Enantioselective inhibition of d-serine transport by (S)-ketamine

Nagendra S Singh; Michel Bernier; Simonetta Camandola; Mohammed A Khadeer; Ruin Moaddel; Mark P Mattson; Irving W Wainer

doi:10.1111/bph.13239

Enantioselective inhibition of d-serine transport by (S)-ketamine

Br J Pharmacol. 2015 Sep;172(18):4546-4559. doi: 10.1111/bph.13239. Epub 2015 Jul 31.

Authors

Nagendra S Singh¹, Michel Bernier², Simonetta Camandola³, Mohammed A Khadeer¹, Ruin Moaddel¹, Mark P Mattson³, Irving W Wainer¹

Affiliations

¹ Laboratory of Clinical Investigation, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, MD, USA.
² Translational Gerontology Branch, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, MD, USA.
³ Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, MD, USA.

Abstract

Background and purpose: Patients with major depressive disorder receiving racemic ketamine, (R,S)-ketamine, experience transient increases in Clinician-Administered Dissociative States Scale scores and a coincident drop in plasma d-serine levels. The results suggest that (R,S)-ketamine produces an immediate, concentration-dependent pharmacological effect on d-serine plasma concentrations. One potential source of this effect is (R,S)-ketamine-induced inhibition of the transporter ASCT2, which regulates intracellular d-serine concentrations. In this study, we tested this hypothesis by examining the effect of (S)- and (R)-ketamine on ASCT2-mediated transport of d-serine in PC-12 and 1321N1 cells and primary neuronal cells in culture.

Experimental approach: Intracellular and extracellular d-serine levels were determined using capillary electrophoresis-laser-induced fluorescence and liquid chromatography-mass spectrometry respectively. Expression of ASCT2, Asc-1 and serine racemase was determined utilizing Western blotting.

Key results: (S)-Ketamine produced a concentration-dependent increase in intracellular d-serine and reduced extracellular d-serine accumulation. In contrast, (R)-ketamine decreased both intracellular and extracellular d-serine levels. The ASCT2 inhibitor, benzyl-d-serine (BDS), and ASCT2 gene knockdown mimicked the action of (S)-ketamine on d-serine in PC-12 cells, while the Asc-1 agonist d-isoleucine reduced intracellular d-serine and increased extracellular d-serine accumulation. This response to d-isoleucine was not affected by BDS or (S)-ketamine. Primary cultures of rat neuronal cells expressed ASCT2 and were responsive to (S)-ketamine and BDS. (S)- and (R)-ketamine increased the expression of monomeric serine racemase in all the cells studied, with (S)-ketamine having the greatest effect.

Conclusions and implications: (S)-Ketamine decreased cellular export of d-serine via selective inhibition of ASCT2, and this could represent a possible source of dissociative effects observed with (R,S)-ketamine.

Published 2015. This article is a U.S. Government work and is in the public domain in the USA.