Novel [18F]-Labeled Meta-Bromobenzylguanidine Derivatives: Potential Positron Emission Tomography Imaging Probes for the Norepinephrine Transporter

To develop novel norepinephrine transporter (NET)-targeting positron emission tomography (PET) probes with optimal pharmacokinetic properties, a series of meta-bromobenzylguanidine derivatives was synthesized. 4-Fluorodiethoxyethane-3-bromobenzylguanidine (compound 12) showed relatively good affinity for the NET (IC50 = 1.00 ± 0.04 μM). The corresponding radiotracer 18F-12 was prepared in high radiochemical purity (>98%) via a three-step method. The in vitro cellular uptake results demonstrated that 18F-12 was specifically taken up by NET-expressing SK-N-SH cells by the uptake-1 mechanism. Biodistribution studies in mice showed that 18F-12 exhibited high cardiac uptake (10.45 ± 0.66 %ID/g at 5 min p.i. and 6.44 ± 0.40 %ID/g at 120 min p.i.), faster liver clearance, and a lower dose of absorbed radiation than [123I]-labeled meta-iodobenzylguanidine ([123I]MIBG). Small animal PET imaging confirmed the high heart-to-background ratio of 18F-12 and the uptake-1 mechanism specific for the NET in rats, indicating its potential as a promising PET radiotracer for cardiac sympathetic nerve imaging.

Profiles of Metabolites and Gene Expression in Rats with Chemically Induced Hepatic Necrosis

This study investigated whether integrated analysis of transcriptomics and metabolomics data increased the sensitivity of detection and provided new insight in the mechanisms of hepatotoxicity. Metabolite levels in plasma or urine were analyzed in relation to changes in hepatic gene expression in rats that received bromobenzene to induce acute hepatic centrilobular necrosis. Bromobenzene-induced lesions were only observed after treatment with the highest of 3 dose levels. Multivariate statistical analysis showed that metabolite profiles of blood plasma were largely different from controls when the rats were treated with bromobenzene, also at doses that did not elicit histopathological changes. Changes in levels of genes and metabolites were related to the degree of necrosis, providing putative novel markers of hepatotoxicity. Levels of endogenous metabolites like alanine, lactate, tyrosine and dimethylglycine differed in plasma from treated and control rats. The metabolite profiles of urine were found to be reflective of the exposure levels. This integrated analysis of hepatic transcriptomics and plasma metabolomics was able to more sensitively detect changes related to hepatotoxicity and discover novel markers. The relation between gene expression and metabolite levels was explored and additional insight in the role of various biological pathways in bromobenzene-induced hepatic necrosis was obtained, including the involvement of apoptosis and changes in glycolysis and amino acid metabolism.

The complete Table 2 is available as a supplemental file online at http://taylorandfrancis.metapress.com/openurlasp?genre=journal&issn=0192-6233 . To access the file, click on the issue link for 33(4), then select this article. A download option appears at the bottom of this abstract. In order to access the full article online, you must either have an individual subscription or a member subscription accessed through www.toxpath.org .

Pharmacokinetics and efficacy of topically applied nonsteroidal anti-inflammatory drugs in retinochoroidal tissues in rabbits

Purpose

To evaluate the pharmacokinetics and efficacy of topically applied nonsteroidal anti-inflammatory drugs (NSAIDs) in the retinochoroidal tissues of rabbits.

Methods

The cyclooxygenase (COX) inhibitory activity of diclofenac, bromfenac, and amfenac, an active metabolite of nepafenac, were determined using human-derived COX-1 and COX-2. Each of the three NSAIDs was applied topically to rabbits, and after 0.5 to 8 hrs, the concentration of each drug in the aqueous humor and the retinochoroidal tissues was measured by liquid chromatography-tandem mass spectrometry. The pharmacokinetics of the drugs in the tissues after repeated doses as is done on patients was calculated by a simulation software. The inhibitory effect of each NSAID on the breakdown of the blood-retinal barrier was assessed by the vitreous protein concentration on concanavalin A-induced retinochoroidal inflammation in rabbits.

