(3E)-1,7,7-trimethyl-3-(4-methylbenzylidene)bicyclo[2.2.1]heptan-2-one

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Justification for type of information:

The dermal absorption factor is reported from a regulatory opinion document from the Scientific Committee on Consumer Products (SCCP). The dermal absorption factor considered in this opinion is used to determine the Margin of Safety (MoS) of 4-methylbenzylidene camphor in sunscreens.

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Version / remarks:

1994, draft

Qualifier:

according to guideline

Guideline:

other: COLIPA Guideline for Percutaneous Absorption/Penetration

Version / remarks:

1995

GLP compliance:

not specified

Remarks:

Study is summarised in a regulatory opinion document; full study details are not available

Radiolabelling:

no

Species:

pig

Sex:

female

Type of coverage:

not specified

Duration of exposure:

24 hours

Doses:

167 to 200 μg test item/cm², corresponding to 4.5 mg formulation/cm² of a 4% test item formulation

No. of animals per group:

8 experiments, performed in triplicate

Details on study design:

SAMPLE COLLECTION
- Skin surface: Gentle scraping with a spatula and/or threefold wiping with cotton wool (corresponds to non-absorbed sample)
- Horny layer: About 15-20 fold stripping with self-adhesive "tesa-film" tape
- Epidermis: Heating of the skin disc (epidermal side for 45 seconds on a 80°C hot plate (Ceram), separation epidermis from dermis with forceps)
- Dermis: 3 punched samples or total dermis
- Receptor fluid: 2 aliquots

ANALYSIS
- Method type(s) for identification: HPLC-DAD
- Limits of detection and quantification: LOD: approximately 0.03 μg/mL, LOQ: approximately 0.1 μg/mL

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: Pig
- Type of skin: Unboiled back skin
- Preparative technique: Skin discs (gently dry-shaved surface, diameter 5 cm)
- Thickness of skin: 3-4 mm

PRINCIPLES OF ASSAY
- Diffusion cell: Glass penetration cell
- Receptor fluid: 0.9% sodium chloride, 1% bovine serum albumin and 0.02% gentamycine sulphate in water
- Solubility of test substance in receptor fluid: Receptor fluid suitable for hydrophilic and lipophilic samples
- Test temperature: 32°C

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Absorption in different matrices:

No test item was detected in the receptor fluid.

Total recovery:

Mean total recovery was 91.8% (range 86.8 to 95.6%).

Key result

Time point:

24 h

Dose:

178 μg/cm²

Parameter:

percentage

Remarks:

1.96 μg/cm² (epidermis+dermis)

Absorption:

1.1 %

Remarks on result:

other: mean of 8 experiments

Table 1. Summary of dermal absorption rates

Test	Applied substance (μg/cm²)	Surface (μg/cm²)	Horny layer (μg/cm²)	Epidermis (μg/cm²)	Dermis (μg/cm²)	Recovery (%)
1	182	125	38.2	2.0	0.34	90.9
2	200	159	26.2	1.3	0.50	93.8
3	172	132	27.6	2.4	0.72	94.7
4	175	119	31.0	1.7	0.90	87.2
5	171	138	23.5	0.7	0.34	95.0
6	167	132	16.2	1.4	0.88	90.0
7	187	144	17.1	0.4	not detectable	86.8
8	173	140	23.5	2.2	not detectable	95.6
Mean	178	136	25.4	1.5	0.46	91.8
Standard deviation	11	12.5	7.2	0.7	0.36	3.5

Conclusions:

Taking into account the values obtained in eight separate experiments, the SCCP consider a mean dermal absorption value of 1.96 μg/cm² as the basis to determine safe use for 4-methylbenzylidene camphor in sunscreen formulations. Based on a mean applied amount of 178 μg/cm², the dermal absorption factor is calculated to be 1.10% (epidermis+dermis).

