Induction of drug metabolizing enzymes by 1,7-phenanthroline and oltipraz in mice is unrelated to Ah-responsiveness

The protective effect of several classes of compounds against the toxic and neoplastic effects of xenobiotics has been attributed to the induction of noncytochrome P450 (P450) drug metabolizing enzymes. Glutathione S-transferases (GST), NAD(P)H: quinone oxidoreductase (QOR), and UDP-glucuronosyltransferases (UGT) play a prominent role in detoxification and can be induced by oltipraz and other N-heterocyclic compounds in rats. In contrast to the induction of these enzymes by aryl hydrocarbon (Ah)-receptor agonists, induction by oltipraz and 1,7-phenanthroline is not accompanied by CYP1A induction. This study investigated the induction of drug metabolizing enzymes following administration of oltipraz and 1,7-phenanthroline in four mouse strains (C57B6A-J, Frings x C57B6J, Frings, CF-1) exhibiting varying degrees of responsiveness to an Ah-receptor agonist. The relative Ah responsiveness was determined in all strains by the induction of hepatic Cypla after three daily doses of 3-methylcholanthrene (20 mg/kg). After treatment with 1,7-phenanthroline and oltipraz (150 mg/kg i.g.) daily for 3 days, all strains showed similar induction of GST and QOR activities for each inducer. Both compounds were equally effective in elevating GST activity, but 1,7-phenanthroline was more effective than oltipraz in elevating QOR activity. In addition to GST and QOR changes, 1,7-phenanthroline significantly elevated UGT (1-naphthol) activity in the Frings strain. Neither compound produced significant changes in Cypla parameters. The independence of 1,7-phenanthroline and oltipraz induction of GST and QOR from Cypla-responsiveness is in line with the concept that N-heterocycle-containing inducers act by mechanisms other than an Ah-receptor-dependent pathway in which the P450 response has been masked or prevented.     

Postnatal effect of smokeless tobacco on phytic acid or the butylated hydroxyanisole-modulated hepatic detoxication system and antioxidant defense mechanism in suckling neonates and lactating mice

The present study evaluates the potential of smokeless tobacco to translactationally modify the chemopreventive efficacy of phytic acid and butylated hydroxyanisole (BHA) via modulation of the hepatic xenobiotic detoxication system and antioxidant defense mechanism in the murine system. Phytic acid (1000 mg/kg b.w./day) by gavage while BHA (1% w/w) in diet induced a significant increase in the levels of glutathione-S-transferase (GST), acid soluble sulfhydryl (-SH), cytochrome b5 (Cyt. b5) and cytochrome P-450 (Cyt. P-450) in lactating dams and suckling pups. The hepatic levels of GST and -SH were significantly depressed whereas microsomal Cyt. b5, Cyt. P-450 and MDA levels were elevated in groups treated with smokeless tobacco (50 or 100 mg/kg b.w./day). The data reveals the inhibitory potential of smokeless tobacco on phytic acid-induced GST/GSH system efficiency besides the significant augmentation by smokeless tobacco on phytic acid or BHA-induced microsomal phase I enzymes. The direct or translactational modulation in the levels of xenobiotic detoxication system enzymes suggests the potential of smokeless tobacco to modify the chemopreventive efficacy of phytic acid or BHA.     

Change in activity of microsomal cytochrome P-450-dependent monooxygenases from rat liver exposed to chronic low doses of radiation

The activity changes of cytochrome P-450-dependent monooxygenases of hepatic microsomal fraction were studied in, experimental animals after prolonged application (1 month) of low radiation doses (0.258 mkl/kg). The obtained results show the increase in catalytic activities of main forms of cytochrome P-450, participating in steroid hydroxylation, as well as the decrease in total content of cytochrome P-450 in hepatic microsomal fraction and the lowering of its demethylase activity.     

Modulation of cytochrome P-450-dependent monooxygenases, glutathione and glutathione S-transferase in rat liver by geniposide from Gardenia jasminoides

Geniposide is an iridoid glycoside extracted from the fruits of Gardenia jasminoides, which are used as a food colorant and as a traditional Chinese medicine for treatment of hepatic and inflammatory diseases. The effects of geniposide and G. jasminoides fruit crude extract on liver cytochrome P-450 (P-450)-dependent monooxygenases, glutathione and glutathione S-transferase were investigated using rats treated orally with the iridoid glycoside (0.1 g/kg body weight/day) or the fruit crude extract (2 g/kg/day) for 4 days. The treatments decreased serum urea nitrogen level but increased liver to body weight ratio, total hepatic glutathione content and hepatic cytosolic glutathione S-transferase activity. Treatments with geniposide and G. jasminoides decreased P-450 content, benzo[a]pyrene hydroxylation, 7-ethoxycoumarin O-deethylation, and erythromycin N-demethylation activities in liver microsomes without affecting aniline hydroxylation activity. The natural products had no effect on glutathione content and monooxygenase activities in kidney microsomes. Immunoblotting analyses of liver microsomal proteins using mouse monoclonal antibody 2-13-1 to rat P4503A1/2 revealed that geniposide and G. jasminoides crude extract decreased the intensity of a P4503A-immunorelated protein. Protein blots probed with mouse monoclonal antibody 1-12-3 to rat P4501A1 and rabbit polyclonal antibody against human P4502E1 showed that both treatments had little or no effect on P4501A and 2E proteins. The present findings demonstrate that geniposide from G. jasminoides has the ability to inhibit a P4503A monooxygenase and increase glutathione content in rat liver.     

Interactions of the bacterial pathogen Listeria monocytogenes with mammalian cells: bacterial factors, cellular ligands, and signaling

Risedronate ([1-hydroxy-2-(3-pyridinyl)-ethylidene[bis]phosphonic acid] monosodium salt) was evaluated for induction of hepatic microsomal drug metabolizing enzymes in male and female Sprague Dawley rats (N = 4/sex/dose group). Main study animals received water (vehicle control), risedronate (0.1, 0.8, 4, or 16 mg/kg/day) or phenobarbital (80 mg/kg/day, positive control) by daily oral gavage for 14 consecutive days. Recovery study animals received water, risedronate (16 mg/kg/day) or phenobarbital (80 mg/kg/day) by daily oral gavage for 14 consecutive days and then were maintained drug-free for 14 days to evaluate the reversibility of any observed effects. At the conclusion of each study the animals were sacrificed, the liver removed, weighed and the microsomal subcellular fraction prepared. The hepatic microsomal fraction was then evaluated for protein content, cytochrome P450, and the activities of aniline hydroxylase, aminopyrine N-demethylase, ethoxycoumarin O-deethylase and p-nitrophenol UDP-glucuronosyltransferase. Risedronate was well tolerated during the dosing phase of the study as evidenced by clinical observations, body weight gain and food consumption which were not significantly different from the vehicle controls. Risedronate did not significantly increase (P > 0.05) liver weight, liver/body weight ratio, protein content, P450, aniline hydroxylase, aminopyrine N-demethylase, ethoxycoumarin O-deethylase or p-nitrophenol UDP-glucuronosyltransferase in rats of either sex when compared to vehicle controls. As expected, the hepatic microsomal enzyme inducer phenobarbital significantly increased (P < 0.05) liver weight, liver/body weight ratio, protein content (males only), P450, aniline hydroxylase (males only), aminopyrine N-demethylase (males only), ethoxycoumarin O-deethylase and p-nitrophenol UDP-glucuronosyltransferase in rats relative to vehicle controls. Following the 14 day drug-free recovery period the induction parameters increased by phenobarbital reversed to vehicle control levels. The results obtained in this well controlled study indicate that risedronate is not an inducer of hepatic microsomal drug metabolizing enzymes in the rat.     