Results

The half-maximal inhibitory concentration (IC₅₀) of diclofenac, bromfenac, and amfenac was 55.5, 5.56, and 15.3 nM for human COX-1, and 30.7, 7.45, and 20.4 nM for human COX-2, respectively. The three NSAIDs were detected in the aqueous humor and the retinochoroidal tissue at all-time points. Simulated pharmacokinetics showed that the levels of the three NSAIDs were continuously higher than the IC₅₀ of COX-2, as an index of efficacy, in the aqueous humor, whereas only the bromfenac concentration was continuously higher than the IC₅₀ at its trough level in the retinochoroidal tissues. The intravitreous concentration of proteins was significantly reduced in rabbits that received topical bromfenac (P = 0.026) but not the other two NSAIDs.

Conclusions

Topical bromfenac can penetrate into the retinochoroidal tissues in high enough concentrations to inhibit COX-2 and exerts its inhibitory effect on the blood-retinal barrier breakdown in an experimental retinochoroidal inflammation in rabbits. Topical bromfenac may have a better therapeutic benefit than diclofenac and nepafenac for retinochoroidal inflammatory diseases.

Bioaccumulation kinetics of polybrominated diphenyl ethers and decabromodiphenyl ethane from field-collected sediment in the oligochaete, Lumbriculus variegatus

The extensive use of polybrominated diphenyl ethers (PBDEs) and decabromodiphenyl ethane (DBDPE) has made them widespread contaminants in abiotic environments, but data regarding their bioavailability to benthic organisms are sparse. The bioaccumulation potential of PBDEs and DBDPE from field-collected sediment was evaluated in the oligochaete Lumbriculus variegatus using a 49-d exposure, including a 28-d uptake and a 21-d elimination phase. All PBDEs and DBDPE were bioavailable to the worms with biota-sediment accumulation factors (BSAFs) ranging from 0.0210 g organic carbon/g lipid to 4.09 g organic carbon/g lipid. However, the bioavailability of highly brominated compounds (BDE-209 and DBDPE) was poor compared with that of other PBDEs, and this was confirmed by their relatively low freely dissolved concentrations (C(free)) measured by solid-phase microextraction. The inverse correlation between BSAFs and hydrophobicity was explained by their uptake (k(s)) and elimination (k(e)) rate constants. While ke changed little for PBDEs, ks decreased significantly when chemical hydrophobicity increased. The difference in bioaccumulation kinetics of brominated flame retardants in fish and the worms was explained by their physiological difference and the presence of multiple elimination routes. The appropriateness of 28-d bioaccumulation testing for BSAF estimation was validated for PBDEs and DBDPE. In addition, C(free) was shown to be a good indicator of bioavailability.

A randomized comparison of to-aqueous penetration of ketorolac 0.45%, bromfenac 0.09% and nepafenac 0.1% in cataract patients undergoing phacoemulsification

OBJECTIVE

To compare the peak to-aqueous penetration of three nonsteroidal anti-inflammatory drugs: ketorolac tromethamine 0.45%, bromfenac 0.09%, nepafenac 0.1%, and amfenac (the active metabolite of nepafenac) in patients undergoing phacoemulsification.

METHODS

A single center, double-masked study randomized 122 patients to receive one of three treatment arms. On-label dosing of ketorolac (BID), bromfenac (BID), and nepafenac (TID) was instructed for 1 day prior to surgery. Patients were instructed to instill one drop the morning of surgery. The patients received four additional doses 1 hour prior to phacoemulsification. After completion of the paracentesis site with a superblade, aqueous humor (0.15 cc) was collected through the peripheral clear cornea with a 30-gauge needle attached to a TB syringe. Following collection, aqueous samples were stored at -40°C prior to analysis. Drug concentrations were analyzed by liquid chromatography tandem mass spectrometry using positive turbo-ion spray ionization and multiple reaction monitoring mode for quantification. An independent sample Student's t-test was used to detect between-group differences.

