1,4-Dihydroxy-2,2,6,6-tetramethylpiperidine

Endpoint summary

Description of key information

Key Study:

28d repeated dose toxicity NOAEL = 250 mg/kg bw/d; OECD 422; Allt (2016)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

27 May 2015 - 02 November 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Study conducted in accordance with international guidelines and in accordance with GLP. All guideline validity criteria were met.

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

Max temperature (exceeded on 1 occasion) and max humidity (exceeded on 17 occasions). It was considered that these deviations had no adverse impact on the scientific purpose of the study.

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

RADIOLABELLING INFORMATION (if applicable)
- Radiochemical purity: n/a
- Specific activity: n/a
- Locations of the label: n/a
- Expiration date of radiochemical substance: n/a

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Stored over silica gel and under nitrogen at low temperature.
- Stability under test conditions: Stable
- Solubility and stability of the test substance in the solvent/vehicle: Stable for at least 16 days once formulated (in Arachis oil BP)
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: No

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: Test item formulated in Arachis oil BP
- Preliminary purification step (if any): No
- Final dilution of a dissolved solid, stock liquid or gel: Formulations prepared at 7.5, 25 and 87.5 (reduced to 62.5 at Day 9+) mg/mL
- Final preparation of a solid: No

FORM AS APPLIED IN THE TEST (if different from that of starting material): Applied as a homegenous liquid formulation.

OTHER SPECIFICS: No

Species:

rat

Strain:

Wistar

Details on species / strain selection:

Wistar Han™:RccHan™:WIST

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Laboratories U.K. Ltd., Blackthorn, Bicester, Oxon, UK
- Females (if applicable) nulliparous and non-pregnant: Yes
- Age at study initiation: ca. 12 weeks old
- Weight at study initiation: Males = 311 - 354 g and females = 177 - 227 g
- Fasting period before study: No
- Housing: Initially, all animals were housed in groups of four in solid floor polypropylene cages with stainless steel mesh lids and softwood flake bedding (Datesand Ltd., Cheshire, UK). During the pairing phase, animals were transferred to polypropylene grid floor cages suspended over trays lined with absorbent paper on a one male: one female basis within each dose group. Following evidence of successful mating, the males were returned to their original cages. Mated females were housed individually during gestation and lactation in solid floor polypropylene cages with stainless steel mesh lids and softwood flakes.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 7 days

DETAILS OF FOOD AND WATER QUALITY: A pelleted diet (Rodent 2018C Teklad Global Certified Diet, Harlan Laboratories U.K. Ltd., Oxon, UK.) was used. Mains drinking water was supplied from polycarbonate bottles attached to the cage. The diet, drinking water, bedding and environmental enrichment was considered not to contain any contaminant at a level that might have affected the purpose or integrity of the study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 ºC
- Humidity (%): 50 ± 20 %
- Air changes (per hr): At least fifteen air changes per hour.
- Photoperiod (hrs dark / hrs light): 12 h:12 h (light: dark)

IN-LIFE DATES: 25 June 2015 (first day of treatment) - 08 August 2015 (final day of necropsy)

Experimental dates: 27 May 2015 - 11 July 2016

Route of administration:

oral: gavage

Details on route of administration:

The test item was administered daily by gavage using a stainless steel cannula attached to a disposable plastic syringe. Control animals were treated in an identical manner with 4 mL/kg of Arachis oil BP.

Vehicle:

arachis oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
For the purpose of this study the test item was prepared at the appropriate concentrations as a suspension in Arachis oil BP. The stability and homogeneity of the test item formulations were determined by Harlan Laboratories U.K. Ltd., Shardlow, UK, Analytical Services. Results show the formulations to be stable for at least sixteen days. Formulations were therefore prepared fortnightly and stored at approximately 4 °C in the dark, under nitrogen and over silica gel.

DIET PREPARATION
- Rate of preparation of diet (frequency): n/a
- Mixing appropriate amounts with (Type of food): n/a
- Storage temperature of food: n/a

VEHICLE
- Justification for use and choice of vehicle (if other than water): Not reported
- Concentration in vehicle: 7.5, 25, 87.5 (62.5 at Day 9+) mg/mL
- Amount of vehicle (if gavage): 4 mL/kg bw
- Lot/batch no. (if required): Not reported
- Purity: Not reported

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The formulations investigated during the study were found to comprimise of the test item in the range of 91 - 101 % and thus the required content limit of ± 10 % with reference to the nominal content was met.

Three validity criteria to demonstrate the validity of the analytical method were met; specifity, linearity (r2 value of calibration cure = 0.998) and accuracy (recoveries = ± 10 % from fortified samples).

