Potential mechanisms underlying a relationship between long-chain polyunsaturated fatty acids and overlapping pain conditions in adults

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Chronic pain therapies typically target one of three pain pathways: nociception, inflammation or psychological processes. The goal is almost always therapeutic, not preventive. We challenge that premise in light of new evidence that chronic pain can be prevented by targeting all three pathways through diets with a favorable balance of omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFAs). The anti-inflammatory effects of long-chain (LC) omega-3 (n-3) PUFAs on pain disorders such as arthritis are well recognized. A more recent discovery is that LC n-3 eicosapentaenoic acid and n-3 docosahexaenoic acid metabolites lower concentrations of pronociceptive derivatives, and increase concentrations of antinociceptive and analgesic derivatives. By contrast, omega-6 (n-6) PUFA metabolites have mostly inflammatory and pronociceptive effects. Furthermore, LC n-3 derivatives have anxiolytic effects, alleviating depressive symptoms and anxiety that are often comorbid with chronic pain. The extent to which n-6 and n-3 PUFAs are synthesized into bioactive LC PUFAs by fatty acid desaturase (FADS) enzymes, encoded by the FADS gene cluster, differs according to genetic variability in key enzymes in PUFA metabolism: delta-5 desaturase (FADS1) and delta-6 desaturase (FADS2). Hence gene-PUFA interactions influence the biosynthesis of PUFA derivatives that have putative and therapeutic effects on chronic pain. We plan to study associations between PUFAs and chronic overlapping pain conditions (COPCs) cross-sectionally using existing data and stored erythrocytes from 655 genotyped adult participants (69% women) in our community-based study named “Orofacial Pain: Prospective Evaluation and Risk Assessment” (OPPERA-II). OPPERA-II assessed overlap of temporomandibular disorder, migraine or tension-type headache, fibromyalgia, low back pain, and irritable bowel syndrome. Aim 1 will evaluate associations between pain conditions and erythrocyte concentrations of PUFAs and their metabolites. PUFAs will be quantified using liquid chromatography tandem mass spectrometry. We hypothesize that high concentrations of the n-6 series, and low concentrations the n-3 series are positively associated with occurrence of each pain condition and the total number of COPCs. Aim 2 will evaluate associations between intermediate phenotypes (nociception, anxiety and depression) and PUFA concentrations. Anxiety and depressive symptoms were measured by psychometrically validated questionnaires. Quantitative sensory testing determined sensitivity to three modalities of nociception: blunt pressure pain, mechanical pain, and thermal heat pain. Aim 3 will assess whether FADS genetic variants modify associations of PUFAs and their metabolites with COPCs. This is a high risk project because community-based studies of pain have never assessed PUFAs’ potential for preventing COPCs. Such a study is a necessary pre-requisite for a future clinical trial. The project has potentially high-reward because current treatments for pain are unsatisfactory whereas n-3 PUFAs have excellent safety profiles and can plausibly be used to prevent chronic pain.