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C J Powell

Publications and source records attributed to C J Powell.

At least 19 recordsLinked to original sources
PubMed2000

Methapyrilene hepatotoxicity is associated with increased hepatic glutathione, the formation of glucuronide conjugates, and enterohepatic recirculation.

The mechanisms by which acute administration of methapyrilene, an H(1)-receptor antihistamine causes periportal necrosis to rats are unknown. This study investigated the role of the hepato-biliary system in methapyrilene hepatotoxicity following daily administration of 150 mg/kg per day over 3 consecutive days. Biliary metabolites of methapyrilene were tentatively identified. In male Han Wistar rats administration of methapyrilene significantly increased hepatic reduced glutathione (GSH) to 140% of control levels 24 h following the last dose. There were no significant changes in the activities of glutathione-related enzymes, glutathione peroxidase (GPx) and reductase (GSH), glutathione S-transferase (GST), and gamma-glutamyl cysteine synthetase (gamma-GCS) over 3 days of methapyrilene administration. Methapyrilene treatment resulted in no significant increase in excretion of biliary oxidized glutathione (GSSG), a sensitive marker of oxidative stress in vivo, following the third dose. [3H]Methapyrilene-derived radioactivity was detected in bile, to a greater extent than in feces, indicating that methapyrilene and/or metabolites underwent enterohepatic recirculation. Cannulation and exteriorization of the bile duct (to interrupt enterohepatic recirculation) afforded some protection against the hepatotoxicity, assessed by clinical chemistry and histopathology. Liquid chromatography-mass spectrometry (LC-MS) analysis of bile indicated the presence of unmetabolized methapyrilene, methapyrilene O-glucuronide and desmethyl methapyrilene O-glucuronide. These data demonstrate that acute methapyrilene hepatotoxicity in vivo is not a consequence of GSH depletion, or oxidative stress, but that enterohepatic recirculation of biliary metabolites may be important. Progressive exposure to non-oxidizing, reactive metabolic intermediates may be responsible for hepatotoxicity.

Alanine Transaminase↗
PubMed1998

Methapyrilene hepatotoxicity is associated with oxidative stress, mitochondrial disfunction and is prevented by the Ca2+ channel blocker verapamil.

Methapyrilene (MP) is an unusual hepatotoxin in that it causes periportal necrosis in rats. The mechanism of acute methapyrilene hepatotoxicity has, therefore, been investigated in cultured male rat hepatocytes. Addition of methapyrilene to rat hepatocytes resulted in a time- and dose-dependent loss in cell viability between 4 and 8 h of incubation as judged by cellular enzyme leakage. The cytochrome P450 (CYP) inhibitor metyrapone protected against methapyrilene-mediated toxicity suggesting that MP is metabolised by CYP for toxicity. The concentration-dependent protection from methapyrilene toxicity afforded by metyrapone correlated with an inhibition of microsomal CYP2C11-associated androstenedione 16alpha hydroxylase activity, and hepatocytes prepared from hypophysectomised rats (containing reduced levels of microsomal immunodetectable CYP2C11 and associated androstenedione 16alpha hydroxylase activity) showed resistance to the toxic effects of methapyrilene. These data suggest that the toxicity of methapyrilene is predominantly dependent on the CYP2C11 isoform. Treatment of hepatocytes with a toxic concentration of MP caused oxidative stress as indicated by increases in NADP+ levels within 2 h and cellular thiol oxidation as evidenced by a reduction--but not complete loss--in glutathione levels. Methapyrilene hepatotoxicity was associated with an early loss in mitochondrial function, as indicated by mitochondrial swelling and significant losses in cellular ATP within 2 h. Co-incubation of methapyrilene-treated hepatocytes with inhibitors of inner mitochondrial transition permeability pore opening--cyclosporin A or the thiol reductant dithiothreitol--abrogated cell death suggesting that pore opening and loss of mitochondrial Ca2+ homeostasis play a significant role in methapyrilene-mediated cell death. Co-incubation of methapyrilene-treated hepatocytes with the phenylalkylamine calcium channel blocker verapamil--but not by treating cells in a nominally calcium-free medium--also abrogated cell death, suggesting that if Ca2+ is involved in cell killing then it is dependent on an intracellular Ca2+ pool. Pre-treatment of hepatocytes for 1 h with verapamil--to inhibit intracellular Ca2+ pool filling--increased the potency of verapamil protection against methapyrilene toxicity by approximately 100-fold. Taken together, these data indicate that methapyrilene intoxication leads to mitochondrial disfunction and suggest a critical role for a loss of mitochondrial Ca2+ homeostasis in this model of hepatocyte death.

