Table 1.
HPLC analysis of the flavonoid samples used in the current study.
Figure 1.
Structures of the different flavonoids used in this study.
Figure 2.
(A) Effect of different flavonoids on Angiotensin Converting Enzyme (ACE) activity.
Purified lung ACE was preincubated at 37°C for 30 min in the presence of 100 µM of flavonoids or DMSO as a control. The results are expressed as the percentage of ACE inhibition. The plot represents the mean result ± SD from three experiments. (B) Effect of different flavonoids on Angiotensin Converting Enzyme (ACE) activity. Purified lung ACE was preincubated at 37°C for 30 min in the presence of 500 µM of flavonoids or DMSO as control. The results are expressed as the percentage of ACE inhibition. The plot represents the mean ± SD from three experiments.
Table 2.
IC50 values obtained for the selected flavonoids.
Figure 3.
Structural diagram which quantitatively assesses the effect of the addition or elimination of different structural elements from the flavonoid core on the ACEI activity of luteolin at 100 µM.
According to these data, the significance order was: double bond C2 = C3 (absence: −91% activity by comparing naringenin vs. apigenin) >4′-O-methoxylation (presence: −78% by comparing diosmetin vs. luteolin) ≈ 4-carbonyl group (absence: −74% by comparing epicatechin vs. luteolin) >3′-hydroxylation (absence: −57% by comparing apigenin vs. luteolin) >3-hydroxylation (presence: −44% by comparing quercetin vs. luteolin) >3-O-glycosylation (presence: -36% by comparing rutin vs. luteolin).
Table 3.
Intermolecular interactions between ACE inhibitors and the tACE binding site.
Figure 4.
Best predicted pose for luteolin (panel A) at the tACE binding site and the relative location to experimental poses for the ACE inhibitors lisinopril (panel B), enalaprilat (panel C), and captopril (panel D).
All of the panels in this figure are in the same relative orientation to allow for easier comparisons between the poses. Residues at the ACE binding site are colored according to the subsite where they belong (i.e., residues from the S2′, S2′/S1′, S1′, S1 and S1/S2 subsites are colored in red, cyan, magenta, green, brown, white and yellow, respectively). Other important residues that have not been classified in any pocket are colored in white. Carbon atoms for the ligands are shown in yellow to make them more easily distinguishable from the binding site residues. Dashed lines are used to show intermolecular hydrogen bonds (in red) or charge-charge interactions (in blue).