Duration of treatment / exposure:

Up to 8 weeks

Frequency of treatment:

Daily

Dose / conc.:

30 mg/kg bw/day (nominal)

Dose / conc.:

100 mg/kg bw/day (nominal)

Dose / conc.:

350 mg/kg bw/day (nominal)

Remarks:

Due to the excessive body weight loss/reduced food consumption during the first week of treatment, and the early termination of one female on Day 9, the high dose level was reduced to 250 mg/kg bw/day from Day 9 onwards.

No. of animals per sex per dose:

12

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on resuts from a prelim test conducted at 50, 100, 250, 500 and 1000 mg/kg bw/day. The effects detected at 1000 and 500 mg/kg bw/day were sufficient to exclude these levels from consideration as high dose levels for the OECD 422 study. The effects at 250 mg/kg bw/day however were insufficient to exclude a dose level close to 250 mg/kg bw/day from further investigation.
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: n/a
- Post-exposure recovery period in satellite groups: n/a

Positive control:

No

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes.
- Time schedule: Immediately before dosing, soon after dosing, and one hour after dosing (except for females during parturition where applicable). Additionally, observations were also made four hours following dosing (not at weekends).

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Prior to the start of treatment and at weekly intervals thereafter. Functional performance tests were also performed on five selected males and females from each dose level, prior to termination, together with an assessment of sensory reactivity to various stimuli.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were recorded on Day 1 (prior to dosing) and then weekly for males until termination and weekly for females until pairing. During pairing phase females were weighed daily until mating was confirmed. Body weights were then recorded for females on Days 0, 7, 14 and 20 post coitum, and on Days 1 and 4 post partum. Body weights were also recorded at terminal kill.

FOOD CONSUMPTION : Yes
- During the pre-pairing period, weekly food consumption was recorded for each cage of adults. This was continued for males after the mating phase. For females showing evidence of mating, food consumption was recorded for the periods covering post coitum Days 0-7, 7-14 and 14-20. For females with live litters, food consumption was recorded on Days 1 and 4 post partum.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes
Food efficiency (the ratio of body weight change/dietary intake) was calculated retrospectively for males throughout the study period (with the exception of the mating phase) and for females during the pre-pairing phase. Due to offspring growth and milk production, food efficiency could not be accurately calculated during gestation and lactation.

WATER CONSUMPTION: Yes
- Time schedule for examinations: Water intake was measured daily during the pre-pairing phase of the study.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: Prior to termination (Day 42 for males and Day 4 post partum for females).
- Anaesthetic used for blood collection: No
- Animals fasted: No
- How many animals: 5 males and 5 females per test/ control group.
- Parameters checked in table 2 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Prior to termination (Day 42 for males and Day 4 post partum for females).
- Animals fasted: No
- How many animals: 5 males and 5 females per test/ control group.
- Parameters checked in table 2 were examined.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: Prior to the start of treatment and at weekly intervals thereafter, all animals were observed for signs of functional/behavioral toxicity. Functional performance tests were also performed on five selected males and females from each dose level, prior to termination
- Dose groups that were examined: All
- Battery of functions tested: sensory activity / grip strength / motor activity.

IMMUNOLOGY: No

OTHER:

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 3)

HISTOPATHOLOGY: Yes (see table 3)

Statistics:

Where considered appropriate, quantitative data was subjected to statistical analysis to detect the significance of intergroup differences from control; statistical significance was achieved at a level of p<0.05. Statistical analysis was performed on the following parameters: Grip Strength, Motor Activity, Body Weight, Body Weight Change, Food Consumption during gestation and lactation, Pre-Coital Interval, Gestation Length, Litter Size, Litter Weight, Sex Ratio, Corpora Lutea, Implantation Sites, Implantation Losses, Viability Indices, Offspring Body Weight, Offspring Body Weight Change, Offspring Surface Righting, Hematology, Blood Chemistry, Absolute Organ Weights, Body Weight-Relative Organ Weights.

Probability values (p) are presented as follows:
p<0.01 **
p<0.05 *
p>0.05 (not significant)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Animals of either sex treated with 350/250 mg/kg bw/day showed incidences of increased salivation from Day 4 until termination (males) and Day 27 (females).

The female that was killed in extremis on Day 9 also had hunched posture on Day 9.

No such effects were evident in animals of either sex treated with 100 or 30 mg/kg bw/day.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One female treated with 350 mg/kg bw/day was killed in extremis due to excessive body weight loss on Day 9. Microscopic examination of this female revealed evidence of inappetance (salivary gland inactive) and depletion in the bone marrow and lymphoid atrophy in the thymus along with metabolic changes in the liver. These are considered non-specific and an actual cause of death could not be established.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Males treated with 350 mg/kg bw/day showed a statistically significant reduction in body weight gain during the first week of treatment. Actual body weight losses were evident in four males on Day 8. Following the reduction of the high dose level on Day 9, recovery was evident in these males during the next two weeks of treatment with a statistically significant increase evident during Week 3. However body weight gain was slightly reduced again during Weeks 4 and 5. Overall body weight gain for these males was 17% lower than controls.

