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Lysophosphatidic acid (LPA) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid Receptors [62, 23, 91, 144]) are activated by the endogenous phospholipid LPA. The first receptor, LPA1, was identified as ventricular zone gene-1 (vzg-1) [46], This discovery represented the beginning of the de-orphanisation of members of the endothelial differentiation gene (edg) family, as other LPA and sphingosine 1-phosphate (S1P) receptors were found. Five additional LPA receptors (LPA2,3,4,5,6) have since been identified [91] and their gene nomenclature codified for human LPAR1, LPAR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and Lpar1, Lpar2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function of their corresponding proteins. The crystal structure of LPA1 [17, 80, 2] and LPA6 [128] are solved and indicate that LPA accesses the extracellular binding pocket, consistent with its proposed delivery via autotaxin [17]. These studies have also implicated cross-talk with endocannabinoids via phosphorylated intermediates that can also activate these receptors. The binding affinities to LPA1 of unlabeled, natural LPA and anandamide phosphate (AEAp) were measured using backscattering interferometry (pKd = 9) [92, 115]. Utilization of this method indicated affinities that were 77-fold lower than when measured using radioactivity-based protocols [143]. Targeted deletion of LPA receptors has clarified signalling pathways and identified physiological and pathophysiological roles. Multiple groups have independently published validation of all six LPA receptors described in these tables, and further validation was achieved using a distinct read-out via a novel TGFα "shedding* assay [54]. LPA has been proposed to be a ligand for GPR35 [103], supported by a study revealing that LPA modulates macrophage function through GPR35 [60]. However chemokine (C-X-C motif) ligand 17 (CXCL17) is reported to be a ligand for GPR35/CXCR8 [85]. Moreover, LPA has also been described as an agonist for the transient receptor potential (Trp) ion channels TRPV1 [96] and TRPA1 [65]. All of these proposed non-GPCR receptor identities require confirmation and are not currently recognized as bona fide LPA receptors.

Sphingosine 1-phosphate (S1P) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid receptors [96]) are activated by the endogenous lipid sphingosine 1-phosphate (S1P). Originally cloned as orphan members of the endothelial differentiation gene (edg) family [16, 123], the receptors are currently designated as S1P1R through S1P5R [73, 16, 123]. Their gene nomenclature has been codified as human S1PR1, S1PR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and S1pr1, S1pr2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function. All S1P receptors (S1PRs) have been knocked-out in mice constitutively and in some cases, conditionally. S1PRs, particularly S1P1, are expressed throughout all mammalian organ systems. Ligand delivery occurs via two known carriers (or "chaperones"): albumin and HDL-bound apolipoprotein M (ApoM), the latter of which elicits biased agonist signaling by S1P1 in multiple cell types [18, 53]. The five S1PRs, two chaperones, and active cellular metabolism have complicated analyses of receptor ligand binding in native systems. Signaling pathways and physiological roles have been characterized through radioligand binding in heterologous expression systems, targeted deletion of the different S1PRs, and most recently, mouse models that report in vivo S1P1R activation [101, 103]. The structures of S1P1 [180, 69, 108, 184], S1P2 [32], S1P3[116, 187], and S1P5 [110, 185] are solved, and confirmed aspects of ligand binding, specificity, and receptor activation, determined previously through biochemical and genetic studies [69, 17]. fingolimod (FTY720), the first FDA-approved drug to target any of the lysophospholipid receptors, binds as a phosphorylated metabolite to four of the five S1PRs, and was the first oral therapy for multiple sclerosis (MS) [35]. Second-generation S1PR modulators siponimod, ozanimod, and ponesimod that target S1P1 and S1P5 are also FDA approved for the treatment of various MS forms [16, 123]. In 2021, ozanimod became the first S1PR modulator to be FDA approved for the treatment of ulcerative colitis [145]. The mechanisms of action of fingolimod and other S1PR-modulating drugs now in development include binding S1PRs in multiple organ systems, e.g., immune and nervous systems, although the precise nature of their receptor interactions requires clarification [141, 37, 63, 64].

Spinal cord injuries (SCIs) irreversibly disrupt spinal connectivity, leading to permanent neurological disabilities. Current medical treatments for reducing the secondary damage that follows the initial injury are limited to surgical decompression and anti-inflammatory drugs, so there is a pressing need for new therapeutic strategies. Inhibition of the type 2 lysophosphatidic acid receptor (LPA

SummaryFTY720 (fingolimod) is a sphingosine 1-phosphate (S1P) receptor modulator and sphingosine analogue approved for multiple sclerosis (MS) therapy, which can functionally antagonize the S1P receptor, S1P1. Vitamin B12 (B12) deficiency produces neurological manifestations resembling MS. Here, we report a new mechanism where FTY720 suppresses neuroinflammation by regulating B12 metabolic pathways. Nuclear RNA-seq of c-Fos-activated astrocytes (called ieAstrocytes) from experimental autoimmune encephalomyelitis (EAE) spinal cords identified up-regulation of CD320, a transcobalamin 2 (TCN2)-B12 receptor, by S1P1 inhibition. CD320 was reduced in MS plaques. Deficiency of CD320 or dietary B12 worsened EAE and eliminated FTY720’s efficacy, while concomitantly down-regulating type I interferon signaling. TCN2 functioned as a chaperone for FTY720 and sphingosine, which induced astrocytic CD320 internalization. An accompanying paper identified a requirement for astrocyte sphingosine kinases in FTY720 efficacy and its altered expression in MS brains, molecularly linking MS and B12 deficiency that can be accessed by sphingolipid/fingolimod metabolic pathways.

