3-mercaptopropionic acid

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Effects on fertility

Link to relevant study records

Reference

Reference 1

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Justification for type of information:

There are no relevant variations in qualitative properties among source substances and the same potency is predicted for all target substances. This is Scenario 4 of the RAAF1. Substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are different alkyl esters of a common acid, 3-mercaptopropionic acid (MPA).
This scenario covers the category approach for which the read-across hypothesis is based on the assumption, that toxicity of compounds in this category are driven by a common toxophore. This approach serves to use existing data on genotoxicity, acute toxicity, repeated-dose toxicity and reproductive toxicity endpoints for substances in this category. For the REACH information requirement under consideration, the property investigated in studies conducted with different source substances is used to predict the property that would be observed in a study with the target substance if it were to be conducted. Similar properties are observed for the different source substances; this may include absence of effects for every member of the category.
There are differences in strength of the effects forming a regular pattern. This corresponds to Scenario 4 of the RAAF. The substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are esters of a common acid, 3-mercaptopropionic acid (3-MPA). All category members share the same mercaptopropionic acid moiety with one free SH group per MPA unit. The MPA unit with free SH is a prerequisite for this category.
The observed differences in effect levels (higher effect levels with increasing carbon chain length were observed in the available acute oral toxicity studies) are assumed to be mainly due to differences in molecular weight (corrections will be made for these differences) and decreasing bioavailability with increasing carbon chain length (no corrections are made for this effect; a worst-case approach is applied here, since based on the available data no exact quantification for bioavailability differences is possible at the moment).
It can be predicted with high confidence that the substances within this category will lead to the same type of effects. The main driver for toxicity is free SH group of the MPA moiety.

Beside structural similarities and the common toxophore, the MPA moiety, category members are also likely to have similar metabolites. As explained in the Toxicokinetics section, substances are predicted to be rapidly hydrolysed into 3-MPA and the respective alcohol after absorption. According to low toxicity of the corresponding alcohols (Table 8), this would support the role of the MPA moiety as toxophore, as well as propose scenario 3 of the RAAF as applicable for this category approach. However, no experimental toxicokinetic data to support this hypothesis are available by now. To proof this hypothesis, simulated gastric acid hydrolysis studies, as well as in-vitro metabolism studies using liver microsomes will be conducted. Based on the results of these studies, scenario selection will be revaluated.

For detaild information refer to section 13.2.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Key result

Dose descriptor:

NOAEL

Effect level:

>= 100 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

mortality

body weight and weight gain

food consumption and compound intake

haematology

clinical biochemistry

gross pathology

neuropathology

histopathology: neoplastic

reproductive function (oestrous cycle)

reproductive function (sperm measures)

reproductive performance

Key result

Dose descriptor:

NOEL

Generation:

F1

Effect level:

ca. 88 mg/kg bw/day

Remarks on result:

other: corrected for molecular weight differences between source and target substance

Reproductive effects observed:

not specified

Conclusions:

NOAEL for reproduction/developmental toxicity was identified to be 100 mg/kg bw/day for MMP. Based on the category approach, 3-MPA is considered to show similar reproduction/developmental effects as MMP. The corresponding NOAEL was corrected for molecular weight differences. Therefore, the reproduction/develpmental toxicity NOEL for 3-MPA was determined to be 88 mg/kg bw/ day.

Reference 2

Endpoint:

screening for reproductive / developmental toxicity

Remarks:

based on test type (migrated information)

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

06-JUN-2006 to 13-JUN-2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: RCC Ltd, Laboratory Animal Services, Wölferstrasse 4, CH-4414 Füllinsdorf / Switzerland
- Age at study initiation: 10 weeks
- Weight at study initiation: Males: 286 - 331 grams, Females: 180 - 207 grams
- Fasting period before study: only before blood sampling
- Housing: Animals were housed in Makrolon cages (type-3) with wire mesh tops and standard granulated softwood bedding. During the pre-pairing period, males and females were housed individually. Cages of males were interspersed amongst those holding females to promote the development of regular estrus cycles. During the pairing period, rats were housed one male/one female in Makrolon pairing cages. After mating or at the end of the pairing period, the males and the females were housed individually again. During the lactation period (until day 4 of lactation), dams were housed together with their litters.
- Diet: Pelleted standard Kliba 3433 rat/mouse maintenance diet (Provimi Kliba AG, CH-4303 Kaiseraugst/Switzerland) available ad libitum
- Water: ad libitum
- Acclimation period: 7 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3°C
- Humidity (%): 30 - 70%
- Air changes (per hr): 10 - 15
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 13-JUN-2006 To: 30-JUL-2006

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test item was weighed into a glass beaker on a tared precision balance and approximately 80% of the vehicle was added (w/v). Using an appropriate homogenizer a homogenous mixture was prepared. Having obtained a homogenous mixture, vehicle was added until the required final volume was achieved. Separate formulations were prepared for each concentration.
During the daily administration period homogeneity of the test item in the vehicle was maintained using a magnetic stirrer.


