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Key value for chemical safety assessment

Effects on fertility

Description of key information
Mesna protected against cytostatic induced reproductive toxicity in female rats (Yeh et al., 2011). Mesna did not affected reproductive organ weights, qualitative and quantitative testicular histological parameters as well as semen characteristics in New Zealand White rabbits during 10- week treatment. 
Effect on fertility: via oral route
Endpoint conclusion:
no adverse effect observed
Quality of whole database:
There are a lot of information on reproductive toxicity of mesna, a nearest analogue to the target chemical.
Additional information
RTECS data (RTECS Number KI7968000) Mesna was studied for its reproductive toxicity potential in rats and in rabbits. Rats received mesna intravenously during pre-mating period (males 9 weeks and females 2 weeks). Thereafter females were treated until day 7 after conception. Mesna at a dose level of 26880 mg/kg bw (total dose) caused effects on fertility. Preimplantation mortality was observed: numbers of implants per female and total number of implants per corpora lutea were reduced. No other maternal effects or effects on embryo or foetus are reported. Rabbits received mesna intravenously during days 6 -18 of gestation. Mesna at a dose level of 7800 mg/kg bw (total dose) caused effects on fertility. Post-implantation mortality (dead or resorbed implants per total number of implants) was reported without further details. Mesna caused no deaths of foetuses. One stunted foetus was observed. The lowest toxic dose (TDLo) of 7800 mg/kg bw (total dose) was reported.

Read-acrossbased on grouping of substances in categories (OECD QSAR Toolbox, v.3.0)

Structurally similar substances to 3-mercaptopropanesulfonic acid, sodium salt (CAS 17636-10-1) with data on reproductive toxicity have been searched with the help of the OECD QSAR Toolbox (v.3.0). The prediction was based on the experimental values of chemicals assigned into the category.The target chemical was profiled as "Thiols "Acute toxicity" by the "US EPA New Chemical Categories". Thiols in general are known to conjugate with proteins via protein thiol-disulfide interchange mechanism. They are also capable to bind covalently proteins via a SN2 reaction at a sulphur atom leading to disulfide bridges. These mechanisms of action are relevant for the investigated endpoint. Therefore, primarily a search for chemicals with the same profiling result was performed. The created category comprised of chemicals which data belong to different units (mg/kg/day, mg/kg bw/day, mg/kg nominal etc.). Hence, the first prediction has been run with chemicals with the most data points (unit/scale "mg/kg bw/day"). The second prediction has been run with unit "mg/kg bw/day (actual dose received)".

The nearest read-across chemicals contain thiol functional groups but no sulfonic groups in their structure. The sulfonic group, however, is not associated with high reactivity as it thiol group does i.e. generation of reactive oxygen species in cells, cysteine peptide depletion or interaction with DNA leading to mutations. Therefore, the category members containing thiol groups are considered to be worst case for the target substance. The chemicals containing other chemical elements in their structure and/or other organic functional groups have not been removed from the domain since they were similar with the target chemical regarding their mechanistic and endpoint specific profiling (= similar reactivity to biomolecules).

Read-across substances have NOAEL for fertility and reproductive toxicity in a similar range (15-200 mg/kg bw). The effects on reproduction observed in animals were associated with systemic toxicity (NOAEL ranged from 15 to 50 mg/kg bw). NOAEL of 80 mg/kg bw for reproductive effects was predicted for the target chemical.

In the second category, the chemicals have been grouped according to the structural similarity in order to verify that all similar chemicals on which reproductive toxicity data exist were considered. Two chemicals were identified: 2-propene-1-sulfonic acid, sodium salt (CAS 2495-39-8) and sulfamic acid, monosodium salt (CAS 13845-18-6). The chemicals do not possess thiol groups which are known to be reactive to biomolecules (proteins and DNA). In place of thiol group, allyl,- or amino group are positioned. However, comparable to the target chemical, they possess a sulfonic group in their structures. The sulfonic group, however, is not associated with high reactivity like thiol group it does i.e. generation of reactive oxygen species in cells, cysteine peptide depletion or interaction with DNA leading to mutations.

Therefore it was decided to run a prediction in order to obtain a toxicity pattern of sulfonic acid derivatives. However, the endpoint specific and the mechanistic profiling of the read-across substances deviate significantly from those of the target chemical. Therefore, the category members with only sulfonic groups can be used for read-across on a limited basis (a detailed assessment of the toxicity pattern is required). The category was not refined since it is based on structural similarity principle only and the toxicity data of the structural analogues are intended to be used for comparison with those of other categories. NOAEL of 1000 mg/kg bw was predicted for the target chemical.

