Effect of intravitreal dexamethasone in treatment of pneumococcal endophthalmitis in rabbits

PURPOSE

To investigate whether corticosteroid therapy would decrease the inflammation and tissue damage associated with pneumococcal endophthalmitis.

METHODS

Albino rabbits were injected intravitreally with 1000 live organisms of Streptococcus pneumoniae and randomized after 24 hours to treatment with intravitreal vancomycin hydrochloride alone (n = 10), combination intravitreal vancomycin and intravitreal dexamethasone (n = 10), or no treatment (n = 10). After 2 weeks, the eyes were examined clinically and enucleated for histopathologic examination.

RESULTS

Eyes treated with vancomycin and dexamethasone had significantly less intraocular inflammation and more preservation of retinal tissue than untreated eyes or eyes treated with vancomycin alone (P < .05, Fisher's exact test). Untreated and vancomycin-treated eyes were indistinguishable on clinical and histologic examination. Marked anterior and posterior segment inflammation with total retinal necrosis was noted in eyes from both groups.

CONCLUSION

Intravitreal corticosteroid therapy may play an important role in minimizing the inflammation and tissue damage associated with pneumococcal endophthalmitis.

Inhibition of benzo[a]pyrene metabolism by insulin, FITC-insulin and an FITC-insulin-antibody conjugate in the human hepatoma cell line HepG2

Benzo[a]pyrene (BaP) can be metabolically activated to an ultimate carcinogen, (+)-anti-BaP-7,8-dihydrodiol-9,10-epoxide [(+)-anti-BaPDE] by cells in culture. This activation involves oxidation by specific isoforms of cytochrome P450s such as CYP1A1. The human hepatoma cell line, HepG2, was used to examine the effect of inhibition of CYP1A1 activity by anti CYP1A1 specific antibodies on BaP metabolism. Metabolism of BaP to water-soluble metabolites by HepG2 cells in culture was 50% lower in fluorescein isothiocyanate (FITC)-insulin-CYP1A1-antibody-conjugate-treated cells than in control cells. However, FITC-insulin (lacking anti CYP1A1 conjugates) or insulin alone also decreased BaP metabolism by 50%. This insulin-induced inhibition of BaP metabolism was observed for cultures treated with a concentration range of FITC-insulin from 50-1000 nM. FITC-conjugated gamma-globulin showed no significant binding to HepG2 cells by fluorescence microscopy, however, FITC-insulin-antibody conjugates bound extensively, suggesting that FITC-insulin conjugates still retain the ability to bind insulin receptors. These results demonstrate that free insulin, FITC-insulin or FITC-insulin conjugated to antibodies are effective inhibitors of BaP metabolism in cells in culture.

Idiopathic subglottic stenosis

OBJECTIVE

To review our patients with subglottic stenosis and describe a rare subclass of patients in whom the cause of subglottic scarring and narrowing remains unknown.

DESIGN

A retrospective chart review and clinical update were performed on all patients seen with the diagnosis of subglottic stenosis.

SETTING

The patient pool represents a collection of primary care patients within a suburb of Boston, Mass, and tertiary referrals from community and out-of-state otolaryngologists.

PATIENTS

The charts of 80 patients were reviewed, and 10 of the 80 patients fulfilled the criteria for idiopathic subglottic stenosis.

INTERVENTION

Diagnostic and therapeutic intervention ranged from laboratory tests, topography, flexible bronchoscopy, rigid endoscopy and biopsy, laser-assisted dilation, and resection and repair of the lesion.

MAIN OUTCOME MEASURES

Attention was directed toward the character of the lesion, treatment modality, and clinical outcome.

RESULTS

From 1985 to 1992, 10 patients with idiopathic subglottic stenosis were treated at the Lahey Clinic, Burlington, Mass. Eight patients required therapy for exertional dyspnea. Endoscopic laser incision and dilation were performed in all eight patients, with good initial results. Four patients were treated successfully with endoscopy alone: three required only one dilation, and the fourth required a second dilation. The remaining four patients, who had longer and more complex stenoses, have had repeated restenosis at intervals ranging from 1.5 to 12 months. Two of these patients have undergone laryngotracheal resection and reconstruction and were without evidence of restenosis 10 and 20 months after surgery.

