Fatty acid amide biosynthesis: a possible new role for peptidylglycine alpha-amidating enzyme and acyl-coenzyme A: glycine N-acyltransferase

Synthesis, Quantification, and Characterization of Fatty Acid Amides from In Vitro and In Vivo Sources

Fatty acid amides are a diverse family of underappreciated, biologically occurring lipids. Herein, the methods for the chemical synthesis and subsequent characterization of specific members of the fatty acid amide family are described. The synthetically prepared fatty acid amides and those obtained commercially are used as standards for the characterization and quantification of the fatty acid amides produced by biological systems, a fatty acid amidome. The fatty acid amidomes from mouse N₁₈TG₂ cells, sheep choroid plexus cells, Drosophila melanogaster, Bombyx mori, Apis mellifera, and Tribolium castaneum are presented.

N-Acyl Amino Acids: Metabolism, Molecular Targets, and Role in Biological Processes

The lipid signal is becoming increasingly crowded as increasingly fatty acid amide derivatives are being identified and considered relevant therapeutic targets. The identification of N-arachidonoyl-ethanolamine as endogenous ligand of cannabinoid type-1 and type-2 receptors as well as the development of different–omics technologies have the merit to have led to the discovery of a huge number of naturally occurring N-acyl-amines. Among those mediators, N-acyl amino acids, chemically related to the endocannabinoids and belonging to the complex lipid signaling system now known as endocannabinoidome, have been rapidly growing for their therapeutic potential. Here, we review the current knowledge of the mechanisms for the biosynthesis and inactivation of the N-acyl amino acids, as well as the various molecular targets for some of the N-acyl amino acids described so far.

Targeting the 5-HT2C Receptor in Biological Context and the Current State of 5-HT2C Receptor Ligand Development

Serotonin (5-HT) 5-HT2C receptor (5-HT2CR) is recognized as a critical mediator of diseaserelated pathways and behaviors based upon actions in the central nervous system (CNS). Since 5-HT2CR is a class A G protein-coupled receptor (GPCR), drug discovery efforts have traditionally pursued the activation of the receptor through synthetic ligands with agonists proposed for the treatment of obesity, substance use disorders and impulse control disorders while antagonists may add value for the treatment of anxiety, depression and schizophrenia. The most significant agonist discovery to date is the FDAapproved anti-obesity medication lorcaserin. In recent years, efforts towards developing other mechanisms to enhance receptor function have resulted in the discovery of Positive Allosteric Modulators (PAMs) for the 5-HT2CR, with several molecule series now reported. The biological significance and context for signaling and function of the 5-HT2CR, and the current status of 5-HT2CR agonists and PAMs are discussed in this review.

Ciliary and cytoskeletal functions of an ancient monooxygenase essential for bioactive amidated peptide synthesis

Many secreted peptides used for cell-cell communication require conversion of a C-terminal glycine to an amide for bioactivity. This reaction is catalyzed only by the integral membrane protein peptidylglycine α-amidating monooxygenase (PAM). PAM has been highly conserved and is found throughout the metazoa; PAM-like sequences are also present in choanoflagellates, filastereans, unicellular and colonial chlorophyte green algae, dinoflagellates and haptophytes. Recent studies have revealed that in addition to playing a key role in peptidergic signaling, PAM also regulates ciliogenesis in vertebrates, planaria and chlorophyte algae, and is required for the stability of actin-based microvilli. Here we briefly introduce the basic principles involved in ciliogenesis, the sequential reactions catalyzed by PAM and the trafficking of PAM through the secretory and endocytic pathways. We then discuss the multi-faceted roles this enzyme plays in the formation and maintenance of cytoskeleton-based cellular protrusions and propose models for how PAM protein and amidating activity might contribute to ciliogenesis. Finally, we consider why some ciliated organisms lack PAM, and discuss the potential ramifications of ciliary localized PAM for the endocrine features commonly observed in patients with ciliopathies.

Primary fatty amides in plasma associated with brain amyloid burden, hippocampal volume, and memory in the European Medical Information Framework for Alzheimer's Disease biomarker discovery cohort

Introduction:

A critical and as-yet unmet need in Alzheimer’s disease (AD) is the discovery of peripheral small molecule biomarkers. Given that brain pathology precedes clinical symptom onset, we set out to test whether metabolites in blood associated with pathology as indexed by cerebrospinal fluid (CSF) AD biomarkers.

Methods:

This study analyzed 593 plasma samples selected from the European Medical Information Framework for Alzheimer’s Disease Multimodal Biomarker Discovery study, of individuals who were cognitively healthy (n = 242), had mild cognitive impairment (n = 236), or had AD-type dementia (n = 115). Logistic regressions were carried out between plasma metabolites (n = 883) and CSF markers, magnetic resonance imaging, cognition, and clinical diagnosis.

Results:

Eight metabolites were associated with amyloid b and one with t-tau in CSF, these were primary fatty acid amides (PFAMs), lipokines, and amino acids. From these, PFAMs, glutamate, and aspartate also associated with hippocampal volume and memory.

Discussion:

PFAMs have been found increased and associated with amyloid b burden in CSF and clinical measures.

Bm-iAANAT and its potential role in fatty acid amide biosynthesis in Bombyx mori

The purpose of this research is to unravel the substrate specificity and kinetic properties of an insect arylalkylamine N-acyltransferase from Bombyx mori (Bm-iAANAT) and to determine if this enzyme will catalyze the formation of long chain N-acylarylalkylamides in vitro. However, the determination of substrates and products for Bm-iAANAT in vitro is no guarantee that these same molecules are substrates and products for the enzyme in the organism. Therefore, RT-PCR was performed to detect the Bm-iAANAT transcripts and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) analysis was performed on purified lipid extracts from B. mori larvae (fourth instar, Bmi4) to determine if long chain fatty acid amides are produced in B. mori. Ultimately, we found that recombinant Bm-iAANAT will utilize long-chain acyl-CoA thioesters as substrates and identified Bm-iAANAT transcripts and long-chain fatty acid amides in Bmi4. Together, these data show Bm-iAANAT will catalyze the formation of long-chain N-acylarylalkylamides in vitro and provide evidence demonstrating that Bm-iAANAT has a role in fatty acid amide biosynthesis in B. mori, as well.

