almost completely. GSH also inhibited the NADPH-dependent reaction but only when added at the beginning of the reaction. In contrast with NADPH-dependent lipid peroxidation, the autocatalytic reaction induced by LAHP was not biphasic, NADPH-dependent or iron-dependent, nor was it inhibited by hydroxyl radical scavengers, catalase or GSH. A synergistic effect on lipid peroxidation was observed when both NADPH and LAHP were added to microsomes. It is concluded that both the fast and slow phases of NADPH-dependent microsomal lipid peroxidation are catalyzed enzymatically and are dependent upon Fe2+, whereas LAHP-dependent lipid peroxidation is autocatalytic. Since the fast phase of enzymatic lipid peroxidation occurred during the fast phase of destruction of cytochrome P-450, it is postulated that iron made available from cytochrome P-450 is sufficient to promote optimal lipid peroxidation. Since catalase and hydroxyl radical scavengers inhibited NADPH-dependent but not LAHP-dependent lipid peroxidation, it is concluded that the hydroxyl radical derived from H2O2 is the initiating active-oxygen species in the enzymatic reaction but not in the autocatalytic reaction.

Depression of cytochrome P-450 and alterations of protein metabolism in mice treated with the interferon inducer polyriboinosinic acid X polyribocytidylic acid

Treatment of mice with the interferon inducer polyriboinosinic acid X polyribocytidylic acid [poly(IC)] results in the depression of several hepatic proteins. In this study we examined synthesis and degradation of the proteins of liver cell organelles in mice treated with poly(IC). Effects on synthesis were determined by using [14C]- and L-[3H]leucine incorporation into control and poly(IC)-treated mice, respectively. At selected times after poly(IC) treatment the 3H/14C ratio was established for preparations of nuclei, mitochondria, lysosomes, smooth endoplasmic reticulum, rough endoplasmic reticulum, and 105,000g supernatant (cytosol). Time-dependent alterations in de novo protein synthesis were greatest in lysosomal and rough endoplasmic reticular fractions; both were depressed 9 h after treatment. The effects of poly(IC) on protein degradation were determined with [14C]bicarbonate. Poly(IC) treatment decreased the time required for disappearance of 50% of 14C-labeled protein (t1/2) of smooth and rough endoplasmic reticula. Examination of endoplasmic reticulum marker enzymes showed depression of cytochromes P-450 and b5 from 9 h onward after poly(IC) administration. Tyrosine aminotransferase activity was elevated 6 h after treatment with poly(IC), and then depressed after 9 h. The other organelle marker enzymes were not affected significantly. We conclude that poly(IC) decreases the content of proteins of the hepatic endoplasmic reticulum, including certain cytochrome P-450 isozymes, by decreasing rates of protein synthesis and increasing rates of protein degradation.

The pharmacology and toxicology of the interferons: an overview

Interferon was discovered three decades ago. The next 20 or more years of research were directed largely toward an understanding of its antiviral activity. The persistent short supply of interferon hampered progress, and the impure preparations available throughout these years clouded interpretation of results. Many of the experiments and clinical studies that interferonologists had dreamed of for 20 or more years became realities when modern technology provided quantities of pure interferon that exceeded expectations. Studies with these pure recombinant interferons removed all doubts that the many pleiotropic effects that had been observed with impure interferon preparations were due to interferon and not to the impurities. The interferons are now acknowledged lymphokines that are involved in many cellular processes. In fact, the antiviral activity of interferon, which led to its discovery, may be an exaggerated adaptive utilization of an interferon-regulated function that plays a more general role in cellular physiology. The ability to isolate, purify, and produce pure interferon has led to the discovery of multiple species of leukocyte interferon. These interferons display different patterns of activity when tested by a variety of systems. This suggests that specific leukocyte interferons may be involved in specific physiological functions. Results of preliminary trials of the interferons as antiviral and antitumor agents have been encouraging and occasionally dramatic. The overall clinical picture is expected to improve when more is learned about the pharmacokinetics of the interferons and which of the interferons are best suited for the treatment of specific tumors and antiviral diseases. There are indications that coadministration of interferons with chemical antineoplastic and antiviral agents may increase the effectiveness of interferon in clinical situations. As might be expected of agents that influence a large number of physiological functions, interferons produce numerous toxic side effects, some of which resemble those inflicted by viral diseases. These side effects are reversible and not life threatening.

