Tier 3 — preclinical

Pharmacokinetics and cerebral distribution of glycine administered to rats

Kawai N, Bannai M, Seki S, Koizumi T, Shinkai K, Nagao K, Matsuzawa D, Takahashi M, Shimizu E
Amino acids 2012 42(6):2129-2137

Bibliography

PubMed
PMID 21647662
DOI
10.1007/s00726-011-0950-y
Funding
Funding was not specified in the indexed abstract; the full funding disclosure has not been verified.
Competing interests
The accessible abstract does not establish the authors' competing interests; absence of a statement is not evidence of no conflicts.

Study snapshot

DesignControlled animal intervention with mechanistic experiments
ModelRats; radiotracer and brain uptake studies
SampleRat pharmacokinetic and autoradiography experiments; sample varies by assay
InterventionRadiolabeled glycine; oral glycine including 2 g/kg and brain uptake experiments
DurationAcute time-course experiments
EndpointsPlasma and cerebrospinal fluid glycine; Brain distribution; Serine metabolism

What the study showed, in plain terms

This rat pharmacokinetic study shows that administered glycine reaches cerebrospinal fluid and brain tissue with different concentration and timing profiles. It helps explain why a rise in blood glycine does not directly specify brain exposure.

Key findings

  • CSF glycine concentrations were roughly one hundredth of plasma concentrations under the tested conditions.
  • Brain tissue concentrations rose more slowly than CSF concentrations.

What this study can and cannot tell us

Rat doses and blood-brain transport cannot define human supplement efficacy or a human dose.

Exposure is a pharmacokinetic finding, not proof of cognitive or sleep improvement.

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction