The effect of food on bromfenac, naproxen sodium, and acetaminophen in postoperative pain after orthopedic surgery

STUDY OBJECTIVES

To evaluate the effect of a standard meal on bioavailability of bromfenac, and on the relative analgesic efficacy and adverse effect liability of bromfenac 25 mg, naproxen sodium 550 mg, and acetaminophen 325 mg in the treatment of pain after orthopedic surgery.

DESIGN

Randomized, double-blind, single-dose, parallel-group.

SETTING

Two wards of the orthopedic surgery department at the Central Hospital, Karlstad, Sweden.

PATIENTS

Three hundred ten patients with steady, moderate, or severe pain within 72 hours after orthopedic surgery.

INTERVENTIONS

Patients were randomly assigned both to receive a standard meal or remain in a fasted state, and to treatment with a single oral dose of bromfenac 25 mg, naproxen sodium 550 mg, or acetaminophen 325 mg, when they experienced steady, moderate, or severe pain that required an analgesic. Using a self-rating record, subjects rated their pain and its relief for up to 8 hours after medicating. Blood samples were obtained from all patients using one of two schedules.

MEASUREMENTS AND MAIN RESULTS

The peak plasma bromfenac concentration for fed patients was only 28% of that of fasted patients. Disregarding food intake, bromfenac 25 mg and naproxen sodium 550 mg were significantly superior to acetaminophen 325 mg for all summary measures of analgesia. Bromfenac and naproxen were superior to acetaminophen by hour 1 and this difference persisted for 8 hours. Food reduced bromfenac's analgesic effect, but not that of naproxen or acetaminophen; treatment by meal interaction was significant for five measures of efficacy. Analgesic response for fed bromfenac recipients, compared with those who were fasted, ranged from 37-71%. The percentage of patients reporting an adverse effect was significantly higher for bromfenac (25%) and naproxen (24%) than for acetaminophen (12%).

CONCLUSIONS

Results of analgesic studies not taking patients' food status into consideration might be misleading. Although bromfenac 25 mg and naproxen sodium 550 mg produced significant analgesia compared with acetaminophen 325 mg, bromfenac's efficacy was significantly reduced when patients ate a standard meal. Adverse effects were transient and consistent with the pharmacologic profiles of the drugs.

Kinetics of the norepinephrine analog [76Br]-meta-bromobenzylguanidine in isolated working rat heart

A related set of kinetic studies of the norepinephrine analog [76Br]-meta-bromobenzylguanidine (MBBG) were performed with an isolated working rat heart preparation. A series of constant infusion studies over a wide range of MBBG concentrations allowed estimation of the Michaelis-Menten constants for transport by the neuronal norepinephrine transporter (uptake1) and the extraneuronal uptake system (uptake2). Pharmacological blocking studies with inhibitors of uptake1, uptake2 and vesicular uptake were performed to delineate the relative importance of these norepinephrine handling mechanisms on the kinetics of MBBG in the rat heart. Bolus injection studies were done to assess the ability of compartmental modeling techniques to characterize the kinetics of MBBG. These studies demonstrate that MBBG shares many of the same uptake mechanisms as norepinephrine in the rat heart. PET imaging studies with MBBG would be useful for assessing sympathetic nerve status in the living human heart.

The influence of bromfenac on the pharmacokinetics and pharmacodynamic responses to glyburide in diabetic subjects

STUDY OBJECTIVE

To assess the effect of bromfenac sodium, a nonnarcotic analgesic drug under development, on the pharmacokinetics and pharmacodynamics of glyburide in patients with type II diabetes.

DESIGN

Randomized, double-blind, placebo-controlled, multiple-dose study with a two-period crossover design.

PATIENTS

Eleven men and one woman (age 36-64 yrs) whose diabetes was responsive to oral sulfonylurea therapy.

INTERVENTIONS

Placebo or bromfenac 50 mg was given as a single oral dose 3 times/day for the first 3 days of the study. On days 4-6, patients received the alternative treatment. For at least 3 months before and during the study, patients took their usual single daily dose of glyburide 10 mg.

MEASUREMENTS AND MAIN RESULTS

Bromfenac concentrations were measured by high-performance liquid chromatography with ultraviolet detection. Glyburide concentrations were measured by gas chromatography with nitrogen-phosphorus detection. Glycemia was measured repeatedly on day 3 of each treatment. Pharmacokinetic analysis was performed with noncompartmental techniques. No significant differences in the pharmacokinetics of glyburide or in the pharmacodynamic response of serum glucose levels were observed between placebo and bromfenac. Intersubject variability of concentrations was modest for glyburide and glucose, with a CV of 43% or less.

CONCLUSION

Glyburide levels are not changed during concomitant administration of bromfenac.

Absolute bioavailability of bromfenac in humans

OBJECTIVE

To estimate absolute bioavailability of bromfenac and to compare its pharmacokinetics after intravenous and oral administration.

DESIGN

This was a randomized, open-label, single-dose, crossover study conducted under fasting conditions with a washout period of at least 48 hours between doses. Each subject received a 50-mg dose of bromfenac both intravenously and orally followed by collection of blood samples at specified time intervals. Bromfenac plasma concentrations were measured by using a validated HPLC method with ultraviolet detection.

SETTING

The study was conducted at the Drug Evaluation Unit. Hennepin County Medical Center, Minneapolis, MN.

SUBJECTS

The participants consisted of 12 healthy subjects between 18 and 45 years of age and within +/-15% of ideal body weight.

RESULTS

The mean +/- SD absolute bioavailability of bromfenac was 67% +/- 20%.

CONCLUSIONS

The pharmacokinetic parameters of bromfenac were similar after intravenous and oral administration, suggesting that the prototype oral dosage form is optimal and that the observed intersubject variability is due to bromfenac itself, not the type of dosage form.

Effects of age and gender on the pharmacokinetics of bromfenac in healthy volunteers

OBJECTIVE

To compare the pharmacokinetic parameters of bromfenac, a nonsteroidal antiinflammatory drug under development, in healthy volunteers of various ages and either gender, after single and multiple doses.

DESIGN

Open-label, single- and multiple-dose, nonrandomized, parallel study.

PARTICIPANTS

Twenty young (18-45 y), 12 young-elderly (65-74 y), and 12 elderly (75-85 y) subjects were studied. Half of the subjects in each group were women.

INTERVENTIONS

Bromfenac was given as a single 50-mg dose and then as 50-mg doses every 12 hours for 3 additional days. Twelve blood samples were collected for 12 hours after the first and last doses.

MAIN OUTCOME MEASURES

Bromfenac concentrations were measured by using an HPLC procedure with ultraviolet detection. Unbound bromfenac concentrations were measured by equilibrium dialysis. Pharmacokinetic analysis was performed by noncompartmental techniques.

RESULTS

No significant differences related to gender were detected. Significant differences were observed in half-life (t1/2), AUC, clearance, and apparent volume of distribution when the elderly group was compared with the young group and in t1/2 when the elderly group was compared with the young-elderly group, although substantial overlap among groups was observed.

CONCLUSIONS

Administration of bromfenac to young-elderly or elderly subjects of either gender does not require a dosage adjustment in acute settings. Consideration should be made to titrating dosages in patients over 75 years of age who require repeated doses.

Bromfenac disposition in patients with impaired kidney function

OBJECTIVES

To compare the pharmacokinetics of bromfenac among normal subjects and renally compromised patients and patients with end-stage renal disease.

METHODS

Bromfenac pharmacokinetics were examined after a single 50 mg oral dose in 18 subjects with normal kidney function, 12 subjects with decreased kidney function, and 10 dialysis-dependent subjects. Protein binding was assessed by equilibrium dialysis.

RESULTS

Mean peak concentrations and areas under the concentration versus time curve ranged from 3.3 to 3.9 micrograms/ml and 5.1 to 6.9 micrograms.hr/ml, respectively. The mean unbound fraction in the subjects receiving dialysis (0.29%) was nearly twice that in the subjects with normal kidney function (0.17%) and in the subjects with impaired kidney function (0.16%), but no differences were detected in clearance, volume of distribution, or their free fraction-corrected counterparts. Bromfenac half-life nearly doubled in the impaired and dialysis groups but was shorter than the anticipated 8-hour dose interval. Eight subjects had a total of 11 study events; none were serious and all were self-limited.

CONCLUSIONS

These findings suggest that no dosage adjustment is necessary in patients with impaired kidney function, but clinical monitoring appropriate for their individual condition is recommended.

