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Inhibitory effects of agmatine on monoamine oxidase (MAO) activity: Reconciling the discrepancies

Loretta Mancinelli
Loretta Mancinelli
, 
Francesco Ragonese
Francesco Ragonese
, 
Samuela Cataldi
Samuela Cataldi
, 
Maria Rachele Ceccarini
Maria Rachele Ceccarini
, 
Rossana G. Iannitti
Rossana G. Iannitti
, 
Cataldo Arcuri
Cataldo Arcuri
 and 
Bernard Fioretti
Bernard Fioretti
   | Apr 25, 2018
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Article Category: Research Article
Published Online: Apr 25, 2018
Page range: 121 - 127
DOI: https://doi.org/10.2478/ebtj-2018-0016
Keywords
© 2018 Loretta Mancinelli, Francesco Ragonese, Samuela Cataldi, Maria Rachele Ceccarini, Rossana G. Iannitti, Cataldo Arcuri, Bernard Fioretti, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Agmatine does not inhibit liver MAO activity. A) Representative experiment showing the absorption spectra without (gray trace) and in presence of tyramine (black trace) or following co-application of 1mM of agmatine (red trace). MAO activity was monitored using the peroxidase-coupling assay (750 μM , pH 7.4 and 30 min). Inset: bar plot showing the mean result of six experiments with tyramine in presence of either 1 mM agmatine (AGM), or the MAO 10 μM of MAO inhibitor tranylcypromine (Tc). AGM and Tc data are normalized with respect to control conditions. Normalization was also applied to SE using error propagation. B) Bar plot showing the mean effects of agmatine (0.1 and 1 mM), idazoxan (0.1 and 1 mM), and tranylcipromine (3 μM) on MAO activity, determined with kinuramine-based assay (see Methods). The asterisk indicates the significant difference with respect to control (p< 0.05).
Agmatine does not inhibit liver MAO activity. A) Representative experiment showing the absorption spectra without (gray trace) and in presence of tyramine (black trace) or following co-application of 1mM of agmatine (red trace). MAO activity was monitored using the peroxidase-coupling assay (750 μM , pH 7.4 and 30 min). Inset: bar plot showing the mean result of six experiments with tyramine in presence of either 1 mM agmatine (AGM), or the MAO 10 μM of MAO inhibitor tranylcypromine (Tc). AGM and Tc data are normalized with respect to control conditions. Normalization was also applied to SE using error propagation. B) Bar plot showing the mean effects of agmatine (0.1 and 1 mM), idazoxan (0.1 and 1 mM), and tranylcipromine (3 μM) on MAO activity, determined with kinuramine-based assay (see Methods). The asterisk indicates the significant difference with respect to control (p< 0.05).

Figure 2

The inhibitory effect of agmatine on MAO activity depends on pH and incubation time. Bar plots showing the effect of 1 mM agmatine on MAO activity when: A) agmatine incubation time is increased to 60 minutes, while the pH is kept constant at 7.4; B) the pH is increased to 9.2, while incubation time is kept constant at 5 min (data showing the effect of agmatine on MAO activity are normalized to the MAO activity at the corresponding pH). Inset shows the increased effect of MAO activity in alkaline condition as consequence of deprotonation of amine (kynuramine) substrate. C) both agmatine incubation time and the pH are increased to 60 minutes and 9.2 respectively. The effects of agmatine (1 mM) on MAO activity are given as compared to those obtained with kynuramine substrate at pH 7.4 and agmatine incubation time fixed at 5 min.
The inhibitory effect of agmatine on MAO activity depends on pH and incubation time. Bar plots showing the effect of 1 mM agmatine on MAO activity when: A) agmatine incubation time is increased to 60 minutes, while the pH is kept constant at 7.4; B) the pH is increased to 9.2, while incubation time is kept constant at 5 min (data showing the effect of agmatine on MAO activity are normalized to the MAO activity at the corresponding pH). Inset shows the increased effect of MAO activity in alkaline condition as consequence of deprotonation of amine (kynuramine) substrate. C) both agmatine incubation time and the pH are increased to 60 minutes and 9.2 respectively. The effects of agmatine (1 mM) on MAO activity are given as compared to those obtained with kynuramine substrate at pH 7.4 and agmatine incubation time fixed at 5 min.

Figure 3

Proprerties of agmatine inhibition of MAO activity. A) Dose-response of agmatine inhibition of MAO activity at pH 9.2 after 60 min incubation. The curve represents the best fit with the Hill equation 100/[1+([Agmatine]/IC50)h] with IC50 and h of 1.3 mM and 0.35, respectively. B) Bar plots showing the lack of the effect of aminoguanidine (AG, 1 mM) in preventing the inhibitory effects of 1 mM agmatine on MAO activity.
Proprerties of agmatine inhibition of MAO activity. A) Dose-response of agmatine inhibition of MAO activity at pH 9.2 after 60 min incubation. The curve represents the best fit with the Hill equation 100/[1+([Agmatine]/IC50)h] with IC50 and h of 1.3 mM and 0.35, respectively. B) Bar plots showing the lack of the effect of aminoguanidine (AG, 1 mM) in preventing the inhibitory effects of 1 mM agmatine on MAO activity.

Figure 1S

A) Peroxidase-coupled assay scheme. Hydrogen peroxide derived from MAO enzyme activity, reacts with chromogenic mixture (4-Aminoantipyrine and vanillic acid) to generate a quinoneimine dye following peroxidase enzyme catalysis. B) Tranylcypromine MAO inhibition estimated by peroxidase-coupled assay. The line represents the best fit with Hill equation providing values for IC50 of 760 nM with a Hill coefficient of 1.8. Single data points represent a mean value ± se (n=6).
A) Peroxidase-coupled assay scheme. Hydrogen peroxide derived from MAO enzyme activity, reacts with chromogenic mixture (4-Aminoantipyrine and vanillic acid) to generate a quinoneimine dye following peroxidase enzyme catalysis. B) Tranylcypromine MAO inhibition estimated by peroxidase-coupled assay. The line represents the best fit with Hill equation providing values for IC50 of 760 nM with a Hill coefficient of 1.8. Single data points represent a mean value ± se (n=6).

Figure 2S

A) Kynuramine-based assay scheme. Deamination of kynuramine catalyzed by MAO providing an aldehyde, followed by non-enzymatic condensation to 4-hydroxyquinoline. B) Dose- dependence inhibition of MAO at various concentration of agmatine (squares, range 0.003 -1 mM, n=3) and Idazoxan (circles, range 0.003 -1 mM, n=3).
A) Kynuramine-based assay scheme. Deamination of kynuramine catalyzed by MAO providing an aldehyde, followed by non-enzymatic condensation to 4-hydroxyquinoline. B) Dose- dependence inhibition of MAO at various concentration of agmatine (squares, range 0.003 -1 mM, n=3) and Idazoxan (circles, range 0.003 -1 mM, n=3).
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