Synaptamide, an ethanolamide metabolite of DHA (22:6n-3), is a specific GPR110 ligand which triggers cAMP-dependent signal transduction leading to potent induction of neurogenesis, neuritogenesis and synaptogenesis in developing neurons. Chemical analogues of synaptamide reveal strong binding of the G-protein coupled receptor 110 (GPR110, ADGRF1) to nM levels of synaptamide which triggers cAMP production. GPR110 selectively acted with synaptamide, in contrast to ethanolamides of 20:4n-6, 20:5n-3, 20:5n-6 and 18:1n-9. Disruption of binding (or GPR110 gene knockout) abolishes synaptamide-induced bioactivity, whereas GPR110 overexpression enhances it. Expression of GPR110 is high in fetal brains, and it rapidly decreases after birth. GPR110 knockout mice show significant deficits in object recognition and spatial memory. GPR110 is a functional synaptamide receptor and a novel target for control of neurodevelopment. Lee JW, Huang BX, Kwon H, Rashid MA, Kharebava G, Desai A, Patnaik S, Marugan J, Kim HY. Orphan GPR110 (ADGRF1) targeted by N-docosahexaenoylethanolamide in development of neurons and cognitive function. Nat Commun. 2016 Oct 19;7:13123. doi: 10.1038/ncomms13123.
Synaptamide increased intracellular cAMP levels, phosphorylation of PKA, and phosphorylation of CREB, and suppressed LPS-induced nuclear translocation of NF-κB p65 and production of TNF-α and NO in cultured microglia cells. Conversely, inhibitors of adenylyl cyclase or PKA abolished the effect of synaptamide on p65 translocation as well as TNF-α and iNOS expression. Administration of synaptamide significantly reduced neuroinflammatory responses to intra-peritoneal LPS, such as microglia activation and mRNA expression of inflammatory cytokines, chemokine, and iNOS in the brain. Park T, Chen H, Kevala K, Lee JW, Kim HY. Docosahexaenoylethanolamine ameliorates LPS-induced neuroinflammation via cAMP/PKA-dependent signaling. J Neuroinflammation. 2016 Nov 4;13(1):284.
Synaptamide increased the average axon length in cultured cortical neurons, inhibited GLI family zinc finger 1 (GLI1) transcription and sonic hedgehog (Shh) gene expression while inducing cAMP elevation. Conversely, Shh antagonized elevation of cAMP and blocked synaptamide-mediated increase in axon length. Adenylate cyclase inhibitor SQ22536 abolished synaptamide-mediated axon growth indicating a requirement of cAMP elevation for this process. Kharebava G, Rashid MA, Lee JW, Sarkar S, Kevala K, Kim HY. N-docosahexaenoylethanolamide regulates Hedgehog signaling and promotes growth of cortical axons. Biol Open. 2015 Nov 6;4(12):1660-70. doi: 10.1242/bio.013425.
N-docosahexaenoylethanolamide (synaptamide), a DHA metabolite, promotes neurite growth, synaptogenesis, and synaptic function. Synaptamide potently induces differentiation of neuronal stem cells (NSCs). Treatment of NSCs with synaptamide at low nM concentrations significantly increased the number of MAP2 and Tuj-1-positive neurons with concomitant induction of protein kinase A (PKA)/cAMP response element binding protein (CREB) phosphorylation. Conversely, PKA inhibitors or PKA knockdown abolished synaptamide-induced neuronal differentiation of NSCs. URB597, a fatty acid amide hydrolase (FAAH) inhibitor, elevated the level of DHA-derived synaptamide and further potentiated the DHA- or synaptamide-induced neuronal differentiation of NSCs. Similarly, NSCs obtained from FAAH-KO mice exhibited greater capacity to induce neuronal differentiation in response to DHA or synaptamide compared to the wild type NSCs. Neither synaptamide nor DHA affected NSC differentiation into glial cells. These results suggest that endogenously produced synaptamide is a potent mediator for neurogenic differentiation of NSCs acting through PKA/CREB activation. Rashid MA, Katakura M, Kharebava G, Kevala K, Kim HY. N-Docosahexaenoylethanolamide is a potent neurogenic factor for neural stem cell differentiation. J Neurochem. 2013 Jun;125(6):869-84. doi: 10.1111/jnc.12255.
Docosahexanoic acid (22:6n-3; DHA) uniquely promotes neurite growth in hippocampal neurons. Inadequate neurite development due to DHA deficiency may contribute to the cognitive impairment associated with n-3 fatty acid deficiency. Calderon F, Kim HY. Docosahexaenoic acid promotes neurite growth in hippocampal neurons. J Neurochem. 2004 Aug;90(4):979-88
DHA aids phosphatidyl serine formation and action in brain.
