Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well-documented publication which meets basic scientific principles. The justification for the Read Across approach has been attached to the Section 13

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2007

Materials and methods

Principles of method if other than guideline:
The primary objectives of these studies were to determine the absorption, distribution, metabolism and elimination of TBBPA-DBPE following oral or intravenous (IV) administration to male Fischer-344 (F-344) rats.
Additional studies with jugular vein cannulated (JVC) animals were conducted to determine the bioavailability of TBBPA-DBPE following oral administration.
Studies using bile duct cannulated (BDC) animals were conducted to investigate hepatic metabolism of TBBPA-DBPE as well as biliary elimination following oral administration.
Metabolism was assessed in vitro with primary cultured hepatocytes (HC) and hepatic microsomal protein (MIC) isolated from male F-344 or Sprague Dawley rat livers.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Radiolabelling:
yes
Remarks:
[14C] phenol ring labelled: TBBA-DBPE, TBBPA and BPA

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Arlan Sprague Dawley, Inc. (Indianapolis, IN)
- Age at study initiation: 8–9 weeks of age
- Weight at study initiation: 161–190 g
- Fasting period before study: From 12 hours prior to 2 hours post the administration; Animals utilized during the repeated dose study were not fasted
- Housing: In University Animal Care, an Association for Assessment and Accreditation for Laboratory Animal Care approved animal care facility; animals were placed hanging steel mesh cages with free access to food and water.
- Metabolism cages: Nalgene® metabolism cages for acclimation 24 h prior to administration and Nalgene® metabolism cages with rat-appropriate parts (floor grate, food hopper, and water bottle) for the duration of experiments.
- Diet (e.g. ad libitum): Ad libitum (Teklad 4 % Rat Diet 7001, Harlan Teklad, Madison, WI)
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 5–7 days; Animals with surgically implanted cannula (JVC or BDC) were acclimatized only 24 h to ensure the cannula would remain unobstructed over the course of the experiment.

ENVIRONMENTAL CONDITIONS
- Temperature: 25 °C
- Photoperiod (hrs dark / hrs light): 12 h/12 h light/dark cycle

Surgical alterations (jugular vein and common bile duct cannulation) were performed at Harlan Sprague Dawley prior to shipment

Administration / exposure

Route of administration:
other: oral and intravenous administration
Vehicle:
other: described case by case
Duration and frequency of treatment / exposure:
Single dose administration
Repeated daily oral doses for 5 or 10 days
Single intravenous administration
Doses / concentrations
Remarks:
Doses / Concentrations:
The doses used in these in vitro studies were based on the results of published toxicity studies (van Esch, 1995[1]). The dose of 20 mg/kg represents a non-toxic dose (approximately 1000- fold lower than published acute LD50 in rats). This lack of acute toxicity was confirmed following a single IV administration of TBBPA-DBPE. Doses selected for in vitro assays (100, 50, or 10 µM) were designed to assay for metabolic product generation, and were therefore based on stable aqueous concentrations of TBBPA-DBPE in the presence of rat hepatocytes or rat liver microsomal protein.

[1]Van Esch, G.J., 1995. Tetrabromobisphenol A dibromopropylether. In: Environmental Health Criteria 172: Tetrabromobisphenol A and derivatives. International Programme on Chemical Safety. World Health Organization, Finland, pp, 71-77.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
The substance is poorly and slowly absorbed across the gut lumen following oral administration of single or multiple (1, 5, or 10 doses). Cmax did not occur until 7.5 h after oral gavage. This slow and limited absorption results in extensive excretion in the foeces. Blood toxicokinetic data revealed that the oral systemic bioavailability of TBBPA-DBPE was 2.2 % of a 20 mg/kg dose. Absorption from the intestines into portal blood was somewhat higher as amounts of TBBPA-DBPE in liver tissues were in the range of 5 – 7 % of the dose. However, that which was absorbed into the systemic compartment was eliminated from the blood slowly.
Details on distribution in tissues:
The slow elimination of the substance, also apparent after IV administration, reflects a restricted, selective tissue disposition. Disposition into the liver appears to be the major mechanism for blood clearance of TBBPA-DBPE.
Based on IV administration data that showed that TBBPA-DBPE is readily extracted from the systemic circulation by the liver, it is anticipated that increases in intestinal absorption of TBBPA-DBPE in the presence of food would not necessarily result in an increase in systemic exposure to TBBPA-DBPE. Evidence indicating that the liver was the major site of disposition was found in all cases, independent of the number of doses or route of administration of TBBPA-DBPE.
Details on excretion:
The primary route of elimination of TBBPA-DBPE was in the foeces. After a single oral bolus dose, the majority of the dose (> 70 %) was eliminated by 24 h. Greater than 85 % of the administered dose was eliminated in the foeces by 96 h. Repeated oral administration of TBBPA-DBPE did not alter the route of elimination of [14C] equivalents.
However, in the course of these studies it was found that fasting prior to oral administration of TBBPA-DBPE increased the rate of elimination of [14C] equivalents in the foeces. When the animals were not fasted, approximately 32 % of the administered dose was eliminated in 24 h as compared to 70 % for fasted animals.
Elimination in the foeces following IV administration was slower than after oral administration. Cumulative foecal excretion of [14C] equivalents did not reach 70 % of the administered dose until 96 h. This excretion appeared linear at about 1 % of dose per hour, up to 48 h.
Excretion in the urine was less than 1 % of the dose in all studies.
Following oral administration of TBBPA-DBPE, excretion of [14C] equivalents in bile was 1 % of the dose after 24 h.

