Induction of cytochrome P-450 mRNA in rainbow trout: in vitro translation and immunodetection

The time course of induction of the rainbow trout microsomal hepatic monooxygenase (MO) system was examined by determination of levels of mRNA and corresponding levels of catalytic activity. Animals were pretreated with beta-naphthoflavone (beta-NF, ip, 100 mg/kg) and terminated at 0, 2, 6, 18, and 48 hr postinjection. Levels of mRNA were determined by immunoprecipitation of in vitro translation products. Levels of mRNA coding for the cytochrome P-450 LM4b isozyme were maximally increased (13-fold) at 18 hr and had decreased almost to pretreatment levels by 48 hr post-treatment. This was in contrast to the catalytic activity in which ethoxyresorufin-O-deethylase (EROD) and ethoxycoumarin-O-deethylase (ECOD) were significantly elevated at both 18 hr (25- and 5-fold, respectively) and 48 hr (46- and 8-fold, respectively). Pretreatment with beta-NF (ip, 100 mg/kg) or 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB, ip, 150 mg/kg) for 18 hr resulted in significant differences in levels of mRNA in only the beta-NF-treated group. The LM2 P-450 isozyme could not be detected by immunoprecipitation with anti-LM2 IgG in trout treated with these same inducers. The results suggest a difference between the time course of induction of the mRNA for cytochrome P-450 LM4b isozyme and the induction of catalytic activity. Under the detection system utilized, the results suggest that the phenobarbital-like inducer, 6-CB, does not induce cytochrome activity nor does it induce the mRNA for cytochrome P-450 LM4b isozyme.     

Pretranslational suppression of cytochrome P-450h (IIC11) gene expression in rat liver after administration of interferon inducers.

Administration of the interferon inducer polyriboinosinic acid.polyribocytidylic acid (poly rl.poly rC) (10 mg/kg, ip) to male rats suppressed the constitutive hepatic expression of the male-specific cytochrome P-450 [AH, reduced-flavoprotein/oxygen oxidoreductase (RH hydroxylating), EC 1.14.14.1] isozyme P450IIC11 (P-450h) to 21% of control levels within 24 hr. The mRNA for P-450h was more rapidly suppressed by the drug, being significantly suppressed to 56% of control values within 6 hr of administration. P-450h mRNA levels were further lowered to 10% of control by 24 hr. The kinetics of suppression of P-450h apoprotein and mRNA by poly rl.poly rC indicate that the primary mechanism(s) is (are) at a pretranslational level. Tilorone analog R11-877DA (TA) (50 mg/kg, ip), also an interferon inducer, produced qualitatively similar effects to those of poly rl.poly rC, although the TA produced lesser (51% and 59%) decreases in P-450h protein and mRNA, respectively, 24 hr after injection. Again, the results indicate a pretranslational mechanism of P-450h suppression. Although both interferon inducers suppressed hepatic P-450h expression, the magnitudes of these effects were not notably greater than those on total hepatic P-450, indicating that suppression of rat liver P-450 isozymes by interferon inducers is not confined to P-450h.     

Endotoxin pretreatment protects against the hepatotoxicity of acetaminophen and carbon tetrachloride: role of cytochrome P450 suppression

Bacterial endotoxin (lipopolysaccharide, LPS) is known to potentiate the toxicity of many hepatotoxicants. However, exposure to a sublethal dose of LPS renders animals tolerant to a lethal dose of LPS, and protects against the toxicity of some chemicals. This study was designed to examine the effects of LPS pretreatment on acetaminophen- and carbon tetrachloride (CCl(4))-induced liver injury in LPS-sensitive C3H/OuJ and LPS-resistant C3H/HeJ mice. Pretreatment of male C3H/OuJ mice with a single injection of LPS (0. 1 mg/kg, ip, for 24 h) protected against the hepatotoxic effects of acetaminophen (400 mg/kg) and carbon tetrachloride (CCl(4), 30 mg/kg), as indicated by serum alanine aminotransferase activity. In contrast, pretreatment of C3H/HeJ mice with 0.1 or 10 mg/kg LPS afforded no protection against the hepatotoxic effects of acetaminophen and CCl(4). In an attempt to determine the mechanism of LPS-induced protection against acetaminophen- and CCl(4)-induced hepatotoxicity in C3H/OuJ mice, liver cytochrome P450 was determined 24 h after LPS injection. LPS treatment caused a 26% decrease in total P450 content in C3H/OuJ but not in C3H/HeJ mice. CYP3A-catalized testosterone 6 beta-, 2 beta-, and 15 beta-hydroxylation was decreased 40% by LPS only in C3H/OuJ mice. To determine whether the differences to LPS-response in the two stains of mice is mediated by a strain-related difference in the release of cytokines, mice were pretreated with interleukin-1 (IL-1 alpha, 5 x 10(5) U/mouse), and the hepatoprotection and hepatic P450 enzymes were examined. IL-1 alpha pretreatment equally protected against the hepatotoxicity of acetaminophen and CCl(4) in both strains, and suppressed the total microsomal P450 and P450 enzyme-catalyzed testosterone hydroxylation to a similar extent. In conclusion, LPS pretreatment suppressed hepatic cytochrome P450 enzymes and protected against the hepatotoxicity of acetaminophen and CCl(4) in LPS-sensitive C3H/OuJ mice, but not in LPS-refractory C3H/HeJ mice. This protective effect of LPS appears to be mediated through the release of cytokines such as IL-1 alpha, which in turn suppresses the cytochrome P450 responsible for the activation of acetaminophen and CCl(4) to reactive metabolites.     

β-Naphthoflavone protects mice from aristolochic acid-l-induced acute kidney injury in a CYPIA dependent mechanism

Aim:

The role of CYP1A in the protection of aristolochic acid (AA)I-induced nephrotoxicity has been suggested. In the present study we investigated the effects of β-naphthoflavone (BNF), a non-carcinogen CYP1A inducer, on AAI-induced kidney injury.

Methods:

Mice were pretreated with 80 mg/kg BNF by daily intraperitoneal injection (ip) for 3 days followed by a single ip of 10 mg/kg AAI. AAI and its major metabolites in blood, liver and kidney, the expression of CYP1A1 and CYP1A2 in microsomes of liver and kidney, as well as the nephrotoxicity were evaluated.

Results:

BNF pretreatment prevented AAI-induced renal damage by facilitating the disposal of AAI in liver. BNF pretreatment induced the expression of CYP1A1 in both liver and kidney; but the induction of CYP1A2 was only observed in liver.

Conclusion:

BNF prevents AAI-induced kidney toxicity primarily through CYP1A induction.     

Effects of ortho- and non-ortho-substituted polychlorinated biphenyl congeners on the hepatic monooxygenase system in scup (Stenotomus chrysops)

Polychlorinated biphenyl congeners that are abundant in environmental samples, and known to induce hepatic monooxygenase isozymes in the P450IA gene subfamily in mammals, were examined for their ability to induce hepatic monooxygenase activity in scup, a marine teleost. Scup were dosed ip with 3,3',4,4'-tetrachlorobiphenyl (congener 77), 2,3,3',4,4'-pentachlorobiphenyl (congener 105), 2,3',4,4',5-pentachlorobiphenyl (congener 118), 2,2',3,4,4',5'-hexachlorobiphenyl (congener 138), 2,2',3,3',4,4'-hexachlorobiphenyl (congener 128), or beta-naphthoflavone and examined for increases in ethoxyresorufin O-deethylase (EROD) activity, immunodetectable cytochrome P450E (the EROD catalyst in scup), and in vitro translatable mRNA for P450E. Monooxygenase parameters were significantly induced only by 3,3',4,4'-tetrachlorobiphenyl (TCB). However, while translatable mRNA for P450E was induced at all doses (1, 5, and 10 mg/kg), EROD activity and P450E were decreased at the 5 and 10 mg/kg doses, relative to the response at 1 mg/kg. A strong relationship between residual TCB concentration in the liver and the decreased EROD activity was evident at the higher doses of TCB. Aminopyrine N-demethylase, a monooxygenase activity not catalyzed by P450E, was unaffected by TCB treatment, indicating a specificity in the TCB effect. Analysis in vitro revealed that TCB was a potent competitive inhibitor of EROD activity, with half-maximal inhibition at 0.3 microM, near the Km for ethoxyresorufin, suggesting one mechanism for the in vivo effect of TCB. These results demonstrate that PCB congeners with ortho-chlorine substitution, and which are effective inducers of AHH and EROD activity in mammals, are ineffective, at the doses tested, as inducers in the teleost scup.     