Adenosine Triphosphate↗
PubMed1998

The LEC rat possesses reduced hepatic selenium, contributing to the severity of spontaneous hepatitis and sensitivity to carcinogenesis.

The hepatic concentrations of copper, zinc, magnesium, calcium, and selenium were measured in LEC rats, which develop a spontaneous form of hepatitis at 3-4 months of age, and compared to trace metal concentrations in the LEA rat, its asymptomatic congenic strain. Consistent with results found by other groups, copper was found to accumulate within the liver of LEC rats to levels more than 50 times those measured in LEA rats. In addition, liver selenium concentration in LEC rats was found to be around 50% of that in LEA rats. The enzyme activity, and RNA for the selenium dependent enzyme, glutathione peroxidase, was also found to be reduced in LEC rat liver. These results indicate that hepatic selenium in the LEC rat is depleted and that, as a result of this, the capacity to protect cells from copper-induced free-radical damage is reduced.

Animals↗
PubMed1998

Effects of induction and inhibition of cytochromes P450 on the hepatotoxicity of methapyrilene.

The mechanisms by which the antihistamine drug methapyrilene causes acute periportal hepatotoxicity in rats are not yet elucidated. This study investigated the effects of modulators of cytochrome P450 (CYP) activity on the hepatotoxicity of methapyrilene and also the effect of methapyrilene on hepatic CYP. Pretreatment of male Han Wistar rats with beta-naphthoflavone, phenobarbitone, butylated hydroxytoluene, piperonyl butoxide, Aroclor 1254, or cobalt protoporphyrin IX, agents known to modify hepatic CYP, all afforded some degree of protection against a hepatotoxic dose of methapyrilene (150 mg/kg x 3 days p.o.), as assessed by clinical chemistry and histology. Total hepatic CYP depletion by cobalt protoporphyrin IX treatment indicated CYP-mediated bioactivation was a prerequisite for methapyrilene-induced hepatotoxicity. Protection against hepatic damage was strongly associated with beta-naphthoflavone induction of CYP1A and phenobarbitone-associated CYP2B induction. However, the role of CYP3A, which is constitutively expressed in the liver and induced by piperonyl butoxide, butylated hydroxytoluene, or Aroclor 1254, was unclear. Modulation of FAD monooxgenase activity by methimazole pretreatment was not associated with increased methapyrilene-induced hepatotoxicity. Methapyrilene treatment alone specifically decreased microsomal enzyme activity markers for CYP2C11, CYP3A, and CYP2A and pretreatment with all the hepatic enzyme-inducing agents specifically prevented the loss of CYP2C11. Together this suggested that CYP2C11 was responsible for the suicide substrate bioactivation of methapyrilene and the toxicologic outcome largely relied upon an abundance of detoxifying enzymes present in the liver.

Animals↗
PubMed1996

Strain-specific enhancement or inhibition of coumarin hepatotoxicity in mice following pretreatment with two different liver enzyme-inducing agents.

Human exposure to coumarin continues despite controversy over its hepatotoxic potential. Greater understanding of human reactions to coumarin may be achieved by studying murine interstrain differences. The metabolic basis of coumarin hepatotoxicity and its modulation by liver enzyme inducers, beta-naphthoflavone (beta NF) and aroclor 1254 (ARO), were investigated in C3H/He and DBA/2 mice. Coumarin (200 mg/kg) was hepatotoxic to both strains, resulting in 2- to 15-fold plasma aminotransferase elevations, mild subcapsular linear hepatocyte necrosis after 24 hr, and, in some C3H/He mice, centrilobular necrosis. In this strain, beta NF pretreatment caused a 2- to 3-fold further increase in plasma aminotransferases and produced periportal necrosis. In contrast, ARO-pretreated C3H/He mice tended to exhibit lower plasma aminotransferases and occasional midzonal damage. Neither pretreatment significantly altered coumarin hepatotoxicity in DBA/2 mice. In C3H/He mice, hepatic microsomal metabolism of [3-14C]-coumarin via the 3-hydroxylation pathway doubled following both beta NF and ARO treatment. The contrasting nonresponsiveness of DBA/2 mice suggested that this pathway is linked to the Ah locus, which is defective in this strain. ARO treatment caused a maximal 5-fold increase in coumarin 7-hydroxylation in C3H/He mice, whereas DBA/2 mice were 30% less responsive. Potentiation of coumarin hepatotoxicity corresponded to an increase in the 3-:7-coumarin hydroxylation ratio. Pretreatment-dependent shifts in the location of hepatocyte damage may be related to changes in the translobular ratio of enzymes involved in activation and detoxication of coumarin. These data highlight how genetic background, individual variation, and xenobiotic-induced alterations in enzyme profiles, factors all relevant to human risk assessment, can influence the consequence of coumarin exposure.

