Propane-1,2-diyl diacetate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Remarks:

toxicokinetic bridging study

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2017

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Objective of study:

other: The objective of this toxicokinetic bridging study was to determine the toxicokinetic parameters of propylene glycol diacetate (PGDA) with relation to propylene glycol (PG) control substance.

Test guideline

Qualifier:

no guideline available

Principles of method if other than guideline:

- Principle of test:The objective of this toxicokinetic bridging study was to determine the toxicokinetic parameters of propylene glycol diacetate (PGDA) with relation to propylene glycol (PG) control substance in Crl:CD(SD) rats following a single administration by oral gavage at equimolar dose levels and equimolar radioactivities. The results of the study determined whether PGDA and PG have similar toxicokinetics due to rapid ester hydrolysis of PGDA to PG, which supports a Read-Across approach for PGDA REACH registration.
- Short description of test conditions:Groups 1 and 3 received a single oral dose of a mixture of 14C-PGDA and PGDA. Groups 2 and 4 received a single oral dose of a mixture of 14C-PG and PG control substances.
Oral gavage was used for this study to characterize biomarkers (parent and/or any metabolite) and other toxicokinetic parameters. Also, many of the key toxicity studies for PG read across were the oral route for test material administration. Therefore, to investigate the toxicokinetics of both PGDA and the control substance PG, oral gavage was used for this study.

- Parameters analysed / observed:
Dose Confirmation and Homogeneity of Dose Preparation
The concentration and homogeneity of PGDA and PG in the dose preparation was determined by LSS analysis of aliquots of the 14C-labeled dose preparation taken from various locations in the vial (top, middle and bottom) was used to confirm the concentration of radioactivity and the homogeneity of the PGDA and PG. The respective dose preparations for Groups 1-4, had radiochemical homogeneity determined prior to administration (via LSS). Concentrations of test material-derived radioactivity in blood and excreta were based on analytically determined test material concentrations in dose formulations.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Propane-1,2-diyl diacetate

EC Number:

210-817-6

EC Name:

Propane-1,2-diyl diacetate

Cas Number:

623-84-7

Molecular formula:

C7H12O4

IUPAC Name:

propane-1,2-diyl diacetate

Test material form:

liquid

Details on test material:

lot F274G29000

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: F274G29000
- Purity test date:The non-GLP purity of the test material was determined to be 99.7 wt%

RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity: The non-GLP radiochemical purity of the test material was determined to be >97% by high performance liquid chromatography
- Specific activity: 2.06 (non-GLP)

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Stability was not tested for PGDA or 14C-PGDA

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

other: Crl:CD (SD)

Details on species / strain selection:

Rats, cannulated in the jugular vein (male)
Crl:CD(SD) rats were selected because of their use in previous toxicological studies related to the control substance (Gaunt et al., 1972). Rats are a suitable species for the analysis of metabolism of chemicals in vivo. The Crl:CD(SD) rats are also suitable due to the availability of historical background data, and the reliability of the commercial supplier.

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (Kingston, New York)
- Age at study initiation: 9 weeks
- Housing: Upon arrival, all animals were single housed in glass Roth-type metabolism cages for acclimation purposes. Roth-type metabolism cages were designed for the separation and collection of urine, feces, CO2, and organic volatiles and are the standard for this study design. During acclimation no excreta was collected.
Following administration of test material all rats continued to be housed singly in glass Roth-type metabolism cages, which were designed for the separation and collection of urine, feces, CO2, and organic volatiles. Air was drawn through the metabolism cages at ~850 mL/minute for groups that had CO2 and organic volatiles collected.
Adequate environmental conditions were targeted in the animal room from the day of arrival until necropsy; however, temporary excursions from these environmental conditions may have occurred on an infrequent basis; all observed ranges will be documented in the study file.
- Diet and Water: Rats were provided LabDiet Certified Rodent Diet #5002 (PMI Nutrition International, St. Louis, Missouri) in pelleted form. Feed was provided ad libitum except access to feed was restricted (1 feed pellet per cage was given) approximately 16 hours prior to the administration of test material. An ad libitum feed was returned about 4 hours post-dosing. Feed was restricted to avoid any interaction of the test compound with the stomach contents, which would affect absorption.
Analyses of the feed were performed by PMI Nutrition International to confirm the diet provides adequate nutrition and to quantify the levels of selected contaminants. Municipal water was supplied to all study animals ad libitum throughout the study. Drinking water obtained from the municipal water source was periodically analyzed for chemical parameters and biological contaminants by the municipal water department. In addition, specific analyses for chemical contaminants were conducted at periodic intervals by an independent testing facility. Copies of these analyses are maintained at Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan.
- Acclimation period:Upon arrival, all animals were acclimated to the laboratory for at least five days prior to the study.
- Enrichment: Enrichment during acclimation included nylon bones and open areas on the cage sides for visualization of other rats. Rats received nylon bones from the day of arrival and during the acclimation period but bones were removed prior to fasting. Nylon bones were removed once animals were administered the 14C-test material, as bones would become contaminated and inhibit the radioactivity mass balance.
-Cannulation: All rats were obtained already cannulated in the jugular vein (JVC) by the supplier (Charles River, Kingston, New York). Patency of the cannulas was verified after at least
5 days of acclimation to the laboratory prior to dosing.



