Can nucleoside and nucleotide precursors become future successful anti-epileptic drugs?
Marek Cieślak1, Michał Komoszyński2
Many examples of experimental epilepsy show that epileptic seizures occur due to release of stimulatory neurotransmitters into intracellular spaces. In CNS adenosine suppresses exocytosis of glutamate and asparginate but guanosine increases the reverse uptake of glutamate by astrocytes and thus lowers it concentration outside the cell. In this process both nucleosides participate in suppressing the epileptic seizures. By decreasing concentration of ectoadenosine and ectoguanosine outside the cell, that compounds can protect neurons from cellular degeneration. It was shown in many animal models for experimental epilepsy that adenosine A 1 and A 2A receptors were involved in the process of stopping the seizures. Moreover, some of the conventional anti-epileptic drugs reveal enhance their therapeutic abilities by interactions with the adenosine receptors, being either agonists or antagonists. These interactions modulate the activity of receptors and consequently regulate the neuroprotection processes. Some agonists of adenosine receptors increase the epileptic episodes reaction to those compounds. Anti-episode action of adenosine and guanosine as well as agonists and antagonists of nucleoside receptors indicate the possibility of applying the knowledge about these processes towards production of new anti-epileptic medication. Successful anti-epileptic medication may be based on compounds that have the ability to increase the concentration of ectoadenosine i.e; adenosine deaminase inhibitors, adenosine kinase inhibitors or compounds with ability to suppress reverse uptake of nucleosides. Another method to increase the concentration of extracellular adenosine is to increase the activity of 5’-nucleotidase. That in effect will increase the amount of ectoadenosine by degradation of ectoAMP. There are very promising results revealed that oral administration of guanosine and GMP as well as guanosine by itself given intraperitoneally and intraventricularly what halted epileptic seizures caused by quinolinic acid which is a glutamate agonist.