Evidence for a predominantly NADH-dependent O-dealkylating system in rat hepatic microsomes

This study compared the NADH- and NADPH-supported p-nitrophenetole (NP) O-deethylase, ethylmorphine (EM) O-deethylase and EM N-demethylase activities of rat hepatic microsomes with respect to dioxygen requirement, inhibition by carbon monoxide, inhibition by classical inhibitors of cytochrome P-450 systems, and the involvement of NADH-cytochrome b5, cytochrome b5 reductase and NADPH-cytochrome P-450 reductase. The results generated the following conclusions and speculations: NADH- and NADPH-supported O-deethylations of NP involve different P-450 hemoproteins. This conclusion was based largely on the observations that the NADPH-supported reaction was inhibited by carbon monoxide and cyanide (5 mM), whereas the NADH-supported reaction was not; the NADH-supported reaction required a relatively high pO2 for maximal activity, whereas the NADPH-supported reaction did not, and the NADPH-supported reaction was depressed in microsomes from rats that had been administered Co2+, Mn2+, allylisopropylacetamide (AIA) or polyriboinosinic acid X polyribocytidylic acid (poly IC), whereas the NADH-supported reaction was not. However, the NADH- and NADPH-supported reactions shared some common features: both were strongly inhibited by alpha-naphthoflavone and weakly inhibited by 2-diethylaminoethyl 2,2-diphenyl valerate HCI (SKF 525-A), both were destroyed by linoleic acid hydroperoxide, and both were induced by 3-methylcholanthrene (MC) and phenobarbital. The use of antibodies against NADPH-cytochrome P-450 reductase, NADH-cytochrome b5 reductase and cytochrome b5 demonstrated that both the NADH- and the NADPH-supported reactions depend on established components of cytochrome P-450 systems. The P-450 hemoproteins involved primarily in both the NADH- and NADPH-supported deethylation of NP are the P1-450 type, i.e. they are markedly induced by MC and inhibited by alpha-napthoflavone. The NADH- and NADPH-supported O-deethylations of NP involve separate electron transfer systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of xanthine oxidase and depression of cytochrome P-450 by interferon inducers: genetic difference in the responses of mice

Interferon and interferon inducing agents depress hepatic cytochrome P-450 systems. They also induce hepatic xanthine oxidase activity. It has been suggested that free radicals produced by xanthine oxidase may cause the loss of P-450. High titers of serum interferon are induced by poly IC (poly riboinosinic acid.polyribocytidylic acid) in both C57Bl/6J and C3H/HeJ mice; Newcastle disease virus (NDV) induces a high titer of interferon in C57Bl/6J mice but not in C3H/HeJ mice. The induction of xanthine oxidase activity by NDV in C3H/HeJ mice was less than half that seen in C57Bl/6J mice, thus demonstrating a relationship between the induction of xanthine oxidase, the depression of P-450 and a genetically determined difference in responsiveness of mice to interferon inducers.

Drug metabolism in the newborn

The duration and intensity of drug action depend not only on the dose of the drug but also on the rates at which drugs are transformed to products that can be excreted readily by the kidney. Two general categories of drug metabolism occur in the liver: phase 1 reactions (oxidations-reductions and hydrolyses) and phase 2 reactions (synthetic conjugations). Phase 1 reactions produce functional groups that can participate in phase 2 reactions. Phase 1 reactions are almost nonexistent in the fetuses of laboratory animals; however, many appear in primates during the first trimester of gestation. Phase 2 reactions are deficient prenatally in both rodents and primates. Parturition triggers a surge of both phase 1 and phase 2 reactions. The lack of uniformity of the development of phase 1 oxidative reactions during the early neonatal period reflects the multiplicity of cytochrome P-450 hemoproteins, the terminal oxidases responsible for most hepatic oxidative biotransformations. The rate of recovery of chemically induced losses of cytochrome P-450 systems is age dependent.

Depression of the hepatic cytochrome P-450 monooxygenase system by treatment of mice with the antineoplastic agent 5-azacytidine

The effects of 5-azacytidine (5-AC) administration on the hepatic cytochrome P-450 systems of mice were studied. A single i.p. dose of 5-AC (25 mg/kg) to male Swiss-Webster mice caused about a 50% depression of microsomal cytochromes P-450 and b5 and of ethylmorphine N-demethylase and ethoxycoumarin O-deethylase activities. Depression was greatest 24 h after treatment; by 48 to 72 h, cytochromes and drug metabolism had returned to near control values. Reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase activity was also depressed by 5-AC, whereas reduced nicotinamide adenine dinucleotide-cytochrome c reductase was not. Incubation of 5-AC with microsomes produced no effect on drug metabolism. The prolongation of hexobarbital sleeping time by 5-AC showed that drug metabolism is also impaired by 5-AC in vivo. These studies may have important clinical implications when certain drugs are coadministered with 5-AC.

