In vitro inhibitory effects of kaempferitrin on human liver cytochrome P450 enzymes

Figures & data

Figure 1. The chemical structure of kaempferitrin.

Table 1. Isoforms tested, marker reactions, incubation conditions, and K_m used in the inhibition study.

CYPs	Marker reactions	Substrate concentration (μM)	Protein concentration (mg/mL)	Incubation time (min)	Estimated Km (μM)
1A2	phenacetin O-deethylation	40	0.2	30	48
3A4	testosterone 6β-hydroxylation	50	0.5	10	53
2A6	coumarin 7-hydroxylation	1.0	0.1	10	1.5
2E1	chlorzoxazone 6-hydroxylation	120	0.4	30	126
2D6	dextromethorphan O-demethylation	25	0.25	20	4.8
2C9	diclofenac 4′-hydroxylation	10	0.3	10	13
2C19	S-Mephenytoin 4-hydroxylation	100	0.2	40	105
2C8	paclitaxel 6α-hydroxylation	10	0.5	30	16

Figure 2. Inhibition of KF on CYP450 enzymes in pooled HLMs. All data represent mean ± S.D. of the triplicate incubations. *p < .05, significantly different from the negative control. Negative control: incubation systems without KF; KF: incubation systems with KF; Positive control: incubation systems with their corresponding positive inhibitors.

Figure 3. Lineweaver-Burk plots (A) and the secondary plot for Ki (B) of inhibition of KF (0–50 μM) on CYP1A2 catalyzed reactions (phenacetin O-deethylation) in pooled HLM. Data are obtained from a 30 min incubation with phenacetin (20–100 μM) in the absence or presence of KF (0–50 μM). The data represent the mean of the incubations (performed in triplicate).

Figure 4. Lineweaver-Burk plots (A) and the secondary plot for Ki (B) of inhibition of KF on CYP3A4 catalyzed reactions (testosterone 6β-hydroxylation) in pooled HLM. Data are obtained from a 30 min incubation with testosterone (20–100 μM) in the absence or presence of KF (0–30 μM). All data represent the mean of the incubations (performed in triplicate).

Figure 5. Lineweaver-Burk plots (A) and the secondary plot for Ki (B) of inhibition of KF on CYP2C9 catalyzed reactions (diclofenac 4'-hydroxylation) in pooled HLM. Data are obtained from a 30 min incubation with diclofenac (2–20 μM) in the absence or presence of KF (0–40 μM). All data represent the mean of the incubations (performed in triplicate).

Figure 6. Time-dependent inhibition investigations of CYP1A2, 3A4, and 2C9 catalyzed reactions by KF (20 μM). All data represent the mean of the incubations (performed in triplicate).

Figure 7. Time and concentration-inactivation of microsomal CYP3A4 activity by KF in the presence of NADPH. The initial rate constant of inactivation of CYP3A4 by each concentration (K_obs) was determined through linear regression analysis of the natural logarithm of the percentage of remaining activity versus pre-incubation time (A). The K_I and K_inact values were determined through non-linear analysis of the K_obs versus the KF concentration (B).