RESULTS

The peak aqueous concentration of ketorolac 0.45% was 10 times the concentration of bromfenac 0.09%, and five times the concentration of and 54% greater than the metabolically inactive nepafenac 0.1%. The mean peak aqueous concentration of ketorolac 0.45% was 688.87 ± 749.6 ng/ml. Bromfenac achieved a mean peak aqueous concentration of 67.64 ± 62.4 ng/ml. The mean peak aqueous concentrations of nepafenac and amfenac were 447.10 ± 225.7 ng/ml and 140.37 ± 56.6 ng/ml, respectively. The peak concentration of ketorolac was statistically significantly greater than bromfenac (P ≤ 0.0005), nepafenac (P ≤ 0.05), and amfenac (P ≤ 0.005). A limitation of this study is that aqueous samples were collected just prior to surgery and not during the postoperative period due to ethical considerations.

CONCLUSIONS

Ketorolac 0.45% achieved significantly greater aqueous concentrations when compared to bromfenac 0.09% and the active metabolite of nepafenac 0.1% (amfenac) in patients undergoing phacoemulsification.

Bioavailability and half-life of decabromodiphenyl ether (BDE-209) in rat

1. The absorption of the flame retardant decabromodiphenyl ether (BDE-209) has been shown by its detection in human plasma, but reported experimental data on its determined in rat, and qualitative analyses by GC/MS of metabolites in plasma were performed. The relative amount of phenolic metabolites was determined in a rat plasma sample obtained after administration of radiolabelled BDE-209. 2. The bioavailability of parent BDE-209 was calculated to be about 26% in rat. The concentrations of phenolic radioactivity in plasma 3 and 7 days after dosing were four times higher than those of the neutral compounds, i.e. parent compound, indicating absorption in rat are inconsistent. The bioavailability and half-life were therefore that total absorption was higher than 26%. 3. Thirteen phenolic metabolites were determined in the plasma and the major phenolic metabolites were characterized as a hydroxy-octaBDE, a hydroxy-nonaBDE and a hydroxy-methoxy-hexaBDE (guaiacol-type). The exposure to the phenolic metabolites seemed higher than the parent compound, BDE-209. 4. The initial elimination phase in plasma t1/2alpha for BDE-209 was 2 h, implying a rapid distribution of BDE-209 to well-perfused tissues. The distribution volume at steady state was 1.4 l kg-1, implying a low tendency for distribution to adipose tissue. The terminal t1/2 for BDE-209 in the intravenously dosed rat was calculated as 2.5 days (58 h).

In vivo pharmacokinetics and in vitro pharmacodynamics of nepafenac, amfenac, ketorolac, and bromfenac

PURPOSE

To evaluate the aqueous humor concentrations and cyclooxygenase (COX) inhibitory activities of nepafenac, amfenac, ketorolac, and bromfenac after topical ocular administration of Nevanac (nepafenac 0.1%), Acular LS (ketorolac 0.4%), or Xibrom (bromfenac 0.09%).

SETTING

Five private ophthalmology practices throughout the United States.

METHODS

Patients requiring cataract extraction were randomized to 1 of 3 treatment groups: Nevanac, Acular LS, or Xibrom. Patients were administered 1 drop of the test drug 30, 60, 120, 180, or 240 minutes before cataract surgery. At the time of paracentesis, an aqueous humor sample was collected and later analyzed for drug concentration. In addition, COX-1 (homeostatic) and COX-2 (inducible) inhibitory activities of nepafenac, amfenac, ketorolac, and bromfenac were determined via the in vitro measurement of prostaglandin E(2) (PGE(2)) inhibition.

RESULTS

Seventy-five patients participated in the study. The prodrug nepafenac had the shortest time to peak concentration and the greatest peak aqueous humor concentration (C(max)). The C(max) of nepafenac was significantly higher than that of the other drugs (P<.05), including the higher-concentration ketorolac (0.4%). The area under the curve (AUC) of nepafenac was significantly higher (P<.05) than the AUCs of amfenac, ketorolac, and bromfenac. The combined AUCs of nepafenac and amfenac were the highest of all drugs tested (P<.05). Ketorolac showed the most potent COX-1 inhibition, whereas amfenac was the most potent COX-2 inhibitor. The PGE(2) aqueous humor levels of each study medication were highly variable; as a result, meaningful interpretation of the data was not possible.

