Isopentyl p-methoxycinnamate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

A short description of the key studies is provided at the beginning of the Discussion section.

Link to relevant study records

Reference

Endpoint:

two-generation reproductive toxicity

Remarks:

based on test type (migrated information)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Germany.
- Age at study initiation: (P) 37 +/- 1 days ;

- Weight at study initiation:
(P) Males: 123.4 (113.1-135.2)g; Females: 108.0 (96.4- 119.0)g;

- Housing:
individually in type DK lll stainless steel wire mesh cages supplied by BECKER& CO., Castrop-Rauxel, Germany (floor area of
about 8 00 cm2)
overnight matings: male and female mating partners housed together in type DK lll cage
gestation day 18- lactation day21: pregnant animals and their litters housed in Makrolon type M lll cages.
nesting material (cellulose wadding) toward the end of gestation
- Use of restrainers for preventing ingestion (if dermal): yes/no
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 9 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24
- Humidity (%): 30-70
- Photoperiod (hrs dark / hrs light): 12 hours( 12h light from 6 .00 a .m. to 6.00 p .m. and
12 h darkness from 6 .00 p .m. to 6.00 a .m.)


IN-LIFE DATES: From: 28.Feb.2002 To: 03.Dec.2002

Route of administration:

oral: feed

Vehicle:

other: unchanged, mixed with diet

Details on exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency): weekly
- Mixing appropriate amounts with (Type of food): ground Kliba maintenance diet mouse/rat "GLP" meal

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: overnight matings for 4d (F0), 6d (F1)
- Proof of pregnancy: sperm in vaginal smear referred to as day 0
- After ... days of unsuccessful pairing replacement of first male by another male with proven fertility.
Mating indices were 100%
- Further matings after two unsuccessful attempts:
no, mating indices were 100%
- After successful mating each pregnant female was caged (how):
From gestation day 18 to lactation day 21: pregnant animals and their litters were housed in
Makrolon type Mlll cages and nesting material (cellulose wadding) was provided.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Feed samples were extracted with acetonitrile. Aliquots of the extracts were used for HPLC-analysis.

Duration of treatment / exposure:

F0 generation: continuous administration of the test substance until or up to
about 16 hours before they were sacrificed (Feb.28- Jul.17.2002)
F1 generation: After weaning, continuous administration of the test substance until or up to
about 16 hours before they were sacrificed. (Jul.3.-Nov.11.2002)
F2 generation: After weaning, continuous administration of the test substance until or up to
about 16 hours before they were sacrificed (Nov.7.-Dec.3.2002)

Frequency of treatment:

continuous administration via diet

Details on study schedule:

- F1 parental animals not mated until at least 74 days after selected from the F1 litters.

for further details, see appendix 1

Remarks:

Doses / Concentrations:
0, 150, 450 ,1000 mg/kg body weight/day
Basis:
nominal in diet

No. of animals per sex per dose:

25

Control animals:

yes, plain diet

Parental animals: Observations and examinations:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: parental animals daily


BODY WEIGHT: Yes
- Time schedule for examinations: weekly
Exeptions for female animals:
During gestation period parental females were weighed on day 0,7,14,20 post coitum.
Females showing no positive evidence of sperm in vaginal smears were not weighed during the mating interval.
Females with litter were weighed on the day after parturition day 1, 4, 7, 14 and 21 post partum.
Females without litter were not weighed during the lactation phase.
After weaning female F0 parental animals were weighed again once weekly (in parallel to male) until scheduled sacrifice.


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculation:
ITx=(FCx*C)/BWy
ITx= TS intake on day x(mg/kg bw/day)
FCx= daily food consumption day x (g)
C= TS concentration (ppm)
BWy= body weight day y (last weighing before day x)

Oestrous cyclicity (parental animals):

Estrous cycle length and normality were evaluate daily (F0 and F1 parental animals)
for a minimum of 3 weeks prior to mating and were continued throughout the mating
period until the female exhibited evidence of mating.