Structural and Mechanistic Analysis of Drosophila melanogaster Agmatine N-Acetyltransferase, an Enzyme that Catalyzes the Formation of N-Acetylagmatine

Agmatine N-acetyltransferase (AgmNAT) catalyzes the formation of N-acetylagmatine from acetyl-CoA and agmatine. Herein, we provide evidence that Drosophila melanogaster AgmNAT (CG15766) catalyzes the formation of N-acetylagmatine using an ordered sequential mechanism; acetyl-CoA binds prior to agmatine to generate an AgmNAT•acetyl-CoA•agmatine ternary complex prior to catalysis. Additionally, we solved a crystal structure for the apo form of AgmNAT with an atomic resolution of 2.3 Å, which points towards specific amino acids that may function in catalysis or active site formation. Using the crystal structure, primary sequence alignment, pH-activity profiles, and site-directed mutagenesis, we evaluated a series of active site amino acids in order to assign their functional roles in AgmNAT. More specifically, pH-activity profiles identified at least one catalytically important, ionizable group with an apparent pK_a of ~7.5, which corresponds to the general base in catalysis, Glu-34. Moreover, these data led to a proposed chemical mechanism, which is consistent with the structure and our biochemical analysis of AgmNAT.

Glycine N-acyltransferase-like 3 is responsible for long-chain N-acylglycine formation in N18TG2 cells

Long-chain fatty acid amides are signaling lipids found in mammals and other organisms; however, details of the metabolic pathways for the N-acylglycines and primary fatty acid amides (PFAMs) have remained elusive. Heavy-labeled precursor and subtraction lipidomic experiments in mouse neuroblastoma N18TG2 cells, a model cell line for the study of fatty acid amide metabolism, establish the biosynthetic pathways for the N-acylglycines and the PFAMs. We provide evidence that the N-acylglycines are formed by a long-chain specific glycine-conjugating enzyme, glycine N-acyltransferase-like 3 (GLYATL3). siRNA knockdown of GLYATL3 in the N18TG2 cells resulted in a decrease in the levels of the N-acylglycines and the PFAMs. This is the first report of an enzyme responsible for long-chain N-acylglycine production in cellula. The production of the PFAMs in N18TG2 cells was reported to occur by the oxidative cleavage of the N-acylglycines, as catalyzed by peptidylglycine α-amidating monooxygenase (PAM). siRNA knockdown of PAM resulted in an accumulation of [(13)C18]N-oleoylglycine and decreased levels of [(13)C18]oleamide when the N18TG2 cells were grown in the presence of [(13)C18]oleic acid. The addition of [1-(13)C]palmitate to the N18TG2 cell growth media led to the production of a family of [1-(13)C]palmitoylated fatty acid amides, consistent with the biosynthetic pathways detailed herein.

Probing the chemical mechanism and critical regulatory amino acid residues of Drosophila melanogaster arylalkylamine N-acyltransferase like 2

Arylalkylamine N-acyltransferase like 2 (AANATL2) catalyzes the formation of N-acylarylalkylamides from the corresponding acyl-CoA and arylalkylamine. The N-acylation of biogenic amines in Drosophila melanogaster is a critical step for the inactivation of neurotransmitters, cuticle sclerotization, and melatonin biosynthesis. In addition, D. melanogaster has been used as a model system to evaluate the biosynthesis of fatty acid amides: a family of potent cell signaling lipids. We have previously showed that AANATL2 catalyzes the formation of N-acylarylakylamides, including long-chain N-acylserotonins and N-acyldopamines. Herein, we define the kinetic mechanism for AANATL2 as an ordered sequential mechanism with acetyl-CoA binding first followed by tyramine to generate the ternary complex prior to catalysis. Bell shaped kcat,app - acetyl-CoA and (kcat/Km)app - acetyl-CoA pH-rate profiles identified two apparent pKa,app values of ∼7.4 and ∼8.9 that are critical to catalysis, suggesting the AANATL2-catalyzed formation of N-acetyltyramine occurs through an acid/base chemical mechanism. Site-directed mutagenesis of a conserved glutamate that corresponds to the catalytic base for other D. melanogaster AANATL enzymes did not produce a substantial depression in the kcat,app value nor did it abolish the pKa,app value attributed to the general base in catalysis (pKa ∼7.4). These data suggest that AANATL2 catalyzes the formation of N-acylarylalkylamides using either different catalytic residues or a different chemical mechanism relative to other D. melanogaster AANATL enzymes. In addition, we constructed other site-directed mutants of AANATL2 to help define the role of targeted amino acids in substrate binding and/or enzyme catalysis.

Altered plasma lysophosphatidylcholines and amides in non-obese and non-diabetic subjects with borderline-to-moderate hypertriglyceridemia: a case-control study

Hypertriglyceridemia (HTG) is a risk factor for atherosclerotic cardiovascular disease (CVD). We investigated alterations in plasma metabolites associated with borderline-to-moderate HTG (triglycerides (TG) 150-500 mg/dL). Using UPLC-LTQ-Orbitrap mass spectrometry analysis, the metabolomics profiles of 111 non-diabetic and non-obese individuals with borderline-to-moderate HTG were compared with those of 111 age- and sex-matched controls with normotriglyceridemia (NTG, TG <150 mg/dL). When compared to the NTG control group, the HTG group exhibited higher plasma levels of lysophosphatidylcholines (lysoPCs), including C14:0 (q = 0.001) and C16:0 (q = 1.8E-05), and several amides, including N-ethyldodecanamide (q = 2.9E-05), N-propyldodecanamide (q = 3.5E-05), palmitoleamide (q = 2.9E-06), and palmitic amide (q = 0.019). The metabolomic profiles of the HTG group also exhibited lower plasma levels of cis-4-octenedioic acid (q<1.0E-9) and docosanamide (q = 0.002) compared with those of the NTG controls. LysoPC 16:0 and palmitoleamide emerged as the primary metabolites able to discriminate the HTG group from the NTG group in a partial least-squares discriminant analysis and were positively associated with the fasting triglyceride levels. We identified alterations in lysoPCs, amides, and cis-4-octenedioic acid among non-diabetic and non-obese individuals with borderline-to-moderate HTG. These results provide novel insights into the metabolic alterations that occur in the early metabolic stages of HTG. This information may facilitate the design of early interventions to prevent disease progression.