VEHICLE
- Justification for use and choice of vehicle (if other than water): corn oil is the vehicle of choice for substances with low water solubility
- Concentration in vehicle: 6.25, 12.50, 25.00 mg/mL
- Amount of vehicle (if gavage): 4 mL/kg bw

Details on mating procedure:

After the animals had received the test item for 14 days, the pairing period was initiated while dosing was continued.
During the pairing period females were housed with males (one male : one female) in special automatic mating cages, i.e. with synchronized timing to initiate the nightly mating period, until evidence of copulation was observed.
This system reduces the variation in the copulation times of the different females.
Females were removed and housed individually if:
a) a copulation plug was observed, and / or
b) the daily vaginal smear was sperm-positive.
This day was designated day 0 post coitum.
Females showing no-evidence of copulation were sacrificed 24-26 days after the last day of the pairing period and, if indicated, the reproductive organs examined histopathologically in order to ascertain the reason for the infertility.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples for determination of concentration, homogeneity and stability (7 days) of the dose formulations were taken during the first week of the administration period. Additionally, samples for determination of concentration and homogeneity were taken during the last week of the administration period.
On each occasion three samples of approximately 2 g were taken from the top, middle and bottom of each formulation and transferred into flat bottomed flasks. The samples were frozen (-25°C to -15°C) pending analysis. Samples were sent on dry ice to Dr. D. Flade, RCC Ltd, Environmental Chemistry & Pharmanalytics, CH-4452 Itingen / Switzerland. Analysis was performed using a method developed by RCC Ltd. After analysis, the analytical results were communicated to the Study Director. Upon receipt and evaluation of these results the Study Director decided about discarding the samples.

Duration of treatment / exposure:

Exposure period: males: at least 28 days; females: for 14 days prior to pairing, through pairing and gestation until day 4 post partum
Premating exposure period (males): 14 days
Premating exposure period (females): 14 days
Duration of test: up to 28 days in males; up to 51 days in females

Frequency of treatment:

daily

Details on study schedule:

see Table 1 (Materials & Methods)

Remarks:

Doses / Concentrations:
25, 50 and 100 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

Post-exposure period: none
- Dose selection rationale: Dose levels were selected in agreement with the Sponsor, based on the results of a dose range-finding study (RCC Study No. A57802) and following discussions with the sponsor.

Positive control:

none

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: mortality, clinical signs. Additionally, the females were observed for signs of difficult or prolonged parturition.


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once prior to the first test item administration and weekly thereafter.


BODY WEIGHT: Yes
- Time schedule for examinations: daily


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood: on the day before or on the day of scheduled necropsy
- Anaesthetic used for blood collection: Yes, isoflurane
- Animals fasted: Yes
- How many animals: 5 per sex per group
- Parameters:
Erythrocyte count, Hemoglobin concentration distribution width, Haemoglobin Platelet count, Haematocrit Total leukocyte count, Mean corpuscular volume, Differential leukocyte count, Red cell volume distribution width, Mean corpuscular hemoglobin concentration, Mean corpuscular haemoglobin
Coagulation: Thromboplastin time, Activated partial thromboplastin time



CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood:on the day before or on the day of scheduled necropsy
- Animals fasted: Yes
- How many animals: 5 per sex per group
- Parameters:
Glucose, Sodium, Urea, Potassium, Creatinine, Chloride, Bilirubin, total Calcium, total Cholesterol, inorganic Phosphorus, Aspartate aminotransferase, total Protein, Alanine aminotransferase, Albumin, Bile acids, Globulin, Alkaline phosphatase, Albumin/Globulin ratio, Gamma-glutamyl-transferase


URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: At one time during the study (males: shortly before scheduled sacrifice; females: on day 3 or 4 post partum) relevant parameters were evaluated for five P generation males and five P generation females randomly selected from each group.
- Dose groups that were examined: all
- Battery of functions tested: Cage side observations, Hand-held observations, Open field observations, Categorical observations, Measurements / Counts: hind limb / fore limb grip strength, landing foot splay, rectal temperature.

Oestrous cyclicity (parental animals):

no

Sperm parameters (parental animals):

no

Litter observations:

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
litter size, live birth, stillbirth and any gross anomalies. The sex ratio of the pups was recorded. The dams were caged together with their litters until day 4 of lactation. Pups were weighed individually (without identification) on days 0 (if possible), 1 and 4 post partum.
The dams and pups were observed daily for survival and behavioural abnormalities in nesting and nursing.