Short description of key information:
In reproductive toxicity studies conducted with the nearest analogue mesna (reported in RTECS), no significant reproductive toxicity was observed. Preimplantation and post-implantation loss was observed only at very high dose levels.
In any category created by the OECD QSAR Toolbox, the read-across chemicals are not reproductive toxicants. The categories consist of chemicals similar to the target chemical mechanistic profiling results (= the same reactivity to biomolecules is expected) and similar functional groups. Based on these data, 3-mercaptopropanesulfonic acid, sodium salt is considered to be not a reproductive toxicant and does not need to be classified for this endpoint.

Justification for selection of Effect on fertility via oral route:
No study is selected because weight-of-evidence approach is used to assess reproductive toxicity of MPS.

Effects on developmental toxicity

Description of key information
The structural analogue mesna at a dose levels of 5 and 30 mg/kg bw was not teratogenic in rats (Slott and Hales, 1986). In teratogenicity studies reported in RTECS, no significant embryo- or foetotoxicity, developmental abnormalities, or effects on newborn animals were reported. Some effects were noted only at very high dose levels. In any category created by the QSAR OECD Toolbox, the read-across chemicals are not developmental toxicants. Therefore, 3-mercaptopropanesulfonic acid, sodium salt is considered to be not a developmental toxicant and does not need to be classified for this endpoint. 
Effect on developmental toxicity: via oral route
Endpoint conclusion:
no adverse effect observed
Quality of whole database:
Numerous studies on the teratogenicity potential of structurally related substance mesna are available in public databases.
Additional information

Teratogenicity data on related substances

Teratogenicity potential of mesna (CAS 19767 -45 -4)

The teratogenicity potential of mesna could be evaluated from the results of a teratogenicity study conducted with cyclophosphamide known anti-cancer drug (Slott and Hales, 1986). The study was designed to determine whether the teratogenic effects of cyclophosphamide and its metabolites could be prevented by mesna. On day 13 of gestation, pregnant Spague Dawley rats were administered mesna intravenously at one of two dose levels (5 and 30 mg/kg bw) in combination with cyclophosphamide or alone. Vehicle control group included animals treated with 0.9% NaCl. Rats were killed on day 20 of gestation and fetuses were examined for gross external malformations, fetal body weight, and skeletal defects. The administration of mesna alone had no significant effects on the incidence of malformations compared to vehicle control (2/62 malformed fetuses in 5 mg/kg bw group and 0/62 malformed fetuses in 30 mg/kg bw dose group). The administration of mesna had no significant effects on the incidence of dead or resorbed fetuses (similar to vehicle control). No effects of mesna treatments were observed on fetal body weights. No skeletal malformations were recorded for mesna treatment groups. Mesna significantly decreased a certain number of fetal malformations induced by cyclophosphamide administration confirming its protective effects against the teratogenic effects of cyclophosphamide.

Mesna was investigated for its toxicity potential in the course of studies covered interference of Mesna with antitumor agents oxazaphosphorines and cytostatics (Brock et al., 1982). A short result about embryotoxicity potential is reported in this article.

In embryotoxicity studies no evidence of adverse effects of mesna on the reproduction process was found in rats at daily oral doses of up to 2000 mg/kg from day 8 to day 15 of gestation inclusive, and in rabbits at daily oral doses of up to 1000 mg/kg from day 7 to day 17 of gestation inclusive.

RTECS data

Mesna was administered to female rats intravenously during days 7-17 of gestation and effects on newborn rats, foetotoxicity and specific developmental abnormalities were evaluated. Mesna caused no deaths of foetuses. One stunted foetus was observed. Viability index (alive at day 4/per born alive) was reduced. Body weight gain of newborn rats was also reduced. Physical and behavioural effects on newborns were reported (without details). Besides this, effects on musculoskeletal system were noted (without details). The lowest toxic doses ((TDLo) of 8800 mg/kg bw, 4400 mg/kg bw and 10400 mg/kg bw were reported. It is very likely that the total doses were reported.

Prediction of teratogenicity by the QSAR OECD Toolbox

Structurally similar substances to 3-mercaptopropanesulfonic acid, sodium salt (CAS 17636-10-1) with data on developmental toxicity have been searched with the help of the OECD QSAR Toolbox (v.3.0). The prediction was based on the experimental values of chemicals assigned into the category. The target chemical was profiled as "Thiols "Acute toxicity" by the "US EPA New Chemical Categories". Thiols in general can conjugate with proteins via a protein-thiol-disulfide-interchange-mechanism. They are also capable to bind proteins covalently via an SN2 reaction at a sulphur atom forming disulfide bridges. These properties can be relevant for the developmental toxicity endpoint. Therefore a search for chemicals with the same profiling results was performed. The created category comprised chemicals whose data belong to different units (mg/kg/day, mg/kg bw/day, mg/kg nominal etc.). The first prediction has been run with chemicals with the most data points (unit/scale: "mg/kg bw").

