Hepatoprotective action of Dendrobium officinale polysaccharide against MAFLD: modulation of gut microbiota-metabolite cascade controls TLR4/NF-κB inflammatory response

Introduction Metabolic dysfunction-associated fatty liver disease (MAFLD) threatens public health worldwide, and Dendrobium officinale polysaccharide (DOP) exhibits promising hepatoprotective potential, yet its regulatory mechanism targeting the gut microbiota-metabolite-TLR4/NF-κB inflammatory axis remains poorly defined. Methods In this study, in-vivo rat and in-vitro HepG2 cell MAFLD models were established. Male Sprague-Dawley (SD) rats received 12-week high-fat diet (HFD) feeding to induce MAFLD; HepG2 cells were exposed to a 1 mmol/L free fatty acid (FFA) mixture (oleic acid/palmitic acid = 2:1) for 24 h to trigger cellular steatosis. Serum, hepatic and cellular biochemical indexes, intestinal permeability factors and inflammatory mediators were detected. Hepatic pathological lesions and lipid accumulation were evaluated via hematoxylin-eosin (HE) and Oil Red O staining. Fecal metagenomics and untargeted metabolomics were applied to profile gut microbes and differential metabolites. RT-qPCR and Western blotting were used to assess tight-junction protein expression and TLR4/NF-κB pathway activation. Results DOP markedly alleviated hepatic lipid accumulation, restored liver function abnormalities and mitigated hepatic pathological damage. DOP reshaped the disturbed gut flora: it reduced lipopolysaccharide (LPS)-enriched Gram-negative bacteria, elevated short-chain fatty acid-producing probiotics, modified intestinal metabolites, repaired the intestinal barrier and prevented intestinal LPS leakage. Both cellular and animal experiments demonstrated that DOP down-regulated TLR4, MyD88 and NF-κB p65 levels, increased IκBα expression and suppressed downstream pro-inflammatory mediators. Discussion Collectively, DOP confers protective effects against MAFLD through remodeling gut microbiota and intestinal metabolites, preserving intestinal-barrier integrity, and inhibiting LPS-provoked hepatic TLR4/NF-κB inflammatory activation.