Rutin protects against H₂O₂-triggered impaired relaxation of placental arterioles and induces Nrf2-mediated adaptation in Human Umbilical Vein Endothelial Cells exposed to oxidative stress

Background: Rutin intake is associated with a reduced risk of cardiovascular disease (CVD). The exact mechanism by which rutin can protect against CVD development is still enigmatic. Since, rutin is a compound with a relatively short half-life, the direct antioxidant effect of rutin cannot explain the long-lasting effect on human health. We hypothesized that rutin next to its direct antioxidant effect that improves endothelial function, may also induce an adaptive response in endogenous antioxidant systems.

Methods and results: In Human Umbilical Vein Endothelial Cells (HUVECs), the direct antioxidant effect was confirmed. During scavenging of Reactive Oxygen Species (ROS), rutin is oxidized into a quinone derivative. HUVECs pretreated with rutin quinone became better protected against a second challenge with oxidative stress 3 h later. LC-MS/MS analysis indicated that rutin quinone targets cysteine 151 of Keapl. Moreover, we found that the quinone is an inhibitor of the selenoprotein thioredoxin reductase 1. These properties correlated with an activation of Nrf2 and, upregulation of Glutamate Cysteine Ligase, the rate-limiting enzyme of glutathione synthesis, while NF-KB and HIF activation became blunted by rutin treatment. Furthermore, rutin was found to prevent hydrogen peroxide from impairing relaxation of human chorionic plate placental vessels, which may help to protect endothelial function.

Conclusion and significance: Rutin functions as an antioxidant and is oxidized into a quinone that upregulates the Nrf2-mediated endogenous antioxidant response. This mechanism suggests that rutin selectively exerts its protective effects in regions with increased oxidative stress, and explains how rutin reduces the risk of developing CVD.

General significance: The newly found mechanism behind the long-term protection of rutin against cardiovas-cular disease, the selective upregulation of endogenous antioxidant systems, contributes to the further understanding why rutin can reduce the risk on developing cardiovascular disease.