Protective effects of some flavonoid derivatives against toxicity of acrolein and glycidol in endothelial cells

Abstract

Lipid-derived foodborne toxicants are worldwide food safety concerns. Dietary exposure to these toxicants has been linked with a variety of adverse implications, particularly cardiovascular disorders. Endothelial cells have been proposed as possible targets of these toxicants. Flavonoids are common food components that have shown potential in protecting against toxicities of lipid-derived foodborne toxicants. Nevertheless, the application of many flavonoids is limited by high effective doses and low bioavailability. This study aimed to investigate the potential endothelial toxicities of two representative lipid-derived toxicants, acrolein and glycidol. In addition, a series of novel flavonoid derivatives were screened for finding effective protective agents against endothelial toxicities of acrolein and glycidol. First, the toxicological effects and mechanisms of acrolein and glycidol were investigated using human umbilical vein endothelial cells (HUVECs). Acrolein was found to induce mitochondrial dysfunction and stimulate mitochondrial ROS production, which promoted oxidative stress and subsequently triggered apoptosis and inflammation. In addition, autophagy was upregulated as evidenced by the increased LC3 II level and concurrently decreased p62 expression. Further analysis indicated that the enhanced autophagy possibly resulted from negative regulation of the Akt/mTOR pathway by ROS. In addition, treatment with 3-methyladenine, an autophagy inhibitor, reduced apoptosis, implying acrolein-induced apoptosis may rely on autophagy. For glycidol, at cytotoxic concentrations, it could lead to endothelial injury as evidenced by enhanced apoptosis and NF-κB-mediated inflammation in HUVECs. The effects were probably regulated by oxidative stress. On the other hand, glycidol at sublethal doses triggered endothelial-to-mesenchymal transition (EndMT), as evidenced by loss of endothelial-specific morphology and markers (CD31, VE-cadherin) and simultaneous acquirement of mesenchymal-like shapes and markers (α-SMA, FSP-1). This process probably involved upregulation of the TGF-β1 signaling. In addition, glycidol significantly promoted phosphorylation of p38 MAPK and ERK. Application of NAC (a ROS scavenger), SB203580 (a p38 MAPK inhibitor), and U0126 (an ERK inhibitor) blocked activation of MAPK kinases, which in turn down-regulated apoptosis and EndMT, suggesting a regulatory role of the ROS-MAPK pathways. Collectively, these findings provide evidence for oxidative stress and related damages like apoptosis and inflammation in coordinating endothelial toxicities of acrolein and glycidol. Next, seven stilbenoid-fused naringenin derivatives were screened for vasoprotective effects against oxidative damage and inflammation in HUVECs and RAW 264.7 macrophages. Data showed that most of the derivatives possessed higher efficacy than naringenin. Among them, one monofluoro-substituted stilbenoid-fused naringenin, Compound 6 exhibited stronger protective potency with low cytotoxicity. Finally, the protective potential of naringenin and Compound 6 were examined and compared in acrolein or glycidol-treated HUVECs. Likewise, Compound 6 exhibited higher efficacy than naringenin against endothelial toxicities caused by acrolein or glycidol. The protective effects of Compound 6 were proposed to be achieved by up-regulation of Phase II enzymes GCLC and HO-1 via the Nrf2 pathway. To conclude, this research provided evidence for the endothelial toxicities of acrolein and glycidol, and discovered a synthesized stilbenoid-fused flavonoid, Compound 6, as an effective protective agent. The findings offered a scientific basis for risk assessment and control of lipid-derived foodborne toxicants and the development of new candidates for cardiovascular protection.