A New VGLUT-Specific Potent Inhibitor: Pharmacophore of Brilliant Yellow

Abstract

The increased concentration of glutamate in synaptic vesicles, mediated by the vesicular glutamate transporter (VGLUT), is an initial vital step in glutamate synaptic transmission. Evidence indicates that aberrant overexpression of VGLUT is involved in certain pathophysiologies of the central nervous system. VGLUT is subject to inhibition by various types of agents. The most potent VGLUT-specific inhibitor currently known is Trypan Blue, which is highly charged, hence membrane-impermeable. We have sought a potent, VGLUT-specific agent amenable to easy modification to a membrane-permeable analog. We provide evidence that Brilliant Yellow exhibits potent, VGLUT-specific inhibition, with a Ki value of 12 nM. Based upon structure-activity relationship studies and molecular modeling, we have defined the potent inhibitory pharmacophore of VGLUT Brilliant Yellow. This study provides new insight into development of a membrane-permeable agent to lead to specific blockade, with high potency, of accumulation of glutamate into synaptic vesicles in neurons.

LSP5-2157 a new inhibitor of vesicular glutamate transporters

“…The 3D homology model build in cytosol open conformation reveals a large binding pore with three successive binding regions: a hydrophilic layer, a hydrophobic layer and another hydrophilic layer. According to this model, the features required for potent inhibition are: two polar moiety linked by a hydrophobic scaffold as observed with known competitive ligands (Pietrancosta et al, 2010;Tamura et al, 2014). Interestingly, as glutamate, small polar ligands such as short Trypan Blue analogs or Xanthurenic acid or other quinolone have low affinity for VGLUT (Carrigan et al, 2002).…”

“…Presently, three major types of VGLUT's inhibitors have been identified (Thompson et al, 2005) : glutamate-like inhibitors (Thompson et al, 2005), substituted quinolines (Bartlett et al, 1998;Carrigan et al, 2002) and dyes (Kehrl et al, 2017;Ozkan and Ueda, 1998;Roseth et al, 1995Roseth et al, , 1998Tamura et al, 2014). Dyes have Ki in the 20nM-10µM range, substituted quinolines (DCQ) in the 40-300µM range and glutamate analogs with IC 50 >230µM.…”

Molecular, Structural, Functional, and Pharmacological Sites for Vesicular Glutamate Transporter Regulation

“…The following has been surmised of these molecules: (1) the negative charge is important for ligand activity and plays the same role as the COO-proximal glutamate moiety; (2) the NH 2 group, present on the polar part of some inhibitors, plays the same role as the amino group of glutamate. This NH 2 does not seem to be essential for glutamate affinity [296]. Currently, azo dyes that inhibit VGLUTs with the best affinity are as follows: Bright Yellow (BY, IC 50 SAR studies have identified important pharmacophoric sites for the affinity of azo dyes (e.g., TB) [296,297].…”

Glutamate Release

“…This regulation would be important in controlling neuronal communication. A number of VGLUT inhibitors have been reported [52,62,70,94,[157][158][159][160][161][162][163][164][165][166][167][168][169][170]172]. However, only three inhibitors have been shown capable of downregulating the amount of exocytotically released glutamate: the vesicular transmitter uptake inhibitory protein factor (IPF) [164], Rose Bengal [165], and ketone bodies, in particular acetoacetic acid [70].…”

“…All the VGLUT-inhibitory keto acids reported are endogenous substances, but not potent. The most potent, highly VGLUT-specific inhibitors known today are Trypan Blue [161] and Brilliant Yellow [172], but these are not membrane-permeable. Thus, membrane-permeable, potent VGLUT-specific inhibitors, which could specifically regulate glutamate release, remain to be developed.…”