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Elucidation of the Specificity of Neuroactive Steroids and Related Compounds at the at the Vesicular Glutamate Transporter

by Smith, Wesley Edward

Abstract (Summary)
As the primary excitatory amino acid, glutamate is essential to proper functioning of the mammalian CNS. Proper regulation of the synaptic release of glutamate, potentially regulated by synaptic vesicle content, is one of many critical aspects to normal excitatory functioning. In particular, the vesicular glutamate transporters (VGLUTs), which load synaptic vesicles with glutamate prior to presynaptic release of neurotransmitter, are distinct from that of the plasma membrane excitatory amino acid transporters (EAAT). The development of a library of compounds which selectively inhibit the uptake of [3H]-L-glutamate into the VGLUTs, has revealed importance of particular structural motifs. Among these structural motifs, one of the most important is that of the "embedded glutamate" which mimics the endogenous substrate of the transporter. With respect to potency, the substitution of a lipophilic moiety at the C6 position seems to be the most important to date, as illustrated by 5,6-napthyl quinoline dicarboxylic acid (5,6-QDC). The structure of this compound strongly resembles that of a steroid molecule. In light of recent research suggesting steroids act within the CNS in a non-genomic manner, this observation prompted the testing of a panel of steroid molecules at VGLUT. These compounds, known as "neuroactive steroids" have been shown to be synthesized, modified, and/or active within the brain. Research from our lab, as well as from the Thompson lab, shows that certain sulfated neuroactive steroids are potent inhibitors of [3H]-L-glutamate uptake into synaptic vesicles. This work identifies pregnenolone sulfate, along with 5,6-QDC, as competitive inhibitors of VGLUT (K i values of 107 and 228 μM, respectively). These two molecules display specificity for VGLUT, with respect to other sites on the synaptic vesicle (i.e., electrochemical gradient), and among other vesicular neurotransmitter transporters (i.e., VGAT, VMAT). Two molecules, 5,6-QDC and Congo Red Fragment (CRF) were aligned to the VGLUT Pharmacophore to illustrate the SAR of these compounds. Biochemical studies have also been conducted to delineate substrate activity of neuroactive steroids and related compounds at VGLUT. The specificity of certain sulfated neuroactive steroids suggest that they could be endogenous regulators of vesicular glutamate uptake.
Bibliographical Information:

Advisor:Dr. Richard J. Bridges; Dr. John M. Gerdes

School:The University of Montana

School Location:USA - Montana

Source Type:Master's Thesis

Keywords:department of biomedical pharm sciences

ISBN:

Date of Publication:09/26/2007

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