At the intersection of cell membrane architecture, intracellular signaling, and the human immune response stands arachidonic acid, an essential bioactive polyunsaturated fatty acid that dictates the initiation, propagation, and resolution of physiological inflammation. Embedded within phospholipid bilayers throughout virtually all mammalian tissues, this versatile molecule serves as both a structural stabilizer and the primary reservoir for enzymatic cascades that govern vascular tone, hemostasis, pain perception, and cellular defense. Understanding its multifaceted biochemistry provides fundamental insights into clinical pharmacology, ranging from the universal therapeutic mechanism of aspirin to cutting-edge interventions in neurodegenerative and cardiovascular diseases.
Arachidonic Acid
1. Concise Definition
Arachidonic acid (AA) is a twenty-carbon polyunsaturated omega-6 fatty acid possessing four cis-double bonds, formally designated as (5Z,8Z,11Z,14Z)-icosa-5,8,11,14-tetraenoic acid or 20:4 (n-6). It is predominantly esterified at the sn-2 position of membrane phospholipids, where it remains biologically latent until mobilized by specific lipolytic enzymes. Upon cleavage, free arachidonic acid acts as the foundational precursor for eicosanoids, a vast class of lipid mediators that regulate local autocrine and paracrine cellular functions.
Beyond its traditional role as a substrate for enzymatic oxygenation, arachidonic acid acts directly as an intracellular secondary messenger, influencing ion channel conductance, protein kinase activation, and membrane fluidity. It maintains homeostatic cellular equilibrium while simultaneously poised to trigger explosive inflammatory signaling cascades when cellular integrity is compromised by trauma, ischemia, or pathogen invasion.
2. Etymology & Linguistic Origin
The term arachidonic acid derives historically and chemically from arachidic acid (the saturated twenty-carbon fatty acid, icosanoic acid), which was first isolated from peanut oil and named after the peanut plant’s botanical genus, Arachis (stemming from the Ancient Greek ἄραχος, meaning a leguminous vetch-like plant). The suffix -idon- reflects early twentieth-century chemical nomenclature conventions denoting unsaturated polyene fatty acid derivatives of corresponding saturated carbon backbones, while -ic acid indicates its terminal carboxylic acid functional group (-COOH).
The systematic International Union of Pure and Applied Chemistry (IUPAC) designation is (5Z,8Z,11Z,14Z)-eicosa-5,8,11,14-tetraenoic acid. In lipidomic literature, shorthand nomenclatures such as 20:4 (n-6) or 20:4 (ω-6) denote the chain length of twenty carbon atoms, four unsaturations, and the position of the initial double bond six carbons from the methyl (omega) terminus.
3. Pronunciation & Grammatical Form
Arachidonic acid is pronounced phonetically in standard scientific English as /əˌrækɪˈdɒnɪk ˈæsɪd/ (American English: uh-RACK-ih-DAHN-ik ASS-id; British English: uh-RACK-ih-DON-ik ASS-id). Grammatically, it functions as an uncountable, non-attributive compound noun phrase.
Its chemical formula is written as C20H32O2, with a corresponding molecular weight of approximately 304.47 g/mol. In biochemical discourse, it is frequently initialized as AA or symbolized in membrane biology alongside associated fatty acyl groups as ARA.
4. Detailed Conceptual Explanation
In resting eukaryotic cells, unesterified arachidonic acid is kept at vanishingly low intracellular concentrations (frequently below 5 micromolar) to prevent untoward cellular toxicity, unregulated cell death, and continuous immune activation. The vast majority of cellular arachidonic acid resides esterified within glycerophospholipids—predominantly phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI)—concentrated strategically at the inner leaflet of the plasma membrane and intracellular organelles such as the endoplasmic reticulum and nuclear envelope.
The mobilization of arachidonic acid represents the rate-limiting gatekeeper for eicosanoid biosynthesis. Upon physiological or pathological activation—such as ligand binding to G-protein-coupled receptors (GPCRs), pathogen-associated molecular pattern (PAMP) engagement, or shear stress—intracellular calcium levels surge. This induces the translocation of cytosolic phospholipase A2 (group IVA cPLA2) from the cytosol to perinuclear membranes, where it selectively hydrolyzes the sn-2 acyl bond, liberating free, unesterified arachidonic acid into the cytoplasm.
