3-methoxybutyl acetate

Carcinogenicity

Description of key information

Limited data are available on 3-methoxybutyl acetate.  However, data from repeat dose studies are available in a range of species and by oral and inhalation routes of exposure for putative metabolites and structurally related chemicals. There is no indication of any adverse effects from these studies, which cover a range of species with some studies extending out to two years exposure, which would indicate a likely carcinogenic effect of 3-methoxybutyl acetate on repeated exposure.
 
This observation is consistent with an assessment of the genotoxicity of 3-methoxybutyl acetate, which concludes that 3-methoxybutyl acetate is unlikely to show any significant genotoxic activity.
 
It is considered that there are sufficient data to make an informed assessment of the likely carcinogenic activity anticipated for 3-methoxybutyl acetate without the conduct of animal studies on the material itself. It is considered that 3-methoxybutyl acetate is unlikely to show a carcinogenic effect on repeated exposure.
 

Justification for classification or non-classification

According to criteria in Regulation (EC) No.1272/2008, the substance is not classified for carcinogenicity. The weight of evidence indicates that 3 -methoxybutyl acetate is unlikely to show a carcinogenic effect on repeated exposure.  

Additional information

Introduction

There are no lifetime animal studies available on 3-methoxybutyl acetate in order to directly investigate for possible carcinogenic activity. However, there is sufficient information available to make a satisfactory assessment of the likely carcinogenic potential of the material. 

Non-testing information relevant for carcinogenicity

Metabolism

From metabolic considerations (CSR Section 5.1), exposure of mammals to 3-methoxybutyl acetate) is likely to lead to its rapid and extensive hydrolysis to 3-methoxybutan-1 -ol and the natural product acetate. The toxicity of the acetate produced is unlikely to be significant due to its incorporation into high-turnover natural processes, such as the citric acid cycle (EU DAR, 2008), and hence the systemic exposure and therefore the toxicity of administered 3-methoxybutan-1-ol and 3 -methoxybutyl acetate will be very similar. 

Systemic 3-methoxybutan-1-ol may be either excreted intact or as a sulphate or glucuronide conjugate or may undergo further metabolism.  Two competing metabolic pathways have been reported for closely related compounds including 2-methoxyethanol and 2 -methoxypropanol (Miller et al., 1984; Jenkins-Sumner et al., 1995; Carney et al., 2003); these involve either initial oxidation or O-demethylation reactions.

Oxidation of 3-methoxybutan-1-ol would produce 3-methoxy butanoic acid. Any 3-methoxy butanoic acid formed would be excreted, probably as the glucuronide conjugate.

O-demethylation would give butane-1,3-diol followed by oxidation to 3-hydroxy-butanoic acid. 3-hydroxy-butanoic acid produced by this route would subsequently enter and be removed by the high turnover pathways of primary metabolism.

SAR

3-Methoxybutyl acetate is a simple alkyl structure containing no structural features or chemical groups that alert to likely genotoxic activity when examined with established structure-activity (SAR) considerations (Tennant and Ashby 1981). The chemical would therefore not be expected to show genotoxic activity in vitro or in vivo, and therefore would also not be expected to show carcinogenic activity due to a genotoxic mechanism. 

The metabolism of 3 -methoxybutyl acetate is expected to be fairly simple (CSR Section 5.1). None of the potential metabolites considered likely to be formed carry alerts for possible genotoxic (and hence likely carcinogenic) activity when considered as above.

3-Methoxybutyl acetate is therefore a simple aliphatic chemical, which, when evaluated using accepted structure activity relationship considerations, has no alerts for genotoxicity or subsequent carcinogenic activity. 

Read-across

In the absence of significant data on 3-methoxybutyl acetate itself, a weight of evidence approach is proposed to assess for carcinogenicity. After consideration of putative metabolism and kinetics, the case for which is presented in more detail in CSR Section 5.1, this summary discusses repeat-dose toxicity data for 3-methoxybutyl acetate and for candidate read-across substances, followed by an overall weight of evidence assessment in respect of potential carcinogenic activity. For 3-methoxybutyl acetate, the candidate read-across substances for repeat-dose toxicity are 3-methoxybutan-1-ol, acetate, butane-1,3-diol, 3-methyl-3-methoxy-1-butanol, n-butyl acetate and n-butanol. These are either proposed metabolites or relevant closely related chemical structures.

Testing data relevant for carcinogenicity  

In vitro data

3-Methoxybutyl acetate has been examined for mutagenicity in vitro using the endpoint of gene mutation in bacteria (the Salmonella mutation assay). Its putative primary metabolite, 3-methoxybutan-1-ol, has also been tested in bacteria (the salmonella mutation assay) and in mammalian cells (L5178Y mouse lymphoma cells). Both substances have shown negative results for mutagenicity in vitro. These data support the above conclusion that 3-methoxybutyl acetate is not mutagenic in vitro. 

