Registration Dossier

Administrative data

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
key study
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:
publication
Title:
Dermal absorption and disposition of 1,3-diphenylguanidine in rats.
Author:
Shah PV, Sumler MR, Ioannou YM, Fisher HL and Hall LL
Year:
1985
Bibliographic source:
Toxicol Environ Health, 15, 623-633.

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Dermal absorption, distribution and metabolism of 1.3 -diphenylguanidine (DPG), was studied in adult female Sprague-Dawley rats
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
1.3-[ring-14C(U)] DPG was purchased from New England Nuclear, Boston, Mass.
Nonradioactive DPG was purchased from Aldrich Chemical Company, Milwaukee, Wis.
Radiochemical purity = 98% (HPLC)
Activity specific = 17.3 mCi/mmol
Radiolabelling:
yes
Remarks:
(1.3-[ring-14C(U)] DPG)

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Farm, Kingston, NY
- Age at study initiation: no data
- Weight at study initiation: 225-250 g
- Fasting period before study: no data
- Housing: individually
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): ad libitum (purina rat chow)
- Water (e.g. ad libitum): ad libitum (not precised)
- Acclimation period: 72h

ENVIRONMENTAL CONDITIONS : no data

Administration / exposure

Type of coverage:
semiocclusive
Vehicle:
acetone
Duration of exposure:
single administration (not rinsed)
Doses:
5 µCi radioactivity and a total dose of 0.3 µmol DPG/animal
No. of animals per group:
No data

Control animals:
no
Details on study design:
TEST SITE
- Area of exposure: tha back of the animals
- % coverage: 5.6 cm²
- Type of wrap if used: no data
- Time intervals for shavings or clipplings: one application only.

TEST MATERIAL and VEHICLE
Acetone solution (150 µl) containing 5 µCi radioactivity and a total dose of 0.3 µmol DPG/animal was carefully applied with a Hamilton syringe aver the prescribed area.

USE OF RESTRAINERS FOR PREVENTING INGESTION: yes. A plastic blister was placed over the treated area with cyanoacrylate adhesive to prevent oral intake, as well as rub-off and contamination of excret.

DOSE PREPARATION
- Method for preparation of dose suspensions: total dose = 0.3 µmol DPG/animal
- Method of storage: no data

APPLICATION OF DOSE: with a hamilton syringe over the prescribed area

VEHICLE : acetone
- Justification for use and choice of vehicle (if other than water): no justification
- Amount(s) applied (volume or weight with unit): 150 µl containing 5 µCi radioactivity
- Purity: no data

TEST SITE
- Preparation of test site: The clipped area was swabbed with acetone to remove dirt and sebaceous-gland secretions.
- Area of exposure: 5.6 cm²
- % coverage: no data
- Type of cover / wrap if used: A plastic blister from a Cathavex single-use filter was placed over the treated area with cyanoacrylate adhesive to prevent oral intake, as well as rub-off and contamination of excreta. Several holes were punched in the blister with a 20-gauge needle to minimize occlusion of the treated site.
- Time intervals for shavings or clipplings: no data

SITE PROTECTION / USE OF RESTRAINERS FOR PREVENTING INGESTION: yes, cyanoacrylate adhesive to prevent oral intake, as well as rub-off and contamination of excreta.

REMOVAL OF TEST SUBSTANCE
- Removal of protecting device: when the animals were killed
- Washing procedures and type of cleansing agent: individual cages were rinsed with a 5% solution of count-off.
- Time after start of exposure: 0.5, 1, 3, 6, 24, 48, 72 and 120h

SAMPLE COLLECTION
- Collection of blood: no
- Collection of urine and faeces: yes
- Collection of expired air: no
- Analysis of organs: yes

SAMPLE PREPARATION AND ANALYSIS
Triplicate urine samples (100 pl) were counted (in a scintillation counter) by adding 15.0 ml Insta-gel scintillation fluid. Air-dried fecal samples were ground with a mortar and pestle. Aliquots of the ground feces were oxidized in a Packard Tri-Carb Sample Oxidizer Mode' B-306 . Carcasses (the remains of the body after removing major organs and tissues) were cut into small pieces, plunged into liquid nitrogen, and ground in a Waring blender (full speed) containing liquid nitrogen. The resultant hygroscopic homogeneous powder was resuspended in distilled water (1:3 ratio), and triplicate samples of the homogenates were oxidized. Other organs and tissues were either processed in toto or minced, and triplicate (200-300 mg) aliquots were oxidized. Ail samples were counted in a Packard Tri-Carb 2660 Spectrometer.

