Inhibitory effects of flavonoids on aldehyde oxidase activity

Figures & data

Figure 1.  The chemical structures of different flavonoid subclasses assayed for their effects on AO activity.

Table I.  The effects of some flavonoids on the oxidation of vanillin and phenanthridine catalyzed by guinea pig liver AO and xanthine oxidation catalyzed by guinea pig liver XO.

Subclass	Systematic names	Substituents	Conc. (μM)	Vanillin	Phenanthridine	Xanthine
Flavon-3-ol
	Myricetin	3,5,7,3′,4′,5′-OH	10	90.5 ± 1.2*	72.9 ± 4.8	84.5 ± 5.8
			1	77.2 ± 8.5	56.3 ± 11.3	71.6 ± 7.9
	Quercetin	3,5,7,3′,4′-OH	10	92.7 ± 6.4	73.4 ± 2.5	95.4 ± 2.4
			1	75.3 ± 11.2	38.2 ± 6.1	82.6 ± 0.7
	Rutin	5,7,3′,4′-OH; 3-O-rutinosyl	10	44.6 ± 7.3	39.9 ± 5.6	21.8 ± 8.2
			1	18.8 ± 3.3	12.1 ± 5.3	9.6 ± 3.4
	Hyperoside	5,7,3′,4′-OH; 3-O-galactoside	10	39.8 ± 7.3	31.0 ± 2.8	25.4 ± 4.9
			1	7.2 ± 2.8	3.3 ± 0.9	9.9 ± 6.3
	Morin	3,5,7,2′,4′-OH	10	76.2 ± 4.9	25.8 ± 1.8	64.5 ± 14.3
			1	23.4 ± 14.5	17.8 ± 9.8	25.4 ± 6.6
Flavan-3-ol
	(+)-Catechin	3,5,7,3′,4′-OH	10	82.7 ± 1.4	67.3 ± 14.5	12.8 ± 6.7
			1	24.9 ± 8.4	21.5 ± 5.3	6.6 ± 7.1
	( − )-Epicatechin	3,5,7,3′,4′-OH	10	75.8 ± 2.4	66.5 ± 10.1	14.6 ± 7.6
			1	22.6 ± 11.5	20.0 ± 9.5	7.1 ± 5.4
Flavanone
	( ± )-Naringenin	5,7,4′-OH	10	77.4 ± 1.9	55.0 ± 6.1	23.9 ± 8.2
			1	34.3 ± 3.3	20.6 ± 8.7	7.5 ± 12.4
	( ± )-Taxifolin	3,5,7,3′,4′-OH	10	67.7 ± 3.1	42.9 ± 1.3	19.9 ± 9.3
			1	16.5 ± 0.8	9.5 ± 1.2	9.5 ± 5.7
	Hesperetin	5,7,3′-OH; 4′-OMe	10	79.2 ± 4.5	60.4 ± 12.3	21.1 ± 5.9
			1	27.1 ± 7.3	23.3 ± 4.5	6.5 ± 5.9
	Hesperidin		100	22.5 ± 6.7	19.4 ± 2.5	14.4 ± 4.8
	Naringin	5, 4′-OH; 7-O- neohespridose	100	31.5 ± 14.5	12.7 ± 8.2	23.6 ± 8.9
Menadione			100	98.5 ± 0.5	98.1 ± 3.1	40.0 ± 7.2 ↑ ^†
			10	89.6 ± 9.3	91.3 ± 4.1	16.6 ± 4.3 ↑
			1	69.4 ± 24.1	43.1 ± 5.7	5.0 ± 6.6 ↑
Allopurinol			100	7.1 ± 4.0	6.2 ± 4.2	94.2 ± 1.4
			10	ND^‡	ND	75.3 ± 8.7
			1	ND	ND	44.1 ± 11.7

* The results are expressed as the percentage inhibition of the initial oxidation rates of vanillin (144.7 ± 28.5 nM/min/mg protein), phenanthridine (49.0 ± 5.4 nM/min/mg protein) and xanthine (6.4 ± 0.6 nM/min/mg protein), mean ± SEM, n = 4–9

^† an increase in the reaction rate

^‡ ND: not determined.

