Pentane-2,4-dione

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Conduction and documentation of study very acceptable. Literature reference available.

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Acute intravenous and inhalation pharmacokinetics of 2,4-pentanedione in the Fischer 344 rat

Author:

Frantz, S.W., Ballantyne, B., Leung, H.W.

Year:

1998

Bibliographic source:

Industrial Health, 14, 413-428

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other:

Principles of method if other than guideline:

Intravenous study: The substance was given to four adult male Fischer 344 rats per dose by single intra-venous injection. Target radioactivity was 2 – 5 mCi. Blood was collected at appropriate intervals from a lateral tail vein until 30 hr post dosing. At 48 hr a cardiac puncture was performed for a final blood sam-ple with all groups. Urine and feces were. For airborne collections, room air was drawn through the me-tabolism cages at approximately 500 ml/min. Expired 14CO2 was trapped.

Inhalation study: A total of fifty animals were exposed 6 hours nose-only to a target concentration and serial groups of 3 animals were removed at the blood sampling intervals during the absorption phase. Included was a group of 4 rats which were monitored by plethysmography during exposure to ensure that there was no excessive peripheral sensory irritation with consequent changes in minute volume. Respira-tory rate was measured. After exposure the animals were transferred to metabolism cages.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Pentane-2,4-dione

EC Number:

204-634-0

EC Name:

Pentane-2,4-dione

Cas Number:

123-54-6

Molecular formula:

C5H8O2

IUPAC Name:

pentane-2,4-dione

Details on test material:

- Name of test material (as cited in study report): 2,4-Pentanedione
- Substance type: Industrial chemical
- Physical state: liquid
- Analytical purity: > 98% (unlabelled material)
- Impurities (identity and concentrations): not reported
- Lot/batch No.: 59F-3413 A3511
- Radiochemical purity (if radiolabelling): > 98%
- Specific activity (if radiolabelling): lot Nos. 119F9234, 2845-085 > 98%
- Stability under test conditions: stable

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague Dawley, Indianapolis, IN
- Age at study initiation: adults
- Weight at study initiation: 0.183 - 0.228 kg
- Fasting period before study: not reported
- Housing: 2/cage for approximately 5 days in stainless steel wire mesh cages
- Individual metabolism cages: yes/no
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 5 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 65 - 77 °F
- Humidity (%): 40 - 70 %
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

other: inhalation: dust and intravenuous

Vehicle:

other: physiol. saline for intravenous, unchanged for inhalation

Duration and frequency of treatment / exposure:

ip: single exposure
inhalation: single 6h exposure

Doses / concentrations

Remarks:

Doses / Concentrations:
4,3; 43; 148.5 and 430 mg/kg bw (i.v.) and 6 h inhalation of 400 ppm

No. of animals per sex per dose / concentration:

4 per dose (ip)
50 (inhalative exposure)

Control animals:

not specified

Positive control reference chemical:

no

Details on study design:

- Dose selection rationale: consultation with sponsor
- Rationale for animal assignment (if not random): random

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, cage washes

Statistics:

not applicable

Results and discussion

Preliminary studies:

Radioactivity totals of 102.4% and 84.3% of the 14C-2,4-Pentanedionegiven by an intravenous dose of 430 mg/kg were recovered by 48 hr, respectively, from the two animals evaluated in this probe study. The majority of the dose (43-57%) was excreted in the urine and a significant amount of 14C was found in the carcass/pelt (6-8%). The disappearance of 14C from plasma after this bolus intravenous dose followed a biexponential behavior which was rapid in the first 15 - 30 min. after injection and showed a slower decline over the remaining 2-48 hr collection period. A t1/2 value for the initial disposition phase was calculated to be 3.9 to 4.5 min, although this was determined from only a minimal numer of measurement intervals, and the terminal dis-position phase had a t1/2 value of 10.5 - 10.9 hours. Based on this disposition pattern, it was decided to expand the number of plasma sample collections in the terminal phase of the curve during the definitive study.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Exposure to a 400 ppm vapor concentration of 14C-labled 2,4-pentanedione resulted in a rapid uptake into the systemic circulation of the male rat. This uptake did not reach a steady-state absorption over a 6-hr exposure period, since 2,4-pentanedione derived 14C-concentrations were still increasing at the end of the exposure. A plasma level which was higher than that measured for the 6-hr interval (end exposure) could be observed for the first 0.5 hr sample in the elimination phase. This was attributed to the fact that 2,4-pentanedione had not reached steady-state levels when the exposure was terminated at 6 hr which vas almost 2-fold higher than Cmax value for the elimination phase.