The data from 3-methoxybutyl acetate have been considered together with the data from relevant structural analogues, and a conclusion drawn based on a weight of evidence that 3 -methoxybutyl acetate does not have any significant genotoxic activity. This is based on data from in vitro gene mutation and cytogenetic assays (including both chromosomal damage and numerical changes) and also data from in vivo cytogenetic assays in both somatic and germ cells (CSR Section 5.7.3 : Summary and discussion of mutagenicity). 

Animal data

3 -Methoxybutyl acetate

An oral gavage OECD 414 embryotoxicity study in which 20 female Wistar rats received daily doses of 3 -methoxybutyl acetate from day 7 to day 16 of pregnancy has reported (Hoechst, 1997; see CSR Section 5.9) that there was no evidence of either maternal or embryo toxicity at the limit dose of 1000 mg/kg (CSR Section 5.9).

Inhalation exposure of groups of 5 rats and 5 guinea pigs, 2 dogs and 2 cats to 1790 ppm (10704 mg/m3) (Hoeschst AG, 1964a) has also been reported for 3-methoxybutyl acetate. Exposure was maintained for 2 hr/day, 5 days/week, for 4 weeks to this near saturated concentration of 3 -methoxybutyl acetate. Dogs and cats were reported to have a small amount of salivation and small degree of irritation of the mucous membrane of the eye at the time of inhalation but between exposures were normal. There were no other adverse clinical observations, clinical chemistry, bodyweight, gross pathological or histopathological changes (CSR Section 5.6).

3 -Methoxybutan-1-ol

Early studies investigating inhalation exposure of groups of 5 rats and 5 guinea pigs, 2 dogs and 2 cats to 1300 and 2430 ppm (5538 and 10351 mg/m3) has been reported for 3-methoxybutan-1-ol (Hoechst AG, 1964b). Exposure was maintained for 2 hr/day, 5 days/week, for 4 weeks to these near saturated concentrations of 3-methoxybutan-1-ol. There were no adverse clinical observations, clinical chemistry, bodyweight, gross pathological or histopathological changes (CSR Section 5.6).

Acetate - The toxicity of the acetate produced is unlikely to be significant due to its incorporation into high-turnover natural processes, such as the citric acid cycle (EU DAR, 2008; Smith et. al., 2007).

n-Butyl acetate and n-butanol

A recent review of n-butanol (ECETOC, 2003) considered a well conducted and reported repeat-dose inhalation study available for n-butyl acetate (David et al 2001) where the substance was administered at dose levels of 500, 1500 and 3000 ppm for 6 hours per day, 5 days per week for 13 weeks to male and female rats. The NOEL was reported as 500 ppm. The effects reported at one or both higher dose levels (1500, 3000 ppm) were transient signs of sedation, reduction in both food intake and body weight, organ weight reductions (liver, kidney, spleen, testes and adrenal gland) and increased lung weight. On histopathological examination, local effects, specific to n-butyl acetate, included degeneration of olfactory epithelium (1500 and 3000 ppm), irritation in the glandular stomach, and necrosis in the non-glandular stomach in female rats (3000 ppm). No effects were observed in the lungs on histopathological examination.

3-methyl-3-methoxy-1-butanol

A well-conducted repeat-dose toxicity study according to a Guideline for the 28 days repeat dose toxicity test in mammalian species (Japan) and done to GLP was reported (RIAS, 2003). Crj:CD(SD)IGS rats (5 animals/sex/dose) were given 3-methyl-3-methoxybutan-1-ol by gavage at doses of 0, 15, 60, 250 or 1000 mg/kg bw/day. The administration period was 28 days, and a 14 day recovery period after administration was also incorporated, with sacrifices on day 29 (end of the administration period) and day 43 (end of the recovery period). Endpoints monitored included observation of general condition, bodyweight gain, food consumption, urinalysis, haematology, and blood biochemistry. Histopathological examinations of the control and highest dose groups of male and female rats were undertaken. No deaths were found in any group and no changes in general condition, body weight gain, food consumption, haematological findings, necropsy findings and histopathological findings were reported. Decreases in blood chloride in males and females at 1000 mg/kg bw/day and increases in albumin/globulin (A/G) ratio and inorganic phosphorus in males at 1000 mg/kg bw/day were reported, however, no such differences remained after the recovery period. There was an increase in the relative kidney weight in males at 250 mg/kg bw/day (11%) and 1000 mg/kg bw/day (15%) and in females at 1000 mg/kg bw/day (16%). In addition an increase in relative weight of the liver in males (10%) and females (13%) at 1000 mg/kg bw/day was reported. However by the end of the recovery period most changes had resolved - only the male liver weight increase at 1000 mg/kg bw/day (7%) had not completely resolved. Based on the increase of relative weight of the kidney in males at 250 mg/kg bw/day and higher, and increases of relative weights of the kidney and liver in females at 1000 mg/kg bw/day, the NOAELs for repeated dose toxicity were considered to be 60 mg/kg bw/day for males and 250 mg/kg bw/day for females.