Once liberated, free arachidonic acid faces divergent metabolic fates driven by competitive enzymatic pathways:
- The Cyclooxygenase (COX) Pathway: Mediated by constitutive COX-1 and inducible COX-2 enzymes (prostaglandin-endoperoxide synthases), which add two molecules of molecular oxygen to form the unstable endoperoxide intermediates prostaglandin G2 (PGG2) and prostaglandin H2 (PGH2). Downstream terminal synthases subsequently convert PGH2 into prostaglandins (PGE2, PGD2, PGF2α), prostacyclin (PGI2), and thromboxane A2 (TxA2).
- The Lipoxygenase (LOX) Pathway: Driven by non-heme iron-containing enzymes (5-LOX, 12-LOX, and 15-LOX) that introduce molecular oxygen at distinct carbon positions, generating hydroperoxyeicosatetraenoic acids (HPETEs) that are reduced to hydroxyeicosatetraenoic acids (HETEs), leukotrienes (such as LTB4 and cysteinyl leukotrienes LTC4, LTD4, LTE4), and anti-inflammatory lipoxins.
- The Cytochrome P450 (CYP) Epoxygenase/ω-Hydroxylase Pathway: Catalyzed by microsomal CYP monooxygenases to synthesize epoxyeicosatrienoic acids (EETs) with potent vasodilatory properties, alongside 20-hydroxyeicosatetraenoic acid (20-HETE), which governs renal and systemic vascular tone.
- Non-Enzymatic Free Radical Peroxidation: Driven by reactive oxygen species (ROS) reacting directly with the bis-allylic methylene carbons of arachidonic acid to yield isoprostanes (e.g., 8-iso-PGF2α), serving as established gold-standard biomarkers of cellular oxidative stress.
- Endocannabinoid Biosynthesis: Arachidonic acid conjugates with ethanolamine or glycerol to yield major endocannabinoids, specifically N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), fundamental to retrograde neurotransmission and neuroprotection.
5. Historical Development
The biochemical identification of arachidonic acid began in 1909 when British physiologist Percival Hartley isolated a polyunsaturated fatty acid containing twenty carbons from the liver lipids of pigs, recognizing its distinct degree of unsaturation compared to known oleic and linoleic acids. During the 1930s and 1940s, researchers such as George Burr and Mildred Burr established the concept of essential fatty acids, documenting that dietary exclusions of polyunsaturated lipids induced fatal deficiency syndromes in murine models, which could be rescued by linoleic or arachidonic acid administration.
In the mid-1930s, Swedish physiologist Ulf von Euler and British-American scientist Maurice Goldblatt independently identified a potent smooth-muscle-contracting and vasodepressor lipid in human seminal plasma, which von Euler christened prostaglandin, believing it originated from the prostate gland. The definitive chemical bridge connecting arachidonic acid to prostaglandins was established in 1964 by Sune Bergström and Bengt Samuelsson at the Karolinska Institute, who proved that arachidonic acid was the obligate precursor substrate for enzymatic prostaglandin synthesis.
A watershed conceptual breakthrough occurred in 1971 when British pharmacologist John Vane demonstrated that ordinary aspirin (acetylsalicylic acid) and nonsteroidal anti-inflammatory drugs (NSAIDs) exert their therapeutic and toxicological effects by inhibiting the cyclooxygenase conversion of arachidonic acid into pro-inflammatory prostaglandins. This discovery earned Vane, Bergström, and Samuelsson the 1982 Nobel Prize in Physiology or Medicine. Subsequent decades witnessed the discovery of leukotrienes by Samuelsson in 1979, the delineation of inducible COX-2 in 1991, and Charles Serhan’s discovery of lipoxins and specialized pro-resolving mediators (SPMs) derived from arachidonic acid, establishing that this lipid orchestrates both the initiation and the programmed resolution of inflammation.
