Dimethyl sulfoxide

Repeated dose toxicity: dermal

Administrative data

Endpoint:

chronic toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Chronic toxicity of DMSO in primates

Author:

Vogin EE, Carson S, Cannon G, Linegar CR, Rubin LF

Year:

1970

Bibliographic source:

Toxicol. Appl. Pharmacol., 16 (3), 606-12

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Dimethyl sulfoxide

EC Number:

200-664-3

EC Name:

Dimethyl sulfoxide

Cas Number:

67-68-5

Molecular formula:

C2H6OS

IUPAC Name:

dimethyl sulfoxide

Details on test material:

Test compound: dimethylsulfoxide
Source: no data
Batch number: no data
Purity: Pharmaceutical-grade

Test animals

Species:

monkey

Strain:

other: Macaca mulatta (rhesus)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: no data
- Diet (e.g. ad libitum): no data
- Water: no data
- Acclimation period:no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): no data

IN-LIFE DATES: no data

Administration / exposure

Type of coverage:

open

Vehicle:

water

Details on exposure:

Topical administration was by direct application to the entire abdominal skin. 
Animals were restrained in a supine position for 1 hour after drug administration to prevent ingestion of the applied solution.
Monkeys was kept in separate rooms to preclude the possibility of inhaling DMSO or its metabolites from treated animals.

Duration of treatment / exposure:

18 months

Frequency of treatment:

daily

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
1 - 3 - 9 ml of 90% DMSO solution/kg bw/d (990 - 2970 - 8910 mg bw/kg/d)
Basis:

Doses / concentrations 2

Remarks:

Doses / Concentrations:
990, 2970 and 8910 mg/kg bw/day
Basis:

No. of animals per sex per dose:

control group: 2 males and 1 female
1 and 3 ml/kg: 2 males and 2 females
9 ml/kg: 3 males and 3 females

Control animals:

other: water, 9 ml/kg

Details on study design:

Post-exposure period: none

Examinations

Observations and examinations performed and frequency:

EXAMINATIONS
Physical signs, behaviour, and survival time were recorded daily.
Examinations included water consumption, electrocardiogram, neurology (reflexes), heart rate, body weight, blood pressure, body temperature, respiratory rate, and ophthalmology. Complete blood counts, serum glutamic-pyruvic transaminase (SGPT), serum alkaline phosphatase (SAP), blood urea nitrogen (BUN), blond glucose, 45-minute sulfobromophthalein (BSP) retention, and endogenous creatinine clearance were measured in all animals. Urinalysis consisted of specific gravity, pH, albumin, glucose, occult blood, ketone bodies, and microscopic examination of the sediment. All of these determinations were performed in accordance with standard procedures.

Because of the need to schedule the broad spectrum of clinical determinations in each animal, starting dates for dosing were staggered over a 6-week period. Surviving monkeys were treated for 74-87 weeks.

Sacrifice and pathology:

NECROPSY AND ORGAN WEIGHT
All animals that died or were sacrificed were submitted to a detailed necropsy. The following organs were weighed: liver, kidneys, heart, brain, gonads, prostate or uterus, adrenals, thyroid, pituitary, and lungs.

HISTOPATHOLOGY
Histomorphologic examinations were performed on the following hematoxylineosin-stained sections of formalin-fixed tissues: liver, spleen, stomach (including fundus and pyloric regions), small intestine (including duodénum, jejunum, and ileum), large intestine (including colon and cecum), pancreas, kidneys, bladder, adrenals, gonads, thyroid, pituitary, thymus, salivary glands, lymph nodes (including cervical and mesenteric), heart, lungs, femoral bone marrow, skin, skeletal muscle, spinal cord, brain, gallbladder, epididymis, seminal vesicles, prostate, uterus, aorta, larynx, trachea, peripheral nerve, diaphragm, and lacrimal glands. The eyes were fixed in formalin or Zenker's fixative. Bone marrow smears were stained with Wright's stain.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Dermal irritation:

effects observed, treatment-related

Description (incidence and severity):

>= 990 mg/kg/day

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

but not biologically relevant

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

no effects observed

Ophthalmological findings:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
Several accidental deaths (self-strangulation) occurred as a result of vigorous attempts to escape by monkeys restrained in a supine position. Two monkeys that died early in the study were replaced. Two in the treated and 2 in the control groups that died or were sacrificed later were not replaced. In no instance was death attributed to the dermal treatment of these animals with DMSO.

All animals treated topically with DMSO exhibited scaling and flaking of the skin in the area of drug application during the initial phases of the study. There were no apparent differences among the various treatment groups. Although several animals had erythema of the skin it did not appear to be related to the dose, and erythema did not occur at regular internals in any animal.
No other adverse behavioural or physical signs were seen that could be attributed to topical application of DMSO.

No DMSO-related changes were found in the treated monkeys during physical examinations. These tests included mean systolic blood pressure, heart rate, respiratory rate, body temperature, 48-hour water consumption, neurological reflexes, and electrocardiograms, performed during weeks 1, 4, 7, 12, 24, 37, 51, and 73 of study.

BODY WEIGHT AND WEIGHT GAIN
Monkeys given 1-9 ml/kg DMSO topically showed slightly less gain in mean body weight compared to the control animals during the study. However, no biologic significance is attached to these differences because of the Iimited number of animals per group and the wide range of initial weights.

OPHTHALMOSCOPIC EXAMINATION
No evidence of refractoriness to Tropicamide mydriasis was seen in any of these monkeys. The typical DMSO lenticular changes described in other species were not visible in any monkey during the course of the experiment. The only ocular abnormality observed was in one animal which had been given 1 ml of DMSO/kg per day dermally for 82 weeks. In the final ocular examination, this animal had a unilateral complete retinal detachment and syneresis of the vitreous humor. There were no biomicroscopically visible changes in the vitreous humor of the remaining animals.

