Eicosanoids have been implicated in a vast number of devastating inflammatory conditions, including arthritis, atherosclerosis, pain, and cancer. Currently, over a hundred different eicosanoids have been identified, with many having potent bioactive signaling capacity. These lipid metabolites are synthesized de novo by at least 50 unique enzymes, many of which have been cloned and characterized. Due to the extensive characterization of eicosanoid biosynthetic pathways, this field provides a unique framework for integrating genomics, proteomics, and metabolomics toward the investigation of disease pathology. To facilitate a concerted systems biology approach, this review outlines the proteins implicated in eicosanoid biosynthesis and signaling in human, mouse, and rat. Applications of the extensive genomic and lipidomic research to date illustrate the questions in eicosanoid signaling that could be uniquely addressed by a thorough analysis of the entire eicosanoid proteome.-Buczynski, M. W., D. S. Dumlao, and E. A. Dennis. An integrated omics analysis of eicosanoid biology.

Persistent pain after resolution of clinically appreciable signs of arthritis poses a therapeutic challenge and immunosuppressive therapies do not meet this medical need. To investigate this conversion to persistent pain, we utilized the K/BxN serum transfer arthritis model, which has persistent mechanical hypersensitivity despite the resolution of visible inflammation. Toll-like receptor (TLR) 4 has been implicated as a potential therapeutic target in neuropathic and other pain models. We compared the relative courses of serum transfer arthritis and mechanical hypersensitivity in wild type (WT) and Tlr4−/− mice. K/BxN serum transfer induced similar joint swelling and inflammation from days 4–22 in WT and Tlr4−/− mice. Unlike WT mice, Tlr4−/− mice displayed a significant reversal in mechanical hypersensitivity and diminished appearance of glial activation markers after resolution of peripheral inflammation. Intrathecal (IT) delivery of a TLR4 antagonist, LPS-RS (10μg), on days 6, 9, and 12 abrogated the transition to persistent mechanical hypersensitivity in WT arthritic mice, while later administration had no impact. We utilized a lipodomics LC/MS/MS methodology to determine spinal cord profiles of bioactive lipid species following early LPS-RS treatment compared to vehicle treated controls. WT arthritic mice had reduced spinal levels of the anti-inflammatory prostaglandin 15d-PGJ2 on day 6, compared to IT LPS-RS treated mice. Direct IT application of 15d-PGJ2 (0.5μg) on day 6 improved mechanical hypersensitivity in arthritic mice within 15 minutes. Hence, TLR4 signaling altered spinal bioactive lipid profiles in the serum transfer model and played a critical role in the transition from acute to chronic post-inflammatory mechanical hypersensitivity.

Cyclic GMP-AMP synthase (cGAS) initiates the innate immune system in response to cytosolic dsDNA. After binding and activation from dsDNA, cGAS uses ATP and GTP to synthesize 2′, 3′ -cGAMP (cGAMP), a cyclic dinucleotide second messenger with mixed 2′-5′ and 3′-5′ phosphodiester bonds. Inappropriate stimulation of cGAS has been implicated in autoimmune disease such as systemic lupus erythematosus, thus inhibition of cGAS may be of therapeutic benefit in some diseases; however, the size and polarity of the cGAS active site makes it a challenging target for the development of conventional substrate-competitive inhibitors. We report here the development of a high affinity (KD = 200 nM) inhibitor from a low affinity fragment hit with supporting biochemical and structural data showing these molecules bind to the cGAS active site. We also report a new high throughput cGAS fluorescence polarization (FP)-based assay to enable the rapid identification and optimization of cGAS inhibitors. This FP assay uses Cy5-labelled cGAMP in combination with a novel high affinity monoclonal antibody that specifically recognizes cGAMP with no cross reactivity to cAMP, cGMP, ATP, or GTP. Given its role in the innate immune response, cGAS is a promising therapeutic target for autoinflammatory disease. Our results demonstrate its druggability, provide a high affinity tool compound, and establish a high throughput assay for the identification of next generation cGAS inhibitors.

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Peripheral inflammation initiates changes in spinal nociceptive processing leading to hyperalgesia. Previously, we demonstrated that among 102 lipid species detected by LC-MS/MS analysis in rat spinal cord, the most notable increases that occur after intraplantar carrageenan are metabolites of 12-lipoxygenases (12-LOX), particularly hepoxilins (HXA 3 and HXB 3 ). Thus, we examined involvement of spinal LOX enzymes in inflammatory hyperalgesia. In the current work, we found that intrathecal (IT) delivery of the LOX inhibitor nordihydroguaiaretic acid prevented the carrageenan-evoked increase in spinal HXB 3 at doses that attenuated the associated hyperalgesia. Furthermore, IT delivery of inhibitors targeting 12-LOX (CDC, Baicalein), but not 5-LOX (Zileuton) dosedependently attenuated tactile allodynia. Similarly, IT delivery of 12-LOX metabolites of arachidonic acid 12(S)-HpETE, 12(S)-HETE, HXA 3 , or HXB 3 evoked profound, persistent tactile allodynia, but 12(S)-HpETE and HXA 3 produced relatively modest, transient heat hyperalgesia. The pronociceptive effect of HXA 3 correlated with enhanced release of Substance P from primary sensory afferents. Importantly, HXA 3 triggered sustained mobilization of calcium in cells stably overexpressing TRPV1 or TRPA1 receptors and in acutely dissociated rodent sensory neurons. Constitutive deletion or antagonists of TRPV1 (AMG9810) or TRPA1 (HC030031) attenuated this action. Furthermore, pretreatment with antihyperalgesic doses of AMG9810 or HC030031 reduced spinal HXA 3 -evoked allodynia. These data indicate that spinal HXA 3 is increased by peripheral inflammation and promotes initiation of facilitated nociceptive processing through direct activation of TRPV1 and TRPA1 at central terminals.eicosanoid | pain | central sensitization T issue injury and inflammation are associated with hyperalgesia mediated by facilitated spinal nociceptive processing that can be modulated by lipids derived from arachidonic acid (AA) and other polyunsaturated fatty acids (PUFA), including eicosanoids synthesized via three enzymatic pathways: (i) cyclooxygenase (COX)-prostaglandins (PG); (ii) 5-, 12-, and 12/15-lipoxygenases (LOX)-leukotrienes, hydroxyeicosatetraenoic acids (HETEs), hepoxilins (HXA 3 and HXB 3 ), lipoxins, resolvins, and protectins; and (iii) cytochrome P450-epoxyeicosatrienoic acids and HETEs (1). Substantial evidence indicates that peripheral injury or direct activation of spinal dorsal horn receptors [Neurokinin 1 (NK1), AMPA, and NMDA] increases eicosanoid formation and that spinal delivery of COX inhibitors reduces the associated hyperalgesia (2, 3). Recently, we reported that paw carrageenan increases spinal production of both COX and 12-LOX metabolites of AA, including 12(S)-HETE in cerebrospinal fluid (CSF) and hepoxilins in the lumbar spinal cord (4).Several groups point to a peripheral role for 5-and 12-LOX in nociception, as shown by antihyperalgesic actions of LOX inhibitors administered via systemic routes (5-9). It has been suggested that spinal 12-LOX may play a r...