SummaryMultiple sclerosis (MS) is an immune-mediated demyelinating disease that alters central nervous system (CNS) functions. Relapsing-remitting MS (RRMS) is the most common form, which can transform into secondary-progressive MS (SPMS) that is associated with progressive neurodegeneration. Single-nucleus RNA sequencing (snRNA-seq) of MS lesions identified disease-related transcriptomic alterations; however, their relationship to non-lesioned MS brain regions has not been reported and which could identify prodromal or other disease susceptibility signatures. Here, snRNA-seq was used to generate high-quality RRMS vs. SPMS datasets of 33,197 nuclei from 8 normal-appearing MS brains, which revealed divergent cell type-specific changes. Notably, SPMS brains downregulated astrocytic sphingosine kinases (SPHK1/2) – the enzymes required to phosphorylate and activate the MS drug, fingolimod. This reduction was modeled with astrocyte-specific Sphk1/2 null mice in which fingolimod lost activity, supporting functionality of observed transcriptomic changes. These data provide an initial resource for studies of single cells from non-lesioned RRMS and SPMS brains.

Spinal cord injuries (SCIs) irreversibly disrupt spinal connectivity, leading to permanent neurological disabilities. Current medical treatments for reducing the secondary damage that follows the initial injury are limited to surgical decompression and anti-inflammatory drugs, so there is a pressing need for new therapeutic strategies. Inhibition of the type 2 lysophosphatidic acid receptor (LPA2) has recently emerged as a new potential pharmacological approach to decrease SCIassociated damage. Toward validating this receptor as a target in SCI, we have developed a new series of LPA2 antagonists, among which compound 54 (UCM14216) stands out as a potent and selective LPA2 receptor antagonist (Emax = 90%, IC50 = 1.9 μM, KD = 1.3 nM; inactive at LPA1,3−6 receptors). This compound shows efficacy in an in vivo mouse model of SCI in an LPA2-dependent manner, confirming the potential of LPA2 inhibition for providing a new alternative for treating SCI.

Ponesimod is a sphingosine 1-phosphate (S1P) receptor (S1PR) modulator that was recently approved for treating relapsing forms of multiple sclerosis (MS). Three other FDA-approved S1PR modulators for MS-fingolimod, siponimod, and ozanimod-share peripheral immunological effects via common S1P

Lysophospholipids are bioactive lipids and can signal through G-protein-coupled receptors (GPCRs). The best studied lysophospholipids are lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P). The mechanisms of lysophospholipid recognition by an active GPCR, and the activations of lysophospholipid GPCR–G-protein complexes remain unclear. Here we report single-particle cryo-EM structures of human S1P receptor 1 (S1P1) and heterotrimeric Gi complexes formed with bound S1P or the multiple sclerosis (MS) treatment drug Siponimod, as well as human LPA receptor 1 (LPA1) and Gi complexes in the presence of LPA. Our structural and functional data provide insights into how LPA and S1P adopt different conformations to interact with their cognate GPCRs, the selectivity of the homologous lipid GPCRs for S1P versus LPA, and the different activation mechanisms of these GPCRs by LPA and S1P. Our studies also reveal specific optimization strategies to improve the MS-treating S1P1-targeting drugs.

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes over 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.15538. G protein-coupled receptors are one of the six major pharmacological targets into which the Guide is divided, with the others being: ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2021, and supersedes data presented in the 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

Lysophosphatidic acid (LPA) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid Receptors [55, 19, 82, 129]) are activated by the endogenous phospholipid LPA. The first receptor, LPA1, was identified as ventricular zone gene-1 (vzg-1) [40], This discovery represented the beginning of the de-orphanisation of members of the endothelial differentiation gene (edg) family, as other LPA and sphingosine 1-phosphate (S1P) receptors were found. Five additional LPA receptors (LPA2,3,4,5,6) have since been identified [82] and their gene nomenclature codified for human LPAR1, LPAR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and Lpar1, Lpar2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function of their corresponding proteins. The crystal structure of LPA1 is solved and indicates that LPA accesses the extracellular binding pocket, consistent with its proposed delivery via autotaxin [13]. These studies have also implicated cross-talk with endocannabinoids via phosphorylated intermediates that can also activate these receptors. The binding affinities to LPA1 of unlabeled, natural LPA and anandamide phosphate (AEAp) were measured using backscattering interferometry (pKd = 9) [83, 104]. Utilization of this method indicated affinities that were 77-fold lower than when measured using radioactivity-based protocols [128]. Targeted deletion of LPA receptors has clarified signalling pathways and identified physiological and pathophysiological roles. Multiple groups have independently published validation of all six LPA receptors described in these tables, and further validation was achieved using a distinct read-out via a novel TGFα "shedding* assay [48]. LPA has been proposed to be a ligand for GPR35 [94], supported by a study revealing that LPA modulates macrophage function through GPR35 [54]. However chemokine (C-X-C motif) ligand 17 (CXCL17) is reported to be a ligand for GPR35/CXCR8 [76]. Moreover, LPA has also been described as an agonist for the transient receptor potential (Trp) ion channels TRPV1 [87] and TRPA1 [58]. All of these proposed non-GPCR receptor identities require confirmation and are not currently recognized as bona fide LPA receptors.

