4‐Octyl Itaconate Attenuates Age‐Induced Parotid Gland Dysfunction Through the Suppression of Fibrosis and Lipid Deposition by AMPKα/PPARα and the Inhibition of Oxidative Stress via the AMPKα/Nrf2 Signaling Pathway

Parotid gland aging is a key factor for reduced salivary production in older individuals. The role of 4-Octyl itaconate (4-OI) in age-related parotid gland dysfunction remains unclear. Thirteen-month-old male mice were administered 4-OI (25 mg/kg) or vehicle once daily for 4 weeks. The salivary flow rate was calculated to assess gland secretion function. Hematoxylin and eosin staining was used to analyze morphological alterations. Masson staining was used to quantify collagen deposition. Oil Red O staining was used to evaluate lipid droplet accumulation. Western blotting was used to detect protein expression levels. Metabolomics, transcriptome, and molecular docking analyses were performed to identify potential mechanisms of action. Functional assays revealed that 4-OI increased the salivary flow rate. AMPKα has been identified as a direct target of 4-OI by molecular docking. 4-OI upregulates AMPKα phosphorylation, decreases lipid droplet deposition, and relieves fibrosis to restore the aging characteristics of the gland. 4-OI regulates fatty acid oxidation (FAO) in the parotid gland through AMPKα/PPARα signaling pathways. The protective effects of 4-OI in aged mice were abolished by Compound C and GW6471, which inhibit AMPKα and PPARα, respectively. In addition, we found that 4-OI treatment ameliorated parotid gland aging-induced oxidative reactions, enhanced mitochondrial biogenesis, and activated the Nrf2 pathway. Moreover, the Nrf2 inhibitor ML385 was used to validate this mechanism. Treatment with 4-OI improved the aging of the parotid gland by increasing gland FAO, decreasing gland fibrosis, and preventing oxidative reactions. This was achieved by upregulating the AMPKα/Nrf2 and AMPKα/PPARα signaling pathways.