Background: ⌬ 9 -Tetrahydrocannabinol (THC) and cannabidiol (CBD) modulate endocannabinoid tone in vivo through unknown mechanisms. Results: THC and CBD bind to fatty acid-binding proteins (FABPs) and reduce endocannabinoid metabolism. Neither THC nor CBD inhibit human fatty acid amide hydrolase activity. Conclusion: FABPs are intracellular transporters of THC and CBD. Significance: These findings identify a new mechanism by which phytocannabinoids influence endocannabinoid signaling.

The endocannabinoid anandamide (AEA) is an antinociceptive lipid that is inactivated through cellular uptake and subsequent catabolism by fatty acid amide hydrolase (FAAH). Fatty acid binding proteins (FABPs) are intracellular carriers that deliver AEA and related N-acylethanolamines (NAEs) to FAAH for hydrolysis. The mammalian brain expresses three FABP subtypes: FABP3, FABP5, and FABP7. Recent work from our group has revealed that pharmacological inhibition of FABPs reduces inflammatory pain in mice. The goal of the current work was to explore the effects of FABP inhibition upon nociception in diverse models of pain. We developed inhibitors with differential affinities for FABPs to elucidate the subtype(s) that contributes to the antinociceptive effects of FABP inhibitors.Inhibition of FABPs reduced nociception associated with inflammatory, visceral, and neuropathic pain. The antinociceptive effects of FABP inhibitors mirrored their affinities for FABP5, while binding to FABP3 and FABP7 was not a predictor of in vivo efficacy. The antinociceptive effects of FABP inhibitors were mediated by cannabinoid receptor 1 (CB1) and peroxisome proliferator-activated receptor alpha (PPARα) and FABP inhibition elevated brain levels of AEA, providing the first direct evidence that FABPs regulate brain endocannabinoid tone. These results highlight FABPs as novel targets for the development of analgesic and anti-inflammatory therapeutics.

Endocannabinoids (eCBs) are lipid-signaling molecules involved in the regulation of numerous behaviors and physiological functions. Released by postsynaptic neurons, eCBs mediate retrograde modulation of synaptic transmission and plasticity by activating presynaptic cannabinoid receptors. While the cellular mechanisms by which eCBs control synaptic function have been well characterized, the mechanisms controlling their retrograde synaptic transport remain unknown. Here, we demonstrate that fatty-acid-binding protein 5 (FABP5), a canonical intracellular carrier of eCBs, is indispensable for retrograde eCB transport in the dorsal raphe nucleus (DRn). Thus, pharmacological inhibition or genetic deletion of FABP5 abolishes both phasic and tonic eCB-mediated control of excitatory synaptic transmission in the DRn. The blockade of retrograde eCB signaling induced by FABP5 inhibition is not mediated by impaired cannabinoid receptor function or reduced eCB synthesis. These findings indicate that FABP5 is essential for retrograde eCB signaling and may serve as a synaptic carrier of eCBs at central synapses.

One contribution of 9 to a Theme Issue 'Towards a systems model of resilience'. The identification of biomarkers for post-traumatic stress disorder (PTSD) and resilience/recovery is critical for advancing knowledge about pathophysiology and treatment in trauma-exposed persons. This study examined a series of glucocorticoid-related biomarkers prior to and in response to psychotherapy. Fifty-two male and female veterans with PTSD were randomized 2 : 1 to receive either prolonged exposure (PE) therapy or a weekly minimal attention (MA) intervention for 12 consecutive weeks. Psychological and biological assessments were obtained prior to and following treatment and after a 12-week naturalistic follow-up. Response was defined dichotomously as no longer meeting criteria for PTSD at post-treatment based on the Clinician Administered PTSD Scale for DSM-IV (CAPS). Clinical improvement on the CAPS was apparent for both PE and MA, with no significant difference according to treatment condition. Biomarkers predictive of treatment gains included the BCLI polymorphism of the glucocorticoid receptor gene. Additional predictors of treatment response were higher bedtime salivary cortisol and 24 h urinary cortisol excretion. Pre-treatment plasma dehydroepiandrosterone/ cortisol ratio and neuropetide Y (NPY) levels were predictors of reductions in PTSD symptoms, and, for NPY only, of other secondary outcomes as well, including anxiety and depression ratings. Glucocorticoid sensitivity changed in association with symptom change, reflecting clinical state. It is possible to distinguish prognostic and state biomarkers of PTSD using a longitudinal approach in the context of treatment. Identified markers may also be relevant to understanding mechanisms of action of symptom reduction.