Membrane bound cytochrome P-450 determines the optimal temperatures of NADPH-cytochrome P-450 reductase and cytochrome P-450-linked monooxygenase reactions in rat and trout hepatic microsomes

The hepatic monooxygenase systems largely responsible for the biotransformation of drugs and other xenobiotics are comprised of NADPH-cytochrome P-450 reductase and multiple forms of cytochrome P-450. Optimal temperatures for these systems in the trout and rat are 26 degrees and 37 degrees, respectively. Purified trout and rat reductases are optimally functional at 26 degrees and 37 degrees, respectively, when added to trout and rat microsomes. However, rat reductase was shown to function optimally at 26 degrees when added to trout microsomes and trout reductase functioned optimally at 37 degrees when added to rat microsomes. Corresponding shifts in optimal temperatures of cytochrome P-450-linked 0-deethylation of 7-ethoxycoumarin occurred when these reductases were added to rat or trout microsomes. It is proposed that the phospholipid annulus surrounding the active site of membrane-bound cytochrome P-450 determines the optimal temperature of cytochrome P-450 systems.

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

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

Effects of the interferon inducing agents tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC) on the hepatic monooxygenase systems of pregnant and fetal rats

Interferon inducing agents, including tilorone and polyriboinosinic acid . polyribocytidylic acid (poly IC), are known to depress hepatic cytochrome P-450-dependent monooxygenase systems and the induction of these systems by phenobarbital (PB) and 3-methylcholanthrene (MC) in mature male rats. The current study investigated the effects of tilorone and poly IC on the cytochrome P-450 systems of non-induced, PB-induced, MC-induced and pregnenolonecarbonitrile (PCN)-induced pregnant rats and their fetuses. Pregnant rats received either tilorone or poly IC and saline, PB, MC or PCN, and microsomes from their livers and those of their fetuses were examined for cytochrome P-450 content, aminopyrine (AP) N-demethylase activity and benzo[a]pyrene (BP) hydroxylase activity. The generalization can be made from these studies that, when the interferon inducing agents caused changes in cytochrome P-450 content or monooxygenase activities of either induced (PB, MC or PCN) or non-induced (saline) animals, decreases were seen in maternal livers and increases in fetal livers. Thus, in maternal livers tilorone depressed cytochrome P-450 and AP N-demethylase activity in non-induced and PB-, MC- and PCN-induced rats and BP hydroxylase activity in the induced animals; BP hydroxylase activity was not depressed in non-induced maternal livers. Poly IC depressed cytochrome P-450 and AP N-demethylase activity in non-induced and PB-induced rats but not in PCN-induced animals. BP hydroxylase was depressed by poly IC in both PB- and PCN-induced animals. Fetal hepatic cytochrome P-450 and monooxygenase activities were increased by tilorone in PB- and PCN-induced rats but not in non-induced or MC-induced animals. Poly IC increased cytochrome P-450 and both monooxygenase activities in PB- and PCN-induced fetal livers, whereas only BP hydroxylase activity was increased in the fetuses of non-induced rats. Several possible explanations are offered for the opposite effects produced by interferon inducing agents in maternal and fetal livers. Unlike maternally administered tilorone, which induced fetal cytochrome P-450 and monooxygenase activities in the liver, intrauterine tilorone depressed cytochrome P-450 and had no effect on AP N-demethylase or BP hydroxylase activities in the fetal liver. Intrauterine poly IC was without effect on the cytochrome P-450 systems of the fetal liver. Treatment of pregnant rats with tilorone on days 17-20 of gestation inhibited normal maternal weight gain and produced overt signs of toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of constitutive and phenobarbital-induced cytochrome P-450 isozymes during the sequential oxidation of benzphetamine. Explanation for the difference in benzphetamine-induced hydrogen peroxide production and 455-nm complex formation in microsomes from untreated and phenobarbital-treated rats

