Gamma-Hydroxybutyrate: Toxicokinetics, Toxicodynamics and Treatment Strategies

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DESCRIPTION (provided by applicant): γ-Hydroxybutyrate (GHB), a popular drug of abuse, is commonly ingested with alcohol at nightclubs and "raves", or as a means of drug-facilitated sexual assault. The range between high recreational doses and overdose is narrow, so that acute intoxications and overdoses are common. Respiratory depression and arrest represent the major cause of death in clinical reports of fatality associated with GHB intoxication. Effective pharmacological treatment for GHB overdoses has yet to be identified. The long-term objective is to identify treatment strategies that improve rates of morbidity and mortality associated with GHB intoxication, when GHB is ingested alone or with ethanol. We have reported that GHB undergoes concentration-dependent reabsorption in the kidney, due to transport by monocarboxylate transporters (MCTs), and that the administration of MCT inhibitors, such as L-lactate, can increase the renal and total clearances of GHB, decrease brain extracellular fluid concentrations of GHB, and decrease sleep time in rats. The purpose of this competing renewal is to determine the therapeutic potential of MCT inhibition as a treatment strategy for GHB overdose, alone and in combination with other potentially effective strategies, using the clinically relevant endpoint of respiratory depression. Our specific aims are: (1) Characterization of GHB-induced respiratory depression and identification of treatment strategies that improve measures of respiration during GHB overdose. The purpose of this aim is to identify the mechanism of GHB-induced respiratory depression using selective neurotransmitter receptor antagonists. (2) Identification of effective treatment strategies for oral GHB overdoses. We hypothesize that MCTs are important for the absorption of GHB from the intestine, and that MCT inhibitors will decrease the bioavailability of GHB, as well as increasing its renal and total clearances following oral GHB intoxication. (3) Characterization of the GHB-alcohol interaction and identification of effective treatment strategies for oral GHB/alcohol overdoses. We hypothesize that high concentrations of ethanol will potentiate GHB-induced respiratory depression, and will increase the risk of fatality due to GHB intoxication. (4) Characterization of the toxicokinetics and toxicodynamics of GHB after multiple exposures and identification of effective treatment strategies. Our hypothesis is that binge use of GHB results in both increased expression of MCTs in tissues leading to altered transport and disposition, as well as tolerance to respiratory depression. Studies in this proposal will evaluate the use of oral and IV administered MCT inhibitors, alone or combined with neurotransmitter receptor antagonists, to improve measures of respiration and prevent fatality with GHB overdoses. This research is significant as it addresses the toxicodynamic effect, respiratory depression, mediating GHB fatality, and applies this endpoint under clinically relevant conditions. By combining treatment strategies with different mechanisms of action, this research will determine which pharmacological interventions have therapeutic potential to treat life-threatening GHB overdoses.