''N''-Arachidonylglycine (NAGly) is a

carboxylic In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

of the

endocannabinoid Cannabinoids () are several structural classes of compounds found in the cannabis plant primarily and most animal organisms (although insects lack such receptors) or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tet ...

anandamide Anandamide (ANA), also known as ''N''-arachidonoylethanolamine (AEA), is a fatty acid neurotransmitter. Anandamide was the first endocannabinoid to be discovered: it participates in the body's endocannabinoid system by binding to cannabinoid rec ...

(AEA). Since it was first synthesized in 1996, NAGly has been a primary focus of the relatively contemporary field of

lipidomics Lipidomics is the large-scale study of pathways and networks of cellular lipids in biological systems The word "lipidome" is used to describe the complete lipid profile within a cell, tissue, organism, or ecosystem and is a subset of the "metabolo ...

due to its wide range of signaling targets in the brain, the immune system and throughout various other bodily systems. In combination with 2‐arachidonoyl glycerol (2‐AG), NAGly has enabled the identification of a family of

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

often referred to as

endocannabinoids Cannabinoids () are several structural classes of compounds found in the cannabis plant primarily and most animal organisms (although insects lack such receptors) or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tet ...

. Recently, NAGly has been found to bind to G-protein coupled receptor 18 (GPR18), the putative

abnormal cannabidiol Abnormal cannabidiol (Abn-CBD) is a synthetic regioisomer of cannabidiol, which unlike most other cannabinoids produces vasodilator effects, lowers blood pressure, and induces cell migration, cell proliferation and mitogen-activated protein kinase ...

receptor. NaGly is an endogenous inhibitor of

fatty acid amide hydrolase Fatty acid amide hydrolase or FAAH (, oleamide hydrolase, anandamide amidohydrolase) is a member of the serine hydrolase family of enzymes. It was first shown to break down anandamide in 1993. In humans, it is encoded by the gene ''FAAH''.; Fun ...

(FAAH) and thereby increases the

ethanolamide Ethanolamides are chemical compounds which are amides formed from carboxylic acids and ethanolamine. Some ethanolamides are naturally occurring, such as anandamide, palmitoylethanolamide and prostamides, which play physiological roles as lipid neur ...

endocannabinoids AEA,

oleoylethanolamide Oleoylethanolamide (OEA) is an endogenous peroxisome proliferator-activated receptor alpha ( PPAR-α) agonist. It is a naturally occurring ethanolamide lipid that regulates feeding and body weight in vertebrates ranging from mice to pythons. O ...

(OEA) and

palmitoylethanolamide Palmitoylethanolamide (PEA) is an endogenous fatty acid amide, and lipid modulator PEA has been studied in ''in vitro'' and ''in vivo'' systems using exogenously added or dosed compound; there is evidence that it binds to a nuclear receptor, thr ...

(PEA) levels. NaGly is found throughout the body and research on its explicit functions is ongoing.

Biosynthesis and degradation

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

. 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.

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. 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. 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. Similar mechanical allydonia induced by partial ligation of the

sciatic nerve The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals which is the largest branch of the sacral plexus and runs alongside the hip joint and down the lower limb. It is the longest and widest si ...

was also reduced by NaGly. 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. NaGly was shown to be endogenous ligand for the G-protein couple receptor GPR92 along with

farnesyl pyrophosphate Farnesyl pyrophosphate (FPP), also known as farnesyl diphosphate (FDP), is an intermediate in the biosynthesis of terpenes and terpenoids such as sterols and carotenoids. It is also used in the synthesis of CoQ (part of the electron transport cha ...

. In the

dorsal root ganglia A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the do ...

(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.

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 Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...

and

IFNγ Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock ...

production, and it shows potential as a therapeutic treatment for chronic inflammation. Moreover, NAGly has been shown to act as a substrate for

cyclooxygenase-2 Prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase) (The HUGO official symbol is PTGS2; HGNC ID, HGNC:9605), also known as cyclooxygenase-2 or COX-2, is an enzyme that in humans is encoded by the ''PTGS2'' gene. ...

(COX-2), the enzyme primarily known for producing

prostaglandins The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derive ...

associated with increases in inflammation and

hyperalgesia Hyperalgesia ( or ; 'hyper' from Greek ὑπέρ (huper, “over”), '-algesia' from Greek algos, ἄλγος (pain)) is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can ...

. 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.

Cell migration

NAGly has been hypothesized to induce cell migration in BV-2

microglia Microglia are a type of neuroglia (glial cell) located throughout the brain and spinal cord. Microglia account for about 7% of cells found within the brain. As the resident macrophage cells, they act as the first and main form of active immune de ...

cells. The same research suggests that this migration occurs through

GPR18 ''N''-Arachidonyl glycine receptor (NAGly receptor), also known as G protein-coupled receptor 18 (GPR18), is a protein that in humans is encoded by the ''GPR18'' gene. Along with the other previously "orphan" receptors GPR55 and GPR119, GPR18 has ...

. This was verified using GPR18 transfected HEK-293 cells. The same migration wasn't witnessed using non-transfected and

GPR55 G protein-coupled receptor 55 also known as GPR55 is a G protein-coupled receptor that in humans is encoded by the ''GPR55'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian unit ...

transfected HEK-293. Additionally,

tetrahydrocannabinol Tetrahydrocannabinol (THC) is the principal psychoactive constituent of cannabis and one of at least 113 total cannabinoids identified on the plant. Although the chemical formula for THC (C21H30O2) describes multiple isomers, the term ''THC'' ...

and NaGly are full

agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...

s at the GPR18 receptors and induce migration in human

endometrial The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional layer ...

HEC-1B cells. Understanding functions of NaGly in such structures provides a promising future in helping treat diseases such as

endometriosis Endometriosis is a disease of the female reproductive system in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus, grow outside the uterus. Most often this is on the ovaries, f ...

Cellular respiration

NAGly powerfully stimulates oxygen consumption in multiple cell lines, including murine C2C12 myoblasts and human HEK293T cells. This respiratory bioactivity of NAGly is by increased uncoupled (state4u) mitochondrial respiration and depends on the presence of fatty acid desaturation. NAGly respiration bioactivity can be also abrogated in the presence of serum albumin, which functions as an NAGly carrier in murine blood plasma.

Other targets

Insulin secretion

NaGly was identified as a novel

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...

secretagogue A secretagogue is a substance that causes another substance to be secreted. The word comes from Greek ''agōgos'', meaning "a leader" or "bringer"; thus "something that brings secretions". The same root is seen in completely unrelated words such as ...

and was shown to increase intracellular calcium concentration through stimulation of voltage dependent calcium channels. Additionally, this action was dependent on extracellular glucose level.

Additional biochemical interactions

NaGly has been shown to inhibit the

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogeni ...

transporter GLYT2a in a non-competitive fashion with

arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''arachi ...

s and secondary messenger systems of GLYT2a, suggesting a novel recognition site for the N-arachodnoyl amino acids, especially because other conjugated amino acids had similar effects.

References

{{DEFAULTSORT:Arachidonylglycine, N- Endocannabinoids Fatty acid amides Glycine reuptake inhibitors Arachidonyl compounds Substances discovered in the 1990s