Details on distribution in tissues:

The lipophilicity of the test substance might lead to a relatively rapid initial loading of the body's fat components, folllowed by a subsequent loading into the blood after the exposure had been terminated.

Details on excretion:

The plasma radioactivity concentrations decreased relatively rapidly (t1/2 = 4.5 hr) during the initial 12 hr of the biphasic elimination phase following exposure, while the decline in the terminal disposition phase was approximately 10-fold slower (t1/2b = 35.8 hr) than the alpha phase in its time course.
The total body clearance of the radioactive body burden resulting from this inhalation dose was roughly completed within the 48-hr period which followed termination of the inhalation exposure. Furthermore, the time-course for the 14C levels recovered in bone marrow indicated that 14C levels in the marrow paralleled that of plasma throughout the 6-hr exposure, but were elevated 5- to 6-fold when compared to plasma levels at the 24- and 54-hr sam-pling intervals (18 and 48 hr after the inhalation exposure had been terminated). It was therefore concluded that accumulation of 2,4-pentanedione-derived radioactivity might occur following mul-tiple exposures to 400 ppm 2,4-pentanedione vapor or higher.
A similar plasma clearance profile has been observed for the 148.5 mg/kg intravenous dose, with a similar urinary radiochromatogram profile observed to that for the inhalation dose. This intravenous dose appeared to correspond to the estimate for 14C body burden calculated from the radioactivity recovered at the 6-hr end exposure group of inhalation animals. The faster time-course for beta phase clearance would be consistent with the less extensive metabolism observed for this intravenous dose when compared to the inhalation dose. It is also reasonable to consider that for an intravenous dose given as a bolus injection, the kinetics may not compare as well as for a dose given by infusion over 6 hr and then terminated in a similar time-course to the inhalation exposure. A bolus injection has comparatively less time to exchange with tissues (e.g., fat) than would a slow infusion or inhalation dose and thus, may compare somewhat differently.

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

The chromatographic data from this study clearly indicate that relatively little of the absorbed 2,4-pentanedione dose remains unchanged before being voided in the urine. Thus, the inhaled dose from this exposure appeared to readily metabolized and excreted as water soluble, polar metabolites in the urine. This finding could suggest that higher concentrations of some 2,4-pentanedione metabolites may be associated with the toxicity attributed to 2,4-pentanedione exposure. These data also showed that 2,4-pentanedione is readily metabolized following an intravenous bolus injection of a similar dose level (148.5 mg/kg), with the same number of urinary peaks observed as for the inhalation dose, although higher 2,4-pentanedione concentrations were detected at later intervals for this intravenous dose. In all, at least 7 different metabolites were detected these radiochromatograms.
These metabolites, by virtue of their appearance in the urine, would generally be water-soluble, and thus more polar than the parent 2,4-pentanedione.
The preliminary intravenous data in this study showed that a linear dose range could be established from 4.3-43 mg/kg for the plasma elimination of 2,4-pentanedione-derived radioactivity. The 43 mg/kg dose was approximately 10-fold higher than the AUCx value for the 4.3 mg/kg dose level, demonstrating linear kinetics. By inference, log-dose decrease of the 400 ppm inhalation dose (e.g., 40 ppm, etc.) should also show linear pharmacokinetic pat-terns, since it was demonstrated that the comparable (148.5 mg/kg) intravenous dose showed dose-proportional pharmacoki-netics to the lower intravenous doses which were evaluated.
However, it should be noted that the plasma data for the 430 mg/kg intravenous dose were not proportional to the lower intravenous doses in terms of plasma clearance kinetics. Thus when the dose was increased from 43 to 430 mg/kg, the increase in AUCx for the 430 mg/kg data was disproportionately higher than expected (18-fold higher than the AUCx for the 43 mg/kg dose), given a 10fold increase in dose. This was consistent with the dose-dependent shift in urinary Vs. CO2 elimination seen for this dose level. This evidence could indicate that a 436 mg/kg intravenous dose is near the lower limit of a non-linear dose range for 2,4-pentanedione.

