Introduction. Dimethyl sulfoxide (DMSO) is a solvent widely used in biomedical research. It is known to interfere with cell signaling, but at a final concentration of 1% or lower is often deemed safe. One of the applications of DMSO is to dissolve hydrophobic compounds. During the characterization of a novel hydrophobic anti-inflammatory compound, we found that dilutions of 4 orders of magnitude of the compound diluted in DMSO, used at a 1% final concentration in cell culture media, strongly inhibited the lipopolysaccharide (LPS) induction of Interleukin (IL)-1b and Tumor Necrosis Factor (TNF)-a secretion without a dose-dependent effect (p<0.001 for all doses).

Hypothesis. We hypothesized that DMSO could inhibit LPS-dependent cytokine release.

Methods. We stimulated mouse macrophages (J774.1 cells) with LPS (1 µg/ml, 6h, to activate NF-kB-dependent gene expression) and administered ATP (5 mM, 30 min). LPS promotes TNF-a secretion and pro-IL-1b intracellular production, while ATP induces caspase-1-dependent IL-1 b maturation and release. Cells were exposed to increasing concentrations of DMSO (0.2, 0.5, 1.0%). We collected the cell supernatants and performed ELISA assays to measure IL-1b and TNF-a production.

Results. The 1% dose of DMSO significantly reduced IL-1β secretion (205±12 vs 709±7 pg/ml; p<0.0001); 0.5% and 0.2% DMSO had no effect. DMSO at concentrations of 1.0% and 0.5% reduced TNF-α (1348±37 and 2672±25 vs 3125±27 pg/ml; all p<0.0001); 0.2% DMSO had no effect on TNF-α release.

Conclusion. DMSO induces a dose-dependent inhibition of IL-1β and TNF-α by reducing LPS/NF-kB-dependent gene expression.