The Inhibitve Effect Of Flavonoid Phytochemicals On The Oxidative Stress-induced Endothelial Injury: A Structure-activity Analysis

Atherosclerosis (AS) has been demonstrated to be the leading cause of death in the western countries, and the prevalence and incidence rates increase rapidly in China. Many researchers are agreed with the response-to-injury hypothesis raised by Ross, in which it implies that endothelial impairment and dysfunction induced by the oxidative stress is the initiating step for AS. And inhibiting endothelial injury could be an effective way for AS prevention and therapy. Oxidized low-density lipoprotein (oxLDL) is recognized as the most important hazard factor for AS, which results in the endothelial injury mainly though the ROS-p38MAPK-NF-κB pathway and by regulating the oxidative stress-related gene expression.Recent research have suggested that AS is closely related to the unhealthy lifestyle, particularly an immoderate dietary patterns. WHO demonstrated that half of patients suffered from AS could be prevented by lifestyle amendment. Epidemiological studies have also found that the intake of flavonoid phytochemicals which are widely distributed in the plant food such as vegetables, fruits, cereals and beans are negatively correlated to the initiation and development of AS and cardiovascular diseases. Many studies have showed that most flavonoid phytochemicals have notably antioxidant activity and some chemicals exert dominantly inhibitive effect on endothelial injury. Thus, it’s implied that these lead compounds might become the effective drugs for AS therapy by structural reconstruction and modification. As many flavonoid phytochemicals have been found in various plant food, It might provide a clue for the drug design based upon the determination of the molecular structures in relation to the inhibitive effects of flavonoid phytochemicals on the endothelial injury and the role of such structural characteristics with regard to the inhibitive activity.In our present study, we firstly established a endothelial injury model induced by oxLDL, measured by the cell viability, cell apoptosis, the level of MDA, LDH, SOD, NO and sICAM-1 as well as the intracellular ROS level, respectively. Furthermore, we chose 21 anthocyanins and 23 flavonoids to compare their inhibitive effects on the endothelial injury, respectively. And then, we analyzed the structure-activity relationships by correlation analysis and paired comparison and clarified the structural characteristics in relation to the inhibitive effects of anthocyanins and flavonoids, respectively. Furthermore, chemicals with dominant activity including 2 anthocyanidin (delphinidin and cyanidin), 2 flavonols (myricetin and quercetin), 2 flavones (luteolin and quercetin) and 2 isoflavones (genistein and daidzein) were screened for the comparison of their effects on the intracellular ROS level, phosphorylation of p38MAPK, nuclear translocation of NF-κB, mRNA expression of oxidative stress-related genes as well as NF-κB and ER-mediated transcriptional activity in the oxLDL-induced endothelial cells, respectively. We tried to reveal the role of such structural characteristics of flavonoid phytochemicals in the inhibition of endothelial injury through ROS-p38MAPK-NF-κB pathway.The main results and conclusions are summarized as follows:(1) oxLDL significantly resulted in the oxidative injury in endothelial cells by decreasing the viability, secretory activity, antioxidant capacity and inducing cell apoptosis as well as increasing lipid peroxidation, inflammatory reaction and the intracellular ROS level in the endothelial cells in a concentration-dependent manner.(2) The number of–OH in total and in B-ring were positively related to the inhibitive effects of anthocyanins in the endothelial injury, respectively. A 3’,4’-ortho-dihydroxyl group on B-ring and a 3-hydroxyl group on C-ring appeared to be closely related to the inhibitive effects of anthocyanins in endothelial injury. Hydroxylation at C5-position showed no significant influence while hydroxylation at C6-position might attenuate the inhibitive effects of anthocyanins in endothelial injury. Sugar moieties substitution in anthocyanins also decreased the inhibitive effects. Delphinidin and cyanidin with dominant activity were chosen for further study.(3) The number of–OH in total and in B-ring were also positively correlated to the inhibitive effects of flavonoids in endothelial injury, respectively. A 3-hydroxyl group on C-ring, a 5,7-meta-dihydroxyl group on A-ring, a 2,3-double bond and B-ring on C3 position of C-ring were all correlated to the inhibitive effects of flavonoids in endothelial injury, respectively. However, hydroxylation on C6-position significantly attenuated the inhibitive effects of flavonoids. 2 flavonols (myricetin and quercetin), 2 flavones (luteolin and apigenin) and 2 isoflavones (genistein and daidzein) were chosen for further study.(4) It’s found that the structural differences significantly affect the inhibitive effects of flavonoid phytochemicals on endothelial injury. A 3’,4’-ortho-dihydroxyl group and a 3-hydroxyl group are the essential molecular characteristics of flavonoid phytochemicals in the inhibition of the ROS-p38MAPK-NF-κB pathway and NF-κB-mediated transcriptional activity as well as the regulation of the oxidative stress-related genes expression in the endothelial cells. A 5,7-meta-dihydroxyl group is closely related to the inhibitive effect of flavonoids on the expression of adhesion and chemotaxis genes mediated by NF-κB. The substituted position of B-ring in C3-position is required for the promotion of eNOS expression and NO release via the estrogen receptor-mediated pathway.In our study, we have analyzed the structure-activity relationship of flavonoid phytochemicals in the inhibition of the oxidative stress-induced endothelial injury. We have also clarified the molecular characteristics in relation to the inhibitive effects and the role of such characteristics in the inhibition of the endothelial injury through ROS-p38MAPK-NF-κB pathway. The biological efficacy of flaovnoid phytochemicals have been the hot spot in the nutritional research field, and some lead compounds might become the sources for drug design. Since there are numerous flavonoid phytochemicals with different structures widely distributed in the edible plants and more and more chemicals will be found in the future, our structure-activity analysis might play an important role in AS prevention by choosing foods with certain flavonoid phytochemicals, and would provide a basis for the drug design for AS therapy by structural reconstruction and modification of such molecular characteristics.