GHB (gamma-hydroxybutyrate) carrier-mediated transport across the blood-brain barrier.

Abstract

gamma-Hydroxybutyrate (sodium oxybate, GHB) is an approved therapeutic agent for cataplexy with narcolepsy. GHB is widely abused as an anabolic agent, euphoriant, and date rape drug. Recreational abuse or overdose of GHB (or its precursors gamma-butyrolactone or 1,4-butanediol) results in dose-dependent central nervous system (CNS) effects (respiratory depression, unconsciousness, coma, and death) as well as tolerance and withdrawal. An understanding of the CNS transport mechanisms of GHB may provide insight into overdose treatment approaches. The hypothesis that GHB undergoes carrier-mediated transport across the BBB was tested using a rat in situ brain perfusion technique. Various pharmacological agents were used to probe the pharmacological characteristics of the transporter. GHB exhibited carrier-mediated transport across the BBB consistent with a high-capacity, low-affinity transporter; averaged brain region parameters were V(max) = 709 +/- 214 nmol/min/g, K(m) = 11.0 +/- 3.56 mM, and CL(ns) = 0.019 +/- 0.003 cm(3)/min/g. Short-chain monocarboxylic acids (pyruvic, lactic, and beta-hydroxybutyric), medium-chain fatty acids (hexanoic and valproic), and organic anions (probenecid, benzoic, salicylic, and alpha-cyano-4-hydroxycinnamic acid) significantly inhibited GHB influx by 35 to 90%. Dicarboxylic acids (succinic and glutaric) and gamma-aminobutyric acid did not inhibit GHB BBB transport. Mutual inhibition was observed between GHB and benzoic acid, a well known substrate of the monocarboxylate transporter MCT1. These results are suggestive of GHB crossing the BBB via an MCT isoform. These novel findings of GHB BBB transport suggest potential therapeutic approaches in the treatment of GHB overdoses. We are currently conducting "proof-of-concept" studies involving the use of GHB brain transport inhibitors during GHB toxicity.