Hepatoprotective Effects of Cipollotto Nocerino Leaf Extract in HepG2 Cells: SIRT1‐Mediated Regulation of Lipid Metabolism and Oxidative Stress

Cipollotto Nocerino (Allium cepa L.), a Protected Designation of Origin (PDO) spring onion from the Campania region (Southern Italy), yields leaves that are a neglected agri-food by-product, typically discarded despite their rich phytochemical profile, and remain largely unexplored, particularly regarding their potential to counteract hepatic steatosis. This study evaluated the hepatoprotective activity of a CN leaf alcoholic extract in HepG2 cells exposed to oleic acid (OA) and palmitic acid (PA) to induce steatosis, in both two- and three-dimensional culture systems. UHPLC-HRMS/MS analysis revealed a complex phytochemical profile comprising polar and apolar lipids, chlorophylls, carotenoids, and flavonoids. These metabolites, known to regulate oxidative stress, inflammation, and lipid metabolism, likely mediate CN’s protective effects against lipotoxicity. In HepG2 cells, CN markedly improved cell viability, attenuated lipid droplet accumulation, restored redox balance, alleviated endoplasmic reticulum (ER) stress, preserved mitochondrial membrane potential, and reduced inflammation markers. Sirtuin 1 (SIRT1) expression and activity were enhanced by CN in the presence of OA/PA, and the pharmacological modulation confirmed its partial involvement in these protective effects. These findings demonstrate that CN counteracts free fatty acid–induced lipotoxicity through an integrated mechanism targeting lipid metabolism, oxidative and ER stress, mitochondrial function, and inflammation, with SIRT1 activation acting as a central, although not exclusive, mediator supporting its potential as a promising, sustainable nutraceutical for the prevention or adjunct management of nonalcoholic fatty liver disease.