Sperm parameters (parental animals):

Parameters examined in [all/P/F1/F2] male parental generations:
testis weight,
epididymis weight,
sperm count in testes,
sperm count in epididymides,
sperm motility,
sperm morphology

Litter observations:

STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: yes
- If yes, maximum of 4/sex/litter as nearly as possible. Standardisation was not performed <= 8 pups /litter
PARAMETERS EXAMINED
The following parameters were examined in [F1 / F2] offspring:
number and sex of pups
stillbirths,
live births
postnatal mortality
presence of gross anomalies
weight gain
physical or behavioural abnormalities



GROSS EXAMINATION OF DEAD PUPS:
yes, for external and internal abnormalities

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals were sacrifieced after weaning period of respective offspring
- Maternal animals: All surviving animals were sacrifieced after weaning period of respective offspring


GROSS NECROPSY
- Gross necropsy consisted of [external and internal examinations including the cervical, thoracic, and abdominal viscera.]


HISTOPATHOLOGY / ORGAN WEIGHTS
The tissues indicated in Appendix 2 were prepared for microscopic examination and weighed, respectively.

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring not selected as parental animals and all F2 offspring were sacrificed after standardization or weaning (14-28d), except for the
group of reared F2 pups, which were sacrificed shortly after achieving sexual maturity (43-56d)

- These animals were subjected to postmortem examinations as follows:
Pups were examined externally and eviscerated their organs were assessed macroscopically

ORGAN WEIGTHS
brain, spleen and thymus of 1 pup/sex and litter from the F1 and F2 pups were weighed.

Statistics:

For statistics of clinical examinations see appendix 3
For statistics of pathology see appendix 4

Reproductive indices:

Male mating Index (%) = (number of males with confirmed mating* / number of males placed with females) x 100
Male fertility Index (%) = (number of fertile males**/number of males placed with females) x100
Female mating index (%) = (number of females mated*/number of females placed with males) x100
Female fertility index (%) = (number of females pregnant***/ number of females mated*) x 100
* animals with vaginal sperm or that gave birth to a litter or with pups/implantations in utero
**defined by a female giving birth to a litter or with pups/implantation in utero
*** defined as the number of females that gave birth to a litter or with pups/implantations in utero

Offspring viability indices:

Gestation Index (%) = (number of females with live pups on the day of birth/number of females pregnant*) x 100
* defined as the number of females that gave birth to a litter or with pups/implantations in utero
Live birth Index (%) = (number of liveborn pups at birth/total number of pups born) x 100
Post lmplantation loss (%) = ((number of implantations - number of pups delivered)/number of implantations) x 100

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One low dose female (150 mg/kg body weight) was found dead: not considered as substance related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In F0 (or P0) 1000 mg/kg bw/day induced eosinophilic homogeneous appearance of the liver cell cytoplasm indicative of enzyme induction

Histopathological findings: neoplastic:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Test substance related findings:

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
1000 mg/kg bw /day:
Males F0: significantly decreased mean bodyweights (16% below control) and body weight gain (average 22 % below control)
Males F1: significantly decreased mean body weights(14% below control) and body weight gain (average 14% below control)
Females F0: decreased mean bodyweights during premating (4 %), gestation (8 %) and early lactation (6 % below control)
Females F1: decreased mean body weights during premating(6 %), gestation(10%) and lactation( 6% below control)
Females F0: decreased body weight gain during premating (9 %) and gestation (18% below control)
Females F1: decreased body weight gain during gestation(1 7% below control)
Males F1: Significantly decreased mean food consumption(4 % below control)
Females F1: significantly decreased mean food consumption during gestation(9%) and mid lactation(11 %) below control.

ORGAN WEIGHTS (PARENTAL ANIMALS):
Test substance related findings with histological correlate:
1000 mg/kg bw/day
F0: Significantly increased mean absolute liver weight in female rats (17% above control)
F0: Significantly increased mean relative liver weight in males/fermales ( 17 and 23% above control, respectively)

HISTOPATHOLOGY (PARENTAL ANIMALS)
1000 mg/kg bw/day
F0/F1: eosinophilic homogeneous appearance of the liver cell cytoplasm indicative of
enzyme induction in males/females
F0/F1: increased amount of hemosiderin in the spleen of males