Sphingosine 1-phosphate (S1P) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid receptors [89]) are activated by the endogenous lipid sphingosine 1-phosphate (S1P). Originally cloned as orphan members of the endothelial differentiation gene (edg) family [16, 112], the receptors are currently designated as S1P1R through S1P5R [69, 16, 112]. Their gene nomenclature has been codified as human S1PR1, S1PR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and S1pr1, S1pr2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function. All S1P receptors have been knocked-out in mice constitutively and in some cases, conditionally. S1PRs, particularly S1P1, are expressed throughout all mammalian organ systems. Ligand delivery occurs via two known carriers (or "chaperones"): albumin and HDL-bound apolipoprotein M (ApoM), the latter of which elicits biased agonist signaling by S1P1 in multiple cell types [18, 49]. The five S1PRs, two chaperones, and active cellular metabolism have complicated analyses of receptor ligand binding in native systems. Signaling pathways and physiological roles have been characterized through radioligand binding in heterologous expression systems, targeted deletion of the different S1PRs, and most recently, mouse models that report in vivo S1P1R activation [94, 96]. A crystal structure of an S1P1-T4 fusion protein confirmed aspects of ligand binding, specificity, and receptor activation, determined previously through biochemical and genetic studies [65, 17]. fingolimod (FTY720), the first FDA-approved drug to target any of the lysophospholipid receptors, binds as a phosphorylated metabolite to four of the five S1PRs, and was the first oral therapy for multiple sclerosis (MS) [33]. siponimod and ozanimod that target S1P1 and S1P5 are also FDA approved for the treatment of various MS forms [16, 112]. The mechanisms of action of fingolimod and other S1PR-modulating drugs now in development include binding S1PRs in multiple organ systems, e.g., immune and nervous systems, although the precise nature of their receptor interactions requires clarification [129, 35, 59, 60].

Lysophosphatidic acid (LPA) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid Receptors [55, 19, 82, 129]) are activated by the endogenous phospholipid LPA. The first receptor, LPA1, was identified as ventricular zone gene-1 (vzg-1) [40], This discovery represented the beginning of the de-orphanisation of members of the endothelial differentiation gene (edg) family, as other LPA and sphingosine 1-phosphate (S1P) receptors were found. Five additional LPA receptors (LPA2,3,4,5,6) have since been identified [82] and their gene nomenclature codified for human LPAR1, LPAR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and Lpar1, Lpar2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function of their corresponding proteins. The crystal structure of LPA1 is solved and indicates that LPA accesses the extracellular binding pocket, consistent with its proposed delivery via autotaxin [13]. These studies have also implicated cross-talk with endocannabinoids via phosphorylated intermediates that can also activate these receptors. The binding affinities to LPA1 of unlabeled, natural LPA and anandamide phosphate (AEAp) were measured using backscattering interferometry (pKd = 9) [83, 104]. Utilization of this method indicated affinities that were 77-fold lower than when measured using radioactivity-based protocols [128]. Targeted deletion of LPA receptors has clarified signalling pathways and identified physiological and pathophysiological roles. Multiple groups have independently published validation of all six LPA receptors described in these tables, and further validation was achieved using a distinct read-out via a novel TGFα "shedding* assay [48]. LPA LPA has been proposed to be a ligand for GPCR35 [94], supported by a recent study revealing that LPA modulates macrophage function through GPR35 [54]. However chemokine (C-X-C motif) ligand 17 (CXCL17) is reported to be a ligand for GPR35/CXCR8 [76]. Moreover, LPA has also been described as an agonist for the transient receptor potential (Trp) ion channels TRPV1 [87] and TRPA1 [58]. All of these proposed non-GPCR receptor identities require confirmation and are not currently recognized as bona fide LPA receptors.

Polyunsaturated fatty acids (PUFAs) are essential FAs for human health. Cytochrome P450 oxygenates PUFAs to produce anti-inflammatory and pain-resolving epoxy fatty acids (EpFAs) and other oxylipins whose epoxide ring is opened by the soluble epoxide hydrolase (sEH/Ephx2), resulting in the formation of toxic and pro-inflammatory vicinal diols (dihydroxy-FAs). Pharmacological inhibition of sEH is a promising strategy for the treatment of pain, inflammation, cardiovascular diseases, and other conditions. We tested the efficacy of a potent, selective sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), in an animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). Prophylactic TPPU treatment significantly ameliorated EAE without affecting circulating white blood cell counts. TPPU accumulated in the spinal cords (SCs), which was correlated with plasma TPPU concentration. Targeted lipidomics in EAE SCs and plasma identified that TPPU blocked production of dihydroxy-FAs efficiently and increased some EpFA species including 12(13)-epoxy-octadecenoic acid (12(13)-EpOME) and 17(18)-epoxy-eicosatrienoic acid (17(18)-EpETE). TPPU did not alter levels of cyclooxygenase (COX-1/2) metabolites, while it increased 12-hydroxyeicosatetraenoic acid (12-HETE) and other 12/15-lipoxygenase metabolites. These analytical results are consistent with sEH inhibitors that reduce neuroinflammation and accelerate anti-inflammatory responses, providing the possibility that sEH inhibitors could be used as a disease modifying therapy, as well as for MS-associated pain relief.