Human FABP5 and FABP7 are intracellular endocannabinoid transporters. SBFI-26 is an α-truxillic acid 1-naphthyl monoester that inhibits the activities of FABP5 and FABP7 and produces antinociceptive and anti-inflammatory effects in mice. The synthesis of SBFI-26 yields several stereoisomers, and it is not known how the inhibitor binds the transporters. Here we report co-crystal structures of SBFI-26 in complex with human FABP5 and FABP7 at a resolution of 2.2 Å and 1.9 Å, respectively. We found that only (S)-SBFI-26 was present in the crystal structures. The inhibitor largely mimics the fatty acid binding pattern, but it also has several unique interactions. Notably, the FABP7 complex corroborates key aspects of the ligand binding pose at the canonical site previously predicted by virtual screening. In FABP5, SBFI-26 was unexpectedly found to bind at the substrate entry portal region in addition to binding at the canonical ligand-binding pocket. Our structural and binding energy analyses indicate that both (R) and (S) forms appear to bind the transporter equally well. We suggest that the (S) enantiomer observed in the crystal structures may be a result of the crystallization process selectively incorporating the (S)-SBFI-26-FABP complexes into the growing lattice, or that the (S)-enantiomer may bind to the portal site more rapidly than to the canonical site, leading to an increased local concentration of the (S) enantiomer for binding to the canonical site. Our work reveals two binding poses of SBFI-26 in its target transporters. This knowledge will guide the development of more potent FABP inhibitors based upon the SBFI-26 scaffold.

BackgroundFatty-acid-binding proteins (FABPs) are intracellular carriers for endocannabinoids, N-acylethanolamines, and related lipids. Previous work indicates that systemically administered FABP5 inhibitors produce analgesia in models of inflammatory pain. It is currently not known whether FABP inhibitors exert their effects through peripheral or central mechanisms. Here, we examined FABP5 distribution in dorsal root ganglia and spinal cord and examined the analgesic effects of peripherally and centrally administered FABP5 inhibitors.ResultsImmunofluorescence revealed robust expression of FABP5 in lumbar dorsal root ganglia. FABP5 was distributed in peptidergic calcitonin gene-related peptide-expressing dorsal root ganglia and non-peptidergic isolectin B4-expressing dorsal root ganglia. In addition, the majority of dorsal root ganglia expressing FABP5 also expressed transient receptor potential vanilloid 1 (TRPV1) and peripherin, a marker of nociceptive fibers. Intraplantar administration of FABP5 inhibitors reduced thermal and mechanical hyperalgesia in the complete Freund’s adjuvant model of chronic inflammatory pain. In contrast to its robust expression in dorsal root ganglia, FABP5 was sparsely distributed in the lumbar spinal cord and intrathecal administration of FABP inhibitor did not confer analgesic effects. Administration of FABP inhibitor via the intracerebroventricular (i.c.v.) route reduced thermal hyperalgesia. Antagonists of peroxisome proliferator-activated receptor alpha blocked the analgesic effects of peripherally and i.c.v. administered FABP inhibitor while antagonism of cannabinoid receptor 1 blocked the effects of peripheral FABP inhibition and a TRPV1 antagonist blocked the effects of i.c.v. administered inhibitor. Although FABP5 and TRPV1 were co-expressed in the periaqueductal gray region of the brain, which is known to modulate pain, knockdown of FABP5 in the periaqueductal gray using adeno-associated viruses and pharmacological FABP5 inhibition did not produce analgesic effects.ConclusionsThis study demonstrates that FABP5 is highly expressed in nociceptive dorsal root ganglia neurons and FABP inhibitors exert peripheral and supraspinal analgesic effects. This indicates that peripherally restricted FABP inhibitors may serve as a new class of analgesic and anti-inflammatory agents.