Females treated with 350 mg/kg bw/day showed a statistically significant reduction in body weight gain during the first week of treatment. Actual body weight losses were evident in four females on Day 8. One female was killed in extremis on Day 9 due to excessive weight loss. This female had lost 17% of her initial body weight. Following the reduction of the high dose level on Day 9, some recovery was evident in these females during the second week of treatment however three females showed an actual body weight loss. No adverse effects were detected in females treated at 350/250 mg/kg bw/day during gestation or lactation.

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day.

Females treated with 100 and 30 mg/kg bw/day showed a statistically significant increase in body weight gain during the first week of treatment. An increase in body weight gain is generally considered not to represent an adverse effect of treatment and the statistical significance attained at these dose levels is most likely due to the lower than expected control values.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Animals of either sex treated with 350 mg/kg bw/day showed a reduction in food consumption efficiency during the first week of treatment. Following the reduction of the high dose level, recovery was evident thereafter.

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day or in any treated female during gestation or lactation.

Food efficiency:

effects observed, treatment-related

Description (incidence and severity):

Animals of either sex treated with 350 mg/kg bw/day showed a reduction in food conversion efficiency during the first week of treatment. Following the reduction of the high dose level recovery was evident thereafter.

Due to offspring growth and milk production, food efficiency could not be accurately calculated during gestation and lactation.

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

effects observed, treatment-related

Description (incidence and severity):

Males treated with 350/250 mg/kg bw/day showed an increase in overall water consumption during maturation. No such effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

There were no toxicologically significant effects detected in the hematological parameters examined.

Females from all treatment groups showed a statistically significant reduction in activated partial thromboplastin time. The majority of individual values were within background control range and in the absence of a true dose related response the intergroup differences were considered not to be of toxicological importance.

Males treated with 350/250 and 100 mg/kg bw/day showed a statistically significant reduction in monocytes. Males treated with 30 mg/kg bw/day showed a statistically significant reduction in total leukocyte count and lymphocytes. All of the individual values were within background control ranges and in the absence of a true dose related response the intergroup differences were considered not to be of toxicological significance.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

There were no toxicologically significant effects detected in the blood chemical parameters examined.

Males treated with 30 mg/kg bw/day showed a statistically significant reduction in phosphorus. All of the individual values were within background control range and in the absence of a similar effect at the high dose group the intergroup difference was considered not to be of toxicological significance.

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There were no treatment-related changes in the behavioural parameters at 30, 100 or 350/250 mg/kg bw/day.

There were no treatment related changes in functional performance considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

There were no inter-group differences in sensory reactivity scores that were considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Males treated with 350/250 mg/kg bw/day showed a statistically significant increase in adrenal weight both absolute and relative to terminal body weight.

No toxicologically significant effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

Males treated with 350/250 mg/kg bw/day showed a statistically significant increase in spleen weight both absolute and relative to terminal body weight. In the absence of any associated microscopic changes in this sex the intergroup difference was considered not to be an adverse effect of treatment.

Females from all treatment groups showed a statistically significant reduction in uterus weight both absolute and relative to terminal body weight. Males treated with 100 mg/kg bw/day showed a statistically significant increase in absolute and relative thyroid weight. In the absence of a true dose related response or any associated histopathological correlates in the uterus or thyroid the intergroup differences were considered not to be of toxicological significance.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

The female that was killed in extremis had an enlarged gastro-intestinal tract at necropsy.

No toxicologically significant effects were detected in terminal kill animals of either sex treated with 350/250, 100 or 30 mg/kg bw/day.

One control female, one male and two females treated with 30 mg/kg bw/day, one female treated with 100 mg/kg bw/day and one male and two females treated with 350/250 mg/kg bw/day had reddened lungs at necropsy. One female treated with 100 mg/kg bw/day had a fluid filled left horn of the uterus. A fully formed feotus was also present in the left horn of the uterus in this female. In the absence of any histopathological correlates the intergroup differences were considered not to be of toxicological importance.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

The following treatment-related microscopic abnormalities were detected:

Adrenals: cortical hypertrophy (zona fasciculata) was present at a minimal or mild level in animals of either sex from all treatment groups.

Spleen: increased hematopoiesis was present in females treated with 350/250 mg/kg bw/day. In two of these females an increase was also present in the bone marrow. A minor increase in hematopoiesis was present in females treated with 100 mg/kg bw/day. No such effects were detected in treated males or in females treated with 30 mg/kg bw/day.