Foeces collected following oral administration of TBBPA-DBPE to fasted or fed animals were extracted and analyzed by HPLC-UV/Vis-radio analysis. Analysis of foecal extracts detected three peaks; a major peak that co-eluted with the TBBPA-DBPE standard at 23.6 min, a minor peak that co-eluted with a contaminant that was present in the dosing solution, and a small but consistently detected peak that eluted at 21.8 min. Relative abundance of each moiety was similar, independent of collection time or feeding regimen. The peak that co-eluted with TBBPA-DBPE accounted for approximately 90 % of the administered radioactivity, the contaminant peak that eluted at 19.4 min accounted for approximately 3 % of the dose (this value closely approximates the known level of contaminant found in the [14C] TBBPADBPE standard), and the unknown (rT = 21.8 min) accounted for approximately 5 % of the administered dose.
HPLC analysis of bile samples resulted in two radioactive peaks that did not co-elute with TBBPA-DBPE. HPLC-radio analysis after incubation with β-glucuronidase revealed a lipophilic moiety that eluted between 18 and 19 min that did not co-elute with the TBBPA-DBPE standard.
It was noted that disposition of [14C] equivalents in the liver in the presence of free biliary outflow (continuously collected bile from bile-cannulated animals; 0.05 % of dose at 24 h) was less than in the absence of free outflow (conventional animals; 0.9 % at 24 h).
Toxicokinetic parametersopen allclose all
Toxicokinetic parameters:
AUC: IV administration = 25.050 µg min/ml
Toxicokinetic parameters:
AUC: Oral administration = 951 µg min/ml
Toxicokinetic parameters:
other: Terminal half life of distribution: oral administration = 2.5 h
Toxicokinetic parameters:
other: Terminal half life for elimination: IV administration = 24.8 h
Toxicokinetic parameters:
other: Terminal half life for elimination: oral administration = 12.3 h
Toxicokinetic parameters:
other: Systemic clearance from blood: IV administration = 0.1 ml/min
Toxicokinetic parameters:
other: Volume of distribution of steady state: IV administration = 4.9 ml
Toxicokinetic parameters:
Cmax: Oral administration = 0.6 µg/ml
Toxicokinetic parameters:
Tmax: Oral administration = 7.5 h
Toxicokinetic parameters:
other: Bioavailability: IV administration = 2.2 %

Metabolite characterisation studies

Metabolites identified:
no
Details on metabolites:
Analysis of radioactivity eliminated in biliary outflow following a single oral administration of TBBPA-DBPE indicated that [14C] equivalents excreted from the liver were due to metabolites formed in the liver. It appears that hepatic metabolism of TBBPA-DBPE is slow, and while the mechanism of metabolite formation is not currently clear, it appears that the metabolite(s) are formed in at least a two-step process. This conclusion is supported by observations of HPLC-radio separations of bile from a treated rat that was incubated in the presence and absence of β-glucuronidase, where the major peak detected in the absence of β-glucuronidase was found to shift to a more hydrophobic moiety following incubation with β-glucuronidase. It was determined that these radiolabeled species were not TBBPA-DBPE, as determined by co-chromatography with [14C] TBBPADBPE.
It must be noted that these metabolites accounted for approximately 1 % of the administered dose recovered in 24 h, a period in which greater than 70 % of the dose was recovered in the foeces. Extraction and radio HPLC analysis of foecal samples also provided some evidence of biotransformation of TBBPA-DBPE. A small peak that did not co-elute with parent or known contaminant was observed. This could reflect a reaction catalysed in the liver and/or by gut microflora. This conclusion is supported by in vitro data that indicate that incubations of TBBPA-DBPE in the presence of either rat hepatocytes or rat liver microsomal protein resulted in no detectable metabolite formation, even when tested at concentrations 100 to 1000-fold higher than the greatest levels detected in liver in vivo. the probability of formation of the carcinogenic moiety DBP was low.