Visual Abstract, Glutamate is the principal excitatory neurotransmitter in the human brain. Following neurotransmission, astrocytes remove excess extracellular glutamate to prevent neurotoxicity. Glutamate neurotoxicity has been reported in multiple neurologic diseases including multiple sclerosis (MS), representing a shared neurodegenerative mechanism. A potential modulator of glutamate neurotoxicity is the bioactive lysophospholipid sphingosine 1-phosphate (S1P) that signals through five cognate G-protein-coupled receptors, S1P1–S1P5; however, a clear link between glutamate homeostasis and S1P signaling has not been established. Here, S1P receptor knock-out mice, primary astrocyte cultures, and receptor-selective chemical tools were used to examine the effects of S1P on glutamate uptake. S1P inhibited astrocytic glutamate uptake in a dose-dependent manner and increased mitochondrial oxygen consumption, primarily through S1P2. Primary cultures of wild-type mouse astrocytes expressed S1P1,2,3 transcripts, and selective deletion of S1P1 and/or S1P3 in cerebral cortical astrocytes, did not alter S1P-mediated, dose-dependent inhibition of glutamate uptake. Pharmacological antagonists, S1P2-null astrocytes, and Gα12 hemizygous-null astrocytes indicated that S1P2-Gα12-Rho/ROCK signaling was primarily responsible for the S1P-dependent inhibition of glutamate uptake. In addition, S1P exposure increased mitochondrial oxygen consumption rates (OCRs) in wild-type astrocytes and reduced OCRs in S1P2-null astrocytes, implicating receptor selective metabolic consequences of S1P-mediated glutamate uptake inhibition. Astrocytic S1P-S1P2 signaling increased extracellular glutamate, which could contribute to neurotoxicity. This effect was not observed with the FDA-approved S1P receptor modulators, siponimod and fingolimod. Development and use of S1P2-selective antagonists may provide a new approach to reduce glutamate neurotoxicity in neurologic diseases.

Lysophosphatidic acid (LPA) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid Receptors [54, 18, 80, 125]) are activated by the endogenous phospholipid LPA. The first receptor, LPA1, was identified as ventricular zone gene-1 (vzg-1) [39], leading to deorphanisation of members of the endothelial differentiation gene (edg) family as other LPA receptors along with sphingosine 1-phosphate (S1P) receptors. Additional LPA receptor GPCRs were later identified. Gene names have been codified as LPAR1, etc. to reflect the receptor function of proteins. The crystal structure of LPA1 was solved and demonstrates extracellular LPA access to the binding pocket, consistent with proposed delivery via autotaxin [12]. These studies have also implicated cross-talk with endocannabinoids via phosphorylated intermediates that can also activate these receptors. The identified receptors can account for most, although not all, LPA-induced phenomena in the literature, indicating that a majority of LPA-dependent phenomena are receptor-mediated. Binding affinities of unlabeled, natural LPA and AEAp to LPA1 were measured using backscattering interferometry (pKd = 9) [81, 102]. Binding affinities were 77-fold lower than than values obtained using radioactivity [124]. Targeted deletion of LPA receptors has clarified signalling pathways and identified physiological and pathophysiological roles. Independent validation by multiple groups has been reported in the peer-reviewed literature for all six LPA receptors described in the tables, including further validation using a distinct read-out via a novel TGFα "shedding" assay [47]. LPA LPA has been proposed to be a ligand for GPCR35 [92], supported by a recent study revealing that LPA modulates macrophage function through GPR35 [53]. However CXCL17 is reported to be a ligand for GPR35/CXCR8 [74]. Moreover, LPA has also been described as an agonist for the transient receptor potential (Trp) ion channel TRPV1 [85] and TRPA1 [57]. All of these proposed non-GPCR receptor identities require confirmation and are not currently recognized as bona fide LPA receptors.

Lysophosphatidic acid (LPA) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid Receptors [54, 18, 80, 125]) are activated by the endogenous phospholipid LPA. The first receptor, LPA1, was identified as ventricular zone gene-1 (vzg-1) [39], leading to deorphanisation of members of the endothelial differentiation gene (edg) family as other LPA receptors along with sphingosine 1-phosphate (S1P) receptors. Additional LPA receptor GPCRs were later identified. Gene names have been codified as LPAR1, etc. to reflect the receptor function of proteins. The crystal structure of LPA1 was solved and demonstrates extracellular LPA access to the binding pocket, consistent with proposed delivery via autotaxin [12]. These studies have also implicated cross-talk with endocannabinoids via phosphorylated intermediates that can also activate these receptors. The identified receptors can account for most, although not all, LPA-induced phenomena in the literature, indicating that a majority of LPA-dependent phenomena are receptor-mediated. Binding affinities of unlabeled, natural LPA and AEAp to LPA1 were measured using backscattering interferometry (pKd = 9) [81, 102]. Binding affinities were 77-fold lower than than values obtained using radioactivity [124]. Targeted deletion of LPA receptors has clarified signalling pathways and identified physiological and pathophysiological roles. Independent validation by multiple groups has been reported in the peer-reviewed literature for all six LPA receptors described in the tables, including further validation using a distinct read-out via a novel TGFα "shedding" assay [47]. LPA LPA has been proposed to be a ligand for GPCR35 [92], supported by a recent study revealing that LPA modulates macrophage function through GPR35 [53]. However CXCL17 is reported to be a ligand for GPR35/CXCR8 [74]. Moreover, LPA has also been described as an agonist for the transient receptor potential (Trp) ion channel TRPV1 [85] and TRPA1 [57]. All of these proposed non-GPCR receptor identities require confirmation and are not currently recognized as bona fide LPA receptors.