Liver: centrilobular hepatocyte hypertrophy was present in three males treated with 350/250 mg/kg bw/day. No such effects were detected in treated females or in males treated with 100 or 30 mg/kg bw/day.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

250 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Remarks on result:

other: The reduced body weight gain/food consumption was considered to be the result of the administration of the higher dose level (350 mg/kg bw/day) and once the dose level had been reduced recovery was evident.

Critical effects observed:

no

Table 4       Mean body weights (BW), body weight gains and % gains

Sex / Day		Bodyweight (g)
		Control	30 mg/kg bw/day	100 mg/kg bw/day	350/ 250 mg/kg bw/day
MALES
Day 1		336.6	329.7	331.3	332.1
Day 8		349.5 (+ 12.9)	342.3 (+ 12.7)	346.3 (+ 15.0)	335.3 (+ 3.2**)
Day 15		359.8 (+ 10.3)	350.8 (+ 8.4)	353.2 (+ 6.8)	344.9 (+ 9.7)
Day 22		365.1 (+ 5.3)	355.9 (+ 5.2)	361.3 (+ 8.2)	355.0 (+ 10.1*)
Day 29		378.2 (+ 13.1)	369.9 (+14.0)	374.6 (+13.3)	364.8 (+ 9.8)
Day 36		389.5 (+ 11.3)	380.8 (+ 10.8)	385.5 (+ 10.9)	372.8 (+ 8.1)
Day 43		395.5 (+ 6.0)	383.2 (+ 2.4)	390.2 (+ 4.7)	380.8 (+ 8.0)
Overall BW gain Day 1 – Day 43 (% gain/ loss)		58.9 (+ 17.5 %)	53.5 (+ 16.2 %)	58.8 (+ 17.7 %)	48.8 (+ 14.7 %)
FEMALES
Day 1		208.2	205.4	201.8	198.8
Day 8		207.6 (- 0.6)	212.9 (+ 7.5**)	208.6 (+ 6.8**)	198.0 (- 0.8**)
Day 9		-	-	-	158.0 (- 4.0)
Day 15		212.3 (+ 4.8)	219.3 (+ 6.4)	210.3 (+ 1.8)	204.7 (+ 3.5)
Day 0	Gestation	216.1	218.6	210.1	206.9
Day 7		241.6	244.2	235.7	231.8
Day 14		265.5	269.3	258.8	255.9
Day 20		317.4	322.9	306.0	308.7
Day 1	Lactation	245.0	250.5	242.3	236.7
Day 4		249.3	256.3	245.5	244.9
Overall BW gain Day 1 – Day 15 (% gain/ loss)		4.2 (+ 2.1 %)	13.9 (+ 6.8 %)	8.5 (+ 4.3 %)	5.2 (+ 2.6 %)
Overall BWG Day 0 – Day 20 gestation period		101.3	104.3	95.9	101.8

* statistically significantly different from control values p < 0.05

** statistically significantly different from control values p < 0.01

Table 5       Haematology, clinical chemistry and pathology findings (P0)

