Gliotoxin-¹³C₁₃is intended for use as an internal standard for the quantification of gliotoxin by GC- or LC-MS. Gliotoxin is an immunosuppressive mycotoxin produced by pathogenic strains ofAspergillusand other fungi with diverse biological activities.^{1,2,3,4,5,6,7,8}It inhibits 20S proteasomal chymotrypsin activity (IC₅₀= 10 μM), blocking the degradation of IκBα and preventing the activation of NF-κB.^2,3Gliotoxin induces apoptosis in monocytes and dendritic cells and reduces phagocytosis by neutrophils.^4,5It suppresses viral infection by Nipah and Hendra virus in HEK293T cells (IC₅₀s = 149 and 579 nM, respectively).⁶Under reducing conditions, gliotoxin inhibits leukotriene A₄hydrolase epoxide hydrolase activity, but not aminopeptidase activity, and leukotriene B₄synthesis in neutrophils and monocytes.⁷In vivo, gliotoxin (5 mg/kg) reduces LTB₄plasma levels and blocks peritoneal neutrophil infiltration in a mouse model of peritonitis induced by zymosan A . It also inhibits geranylgeranyltransferase I and farnesyltransferase (IC₅₀s = 17 and 80 μM, respectively).⁸

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