Antibody specificity and sensitivity is required in basic and clinical research for ensuring scientific rigor and reproducibility, while off-target cross-reactivity could generate erroneous conclusions. Lysophosphatidic acid (LPA) is a bioactive lipid being targeted clinically by antibody strategies. Here, we reexamined binding properties of a commercially available monoclonal antibody (504B3) reported as specific for LPA using a free-solution assay measured in a compensated interferometric reader. The antibody showed comparable binding affinities to LPA and non-LPA lipids including phosphatidic acid (PA) and lysophosphatidylcholine (LPC). These results may alter conclusions drawn from current and past basic and clinical studies employing anti-LPA antibodies.

Lipids are essential for life. They store energy, constitute cellular membranes, serve as signaling molecules, and modify proteins. In the long history of lipid research, many drugs targeting lipid receptors and enzymes that are responsible for lipid metabolism and function have been developed and applied to a variety of diseases. For example, non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed medications for fever, pain, and inflammation. The NSAIDs block prostaglandin production by inhibiting cyclooxygenases. A recent innovative breakthrough in drug discovery for the lipid biology field was the development of the sphingosine 1-phosphate receptor modulators (fingolimod, siponimod and ozanimod) for the treatment of multiple sclerosis, which were approved by the United States Food and Drug Administration in 2010, 2019 and 2020, respectively. This review series of "Druggable Lipid Signaling Pathways" provides 9 outstanding reviews that summarize the currently available drugs that target lipid signaling pathways and also outlines future directions for drug discovery. The review chapters include lipid signaling pathways (prostanoids, leukotrienes, epoxy fatty acids, sphingolipids, lysophospholipids, endocannabinoids, and phosphoinositides) and lipid signaling proteins (lysophospholipid acyltransferases, phosphoinositide 3-kinase, and G protein-coupled receptors (GPCRs)). Drugs targeting lipid signaling pathways promise to be life changing magic for the future of human health and well-being.

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

IntroductionGiven an increasing use of dipeptidyl peptidase-4 (DPP-4) inhibitors to treat patients with type 2 diabetes mellitus in the real-world setting, we conducted a prospective observational study (Japan-based Clinical Research Network for Diabetes Registry: J-BRAND Registry) to elucidate the safety and efficacy profile of long-term usage of alogliptin.Research design and methodsWe registered 5969 patients from April 2012 through September 2014, who started receiving alogliptin (group A) or other classes of oral hypoglycemic agents (OHAs; group B), and were followed for 3 years at 239 sites nationwide. Safety was the primary outcome. Symptomatic hypoglycemia, pancreatitis, skin disorders of non-extrinsic origin, severe infections, and cancer were collected as major adverse events (AEs). Efficacy assessment was the secondary outcome and included changes in hemoglobin A1c (HbA1c), fasting blood glucose, fasting insulin and urinary albumin.ResultsOf the registered, 5150 (group A: 3395 and group B: 1755) and 5096 (3358 and 1738) were included for safety and efficacy analysis, respectively. Group A patients mostly (>90%) continued to use alogliptin. In group B, biguanides were the primary agents, while DPP-4 inhibitors were added in up to ~36% of patients. The overall incidence of AEs was similar between the two groups (42.7% vs 42.2%). Kaplan-Meier analysis revealed the incidence of cancer was significantly higher in group A than in group B (7.4% vs 4.8%, p=0.040), while no significant incidence difference was observed in the individual cancer. Multivariate Cox regression analysis revealed that the imbalanced patient distribution (more elderly patients in group A than in group B), but not alogliptin usage per se, contributed to cancer development. The incidence of other major AE categories was with no between-group difference. Between-group difference was not detected, either, in the incidence of microvascular and macrovascular complications. HbA1c and fasting glucose decreased significantly at the 0.5-year visit and nearly plateaued thereafter in both groups.ConclusionsAlogliptin as a representative of DPP-4 inhibitors was safe and durably efficacious when used alone or with other OHAs for patients with type 2 diabetes in the real world setting.

BACKGROUND Rapid urinary trypsinogen-2 dipstick test and levels of urinary trypsinogen-2 and trypsinogen activation peptide (TAP) concentration have been reported as prognostic markers for the diagnosis of acute pancreatitis. AIM To reconfirm the validity of all these markers in the diagnosis of acute pancreatitis by undertaking a multi-center study in Japan. METHODS Patients with acute abdominal pain were recruited from 17 medical institutions in Japan from April 2009 to December 2012. Urinary and serum samples were collected twice, at enrollment and on the following day for measuring target markers. The diagnosis and severity assessment of acute pancreatitis were assessed based on prognostic factors and computed tomography (CT) Grade of the Japanese Ministry of Health, Labour, and Welfare criteria. RESULTS A total of 94 patients were enrolled during the study period. The trypsinogen-2 dipstick test was positive in 57 of 78 patients with acute pancreatitis (sensitivity, 73.1%) and in 6 of 16 patients with abdominal pain but without any evidence of acute pancreatitis (specificity, 62.5%). The area under the curve (AUC) score of urinary trypsinogen-2 according to prognostic factors was 0.704, which was highest in all parameter. The AUC scores of urinary trypsinogen-2 and TAP according to CT Grade were 0.701 and 0.692, respectively, which shows higher than other pancreatic enzymes. The levels of urinary trypsinogen-2 and TAP were significantly higher in patients with extended extra-pancreatic inflammation as evaluated by CT Grade. CONCLUSION We reconfirmed urinary trypsinogen-2 dipstick test is useful as a marker for the diagnosis of acute pancreatitis. Urinary trypsinogen-2 and TAP may be considered as useful markers to determine extra-pancreatic inflammation in acute pancreatitis.