Alanine Transaminase↗
PubMed1996

A novel hypothalamic peptide, pituitary adenylate cyclase-activating peptide, regulates the function of rat granulosa cells in vitro.

Pituitary adenylate cyclase-activating peptide (PACAP) is a novel peptide that was isolated from ovine hypothalamic tissue on the basis of its ability to stimulate cAMP accumulation in cultured rat pituitary cells. Recently we demonstrated that PACAP can stimulate cAMP accumulation and secretory function in cultured rat Sertoli cells. Since ovarian granulosa cells share many properties with Sertoli cells, we have examined the effect of PACAP (consisting of 38 or 27 amino acid residues) on cultured granulosa cell function. Granulosa cells were obtained from the ovaries of 25-day-old rats implanted with a silastic capsule containing diethylstilbestrol 5 days prior to culture. PACAP 38 (0.1 microM-0.01 pM), both alone and in the presence of the phosphodiesterase inhibitor, methylisobutylxanthine, stimulated cAMP accumulation 4-8-fold with an ED50 of approximately 100 pM. Maximal PACAP 38 or PACAP 27 stimulation of granulosa cell cAMP was significantly greater than that produced by a maximally effective concentration of FSH. Because PACAP 38 and 27 have 68% sequence homology with vasoactive intestinal peptide (VIP), and since VIP stimulates granulosa cell cAMP accumulation and estradiol and progesterone secretion, we examined the possibility that PACAP could be acting via the VIP receptor. VIP stimulated cAMP only at concentrations of 10 nM or greater, whereas the PACAP stimulation was evident at 10 pM. Moreover, only one of three potent VIP antagonists inhibited VIP stimulation of cAMP accumulation, and only at 1 microM or greater. This VIP antagonist did not inhibit PACAP 38 action at 2000-fold excess concentration. Interestingly PACAP 38 was more effective than PACAP 27 with regard to steroid secretion and the ability to induce LH responsiveness. PACAP and VIP stimulation of granulosa cell cAMP accumulation or estradiol or progesterone secretion was not additive. Thus, these data support the hypothesis that granulosa cells have specific PACAP 38 receptors and that VIP acts via these receptors. In addition, PACAPs 38 and 27 are more potent stimulators of cAMP accumulation in luteinized granulosa cells than LH. These results both pre- and postovulation, along with previous data indicating that the PACAPs are found in the ovaries, suggest a role for PACAP in the regulation of ovarian function.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Biochemical and morphological effects of contrast media on the kidney.

The intravenous use of roentgen contrast media (CM) is associated with a low incidence of renal impairment. This paper considers the intravascular handling and retention of CM in relation to effects on renal function - specifically the ability of the kidney to reabsorb and catabolise low molecular weight proteins. Renal morphology following experimental administration of a high dose of an isotonic dimeric CM (iodixanol at 3 g I/kg) in rats showed numerous, large, protein-containing vacuoles or droplets in the cells of the proximal convoluted tubule. These were fully formed within 3.5 hours. The process of vacuole-formation involving the uptake of CM appears to be analogous to dextran uptake that occurs via fluid phase endocytosis. These vacuoles or CM droplets are abundant for 7 days but then slowly decline over several weeks. The quantitative recovery of (14)C iodixanol (3g I/kg) from the kidneys between 3.5 hours to 7 days after administration was about 1% of the dose, with some 0.2% of the original dose still present at 28 days. Subcellular analysis to determine the site of the radiolabel showed that the (14)C was associated with lysosomal marker enzymes. The CM-induced vacuoles/droplets are most probably giant lysosomes, which contain the intracellularly retained CM. Co-administration of tracer doses of (125)I-labelled cytochrome C with iodixanol showed some impairment of low molecular weight protein reabsorption, but remarkably this process was not effected when the vacuoles were fully formed. The conspicuous morphology of the vacuoles, the CM retention and the transient proteinuria and enzymuria cannot presently be associated with any functionally significant impairment of tubular or cellular processes.

