Farnesol

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dermal absorption in vitro / ex vivo

Remarks:

Including in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline followed

Principles of method if other than guideline:

Dermal absorption of farnesol was investigated in guinea pigs in an in vivo test using radiolabelled material and also in an in vitro study by mounting skin grafts in diffusion cells and measuring receptor fluid fractions.

GLP compliance:

no

Radiolabelling:

yes

Remarks:

Radiochemical purity greater than 99% and a specific activity of 20.0 mCi/mmol

Species:

guinea pig

Strain:

Hartley

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Housing: Single
- Individual metabolism cages: polycarbonate shoe box cages on hardwood chip contact bedding
- Diet: ad libitum pelleted guinea pig chow
- Water: ad libitum
- Acclimation period: 3-days in quarantine

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21±1°C
- Humidity (%): 50±10 % relative humidity
- Air changes (per hr): 10 complete room changes per hour
- Photoperiod (hrs dark / hrs light): 12 hours light/dark full spectrum lighting cycle (no twilight)

Type of coverage:

occlusive

Vehicle:

other: oil-in-water emulsion prepared with: 3% polyglycerate distearate; 3% cetyl stearyl alcohol; 10% light mineral oil; 5% propylene glycol; 0.5% propyl-p-hydroxybenzoate; 0.5% methyl-p-hydroxybenzoate and 78% water

Doses:

An oil-in-water emulsion containing 5.0% of unlabelled farnesol, spiked with 3H-farnesol so that approximately 0.5 µCi of radiolabelled farnesol was applied per cm2 of skin in vivo or to the skin in vitro diffusion cell. The emulsion was applied to the skin at a dosage of 1 mg/cm2.

No. of animals per group:

3

Control animals:

no

Details on study design:

In vivo skin absorption study - A 3.0 x 3.0 cm treatment site was marked on the mid-scapular region of the guinea pig’s back and enclosed with a Stomahesive® patch glued directly to the animal’s skin, the dosing area and patch were then covered with a vinyl coated fibreglass screen (to prevent dosing formulation being rubbed off the skin) and carbon impregnated filter paper to trap volatile test material. In vivo skin absorption was determined 24-hours after dosing. Urine and faeces were collected throughout the study duration. Animals were euthanized with Isoflurane. The skin at the treatment site, ovaries, liver and kidneys were excised and dissoluted in potassium hydroxide (5M). Radioactivity was measured by liquid scintillation counting.

Details on in vitro test system (if applicable):

Skin grafts (200-300 µm thick) were obtained from hairless guinea pigs euthanized with carbon dioxide. The skin was washed with 1% (v/v) liquid detergent solution, rinsed with distilled water and patted dry. Diffusion cells (0.64 cm2) and the perfusion system were prepared and flushed with 70% (v/v) ethanol solution and the receptor fluid was sterilised by vacuum filtration through a 0.2 µm filter. The skin was mounted in the diffusion cell and equilibrated to the test conditions (1.5 ml/hour) and the dosing was applied to the surface, in a manner comparable to the in vivo tests (oil-in-water emulsion). Receptor fluid fractions were collected at 6-hour intervals for 24-72 hours.

Signs and symptoms of toxicity:

not examined

Dermal irritation:

not examined

Absorption in different matrices:

In vivo absorption of farnesol in three animals, 24 hours after dermal application, resulted in systematic absorption of 39.8±2.5 %AD (mean ± SEM) percent of the applied dose (% AD). At 24-hours, 2.1±0.2 %AD of farnesol remained in the skin and 5.0±2.2 %AD was extracted from carbon impregnated filter papers. The total penetration (systemically absorbed + skin absorption + recovery of materials in skin around the dosing site) corresponded to 44.1 ± 2.2% AD, 5.4 ± 1.3%AD was recovered in the urine. The total recovery (mass balance) corresponded to 65.9 ± 6%.


Twenty-four hour in vitro absorption studies suggested total penetration of farnesol to be 69.9±4.3 %AD, with 43.5 ± 3.3%AD in the receptor fluid, with 26.4 ± 4.1%AD remaining in the skin (approximately 19.2 ± 4.6%AD in the viable skin and 7.2 ± 1.3%AD in the stratum corneum). Extended 72-hour studies found 77.5±4.7 %AD in the receptor fluid with 8.0±1.9 %AD remaining in the skin (approximately 2.8 ± 0.7%AD in the viable skin and 5.2 ± 1.2%AD in the stratum corneum). The total 72-hour in vitro penetration of farnesol was calculated to be 85.5±6.7 %AD. The total recovery was 105.8 ± 6.2% at 72 h.

Total recovery:

The systemic in vivo absorption value coincided with the 24 -hour in vitro absorption value. However, the evaporation test for 3H-Farnesol suggested that there is a potential for evaporative loss.

Conclusions:

As a lipophilic compound, farnesol has been shown to be readily absorbed and distributed in Hartley guinea pigs in vitro and in vivo.

