Protective effects of luteolin against oxidative stress and mitochondrial dysfunction in endothelial cells

Abstract

Background and aims: Luteolin is a common flavonoid that is abundantly present in various edible plants, it is known to exhibit beneficial effects on cardiovascular system. However, the mechanisms which underlie the protective effects of luteolin on endothelial cell damage caused by oxidative stress remains unclear. The purpose of this study is to test the hypothesis which states that luteolin protects against H₂O₂-induced oxidative stress via modulating ROS-mediated P38 MAPK/NF-κB and calcium-evoked mitochondrial apoptotic signalling pathways.

Methods and results: Human umbilical vein endothelial cells (HUVECs) were pretreated with luteolin prior to being stimulated by 600 μM H₂O₂ for another 24 h. The expression of native and phosphorylated-P38, IκB, NF-κB, native eNOS, phosphorylated-eNOS, iNOS and several apoptosis-related proteins were analyzed by Western blot. In addition, intracellular calcium was determined by fura-2 AM and mitochondrial membrane potential was examined by using JC1. Using the data gathered, we found indications that H₂O₂ induced P38 MAPK/NF-κB activation. H₂O₂ downregulated the expression of eNOS and upregulated iNOS, which in turn contribute to an elevated NO generation and protein nitrosylation. However, pretreatment with luteolin markedly reversed all of these alterations dose-dependently. Additionally, an intracellular calcium rise and subsequent mitochondrial membrane potential collapse, P53 phosphorylation, reduced BcL-2/Bax ratio in the mitochondrial membrane, release cytochrome c from mitochondria, leading to the subsequent activation of caspase 3 activation by H₂O₂ were all markedly suppressed in the presence of luteolin.

Conclusion: Results from this study may provide the possible molecular mechanisms underlying cardiovascular protective effects of luteolin.

Keywords: Apoptosis; Luteolin; Mitochondrial dysfunction; Oxidative stress; oxLDL.