Dimethyl sulfoxide

Immunotoxicity

Key value for chemical safety assessment

Effect on immunotoxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

NOAEC

2 800 mg/m³

Additional information

As part of a 13-week inhalation toxicity study (Kenny, 2000, see section 7.5.3), four satellite groups of Sprague-Dawley rats (5/sex/group) were exposed snout-only, 6 h/day, 7 d/week, for 28 days to mean analyzed chamber concentrations of 0, 0.310, 0.964 and 2.783 mg DMSO/l. To act as a positive control, a further group of satellite animals were injected i.p. with cyclophosphamide at a dose of 50 mg/kg 2 days prior to termination. The study was designed to comply with OECD/US EPA OPPTS guidelines and GLP regulations. Sheep Red Blood Cell (SRBC)-specific antibody secreting cells (ASCs) were enumerated using a modification of the Jerne Plaque Forming Cell (PFC) assay. Inhalation exposure to DMSO led to an apparent increase in the number of antibody secreting cells in male rats, compared with controls. Changes in the total number of antibody secreting cells in the spleen (PFC/spleen) and also changes in the relative numbers of antibody secreting cells, associated with changes in other spleen cell populations (PFC/10e⁶ cells) were measured. Since DMSO increased both PFC/10e⁶ cells and PFC/spleen in male rats, the effect is likely to be a genuine enhancement, not simply a broad spectrum increase in spleen cell numbers. It is worth noting that there was a high degree of inter-animal variation in the PFC response. This is almost certainly linked to the genetic background of the Sprague-Dawley rats, which are an outbred population. The adaptive immune response is known to have strong genetic linkage and work from other sources has shown that whilst outbred species are popular models in toxicology they have an inherent variability in immune responses. Based in the high variability observed in male rats, the lack of effects in female rats and the lack of effect on the other end-points relevant for immunotoxicity (spleen and thymus weights, lymphocyte count) reported in the 13-week study, these data doesn't desmonstrate any effects of toxicological significance on the immune system (Kenny, 2000; reliability 1).

Autoimmune strain MRL/lpr, CH3/lpr, and male BXSB mice were placed on a continuous treatment with 3% DMSO (8-10 g/kg bw/d) in the drinking water, commencing at 1 to 2 months of age, before spontaneous disease development could be detected. DMSO provides significant protection against the development of murine autoimmune lymphoproliferative disease (Morton & Siegel, 1986).

Mice were injected i.p. daily with 1.3-2.5 g/kg 100% DMSO or sterile saline for 5 weeks. All mice were immunized twice with sheep red blood cells (days 13 and 24), and bled twice by caudal incision (days 20 and 29). Haematocrits were significantly decreased but still within the normal range. The primary and secondary antibody response to sheep red blood cells, leukocytes counts, body weight, and the size of the heart, lungs, spleen, thymus, and kidneys were not affected. DMSO treatment resulted in significant liver enlargement (Caren et al., 1985).

Justification for classification or non-classification

Based on the available data, no classification for repeated toxicity has to be applied for DMSO according to EU Directive 67/584/EEC and EU regulation (EC) No 1272/2008 (CLP).