Bioactive Lipids in Nociception Ermund, Anna 2008 Link to publication Citation for published version (APA): Ermund, A. (2008). Bioactive Lipids in Nociception. [Doctoral Thesis (compilation), Faculty of Medicine]. Clinical Chemistry and Pharmacology, Dept of Laboratory Medicine. 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LUND UNIVERSITY PO Box 117 221 00 Lund +46 46-222 00 00 Bioactive Lipids in Nociception Anna Ermund Clinical Chemistry and Pharmacology Department of Laboratory Medicine Faculty of Medicine Lund University Lund 2008 Contents Original articles Abbreviations Introduction The somatosensory system Nociception TRPV1 Acetaminophen Long-chain N-acylamines and glycerols Aims of the thesis Materials and methods Tension recordings Voltage-clamp electrophysiology Mass-spectrometry Nociceptive in vivo tests Enzyme immunoassays Calculations and statistics Drugs Results and discussion Formation of AM404 from acetaminophen (study I) Differential action of acetaminophen and ibuprofen (study II) Activation of TRPV1 by 2-arachidonoylglycerol (study III) General discussion Conclusions Svensk sammanfattning (Swedish summary) Acknowledgements References Appendix I-III 2 Original articles The thesis is based on the following studies, which are referred to in the text by their Roman numerals: I. Högestätt ED, Jönsson BA, Ermund A, Andersson DA, Björk H, Alexander JP, Cravatt BF, Basbaum AI, Zygmunt PM. Conversion of acetaminophen to the bioactive N-acyl phenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. J. Biol. Chem. 2005, 280:31405-12. II. Ermund A, Jönsson BA, Mallet C, Eschalier A, Zygmunt PM, Högestätt, ED. Analgesic and biochemical effects of acetaminophen and ibuprofen in vivo. Submitted. III. Ermund A, Movahed P, Jönsson BA, Andersson D, Birnir B, Kanje M, Bevan S, Zygmunt PM, Högestätt ED. Activation of TRPV1 by endogenous monoacylglycerols. Submitted. Copyright holder of published work © American Society for Biochemistry and Molecular Biology 3 Abbreviations 1-AG: 1-Arachidonoylglycerol 2-AG: 2-Arachidonoylglycerol AM404: N-Arachidonoylphenolamine ATP: Adenosine-5´-triphosphate AUC: Area under curve cDNA: Complementary deoxynucleic acid CHO cell: Chinese hamster ovary cell CGRP: Calcitonin gene-related peptide COX: Cyclooxygenase DAG: Diacylglycerol DMSO: Dimethylsulphoxide EDTA: Ethylenediaminetetraacetic acid EGTA: Ethyleneglycol tetraacetic acid FAAH: Fatty acid amide hydrolase FAAH-/-: Fatty acid amide hydrolase gene knock-out HEK293 cell: Human embryonic kidney cell 293 HEPES: 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid HPLC: High-performance liquid chromatography i.p.: intraperitoneal MAFP: Methylarachidonoylfluorophosponate nPA: normalized peak area 2-OG: 2-oleoylglycerol PEA: N-Palmitoylethanolamine PGD : Prostaglandin D 2 2 PGE : Prostaglandin E 2 2 PKC: Protein kinase C PLC: Phospholipase C PMSF: Phenymethylsulfonylfluoride p.o.: per os s.c.: subcutaneous TES: N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid THC: Δ9-Tetrahydrocannabinol TRP: Transient receptor potential TRPV1: Transient receptor potential vanilloid 1 TRPV1-/-: Transient receptor potential vanilloid 1 gene knock-out TRPA1: Transient receptor potential ankyrin 1 TXB : Thromboxane B 2 2 4 Introduction The somatosensory system Organisms receive information about the external and internal environment through various sensory systems, including the visual (vision), auditory (hearing), gustatory (taste), olfactory (smell) and somatosensory systems. In contrast to the other systems, the somatosensory system extends to most parts of the body. The skin, mucous membranes, skeletal muscles, joints, visceral organs and the cardiovascular system are all innervated by somatosensory nerve fibres, which convey a variety of sensory modalities such as touch, pressure, temperature, proprioception and nociception. The Latin word proprius means one’s own and proprioception refers to the ability to sense the relative position of one´s own body parts. Nociception comprises the ability to detect potentially noxious stimuli and the Latin word noceo