A microdialysis study of glycinamide, glycine and other amino acid neurotransmitters in rat frontal cortex and hippocampus after the administration of milacemide, a glycine pro-drug

Increasing the antinociceptive effect of ingested glycinamide in female rats by increasing its palatability

BACKGROUND

These studies were undertaken to investigate whether the ingestion of glycinamide, a precursor of glycine, made more palatable by mixing with a chocolate suspension, improves antinociception in rats.

METHODS

Two nociception threshold models were employed: the tail-flick latency and vocalization to tail shock, in restricted and freely-moving rats. Glycinamide in a highly palatable commercial chocolate aqueous suspension was provided for ad-lib ingestion after 24 hours of water deprivation. Antinociception threshold testing was performed before and 10, 30, 60, 90, 120, 180, and 240 minutes after the ingestion of the chocolate-glycinamide mixture.

RESULTS

Ingestion of the glycinamide-in-chocolate suspension induced antinociception based on the tail shock vocalization and tail-flick latency tests. Ingestion of the glycinamide-in-chocolate suspension induced an 80% elevation in the antinociceptive threshold that persisted for 4 hours.

CONCLUSIONS

Rats readily ingest the glycine precursor, glycinamide, in an aqueous chocolate mixture, which induces potent and prolonged antinociception.

Amino Acids in the Development of Prodrugs

Although drugs currently used for the various types of diseases (e.g., antiparasitic, antiviral, antibacterial, etc.) are effective, they present several undesirable pharmacological and pharmaceutical properties. Most of the drugs have low bioavailability, lack of sensitivity, and do not target only the damaged cells, thus also affecting normal cells. Moreover, there is the risk of developing resistance against drugs upon chronic treatment. Consequently, their potential clinical applications might be limited and therefore, it is mandatory to find strategies that improve those properties of therapeutic agents. The development of prodrugs using amino acids as moieties has resulted in improvements in several properties, namely increased bioavailability, decreased toxicity of the parent drug, accurate delivery to target tissues or organs, and prevention of fast metabolism. Herein, we provide an overview of models currently in use of prodrug design with amino acids. Furthermore, we review the challenges related to the permeability of poorly absorbed drugs and transport and deliver on target organs.