Identification of the mechanical impedance at the human finger tip

The present study evaluates the potential of smokeless tobacco to modify the chemopreventive efficacy of minor dietary constituents, including garlic, mace or black mustard, via modulating the competing pathways of hepatic detoxication system and antioxidant defense mechanism in murine system. Garlic (100 mg/kg b.w. per day) by gavage and mace (1% w/w) or black mustard (1% w/w) in diet induced a significant increase in the levels of glutathione-S-transferase (GST), acid-soluble sulfhydryl (-SH), cytochrome b5 (Cyt.b5) and cytochrome P-450 (Cyt.P-450) in murine liver. The hepatic levels of GST and -SH were significantly depressed whereas microsomal Cyt.b5, Cyt.P-450 and MDA levels were elevated in groups treated with smokeless tobacco (50 or 100 mg/kg b.w. per day). The data revealed the inhibitory potential of smokeless tobacco on garlic-induced hepatic GST/GSH system besides the significant augmentation by smokeless tobacco on garlic or mace or black mustard-induced microsomal cytochromes. The possible implications of modulation in competing bioactivation and detoxication pathways in the process of chemical carcinogenesis are discussed.     

Bronchoalveolar lavage studies in children without parenchymal lung disease: cellular constituents and protein levels

The hepatotoxicity of acetaminophen overdose depends on the metabolic activation to a toxic reactive metabolite by the hepatic mixed function oxidases. There is evidence that an increase in cytosolic Ca2+ is involved in acetaminophen hepatotoxicity. The effects of the Ca2+-antagonists nifedipine (NF), verapamil (V), diltiazem (DL) and of the calmodulin antagonist trifluoperazine (TFP) on the activity of some drug-metabolizing enzyme systems, lipid peroxidation and acute acetaminophen toxicity were studied in male albino mice. No changes in the drug-metabolizing enzyme activities studied and in the cytochrome P-450 and b5 contents were observed 1 h after oral administration of V (20 mg/kg). DL (70 mg/kg) and TFP (3 mg/kg). NF (50 mg/kg) increased cytochrome P-450 content, NADPH-cytochrome c reductase and ethylmorphine-N-demethylase activities. DL and TFP significantly decreased lipid peroxidation. NF, V, DL and TFP administered 1 h before acetaminophen (700 mg/kg orally) increased the mean survival time of animals. A large increase of serum aspartate aminotransferase(AST), and liver weight and depletion of liver reduced glutathione (GSH) occurred in animals receiving toxic acetaminophen dose. NF, V and DL prevented and TFP decreased the acetaminophen-induced hepatic damage measured both by plasma AST and by liver weight. NF, V, DL and TFP changed neither the hepatic GSH level nor the GSH depletion provoked by the toxic dose of acetaminophen. This suggests that V, DL and TFP do not influence the amount of the acetaminophen toxic metabolite formed in the liver. The possible mechanism of the protective effect of NF, V, DL and TFP on the acetaminophen-induced toxicity is discussed.     

Effects of motorcycle exhaust on cytochrome P-450-dependent monooxygenases and glutathione S-transferase in rat tissues