Animals↗
PubMed1994

The dose-dependent effect of BHT (butylated hydroxytoluene) on vitamin K-dependent blood coagulation in rats.

Earlier studies have reported a reduction of vitamin K-dependent blood clotting factor activity and incidence of haemorrhagic death in rats fed butylated hydroxytoluene (BHT); however, the vitamin K status of the animals used in these studies was claimed to be inadequate. The aim of the study reported here was to determine the effect of BHT on vitamin K-dependent clotting factors in vitamin K-sufficient and vitamin K-supplemented rats. Rats given BHT (3000 mg/kg body weight) for up to 21 days, in a diet containing a minimum of 3 ppm vitamin K3 (six times the recommended requirement), showed decreased vitamin K-dependent blood clotting factor activities, demonstrated by increases in factor-specific clotting time assays. Clotting times were prolonged within 7 days, significantly increased within 14 days (P < 0.001) and maximally increased 5.5-fold at 21 days (P < 0.05). Supplementation with a further 250 ppm vitamin K3 reversed this effect. BHT did not increase prothrombin time (PT), the usual index of clotting. However, in a similar 14-day investigation, a small but significant increase in PT (up to 151%, P < 0.005) was seen within 7 days. Further vitamin K supplementation was incapable of reversing this effect completely. A similar trend was shown by activated partial thromboplastin time. The 1/51 dilution Thrombotest, a more sensitive indicator of vitamin K-dependent clotting factor activity in the rat, was significantly increased (more than four fold, P < 0.01) within 7 days. This increase was fully reversed by further vitamin K supplementation. Prolongation of Thrombotest time was significant at a BHT dose level of 600 mg/kg body weight per day and this could be reversed by further supplementation of only 3.0 ppm vitamin K. However, at dose levels of 125 mg BHT/kg body weight per day or less, no clotting defects were observed. These studies confirm that chronic administration of more than 600 mg BHT/kg/day to rats supplied with recommended amounts of vitamin K can depress clotting factors and precipitate haemorrhagic deaths. When further vitamin K is provided, these deaths could be prevented even though not all clotting abnormalities may be reversed. This study disapproves the proposal that BHT-related clotting factor defects are confined to rats of inadequate vitamin K status, but shows that such effects do not occur at dose levels lower than 600 mg/kg/day. The results further indicate that rats receiving a high dose of BHT have a higher vitamin K requirement than would otherwise be considered necessary. However, as BHT produces no clotting defects in these animals receiving an intake 1000 times the acceptable daily intake, such clotting effects are most unlikely to indicate a human safety problem for BHT.

Animals↗
PubMed1994

Local immune response and protection in the guinea pig keratoconjunctivitis model following immunization with Shigella vaccines.

This study used the guinea pig keratoconjunctivitis model to examine the importance of route of administration (mucosal versus parenteral), frequency and timing of immunization (primary versus boosting immunization), and form of antigen given (live attenuated vaccine strain versus O-antigen-protein conjugate) on the production of protective immunity against Shigella infection. Since local immune response to the lipopolysaccharide (LPS) O-antigen of Shigella spp. is thought to be important for protection against disease, O-antigen-specific antibody-secreting cells (ASC) in the spleen and regional lymph nodes of immunized animals were measured by using an ELISPOT assay. Results indicated that protective efficacy was associated with a strong O-antigen-specific ASC response, particularly in the superficial ventral cervical lymph nodes draining the conjunctivae. In naive animals, a strong ASC response in the cervical lymph nodes and protection against challenge were detected only in animals that received a mucosal immunization. Protection in these animals was increased by a boosting mucosal immunization. While parenteral immunization alone with an O-antigen-protein conjugate vaccine did not protect naive animals against challenge, a combined parenteral-mucosal regimen elicited enhanced protection without the addition of a boosting immunization. Although O-antigen-specific serum immunoglobulin A titers were significantly higher in animals receiving a mucosal immunization, there was no apparent correlation between levels of serum antibody and protection against disease.

Animals↗
PubMed1994

Cocaine hepatotoxicity: a study on the pathogenesis of periportal necrosis.