CONCLUSION

Nepafenac showed significantly greater ocular bioavailability and amfenac demonstrated greater potency at COX-2 inhibition than ketorolac or bromfenac.

Dietary exposure of juvenile rainbow trout (Oncorhynchus mykiss) to 1,2-bis(2,4,6-tribromophenoxy)ethane: bioaccumulation parameters, biochemical effects, and metabolism

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed in the laboratory to an environmentally relevant dose of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) via their diet for 49 days, followed by 154 days of untreated food to examine bioaccumulation parameters, potential biochemical effects, and metabolic products. There was a linear increase in the amount of BTBPE in fish during the uptake phase of the experiment, and an uptake rate constant of 0.0069 +/- 0.0012 (arithmetic mean +/- 1 x standard error) nmoles per day was calculated. The elimination of BTBPE from the fish obeyed first-order depuration kinetics (r2 = 0.6427, p < 0.001) with a calculated half-life of 54.1 +/- 8.5 days. The derived biomagnification factor of 2.3 +/- 0.9 suggests that this chemical has a high potential for biomagnification in aquatic food webs. Debrominated and hydroxylated metabolites were not detected in liver extracts and suggest that either biotransformation or storage of BTBPE-metabolites in the hepatic system of fish is minor or that our exposure time frame was too short. Similar concentrations of circulating thyroid hormones, liver deiodinase enzyme activity, and thyroid glandular histology suggest that BTBPE is not a potent thyroid axis disruptor.

The effect of selected aromatic bromine derivatives on the activity of glutathione peroxidase and transferase

OBJECTIVES

Glutathione (GSH) is an important element of antioxidative barrier. Its biological function consists in eliminating oxygen free radicals. It also acts as a co-substrate in numerous enzymatic reactions catalyzed by glutathione peroxidase (GPx) and glutathione S-transferase (GST). In our study we attempted to assess the effect of hexabromobenzene (HBB) and its metabolites on the level of GSH and related enzymes, GPx and GST.

MATERIALS AND METHODS

The experiments were performed on female Wistar rats. The investigated compounds (HBB, 1,2,4,5-tetraBB, 1,2,4- and 1,3,5-triBB) were administered intragastrically in three different doses (HBB: 15, 75, and 375 mg/kg; 1,2,4,5-tetraBB and 1,2,4-triBB: 8, 40, and 200 mg/kg; 1,3,5-triBB: 12, 60, and 300 mg/kg) for 7, 14, 21 or 28 days. GSH level and activity of GST and GPx were determined in the obtained material.

RESULTS

The highest activity of GPx and GSTwas observed after a 7-fold administration of all investigated compounds. Prolonged time of exposure caused the return to the control values.

CONCLUSIONS

The study revealed that repeated exposure to aromatic bromine derivatives increases GPx and GST activity only in the initial phase of the experiment.

Effects of nonsteroidal anti-inflammatory drugs on experimental allergic conjunctivitis in Guinea pigs

The effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on experimental allergic conjunctivitis, induced by ocular challenge with antigen in actively sensitized guinea pigs, were investigated. NSAIDs reduced the increase in prostaglandin D2 (PGD2) and E2 (PGE2) in the ocular lavage fluid. The inhibition of NSAIDs to these increases was approximately 90%-95%. NSAIDs also lowered itch-scratch response (ISR) to approximately one-third to one-half of the vehicle-treated group. However, these drugs scarcely affected plasma exudation in the conjunctiva. Ketotifen, an H1 histamine receptor antagonist, inhibited both pathophysiological changes (inhibition: 70%-80%). However, this drug was less efficacious than NSAIDs in reducing PGD2 and PGE2 levels. Moreover, topical administration of histamine induced ISR and plasma exudation; in contrast, PGD2 induced ISR exclusively. These results suggest that a part of antigen-induced ISR may be attributable to PGs. However, PGs may not play a key role in plasma exudation; other mediators such as histamine may be involved.

