Natural Flavonoid Buddleoside Reverses Fatty Liver Disease via AMPK-TFEB Pathway
Buddleoside activates AMPK, suppresses MTORC1, and restores autophagy to combat nonalcoholic steatohepatitis in mice.
Summary
Nonalcoholic steatohepatitis (NASH) combines fatty liver, inflammation, and fibrosis with no approved drug treatments. Researchers at Jilin University tested buddleoside (Bud), a natural flavonoid, in mice fed a high-fat, high-cholesterol diet. Bud reduced hepatic fat accumulation, insulin resistance, inflammation, and fibrosis. Mechanistically, Bud bound the PRKAB1 subunit of AMPK at specific residues (Val81, Arg83, Ser108), activating AMPK, which in turn phosphorylated RPTOR to suppress MTORC1. This freed transcription factor TFEB to enter the nucleus and upregulate the autophagy-lysosomal pathway. Blocking AMPK or knocking out hepatic Tfeb abolished Bud's benefits, confirming the pathway's necessity. These findings position buddleoside as a promising candidate for NASH therapy.
Detailed Summary
Nonalcoholic fatty liver disease (NAFLD) affects hundreds of millions worldwide, and its progressive form—nonalcoholic steatohepatitis (NASH)—combines steatosis, hepatic inflammation, and fibrosis, significantly raising the risk of cirrhosis and hepatocellular carcinoma. Despite this burden, no pharmacological treatments have yet been approved specifically for NASH, making the identification of effective compounds an urgent research priority.
Researchers from Jilin University investigated buddleoside (Bud), a naturally occurring flavonoid with emerging hepatoprotective properties. They fed mice a high-fat and high-cholesterol (HFHC) diet to induce NASH-like pathology and treated them with Bud. In parallel, cell-based experiments used palmitic acid (PA) to model lipotoxicity in hepatocytes. Both in vivo and in vitro systems were employed to characterize Bud's effects on steatosis, insulin resistance, inflammation, and fibrosis, as well as its molecular mechanism.
Bud treatment significantly alleviated all hallmarks of HFHC-induced NASH: hepatic fat deposition, markers of insulin resistance (assessed by glucose-tolerance and insulin-tolerance tests, HOMA-IR), inflammatory signaling (NFKB pathway), and fibrosis (collagen deposition, SMAD2/3 phosphorylation). Crucially, Bud activated AMP-activated protein kinase (AMPK), inhibited MTOR complex 1 (MTORC1), and enhanced the nuclear translocation and transcriptional activity of TFEB, which governs the autophagy-lysosomal pathway (ALP). Autophagic flux markers (MAP1LC3/LC3, SQSTM1) confirmed restored autophagy.
Mechanistic studies using drug affinity responsive target stability (DARTS) assays, cellular thermal shift assays (CETSA), and molecular docking revealed that Bud physically binds to the PRKAB1 (β1) regulatory subunit of AMPK at residues Val81, Arg83, and Ser108—a site consistent with the allosteric drug and metabolite (ADaM) binding pocket. This interaction activates AMPK, which then phosphorylates RPTOR (a component of MTORC1), suppressing MTORC1 kinase activity. Reduced MTORC1 activity releases TFEB from inhibitory cytoplasmic sequestration, allowing nuclear entry and transcription of autophagy and lysosomal genes. Genetic confirmation came from experiments using the AMPK inhibitor compound C and hepatocyte-specific Tfeb knockout (tfeb-HKO) mice: both interventions abolished Bud's protective effects, demonstrating that the AMPK→MTORC1→TFEB axis is essential for Bud's mechanism of action.
These findings carry important translational implications. Buddleoside is a well-characterized natural compound with an established safety profile, making it an attractive lead for drug development. Its ability to target AMPK at the PRKAB1 subunit rather than the catalytic site may confer selectivity advantages. However, the study was conducted exclusively in rodent models and cell lines; human pharmacokinetics, long-term safety, and clinical efficacy remain to be established. Additionally, NASH involves complex multicellular pathophysiology—including stellate cells and immune cells—that may not be fully captured in the hepatocyte-centric experiments performed here.
Key Findings
- Buddleoside reduced hepatic steatosis, insulin resistance, inflammation, and fibrosis in HFHC diet-fed mice.
- Bud directly binds AMPK's PRKAB1 subunit at Val81, Arg83, and Ser108, activating the kinase.
- AMPK activation by Bud suppresses MTORC1 via RPTOR phosphorylation, freeing TFEB for nuclear entry.
- Hepatocyte-specific Tfeb knockout or AMPK inhibition completely abolished Bud's hepatoprotective effects.
- Bud restored autophagic flux, confirmed by improved LC3-II turnover and reduced SQSTM1 accumulation.
Methodology
Mouse NASH was induced by high-fat, high-cholesterol diet; cell models used palmitic acid-treated hepatocytes. Target engagement was confirmed by DARTS, CETSA, and molecular docking. Genetic validation employed hepatocyte-specific Tfeb knockout mice and pharmacological AMPK inhibition with compound C.
Study Limitations
All experiments were performed in rodent models and cultured hepatocytes; human pharmacokinetics and clinical efficacy are unknown. The study focused primarily on hepatocytes, potentially underrepresenting contributions of hepatic stellate cells, Kupffer cells, and systemic metabolic factors to NASH pathogenesis.
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