4-hydroxy-2,5-dimethylfuran-2(3H)-one

Carcinogenicity

Description of key information

Carcinogenicity study (chronic) (OECD 451, GLP, K, Rel.1):

No oncogenic effects due to the substance were observed.

LOAEL = 400 mg/kg bw/day (corresponding to actual doses of 388.85 mg/kg bw/day in males and 389.28 mg/kg bw/day in females), based on reduced body weight gains in males and females at 400 mg/kg bw/day and decreased survival in males at 400 mg/kg bw/day.

NOEL = 200 mg/kg bw/day (corresponding to actual doses of 194.25 mg/kg bw/day in males and 195.90 mg/kg bw/day in females).

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

07 February 2000 to 15 January 2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

GLP study conducted according to OECD Guideline 451 without deviations.

Qualifier:

according to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes

Species:

rat

Strain:

other: Crl:CD® (SD) IGS BR

Details on species / strain selection:

The rat is an animal model commonly utilized in toxicity studies. In addition, a historical data base is available for comparative evaluation.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Kingston, New York 12484.
- Females were nulliparous and non-pregnant: Yes
- Age at study initiation: approximately 6 weeks
- Weight at study initiation: Male: 212 g (178-250 g); Female: 157 g (121-202 g); Individual weights of animals placed on test were within ±20% of the mean weight for each sex.
- Housing: Animals were doubly housed in elevated, stainless steel, wire mesh cages during the first week of the acclimation period and individually housed thereafter.
- Diet: Certified Rodent Diet, No. 5002; (Meal) (PMI Nutrition International, St. Louis, Missouri) was available without restriction. Fresh feed was presented twice per week as required.
- Water: Water (Elizabethtown Water Company, Westfield, New Jersey) was available without restriction via an automated watering system.
- Acclimation period: approximately 2 weeks

DETAILS OF FOOD AND WATER QUALITY:
There were no known contaminants in the feed and water that were expected to interfere with the results of this study.

ENVIRONMENTAL CONDITIONS
- Temperature: 20-28 °C
- Humidity: 4-85 %
- Photoperiod: 12 h dark / 12 h light

IN-LIFE DATES: 07 February 2000 to 15 January 2003

Route of administration:

oral: feed

Vehicle:

other: 0.2% ascorbic acid in propylene glycol

Details on exposure:

STOCK SOLUTION WITH TEST ITEM
- In a nitrogen-filled glovebox, an appropriate amount of test item was weighed onto a weigh boat/paper or directly into a calibrated beaker. The total final volume was achieved by adding an appropriate amount of control item solution. The mixture was stirred for at least one hour or until a clear solution was obtained. The stock solution was nitrogen-capped after each use. A new package of test item was used for each weighing interval, through January 2001 at which time larger packages were received. From January 2001 until the end of the study, partial packages of test item were retained for additional mixes and were nitrogen capped between uses.

DIET PREPARATION
- Dietary concentrations were adjusted weekly for the first 16 weeks and monthly thereafter, based on body weight and feed consumption data from the preceding week. The amount of untreated Certified Rodent Diet No. 5002 was weighed and added to appropriately labeled dose group buckets. 10% additional test item was added to the Group 4 diet in order to achieve targeted concentrations after 4 days of feed presentation. Control animals received untreated diet with the same volume of 0.2% ascorbic acid in propylene glycol that was used as the premix for the high dose group.
- Premix for Groups 1-4: Approximately 2 kg of untreated diet were placed into the bowl of a Hobart mixer. The test item solution was poured into the layer of feed in the bowl of the Hobart mixer. The test item container was rinsed with several grams of untreated diet, and this also was added to the bowl of the Hobart mixer. Approximately 2 kg of untreated diet then was added to the bowl of the Hobart mixer. Using a paddle blade, the mixer was run for approximately 15 minutes.
- General mix for Groups 1-4: Approximately half of the remaining diet was poured into a PK-Twin-shell mixer, and the mixture prepared in the Hobart mixer was added to the PK-Twin-shell. The bowl and paddle blade of the Hobart mixer were rinsed with several grams of untreated diet, and this also was added to the PK-Twin-shell. The remaining untreated diet was poured into the PK-Twin-shell, which then was run for approximately 15 minutes. Fresh diets were prepared twice weekly.

