Registration Dossier

Administrative data

Endpoint:
specific investigations: other studies
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study was conducted prior to GLPs; study was generally conducted according to acceptable scientific standards

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1969
Report Date:
1969

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
TXIB was provided to rats ad libitum in the diet at concentrations up to 1% for 51-99 days. Rats were also administered concentrations up to 100 mg/kg bw of TXIB or TMPD (2,2,4-trimethyl-1,3-pentanediol), a known metabolite of TXIB, by intraperitoneal injection for 7 days. All rats were euthanized the following day; livers were removed and immediately frozen on dry ice. Livers were later thawed for liver microsomal enzyme determination.
GLP compliance:
no
Remarks:
Study was conducted prior to GLPs
Type of method:
in vivo
Endpoint addressed:
not applicable

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Type:
Constituent
Details on test material:
-Name of test materials (as cited in study report): 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB) and 2,2,4-trimethyl-1,3-pentanediol (TMPD)
- no other details on test substance were provided

Test animals

Species:
rat
Strain:
not specified
Sex:
male/female
Details on test animals and environmental conditions:
Feeding study:
-Diet: ground Purina Laboratory Chow containing 0, 0.1 or 1% TXIB dissolved in 5% (w/w) Mazola oil (ad libitum)
-Test animals: both sexes
-Animal weight at study initiation: no information
-Housing: no information

I.P study:
-Diet: ground Purina Laboratory Chow (ad libitum)
-Test animals: males only
-Animal weight at study initiation: 250-300 g
-Housing: six per large stainless steel cage

Administration / exposure

Route of administration:
other: Oral: feed; Intraperitoneal
Vehicle:
other: Feed Study: TXIB dissolved in corn oil added to feed; Intraperitoneal Study: Corn Oil
Details on exposure:
Feeding Studies:
-1.0% TXIB 51-day study: TXIB dissolved in corn oil and added to the diet to give a final concentration of 1%; administered ad libitum to rats of both sexes for 51 days.
-0.1% and 1% TXIB 99-day study: TXIB dissolved in corn oil and added to the diet to give final concentrations of 0.1 or 1%; administered ad libitum in the diet to rats of both sexes for 99 days.
-1.0% TXIB recovery study: TXIB dissolved in corn oil and added to the diet to give a final concentration of 1%; administered ad libitum to rats of both sexes for 52 days; then rats returned to the control diet for 47 days.

Intraperitoneal study:
-Male rats divided into 5 groups: corn oil controls (8); 25 mg/kg bw TXIB (5), 100 mg/kg bw TXIB (6), 25 mg/kg bw TMPD (5), and 100 mg/kg bw TMPD (6). All injections were 1X/day as 0.5-0.7 mL corn oil doses for 7 days.
Analytical verification of doses or concentrations:
no
Duration of treatment / exposure:
Feeding studies: Up to 99 days
IP study: 7 days
Frequency of treatment:
ad libitum for feeding studies; 1X/day for IP study
Post exposure period:
Feed study: One group of animals was administered TXIB for 52 days with a 47 day post-exposure period
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0.1% TXIB in corn oil in Purina Laboratory Chow
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
1.0% TXIB in corn oil in Purina Laboratory Chow
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
25 mg/kg bw TXIB or TMPD
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
100 mg/kg bw TXIB or TMPD
Basis:
nominal conc.
No. of animals per sex per dose:
Feed study: 5 rats/sex/group
IP: 0 mg/kg TXIB or TMPD (8 males)
IP: 25 mg/kg TXIB or TMPD (5 males)
IP: 100 mg/kg TXIB or TMPD (6 males)
Control animals:
yes, concurrent vehicle
Details on study design:
At study termination, livers were removed, immediately frozen on dry ice, and maintained at -60 °F. For analysis, livers were thawed for immediate fractionation and enzyme determination. Microsomal fractions from the feeding studies were derived from 2 pooled livers. For enzyme assays for the IP study, microsomes were prepared from each liver.

Examinations

Examinations:
-Preparation of microsomes followed procedure of Schneider et al. (1948) with cell disruption done with a close fitting plastic pestle homogenizer using 0.25 M sucrose as the suspending material.

-Microsomal protein determinations followed procedure of Gornall et al. (1949) using Pentex Bovine serum albumin as the standard.

-p-NO2-anisole demethylase (p-NADase) activity measurement followed procedure of Netter and Seidel (1964) with velocity measurements taken from the initial, most linear portion of the reaction curve. NADPH was added in excess to a 3 ml volume to start the reaction.

-Glucose-6-phosphatase (G-6-Ptase) activity measurement followed procedure of Harper (1963) with L-histidine (pH 6.5) as the buffer; incubation volume was 2 ml for 15 minutes at 37°C. Inorganic phosphate determination followed procedure of Bartlett (1959).

- p-Aminophenol glucuronyl transferase (AP-Gluc.) activity measurement followed a modification of procedure of Dutton and Storey (1962). In the current study, ATP and UDP-N-AG were added to the mixture to protect the substrate, UDPGA from destruction by rat liver microsomes. Incubation time was 30 minutes at 37°C in a volume of 1.0 ml; color formation was read at a wavelength of 575 mµ.

