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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1992
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: well performed and documented publication

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1992
Report Date:
1992

Materials and methods

Objective of study:
metabolism
Principles of method if other than guideline:
metabolism in perfused livers
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Details on test material:
- Name of test material (as cited in study report): R- and S-1,3-butanediol
- Specific activity (if radiolabelling): R-[3-14C]1,3-butanediol: 11920 dpm/µmol; S-[3-14C]1,3-butanediol: 26650 dpm/µmol;
Radiolabelling:
yes
Remarks:
R- and S-[3-14C]1,3-butanediol

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River
- Diet: Charles River laboratory chow from 7:00 to 10:00 h
- Water (e.g. ad libitum): no data
- feeding period: 3 weeks
- animals were used during the third week of the feeding schedule when they were in the weight range 210-280 g
- experiments were started between 10:00 and 11:00 h, corresponding to the maximum rate of fatty acid and steroid synthesis under these feeding conditions
- Fasting period before study: "starved" rats received their last meal 48 h before the experiment


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-24°C


Administration / exposure

Route of administration:
other: perfusion of isolated rat liver
No. of animals per sex per dose:
about 4-8 animals per group (for details see below)
Control animals:
yes
Details on study design:
Liver perfusion:
- with 210 ml of recirculating Krebs-Ringer bicarbonate buffer containing 4% dialysed BSA and glucose (15 or 4 mM in perfusions of livers from fed or starved rats, respecively)
- equilibration time: 30 min
- treatment time: 120 min
- treatment concentrations: R- or S-[3-14C]1,3-butylene glycol (fed, 5 mM, starved, 7.5 mM), 80 µmol of [3,4-13C2]acetoacetate and 25mCi of 3-H2O
- at the end of the treatment period livers were freeze-clamped and kept at -80°C
Details on dosing and sampling:
-Samples of perfusate were assayed for concentrations and specific radioactivity of R-hydroxybutyrate and acetoacetate.
- Acetoacetate isolated by column chromatography was degraded to acetone and carbon dioxide, which were trapped in hydrazine-lactate and sodium hydroxide respectively before counting of radioactivity.
-Total rates of fatty acid and 3-beta-hydroxysterol synthesis in the liver and the contribution of [3-14C]1,3-butylene glycol to lipogenesis were calculated from the incorporation of 3H and 14C respectively.
- Ketone body production in perfused livers was calculated from the dilution of the specific radioactivities of R-[3-14C]hydroxybutyrate or [3-14C]acetoacetate following addition of a tracer of either R-[3-14C]hydroxybutyrate or [3-14C]acetoacetate to the perfusate.

Results and discussion

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
R- and S-1,3-butylene glycol are taken up at identical rates by perfused livers from fed and starved rats. Ketogenesis was increased 9- and 3.5-fold by R-1,3-butylene glycol and S-1,3-butylene glycol respectively in livers from fed rats. In livers from starved rats ketogenesis was increased 3.5- and 1.5-fold by R-1,3-butylene glycol and S-1,3-butylene glycol respectively. Accumulation of R-hydroxybutyrate and acetoacetate accounted for 76-96% of ketone body production. The difference between total ketogenesis and ketone body accumulation is accounted for by a) conversion of acetoacetate to acetone and b) incorporation of acetoacetate into fatty acids, sterols and carbon dioxide.
Total ketogenesis (measured by isotopic dilution) amounted to 80 to 102% of R-1,3-butylene glycol uptake after addition of R-1,3-butylene glycol to the perfusate. In the presence of S-1,3-butanediol total ketogenesis amounted to only 29-38% of S-1,3-butylene glycol uptake.
R-[3-14C]1,3-butylene glycol contributed 86% and 98% of total ketogenesis in livers from starved and fed rats repectively, and S-[3-14C]1,3-butylene glycol contributed 47% and 75% of total ketogenesis in livers from starved and fed rats.
Values for the formation of fatty acids, sterols, carbon dioxide and acetone are presented in the tables shown below.
R-1,3-butylene glycol contributed 13% and 27% of the carbon incorporated into fatty acids and sterols respectively. In livers from fed rats, S-1,3-butylene glycol contributed equally (24%) to both fatty acid and sterol synthesis.
The increase in fatty acid synthesis over controls was equal to the amount of S-1,3-butylene glycol incorporated in livers from fed rats perfused with S-1,3-butylene glycol. In livers from starved rats, fatty acid and sterol synthesis were increased 3.5 and 2.5 fold by the R- and S-enantiomere, respecitvely, but remained below the rates measured in livers from fed rats.

Any other information on results incl. tables

Cumulative rates from liver perfusates expressed as µmol of 1,3-butylene glycol/90 min per g dry weight (mean +/- S.E.M.)

      fed     starved
   R-1,3 -butylene glycol (n=6)   S-1,3 -butylene glycol (n=5-7)  R-1,3 -butylene glycol (n=5-7)    S-1,3 -butylene glycol (n=4)
 uptake of 1,3 -butylene glycol  380 +/- 40  386 +/- 22  355 +- 17  409 +/- 30
 Incorporation of 1,3 -butylene glycol intol:      
 R-hydroxybutyrate and acetoacetate    247 +/- 31   76 +/- 7.8   282 +/- 9   67 +/- 7.5
 S-hdroxybutyrate   -   224 +/- 22  -   231 +/- 12
 fatty acids and sterols  5.38 +/- 0.57  14.2 +/- 1.7  0.21 +/- 0.03  0.18 +/- 0.01
 carbon dioxide  3.35 +/- 0.48  11.6 +/- 2.4 1.28 +/- 0.11   4.07 +/- 0.59
 acetone  39.4 +/- 6.1 8.70 +/- 1.08   27.5 +/- 1.5  5.25 +/- 0.72
 total 1,3 -butylene glycol incorporated  294 +/- 36  331 +/- 31  311 +/- 9  307 +/- 53
 amount of 1,3 -butylene glycol uptake accounted for (%)  89 +/- 13  81 +/- 4  89 +/- 5  75 +/- 4