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
F0: One low dose female (150 mg/kg body weight) was found dead: not considered as substance related.
F1: Mortality in two mid dose females (found dead/ sacrificed for to humane reasons): not considered as substance related.
F0: Urine-smeared fur around the anogenital region in 2 animals (1000 mg/kg bw/day)
F1: Urine-smeared fur around the anogenital region in 3 animals (1000 mg/kg bw/day)
REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
F0: mean number of implantation sites was statistically significantly lower for the high dose group (12.0; 12.3; 11.3; 10.0 implants/dam for test group 0;150; 450; 1000 mg/kg bw/day, respectively)
F1: mean number of implantation sites was statistically significantly lower for mid/ high dose group (12.4; 11.5; 10.7; 10.3 implants/dam for test
group 0;150; 450; 1000 mg/kg bw/day, respectively)
F0: mean number of F1 pups delivered/dam was statistically significantly lower for the high dose group (11 .0 ; 11.9; 10.9; 9.2 for test group 0; 150; 450; 1000 mg/kg bw/day, respectively)


GROSS PATHOLOGY (PARENTAL ANIMALS)
F0:Erosion/ulcer in the mucosa of the glandular stomach ( 0/1/3/4 females for test group 0; 150; 450; 1000 mg/kg bw/day, respectively)
F1:Erosion/ulcer in the mucosa of the glandular stomach ( 0/0/0/4 males and 3/3/2/4 females for test group 0; 150; 450; 1000 mg/kg bw/day, respectively)

Dose descriptor:

NOAEL

Remarks:

systemic parental toxicity

Effect level:

450 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: overall effects: body weight; gross pathology; organ weights; histopathology;

Remarks on result:

other: Generation: P/F1 (migrated information)

Dose descriptor:

NOAEL

Remarks:

Fertility and reproduction parameters

Effect level:

450 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: overall effects: secondary number of implantation sites; secondary delayed sexual maturation

Remarks on result:

other: Generation: P/F1 (migrated information)

Dose descriptor:

NOAEL

Remarks:

developmental toxicity

Effect level:

450 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: overall effects: pup weights

Remarks on result:

other: Generation: F1/F2 (migrated information)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Urine-smeared fur around the anogenital region in 3 animals (1000 mg/kg bw/day)

Mortality:

mortality observed, non-treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Reproductive function: oestrous cycle:

not specified

Reproductive function: sperm measures:

not specified

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

Mean number of implantation sites was statistically significantly lower for mid/ high dose group (12.4; 11.5; 10.7; 10.3 implants/dam for test group 0;150; 450; 1000 mg/kg bw/day, respectively).

Dose descriptor:

NOAEL

Remarks:

Fertility and reproduction parameters

Effect level:

<= 450 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: reduced number of implantation sites; secondary delayed sexual maturation

Dose descriptor:

NOAEL

Remarks:

Systemic parental (F1/P1) toxicity

Effect level:

<= 450 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality / viability:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Sexual maturation:

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Test substance related findings:

BODY WEIGHT (OFFSPRING)
1000 mg/kg bw/day
F1: significantly decreased mean body weights( 13% below control at weaning) and body
weight gain( 15% below control) males/females during lactation
F2: significantly decreased mean body weights( 16% below control at weaning) and body
weight gain(20% below control) males/females during lactation.
F2 reared: significantly decreased mean body weights (final weight 12% below control) and body
weight gain (average 10% below control) in males
F2 reared: significantly decreased mean body weights (final weight 6% below control) in females

SEXUAL MATURATION (OFFSPRING)
1000 mg/kg bw/day
F1: slight delay of preputial separation in males (average age 45.4d vs.43.6 d in control) exceeds historical control (42.5- 45.0d), secondary to delayedbody weight development
F2 reared: slight delay of preputial separation in males (average age 45.1d vs.42.8 d in control) exceeds historical control (42.5- 45.0d), secondary to delayed body weight development
F1: apparent slight delay of vaginal patency in females (average age 33.8d vs. 31.3d in control) within historical control (30.8d- 33.8d), secondary to
delayed body weight development
F2 reared: apparent slight delay of vaginal patency in females (average age 35.5d vs. 32.9d in control) within historical control (30.8d- 33.8d),
secondary to delayed body weight development.

