Galanin receptors modulate seizures

Synergistic effects of the galanin analog 810-2 with the antiseizure medication levetiracetam in rodent seizure models

OBJECTIVE

The use of many antiseizure medications (ASMs) is limited due to pharmacoresistance and dose-limiting side effects, suggesting an unmet need for novel therapeutic approaches. The neuropeptide galanin reduces seizures in several preclinical seizure and epilepsy models, but its clinical utility is limited due to rapid metabolism and poor blood-brain barrier penetration. The lead galanin analog 810-2 is systemically bioavailable and reduces seizures when administered alone. Further development of this analog, with the potential for use as an add-on therapy in patients with epilepsy, requires a better understanding of the use of this analog in combination with approved ASMs. We sought to evaluate 810-2 in combination with commonly used ASMs in rodent models of seizures.

METHODS

The mouse 6-Hz seizure assay was used to test efficacy of 810-2 in combination with levetiracetam (LEV), valproic acid (VPA), or lacosamide (LCM) using a 1:1 dose ratio in isobolographic studies. Further characterization was performed for the combination of 810-2 and LEV in the mouse corneal kindling and rat 6-Hz assays.

RESULTS

Whereas the combination of 810-2 with VPA and LCM yielded additive interactions, the combination of 810-2 with LEV demonstrated a synergistic interaction in the mouse 6-Hz assay. Supra-additive effects were also observed in the mouse corneal kindling and rat 6-Hz assays for this combination.

SIGNIFICANCE

The combination of 810-2 with LEV suggests the potential for this galanin analog to be further developed as an add-on therapy for patients with epilepsy, particularly when coadministered with LEV.

CSF levels of a set of neurotrophic factors (brain-derived neurotrophic factor, nerve growth factor) and neuropeptides (neuropeptide Y, galanin) in epileptic children

This paper aims to investigate the possible roles of a set of neurotrophic factors (brain-derived neurotrophic factor-BDNF, nerve growth factor-NGF) and neuropeptides (neuropeptide Y-NPY, and galanin) in children with active epileptogenesis. The cerebrospinal fluid (CSF) levels of BDNF, NPY, NGF and galanin were measured with enzyme-linked immunosorbent assays in epileptic children (n = 73) and controls (n = 64). There were no significant alterations in the CSF levels of BDNF, NPY and NGF in epileptic children with active clinical seizures compared with the levels of controls. However profoundly depressed galanin levels were found in infants with epileptic encephalopathy (mean ± SD:0.63 ± 0.19 pg/ml) and significantly increased galanin levels were measured in children with drug resistant epilepsy during the period of status epilepticus (mean ± SD: 6.92 ± 1.19, pg/ml pg/ml) compared with the levels of controls. Depressed levels of galanin might reflect a defective anti-epileptogenic effect of galanin in infants with epileptic encephalopathy. On the contrary, increased CSF levels of galanin might be a result of anti-epileptogenic effects of this peptide in epileptic children with status epilepticus.

The potential effects of anticonvulsant drugs on neuropeptides and neurotrophins in pentylenetetrazol kindled seizures in the rat

Purpose: Neuropeptides and neurotrophic factors are thought to be involved in epileptogenesis. This study aims to investigate the potential effects of anticonvulsant drugs on neuropeptides (galanin and neuropeptide Y) and neurotrophic factors (BDNF and NGF) in pentylenetetrazol (PTZ)-kindled seizures in the rat.Methods: Forty-eight adult male Sprague-Dawley rats were included in the study. The animals were divided into 8 groups of six rats. Group 1 was defined as naïve control, and received no medication. Group 2 (PTZ + saline) was treated with sub-convulsive doses of PTZ (35 mg/kg) and saline i.p. for 14 days. For anticonvulsant treatments, Groups 3-8 were treated with 200 mg/kg levetiracetam (PTZ + LEV), 1 mg/kg midazolam (PTZ + MDZ), 80 mg/kg phenytoin (PTZ + PHT), 80 mg/kg topiramate (PTZ + TPR), 40 mg/kg lamotrigine (PTZ + LMT) and 50 mg/kg sodium valproate (PTZ + SV), respectively. All anticonvulsant drugs were injected 30 min prior to PTZ injection throughout 14 days. Following treatment period, behavioral, biochemical and immunohistochemical studies were performed.Results: PTZ + saline group revealed significantly decreased galanin, NPY, BDNF and NGF levels compared to control. PTZ + MDZ group had significantly increased galanin, BDNF and NGF levels compared to saline group. Also, PTZ + LEV group showed increased BDNF levels. PTZ + saline group revealed significantly lower neuron count and higher GFAP (+) cells in hippocampal CA1-CA3 regions. All anticonvulsants significantly reduced hippocampal astrogliosis whereas only midazolam, levetiracetam, sodium valproate and lamotrigine prevented neuronal loss.Conclusion: Our results suggested that anticonvulsant drugs may reduce the severity of seizures, and exert neuroprotective effects by altering the expression of neuropeptides and neurotrophins in the epileptogenic hippocampus.

Positive allosteric modulators to peptide GPCRs: a promising class of drugs

The task of finding selective and stable peptide receptor agonists with low molecular weight, desirable pharmacokinetic properties and penetrable to the blood-brain barrier has proven too difficult for many highly coveted drug targets, including receptors for endothelin, vasoactive intestinal peptide and galanin. These receptors and ligand-gated ion channels activated by structurally simple agonists such as glutamate, glycine and GABA present such a narrow chemical space that the design of subtype-selective molecules capable of distinguishing a dozen of glutamate and GABA receptor subtypes and possessing desirable pharmacokinetic properties has also been problematic. In contrast, the pharmaceutical industry demonstrates a remarkable success in developing 1,4-benzodiazepines, positive allosteric modulators (PMAs) of the GABAA receptor. They were synthesized over 50 years ago and discovered to have anxiolytic potential through an in vivo assay. As exemplified by Librium, Valium and Dormicum, these allosteric ligands of the receptor became the world's first blockbuster drugs. Through molecular manipulation over the past 2 decades, including mutations and knockouts of the endogenous ligands or their receptors, and by in-depth physiological and pharmacological studies, more peptide and glutamate receptors have become well-validated drug targets for which an agonist is sought. In such cases, the pursuit for PAMs has also intensified, and a working paradigm to identify drug candidates that are designed as PAMs has emerged. This review, which focuses on the general principles of finding PAMs of peptide receptors in the 21st century, describes the workflow and some of its resulting compounds such as PAMs of galanin receptor 2 that act as potent anticonvulsant agents.