6. Theoretical Foundations
The biology of arachidonic acid is anchored within the modern Fluid Mosaic Model of cellular membranes and the paradigm of stimulus-response lipid remodeling. Biological membranes are not static barriers but dynamic signaling reservoirs. The incorporation of polyunsaturated fatty acids like arachidonic acid, with its four non-conjugated double bonds separated by methylene carbons, introduces structural kinks that disrupt tight hydrocarbon packing, thereby maintaining membrane fluidity, governing membrane curvature, and modulating the spatial organization of integral membrane receptors.
A second foundational theory is the Lands Cycle (the phospholipid deacylation-reacylation cycle proposed by William E.M. Lands). Rather than synthesizing membrane lipids de novo for signaling, cells continuously remodel phospholipid fatty acid composition. cPLA2 selectively cleaves arachidonic acid upon demand, while lysophospholipid acyltransferases (LPLATs) re-esterify free fatty acids back into the bilayer. This cyclic flux prevents sustained intracellular toxicity while maintaining a loaded, primed trigger for inflammatory signaling.
Finally, arachidonic acid operates within the framework of competitive substrate inhibition and lipid mediator class switching. Polyunsaturated omega-3 fatty acids, notably eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), directly compete with arachidonic acid for incorporation into the sn-2 phospholipid position and for binding sites within COX and LOX catalytic channels. Because omega-3-derived downstream mediators (such as 3-series prostaglandins and 5-series leukotrienes) typically exhibit markedly lower inflammatory potency than their 2-series and 4-series arachidonic acid counterparts, the stoichiometric ratio of arachidonic acid to omega-3 fatty acids establishes the baseline cellular threshold for acute and chronic inflammatory reactivity.
7. Key Components, Types & Dimensions
To analyze the architectural role and physiological signaling pathways driven by arachidonic acid, researchers categorize its functional dimensions into enzymatic cascades, non-enzymatic products, and lipid classes:
- Cyclooxygenase Prostanoid Spectrum:
- Prostaglandin E2 (PGE2): Potent mediator of hyperalgesia, pyrexia (fever induction via hypothalamic EP3 receptors), arterial vasodilation, and gastric mucosal cytoprotection.
- Prostacyclin (PGI2): Synthesized primarily by vascular endothelial cells; promotes potent systemic vasodilation and suppresses platelet aggregation via cyclic AMP elevation.
- Thromboxane A2 (TxA2): Produced predominantly by activated platelets via thromboxane synthase; acts as a physiological antagonist to PGI2 by inducing vasoconstriction and triggering platelet activation and thrombosis.
- Prostaglandin D2 (PGD2) & F2α (PGF2α): Mediators of bronchoconstriction, sleep architecture, smooth muscle contractility, and uterine contractions during labor.
- Lipoxygenase Leukotriene and Lipoxin Spectrum:
- Leukotriene B4 (LTB4): A potent chemotactic factor for neutrophils, directing leukocyte extravasation, degranulation, and superoxide generation.
- Cysteinyl Leukotrienes (LTC4, LTD4, LTE4): Formerly identified as the slow-reacting substance of anaphylaxis (SRS-A); potent bronchoconstrictors and promoters of microvascular hyperpermeability in bronchial asthma.
- Lipoxins (LXA4 and LXB4): Endogenous anti-inflammatory, pro-resolving lipid mediators generated via transcellular biosynthesis that halt neutrophil recruitment and stimulate non-phlogistic macrophage phagocytosis of apoptotic debris.
- Cytochrome P450 Metabolites:
- Epoxyeicosatrienoic Acids (5,6-, 8,9-, 11,12-, and 14,15-EET): Endothelial-derived hyperpolarizing factors (EDHFs) that promote vascular relaxation, stimulate angiogenesis, and protect cardiac tissues against ischemia-reperfusion injury.
- 20-Hydroxyeicosatetraenoic Acid (20-HETE): A vasoconstrictor lipid acting on renal vasculature that regulates natriuresis, microvascular tone, and systemic blood pressure homeostasis.