Any other information on results incl. tables

Intravenous study: After a single intravenous injection the plasma concentration of 14C-labeled-TS derived radioactivity declined in a biexponential fashion, with a rapid initial phase followed by a slower terminal phase. The pharmacokinetic parameters derived were: initial elimination rate constants (k alpha (hr-1)) of 2.30; 0.97; 1.32 and 26.02; initial half-life (alpha t1/2 (hr)) of 0.30; 0.71; 0.53 and 0.03; terminal elimination constants (k beta (hr-1)) of 0.045; 0.037; 0.053 and 0.065; terminal half-life (beta t1/2 (hr)) of 15.40; 18.73; 13.08 and 10.66; maximum plasma concentrations (Cmax (μg/g)) of 16.13; 110.8; 499.40 and 4369.46; apparent volumes of distribution (Vd (l/kg)) of 1.79; 2.49; 1.28 and 0.78, mean residence time (MRT (hr)) of 12.8; 12.1; 10.3 and 10.5; and areas under the curve to infinity (AUC (μg hr/g)) of 53.28; 467.09; 2196.61 and 8505.12 for the 4.3; 43; 148.5 and 430 mg/kg doses, respectively.

The overall form of the 14C plasma concentration-time curves and derived pharmacokinetic parameters indicated that dose-linear kinetics occurred in the dose range of 4.3 - 148.5 mg/kg, but not with 433 mg/kg. Metabolism of 2,4-pentanedione was quite rapid as the concentration of unmetabolized TS declined steadily to undetectable amounts after 8 hr in the 430 mg/kg dose group. 14C -TS derived radioactivity was eliminated mainly as 14CO2 and in urine. For the 4.3; 43 and 148.5 mg/kg doses 14CO2 elimination was relatively constant (36.8; 38.8 and 42.3 % in 48 hr samples, respectively) and greater than urinary excretion (17.9; 14.3 and 29.6 % in 48 hr samples, respectively). At 430 mg/kg there was a reversal of the excretion pattern, with urine 14C excretion (54.7 %) becoming greater than that for 14CO2 (27.3 %). Excretion in expired volatiles and faeces was small. Radio chromatograms of urine showed free 2,4-pentanedione in the 12 hr sample, together with 7 other metabolites. Most of the urinary radiolable was excreted within the first 24 hr post dosing. Unmetabolized 2,4- pentanedione and 6 of the metabolites decreased or were not detectable in the 24 or 48 hr urine samples, but one peak was still detectable in this samples. Carcass radioactivity ranged from 5.32 to 9.07 %. Total recovery ranged from 69.0 % at the 4.3 mg/kg dose to 95.18 % at the 430 mg/kg dose.

Inhalation study: Nose-only exposure to 400 ppm 14C-labeled 2,4- pentanedione produced mean decrease in breathing rate of 20.1 %, which was constant and sustained throughout exposure, due to a lengthening of the expiratory phase of the respiratory cycle, and therefore suggesting a peripheral sensory irritant effect. 14C -2,4-pentanedione was rapidly absorbed during the first 3 hr of exposure, than began to plateau, but did not reach a steady state. Postexposure elimination of 14 C from plasma followed a biphasic pattern, which was quantitatively similar to that for the intravenous studies. The pharmacokinetic parameters derived were:

initial elimination rate constants (k alpha (hr-1)) of 0.162; initial half-life (alpha t1/2 (hr)) of 4.26; terminal elimination constants (k beta (hr-1)) of 0.023; terminal half-life (beta t1/2 (hr)) of 31.5; mean residence time (MRT (hr)) of 13,9; and areas under the curve for the first 6 hr, for 6 hr to infinity and total (AUC (μg hr/g)) of 703.02; 2751.94 and 3454.96, respectively.