CONTROL ITEM SOLUTION
The appropriate amount of ascorbic acid was weighed onto a weigh boat/paper or directly into a calibrated beaker. A 0.2% solution was achieved by adding an appropriate volume of propylene glycol. The mixture was stirred overnight, using a stirbar and stir plate, until a clear solution was obtained. The mixture was protected from light and nitrogen-capped while stirring. The control item solution was prepared weekly and stored refrigerated, protected from light and nitrogen-capped.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Prior to initiation of the study, homogeneity of diet batches prepared using the proposed preparation procedure was demonstrated by taking 3 top, 3 middle and 3 bottom samples (9 samples per batch) from diet batches of concentrations that bracket the expected concentrations for the study. Stability (4 days) under storage conditions used in the study was determined in a previous 90-day range-finding study in rats (HLS Study No. 99-2609). Dietary confirmation analyses were performed in duplicate for the first 4 weeks and every two months thereafter.
Analyses were performed by the Testing Facility. The analytical procedure was based on a GC method validated in HLS Study No. 99-2609.
Fresh concurrent fortified control samples were run with each set of analyses at the highest and lowest concentrations being tested. At least one standard solution was run at the beginning and end of each set of samples to ensure that the standard curve was valid.

Duration of treatment / exposure:

24 months

Frequency of treatment:

Each animal received the appropriate amount of the test item, ad libitum, 7 days per week, for 24 months.

Dose / conc.:

0 mg/kg bw/day (actual dose received)

Remarks:

Group 1 (control)

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

Group 2

Dose / conc.:

200 mg/kg bw/day (nominal)

Remarks:

Group 3

Dose / conc.:

400 mg/kg bw/day (nominal)

Remarks:

Group 4

No. of animals per sex per dose:

60

Control animals:

other: Control animals received untreated diet, and the same volume of 0.2% ascorbic acid in propylene glycol that was used as the premix for the high dose group.

Details on study design:

- Dose selection rationale: Doses were selected by the Sponsor based on a 3-month dietary range-finding study in rats (HLS Study No. 99-2609).
- Rationale for animal assignment: More animals than required for the study were purchased and acclimated. Animals considered unsuitable for the study on the basis of pretest physical examinations or outlying body weight data were eliminated prior to random selection for group assignment. Animals considered suitable for study were distributed into 4 groups of 60 animals per sex by a computerized random sort program so that body weight means for each group were comparable.

Positive control:

Not applicable

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Observations were made once per day concurrently with one of the viability checks, for any signs of poor health or toxic or pharmacologic effects (e.g., abnormalities in general condition, appearance, activity, behavior, respiration, etc.).
Animals were observed in their cages twice daily for mortality and signs of severe toxic or pharmacologic effects. Animals in extremely poor health or in a possible moribund condition were identified for further monitoring and possible euthanasia.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Each animal was removed from its cage and examined twice pretest and once weekly during the study period. Examinations included observations of general condition, skin and fur, eyes, nose, oral cavity, abdomen and external genitalia, occurrence of secretions and excretions, and autonomic activity (e.g., lacrimation, piloerection, pupil size, unusual respiratory pattern). Changes in gait, posture and response to handling as well as the presence of clonic or tonic movements, stereotypy (e.g., excessive grooming, repetitive circling) or bizarre behavior (e.g., self-mutilation, walking backward) was recorded.

BODY WEIGHT: Yes
- Time schedule for examinations: Animals were removed from their cages and weighed twice pretest, twice weekly for the first 16 weeks, and twice monthly thereafter. Terminal, fasted body weights were obtained just prior to necropsy.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Feed was available without restriction 7 days/week. Animals were presented with full feeders of a known weight twice per week for the first 16 weeks and once per month thereafter (includes weight of feed, jar and lid). After 3 or 4 days, feeders were reweighed and the resulting weight was subtracted from the full feeder weight to obtain the grams consumed per animal over the 3 or 4-day period. Feed consumption was measured for all animals twice during the week prior to treatment initiation, twice weekly for the first 16 weeks and once monthly thereafter. Measurements were obtained over a 3-day and a 4-day interval each week.
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
Calculation: grams of feed consumed/kilogram of body weight/day (g/kg bw/day) = grams of feed consumed/body weight (kg)*/3 or 4 days
* An average of the current and previous weight was used.
TEST ITEM INTAKE
Calculated from feed consumption data and based on nominal dietary concentrations.
Calculation: milligrams of test item consumed/kilogram of body weight/day (mg/kg bw/day) = feed consumed (g/kg bw/day) x dietary concentration (mg test item/g diet)

WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: All surviving animals at Months 12 and 18, and at study termination.
- Anaesthetic used for blood collection: Yes; Blood obtained via the orbital sinus (retrobulbar venous plexus) under light CO2/O2 anesthesia.
- For the terminal interval, blood samples that were redrawn due to clotting were collected from the abdominal aorta during the necropsy of the animal.
- Animals fasted: Yes; Animals were fasted overnight prior to each blood collection interval.
- Parameters:
Blood for hematology studies was collected (approximately 0.5 mL) into tubes containing EDTA anticoagulant. Blood samples were analyzed as follows: ADVIA 120 HematologyAnalyzer, Bayer Corporation
Hemoglobin concentration, Hematocrit, Erythrocyte count, Platelet count, Mean corpuscular volume, Mean corpuscular hemoglobin, Mean corpuscular hemoglobin concentration, Total leukocyte count, Reticulocyte count, Differential leukocyte count, Erythrocyte and platelet morphology (Henry, 1991)
Coagulation parameters: Prothrombin time and Activated partial thromboplastin time

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

NECROPSY INFORMATION
Necropsy was performed on all surviving animals after 24 months of treatment. Animals were fasted overnight prior to necropsy. A necropsy schedule was established to ensure that approximately equal numbers of males and females were examined on each day of necropsy and that examination of animals of both sexes were performed at similar times of the day throughout the necropsy period.
Method of Euthanasia: Exsanguination following carbon dioxide inhalation.

GROSS PATHOLOGY: Yes; Complete macroscopic examinations were performed on all animals. The macroscopic examination included examination of the external surface and all orifices; the external surfaces of the brain and spinal cord; the organs and tissues of the cranial, thoracic, abdominal and pelvic cavities and neck; and the remainder of the carcass for the presence of macroscopic morphologic abnormalities. Animals who died unscheduled deaths were similarly examined as soon as it was practically possible.

ORGAN WEIGHTS: Organs indicated in Table 7.7/1 were weighed for all animals at the scheduled sacrifice interval. Prior to weighing, the organs were carefully dissected and properly trimmed to remove adipose and other contiguous tissues in a uniform manner. Organs were weighed as soon as possible after dissection in order to avoid drying. Paired organs were weighed together.

HISTOPATHOLOGY: Yes; The tissues listed in Table 7.7/1 were obtained at the scheduled sacrifice interval and preserved for all animals. In addition, slides of the indicated tissues were prepared and examined microscopically for all animals in the control and high-dose groups, and for animals in the low- and mid-dose groups that died or were sacrificed prior to study termination. Any abnormalities not noted during macroscopic examinations that were seen during histology processing were recorded.
Preservatives: All tissues - 10% neutral buffered formalin; Eyes were placed in glutaraldehyde/paraformaldehyde initially and then retained in 10% formalin. Testes and epididymides were placed in Bouin's solution. Lungs and urinary bladder were infused with formalin prior to their immersion into a larger volume of the same fixative.
Smear preparations of the marrow from the rib were air dried, fixed in absolute methanol, and archived without examination.
Processing: After fixation, the tissues and organs from all animals were routinely processed, embedded in paraffin, cut at a microtome setting of 4-7 microns, mounted on glass slides, stained with hematoxylin and eosin and examined by light microscopy. The bones were decalcified in Decalcifier.

Other examinations:

None

Statistics:

See "Any other information on materials and methods incl. tables"

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

The observations recorded during the weekly physical observations are common findings in laboratory rats and/or they occurred sporadically, and were not related to dietary administration of test item.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Survival rates of the test item-treated groups were in general comparable to or greater than control survival rates with the exception of males treated with the highest dose (400 mg/kg bw/day). Pituitary adenomas of the pars distalis accompanied by compression of the hypothalmic area within the brain may have contributed to the decreased survival rate in this group late in the study.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

- Mean body weights and body weight gains of males and females administered 400 mg/kg bw/day were decreased relative to control weights after 24 months of treatment. After 24 months of treatment, body weight gains, were decreased by approximately 12 and 24%, respectively for males and females administered 400 mg/kg bw/day.
- Mean body weights and body weight gains of all other test item-treated groups were considered comparable to control values during the study.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

- Feed consumption values of males and females administered test item were considered comparable to or slightly greater than control values.
- Mean test item intake values were 97.27, 194.25 and 388.85 mg/kg bw/day (males) & 97.90, 195.90 and 389.28 mg/kg bw/day (males)corresponding to 100, 200 and 400 mg/kg bw/day, respectively.