The following pathway for benzphetamine (Bz) metabolism in rat hepatic microsomes was established: Bz leads to norbenzphetamine (NorBz) leads to N-hydroxynorbenzphetamine leads to N-benzylethyl-alpha-phenylnitrone leads to 2-nitroso-1-phenylpropane. The last product forms a complex with cytochrome P-450 with an absorbance maximum at 455 nm. Steps 1, 2, and 4 are cytochrome P-450-dependent; Step 3 appears to involve the flavoprotein, mixed-function amine oxidase. Step 2 is partially uncoupled, producing H2O2 at approximately 3 times the rate of N-hydroxylation. Bz is oxidized to NorBz in microsomes from both untreated rats (U-microsomes) and phenobarbital (PB)-treated rats (PB-microsomes), but the 455-nm peak does not appear in U-microsomes until almost all of the Bz has been converted to NorBz; i.e., Bz inhibits the oxidation of NorBz in U- but not in PB-microsomes. The inhibition is competitive. Bz inhibits the oxidation of the nitrone to 2-nitroso-1-phenylpropane in both U- and PB-microsomes; NorBz inhibits this reaction in U-microsomes only. These results can be explained as follows. The substrate affinities of the cytochrome P-450 primarily responsible for the N-demethylation of Bz in U- and PB-microsomes differ markedly. The constitutive cytochrome(s) in U-microsomes has a high affinity for Bz; PB induces both this form and a cytochrome(s) with a lower affinity for Bz. The substrate affinities of these two cytochromes P-450 for NorBz do not differ appreciably. Thus, although both forms of cytochrome P-450 can oxidize Bz and NorBz in PB-microsomes, Bz is primarily oxidized by the constitutive form, whereas NorBz is oxidized primarily by the induced form, thereby relieving competition and increasing the over-all sequential oxidation of Bz. The nitrone appears to be oxidized exclusively by the constitutive form in both U- and PB-microsomes. The current study shows that PB induction of monooxygenase activity need not be due entirely to an increase in the amount of cytochrome P-450 or the substrate selectivity of cytochrome P-450 isozyme(s) responsible for that activity, but that, in at least one case, the metabolism of Bz, PB-induced activity can be due, at least in part, to the induction of a cytochrome P-450 isozyme that relieves substrate inhibition.

Hepatic cytochrome P-450-dependent monooxygenase systems of the trout, frog and snake--I. Components

1. Components of the hepatic monooxygenase systems (cytochrome P-450, cytochrome b5, NADPH cytochrome P-450- or c-reductase) of the brown trout (Salmo trutta), leopard frog (Rana pipiens) and garter snake (Thamnophis) were considerably lower than those found in the rat. 2. Reactivity of snake NADPH-cytochrome P-450-reductase with cytochrome P-450 was about twice that of the rat reductase; reactivities of trout and frog reductases were similar, but lower than that of the rat. The optimal temperature for the rat, frog and snake reductase activity was 37 degrees C, but 26 C for the trout reductase, regardless of whether cytochrome P-450 or cytochrome c was the electron acceptor for the reaction. 3. A type I substrate (benzphetamine) and a type II substrate (aniline) were less reactive with P-450 cytochrome from the trout, frog and snake than with P-450 cytochrome from the rat. 4. Qualitative differences were seen in the ethylisocyanide spectrum of microsomes from the rat, trout, frog and snake; these differences reflect qualitative differences in the populations of P-450 cytochromes among each of the four species.

Hepatic cytochrome P-450-dependent monooxygenase systems of the trout, frog and snake--II. Monooxygenase activities

1. Activities of hepatic monooxygenase systems (aminopyrine N-demethylase, benzo[a]pyrene hydroxylase and p-nitrophenetole O-deethylase) of the brown trout (Salmo trutta), leopard frog (Rana pipiens) and garter snake (Thamnophis) were observed to be considerably lower than those of the rat. The specific activities of their P-450 cytochromes relative to rates of product formation were also much lower than those of the rat, except benzo[a]pyrene hydroxylation by frog microsomes, in which case, the value was about the same as that for the rat. 2. The monooxygenase systems of the trout, frog and snake were identified as cytochrome P-450 systems by the inhibitory effects of carbon monoxide, SKF 535-A, alpha-naphthoflavone and by the requirement for NADPH. 3. NADH synergism of NADPH-supported monooxygenase activities of hepatic microsomes of the trout, frog and snake suggest the participation of cytochrome b5 in these reactions. For the trout, p-nitrophenetole metabolism was supported almost as well by NADH as by NADPH, which suggests that in this species, cytochrome b5 may play an important role in certain monooxygenase reactions. 4. Qualitative differences in the P-450 cytochromes of the trout, frog, snake and rat were indicated by differences in the inhibitory effects of SKF 525-A and alpha-naphthoflavone on monooxygenase activities.

