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Arachidonic acid metabolism

Clinical review pending

Arachidonic acid gives rise to messengers for inflammation, blood clotting and vascular function. How COX, LOX and omega-3 fatty acids are involved.

Editorial draft. The text has been read in full and copyedited. Clinical review and source verification are still pending.

Arachidonic acid metabolism is a biochemical cascade that converts arachidonic acid, an omega-6 fatty acid stored in cell membranes, into pro-inflammatory signaling molecules such as prostaglandins, leukotrienes and thromboxanes. This cascade is one of the central mechanisms of the acute inflammatory response and is relevant to conditions ranging from joint pain to cardiovascular risk. The balance between omega-6 and omega-3 fatty acids has a major influence on how active this pathway is.

Why the arachidonic acid pathway matters

Inflammation arises from several interconnected molecular processes. One clinically important cascade is arachidonic acid (AA) metabolism: it produces the molecules that trigger pain, swelling, fever and platelet aggregation in response to injury or immune activation. This pathway is also the target of nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin, which work by blocking key enzymes in the cascade. Source

Persistent, low-grade activation of the AA cascade is linked to cardiovascular disease, metabolic disorders and chronic pain. It differs from an acute inflammatory response, which subsides afterward. The dietary and metabolic influences that drive or suppress this pathway are measurable and modifiable.

How the arachidonic acid pathway works

Where does arachidonic acid come from?

Arachidonic acid is a polyunsaturated omega-6 fatty acid with 20 carbon atoms. It is stored in the phospholipid bilayer of nearly all cell membranes. The body gets it from animal foods or makes it from linoleic acid, an omega-6 fatty acid found in vegetable oils. In this process, enzymes lengthen linoleic acid step by step and add extra double bonds. Source

When a cell is injured or receives the right immune signal, an enzyme called phospholipase A2 (PLA2) cleaves arachidonic acid from the membrane and releases it into the cytoplasm. That starts the downstream cascade. Without this release step, the downstream inflammatory molecules cannot be produced. Source

The COX pathway: prostaglandins and thromboxanes

Once arachidonic acid is released, it is metabolized by one of two large enzyme families. Cyclooxygenase enzymes (COX-1 and COX-2) convert AA into prostaglandins and thromboxanes. These molecules mediate pain sensitization, fever, vasodilation at sites of inflammation and platelet aggregation. COX-1 is active even without an inflammatory stimulus; it plays a protective role for the stomach lining and a role in platelet function. COX-2 is induced by inflammatory stimuli and is particularly associated with the inflammatory response. Source

NSAIDs inhibit both COX enzymes to varying degrees. Aspirin inhibits COX-1 and COX-2 irreversibly, which is why low-dose aspirin reduces platelet aggregation. Selective COX-2 inhibitors (such as celecoxib) were developed to reduce inflammatory symptoms while sparing the stomach-protecting effect of COX-1.

The LOX pathway: leukotrienes

The second main branch uses lipoxygenase (LOX) enzymes to convert arachidonic acid into leukotrienes. These molecules play an important role in allergic inflammation, asthma and the sustained phase of the inflammatory response. Leukotrienes increase vascular permeability, recruit neutrophils and eosinophils to sites of inflammation and contribute to bronchoconstriction in asthma. Leukotriene-modifying drugs (such as montelukast) specifically target this branch of the pathway. Source

The omega-3 counterweight

Omega-3 fatty acids, especially EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), compete with arachidonic acid at several steps along this pathway. EPA competes with AA for the COX and LOX enzymes. EPA gives rise to eicosanoids that are described as less pro-inflammatory. With adequate omega-3 intake, a larger share of the resulting signaling molecules comes from EPA rather than AA, which leads to a less pro-inflammatory eicosanoid profile. Source

A 2024 systematic review in Nutrients reports that omega-3 supplementation can reduce post-exercise inflammation and lower markers of muscle damage. These effects are mediated partly through competitive inhibition of the arachidonic acid pathway. The dietary ratio of omega-6 to omega-3 fatty acids is therefore a meaningful factor in baseline inflammatory activity. Source

Chronic activation and its consequences

The arachidonic acid pathway is involved in acute inflammation that subsides afterward. Chronic stimulation, triggered by high omega-6 intake, excess fat tissue (which itself produces inflammatory cytokines), persistent infections or metabolic disorders, keeps the pathway in a chronically active state. The resulting low-grade inflammatory environment is associated with cardiovascular risk, insulin resistance and the progression of conditions such as atherosclerosis and inflammatory joint disease.

