Heather B. Bradshaw

The expanding field of cannabimimetic and related lipid mediators

The discovery of the endogenous cannabimimetic lipid mediators, anandamide and 2‐arachidonoyl glycerol, opened the door to the discovery of other endogenous lipid mediators similar in structure and function. The majority of these compounds do not bind appreciably to known cannabinoid receptors; yet some of them produce cannabimimetic effects while others exert actions through novel mechanisms that remain to be elucidated. This review explores the growing diversity of recently discovered putative lipid mediators and their relationship to the endogenous cannabinoid system. The possibility that there remain many unidentified signalling lipids coupled with the evidence that many of these yield bioactive metabolites due to actions of known enzymes (e.g. cyclooxygenases, lipoxygenases, cytochrome P450s) suggests the existence of a large and complex family of lipid mediators about which only little is known at this time. The elucidation of the biochemistry and pharmacology of these compounds may provide therapeutic targets for a variety of conditions including sleep dysfunction, eating disorders, cardiovascular disease, as well as inflammation and pain.

Targeted lipidomics: Discovery of new fatty acyl amides

The discovery of endogenous fatty acyl amides such asN-arachidonoyl ethanolamide (anandamide),N-oleoyl ethanolamide (OEA), andN-arachidonoyl dopamine (NADA) as important signaling molecules in the central and peripheral nervous system has led us to pursue other unidentified signaling molecules. Until recently, technical challenges, particularly those associated with lipid purification and chemical analysis, have hindered the identification of low abundance signaling lipids. Improvements in chromatography and mass spectrometry (MS) such as miniaturization of high-performance liquid chromatography components, hybridization of multistage mass spectrometers and time-of-flight technology, the development of electrospray ionization (ESI) and of information-dependent acquisition, now permit rapid identification of novel, low abundance, signaling lipids.

The biosynthesis of N-arachidonoyl dopamine (NADA), a putative endocannabinoid and endovanilloid, via conjugation of arachidonic acid with dopamine

N-arachidonoyl dopamine (NADA) is an endogenous ligand that activates the cannabinoid type 1 receptor and the transient receptor potential vanilloid type 1 channel. Two potential biosynthetic pathways for NADA have been proposed, though no conclusive evidence exists for either. The first is the direct conjugation of arachidonic acid with dopamine and the other is via metabolism of a putative N-arachidonoyl tyrosine (NA-tyrosine). In the present study we investigated these biosynthetic mechanisms and report that NADA synthesis requires TH in dopaminergic terminals; however, NA-tyrosine, which we identify here as an endogenous lipid, is not an intermediate. We show that NADA biosynthesis primarily occurs through an enzyme-mediated conjugation of arachidonic acid with dopamine. While this conjugation likely involves a complex of enzymes, our data suggest a direct involvement of fatty acid amide hydrolase in NADA biosynthesis either as a rate-limiting enzyme that liberates arachidonic acid from AEA, or as a conjugation enzyme, or both.

The Non-Psychoactive Plant Cannabinoid, Cannabidiol Affects Cholesterol Metabolism-Related Genes in Microglial Cells

Cannabidiol (CBD) is a non-psychoactive plant cannabinoid that is clinically used in a 1:1 mixture with the psychoactive cannabinoid Δ9-tetrahydrocannabinol (THC) for the treatment of neuropathic pain and spasticity in multiple sclerosis. Our group previously reported that CBD exerts anti-inflammatory effects on microglial cells. In addition, we found that CBD treatment increases the accumulation of the endocannabinoid N-arachidonoyl ethanolamine (AEA), thus enhancing endocannabinoid signaling. Here we proceeded to investigate the effects of CBD on the modulation of lipid-related genes in microglial cells. Cell viability was tested using FACS analysis, AEA levels were measured using LC/MS/MS, gene array analysis was validated with real-time qPCR, and cytokine release was measured using ELISA. We report that CBD significantly upregulated the mRNAs of the enzymes sterol-O-acyl transferase (Soat2), which synthesizes cholesteryl esters, and of sterol 27-hydroxylase (Cyp27a1). In addition, CBD increased the mRNA of the lipid droplet-associated protein, perilipin2 (Plin2). Moreover, we found that pretreatment of the cells with the cholesterol chelating agent, methyl-β-cyclodextrin (MBCD), reversed the CBD-induced increase in Soat2 mRNA but not in Plin2 mRNA. Incubation with AEA increased the level of Plin2, but not of Soat2 mRNA. Furthermore, MBCD treatment did not affect the reduction by CBD of the LPS-induced release of the proinflammatory cytokine IL-1β. CBD treatment modulates cholesterol homeostasis in microglial cells, and pretreatment with MBCD reverses this effect without interfering with CBD’s anti-inflammatory effects. The effects of the CBD-induced increase in AEA accumulation on lipid-gene expression are discussed.

Broad impact of deleting endogenous cannabinoid hydrolyzing enzymes and the CB1 cannabinoid receptor on the endogenous cannabinoid-related lipidome in eight regions of the mouse brain.