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

- No test item related changes were seen in the hematological and coagulation parameters examined after 12, 18 and 24 months of treatment.
- Statistically significant differences that occurred were considered due to normal biological variability and unrelated to test item administration.

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

- Organ weight data was considered comparable between the control and test item-treated groups at termination of the study.
- Statistically significant differences noted in the organ weight data were attributed to normal biologic variability and differences in body weight between the control and high-dose group.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

- At the end of the study, overall, there were no test item-related macroscopic findings; the incidental findings occurred with comparable incidence and severity in the control and test item treated groups or they occurred sporadically. The incidence of discoloration of the lungs in females at 400 mg/kg bw/day was slightly greater than in the comparable controls. These were primarily small, scattered red and/or tan foci. Microscopically the red foci were small agonal hemorrhages; the tan foci were small focal collections of alveolar macrophages normally present in the lungs. These pulmonary discolorations also were not considered to be test item related.
- In animals dying during the course of the study, the number of pituitary masses was greater in test item-treated males than in controls with the highest incidence at 400 mg/kg bw/day but differences were not statistically significant from controls. There was no similar effect in females. This may have contributed to the decreased survival in the high-dose male group.

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

- At the end of the study, overall, there were no test item-related non-neoplastic findings. The findings occurred with comparable incidence and severity in the control and test item-treated groups or they occurred sporadically. These incidental findings have been seen in untreated control rats of this strain and age used in similar studies conducted in this facility.
- A number of tissues and organs (e.g. lungs, liver and kidneys) from the decedents of all groups, including the controls, had vascular congestion. In a few instances, the incidence in the test item treated groups was slightly greater than in the controls. However, this is commonly seen in rats that are not exsanguinated (found dead or accidental deaths) or incompletely exsanguinated (sacrificed in extremis) prior to postmortem examination. This finding was not related to the dietary administration of test item.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

- At the end of the study, overall there were no test item-related neoplastic findings. The total number of primary neoplasms and the total number of animals affected were comparable for both males and females at 0 and 400 mg/kg bw/day. Individual neoplasms occurred with comparable incidence in the control and test item-treated groups or they occurred sporadically. These incidental neoplasms have been seen in untreated control rats of this strain and age used in similar studies conducted in this facility.
- In rats dying prior to the terminal necropsy, the incidence of adenoma of the pars distalis of the pituitary, was greater in the test item-treated males than controls with the highest incidence at 400 mg/kg bw/day, but differences from controls were not statistically significant by Fischer's exact test (p< 0.05%). The increased incidence of adenomas in treated males was proportional to the increased mortality observed in these groups when compared to control male mortality. The incidence in females was considered comparable between control and test item-treated groups. Adenoma of the pars distalis with subsequent compression of the hypothalmic area of the brain was considered to have contributed to the cause of death in a number of these affected rats.
- Adenomas of the pars distalis of the pituitary gland are a common finding in aging and aged rats. They usually begin to appear between 13 and 24 months (Stefaneu and Kovacs, 1994). In this study; 1) all the decedent males and almost all of the decedent females with adenomas of the pars distalis died late in the study (approximately 18 months or later); 2) the incidence of this finding in the high dose males (53%) was well within historical control data ranges for the testing facility as well as within the maximum incidence rates of Charles River Laboratories Sprague-Dawley male historical control data (Giknas and Clifford, 2001) and was within reported ranges in the literature for this age and strain of rat (McComb, et al, 1984); 3) results of Peto analysis of pituitary (pars ditalis) tumors, which examines the tumor rates and time to tumor formation did not reveal any statistically significant results between control and high dose males and females. Therefore, these adenomas were considered a common spontaneous tumor and unrelated to test item administration.