HAEMATOLOGY - CLINICAL CHEMISTRY - URINALYSIS
The mean hematological results at approximately 6-month intervals are presented for the topically treated control and 9 ml/kg groups in Table 1. Table 2 shows the biochemical data for the same groups. No significant differences were found between the DMSO-treated and control monkeys in any of the hematological or biochemical parameters evaluated. Animals given 1 or 3 ml/kg responded in a similar manner.

Further, no significant differences were seen in erythrocyte sedimentation rate (ESR), BSP retention, creatinine clearance and urinalysis between the treated and control animals.

ORGAN WEIGHTS
No significant differences were seen in absolute or relative organ weights between the treated and control animals.

HISTOPATHOLOGY: NON-NEOPLASTIC
No significant lesions attributable to DMSO were found upon gross examination at necropsy. Microscopic examination of the tissues showed tuberculosis in a control monkey in the dermally dosed group. This animal was sacrificed in week 41 because of a positive tuberculin reaction. Epidermal thickening and focal chronic hyperkeratosis were seen in skin sections of the abdomen from monkeys which had DMSO or water applied. This is often seen in animals treated dermally with aqueous solutions, and it is a result of constant application of fluid to the epidermis.
No histological changes were visible in the lenses of treated animals with the exception of the monkey with retinal detachment. In this animal, there appeared to be several swollen lenticular fibers in the equatorial portion of the lens in the affected eyes. The retina was undergoing cystic changes and the outer limbs of the neuroepithelial cells were sticky. There was no indication of inflammatory activity within the eye although there was an accumulation of inflammatory cells in the periphery of the optic nerve near the globe.

Effect levels

1

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

>= 8 910 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical biochemistry

clinical signs

food consumption and compound intake

gross pathology

haematology

histopathology: non-neoplastic

mortality

ophthalmological examination

urinalysis

2

Dose descriptor:

LOAEL

Remarks:

skin irritation

Effect level:

990 mg/kg bw/day

Basis for effect level:

dermal irritation

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Rhesus monkeys can tolerate DMSO administered daily for approximately 18 months at doses up to 9ml/kg dermally without frank intolerance.
Under these experimental conditions, the NOAEL was 8910 mg/kg in monkey after repeated dermal application.

Executive summary:

Daily doses of 0, 1, 3, or 9 ml/kg b.w. of a 90% aqueous DMSO solution were administered dermally to 4 groups of rhesus monkeys, 7 days per week, over an 18-month period. Dosages administered were equivalent to 990, 2970, and 8910 mg/kg bw/d. There were 2 males and 1 female in the control group, 2 animals of each sex in the groups treated with 1 and 3 ml/kg, and 3 animals of each sex in the groups receiving 9 ml/kg per day of DMSO. Physical signs, behaviour, and survival time were recorded daily. Examinations included 48-hour water consumption, electrocardiogram, neurology (reflexes), heart rate, body weight, blood pressure, body temperature, respiratory rate (on weeks 1, 4, 7, 12, 24, 37, 51, and 73 of study) and ophthalmology. Complete blood counts, SGPT, serum alkaline phosphatase (SAP), BUN, blood glucose, 45-minute sulfobromophthalein (BSP) retention, and endogenous creatinine clearance were measured in all animals. Urinalysis consisted of specific gravity, pH, albumin, glucose, occult blood, ketone bodies, and microscopic examination of the sediment. All animals that died or were sacrificed were submitted to a detailed necropsy. The following organs were weighed: liver, kidneys, heart, brain, gonads, prostate or uterus, adrenals, thyroid, pituitary, and lungs. Histomorphologic examinations were performed on the following tissues: liver, spleen, stomach (including fundus and pyloric regions), small intestine (including duodénum, jejunum, and ileum), large intestine (including colon and cecum), pancreas, kidneys, bladder, adrenals, gonads, thyroid, pituitary, thymus, salivary glands, lymph nodes (including cervical and mesenteric), heart, lungs, femoral bone marrow, skin, skeletal muscle, spinal cord, brain, gallbladder, epididymis, seminal vesicles, prostate, uterus, aorta, larynx, trachea, peripheral nerve, diaphragm, and lacrimal glands.All animals treated topically with DMSO exhibited scaling and flaking of the skin in the area of drug application during the initial phases of the study. There were no apparent differences among the various treatment groups. Although several animals had erythema of the skin, it did not appear to be related to dose, and did not occur at regular internals. No other adverse behavioural or physical signs were seen that could be attributed to topical application of DMSO. No DMSO-related changes were found in the treated monkeys during physical examinations. No evidence of refractoriness to Tropicamide mydriasis was seen in any of these monkeys. The typical DMSO lenticular changes described in other species were not visible in any monkey during the course of the experiment. No significant differences were found between the DMSO-treated and control monkeys in any of the haematological or biochemical parameters evaluated. Further, no significant differences were seen in erythrocyte sedimentation rate (ESR), BSP retention, creatinine clearance and urinalysis between the treated and control animals.

No significant differences were seen in absolute or relative organ weights between the treated and control animals. No significant lesions attributable to DMSO were found upon gross examination at necropsy. No histological changes were visible in the lenses of treated animals with the exception of a monkey that had retinal detachment. The authors concluded that Rhesus monkeys can tolerate DMSO at doses up to 9 ml/kg/day administered dermally for approximately 18 months.

Consequently, the NOAEL for the systemic effects is higher than 8910mg/kg bw/day based on the lack of systemic toxicity and changes in the lens of the eyes. The LOAEL for skin irritation is 990 mg/kg bw/day.