Executive summary:

Data on the dermal absorption of 4 -methylbenzylidene camphor is available in a regulatory opinion document from the Scientific Committee on Consumer Products (SCCP). Taking into account the values obtained in eight separate in vitro experiments using pig skin, the SCCP consider a mean dermal absorption value of 1.96 μg/cm² as the basis to determine safe use for 4-methylbenzylidene camphor in sunscreen formulations. Based on a mean applied amount of 178 μg/cm², the dermal absorption factor is calculated to be 1.10% (epidermis+dermis). The reliability of this data source cannot be assigned (Klimisch 4) as it is a secondary source reporting from a summary of eight individual experiments. The original studies were not obtained for reliability and relevance assessment, however as the data is used in a regulatory opinion, it is assumed to be sufficiently reliable.

Description of key information

In a study by Schauer et al (2006), plasma levels and toxicokinetics were investigated in both human subjects and rats following dermal exposure:

The toxicokinetics of 4-methylbenzylidene camphor after dermal administration were investigated in humans. Humans (3 male and 3 female subjects) were exposed to 4-MBC by topical application of a commercial sunscreen formulation containing 4% 4-MBC (w/w), covering 90% of the body surface and resulting in a mean dermal 4-MBC dose of 22 mg/kg bw. Concentrations of 4-MBC and its metabolites were monitored over 96 h in plasma and urine. Peak plasma levels (Cmax) of 4-MBC were reached 6 h after dermal application (200 pmol/mL in males and 100 pmol/mL in females). After the 6 h sampling point, 4-MBC concentrations decreased following 1st order kinetics with a half-life of 9 h to reach the limit of quantitation at 48 h (males) or 36 h (females) after the application. The AUC values were 3884 and 1909 pmol/mL h in males and females, respectively. In plasma, 3-(4-carboxybenzylidene)camphor is the major metabolic product, whereas, in urine, 3-(4-carboxybenzylidene)-6-hydroxycamphor and a glucuronide of 3-(4-carboxybenzylidene)camphor are major metabolites. Less than 1% of the applied dose of 4-MBC was recovered in urine as metabolites.

The toxicokinetics of 4-methylbenzylidene camphor after dermal administration were investigated in rats. Wistar rats (3 male and 3 female subjects) were exposed to dermal 4-MBC doses of 400 and 2000 mg/kg bw applied in a formulation using an occlusive patch for 24 h. Concentrations of 4-MBC and its metabolites were monitored over 96 h in plasma. Peak plasma levels of 4-MBC were 200 (dose of 400 mg/kg bw) and 1200 pmol/mL (dose of 2000 mg/kg bw) in male and female rats. These levels remained constant for up to 24–48 h after dermal application. Two major metabolites were identified in the plasma of rats after dermal application: 3-(4-carboxybenzylidene)-6-hydroxycamphor and 3-(4-carboxybenzylidene)camphor.

In an opinion document on 4-MBC by the Scientific Committee on Consumer Products (SCCP, 2008) a toxicokinetic approach was used to derive a Margin of Safety (MoS) for 4-MBC. A mean dermal absorption value of 1.96 μg/cm² from an applied substance amount of 178 μg/cm² yielded a calculated dermal absorption value of 1.10%.

Key value for chemical safety assessment

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

1.1

Absorption rate - inhalation (%):

100

Additional information

The study by Schauer et al. (2006) concluded that the biotransformation of 4-MBC in humans and rats after dermal administration is identical and occurs by a series of cytochrome P450-catalyzed oxidations of 4-MBC followed by formation of glucuronides. Also the kinetics following dermal exposure to 4-MBC was considered to be similar between rats and humans with peak plasma levels being reached approximately 6 hours following the exposure and plasma levels regressing towards the limit of quantification at around 48 hours post-exposure. As no new dermal absorption studies have been identified with adequate reliability, a dermal absorption factor of 1.10% is used in line with the current regulatory opinion (SCCP 2008).