Cerebral edema is a life-threatening neurological condition characterized by brain swelling due to the accumulation of excess fluid both intracellularly and extracellularly. Fulminant hepatic failure (FHF) develops cerebral edema by disrupting blood-brain barrier (BBB). However, the mechanisms by which mediator induces brain edema in FHF remain to be elucidated. Here, we assessed a linkage between brain edema and lysophosphatidic acid (LPA) signaling by utilizing an animal model of FHF and in vitro BBB model. Azoxymethane-treated mice developed FHF and hepatic encephalopathy, associated with higher autotaxin (ATX) activities in serum than controls. Using in vitro BBB model, LPA disrupted the structural integrity of tight junction proteins including claudin-5, occludin, and ZO-1. Furthermore, LPA decreased transendothelial electrical resistances in in vitro BBB model, and induced cell contraction in brain endothelial monolayer cultures, both being inhibited by a Rho-associated protein kinase inhibitor, Y-27632. The brain capillary endothelial cells predominantly expressed LPA6 mRNA, whose knockdown blocked the LPA-induced endothelial cell contraction. Taken together, the up-regulation of serum ATX in hepatic encephalopathy may activate the LPA-LPA6-G12/13-Rho pathway in brain capillary endothelial cells, leading to enhancement of BBB permeability and brain edema.

Lipids are essential for life. They store energy, constitute cellular membranes, serve as signaling molecules, and modify proteins. In the long history of lipid research, many drugs targeting lipid receptors and enzymes that are responsible for lipid metabolism and function have been developed and applied to a variety of diseases. For example, non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed medications for fever, pain, and inflammation. The NSAIDs block prostaglandin production by inhibiting cyclooxygenases. A recent innovative breakthrough in drug discovery for the lipid biology field was the development of the sphingosine 1-phosphate receptor modulators (fingolimod, siponimod and ozanimod) for the treatment of multiple sclerosis, which were approved by the United States Food and Drug Administration in 2010, 2019 and 2020, respectively. This review series of “Druggable Lipid Signaling Pathways” provides 9 outstanding reviews that summarize the currently available drugs that target lipid signaling pathways and also outlines future directions for drug discovery. The review chapters include lipid signaling pathways (prostanoids, leukotrienes, epoxy fatty acids, sphingolipids, lysophospholipids, endocannabinoids, and phosphoinositides) and lipid signaling proteins (lysophospholipid acyltransferases, phosphoinositide 3-kinase, and G protein-coupled receptors (GPCRs)). Drugs targeting lipid signaling pathways promise to be life changing magic for the future of human health and well-being.

Neuropathic pain (NP) is a complex chronic pain state with a prevalence of almost 10% in the general population. Pharmacological options for NP are limited and weakly effective, so there is a need to develop more efficacious NP attenuating drugs. Activation of the type 1 lysophosphatidic acid (LPA(1)) receptor is a crucial factor in the initiation of NP. Hence, it is conceivable that a functional antagonism strategy could lead to NP mitigation. Here we describe a new series of LPA(1) agonists among which derivative (S)-17 (UCM-05194) stands out as the most potent and selective LPA(1) receptor agonist described so far (E(max) = 118%, EC(50) = 0.24 µM, K(D) = 19.6 nM; inactive at autotaxin and LPA(2-6) receptors). This compound induces characteristic LPA(1)-mediated cellular effects and prompts the internalization of the receptor leading to its functional inactivation in primary sensory neurons and to an efficacious attenuation of the pain perception in an in vivo model of NP.

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

Neuropathic pain (NP) is a complex chronic pain state with a prevalence of almost 10% in the general population. Pharmacological options for NP are limited and slightly effective, so there is a need of developing more efficacious NP attenuating drugs. Activation of the type 1 lysophosphatidic acid (LPA(1)) receptor is a crucial factor in the initiation of NP. Hence, it is conceivable that a functional antagonism strategy could lead to NP mitigation. Here we describe a new series of LPA(1) agonists among which derivative (S)-17 (UCM-05194) stands out as the most potent and selective LPA(1) receptor agonist described so far (E(max)=118%, EC(50)=0.24 μM, K(D)=19.6 nM; inactive at autotaxin and LPA(2–6) receptors). This compound induces characteristic LPA(1)-mediated cellular effects and prompts the internalization of the receptor leading to its functional inactivation in primary sensory neurons and to an efficacious attenuation of the pain perception in an in vivo model of NP.

