Vojtech Kapras

Neurosteroid modulation of N-methyl-D-aspartate receptors: Molecular mechanism and behavioral effects

Glutamate is the main neurotransmitter released at synapses in the central nervous system of vertebrates. Its excitatory role is mediated through activation of specific glutamatergic ionotropic receptors, among which the N-methyl-D-aspartate (NMDA) receptor subtype has attracted considerable attention in recent years. Substantial progress has been made in elucidating the roles these receptors play under physiological and pathological conditions and in our understanding of the functional, structural, and pharmacological properties of NMDA receptors. Many pharmacological compounds have been identified that affect the activity of NMDA receptors, including neurosteroids. This review summarizes our knowledge about molecular mechanisms underlying the neurosteroid action at NMDA receptors as well as about the action of neurosteroids in animal models of human diseases.

Access of inhibitory neurosteroids to the NMDA receptor

NMDA receptors are glutamatergic ionotropic receptors involved in excitatory neurotransmission, synaptic plasticity and excitotoxic cell death. Many allosteric modulators can influence the activity of these receptors positively or negatively, with behavioural consequences. 20‐Oxo‐5β‐pregnan‐3α‐yl sulphate (pregnanolone sulphate; PA‐6) is an endogenous neurosteroid that inhibits NMDA receptors and is neuroprotective. We tested the hypothesis that the interaction of PA‐6 with the plasma membrane is critical for its inhibitory effect at NMDA receptors.

Cellular and behavioural effects of a new steroidal inhibitor of the N-methyl-D-aspartate receptor 3α5β-pregnanolone glutamate

Preclinical studies have demonstrated a considerable role for N-methyl-d-aspartate (NMDA) receptors in excitotoxicity and the concurrent neuroprotective effect of NMDA receptor antagonists. Because NMDA receptors are one of the most widespread receptors in the central nervous system, application of their antagonist often leads to serious side effects ranging from motor impairment to induction of schizophrenic-like psychosis. Therefore, we have initiated development and testing of a novel synthetic NMDA receptor antagonist derived from naturally occurring neurosteroids. 20-oxo-5β-pregnan-3α-yl-l-glutamyl-1-ester (3α5βP-Glu) is a novel synthetic steroidal inhibitor of the NMDA receptor. Our results show that 3α5βP-Glu preferentially inhibits tonically activated NMDA receptors, is able to cross the blood brain barrier, does not induce psychotomimetic symptoms (such as hyperlocomotion and sensorimotor gating deficit) and reduced an excitotoxic damage of brain tissue and subsequent behavioural impairment in rats. In particular, 3α5βP-Glu significantly ameliorated neuronal damage in the dentate gyrus and subiculum, and improved behavioural performance in active allothetic place avoidance tasks (AAPA, also known as the carousel maze) after bilateral NMDA-induced lesions to the hippocampi. These findings provide a possible new therapeutic approach for the treatment of diseases induced by NMDA receptor overactivation.

Synthesis of C3, C5, and C7 pregnane derivatives and their effect on NMDA receptor responses in cultured rat hippocampal neurons

The synthesis of several novel 5alpha- and 5beta-20-oxo-pregnane derivatives substituted in the position 3 and 7 of the steroid skeleton is described. Activity of synthesized compounds was studied in voltage-clamped cultured rat hippocampal neurons. Substituted derivatives inhibited NMDA-elicited neuronal activity. The relationship between biological activity and structure is discussed.

Total Synthesis of ent-Pregnanolone Sulfate and Its Biological Investigation at the NMDA Receptor

A unique asymmetric total synthesis of the unnatural enantiomer of pregnanolone, as well as a study of its biological activity at the NMDA receptor, is reported. The asymmetry is introduced by a highly atom-economic organocatalytic Robinson annulation. A new method for the construction of the cyclopentane D-ring consisting of CuI-catalyzed conjugate addition and oxygenation followed by thermal cyclization employing the persistent radical effect was developed. ent-Pregnanolone sulfate is surprisingly only 2.6-fold less active than the natural neurosteroid.