Other effects:

no effects observed

Key result

Dose descriptor:

NOEL

Effect level:

200 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

gross pathology

haematology

histopathology: neoplastic

histopathology: non-neoplastic

mortality

organ weights and organ / body weight ratios

Key result

Critical effects observed:

no

Analytical chemistry:

Analysis of preliminary mixes confirmed that the preparation procedure used for this study produced homogeneous mixtures and that the test item was stable in the diet, under storage conditions used in this study, for at least 4 days. Analyses conducted during the treatment period confirmed that diets of appropriate concentrations were administered. Mean analytical concentrations, expressed as percent of nominal (desired) concentrations were as follows:

 

Group	Nominal concentration (mg/kg bw/day)	Analytical concentration (% of nominal)
2	100	98.5
3	200	96.7
4	400	103.0

 

Conclusions:

Under the test conditions, no oncogenic effects were attributed to dietary administration of test item to rats for 24 months. The LOAEL was 400 mg/kg bw/day (corresponding to actual doses of 388.85 mg/kg bw/day in males and 389.28 mg/kg bw/day in females) and the NOEL was 200 mg/kg bw/day(corresponding to actual doses of 194.25 mg/kg bw/day in males and 195.90 mg/kg bw/day in females), based on reduced body weight gains in males and females at 400 mg/kg bw/day and decreased survival in males at 400 mg/kg bw/day.

Executive summary:

In a carcinogenicity study conducted according to the OECD Guideline 451 and in compliance with GLP, test item was administered orally, via dietary admixture, to Sprague-Dawley CD^® rats (60/sex/group) at dose levels of 100, 200 and 400 mg/kg bw/day for 24 months. Control animals (60/sex) received untreated standard laboratory diet. Examinations during the study included: mortality, clinical signs, body weight change, food consumption, hematology, macroscopic examination and histopathology. Analyses conducted during the treatment period confirmed that diets of the appropriate concentrations were administered. Mean test item actual intake values were 97.27, 194.25 and 388.85 mg/kg bw/day (males) & 97.90, 195.90 and 389.28 mg/kg bw/day (males) corresponding to 100, 200 and 400 mg/kg bw/day, respectively.

 

The observations recorded during the weekly physical observations are common findings in laboratory rats and/or they occurred sporadically, and were not related to dietary administration of test item.

 

Mean body weights and body weight gains of males and females at 400 mg/kg bw/day were decreased relative to control weights after 24 months of treatment. Feed consumption values of males and females administered test item were considered comparable to or slightly greater than control values.

 

No test item related changes were seen in the hematological and coagulation parameters examined after 12, 18 and 24 months of treatment. Organ weight data was considered comparable between the control and test item-treated groups at termination of the study.

 

Mean survival rate of males at 400 mg/kg bw/day was approximately 20% lower than the control male survival rate after 24 months of treatment. This may be due in part to an increased incidence of adenomas of the pars distalis of the pituitary with subsequent compression of the hypothalmic region within the brain in males dying prior to the end of the study. Pituitary adenoma is considered a common finding in aging and aged rats and usually appears between 13 and 24 months. In this study, 1) all the decedent males and almost all of the decedent females with adenomas of the pars distalis died late in the study (approximately 18 months or later), 2) the incidence of this finding was well within historical control data ranges as well as within reported ranges in the literature for this age and strain of rat and 3) results of Peto analysis of pituitary (pars distalis) tumors did not reveal any statistically significant results between control and test item-treated males and females. Therefore, these adenomas were considered a common spontaneous tumor and unrelated to test item administration. At the end of the study, overall there were no macroscopic or microscopic test item-related findings.

 

In conclusion, treatment with test item for 24 months resulted in reduced body weight gains in males and females at 400 mg/kg bw/day and decreased survival in males at 400 mg/kg bw/day. No oncogenic effects were attributed to dietary administration of test item. Therefore, under conditions of this study, following dietary administration of test item to Sprague-Dawley rats, the LOAEL was 400 mg/kg bw/day (corresponding to actual doses of 388.85 mg/kg bw/day in males and 389.28 mg/kg bw/day in females) and the NOEL was 200 mg/kg bw/day(corresponding to actual doses of 194.25 mg/kg bw/day in males and 195.90 mg/kg bw/day in females).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LOAEL

388.85 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Klimisch reliability grade 1, GLP study.