Stereoselectivity and interaction between the glucuronidation of S-(-)- and R-(+)-propranolol in rat hepatic microsomes pretreated with different inducers

Phase II glucuronidation metabolism of side-chain propranolol was studied using microsomes from rats treated with the inducers beta-naphthoflavone (BNF) or dexamethasone (Dex). The glucuronide concentrations of propranolol enantiomers were assayed by RP-HPLC. The kinetic constants of glucuronidation, Km, Vmax and Clint were determined. There are significant differences between the R- and S-enantiomeric glucuronide in Km, Vmax and Clint P < 0.05, P < 0.01 and P < 0.05 in control microsome. There are significant differences in Km and Clint (P < 0.01 or P < 0.001) but no significant differences in Vmax (P > 0.05) between R and S-enantiomeric glucuronide in the microsomes induced with Dex and BNF. The formation of S-(-)-propranolol glucuronide was inhibited by R-(+)-propranolol from the rat microsomes pretreated with BNF and Dex. The glucuronidation metabolism of propranolol enantiomers exhibited the stereoselectivity in rat hepatic microsomes induced with BNF or Dex. Multiple UGT1A and 2B may be involved in stereoselective O-glucuronidation of propranolol enantiomers in rat liver microsomes. The glucuronides produced were in favor of the R-enantiomer. There is an interaction between the glucuronidation of R- and S-enantiomer.     

Effect of cytochrome P450 inducers on the metabolism and toxicity of thiram in rats

Thiram is a dithiocarbamate compound widely used as an agricultural fungicide. This study examined the effect of cytochrome P450 (CYP) inducers on the metabolism and toxicity of thiram in rats. Rats were pretreated with 3-methyl cholathrene (3-MC), phenobarbital (PB), isoniazid (INH), or pregnenolone-16a-carbonitrile (PCN) as selective inducers of CYP 1A1, 2B1, 2E1 and 3A2, respectively. Thiram was administered ip to induced rats at 0.1 or 0.5 mmol/kg, and the animals were sacrificed 3 or 24 h later to assess P450 interaction and liver damage, respectively. No significant inhibition of 3-me-induced CYP1A1 was observed with either thiram dose at 3 or 24 h after treatment; similar results were noted for rats induced with PB or PCN. By contrast, when INH was the selective inducer of CYP2E1, there was significant inhibition by thiram 3 h and 24 h after treatment, suggesting that thiram was metabolized by the induced CYP2E1; there was a significant increase in ALT activity reflective of liver damage in the rats treated with thiram. The results suggest that CYP2EI induced by INH may be significantly involved in the metabolism of thiram, and the associated liver damage.     

Induction of renal and hepatic mixed function oxidases in the hamster and guinea pig

A marked species difference exists in the induction of renal and hepatic mixed function oxidase (MFO) activity between rats and rabbits. However, little is known about MFO induction in these organs from other laboratory animals. Male Golden Syrian hamsters and male Hartley guinea pigs were administered phenobarbital (PB) or beta-napthoflavone (BNF) at 70 and 40 mg/kg, respectively, as daily i.p. injections for 4 days. Polybrominated biphenyl (PBB) (Firemaster BP-6) was given as a single i.p. injection (50 mg/kg). Hamster hepatic microsomal ethoxyresorufin-O-deethylase (EROD) and benzphetamine-N-demethylase (BPND) were selectively induced by BNF and PB, respectively. PBB administration induced both hamster hepatic EROD and BPND. In contrast, hepatic microsomal MFO activity from the guinea pig was inducible by PB, PBB and BNF. Renal microsomal MFO activity in both species was inducible by BNF and PBB as arylhydrocarbon hydroxylase and EROD were induced approximately 10-fold. On the other hand, hamster BPND was induced by PB whereas guinea pig MFO activity was unaffected. Total renal cytochrome P-450 content was not affected by any of these inducers in either species. These data demonstrate selective patterns of induction in both hamster and guinea pig liver and kidney suggesting the involvement of multiple forms of cytochrome P-450.     