Doses (mg/kg/day)	Control	30	100	350/250	Control	30	100	350/250
	male				female
Number of animals/group	5	5	5	5	5	5	5	5
Haematology(day 44 for males and day 5 post-partum for females)
- Hb (g/dl)	16.64	16.80	16.68	16.54	14.08	14.16	13.82	16.50
- RBC (10^12/L)	8.862	9.128	9.058	8.836	7.234	7.450	6.980	6.790
- Hct (%)	47.86	48.84	48.20	48.16	41.62	41.84	41.00	40.14
- MCH (pg)	18.80	18.42	18.42	18.74	19.50	19.04	19.82	19.94
- MCV (fl)	54.04	53.54	53.26	54.58	57.62	56.24	58.84	59.26
- MCHC (g/df)	34.76	34.40	34.60	34.34	33.84	33.84	33.70	33.68
- WBC (10^9/L)	7.92	5.70*	6.44	7.40	6.28	6.20	5.98	6.40
- Neut (10^9/L)	1.090	1.104	1.042	1.278	1.714	1.620	1.682	1.510
- Lymph (10^9/L)	6.770	4.506*	5.350	6.048	4.558	4.580	4.278	4.868
- Mono (10^9/L)	0.030	0.000	0.000	0.000	0.000	0.000	0.000	0.000
- Eos (10^9/L)	0.036	0.088	0.048	0.074	0.012	0.000	0.022	0.026
- Bas (10^9/L)	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
- CT (secs)	8.26	8.32	8.66	8.64	8.60	8.84	8.54	8.56
- PLT (10^9/L)	567.0	610.0	568.4	569.6	838.6	851.2	824.4	904.0
- APTT (secs)	12.44	13.06	12.98	13.18	14.88	13.28*	13.48*	12.54**
Blood chemistry(day 44 and day 5 post-partum for females)
- Urea (mg/dl)	47.0	43.8	47.6	46.2	73.6	61.8	47.6	56.2
- Glucose (mg/dl)	156.8	172.2	163.0	157.6	148.2	160.8	148.8	146.6
- Tot. Prot. (g/dl)	6.772	6.928	6.962	6.992	6.140	6.400	6.584	6.380
- Albumin (g/dl)	3.72	3.88	3.84	3.80	3.56	3.76	3.78	3.62
- A/G ratio	1.240	1.270	1.236	1.186	1.366	1.418	1.364	1.328
- Na+ (mmol/L)	149.6	147.4	148.2	147.0	146.2	146.6	145.0	146.2
- K+ (mmol/L)	4.582	4.052	4.302	4.472	6.382	5.016	4.322	4.500
- Cl- (mmol/L)	101.0	103.6	102.6	101.4	106.2	105.0	104.6	106.0
- Ca++ (mmol/L)	2.678	2.712	2.758	2.702	2.788	2.698	2.462	2.616
- P (mmol/L)	2.00	1.56*	2.08	2.16	0.84	1.32	0.98	0.98
- ASAT (IU/L)	109.2	87.0	72.8	88.2	87.8	79.4	82.4	100.8
- ALAT (IU/L)	60.4	59.6	55.4	63.2	67.6	55.6	69.0	73.0
- AP (IU/L)	149.2	134.0	148.2	147.8	124.4	100.2	127.2	123.2
- Creat (mg/dL)	0.664	0.670	0.664	0.664	1.132	0.876	0.718	0.820
- Chol (mg/dL)	90.8	86.6	90.4	108.2	83.8	75.8	79.2	74.6
- Bili (mg/dL)	0.112	0.086	0.096	0.106	0.086	0.074	0.076	0.070
- Bile acid (µmol/L)	5.66	7.26	7.78	17.00	32.10	11.32	31.30	15.34
Pathology	male				female
Number of animals/group	12	12	12	12	12	12	12	11^a
- Lung;red discolouration	0	1	0	1	1	2	1	2
- Uterus and cervix; fluid filled and foetus removed from left horn	-	-	-	-	0	0	1	0
- No abnormalities	12	11	12	11	11	10	11	9

Statistics: Anova + Dunnetts tests (two sided): * P<0.05, ** P<0.01^aone female killed in extremis on Day 9 exhibited the following pathological signs; caecum (enlarged), duodenum, (enlarged), ileum (enlarged), jejunum (enlarged)

Table 6       Absolute and relative organ weights (P0)

		Males				Females
DAILY DOSE (mg/kg bw/day)		Control	30	100	350/250	Control	30	100	350/250
BODY WEIGHT (g)^a		396.5	384.8	391.9	381.0	248.2	258.4	246.8	239.0
BRAIN (n=5)^b
Absolute Weight^a	g	1.92608	1.95708	1.90928	1.85856	1.79188	1.86194	1.77998	1.73266
Per Body Weight^a	%	0.500	0.513	0.486	0.497	0.740	0.759	0.727	0.716
ADRENALS (n=5)^b
Absolute Weight^a	g	0.06980	0.07874	0.07754	0.08756*	0.09182	0.09620	0.09606	0.10156
Per Body Weight^a	%	0.018	0.020	0.020	0.023*	0.038	0.039	0.039	0.042
EPIDIDYMIDES (n=12)^b
Absolute Weight^a	g	1.67668	1.64823	1.61638	1.66668	-	-	-	-
Per Body Weight^a	%	0.424	0.429	0.413	0.438	-	-	-	-
HEART (n=5)^b
Absolute Weight^a	g	1.11314	1.17090	1.10540	1.09980	0.82250	0.79110	0.79618	0.91182
Per Body Weight^a	%	0.288	0.307	0.281	0.294	0.339	0.322	0.324	0.374
KIDNEYS (n=5)^b
Absolute Weight^a	g	2.32086	2.33974	2.19380	2.23120	1.49388	1.52330	1.51554	1.51430
Per Body Weight^a	%	0.603	0.612	0.558	0.596	0.612	0.621	0.616	0.626
LIVER (n=5)^b
Absolute Weight^a	g	12.5039	12.1590	12.9510	13.3185	10.2267	10.5920	11.1381	10.0943
Per Body Weight^a	%	1.06219	1.70258	1.27713	1.56141	2.16809	1.76456	2.13278	1.45328
SPLEEN (n=5)^b
Absolute Weight^a	g	0.72426	0.71644	0.74192	0.86198*	0.66304	0.61726	0.73818	0.64746
Per Body Weight^a	%	0.188	0.187	0.188	0.230*	0.275	0.250	0.300	0.266
TESTES (n=12)^b
Absolute Weight^a	g	3.73889	3.65588	3.68240	3.74103	-	-	-	-
Per Body Weight^a	%	0.943	0.951	0.941	0.983	-	-	-	-
PROSTATE (n=12)^b
Absolute Weight^a	g	0.67028	0.61158	0.69047	0.59546	-	-	-
Per Body Weight^a	%	0.171	0.159	0.177	0.156	-	-	-	-
SEMINAL VESICLES (n=12)^b
Absolute Weight^a	g	1.92255	1.90243	2.04975	2.08725	-	-	-	-
Per Body Weight^a	%	0.485	0.494	0.523	0.550	-	-	-	-
THYROID / PARATHYROID (n=5)^b
Absolute Weight^a	g	0.02206	0.02156	0.02976*	0.02234	0.02348	0.02404	0.01938	0.02312
Per Body Weight^a	%	0.006	0.006	0.008*	0.006	0.010	0.010	0.008	0.009
THYMUS (n=5)^b
Absolute Weight^a	g	0.38374	0.36892	0.43906	0.34442	0.27284	0.25900	0.26726	0.20460
Per Body Weight^a	%	0.100	0.096	0.111	0.092	0.112	0.105	0.108	0.085
OVARIES (n=10, 12, 10, 11 for 0, 30, 100 and 350/ 250 mg/kd bw/day, respectively)^b
Absolute Weight^a	g	-	-	-	-	0.10111	0.11443	0.10881	0.11550
Per Body Weight^a	%	-	-	-	-	0.040	0.044	0.044	0.047
UTERUS AND CERVIX (n=10, 12, 10, 11 for 0, 30, 100 and 350/ 250 mg/kd bw/day, respectively)^b
Absolute Weight^a	g	-	-	-	-	0.81859	0.68867*	0.69113*	0.65409*
Per Body Weight^a	%	-	-	-	-	0.329	0.269*	0.280*	0.266*
PITUITARY (n=12)^b
Absolute Weight^a	g	0.01139	0.01057	0.01095	0.01247	0.01404	0.01533	0.01431	0.01394
Per Body Weight^a	%	0.003	0.003	0.003	0.003	0.006	0.006	0.006	0.006