- Free Radical Peroxidation Products:
- F2-Isoprostanes: Prostaglandin-like compounds generated independently of cyclooxygenase enzymes via free-radical-catalyzed peroxidation of membrane-bound arachidonic acid.
8. Examples & Illustrative Cases
The dynamic engagement of arachidonic acid is evident across daily physiological events and classic pathological states:
Case 1: The Classic Acute Inflammatory Cascade in Tissue Trauma
When an individual sustains an acute mechanical injury, such as a lateral ankle sprain, blunt mechanical force compromises local endothelial and stromal cell membranes. Disrupted membrane integrity stimulates an immediate flux of extracellular calcium into the cytosol, activating cPLA2. Within seconds, membrane phospholipids release free arachidonic acid, which is rapidly captured by COX-2 and 5-LOX enzymes in infiltrating granulocytes and local mast cells. The immediate production of PGE2 and PGI2 induces local arteriolar vasodilation and sensitizes nociceptive C-fiber nerve terminals (erythema, heat, and throbbing pain), while LTB4 guides directed neutrophil diapedesis into the interstitial injury site (edema and cellular infiltration).
Case 2: Pharmacological Inhibition and Aspirin-Exacerbated Respiratory Disease (AERD)
In susceptible individuals with asthma and chronic rhinosinusitis with nasal polyps, the administration of standard nonselective COX inhibitors (such as aspirin or ibuprofen) produces severe bronchospasm rather than analgesia. This phenomenon, known as Samter’s Triad or AERD, occurs due to biochemical shunting of liberated arachidonic acid. When the cyclooxygenase pathway is blocked, excess substrate is forced into the parallel 5-lipoxygenase pathway. This uninhibited surge generates massive quantities of cysteinyl leukotrienes (LTC4, LTD4, LTE4), which bind CysLT1 receptors on bronchial smooth muscle, causing profound, potentially life-threatening bronchoconstriction and airway mucosal edema.
Case 3: Gastric Ulcerogenesis from Chronic NSAID Therapy
Constitutive COX-1 expression in gastric mucosal epithelial cells continuously processes endogenous arachidonic acid into baseline quantities of PGE2 and PGI2. These prostanoids tonically inhibit parietal cell gastric acid secretion, stimulate bicarbonate secretion, and maintain microvascular mucosal blood flow. When a patient takes chronic nonselective NSAIDs for osteoarthritis, systemic suppression of COX-1 starves the gastric lining of protective prostanoids, leading directly to mucosal ischemia, chemical ulceration, and severe upper gastrointestinal bleeding.
9. Measurement & Assessment
Assessing arachidonic acid status and its metabolic pathways requires distinguishing between structural fatty acid pools (membrane composition), unesterified circulating concentrations, and downstream oxygenated metabolites:
- Gas Chromatography-Flame Ionization Detection (GC-FID) and GC-Mass Spectrometry (GC-MS): Considered the gold standard for measuring total fatty acid profiles in plasma, red blood cell (RBC) membranes, and tissue biopsies. Lipids are extracted and converted to fatty acid methyl esters (FAMEs), providing an exact quantification of arachidonic acid as a percentage of total cellular fatty acids.
- Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS): High-throughput targeted lipidomics utilized to measure free, unesterified arachidonic acid and its complex downstream eicosanoid cascades simultaneously. LC-MS/MS offers picomolar sensitivity, resolving positional isomers such as specific HETEs, leukotrienes, and prostaglandins in plasma, urine, and cerebrospinal fluid.
- Urine and Plasma F2-Isoprostane Assays: Quantification of 15-F2t-isoprostane via LC-MS/MS or gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICI-MS) represents the internationally validated benchmark for determining systemic in vivo lipid peroxidation and endogenous oxidative stress.
- The Omega-3 Index and AA/EPA Ratio: A widely deployed clinical diagnostic tool measuring the ratio of arachidonic acid to eicosapentaenoic acid in red blood cell membranes. Elevated AA/EPA ratios (often exceeding 15:1 in modern populations) serve as a clinical surrogate biomarker for systemic, low-grade inflammatory states and cardiovascular risk stratification.
