BDK inhibition acts as a catabolic switch to mimic fasting and improve metabolism in mice.

OBJECTIVE: Branched chain amino acid (BCAA) catabolic defects are implicated to be causal determinates of multiple diseases. This work aimed to better understand how enhancing BCAA catabolism affected metabolic homeostasis as well as the mechanisms underlying these improvements. METHODS: The rate limiting step of BCAA catabolism is the irreversible decarboxylation by the branched chain ketoacid dehydrogenase (BCKDH) enzyme complex, which is post-translationally controlled through phosphorylation by BCKDH kinase (BDK). This study utilized BT2, a small molecule allosteric inhibitor of BDK, in multiple mouse models of metabolic dysfunction and NAFLD including the high fat diet (HFD) model with acute and chronic treatment paradigms, the choline deficient and methionine minimal high fat diet (CDAHFD) model, and the low-density lipoprotein receptor null mouse model (Ldlr-/-). shRNA was additionally used to knock down BDK in liver to elucidate liver-specific effects of BDK inhibition in HFD-fed mice. RESULTS: A rapid improvement in insulin sensitivity was observed in HFD-fed and lean mice after BT2 treatment. Resistance to steatosis was assessed in HFD-fed mice, CDAHFD-fed mice, and Ldlr-/- mice. In all cases, BT2 treatment reduced steatosis and/or inflammation. Fasting and refeeding demonstrated a lack of response to feeding-induced changes in plasma metabolites including insulin and beta-hydroxybutyrate and hepatic gene changes in BT2-treated mice. Mechanistically, BT2 treatment acutely altered the expression of genes involved in fatty acid oxidation and lipogenesis in liver, and upstream regulator analysis suggested that BT2 treatment activated PPARα. However, BT2 did not directly activate PPARα in vitro. Conversely, shRNA-AAV-mediated knockdown of BDK specifically in liver in vivo did not demonstrate any effects on glycemia, steatosis, or PPARα-mediated gene expression in mice. CONCLUSIONS: These data suggest that BT2 treatment acutely improves metabolism and liver steatosis in multiple mouse models. While many molecular changes occur in liver in BT2-treated mice, these changes were not observed in mice with AAV-mediated shRNA knockdown of BDK. All together, these data suggest that systemic BDK inhibition is required to improve metabolism and steatosis by prolonging a fasting signature in a paracrine manner. Therefore, BCAA may act as a "fed signal" to promote nutrient storage and reduced systemic BCAA levels as shown in this study via BDK inhibition may act as a "fasting signal" to prolong the catabolic state.

Acetyl-CoA Carboxylase Inhibition Improves Multiple Dimensions of NASH Pathogenesis in Model Systems.

BACKGROUND & AIMS: Disordered metabolism, steatosis, hepatic inflammation, and fibrosis contribute to the pathogenesis of nonalcoholic steatohepatitis (NASH). Acetyl-CoA carboxylase (ACC) catalyzes the first committed step in de novo lipogenesis (DNL) and modulates mitochondrial fatty acid oxidation. Increased hepatic DNL flux and reduced fatty acid oxidation are hypothesized to contribute to steatosis. Some proinflammatory cells also show increased dependency on DNL, suggesting that ACC may regulate aspects of the inflammatory response in NASH. PF-05221304 is an orally bioavailable, liver-directed ACC1/2 inhibitor. The present studies sought to evaluate the effects of PF-05221304 on NASH pathogenic factors in experimental model systems. METHODS: The effects of PF-05221304 on lipid metabolism, steatosis, inflammation, and fibrogenesis were investigated in both primary human-derived in vitro systems and in vivo rodent models. RESULTS: PF-05221304 inhibited DNL, stimulated fatty acid oxidation, and reduced triglyceride accumulation in primary human hepatocytes, and reduced DNL and steatosis in Western diet-fed rats in vivo, showing the potential to reduce hepatic lipid accumulation and potentially lipotoxicity. PF-05221304 blocked polarization of human T cells to proinflammatory but not anti-inflammatory T cells, and suppressed activation of primary human stellate cells to myofibroblasts in vitro, showing direct effects on inflammation and fibrogenesis. Consistent with these observations, PF-05221304 also reduced markers of inflammation and fibrosis in the diethylnitrosamine chemical-induced liver injury model and the choline-deficient, high-fat-fed rat model. CONCLUSIONS: The liver-directed dual ACC1/ACC2 inhibitor directly improved multiple nonalcoholic fatty liver disease/NASH pathogenic factors including steatosis, inflammation, and fibrosis in both human-derived in vitro systems and rat models.