Depriving pregnant mice of n-3 nutrients decreased DHA in the brain of their offspring by >50%. Continued feeding the deficient diet to the offspring gave significantly worse learning and memory at 6 mo than in groups fed an adequate diet. Changing mice to the adequate diet at 3 wk, 2 mo, or 4 mo of age restored brain DHA to the age-matched adequate concentration. However, deficits in hippocampal synaptic protein expression and spatial learning and memory were normalized only when the diet was changed at 3 wk. Deprivation of brain DHA during development of mice may have a lasting impact on cognitive function if not corrected at an early age. Lozada LE, Desai A, Kevala K, Lee JW, Kim HY. Perinatal Brain Docosahexaenoic Acid Concentration Has a Lasting Impact on Cognition in Mice. J Nutr. 2017 Sep;147(9):1624-1630. doi: 10.3945/jn.117.254607.
Phosphatidylserine (PS), the major anionic phospholipid in eukaryotic cell membranes, is synthesized by the integral membrane enzymes PS synthase 1 (PSS1) and 2 (PSS2). PSS2 is highly expressed in specific tissues, such as brain and testis, where docosahexaenoic acid (DHA, 22:6n-3) is also highly enriched. Flag-tagged PSS2 was expressed in HEK cells and immunopurified in a functionally active form. Purified PSS2 utilized both PE plasmalogen and diacyl PE as substrates. The latter was six times better utilized, indicating the importance of an ester linkage at the sn-1 position. Although no sn-1 fatty acyl preference was noted, PSS2 exhibited significant preference toward DHA compared with 18:1 or 20:4 at the sn-2 position. PSS2 may play a key role in PS accumulation in brain and testis through high activity toward DHA-containing substrates that are abundant in these tissues. Kimura AK, Kim HY. Phosphatidylserine synthase 2: high efficiency for synthesizing phosphatidylserine containing docosahexaenoic acid. J Lipid Res. 2013 Jan;54(1):214-22. doi: 10.1194/jlr.M031989.
Docosahexaenoic acid (DHA; 22:6n-3), promotes neuronal survival by facilitating membrane translocation/activation of Akt through its ability to increase phosphatidylserine (PS), the major acidic phospholipid in cell membranes. Docosapentaenoic acid (DPA; 22:5n-6), which replaces DHA during n-3 fatty acid deficiency, was less effective in accumulating PS and translocating Akt and thus less effective in preventing apoptosis. Dietary depletion of n-3 fatty acids consistently decreased hippocampal PS and increased neuronal susceptibility to apoptosis in cultures. This process may contribute to neurological deficits associated with n-3 fatty acid deficiency. Akbar M, Calderon F, Wen Z, Kim HY. Docosahexaenoic acid: a positive modulator of Akt signaling in neuronal survival. Proc Natl Acad Sci U S A. 2005 Aug 2;102(31):10858-63.
Microsomes from the cerebral cortex synthesized PS from 18:0,22:6-PC most favorably among the PC substrates tested, followed by 18:0,22:5-PC, resulting in the PC substrate preference in the order of 18:0,22:6 > 18:0,22:5 > 18:0,20:4 = 18:0,18:1. Liver microsomes also preferred 18:0,22:6-PC, but the 18:0,22:5-PC species was converted to PS at the similar extent as 18:0,20:4- or 18:0,18:1-PC species. Both brain and liver microsomes showed a preference for 18:0 over 16:0 as the sn-1 fatty acid. The distinctive preference for 18:0,22:5-PS in brain microsomes may help maintain PS at a high level in the brain when 22:6n-3 is replaced by 22:5n-6 as in the case of n-3 fatty acid deficiency. Kim HY, Bigelow J, Kevala JH. Sub strate preference in phosphatidylserine biosynthesis for docosahexaenoic acid containing species. Biochemistry. 2004 Feb 3;43(4):1030-6.
