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.