Two read-across substances sodium salt of thioglycolic acid (CAS 367-51-1) and mercaptosuccinic acid (No CAS available) were identified. The second prediction has been run with "mg/kg bw/day". One suitable chemical thioglicolic acid ammonium salt (CAS 5421-46-5) was identified. The read-across chemicals contain thiol and carboxyl functional groups but no sulfonic group in their structure. Carboxylic and sulfonic groups, however, are not associated with a high reactivity i.e. generation of reactive oxygen species in cells, cysteine peptide depletion or interaction with DNA leading to mutations. Therefore, two category members with thiol groups are considered to be the worst-case for the target chemical. The read-across chemicals are similar to the target chemical regarding their mechanistic and endpoint specific profiling (= similar reactivity to biomolecules). The read-across chemicals are not developmental toxicants. A NOAEL of 181 mg/kg bw and 45 mg/kg bw for developmental effects were predicted for the target chemical in the first and the second predictions, respectively.

A second category was created based on structural similarity in order to verify that all similar chemicals with developmental toxicity data were considered. Three chemicals were identified: 2-propene-1-sulfonic acid, sodium salt (CAS 2495-39-8), sulfamic acid, monosodium salt (CAS 13845-18-6) and sodium 2 -hydroxyethanesulfonate (CAS 1562-00-1). The chemicals do not possess thiol groups which are known to be reactive to biomolecules (proteins and DNA). In place of thiol group, allyl,- amino,- or hydroxyl groups are positioned. However, comparable to the target chemical, they possess a sulfonic group in their structures. Sulfonic groups, however, are not associated with a high reactivity like thiol groups, i.e. generation of reactive oxygen species in cells, cysteine peptide depletion or interaction with DNA leading to mutations.

Therefore it was decided to run a prediction in order to obtain a toxicity pattern of sulfonic acid derivatives. However, the endpoint specific and the mechanistic profiling of the read-across substances deviate significantly from those of the target chemical. Therefore, the category members with only sulfonic groups can be used for read-across on a limited basis (a detailed assessment of the toxicity pattern is required). The category was not refined since it is based on structural similarity principle only and the toxicity data of the structural analogues are intended to be used for comparison with those of other categories. The read-across chemicals are not developmental toxicants. A NOAEL of 1000 mg/kg bw was predicted for the target chemical.

Justification for selection of Effect on developmental toxicity: via oral route:
No study is selected because weight-of-evidence approach is used to assess reproductive toxicity of MPS.

Toxicity to reproduction: other studies

Additional information

The influence of mesna (CAS 19767 -45 -4) on reproductive toxicity induced by cytostatic drugs

Cisplatin induced reproductive toxicity

The influence of Mesna on the cisplatin induced reproductive toxicity was studied in rats (Yeh at el., 2011). Cisplatin, a chemotherapeutic agent, is known to cause damage to ovaries in rats and a variety of adverse effects in foetuses of rats and mice. In humans, cisplatin caused damage to ovaries as well. Therefore, the administration of mesna prior to multiple doses of cisplatin was believed to offer protection from the loss of fertility induced by cisplatin. Adult female Sprague Dawley rats were injected with saline, cisplatin alone (4.5 mg/kg bw), mesna alone (200 mg/kg bw), mesna + saline or mesna + cisplatin, and mated with males. The female rats were divided into two groups. Group 1 served as cisplatin mating group, in which effects of cisplatin on reproductive performance of females were studied and group 2 served as the mesna + cisplatin mating group in which effects of mesna on cisplatin induced reproductive toxicity were studied. Group 1 was sub-divided into two treatment sub-groups, the saline control sub-group and the cisplatin treated sub-group. Group 2 was divided into four sub-groups, the control (saline) sub-group, the mesna + saline control subgroup, mesna + cisplatin treatment sub-group, and cisplatin only treatment sub-group. The animals were given two i.p. injections one week apart, (mesna 30 minute pretreatment with saline or cisplatin) followed by mating up to ten days after treatment. The animals were euthanized on gestational day 17 and the number corpora lutea, implantation and resorptions sites, viable and non-viable fetuses, fetal weights, and the level of progesterone per corpus luteum were determined.