Evaluation of pharmacokinetic interaction between bromfenac and phenytoin in healthy males

An open-label, nonrandomized, multiple-dose, inpatient study was conducted in healthy male volunteers to compare the pharmacokinetics of bromfenac and phenytoin when the drugs are given individually and concomitantly. Twelve men received multiple oral doses of bromfenac for 4 days and then oral phenytoin for up to 14 days followed by concomitant administration of bromfenac and phenytoin for 8 days. Concomitant administration of the two drugs caused an approximate 40% decrease in the mean peak plasma concentration (Cmax) and the interdose area under the concentration-time curve (AUC) of bromfenac. The oral clearance (Clpo) of bromfenac doubled and the volume of distribution increased by 77%. For phenytoin, the mean peak serum concentration and the AUC increased by 9% and 11%, respectively, in the presence of bromfenac. The only change in unbound phenytoin was a 16% increase in the AUC. Although statistically significant, the changes in the pharmacokinetic parameters of phenytoin and unbound phenytoin were small. Adjustments in the dose of phenytoin should not be required during concomitant administration of bromfenac, although each patient's clinical status should be evaluated individually.

Pharmacokinetic-pharmacodynamic relationships of bromfenac in mice and humans

The relationship between pharmacodynamic effect and plasma concentrations of the analgesic bromfenac was assessed retrospectively. The drug was administered in single doses of 5, 10, 25, 50, or 100 mg to patients with oral surgery pain. Concentration-effect curves were generated by a semiparametric pharmacokinetic-pharmacodynamic procedure. The bromfenac EC50 (the effect site concentration giving 50% of the maximum effect) was estimated to be 0.36 microgram/ml in patients when all five dose groups were combined, and an Emax model was used for pharmacodynamic response. A similar EC50 value, 0.40 microgram/ml, was obtained when bromfenac was tested in a mouse pain model. On the basis of combined-dose data, effect site concentrations were predicted to be above the analgesic EC50 for approximately 7-8 hours after a 50-mg bromfenac dose was taken in the fasting state. Predictions based on a pharmacokinetic-pharmacodynamic modeling procedure were in reasonable agreement with the clinical observations.

Lack of interaction between bromfenac and methotrexate in patients with rheumatoid arthritis

OBJECTIVE

To compare the pharmacokinetics of methotrexate (MTX) and bromfenac administered separately or coadministered in patients with rheumatoid arthritis (RA).

METHODS

Patients received their usual weekly oral dose of MTX on Days 1 and 8 and bromfenac 50 mg every 8 h from Days 4 to 9. On Days 1 and 8 serial blood and urine samples were collected to study the pharmacokinetics of MTX and 7-hydroxymethotrexate (7-OHMTX). Bromfenac pharmacokinetics were studied on Days 7 and 8. Concentrations of the analytes were assayed using validated high performance liquid chromatography methods.

RESULTS

Nine patients, 5 women and 4 men, completed the study. No statistically significant changes were observed in any of the pharmacokinetic variables evaluated for bromfenac with or without MTX. Bromfenac also did not alter the pharmacokinetics of low dose MTX. However, some significant changes were observed in the pharmacokinetics of 7-hydroxymethotrexate: a 30% increase in dose normalized area under the serum concentration time curve (mean +/- SD) to 3102 +/- 1397 micrograms.h/l and a 16% decrease in renal clearance to 10.0 +/- 6.7 ml/h/kg. Eight patients had mild or moderate adverse events: most were considered unrelated to the study drug by the investigator. One patient did not complete the study because of moderate hypertension. No patient had clinically important abnormal laboratory test results.

CONCLUSION

No clinically significant changes in MTX pharmacokinetics were detected in patients with RA when bromfenac was added to MTX therapy. Although 7-OHMTX concentrations were elevated, the changes were small and unlikely to be of clinical significance. MTX did not alter the pharmacokinetics of bromfenac.

Dietary uptake of superlipophilic compounds by earthworms (Eisenia andrei)

The uptake and elimination of three superlipophilic compounds (hexabromobenzene, PCB153, and octachloronaphthalene) after dietary uptake was studied in earthworms (Eisenia andrei). All three compounds were taken up from the food, although they did not significantly accumulate despite their hydrophobicity. Both uptake efficiencies (E) and biomagnification factors (BMF) were low. E varied between 0.70 and 7.5%, while BMF values were all below 0.17. The elimination of the compounds was slow, with elimination rate constants k2 varying between 0.04 and 0.09 day-1.

