Compounds Contributing to the Modulation of Visceral Adiposity and Hepatic Lipid Metabolism in High-Fat-Diet-Fed Rats by Pometia pinnata (Matoa) Peel Powder: Identification of Pancreatic Lipase Inhibitors

Background: Pometia pinnata (matoa) peel powder attenuates high-fat diet-induced adiposity and hepatic lipid accumulation in rats, but the responsible compounds remain unclear. This study aimed to identify the bioactive compounds that may contribute to this phenotype, with an emphasis on pancreatic lipase inhibition as a candidate mechanism. Methods: Rats received high-fat diets containing matoa peel powder, or its water- or ethanol extraction residue. Visceral fat accumulation, hepatic lipid deposition, and serum lipid profiles were evaluated. An ethanol extract was fractionated by activity-guided column chromatography based on pancreatic lipase-inhibitory activity, and structures were identified by nuclear magnetic resonance analysis. Static in vitro gastrointestinal digestion was performed to assess inhibition of fatty acid release by the extract or isolated compounds. Results: The visceral adiposity- and hepatic lipid-modulating effects observed with matoa peel powder were retained in the water extraction residue but not in the ethanol extraction residue, suggesting removal of bioactive constituents by ethanol extraction. The ethanol extract inhibited pancreatic lipase (IC50 = 740 µg/mL). Two active compounds—hederagenin saponin and protocatechuic acid—were isolated, and both inhibited pancreatic lipase (IC50 = 149 µmol/L and 404 µmol/L, respectively). Under simulated digestion in vitro, the ethanol extract and protocatechuic acid reduced free fatty acid release, whereas hederagenin saponin did not. Conclusions: Matoa peel powder contains ethanol-soluble constituents, including pancreatic lipase-inhibitory compounds that may contribute to the modulation of adiposity and hepatic lipid metabolism in high-fat-diet-fed rats. The attenuation of individual-compound activity under simulated digestion is consistent with matrix- and intestinal milieu-dependent effects, and supports a multi-component mechanism involving saponins, phenolics (protocatechuic acid), and their intestinal biotransformation products.