Dimethoxymethylsilane

Repeated dose toxicity: dermal

Administrative data

Endpoint:

short-term repeated dose toxicity: dermal

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference Type:

publication

Title:

Granulomatous Dermatitis in New Zealand White Rabbits following 9-Day repeated cutaneous exposure to Methyldimethoxysilane

Author:

Losco P.E., Hermansky S.J., Weaver E.V., Ballantyne B.

Year:

1996

Bibliographic source:

Journal of Toxicology - Cutaneous & Occular Toxicology, 15 (3), 261 - 276

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rabbits were exposed dermally (occlusive) to the test substance for 9 doses over a time of 11 days. Animals were euthanized at the end of exposure period. 5 animals from high-dose and control group were kept as satellite groups for 2 weeks of recovery. Observations were made for clinical effects, gross and macroscopic lesions, haematology, clinical chemistry and urinalysis.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Dimethoxymethylsilane

EC Number:

240-914-9

EC Name:

Dimethoxymethylsilane

Cas Number:

16881-77-9

Molecular formula:

C3H10O2Si

IUPAC Name:

Dimethoxy(methyl)silane

Details on test material:

- Name of test material (as cited in study report): Methyldimethoxysilane (MDMS)

Test animals

Species:

rabbit

Strain:

New Zealand White

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Hazelton Research Products, Inc., Denver
- Age at study initiation: 17 - 19 weeks old
- Weight at study initiation: 3.0 - 4.0 kg
- Housing: individually in stainless steel cages with wire mesh floors
- Diet: Agway Pro-Lab Certified Rabbit Formula (Agway Inc. Waverly, NY), ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 16 - 21 °C
- Humidity (%): 40 - 70%
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on exposure:

TEST SITE
- Type of wrap if used: polyethylene sheeting, secured with waterproof tape before treatment; after application of test substance usig a syringe with gavage needle, entire treatment area was overwrapped with VETRAP bandaging tape
- Area of exposure: no data
- % coverage: no data
- Time intervals for shavings or clipplings: no details given

REMOVAL OF TEST SUBSTANCE
- Washing: no washing, area was cleaned by wiping with a dry cloth
- Time after start of exposure: 6 h

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

11 days, and 2 weeks post exposure (satellite control and high dose groups)

Frequency of treatment:

5 consecutive days of exposure, followed by a 2 days rest period, followed by 4 consecutive days of exposure
6 hours per day

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.05 other: mL/kg bw (nominal)

Doses / concentrations 2

Dose / conc.:

0.1 other: mL/kg bw (nominal)

Doses / concentrations 3

Dose / conc.:

0.2 other: mL/kg bw (nominal)

Doses / concentrations 4

Dose / conc.:

43 mg/kg bw/day (nominal)

Doses / concentrations 5

Dose / conc.:

85 mg/kg bw/day (nominal)

Doses / concentrations 6

Dose / conc.:

171 mg/kg bw/day (nominal)

No. of animals per sex per dose:

10 per gender
5 per gender for 43 mg/kg dose group

Control animals:

yes, sham-exposed

Details on study design:

- Post-exposure recovery period in satellite groups: 14 days

Examinations

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily before dosing

DERMAL IRRITATION (if dermal study): Yes
- Time schedule for examinations: daily before dosing

BODY WEIGHT: Yes
- Time schedule for examinations: on day 1, 8 and 12 during dosing and weekly during recovery period

FOOD CONSUMPTION:
- Food consumption for each animal determined throughout the study

WATER CONSUMPTION: Yes
- Time schedule for examinations: determined throughout the study

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at termination of study
- Anaesthetic used for blood collection: No data
- Animals fasted: No
- How many animals: all
- Parameters checked in table [No.1] were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at termination of study
- Animals fasted: No
- How many animals: all
- Parameters checked in table [No.1] were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: at termination of study
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- Parameters checked in table [No.1] were examined.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (selected tissues, not further specified, wet weights of brain, liver, kidneys, heart, spleen, adrenals and testes)
HISTOPATHOLOGY: Yes (selected tissues, not further specified but including skin)

Other examinations:

scanning electron microscopy/energy-dispersive x-ray analysis (SEM/EDX) was performed on treated skin of one high-dose rabbit per gender from the recovery group to determine the nature of the pigmented material observed in the skin by light microscopy.

