The biosynthesis and degradation of NaGly is not completely understood. Using biochemical approaches, two proposed pathways include: 1) enzymatic conjugation of arachidonic acid and glycine and 2) the oxidative metabolism of the endogenous cannabinoid
anandamide.[8][9] In support of the former "direct" pathway of arachidonic acid and glycine conjugation and hydrolysis, the secreted enzyme
PM20D1 and the intracellular amidase
FAAH has been identified as enzymatic regulators of NAGly metabolism in mice.[10][11]
Research
Effects on the nervous system
NAGly has been hypothesized to have a neurophysiological function of pain suppression, supported by evidence that it suppresses formalin-induced pain behavior in rats.[12] In particular, peripherally administered NAGly inhibited phase 2 pain behavior, suggesting either a direct suppression of nociceptive afferents on the nerve or an indirect modulation of the afferents' interstitial environment.[12] In either case, these findings hold promise for NAGly as a means of mitigating postoperative or chronic pain. NAGly is also effective in acute pain models, reducing mechanical allodynia and thermal hyperalgesia induced by intraplantar injection of
Fruend's complete adjuvant.[13] Similar mechanical allydonia induced by partial ligation of the
sciatic nerve was also reduced by NaGly.[14] Other arachidonic acid-amino acid conjugates did not have the same effects and the actions of NaGly were not affected by cannabinoid receptor agonists in either study, suggesting a novel non-cannabinoid receptor mediated approach to alleviate inflammatory pain.[13][14]
NaGly was shown to be endogenous ligand for the G-protein couple receptor GPR92 along with
farnesyl pyrophosphate.[15] In the
dorsal root ganglia (DRG), where GPR92 was found to be localized NaGly increased intracellular calcium levels in DRG neurons, indicating a role of NaGly in the sensory nervous system through the activation of GPR92.[15]
Effects on the immune system
NAGly has been the focus of research on the immune system because of its antinociceptive effects and inhibitory action on components of the immune system. Specifically, it significantly inhibited
TNFα and
IFNγ production, and it shows potential as a therapeutic treatment for chronic inflammation.[16] Moreover, NAGly has been shown to act as a substrate for
cyclooxygenase-2 (COX-2), the enzyme primarily known for producing
prostaglandins associated with increases in inflammation and
hyperalgesia. In many mammalian tissues that express COX-2, significant levels of NAGly are naturally present, and in these tissues COX-2 selectively metabolizes NAGly prostaglandin (PG) H2 glycine and HETE-Gly.[17]
Cell migration
NAGly has been hypothesized to induce cell migration in BV-2
microglia cells.[5] The same research suggests that this migration occurs through
GPR18. This was verified using GPR18 transfected
HEK-293 cells. The same migration wasn't witnessed using non-transfected and
GPR55 transfected
HEK-293.[5] Additionally,
tetrahydrocannabinol and NaGly are full
agonists at the GPR18 receptors and induce migration in human
endometrial HEC-1B cells.[18] Understanding functions of NaGly in such structures provides a promising future in helping treat diseases such as
endometriosis.
Cellular respiration
NAGly powerfully stimulates oxygen consumption in multiple cell lines, including murine C2C12 myoblasts and human HEK293T cells.[19] This respiratory bioactivity of NAGly is by increased uncoupled (state4u) mitochondrial respiration and depends on the presence of fatty acid desaturation.[20] NAGly respiration bioactivity can be also abrogated in the presence of serum albumin, which functions as an NAGly carrier in murine blood plasma.[21]
Other targets
Insulin secretion
NaGly was identified as a novel
insulinsecretagogue and was shown to increase intracellular calcium concentration through stimulation of voltage dependent calcium channels.[22] Additionally, this action was dependent on extracellular glucose level.[22]
Additional biochemical interactions
NaGly has been shown to inhibit the
glycine transporter GLYT2a in a non-competitive fashion with
arachidonic acid and secondary messenger systems of GLYT2a, suggesting a novel recognition site for the N-arachidonyl amino acids, especially because other conjugated amino acids had similar effects.[23]
^Kohno M, Hasegawa H, Inoue A, Muraoka M, Miyazaki T, Oka K, Yasukawa M (September 2006). "Identification of N-arachidonylglycine as the endogenous ligand for orphan G-protein-coupled receptor GPR18". Biochemical and Biophysical Research Communications. 347 (3): 827–32.
doi:
10.1016/j.bbrc.2006.06.175.
PMID16844083.
^WO application 9738688, Ferrante A, Poulos A, Pitt M, Easton C, Sleigh M, Rathjen D, Widmer F, "Methods of Treating Immunopathologies Using Polyunsaturated Fatty Acids", published 23 October 1997, assigned to Peptide Technology Pty Ltd. and Women's and Children's Hospital Adelaide
^Prusakiewicz JJ, Kingsley PJ, Kozak KR, Marnett LJ (August 2002). "Selective oxygenation of N-arachidonylglycine by cyclooxygenase-2". Biochemical and Biophysical Research Communications. 296 (3): 612–7.
doi:
10.1016/s0006-291x(02)00915-4.
PMID12176025.