Hepatic cytochrome P-450-dependent monooxygenase systems of the trout, frog and snake--III. Induction

1. 3-Methylcholanthrene administration increased levels of cytochrome P-450, benzo[a]pyrene hydroxylase activity and p-nitrophenetole O-deethylase activity in hepatic microsomes from the brown trout (Salmo trutta), leopard frog (Rana pipiens) and the garter snake (Thamnophis). The level of aminopyrine N-demethylase activity was increased in trout microsomes, but not in those from the frog, snake or rat. 2. The shift in the Soret maximum of the reduced carbon monoxide difference spectrum of cytochrome P-450 from 450 to 448 nm, which is observed when 3-methylcholanthrene is administered to rats, was not seen in microsomes from the trout, frog or snake. 3. Benzo[a]pyrene hydroxylase activity induced by 3-methylcholanthrene in the trout, frog and snake was inhibited by relatively low concentrations of SKF 525-A, but that induced in the rat was not. alpha-Naphthoflavone inhibited 3-methylcholanthrene-induced benzo[a]pyrene hydroxylase activity in the trout, frog and rat, but not in the snake. 4. 3-Methylcholanthrene induced an increase in the 455/430 nm peak height ratio of the reduced ethylisocyanide spectrum of microsomes in the rat and trout, but not in the frog or snake. 5. These observations (items 1--4 of the abstract) show that different species of cytochrome P-450 are induced by 3-methylcholanthrene in the four vertebrates. 6. Phenobarbital did not alter the components or the activities of hepatic monooxygenase systems in the trout, frog or snake, even though it was shown to accumulate in the livers of these vertebrates as readily as it does in the liver of the rat.

Effects of interferon-inducing agents on hepatic cytochrome P-450 drug metabolizing systems

Duration and intensity of drug action are greatly influenced by the rates of which drugs are biotransformed by the cytochrome P-450-linked monooxygenase systems of the hepatic endoplasmic reticulum. Several interferon-inducing agents (poly rI.rC, tilorone, vaccines, viruses, endotoxin) are shown to markedly depress hepatic P-450 systems when administered to rodents. The interferon (IF) inducers that depress hepatic drug metabolism also modulate certain immune responses; it is therefore not known whether the depression of P-450 is due to IF per se or to the action of IF-inducing agents on one or more components of the immune system. The loss of cytochrome P-450 elicited by IF-inducing agents is accompanied by a perturbation of heme metabolism associated with the dissociation of heme from cytochrome P-450. The agents also cause losses of hepatic catalase and tryptophan 2,3-dioxygenase. These studies predict that viral infections, vaccinations, and treatment with IF-inducing agents will be shown to seriously impair the metabolism of drugs in humans.

Species, sex, and developmental differences in the O- and N-dealkylation of ethylmorphine by hepatic microsomes

3-O-[1'-14C]Ethylmorphine and ethylmorphine, respectively, were used to measure O- and N-dealkylase activities of hepatic microsomes. The well-known sex difference in the rate of N-delakylation in mature rats was not observed with O-dealkylation, nor did O-dealkylase activity increase as male rats reached maturity, as is the case with N-dealkylase activity. Accordingly, O-dealkylation represents only about 20% of the total dealkylase activity (O- + N-) in mature male rats, but about 50% in mature female rats. A comparison of the O- and N-dealkylating activities of hepatic microsomes from rats, mice, guinea pigs, and rabbits showed that both the rates of O- and N-dealkylation and the ratio of the two reactions vary greatly among animal species. These studies contribute to the evidence that different cytochrome P-450-dependent mono-oxygenase systems are involved in the O- and N-dealkylation of opium alkaloids.

Depression of the hepatic cytochrome P-450 mono-oxygenase system by administered tilorone (2,7-bis(2-(diethylamino)ethoxy)fluoren-9-one dihydrochloride)

The oral administration of the antiviral agent, tilorone-HCl (50 mg/day for 4 days) to rats caused losses of hepatic microsomal ethylmorphine N-demethylase, benzo(a)pyrene hydroxylase and aniline hydroxylase activities of 50, 44 and 22%, respectively. Microsomal levels of cytochrome P-450 and NADPH-cytochrome c reductase were lowered by 40 and 20% respectively, but levels of cytochrome b5 and NADH-cytochrome c reductase remained unchanged. After a single oral dose of tilorone-HCl (50 mg/kg) a loss of 38% of the microsomal cytochrome P-450 and 25% of the ethylmorphine N-demethylase activity was observed within 24 hr; recovery was complete within 8 to 10 days. Hexobarbital sleeping times and blood levels were elevated after tilorone administration (20 or 50 mg/kg/day for 4 days). In vitro, tilorone-HCl showed no inhibitory effect on microsomal drug metabolism nod did it affect the cytochrome P-450 content of the microsomes. The rate of incorporation of delta-amino(3H)levulinic acid into cytochrome P-450 was not affected by tilorone-HCl.