Oral administration of D-alanine in monkeys robustly increases plasma and cerebrospinal fluid levels but experimental D-amino acid oxidase inhibitors had minimal effect

Camilo Rojas, Jesse Alt, Nancy A Ator, Heather Wilmoth, Rana Rais, Niyada Hin, Michael Devivo, Michael Popiolek, Takashi Tsukamoto, Barbara Slusher

Research output: Contribution to journalArticlepeer-review

Abstract

Hypofunction of the N-methyl-d-aspartate (NMDA) receptor is thought to exacerbate psychosis in patients diagnosed with schizophrenia. Consistent with this hypothesis, D-alanine, a co-agonist at the glycine site of the NMDA receptor, was shown to improve positive and cognitive symptoms when used as add-on therapy for schizophrenia treatment. However, D-alanine had to be administered at high doses (∼7 g) to observe clinical effects. One possible reason for the high dose is that D-alanine could be undergoing oxidation by D-amino acid oxidase (DAAO) before it reaches the brain. If this is the case, the dose could be reduced by co-administration of D-alanine with a DAAO inhibitor (DAAOi). Early studies with rodents showed that co-administration of D-alanine with 5-chloro-benzo[d]isoxazol-3-ol (CBIO), a prototype DAAOi, significantly enhanced the levels of extracellular D-alanine in the frontal cortex compared with D-alanine alone. Further, the use of CBIO reduced the dose of D-alanine needed to attenuate prepulse inhibition deficits induced by dizocilpine. The objective of the work reported herein was to confirm the hypothesis that DAAO inhibition can enhance D-alanine exposure in a species closer to humans: non-human primates. We report that while oral D-alanine administration to baboons (10 mg/kg) enhanced D-alanine plasma and CSF levels over 20-fold versus endogenous levels, addition of experimental DAAOi to the regimen exhibited a 2.2-fold enhancement in plasma and no measurable effect on CSF levels. The results provide caution regarding the utility of DAAO inhibition to increase D-amino acid levels as treatment for patients with schizophrenia.

Original languageEnglish (US)
Pages (from-to)887-895
Number of pages9
JournalJournal of Psychopharmacology
Volume30
Issue number9
DOIs
StatePublished - Sep 1 2016

Keywords

  • D-amino acid oxidase inhibition
  • NMDA receptor
  • Schizophrenia

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health
  • Pharmacology (medical)

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