Registration Dossier

Administrative data

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1987
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1987
Report Date:
1987

Materials and methods

Test guideline
Qualifier:
no guideline followed
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified
Details on test material:
2,5-[ 1,2,5,6-14C]Hexanedione, specific activity of 5. 1 mCi/
mmol, was prepared by Amersham Corp., Arlington Heights, IL. Radiochemical
purity was determined by gas-liquid chromatography to be
97%. 2,5-Hexanedione (2,5-HD, 98% pure) was obtained from Eastman
Kodak Co., Rochester, NY. 2,5-Dimethylfuran (99%) was purchased
from Aldrich Chemical Co., Milwaukee, WI. 5-Hydroxy-2-hexanone was
a gift from Dr. G. D. DiVincenzo, Eastman Kodak Company, Rochester
NY. Amberlite XAD-4 resin was obtained from Supelco Inc., Bellefonte,
PA. All other chemicals used in this study were obtained in the highest
purity available.
Radiolabelling:
yes
Remarks:
14 C

Test animals

Species:
hen
Strain:
other: Gallus gallus domesticus
Sex:
female
Details on test animals and environmental conditions:
Laying hens (Gallus gallus domesticus),
18 months old with average weights of 1.6 ± 0.04 kg (mean ± SE), were
obtained from Featherdown Farm, Raleigh, NC. Fifteen hens were each
given a dermal dose of 50 mg (7.5 uCi) of 2,5-HD/kg of body weight.
To avoid evaporation of 2,5-HD, the dose was injected through a rubber
septum that was attached to a round glass vial (2.5 cm in diameter) glued
over the midthoracic region of the chicken. The birds were housed in
individual metabolism cages (1 .5 x 2.5 feet, custom-made), which were
made of glass and contained coarse-mesh screens to isolate excrement.
The cages were placed in a temperature-controlled room (2 1-23#{176}wC)ith
a I 2-hr light cycle and free access to feed (Layena chicken feed, Ralston
Purina Co., St. Louis, MO) and water. Two consecutive traps were
connected to the metabolism cages. The first contained 50 g of Amberlite
XAD-4 to trap volatile organic compounds (20-22), and the second trap
had 250 ml of a mixture of ethanolamine:ethylene glycol monomethyl
ether (1:2 v/v) to collect 14C02. The Amberlite XAD-4 trap and carbon
dioxide trap were collected at 2, 4, 8, and 24 hr following treatment,
while excreta and eggs were collected daily. Three treated hens were
killed at each of the following time points: 4, 8, 24, 36, and 48 hr. In
addition, two hens were killed 2 hr following dosing to further determine
the peak distribution of 2,5-HD. Birds were anesthetized with an intraperitoneal
injection ofsodium pentobarbital solution (Nembutal, Abbott
Laboratories, North Chicago, IL). The blood was collected by a heparinized
syringe via heart puncture and centrifuged to separate plasma from
red blood cells. Individual organs and tissues were removed and weighed.
Skin and adipose tissue samples were obtained from three sites, one from
the anterior portion ofeach thigh and one from the thorax. Spinal cords
were sampled at three sites, with one sample from each site (cervical,
thoracic, and sacral segments). The contents of the gastrointestinal tract
parts, e.g. crop, proventriculus, ventriculus, small intestine, ceca and
large intestine, were collected and homogenized separatetely.

Administration / exposure

Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
To avoid evaporation of 2,5-HD, the dose was injected through a rubber septum that was attached to a round glass vial (2.5 cm in diameter) glued over the midthoracic region of the chicken. Three treated hens were killed at each of the following time points: 4, 8, 24, 36, and 48 hr. In addition, two hens were killed 2 hr following dosing to further determine the peak distribution of 2,5-HD.
Doses:
dermal dose of 50 mg (7.5 µCi) of 2,5-HD/kg of body weight
No. of animals per group:
Fifteen hens
Control animals:
no

Results and discussion

Signs and symptoms of toxicity:
no effects
Dermal irritation:
not examined
Total recovery:
The disappearance of 2,5-HD from the dosing site of treated hens followed a monoexponential kinetics with a half-life of 6.09 hr. By the end of the experiment, only 0.41 % of the radioactive dose was recovered from the dosing site.

Applicant's summary and conclusion

Conclusions:
The disappearance of 2,5-HD from the dosing
site of treated hens followed a monoexponential kinetics
with a half-life of 6.09 hr. By the end of the experiment, only
0.41% of the radioactive dose was recovered from the dosing
site.
2,5-Hexanedione (2,5-HD) was readily absorbed from the skin
of the treated hen as indicated by its disappearance from the
dosing site and the concurrent detection of radioactivity in the
plasma and all tissues analyzed.
2,5-HD was the predominant compound present in liver,
lungs, and kidneys at 4- and 24-hr time points. Again, this is
probably due to the high rate of excretion of 5-hydroxy-2-
hexanone and/or its oxidation to 2,5-HD by these tissues.
This study concludes that 2,5-HD is metabolized in the hen
to 5-hydroxy-2-hexanone and 2,5-dimethylfuran which are common
metabolites of some other aliphatic hexacarbons. 2,5-HD
is readily absorbed from the skin and subsequently distributed
throughout the body of the hen. Low concentrations of radioactivity
were observed in the target tissues, i. e. the neural tissues,
after a single administration.
Executive summary:

A dermal dose of 50 mg/kg (7.5 MCi/kg) of [14C]2,5-hexanedione (2,5-HD) was applied on a protected area on the backs of hens. Five groups of three hens were killed after 4, 8, 24, 36, and 48 hr. 2,5-HD disappeared monoexponentially from the application sfte with a halflife of 6 hr. After 48 hr, 35% of the radioactivfty was expired as volatile material, largely as 2,5-HD. The combined urinary fecal excreta accounted for 15% of the eliminated radioactivity, while the 14CO2 accounted for 11.9% of the radioactive dose. The highest concentration of 14C was detected in the bile. Among tissues analyzed, liver and kidney contained the highest concentrations of radioactivfty, whereas the brain, spinal cord, and peripheral nerves showed smaller concentrations. The half-lives for the elimination of 14C were longest for muscle (71 hr) and shortest for adipose tissue (12 hr), while the remaining tissues showed half-lives ranging from 20 to 30 hr. Radioactivfty in the plasma reached a peak at 4 hr. Most of this radioactivity was identified as 5-hydroxy-2-hexanone followed by 2,5-HD and 2,5-dimethylfuran; these chemicals then disappeared biexponentially with terminal half-lives of 7.6 hr, 12.6 hr, and 28.6 hr, respectively. 2,5-HD was the most accounted chemical found in the liver, lung, and kidney, while 5-hydroxy-2-hexanone was found to be most abundant in the combined urinary-focal excreta.