C-terminal modification of monoclonal antibody drugs: amidated species as a general product-related substance

Twelve therapeutic mAbs, comprising 10 IgG1s and 2 IgG4s, were analyzed by a peptide mapping technique to detect and quantify C-terminal modifications. C-terminal amidated structures were found in 8 out of the 12 mAbs. An in vitro study using a commercially available peptidylglycine alpha-amidating monooxygenase (PAM) revealed that both IgG1 and IgG4 can be substrates for PAM. This study showed that C-terminal amidation is a general C-terminal modification on the heavy chains of therapeutic mAbs and that C-terminal amidation of mAbs can be catalyzed by a certain PAM(s) in the Chinese hamster ovary (CHO) cells that are widely used for manufacturing therapeutic mAbs.

A "neural" enzyme in nonbilaterian animals and algae: preneural origins for peptidylglycine α-amidating monooxygenase

Secreted peptides, produced by enzymatic processing of larger precursor molecules, are found throughout the animal kingdom and play important regulatory roles as neurotransmitters and hormones. Many require a carboxy-terminal modification, involving the conversion of a glycine residue into an α-amide, for their biological activity. Two sequential enzymatic activities catalyze this conversion: a monooxygenase (peptidylglycine α-hydroxylating monooxygenase or PHM) and an amidating lyase (peptidyl-α-hydroxyglycine α-amidating lyase or PAL). In vertebrates, these activities reside in a single polypeptide known as peptidylglycine α-amidating monooxygenase (PAM), which has been extensively studied in the context of neuropeptide modification. Bifunctional PAMs have been reported from some invertebrates, but the phylogenetic distribution of PAMs and their evolutionary relationship to PALs and PHMs is unclear. Here, we report sequence and expression data for two PAMs from the coral Acropora millepora (Anthozoa, Cnidaria), as well as providing a comprehensive survey of the available sequence data from other organisms. These analyses indicate that bifunctional PAMs predate the origins of the nervous and endocrine systems, consistent with the idea that within the Metazoa their ancestral function may have been to amidate epitheliopeptides. More surprisingly, the phylogenomic survey also revealed the presence of PAMs in green algae (but not in higher plants or fungi), implying that the bifunctional enzyme either predates the plant/animal divergence and has subsequently been lost in a number of lineages or perhaps that convergent evolution or lateral gene transfer has occurred. This finding is consistent with recent discoveries that other molecules once thought of as "neural" predate nervous systems.

Primary fatty acid amide metabolism: conversion of fatty acids and an ethanolamine in N18TG2 and SCP cells

Primary fatty acid amides (PFAM) are important signaling molecules in the mammalian nervous system, binding to many drug receptors and demonstrating control over sleep, locomotion, angiogenesis, and many other processes. Oleamide is the best-studied of the primary fatty acid amides, whereas the other known PFAMs are significantly less studied. Herein, quantitative assays were used to examine the endogenous amounts of a panel of PFAMs, as well as the amounts produced after incubation of mouse neuroblastoma N(18)TG(2) and sheep choroid plexus (SCP) cells with the corresponding fatty acids or N-tridecanoylethanolamine. Although five endogenous primary amides were discovered in the N(18)TG(2) and SCP cells, a different pattern of relative amounts were found between the two cell lines. Higher amounts of primary amides were found in SCP cells, and the conversion of N-tridecanoylethanolamine to tridecanamide was observed in the two cell lines. The data reported here show that the N(18)TG(2) and SCP cells are excellent model systems for the study of PFAM metabolism. Furthermore, the data support a role for the N-acylethanolamines as precursors for the PFAMs and provide valuable new kinetic results useful in modeling the metabolic flux through the pathways for PFAM biosynthesis and degradation.

N-acylethanolamines as novel alcohol dehydrogenase 3 substrates

N-acylethanolamines (NAEs) are members of the fatty acid amide family. The NAEs have been proposed to serve as metabolic precursors to N-acylglycines (NAGs). The sequential oxidation of the NAEs by an alcohol dehydrogenase and an aldehyde dehydrogenase would yield the N-acylglycinals and/or the NAGs. Alcohol dehydrogenase 3 (ADH3) is one enzyme that might catalyze this reaction. To define a potential role for ADH3 in NAE catabolism, we synthesized a set of NAEs and evaluated these as ADH3 substrates. NAEs were oxidized by ADH3, yielding the N-acylglycinals as the product. The (V/K)(app) values for the NAEs included here were low relative to cinnamyl alcohol. Our data show that the NAEs can serve as alcohol dehydrogenase substrates.

Identification of glycine N-acyltransferase-like 2 (GLYATL2) as a transferase that produces N-acyl glycines in humans

The discovery of glycine conjugates of long-chain fatty acids (N-acyl glycines) in the brain and other non-neuronal tissues has led to the identification of an emerging class of bioactive lipids. The biological activities of N-acyl glycines include antinociceptive, anti-inflammatory and antiproliferative effects, and activation of G-protein-coupled receptors. However, despite the fact that N-acyl glycines are emerging as a distinct lipid signaling family, pathways for their production are not fully elucidated. Here we report on the characterization of human glycine N-acyltransferase-like 2 (hGLYATL2), a member of a gene family of 4 putative glycine conjugating enzymes, and show that it synthesizes various N-acyl glycines. Recombinantly expressed hGLYATL2 efficiently conjugated oleoyl-CoA, arachidonoyl-CoA, and other medium- and long-chain acyl-CoAs to glycine. The enzyme was specific for glycine as an acceptor molecule, and preferentially produced N-oleoyl glycine. The hGLYATL2 enzyme is localized to the endoplasmic reticulum, and the mRNA shows highest expression in salivary gland and trachea, but is also detected in spinal cord and skin fibroblasts. The expression pattern and the identification of high levels of N-acyl glycines in skin and lung may indicate a role for N-acyl glycines in barrier function/immune response and the potential role of hGLYATL2 in this regard is discussed.

