γ-Glutamyl-dipeptides: Easy tools to rapidly probe the stereoelectronic properties of the ionotropic glutamate receptor binding pocket

Comprehensive Review of γ-Glutamyl Peptides (γ-GPs) and Their Effect on Inflammation Concerning Cardiovascular Health

γ-Glutamyl peptides (γ-GPs) are a group of peptides naturally found in various food sources. The unique γ-bond potentially enables them to resist gastrointestinal digestion and offers high stability in vivo with a longer half-life. In recent years, these peptides have caught researchers' attention due to their ability to impart kokumi taste and elicit various physiological functions via the allosteric activation of the calcium-sensing receptor (CaSR). This review discusses the various food sources of γ-glutamyl peptides, different synthesis modes, allosteric activation of CaSR for taste perception, and associated multiple biological functions they can exhibit, with a special emphasis on their role in modulating chronic inflammation concerning cardiovascular health.

The Glutathione Metabolite γ-Glutamyl-Glutamate Partially Activates Glutamate NMDA Receptors in Central Neurons With Higher Efficacy for GluN2B-Containing Receptors

Gamma-L-glutamyl-L-glutamate (γ-Glu-Glu) was synthetized and further characterized for its activity on cultured neurons. We observed that γ-Glu-Glu elicited excitatory effects on neurons likely by activating mainly the N-methyl-D-aspartate (NMDA) receptors. These effects were dependent on the integrity of synaptic transmission as they were blocked by tetrodotoxin (TTX). We next evaluated its activity on NMDA receptors by testing it on cells expressing these receptors. We observed that γ-Glu-Glu partially activated NMDA receptors and exhibited better efficacy for NMDA receptors containing the GluN2B subunit. Moreover, at low concentration, γ-Glu-Glu potentiated the responses of glutamate on NMDA receptors. Finally, the endogenous production of γ-Glu-Glu was measured by LC-MS on the extracellular medium of C6 rat astroglioma cells. We found that extracellular γ-Glu-Glu concentration was, to some extent, directly linked to GSH metabolism as γ-Glu-Glu can be a by-product of glutathione (GSH) breakdown after γ-glutamyl transferase action. Therefore, γ-Glu-Glu could exert excitatory effects by activating neuronal NMDA receptors when GSH production is enhanced.