The effects of motorcycle exhaust (ME) on cytochrome P-450 (P-450)-dependent monooxygenases were determined using rats exposed to the exhaust by either inhalation, intratracheal, or intraperitoneal administration. A 4-wk ME inhalation significantly increased benzo[a]pyrene hydroxylation, 7-ethoxyresorufin O-deethylation, and NADPH-cytochrome c reductase activities in liver, kidney, and lung microsomes. Intratracheal instillation of organic extracts of ME particulate (MEP) caused a dose- and time-dependent significant increase of monooxygenase activity. Intratracheal treatment with 0.1 g MEP extract/kg markedly elevated benzo[a]pyrene hydroxylation and 7-ethoxyresorufin O-deethylation activities in the rat tissues 24 h following treatment. Intraperitoneal treatment with 0.5 g MEP extract/kg/d for 4 d resulted in significant increases of P-450 and cytochrome b5 contents and NADPH-cytochrome c reductase activity in liver microsomes. The intraperitoneal treatment also markedly increased monooxygenases activities toward methoxyresorufin, aniline, benzphetamine, and erythromycin in liver and benzo[a]pyrene and 7-ethoxyresorufin in liver, kidney, and lung. Immunoblotting analyses of microsomal proteins using a mouse monoclonal antibody (Mab) 1-12-3 against rat P-450 1A1 revealed that ME inhalation, MEP intratracheal, or MEP intraperitoneal treatment increased a P-450 1A protein in the hepatic and extrahepatic tissues. Protein blots analyzed using antibodies to P-450 enzymes showed that MEP intraperitoneal treatment caused increases of P-450 2B, 2E, and 3A subfamily proteins in the liver. The ME inhalation, MEP intratracheal, or MEP intraperitoneal treatment resulted in significant increases in glutathione S-transferase activity in liver cytosols. The present study shows that ME and MEP extract contain substances that can induce multiple forms of P-450 and glutathione S-transferase activity in the rat.     

Role of metabolism by esterase and cytochrome P-450 in cocaine-induced suppression of the antibody response

To investigate the role of metabolism in cocaine-induced immunosuppression, diazinon and beta-ionone were administered as an esterase inhibitor and a cytochrome P-450 (P-450) inducer, respectively, to B6C3F1 female mice. When 10 or 30 mg/kg of diazinon was administered 30 min before cocaine (30 mg/kg) was administered i.p. for 7 consecutive days, the suppression of the T-dependent antibody response to sheep red blood cells was potentiated greatly when compared to the suppression by cocaine alone. Spleen and thymus weights were decreased significantly and serum glutamate-pyruvate transaminase activities were elevated dramatically when cocaine and diazinon were administered together. beta-Ionone was administered s.c. for 7 consecutive days and the P-450 activities were determined 3 days after the last administration. beta-Ionone induced cocaine N-demethylation, which is the first step in the activation of cocaine to the metabolites capable of producing hepatotoxicity, as well as P-450IA1- and P-450IIB1-specific monooxygenases. The inductive effects of beta-ionone on P-450IA1/2 and P-450IIB1/2 proteins were confirmed by using Western immunoblotting with selective monoclonal antibodies. In addition, when beta-ionone (600 mg/kg) was administered with cocaine for 7 days, the suppression of the antibody response was potentiated greatly, thymus weight was decreased significantly and serum glutamate-pyruvate transaminase was elevated. Our present results suggest that inhibition of the esterase pathway of cocaine shunts the metabolism of cocaine into an immunotoxic pathway, and that the metabolism of cocaine by P-450 may be the critical pathway for the generation of the metabolites capable of suppressing the antibody response.     

Nitroreduction of 2,4-dinitrotoluene in vitro by cytochrome P-450 induced H4IIE cells

Conditions have been established for H4IIE rat hepatoma cell cultures in which effects of cytochrome P-450 induction on the metabolism of a munitions wastestream pollutant can be studied. Under these conditions, the polychlorinated hydrocarbon 2,3,4,7,8-pentachlorodibenzfuran (PCDBF) induced cytochrome P-450 (1A1) aryl hydrocarbon hydroxylase (AHH) activity over a wide range of concentrations without significant cytotoxic effects. The munition pollutant 2,4-dinitrotoluene (2,4-DNT) did not induce AHH activity itself, but its metabolism was considerably altered when applied to PCDBF induced cultures. Production of amino nitrotoluene isomers was greatly enhanced in induced cultures as compared to uninduced controls, as was the conversion of radiolabeled 2,4-DNT to relatively more polar metabolites. To some extent, the results with H4IIE cells parallel those reported for animals exposed to 2,4-DNT after induction of cytochrome P-450 AHH activity. The preliminary findings suggest that with further development and validation, H4IIE cultures could be of use in characterizing metabolites that result from exposure to chemical mixtures involving a P-450 (1A1) inducer.     