Metabolism, tissue disposition, and excretion of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) in male Sprague-Dawley rats

A single oral dose of [14C] 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) was administered to conventional and bile-duct cannulated male Sprague-Dawley rats. Tissue disposition, excretion and metabolism was determined. BTBPE is a low-volume brominated flame retardant used in resins or plastics, and toxicity data in peer-reviewed journals is extremely limited. BTBPE was fairly insoluble in lipophilic solutions, which made dose preparation difficult. The great majority of 14C (>94%) was excreted in the feces of both groups of rats at 72 h, and tissue retention was minimal. Lipophilic tissues contained the highest concentrations of BTBPE, e.g. thymus, adipose tissue, adrenals, lung, and skin. Metabolites were excreted in the urine, bile and feces, but at a very low level. Fecal metabolites were characterized as monohydroxylated, monohydroxylated with debromination, dihydroxylated/debrominated on a single aromatic ring, monohydroxylated on each aromatic ring with accompanying debromination, and cleavage on either side of the ether linkage to yield tribromophenol and tribromophenoxyethanol. Despite a limited quantity of stable metabolites extractable in the feces, non-extractable 14C levels were relatively high (39% of the 0-24 h fecal 14C), which suggested that BTBPE could be metabolically activated in the rat and covalently bound to fecal proteins and/or lipids. It was concluded that limited absorption and metabolism of BTBPE would occur by ingestion in mammals.

Debromination of the flame retardant decabromodiphenyl ether by juvenile carp (Cyprinus carpio) following dietary exposure

The congener 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE 209) is the primary component in a commonly used flame retardant known as decaBDE. This flame retardant constitutes approximately 80% of the world market demand for polybrominated diphenyl ethers (PBDEs). Because this compound is very hydrophobic (log K(ow) approximately 10), it has been suggested that BDE 209 has very low bioavailability, although debromination to more bioavailable metabolites has also been suggested to occur in fish tissues. In the present study, juvenile carp were exposed to BDE 209 amended food on a daily basis for 60 days, followed by a 40-day depuration period in which the fate of BDE 209 was monitored in whole fish and liver tissues separately. No net accumulation of BDE 209 was observed throughout the experiment despite an exposure concentration of 940 ng/day/fish. However, seven apparent debrominated products of BDE 209 accumulated in whole fish and liver tissues over the exposure period. These debrominated metabolites of BDE 209 were identified as penta- to octaBDEs using both GC/ECNI-MS and GC/HRMS. Using estimation methods for relative retention times of phenyl substitution patterns, we have identified possible structures for the hexa- and heptabromodiphenyl ethers identified in the carp tissues. Although exposure of carp to BDE 209 did not result in the accumulation of BDE 209 in carp tissues, our results indicate evidence of limited BDE 209 bioavailability from food in the form of lower brominated metabolites.

Comparison of tissue distribution and metabolism of 1,2- and 1,4-dibromobenzenes in female rats

The distribution, excretion and metabolism of 1,4-dibromobenzene (1,4-DBB) and 1,2-dibromobenzene (1,2-DBB), following a single intraperitoneal administration to female Wistar rats, were investigated using radiotracer 3H and GC-MS technique. The maximum level of 3H after 1,4-DBB administration was detected in all examined rat tissues between 4 and 24 h foltowing the injection. The highest concentrations of 3H were found in fat tissue, muscles, adrenal glands and sciatic nerve. About 50% of administered dose was still retained in the rat 72 h after injection. For 1,2-DBB, the highest level of 3H was in the liver, kidneys and fat tissue 4 and 8 h after administration. Three days after injection, less than 2% of the given dose was retained in the rat body. Urine turned out to be the main route of 3H excretion following the injection of both compounds (30% and 82%, after 1,4-DBB and 1,2-DBB, respectively), and about 4% of the given dose was excreted in feces. In urine of rats the following substances were identified (in sequence 1,4-dBB and 1,2-dBB): (1) unchanged parent compounds (5 and 11%); (2) dibromophenols (84 and 73%); (3) dibromothiophenols (5 and 10%) and (4) monobromophenols (1.9 and 0.7%). This study suggests that 1,2-DBB is characterized by a relatively high turnover rate, whereas 1,4-DBB shows a tendency for long-term retention in the body.

