Supersensitivity to anandamide and enhanced endogenous cannabinoid signaling in mice lacking fatty acid amide hydrolase

Abstract

The medicinal properties of marijuana have been recognized for centuries, but clinical and societal acceptance of this drug of abuse as a potential therapeutic agent remains fiercely debated. An attractive alternative to marijuana-based therapeutics would be to target the molecular pathways that mediate the effects of this drug. To date, these neural signaling pathways have been shown to comprise a cannabinoid receptor (CB1) that binds the active constituent of marijuana, tetrahydrocannabinol (THC), and a postulated endogenous CB1 ligand anandamide. Although anandamide binds and activates the CB1 receptor in vitro, this compound induces only weak and transient cannabinoid behavioral effects in vivo, possibly a result of its rapid catabolism. Here we show that mice lacking the enzyme fatty acid amide hydrolase (FAAH ؊/؊ ) are severely impaired in their ability to degrade anandamide and when treated with this compound, exhibit an array of intense CB1-dependent behavioral responses, including hypomotility, analgesia, catalepsy, and hypothermia. FAAH ؊/؊ -mice possess 15-fold augmented endogenous brain levels of anandamide and display reduced pain sensation that is reversed by the CB1 antagonist SR141716A. Collectively, these results indicate that FAAH is a key regulator of anandamide signaling in vivo, setting an endogenous cannabinoid tone that modulates pain perception. FAAH may therefore represent an attractive pharmaceutical target for the treatment of pain and neuropsychiatric disorders.T he endogenous cannabinoid system has been the focus of intense research over the past decade (1-3). Cannabinoid receptors that recognize the active component of marijuana, ⌬ 9 -tetrahydrocannabinol (THC) (4), have been identified in both the brain (CB 1 receptor) and immune system (CB 2 receptor) (5). Additionally, a natural brain lipid, N-arachidonoyl ethanolamine, or anandamide, has been characterized as a possible endogenous ligand for the CB 1 receptor (6). Consistent with its postulated role as an endocannabinoid, anandamide (i) binds and activates the CB 1 receptor in vitro (6, 7), (ii) is produced in the brain in response to peripheral pain stimuli (8), and (iii) induces some cannabinoid behavioral effects in vivo, including hypothermia, analgesia, and motor defects (9-11).Although a number of biochemical and cell biological studies have provided evidence that anandamide acts as an endogenous CB 1 ligand (6,7,12,13), the behavioral effects induced by this compound are very weak and transient, especially when compared with those elicited by exocannabinoids like THC (11). Additionally, efforts to block the behavioral effects of anandamide with the CB 1 antagonist SR141716A have met with mixed success (14, 15). Most recently, anandamide was found to produce significant behavioral effects in CB 1 receptor-knockout (CB 1 Ϫ/Ϫ ) mice (16), suggesting that an alternative site(s) of action for this compound may exist in vivo. On this note, anandamide affects multiple receptor systems in addition to the CB 1 receptor in vitro, i...

Assignment of Endogenous Substrates to Enzymes by Global Metabolite Profiling

“…Key to the implementation of discovery metabolite profiling (DMP) was the supposition that the absolute mass ion intensities measured during LC-MS analysis could be used in a broad mass-scanning mode to quantify the relative levels of metabolites in tissue samples and thereby obviate the need for internal standards ( Figure 1B). To test this premise, we compared the LC-MS metabolite profiles of central nervous system (CNS) tissues from wild-type mice and mice lacking the enzyme FAAH (9) [FAAH(-/-) mice], which degrades several neural signaling lipids in ViVo (10), (10,12) and thus provided an excellent model for testing the capacity of DMP to identify both known changes in the levels of specific FAAH substrates and potentially novel metabolites regulated by this enzyme in ViVo.…”

The faah gene is the first direct target of estrogen in the testis: role of histone demethylase LSD1

“…Both endocannabinoids affect male reproductive functions: 2-arachidonoylglycerol has a pivotal role in spermatogenesis, by promoting the meiotic progression of germ cells [16]; AEA controls sperm functionality by reducing motility, capacitation, and acrosome reaction [17,18], and it also reduces the spermatogenic output by inducing apoptosis of Sertoli cells [15]. AEA signaling depends on its endogenous content, that in vivo is strongly controlled by FAAH [19]. Remarkably, recent studies have shown that among the different components of the ''endocannabinoid system'' (i.e., AEA-binding receptors and metabolic enzymes) in Sertoli cells, only FAAH is a target of follicle-stimulating hormone (FSH) [14,15].…”

Inhibition of Fatty-Acid Amide Hydrolase Accelerates Acquisition and Extinction Rates in a Spatial Memory Task

“…FAAH (À/À) mice have been shown to possess quantities of anandamide and other FAAs (eg, oleamide, PEA, OEA) in the brain and other areas more than 10 times the levels seen in wild-type mice. Accordingly, FAAH (À/À) mice represent a useful tool to evaluate the physiological function of these lipid signaling molecules (Cravatt et al, 2001;Clement et al, 2003). In addition to displaying dramatically enhanced responses to intraperitoneal injections of anandamide, FAAH (À/À) mice display CB 1 receptor mediated hypoalgesic responses to radiant heat and inflammatory stimuli (Cravatt et al, 2001;Lichtman et al, 2004b).…”

“…Accordingly, FAAH (À/À) mice represent a useful tool to evaluate the physiological function of these lipid signaling molecules (Cravatt et al, 2001;Clement et al, 2003). In addition to displaying dramatically enhanced responses to intraperitoneal injections of anandamide, FAAH (À/À) mice display CB 1 receptor mediated hypoalgesic responses to radiant heat and inflammatory stimuli (Cravatt et al, 2001;Lichtman et al, 2004b). In parallel with the transgenic models, several pharmacological inhibitors of FAAH have been developed and shown to elicit cannabinoid-receptor mediated analgesia, notably reversible a-ketoheterocyle inhibitors (eg, OL-135), and irreversible carbamate inhibitors (eg, URB-597).…”