Structural Characterization and Lipid-lowering Mechanisms of a Novel Acidic Polysaccharide from Wild Bitter Melon (Momordica charantia L. var. abbreviata) in a High-fat diet Zebrafish Model

Background: Wild bitter melon (Momordica charantia L. var. abbreviata Ser., WBM) is a traditional food-medicine homologous plant endemic to southern China, known for its excellent antidiabetic and lipid-lowering properties. However, the structural characteristics and precise metabolic mechanisms of its polysaccharides remain underexplored. This study aimed to isolate and structurally characterize a novel acidic polysaccharide from WBM and evaluate its lipid-lowering effects both in vitro and in vivo. Methods: A polysaccharide fraction WBP75-3-1 was isolated using DEAE-Sepharose Fast Flow and Sephadex G-75 chromatography. Its structure was characterized using high-performance gel permeation chromatography (HPGPC), ion chromatography, methylation analysis, and Nuclear Magnetic Resonance (NMR) spectroscopy. The lipid-lowering potential was assessed by measuring its in vitro fat-, bile acid-, and cholesterol-binding capacities as well as pancreatic lipase inhibition. Oleic acid–induced hyperlipidemic HepG2 cells and high-fat diet zebrafish models were used to evaluate its lipid metabolism-improving effects. Transcriptome analysis and RT-qPCR/Western blot were performed to elucidate potential mechanisms. Results: WBP75-3-1 was identified as a 5.25 kDa low-molecular-weight acidic polysaccharide mainly composed of galacturonic acid, galactose, rhamnose, and arabinose, with a backbone of →4)-α-GalpA-(1→ and branched arabinofuranose and galactose residues. It showed notable in vitro fat (55.83% ± 1.67%), bile acid (18.85% ± 1.38%), and cholesterol-binding capacities (52.81% ± 1.58%), and effectively inhibited pancreatic lipase. In OA-induced HepG2 cells and hyperlipidemic zebrafish, WBP75-3-1 significantly reduced TC, TG, and LDL-C levels, increased HDL-C, and improved oxidative stress markers. Transcriptomic and protein analyses revealed that it modulates multiple pathways, including SREBP2, HMGCR, SOAT2, ABCG8, PLTP, and SORT1, indicating multitarget regulation of lipid metabolism. Conclusions: WBP75-3-1 is a GalA-rich acidic polysaccharide that exerts potent lipid-lowering effects by simultaneously regulating lipid synthesis, storage, transport, and excretion pathways. These findings highlight the potential of WBP75-3-1 as a natural hypolipidemic agent for managing metabolic disorders.