Quetiapine and novel PDE10A inhibitors potentiate the anti-BuChE activity of donepezil

Figures & data

Figure 1. The chemical structure of quetiapine and PDE10A inhibitors, CPL500036-01 and CPL500036-02.

Figure 2. The effects of quetiapine (A) and CPL500036-01 (B) and CPL500036-02 (C) on AChE activity expressed as the percentage of enzyme inhibition in comparison to control (100% of activity). Each data point represents mean ± SD for at least three independent experiments conducted in duplicates.

Figure 3. The effects of quetiapine (A) and CPL500036-01 (B) and CPL500036-02 (C) on BuChE activity expressed as the percentage of enzyme inhibition in comparison to control (100% of activity). Each data point represents mean ± SD for at least three independent experiments conducted in duplicates. Subsequent calculations using logarithmic equations from each conducted experiment allowed to determine the IC₅₀ value for quetiapine.

Table 1. Effects of quetiapine and donepezil on the human erythrocyte acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BuChE) activity.

Compound	IC50 (µmol/L)
	AChE	BuChE
Quetiapine	NE	6.08 ± 1.64
Donepezil	0.025 ± 0.004	12.8 ± 1.52

The values are given as mean ± SD in three independent experiments conducted in duplicates on various biological samples. NE: non estimated (>100 µmol/L).

The value of CI below 1 gives evidence of synergism between the examined binary mixtures (don. + quet., don. + CPL500036-01, don. + CPL500036-02) in the case of BuChE inhibition. The results regarding AChE seem to be complex: higher concentrations mixtures also indicate synergistic activity.

Figure 4. Determination of kinetic parameters of BuChE enzymatic reactions. Hanes-Woolf plots we used to calculate the Michaelis constant (K_m) and maximal velocity (V_max). Quetiapine was used at the concentration of 12.8 µmol/L. Presented data constitute the results of one exemplary experiment conducted in duplicates. The results of kinetic studies conducted in three independent experiments and calculated kinetic parameters are enclosed in Table 2.

Table 2. Kinetic parameters of BuChE enzymatic reaction.

Drug	Km (µmol/L)	Vmax (A/min)	Km(i) (µmol/L)	Vmax(i) (A/min)
Quetiapine	92.7 ± 17.4	0.182 ± 0.041	103.5 ± 29.5	0.137 ± 0.036
Donepezil	85.3 ± 6.7	0.245 ± 0.069	149.7 ± 6.9	0.098 ± 0.032

The values are given as mean ± SD in three independent experiments.

Table 3. Effects of the mixture of donepezil and quetiapine, or two new compounds on the human erythrocyte acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BuChE) activity.

Compound	IC50
	AChE (nmol/L)	BuChE (µmol/L)
Donepezil + Quetiapine	25.41 ± 1.82	9.82 ± 2.21
Donepezil + CPL500036-01	27.19 ± 2.66	2.13 ± 1.45
Donepezil + CPL500036-02	21.72 ± 0.48	3.78 ± 0.54
Donepezil	25.58 ± 4.56	12.81 ± 1.52

The values are given as mean ± SD in three independent experiments conducted in duplicates on various biological samples. Donepezil was used at the concentration between 0.01 and 100 nmol/L for AChE inhibition, and 0.2 to 100 µmol/L for BuChE activity assessment. Quetiapine, CPL500036-01, and CPL500036-02 were used at the following constant concentrations: 200 ng/mL (400 nmol/L) for quetiapine, 25 µmol/L for CPL500036-01, and CPL500036-02.

Figure 5. Analysis of potential synergism between donepezil and quetiapine, CPL500036-01, and CPL500036-02 by the median effect principle. Data from the AChE (A) and BuChE (B) inhibitory activities assay were analysed by means of the Chou–Talalay method. The results are depicted using Fa-CI plots, where Fa is Fraction affected, and CI is combination index.