CONCLUSIONS

There exists a subclass of patients with subglottic stenosis of unknown cause. Symptomatic idiopathic subglottic stenosis may be treated successfully with laser incision and dilation if the stenosis is simple and short. More complex, longer stenoses are prone to recurrence and are more definitively managed by resection and reconstruction of the narrowed area.

Posterior segment complications after vitrectomy for macular hole

PURPOSE

The purpose of this study is to assess the rate of posterior segment complications after vitreous surgery for macular holes and to evaluate the effect of such complications on final visual outcome.

METHODS

The authors reviewed retrospectively all cases of vitreous surgery for macular holes performed between June 1990 and October 1993. Among 98 patients with a followup of 3 months or more, all patients with posterior segment complications during the postoperative course were identified. The rate of complications was compared with that seen after vitreous surgery for macular pucker performed by the same surgeons.

RESULTS

Posterior segment complications were noted in 23 (23%) of 98 patients. These included peripheral retinal breaks (3%), rhegmatogenous retinal detachment from a peripheral retinal break (14%), enlargement of the hole (2%), late reopening of the hole (2%), retinal pigment epithelium loss under the hole (1%), photic toxicity (1%), and endophthalmitis (1%). In 40% of these eyes, the final visual acuity was two lines or more below preoperative visual acuity. When compared with the macular pucker group, the rate of posterior segment complications, in particular the rate of peripheral retinal tears and detachments, was significantly higher (P < or = 0.05).

CONCLUSIONS

The authors conclude that visually significant posterior segment complications may occur after vitrectomy for macular hole, and the rate of these complications appears to be higher than expected.

Treatment of exogenous Candida endophthalmitis in rabbits with oral fluconazole

We investigated the efficacy of oral fluconazole, alone or in combination with oral flucytosine (5FC), in treating Candida endophthalmitis using a rabbit model. Albino rabbits were infected with an intravitreal inoculation of 1,000 CFU of susceptible Candida albicans and randomized 5 days later to receive treatment with oral fluconazole alone (80 mg/kg of body weight per day), a combination of fluconazole and 5FC (100 mg/kg/12 h), or no treatment. The treatment effect was assessed at 2 and 4 weeks after therapy by funduscopy, quantitative vitreous culture, and histopathology. Intravitreal levels of fluconazole, 2 to 24 h after the first dose, were measured to be > 10 times the MIC of the drug for C. albicans. Among rabbits treated with fluconazole for 2 weeks, 67% had a > 90% reduction in fungal load (P < 0.05) and 33% were sterile. After 4 weeks, all had a > 99% reduction in fungal load (P < 0.05) and 75% were sterile (P = 0.01). This treatment effect was unchanged 4 weeks after discontinuation of fluconazole. Among rabbits treated with fluconazole and 5FC for 2 weeks, 67% died during therapy. Among the surviving rabbits, 75% had a > 90% reduction in fungal load (P < 0.05) and 25% were sterile. We conclude that oral fluconazole may be useful for treatment of Candida endophthalmitis. Addition of 5FC was associated with high toxicity and minimal additional antifungal effect in our rabbit model.

Tracheopathia osteoplastica simulating asthmatic symptoms. Diagnosis by bronchoscopy and computerized tomography

Tracheopathia osteoplastica (TO) is a relatively rare benign disease of the trachea and major bronchi, characterized by cartilaginous and bony submucosal nodules covered by intact mucosa, which may cause narrowing and rigidity of the upper airways. The diagnosis of TO is rarely considered because of a lack of awareness of this entity, rather than the reported rare occurrence. We intend to report herein a case initially misinterpreted as bronchial asthma but later disclosed through computerized tomography (CT) and bronchoscopic biopsies as TO.