Statistics:

The data for quantitative continuous variables were intercompared for the three treatment groups and the control group by use of Levene's test for equality of variances, analysis of variance (ANOVA) and t-test. The t-test was used when the F-value from the ANOVA was significant. When Levene's test indicated simialr variances and the ANOVA was significant a pooled t-test was used for pairwise comparisons. When Levene's test indicated heterogenous variances, all groups were compared by an ANOVA for unequal variances followed when necessary by a separate variance test for pairwise comparison.
Nonparametric data were statistically evaluated using the Kruskal-Wallis test followed by Mann-Whitney U test when appropriate. Incidence data were compared using the Fisher's exact test. For all statistical tests, the probability value of p<0.05 (two-tailed) was used as the critical level of significance.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Dermal irritation:

effects observed, treatment-related

Description (incidence and severity):

moderate to severe skin irritation, females more affected than males, lesion severity correlated with dose

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not specified

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

no effects observed

Ophthalmological findings:

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

no treatment-related effects, except decrease in monocytes for high dose group males, which may have been due to sequestration of circulating leukocytes at the site of skin irritation

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

the only finding were lesions to the skin

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

skin lesions were found

Histopathological findings: neoplastic:

not specified

Details on results:

CLINICAL SIGNS AND MORTALITY
Treatment-related clinical lesions were limited to the the treated skin. Females tended to be affected slightly more than males. There was moderate to severe skin irritation as evidenced by exfoliation, fissures, and ecchymoses for both genders in the high-dose group, with ulceration and necrosis found only in high-dose group females. In addition, Draize scoring of skin irritation revealed barely perceptible to well-defined erythema and edema in the mid- and high-dose groups of male animals and barely perceptible to moderate erythema in all dose groups of female animals. In general, lesion severity correlated with dose.

HAEMATOLOGY
In animals euthanised after a 2 week recovery period, the only noteworthy finding was a statistically significant decrease in monocytes for high-dose group males, which may have been due to sequestration of circulating leukocytes at the site of skin irritation.

GROSS PATHOLOGY
The only gross lesions found involved the treated skin of rabbits of both genders from all exposure groups at both necropsies. Necropsy findings were similar to clinical observations. The most common lesion was exfoliation or scaling, which was present in most intermediate and high-dose group rabbits, and five of five females and one of five males from the low-dose group from the primary necropsy, as well as in four of five high-dose group rabbits/gender from the recovery group necropsy. Discoloration of the skin, either erythema or ecchymoses, was observed sporadically (more frequently in females) in intermediate and high-dose group rabbits euthanized on day 12, but not observed in the recovery group animals. Lesions indicative or more serious skin irritation, such as ulceration and necrosis (females only), or fissures (both sexes), were noted sporadically in the high-dose group animals euthanized on day 12. Four intermediate dose group females also had fissures and one had ulceration as well.

HISTOPATHOLOGY: NON-NEOPLASTIC
Statistically significant treatment-related microscopic lesions were observed in the treated skin of MDMS-exposed rabbits from all three dose groups of female animals and from the interrnediate and high-dose groups of male animals euthanized immediately following the exposure period. Lesions indicative of treatment-induced irritation of the skin included hyperkeratosis (corresponding to the exfoliation reported grossly), acanthosis, dermal congestion, edema, hemorrhage, epidermitis, ulceration, dermatitis, and dermal fibrosis. The only lesions seen in low-dose group rabbits were hyperkeratosis and dermatitis. Slight dermatitis (lymphocytic infiltrates) was also seen in a few control group rabbits. Acute inflammation in the intermedite and high-dose group animals was often most intense at the epidermal junction, even when the overlying epidermis was intact. Dermal fibrosis was associated with phagocytosed foreign material within macrophages, which appeared as a brown crystalline substance (dermal pigmentation) on H & E-stained sections. Significant residual lesions of treated skin were also present in all high-dose group rabbits euthanized after the 2-week recovery period. Lesions included hyperkeratosis, dermal fibrosis, and granulomatous dermatitis, in which phagocytic giant cells containing pigmented foreign material were prominent.
Scanning electron microscopy of the superficial dermis revealed numerous electron-dense deposits that were proven by elemental analysis to contain silicon. This material is believed to represent a polymer derived from absorbed MDMS or its breakdown products.

