New Synthetic Caffeine Analogs as Modulators of the Cholinergic System

Abstract

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder. Since cholinergic deficit is a major factor in this disease, two molecular targets for its treatment are the acetylcholinesterase (AChE) and the nicotinic acetylcholine receptors (nAChRs). Given that caffeine is a natural compound that behaves as an AChE inhibitor and as a partial agonist of nAChRs, the aim of this work was to synthetize more potent bifunctional caffeine analogs that modulate these two molecular targets. To this end, a theophylline structure was connected to a pyrrolidine structure through a methylene chain of different lengths (3 to 7 carbon atoms) to give compounds 7-11. All caffeine derivatives inhibited the AChE, of which compound 11 showed the strongest effect. Electrophysiological studies showed that all compounds behave as agonists of the muscle and the neuronal α7 nAChR with greater potency than caffeine. To explore if the different analogs could affect the nAChR conformational state, the nAChR conformationalsensitive probe crystal violet (CrV) was used. Compounds 9 and 10 conduced the nAChR to a different conformational state comparable with a control nAChR desensitized state. Finally, molecular docking experiments showed that all derivatives interacted with both the catalytic and anionic sites of AChE and with the orthosteric binding site of the nAChR. Thus, the new synthetized compounds can inhibit the AChE and activate muscle and α7 nAChRs with greater potency than caffeine, which suggests that they could be useful leaders for the development of new therapies for the treatment of different neurological diseases.

New Multitarget Molecules Derived from Caffeine as Potentiators of the Cholinergic System

“…Differences in K D values from samples before and after incubation with carb indicate different conformational states of the receptor and, indirectly, functional response of the nAChR to carb. 30,31 We observed that, when caffeine analogues were incubated with carb, the K D values were similar in all cases, indicating that receptor desensitization occurred (Figure 6). However, in the absence of carb, we observed that only compound 12 at 1 μM (n = 4) and 100 μM (n = 4) caused conformational changes of the nAChR, stabilizing it in a desensitized state (Figure 6).…”

“…The reduction of the mean open time by the increase of the compound concentration could be due to an open channel block as described for caffeine and compound 9. 30,31 In contrast to the low activity of the former analogues, high channel activity was detected with compounds 12 and 15. Although the frequency of openings was high in the presence of both compounds, clusters could not be distinguished.…”

“…31,44,45 Cluster duration was 145 ± 6 ms (n = 6 and N = 5), as described before. 31 The main intracluster closed component showed a mean duration of 6.8 ± 0.7 ms (n = 6 and N = 5) (Figure 3).…”

“…However, all these molecules behaved as partial muscle nAChR agonists. 30,31 In the present work, we analyzed possible conformational changes of nAChR in the presence of the new caffeine analogues. To this end, we used the crystal violet (CrV) fluorescent probe, a nAChR open-channel blocker which exhibits higher affinity for the desensitized (D) state compared to the resting (R) state.…”

“…32−35 This strategy, involving the combination of diverse pharmacophores or functional groups derived from theophylline and its derivatives, has proven effective in enhancing the activity of the original pharmacological compounds, as demonstrated in our previously synthesized series of caffeine derivatives. 31 However, these reports evaluated only the effect on AChE and not on nAChR. Furthermore, almost all of these compounds exhibited lower AChE inhibitory potency than our previous caffeine analogues.…”