Piperine effects on the expression of P4502E1, P4502B and P4501A in rat

1. Treatment of rat with piperine (PIP) (1.4 mmol/kg, 3 days ip injections) resulted in an approximate two-fold increase in total liver microsomal P450 content relative to that in uninduced animals. 2. 4-Nitrophenol and aniline hyroxylase activities in the hepatic microsomes prepared from rat treated with PIP decreased by 30 and 28% respectively as compared with control. Immunoblot analyses also revealed decreased P4502E1 levels in hepatic microsomes from PIP-treated animals. 3. In contrast with P4502E1 suppression, hepatic 2B1 and 2B2 levels were significantly increased in PIP-induced animals, as evidence by both metabolic activity and immunoblot analysis of the liver microsomal fractions. The rate of hexobarbital hydroxylase activity in microsomes from PIP-treated animals was markedly elevated and was inhibited by approximately 62% in the presence of monoclonal anti-P4502B IgG. Immunoblot analyses demonstrated that P4502B1 and 2B2 levels in hepatic microsomes from PIP-treated animals were comparable with those from phenobarbital-treated animals. 4. 7-Ethoxycoumarin deethylase activity was elevated approximately two-fold in PIP-induced animals and was 17% of that derived from 3-methylcholanthrene-induced animals. 7-ethoxycoumarin deethylase activity in PIP-induced hepatic microsomes was inhibited 63% in the presence of monoclonal anti-P4501A antibody. Immunoblot analysis confirmed the increase in P4501A levels by PIP, which was 15% of that in hepatic microsomes from 3-methylcholanthrene-induced animals. 5. PIP treatment failed to affect microsomal epoxide hydrolase (mEH) and glutathione S-transferases (GST) expression, as indicated by immunoblot analyses using polyclonal antibodies toward mEH and GST subunits Ya, Yb1, Yb2 and Yc. 6. These results demonstrate that PIP treatment suppressed P4502E1 expression and enhanced 2B and 1A expression, whereas this agent failed to affect hepatic mEH and GST expression.

Induction of cytochrome CYPIA1 and formation of toxic metabolites of benzo[a]pyrene by rat aorta: a possible role in atherogenesis

Cigarette smoking is a leading risk factor for atherosclerosis. Endothelial injury may be the initial event in this process. The carcinogenic metabolites of the polycyclic aromatic hydrocarbons found in cigarette smoke tars could cause this injury. We tested this model by examining the effect of 3-methylcholanthrene administration on aortic polycyclic aromatic hydrocarbon metabolism. Immunoblotting with a monoclonal antibody (mAb 1-7-1) specific for cytochromes CYPIA1 and CYPIA2 showed that aortic microsomes from treated, but not from control, animals contained CYPIA1; the CYPIA1 was primarily in the endothelium. Aortic microsomes from induced animals metabolized benzo[a]pyrene (BaP) to the 7R,8S,9,10-tetrahydrotetrol-, 7,8-dihydrodiol-, 1,6 quinone-, 3,6 quinone-, 6,12 quinone-, 3-hydroxy-, and 9-hydroxy-BaP. mAb 1-7-1 inhibited the formation of the tetrahydrotetrol, the dihydrodiol-BaP, and the 3-hydroxy-BaP but did not inhibit the quinones or the 9-hydroxy-BaP. Arachidonic acid did not affect metabolism. These data suggest that the aortas of induced animals metabolize the BaP in cigarette smoke to carcinogenic and toxic products and that this metabolism may initiate vessel injury and lead to the accelerated atherosclerosis seen in cigarette smokers.

Malotilate, a hepatoprotectant, suppresses CYP2E1 expression in rats

The expression of CYP2E1 was examined in hepatic tissue from rats treated with malotilate (MT), a hepatoprotectant. Microsomal p-nitrophenol hydroxylase activity in MT-treated rats was decreased to 66% and 47% of control activity at day 2 and 3 post-treatment. SDS-PAGE and immunoblot analyses of hepatic microsomes prepared from MT-treated rats showed that CYP2E1 levels were decreased below the limit of detectability. In contrast, CYP2B1 levels were increased in MT-treated microsomes, as assessed by immunoblot analyses. MT, however, failed to modulate CYP1A expression. RNA hybridization analysis revealed that CYP2E1 mRNA levels failed to change significantly by day 2 or 3 post-treatment, whereas microsomal epoxide hydrolase mRNA levels were elevated approximately 3-fold at the same time points. These results demonstrate that MT effectively suppresses CYP2E1 expression in the absence of transcriptional inactivation.