Effect levels

1

Dose descriptor:

NOAEL

Remarks:

systemic

Effect level:

171 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no systemic effects observed at the highest dose tested, the only abnormal finding involved the treated skin

2

Dose descriptor:

LOAEL

Remarks:

local effects

Effect level:

43 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

dermal irritation

3

Dose descriptor:

LOAEL

Remarks:

local effects

Effect level:

0.051 mg/cm² per day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: see 'Remark'

Target system / organ toxicity

Critical effects observed:

no

Any other information on results incl. tables

table1: Summary of clinical observations of rabbits

	Males				Females
group [mg/kg bw]	0	43	85	171	0	43	85	171
Treated skin
total number examined	10	5	10	10	10	5	10	10
Number affected
Exfoliation	0	1	10	10	0	5	10	10
Ecchymoses	0	0	0	3	0	0	3	9
Ulceration	0	0	0	0	0	0	0	2
Fissures	0	0	0	8	0	0	4	10
Necrosis	0	0	0	0	0	0	0	3

table2: Necropsy Findings for rabbits euthanized on day 12

	Males				Females
group [mg/kg bw]	0	43	85	171	0	43	85	171
treated skin
total number examined	5	5	10	5	5	5	10	5
Number affected
Exfoliation	0	1	9	5	0	5	10	5
Excoriation	1	0	0	1	0	0	0	0
Erythema	0	0	1	1	0	0	4	0
Ecchymoses	0	0	0	1	0	0	2	2
Ulceration	0	0	0	0	0	0	0	1
Fissures	0	0	0	2	0	0	4	5
Necrosis	0	0	0	0	0	0	1	2

table3: Necropsy Findings for rabbits euthanized on day 29

	Males				Females
group [mg/kg bw]	0	43	85	171	0	43	85	171
treated skin
total number examined	5	-	-	5	5	-	-	5
number affected
Exfoliation	0	-	-	4	0	-	-	4
Papule	0	-	-	1	0	-	-	0

table4: Microscopic Findings for rabbits euthanized on day 12

	Males				Females
group [mg/kg bw]	0	43	85	171	0	43	85	171
treated skin
total number examined	5	5	10	5	5	5	10	5
examined, unremarkable	3	0	0	0	4	0	0	0
number affected
Hyperkeratosis	0	2	10**	5**	0	5**	10**	5**
Acanthosis	1	0	10**	5*	0	1	7*	5**
Congestion	0	0	4	0	0	0	6*	4*
Epidermitis	0	0	7*	4*	0	0	9**	5**
Ulceration	1	0	3	2	0	0	3	4*
Dermal edema	0	0	0	0	0	0	1	3
Dermal hemorrhage	0	0	4	3	0	0	7*	5**
Dermatitis	2	5	10*	5	1	4	10**	4
Dermal fibrosis	0	0	10**	4*	0	0	8**	5**
Dermal pigmentation	0	0	10**	4*	0	0	9**	5**

Significantly different from control group, *p<0.05, **p<0.01

table5: Microscopic Findings for rabbits euthanized on day 29

	Males				Females
group [mg/kg bw]	0	43	85	171	0	43	85	171
treated skin
total number examined	5	0	0	5	5	0	0	5
examined, unremarkable	4	-	-	0	1	-	-	0
number affected
Hyperkeratosis	0	-	-	5**	0	-	-	5**
Acanthosis	0	-	-	0	0	-	-	2
Ulceration	0	-	-	0	1	-	-	0
Dermal hemorrhage	0	-	-	0	1	-	-	1
Dermatitis	1	-	-	5*	3	-	-	4
Granulomatous dermatitis	0	-	-	4*	0	-	-	5**
Dermal fibrosis	0	-	-	2	0	-	-	5**
Dermal pigmentation	0	-	-	5**	0	-	-	5**

Significantly different from control group, *p<0.05, **p<0.01

Applicant's summary and conclusion

Conclusions:

Repeated dermal application of the test substance did not result in systemic toxicity. The only abnormal findings involved the treated skin.