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ToxSci Advance Access originally published online on June 2, 2005
Toxicological Sciences 2005 87(1):75-85; doi:10.1093/toxsci/kfi215
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© The Author 2005. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org

Sodium Methyldithiocarbamate Inhibits MAP Kinase Activation through Toll-like Receptor 4, Alters Cytokine Production by Mouse Peritoneal Macrophages, and Suppresses Innate Immunity

Stephen B. Pruett1, Qiang Zheng, Carlton Schwab and Ruping Fan

Department of Cellular Biology and Anatomy, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130

Received April 28, 2005; accepted May 27, 2005

Sodium methyldithiocarbamate (SMD; trade name, Metam Sodium) is an abundantly used soil fumigant that can cause adverse health effects in humans, including some immunological manifestations. The mechanisms by which SMD acts, and its targets within the immune system are not fully understood. Initial experiments demonstrated that SMD administered by oral gavage substantially decreased IL-12 production and increased IL-10 production induced by lipopolysaccharide in mice. The present study was conducted to further characterize these effects and to evaluate our working hypothesis that the mechanism for these effects involves alteration in signaling through toll-like receptor 4 and that this would suppress innate immunity to infection. SMD decreased the activation of MAP kinases and AP-1 but not NF-{kappa}B in peritoneal macrophages. The expression of mRNA for IL-1{alpha}, IL-1ß, IL-18, IFN-{gamma}, IL-12 p35, IL-12 p40, and macrophage migration inhibitory factor (MIF) was inhibited by SMD, whereas mRNA for IL-10 was increased. SMD increased the IL-10 concentration in the peritoneal cavity and serum and decreased the concentration of IL-12 p40 in the serum, peritoneal cavity, and intracellularly in peritoneal cells (which are >80% macrophages). Similar effects on LPS-induced cytokine production were observed following dermal administration of SMD. The major breakdown product of SMD, methylisothiocyanate (MITC), caused similar effects on cytokine production at dosages as low as 17 mg/kg, a dosage relevant to human exposure levels associated with agricultural use of SMD. Treatment of mice with SMD decreased survival following challenge with non-pathogenic Escherichia coli within 24–48 h, demonstrating suppression of innate immunity.

Key Words: sodium methyldithiocarbamate; immune system; toll-like receptor 4; methylisothiocyanate; Escherichia coli.


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