Docosahexaenoic acid (22:6n-3, DHA) is essential for proper brain function. We show that staurosporine (ST) induces apoptosis in Neuro 2A cells, and DHA enrichment prior to the ST treatment significantly inhibits the apoptotic cell death. Enrichment with other fatty acids such as oleic and arachidonic acids did not exert such an effect. Phosphatidylinositol 3-kinase (PI3-K) inhibitors, wortmanin, and LY-294002 abolished the protective effect of DHA in ST-induced apoptosis. Concurrently, ST-treatment significantly decreased the phosphorylation status of Akt at Ser-473 and Thr-308 as well as Akt activity, and this reduction was partially prevented by DHA enrichment. DHA enrichment uniquely protects ST-induced apoptosis in a PS- and PI3-K-dependent manner. The anti-apoptotic effect of DHA is mediated at least in part through the PI3-K/Akt pathway, facilitated by DHA-induced PS accumulation. Akbar M, Kim HY. Protective effects of docosahexaenoic acid in staurosporine-induced apoptosis: involvement of phosphatidylinositol-3 kinase pathway. J Neurochem. 2002 Aug;82(3):655-65.
Through effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Progress in recent nuclear magnetic resonance studies delineate differences in molecular structure and order in biomembranes due to small differences in phospholipid unsaturation. Salem N Jr, Litman B, Kim HY, Gawrisch K. Mechanisms of action of docosahexaenoic acid in the nervous system. Lipids 2001 Sep;36(9):945-59
Enrichment of neuronal cells with 22:6n-3 increases the PS content and Raf-1 translocation, down-regulates caspase-3 activity, and prevents apoptotic cell death. Hindering PS accumulation by a serine-free medium diminished the protective effect of 22:6n-3. Both the antiapoptotic effect of 22:6n-3 and Raf-1 translocation are sensitive to 22:6n-3 enrichment-induced PS accumulation in neuronal membranes. Kim HY, Akbar M, Lau A, Edsall L. Inhibition of neuronal apoptosis by docosahexaenoic acid (22:6n-3). Role of phosphatidylserine in antiapoptotic effect. J Biol Chem 2000 Nov 10;275(45):35215-23.
Neuronal membranes are highly enriched with docosahexaenoic acid (22:6n-3). Electrospray liquid chromatography-mass spectrometry analysis revealed that cells treated with 22:6n-3 had more PS compared to nonenriched or 20:4n-6-enriched cells. After cells were exposed to 20 or 50 mM ethanol for 4 wk, accumulation of 18:0,22:6-PS upon 22:6n-3 supplementation was significantly lower, resulting in a drastic reduction of total PS. Attenuated accumulation of 22:6n-3 in PS and the reduction of PS thus may have significant implications in pathophysiological effects of ethanol, especially in tissues with abundant 22:6n-3. Kim HY, Hamilton J. Accumulation of docosahexaenoic acid in phosphatidylserine is selectively inhibited by chronic ethanol exposure in C-6 glioma cells. Lipids 2000 Feb;35(2):187-95
Brain microsomes from offspring of rats reared on an n-3-deficient diet have low 22:6n-3 content (1.7 +/- 0.1%) compared with control animals (15.0 +/- 0.2%). The decrease was accompanied by an increase in docosapentaenoic acid (22:5n-6) content, which replaced the 22:6n-3 phospholipids with 22:5n-6 molecular species, as demonstrated using HPLC/electrospray mass spectrometry. The n-3 deficiency did not affect the total amount of polyunsaturated phospholipids in brain microsomes; however, it was associated with a decrease in the total polyunsaturated PS content and with increased levels of 1-stearoyl-2-docosapentanoyl (18:0/22:5n-6) species, particularly in phosphatidylcholine. Incorporation of [3H]serine into PS in rat brain microsomes from n-3-deficient animals was slightly but significantly less than that of the control animals. Similarly, C6 glioma cells cultured for 24 h in 22:6n-3-supplemented media (10-40 microM) showed a significant increase in the synthesis of [3H]PS when compared with unsupplemented cells. Neuronal and glial PS synthesis is sensitive to changes in the docosahexaenoate levels of phospholipids. Garcia MC, Ward G, Ma YC, Salem N Jr, Kim HY. Effect of docosahexaenoic acid on the synthesis of phosphatidylserine in rat brain in microsomes and C6 glioma cells. J Neurochem 1998 Jan;70(1):24-30.