- Enzyme-Linked Immunosorbent Assays (ELISA): Commercially widespread immunoassays designed for clinical and research quantification of individual metabolites, including urinary 11-dehydro-thromboxane B2 (assessing in vivo platelet activation and aspirin resistance) and PGE2 metabolites.
10. Applications & Practical Significance
The manipulation of arachidonic acid metabolism represents one of the most widely utilized therapeutic strategies in human medicine, spanning multiple drug categories and clinical contexts:
Pharmacology and Therapeutics:
Nonsteroidal anti-inflammatory drugs (NSAIDs)—such as ibuprofen, naproxen, and indomethacin—act as competitive inhibitors of the COX catalytic channel, preventing arachidonic acid binding. Aspirin is unique in that it permanently and irreversibly acetylates a serine residue within the catalytic channel (Ser529 in COX-1, Ser516 in COX-2). In platelets, which lack nuclear DNA and cannot synthesize new proteins, this irreversible inhibition suppresses thromboxane A2 production for the entire 8- to 10-day lifespan of the platelet, establishing aspirin as a cornerstone antiplatelet therapy for secondary prevention of myocardial infarction and ischemic stroke.
Selective COX-2 inhibitors (coxibs, such as celecoxib) were engineered to spare gastroprotective COX-1 prostanoids while suppressing pro-inflammatory COX-2 mediators at sites of arthritis and injury. However, selective COX-2 inhibition depresses endothelial PGI2 synthesis without suppressing platelet-derived TxA2 synthesis, creating an unmitigated pro-thrombotic milieu that can increase myocardial infarction and thrombotic cardiovascular events.
Pulmonology and Asthma Management:
Targeting the lipoxygenase branch of arachidonic acid metabolism has yielded important pharmacological therapies. 5-LOX inhibitors (e.g., zileuton) suppress the upstream production of leukotrienes, while selective leukotriene receptor antagonists (LTRAs, such as montelukast and zafirlukast) competitively block the CysLT1 receptor, serving as established maintenance treatments for chronic asthma, allergic rhinitis, and exercise-induced bronchospasm.
Neurology and Cognitive Development:
Arachidonic acid comprises roughly 10% to 12% of the total fatty acid content of the mammalian brain, enriched alongside docosahexaenoic acid (DHA) within synaptic membrane phospholipids. Free arachidonic acid and its downstream endocannabinoid derivatives are indispensable for retrograde neurotransmission, long-term potentiation (LTP), and dendritic arborization. Consequently, international pediatric guidelines mandate the fortification of infant formulas with balanced arachidonic acid and DHA to support optimal neurocognitive development and visual acuity in term and preterm infants.
11. Research & Empirical Evidence
Substantial clinical and basic science research over the past several decades has shifted the scientific perception of arachidonic acid from that of a purely destructive pro-inflammatory molecule to a highly nuanced, tightly coordinated metabolic regulator:
A classic epidemiological debate concerns dietary arachidonic acid intake and systemic inflammatory biomarkers. Early mechanistic hypotheses assumed that higher dietary intake of linoleic acid (LA) or preformed arachidonic acid would directly accelerate systemic inflammation by driving prostanoid synthesis. However, rigorous human randomized controlled trials, summarized by Rett and Whelan (2011), demonstrated that increasing dietary linoleic acid up to sixfold does not significantly alter plasma or tissue arachidonic acid concentrations, nor does it elevate circulating inflammatory markers such as C-reactive protein (CRP), interleukin-6 (IL-6), or tumor necrosis factor-alpha (TNF-α).
Work by Charles Serhan and colleagues has illuminated the dual pro- and anti-inflammatory roles of arachidonic acid in inflammatory resolution. Arachidonic acid serves as the direct precursor to lipoxins (LXA4 and LXB4). During an acute inflammatory response, a programmed “lipid mediator class switch” occurs: early PGE2 and PGD2 signaling upregulates 15-lipoxygenase expression in leukocytes, diverting subsequent arachidonic acid metabolism from neutrophil-recruiting leukotrienes toward pro-resolving lipoxins, thereby actively terminating acute inflammation and preventing chronic tissue damage.