Assessing intratumor distribution and uptake with MBBG versus MIBG imaging and targeting xenografted PC12-pheochromocytoma cell line

The heterogeneity of tumor uptake is likely to substantially limit the effectiveness of metaiodobenzylguanidine (MIBG) therapy. This study was done to establish whether metabromobenzylguanidine (MBBG) can target neuroendocrine tumors and to provide intratumor biodistribution and uptake information in comparison to MIBG.

METHODS

MBBG and MIBG tumor uptake and kinetic studies were performed in experimental PC-12 pheochromocytoma grown in nude mice. Intratumor distribution studies were performed using autoradiography and secondary ion mass spectrometry (SIMS) microscopy, because the latter technique can detect and potentially quantify both drugs concomitantly within the same tumor specimen.

RESULTS

MBBG uptake in PC12 tumors was early (2 hr) and intense (80% ID/g). Retention values were similar for both drugs 24 hr postinjection. At the cellular level, MBBG mostly accumulated in the cytosol. At the multicellular level, cells exhibited staining, but in many areas, SIMS images of both drugs were not spatially correlated.

CONCLUSION

MBBG targeted experimental pheochromocytoma efficiently with high early uptake values. Bromine-76-MBBG is a promising means of imaging and quantifying tumor uptake with PET. Both drugs were localized in the cytosol, but the correlation between the two distributions, as assessed by the values of the standardized local concentrations, was weak although significant multicellularly.

Biotransformation and toxicity of halogenated benzenes

1. Multiple potentially harmful metabolites can be distinguished in the metabolic activation of halogenated benzenes: epoxides, phenols, benzoquinones and benzoquinone-derived glutathione conjugates. 2. The role of these (re-) active metabolites in the toxic effects induced by halogenated benzenes such as hepatotoxicity, nephrotoxicity, porphyria and thyroid toxicity is discussed. 3. Evidence is presented suggesting that the formation of reactive benzoquinone metabolites rather than the traditional epoxides is linked to halogenated benzene-induced hepatotoxicity. 4. A crucial role for the benzoquinone-derived glutathione adducts in halogenated benzene-induced nephrotoxicity is clearly established. 5. Although metabolic activation appears to be involved in porphyria, the nature of the ultimate porphyrinogenic metabolite has not been elucidated yet. 6. Disturbances in thyroid hormone (and retinoid) homeostasis can be (at least partially) explained by the formation of halogenated phenol metabolites. 7. In conclusion, for a relevant prediction of the ultimate fate of a compound in a living organism, one should know the chemical characteristics and reactivity of the parent compound and its metabolites, together with insight into the formation mechanism of each of the suspected metabolites, and an understanding of the interaction between a specific chemical (reactive) structure and its target molecule.

Interindividual variation in biotransformation and cytotoxicity of bromobenzene as determined in primary hepatocyte cultures derived from monkey and human liver

1. Bromobenzene-evoked hepatotoxicity resulting from cytochrome P450-mediated epoxidation has been studied extensively in rodents in vivo and in rodent hepatocytes. In this paper we present data concerning the formation of bromphenols, glutathione (GSH) depletion and cytotoxicity observed in primate hepatocytes in primary culture after exposure to bromobenzene (BrB). 2. After pre-incubation for 2 or 24 h, hepatocytes were exposed to BrB in concentrations up to 2 mM for 4 or 24 h. 3. In both human and cynomolgus monkey hepatocytes BrB cytotoxicity and GSH depletion were found after exposure to 2 mM BrB. The degree of the observed effects was not influenced by the duration of pre-incubation and/or exposure periods. 4. Major inter-individual differences were observed, which could not be attributed to differences in cytochrome P450-mediated bioactivation rates. This suggests that the variation in individual susceptibility to BrB may be related to inter-individual differences in the activity of de-activating (metabolic) pathways. 5. The study of the background of these inter-individual differences may contribute to a more complete understanding of the factors ruling sensitivity to BrB or related chemicals.