ENVIRONMENTAL CONDITIONS
- Temperature (°C):22°C with a range of 21°C-26°C
- Humidity (%): 54% with a range of 46-71%
- Air changes (per hr): 10-15 air changes/hour
- Photoperiod (hrs dark / hrs light):12-hour light/dark (on at 6:00 a.m. and off at 6:00 p.m.)

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:The equal molar level of both radiolabeled- and unlabeled-test material was used. The dose preparation was administered neat; the target radioactivity was ~500 µCi/kg bw (The specific activity of both 14C-PGDA and 14C-PG was similar). Radioactivity in the dose mixture was quantified by LSS.

The oral dose was administered via a ball-tipped gavage needle attached to a glass syringe. Animals from Groups 1-4, received a single oral dose. The volume of radiolabeled dose formulation to be administered to each animal was calculated based on the body weight taken on the day of dose administration. The actual amount of formulation administered to each animal was determined by weighing the dose syringe before and after dose administration.

Animals from Groups 1-4, received a single oral dose.
Groups 2 and 4 received a single oral dose of a mixture of 14C-PG and PG control substances.

Duration and frequency of treatment / exposure:

Groups 1 and 3 received a single oral dose of a mixture of 14C-PGDA and PGDA. Groups 2 and 4 received a single oral dose of a mixture of 14C-PG and PG control substances.

Doses / concentrations

Dose / conc.:

500 mg/kg bw/day

Remarks:

PGDA

No. of animals per sex per dose / concentration:

Time-Course blood Test groups 3
Cmax Test groups 1

Control animals:

yes

Details on study design:

- Dose selection rationale:
- Rationale for animal assignment: Random

Details on dosing and sampling:

Stage 1:
Two groups of 3 male rats, with cannula implanted in the jugular vein, were administered either radioactive 14C-PGDA (the PG portion was labeled) or 14C-PG control substance individually, via oral gavage, at equal molar dose levels. Repetitive blood samples were taken from each rat at 0.08, 0.17, 0.25, 0.5, 1, 2, 3, 6, 12, 24, 48, 72, 96, 120, 144, and 168 hrs post-dosing. All urine voided during the study was collected in dry-ice cooled traps. The urine traps were changed at 12-, 24- and 48-hour post-dosing followed by 24-hour intervals for the remainder of the study. Feces were collected in dry-ice chilled containers at 24-hour intervals. Expired volatiles including CO2 were first passed through charcoal traps which were changed at 12-hr intervals for the first 24 hrs followed by 24-hr intervals for the remaining collection time. The potential untrapped CO2 was further passed through a solution of monoethanolamine/1-methoxy-2-proponol (3:7 v/v) (CO2 trapping solution). Total radioactivities in blood, urine, feces, charcoal, skin/carcass and the CO2 trapping solution were counted by LSS (Liquid Scintillation Spectrometry). Toxicokinetic analysis was conducted on the total radioactivity from each blood sample to calculate TK parameters (absorption and elimination half-lives of the total radioactivity in blood, as well as AUC). The urinary and fecal excretion of both test materials was also calculated based on the radioactivity of urine and fecal samples, respectively. Based on the quick hydrolysis assumption, it was expected that comparable TK parameters plus additional urinary and fecal excretion data would be generated from both 14C-PGDA and 14C-PG. The resulting comparable toxicokinetic data between 14C-PGDA and 14C-PG were sufficient to support a Read-Across approach for PGDA REACH registration due to the rapid ester hydrolysis of PGDA to PG.
Stage 2:
In this stage, two groups of 1 male rat/group with cannula implanted in the jugular vein, were administered either radioactive 14C-PGDA (PG was labeled) or 14C-PG control substance individually, via oral gavage, at equal molar dose levels (similar to Stage 1). Repetitive blood samples were taken at Cmax, 1/2Cmax and 1/5Cmax (determined from Stage 1) post-dosing. These blood samples were profiled. Comparable metabolite profiling from both test materials further strengthens the Read-Across approach for PGDA REACH registration.


