Preliminary Comparative And Mechanistic Investigation Of A Series Of Flavonoids On The Platelet Aggregation, Free Radical Removal And Interaction With Bovine Serum Albumin

Dramatic attentions have been attracted in the research fields of dietary chemical compounds such as plant polyphenols due to their important and potential therapeutic and biological values in recent years. As one important type of plant polyphenols, flavonoids have gradually been studied comprehensively. Flavonoids are widely distributed in a variety of fruits and vegetables including celery, apple, onion, capsicum pepper, etc. Flavonoids are reported to have anti-tumor, anti-inflammation, free radical scavenging, anti-hypertension, atherosclerosis and cardiovascular disease prevention effects. Although there are so many kinds of flavonoids, they show the basic structure core of 2-phenylchromone. And the different types of substituents are formed based on this core structure. Therefore, different types of flavonoids might have varied biological activities due to their structural differences. In current work, the effects of a series of flavonoids on the platelet aggregation, free radical removal and their interactions with bovine serum albumin were investigated. The corresponding mechanisms were also discussed. The dissertation consists of three sections:Section 1: The aim of this part was to assay the effects of eight flavonoid compounds on the rat blood platelet aggregation in vitro and to compare the differences on platelet aggregation among them. Rat blood platelet aggregation was induced by adenosine diphosphate (ADP). The rate of platelet aggregation was assayed by turbidity method with an LBY-NJ blood condense-meter. The results indicated that all the eight flavonoid compounds could significantly inhibit the platelet aggregation induced by ADP. Quercetin and icariin showed the strongest and weakest inhibiting effects on rat blood aggregations among the eight compounds tested, with the inhibitory rates of 68.33±2.43% and 20.94±3.20%, respectively. Preliminary conclusion is then made that the different inhibiting effect of individual flavonoid compound on blood platelet aggregation might be caused due to its particular structure. And the contributions to anti-blood platelet aggregation from the groups of flavonoid compounds are most probably from the C7 hydroxyl of A ring and catechol moiety of B ring. The C3 might also contribute certain inhibiting effect that should be much less effective than the former two factors.Section 2: This part is aimed to study the anti-oxidation activities of the eight flavonoid compounds and to compare their differences. The scavenging effect of these eight flavonoid compounds on hydroxyl free radical produced by Fenton reaction was studied. The results showed that quercetin could significantly remove hydroxyl free radical with a dose-dependent effect. Among all the eight flavonoid compounds tested in current study, quercetin showed the strongest anti-oxidation activity by removing 30.69% of hydroxyl free radical, followed by rutin (13.70 %) and isoquercitin (10.23 %). Controversially, icariin was found to promote the hydroxyl radical by 4.29%. Based on the results obtained above, we conclude that the principal functional groups attributed to anti-oxidant activity of flavonoid compounds should be the C3 hydroxyl of A ring and catechol moiety of B ring.Section 3: The binding affinities and binding site numbers of the eight flavonoid compounds to bovine serum albumin (BSA) were determined by fluorescence spectroscopy. The binding sites number (n) and the apparent association constant (KA) were derived from the plots made following the static quenching mechanism of BSA fluorescence. The results are given below: quercetin (KA=4.94×10~5, n=0.97), isoquercitrin (KA=4.66×10~4 , n=0.92), rutin (KA=1.65×10~4 , n=0.86), hesperetin (KA=5.59×10~5,n=1.08), hesperidin (KA=2.5×10~3,n=0.74), naringenin (KA=3.04×10~5,n=1.06), naringin (KA=8.7×10~2,n=0.63) and icariin (KA=3.6×10~4,n=0.95). The interaction between flavonoid compound and BSA is influenced by the structural variety of individual flavonoid molecule. The substituted group of C7 in A ring is the key acting group in the interaction of BAS with flavonoids, as the A ring is the key structure connecting the hydrophobic region of BSA.