A 2024 study in the New England Journal of Medicine confirmed that a combined assessment of inflammation (hs-CRP), LDL cholesterol and lipoprotein(a) predicted cardiovascular events in women over a 30-year period, which highlights the link between inflammation and long-term cardiovascular risk. Source

Which biomarkers reflect arachidonic acid pathway activity?

No single test in routine clinical practice measures arachidonic acid pathway activity directly, but several markers reflect the downstream consequences of chronic activation of the inflammatory cascade and the dietary influences that modulate it.

  • hs-CRP: an inflammatory marker made in the liver; it rises in response to cytokines produced in connection with the AA pathway Source

  • Omega-6 to omega-3 ratio: a direct measure of the fatty acid balance that determines how inflammation-related the resulting eicosanoids are; available through a fatty acid panel when ordered by a physician for a clinical reason

  • Homocysteine: elevated levels are linked to vascular inflammation and endothelial dysfunction Source

  • Apolipoprotein B: a marker of the number of atherogenic lipoprotein particles; more sensitive than LDL for cardiovascular risk in inflammatory states Source

  • Fasting insulin: insulin resistance drives chronic activation of the AA pathway through inflammatory adipokines Source

  • HbA1c: chronic hyperglycemia activates inflammatory pathways, including upregulation of COX-2 Source

The source article names hs-CRP, HbA1c and ApoB for a complementary assessment of inflammation and metabolism. These values do not measure the arachidonic acid pathway directly. Source

What influences arachidonic acid pathway activity?

The main modifiable factors in the AA pathway include the composition of dietary fats (especially the ratio of omega-6 to omega-3), body fat percentage, blood sugar regulation and the presence or absence of chronic infection or autoimmune activation. The source article discusses fewer linoleic acid-rich vegetable oils relative to omega-3 sources, better metabolic health and treating the causes of chronic low-grade inflammation as possible starting points. Dietary recommendations derived from this require a separate clinical assessment.

None of this replaces a clinical assessment. Elevated hs-CRP, insulin resistance or dyslipidemia require investigation of their specific causes before any conclusions can be drawn about the role of the AA pathway in a person’s health.

This article explains biological relationships. The linked test offerings document the source article and do not replace a medical assessment.

Frequently asked questions

What is the arachidonic acid pathway and why does it matter for health?

The arachidonic acid pathway is a biochemical cascade in which the omega-6 fatty acid arachidonic acid is converted into eicosanoids, signaling molecules that regulate inflammation, blood clotting and immune function. The pathway matters for health because an imbalance in it is associated with chronic, low-grade inflammation, which is linked to cardiovascular problems, metabolic disorders and other long-term health problems.

What is arachidonic acid, and is it an omega-3 or an omega-6 fatty acid?

Arachidonic acid (AA) is a polyunsaturated omega-6 fatty acid with 20 carbon atoms that occurs in cell membranes throughout the body. It is obtained directly from animal foods such as eggs, poultry and red meat, and the body can also synthesize it from linoleic acid, another omega-6 fatty acid that is common in vegetable oils. It is required for normal cell function. Its ratio to omega-3 fatty acids such as EPA is discussed as an influence on how inflammatory responses are regulated.

What are the three main branches of the arachidonic acid pathway?

The three main enzymatic branches are the cyclooxygenase (COX) pathway, the lipoxygenase (LOX) pathway and the cytochrome P450 pathway. The COX pathway produces prostaglandins and thromboxanes, which are involved in inflammation and blood clotting. The LOX pathway generates leukotrienes, which contribute to immune and allergic reactions. The cytochrome P450 pathway produces epoxyeicosatrienoic acids (EETs), which may help support vascular function.