In cardiovascular biology, the prospective Framingham Offspring Study and large-scale meta-analyses led by researchers such as Dariush Mozaffarian have demonstrated that higher circulating biomarkers of omega-6 fatty acids, including arachidonic acid, are not correlated with increased risks of coronary artery disease. In some cohorts, higher circulating AA levels are inversely associated with primary ischemic stroke, challenging simplistic assumptions that dietary omega-6 polyunsaturated fatty acids are fundamentally atherogenic.
12. Cultural & Cross-Cultural Considerations
Human dietary intake of arachidonic acid varies widely across geographic regions, evolutionary lineages, and cultural food systems. Because preformed arachidonic acid is found almost exclusively in foods of animal origin—such as egg yolks, poultry, red meat, organ meats, and marine organisms—strict vegetarian and vegan populations consume virtually zero preformed dietary arachidonic acid. These populations depend entirely on endogenous biosynthesis from the plant-derived precursor linoleic acid (18:2 n-6) via sequential desaturation and elongation enzymes catalyzed by fatty acid desaturase 1 (FADS1), fatty acid desaturase 2 (FADS2), and elongase enzymes (ELOVL5).
Modern anthropological genomics has uncovered striking evolutionary adaptations within the human FADS gene cluster. Populations with long ancestral histories of plant-based agriculture—such as certain indigenous populations in South Asia and Africa—exhibit a high prevalence of genetic variants that upregulate FADS1 and FADS2 activity, enabling efficient conversion of dietary plant linoleic acid into arachidonic acid to maintain cognitive and immune functions. Conversely, traditional marine-dependent populations, such as the Greenland Inuit, who historically consumed massive amounts of preformed marine polyunsaturated fatty acids, harbor unique FADS variants that suppress endogenous desaturation, protecting them from excessive lipid accumulation.
Furthermore, the industrialization of the global food supply has dramatically skewed the dietary ratio of omega-6 to omega-3 fatty acids. While ancestral human diets are estimated to have possessed an omega-6 to omega-3 ratio of approximately 1:1 to 2:1, the modern Western diet—dominated by mass-produced refined seed oils (such as soybean, corn, and sunflower oils)—exhibits ratios ranging from 15:1 to 20:1. This imbalance saturates membrane incorporation sites with omega-6 precursors, establishing a biological environment primed for prolonged pro-inflammatory signaling when challenged by metabolic stress.
13. Criticisms, Debates & Limitations
The primary controversy surrounding arachidonic acid centers on the long-standing “Omega-6 Hypothesis” of chronic disease. For decades, nutritional and cardiovascular literature advanced the view that high omega-6 fatty acid consumption is inherently toxic and directly responsible for the modern epidemic of chronic non-communicable inflammatory diseases, including atherosclerosis, non-alcoholic fatty liver disease, and rheumatoid arthritis. Critics argue that evaluating fatty acids through such broad classifications ignores the complex local kinetics of eicosanoid metabolism. Unesterified arachidonic acid is tightly controlled and does not spill indiscriminately into pro-inflammatory pathways; rather, downstream synthases are regulated by distinct intracellular transcriptional programs and calcium dynamics.
A second major debate centers on the safety profiles of selective COX-2 inhibitors versus traditional nonselective NSAIDs. The high-profile market withdrawal of rofecoxib (Vioxx) in 2004 underscored the hazard of artificially uncoupling the balanced pathways of arachidonic acid metabolism. By suppressing endothelial prostacyclin (a potent vasodilator and platelet inhibitor) while leaving platelet thromboxane production unchecked, selective pharmacological intervention exposed thousands of patients to elevated risks of thrombotic events. This episode serves as a cautionary paradigm in pharmacology regarding the hazards of selective intervention within branched biochemical networks.
Finally, a critical limitation in current research is the frequent reliance on circulating plasma fatty acid concentrations rather than localized, organ-specific tissue measurements. Plasma concentrations of arachidonic acid fluctuate based on recent dietary intake and hepatic export, poorly reflecting the true bioactive membrane composition of microvascular beds, synovial membranes, or central nervous system parenchyma.
