Dimethyl sulfoxide

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

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:

The toxicity of dimethyl sulphoxide (DMSO) for the dog, pig, rat and rabbit

Author:

Noel PRB, Barnett KC, Davies RE, Jolly DW, Leahy JS, Mawdesley-Thomas LE, Shillam KWG, Squires PF, Street AE, Tucker WC and Worden AN

Year:

1975

Bibliographic source:

Toxicology, 3 (2), 143-69

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

Deviations:

yes

Remarks:

The blood chemistry parameters and the organs (excepted the eyes) subject to the histopathological examination are not reported.

GLP compliance:

not specified

Limit test:

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: Crown Zellerbach Corporation
Batch number: no data
Purity: Pharmaceutical-grade

Test animals

Species:

dog

Strain:

other: Pembrokeshire Corgis

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: HRC's regular supplier. Inoculated against canine distemper, canine hepatitis and leptospirosis, dosed with piperazine
- Age at study initiation: 4-5 months
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: individuel pens with underfloor heating
- Diet (e.g. ad libitum): fed twice daily with a dry diet (Spillers P 62) at the rate of 300 g/dog/day, and were provided in addition with 200 ml/dog/day of fresh cow's milk
- Water: ad libitum
- 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: From 1965 to 1967

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

Gastric intubation with a 50% aqueous solution of DMSO

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

2 years

Frequency of treatment:

5 days/wk

Doses / concentrations

Remarks:

Doses / Concentrations:
1, 3 and 9 ml/kg bw/d (1100 - 3300 - 9900 mg /kg bw/day)
Basis:
actual ingested

No. of animals per sex per dose:

5 males and 5 females

Control animals:

other: 1 ml/kg water

Details on study design:

After 18 weeks of treatment, unexpected eye changes were observed. Dosing was continued for half the dogs in each group for the remaining 86 weeks; the other half was not treated but  observed for signs of recovery. The total interval of dosing was 2 years.

Positive control:

Not appropriate

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily and all animals were subjected to regular veterinary examinations

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes, twice weekly

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: three times before dosing and then on months 1, 3, 4.5, 6, 9, 12, 18, and 24
- Dose groups that were examined: all

HAEMATOLOGY: Yes
- Time schedule for collection of blood: three times before dosing and then on months 1, 3, 4.5, 6, 9, 12, 18, and 24
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- Parameters checked: ESR, PCV, haemoglobin, total red and white cell counts with differential, reticulocyte and platelet counts, prothrombin, clotting times

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: three times before dosing and then on months 1, 3, 4.5, 6, 9, 12, 18, and 24
- Animals fasted: No data
- Parameters checked: plasma urea, total reducing substances, total serum proteins and electrophoresis, SAP, SGPT and SGOT, serum isocitric dehydrogenase and serum cholesterol

URINALYSIS: Yes
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
-  A routine series of qualitative urinalysis tests were performed, together with microscopy of the spun deposit.

Sacrifice and pathology:

POST-MORTEM EXAMINATION: All animals were then sacrificed humanely and a detailed macroscopic postmortem examination made, during which the principal organs were weighed and tissues taken for routine histopathological examination.
The eye was subjected to a specific procedure: both eyes were enucleated, placed in normal saline, examined and then photographed, using either the slit-lamp microscope or a Rayner-Wray close-up camera. Aqueous humour was removed by needle puncture and the volume of liquid measured. The lenses were removed, weighed and subjected to extensive biochemicals and histological examinations.

Other examinations:

Additional studies performed prior to termination included bone radiography, BSP tests, serum and urine electrolytes and red cell fragility. 
ECG  was performed on all dogs three times before dosing commenced and then after 1, 3, 4.5, 6, 9, 12, 18, and 24 months'administration. 