The toxicology of the three commercial polybrominated diphenyl oxide (ether) flame retardants

Three commercial polybrominated diphenyl oxide flame retardants (PBDPO, PBDE) are manufactured: decabromodiphenyl oxide (DBDPO), octabromodiphenyl oxide (OBDPO) and pentabromodiphenyl oxide (PeBDPO). The composition, production volumes, uses and toxicology of the three products differ. In 1999, DBDPO accounted for approximately 82% of the global PBDPO usage. DBDPO has been extensively tested. DBDPO was not acutely toxic, was not irritating to the skin or eye, and did not induce skin sensitization. No evidence of genotoxic effects was detected in the Ames Salmonella, chromosome aberration, mouse lymphoma, or sister chromatid exchange tests. No cytogenic changes were observed in the bone marrow of rats (parents and offspring) undergoing a one-generation reproduction test. DBDPO did not adversely affect development or reproduction in rats. DBDPO's no-adverse-effect-level (NOAEL) in repeated dose studies was > or = 1000 mg/kg body weight. No, equivocal, or some evidence of carcinogenicity, dependent on genus and sex, was found in mice and rats at 2.5% and 5% of the diet administered for 2 years. DBPDO was poorly absorbed from the gastrointestinal tract (< 0.3-2% oral dose), had a short half-life (< 24 h) compared to PCB 153 (only 2% of an oral dose eliminated by rats in 21 days), and was rapidly eliminated via the feces (> 99% in 72 h). In contrast, components of the PeBDPO product were well absorbed and slowly eliminated, OBDPO's effect level in a 90-day study was approximately 100 mg/kg, PeBDPO's no-effect-level (NOEL) in a 30-day study was 1 mg/kg, and OBDPO induced developmental toxicity in the rat. In aquatic species, neither DBDPO nor OBDPO were toxic to aquatic organisms or bioconcentrating. Components of the PeBDPO product bioconcentrated in fish but produced little evidence of adverse effects.

In vitro dermal absorption of flame retardant chemicals

Flame retardant chemicals may be used in furniture fabric in the future to reduce the flammability of the fabric. As a part of the process to evaluate the potential for exposure to these chemicals, this study examined the in vitro dermal absorption of two flame retardant chemicals. The chemicals were [14C]decabromodiphenyl oxide (DBDPO) and [14C]tris-(1,3-dichloro-2-propyl)phosphate (TDCP). Skin from the adult hairless female mouse (SKH1) was removed and mounted in flow-through diffusion cells. The chemicals, at three dose levels (DBDPO: 6, 30 and 60 nmol; TDCP: 20, 100 and 200 pmol), were applied in a volatile vehicle (tetrahydrofuran for DBDPO; acetone for TDCP) to the skin. Fractions of receptor fluid, pumped below the skin, were collected over a 24-h period. The skin was washed with solvent (tetrahydrofuran for DBDPO; ethanol for TDCP) to remove unabsorbed chemical 24 h after application. The receptor fluid, skin wash and skin were analyzed for chemical-derived radioactivity. The skin from the high-dose group of both chemicals, and the receptor fluid from TDCP high-dose samples, were analyzed for parent compound and metabolites by HPLC. The 24-h cumulative percent of the dose of DBDPO in the receptor fluid was very low (0.07-0.34%). The applied dose of DBDPO detected in the skin ranged from 2 to 20%. The lowest dose of DBDPO had the highest percentage of the dose (20%) in the skin. The major portion of the applied dose was removed by washing the skin 24 h after application of DBDPO, and ranged from 77 to 92%. HPLC analysis of homogenate extract prepared from the high-dose of DBDPO-treated skin showed the presence of DBDPO and a minor unknown peak. TDCP was readily detected in the receptor fluid; 39-57% of the applied dose of TDCP was in the receptor fluid by 24 h. The solvent wash removed 11-25% of the dose from the skin and 28-35% remained in it. HPLC analysis of the skin homogenate extract and receptor fluid extract from the TDCP high-dose treated samples showed the presence of parent compound and a minor unknown peak. TDCP more readily penetrated hairless mouse skin and diffused into the receptor fluid than DBDPO. TDCP has a lower molecular weight and log octanol:water partition coefficient than DBDPO. The differences in the physico-chemical properties of these two chemicals most likely explains their dissimilar absorption through hairless mouse skin.