Details on dosing and sampling
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled : urine, feces, liver, kidney, intestine, fat, skin, ear, bladder, spleen, lung, stomach, heart, brain
- Time and frequency of sampling: 0.5 , 1 , 3, 6, 24 , 48 , 72 and 120h after the administration

METABOLITE CHARACTERISATION STUDIES
Because of the low radioactivity in other organs, only urine, feces, and treated skin samples were used for metabolism studies. The relative amounts of DPG and metabolite(s) from urine samples and extracts from fecal and treated skin samples were determined on HPLC.

Statistics
The organ distribution and excretion results are expressed as a fraction of the recovered dose, which is defined as the cum of radioactivity recovered in organs, excreta, treated skin, and carcass at each kill point. The regression curves and other statistical parameters were determined by using a general linear model in SAS.

Results and discussion

Absorption in different matrices:
Only 10% of the 14C activity penetrated the shaven skin of the back within 5 days with an apparent first-order dermal absorption rate of 0.021 ± 0.002 d-1 and a t½ of 33.6 days. Distribution throughout the entire organism also occurred here.
Percutaneous absorption
Dose:
0.3 µmol DPG/animal
Parameter:
percentage
Absorption:
ca. 10 %
Remarks on result:
other: 5 day

Any other information on results incl. tables

Details on distribution in tissues  
Approximately 13% of  the absorbed dose remained in the body in 5 d. Retention in skin, muscle,  liver, intestine and fat contributed most to the body burden of  DPG-derived radioactivity in 5 d. All tissues showed tissue to blood ratios greater than 1, with liver and intestine ratios of 26 at 5 d.
Most organs and tissues examined showed the highest concentration at 6h following dermal application, except for fat, skin and ear. Maximum concentration in descending order are : intestine and its contents > skin > bladder > liver > spleen and kidney.

Details on excretion
Approximately 61% of the absorbed dose was eliminated into urine and 27%  into feces in 5 d showing rapid clearance of absorbed DPG from the body.  High-pressure liquid chromatography (HPLC) analysis of urine revealed two  major peaks (parent compound and metabolite(s)). Within 72h,  approximately 50% of the DPG-derived radioactivity excreted in the urine  was parent compound. After 72 h, the DPG-derived radioactivity in the  urine was present in the form of a single metabolite, and no parent  compound was detected. No parent compound was detected in feces. Two  metabolites, neither of which occurred in urine, were detected in feces.  The HPLC analysis of the radioactivity at the application site showed  only parent compound.

Details on metabolites
During the first 72h following dermal application, approximately 50% of the urinary radioactivity was parent compound, while the remainder was in the form of a single DPG metabolite. This metabolite (II) accounted for all the radioactivity in the urine after 72h. HPLC analysis of the fecal extracts shows two metabolites (IV and V), both of which were different from those in urine, and no parent DPG was detected. At 24h, only metabolite V was present in feces. At 120h, about 75% of the radioactivity in feces was metabolite V and about 25% was metabolite IV. The extractable radioactivity at the application site was examined for metabolites at 6, 48 and 120 h, and only parent compound was detected.

Applicant's summary and conclusion

Conclusions:
This study has shown slow penetration of DPG through rat skin, demonstrating that the skin is an incomplete barrier to DPG. Dermally absorbed DPG was readily distributed to all tissues examined and rapidly eliminated in urine and feces. Throughout the study, only parent compound was found at the application site, showing the stability of DPG on and in the skin, suggesting that the parent compound penetrates through the skin.
Executive summary:

Dermal absorption, distribution and metabolism of 1.3 -diphenylguanidine (DPG), widely used as an accelerator in processing rubber and in food packaging, was studied in adult female Sprague-Dawley rats. DPG shows 10% penetration through clipped back skin of the rats in 5 days. The first-order dermal absorption rate constant as determined by least square method was 0.021 +/- 0.002 d-1 (T1/2 = 33.6 days). Approximately 13% of the absorbed dose remained in the body in 5 days. Retention in skin, muscle, liver, intestine and fat contributed most to the body burden of DPG-derived radioactivity in 5 days. All tissues showed tissue to blood ratios greater than 1, with liver and intestine ratios of 26 at 5 days. Approximately 61% of the absorbed dose was eliminated into urine and 27% into feces in 5 days showing rapid clearance of absorbed DPG from the body. HPLC analysis of urine revealed two major peaks (parent compound and metabolite(s)). Within 72h, approximately 50% of the DPG-derived radioactivity excreted in the urine was parent compound. After 72h, the DPG-derived radioactivity in the urine was present in the form of a single metabolite, and no parent compound was detected. No parent compound was detected in feces. Two metabolites, neither of which occurred in urine, were detected in feces. The HPLC analysis of the radioactivity at the application site showed only parent compound.

Even though DPG shows slow dermal penetration, this route of exposure needs to be considered in the risk assessments besause of the suspected chronic toxicity of DPG.