5s-12r-18r-trihydroxy-6z-8e-10e-14z-16e-eicosapentaenoic-acid and Pain

Endogenous pain-inhibitory substances have rarely been found. A group of powerful pain suppressor molecules that are endogenously generated are now emerging: resolvins and related compounds including neuroprotectins and maresins. These molecules began to be unveiled in a series of inflammation studies more than a decade ago, rapidly shifting the paradigm that explains the mechanism for the inflammatory phase switch. The resolution phase was considered a passive process as proinflammatory mediators disappeared; it is now understood to be actively drawn by the actions of resolvins. Surprisingly, these substances potently affect the pain state. Although this research area is not fully matured, consistently beneficial outcomes have been observed in a various in vivo and in vitro pain models. Furthermore, multiple hypotheses on the neuronal and molecular mechanisms for alleviating pain are being tested, deriving inspiration from existing inflammation and pain studies. This paper serves as a brief summary of the proresolving roles of resolvins and related lipid mediators in inflammation and also as a review for accumulated information of their painkilling actions. This also includes potential receptor-mediated mechanisms and discusses future scientific perspectives. Further diverse approaches will help to construct a hidden axis of natural protection principles and establish proofs of concept for pain relief.

Topics: Calcium Channels; Docosahexaenoic Acids; Eicosapentaenoic Acid; Humans; Inflammation; Inflammation Mediators; Nerve Tissue Proteins; Pain; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPV Cation Channels

Resolvins, including D and E series resolvins, are endogenous lipid mediators generated during the resolution phase of acute inflammation from the omega-3 polyunsaturated fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Resolvins have potent anti-inflammatory and pro-resolution actions in several animal models of inflammation. Recent findings also demonstrate that resolvin E1 and resolvin D1 can each potently dampen inflammatory and postoperative pain. This review focuses on the mechanisms by which resolvins act on their receptors in immune cells and neurons to normalize exaggerated pain via regulation of inflammatory mediators, transient receptor potential (TRP) ion channels, and spinal cord synaptic transmission. Resolvins may offer novel therapeutic approaches for preventing and treating pain conditions associated with inflammation.

Topics: Analgesics; Animals; Docosahexaenoic Acids; Eicosapentaenoic Acid; Humans; Inflammation; Neurons; Pain; Pain, Postoperative

Inflammatory pain such as arthritic pain is typically treated with opioids and cyclo-oxygenase-2 inhibitors with well known side effects. Transient receptor potential subtype vanilloid 1 (TRPV1) and TRP ankyryn 1 (TRPA1) contribute importantly to the genesis of inflammatory pain via both peripheral mechanisms (peripheral sensitization) and spinal cord mechanisms (central sensitization). Although these TRP channels have been intensively studied, little is known about their endogenous inhibitors. Recent studies have demonstrated that the endogenous lipid mediators resolvins (RvE1 and RvD1), derived from ω-3 unsaturated fatty acids, are potent inhibitors for inflammatory pain, without noticeable side effects. However, the molecular mechanisms underlying resolvins' distinct analgesic actions in mice are unclear. RvD2 is a novel family member of resolvins. Here we report that RvD2 is a remarkably potent inhibitor of TRPV1 (IC(50) = 0.1 nm) and TRPA1 (IC(50) = 2 nm) in primary sensory neurons, whereas RvE1 and RvD1 selectively inhibited TRPV1 (IC(50) = 1 nm) and TRPA1 (IC(50) = 9 nm), respectively. Accordingly, RvD2, RvE1, and RvD1 differentially regulated TRPV1 and TRPA1 agonist-elicited acute pain and spinal cord synaptic plasticity [spontaneous EPSC (sEPSC) frequency increase]. RvD2 also abolished inflammation-induced sEPSC increases (frequency and amplitude), without affecting basal synaptic transmission. Intrathecal administration of RvD2 at very low doses (0.01-1 ng) prevented formalin-induced spontaneous pain. Intrathecal RvD2 also reversed adjuvant-induced inflammatory pain without altering baseline pain and motor function. Finally, intrathecal RvD2 reversed C-fiber stimulation-evoked long-term potentiation in the spinal cord. Our findings suggest distinct roles of resolvins in regulating TRP channels and identify RvD2 as a potent endogenous inhibitor for TRPV1/TRPA1 and inflammatory pain.

Topics: Animals; Docosahexaenoic Acids; Eicosapentaenoic Acid; Ganglia, Spinal; Inflammation; Male; Mice; Neuronal Plasticity; Neurons; Pain; Spinal Cord; TRPV Cation Channels

Inflammatory pain, such as arthritis pain, is a growing health problem. Inflammatory pain is generally treated with opioids and cyclooxygenase (COX) inhibitors, but both are limited by side effects. Recently, resolvins, a unique family of lipid mediators, including RvE1 and RvD1 derived from omega-3 polyunsaturated fatty acid, have shown marked potency in treating disease conditions associated with inflammation. Here we report that peripheral (intraplantar) or spinal (intrathecal) administration of RvE1 or RvD1 in mice potently reduces inflammatory pain behaviors induced by intraplantar injection of formalin, carrageenan or complete Freund's adjuvant (CFA), without affecting basal pain perception. Intrathecal RvE1 injection also inhibits spontaneous pain and heat and mechanical hypersensitivity evoked by intrathecal capsaicin and tumor necrosis factor-alpha (TNF-alpha). RvE1 has anti-inflammatory activity by reducing neutrophil infiltration, paw edema and proinflammatory cytokine expression. RvE1 also abolishes transient receptor potential vanilloid subtype-1 (TRPV1)- and TNF-alpha-induced excitatory postsynaptic current increases and TNF-alpha-evoked N-methyl-D-aspartic acid (NMDA) receptor hyperactivity in spinal dorsal horn neurons via inhibition of the extracellular signal-regulated kinase (ERK) signaling pathway. Thus, we show a previously unknown role for resolvins in normalizing the spinal synaptic plasticity that has been implicated in generating pain hypersensitivity. Given the potency of resolvins and the well-known side effects of opioids and COX inhibitors, resolvins may represent new analgesics for treating inflammatory pain.

Topics: Analgesics; Animals; Docosahexaenoic Acids; Eicosapentaenoic Acid; Inflammation; Injections, Spinal; Male; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Knockout; Pain; Posterior Horn Cells

Topics: Analgesics; Docosahexaenoic Acids; Eicosapentaenoic Acid; Humans; Inflammation; Models, Biological; Molecular Structure; Pain