Bioaccessibility

Bioaccessibility testing results:
Following IV or oral administration of [14C] TBBPADBPE, only one radioactive peak was detected in the blood at all time points. The retention time of the radioactive peak (rT = 23.6 min) was the same as that of the TBBPA-DBPE standard. Disappearance of [14C] equivalents from the blood was slow and found to be best described by a bi-exponential curve. This conclusion was supported by a long calculated half-life of elimination (t1/2β: 24.8 h) and slow clearance of radioactivity from blood (CLb: 0.1 ml/min).
Following oral administration, TBBPA-DBPE was poorly absorbed into the systemic circulation. Additionally, this uptake into the blood compartment from the intestine appeared to be slow. The Cmax (0.6 µg/ml) was not achieved until 7.4 h, with an absorption half-life of 2.5 h. Once the TBBPA-DBPE was absorbed, the half-life of elimination from blood was relatively long (t1/2β: 13.9 h). The maximum systemic bioavailability following oral administration was calculated to be 2.2 %.

Any other information on results incl. tables

In vitro metabolism of TBBPA-DBPE

Following incubations of rat MIC (1, 2, or 5 mg/ml) in a NADP+ recycling system with 100 µM TBBPA-DBPE, HPLC-UV/Vis-radio analysis detected only one peak that co-eluted with TBBPA-DBPE. However, after 15 min of incubation, losses in the parent compound peak area were observed with time.

After it was determined that these losses were not due to protein binding or adsorption to the reaction vessel(s), it was concluded that this apparent loss was due to the poor solubility of TBBPA-DBPE in aqueous media. In order to maximize solution stability, the concentration of TBBPA-DBPE was reduced to 10 µM. In the presence of protein (1 mg/ml), this concentration of TBBPA-DBPE formed a stable incubation system. However, even in this stable system, evidence of TBBPA-DBPE metabolism was not obtained. HPLC-UV/Vis-radio analyses of samples from all time points were found to contain a single [14C] labeled peak that coeluted with the parent molecule. Identical results were obtained from studies that utilized rat MIC isolated from male Sprague Dawley rats that were pretreated with phenobarbital (> 10-fold enrichment of CYP2B levels).

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): low bioaccumulation potential based on study results
The results of these studies show that the likelihood of systemic exposure following ingestion of TBBPA-DBPE is low. Additionally, disposition in liver tissue was minimal, and metabolite formation was slow.
In summary, these data show that TBBPA-DBPE was poorly absorbed across the gut lumen following oral administration.
However, the absorbed amount was rapidly sequestered in the liver, slowly metabolized, and finally eliminated in the bile for foecal excretion.
Executive summary:

Method

Male Fischer-344 rats were dosed with TBBPA-DBPE (20 mg/kg) by oral gavage or IV administration. Following a single oral administration of TBBPA-DBPE, elimination of [14C] equivalents in the foeces was extensive and rapid (95 % of dose by 36 h). Following repeated daily oral doses for 5 or 10 days, route and rate of elimination was similar to single administrations of TBBPA-DBPE. After IV administration, foecal excretion of [14C] equivalents was much slower (27 % of dose eliminated by 36 h, 71 % by 96 h). Urinary elimination was minimal (< 0.1 %) following oral or IV administration. A single peak that co-eluted with the standard of TBBPA-DBPE was detected in extracts of whole blood following oral or IV administration. TBBPA-DBPE elimination from the blood was slow. Kinetic constants following IV dosing were: t1/2β= 24.8 h; CLb= 0.1ml/min. Kinetic constants following oral dosing were: t1/2a= 2.5 h; t1/2β= 13.9 h; CLb= 4.6 ml/min. Systemic bioavailability was 2.2%. Liver was the major site of disposition following oral or IV administration.

Results

After oral administration, 1 % of the dose was eliminated in bile in 24 h (as metabolites). In the in vitro experiments utilizing hepatocytes or liver microsomal protein, no detectable metabolism of TBBPA-DBPE occurred. These data indicate that TBBPA-DBPE is poorly absorbed from the gastrointestinal tract. Compound which is absorbed is sequestered in the liver, slowly metabolized, and eliminated in the foeces.