^aGroup means at the end of terminal necropsy are shown

^bnumber of replicates per test group

* p<0.05 statistically significantly different from control

Conclusions:

A No Observed Effect Level (NOEL) for systemic toxicity could not be established due to observed toxic effects at the lowest tested concentration (microscopic changes in the adrenals of both sexes).

The reduced body weight gain/food consumption was considered to be the result of the administration of the higher dose level (350 mg/kg bw/day) and once the dose level had been reduced recovery was evident. All of the microscopic changes observed were considered to either be stress related or an adaptive change. For these reasons, the No Observed Adverse Effect Level (NOAEL) was considered to be 250 mg/kg bw/day.

Executive summary:

In a combined repeat dose toxicity study with reproductive toxicity screening (OECD 422) 1,4-Dihydroxy-2,2,6,6-tetramethyl-4-piperidinol was administered to 36 male and 36 female Wistar Han:RccHan:WIST strain rats by gavage at dose levels of 30, 100 and 350 (reduced to 250 at Day 9 onwards) mg/kg bw/day for up to 44 consecutive days. In addition, 12 male and 12 female control rats were dosed with vehicle (Arachis oil BP) alone.

 

A summary of adult responses to the test item are described below;

 

Mortality- One female treated with 350 mg/kg bw/day was killed in extremis due to excessive body weight loss on Day 9. Microscopic examination of this female revealed evidence of inappetance (salivary gland inactive) and depletion in the bone marrow and lymphoid atrophy in the thymus along with metabolic changes in the liver. These are considered non-specific and an actual cause of death could not be established. There were no further unscheduled deaths.

 

Clinical signs- Animals of either sex treated with 350/250 mg/kg bw/day showed incidences of increased salivation from Day 4. The female that was killed in extremis on Day 9 also had hunched posture on Day 9.

 

No such effects were evident in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Behavioural assessments- There were no treatment-related changes in the behavioural parameters at 30, 100 or 350/250 mg/kg bw/day.

 

Functional performance- There were no treatment related changes in functional performance considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

 

Sensory reactivity assessments- There were no inter-group differences in sensory reactivity scores that were considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

 

Bodyweight- Animals of either sex treated with 350 mg/kg bw/day showed a reduction in body weight gain during the first week of treatment. Actual body weight losses were evident in four males and four females on Day 8 and one female was killed in extremis on Day 9 due to excessive weight loss. Following the reduction of the high dose level on Day 9, recovery was evident in males during the next two weeks of treatment however body weight gain was reduced again during Weeks 4 and 5 and overall body weight gain for these males was lower than controls. Following the reduction of the high dose level some recovery was evident in females during the second week of treatment however three females showed an actual body weight loss. No adverse effects were detected in treated females during gestation or lactation.