Evaluation of the developmental toxicity of 4-bromobenzene using frog embryo teratogenesis assay--Xenopus: possible mechanisms of action

Potential mechanisms of 4-bromobenzene-induced developmental toxicity were evaluated using frog embryo teratogenesis assay-Xenopus (FETAX). Early X, laevis embryos were exposed to 4-bromobenzene in two separate definitive concentration-response tests with and without an exogenous metabolic activation system (MAS) or selectively inhibited MAS. The MAS was treated with carbon monoxide (CO) to modulate P-450 activity, cyclohexene oxide (CHO) to modulate epoxide hydrolase activity, and diethyl maleate (DM) to modulate glutathione conjugation. Addition of the intact MAS, and particularly the CHO- and DM-inhibited MASs, dramatically increased the embryo lethal potential of 4-bromobenzene. Addition of the CO-inhibited MAS decreased the developmental toxicity of activated 4-bromobenzene to levels approximating that of the parent compound. Results from these studies suggested that a highly toxic arene oxide intermediate of 4-bromobenzene formed as the result of mixed function oxidase (MFO)-mediated metabolism may play an important role in the development toxicity of 4-bromobenzene in vitro. Furthermore, both epoxide hydrolase and glutathione conjugation appeared to be responsible for activated 4-bromobenzene detoxification.

The disposition and metabolism of 1,3-dibromobenzene in the rat

The distribution, excretion and metabolism of 1,3-dibromobenzene following a single i.p. administration to rats 100 or 300 mg/kg was investigated using radiotracer [3H] and GC-MS technique. After 72 hours about 74 to 90% were excreted in urine. The highest radioactivity was observed in the liver, kidneys and fat tissue. Later on a steady decline of radioactivity was apparent in all investigated tissues except for blood cells and the sciatic nerve, where constant levels were noted. In urine the following substances were identified and quantified by GC peak areas: unchanged 1,3-DBB (18%), dibromophenols (34%), dibromothiophenols (28%), dibromothioanisole (1.8%), bromophenol (5.5%), bromohydroxythiophenols (5%), and bromohydroxythioanisole (7.5%).

Comparison of tilidine/naloxone, tramadol and bromfenac in experimental pain: a double-blind randomized crossover study in healthy human volunteers

AIM

The analgesic efficacy and safety of single oral doses of two centrally acting compounds, the combination of 50 mg tilidine and 4 mg naloxone (Valoron N) and 50 mg tramadol (Tramal), were compared to 25, 50 and 75 mg of the non-steroidal antiinflammatory bromfenac in experimental pain.

SUBJECTS AND METHODS

It was a placebo-controlled double-blind 6-way crossover study design with 12 human volunteers. Acute pain was generated by electrical tooth pulp stimulation. Treatment effects were determined by recording somatosensory-evoked potentials and by subjective pain rating.

RESULTS

The tilidine/naloxone combination clearly was the most potent medication in this study, followed by bromfenac 75 mg, which produced an early pain relief. Tramadol produced poor analgesia, as did bromfenac 25 and 50 mg. There was no dose-response relationship for bromfenac. Control of plasma levels revealed pronounced interindividual differences in peak plasma concentrations for bromfenac, but not for tramadol. Tilidine/naloxone exerted adverse effects in 9, tramadol in 3 volunteers. Under medication with 25 and 50 mg bromfenac, respectively, only one subject reported adverse effects. No adverse effects were experienced with 75 mg bromfenac or placebo.

CONCLUSION

The results support previous conclusions about the analgesic efficacy of tilidine/naloxone and tramadol in experimental pain. Moreover, the findings suggest that 75 mg bromfenac might be suitable for fast but short relief of pain of non-inflammatory genesis.