GROSS EXAMINATION OF DEAD PUPS:
yes

Postmortem examinations (parental animals):

GROSS PATHOLOGY: Yes
The testes and epididymides of all parental males were weighed.
In addition for five adult males and females, randomly selected from each group, the following organs were trimmed from any adherent tissue, as appropriate, and their wet weight taken:
liver, spleen, adrenals, brain, thymus, heart, kidneys

HISTOPATHOLOGY: Yes
prostate, testes, seminal vesicles with coagulation gland, epididymides, ovaries, gross lesions, heart, brain, thymus, spinal cord, thyroid, small and large intestines (incl. Peyer's patches), trachea and lungs, stomach, uterus (with vagina), liver, urinary bladder, kidneys, lymph nodes, adrenals, peripheral nerve, spleen, bone marrow

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring were sacrificed at 4 days of age.
- These animals were subjected to macroscopic postmortem examination.


GROSS NECROPSY
- Gross necropsy consisted of external examinations.

Statistics:

The following statistical methods were used to analyze body weights, food consumption, reproduction and skeletal examination data:
• Means and standard deviations of various data were calculated and included in the report.
• If the variables could be assumed to follow a normal distribution, the Dunnett t-test, based on a pooled variance estimate, was used for intergroup comparisons (i.e. single treatment groups against the control group).
• The Steel test (rank test) was applied when the data could not be assumed to follow a normal distribution.
• Fisher's Exact test for 2x2 tables was applied if the variables could be dichotomized without loss of information.

Reproductive indices:

Mating index: no. of females mated/ no. of females paired
Fertility index: no. of pregnant females / no. of females mated
Gestation index: no. of litters with live pups / no. of pregnant females

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

not examined

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
All animals survived until scheduled necropsy. In group 4, all animals pushed their heads through the bedding after administration of the test item starting on day 5 of the prepairing period and continuing until the end of the treatment period.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
unaffected

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)
no data

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
no data

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS): see Table 2

ORGAN WEIGHTS (PARENTAL ANIMALS): see Table 3
For groups 3 and 4 males, liver weights relative to body weights and brain weights were dose-dependently increased. Liver weights relative to the brain weights did not reach statistical significance in group 3.
In the absence of a histopathological correlation these higher weights were considered to be of no adverse character.
In females, mean absolute organ weights as well as organ/body weight ratios and organ/brain weight ratios were not affected by exposure to the test item.


GROSS PATHOLOGY (PARENTAL ANIMALS)
During necropsy of parent animals no test item-related findings were noted.

HISTOPATHOLOGY (PARENTAL ANIMALS): see Table 4
A minimal to slight hyperplasia of the forestomach squamous epithelium partly associated with a minimal to slight hyperkeratosis and minimal inflammatory cell infiltrations was recorded in four males and four females in group 4. Proliferative lesions of the rodent non-glandular stomach region are relatively common in gavage and feeding studies ranging from mild hyperplasia of the keratinized stratified squamous epithelium to extensive papillomatous hyperplasia. As no similar findings were noted in the forestomach epithelium of the control group, this finding was considered to be test item-related.
All other microscopic findings recorded in various organs of all groups treated with the test item did not differ significantly from the control group. All findings were considered to be spontaneous in nature and within the normal background pathology commonly seen in rats of this strain and age.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 100 mg/kg bw/day

Sex:

male/female

Basis for effect level:

clinical signs

mortality

body weight and weight gain

food consumption and compound intake

haematology

clinical biochemistry

gross pathology

neuropathology

histopathology: neoplastic

reproductive function (oestrous cycle)

reproductive function (sperm measures)

reproductive performance

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

not examined

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

>= 100 mg/kg bw/day

Sex:

male/female

Basis for effect level:

body weight and weight gain

gross pathology

other:

Remarks on result:

other: no treatment related effects on reproductive toxicity were observed

Reproductive effects observed:

not specified

Result: no effects on reproduction at the highest dose tested (100 mg/kg bw/d)
The fertility rate was high resulting in 9, 8, 9 and 10 litters in order of ascending dose levels for evaluation of reproduction data. At all concentrations, there were no treatment-related effects on precoital time, fertility indices, mean duration of gestation, number of implantations, or post-implantation loss. The mean number of
corpora lutea per dam (determined at necropsy) was similar in all groups and gave no indication of a test item-related
effect.