Substituted hippurates and hippurate analogs as substrates and inhibitors of peptidylglycine alpha-hydroxylating monooxygenase (PHM)

Peptidyl alpha-hydroxylating monooxygenase (PHM) functions in vivo towards the biosynthesis of alpha-amidated peptide hormones in mammals and insects. PHM is a potential target for the development of inhibitors as drugs for the treatment of human disease and as insecticides for the management of insect pests. We show here that relatively simple ground state analogs of the PHM substrate hippuric acid (C(6)H(5)-CO-NH-CH(2)-COOH) inhibit the enzyme with K(i) values as low as 0.5microM. Substitution of sulfur atom(s) into the hippuric acid analog increases the affinity of PHM for the inhibitor. Replacement of the acetylglycine moiety, -CO-NH-CH(2)-COOH with an S-(thioacetyl)thioglycolic acid moiety, -CS-S-CH(2)-COOH, yields compounds with the highest PHM affinity. Both S-(2-phenylthioacetyl)thioglycolate and S-(4-ethylthiobenzoyl)thioglycolic acid inhibit the proliferation of cultured human prostate cancer cells at concentrations >100-fold excess of their respective K(i) values. Comparison of K(i) values between mammalian PHM and insect PHM shows differences in potency suggesting that a PHM-based insecticide with limited human toxicity can be developed.

In vitro synthesis of oleoylglycine by cytochrome c points to a novel pathway for the production of lipid signaling molecules

Long chain fatty acyl glycines represent a new class of signaling molecules whose biosynthetic pathway is unknown. Here we report that cytochrome c catalyzes the formation of oleoylglycine from oleoyl-CoA and glycine, in the presence of hydrogen peroxide. The identity of oleoylglycine product was confirmed by isotope labeling and fragmentation mass spectrometry. Synthesis of oleoylglycine by cytochrome c was dependent upon substrate concentration and time. Other heme-containing proteins, myoglobin and hemoglobin, did not catalyze oleoylglycine synthesis. The functional properties of the reaction closely resemble those observed for the ability of cytochrome c to mediate the synthesis of oleamide from oleoyl-CoA and ammonia, in the presence of hydrogen peroxide (Driscoll, W. J., Chaturvedi., S., and Mueller, G. P. (2007) J. Biol. Chem. 282). The ability of cytochrome c to catalyze the formation of oleoylglycine experimentally indicates the potential importance of cytochrome c as a novel mechanism for the generation of long chain fatty acyl glycine messengers in vivo.

Oleamide synthesizing activity from rat kidney: identification as cytochrome c

Oleamide (cis-9-octadecenamide) is the prototype member of an emerging class of lipid signaling molecules collectively known as the primary fatty acid amides. Current evidence suggests that oleamide participates in the biochemical mechanisms underlying the drive to sleep, thermoregulation, and antinociception. Despite the potential importance of oleamide in these physiologic processes, the biochemical pathway for its synthesis in vivo has not been established. We report here the discovery of an oleamide synthetase found in rat tissues using [(14)C]oleoyl-CoA and ammonium ion. Hydrogen peroxide was subsequently found to be a required cofactor. The enzyme displayed temperature and pH optima in the physiologic range, a remarkable resistance to proteolysis, and specificity for long-chain acyl-CoA substrates. The reaction demonstrated Michaelis-Menten kinetics with a K(m) for oleoyl-CoA of 21 microm. Proteomic, biochemical, and immunologic analyses were used to identify the source of the oleamide synthesizing activity as cytochrome c. This identification was based upon peptide mass fingerprinting of isolated synthase protein, a tight correlation between enzymatic activity and immunoreactivity for cytochrome c, and identical functional properties shared by the tissue-derived synthetase and commercially obtained cytochrome c. The ability of cytochrome c to catalyze the formation of oleamide experimentally raises the possibility that cytochrome c may mediate oleamide biosynthesis in vivo.

In vivo evidence that N-oleoylglycine acts independently of its conversion to oleamide

Oleamide (cis-9-octadecenamide) is a member of an emerging class of lipid-signaling molecules, the primary fatty acid amides. A growing body of evidence indicates that oleamide mediates fundamental neurochemical processes including sleep, thermoregulation, and nociception. Nevertheless, the mechanism for oleamide biosynthesis remains unknown. The leading hypothesis holds that oleamide is synthesized from oleoylglycine via the actions of the peptide amidating enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The present study investigated this hypothesis using pharmacologic treatments, physiologic assessments, and measurements of serum oleamide levels using a newly developed enzyme-linked immunosorbant assay (ELISA). Oleamide and oleoylglycine both induced profound hypothermia and decreased locomotion, over equivalent dose ranges and time courses, whereas, closely related compounds, stearamide and oleic acid, were essentially without effect. While the biologic actions of oleamide and oleoylglycine were equivalent, the two compounds differed dramatically with respect to their effects on serum levels of oleamide. Oleamide administration (80mg/kg) elevated blood-borne oleamide by eight-fold, whereas, the same dose of oleoylglycine had no effect on circulating oleamide levels. In addition, pretreatment with the established PAM inhibitor, disulfiram, produced modest reductions in the hypothermic responses to both oleoylglycine and oleamide, suggesting that the effects of disulfiram were not mediated through inhibition of PAM and a resulting decrease in the formation of oleamide from oleoylglycine. Collectively, these findings raise the possibilities that: (1) oleoylglycine possesses biologic activity that is independent of its conversion to oleamide and (2) the increased availability of oleoylglycine as a potential substrate does not drive the biosynthesis of oleamide.

Thematic review series: Lipid Posttranslational Modifications. Lysosomal metabolism of lipid-modified proteins

Much is now understood concerning the synthesis of prenylated and palmitoylated proteins, but what is known of their metabolic fate? This review details metabolic pathways for the lysosomal degradation of S-fatty acylated and prenylated proteins. Central to these pathways are two lysosomal enzymes, palmitoyl-protein thioesterase (PPT1) and prenylcysteine lyase (PCL). PPT1 is a soluble lipase that cleaves fatty acids from cysteine residues in proteins during lysosomal protein degradation. Notably, deficiency in the enzyme causes a neurodegenerative lysosomal storage disorder, infantile neuronal ceroid lipofuscinosis. PCL is a membrane-associated flavin-containing lysosomal monooxygenase that metabolizes prenylcysteine to prenyl aldehyde through a completely novel mechanism. The eventual metabolic fates of other lipidated proteins (such as glycosylphosphatidylinositol-anchored and N-myristoylated proteins) are poorly understood, suggesting directions for future research.

