Comparative study of the inhibitory effect of antidepressants on cholinesterase activity in Bungarus sindanus (krait) venom, human serum and rat striatum

Figures & data

Figure 1.  Chemical structure of paroxetine (A), sertraline (B), imipramine (C) and clomipramine (D).

Figure 2.  Acetylcholinesterase (AChE) and butrylcholinesterase (BChE) experiments in the presence of 0.5 mM of antidepressants (Clom; clomipramine, Sert; sertraline, Paro; paroxetine and Imip; imipramine). Hydrolysis rates were measured at 412 nm by using 0.4 mM substrate in 1 mL assay solutions with 62 mM phosphate buffer (pH 7.5) and 1 mM DTNB [5,5-dithiobis(2-nitronenzoic acid)]. Enzyme was preincubated for 30 min before 0.4 mM substrate addition. For AChE activity, 0.06 mM ethopropazine (specific inhibitor of BChE) was used to inhibit the activity of BChE in snake venom. All experiments were repeated at least three times and similar results were obtained. For snake venom AChE *P < 0.05 and for human serum BChE *P < 0.038. Significantly different from control.

Figure 3.  The graphs show rat brain striatum acetylcholinesterase experiments in the presence of 0.5 mM different antidepressants (Clom; clomipramine, Sert; sertraline, Paro; paroxetine and Imip; imipramine). Hydrolysis rates were measured at 412 nm by using 0.4 mM substrate in 1 mL assay solutions with 62 mM phosphate buffer (pH 7.5), and 1 mM DTNB [5,5-dithiobis(2-nitronenzoic acid)]. Enzyme was preincubated for 30 min before 0.4 mM substrate addition. 0.06 mM ethopropazine (specific inhibitor of BChE) was used to inhibit BChE activity. All experiments were repeated at least three times and similar results were obtained.

Figure 4.  Kinetic analysis of inhibition of snake venom acetylcholinesterase by Paroxetine (A) Sertraline (B) Imipramine (C) and Clomipramine (D).

Table I.  K_i and IC₅₀ values for venom acetylcholinesterase.

	Imipramine	Paroxetine	Clomipramine	Sertraline
IC50(mM)	0.3	0.38	0.34	0.35
Ki (mM)	0.35	0.41	0.38	0.4

The K_i values were obtained using Cornish-Bowden plots of S/V vs. [I] and IC₅₀ was calculated according to the Dixon and Webb plot using 1/V vs. [I]. The values were obtained for at least three experiments with standard deviation lower than 10%.