Staurosporine (ST) induces apoptotic cell death of Neuro 2A cells, which is significantly inhibited by prior enrichment with DHA, but not oleic and arachidonic acids. Phosphatidylinositol 3-kinase (PI3-K) inhibitors, wortmanin, and LY-294002 abolished the protective effect of DHA. The extent of the antiapoptotic effect of DHA is mediated at least in part through the PI3-K/Akt pathway, facilitated by DHA-induced PS accumulation. Akbar M, Kim HY. Protective effects of docosahexaenoic acid in staurosporine-induced apoptosis: involvement of phosphatidylinositol-3 kinase pathway. J Neurochem 2002 Aug; 82(3): 655-65
DHA enrichment increased PS in cultured neuronal cells and protected against apoptotic cell death (cell suicide) in a subsequent absence of growth factors. Kim HY, Akbar M, Lau A, Edsall L. Inhibition of neuronal apoptosis by docosahexaenoic acid (22:6n-3): Role of phosphatidylserine in antiapoptotic effect. J Biol Chem 2000; M004446200
Docosahexaenoic acid (22:6n-3) is the major polyunsaturated fatty acid (PUFA) in the CNS and it accumulates particularly in phosphatidylserine (PS). Brain microsomes from offspring of rats artificially reared on an n-3-deficient diet had much lower 22:6n-3 content (1.7 +/- 0.1%) compared with control animals (15.0 +/- 0.2%). The decrease was accompanied by an increase in docosapentaenoic acid (22:5n-6) content, which replaced the 22:6n-3 phospholipids with 22:5n-6 molecular species, as demonstrated using HPLC/electrospray mass spectrometry. The total polyunsaturated phospholipids in brain microsomes was unchanged however, as a decrease in total PS accompanied increased 1-stearoyl-2-docosapentanoyl (18:0/22:5n-6) species of phosphatidylcholine. Garcia MC, Ward G, Ma YC, Salem N Jr, Kim HY. Effect of docosahexaenoic acid on the synthesis of phosphatidylserine in rat brain in microsomes and C6 glioma cells. J Neurochem 1998 Jan;70(1):24-30.
Reversed phase HPLC-electrospray ionization mass spectrometry showed that depleting n-3 fatty acids from the diet gave 70-80% reduction of 22:6n-3 molecular species in phosphatidylcholine (PC), phosphatidylethanolamine (PE), PE-plasmalogens (PLE), and phosphatidylserine (PS). In general, 22:6n-3 was replaced with 22:5n-6 but the replacement at the molecular species level did not always occur in a reciprocal manner, especially in PC and PLE. While the total PL content was not affected by n-3 deficiency, the relative distribution of PS decreased by 28% with a concomitant increase in PC. Murthy M, Hamilton J, Greiner RS, Moriguchi T, Salem N Jr, Kim HY. Differential effects of n-3 fatty acid deficiency on phospholipid molecular species composition in the rat hippocampus. J Lipid Res 2002 Apr;43(4):611-7
Phospholipid molecular species analysis revealed that in brain cortex, mitochondria, and olfactory bulb 18:0,22:6n-3 was the most abundant species representing 45-65% of total PS. In nonneuronal tissues such as liver and adrenal, 18:0,20:4n-6 was the major PS species. Dietary depletion of n-3 fatty acids during prenatal and postnatal developmental periods decreased the brain 22:6n-3 content by more than 80%, with an approximately 30-35% reduction in total PS in rat brain cortex, brain mitochondria, and olfactory bulb. PS levels in liver and adrenal were unchanged. The observed reduction of PS content in neuronal membranes appears to be due to a dramatic reduction of 18:0,22:6n-3-PS without complete replacement by 18:0,22:5n-6-PS. Hamilton L, Greiner R, Salem N Jr, Kim HY. n-3 fatty acid deficiency decreases phosphatidylserine accumulation selectively in neuronal tissues. Lipids 2000 Aug;35(8):863-9
Brain microsomes from offspring of rats artificially reared on an n-3 deficient diet had much lower 22:6n-3 content (1.7 +/ 0.1%) compared with control animals (15.0 +/ 0.2%). The decrease was accompanied by an increase in docosapentaenoic acid (22:5n-6) content, which replaced the 22:6n-3 phospholipids with 22:5n-6 molecular species, as demonstrated using HPLC/electrospray mass spectrometry. The n-3 deficiency was associated with a decrease in the total polyunsaturated PS content and with increased levels of 1 stearoyl 2 docosapentanoyl (18:0/22:5n-6) species, particularly in phosphatidylcholine. Incorporation of 3H-serine into PS in rat brain microsomes from n-3 deficient animals was slightly but significantly less than that of the control animals. Neuronal and glial PS synthesis is sensitive to changes in the docosahexaenoate levels of phospholipids, and 22:6n-3 may modulate PS synthesis. Garcia MC; Ward G; Ma YC; Salem N; Kim HY. Effect of docosahexaenoic acid on the synthesis of phosphatidylserine in rat brain microsomes and C6 glioma cells. J Neurochem 1998; 70: 24-30.
updated October, 2017