Cardamonin protects against diabetic cardiomyopathy by activating macrophage NRF2 signaling through molecular interaction with KEAP1

Diabetic cardiomyopathy (DCM) contributes to a large proportion of heart failure incidents in the diabetic population, but effective therapeutic approaches are rare. Cardamonin (CAD), a flavonoid found in Alpinia, possesses anti-inflammatory and anti-oxidative activities. Here we report a profound protective effect of CAD on DCM in a mouse model of type 2 diabetes induced by streptozotocin and a high-fat diet, in which gavage with CAD improved hyperglycemia and glucose intolerance and mitigated diabetic cardiac injuries including cardiac dysfunction, hypertrophy, apoptotic cell death and infiltration of inflammatory cells, especially M1 polarized macrophages. To verify whether CAD could protect against cardiomyocyte injury through inhibiting macrophage M1 polarization, M1 polarized macrophages were treated with CAD, followed by washing out and co-culturing with cardiomyocytes, showing that CAD remarkably inhibited macrophage M1 polarization and the following cardiomyocyte injury, along with activation of the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant signaling pathway. Molecular docking and surface plasmon resonance assays found Kelch-like ECH-associated protein 1 (KEAP1) as the molecular target of CAD. Both CAD and the Kelch domain inhibitor Ki696 promoted the nuclear translocation of nuclear factor erythroid 2-related factor 2 (NRF2). This work may provide CAD as a novel NRF2 activator in future interventions for DCM.