地非三唑在鼠肝微粒体中的体外代谢

目的　为了解地非三唑 (Dip)在不同预处理的鼠肝微粒体中主要受何种酶代谢影响 ,为其临床合理应用和进一步开发利用提供科学依据。方法　将Dip与 6种不同诱导剂〔苯巴比妥 (PB)、地塞米松(Dex)、β 萘黄酮 (BNF)、Dip、吡啶和空白对照〕诱导的鼠肝微粒体进行体外共孵育 ,用氯仿终止反应 ,以地西泮为内标 ,采用反相高效液相色谱 (RP HPLC)法测定孵育后剩余的Dip的含量。结果　BNF诱导的鼠肝微粒体对Dip代谢具有强烈的催化活性 ,Dip诱导的微粒体的催化能力次之 ,PB诱导组也有一定的催化能力 ,其他几种诱导剂诱导的微粒体对Dip代谢能力与对照组无明显差别。测得Dip在BNF诱导的鼠肝微粒体中的Km 为 (6 0 .5± 1.3) μmol·L- 1,vm 为 (5 .6± 0 .4 )mmol·g- 1·min- 1。结论　由BNF诱导的鼠肝微粒体 (主要为细胞色素P4 5 0 1A)和PB诱导的鼠肝微粒体 (主要为细胞色素P4 5 0 2B)在Dip的体外代谢中可能起主导作用 ;Dip诱导的鼠肝微粒体对其自身的代谢也起了重要作用。     

In vivo metabolism of CCl4 by rats pretreated with chlordecone, mirex, or phenobarbital

The propensity of chlordecone (CD) to potentiate hepatotoxic and lethal effects of CCl4 is well established. Mirex (M), a close structural analogue of CD, or phenobarbital (PB), powerful inducers of hepatic microsomal drug metabolizing enzymes, are much weaker potentiators of CCl4 toxicity. The purpose of this study was to test the possibility that CD potentiates the toxicity of CCl4 by increasing the metabolism of CCl4 to a greater degree than either PB or M. We compared the in vivo metabolism of CCl4 in rats pretreated with CD, M, or PB, by measuring the hepatic content of 14CCl4, the expiration of 14CCl4, expiration of 14CCl4-derived 14CO2, and lipid peroxidation. Male Sprague-Dawley rats (250-270 g) were pretreated with a single oral dose of CD (10 mg/kg), M (10 mg/kg), or corn oil vehicle (1 ml/kg). PB pretreatment consisted of an ip injection of sodium PB (80 mg/kg) in saline (0.9%) for 2 successive days. Twenty-four hours later, 14CCl4 (0.1 ml/kg; sp act: 0.04 mCi/mmol) was administered ip in corn oil and the radioactivity present in the expired air was collected for 6 hr. Excretion of the parent compound as represented by the 14C label in the toluene trap was unchanged by any of the pretreatments. Expiration of 14CO2 measured during the 6 hr after CCl4 administration was increased in animals pretreated with PB or CD. In vivo lipid peroxidation measured as diene conjugation in lipids extracted from the livers was increased to a similar extent in animals pretreated with PB and CD, whereas the serum transaminases (ALT, AST) were significantly elevated only in animals pretreated with CD.M did not affect 14CO2 production and was without a significant effect on the lipid peroxidation. The radiolabel present in the liver at 6 hr showed no difference in hepatic content of free 14CCl4 among the groups, but the covalently bound label present in the lipid fractions of the livers pretreated with PB was elevated in comparison to CD and M treatments. These data indicate that a single oral administration of CD (10 mg/kg) 24 hr prior to CCl4 administration (100 microliter/kg) enhances the oxidative metabolism of CCl4 but to a lesser extent than PB (80 mg/kg, ip, twice), which is in inverse relationship to the potentiation of the hepatotoxic and lethal effects of CCl4 associated with these pretreatments.     