 

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Food consumption and efficiency- Animals of either sex treated with 350 mg/kg bw/day showed a reduction in food consumption during the first week of treatment. Following the reduction of the high dose level recovery was evident thereafter.

 

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Water consumption- Males treated with 350/250 mg/kg bw/day showed an increase in overall water consumption during maturation. No such effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Reproductive performance;

Mating- No treatment-related effects were detected in mating performance.

 

Fertility- No treatment-related effects were detected in fertility.

 

Gestation length- Gestation lengths were between 22 and 23ó days and the distribution of gestation lengths for treated females was essentially similar to control. One control female and one female treated with 100 mg/kg bw/day that had a total litter loss had a gestation length of 24ó and 24 Days (respectively).

 

Litter size, viability, development- Of the litters born, litter size at birth and subsequently on Days 1 and 4 post partum were comparable to controls.

 

Offspring body weight gain and litter weights at birth and subsequently on Days 1 and 4 post partum were comparable to control litters. Sex ratio and surface righting were also comparable to controls.

 

The clinical signs apparent for offspring on the study were typical for the age observed. Neither the incidence nor distribution of these observations indicated any adverse effect of maternal treatment on offspring development at 30, 100 and 350/250 mg/kg bw/day.

 

Haematology- There were no toxicologically significant effects detected in the hematological parameters examined.

 

Blood Chemistry- There were no toxicologically significant effects detected in the blood chemical parameters examined.

 

Necropsy- The female that was killed in extremis had an enlarged gastro-intestinal tract at necropsy.

 

No toxicologically significant effects were detected in terminal kill animals of either sex treated with 350/250, 100 or 30 mg/kg bw/day.

 

Organ weights- Males treated with 350/250 mg/kg bw/day showed a statistically significant increase in adrenal weight both absolute and relative to terminal body weight. No toxicologically significant effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Histopathological changes;

 

The following treatment-related microscopic abnormalities were detected:

 

Adrenals: Cortical hypertrophy (zona fasciculata) was present at a minimal or mild level in animals of either sex from all treatment groups.

 

Spleen: Increased hematopoiesis was present in females treated with 350/250 mg/kg bw/day. In two of these females an increase was also present in the bone marrow. A minor increase in hematopoiesis was present in females treated with 100 mg/kg bw/day. No such effects were detected in treated males or in females treated with 30 mg/kg bw/day.

 

Liver: Centrilobular hepatocyte hypertrophy was present in three males treated with 350/250 mg/kg bw/day. No such effects were detected in treated females or in males treated with 100 or 30 mg/kg bw/day.

 

In conclusion, a ‘No Observed Effect Level’ (NOEL) for systemic toxicity could not be established due to observed toxic effects at the lowest tested concentration (microscopic changes in the adrenals of both male and female rats). The reduced body weight gain/food consumption was considered to be the result of the administration of the higher dose level (350 mg/kg bw/day) and once the dose level had been reduced recovery was evident. All of the microscopic changes observed were considered to either be stress related or an adaptive change. For these reasons, the No Observed Adverse Effect Level (NOAEL) was considered to be 250 mg/kg bw/day.

The ‘No Observed Effect Level’ (NOEL) for reproductive and developmental toxicity was considered to be 250 mg/kg bw/day.

 

This combined toxicity study with reproduction screening in the rat is acceptable and satisfies the guideline requirements for an OECD 422 in the rat.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

250 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The sub-acute repeated dose toxicity study conducted on the registered substances was considered reliable, with a Klimisch rating of 1.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

OECD 422

In a combined repeat dose toxicity study with reproductive toxicity screening (OECD 422) 1,4-Dihydroxy-2,2,6,6-tetramethyl-4-piperidinol was administered to 36 male and 36 female Wistar Han:RccHan:WIST strain rats by gavage at dose levels of 30, 100 and 350 (reduced to 250 at Day 9 onwards) mg/kg bw/day for up to 44 consecutive days. In addition, 12 male and 12 female control rats were dosed with vehicle (Arachis oil BP) alone.

 

A summary of adult responses to the test item are described below;

 

Mortality- One female treated with 350 mg/kg bw/day was killed in extremis due to excessive body weight loss on Day 9. Microscopic examination of this female revealed evidence of inappetance (salivary gland inactive) and depletion in the bone marrow and lymphoid atrophy in the thymus along with metabolic changes in the liver. These are considered non-specific and an actual cause of death could not be established. There were no further unscheduled deaths.

 

Clinical signs- Animals of either sex treated with 350/250 mg/kg bw/day showed incidences of increased salivation from Day 4. The female that was killed in extremis on Day 9 also had hunched posture on Day 9.

