Date of Award
Doctoral Dissertation - Restricted (NYMC/Touro only) Access
Doctor of Philosophy
Infantile spasms represent a devastating epilepsy syndrome during early life (incidence of IS is 1:3,200-3,400 live births). The syndrome consists of a triad of spasms (stretch-like seizures) in clusters, electroencephalogram pattern of hypsarrhythmia and neurobehavioral regress. Current Food and Drug Administration approved medications (adrenocorticotropic hormone and vigabatrin) are not completely effective (40% of patients do not respond to the treatments) and have side effects that may severely affect quality of life or even be life-threatening. Therefore, new improved treatments for infantile spasms are needed.
Sigma-1 receptor is a specific protein found at the mitochondrion-endoplasmic reticulum junction. Activation of sigma-1 receptor can modulate cellular properties in multiple ways. Though, the exact mechanisms of sigma-1 receptor action are still not well understood, sigma-1 receptors play important roles in neuronal physiology and are involved in the cell protective mechanisms in neurodegenerative disorders. Studies show that many sigma-1 receptor agonists have anticonvulsant effects in multiple models of acutely induced seizures. We used a biological model of infantile spasms developed in rats consisting of prenatal betamethasone exposure and postnatal trigger of spasms by N-methyl-D-aspartate. This model has been developed in our laboratory, repeatedly validated and reproduced in five independent laboratories worldwide. We primarily tested a sigma 1 receptor agonist, ANAVEX®2-73, as a potential infantile spasms treatment but also included additional sigma-1 receptor agonists to determine whether this class of small molecules may offer a new treatment approach for infantile spasms.
ANAVEX®2-73 was applied in both acute and chronic settings in postnatal day 12-15 rats. In the acute experiment, the drug was administered as a single pretreatment before a single trigger of spasms. In the chronic experiment, the drug administration was randomized in a prospective trial over several days with repeated treatments initiated only after the first bout of spasms. The results indicate that ANAVEX®2-73 has strong activity against the spasms in both approaches. However, while testing this drug together with commercially available sigma-1 receptor antagonist, there was no loss of effect. Similarly, a commercially available sigma-1 receptor agonist (PRE-084) was ineffective in the model. Both these failures indicate that either ANAVEX®2-73 is using different conformational states of sigma-1 receptor in comparison to PRE-084 leading to activation of different cellular effectors, or, the ANAVEX®2-73 has additional effects outside sigma-1 receptor domain.
In the animals undergoing treatment in the chronic model, we further investigated whether introduction of ANAVEX®2-73 affects animal behaviors (as a rat correlate of human neurodevelopment). In the studies we found that those animals experiencing spasms are less fearful and explore an open space more than naïve animals. Treatment with ANAVEX®2-73 however did not change this behavior.
As neurodevelopmental and learning problems observed in infants with infantile spasms may be the result of impaired neuronal plasticity, specifically long-term potentiation after the spasms, we also investigated hippocampal long-term potentiation in the stratum radiatum of CA1 and dentate gyrus molecular layers. The spasms with NMDA in our infantile spasms model caused impairments of long term potentiation in the dentate gyrus but not in the CA1 hippocampal region during adolescence (25 to 30 days old rats). ANAVEX®2-73 recovered the lost plasticity in the dentate gyrus.
Our data indicate that ANAVEX®2-73 significantly suppresses spasms in our animal model of infantile spasms. Whether this effect also includes additional S1R agonists or is due to cholinergic effects of ANAVEX®2-73 is yet to be determined. Spasms elicited changes in behavior of the rats such as anxiolytic effects seen as loss of fear in open space. Interestingly, ANAVEX®2-73 was able to recover some impairments in the long-term potentiation despite not affecting behavioral outcome. It is possible that a longer period of behavioral follow-up would return positive results with ANAVEX®2-73 treatment.
Chern, Chian-Ru, "Assessment of AN2-73, a Putative Sigma 1 Receptor (S1R) Agonist in a Model of Infantile Spasms" (2022). NYMC Student Theses and Dissertations. 62.