A glutamine synthetase inhibitor increases survival and decreases cytokine response in a mouse model of acute liver failure

Background: Acute liver failure (ALF) can be induced in mice by administering Escherichia coli lipopolysaccharide (LPS) and D-galactosamine (D-GalN), which induce an inflammatory response involving tumour necrosis factor (TNF)-alpha production and a hepatocyte-specific transcriptional block. Under these conditions, binding of TNF-alpha to its cognate receptor on hepatocytes eventually leads to their apoptosis. Aims: As part of an effort to identify drugs to treat this disease model, we have investigated whether the glutamine synthetase inhibitor methionine sulfoximine (MSO) could play a protective role, given its effectiveness in the inhibition of brain swelling associated with hyperammonaemia. Methods: Mouse survival, glutamine synthetase activity, hepatocyte apoptosis and induction of inflammatory cytokines were measured in mice treated with MSO before an intraperitoneal injection of LPS/D-GalN. The effect of MSO on viability and on TNF-alpha release was also assessed on inflammatory and liver cells. Results: We have found that, in mice treated with LPS/D-GalN, MSO (i) drastically increases animal survival; (ii) sharply reduces glutamine synthetase activity, without inhibiting its other target, gamma-glutamyl cysteine synthetase; (iii) inhibits death receptor-mediated apoptosis in hepatocytes upstream to cytokine binding; (iv) strongly reduces the overall inflammatory cytokine response, including a significant decrease in TNF-alpha induction in vivo and ex vivo, and in the interferon-gamma level and signalling. Conclusions: These results demonstrate that the MSO target glutamine synthetase is required for the early steps of the cytokine response to endotoxins, and that its pharmacological inhibition may be exploited to treat inflammation.