Plasma unmetabolized 2,4 -pentanedione was present throughout the whole of the exposure phase, but was significantly less than total 14C. Post exposure, plasma unmetabolized TS declined rapidly to undetectable concentrations by 12 hr. 14C excretion was approximately equivalent in urine (37.6 % over 48 hr) and expired 14CO2 (36.3 % over 48 hr), which most part of the radioactivity was eliminated in the first 12 hours. Expired volatiles, feces, tissues and carcass accounted for 2.29; 2.78; 1.66 and 17.15 % of the administered dose 48 hr post dosing, respectively. Urine radio chromatograms showed a minor 2,4 -pentanedione peak, along with 7 other peaks representing metabolites. Immediately post exposure, radioactivity was present in all tissues examined, but on a concentration basis (μg equivalents/g) there was no preferential accumulation of 14C in any tissue or organ. On a total basis, highest contents were in liver and kidneys. By 48 hr post exposure, concentrations had decreased in all tissues except fat, presumably due to lipophilicity of 14C residues.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results
In summary, it was demonstrated that male Fischer 344 rats readily absorbed 2,4-pentanedione from exposure to 400 ppm vapor over a 6-hr exposure period and that it was steadily eliminated from the plasma during the 48-hr postexposure sampling period. The majority of the dose was excreted in the urine within the first 12-24 hr after the exposure, and chromatographic analysis of the urine demonstrated that 2,4-pentanedione was readily metabolized to several, more polar molecules prior to being voided in the urine. In addition, a similar plasma clearance profile was observed for the 148.5 mg/kg intravenous bolus dose, a dose which is comparable to the inhalation exposure dose at 6 hr, with a similar urinary metabolite profile observed to that for the inhalation dose. Thus, the time course for 2,4-pentanedione itself indicates that it is not present at high levels in the bloodstream for long after the termination of an inhalation exposure.

Executive summary:

The pharmacokinetics of 14C-2.4 -Pentanedione (CAS RN 123-54-6) were determined following nose-only inhalation exposure of male Fischer 344 rats to 400 ppm vapor over a 6 hr period. Groups of 3 animals were removed serially from a Cannon-nose-only chamber and blood samples were obtained by cardiac puncture at 15 and 30 minutes, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 and 6 hours after the start of the 6 hr inhalation exposure. A mean respiratory rate decrease of 18.4% which occurred shortly after exposure initiation and remained depresses over the entire exposure, was attributed to a lengthening of the expiratory phase of breathing. At termination of exposure, a group of 4 rats were moved to metabolism cages and blood samples were obtained at 0.5-, 1-, 2-, 4-, 6-, 12-, 18-, 24- and 48 hours postexposure. Elimination of excreta and tissue 14C was followed in these animals for 48 hours postexposure. For comparison, a bolus dose of 148.5 mg/kg was given by the intravenous route (equivalent to the inhalation exposure dose for a 6 hour exposure) for the purpose of providing additional interpretative pharmacokinetic information. Blood smples for this intravenous study were collected via a lateral vein in 15 and 30 minutes, 1-, 2-, 4-, 6-, 12-, 18-, 24-, 30- and 48 hours postdosing.

This study demonstrated that male rats readily absorbed 2, 4-Pentanedione vapor over a 6 hour exposure period and that it was steadily eliminated from the plasma during the 48 hour sampling period which followed. The majority of the absorbed dose was excreted in the urine within the first 12 – 24 hours after the exposure ended. Chromatographic analysis of the urine demonstrated that inhaled 2,4-Pentanedione was readily metabolized to several, more polar molecules prior to being voided in the urine. A plasma clearance profile, similar to that for the inhalation route, was observed for the 148.5 mg/kg intravenous dose, and with similar urinary metabolite profile. A preliminary time-course established for the bone marrow during the inhalation exposure demonstrated that 2, 4-Pentanedione derived 14C paralleled that of the plasma throughout the 6 hour exposure, but was 5- 6-fold higher than plasma levels at 18 and 48 hours (terminal half live time value of 31.5 hours) after the inhalation exposure had been terminated. Chromatographic analysis of plasma samples obtained from the inhalation dose group showed that 2,4-Pentanedione was rapidly metabolized and was present as unmetabolized 2,4-Pentanedione at much lower levels in the bloodstream than for 14C concentrations during the inhalation exposure. Unmetabolized 2,4-Pentanedione levels decreased dramatically after exposure to non-detectable levels of 2,4-pentanedione by 18 hours postexposure. Correspondingly lower levels of 2,4-Pentanedione were detected in the urine during the 48 hours period which followed exposure. Unmetabolized 2,4-Pentanedione also disappeared rapidly from the plasma after intravenous injection of a comparable dose, indicating a consistent pharmacokinetic pattern between routes. Also, the mass balances for both routes indicated that 14CO2 exhalation was the predominant excretion route.

Thus, the time course of 2,4-Pentanedione itself following exposure to 400 ppm indicated that it is present at high levels in the bloodstream for only a short period after the termination of the exposure, due to extensive metabolism of 2,4-Pentanedione that occurs prior to its elimination.