Activities of conjugating and antioxidant enzymes following endotoxin exposure

Endotoxin exposure elicits various responses in mammals including the acute phase response that has been shown to cause changes in the activity of several forms of cytochrome P450s and other enzymes. Therefore, the hepatic conjugating enzyme, glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT), the antioxidant enzymes, glutathione peroxidase (GSHPx), catalase, and superoxide dismutase (SOD), as well as lipid peroxidation were investigated following the administration of endotoxin to male Sprague-Dawley rats (8 mg/kg body weight). Rats were euthanized at various times following endotoxin administration and the livers removed and processed to assess various enzyme activities. Glutathione S-transferase, UDPGT, and GSHPx activity showed statistically significant decreases after 24 hours and remained lower than controls for the duration of the study. Decreases in total SOD and catalase activities were seen at 24, 48, and 72 hours following endotoxin administration; however, only catalase activity showed statistically significant differences between control and treated samples at those time points, and total SOD activity showed a statistically significant decrease at 24 hours. No statistically significant changes were seen in the level of lipid peroxidation in the liver microsomes from endotoxin-treated animals. Changes in the conjugative enzymes and the free-radical scavenging enzymes following endotoxin exposure may alter the host's metabolism and response to free radicals.     

Genotoxic effect of triarylmethane dye--acid green 16 after chronic ethanol consumption in mice

Genotoxic effect and hepatic microsomal monooxygenase activities were assessed in mice treated with Acid Green 16 (single i.p. injection at dose 75 mg/kg) superimposed on prolonged ethanol consumption (10% solution in drinking water for 2-4 months). Treatment of mice with Acid Green 16 led to an increased frequency of micronucleated erythrocytes in bone marrow. In animals pretreated with ethanol the frequency of micronucleated erythrocytes, produced by Acid Green 16, was significantly higher. The changes in frequency of micronucleated erythrocytes were accompanied by the enhanced activity of microsomal monooxygenases manifested by higher activity of 7-ethoxycoumarin o-deethylase (the level of cytochrome P-450 was not altered). The obtained results showed that ethanol tended to increase the genotoxic effect of Acid Green 16. However, the slight inductive effect of ethanol on microsomal monooxygenases did not provide clear evidence that the genotoxic effect of Acid Green 16 was associated with ethanol stimulation of the metabolic activation of the dye in the liver.     

Relationship between cytochrome P-450 induction by rifampicin, hepatic volume and portal blood flow in man

OBJECTIVE: Induction of hepatic cytochrome P-450-dependent oxidative metabolism is related to an almost identical increase (30%) in both the liver weight and portal blood flow in animals. In humans by contrast, an increased liver blood flow (44%) but no significant increase in liver volume has been reported. DESIGN: Therefore, we studied prospectively the relationship between P-450 induction by rifampicin, hepatic volume and portal blood flow in 10 healthy volunteers. METHODS: After a pre-treatment phase (day 1 to 7) the 10 volunteers received 600 mg/day of rifampicin from day 7 to 12. The urinary 6-beta-hydroxycortisol output as a measure of oxidative metabolism (CYP3A4) and portal blood flow (pulsed Doppler ultrasound) were determined on days 1, 7, 11 and 13. Hepatic magnetic resonance volumetry was performed on days 1 and 13. RESULTS: Urinary 6-beta-hydroxycortisol output increased in all volunteers (P = 0.0051) from a median of 2.15 micrograms/day/kg (1.8-3.3 micrograms/day/kg) on day 1 to 9.9 micrograms/day/kg (5.7-14 micrograms/day/kg) on day 13. In 9 of 10 volunteers induction by rifampicin was related to an increase (P = 0.0218) in liver volume from a median of 1570 cm3 (1390-1830 cm3) to a median of 1690 cm3 (1420-1860 cm3). The portal flow as assessed by colour Doppler ultrasound did not change significantly between day 1 (median 22 cm/s (15-35 cm/s)) and day 13 (median 19 cm/s (16-39 cm/s)). CONCLUSION: A fourfold increase of urinary 6-beta-hydroxycortisol output after induction of cytochrome P-450 by rifampicin is associated with a significant but less than 10% increase in human liver volume. No increase of portal perfusion as assessed by Doppler ultrasound could be detected in this study.     