OTHER FINDINGS (OFFSPRING)
F2 reared: Significantly decreased mean food consumption(10 % below control) in males

Dose descriptor:

NOAEL

Remarks:

General toxicity (F1)

Generation:

F1

Effect level:

<= 450 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Sexual maturation:

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings:

not specified

Dose descriptor:

NOAEL

Generation:

F2

Effect level:

<= 450 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

sexual maturation

body weight and weight gain

food consumption and compound intake

Reproductive effects observed:

not specified

Reproductive effects observed:

yes

Lowest effective dose / conc.:

1 000 mg/kg bw/day (nominal)

Treatment related:

yes

Relation to other toxic effects:

reproductive effects as a secondary non-specific consequence of other toxic effects

Dose response relationship:

no

Relevant for humans:

yes

Conclusions:

Al the highest dose of 1,000 mg/kg bw/d, reduced food consumption and body weight (-14% to -16% in males, -4% to -5% females), increased liver weight, produced hepatic cytoplasmic eosinophilia and erosion/ulceration of glandular stomach mucosa were observed in parental animals. This was accompanied by a slight decrease in implantation rate in the high-dose F0 and F1 dams.
The NOAEL (no observed adverse effect level) for fertility and reproductive performance, for systemic parental and developmental toxicity was thus determined to be 450 mg/kg bw/d.

Executive summary:

The potential reproductive toxicity of 2-ethylhexyl 4-methoxycinnamate, a compound that is structurally similar to isopentyl p-methoxycinnamate, was investigated in a two-generation reproductive toxicity study in rats.

In this study, wistar rats (25 animals per sex and dose group) continuously received the test compound in the diet through two successive generations at nominal doses of 150, 450, or 1,000 mg/kg bw/d. OMC had no adverse effects on oestrous cycles, mating behaviour, conception, parturition, lactation and weaning, sperm and follicle parameters, macropathology, and histopathology of the sexual organs.

 

1000 mg/kg bw/d reduced parental food consumption and body weight (-14% to -16% in males, -4% to -5% females), increased liver weight, produced hepatic cytoplasmic eosinophilia and erosion/ulceration of glandular stomach mucosa, and led to a slightly decreased implantation rate in the top dose F0 and F1 dams. The high dose F1 and F2 pups had reduced lactation weight gain and organ weights and delayed sexual maturation landmarks. There was no evidence of a selective influence of the test compound on pups' sexual landmarks.

 

The NOAEL (no observed adverse effect level) is 450 mg/kg bw/d for fertility and reproductive performance, for systemic parental and developmental toxicity.

 

Due to the high degree of structural similarity between isopentyl p-methoxycinnamate and 2-ethylhexyl 4-methoxycinnamate, the negative findings obtained with 2-ethylhexyl 4-methoxycinnamate in this study suggest that isopentyl p-methoxycinnamate would also not show any reproductive or developmental toxicity.

Effect on fertility: via oral route

Dose descriptor:

NOAEL

450 mg/kg bw/day

Species:

rat

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

In the two-generation reproduction toxicity study conducted with 2-ethylhexyl 4-methoxycinnamate, Wistar rats continuously received the test compound in the diet through two successive generations at nominal doses of 0, 150, 450 or 1000 mg/kg bw/day (Schneider et al. 2005; see also section 7.8.1 of this IUCLID dataset). The study was performed according to OECD guideline no. 416.

At the highest dose level, reductions in food consumption and body weight, increases in liver weight, hepatic cytoplasmic eosinophilia and erosion/ulceration of glandular stomach mucosa were observed in the parental animals. A slightly decreased implantation rate was also observed in the top dose F0 and F1 females, although the implantation rate was within or close to the historical control range. A slightly decreased implantation rate at the highest dose, at which parental animals show signs of toxicity, is not unusual and was considered most likely to be secondary to the maternal toxicity observed. High dose F1 and F2 pups had reduced lactation weight gain and organ weights and delayed sexual maturation landmarks. There was no evidence of a selective influence of the test compound on pups sexual landmarks. Rather, the delay in sexual maturation was considered to be secondary to the reduced pup weight gain, since body weights at time of sexual maturity were similar between controls and treated pups. Body weight rather than calendar age is the main factor driving sexual maturity.

