Novel Choline-Deficient and 0.1%-Methionine-Added High-Fat Diet Induces Burned-Out Metabolic-Dysfunction-Associated Steatohepatitis with Inflammation by Rapid Immune Cell Infiltration on Male Mice

<b>Background:</b> Metabolic-dysfunction-associated steatotic liver disease (MASLD) is a progressive liver disorder that possesses metabolic dysfunction and shows steatohepatitis. Although the number of patients is globally increasing and many clinical studies have developed medicine for MASLD, most of the studies have failed due to low efficacy. One reason for this failure is the lack of appropriate animal disease models that reflect human MASLD to evaluate the potency of candidate drugs. <b>Methods:</b> We developed a novel choline-deficient and 0.11%-methionine-added high-fat diet (CDAHFD)-based (MASH) diet that can induce murine metabolic-dysfunction-associated steatohepatitis (MASH) without severe body weight loss. We performed kinetic analyses post-feeding and proposed an appropriate timing of MASH pathogenesis by quantitatively analyzing steatosis, inflammation, and fibrosis. <b>Results:</b> This MASH diet induced liver fibrosis earlier than the conventional CDAHFD model. In brief, lipid accumulation, inflammation, and fibrosis started after 1 week from feeding. Lipid accumulation increased until 8 weeks and declined thereafter; on the other hand, liver fibrosis showed continuous progression. Additionally, immune cells, especially myeloid cells, specifically accumulated and induced inflammation in the initiation stage of MASH. <b>Conclusions:</b> The novel MASH diet promotes the dynamics of lipid deposition and fibrosis in the liver, similar to human MASH pathophysiology. Furthermore, immune-cell-derived inflammation possibly contributes to the initiation of MASH pathogenesis. We propose this model can be the new pre-clinical MASH model to discover the drugs against human MASH by evaluating the interaction between parenchymal and non-parenchymal cells.