Identification of GSK-3 as a Potential Therapeutic Entry Point for Epilepsy

Abstract

In view of the clinical need for new anti-epileptic drugs (AEDs) with novel modes of action, we used a zebrafish seizure model to screen the anticonvulsant activity of medicinal plants used for traditional epilepsy treatment in the Congo, identifying 4 crude plant extracts that inhibited pentylenetetrazol (PTZ)-induced seizures in zebrafish larvae. Zebrafish bioassay-guided fractionation of an anticonvulsant Fabaceae species, Indigofera arrecta, identified indirubin, an bis-indole alkaloid with known inhibitory activity at glycogen synthase kinase (GSK)-3, a well known protein kinase. Target validation experiments with partial loss of function of GSK-3 via antisense knockdown in zebrafish showed anticvonvulant activity against PTZ-induced seizures. Subsequently, indirubin, together with the more potent and GSK-3 specific derivative 6-bromoindirubin-3'-oxime (BIOacetoxime) and the structurally unrelated GSK-3β inhibitor 2-methyl-5-[3-[4-(methylsulfinyl)phenyl]-5-benzofuranyl]-1,3,4-oxadiazole (TCS2002), were tested in zebrafish and rodent seizure assays. All 3 compounds revealed anticonvulsant activity in PTZ-treated zebrafish larvae, with electroencephalographic recordings revealing reduction of epileptiform discharges. All 3 compounds also showed anticonvulsant activity in the pilocarpine rat model for limbic seizures and in the 6-Hz psychomotor refractory seizure mouse model. Moreover, BIOacetoxime, the most potent GSK-3 inhibitor was also able to exert anticonvulsant actions in 6-Hz fully kindled mice. Our findings provide the first evidence for anticonvulsant activity of selective GSK-3 inhibitors, thereby implicating GSK-3 as a potential new drug target for epilepsy. Our results also support the use of zebrafish bioassay-guided fractionation of anti-epileptic medicinal plant extracts as an effective strategy for the discovery of new AEDs with novel mechanisms of action.

GSK3β and Tau Protein in Alzheimer’s Disease and Epilepsy

“…In this report, PTZ-treated zebrafish larvae were treated with both compounds, which exhibited anticonvulsant activity, with a reduction of epileptiform discharges. In the same way, indirubin and BIO-acetoxime showed anticonvulsant activity in the 6-Hz refractory seizure mouse model (Aourz et al, 2019).…”

“…Memantine and ifendropil are NMDAR antagonists and have been demonstrated to conduct to GSK3β inactivation and reduction of tau phosphorylation (Liu et al, 2017). Recently, the use of potent and selective GSK3β inhibitors such as indirubin and BIO-acetoxime showed anticonvulsant properties (Aourz et al, 2019). In this report, PTZ-treated zebrafish larvae were treated with both compounds, which exhibited anticonvulsant activity, with a reduction of epileptiform discharges.…”

“…Even though GSK3β has not been demonstrated to produce epilepsy in itself, there is evidence showing that GSK3β inhibition does result in anticonvulsant activity, even after brain excitability has been altered from normal, healthy conditions into a ''proepileptic'' state (Aourz et al, 2019). Furthermore, GSK3β alterations do increase seizure susceptibility, and increased GSK3β activity has been evidenced in other epilepsy models (Lohi et al, 2005;Tripathi et al, 2010;Lee et al, 2012).…”

Anticonvulsant Activity of Pterostilbene in Zebrafish and Mouse Acute Seizure Tests

“…In our study, the anticonvulsant potential of PTE was first evaluated in the zebrafish PTZ seizure test [ 10 , 13 , 21 ] and this assay demonstrated its evident seizure-suppressing activity. Interestingly, exposure time of 2 h was sufficient to detect its bioactivity, whereas most of the compounds required longer, usually 18 h, incubation to exhibit its properties.…”

A theoretical and spectroscopic (NMR and IR) study of indirubin in solution and in the solid state

“…Very recently, a group of authors from different countries have identified indirubin as the active principle responsible for the anticonvulsant properties of Indigofera arrecta (a traditional medicinal plant from Congo). Indirubin itself and 6‐bromoindirubin‐3‐acetoxime, both potent GSK‐3 inhibitors, are a new therapeutic entry point for epilepsy …”