Fatty acid binding proteins (FABPs) serve as critical modulators of endocannabinoid signaling by facilitating the intracellular transport of anandamide and whose inhibition potentiates anandamide signaling. Our previous work has identified a novel small-molecule FABP inhibitor, α-truxillic acid 1-naphthyl monoester (SB-FI-26, 3) that has shown efficacy as an antinociceptive and anti-inflammatory agent in rodent models. In the present work, we have performed an extensive SAR study on a series of 3-analogs as novel FABP inhibitors based on computer-aided inhibitor drug design and docking analysis, chemical synthesis and biological evaluations. The prediction of binding affinity of these analogs to target FABP3, 5 and 7 isoforms was performed using the AutoDock 4.2 program, using the recently determined co-crystal structures of 3 with FABP5 and FABP7. The compounds with high docking scores were synthesized and evaluated for their activities using a fluorescence displacement assay against FABP3, 5 and 7. During lead optimization, compound 3l emerged as a promising compound with the Ki value of 0.21 μM for FABP 5, 4-fold more potent than 3 (Ki, 0.81 μM). Nine compounds exhibit similar or better binding affinity than 3, including compounds 4b (Ki, 0.55 μM) and 4e (Ki, 0.68 μM). Twelve compounds are selective for FABP5 and 7 with >10 μM Ki values for FABP3, indicating a safe profile to avoid potential cardiotoxicity concerns. Compounds 4f, 4j and 4k showed excellent selectivity for FABP5 and would serve as other new lead compounds. Compound 3a possessed high affinity and high selectivity for FABP7. Compounds with moderate to high affinity for FABP5 displayed antinociceptive effects in mice while compounds with low FABP5 affinity lacked in vivo efficacy. In vivo pain model studies in mice revealed that exceeding hydrophobicity significantly affects the efficacy. Thus, among the compounds with high affinity to FABP5 in vitro, the compounds with moderate hydrophobicity were identified as promising new lead compounds for the next round of optimization, including compounds 4b and 4j. For select cases, computational analysis of the observed SAR, especially the selectivity of new inhibitors to particular FABP isoforms, by comparing docking poses, interaction map, and docking energy scores has provided useful insights.

Fatty acid binding proteins (FABPs) are intracellular lipid carriers that regulate inflammation, and pharmacological inhibition of FABP5 reduces inflammation and pain. The mechanism(s) underlying the anti-inflammatory effects associated with FABP5 inhibition are poorly understood. Herein, we identify a novel mechanism through which FABP5 modulates inflammation. In mice, intraplantar injection of carrageenan induces acute inflammation that is accompanied by edema, enhanced pain sensitivity, and elevations in pro-inflammatory cytokines and prostaglandin E2 (PGE2). Inhibition of FABP5 reduced pain, edema, cytokine, and PGE2 levels. PGE2 is a major eicosanoid that enhances pain in the setting of inflammation and we focused upon the mechanism(s) through which FABP5 modulates PGE2 production. Cyclooxygenase-2 and microsomal prostaglandin E synthase-1 (mPGES-1) are enzymes upregulated at the site of inflammation and account for the bulk of PGE2 biosynthesis. Pharmacological or genetic FABP5 inhibition suppressed the induction of mPGES-1 but not COX-2 in carrageenan-injected paws, which occurred predominantly in macrophages.The cytokine interleukin 1β (IL-1β) is a major inducer of mPGES-1 during inflammation. Using A549 cells that express FABP5, IL-1β stimulation upregulated mPGES-1 expression, and mPGES-1 induction was attenuated in A549 cells bearing a knockdown of FABP5. IL-1β upregulates mPGES-1 via NF-kB, which activates the mPGES-1 promoter. Knockdown of FABP5 reduced the activation and nuclear translocation of NF-kB, and attenuated mPGES-1 promoter activity. Deletion of NF-kB binding sites within the mPGES-1 promoter abrogated the ability of FABP5 to inhibit mPGES-1 promoter activation. Collectively, these results position FABP5 as a novel regulator of mPGES-1 induction and PGE2 biosynthesis during inflammation. ________________________________________ Pain is a frequent reason for seeking medical care and approximately thirty percent of older adults experience chronic pain (1-3). Nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids are mainstay treatments for chronic pain. However, chronic NSAID use is associated with gastrointestinal hemorrhage and even acute NSAID use increases the incidence of myocardial FABP5 regulates mPGES-1 during inflammation2 infarctions (4,5). Chronic opioid use is associated with significant addiction and overdose liability (6)(7)(8). Consequently, there is a need to develop novel efficacious non-opioid analgesics.Fatty acid binding proteins (FABPs) are intracellular carriers for fatty acids and related bioactive lipids such as the endocannabinoid anandamide (9-11). In addition to the cytosolic transport of lipids, FABPs deliver ligands to the nucleus wherein they activate nuclear receptors (10,(12)(13)(14). There are ten FABP isoforms expressed in mammals and we previously demonstrated that pharmacological inhibition of FABP5 produces analgesic effects by enhancing endocannabinoid signaling (15)(16)(17)(18). We also demonstrated that FABP5 is expressed in nociceptors, p...