means hurt. Sensory nerve fibers can be divided into three categories: (1) Myelinated, rapidly conducting Aβ fibers, originating from large diameter cell bodies, which mostly convey innocuous low- threshold stimuli, (2) the thinly myelinated Aδ fibers, originating in medium size cell bodies, which convey fast, sharp pain, but also innocuous stimuli, and (3) unmyelinated, slowly conducting C fibers, originating in small diameter cell bodies and which participate in the detection of dull, diffuse pain. Traditionally, nocieptive nerve cells are defined as cells sensitive to the plant-derived irritant capsaicin (Szolcsanyi, 2004). A nerve consists of bundles of axons, their myelin sheaths and blood vessels supplying the axons and Schwann cells with oxygen and nutrients. The primary sensory neurons have their cell bodies in dorsal root ganglia, nodose ganglia or trigeminal ganglia. After reaching the dorsal root ganglia, the nociceptive signal passes into the dorsal horn of the spinal cord, where the signal may be relayed simultaneously to interneurons, involved in protective reflexes, and ascending secondary neurons for supraspinal processing and initiation of pain (Fig. 1). 5 Figure 1: The withdrawal reflex protects the limb from being damaged by potentially harmful stimuli. Source: http://www.mhhe.com/socscience/intro/ibank/set1.htm (November 16 2005). The sensory nerve endings enter a variety of specialized structures, most of them in the skin muscle and tendons. Free nerve endings are the major detectors of noxious stimuli in both the skin and viscera, but free nerve endings are also involved in sensing temperature and itch. Nociception One important role of the somatosensory system is to detect injury or potentially harmful stimuli, a process generally referred to as nociception. In the periphery there are molecular sensors situated on primary sensory nerve terminals. These sensors are activated in response 6 to high-threshold stimuli, more specifically noxious heat, cold and mechanical stress, as well as certain chemicals. These nerve terminals can also be activated or sensitized by protons and various inflammatory mediators. Many of these neurons or nociceptors are polymodal, which means that they can be activated by more than one of the above mentioned stimuli. The ability of an organism to detect harmful stimuli and hence to avoid tissue injury is crucial for survival. Pain in response to a noxious stimulus or injury is generally referred to as nociceptive pain. As described above, nociceptors detect potentially harmful stimuli and transmit this information as action potentials to the central nervous system (afferent function). When activated, nociceptors also release neurotransmitters, such as calcitonin gene-related peptide (CGRP), substance P and neurokinin A, from their peripheral terminals (efferent function). These neuropeptides induce vasodilatation and plasma extravasation (Louis et al., 1989) as well as mast cells and neutrophil activation, which may initiate a neurogenic inflammation (Julius et al., 2001). Several inflammatory mediators, such as histamine, prostaglandins, bradykinin, ATP, cytokines and neurotrophic factors, are able to activate or sensitize sensory neurons (Rang et al., 2003). This may not only induce pain and hyperalgesia, but it could also create a positive feedback loop reinforcing inflammation via release of neurotransmitters from peripheral nerve endings. TRPV1 The recent finding that certain TRP ion channels, including TRPV1, TRPV2, TRPA1 and TRPM8, have unique expression patterns in sensory neurons has opened-up new avenues for understanding nociceptive signaling at a molecular level. The first TRP ion channel was identified in the phototransduction pathway of a blind Drosophila mutant (Cosens et al., 1969; Montell, 2005). The photoreceptor cells in this mutant responded with a transient rather than a sustained receptor potential when exposed to continuous light (Cosens et al., 1969). The mutant was therefore named trp. The trp gene encodes a calcium permeable ion channel, which is the founding member of