Thiorphan, tiopronin, and related analogs as substrates and inhibitors of peptidylglycine α-amidating monooxygenase (PAM)

Peptidyglycine alpha-amidating monooxygenase is a copper- and zinc-dependent, bifunctional enzyme that catalyzes the cleavage of glycine-extended peptides or N-acylglycines to the corresponding amides and glyoxylate. This reaction is a key step in the biosynthesis of bioactive alpha-amidated peptides and, perhaps, the primary fatty acids amides also. Two clinically useful N-acylglycines are thiorphan and tiopronin, each with a thiol moiety attached to the acyl group. We report here that thiorphan and tiopronin are substrates for PAM, exhibiting relatively low K(M,app) and V(MAX,app) values. The low V(MAX,app) values result, most likely, from a decrease in active PAM.2Cu(II) as the enzyme competes ineffectively with thiorphan and tiopronin for free copper.

Structure and function of fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) is a mammalian integral membrane enzyme that degrades the fatty acid amide family of endogenous signaling lipids, which includes the endogenous cannabinoid anandamide and the sleep-inducing substance oleamide. FAAH belongs to a large and diverse class of enzymes referred to as the amidase signature (AS) family. Investigations into the structure and function of FAAH, in combination with complementary studies of other AS enzymes, have engendered provocative molecular models to explain how this enzyme integrates into cell membranes and terminates fatty acid amide signaling in vivo. These studies, as well as their biological and therapeutic implications, are the subject of this review.

Use of reversed phase HP liquid chromatography to assay conversion of N-acylglycines to primary fatty acid amides by peptidylglycine-alpha-amidating monooxygenase

Primary fatty acid amides (R-CO-NH2) and N-acylglycines (R-CO-NH-CH2-COOH) are classes of compounds that have only recently been isolated and characterized from biological sources. Key questions remain regarding how these lipid amides are produced and degraded in biological systems. Relative to the fatty acids, little has been done to develop methods to separate and quantify the fatty acid amides and N-acylglycines. We describe reversed phase HPLC methods for the separation of C2-C12 primary fatty acid amides and N-acylglycines and also C12-C22 fatty acid amides. Separation within each class occurs primarily on the basis of simple interactions between the acyl chain and the chromatographic stationary phase, but the polar headgroups on these and related fatty acids and N-acylethanolamides modulate the absolute retention in reversed phase mode. We use these methods to measure the enzyme-mediated, two-step conversion of N-octanoylglycine to octanoamide.

Quantification of primary fatty acid amides in commercial tallow and tallow fatty acid methyl esters by HPLC-APCI-MS

Primary fatty acid amides are a group of biologically highly active compounds which were already identified in nature. Here, these substances were determined in tallow and tallow fatty acid methyl esters for the first time. As tallow is growing in importance as an oleochemical feedstock for the soap manufacturing, the surfactant as well as the biodiesel industry, the amounts of primary fatty acid amides have to be considered. As these compounds are insoluble in tallow as well as in the corresponding product e.g. tallow fatty acid methyl esters, filter plugging can occur. For the quantification in these matrices a purification step and a LC-APCI-MS method were developed. Although quantification of these compounds can be performed by GC-MS, the presented approach omitted any derivatization and increased the sensitivity by two orders of magnitude. Internal standard calibration using heptadecanoic acid amide and validation of the method yielded a limit of detection of 18.5 fmol and recoveries for the tallow and fatty acid methyl ester matrices of 93% and 95%, respectively. A group of commercially available samples were investigated for their content of fatty acid amides resulting in an amount of up to 0.54%m/m (g per 100 g) in tallow and up to 0.16%m/m (g per 100 g) in fatty acid methyl esters.

Oleic acid derived metabolites in mouse neuroblastoma N18TG2 cells

Oleamide is an endogenous sleep-inducing lipid that has been isolated from the cerebrospinal fluid of sleep-deprived mammals. Oleamide is the best-understood member of the primary fatty acid amide family. One key unanswered question regarding oleamide and all other primary acid amides is the pathway by which these molecules are produced. One proposed pathway involves oleoyl-CoA and N-oleoylglycine as intermediates: oleic acid --> oleoyl-CoA --> N-oleoylglycine --> oleamide. The first and third reactions are known reactions, catalyzed by acyl-CoA synthetase and peptidylglycine alpha-amidating monooxygenase (PAM). Oleoyl-CoA formation from oleic acid has been demonstrated in vitro and in vivo while, to date, N-oleoylglycine cleavage to oleamide has been established only in vitro. PAM catalyzes the final step in alpha-amidated peptide biosynthesis, and its proposed role in primary fatty acid amide biosynthesis has been controversial. Mouse neuroblastoma N(18)TG(2) cells are an excellent model system for the study of oleamide biosynthesis because these cells convert [(14)C]-oleic acid to [(14)C]-oleamide and express PAM in a regulated fashion. We report herein that growth of the N(18)TG(2) cells in the presence of [(14)C]-oleic acid under conditions known to stimulate PAM expression generates an increase in [(14)C]-oleamide or in the presence of a PAM inhibitor generates [(14)C]-N-oleoylglycine. This represents the first identification of N-oleoylglycine from a biological source. In addition, N(18)TG(2) cell growth in the presence of N-oleoylglycine yields oleamide. These results strongly indicate that N-oleoylglycine is an intermediate in oleamide biosynthesis and provide further evidence that PAM does have a role in primary fatty acid amide production in vivo.