Bromobenzene detoxification in the human liver-derived HepG2 cell line

1. The applicability of the human hepatoma cell line, HepG2, as a cell culture model for studying xenobiotic liver toxicity has been investigated using the well-characterized hepatotoxic chemical, bromobenzene. 2. Bromobenzene caused a concentration- (0-10 mM) and time-dependent (0-180 min) decrease in HepG2 cell viability. The degree of toxicity was dependent upon the culture medium composition and the state of cell growth. Toxicity in Modified Earle's and Williams' E Media was maximal at 7 days growth compared with 3 and 10 days, and was greater in Williams' than in Earle's medium. Toxicity in Dulbecco's medium was apparent only at 10 days growth and was less than the maximum toxicity in the other media. 3. Bromobenzene was detoxified by epoxide hydrase. The question of metabolic activation by P450 remained unresolved, but any involvement of P450 was by forms not inhibited by ketoconazole. 4. The mechanism of bromobenzene toxicity did not appear to involve lipid peroxidation, depletion of reduced glutathione, calcium-mediated proteolysis or metabolic activation by prostaglandin synthetase, but may have involved direct solvent-induced cell damage. 5. This study demonstrates the potential usefulness of HepG2 cells in toxicity testing and highlights the importance of standardizing culture conditions.

Metabolites of ebrotidine, a new H2-receptor antagonist, in human urine

Ebrotidine is a new H2-receptor antagonist which exhibits a remarkable ability for gastric mucosal protection. A preliminary metabolic pathway for this compound was proposed and the hypothetic metabolites were synthesized. The presence of ebrotidine and its metabolites ebrotidine S-oxide and 4-bromobenzenesulfonamide in human urine has been confirmed by HPLC separation and spectroscopic characterization of the collected fractions by FT-IR and 1H NMR. Ebrotidine S,S-dioxide has been identified by HPLC using diode-array detection.

Preparation and pharmacological characterization of [76Br]-meta-bromobenzylguanidine ([76Br]MBBG)

[76Br]-meta-Bromobenzylguanidine ([76Br]MBBG) was prepared from the iodinated analog (MIBG) and [76Br]NH4 using a Cu(+)-assisted halogen exchange reaction. [76Br]MBBG was produced in a 60-65% radiochemical yield with a specific activity of 20 MBq/nmol. In rats, biodistribution kinetic studies showed a high uptake of [76Br]MBBG in heart tissues with its maximum of 5% ID/S at 2 h p.i.; whereas 4 h p.i., the maximum of the heart-to-lung concentration ratio of 8 was observed. Metabolic studies in rats indicated that [76Br]MBBG was rapidly metabolized in plasma. However in heart tissue, 25 h p.i., 85% of the radioactivity still represented unchanged radiotracer. Pharmacological studies in rats showed that the myocardial uptake of [76Br]MBBG was similar to that of norepinephrine. After pretreatment of the rats, the uptake of [76Br]MBBG was reduced 4 h p.i. to the following values: after desipramine (DMI) to 37%, after dexamethasone (DXM) to 88% and after 6-hydroxydopamine (6-OHDA) to 16%. These preliminary results suggest that [76Br]MBBG can be useful for the assessment of heart catecholamine reuptake disorders with PET.

Bromine-76-metabromobenzylguanidine: a PET radiotracer for mapping sympathetic nerves of the heart

Iodine-123-metaiodobenzylguanidine (MIBG) is used to qualitatively assess heart innervation with single-photon emission computed tomography (SPECT). This approach is clinically useful in the prognostic evaluation of congestive heart failure. To improve quantification of uptake of the tracer using positron emission tomography (PET), we studied the characteristics of the bromoanalog of MIBG. Bromine-76-metabromobenzylguanidine (76Br-MBBG) was prepared from a heteroisotopic exchange between radioactive bromine atoms (noncarrier-added (76Br) BrNH4) and the cold iodine atoms of the precursor metaiodobenzylguanidine. Biodistribution was studied in rats and PET cardiac imaging performed in dogs. Myocardial uptake was high and prolonged in both species (mean half-life in dogs: 580 min). In rats, myocardial uptake was inhibited by desipramine by 64%, whereas after pretreatment with 6-hydroxydopamine uptake was reduced by 84%. In dogs pretreated with 6-hydroxydopamine or with desipramine, a steep washout of the tracer occurred (mean half-life: 136 min and 118 min, respectively). The non-specific uptake plus the passive neuronal diffusion of the tracer could be estimated at about 25%-30% of the total fixation. In dogs, analysis of unchanged 76Br-MBBG in plasma showed that radiotracer metabolism was slow: 60 min after injection, 80% of the radioactivity was related to unchanged 76Br-MBBG. These preliminary findings suggest that 76Br-MBBG could be used to quantitatively assess adrenergic innervation in heart disease using PET. When combined with use of 11C-CGP 12177, cardiac adrenergic neurotransmission can be assessed.