a large family of cation channels present in worms, insects, fish and mammals (Montell, 2005; Nilius et al., 2007). TRP ion channels have six transmembrane domains and N- and C-termini facing the cytoplasm (Fig. 2) (Caterina et al., 1997). The loop between transmembrane 7 segment 5 and 6 is considered to form the ion pore after tetramerization of the protein. Among mammalian TRP ion channels, the TRPC subfamily shows the largest similarity with the original Drosophila TRP channel (Desarnaud et al., 1995; Wes et al., 1995; Zhu et al., 1995). Figure 2: TRP ion channel structure. The ion channel protein has six putative transmembrane regions and a pore loop between transmembrane segment 5 and 6. The N- and C-termini are intracellular. The number of ankyrin repeats (A) in the N-terminal region of the protein varies among the different subgroups. Some members of the TRP ion channel family also contain a TRP box localized C-terminally. The activation of sensory neurons by the pungent component in hot chili peppers, capsaicin, has been studied thoroughly by Szolcsányi and colleagues (Szolcsanyi, 2004). Not until 1997 was the target protein for capsaicin identified by Julius and co-workers, using an expression cloning strategy with capsaicin-induced calcium responses as a selection instrument (Caterina et al., 1997). The ion channel was named transient receptor potential vanilloid 1 (TRPV1) to indicate its sensitivity to vanilloid compounds such as capsaicin (Fig. 3). As shown in calcium imaging experiments, TRPV1-mediated responses can be seen in small and medium diameter dorsal root ganglion neurons (Fig. 3). Aside from being activated by various vanilloid compounds, TRPV1 is also gated by noxious heat (threshold ~43°C) and protons (Caterina et al., 1997). Protons also potentiate TRPV1 responses to chemical activators (Jordt et al., 2000) and temperature (Tominaga et al., 1998). Thus, TRPV1 integrates stimuli of many different modalities and has therefore been termed a polymodal molecular sensor (Caterina et al., 1997). 8 TRPV1 can be positively modulated downstream of surface receptors coupled to phospholipase C (PLC) (Chuang et al., 2001; Premkumar et al., 2000). Phosphatidylinositol 4,5-bisphosphate (PIP ) has been suggested to act as a brake on the channel and when PIP is 2 2 cleaved by PLC to inositol 1,4,5-trisphosphate (IP ) and diacylglycerol (DAG), TRPV1 is 3 released from this inhibition (Chuang et al., 2001). However, when directly applied to an inside out patch from a cell heterologously expressing TRPV1, PIP causes activation of 2 TRPV1. It has therefore been suggested that the PIP -mediated inhibition of TRPV1 is an 2 indirect effect (Lukacs et al., 2007). Phosphorylation of the channel by DAG-activated PKCε can also cause activation or sensitization of TRPV1 (Premkumar et al., 2000). Other proteins affecting the phosphorylation state and activity of TRPV1 are calcium/calmodulin dependent kinase II (Jung et al., 2004; Price et al., 2005a; Rosenbaum et al., 2003) and cAMP-dependent protein kinase A (Bhave et al., 2002; Mohapatra, 2003). Furthermore, the cyclosporine- sensitive phosphatase calcineurin is involved in desensitization of TRPV1-mediated activity (Jung et al., 2004; Mohapatra et al., 2005). Interestingly, the TRPV1 knock-out mouse fails to develop inflammation-induced thermal hyperalgesia (Caterina et al., 2001; Caterina et al., 2000), which is consistent with the view that TRPV1 is a downstream target for many inflammatory mediators acting on PLC-coupled surface receptors. Several endogenous lipids, including long chain N-acylethanolamines and certain lipoxygenase products, are able to activate TRPV1 and may have a role as TRPV1 sensitizers during inflammation or tissue injury (Hwang et al., 2000; Zygmunt et al., 1999). Inflammation also triggers the expression of TRPV1 in sensory neurons (Ji et al., 2002; Winston et al., 2001). As TRPV1 is involved in inflammatory pain, it is not surprising that the pharmaceutical industry considers this ion channel an interesting drug target for novel analgesics (Caterina et al., 2000). 9