– 4-Hydroxynonenal (4-HNE) is an ?,? unsaturated hydroxyalkenal and an oxidative/nitrosative stress biomarker. 4-Hydroxynonenal is a substrate and an inhibitor of acetaldehyde dehydrogenase 2 (ALDH2). 4-Hydroxynonenal can modulate a number of signaling processes mainly through forming covalent adducts with nucleophilic functional groups in proteins, nucleic acids, and membrane lipids. 4-Hydroxynonenal plays an important role in cancer through mitochondria.