Table II.  IC₅₀ values for the inhibition of guinea pig liver AO and XO by various flavonoids, menadione and allopurinol.

		IC50 value (μM)
Subclass	Compounds Systematic name	Vanillin (50 μM)	Phenanthridine (50 μM)	Xanthine (50 μM)
Flavonol
	Myricetin	0.4 ± 0.2*	0.7 ± 0.2	0.7 ± 0.1
	Quercetin	0.4 ± 0.2	2.1 ± 0.2	0.4 ± 0.1
	Rutin	17.8 ± 3.2	22.2 ± 7.4	30.1 ± 1.5
	Hyperoside	20.8 ± 4.4	24.3 ± 7.5	35.0 ± 6.8
	Morin	3.7 ± 1.8	30.1 ± 7.4	6.9 ± 1.9
Flavanol
	(+)-Catechin	2.5 ± 0.1	6.1 ± 2.7	70.9 ± 6.8
	( − )-Epicatechin	5.7 ± 1.1	6.1 ± 3.3	59.2 ± 31.2
Flavanone
	( ± )-Naringenin	3.4 ± 2.5	8.8 ± 7.6	25.1 ± 2.5
	( ± )-Taxifolin	4.1 ± 0.3	14.7 ± 3.9	28.5 ± 10.0
	Hesperetin	4.3 ± 2.2	9.8 ± 6.1	26.6 ± 10.2
	Hesperidin	100 <	100 <	100 <
	Naringin	100 <	100 <	100 <
Menadione		0.4 ± 0.1	1.9 ± 0.4	Increased activity
Allopurinol		100 <	100 <	3.2 ± 0.9

* The results are expressed as mean ± SEM (n = 4–7).

The obtained initial velocities for phenanthridine, vanillin and xanthine were 49.0 ± 5.4, 144.7 ± 28.5 and 6.4 ± 0.6 nM/min/mg protein, respectively.

Table III.  Kinetic characteristics of the inhibitory activity of flavonoids on the oxidation of vanillin and phenanthridine by guinea pig liver AO.

	Vanillin			Phenanthridine
Inhibitors	KI (μM)	Ki (μM)	Mode of inhibition	KI(μM)	Ki(μM)	Mode of inhibition
Flavonol
Myricetin	0.3 ± 0.1*	0.7 ± 0.1	Mixed	2.5 ± 1.3	0.7 ± 0.3	Mixed
Quercetin	0.4 ± 0.1	0.5 ± 0.1	Mixed	1.7 ± 1.1	0.8 ± 0.1	Mixed
Rutin	25.5 ± 4.8	12.5 ± 3.9	Mixed	27.4 ± 1.9	13.9 ± 11.4	Mixed
Hyperoside	27.8 ± 5.4	15.8 ± 4.3	Mixed	17.6 ± 6.2	4.7 ± 1.3	Mixed
Morin	5.0 ± 1.4	4.6 ± 0.9	Mixed	18.5 ± 6.1	17.3 ± 4.3	Mixed
Flavanol
(+)-Catechin	2.3 ± 0.2	–	Non-competitive	–	1.3 ± 0.1	Competitive
( − )-Epicatechin	4.2 ± 0.1	–	Non-competitive	–	2.4 ± 0.1	Competitive
Flavanone
( ± )-Naringenin	2.0 ± 0.3	–	Non-competitive	3.9 ± 1.2	1.6 ± 0.9	Mixed
Hesperetin	2.6 ± 0.7	–	Non-competitive	4.5 ± 3.8	1.9 ± 1.5	Mixed
( ± )-Taxifolin	3.4 ± 0.6	–	Non-competitive	10.0 ± 2.3	4.1 ± 1.1	Mixed

* The values are expressed as mean ± SEM, n = 3–4.

Figure 2.  Typical Lineweaver-Burk plots for inhibitory activity of myricetin and catechin on the oxidation of vanillin (A and C, respectively) and phenanthridine (B and D, respectively) catalyzed by guinea pig liver AO. The enzyme assays were performed as described in materials and methods. The data represent the average of 4–8 experiments.