Induction and regulation of CYP2E1 in murine liver after acute and chronic acetone administration

The effects of acute and chronic acetone administration on hepatic Cyp2e1 were investigated in mice. Acute treatment consisted of a single dose of acetone (5 ml/kg) given intragastrically, whereas the chronic regimen consisted of 1% acetone in drinking water for 8 days. We examined 1) relative induction of Cyp2e1 protein by immunoblotting, 2) relative induction of enzyme catalytic activity (p-nitrophenol hydroxylation), and 3) Cyp2e1 mRNA levels associated with acute and chronic treatment regimens. Western immunoblotting, using a monoclonal antibody (Mab 1-98-1) specific for rat ethanol-inducible P-450, detected a band of M(r) 51,000 in liver microsomes of both control and acetone-treated mice. Densitometric quantitation showed significant enhancement of the intensity of this band by 4.4- and 5.3-fold after acute and chronic acetone treatments, respectively. Hydroxylation of p-nitrophenol was increased 2.3-fold in microsomes from livers exposed acutely to acetone, as compared with an increase of 3.7-fold in microsomes from livers exposed chronically. The induction of Cyp2e1 protein, as well as of catalytic activity, by acetone was not accompanied by significant alterations in the levels of Cyp2e1 mRNA. These results demonstrate a difference in induced increases of Cyp2e1 between acute and chronic acetone treatments: significantly higher induction of both protein and catalytic activity is induced by treatment under chronic vs. acute conditions.

Long-term effects of pentobarbital anesthesia on the atrial natriuretic peptide system in rats

A long-term effect of pentobarbital treatment on the storage and release of atrial natriuretic peptide (ANP) was investigated in rats. The experimental group was treated with pentobarbital (50 mg/kg, ip), and the control group was injected with the vehicle only. They were used one week after the treatment. Male and female rats were used separately to see if there exists a sex difference in the response to pentobarbital. In male rats, the plasma ANP measured in a conscious state was significantly higher in the experimental group than in the control. The ANP content as well as the number of specific granules in the atrial tissue was significantly lower in the experimental group. In response to extracellular volume expansion (VE), amounting up to 5% of the body weight over 30 min, while the plasma ANP increased in the control, it did not significantly change in the experimental group. Urinary responses to the exogenous infusion of ANP did not differ in magnitude between the two groups. In female rats, neither the plasma level nor the atrial content of ANP (or the atrial granularity) was different between the experimental and control groups. Nor did the increase of plasma ANP in response to VE differ in magnitude between the two groups in female rats. These results indicate that pentobarbital may have a long-term effect on the storage and release of ANP.

Involvement of P450 1A1 in benzo(a)pyrene but not in benzo(a)pyrene-7,8-dihydrodiol activation by 3-methylcholanthrene-induced mouse liver microsomes

Synchronous fluorescence spectrophotometry for benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE)-DNA adducts was used to study the activation pathway of benzo(a)pyrene in C57BL/6 mice. Benzo(a)pyrene but not benzo(a)pyrene-7,8-diol activation by 3-methylcholanthrene-induced mouse liver microsomes was inhibited by a monoclonal antibody (Mab 1-7-1) against CYP1A1/2 suggesting that 1A1 probably takes part in the first P450 reaction. However, aryl hydrocarbon hydroxylase activity, a classical measure of benzo(a)pyrene metabolism, was not inhibited by the same concentration of Mab 1-7-1. None of the other antibodies used, detecting 2A, 2B, 2C or 2E subfamilies, inhibited the adduct formation. Troleandomycin and gestodene, chemical inhibitors of human 3A4, inhibited benzo(a)pyrene-7,8-diol activation by 3-methylcholanthrene-induced microsomes to some extent only in high concentrations. Although liver microsomes from 3-methylcholanthrene-induced mice catalyzed the formation of BPDE-DNA in vitro clearly more than uninduced microsomes, 3-methylcholanthrene pretreatment in vivo decreased the adduct formation in benzo(a)pyrene-treated mice. These results emphasize the significance of detoxicating and DNA-repairing pathways in vivo. Finally, synchronous fluorescence spectrophotometry for BPDE-DNA measures the end-point of the three-step activation pathway while aryl hydrocarbon hydroxylase measures a one-step hydroxylation. Thus, these methods should be used rather as corroborative than mutually exclusive assays.