In the cisplatin mating group (group 1), cisplatin caused a decrease in the percentage of females that mated to males but there was no change in the fecundity index in the animals treated with cisplatin alone and in the saline control animals. Cisplatin treated animals had an increase in the number of resorption sites and the presence of a non-viable fetus as well as an increase in the percentage of pre-implantation and post-implantation losses in comparison to the control animals. The total number of resorptions per pregnant animal was increased. There was a significant decrease in the number of viable fetuses but no significant differences were found in the fetal weight between the saline controls and the cisplatin treated sub-group. The total number of corpora lutea was similar in animals of both groups. The progesterone level per CL between control and cisplatin sub-groups were not statistically different. This suggests that the fetal loss was not directly associated with corpus luteum progesterone production.

The administration of mesna + saline did not effect any of the reproductive outcomes compared to the saline control. In the mesna + cisplatin mating group, there was a non-significant change in the percentage of females that mated to a male. Of the females that mated with a male, there was no difference in the fecundity index for all sub-three groups. Mesna protected against the pre-implantation and post-implantation losses of the fetuses induced by cisplatin. There was a statistically significant difference in the number of resorptions seen among the control, mesna + cisplatin, and cisplatin sub-groups. Treatment with mesna leads to an increase in the total number of viable fetuses in the mesna + cisplatin compared to cisplatin. The weight of the viable fetuses was not statistically different among the three sub-groups. After mesna and cisplatin administration, there was no difference in the total number of corpora lutea found in the saline, mesna + cisplatin and cisplatin sub-groups. The measurement of progesterone revealed that there was no difference in the progesterone level per corpus luteum in any of the three sub-groups.

In conclusion, prior exposure to cisplatin caused significant adverse effects on fertility as evidenced by the decreased implantation due to increased fetal loss. The administration of mesna appeared to temper cisplatin damage by lessening the cisplatin effects on fetal resorption.

Ifosfamide induced reproductive toxicity

Ifosfamide, a chemotherapeutic agent with a broad spectrum of antineoplastic activity, is concurrently administered with the uroprotectant mesna to avoid the urotoxic effect. This study was undertaken to investigate possible effects of ifosfamide-mesna treatment on the testes and semen characteristics in rabbits. Sexually mature New Zealand White male rabbits received intravenously 10 weekly treatments of ifosfamide + mesna (groups A, B and C received 30, 45 or 60 mg/kg of body weight ifosfamide + 6, 9 or 12 mg/kg of body weight mesna, respectively, followed by a second equal dose of mesna 4 h later); groups MA, MB and MC received mesna alone at the corresponding doses; and group S received normal saline. Reproductive organ weights as well as various qualitative and quantitative parameters of testis histology (minor diameter of seminiferous tubules, the most advanced germ cell type in seminiferous tubule identified in cross sections, and the number of germ cells per stage 1 seminiferous tubule cross section) were determined on day 1 and 20 weeks after the treatment period, while semen quality (sperm count, sperm morphology and sperm progressive motility) and libido were evaluated on a weekly basis.

Changes were noted only in the ifosfamide - mesna treated animals. Reproductive organ weights were decreased on the first day after treatment. Major histopathological lesions were not found; however, quantitative histological endpoints were altered in groups A-C. Transient oligospermia and teratozoospermia were noted in groups B and C, while asthenozoospermia was observed in group C only. The time course of these sperm alterations suggested a possible bioaccumulation and residual activity of ifosfamide. Libido remained normal. The decrease in reproductive organ weights persisted in groups B and C to 20 weeks after treatment but only one quantitative histological endpoint, the number of the round spermatids per stage 1 seminiferous tubule cross section, remained decreased in group C. These results suggest that subchronic treatment with ifosfamide-mesna suppressed spermatogenesis and epididymal sperm maturation in the rabbit. Germinal epithelium recovery was not complete because although sperm characteristics returned to pretreatment values, not all histological alterations were ameliorated.

No treatment related changes in any parameter tested were noted in the mesna-alone groups. Reproductive organ weights (testes, epididymides and accessory glands) were comparable to control. No gross histopathological lesions were observed. Quantitative testicular histological examinations revealed no significant changes in the mesna groups compared to controls. Sperm characteristics remained unaffected in the mesna groups.

Justification for classification or non-classification

The nearest analogue mesna (CAS 19767-45-4) did not induce significant reproductive and developmental toxicity in rats and in rabbits at very high dose levels (4400 -10400 mg/kg bw; RTECS data) . In opposition to any toxicity, it protected against cytostatic induced reproductive toxicity and is widely used during course of anticancer therapy. The structural analogue chemicals identified by the OECD QSAR Toolbox, which possess thiol groups and therefore are believed to act in the same manner with biomolecules as the target chemical, are all not reproductive or developmental toxicants.

Based on the experimental data on reproductive and developmental toxicity studies conducted with the read-across chemicals, sodium 3 -mercaptopropanesulfonic acid is not subject to classification and labelling as reproductive or developmental toxicant according to the Regulation No 1272/2008 (CLP).