 

The NOAEL of 2-ethylhexyl 4-methoxycinnamate by continuous dietary administration was thus determined to be 450 mg/kg bw/day for fertility and reproduction parameters, for systemic parental and developmental toxicity. This is based on reduced body weights, increased liver weight and hepatic cytoplasmic eosinophilia in the parents, a secondary reduction in implantation rate, and reduced body weights and delayed sexual maturation of the pups at 1000 mg/kg bw/day.

Short description of key information:
The effects of isopentyl p-methoxycinnamate on fertility were not studied.

However, information on this endpoint is available from a two-generation reproduction toxicity in rats which was performed with 2-ethylhexyl 4-methoxycinnamate, a compound that is structurally similar to isopentyl p-methoxycinnamate (Schneider et al. 2005; see also section 7.8.1 of this IUCLID dataset and the section "discussion" below for further information).

In addition, in an oral subchronic 90-day study performed with isopentyl p-methoxycinnamate in the rat, histopathological examination did not reveal any significant effects on reproductive organs upon oral dosing at up to 2,000 mg/kg bw/day (see section 7.5.1 of this IUCLID dataset).

Justification for selection of Effect on fertility via oral route:
Read-across study with 2-ethylhexyl 4-methoxycinnamate

Effects on developmental toxicity

Description of key information

The embryotoxic and/or teratogenic potential of isopentyl p-methoxycinnamate was evaluated in Wistar rats (Study no. 1988034). The study was conducted in accordance with OECD guideline no. 414. Mated females (n=20 per dose) received daily oral doses of 0.25, 0.75, and 2.25 mL/kg/d isopentyl p-methoxycinnamate in olive oil or the vehicle only from day 6 post coitum up to and including day 15 post coitum. Tretinoin was used as a positive control. The animals were sacrificed at day 20 post coitum and subjected to necropsy.
No teratogenic effects were observed at any of the dose levels tested. Embryotoxicity was observed at the highest dose level (2.25 mg/kg/d). However, this effect was considered to be a consequence of the high degree of maternal toxicity that was observed at this dose level and was not considered to be due to a specific embryotoxic action of the test item. Accordingly, it can be concluded that no teratogenic or specifically embryotoxic effects of isopentyl p-methoxycinnamate were observed in this study.
When strict criteria of general maternal toxicity were applied, the no observed adverse effect level (NOAEL) for maternal toxicity was determined at 0.25 mL/kg/d. However, as the only relevant adverse effect that was observed at the intermediate dose level of 0.75 mL/kg/d was hair loss, which may be considered a minor adverse effect, the intermediate dose level of 0.75 mL/kg/d might be considered as NOAEL in this case.

Effect on developmental toxicity: via oral route

Dose descriptor:

NOAEL

0.75

Species:

rat

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Mated female Wistar rats were treated with daily oral doses of 0.25, 0.75, and 2.25 mL/kg/d isopentyl p-methoxycinnamate from day 6 post coitum to day 15 post coitum. No teratogenic effects were observed at any of the dose levels tested. Embryotoxicity observed at the highest dose level (2.25 mg/kg/d) were attributed to the high degree of maternal toxicity that was observed at this dose level and was not considered to be a consequence of a specific embryotoxic effect of the test item. Accordingly, no teratogenic or specific embryotoxic effects of isopentyl p-methoxycinnamate were observed in this study.

As hair loss was the only relevant toxic effect observed in mothers at 0.75 mL/kg/d, this intermediate dose level may be considered as the NOAEL.

Justification for selection of Effect on developmental toxicity: via oral route:
Guideline study

Toxicity to reproduction: other studies

Additional information

UTEROTROPHIC ASSAY IN IMMATURE FEMALE RATS (IN VIVO) (STUDY NO. 2001155)

In this assay, juvenile female Wistar rats (n=6 per dose level) received daily subcutaneous injections of isopentyl p-methoxycinnamate (200 or 1000 mg/kg in corn oil) for 3 consecutive days. Two positive control groups of 6 juvenile female rats each were treated daily for 3 consecutive days with 0.3 or 1.0 µg/kg 17alpha-ethinyloestradiol, two further groups of 6 juvenile female rats received the vehicle alone or were left untreated. The study was performed in accordance with the OECD Draft protocol B - Immature female rats with subcutaneous administration. No effects on uterine weight were observed at 200 and 1000 mg/kg isopentyl p-methoxycinnamate. An enlargement of uterus and increased uterine weights were observed with the positive control. In conclusion, the test item did not show any estrogenic effects in this assay.