Effect of cobalt on the synthesis of liver microsomal cytochromes

1. The amount of cytochrome b5 was not changed significantly by a single injection of cobalt (60 mg/kg body weight) or by daily injection of cobalt (30 mg/kg body weight) for 4 days or 8 days. On the other hand, the amount of cytochrome P-450 was depressed strongly by both cobalt treatments. 2. The incorporations of [3H]leucine as well as 5-amino[3H]levulinate into cytochrome b5 in cobalt-treated animals were almost the same as those in the controls 5 h after injections of the radioisotopes, whereas the radioactivity of heme labelled with 5-amino[3H]levulinate in microsomal residues after trypsin digestion, which would consist mainly of cytochrome P-450, was higher in the controls than in cobalt-treated animals after 5 h.     

Rosemary extract and carnosol stimulate rat liver glutathione-S-transferase and quinone reductase activities

The effects of dietary intake and intraperitoneal (i.p.) administration of an extract of the spice rosemary and of the rosemary constituent carnosol on the liver activities of glutathione-S-transferase (GST) and NAD(P)H-quinone reductase (QR) in the female rat were evaluated. Rosemary extract at concentrations from 0.25 to 1.0% (by wt.) in the diet resulted in a significant 3.5- to 4.5-fold increase in liver GST and a 3.3- to 4.0-fold increase in liver QR activities compared to controls. Carnosol supplemented in the diet at levels from 0.01 to 1.0% did not enhance GST activity. When rosemary extract and carnosol were administered i.p. there was a significant increase in liver GST and QR activities. The injection of rosemary extract (200 mg/kg) was associated with 1.5-fold and 3.2-fold increases in GST and QR activities, respectively, compared to controls. The injection of carnosol at doses from 100 to 400 mg/kg was associated with 1.6- to 1.9-fold increases in GST activity and 3.1- to 4.8-fold increases in QR activity, compared to controls. These data indicate that rosemary extract in the diet or injected i.p. and carnosol administered i.p. are effective enhancers of the in vivo activity of liver GST and QR in the female rat.     

Pharmacokinetics of antipyrine in calves at neonatal period fed with casein supplemented food

The purpose of the studies was to evaluate (on the basis of pharmacokinetics of antipyrine) hepatic biotransformation rate in calves in neonatal period, which received supplementary casein dose in their food. It was found that 25% increase in protein content in food ration of the examined animals significantly increased hepatic biotransformation rate (activity of monooxygenases dependent on cytochrome P-450). The results obtained also indicate that a protein-rich diet may significantly increase metabolism of other xenobiotics in MFO-P-450 enzymatic system, provided that they undergo the same biotransformation process as antipyrine.     