Statistics:

Numerical results were subjected to statistical analysis, comprising analysis of variance followed by Student's 't' test. The result of the analysis was usually expressed as the least difference that had to exist between test and control group means before a 5% or 1% level of significance was reached

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

at 9 ml/kg/d

Mortality:

mortality observed, treatment-related

Description (incidence):

at 9 ml/kg/d

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

effects observed, treatment-related

Description (incidence and severity):

>= 1 ml/kg/d

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

at 9 ml/kg/d

Clinical biochemistry findings:

not specified

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

>= 3 ml/kg/d

Behaviour (functional findings):

not examined

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
There were no marked clinical signs and only one death occurred, after the 4th dose at the intermediate level. This was caused by accidental inspiration of DMSO, leading to a severe pulmonary reaction; the animal was replaced. Occasional isolated bouts of vomiting were seen at 9 ml/kg/day and transitory "head shaking" was temporarily observed during weeks 11 and 12 at this and the 3 ml/kg/day level. 

BODY WEIGHT AND WEIGHT GAIN - FOOD CONSUMPTION
No adverse effects on bodyweight and food intake were recorded. 

OPHTHALMOSCOPIC EXAMINATION
Ocular effects (Table II) were observed after 5-10 weeks dosing in the dogs receiving 9 ml/kg including central (nuclear) lenticular changes with alteration of the refractive index (myopia) and by the fifth month, transitory equatorial opacities, central (nuclear) opalescence, and changes in the vitreous humour. Similar effects were observed in dogs receiving 1 and 3 ml/kg but they occurred more slowly.
No abnormalities, other than those in the eye, were detected during macroscopic or microscopic examination of organs. The retina was normal. Changes in the lens included an increase in insoluble protein at all dose levels and a reduction of water content in the 3 and 9 ml/kg group. There was a significant reduction of soluble protein and a reduction in glutathione content in the 9 ml/kg group.

HAEMATOLOGY
The only other change related to red cells (Table I): there were persistently increased PCV and haemoglobin levels, and total red cell count, at 9 ml/kg (Table 1). The red cells had normal haemoglobin concentrations (MCHC) and were of normal size (MCV). Bone marrow examination prior to termination revealed no evidence of toxic changes.

URINALYSIS
Laboratory investigations confirmed the persistence of diuresis in dogs receiving 3 ml/kg and above (increased "overnight" urine volumes, reduced SG and increased water intake during periods of measurement). No renal damage resulted; normal function was demonstrated by the sensitive urine concentration tests and normal plasma urea levels.
It seemed possible that the constant diuresis had resulted in a balance with a slightly higher degree of haemoconcentration than is normally found. No increase in serum proteins could be demonstrated to confirm this possibility.

OTHER FINDINGS
ECG records were normal throughout except for a transient, minimal slowing of the heart rate in recordings made after 4 weeks.
Terminal radiology of excised bone showed no evidence of osteoporosis.

Effect levels

1

Dose descriptor:

LOAEL

Remarks:

ocular effects

Effect level:

1 100 other: mg/kg bw/day

Sex:

male/female

Basis for effect level:

ophthalmological examination

2

Dose descriptor:

NOAEL

Remarks:

other systemic effects excluding ocular effects

Effect level:

1 100 other: mg/kg bw/day

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

haematology

mortality

3

Dose descriptor:

LOAEL

Remarks:

other systemic effects excluding ocular effects

Effect level:

3 300 other: mg/kg bw/day

Sex:

male/female

Basis for effect level:

clinical signs

haematology

urinalysis

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Under the experimental conditions, the Lowest Observed Adverse Effect Level (LOAEL) is 1100 mg/kg/day.

Executive summary:

The potential toxicity of DMSO was evaluated following repeated oral administration for 104 weeks. Dogs were pure-bred Pembrokeshire Corgis obtained at the age of 4-5 months and were assigned to groups; 5 males and 5 females per group. Dogs were dosed orally, once per day for 5 days a week, by gastric intubation with a 50% aqueous solution of DMSO. Groups received 9, 3, or 1 ml/kg/day. A control group received 1 ml distilled water/kg/day.