Executive summary:

The dermal absorption of farnesol was investigated in Hartley guinea pigs in vivo using radiolabelled material and in vitro by mounting skin grafts in diffusion cells and measuring receptor fluid fractions. Comparable in vitro and in vivo dermal absorption of farnesol was observed. The in vivo absorption of farnesol led to systematic absorption of 39.8±2.5 % of the applied dose (AD) (mean ± SEM). At 24-hours, 2.1±0.2 %AD of farnesol remained in the skin and 5.0±2.2 %AD was extracted from carbon impregnated filter papers. In vitro farnesol absorption studies suggested penetration of 69.9±4.3 %AD. Extended 72-hour studies found 77.5±4.7 %AD in the receptor fluid with 8.0±1.9 %AD remaining in the skin. The total 72-hour in vitro penetration of farnesol was calculated to be 85.5±6.7 %AD. Under the experimental conditions stated, farnesol is readily absorbed and systemically distributed. This study is considered to be reliable without restriction (Klimisch 1) as it was a published study with adequate experimental design and sufficient reporting.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The study was not of guideline design including just two treatment groups and a control, and was not conducted to GLP

Objective of study:

absorption

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study design was similar to an OECD 407 28-day repeated dose toxicity study although only two treated groups were included together with a standard vehicle control group. The numbers of animals per group complied with guideline requirements for studies of this type along with the experimental conditions. Half the animals from each group were terminated after 28 days of oral dosing whilst the remaining animals were terminated after a further 28-day period without treatment to assess recovery from any toxicities. Blood samples were taken from all animals at termination for the determination of plasma farnesol levels.

GLP compliance:

not specified

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Rats were individually housed in stainless steel cages suspended over absorbent cage boards, and were held in a temperature-controlled room maintained on a 12 h light/dark cycle. Rats were permitted free access to drinking water (supplied by automatic watering system) at all times during the study; rats were also allowed free access to Purina Certified Rodent Diet 5002 (PMI Nutrition International Inc., Brentwood, MO) throughout the study, except during an overnight fast prior to scheduled necropsies.

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
- Dose levels of 500 or 1000 mg/kg/day were selected on the basis of a previous pre-clinical 28-day toxicity study without recovery

VEHICLE
- Justification for use and choice of vehicle (if other than water): Not stated
- Concentration in vehicle: Not stated
- Amount of vehicle (if gavage): 5 mL/Kg
- Lot/batch no. (if required): Not stated
- Purity: Not stated

Duration and frequency of treatment / exposure:

28 days followed by a 28-day recovery period

Dose / conc.:

100 other: mg/mL

Dose / conc.:

200 other: mg/mL

No. of animals per sex per dose / concentration:

20 male and 20 female rats per group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Dose levels of 500 and 1000 mg/kg/day were selected by the National Cancer Institute on the basis of a previous preclinical 28-day toxicity study
- Rationale for animal assignment (if not random): animals randomly assigned to groups
- Rationale for selecting satellite groups: not stated
- Post-exposure recovery period in satellite groups: 28-day recovery period

Details on dosing and sampling:

PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: plasma
- Time and frequency of sampling: Blood samples taken from all animals killed at the end of 28-days of treatment
- Method type(s) for identification: Gas chromoatography/mass spectrometry
- Limits of detection and quantification: cis, cis-farnesol (0.233 umol/l); cis, trans-farnesol (0.527 umol/l); trans, cis-farnesol (0.516 umol/l); trans,
trans-farnesol (0.814 umol/l).

Type:

absorption

Results:

Plasma levels of total farnesol and individual farnesol isomers in rats receiving daily exposure to farnesol at doses of 500 or 1000 mg/kg/day

Details on absorption:

Total plasma farnesol levels, and plasma levels of individual farnesol isomers in samples collected from study animals at approximately two hours post-dosing during the final week of farnesol administration are summarised in Table 1. As expected, plasma levels of total farnesol (all isomers) and individual farnesol isomers increased with increasing farnesol dose. Despite the fact that farnesol is an endogenous compound, plasma farnesol levels were not detectable in all animals in the vehicle control group (data not shown) as the levels were probably below the detection limit of the assay.

