Complex I Modulator BI4500 Reduces MASH by Limiting Oxidative Stress and Reprogramming Lipid Metabolism via AMPK in MCD Rats

BACKGROUND: Metabolic-dysfunction-associated steatotic liver disease (MASLD) is a multifactorial liver disease in which mitochondrial dysfunction, oxidative stress, and inflammation play key roles in driving the progression toward metabolic dysfunction-associated steatohepatitis (MASH) and hepatocellular carcinoma (HCC). Dysfunctional mitochondria generate excess reactive oxygen species (ROS), impair antioxidant defenses, activate pro-inflammatory pathways and hepatic stellate cells, and perpetuate liver injury. Mitochondrial Complex I is a major ROS source, particularly under conditions of dysregulated energy metabolism. Since Complex I inhibition by metformin was shown to reduce ROS and activate the adenosine monophosphate-activated protein kinase (AMPK), this study aimed to evaluate whether a novel Complex I Modulator (CIM, BI4500) could attenuate oxidative stress, inflammation, and consequently reduce lipid accumulation and fibrosis in a methionine- and choline-deficient diet (MCD)-fed rat model of MASH. METHODS: Rats were fed an MCD or an isocaloric control diet for six weeks. From week four, animals received daily oral treatment with CIM (10 mg/kg) or vehicle (Natrosol). At the endpoint, liver tissue was collected for histological, biochemical, and molecular analyses. Lipid droplet area, inflammatory infiltration, and collagen deposition were evaluated on tissue sections; total lipid content and oxidative stress markers were assessed in homogenates and isolated mitochondria. Molecular pathways related to oxidative stress, lipid metabolism, and fibrosis were assessed at protein and mRNA levels. RESULTS: CIM treatment significantly reduced oxidative stress (ROS, lipid peroxidation, nitrogen species), promoting AMPK activation and metabolic reprogramming. This included increased expression of peroxisome proliferator-activated receptor alpha (PPAR-α) and its target genes, and decreased sterol regulatory element binding protein-1c (SREBP-1c)-driven lipogenesis. These changes halted fibrosis progression, as confirmed by Picro-Sirius Red staining and fibrosis markers. CONCLUSIONS: these findings indicate that Complex I modulation may represent a promising strategy to counteract MASLD progression toward MASH.