Kainic acid receptor

Trigonelline, an alkaloid found in the seeds of Trigonella foenum-graecum L. (fenugreek), has been recognized for its potential in treating various diseases. Notably, trigonelline has demonstrated a neuroprotective impact by reducing intrasynaptosomal calcium levels, inhibiting the production of reactive oxygen species (ROS), and regulating cytokines. Kainic acid, an agonist of kainic acid receptors, is utilized for inducing temporal lobe epilepsy and is a common choice for establishing kainic acid-induced status epilepticus, a widely used epileptic model. The neuroprotective effect of trigonelline in the context of kainic acid-induced epilepsy remains unexplored. This study aimed to induce epilepsy by administering kainic acid (10 mg/kg, single subcutaneous dose) and subsequently evaluate the potential anti-epileptic effect of trigonelline (100 mg/kg, intraperitoneal administration for 14 days). Ethosuccimide (ETX) (187.5 mg/kg) served as the standard drug for comparison. The anti-epileptic effect of trigonelline over a 14-day administration period was examined. Behavioral assessments, such as the Novel Object Recognition (NOR) test, Open Field Test (OFT), and Plus Maze tests, were conducted 2 h after kainic acid administration to investigate spatial and non-spatial acquisition abilities in rats. Additionally, biochemical analysis encompassing intrasynaptosomal calcium levels, LDH activity, serotonin levels, oxidative indicators, and inflammatory cytokines associated with inflammation were evaluated. Trigonelline exhibited significant behavioral improvements by reducing anxiety in open field and plus maze tests, along with an amelioration of memory impairment. Notably, trigonelline substantially lowered intrasynaptosomal calcium levels and LDH activity, indicating its neuroprotective effect by mitigating cytotoxicity and neuronal injury within the hippocampus tissue. Moreover, trigonelline demonstrated a remarkable reduction in inflammatory cytokines and oxidative stress indicators. In summary, this study underscores the potential of trigonelline as an anti-epileptic agent in the context of kainic acid-induced epilepsy. The compound exhibited beneficial effects on behavior, neuroprotection, and inflammation, shedding light on its therapeutic promise for epilepsy management.

The majority of excitatory neurotransmission in vertebrate CNS is mediated by glutamate binding to different types of receptors. Among them, a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and kainite receptors (KAR) are ionotropic receptors playing important pathophysiological roles. A number of small molecules acting as positive allosteric modulators (PAM) of AMPAR have been proposed as drugs for neurological disorders, however, there is no such abundance of ligands capable of modulating KARs activity. We investigated the ability of IDRA21 and of its derivative, compound 2 (c2), to modulate glutamate-evoked currents at native and recombinantly expressed AMPA and KA receptors. By using the patch clamp technique we analyzed the activity of the two compounds in primary cultures of cerebellar granule neurons and in HEK293 cells transiently transfected with KARs and AMPAR subunits. It resulted that both benzothiadiazine derivatives potentiate AMPAR and KAR mediated currents in native and recombinant receptors, c2 being always more potent and efficacious than IDRA21. The potency of both compounds was higher in native receptors than in recombinant receptors. In HEK293 cells transfected with AMPAR subunits, the efficacy of IDRA21 and c2 was much higher in GluA1 than in GluA2 homomeric receptors while their potency did not change. In recombinant KAR, both compounds had a potency in the high micromolar range, while the efficacy reached a maximum in the GluK2 expressing cells. The benzothiadiazine effect, both in native and recombinant receptors, was detected mainly on plateau current, involving a decrease in AMPAR and KAR desensitization. Our study demonstrates for the first time that two positive allosteric modulators of AMPAR, IDRA21 and its derivative, c2, potentiate KAR activity. Furthermore, we highlighted their subunit selectivity that may enable the design of potent and selective PAMs, which could be relevant for the development of new drugs and for a better understanding of KAR functions in the CNS.

Discovery of chemical tools for the ionotropic glutamate receptors continues to be a challenging task. Herein we report a diversity-oriented approach to new 2,3-trans-l-proline analogs whereby we study how the spatial orientation of the distal carboxylate group influences the binding affinity and receptor class and subtype selectivity. In total, 10 new analogs were synthesized and 14 stereoisomers characterized in binding assays at native rat ionotropic glutamate receptors, and at cloned human homomeric kainic acid (KA) receptor subtypes GluK1-3. The study identified isoxazole analogs 3d,e, which displayed selectivity in binding at native N-methyl-d-aspartate (NMDA) receptors over native α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and KA receptors, in the high nanomolar to low micromolar range. Furthermore, analogs 3i-A/B showed a preference in binding affinity for GluK3 over GluK1,2. Finally, analog 3j displayed high nanomolar affinity for native NMDA receptors as well as for homomeric GluK3 receptors.