Fatty acid amide hydrolase in brain ventricular epithelium: mutually exclusive patterns of expression in mouse and rat

Fatty acid amides and fatty acid ethanolamides are novel signalling molecules exemplified by the sleep-inducing lipid oleamide and the endocannabinoid anandamide, respectively. These substances are inactivated by fatty acid amide hydrolase (FAAH), an enzyme that is expressed by neurons and non-neuronal cells in the brain. In the rat, FAAH-immunoreactivity has been detected in epithelial cells of the choroid plexus and, in accordance with this finding, here we report FAAH mRNA expression in rat choroid plexus epithelium using in situ hybridisation methods. Surprisingly, a comparative analysis of mouse brain did not reveal FAAH mRNA expression or FAAH-immunoreactivity in the choroid plexus of this species. FAAH-immunoreactivity was, however, detected in non-choroidal ventricular ependymal cells in the mouse brain and the specificity of this immunostaining was confirmed by analysis of FAAH-knockout mice. FAAH-immunoreactivity was detected in ependymal cells throughout the ventricles of the mouse brain but with regional variation in the intensity of immunostaining. Intriguingly, in rat brain, although FAAH expression is observed in choroid plexus epithelial cells, little or no FAAH-immunoreactivity is present in the ventricular ependyma. Thus, there are mutually exclusive patterns of FAAH expression in the ventricular epithelium of rat and mouse brain. Our observations provide the basis for an experimental analysis that exploits differences in FAAH expression in rat and mouse to investigate FAAH function in ventricular epithelial cells and, in particular, the role of FAAH in regulating the sleep-inducing agent oleamide in cerebrospinal fluid.

Glutathione, S-substituted glutathiones, and leukotriene C4 as substrates for peptidylglycine alpha-amidating monooxygenase

The C-terminal alpha-amide moiety of most peptide hormones arises by the posttranslational cleavage of a glycine-extended precursor in a reaction catalyzed by bifunctional peptidylglycine alpha-amidating monooxygenase (PAM). Glutathione and the S-alkylated glutathiones have a C-terminal glycine and are, thus, potential substrates for PAM. The addition of PAM to glutathione, a series of S-alkylated glutathiones, and leukotriene C(4) results in the consumption of O(2) and the production of the corresponding amidated peptide and glyoxylate. This reaction proceeds in two steps with the intermediate formation of a C-terminal alpha-hydroxyglycine-extended peptide. Amidated glutathione (gammaGlu-Cys-amide) is a relatively poor substrate for glutathione S-transferase with a V/K value that is 1.3% of that for glutathione. Peptide substrates containing a penultimate hydrophobic or sulfur-containing amino acid exhibit the highest (V/K)(app) values for PAM-catalyzed amidation. The S-alkylated glutathiones incorporate both features in the penultimate position with S-decylglutathione having the highest (V/K)(app) of the substrates described in this report.

Cannabinoid receptor-inactive N-acylethanolamines and other fatty acid amides: metabolism and function

Although it is now generally accepted that long-chain N-acylethanolamines and their precursors, N-acylethanolamine phospholipids, exist as trace constituents in virtually all vertebrate cells and tissues, their possible biological functions are just emerging. While anandamide (N-arachidonoylethanolamine) has received much attention due to its ability to bind to and activate cannabinoid receptors, the saturated and monounsaturated N-acylethanolamines, which usually represent the vast majority, are cannabinoid receptor-inactive but appear to interact with endocannabinoids and to have other signaling functions as well. Also, primary fatty acid amides, including the amide of oleic acid, which acts as a sleep-inducing agent, do not interact with cannabinoid receptors but are catabolically related to endocannabinoids. Here we review published information on the occurrence, metabolism, and possible signaling functions of the cannabinoid receptor-inactive N-acylethanolamines and primary fatty acid amides.

Proteins regulating the biosynthesis and inactivation of neuromodulatory fatty acid amides

Fatty acid amides (FAAs) represent a growing family of biologically active lipids implicated in a diverse range of cellular and physiological processes. At present, two general types of fatty acid amides, the N-acylethanolamines (NAEs) and the fatty acid primary amides (FAPAs), have been identified as potential physiological neuromodulators/neurotransmitters in mammals. Representative members of these two subfamilies include the endocannabinoid NAE anandamide and the sleep-inducing FAPA oleamide. In this Chapter, molecular mechanisms proposed for the biosynthesis and inactivation of FAAs are critically evaluated, with an emphasis placed on the biochemical and cell biological properties of proteins thought to mediate these processes.

Amidation of salicyluric acid and gentisuric acid: a possible role for peptidylglycine alpha-amidating monooxygenase in the metabolism of aspirin

Bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the copper-, ascorbate-, and O2-dependent cleavage of C-terminal glycine-extended peptides, N-acylglycines, and the bile acid glycine conjugates to the corresponding amides and glyoxylate. Two known metabolites of aspirin, salicyluric acid and gentisuric acid, are also substrates for PAM, leading to the formation of salicylamide and gentisamide. The time course for O2 consumption and glyoxylate production indicates that salicylurate amidation is a two-step reaction. Salicylurate is first converted to N-salicyl-alpha-hydroxyglycine, which is ultimately dealkylated to salicylamide and glyoxylate. The enzymatically generated salicylamide and N-salicyl-alpha-hydroxyglycine were characterized by mass spectrometry and two-dimensional 1H-13C heteronuclear multiple quantum coherence NMR.

Oxidative metabolism of anandamide

In addition to the well studied hydrolytic metabolism of anandamide, a number of oxidative processes are also possible. Several routes somewhat analogous to the metabolism of free arachidonic acid have been reported. These involve mediation by various lipoxygenases and COX-2 and lead to ethanolamide analogs of the prostaglandins and HETES. The physiological significance of these products is not well understood at this time. There are also preliminary data suggesting a pathway involving oxidation of the hydroxy group of anandamide to a putative metabolite, N-arachidonyl glycine (AA-gly). This molecule displays activities in experimental models that suggest that it may play a role in some of the activities attributed to its precursor, anandamide.