Mode of Action Analysis / Human Relevance Framework

The substance has been identified as a somatic cell clastogen in mammlian in vivo studies, but as negative in reliable mammalian in vivo germ-cell assays. In vitro and in vivo assays have demonstrated clear evidence for a threshold oxidative mode of action as a cause of the positive results observed in some genotoxicity assays. Consequently, the positive genotoxicity results have no relevance to human exposure.

Justification for classification or non-classification

Harmonized classification:

The test material has no harmonized classification for human health according to the Regulation (EC) No. 1272/2008.

Self-classification:

Based on the available data, no additional classification is proposed regarding carcinogenicity according to the Regulation (EC) No. 1272/2008 (CLP).

The ECHA Guidance on CLP, Version 5, July 2017, section 3.6.2.4 includes the statement “As mentioned throughout, classification as a carcinogen is based on consideration of the strength of evidence with additional considerations (weight of evidence) being taken into account as appropriate. It is recognised that, in most cases, expert judgment is necessary to determine the classification category.”For this substance, there is a good quality carcinogenicity study in rats that provided a negative result and therefore it may be concluded not necessary to classify as a carcinogen. There is provision to use genotoxicity data to classify as a carcinogen but in this case, as a weight of evidence argument may be used against classification as a germ-cell mutagen, this argument is also be used as an additional against classification as a carcinogen.

The conclusion is "no classification for carcinogenicity."

Additional information

In a carcinogenicity study conducted according to the OECD Guideline 451 and in compliance with GLP, test item was administered orally, via dietary admixture, to Sprague-Dawley CD^®rats (60/sex/group) at dose levels of 100, 200 and 400 mg/kg bw/day for 24 months. Control animals (60/sex) received untreated standard laboratory diet.Examinations during the study included: mortality, clinical signs, body weight change, food consumption, hematology, macroscopic examination and histopathology. Analyses conducted during the treatment period confirmed that diets of the appropriate concentrations were administered. Mean test item intake values were 97.27, 194.25 and 388.85 mg/kg bw/day (males) & 97.90, 195.90 and 389.28 mg/kg bw/day (males) corresponding to 100, 200 and 400 mg/kg bw/day, respectively.

 

The observations recorded during the weekly physical observations are common findings in laboratory rats and/or they occurred sporadically, and were not related to dietary administration of test item.

 

Mean body weights and body weight gains of males and females at 400 mg/kg bw/day were decreased relative to control weights after 24 months of treatment. Feed consumption values of males and females administered test item were considered comparable to or slightly greater than control values.

 

No test item related changes were seen in the hematological and coagulation parameters examined after 12, 18 and 24 months of treatment. Organ weight data was considered comparable between the control and test item-treated groups at termination of the study.

 

Mean survival rate of males at 400 mg/kg bw/day was approximately 20% lower than the control male survival rate after 24 months of treatment. This may be due in part to an increased incidence of adenomas of the pars distalis of the pituitary with subsequent compression of the hypothalmic region within the brain in males dying prior to the end of the study. Pituitary adenoma is considered a common finding in aging and aged rats and usually appears between 13 and 24 months. In this study, 1) all the decedent males and almost all of the decedent females with adenomas of the pars distalis died late in the study (approximately 18 months or later), 2) the incidence of this finding was well within historical control data ranges as well as within reported ranges in the literature for this age and strain of rat and 3) results of Peto analysis of pituitary (pars distalis) tumors did not reveal any statistically significant results between control and test item-treated males and females. Therefore, these adenomas were considered a common spontaneous tumor and unrelated to test item administration. At the end of the study, overall there were no macroscopic or microscopic test item-related findings.

 

In conclusion, treatment with test item for 24 months resulted in reduced body weight gains in males and females at 400 mg/kg bw/day and decreased survival in males at 400 mg/kg bw/day. No oncogenic effects were attributed to dietary administration of test item. Therefore, under conditions of this study, following dietary administration of test item to Sprague-Dawley rats,the LOAEL was 400 mg/kg bw/day (corresponding to actual doses of 388.85 mg/kg bw/day in males and 389.28 mg/kg bw/day in females) and the NOEL was 200 mg/kg bw/day(corresponding to actual doses of 194.25 mg/kg bw/day in males and 195.90 mg/kg bw/day in females).