-Bilirubin glucuronyl transferase (Bilir.-Gluc.) activity measurement followed the procedure of van Roy and Heirwegh (1968) using system I. Incubation time was 30 minutes at 37°C with TRIS buffer (pH 7.4) in a volume of 1.0 ml; color formation was read at a wavelength of 540 mµ.

Results and discussion

Details on results:
MICROSOMAL ENZYME ACTIVITIES – 51 DAY TXIB FEEDING STUDIES
p-NADase Activity:
At 1% TXIB, there was a statistically significant 2-3 fold increase in activity for both sexes (see Table 1).

G-6-Ptase Activity:
In male rats exposed to 1% TXIB, there was a slight decrease compared to control while females had a slight increase in activity. Neither value reached statistical significance (see Table 1).

AP-Gluc. Activity:
At 1% TXIB, a statistically significant increase in glucuronide transferase reaction with p-aminophenol by ether conjugation occurred in both sexes (see Table 1).

Bilir.-Gluc. Activity:
At 1% TXIB, a statistically significant increase in glucuronide transferase reaction with bilirubin by ester conjugation occurred in both sexes (see Table 1).

MICROSOMAL ENZYME ACTIVITIES – 99 DAY TXIB FEEDING STUDIES
p-NADase Activity:
Dose-dependent increase in activity was seen with the highest activity observed in animals exposed to 1% TXIB for 99 days (reached statistical significance). Activity returned to near control values when animals were exposed to TXIB for 52 days and then returned to the control diet for 47 days (see Table 2).

Bilir.-Gluc. Formation:
Dose-dependent increase in activity was seen with the highest activity observed in animals exposed to 1% TXIB for 99 days (reached statistical significance in females). Activity returned to slightly below control values when animals were exposed to TXIB for 52 days and then returned to the control diet for 47 days (see Table 2).

MICROSOMAL ENZYME ACTIVITIES – 7 DAY IP STUDIES WITH TXIB and TMPD
p-NADase Activity:
At 25 mg/kg bw, activity for both chemicals was similar to control; at 100 mg/kg bw, there was statistically significant increased activity for both (see Table 3).

Bilir.-Gluc. Formation:
There was no statistically significant effect for either TXIB or TMPD at either dose level (see Table 3).

Any other information on results incl. tables

Table 1
p-NADase G-6-Ptase AP-Gluc. Bilir.-Gluc.
Male        
Control 161 2.16 11.5 8
1.0% TXIB 407* 1.88 22.2* 14.0*
         
Female        
Control 137 1.45 5 8.9
1.0% TXIB 397* 1.78 7.4* 14.8*

*Statistically significant at p≤ 0.05

Table 2 Control (Purina Laboratory Chow with Corn Oil) Diet 0.1% TXIB in Control Diet 1% TXIB in Control Diet 1% TXIB for 52 days in Control Diet and 47 days Control Diet Alone
99 Day 99 Day

Males

       

p-NADase

171 230 389* 199

Females

       

p-NADase

159 188 355* 180

Males

       

Bilir.-Gluc.

17.4 20.3 21 16.9

Females

       

Bilir.-Gluc.

17 18.7 22.4* 16.3

*Statistically significant at p≤ 0.05

Table 3 Control (Corn Oil) 25 mg/kg TXIB 100 mg/kg TXIB 25 mg/kg TMPD 100 mg/kg TMPD
p-NADase 183 190 315* 184 256*
Bilir.-Gluc. 14.2 13.4 17.7 12.7 13.4

*Statistically significant at p≤ 0.05

Applicant's summary and conclusion

Conclusions:
Under conditions of this study, repeated exposure to high concentrations of TXIB by the oral or intraperitoneal routes caused transitory reversible elevations in activities of certain liver enzymes in male and/or female rats.
Executive summary:

To investigate the potential for TXIB and the potential metabolite TMPD to affect the activity of certain liver enzymes, up to 1% of each chemical was repeatedly administered to groups of male and/or female rats by the oral and intraperitoneal routes for up to 99 days. For male and female rats fed 1.0% TXIB in the diet for 51 days, there was a statistically significant increase in p-NO2-anisole demethylase, UDP-aminophenol, and UDP-bilirubin glucuronyl transferase activities while glucose-6-phosphatase activity remained at control levels. When 0.1% or 1% TXIB was fed to both sexes for 99 days, p-NO2-anisole demethylase activity was statistically significantly increased for both sexes at the high dose while bilirubin glucuronyl transferase activity was elevated only for high-dose females. When both sexes were treated with 1.0% TXIB in the diet for 52 days and then returned to the control diet for 47 days, p-NO2-anisole demethylase and bilirubin glucuronyl transferase activities returned to control levels. In a study in male rats in which TXIB or TMPD was administered by intraperitoneal injection for 7 days at dose levels of 25 mg/kg bw or 100 mg/kg bw, and then liver microsomes examined for p-NO2-anisole demethylase and bilirubin glucuronyl transferase activity, there was a statistically significant increase in demethylase activity in animals treated with either TMPD or TXIB at 100 mg/k bw. Bilirubin glucuronyl transferase activity was not affected at either dose level.

Under conditions of this study, repeated exposure to high doses of TXIB appeared to cause reversible adaptive changes in the livers of male and female rats. Increases in enzymatic activity observed at high oral doses were reversed and returned to control levels when TXIB was removed from the diet. These changes correlated well with reversible liver enlargement observed in other studies by the same laboratory following prolonged high dosing with TXIB.