BACKGROUND AND PURPOSEnThe enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) hydrolyze endogenous cannabinoids (eCBs), N-arachidonoyl ethanolamine (AEA) and 2-arachidonoyl glycerol (2-AG), respectively. These enzymes also metabolize eCB analogs such as lipoamines and 2-acyl glycerols, most of which are not ligands at CB1. To test the hypothesis that deleting eCB hydrolyzing enzymes and CB1 shifts lipid metabolism more broadly and impacts more families of eCB structural analogs, targeted lipidomics analyses were performed on FAAH KO, MAGL KO, and CB1 KO mice and compared to WT controls in 8 brain regions.nnnEXPERIMENTAL APPROACHnMethanolic extracts of discrete brain regions (brainstem, cerebellum, cortex, hippocampus, hypothalamus, midbrain, striatum and thalamus) were partially purified on C-18 solid-phase extraction columns. Over 70 lipids per sample were then analyzed with HPLC/MS/MS.nnnKEY RESULTSnAEA and 2-AG were unaffected throughout the brain in CB1 KO mice; however, there was an increase in the arachidonic acid (AA) metabolite, PGE2 in the majority of brain areas. By contrast, PGE2 and AA levels were significantly reduced throughout the brain in the MAGL KO corresponding to significant increases in 2-AG. No changes in AA or PGE2 were seen throughout in the FAAH KO brain, despite significant increases in AEA, suggesting AA liberated by FAAH does not contribute to steady state levels of AA or PGE2. Changes in the lipidome were not confined to the AA derivatives and showed regional variation in each of the eCB KO models.nnnCONCLUSIONS AND IMPLICATIONSnAEA and 2-AG hydrolyzing enzymes and the CB1 receptor link the eCB system to broader lipid signaling networks in contrasting ways, potentially altering neurotransmission and behavior independently of cannabinoid receptor signaling.

Distribution of endogenous farnesyl pyrophosphate and four species of lysophosphatidic acid in rodent brain.

Lysophosphatidic acid (LPA) is the umbrella term for lipid signaling molecules that share structural homology and activate the family of LPA receptors. Farnesyl Pyrophosphate (FPP) is commonly known as an intermediate in the synthesis of steroid hormones; however, its function as a signaling lipid is beginning to be explored. FPP was recently shown to an activator of the G-protein coupled receptor 92 (also known as LPA5) of the calcium channel TRPV3. The LPA receptors (including GPR92) are associated with the signal transduction of noxious stimuli, however, very little is known about the distribution of their signaling ligands (LPAs and FPP) in the brain. Here, using HPLC/MS/MS, we developed extraction and analytical methods for measuring levels of FPP and 4 species of LPA (palmitoyl, stearoyl, oleoyl and arachidonoyl-sn-glycerol-3 phosphate) in rodent brain. Relative distributions of each of the five compounds was significantly different across the brain suggesting divergent functionality for each as signaling molecules based on where and how much of each is being produced. Brainstem, midbrain, and thalamus contained the highest levels measured for each compound, though none in the same ratios while relatively small amounts were produced in cortex and cerebellum. These data provide a framework for investigations into functional relationships of these lipid ligands in specific brain areas, many of which are associated with the perception of pain.

Endogenous Cannabinoid Production in the Rat Female Reproductive Tract Is Regulated by Changes in the Hormonal Milieu

The endogenous cannabinoid (eCB) system is emerging as an important component of female reproductive tract physiology. The eCBs anandamide (AEA), 2-arachidonoyl glycerol (2-AG), and N-arachidonoyl glycine (NAGly) were measured in the rat reproductive tract at five time points in the four-day estrous cycle, in acyclic retired breeders (RB), after ovariectomy (OVX), OVX + estrogen (E2), OVX + progesterone (P4), or OVX with E2+P4. eCBs were measured in the uterus, uterine adipose, ovaries, and ovarian adipose using HPLC/MS/MS. Levels of AEA, 2-AG, and NAGly were highest in the estrus phase of the estrous cycle in the uterus, whereas, only NAGly had differences in production in the ovaries across the cycle. All eCBs were lower in RB ovaries; however, the production of eCBs in the uterus of RB and OVX groups was more varied with NAGly showing the lowest levels of production in these groups. Levels of AEA in uterine fat were significantly higher or equivalent to levels in the uterus. However, levels of 2-AG and NAGly were dramatically lower in uterine fat verses the organ. Ovarian fat had significantly lower levels of all three eCBs. These data provide evidence that the hormonal milieu plays a significant and complex role in the production of eCBs in the female rat reproductive tract.

