Capsaicin acts as a novel NRF2 agonist to suppress ethanol induced gastric mucosa oxidative damage by directly disrupting the KEAP1-NRF2 interaction

Abstract

Ethanol induced oxidative damage to the gastric mucosa is one of the causes of gastritis and gastric ulcers. The KEAP1/NRF2 system stands as the principal regulator of reactive oxygen stress (ROS). Capsaicin (CAP), a naturally small molecule from chili, is recognized for its antioxidant and anti-inflammatory attributes. Yet, the mechanistic action remains largely unknown. In the study, we established an in vitro oxidative stress model using ethanol-exposed human gastric mucosal epithelial (GES-1) cells. We found that CAP pretreatment effectively mitigated ROS levels and preserved mitochondrial integrity. Proteomic analysis indicated a significant enrichment of antioxidant-associated pathways. Intriguingly, CAP augmented NRF2 protein expression and facilitated its nuclear translocation, thereby amplifying the transcription and translation of downstream antioxidant response elements (ARE), such as HO-1, NQO1, Trx and GSS. These observations were congruent in hydrogen peroxide-exposed mesenchymal stem cells, which indicates the universality of its antioxidant ability. Furthermore, CAP was found to inhibit the KEAP1-NRF2 interaction, and it failed to trigger the activation of NRF2 after KEAP1 knockout in 293T. CAP specifically interacts with the Kelch domain of KEAP1 and binds to allosteric sites. To enhance drug safety, we also formulated and characterized IR-HSA@CAP nanoparticles. In vivo assessments corroborated that CAP markedly curtailed ROS and invigorated the NRF2/ARE pathway. Additionally, CAP modulated inflammatory markers, reducing IL-1β, TNF-α, IL-6, and CXCL1/KC(IL-8), while elevating IL-10 in gastric tissues. Given that the non-covalent binding modality of natural compounds to KEAP1 remains underreported, CAP may emerge as a pioneering direct inhibitor of the KEAP1-NRF2 interaction.