Specimen Collection
Time-Course Blood Collection
The rats of Groups 1-4 were fitted with indwelling jugular vein cannulae (JVC) and blood 14C concentration-time course was determined on Groups 1 and 2.
For Groups 1-2, approximately 0.1-0.2-mL blood was individually collected at the chosen times: 0.08, 0.17, 0.25, 0.5, 1, 2, 3, 6, 12, and 24 h as well as every 24 hours post-dosing thereafter up to study termination (seven days post-dosing). Instruments used to manipulate cannulas were sanitized prior to use and between each collection. The blood was oxidized and analyzed for radioactivity via LSS.
For Groups 3-4, approximately 0.5-mL blood was individually collected at Cmax, 1/2Cmax and 1/5Cmax (determined from Groups 1-2). From an aliquot, blood was oxidized and the blood analyzed for radioactivity via LSS. Moreover, as a larger blood volume could be obtained from each time point interval, blood that was not immediately analyzed for radioactivity was prepared (i.e., placed in extraction solvent of acetonitrile) and stored in -80ºC until chemical analysis (Stage 2 per sponsor approval).

Urine
Groups 1-2: All rat urine voided during the study was collected in dry ice-cooled traps. The urine traps were changed at 12- and 24-hour post-dosing followed by 24-hour intervals for the remainder of the study. The cages were rinsed with water at the time the traps were changed and the rinse collected. Each urine specimen and urine/cage rinse was weighed, and a weighed aliquot of each sample was analyzed for radioactivity via LSS. Urine was stored in -80ºC for future potential analysis.
Groups 3-4: No urine was collected from these groups of animals.

Feces
Groups 1-2: Feces were collected in dry ice-chilled containers at 24-hour intervals up to termination (168 hours post-dosing). Shortly after collection, an aqueous homogenate (~25% w/w) was prepared (shaken for > 4 hours) and weighed aliquots of these homogenates were oxidized, (OxiMate 80 Sample Oxidizer, PerkinElmer Life Sciences, Inc., Boston, Massachusetts) and quantitated for radioactivity via LSS. Fecal homogenates were stored in -80ºC, but were not chemically analyzed.
Groups 3-4: No fecal samples will be collected from these groups of animals.

Expired Volatiles
Groups 1-2: Air was drawn through the cage at approximately 850 ml/minute. The air exiting the cage was passed through charcoal to trap expired volatiles. These charcoal traps were changed at 24-hour intervals. The charcoal was ground with a blender. Weighed aliquots of the charcoal were oxidized and analyzed for radioactivity via LSS. Because <1% of the administered dose was detected in the 24, 48 and 72 hour charcoal traps, the replacement traps for the later collections were not analyzed for radioactivity.
Groups 3-4: Expired volatiles were not collected.

Expired CO2
Groups 1-2: Following the charcoal traps (described above) the expired air was passed through a solution of monoethanolamine:1-methoxy-2-propanol (3:7 v/v) to trap expired CO2 and analyzed for radioactivity via LSS. The CO2 traps were changed at the 12- and 24-hour time points followed by 24-hour intervals for the remainder of the study.
Groups 3-4: Expired CO2 was not collected.