Posthemorrhagic hydrocephalus (PHH) in premature infants is a common neurological disorder treated with invasive neurosurgical interventions. Patients with PHH lack effective therapeutic interventions and suffer chronic comorbidities. Here, we report a murine lysophosphatidic acid (LPA)–induced postnatal PHH model that maps neurodevelopmentally to premature infants, a clinically accessible high-risk population, and demonstrates ventriculomegaly with increased intracranial pressure. Administration of LPA, a blood-borne signaling lipid, acutely disrupted the ependymal cells that generate CSF flow, which was followed by cell death, phagocytosis, and ventricular surface denudation. This mechanism is distinct from a previously reported fetal model that induces PHH through developmental alterations. Analyses of LPA receptor–null mice identified LPA1 and LPA3 as key mediators of PHH. Pharmacological blockade of LPA1 prevented PHH in LPA-injected animals, supporting the medical tractability of LPA receptor antagonists in preventing PHH and negative CNS sequelae in premature infants.

Bioactive lipids, or lipid mediators, are utilized for intercellular communications. They are rapidly produced in response to various stimuli and exported to extracellular spaces followed by binding to cell surface G protein-coupled receptors (GPCRs) or nuclear receptors. Many drugs targeting lipid signaling such as non-steroidal anti-inflammatory drugs (NSAIDs), prostaglandins, and antagonists for lipid GPCRs are in use. For example, the sphingolipid analog, fingolimod (also known as FTY720), was the first oral disease-modifying therapy (DMT) for relapsing-remitting multiple sclerosis (MS), whose mechanisms of action (MOA) includes sequestration of pathogenic lymphocytes into secondary lymphoid organs, as well as astrocytic modulation, via down-regulation of the sphingosine 1-phosphate (S1P) receptor, S1P

Sphingosine 1-phosphate (S1P) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid receptors [70]) are activated by the endogenous lipid sphingosine 1-phosphate (S1P). Originally cloned as orphan members of the endothelial differentiation gene (edg) family, current gene names have been designated as S1P1R through S1P5R [52]. S1PRs, particularly S1P1, are expressed throughout all mammalian organ systems. Ligand delivery occurs via two known carriers (or "chaperones"): albumin and HDL-bound apolipoprotein M (ApoM), the latter of which elicits biased agonist signaling by S1P1 in multiple cell types [15, 39]. The five S1PRs, two chaperones, and active cellular metabolism have complicated analyses of receptor ligand binding in native systems. Signaling pathways and physiological roles have been characterized through radioligand binding in heterologous expression systems, targeted deletion of the different S1PRs, and most recently, mouse models that report in vivo S1P1R activation [74, 76]. A crystal structure of an S1P1-T4 fusion protein confirmed aspects of ligand binding, specificity, and receptor activation determined previously through biochemical and genetic studies [48, 14]. fingolimod (FTY720), the first drug to target any of the lysophospholipid receptors, binds to four of the five S1PRs, and was the first oral therapy for multiple sclerosis [26]. The mechanisms of action of fingolimod and other S1PR modulating drugs in development include binding S1PRs in multiple organ systems, e.g., immune and nervous systems, although the precise nature of their receptor interactions requires clarification [107, 28, 43, 44].

In the accompanying comment1, Kim et al. concluded that somatic gene recombination (SGR) and amyloid precursor protein (APP) genomic complementary DNAs (gencDNAs) in brain are contamination artifacts and do not naturally exist. We disagree. Here we address the three types of analyses used by Kim et al. to reach their conclusions: informatic contaminant identification, plasmid PCR, and single-cell sequencing. Additionally, Kim et al. requested “reads supporting novel APP insertion breakpoints,” and we now provide 10 different examples that support APP gencDNA insertion within eight chromosomes beyond wildtype APP on chromosome 21 from Alzheimer’s disease (AD) samples. If SGR exists as experimentally supported here and previously2,3, contamination scenarios become moot. Our informatic analyses of data generated by an independent laboratory (Park et al.)4, complement and are entirely consistent with what Lee et al.2 presented via nine distinct lines of evidence, in addition to three from a prior publication3. Plasmid contamination was identified in a single pull-down dataset after publication of Lee et al.2; however subsequent analyses did not alter any of our conclusions including those of our prior publications3,5 and plasmid contamination-free replication of this approach by ourselves and others supported the original conclusions. Novel retro-insertion sites, alterations of APP gencDNA number and form with cell type from the same brain and pathogenic SNVs occurring only in AD, all support the existence of APP gencDNAs produced by SGR.