How are arachidonic acid and inflammation connected?

Arachidonic acid is the main substrate for producing pro-inflammatory eicosanoids such as prostaglandin E2 and leukotriene B4. When arachidonic acid levels are high relative to anti-inflammatory omega-3 fatty acids, the body may produce more of these pro-inflammatory mediators. This shift is associated with a heightened inflammatory state that can, over time, lead to tissue damage and chronic disease.

What does an arachidonic acid blood test measure?

An arachidonic acid blood test typically measures the concentration of arachidonic acid in red blood cell membranes or in blood plasma, often reported together with other fatty acids. Many fatty acid profiles also calculate the AA/EPA ratio, which compares the arachidonic acid level with the eicosapentaenoic acid (EPA) level. This ratio is used as a marker of omega-6 to omega-3 balance and may reflect inflammatory activity.

What is the AA/EPA ratio and why does it matter?

The AA/EPA ratio compares the amount of arachidonic acid (an omega-6 fat) with eicosapentaenoic acid (an omega-3 fat) in the blood. A higher ratio indicates a larger share of pro-inflammatory omega-6 relative to anti-inflammatory omega-3, which is associated with increased inflammatory activity. Repeat measurements can show whether the fatty acid ratio changes after a change in diet, for example eating more fish or taking an omega-3 supplement.

What is a normal arachidonic acid level or a normal AA/EPA ratio?

Reference ranges can vary by lab and population, but an AA/EPA ratio below 5 is generally considered favorable, and some researchers suggest an optimal range between 1.5 and 3. Because of high omega-6 intake and low omega-3 consumption, the typical Western diet often leads to ratios well above 10. Results should be interpreted by a physician in the context of a person’s health.

What can an elevated arachidonic acid level mean?

Elevated arachidonic acid levels or a high AA/EPA ratio can indicate that pro-inflammatory precursors outweigh anti-inflammatory ones. This imbalance is linked to raised risk markers for cardiovascular problems, joint complaints and other inflammation-related conditions. Dietary changes, especially more omega-3-rich foods, can help support a more balanced fatty acid profile.

Sources

  • Ricciotti E, FitzGerald GA (2011). Prostaglandins and inflammation. Arteriosclerosis, thrombosis, and vascular biology, 31(5), 986-1000. https://doi.org/10.1161/ATVBAHA.110.207449 Source

  • Wang B, Wu L, Chen J, Dong L, Chen C, Wen Z, Hu J, Fleming I, Wang DW (2021). Metabolism pathways of arachidonic acids: mechanisms and potential therapeutic targets. Signal transduction and targeted therapy, 6(1), 94. https://doi.org/10.1038/s41392-020-00443-w Source

  • Murakami M, Kudo I (2002). Phospholipase A2. Journal of biochemistry, 131(3), 285-92. https://doi.org/10.1093/oxfordjournals.jbchem.a003101 Source

  • Calder PC (2017). Omega-3 fatty acids and inflammatory processes: from molecules to man. Biochemical Society transactions, 45(5), 1105-1115. https://doi.org/10.1042/BST20160474 Source

  • Fernández-Lázaro D, Arribalzaga S, Gutiérrez-Abejón E, Azarbayjani MA, Mielgo-Ayuso J, Roche E (2024). Omega-3 Fatty Acid Supplementation on Post-Exercise Inflammation, Muscle Damage, Oxidative Response, and Sports Performance in Physically Healthy Adults-A Systematic Review of Randomized Controlled Trials. Nutrients, 16(13). https://doi.org/10.3390/nu16132044 Source

  • Ridker PM, Moorthy MV, Cook NR, Rifai N, Lee IM, Buring JE (2024). Inflammation, Cholesterol, Lipoprotein(a), and 30-Year Cardiovascular Outcomes in Women. The New England journal of medicine, 391(22), 2087-2097. https://doi.org/10.1056/nejmoa2405182 Source