Cloning, expression and characterization of a murine-human chimeric antibody with specificity for pre-S2 surface antigen of hepatitis B virus

The cloning, expression and characterization of a murine-human chimeric antibody with specificity for the pre-S2 surface antigen (Ag) of hepatitis B virus (HBV) is described. The heavy and light chain variable region (VH and VL) genes encoding the murine monoclonal antibody (mAb) were isolated and combined with human gamma 1 and kappa constant region genes, respectively. The expression vectors containing the chimeric heavy and light chain genes were sequentially electroporated into murine Sp2/0 hybridoma cells and transfectomas secreting chimeric antibody were isolated. The chimeric antibody was purified and characterized by ELISA, Western analysis and competition immunoassay, demonstrating that the transfectoma functionally express and secrete murine-human chimeric antibody which retained the specificity and affinity of the parental murine mAb.

Specific induction of hepatic cytochrome P4501a-2 in C57BL/6 and DBA/2 mice treated with 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)

The food mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is activated by cytochrome p4501a-2 via N-hydroxylation; various P450s may contribute to detoxification via ring hydroxylation. Alterations in P450 levels by IQ treatment might therefore influence its toxicity. To examine the role of Ah locus genotype on the biochemical effects of IQ, C57BL/6 (AhbAhb; p450Ia-1/2 inducible) and DBA/2 (AhdAhd, noninducible) mice of both sexes were given IQ at varying doses, with different vehicles and routes of administration. Livers taken after 24 hours were assessed for total cytochrome p450 and activities of ethoxyresorufin-O-deethylase (EROD, a p4501a-1 activity, inducible in Ahb mice), methoxyresorufin-O-demethylase (MROD, a p4501a-2 activity), and benzyloxyresorufin-O-dealkylase (BzROD, an activity of p4502b). There was little effect on total cytochrome p450, but all three enzyme activities were often induced, a maximum of 2.5-fold, in both sexes and in DBA/2 as well as C57BL/6 mice. However, Western immunoblot analysis with monoclonal antibodies demonstrated an increase only in p4501a-2 protein. p4501a-1 remained undetectable. A monoclonal antibody to p4502-b recognized one protein band in liver microsomes from males and two bands in female mice of both strains. Amounts of these proteins were not altered by IQ treatment. Thus, IQ specifically, if moderately, induces its activating enzyme, p4501a-2, in a process that was not clearly related to Ah responsiveness.

Flow-regulatory function of upper airway in health and disease: a unified pathogenetic view of sleep-disordered breathing

Although the Starling resistor behavior of the upper airway during sleep has been well established in health and disease, its physiological implications have not been fully appreciated. The purposes of the present communication are to reassess the current state of knowledge within the framework of the Starling resistor concept and to examine the implications of the concept on homeostatic feedback respiratory control and the pathogenesis of the sleep apnea syndrome. The main inferences drawn from the assessment include: (1) Owing to the Starling resistor properties of the upper airway and the well-organized neurochemical control mechanism, the upper airway performs important homeostatic flow regulatory function; it appropriately dampens the potentially unstable breathing during sleep and prevents the PaCO2 from falling below the apneic threshold; (2) Under certain conditions, the upper airway flow regulatory function fails to achieve appropriate dampening, leading to development of a variety of sleep-related breathing disorders that include underdamping due to overly sensitive central chemoresponsiveness and/or excessive lung to chemoreceptor transport lag--central sleep apnea; overdamping due to upper airway obstructive dysfunction--obstructive sleep apnea and/or hypopnea; and, finally, conditions with mixed features of central underdamping with coexisting collapsible upper airway; and (3) Successful treatment of these conditions requires restoration of appropriate damping. The overdamping imposed by the faulty upper airway is effectively reduced by surgical and medical approaches, and by application of nasal continuous positive airway pressure (CPAP). Reduction of PaCO2 by use of acetalzolamide and/or aminophylline reduces the plant gain, thus effectively offsetting the underdamping of central origin. Owing to the dual effect of nasal CPAP on the upper airway and respiratory pump, use of nasal CPAP can also effectively reduce the plant gain, accounting for the therapeutic effect of nasal CPAP on the central sleep apnea.