Contribution of 1,3 -butylene glycol to total ketogenesis. Cumulative rates are expressed as µmol of 1,3-butylene glycol/90 min per g dry weight (mean +/- S.E.M.)

      control     R-1,3 -butylene glycol      S-1,3 -butylene glycol
   fed (n=7)  starved (n=7)  fed (n=6)  starved (n=5)  fed (n=6)  starved (n=4)
 total ketogenesis (A)  33.5 +/- 4.0  107 +/- 9  305 +/- 20  361 +/- 14  112 +/- 14  156 +/- 23
ketone body accumulation (B)   17.9 +/- 4.1  61.9 +/- 11.6  279 +/- 24  347 +/- 9  85.4 +/- 10.8  126.7 +/- 8.6
 ketone body uptake (A-B)  15.6 +/- 2.7  45.9 +/- 16.4  38.8 +/- 5.2  13.7 +/- 15.7  31.7 +/- 6.3  29.3 +/- 20.4
 (A-B)/A x 100  53.1 +/- 6.1  42.6 +/- 4.9  13.8 +/- 2.2  2.97 +/- 3.82  27.9 +/- 5.0  22.3 +/- 8.3
 1,3 -butylene glycol contribution to total ketogenesis (%) 97.7 +/- 8.3  86.4 +/- 3.1  75.2 +/- 9.2   47.5 +/- 8.7

Total rates of fatty acid and sterol synthesis. All rates are expressed as µmol acetyl incorporated/90 min per g dry weight (means +/- S.E.M)

         fed        starved
   control (n=6)  R-1,3 -butylene glycol (n= 7 -8)   S-1,3 -butylene glycol (n= 7 -8) control (n=6)    R-1,3 -butylene glycol (n= 7 -8)  S-1,3 -butylene glycol (n= 5) 
 fatty acid synthesis            
A) total  85.6 +/- 13.4  75.5 +/- 12.8 110 +/- 16   1.64 +/- 0.16  5.79 +/- 0.50  4.13 +/- 0.53
B) from diol   9.00 +/- 1.14  25.7 +/- 3.20  -  0.37 +/- 0.05  0.32 +/- 0.04
C) from other than diol (A-B)  85.6 +/- 13.4 66.5 +/- 11.2   84.1 +/- 13.2   1.64 +/- 0.16  5.66 +/- 0.48 3.66 +/- 0.60 
D) (B/A)x100  -  12.9 +/- 1.0  24.1 +/- 1.8  -  6.26 +/- 0.52  7.93 +/- 0.30
 sterol synthesis            
E) total  9.91 +/- 1.11  6.97 +/- 0.90  10.4 +/- 1.5  0.42 +/- 0.12  0.81 +/- 0.18  0.43 +/- 0.19
F) from diol  -  1.76 +/- 0.17  2.60 +/- 0.46  -  0.06 +/- 0.01  0.032 +/- 0.01
G) from other than diol (E-F)  9.91 +/- 1.11  5.20 +/- 0.79  7.84 +/- 1.10  0.42 +/- 0.12  0.75 +/- 0.16  0.41 +/- 0.18 
H) (F/E) x 100  -  26.8 +/- 2.9  24.3 +/- 1.9  -  6.78 +/- 0.58  7.92 +/- 0.78

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): low bioaccumulation potential based on study results concluded by submitter
R- and S-1,3-butylene glycol are taken up by the isolated liver of fed or starved rats at the same rate. R-1,3-butylene glycol is mainly transformed to the physiological ketone bodies R-3-hydroxybutyrate and acetoacetate. Only 29-38&% of the S-enantiomer are converted into physiological ketone bodies. The S-enantiomer is further metabolised to S-3-hydroxybutyrate (not a natural compound), lipids and carbon dioxide. Based on these results it can be concluded that the test item is metabolised via physiological pathways, suggesting that it has a low potential to accumulate.
Executive summary:

Livers from fed and starved rats were perfused with buffer containing radiolabelled R- or S-1,3-butylene glycol. The following parameters were determined: a) uptake of the diol, b) contribution of the diol to ketogenesis, c) contribution of the diol to total fatty acid plus sterol synthesis, and d) conversion of S-1,3-butylene glycol into the (non physiological) metabolite S-3-hydroxybutyrate. Both enantiomers were taken up by the livers of fed or starved rats at the same rate. R-1,3-butylene glycol is mainly transformed to the physiological ketone bodies R-3-hydroxybutyrate and acetoacetate. Only 29-38% of the S-enantiomer are converted into physiological ketone bodies. The S-enantiomer is further metabolised to S-3-hydroxybutyrate (not a natural compound), lipids and carbon dioxide (Desrochers et al., 1992).

Using radiolabelled substrate they could demonstrate that the R-1,3-butylene glycol is metabolised to physiological ketone bodies and the S-enantiomer to S-3 -hydroxybutyrate , lipids and carbon dioxide. Based on the results obtained it was concluded that the test item is metabolised via physiological pathways, suggesting that the substance is not accumulate in the body.