The enzymatic formation of novel bile acid primary amides

Bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the copper-, ascorbate-, and O(2)-dependent cleavage of C-terminal glycine-extended peptides and N-acylglycines to the corresponding amides and glyoxylate. The alpha-amidated peptides and the long-chain acylamides are hormones in humans and other mammals. Bile acid glycine conjugates are also substrates for PAM leading to the formation of bile acid amides. The (V(MAX)/K(m))(app) values for the bile acid glycine conjugates are comparable to other known PAM substrates. The highest (V(MAX)/K(m))(app) value, 3.1 +/- 0.12 x 10(5) M(-1) s(-1) for 3-sulfolithocholylglycine, is 6.7-fold higher than that for d-Tyr-Val-Gly, a representative peptide substrate. The time course for O(2) consumption and glyoxylate production indicates that bile acid glycine conjugate amidation is a two-step reaction. The bile acid glycine conjugate is first converted to an N-bile acyl-alpha-hydroxyglycine intermediate which is ultimately dealkylated to the bile acid amide and glyoxylate. The enzymatically produced bile acid amides and the carbinolamide intermediates were characterized by mass spectrometry and two-dimensional (1)H-(13)C heteronuclear multiple quantum coherence NMR.

Induction of peptidylglycine alpha-amidating monooxygenase in N(18)TG(2) cells: a model for studying oleamide biosynthesis

The fatty-acid primary amide, oleamide, is a novel signaling molecule whose mechanism of biosynthesis is unknown. Recently, the N(18)TG(2) cell line was shown to synthesize oleamide from oleic acid, thereby demonstrating that these cells contain the necessary catalytic activities for generating the fatty-acid primary amide. The ability of peptide alpha-amidating enzyme, peptidylglycine-alpha-amidating monooxygenase (PAM; EC 1.14.17.3), to catalyze the formation of oleamide from oleoylglycine in vitro suggests this as a function for the enzyme in vivo. This investigation shows that N(18)TG(2) cells, in fact, express PAM and that cellular differentiation dramatically increases this expression. PAM expression was confirmed by the detection of PAM mRNA, PAM protein, and enzymatic activity that exhibits the functional characteristics of PAM isolated from mammalian neuroendocrine tissues. The regulated expression of PAM in N(18)TG(2) cells is consistent with the proposed role of PAM in the biosynthesis of fatty-acid primary amides and further establishes this cell line as a model for studying the pathway.

A molluscan peptide alpha-amidating enzyme precursor that generates five distinct enzymes

Mechanisms underlying the specificity and efficiency of enzymes, which modify peptide messengers, especially with the variable requirements of synthesis in the neuronal secretory pathway, are poorly understood. Here, we examine the process of peptide alpha-amidation in individually identifiable Lymnaea neurons that synthesize multiple proproteins, yielding complex mixtures of structurally diverse peptide substrates. The alpha-amidation of these peptide substrates is efficiently controlled by a multifunctional Lymnaea peptidyl glycine alpha-amidating monooxygenase (LPAM), which contains four different copies of the rate-limiting Lymnaea peptidyl glycine alpha-hydroxylating monooxygenase (LPHM) and a single Lymnaea peptidyl alpha-hydroxyglycine alpha-amidating lyase. Endogenously, this zymogen is converted to yield a mixture of monofunctional isoenzymes. In vitro, each LPHM displays a unique combination of substrate affinity and reaction velocity, depending on the penultimate residue of the substrate. This suggests that the different isoenzymes are generated in order to efficiently amidate the many peptide substrates that are present in molluscan neurons. The cellular expression of the LPAM gene is restricted to neurons that synthesize amidated peptides, which underscores the critical importance of regulation of peptide alpha-amidation.

Arachidonoylserotonin and other novel inhibitors of fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) catalyzes the hydrolysis of bioactive fatty acid amides and esters such as the endogenous cannabinoid receptor ligands, anandamide (N-arachidonoyl-ethanolamine) and 2-arachidonoylglycerol, and the putative sleep inducing factor cis-9-octadecenoamide (oleamide). Most FAAH blockers developed to date also inhibit cytosolic phospholipase A2 (cPLA2) and/or bind to the CB1 cannabinoid receptor subtype. Here we report the finding of four novel FAAH inhibitors, two of which, malhamensilipin A and grenadadiene, were screened out of a series of thirty-two different algal natural products, and two others, arachidonoylethylene glycol (AEG) and arachidonoyl-serotonin (AA-5-HT) were selected out of five artificially functionalized polyunsaturated fatty acids. When using FAAH preparations from mouse neuroblastoma N18TG2 cells and [14C]anandamide as a substrate, the IC50s for these compounds ranged from 12.0 to 26 microM, the most active compound being AA-5-HT. This substance was also active on FAAH from rat basophilic leukaemia (RBL-2H3) cells (IC50 = 5.6 microM), and inhibited [14C]anandamide hydrolysis by both N18TG2 and RBL-2H3 intact cells without affecting [14C]anandamide uptake. While AEG behaved as a competitive inhibitor and was hydrolyzed to arachidonic acid (AA) by FAAH preparations, AA-5-HT was resistant to FAAH-catalyzed hydrolysis and behaved as a tight-binding, albeit non-covalent, mixed inhibitor. AA-5-HT did not interfere with cPLA2-mediated, ionomycin or antigen-induced release of [3H]AA from RBL-2H3 cells, nor with cPLA2 activity in cell-free experiments. Finally, AA-5-HT did not activate CB1 cannabinoid receptors since it acted as a very weak ligand in in vitro binding assays, and, at 10-15 mg/kg body weight, it was not active in the 'open field', 'hot plate' and rectal hypothermia tests carried out in mice. Conversely AEG behaved as a cannabimimetic substance in these tests as well as in the 'ring' immobility test where AA-5-HT was also active. AA-5-HT is the first FAAH inhibitor reported to date which is inactive both against cPLA2 and at CB1 receptors, whereas AEG represents a new type of cannabinoid receptor agonist.

'Endocannabinoids' and other fatty acid derivatives with cannabimimetic properties: biochemistry and possible physiopathological relevance

The only endogenous substances isolated and characterised so far that are capable of mimicking the pharmacological actions of the active principle of marijuana, (-)-Delta9-tetrahydrocannabinol, are amides and esters of fatty acids. Some of these compounds, like anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol, act as true 'endogenous cannabinoids' by binding and functionally activating one or both cannabinoid receptor subtypes present on nervous and peripheral cell membranes. The metabolic pathways and molecular mode of actions of these metabolites, as well as their possible implication in physiopathological responses, are reviewed here.