14. Related Terms & Distinctions
To avoid conceptual confusion, arachidonic acid must be carefully distinguished from structurally and metabolically related lipid species:
- Linoleic Acid (LA, 18:2 n-6): An essential 18-carbon dietary omega-6 fatty acid with two double bonds. LA is the upstream dietary precursor from which the human body biosynthesizes arachidonic acid through desaturation and elongation. Unlike arachidonic acid, linoleic acid cannot be directly converted by COX or LOX into standard 2-series prostanoids or 4-series leukotrienes.
- Eicosapentaenoic Acid (EPA, 20:5 n-3): A 20-carbon omega-3 polyunsaturated fatty acid with five double bonds. EPA directly competes with arachidonic acid for COX, LOX, and CYP enzymes, yielding alternative 3-series prostanoids and 5-series leukotrienes that exhibit markedly lower biological inflammatory potency.
- Docosahexaenoic Acid (DHA, 22:6 n-3): A 22-carbon omega-3 fatty acid possessing six double bonds. Along with arachidonic acid, DHA is one of the two dominant structural polyunsaturated fatty acids in the mammalian brain, though it does not serve as a substrate for cyclooxygenase.
- Arachidic Acid (20:0): A twenty-carbon completely saturated fatty acid without double bonds, found naturally in peanut and vegetable oils. Despite the similarity in nomenclature, arachidic acid lacks the conformational flexibility, unsaturations, and signaling functions of arachidonic acid.
- Anandamide (N-arachidonoylethanolamine / AEA): An endogenous cannabinoid neurotransmitter synthesized via the enzymatic condensation of arachidonic acid and ethanolamine, which binds CB1 and CB2 cannabinoid receptors throughout the nervous and immune systems.
15. Summary / Key Takeaways
Arachidonic acid (20:4 n-6) is a critical biological fatty acid that functions as a fundamental structural component of cell membranes and the indispensable source of eicosanoid signaling cascades. Residing esterified within membrane phospholipids, its release via phospholipase A2 represents the rate-limiting step in generating prostaglandins, thromboxanes, leukotrienes, lipoxins, and endocannabinoids. While historically categorized primarily as an agent of acute inflammation and pain, contemporary biomedical research demonstrates that arachidonic acid also orchestrates active anti-inflammatory resolution, regulates vascular and renal tone, and supports synaptic neuroplasticity.
In clinical practice, the therapeutic modulation of arachidonic acid metabolism remains a central pillar of modern medicine, governing the actions of everyday analgesics, antithrombotic therapies, and asthma medications. Ultimately, arachidonic acid embodies the delicate biological equilibrium between host defense and tissue preservation, demonstrating that physiological wellness depends not on the complete eradication of inflammatory signals, but on their precise, homeostatic coordination.
References
- Bergström, S., Danielsson, H., & Samuelsson, B. (1964). The enzymatic formation of prostaglandin E2 from arachidonic acid. Biochimica et Biophysica Acta, 90(1), 207–210. https://pubmed.ncbi.nlm.nih.gov/14201168/
- Calder, P. C. (2015). Marine omega-3 fatty acids and inflammatory processes: Effects, mechanisms and clinical relevance. Biochimica et Biophysica Acta (BBA) – Molecular and Cell Biology of Lipids, 1851(4), 469–484. https://pubmed.ncbi.nlm.nih.gov/25149823/
- Dennis, E. A., & Norris, P. C. (2015). Eicosanoid storm in infection and inflammation. Nature Reviews Immunology, 15(8), 511–523. https://pubmed.ncbi.nlm.nih.gov/26139350/
- Rett, B. S., & Whelan, J. (2011). Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consumed ad libitum: A systematic review. Prostaglandins, Leukotrienes and Essential Fatty Acids, 85(2), 81–91. https://pubmed.ncbi.nlm.nih.gov/21664121/
- Serhan, C. N. (2014). Pro-resolving lipid mediators are leads for resolution physiology. Nature, 510(7503), 92–101. https://pubmed.ncbi.nlm.nih.gov/24899309/
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