The Neuroprotective Role of Origanum syriacum L. and Lavandula dentata L. Essential Oils through Their Effects on AMPA Receptors.

Lavandula dentata L. and Origanum syriacum L. essential oils have numerous health benefits and properties, such as possessing common components with a variant degree of depressive actions in the central nervous system. We investigated the depressive property of these oils on AMPA receptors, which are responsible for most of the fast-excitatory neurotransmission in the CNS and play a critical role in synaptic plasticity. Since excessive activation of AMPARs has been linked to neurotoxicity leading to various pathologies, we hypothesize that these oils have a neuroprotective role by acting directly on the kinetics of AMPARs. Using Gas Chromatography-Mass Spectrometry (GC/MS) and patch-clamp electrophysiology, the essential oils of L. dentata flowers and O. syriacum leaves were characterized and the whole cell currents were measured with and without the administration of the oils onto HEK293 cells. The current study results showed that the biophysical properties of AMPA receptor subunits showed a decrease in desensitization rate of GluA1 and GluA2 homomers, using O. syriacum, while administering L. dentata oil decreased the desensitization rate of GluA1 and GluA2 homomers, as well as GluA1/2 heteromers. As for the deactivation rate, both oils slowed the deactivation kinetics of all AMPA receptor subunits. Intriguingly, between the two oils, the effect of desensitization and deactivation was of a greater significance for L. dentata oil than O. syriacum. Our data suggest that the two oils contain components that are essential to identify, as those active components underlie the oils' neuronal depressive properties reported, and to extract them to synthesize a potent neuroprotective drug to treat neurological diseases potentially.

The inhibitory role of curcumin derivatives on AMPA receptor subunits and their effect on the gating biophysical properties.

Curcumin is a natural polyphenol that has a broad spectrum of therapeutic characters, including neuroprotective actions against various neurological diseases. However, the molecular mechanism behind its neuroprotective properties remains obscure. The current study investigated the neuroprotective properties of 7 different curcumin derivatives on the gating biophysical properties of AMPA receptors, specifically on the calcium-permeable homomeric GluA1 and calcium impermeable heteromeric GluA1/A2 subunits. Due to the association between excessive activation of AMPARs and neurotoxicity linked to numerous pathologies, we aim to target and manipulate the kinetics of AMPARs through these derivatives. The current study used patch-clamp electrophysiology to measure the whole-cell currents in the presence and absence of the curcumin derivatives onto HEK293 cells expressing AMPA subunits. Our results showed that some of the curcumin derivatives showed an inhibitory effect and altered the gating biophysical properties, namely, deactivation and desensitization. In the presence of those derivatives, the peak current measured was significantly reduced, and the desensitization and deactivation rates decreased as well, achieving slower kinetics of the receptor and depressing its activity. These results suggest that the two most promising derivatives have inhibitory actions and act as allosteric modulators. Many neurological diseases like epilepsy, ALS, and strokes are associated with overactivation of AMPA receptors. We can potentially synthesize a more potent neuroprotective drug to treat those neurological diseases, by understanding the most stable chemical interaction between the derivative and the receptor underlying the reported neuronal depressive properties.

Inhibition and assessment of the biophysical gating properties of GluA2 and GluA2/A3 AMPA receptors using curcumin derivatives.

The development of efficacious and safe drugs for the treatment of neurological diseases related to glutamate toxicity has been a focus in neuropharmacological research. Specifically, discovering antagonists to modulate the activity and kinetics of AMPA receptors, which are the fastest ligand-gated ion channels involved in excitatory neurotransmission in response to glutamate. Thus, the current study investigated novel curcumin derivatives on the biophysical properties of AMPA receptors, specifically on the homomeric GluA2 and the heteromeric GluA2/A3 subunits and assessed for inhibitory actions. The biophysical parameter (i.e., desensitization, deactivation, and peak currents) were measured by using whole-cell patch clamp electrophysiology with and without the administration of the derivatives onto HEK293 cells. CR-NN, CR-NNPh, CR-MeNH, and CR-NO of the tested derivatives showed inhibition on all AMPA receptors up to 6 folds. Moreover, the inhibitory derivatives also increased desensitization and deactivation, which further intensifies the compounds' neuroprotective effects. However, CR-PhCl, CR-PhF, and CR-PhBr did not show any significant changes on the peak current, deactivation or desensitization rates. By comparison to other discovered and widely used antagonist, the prepared curcumin derivatives are not selective to a specific AMPA subunit, instead implement its effect in the same way between all types of AMPA receptors. Additionally, the obtained results provide derivatives that not only noncompetitively inhibit AMPARs but also decrease its biophysical kinetics, specifically desensitization and deactivation rates. Hence, to potentially serve as a new AMPAR inhibitor with therapeutic potential, the current study provides compounds that are non-selective and non-competitive antagonist, which also effect the desensitization and deactivation rates of the receptor.