Nrf-2 mediated heme oxygenase-1 expression, an antioxidant-independent mechanism, contributes to anti-atherogenesis and vascular protective effects of Ginkgo biloba extract

Aims: Vascular protective effects of Ginkgo biloba extract (GBE) may involve both antioxidant-related and anti-inflammatory mechanisms. GBE was recently suggested as a heme oxygenase (HO)-1 inducer. The role of HO-1 in anti-atherogenesis and related vascular protective effects of GBE awaited further clarification. Methods and results: Tumor necrosis factor (TNF)-α was used to stimulate adhesiveness of human aortic endothelial cells (HAECs) to monocytes, an in vitro sign simulating atherogenesis. Pretreatment with GBE reduced TNF-α-stimulated endothelial adhesiveness, which could be attenuated by HO-1 inhibitors ZnPP IX or SnPP IX. GBE increased HO-1 expression and enzyme activity in HAECs. Pretreatment with MAP kinase inhibitor SB203580 significantly reduced GBE-induced HO-1 expression. Furthermore, GBE activated the translocation of the transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2), and increased its binding to the antioxidant response element (ARE) of the HO-1 gene. Pretreatment with PEG-SOD or other antioxidant reagents did not alter GBE-induced endothelial HO-1 expression. In vivo study also showed that GBE treatment could reduce leukocyte adherence to injury arteries, and enhance HO-1 expression in circulating monocytes and in arteries after wire injury, suggesting the in vivo induction of HO-1 by GBE. Conclusion: GBE could inhibit cytokine-induced endothelial adhesiveness by inducing HO-1 expression via the activation of p38 and Nrf-2 pathways, a mechanism in which oxidative stress is not directly involved. GBE might exert its anti-atherogenesis and vascular protective effects by inducing vascular HO-1 expression.