Table 1 - Plasma levels of total farnesol and individual farnesol isomers in rats receiving daily exposure to farnesol at doses of 500 or 1000 mg/kg/day

		Concentration (µmol/L)
		Male, 500^a	Male, 1000^a	Female, 500^a	Female, 1000^a
Total Farnesol	Mean±SD^b Range^c N^d	3.75±2.02 1.29-6.68 8	7.82±1.60 5.12-9.64 10	5.89±3.38 2.76-11.3 9	8.75±2.91 5.74-13.6 10
cis,cisFarnesol	Mean±SD^b Range^c N^d	0.676±0.267 0.283-0.931 5	1.09±0.393 0.603-1.57 10	0.485±0.178 0.234-0.729 5	0.929±0.336 0.576-1.57 10
cis,transFarnesol	Mean±SD^b Range^c N^d	0.801 0.801 1	1.28±0.714 0.553-2.17 4	2.01 2.01 1	1.01±0.183 0.881-1.14 2
trans,cisFarnesol	Mean±SD^b Range^c N^d	0.846±0.197 0.06-0.985 2	0.814±0.339 0.522-1.25 8	1.03±0.409 0.742-1.32 2	0.665±0.089 0.562-0.765 5
trans,transFarnesol	Mean±SD^b Range^c N^d	3.02±1.44 1.29-4.95 8	5.57±1.00 4.08-6.97 10	5.18±2.64 2.76-10.0 9	7.29±2.27 4.90-11.6 10

Blood samples were collected approximately 2h post-dosing during the fourth week of farnesol administration. Plasma farnesol levels in all samples collected from vehicle controls were not detectable

a Sex and dose (mg/kg/day)

b Mean concentration (+/- standard deviation) for animals with quantifiable levels within the group

c Concentration range among animals with quantifiable levels within the group

d Number of animals (out of 10) with quantifiable levels within the group

Conclusions:

Plasma concentrations of farnesol and associated isomers increased with increasing dose concentration following oral exposure in rats.

Executive summary:

Male and female rats received daily exposure to farnesol at doses of 500 or 1000 mg/kg/day, alongside a vehicle control, for 28 days followed by a 28-day recovery period. Total plasma farnesol levels and plasma levels of individual farnesol isomers were analysed at approximately two hours post-dosing during the final week of farnesol administration. Plasma levels of total farnesol (all isomers) and individual farnesol isomers increased with increasing farnesol dose. This study is considered to be reliable with restriction (Klimisch 2) as it was a published study conducted similar to an OECD 407 28-day repeated dose toxicity study, with minor limitations in reporting.

Description of key information

The in vivo absorption of farnesol led to systematic absorption of 39.8±2.5 % of the applied dose (mean ± SEM) in Harley guinea pigs. As the total recovery (mass balance) corresponded only to 65.9 ± 6%, in vitro information was used as key information. Here, the total recovery corresponded to 105.8 ± 6.2% at 72 h and the in vitro absorption of farnesol was 85.5%. Under the experimental conditions of the test, farnesol is readily absorbed and systemically distributed.

Key value for chemical safety assessment

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

39.8

Absorption rate - inhalation (%):

100

Additional information

Doan et al. (2010) investigated the dermal absorption of farnesol in Hartley guinea pigs in vivo using radiolabelled material and in vitro by mounting skin grafts in diffusion cells and measuring receptor fluid fractions. Comparable in vitro and in vivo dermal absorption of farnesol was observed. The in vivo absorption of farnesol led to systematic absorption of 39.8±2.5 % of the applied dose (AD) (mean ± SEM). At 24-hours, 21±0.2 % AD of farnesol remained in the skin and 5.0±2.2 %AD was extracted from carbon impregnated filter papers. The total recovery (mass balance) corresponded only to 65.9 ± 6%.

In vitro farnesol absorption studies suggested penetration of 69.9±4.3 %AD. Extended 72-hour studies found 77.5±4.7 %AD in the receptor fluid with 8.0±1.9 %AD remaining in the skin. The total 72-hour in vitro penetration of farnesol was calculated to be 85.5±6.7 %AD. Under the experimental conditions stated, farnesol is readily absorbed and systemically distributed. The systemic in vivo absorption value coincided with the 24 -hour in vitro absorption value. However, an evaporation test for 3H-Farnesol suggested that there is a potential for evaporative loss. This study is considered to be reliable without restriction (Klimisch 1) as it was a published study with adequate experimental design and sufficient reporting.

Horn et al. (2005) investigated the levels of farnesol in plasma in a study conducted similar to an OECD 407 28-day oral repeated dose toxicity study. Male and female rats received daily exposure to farnesol at doses of 500 or 1000 mg/kg/day by oral gavage, alongside a vehicle control, for 28 days followed by a 28-day recovery period. Total plasma farnesol levels and plasma levels of individual farnesol isomers were analysed at approximately two hours post-dosing during the final week of farnesol administration. Plasma levels of total farnesol (all isomers) and individual farnesol isomers increased with increasing farnesol dose. However, these plasma levels are probably confounded by the fact that farnesol is an endogenous compound which is rapidly metabolised and may be sequestered by intracellular and extracellular binding proteins. In the absence of elimination data, the actual quantification of absorption cannot be performed. However, dermal absorption has been determined at 85.5% and it can be considered that absorption from oral exposure would exceed this level. Consequently, the absorption rate for the oral route is estimated at 100%. This study is considered to be reliable with restriction (Klimisch 2) as it was a published study with minor limitations in reporting.

There are no data covering the kinetics of inhalation exposure so the default of 100% absorption by this route is given.