Use of methionine sulfoximine to dissect the role of glutamine synthetase and glutamine in progression of acute liver failure

Methionine sulfoximine (MSO) is a modified amino acid and a well characterized irreversible inhibitor of glutamine synthetase (GS) enzyme. Glutamine is synthesized by GS enzyme and it is the most abundant amino acid in the body. Glutamine is required by immune cells for generation, propagation and maintenance of an immune response. To induce acute liver failure (ALF) in mice, animals were given intraperitoneal injections of E. coli lipopolysaccharides (LPS) and sugar D-galactosamine (D-GalN). When these animals were pretreated with MSO, 80% of the animals were completely rescued from liver failure. Moreover, when we characterized the immune response generated during ALF using cytokine antibody microarrays, we observed 1) that the macrophages and neutrophils appeared to be responsible for the cytokine storm generated during ALF, and 2) MSO pretreatment reduced the entire measured cytokine response. Using ELISA assays we observed that MSO pretreatment reduced plasma cytokine values of TNF-α, IFN-γ and IL-6 by more than 50%. MSO inhibited GS by more than 90% in liver extracts and reduced plasma glutamine by around 75%. MSO pretreatment had no effect on GS protein levels and on kupffer cell (liver macrophages) infiltration in liver. GS and TNF-α transcript levels were unaffected by MSO pretreatment. Also, preliminary results show that MSO does not inhibit cellular and secreted protein synthesis globally in LPS stimulated peritoneal macrophage cell culture. However, MSO treatment reduces TNF-α production in the LPS stimulated peritoneal macrophages. Thus, it seems that inhibiting GS during stress conditions such that low levels of plasma glutamine are maintained can lead to a reduction in inflammatory cytokines. Also, MSO might have targets other than glutamine synthetase. These results show a novel use for MSO in attenuating the overall immune inflammatory response in liver