 

ANDROGEN RECEPTOR BINDING ASSAY (IN VITRO) (STUDY NO. 2002031)

In the in vitro androgen receptor binding assay, the potential interaction of the test item with the androgen receptor was investigated using a rat recombinant fusion protein containing both the hinge region and ligand binding domain of the androgen receptor and radiolabelled methyltrienolone as ligand.

Isopentyl p-methoxycinnamate only weakly displaced methyltrienolone from the androgen receptor (25% and 35%, respectively, at 100 µM in two independent experiments) and no IC50 value could be established. These results did not suggest a specific interaction of the test item with the androgen receptor.

 

ESTROGEN RECEPTOR BINDING ASSAY (IN VITRO) (STUDY NO. 2002077)

In this assay, the potential interaction of the test item with the estrogen receptor was investigated using a human recombinant estrogen receptor of the alpha-subtype and radiolabelled estradiol as ligand. In this assay, the test item did not show any affinity to the estrogen receptor at concentrations ranging from 0.1 to 100 µM.

YEAST TRANSCRIPTIONAL ACTIVATION ASSAY (IN VITRO) (Kunz et al. 2006)

In this published study, Kunz et al. (2006) investigated thein vitro oestrogenic activity of isopentyl p-methoxycinnamate in two yeast transactivational assays. A recombinant yeast was employed, which was stably transfected with either the oestrogen receptor alpha of rainbow trout or the human oestrogen receptor alpha. The test item did not result in any transactivational effects with either oestrogen receptor, indicating that it does not have any agonistic estrogenic activity in either of these two assay systems at concentrations ranging from 10^-9 to 10^-3 M.

YEAST TRANSCRIPTIONAL ACTIVATION ASSAY (IN VITRO) (Kunz and Fent 2006)

In this published study, Kunz and Fent (2006) systematically investigated the in vitro (anti-)oestrogenic and (anti-)androgenic activity of isopentyl p-methoxycinnamate in a transactivational assay. The recombinant yeast (S. cerevisiae) was employed, which was stably transfected with either the hERa or the human androgen receptor (hAR). The tested concentration range was 10^-7to 10^-2M. No oestrogenic transactivation was measureable in the oestrogen agonism assay. However, multiple hormonal activity was observed, with effects in the anti-oestrogenic, androgenic and anti-androgenic assays. Complete inhibition of E2-induced activity was measured at the highest concentration tested and a full dose-response curve was obtained. The IC50 was determined as 297 µM, which represented a potency 540 times lower than the known anti-oestrogen 4-hydroxytamoxifen. Isopentyl p-methoxycinnamate displayed partial agonistic activity in the androgen assay, indicated by a sub-maximal dose-response curve (curve height was 52% that of DHT). The EC50 was determined as 429 µM, representing a potency 260,000 times lower than the natural ligand DHT. A full dose-response curve with complete inhibition of DHT was observed in the anti-androgenic assay. The IC50 was determined as 8.12 µM, which represents a potency 3.5 less than the anti-androgen reference standard flutamide.

The five studies summarised in this section (Toxicity to reproduction: other studies) address the potentialin vitro andin vivo screening level (anti-)estrogenic and (anti-)androgenic activity of isopentyl p-methoxycinnamate.

The results from threein vitro studies (Freyberger 2002a, Kunz et al. 2006, Kunz and Fent 2006), as well as the uterotrophic assay (Krötlinger 2002), provide evidence that isopentyl p-methoxycinnamate does not have any oestrogenic potential.