After 18 weeks, unexpected eye changes were observed. Dosing was continued for half the dogs in each group for the remaining 86 weeks; the other half was not treated but observed for signs of recovery.

Clinical signs were recorded daily and all animals were subjected to regular veterinary examinations, including ophthalmoscopy. Bodyweight was recorded once a week. Food intake was measured twice daily. ECG and laboratory investigations were performed on all dogs three times before dosing commenced and then after 1, 3, 4.5, 6, 9, 12, 18, and 24 months' administration. Laboratory monitoring comprised haematological assessments including ESR, PCV, haemoglobin, total red and white cell counts with differential, reticulocyte and platelet counts, prothrombin and clotting times; biochemical investigation, mainly by auto-analytical techniques, included plasma urea, total reducing substances, total serum proteins and electrophoresis, SAP, SGPT and SGOT, serum isocitric dehydrogenase and serum cholesterol. A routine series of qualitative urinalysis tests were performed, together with microscopy of the spun deposit. Additional studies performed prior to termination included bone radiography, BSP tests, serum and urine electrolytes and red cell fragility. All animals were then sacrificed humanely and a detailed macroscopic post-mortem examination made, during which the principal organs were weighed and tissues taken for routine histopathological examination.  The eye was subjected to a specific procedure: both eyes were enucleated, placed in normal saline, examined and then photographed, using either the slit-lamp microscope or a Rayner-Wray close-up camera. Aqueous humour was removed by needle puncture and the volume of liquid measured. The lenses were removed, weighed and subjected to extensive biochemical and histological examinations.

There were no marked clinical signs and only one death occurred, after the 4th dose at the intermediate level. This was caused by accidental inspiration of DMSO, leading to a severe pulmonary reaction; the animal was replaced. Occasional isolated bouts of vomiting were seen at 9 ml/kg/day and transitory "head shaking" was temporarily observed during weeks 11 and 12 at this and the 3 ml/kg/day level.

No adverse effects on bodyweight and food intake were recorded.

Ocular effects were observed after 5-10 weeks dosing in the dogs receiving 9 ml/kg including central (nuclear) lenticular changes with alteration of the refractive index (myopia) and by the fifth month, transitory equatorial opacities, central (nuclear) opalescence, and changes in the vitreous humour. Similar effects were observed in dogs receiving 1 and 3 ml/kg but they occurred more slowly.

No abnormalities, other than those in the eye, were detected during macroscopic or microscopic examination of organs. The retina was normal. Changes in the lens included an increase in insoluble protein at all dose levels and a reduction of water content in the 3 and 9 ml/kg group. There was a significant reduction of soluble protein and a reduction in glutathione content in the 9 ml/kg group.

The only other change related to red cells: there were persistently increased PCV and haemoglobin levels, and total red cell count, at 9 ml/kg (Table 1). The red cells had normal haemoglobin concentrations (MCHC) and were of normal size (MCV). Bone marrow examination prior to termination revealed no evidence of toxic changes.

Laboratory investigations confirmed the persistence of diuresis in dogs receiving 3 ml/kg and above (increased "overnight" urine volumes, reduced SG and increased water intake during periods of measurement). No renal damage resulted; normal function was demonstrated by the sensitive urine concentration tests and normal plasma urea levels.

It seemed possible that the constant diuresis had resulted in a balance with a slightly higher degree of haemoconcentration than is normally found. No increase in serum proteins could be demonstrated to confirm this possibility.

ECG records were normal throughout except for a transient, minimal slowing of the heart rate in recordings made after 4 weeks.

Terminal radiology of excised bone showed no evidence of osteoporosis.

Consequently, the NOAEL for the systemic effects, excluding the ocular effects, is 1100 mg/kg bw/day. The LOAEL for the ocular effects is 1100 mg/kg bw/day and the LOAEL for the other systemic effects is 3300 mg/kg bw/day based on clinical signs, heamatological changes and increased diuresis.