Table 2: Reproductive performance

	Group 1 0 mg/kg/d	Group 2 25 mg/kg/d	Group 3 50 mg/kg/d	Group 4 100 mg/kg/d
Mating index (%)	100.0	100.0	100.0	100.0
Fertility index (%)	90.0	80.0	90.0	100.0
Conception rate (%)	90.0	80.0	90.0	100.0
Gestation index (%)	100.0	100.0	100.0	100.0

 

Table 3: Organ weights P-generation males

MALES	Group 1 0 mg/kg/d	Group 2 25 mg/kg/d	Group 3 50 mg/kg/d	Group 4 100 mg/kg/d
BODY W. [g]	342.3	360.3	352.1	355.9
ST.DEV.	17.8	17.2	23.9	23.4
N	10	10	10	10
BRAIN [g]	2.02	2.01	2.08	1.97
% BW	0.60	0.57	0.59	0.57
N	5	5	5	5
HEART [g]	0.95	1.02	1.04	1.01
% BW	0.28	0.29	0.29	0.29
N	5	5	5	5
LIVER[g]	8.30	8.62	9.40	9.38
% BW	2.46	2.43	2.65*	2.70*
N	5	5	5	5
THYMUS[g]	0.306	0.364	0.287	0.348
% BW	0.091	0.103	0.082	0.099
N	5	5	5	5
KIDNEYS[g]	2.26	2.23	2.34	2.40
% BW	0.67	0.63	0.66	0.69
N	5	5	5	5
ADRENALS[g]	0.074	0.081	0.081	0.088
% BW	0.022	0.023	0.023	0.025
N	5	5	5	5
SPLEEN[g]	0.69	0.72	0.76	0.68
% BW	0.21	0.21	0.22	0.20
N	5	5	5	5
TESTES[g]	3.63	3.69	3.76	3.83
% BW	1.06	1.02	1.07	1.08
N	10	10	10	10
EPIDIDYMIDES[g]	1.225	1.231	1.240	1.275
% BW	0.358	0.342	0.352	0.359
N	10	10	10	10

*/**: Dunnett-test based on pooled variance sig. at 5% or 1% level.

Table 4: Histopathology

Dose group	1	2	3	4	1	2	3	4
Sex	Males				Females
Stomach No. examined	5	5	5	5	5	5	5	5
epithelial hyperplasia	–	–	–	4	–	–	–	4
grade 1	–	–	–	1	–	–	–	1
grade 2	–	–	–	3	–	–	–	3
hyperkeratosis	–	–	–	3	–	–	–	1
grade 1	–	–	–	3	–	–	–	–
grade 2	–	–	–	–	–	–	–	1
mononuclear infiltrate	–	–	–	1	–	–	1	2
grade 1	–	–	–	1	–	–	1	2
inflammation	–	–	–	2	–	–	–	3
grade 1	–	–	–	2	–	–	–	3

Conclusions:

No treatment-related effects on reproduction were evident.
The NOEL for reproductive toxicity was considered to be 100 mg/kg bw/d.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

88.3 mg/kg bw/day

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Data gaps for the endpoint toxicity to reproduction (screening study) were identified for 3-MPA, BuMP, and EHMP.
These data gaps can in part be filled by read-across. The reproductive/developmental NOAELs for 3-MPA, BuMP, and EHMP were calculated from the NOAEL obtained for MMP by correcting for molecular weight differences.

These predictions do not take into consideration potential differences in bioavailability. As shown for acute toxicity, the prediction was rather conservative and in general overestimated toxicity when compared to experimental data.

As demonstrated for acute toxicity, the alcohol does not contribute to a large extent to the overall toxicity of the substances. The main driver for toxicity of the substances within this category is the MPA moity with the free SH group. This is also hypothesised for toxicity on reproduction. Not for all alcohols, data on reproductive toxicity were identified in the public literature. However, based on these data and the data assessed in the Oxo Alcohols C9 to C13 Category (OECD, 2006) no hazard for toxicity to reproduction was identified for linear of branched alcohols. “In the 14-day repeat dose studies of isononanol, isodecanol and isotridecanol, no changes in testicular weight were observed. These data support the conclusion that members of the Oxo Alcohols C9 to C13 category are not selective reproductive toxicants.” (OECD, 2006).
Overall, neither 3-MPA, nor the alcohols require classification for toxicity to reproduction based on the available data.
Based on the considerations above, the reproduction toxicity data generated with MMP will be used to fill the data gaps identified for 3-MPA and BuMP.

A Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test according to OECD TG 422 will be additionally conducted with EHMP to add another anchor point to the category and thereby improve the robustness of the category and to further support the hypothesis, that the presence of branchings in the alcohol moiety does not alter the toxicological properties to a relevant extent.

Effects on developmental toxicity

Description of key information

No effects on  pre-natal development were noted in a screening study with the methyl ester of MPA, MMP, according to OECD 422. A study according to OECD 414 is proposed to fill the data gap for 3-MPA.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available (further information necessary)

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

No prenatal developmental toxicity studies are available for the category. A data gap was identified for 3-MPA. Testing will be proposed accordingly. Since 3-MPA is an acid, this substance might lead to problems when orally administered over a longer period of time. Therefore, testing (according to OECD TG 414) will be proposed for an alternative substance. Currently, research is ongoing to find a structurally similar substance without the acidic properties of 3-MPA. If no alternative can be identified, testing will be proposed with neutralized 3-MPA, e.g. sodium mercaptopropionate.