Central functional response to the novel peptide cannabinoid, hemopressin
Introduction
To date, all known endogenous cannabinoids, such as 2-arachidonoylglycerol (2-AG) and anandamide, are eicosanoid fatty acid derivatives (Bisogno, 2008; Petrosino and Di Marzo, 2010). These endocannabinoids are released by postsynaptic neurons “on demand,” following the Ca2+ influx produced in response to postsynaptic depolarization or activation of metabotropic receptors (Kano et al., 2009). When released into the synaptic cleft, endocannabinoids activate presynaptic cannabinoid 1 (CB1) receptors, and impart an inhibitory action on further presynaptic transmission (Di Marzo et al., 2004; Wilson and Nicoll, 2002). Pharmacological manipulation, coupled with expression studies, has implied integral roles for CB1 in a diverse range of physiological functions, including memory, cognition, reward, appetite and nociception (Pertwee, 2005; Valverde et al., 2005). Due to this diverse functionality, CB1 receptors have immense therapeutic potential and are, in fact, established targets particularly in nociceptive and metabolic disorders (Di Marzo, 2011; Di Marzo et al., 2011; Walker and Hohmann, 2005).
The development of CB1-based therapies, particularly as anti-obesity treatments, has been hindered following the withdrawal of rimonabant (Acomplia; SR141716) by the European Medicines Agency. Rimonabant is a synthetic CB1 inverse agonist, capable of producing weight-reducing effects over extended periods in rodents and humans (Di Marzo, 2008; Van Gaal et al., 2005). Rimonabant antagonises central CB1 receptors to acutely reduce motivational appetite (Griebel et al., 2005; Thornton-Jones et al., 2005, 2007). This effect involves a corticostriatal–hypothalamic pathway thought to provide a link whereby reward/motivational circuits impinge on the hypothalamic control of feeding (Dodd et al., 2009; Kelley et al., 2005). In addition to affecting motivational appetite, rimonabant reduces body-fat mass via peripheral interaction with lipid mobilization pathways in adipose tissue and liver, and via energy expenditure and cellular glucose uptake (Di Marzo, 2008; Dodd et al., 2009; Kunos et al., 2009; Nogueiras et al., 2008). Despite being an effective anti-obesity treatment, the withdrawal of rimonabant was a consequence of undesirable central nervous system effects resulting in depression, anxiety or suicidality (Christensen et al., 2007). The discovery of selective CB1 antagonists capable of maintaining therapeutic benefits whilst lacking these adverse side effects is highly coveted.
Hemopressin is a nine-amino acid peptide, derived from the alpha chain of haemoglobin, which was discovered originally using substrate capture on rat brain homogenates (Heimann et al., 2007; Rioli et al., 2003). Hemopressin acts in vitro to functionally antagonise CB1 receptors, and demonstrates selective CB1 inverse agonism with sub-nanomolar potency (Dodd et al., 2010b; Heimann et al., 2007). Like rimonabant, hemopressin inhibits food intake in both normal and obese rodent models, and hemopressin can block CB1 agonist-induced hyperphagia in vivo (Dodd et al., 2010b). Interestingly, whereas rimonabant's anorectic effects are by inhibiting hedonic motivation, hemopressin appears to have a specific effect on satiety rather than on reward, and does not exhibit some of rimonabant's off-target behavioural side effects, at least in rodents (Dodd et al., 2009, 2010b; Kirkham, 2009). Hemopressin also induces robust non-opioid antinociception (Heimann et al., 2007), again devoid of non-selective behavioural effects, such as hypothermia, catalepsy and hypoactivity, seen previously with synthetic CB1 ligands (Hama and Sagen, 2011b; Rahn and Hohmann, 2009). Taken together, these studies suggest that hemopressin may confer its anorectic and antinociceptive actions via more defined CB1-mediated mechanisms. However, owing to its small size and high sequence homology with haemoglobin, hemopressin's expression, mode of action, and the neuronal targets underlying the peptide's behavioural effects are yet to be explored fully. Understanding the central circuits mediating hemopressin's action at a whole-brain level may be of high significance as it will offer a deeper insight into modes of CB1 receptor antagonism.
By using the complementary techniques of c-Fos immunohistochemical activity mapping and blood-oxygen-level-dependent (BOLD), pharmacological-challenge magnetic resonance imaging (phMRI), we aim to describe the central circuitry modulated by hemopressin in rodents. Through comparison with the effects in CB1−/− mice and to that of the rimonabant structural analogue, AM251, we hypothesise that hemopressin may act as a functional antagonist at CB1 receptors capable of selectively modulating the activity of hypothalamic appetite centres in the brain.