Evidence of high expression of peptidylglycine alpha-amidating monooxygenase in the rat uterus: estrogen regulation

In the present study, high levels of peptidylglycine alpha-amidating monooxygenase (PAM), which catalyzes the two-step formation of bioactive alpha-amidated peptides from their glycine-extended precursors, have been found in the uterus. Expression of PAM was evaluated in the uterus of intact cycling adult female rats and after experimental manipulation of the estrogen status of the rats. During the estrous cycle, PAM mRNA levels exhibited striking changes inversely related to the physiological variations of plasma estrogen levels. The levels of PAM transcripts changed markedly during the estrous cycle, reaching the highest levels at metestrus. There was a 15-fold increase in the abundance of PAM mRNA between metestrus and proestrus. Chronic treatment of ovariectomized rats with 17beta-estradiol decreased PAM mRNA levels to values comparable with those found in intact rats at proestrus. Progesterone was without effect on PAM mRNA levels, indicating that the effect was specific for estradiol. In situ hybridization studies were conducted to determine the tissue disposition and cell types expressing PAM. High levels of PAM mRNA were localized in the endometrium at the level of luminal and glandular cells. A weak signal was observed in stromal cells, and the myometrium cells were negative. 17beta-Estradiol treatment induced an overall decrease of the hybridization signal, as compared with ovariectomized rats. These results demonstrate the presence of high levels of PAM in the uterus and indicate that estrogens are involved in regulating the expression of the enzyme in this tissue. However, the present study provides no information regarding whether this regulation takes place at the level of transcription or influences mRNA stability.

Chemical requirements for inhibition of gap junction communication by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and has been shown to effect serotonergic systems and block gap junction communication in a structurally specific manner. Herein, the structural features of oleamide required for inhibition of the gap junction-mediated chemical and electrical transmission in rat glial cells are defined. The effective inhibitors fall into two classes of fatty acid primary amides of which oleamide and arachidonamide are the prototypical members. Of these two, oleamide constitutes the most effective, and its structural requirements for inhibition of the gap junction are well defined. It requires a chain length of 16-24 carbons of which 16-18 carbons appears optimal, a polarized terminal carbonyl group capable of accepting but not necessarily donating a hydrogen bond, a Delta9 cis double bond, and a hydrophobic methyl terminus. Within these constraints, a range of modifications are possible, many of which may be expected to improve in vivo properties. A select set of agents has been identified that serves both as oleamide agonists and as inhibitors of fatty acid amide hydrolase, which is responsible for the rapid inactivation of oleamide.

Structural requirements for 5-HT2A and 5-HT1A serotonin receptor potentiation by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and that has been shown to effect serotonergic receptor responses and block gap junction communication. Herein, the potentiation of the 5-HT1A receptor response is disclosed, and a study of the structural features of oleamide required for potentiation of the 5-HT2A and 5-HT1A response to serotonin (5-HT) is described. Of the naturally occurring fatty acids, the primary amide of oleic acid (oleamide) is the most effective at potentiating the 5-HT2A receptor response. The structural features required for activity were found to be highly selective. The presence, position, and stereochemistry of the delta9-cis double bond is required, and even subtle structural variations reduce or eliminate activity. Secondary or tertiary amides may replace the primary amide but follow a well defined relationship requiring small amide substituents, suggesting that the carboxamide serves as a hydrogen bond acceptor but not donor. Alternative modifications at the carboxamide as well as modifications of the methyl terminus or the hydrocarbon region spanning the carboxamide and double bond typically eliminate activity. A less extensive study of the 5-HT1A potentiation revealed that it is more tolerant and accommodates a wider range of structural modifications. An interesting set of analogs was identified that inhibit rather than potentiate the 5-HT2A, but not the 5-HT1A, receptor response, further suggesting that such analogs may permit the selective modulation of serotonin receptor subtypes and even have opposing effects on the different subtypes.

The sleep inducing factor oleamide is produced by mouse neuroblastoma cells

Cis-9,10-octadecenoamide (oleamide) was isolated from the cerebrospinal fluid of sleep-deprived mammals and shown to induce sleep in rats. The enzyme catalyzing the hydrolysis of the amide bond of oleamide as well as of anandamide, the putative endogenous ligand of cannabinoid receptors, was purified from rat liver, cloned, shown to be expressed also in brain and named fatty acid amide hydrolase (FAAH). The enzymatic synthesis of oleamide from oleic acid and ammonia by rat brain microsomes has been also described. However, no evidence has been reported so far on the neuronal origin of oleamide, necessary in order to postulate for this compound a role as a neuromodulator. Here we show for the first time that oleamide is produced by a neuronal cell type and that its biosynthesis in intact neurons is not likely to occur through the direct condensation of oleic acid and ammonia. A lipid metabolite was extracted and purified from mouse neuroblastoma N18TG2 cells through a sequence of chromatographic steps and characterized as oleamide by means of gas chromatography/electron impact mass spectrometry (GC/EIMS). The amount of oleamide, as estimated by GC analyses carried out in comparison with known amounts of synthetic oleamide, was 55.0+/-09.5 pmols/10(7) cells, compared to less than 0.7 pmol/10(7) cells for anandamide in the same cells. When N18TG2 cells were prelabeled with [14C]oleic acid and the lipids extracted and purified, a radioactive component with the same chromatographic behavior as oleamide was found whose levels: (1) were not significantly influenced by stimulation with ionomycin; (2) were slightly increased by incubation with FAAH inhibitor phenyl-methyl-sulphonyl-fluoride (PMSF); (3) appeared to correlate with [14C]oleic acid incorporation into phospholipids but not with free [14C]oleic acid levels. N18TG2 cell membranes were shown to contain an enzymatic activity catalyzing the synthesis of oleamide from oleic acid and ammonia. This activity was inhibited by FAAH selective inhibitors arachidonoyltrifluoromethylketone and methylarachidonoylfluorophosphonate, as well as by an excess of anandamide, and by PMSF at the same concentration which increased oleamide formation in intact cells. These data suggest that a FAAH-like enzyme working "in reverse" may be responsible for the formation of oleamide in cell-free preparations but not in whole cells.