Effect of pretreatment of cytochrome P450 (P450) modifiers on neurobehavioral toxicity induced by deltamethrin.

To investigate the involvement of cytochrome P450 (P450) enzyme induction and the effect of different P450 modifiers in the neurobehavioral toxicity of deltamethrin, deltamethrin (10 mg/kg; orally for 1 day) was administered to young male albino Wistar rats, or in rats pretreated with phenobarbital (PB; 80 mg/kg, ip for 5 days), an inducer of P450 2B1/2B2 or 3-methylcholanthrene (MC; 30 mg/kg, ip for 5 days), an inducer of P450 1A1/1A2 or cobalt chloride (CoCl(2); sc for 2 days), a depletor of P450s. The administration of PB or MC or CoCl(2) alone did not produced any symptoms of neurobehavioral toxicity. While a single oral administration of deltamethrin produced tremors in two out of 10 rats and decreased the spontaneous locomotor activity, pretreatment with MC or PB potentiated the deltamethrin induced neurobehavioral toxicity with 50% of the treated rats exhibiting tremors. Half of the animals pretreated with MC prior to exposure to deltamethrin also exhibited choreoathetosis. The decrease in the spontaneous locomotor activity was found to be much more significant in PB- or MC-pretreated animals exposed to deltamethrin. In contrast to the pretreatment with inducers, rats pretreated with CoCl(2) exhibited no symptoms of tremors or choreoathetosis, indicating that a reactive metabolite of deltamethrin is formed by P450 catalysed reactions which is involved in the neurobehavioral toxicity of deltamethrin.     

Effect of monensin on liver glutathione, glutathione S-transferase and monooxygenases in rats.

Monensin administered ip to male rats at a dosage of 2.5 mg/kg/d for 3 consecutive days did not change the liver levels of glutathione, but depressed significantly the amount of cytochrome P-450 and the activities of aniline hydroxylase and a cytosolic CDNB-specific glutathione S-transferase. There was a marked decrease in the aminopyrine N-demethylase activity and a significant increase in the pentobarbital sleeping time in rats treated with monensin. In contrast, no change in these parameters was found 2 h after a single ip dose (7.5 mg/kg) of monensin. The results suggest that monensin-induced inhibition of the liver cytosolic glutathione S-transferase and microsomal monooxygenases is non-specific.     

Renal and hepatic microsomal enzymes responsible for bioactivation of 3-methoxy-4-aminoazobenzene in the rodent

Activities of the renal and hepatic microsomal enzymes responsible for the N-hydroxylation and mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) were examined in male mice, rats, hamsters and guinea pigs. In all these rodent species, hepatic microsomes showed definite N-hydroxylation of 3-MeO-AAB, whereas the renal activity was detected only in mice. The hepatic enzyme responsible for N-hydroxylation of 3-MeO-AAB (3-MeO-AAB N-hydroxylase) was induced in all species except mice by phenobarbital and selectively in mice and hamsters by 3-methylcholanthrene, whereas these cytochrome P450 inducers did not affect the renal enzyme in mice, rats or hamsters. In individual microsome samples, activities for N-hydroxylation and mutagenic activation of 3-MeO-AAB correlated well. These results indicate that the renal and hepatic enzymes responsible for the metabolic activation of 3-MeO-AAB differed among different species of rodent animals in terms of their activity and inducibility with cytochrome P450 inducers.     

Aryl hydrocarbon hydroxylase activity levels in the hepatic microsomal fraction from MC- or TCDD-treated mice: a comparison between aromatic hydrocarbon responsive and non-responsive strains

The effects of in vivo administration of polycyclic aromatic hydrocarbons on the levels of aryl hydrocarbon hydroxylase (AHH) activity in aromatic hydrocarbon (Ah) responsive and non-responsive strains of mice were studied using the hepatic microsomal fraction. Injection of 3-methylcholanthrene (MC; 42 mg/kg body wt.) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 120 micrograms/kg body wt.) into both strains produced marked enhancement of AHH activity except for MC treatment of Ah non-responsive strains. Addition of 7,8-benzoflavone (BNF) to the microsomal AHH assay mixture prepared from mice previously injected with vehicle (olive oil) alone caused an increase in activity when the mice were responsive, while BNF lowered the activity in non-responsive strains. With regard to MC-injected mice, BNF and 3-methyl-sulphonyl-4,5,3',4'-tetrachlorobiphenyl (3-MSF-TCB) decreased microsomal AHH activity in Ah-responsive mice, whereas these drugs enhanced the activity in Ah-non-responsive strains. 3-MSF-TCB also had inhibitory potency on AHH activity, but the mechanism of inhibition seems to be somewhat different from that of BNF. It may also suggest that cytochrome P-450 isozymes inhibited by BNF are different from those inhibited by 3-MSF-TCB.     

