Alpinetin inhibits macrophage infiltration and atherosclerosis by improving the thiol redox state: Requirement of GSk3β/Fyn-dependent Nrf2 activation.

Alpinetin is a plant flavonoid isolated from Alpinia katsumadai Hayata with antioxidant and anti-inflammatory properties. Monocyte infiltration into the intima promotes atherosclerotic development and causes plaque instability at the later stage, which is profoundly influenced by various oxidants. In this study, we investigated whether alpinetin restores the redox state to inhibit monocyte infiltration and ameliorates atherosclerosis. ApoE-deficient (ApoE-/- ) mice were fed a high-fat diet and treated with alpinetin. We found that alpinetin significantly attenuated atherosclerotic lesions and reduced necrotic core size associated with the reduction in infiltrated macrophages within the plaques. Alpinetin inhibited macrophage adhesion and migration, and the expression of chemokines and adhesion molecules, such as MCP-1, VCAM-1, and ICAM-1. Intraplaque MMP2 and MMP9 were reduced, while collagen contents were increased and elastin fiber was prevented from degradation in the alpinetin-treated mice. Data further showed that alpinetin reduced reactive oxygen species generation and promoted thiol-dependent glutathione and thioredoxin antioxidant systems in macrophages. Alpinetin activated Nfr2, an upstream activator of the thiol-dependent redox signaling by increasing the nuclear translocation. The nuclear accumulation of Nrf2 was enhanced by reducing nuclear export, which was achieved through the regulation of the GSk3β/Fyn pathway. Finally, inhibition of Nrf2 in HFD-apoE-/- mice blockaded the effect of alpinetin, which increased aortic macrophage recruitment and aggravated atherosclerosis concurrently with elevating the expression of MCP-1, VCAM-1, and ICAM-1. Altogether, these findings indicated that alpinetin improved Nrf2-mediated redox homeostasis, which consequently inhibited macrophage infiltration and atherosclerosis, suggesting a useful compound for treating atherosclerosis.