Glutamate is the principal excitatory neurotransmitter in the human brain. Following neurotransmission, astrocytes remove excess extracellular glutamate to prevent neurotoxicity. Glutamate neurotoxicity has been reported in multiple neurological diseases including multiple sclerosis (MS), representing a shared neurodegenerative mechanism. A potential modulator of glutamate neurotoxicity is the bioactive lysophospholipid sphingosine 1-phosphate (S1P) that signals through five cognate G protein-coupled receptors (GPCRs), S1P1 - S1P5, however, a clear link between glutamate homeostasis and S1P signaling has not been established. Here, S1P receptor knock-out mice, primary astrocyte cultures, and receptor-selective chemical tools were used to examine the effects of S1P on glutamate uptake. S1P inhibited astrocytic glutamate uptake in a dose-dependent manner and increased mitochondrial oxygen consumption, primarily through S1P2. Primary cultures of wild-type mouse astrocytes expressed S1P1,2,3 transcripts, and selective deletion of S1P1 and/or S1P3 in cerebral cortical astrocytes, did not alter S1P-mediated, dose-dependent inhibition of glutamate uptake. Pharmacological antagonists, S1P2-null astrocytes, and Gα12 hemizygous-null astrocytes indicated that S1P2-Gα12-Rho/ROCK signaling was primarily responsible for the S1P-dependent inhibition of glutamate uptake. In addition, S1P exposure increased mitochondrial oxygen consumption rates (OCRs) in wild-type astrocytes, and reduced OCRs in S1P2-null astrocytes, implicating receptor selective metabolic consequences of S1P-mediated glutamate uptake inhibition. Astrocytic S1P-S1P2 signaling increased extracellular glutamate, which could contribute to neurotoxicity. This effect was not observed with the FDA-approved S1P receptor modulators, siponimod and fingolimod. Development and use of S1P2-selective antagonists may provide a new approach to reduce glutamate neurotoxicity in neurological diseases. Significance statement Extracellular glutamate is excitotoxic and its levels are controlled by astrocyte uptake. Sphingosine 1-phosphate (S1P) is a bioactive lipid originating from cell membrane sphingolipids that associates with carrier molecules like albumin, ApoM, and ApoA4 to produce cellular effects. S1P signals extracellularly through five GPCRs and it is found in higher concentrations in neurological diseases like multiple sclerosis where excitotoxic neurodegeneration has been implicated. Here we show that astrocytic S1P2 activation by S1P results in glutamate uptake inhibition to promote excitotoxic damage. S1P receptor modulators, including approved drugs for treating multiple sclerosis (e.g., fingolimod (FTY720) and siponimod (BAF312)), do not engage S1P2, thus avoiding glutamate uptake inhibition. S1P2 antagonists may provide a means to reduce S1P-induced glutamate neurotoxicity and ameliorate neurological diseases.

Arachidonic acid (AA), a representative ω6-polyunsaturated fatty acid (PUFA), is a precursor of 2-series prostaglandins (PGs) that play important roles in inflammation, pain, fever, and related disorders including cardiovascular diseases. Eating fish or supplementation with the ω3-PUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is widely assumed to be beneficial in preventing cardiovascular diseases. A proposed mechanism for a cardio-protective role of ω3-PUFAs assumes competition between AA and ω3-PUFAs for cyclooxygenases (COX), leading to reduced production of 2-series PGs. In this study, we have used a systems biology approach to integrate existing knowledge and novel high-throughput data that facilitates a quantitative understanding of the molecular mechanism of ω3- and ω6-PUFA metabolism in mammalian cells. We have developed a quantitative computational model of the competitive metabolism of AA and EPA via the COX pathway through a two-step matrix-based approach to estimate the rate constants. This model was developed by using lipidomic data sets that were experimentally obtained from EPA-supplemented ATP-stimulated RAW264.7 macrophages. The resulting model fits the experimental data well for all metabolites and demonstrates that the integrated metabolic and signaling networks and the experimental data are consistent with one another. The robustness of the model was validated through parametric sensitivity and uncertainty analysis. We also validated the model by predicting the results from other independent experiments involving AA- and DHA-supplemented ATP-stimulated RAW264.7 cells using the parameters estimated with EPA. Furthermore, we showed that the higher affinity of EPA binding to COX compared with AA was able to inhibit AA metabolism effectively. Thus, our model captures the essential features of competitive metabolism of ω3- and ω6-PUFAs.

LPA, a blood-borne signaling lipid, induces neonatal hydrocephalus by damaging ependymal cells through LPA1/3 overactivation., Posthemorrhagic hydrocephalus (PHH) in premature infants is a common neurological disorder treated with invasive neurosurgical interventions. Patients with PHH lack effective therapeutic interventions and suffer chronic comorbidities. Here, we report a murine lysophosphatidic acid (LPA)–induced postnatal PHH model that maps neurodevelopmentally to premature infants, a clinically accessible high-risk population, and demonstrates ventriculomegaly with increased intracranial pressure. Administration of LPA, a blood-borne signaling lipid, acutely disrupted the ependymal cells that generate CSF flow, which was followed by cell death, phagocytosis, and ventricular surface denudation. This mechanism is distinct from a previously reported fetal model that induces PHH through developmental alterations. Analyses of LPA receptor–null mice identified LPA1 and LPA3 as key mediators of PHH. Pharmacological blockade of LPA1 prevented PHH in LPA-injected animals, supporting the medical tractability of LPA receptor antagonists in preventing PHH and negative CNS sequelae in premature infants.

Fingolimod (FTY720, Gilenya) was the first US Food and Drug Administration–approved oral therapy for relapsing forms of multiple sclerosis (MS). Research on modified fungal metabolites converged with basic science studies that had identified lysophospholipid (LP) sphingosine 1-phosphate (S1P) receptors, providing mechanistic insights on fingolimod while validating LP receptors as drug targets. Mechanism of action (MOA) studies identified receptor-mediated processes involving the immune system and the central nervous system (CNS). These dual actions represent a more general theme for S1P and likely other LP receptor modulators. Fingolimod's direct CNS activities likely contribute to its efficacy in MS, with particular relevance to treating progressive disease stages and forms that involve neurodegeneration. The evolving understanding of fingolimod's MOA has provided strategies for developing next-generation compounds with superior attributes, suggesting new ways to target S1P as well as other LP receptor modulators for novel therapeutics in the CNS and other organ systems.