CB1-induced side effects of specific COX-2 inhibitors: A feature, not a bug

In the current issue of Pain, Telleria-Diaz and colleagues [6] shed novel light on the mechanism of action of cyclooxygenase-2 (COX-2) showing that a ‘‘side-effect” of specific COX-2 inhibitors is the significant reduction in the metabolism/degradation of the endogenous cannabinoid (eCB), 2-arachidonoyl glycerol (2-AG). The late Michael Walker’s group first showed that the eCB, anandamide, was released in the periaqueductal grey (PAG) during noxious peripheral stimulation and that eCB levels correlated with analgesia [7]. Subsequently, Andrea Hohmann and colleagues [2] demonstrated another and more abundant eCB, 2-AG, is the most likely candidate for the non-opioid component of stress-induced analgesia in the PAG. These data placed the endogenous cannabinoid system as a primary player in the regulation of pain at the CNS level. Biochemical relationships between the eCB system and overthe-counter pain medication are an emerging field of interest. In 2005, Hogestatt and colleagues [1] proposed that an analgesic property of acetaminophen (also called paracetamol) arose from metabolic production of N-arachidonoyl-4-aminophenol (AM404) by conjugation of arachidonic acid to exogenously administered p-acetamidophenol. AM404 works as an eCB hydrolytic enzyme inhibitor that elevates or blocks the degradation of eCBs. Some of my colleagues and I who were studying both endogenous cannabinoids and pain joked at the time that while these results were fascinating and encouraging, we almost hoped that no one in the media would pick up on this fact. We feared that a media report that acetaminophen was, in fact, a cannabimimetic drug would lead to its removal from the shelves. Funnily enough, the popular media did not seem to notice and the interactions of NSAIDS and the eCB system on pain remained firmly in the minds of a relatively small group of scientists. In a separate but related area of research, Marnett’s group demonstrated that 2-AG is readily oxidized by COX-2 in vitro and introduced a potential metabolite of 2-AG, PGE2-G, that may act more like a prostaglandin than an eCB [4]. We later showed that PGE2G is produced endogenously, is pro-nociceptive, and acts through an as yet unidentified receptor [3]. Data presented here by Telleria-Diaz suggest that it is primarily the activation of 2-AG at CB1 receptors that inhibits the central sensitization driven by the continuous sensory input of sustained inflammation. More recently, Marnett’s group [5] added another caveat to this beautifully complex system. They used in vitro recombinant COX-2 and showed that COX-2 inhibitors, at low doses that still allow arachidonic acid metabolism into PGE2, will block 2-AG metabolism into PGE2-G.

Environmental toxin acrolein alters levels of endogenous lipids, including TRP agonists: A potential mechanism for headache driven by TRPA1 activation

Exposure to airborne toxins can trigger headaches, but the mechanisms are not well understood. Some environmental toxins, such as acrolein, activate transient receptor potential ankyrin 1 (TRPA1), a receptor involved in pain sensation that is highly expressed in the trigeminovascular system. It has been shown in rat models that repeated exposure to acrolein induces trigeminovascular sensitization to both TRPA1 and TRP vanilloid 1 (TRPV1) agonists, a phenomenon linked to headache. In this study, we test the hypothesis that the sensitization of trigeminovascular responses in rats after acrolein exposure via inhalation is associated with changes in levels of endogenous lipids, including TRPV1 agonists, in the trigeminal ganglia, trigeminal nucleus, and cerebellum. Lipidomics analysis of 80 lipids was performed on each tissue after acute acrolein, chronic acrolein, or room air control. Both acute and chronic acrolein exposure drove widespread alterations in lipid levels. After chronic acrolein exposure, levels of all 6 N-acyl ethanolamines in the screening library, including the endogenous cannabinoid and TRPV1 agonist, N-arachidonoyl ethanolamine, were elevated in trigeminal tissue and in the cerebellum. This increase in TRPV1 ligands by acrolein exposure may indicate further downstream signaling, in that we also show here that a combination of these TRPV1 endogenous agonists increases the potency of the individual ligands in TRPV1-HEK cells. In addition to these TRPV1 agonists, 3 TRPV3 antagonists, 4 TRPV4 agonists, and 25 orphan lipids were up and down regulated after acrolein exposure. These data support the hypothesis that lipid signaling may represent a mechanism by which repeated exposure to the TRPA1 agonist and environmental toxin, acrolein, drives trigeminovascular sensitization.

N -Acyl Amides: Ubiquitous Endogenous Cannabimimetic Lipids That Are in the Right Place at the Right Time

Abstract N -Arachidonyl ethanolamide (also known as anandamide) is arguably the world’s most famous molecule in a very specific class of molecules structurally referred to as N -acyl amides. While it is true that N -acyl amide are not yet particularly well known throughout scientific communities, we will argue that they are quite well known throughout all of the plant and animal kingdoms in that they are ubiquitous molecules that are formed from simple fatty acids and amines and are likely present in most – if not all – forms of life. This presence provides an opportunistic situation for them to be used as signaling molecules and as metabolic precursors to additional signaling molecules. How they are synthesized, metabolized, and what they do in each of these systems is largely unknown. Given their ubiquitous nature, it is actually a narrow view that they are most specifically endogenous cannabinoids; however, it is the case that our understanding of their signaling properties currently stems from the work of how some are endogenous counterparts to the wide range of cannabis plant lipids that activate both GPCR and ion channels. Here, we provide a glimpse into the world of N -acyl amide lipids and how they act to create a system of cellular signaling that provides some clues as to how Cannabis has so many varied effects on the brain and body.