Pharmacokinetics of bromfenac in healthy subjects after single oral administration of three different doses

The pharmacokinetic profile of bromfenac (2-amino-3-(4-bromobenzoyl) benzeneacetic acid, CAS91714-93-1) has been investigated in 12 healthy subjects (6 male and 6 female) after single oral doses of 25, 50 and 75 mg. Plasma concentrations were determined by a sensitive HPLC method with spectrophotometric detection. Sampling was performed up to 300 min after drug ingestion. Linear pharmacokinetics could be verified for this dose-range; there was a clear, positive dose-plasma concentration relationship. Bromfenac exhibits a cmax of 3.49 +/- 1.65-8.81 +/- 3.45 micrograms/ml at tmax 52 +/- 27-42 +/- 15 min. The elimination half-life was 39.8 +/- 7.3-34.2 +/- 8.0 min with a clearance (Cl/f) of 120.6 +/- 51.6-135.3 +/- 34.6 ml/min and a volume of distribution (Vd/f) 6.82 +/- 2.88-6.64 +/- 2.29 l. The results obtained show a fast absorption and rapid elimination of bromfenac when administered orally. The short plasma half-life of bromfenac apparently presents no direct relationship to its clinical effectiveness.

Disposition of the flame retardant 1,2-bis(2,4,6-tribromophenoxy)ethane in rats following administration in the diet

[14C]1,2-Bis(2,4,6-tribromophenoxy)ethane (FF-680) was administered at 0.05, 0.5, or 5% in the diet for 1 day to three groups (four rats per group) of rats, and daily at 0.05% in the diet for 10 days to another group of five rats. In addition, another group of four rats were given a single oral gavage dose of 200 mg/kg of [14C]FF-680 in corn oil and were used for bile collection. At all dose levels, [14C]FF-680-derived radioactivity was excreted almost totally via the fecal route (> 99% of the total excreted 14C), with < 1% recovered in the urine. No radioactivity was detected in the expired air, and very little radioactivity was excreted in the bile (ca. 0.04% of the dose). At 4 days after the start of administration of the dosed diet for 1 day, no radioactivity was detected in any tissue analyzed, except adipose tissue, skin, and thymus, in which trace concentrations of radioactivity were detected in some animals. At 10 days after the start of administration of dosed diet to rats dosed for 10 days, trace but detectable levels of radioactivity were observed in all tissues analyzed except the brain of some animals. Excluding the gastrointestinal tract, adipose tissue contained the highest concentration of 14C radioactivity, followed by kidney, skin, and thymus, whereas brain, testes, and spleen contained the lowest concentrations of radioactivity. No parent compound was detected in the urine, while fecal radioactivity was identified as the parent compound. Mean recovery of radioactivity ranged from ca. 86-101% of the [14C]FF-680 consumed. The data indicate that FF-680 was very poorly absorbed from the gastrointestinal tract. However, following daily administration for 10 days, trace amounts of radioactivity accumulated in tissues to provide detectable levels.

Effect of p-xylene inhalation on the bioactivation of bromobenzene in rat lung and liver

