TLR4 is a receptor for PAMPs and DAMPs, and TLR4 deficient mice have

reduced liver injury in ASH models. Broad spectrum antibiotics almost normalized liver histology and transaminases, arguing for a very significant role for PAMPs.[34-36] The recent data showing a role for the microbiome in regulating liver disease also suggest that both PAMPs and DAMPs are present in the liver, and there is a relationship between cancer metabolism inhibitor intestinal PAMPs and endogenous DAMPs.[37] Downstream of TLR4 the MyD88/NF-κB pathway does not have a significant role in ASH, but the TRIF/IRF3 pathway has a critical role through up-regulation of TNF-α.[38, 39] This points away from the inflammasome having a direct role in ASH as up-regulation of pro-IL-1β and other inflammasome components is via the MyD88/NF-κβ pathway.[40] Direct evidence supporting an inflammasome and IL-1β-mediated

pathway in ALD comes from studies showing that mice lacking caspase-1 or IL-1R have reduced steatosis and inflammation, and Torin 1 in vitro this was further supported by the ability of the IL-1R antagonist to duplicate this in wild-type mice.[41] Acute and chronic exposure to large amounts of alcohol has opposite results on inflammation. A single acute dose of alcohol significantly attenuates production of IL-1β and TNF-α.[42] In contrast exposure of monocytes to alcohol for more than four days was associated with augmented LPS-induced cytokine production.[42] This poses the question if the contrasting effects of acute and chronic alcohol on liver inflammation have any interactions with Elongation factor 2 kinase other inflammatory liver conditions. Elevations in serum TLR4 ligands have been demonstrated in rodent models, and in human NASH.[43]

In humans, there is also an elevation of free fatty acids, which have been reported to be ligands for TLR4.[44] Many aspects of NASH including histological score, hepatocyte apoptosis, ALT, and fibrogenic markers are reduced in mice lacking TLR4 and TLR9.[45-47] Furthermore, TLR9 is required for normal amounts of IL-1β production from Kupffer cells in NASH, which induces hepatocyte death and hepatic stellate cell activation. Crucially, IL-1β also induces lipid metabolism and hepatocyte steatosis. It was recently demonstrated that although IL-1β cannot induce cell death by itself, it sensitizes hepatocytes to signals from conventional cell death signals such as TNF-α.[45, 48] A direct role for the TLR adaptor protein MyD88 has been demonstrated in MCD model of NASH and results in up-regulation of the AIM2 inflammasome.[45] There was a requirement of MyD88 on bone marrow-derived cells suggesting along with other studies a central role of Kupffer cells in liver SI. The recent demonstration of an important role for the NLRP6 inflammasome in the colonic epithelium in regulating the microbiome was given surprising relevance in NASH.