Section snippets
Animals
Experiments were carried out using adult male Sprague–Dawley rats, CD1 mice (Charles River Laboratories, Inc., Sandwich, UK) and CB1+/+ and CB1−/− littermate mice (Marsicano et al., 2002). Animals were group housed in The University of Manchester animal unit in a constant environment of 21 ± 2 °C and 45 ± 10% humidity, on a 12:12 h light–dark cycle with the dark phase commencing at 20:00. Chow (Beekay International, Hull, UK) and tap water were available ad libitum. All procedures conformed
Effects of hemopressin and the synthetic CB1 inverse agonist, AM251, on c-Fos immunoreactivity
To demonstrate that hemopressin and AM251 were effective in these animals, food intake was significantly decreased 90 min after injection (vehicle: 1.3 ± 0.1 g, hemopressin: 0.8 ± 0.1 g, p < 0.05; vehicle: 1.2 ± 0.2 g, AM251: 0.4 ± 0.1 g, p < 0.05). Quantitative analysis of the number of c-Fos-positive neurones in the brain regions of interest revealed a significant increase in counts following hemopressin (Figs. 1 and 3) administration. Hemopressin, when compared with vehicle injection,
Discussion
Despite growing evidence suggesting that hemopressin plays a behaviourally selective role in both CB1-mediated nociception and appetite (Dodd et al., 2010a; Heimann et al., 2007), nothing is known of the underlying neuronal mechanisms. To address this at the ‘whole-brain’ level, we have employed complementary BOLD phMRI and c-Fos protein functional activity mapping to spatially resolve the underlying neuronal circuitry modulated by hemopressin and the synthetic CB1 inverse agonist, AM251. Our
Disclosure statement
The authors Garron T. Dodd, Amy A. Worth, Duncan J. Hodkinson, Raj K. Srivastava, Beat Lutz, Steven R. Williams, and Simon M. Luckman all declare no conflict of interest.
Acknowledgements
The authors wish to thank the technical assistance of Miss Katie Murray for assistance with femoral artery cannulations, and Ms Karen Davies for maintenance of the MRI magnet and console. This work was supported by a Biotechnology and Bioscience Research Council grant.
References (69)
- et al.
Regional differences in naloxone modulation of Delta(9)-THC induced Fos expression in rat brain
Neuropharmacology
(2003) - et al.
Synaptic input and output of parvalbumin-immunoreactive neurons in the neostriatum of the rat
Neuroscience
(1994) - et al.
Efficacy and safety of the weight-loss drug rimonabant: a meta-analysis of randomised trials
Lancet
(2007) - et al.
Central cannabinoid signaling mediating food intake: a pharmacological-challenge magnetic resonance imaging and functional histology study in rat
Neuroscience
(2009) - et al.
Effects of the cannabinoid CB1 receptor antagonist rimonabant in models of emotional reactivity in rodents
Biol. Psychiatry
(2005) - et al.
Chronic food restriction increases D-1 dopamine receptor agonist-induced phosphorylation of extracellular signal-regulated kinase 1/2 and cyclic AMP response element-binding protein in caudate–putamen and nucleus accumbens
Neuroscience
(2004) - et al.
Activation of spinal and supraspinal cannabinoid-1 receptors leads to antinociception in a rat model of neuropathic spinal cord injury pain
Brain Res.
(2011) - et al.
Centrally mediated antinociceptive effects of cannabinoid receptor ligands in rat models of nociception
Pharmacol. Biochem. Behav.
(2011) - et al.
Coexpression of the cannabinoid receptor type 1 with dopamine and serotonin receptors in distinct neuronal subpopulations of the adult mouse forebrain
Neuroscience
(2002) - et al.
Corticostriatal–hypothalamic circuitry and food motivation: integration of energy, action and reward
Physiol. Behav.
(2005)
Feeding induced by blockade of AMPA and kainate receptors within the ventral striatum: a microinfusion mapping study
Behav. Brain Res.
Should peripheral CB(1) cannabinoid receptors be selectively targeted for therapeutic gain?
Trends Pharmacol. Sci.
Anatomical basis for cannabinoid-induced antinociception as revealed by intracerebral microinjections
Brain Res.
An examination of the central sites of action of cannabinoid-induced antinociception in the rat
Life Sci.