Changes in pentobarbital hypnosis and hepatic metabolism in streptozotocin-diabetic mice

The present study deals with the hypnotic effect of pentobarbital (Pento) in relation to its metabolism in hepatic microsomes in streptozotocin (STZ, 170 mg/kg, i.p.) injected mice. Liver weight (mg/10 g body wt.) of STZ-treated mice was larger than that of the controls throughout the experimental period. Although the shortening of sleeping time induced by Pento (60 mg/kg, i.p.) was always observed, Pento-metabolizing enzyme activity (by the method of Kato et al., 1964) increased in mice with diabetes for 2 and 4 weeks but decreased in mice with diabetes for 8 weeks. Induction following phenobarbital (100 mg/kg, s.c.) and inhibition by SKF 525-A (10 mg/kg, i.p.) of hepatic metabolizing enzyme were found in both control and mice with diabetes for 2, 4 and 8 weeks, but these were not definitely correlated to their hepatic Pento-metabolizing enzyme activities. STZ-induced hyperglycemia and shortening of sleeping time by Pento were completely prevented by the pretreatment with nicotinamide (500 mg/kg, i.p.). NPH-insulin injection partially decreased hyperglycemia in STZ-diabetic mice, but sleeping time by Pento was not significantly affected. These results suggest that the hyposensitivity to Pento in STZ-diabetic mice is partially related to an abnormality of metabolism in liver such as the hyperglycemic state.     

六氯对二甲苯对豚鼠肝药酶的抑制作用

六氯对二甲苯(HCX)单剂(50-100mg/kg)或多剂(100mg/kg,qd×6d或50mg/kg,qd×14d,ip)均能极显著延长豚鼠戊巴比妥钠催眠时间,HCX 100mg/kg ip使豚鼠血浆戊巴比妥t 1/2 β延长3.2倍,并使豚鼠肝匀浆内戊巴比妥侧链羟化酶和氨基比林N-脱甲基酶活性明显降低。表明HCX是豚鼠肝药酶的抑制剂。而大鼠ip HCX 100mg/kg对其血浆戊巴比妥t 1/2 β确无明显影响。     

Effect of ozone on drug-induced sleeping time in mice pretreated with mixed-function oxidase inducers and inhibitors

Prior studies have shown that ozone (O₃) increases pentobarbital (PEN)-induced sleeping time (S.T.) in female mice, rats, and hamsters. To investigate some potential mechanisms producing these effects, we measured zoxazolamine-induced paralysis time and thiopental- and hexobarbital-induced S.T., all of which were prolonged significantly in mice following a 5-hr exposure to 1960 μg O₃/m³ (1 ppm). To probe the effect of O₃ exposure on the drug metabolism microsomal monooxygenase system, CD-1 mice were pretreated with mixed-function oxidase inducers [PEN, phenobarbital, pregnenolone-16α-carbonitrile, and β-naphthoflavone (BNF)] or inhibitors (SKF 525A and piperonyl butoxide) prior to a 5-hr exposure to 1960 μg O₃/m³ (1 ppm). In CD-1 mice, pretreatment with PEN caused no effects on PEN-induced S.T. For all other compounds, the PEN-induced S.T. of CD-1 mice was significantly decreased, irrespective of whether the animals were exposed to air or O₃. Ozone exposure significantly increased PEN-induced S.T. equivalently in the vehicle- and inducer-pretreated animals. Similar studies were conducted in DBA and C57BL mice pretreated with BNF. DBA mice responded similarly to CD-1 mice. However, with C57BL mice, O₃ significantly increased PEN-induced S.T. in the vehicle, but not in the BNF group. When CD-1 mice were pretreated with inhibitors, a generally increased magnitude of the O₃ effect was observed with increasing doses of inhibitor. These data suggest that O₃ exposure may affect several aspects of drug metabolism and distribution.     