Statistics:

Descriptive statistics were used, i.e., mean ± standard deviation. All calculations in the database were conducted using Microsoft Excel (Microsoft Corporation, Redmond, Washington) spreadsheets and databases in full precision mode (15 digits of accuracy). Certain toxicokinetic parameters were estimated from blood data, including AUC (area-under-the-curve), Cmax, 1/2Cmax and 1/5Cmax and elimination rate constants, using a toxicokinetic computer modeling program PK Solutions (v.2.0.6., Summit Research Services, Montrose, Colorado).

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Time-Course Concentration of Radioactivity and Toxicokinetic Parameters in Blood
Overall, blood time courses are similar for both PGDA and PG, indicating that PGDA and the control substance PG have similar toxicokinetics in rats after single oral gavage dose. Based on further toxicokinetic analyses of the blood time courses, the major toxicokinetic parameters for both PGDA and PG were calculated using PK solutions (a toxicokinetic computer modeling program, version 2.0.6., Summit Research Services, Montrose, Colorado). Toxicokinetic parameters from individual animals are very similar except Tmax, Cmax and AUC which were ~50% higher for PGDA. In terms of absorption, both PGDA and the control substance PG had absorption half-lives of less than 12 min., with PG being absorbed quicker. As 14C-labeled position in PGDA was in propylene glycol group (the same position as in 14C-labeled PG), the similarity of toxicokinetic parameters from both PGDA and PG indicated that PGDA was quickly hydrolyzed to PG in rats after oral gavage dosage and resulted in similar toxicokinetics to PG control substance.

Details on excretion:

After a single oral dose of 14C-PGDA (at 500 mg/kg) or 14C-PG (at 237 mg/kg) in male rats, the recovery values of radioactive dose in urine, feces, blood, charcoal and CO2 trapping solution collected at different time points was evaluated. The corresponding recoveries from urine, feces, CO2 trapping solution at each collection time point are very similar for both PGDA and the control substance PG. The majority of radioactivity was captured as CO2 which was recovered in the first 12 hours post-dosing and which was similar for both PGDA and PG, indicating again that PGDA was quickly hydrolyzed in the rat to form the control substance PG, which was further metabolized to radioactive CO2. The final total average recoveries from both PGDA and PG are similar (75% for PGDA and 82% for PG). This relatively low total radioactivity recoveries are possibly due to the metabolite 14C-CO2 loss caused by the frequent lid openings of the metabolism cage during the blood sample collections (especially in the first 12 hours post-dosing).

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

Selected blood samples (Cmax, 1/2Cmax and 1/5Cmax) were collected from Crl:CD(SD) rats orally dosed with 14C-PGDA or 14C-PG control substance. Both 1/2Cmax and 1/5Cmax extracts had extremely low radioactivity; therefore, only the blood extracts from Cmax were analyzed (profiled) via HPLC separation with radioactivity monitoring (RAM) detection and fraction collection (20 second fractions of eluent collected post-column) followed by LSS assay of the fractions. Only one peak was detected from the Cmax blood samples collected from rats administered either 14C-PGDA or 14C-PG. No PGDA was detected from Cmax blood samples from 14C-PGDA or 14C-PG. Peak A eluted at 3.0 min which did not match the retention time of 14C-PGDA; however the retention time of peak A did match the retention time of 14C-PG, indicating that 14C-PGDA was quickly hydrolyzed in rats after oral gavage administration of 14C-PGDA to form the same blood metabolite profile as the control substance PG. In consideration of the possibility that PGDA can also be hydrolyzed to propylene glycol monoacetate (PGA), the standard of PGA (a mixture of 1-hydroxy or 2-hydroxy acetylated PG) were commercially acquired and analyzed by LC/Q-TOF HRMS (high-resolution mass spectrometry) along with PG and PGDA in both solvent and control blood matrix (extract of the control blood). The peak of PGA was eluted between PG and PGDA and was not overlapped either with PG or PDGA. This further experiment confirmed that PGA was not present in any Cmax samples. Overall, the metabolite profiling results further support the hypothesis that 14C-PGDA was quickly hydrolyzed to 14C-PG in vivo, resulting in similar toxicokinetics between 14C-PGDA and 14C-PG. Further indication that PGDA was rapidly hydrolyzed to PG is evident by comparing the lack of PGDA at the 1 hr Cmax and the absorption t1/2. Based on no PGDA being present after 1 hr (metabolic steady state) and knowing it takes 5 half-lives to reach steady state, the metabolic t1/2 can be calculated at 0.2 hr. Since this is identical to the absorption t1/2 (0.192 hr), this indicates that PGDA is metabolized shortly after it is absorbed. These study results demonstrate quick hydrolysis of PGDA to the read across material PG.