Methoxyresorufin and benzyloxyresorufin: substrates preferentially metabolized by cytochromes P4501A2 and 2B, respectively, in the rat and mouse

The cytochrome P450 isozyme specificity for the O-dealkylation of methoxyresorufin (MTR) and benzyloxyresorufin (BZR) in the rat and mouse was investigated. The induction of various alkoxyresorufin O-dealkylation activities was measured in male F344/NCr rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3,4,5,3',4',5'-hexachlorobiphenyl. MTR and ethoxyresorufin (ETR) O-dealkylation activities were induced 30- and 80-fold, respectively, in the liver. ETR O-dealkylation activity was induced > 250-fold in the kidney, whereas the metabolism of MTR was induced only 30-fold in this extrahepatic tissue. Phenacetin, a fairly specific CYP1A2 inhibitor, caused concentration-dependent competitive inhibition of MTR O-dealkylation (ki approximately 20 microM at 0.5 microM substrate) in hepatic microsomes from 3,4,5,3',4',5'-hexachlorobiphenyl-treated rats. The corresponding ki for inhibition of ETR O-dealkylation by phenacetin was > or = 333 microM at a 0.5 microM substrate concentration. A monoclonal antibody displaying inhibitory activity against rat CYP1A1 inhibited ETR O-dealkylation activity, whereas it failed to inhibit MTR O-dealkylation activity. In contrast, a monoclonal antibody reactive with both CYP1A1 and CYP1A2 inhibited both O-dealkylation activities to an equal extent. Similar experiments, employing phenacetin or specific monoclonal antibodies, yielded comparable results when performed with mouse microsomes. The maximal induction of MTR O-dealkylation activity in mice was > 100-fold. The P450 isozyme specificity of BZR O-dealkylation was also examined in both rats and mice. Pregnenolone-alpha-carbonitrile, a strong inducer of CYP3A, only weakly induced BZR O-dealkylation activity. In addition, a monoclonal antibody that specifically inhibits CYP2B caused inhibition of BZR metabolism in microsomes from phenobarbital- or dexamethasone-pretreated rats. In B6C3F1 mice exposed to dietary Aroclor 1254, significant induction of hepatic MTR O-dealkylation activity was observed at concentrations lower than those required for the induction of ETR or BZR O-dealkylation. In summary, it would appear that MTR is a relatively specific substrate for CYP1A2 activity in rodents, while BZR appears to be relatively specific for CYP2B.

Monoclonal antibody-directed assessment of toluene induction of rat hepatic cytochrome P450 isozymes

Cytochrome P450 isozymes induced in rat liver by a range of concentrations of toluene were studied with monoclonal antibodies (MAbs) to specific P450 isozymes and by enzyme assays. Nitrosodimethylamine demethylase activity was significantly increased in microsomes from rats exposed to more than 1000 ppm of toluene, an increase that was dose-dependent. Anti-CYP2E1 significantly inhibited the metabolism of toluene to benzyl alcohol (BA) by about 50%, in microsomes from 1000 to 4000 ppm toluene-exposed rats, at low substrate concentration (0.2 mM). With anti-CYP2B1/2, the rate of BA formation was decreased by 15-17% in microsomes from rats of 2000 and 4000 ppm toluene exposures at high substrate concentration (5.0 mM). On the other hand, anti-CYP2C11/6 inhibited the rate of formation of BA in all of the microsomes, but the extent of inhibition was progressively decreased from 55% in control to 33% in 4000 ppm exposure. Immunoblot analysis with anti-CYP2E1 and anti-CYP2B1/2 revealed stronger immunoreactive bands in microsomes from rats exposed to more than 1000 and 2000 ppm of toluene, respectively. Stronger bands were also observed in microsomes from rats of 2000-4000 ppm toluene exposures with anti-CYP3A1/2, but no immunoreactivity appeared with anti-CYP1A1/2. These results suggest that toluene induces CYP2E1, CYP2B1/2 and CYP3A1/2, but reduces CYP2C11/6, and has no effect on CYP1A1/2.