Effects of singly administered betaine on hepatotoxicity of chloroform in mice

Effects of a single dose of betaine on the chloroform-induced hepatotoxicity were examined in adult male ICR mice. Administration of betaine (1000 mg/kg, ip) 1 to 7 hr prior to a chloroform challenge (0.25 ml/kg, ip) resulted in remarkable enhancement of hepatotoxicity as indicated by increases in serum sorbitol dehydrogenase (SDH), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. The potentiation of hepatotoxicity was most significant when mice were treated with betaine 4 hr earlier than chloroform. However, a 24 hr prior administration of betaine protected the animals from induction of the chloroform hepatotoxicity. Thus, its effect appeared to be highly dependent on the time lapse from the betaine pretreatment to the challenge of mice with chloroform. Betaine treated either 4 or 24 hr prior to sacrifice did not alter the hepatic contents of cytochrome P-450, cytochrome b5, or NADPH cytochrome P-450 reductase activity. Accordingly the hepatic microsomal p-nitroanisole O-demethylase, aminopyrine N-demethylase, or p-nitrophenol hydroxylase activities were not influenced by the betaine pretreatment. Betaine was shown not to affect any of the enzyme activities associated with glutathione (GSH) conjugation reaction, such as glutathione S-transferases (GSTs), glutathione disulfide (GSSG) reductase and GSH peroxidase irrespective of the time of its administration. When betaine was administered to mice 2-6 hr prior to sacrifice, hepatic GSH level, but not plasma GSH, was decreased significantly. Enhancement of the chloroform hepatotoxicity by betaine correlated well with the reduction in hepatic GSH levels. Both hepatic and plasma GSH levels were elevated in mice 24 hr following the betaine treatment. The results suggest that betaine affects induction of the chloroform hepatotoxicity by modulating the availability of hepatic GSH, which appears to be associated with its role in the transsulfuration pathway in the liver.     

The effect of 1,2,3,4-tetrachlorodibenzo-p-dioxin on drug-metabolizing enzymes in the rat liver

The effects of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) on drug-metabolizing enzymes were studied in male and female rats. 1,2,3,4-TCDD (25, 50, 100 and 200 mumol/kg) was administered by i.p. injection once. Among the cytochrome P-450 (P450)-mediated monooxygenase activities tested, 7-ethoxyresorufin O-deethylase (EROD) activities in both male and female rats, which are associated with CYP1A1, were remarkably induced by all doses of 1,2,3,4-TCDD. The relative induction to each control activity were from 3.0- to 24.5-fold and from 2.2- to 16.5-fold, respectively. Also, 1,2,3,4-TCDD increased other CYP1A-mediated monooxygenase activities such as 7-ethoxycoumarin O-deethylase (ECOD) and 7-methoxyresorufin O-demethylase (MROD) in male and female rats dose-dependently (1.4- to 4.3-fold). Western immunoblotting showed that the levels of CYP1A1 and CYP1A2 proteins in liver microsomes were increased by 1,2,3,4-TCDD. Although the activities of other P450-mediated monooxygenases, namely 7-pentoxyresorufin O-depentylase (PROD), 7-benzyloxyresorufin O-debenzylase (BROD), aminopyrine N-demethylase (APND) and nitrosodimethylamine N-demethylase (NDAND) in both male and female rats were induced at high doses (> or = 50 mumol/kg) of 1,2,3,4-TCDD, the relative level was low compared with those of the CYP1A-mediated monooxygenase such as EROD, ECOD or MROD. In addition to P450-mediated monooxygenase, there was significant induction in the activities of the Phase II drug-metabolizing enzymes, UDP-glucuronyltransferase (UGT) activities towards 4-nitrophenol (4-NP) and 7-hydroxycoumarin (7-HC) and glutathione S-transferase (GST) towards 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and DT-diaphorase. These results indicate that 1,2,3,4-TCDD induces both Phase I (CYP1A-mediated monooxygenase) and Phase II drug-metabolizing enzymes (UGT, GST, DT-diaphorase) in the male and female rat liver, and that the alterations of drug-metabolizing enzyme are characteristic of PCDD toxicity.     