Cocaine is reported to produce either periportal or mid-zonal necrosis in mice pretreated with the enzyme inducer phenobarbitone (James et al. 1987; Powell et al. 1991; Charles & Powell 1992). Dose-response and time course experiments were performed in phenobarbitone treated male DBA/2Ha mice to study the pathogenesis of this unusual cocaine induced lesion. An increase in the dose of cocaine from 60 to 90 or 120 mg/kg produced more extensive and severe periportal and linking portal damage and elevated plasma aspartate (AST) and alanine (ALT) aminotransferases in a dose dependent manner. Scattered hepatocyte degeneration began at the edge of the periportal region and was detectable by electron microscopy within 30 minutes of administration of 60 mg/kg of cocaine, with conspicuous disorganization of the endoplasmic reticulum being one of the earliest changes. Significant elevations of plasma AST and ALT were observed 3 hours after cocaine administration and were sustained for 12 hours, at which time progressive hepatocyte damage had developed into a network of confluent necrosis at the periphery of the periportal region. The rapidity of organelle derangement and subsequent cell death, and absence of any effect on total cytochrome P-450 or FAD-mono-oxygenase levels, appear to distinguish this periportal lesion from previous reports of cocaine induced centrilobular necrosis in non-enzyme induced mice, suggesting that the two types of damage may develop by different mechanisms. The observation that periportal lesions commence at the periphery of the periportal area, progressing portalwards with increasing dose and time, offers an explanation for the previously conflicting reports of cocaine induced mid-zonal and/or periportal lesions in phenobarbitone treated mice.

Alanine Transaminase↗
PubMed1993

Effects of mono(2-ethylhexyl) phthalate, a testicular toxicant, on follicle-stimulating hormone binding to membranes from cultured rat Sertoli cells.

The widely used plasticizer di(2-ethylhexyl) phthalate (DEHP) is a male reproductive toxicant. Its toxicity has been shown to be due primarily to the action of its metabolite mono(2-ethylhexyl) phthalate (MEHP) on Sertoli cells. We have previously shown that at least one of the sites of action of MEHP on the Sertoli cell is the cAMP second messenger system. MEHP inhibits the ability of FSH but not isoproterenol, forskolin, or cholera toxin to stimulate cAMP accumulation in cultured Sertoli cells in a dose- and time-dependent manner. To further characterize this effect of MHP, we prepared a light membrane fraction from control and MEHP-treated Sertoli cells cultured from 18-day-old Fischer 344 rats and measured FSH binding in a radioligand receptor assay using 125I-labeled human FSH (125I-hFSH). MEHP inhibited FSH binding when preincubated with Sertoli cells in culture but not when added simultaneously with 125I-hFSH to the purified membrane preparation. Attenuation of FSH binding was evident after a 3-h preincubation with 100 microM MEHP (18%) and was maximal after 15-24 h of preincubation (70-90%). Preincubation of Sertoli cells for 24 h with 100 microM DEHP had no effect on FSH binding. Half-maximal inhibition occurred at approximately 0.1 microM MEHP. Scatchard analysis indicated a four-fold decrease in FSH affinity with no change in receptor concentration. Exposure of Sertoli cells to MEHP amplified the attenuating effect of guanosine triphosphate (GTP) on FSH binding, suggesting that the action of MEHP may be at the level of the GTP-binding protein that couples the FSH receptor to the adenylate cyclase catalytic subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Phthalate ester effects on rat Sertoli cell function in vitro: effects of phthalate side chain and age of animal.

Mono(2-ethylhexyl) phthalate (MEHP), the active metabolite of the testicular toxicant di(2-ethylhexyl) phthalate, inhibits FSH-stimulated rat Sertoli cell cAMP accumulation, stimulates basal lactate production, and decreases intracellular ATP levels in vitro. Dibutyl phthalate and dipentyl phthalate but not diethyldimethyl or dipropyl are also age-dependent testicular toxicants in vivo. We therefore examined the effect of animal age and phthalate monoester on the Sertoli cell FSH-stimulated cAMP accumulation, lactate secretion, and ATP levels in order to determine if these effects are part of the mechanism of action of phthalate esters in vivo. MEHP, monobutyl and monopentyl phthalates but not the monoethyl, monomethyl, or monopropyl phthalates inhibited FSH-stimulated cAMP accumulation, a segregation which matches the in vivo toxicity potential of these agents. MEHP and monopentyl, but not monobutyl phthalates, also stimulated Sertoli cell lactate secretion. The effect of the active phthalates on FSH-stimulated cAMP accumulation and lactate secretion is not dependent on age of animal over a range of 13-80 days, suggesting that the age-related toxicity in vivo may be related to differences in metabolism and disposition rather than tissue sensitivity. Since the ED50 of MEHP inhibition of cAMP accumulation and lactate secretion is similar, these two effects may be related to a common initial effect of the active phthalates. Inhibition of intracellular ATP levels is specific for MEHP and is lost with age (greater than 28 days of age) and thus is not likely to be an essential part of the in vivo mechanism of action of phthalate diesters.

