In Vitro and In Vivo Evidence for Active Brain Uptake of the GHB Analog HOCPCA by the Monocarboxylate Transporter Subtype 1.

Abstract

γ-Hydroxybutyric acid (GHB) is a recreational drug, a clinically prescribed drug in narcolepsy and alcohol dependence, and an endogenous substance that binds to both high- and low-affinity sites in the brain. For studying the molecular mechanisms and the biologic role of the GHB high-affinity binding sites, ligands with high and specific affinity are essential. The conformationally restricted GHB analog HOCPCA (3-hydroxycyclopent-1-enecarboxylic acid) is one such compound. The objective of this study was to investigate the transport of HOCPCA across the blood-brain barrier in vitro and in vivo and to investigate the hypothesis that HOCPCA, like GHB, is a substrate for the monocarboxylate transporters (MCTs). For in vitro uptake studies, MCT1, -2, and -4 were recombinantly expressed in Xenopus laevis oocytes, and the previously reported radioligand [(3)H]HOCPCA was used as substrate. HOCPCA inhibited the uptake of the endogenous MCT substrate l-[(14)C]lactate, and [(3)H]HOCPCA was shown to act as substrate for MCT1 and 2 (Km values in the low- to mid-millimolar range). Introducing single-point amino acid mutations into positions essential for MCT function supported that HOCPCA binds to the endogenous substrate pocket of MCTs. MCT1-mediated brain entry of HOCPCA (10 mg/kg s.c.) was further confirmed in vivo in mice by coadministration of increasing doses of the MCT inhibitor AR-C141990 [(R)-5-(3-hydroxypyrrolidine-1-carbonyl)-1-isobutyl-3-methyl-6-(quinolin-4-ylmethyl)thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione], which inhibited brain penetration of HOCPCA in a dose-dependent manner (ID50 = 4.6 mg/kg). Overall, our study provides evidence that MCT1 is an important brain entry site for HOCPCA and qualifies for future in vivo studies with HOCPCA.

• Authors: Louise Thiesen, Jan Kehler, Rasmus P Clausen, Bente Frølund, Christoffer Bundgaard, Petrine Wellendorph
• Journal: The Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 354 Issue 2 Pg. 166-74 (Aug 2015) ISSN: 1521-0103 [Electronic] United States
• PMID: 25986445 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.

Chemical References

• 3-hydroxycyclopent-1-enecarboxylic acid
• Carboxylic Acids
• Cyclopentanes
• Monocarboxylic Acid Transporters
• Symporters
• monocarboxylate transport protein 1
• Sodium Oxybate

Topics

• Animals
• Blood-Brain Barrier (metabolism)
• Brain (metabolism)
• Carboxylic Acids (chemistry, metabolism)
• Cyclopentanes (chemistry, metabolism)
• Dogs
• Humans
• Madin Darby Canine Kidney Cells
• Male
• Mice
• Monocarboxylic Acid Transporters (metabolism)
• Rats
• Sodium Oxybate (analogs & derivatives, metabolism)
• Symporters (metabolism)
• Xenopus laevis