Clinical pharmacokinetics and pharmacodynamics of bromfenac

Bromfenac is a nonsteroidal anti-inflammatory drug whose peak plasma concentration is reached 0.5 hours after oral administration. Bromfenac binds extensively to plasma albumin. The area under the plasma concentration-time curve is linearly proportional to the dose for oral doses up to 150 mg. The relationship between the total plasma and analgesic effect has been established. Only small amounts of bromfenac are eliminated unchanged, with the remaining drug being biotransformed into glucuronide metabolites which are excreted in urine and bile. Rapid elimination occurs in healthy individuals (half-life 0.5 to 4.0 h). Renal disease, hepatic disease and aging alter the disposition kinetics of bromfenac, and dosage adjustment may be advisable. Bromfenac modestly decreases free phenytoin concentrations. Bromfenac can cause idiosyncratic hepatic toxicity and has been withdrawn by its manufacturer pending further investigation of these case reports.

Metabolic disposition of 14C-bromfenac in healthy male volunteers

The metabolic disposition of 14C-bromfenac, an orally active, potent, nonsteroidal, nonnarcotic, analgesic agent was investigated in six healthy male subjects after a single oral 50-mg dose. The absorption of radioactivity was rapid, producing a mean maximum plasma concentration (Cmax) of 4.9 +/- 1.8 microg x equiv/mL, which was reached 1.0 +/- 0.5 hours after administration. Unchanged drug was the major component found in plasma, and no major metabolites were detected in the plasma. Total radioactivity recovered over a 4-day period from four of the six subjects averaged 82.5% and 13.2% of the dose in the urine and feces, respectively. Excretion into urine was rapid; most of the radioactivity was excreted during the first 8 hours. Five radioactive chromatographic peaks, a cyclic amide and four polar metabolites, were detected in 0- to 24-hour urine samples. Similarity of metabolite profiles between humans and cynomolgus monkeys permitted use of this animal model to generate samples after a high dose for structure elucidation. Liquid chromatography/mass spectrometry (LC/MS) analysis of monkey urine samples indicated that the four polar metabolites were two pairs of diastereoisomeric glucuronides whose molecular weight differed by two daltons. Enzyme hydrolysis, cochromatography, and LC/MS experiments resulted in the identification of a hydroxylated cyclic amide as one of the aglycones, which formed a pair of diastereoisomeric glucuronides after conjugation. Data also suggested that a dihydroxycyclic amide formed by the reduction of the ketone group that joins the phenyl rings formed the second pair of diastereoisomeric glucuronides. Further, incubation of various reference standards in control (blank) urine and buffer with and without creatinine indicated that the hydroxy cyclic amide released from enzyme hydrolysis can undergo ex vivo transformations to a condensation product between creatinine and an alpha-keto acid derivative of the hydroxy cyclic amide that is formed by oxidation and ring opening. Further experiments with a dihydroxylated cyclic amide after reduction of the keto function indicated that it too can form a creatinine conjugate.

The distribution and excretion of hexabromobenzene after a single administration in rat

The aim of this study was to investigate the disposition of [1-14C]-hexabromobenzene (HBB) in rats. The experiments were performed on 76 female Outbred IMP: Wist rats with body weight of 200 g +/- 20%. The compound was given orally in a single dose of 600 mg/kg and 4500 mg/kg. 14C radioactivity was traced in selected tissues, blood, urine and faeces, 0-72 hours following the administration. Maximum concentration of the 14C in blood was observed during the 2nd hour after the compound administration. The accretion of 14C in plasma proceeded with kinetic constant of 1.35/hour, whereas 14C-decline was biphasic. Half-lives for phase I and II were 1.2- and 440 hours, respectively. No substantial differences were noted in relation to the HBB dose. In tissues the highest radioactivity was observed in the fat tissue, adrenals and sciatic nerve. About 16 to 24% of the administered radioactivity was still retained in the rat body, 72 hours after administration of the compound. Faeces turned out to be the main route of excretion (about 75% of the given dose); only 1% was excreted in urine. Following on the literature data and our total balance of 14C elimination with faeces, we concluded, that almost 70% of 14C found in the faeces were composed of other metabolites than HBB and its lower-brominated derivatives. The above data indicate that HBB, especially in the case of chronic exposure, might accumulate in the body.

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.