Induction and inhibition of cytochrome P-450-dependent monooxygenases in hamster tissues by ethanol

The effects of ethanol on hamster hepatic and extrahepatic monooxygenases were determined in the present study. Chronic ethanol administration increased cytochrome P-450 (P-450) content and monooxygenase activities towards aniline, N-nitrosodimethylamine, and 7-ethoxyresorufin. In contrast, benzphetamine and benzo(a)pyrene oxidation rates were decreased 21-24% by ethanol. In kidney, ethanol pretreatment increased P-450 content, aniline and N-nitrosodimethylamine oxidation activities. In lung, ethanol ingestion selectively increased aniline hydroxylation without affecting other monooxygenase activities. Intestinal monooxygenase activity was refractory to ethanol induction. Immunoblotting of the microsomal proteins showed that ethanol induced a protein cross-reactive with rabbit antibody raised against human P-450 2E1 in hamster liver, kidney, and lung. Immunoblotting analysis using mouse monoclonal antibody 1-12-3 raised against scup P-450 1A1 revealed that ethanol induced an immunorelated protein in hamster liver, kidney, and lung. Induction of P-450 2E1 and 1A was not observed with intestinal protein blots. Immunoblotting analysis using mouse monoclonal antibody 2-66-3 against rat P-450 2B1 showed inhibition of an immunorelated protein in ethanol-treated hamster liver. The inhibitory effect on P-450 2B was not observed with extrahepatic tissues. These results suggest that ethanol has the ability to induce P-450s 2E1 and 1A and to inhibit P-450 2B in hamster tissues.

Metabolism of the antimammary cancer antiestrogenic agent tamoxifen. I. Cytochrome P-450-catalyzed N-demethylation and 4-hydroxylation

Previous studies suggested that the therapeutic effect of the antimammary cancer agent tamoxifen might be related to its metabolism. This study examined the cytochrome P-450 enzymes in rat and human liver catalyzing the metabolism of tamoxifen. Incubations of tamoxifen with rat liver microsomes yielded three major polar metabolites identified as the N-oxide, N-desmethyl, and 4-hydroxy derivatives. N-Oxide formation was catalyzed by the flavin-containing monooxygenase (see part II). Carbon monoxide, SKF-525A, metyrapone, and benzylimidazole strongly inhibited N-demethylation and 4-hydroxylation, indicating the participation of P-450 monooxygenase in these reactions. Antibodies to NADPH-P450 reductase inhibited N-demethylation and 4-hydroxylation. Comparison of the metabolism of tamoxifen in untreated male and female rats demonstrated some sexual dimorphism. N-Demethylation was higher in the male rat and 4-hydroxylation was higher in the female. Treatment of rats with phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN), and methylcholanthrene (MC) enhanced N-demethylation, demonstrating the potential participation of multiple P-450s in N-demethylation. Evidence strongly indicates that CYP3A enzyme(s) catalyzes N-demethylation in liver microsomes of PB- and PCN-treated rats (PB and PCN microsomes, respectively): i) N-demethylation was inhibited by cortisol and erythromycin (alternate substrates) and a time-dependent inhibition was observed with troleandomycin (TAO) in vitro; ii) treatment of female rats with TAO, followed by dissociation of the microsomal TAO-P-450 complex, elevated N-demethylation; iii) treatment of PCN-induced female rats with chloramphenicol inhibited N-demethylation; and iv) polyclonal antibodies (PAbs) to CYP3A1 inhibited N-demethylation in PCN- and PB-treated female rats. Although we were unable to reconstitute the N-demethylation activity with purified CYP3A1, which is difficult to reconstitute, collectively the evidence demonstrated that CYP3A enzymes catalyze N-demethylation in PB and PCN microsomes. By contrast, antibodies against CYP2B1/B2 did not inhibit N-demethylation and reconstituted 2B1 did not catalyze N-demethylation of tamoxifen, indicating that 2B1 was not involved. The increase in N-demethylation by MC treatment appears to be due to elevation of CYP1A1/1A2 (P-450c/d). Alternate substrates of CYP1A1/1A2 inhibited N-demethylation and reconstituted rat CYP 1A1-catalyzed N-demethylation. Surprisingly, monoclonal antibodies (MAbs) against CYP1A1/1A2 only partially inhibited, and PAbs against CYP1A1 did not inhibit N-demethylation in MC microsomes, indicating that in MC microsomes, 1A1 does not contribute significantly to that reaction. Mab anti-CYP2C11/2C6 (P-450h/k) inhibited N-demethylation in PB, PCN, and control male rat liver microsomes, suggesting that CYP2C11 and/or CYP2C6 catalyze this reaction to some extent.(ABSTRACT TRUNCATED AT 400 WORDS)