 

No such effects were evident in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Behavioural assessments- There were no treatment-related changes in the behavioural parameters at 30, 100 or 350/250 mg/kg bw/day.

 

Functional performance- There were no treatment related changes in functional performance considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

 

Sensory reactivity assessments- There were no inter-group differences in sensory reactivity scores that were considered to be related to treatment at 30, 100 or 350/250 mg/kg bw/day.

 

Bodyweight- Animals of either sex treated with 350 mg/kg bw/day showed a reduction in body weight gain during the first week of treatment. Actual body weight losses were evident in four males and four females on Day 8 and one female was killed in extremis on Day 9 due to excessive weight loss. Following the reduction of the high dose level on Day 9, recovery was evident in males during the next two weeks of treatment however body weight gain was reduced again during Weeks 4 and 5 and overall body weight gain for these males was lower than controls. Following the reduction of the high dose level some recovery was evident in females during the second week of treatment however three females showed an actual body weight loss. No adverse effects were detected in treated females during gestation or lactation.

 

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Food consumption and efficiency- Animals of either sex treated with 350 mg/kg bw/day showed a reduction in food consumption during the first week of treatment. Following the reduction of the high dose level recovery was evident thereafter.

 

No such effects were detected in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Water consumption- Males treated with 350/250 mg/kg bw/day showed an increase in overall water consumption during maturation. No such effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Reproductive performance;

Mating- No treatment-related effects were detected in mating performance.

 

Fertility- No treatment-related effects were detected in fertility.

 

Gestation length- Gestation lengths were between 22 and 23ó days and the distribution of gestation lengths for treated females was essentially similar to control. One control female and one female treated with 100 mg/kg bw/day that had a total litter loss had a gestation length of 24ó and 24 Days (respectively).

 

Litter size, viability, development- Of the litters born, litter size at birth and subsequently on Days 1 and 4 post partum were comparable to controls.

 

Offspring body weight gain and litter weights at birth and subsequently on Days 1 and 4 post partum were comparable to control litters. Sex ratio and surface righting were also comparable to controls.

 

The clinical signs apparent for offspring on the study were typical for the age observed. Neither the incidence nor distribution of these observations indicated any adverse effect of maternal treatment on offspring development at 30, 100 and 350/250 mg/kg bw/day.

 

Haematology- There were no toxicologically significant effects detected in the hematological parameters examined.

 

Blood Chemistry- There were no toxicologically significant effects detected in the blood chemical parameters examined.

 

Necropsy- The female that was killed in extremis had an enlarged gastro-intestinal tract at necropsy.

 

No toxicologically significant effects were detected in terminal kill animals of either sex treated with 350/250, 100 or 30 mg/kg bw/day.

 

Organ weights- Males treated with 350/250 mg/kg bw/day showed a statistically significant increase in adrenal weight both absolute and relative to terminal body weight. No toxicologically significant effects were detected in females treated with 350/250 mg/kg bw/day or in animals of either sex treated with 100 or 30 mg/kg bw/day.

 

Histopathological changes;

 

The following treatment-related microscopic abnormalities were detected:

 

Adrenals: Cortical hypertrophy (zona fasciculata) was present at a minimal or mild level in animals of either sex from all treatment groups.

 

Spleen: Increased hematopoiesis was present in females treated with 350/250 mg/kg bw/day. In two of these females an increase was also present in the bone marrow. A minor increase in hematopoiesis was present in females treated with 100 mg/kg bw/day. No such effects were detected in treated males or in females treated with 30 mg/kg bw/day.

 

Liver: Centrilobular hepatocyte hypertrophy was present in three males treated with 350/250 mg/kg bw/day. No such effects were detected in treated females or in males treated with 100 or 30 mg/kg bw/day.

 

In conclusion, a ‘No Observed Effect Level’ (NOEL) for systemic toxicity could not be established due to observed toxic effects at the lowest tested concentration (microscopic changes in the adrenals of both male and female rats). The reduced body weight gain/food consumption was considered to be the result of the administration of the higher dose level (350 mg/kg bw/day) and once the dose level had been reduced recovery was evident. All of the microscopic changes observed were considered to either be stress related or an adaptive change. For these reasons, the No Observed Adverse Effect Level (NOAEL) was considered to be 250 mg/kg bw/day.

The ‘No Observed Effect Level’ (NOEL) for reproductive toxicity was considered to be 250 mg/kg bw/day.

 

This combined toxicity study with reproduction screening in the rat is acceptable and satisfies the guideline requirements for an OECD 422 in the rat.

Justification for classification or non-classification

The substance did not meet the criteria for classification for specific target organ toxicity (repeated exposure), in accordance with Regulation (EC) No 1272/2008 (CLP).