The rationale, evolution and clinical application of the self-ligating bracket

The binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with the aryl hydrocarbon (AH) receptor and subsequent changes in gene expression have been studied intensively, but the mechanisms by which these lead to toxicity are unclear. We investigated the influence of iron, previously implicated in TCDD-induced hepatic porphyria, in mice with alleles of Ahr that encode receptors with varied affinity for TCDD. The administration of iron to Ahrb-1 C57BL/6J (AH-responsive) mice before a single dose of TCDD (75 micrograms/kg) markedly potentiated not only the hepatic porphyria but also general hepatocellular damage and elevation of plasma hepatic enzymes. The formation of hydroxylated and peroxylated derivatives of uroporphyrins formed from uroporphyrinogen and the induction of a mu-glutathione transferase (GST) were consistent with the operation of an oxidative mechanism. In a comparison of C57BL/6J mice with Ahrb-2 BALB/c (AH-responsive) and Ahrd SWR and DBA/2 (AH-nonresponsive) mice, iron overcame the weak hepatic porphyria and toxicity responses in BALB/c and SWR strains but not in DBA/2. CYP1A isoforms are strongly implicated in the mechanism of porphyria, but activities were lowered by 20-30% with iron treatment, and a comparison of levels between strains did not fully account for the resistance of DBA/2 mice. Studies with the use of gel shift assays and cytosolic aconitase of the capacity of the iron regulatory protein controlling the translation of some iron metabolism proteins showed a significant difference between C57BL/6J and DBA/2 mice after the administration of TCDD. We conclude that iron potentiates both the hepatic porphyria and toxicity of TCDD in susceptible mice in an oxidative process with disturbance of iron regulatory protein capacity. Iron even overcomes the AH-nonresponsive Ahrd allele in the SWR strain but not in DBA/2 mice, which remain resistant.     

PMP-22 expression in the central nervous system of the embryonic mouse defines potential transverse segments and longitudinal columns

Treatment of rats with p-chlorotoluene (PCT, 1 g/kg, ip) resulted in peak PCT blood and lung concentrations at 4 h, which declined to very low levels at 12 h. The concentration of PCT in the liver attained its highest value at 1 h and also declined to low levels at 12 h. In the dose-response study, PCT significantly decreased hepatic and pulmonary AHH activities at 0.5 g/kg, 1 h. Maximum inhibition was attained at 1 g/kg, 1 h, and further increase in the dose did not enhance the enzyme inhibition in the time-course investigation, PCT (1 g/kg) maximally inhibited hepatic and pulmonary aryl hydrocarbon hydroxylase (AHH) activities at 1 h and the decrease in enzyme activity was sustained through 12 h. Administration of PCT (1 g/kg, 1 h) also markedly decreased pulmonary cytochrome P-450 content, while hepatic cytochrome P-450 content was only slightly reduced. The partial decrease in cytochrome P-450 content indicated altered levels of the P-450 isozymes, which may have profound effects on the metabolic disposition of benzo[a]pyrene [BaP]. BaP is regioselectively metabolized by two major isoforms of P-450 to toxic dihydrodiols and nontoxic phenol derivatives and there is a balance between these two metabolite groups. PCT (1 g/kg, 1 h) significantly inhibited the phenolic 3-OH BaP formation in both lung (52%) and liver (56%). The formations of BaP 7,8-dihydrodiol (146%) and 9,10-dihydrodiol (90%) were significantly elevated in the lung. The toxication to detoxication ratios were significantly elevated in both organs. Total quinone formation was markedly enhanced in the liver. Since PCT inhibited phenolic metabolite formation and increased dihydrodiol production, the activities of the isozymes that are responsible for their formations were determined. PCT (1 g/kg, 1 h) significantly inhibited cytochrome P-4502B1 in the lung (50%) and 2B1/2B2 in the liver (40%), while cytochrome P-4501A activity was not altered in either lung or liver. PCT increased phospholipid (PL) levels (45%) and conjugated diene (CD) formation (58%) in lung but not in liver, while membrane fluidity was increased [phospholipid/cholesterol (PL/CL) ratio; diphenylhexatriene (DPH) and trimethylammonium DPH (TMA-DPH) fluorescence polarization] in both organs. There was no apparent relationship between these membrane changes and alterations in MFO activity. Taken together the results suggest that PCT is capable of nonselectively inactivating the hepatic and pulmonary isozymes of P-450 that are responsible for the detoxication of BaP. The observed shift in the metabolism of BaP toward potentially more toxic metabolites suggests that concurrent exposure to BaP and PCT may result in greater toxicity, compared to exposure to BaP alone.