GABA Transporters and GABA-Transaminase as Drug Targets

The fine-tuning and homeostatic balance of the GABAergic inhibitory tone in the central nervous system (CNS) is a prerequisite for controlling the excitatory neurotransmission. This principal mechanism for controlling excitation is inhibition which has been the topic of intensive research covering all known functional entities of the GABAergic synapse. The therapeutical scope for targeting the GABA system covers a large number of neurological and psychiatric disorders. This review focuses on the major inactivation systems for GABAergic neurotransmission, the GABA transporters (GATs) and the GABA catabolic enzyme GABA-transaminase (GABA-T) as drug targets. Tiagabin and Vigabatrin, two anti-epileptic drugs on the market today, specifically inhibit GABA transport and metabolism, respectively. However, previous and recent evidence has clearly demonstrated the importance and differential functional roles of glial and neuronal GABA uptake and the metabolic fate of the sequestered neurotransmitter GABA in these cells. Moreover, the diverse expression patterns of the GABA transporters, in combination with development of GAT inhibitors with novel pharmacological profiles may initiate a renaissance for these inactivation systems as drugs targets. In particular, further research to elucidate the specialized physiological function of the GATs combined with their differential spatial expression could be of fundamental importance for the understanding of concerted action with regard to the fine-tuning of the GABAergic inhibitory tone. As such, selective targeting and modulation of GABA transporter subtypes and cell-specific GABA uptake and metabolism is of therapeutical interest in GABA-related CNS disorders, including epilepsy.