Adenosine Triphosphate↗
PubMed1992

Rapidly developing cocaine-induced peripheral portal liver damage.

Cocaine administration to phenobarbitone treated DBA/2Ha mice caused scattered peripheral portal cell necrosis within 2 h. At 3 h, when this initial lesion had become more widespread, and plasma membrane integrity had been compromised, 15-fold elevations in plasma levels of liver enzymes were observed. Biochemical analysis of liver microsomes showed no changes in the levels of total cytochrome P-450 during the development of hepatic damage, and there was no correlation between microsomal malondialdehyde (MDA), an indicator of lipid peroxidation, and liver damage. These results indicate that as liver damage occurs only 2 h after cocaine administration, prompt action is warranted when cocaine overdose is suspected.

Animals↗
PubMed1992

A novel hypothalamic peptide, pituitary adenylate cyclase activating peptide, modulates Sertoli cell function in vitro.

Pituitary adenylate cyclase-activating peptide (PACAP), a novel hypothalamic peptide that has been shown to exist in several tissues including the testis, was examined for its effects on cultured rat Sertoli cells. PACAP stimulates cAMP accumulation in Sertoli cells cultured from 15-day-old rats in the presence or absence of methylisobutylxanthine, a phosphodiesterase inhibitor, and in the presence of pertussis toxin, a blocker of the adenylate cyclase inhibitory pathway. Maximal stimulation, which is 20-40% of that attainable with FSH, occurs at PACAP concentrations of 10 nM: the ED50 is approximately 100 pM. The ability of PACAP to stimulate Sertoli cell cAMP declines with increasing age of donor animals (15-60 days of age) in a fashion similar to the FSH effect. PACAP stimulation of Sertoli cell cAMP accumulation is additive with submaximal, but not maximal, concentrations of FSH or forskolin. PACAP also stimulates the secretion of lactate, estradiol, and inhibin in a concentration-dependent manner. The stimulation of Sertoli cell cAMP accumulation by PACAP is not altered by a vasoactive intestinal peptide antagonist, and vasoactive intestinal peptide alone does not stimulate cAMP accumulation, indicating that PACAP is not acting via vasoactive intestinal peptide receptors. Further experiments are needed to determine whether PACAP is synthesized within the testis and if so, in which cell types; however, the present data clearly demonstrate that PACAP can modulate Sertoli cell function in vitro.

Age Factors↗
PubMed1991

The site specificity and sensitivity of the rat liver to butylated hydroxytoluene-induced damage.

The food additive butylated hydroxytoluene (BHT) is capable of damaging centrilobular or periportal cells in the liver according to the dose and duration of treatment. The effect of two hepatotoxicity potentiating agents on the site specificity of acute cell damage was investigated in Sprague-Dawley rats. A 500 mg/kg oral dose of BHT did not cause overt hepatic necrosis or alter the cytochrome P450 concentration, but increased ethoxycoumarin-O-deethylation, implying an alteration in the ratio of P450 isoenzymes. Pretreatment with either phenobarbitone (3 X 80 mg/kg, ip) or the glutathione depleting agent buthionine sulfoximine (900 mg/kg, ip) produced liver necrosis in approximately 50% of animals: mainly in centrilobular areas, but with some necrosis in midzonal or periportal areas. Phenobarbitone and BHT did not significantly change the cytochrome P450 concentration, but did alter the ratio of P450 isoenzymes. In phenobarbitone-pretreated rats centrilobular hepatocyte damage was clearly localized in cells with high immunocytochemical staining for the cytochrome P450IIB subfamily. Buthionine sulfoximine and BHT reduced the cytochrome P450 concentration without reducing ethoxycoumarin-O-deethylase activity, implying a different alteration in the ratio of P450 isoenzymes. These results indicate that phenobarbitone-inducible enzymes are capable of activating high doses of BHT to reactive oxidizing intermediates, which in the absence of adequate glutathione can cause cell death. Enzymes of the P450IIB subfamily are implicated in this mechanism.

Animals↗