It is unclear whether the pneumotoxicity observed with bromobenzene (BB) in phenobarbital-induced rats is related to BB bioactivation in lung, liver or both. To help differentiate pulmonary from hepatic bioactivation, BB was administered alone and in combination with p-xylene, which inhibits pulmonary but induces hepatic cytochromes P450. Exposure to p-xylene alone (3400 ppm for 4 hr) produced no changes in bronchoalveolar lavage fluid (BALF) measurements (gamma-glutamyl transpeptidase, lactate dehydrogenase, protein, white blood cell count) or serum sorbitol dehydrogenase. p-Xylene increased hepatic microsomal benzyloxy- (BROD), pentoxy- (PROD), and ethoxy- (EROD) resorfuin O-dealkylase activities but decreased pulmonary microsomal BROD and PROD. Immunoblot analysis revealed an induction of hepatic but not pulmonary microsomal P450IIB apoprotein. When rats were exposed to p-xylene (2800 ppm) or room air for 4 hr, treated 12 hr later with BB (0.5 ml/kg, ip) or corn oil, and killed after 12 hr, p-xylene increased hepatic P450IIB (27-fold) concomittant with a similar increase in BROD activity. p-Xylene also increased hepatic P450IA apoprotein (3.4-fold) with a complimentary increase in EROD activity. p-Xylene potentiated BB-induced hepatotoxicity. In pulmonary microsomes p-xylene and BB each produced similar decreases in both EROD and BROD activities. The combination of p-xylene and BB had an additive effect on pulmonary P450IA1 reduction. BALF analysis and histopathology revealed no pneumotoxicity with any treatment. p-Xylene potentiation of BB-induced hepatotoxicity without pneumotoxicity suggests that the liver does not produce metabolites of BB which are directly involved in pulmonary damage.

Bromobenzene-glutathione excretion into bile reflects toxic activation of bromobenzene in rats

This investigation was designed to determine whether biliary excretion of bromobenzene(BB)-glutathione(GSH) conjugate can be used as an index of in vivo activation of BB. In order to test this hypothesis, the effect of chemicals known to alter the toxicity and biotransformation of BB (i.e., cytochrome P-450 inducers and inhibitors) on the biliary excretion of BB-GSH was studied in rats. BB-GSH was the major BB metabolite in bile. A linear relationship was observed between the dosage of BB administered and BB-GSH excreted into bile, up to a dosage of 250 mumol/kg of BB. Of the inducers tested, phenobarbital, which is known to increase the toxicity of BB, dramatically increased (700%) the rate of biliary excretion of BB-GSH over that in control animals. In contrast, 3-methylcholanthrene, which is known to decrease the hepatotoxicity of BB, decreased the biliary excretion of BB-GSH (56%). Inhibitors of P-450, such as SKF 525-A and piperonyl butoxide which are known to decrease the activation and hepatotoxicity of BB, also decreased the biliary excretion of BB-GSH. These findings are in agreement with the hypothesis that the biliary excretion of BB-GSH reflects the formation of the reactive BB metabolite in liver and the rate of biliary excretion can be used to determine factors that are important in determining the toxicity of BB.

Metabolic activation of halogenated hydrocarbons in the conjunctival epithelium and excretory ducts of the intraorbital lacrimal gland in mice

Autoradiographic studies were performed to determine the localization of irreversibly bound radioactivity in the eyes and accessory structures of mice exposed to 14C-labelled organic solvents in vivo or in vitro. A selective localization of bound radioactivity was observed in the conjunctival epithelium of mice given i.v. injections of 1,2-dibromoethane, chloroform, carbon tetrachloride or bromobenzene. Similar results were observed after instillation of chloroform or carbon tetrachloride in the conjunctival sac and after incubation of eyelids with the labelled compounds in vitro. A high level of irreversibly bound radioactivity was also observed in the excretory ducts of the intraorbital lacrimal glands of mice exposed to 1,2-dibromoethane in vivo and in vitro. After incubation of 14C-labelled 1,2-dibromoethane or chloroform with homogenates prepared from rat conjunctiva, the presence of irreversibly protein-bound radioactivity was detected. The results indicate that the conjunctival epithelium can metabolically activate halogenated organic solvents into products that bind to the tissue. The significance of a metabolic activation of chemicals in the pathogenesis of chemically induced lesions in the conjunctiva merits further attention.

Short term inhalation of bromobenzene: methodology and absorption characteristics in mouse, rat and rabbit

In a dynamic inhalation system, mice, rats and rabbits were exposed to bromobenzene vapour (250-3400 p.p.m.) for 4 hr. Blood concentrations of bromobenzene were determined by head-space gas chromatography. After inhalation of 1000 p.p.m. for 4 hr, concentrations of 153, 102 and 47 micrograms bromobenzene/ml blood were found in mice, rats and rabbits, respectively. In vitro experiments showed a blood/air partition coefficient at 37 degrees of approximately 200, which was reflected by a linear uptake of bromobenzene up to an air concentration of 2500 p.p.m. Compared with results obtained previously by intraperitoneal bromobenzene administration inhalation resulted in higher blood concentrations.