The results from an androgen receptor binding study indicated that isopentyl p-methoxycinnamate only had weak affinity for the androgen receptor; although a concentration response curve was observed, the curve was flat and displacement of the ligand did not exceed a mean of 30% (Freyberger 2002b). However, in a further study isopentyl p-methoxycinnamate displayed multiple hormonal activities, with positive results in the anti-oestrogenic, androgenic and anti-androgenic assays (Kunz and Fent 2006). The relative anti-oestrogenic and androgen activities were quite weak. The greatest effect was found in the anti-androgenic assay, in which the anti-androgenic potency of isopentyl p-methoxycinnamate was determined to be 3.5-fold less than the reference compound flutamide. Noin vivo screening data from a Hershberger assay were available, which would have clarified whether the anti-androgenic activity measured for isopentyl p-methoxycinnamatein vitro is also inducedin vivo.

For a substance to be considered as an endocrine disrupter, any in vitro or in vivo screening level activity observed must be plausibly linked to an adverse effect observed in an apical study. Results from a 90-day repeat dose study and a prenatal developmental toxicity study are available, which fall in Level 4 of the OECD Conceptual Framework for the assessment of endocrine disruption. Although these studies are not specifically designed to detect endocrine disrupting effects, they provide relevant information on endpoints such as weight and histopathology of the gonads, and reproductive and developmental parameters. No effects on testes weight or histopathology were observed in a 90-day rat oral toxicity study (Suberg and Schilde 1987; see Section 7.5.1). The main relevant effect found in the prenatal developmental toxicity study was increased intra-uterine mortality at the highest dose, but this was related to the significant maternal toxicity observed at this dose (Kemper and Jekat 1988; see Section 7.8.2). No other effects consistent with any potential endocrine activity were observed. No gross abnormalities of the genitalia were reported. No effects that would be consistent with a potent anti-androgen were noted in any of these studies.

No data from a two-generation reproduction study are available for isopentyl p-methoxycinnamate, which would confirm whether there are any longer term functional consequences from the potentialin vitro activity observed. However, a two-generation reproduction toxicity study is available for 2-ethylhexyl 4-methoxycinnamate, which has been submitted as a read-across study for this endpoint (Schneiders et al. 2005; see Section 7.8.1 of this IUCLID dataset). Wistar rats continuously treated with 2-ethylhexyl 4-methoxycinnamate at doses up to 1000 mg/kg bw/day through two successive generations showed no adverse effects on estrous cycles, mating behaviour, conception, parturition, lactation and weaning, sperm and follicle parameters, macropathology and histopathology of the sexual organs.The only potentially relevant effects observed were a slight reduction in the number of implantation sites in the top dose F0 and F1 females and

delayed sexual development in pups at the highest dose. However, the slightly lower implantation rate was within the historical control range and these effects occurred at the highest dose, at which other systemic toxicity was observed. They are therefore considered to be secondary to the toxicity observed at the highest dose. Similarly, lower body weight gain in the high dose pups was considered to be the most likely cause for the slight delay in sexual development, since body weights at the time of sexual maturity were similar between controls and high dose pups, and because body weight rather than calendar age is the essential component driving sexual maturation.

A full weight of evidence review of all data relevant for the assessment of potential endocrine disruption is presented in Section 13 of this IUCLID dossier for both isopentyl p-methoxycinnamate and 2-ethylhexyl 4-methoxycinnamate. The conclusion from this weight of evidence evaluation is that although both substances may exhibitin vitro hormonal activity, the evidence for adverse effects in apicalin vivo studies is absent or weak. Based on the results of the prenatal developmental toxicity studies and the read across from the two generation study, it can be concluded that neither substance result in clear or consistent adverse effects relevant for the assessment of endocrine disruption. They therefore do not fulfil the WHO definition of an endocrine disrupter, which requires the demonstration of relevant adverse effects that can be plausibly linked to an endocrine mode of action.

Justification for classification or non-classification

The results obtained from the embryotoxicity/teratogenicity study in Wistar rats indicate that isopentyl p-methoxycinnamate is non-teratogenic and non-embryotoxic. The lack of overt reproductive effects induced by isopentyl p-methoxycinnamate is further substantiated by the negative results obtained in the uterotrophic assay in immature Wistar rats in vivo and from the androgen and estrogen receptor binding studies.

Based on the study results outlined above, isopentyl p-methoxycinnamate is not classified as reproductive toxicant as specified in the current EU-CLP Regulation.