Mirtazapine antagonises the subjective, hormonal and neuronal effects of m-chlorophenylpiperazine (mCPP) infusion: a pharmacological-challenge fMRI (phMRI) study
Neuroimage
CB1 receptor mediated analgesia from the Nucleus Reticularis Gigantocellularis pars alpha is activated in an animal model of neuropathic pain
Brain Res.
About being BOLD
Brain Res. Rev.
Changes in spinal and supraspinal endocannabinoid levels in neuropathic rats
Neuropharmacology
Cannabinoids as pharmacotherapies for neuropathic pain: from the bench to the bedside
Neurotherapeutics
Novel natural peptide substrates for endopeptidase 24.15, neurolysin, and angiotensin-converting enzyme
J. Biol. Chem.
A stereotaxic MRI template set for the rat brain with tissue class distribution maps and co-registered anatomical atlas: application to pharmacological MRI
Neuroimage
Modulation of morphine-induced Fos-immunoreactivity by the cannabinoid receptor antagonist SR 141716
Neuropharmacology
Functional magnetic resonance imaging and c-Fos mapping in rats following an anorectic dose of m-chlorophenylpiperazine
Neuroimage
Effects of the cannabinoid-1 receptor blocker rimonabant on weight reduction and cardiovascular risk factors in overweight patients: 1-year experience from the RIO-Europe study
Lancet
Endogenous cannabinoids: structure and metabolism
J. Neuroendocrinol.
Regional differences in cannabinoid receptor/G-protein coupling in rat brain
J. Pharmacol. Exp. Ther.
Optimization of neuropeptide extraction from the mouse hypothalamus
J. Proteome Res.
Glutamate and the neural basis of the subjective effects of ketamine: a pharmaco-magnetic resonance imaging study
Arch. Gen. Psychiatry
The endocannabinoid system in obesity and type 2 diabetes
Diabetologia
Endocannabinoids: an appetite for fat
Proc. Natl. Acad. Sci. U. S. A.
The endocannabinoid system and its therapeutic exploitation
Nat. Rev. Drug Discov.
Cannabinoids and endocannabinoids in metabolic disorders with focus on diabetes
Handb. Exp. Pharmacol.
The peptide hemopressin acts through CB1 cannabinoid receptors to reduce food intake in rats and mice
J. Neurosci.
Functional magnetic resonance imaging and c-Fos mapping in rats following a glucoprivic dose of 2-deoxy-D-glucose
J. Neurochem.
Cited by (34)
Intracellular peptides as drug prototypes
2022, Peptide and Peptidomimetic Therapeutics: From Bench to BedsideCharacterization of pepcan-23 as pro-peptide of RVD-hemopressin (pepcan-12) and stability of hemopressins in mice
2021, Advances in Biological RegulationHemopressin as a breakthrough for the cannabinoid field
2021, NeuropharmacologyCitation Excerpt :In contrast to the CB1R antagonist, AM251, the anorectic effects of hemopressin do not involve the brain reward centers, such as the ventral tegmental area, nucleus accumbens, and orbitofrontal cortex, which normally form a functional activity signature for the central action of synthetic CB1R inverse agonists (Dodd et al., 2013). Thus, hemopressin may offer behaviorally selective effects on nociception and appetite, without engaging reward pathways (Dodd et al., 2010, 2013). Interestingly, intraperitoneal (Leone et al., 2018) or intracerebral (Recinella et al., 2018) injection of RVD-HP also showed anorexigenic properties in rats, a mechanism that could be partially mediated by lowering of levels of orexin-A, proopiomelanocortin, and agouti-related peptide gene expression (Leone et al., 2018; Recinella et al., 2018).
The potential anti-inflammatory and anti-nociceptive effects of rat hemopressin (PVNFKFLSH) in experimental arthritis
2021, European Journal of PharmacologyHemoglobin-derived peptides and mood regulation
2020, PeptidesNFKF is a synthetic fragment derived from rat hemopressin that protects mice from neurodegeneration
2020, Neuroscience LettersCitation Excerpt :Subsequently, characterization of a large number of endogenous HP-derived/HP-containing peptides with cannabinoid activity suggested the existence of new players on the endocannabinoid system [4–8]. Despite of the still elusive biological significance of having two distinctive endocannabinoid systems (i.e. protein-derived and lipid-derived endocannabinoids), HP and the smaller CB1R-active synthetic peptide NFKF were shown to have oral pharmacological activity [4,1,2,9,10]. One of the pharmacological activities shown for both HP and NFKF was to delay the symptoms and seizures of pilocarpine-induced seizures in mice [4].