The role of cytochrome P-450-inducing agents in potentiaing the toxicity of fluroxene (2,2,2-trifluoroethyl vinyl ether)

The effects of the hepatic microsomal cytochrome P-450-inducing agents 3-methylcholanthrene (MC), benzo[α]pyrene (BP), β-naphthoflavone (BNF), mirex, 8-hydromirex, Kepone, spironolactone, pregnenolone-16α-carbonitrile (PCN), barbital, phenobarbital (PB), mephobarbital, hexobarbital, and pentobarbital in potentiating the toxicity of the anesthetic fluroxene (2,2,2-trifluoroethyl vinyl ether) in male rats have been investigated. The toxicity was expressed as death, hepatic necrosis, or destruction of hepatic cytochrome P-450. Only PCN, mephobarbital, and phenobarbital induction caused death within 48 hr of the administration of fluroxene (2.5 g/kg, ip), and this was prevented by administration of cytochrome P-450 inhibitors. With PB induction the percentage of mortality correlated with the induced cytochrome P-450 concentrations. Fluroxene destroyed microsomal cytochrome P-450 in vivo, within 90 min of administration, and this destruction was enhanced over twofold by pretreatment of the rats with MC, BP, and all the barbiturates, and less significantly with BNF, Kepone, and PCN. Only the livers of mirex-, 8-hydromirex-, or MC-induced rats showed necrosis within 48 hr of administration of fluroxene, with 8-hydromirex-induced livers showing the most widespread necrosis. We conclude that a number of different forms of cytochrome P-450 can metabolize fluroxene to toxic products. Some forms of cytochrome P-450, particularly cytochrome P-448, are highly susceptible to destruction by fluroxene metabolites which probably arise from metabolism of the fluroxene vinyl group. Fluroxene-induced liver necrosis is not related to the destruction of cytochrome P-450, nor to the death of the experimental animals. Thus, the three aspects of fluroxene toxicity—mortality, cytochrome P-450 destruction and hepatic necrosis—are differentially affected.     

对氨基二苯醚类似物抑制细胞色素P－450的定量构效关系

测定了一组对氨基二苯醚类似物延长小鼠戊巴比妥睡眠时间和体外抑制未经处理的小鼠肝微粒体催化氧化对硝基茴香醚脱甲基的活性。用逐步多元回归分析法导出了这些类似物体内和体外抑制细胞色素Ｐ－４５０（Ｐ－４５０）的活性与量化指数的定量构效关系（ＱＳＡＲ）。结果表明：对氨基二苯醚类似物体内和体外抑制Ｐ－４５０的活性均与最低未占据分子轨道能级（ＥＬＵＭＯ）、氨基氮原子的亲核超离域度（ＳＮ（Ｎ））和醚氧原子的亲核超离域度（ＳＮ（Ｏ））相关。这些类似物的代谢中间体（ＭＩ）与Ｐ－４５０形成Ｐ－４５０代谢中间体络合物（Ｐ－４５０－ＭＩ）可能是它们能够抑制Ｐ－４５０的主要原因。     

四氯化碳致大鼠肝损伤的机理

给大鼠一次po四氯化碳(CCl_4)23 mmol/kg后,血清ALT分别于3和12 h起逐渐增高;肝微粒体细胞色素P450同时下降。染毒后24和48 h肝线粒体GSH明显降低,胞液GSH则未见明显变化。血清脂质过氧化物丙二醛(MDA)经时过程呈双相,即染毒后3～24 h明显降低,至48 h则显著增高。染毒后12～48 h肝线粒体和微粒体MDA明显增高;同时膜脂流动性增高.8-甲氧补骨脂素预处理可显著降低CCl_4引起的肝匀浆MDA和血清ALT增高。结果提示CCl_4均裂产物启动的膜脂过氧化和流动性增高可能是CCl_4致肝损伤的二次反应。