Any other information on results incl. tables

Dose Solution (Concentration, Administration and Recovery of the Dose)

The concentrations of PGDA or PG control substance in the doses are shown in Table 1. The concentration of radioactivity in each of the doses was within 80-95% of the target radioactivity.

At the time of test material administration, the body weights of male rats ranged from 0.244-0.273 kg. The administered dose of¹⁴C-PGDA or¹⁴C-PG administered to various groups ranged from 405-465 mg/kg bw for the targeted 500 mg/kg bw dose and 229-239 mg/kg bw for the targeted 237 mg/kg bw dose. A mean range of 401-460 µCi/kg bw (or ~104-112 µCi per rat) or 478-498 µCi/kg bw (or ~126-132 µCi per rat) was administered to rats of the 500 or 237 mg/kg bw oral dose groups, respectively. The actual radioactivity administered through oral dosing was consistent with the targeted dose range of ~500 µCi/kg bw. The difference between the target and actual doses administered had no effects on the results of this study.

In-life Parameters

There were no signs of toxicity observed in any animals following oral administration of¹⁴C-PGDA or¹⁴C-PG.

Applicant's summary and conclusion

Conclusions:

Similar blood kinetics, mass balance (urine, CO2 and feces), remaining radioactivity in the skin/carcass, and metabolite profiles from Cmax blood samples were observed in rats administered 14C-PGDA or 14C-PG control substance at equal molar dose levels. No detectable 14C-PGDA levels were found in any Cmax, 1/2Cmax and 1/5Cmax blood samples. Finally, based on the lack of PGDA at the 1 hr Cmax, equating to a metabolic t1/2 of 0.2 hr and comparing this to the absorption t1/2, indicates that PGDA is metabolized rapidly after it is absorbed. These study results support the REACH registration Read-Across approach where PGDA was quickly hydrolyzed via the ester hydrolysis to PG in rats.

Executive summary:

The compound propylene glycol diacetate (PGDA) undergoes rapid ester hydrolysis to form propylene glycol (PG). To support the read-across of PGDA to PG as part of REACH registration, the absorption, metabolism, and excretion of¹⁴C-PGDA was compared to the control substance¹⁴C-propylene glycol (PG) following a single oral dose administrationviagavage. Both compounds were labeled at the same¹⁴C-labeled position of the methyl group of PG moiety. Two groups of 3 male Crl:CD(SD) rats were dosed at molar equivalents (500 or 237 mg/kg body weight of PGDA and PG, respectively). The major toxicokinetic parameters resulting from the blood time-courses, excretion (in urine, feces, volatiles and CO₂), and the radioactivity in the final skin/carcass were determined. After determination of the C_max(1 hr),¹/₂C_max(6 hr) and¹/₅C_max(12 hr), two additional male Crl:CD(SD) rats (one/compound) were dosed with PGDA and PG at molar equivalents (500 or 237 mg/kg body weight of PGDA and PG, respectively), blood samples were collected at these times and analyzed by HPLC separation with radioactivity monitoring (RAM) detection or fraction collection (20 second fractions of eluent post-column) followed by liquid scintillation spectrometry (LSS). Very similar blood kinetics, mass balance (urine, CO₂and feces), remaining radioactivity (caused by uptake of radiolabeled pyruvate in the Kreb’s cycle) in skin/carcass, and metabolite profiles from C_maxblood samples were observed in rats administered¹⁴C-PGDA or¹⁴C-PG at molar equivalent dose levels. No detectable¹⁴C-PGDA levels were found in C_maxblood samples, supporting its absence from blood at all later time points (i.e.,¹/₂C_maxand¹/₅C_max). Finally, based on the lack of PGDA at the 1 hr C_max, equating to a metabolic t_1/2of 0.2 hr and comparing this to the absorption t_1/2, indicates that PGDA is metabolized rapidly after it is absorbed. These study results support theREACH registration Read-Across approach where PGDA was proposed to be quickly hydrolyzedviaester hydrolysis to PG in rats.