Butane-1,3-diol

Butane-1,3-diol has been approved as a substance used in foodstuffs by The Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in contact with Food, (AFC,2005). There are several long-term repeat-dose studies reported for butane-1,3-diol during earlier evaluations of its potential use in synthetic diets in several species (Miller & Dymsza, 1967 (CSR Section 5.6), Scala & Paynter, 1967, Hess et al., 1981 (CSR Section 5.6).

The aim of the series of studies of Miller and Dymsza (1967) was to consider butane-1,3-diol as a synthetic energy source. Male and female rats and mice were fed butane-1,3-diol for up to 30 weeks at dietary incorporation levels of up to 30% (15,000 mg/kg bodyweight). The main effect reported in the 30-week study was an impairment of the utilisation of the diet when the substance was fed at the 30% level. However, at an incorporation level of 20%, (10,000 mg/kg bodyweight) no such impairment was reported. Other clinical chemistry examinations, such as quantification of ketone-bodies in urine and serum, revealed no changes after the 30 week feeding period. Food intake and bodyweight gain are reported with reduced intake and bodyweight gain at the higher, relative to the lower dose levels. Little other information of significance with respect to toxicology of butane-1,3-diol is available from this study.

In the studies of Scala and Payntner (1967) butane-1,3-diol was incorporated into the diet of 60 male and female rats (100,000 ppm; 5,000mg/kg bodyweight) with 30 male and female rats each receiving a control diet. Animals received the test diets for 2 years. Bodyweight, food and test substance consumption and observations for potential pharmacological effects were regularly recorded. Some clinical chemistry examinations of blood and urine were recorded 6 times during the 2-year study. After one year, 10 animals from each group, and at 2 years all surviving animals were autopsied. Representative organs were weighed and sections of brain, pituitary, thyroid, lung, heart, spleen, kidney, adrenal, pancreas, stomach, small and large intestine, urinary bladder, gonads, bone and bone marrow were examined by histopathology.

Four groups of 4 male and female dogs were fed diets containing butane-1,3-diol at 0, 0.5, 1 or 3% (3% is equivalent to 30,000 ppm; 750 mg/kg bodyweight) for 2 years with an interim sacrifice following 1 year. Daily or weekly records were taken of appetite, appearance, elimination, signs of pharmacological effect, bodyweight and food and substance consumption. Clinical chemistry examinations of blood and urine were undertaken 8 times during the 2-year study. After 1 year, 2 animals from each group were sacrificed and the remainder sacrificed after 2 years. At both time points, autopsies were performed and representative organs weighed. Samples of brain, pituitary, thyroid, lung, heart, lymph nodes, liver, spleen, kidney, adrenal, pancreas, stomach, large and small intestine, gall bladder, urinary bladder, gonads, bone and bone marrow were examined by histopathology.

Although the detailed histopathology results of the study were not reported and only summary body and organ weight information was reported, the authors concluded in their report that throughout the 2-year tests in both species, the feeding of butane-1,3-diol caused no discernable toxic effects at any level of dietary incorporation up to 3% (750 mg/kg bodyweight) in dogs and 10% (5,000mg/kg bodyweight) in rats. All dose conversions are taken from AFC, 2005.

Histopathological examination of the testes, ovaries and pituitary glands revealed no treatment-related changes following 5 successive mating cycles (over 77 weeks) of the F1A generation (Hess et al., 1981).

In humans, short-term metabolic studies indicate that butane-1,3-diol can supply up to 10% of total dietary energy without toxic effects (Tobin et al, 1974; Altschule et al 1977), consistent with the data from animal studies.

Discussion

From metabolic considerations (see section on Toxicokinetics), exposure of mammals to 3-methoxybutyl acetate is likely to lead to its rapid hydrolysis to 3-methoxybutan-1-ol and the natural product acetate. The toxicity of the acetate produced is unlikely to be significant due to its incorporation into high-turnover natural processes, such as the citric acid cycle (EU DAR, 2008).

Data are available for repeat dose studies on 3-methoxybutyl acetate and relevant related chemicals as summarised below:

3 -Methoxybutyl acetate:

28 day; rabbit gavage

4 weeks; rat, guinea pig, dog, cat inhalation

3-Methoxybutan-1-ol

4 weeks; rat, guinea pig, dog, cat inhalation

n-Butyl acetate

               13 weeks; rat inhalation

3-methoxy-3-methyl-1 -butanol

               28 day; rat gavage

Butane-1,3-diol

               30 week; rat, mouse dietary

               2 year; rat dietary

               2 year; dog dietary

2 year; rat 5 -generation study

The only histopathological changes reported were from local effects in the nose and stomach in rats following 13 weeks inhalation of n-butyl acetate, with a NOEL of 500 ppm. These changes along with the other changes reported in the above studies, including some minor clinical chemistry changes and organ weight changes, are not considered to indicate a likely carcinogenic effect for 3-methoxybutyl acetate. The studies available include administration of high dose levels and for time periods extending out to 2 years. 

 

References

Ashby J and Tennant RW (1988) Chemical structure, Salmonella mutagenicity and extent of carcinogenicity as indicators of genotoxic carcinogenesis among 222 chemicals tested in rodents by the U.S. NCI/NTP. Mutat Res 204: 17-115.