University of Colorado-Boulder

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1 University of Colorado-Boulder Activated Glia as Culprits in Opposing Opioid Analgesia & Driving Tolerance, Dependence & Reward: Role of a Non-classical Non-classical Opioid Receptor Linda R. Watkins Psychology & Center for Neuroscience University of Colorado at Boulder 1

2 CU-Boulder: Kim Brown Ben Coats Susannah Lewis Steven Maier Alexis Northcutt Niloofar Rezvani University of Adelaide Mark Hutchinson University of Sydney Ian Johnston National Institute Drug Abuse/NIH Kenner Rice Global Concepts Views of pain & opioid effects are changing Glia (microglia (microglia & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor 2

3 Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor 3

4 Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor 4

5 Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor Global Concepts Views of pain & opioid effects are changing Glia (microglia( & astrocytes) in CNS are key players in: * pain amplification, including pathological pain * making acute opioids (such as morphine) less effective for pain control * causing chronic morphine to lose effect, contributing to opioid tolerance * driving morphine dependence/withdrawal * driving morphine reward, linked to drug craving * driving other opioid-induced negative side effects Opioids activate glia via a non-classical opioid receptor 5

6 Neuropathic Pain Glial Dysregulation of Pain Activation of: *Microglia *Astrocytes Release of: *Interleukin-1 *Interleukin-6 *Tumor Necrosis factor Each Enhance Pain Effects Synergize Watkins et al., Brain Research Reviews

7 Glial Dysregulation of Opioids Activation of: *Microglia *Astrocytes Release of: *Interleukin-1 *Interleukin-6 *Tumor Necrosis factor Each Enhance Pain Results in: * Analgesia * Naïve tolerance * Tolerance * Dependence * Reward * Side Effects Effects Synergize Hutchinson et al., TheScientificWorldJournal 2007 The initial discovery of glial regulation of opioid actions was made in the context of Morphine Tolerance 7

8 Glial Activation by Repeated Morphine GFAP: Spinal Cord Saline Morphine Close Up Of Glia Song & Zhao, Neurosci. Research 2001 Chronic i.t. Morphine Increases Spinal Cord Interleukin-1 Johnston et al., Journal of Neuroscience 04 8

9 Spinal : i.t. Morphine Tolerance & Withdrawal-Induced Pain Facilitation (Johnston et al. Journal of Neuroscience 04) Tailflick Latency (sec) Based on these hints, we began exploring glial regulation of Acute Morphine Analgesia 9

10 Glial Activation Opposes the Analgesic Efficacy of Both Acute i.t. Morphine & i.t. Methadone Percent of Maximal Possible Effect BL Timecourse (Minutes) BL Timecourse (Minutes) Hutchinson et al., MS in review Spinal Glial Activation Opposes the Analgesic Efficacy of Systemic Morphine, Too! Hutchinson et al., MS in review 10

11 Intrathecal ra Unmasks Morphine Analgesia Analgesia Morphine Behavioral output =Morphine + Pain Interleukin-1 Intrathecal ra Unmasks Morphine Analgesia Analgesia Morphine Pain ra Interleukin-1 11

12 Spinal Glial Opposition of Morphine: involvement of multiple proinflammatory cytokines Hutchinson et al., MS in review Spinal Glial Opposition of Morphine: Microglia implicated - Hutchinson et al., MS in review Hutchinson et al., Society for Neuroscience,

13 i.t. ra Enhances Morphine: Leftward Dose-Response Shift Hutchinson et al., MS in review i.t. ra Amplifies i.t. Morphine: Leftward Dose-Response Shift Hutchinson et al., MS in review 13

14 i.t. ra: Enhanced Efficacy of Morphine: NOT Due to Altered Pharmacokinetics Circles: Morphine in CSF (ng/ul) With IL1ra; Without IL1ra Squares: Morphine in Spinal Cord (ng/mg) With IL1ra; Without IL1ra Hutchinson et al., MS in review 2007 Does Glial Dysregulation of Opioids Only Occur in Spinal Cord? Might suppressing glial activation impact brain mediated: * Dependence/withdrawal? * Reward? * Other negative side effects? 14

15 AV411 Blocks Naloxone-Precipitated Morphine Withdrawal (Hutchinson et al., MS in review 2008) Behavioral Withdrawal Score Naltrexone to Precipitate Withdrawal Vehicle + Morphine Timecourse (Minutes) AV411 Blunts Morphine-Induced Release of Nucleus Accumbens Dopamine, by In Vivo Microdialysis 5 days of twice daily: Morphine + Vehicle Bland et al. MS in prep 08 Morphine + AV411 Reward Vehicle or AV411 + Saline Dopamine Timecourse (20 min collection intervals) 15

16 AV411 Blunts Morphine-Induced Release of Nucleus Accumbens Dopamine, by In Vivo Microdialysis 5 days of twice daily: Morphine + Vehicle Bland et al. MS in prep 08 Morphine + AV411 Reward Vehicle or AV411 + Saline Dopamine Timecourse (20 min collection intervals) Glia & Opioid Reward: Conditioned Place Preference Morphine/Saline Test Pre-exposure place preference Saline Morphine Saline paired Saline paired 16

17 Inhibiting Glial Activation Suppresses Morphine Reward as Measured by CPP Reward Hutchinson et al., MS in review 08 Glial Inhibitor Suppresses Respiratory Depression Morphine + Vehicle Mor + 25 mg/kg Minocycline Mor + 50 mg/kg Minocycline Minute Volume v Veh + 50 mg/kg Mino Vehicle + Vehicle Inspiratory Force Hutchinson et al. MS in review 08 17

18 Opioid Effects are Different for Neurons & Glia Neuronal Receptors are Stereoselective: [-]Methadone: [+]Methadone: Active Agonist INActive Agonist at Classical Opioid Receptor at Classical Opioid Receptor Opioid Effects are Different for Neurons & Glia Neuronal Receptors are Stereoselective: [-]-Naloxone: [+]-Naloxone: Active Antagonist INactive Antagonist at Classical Opioid Receptor at Classical Opioid Receptor This Point is KEY 18

19 Classical view of opioid-induced analgesia Neuron (+)-Opioid ANALGESIA Opioid Effects are Different for Neurons & Glia GLIAL Receptors are Not Stereoselective! [-]& [+] Isomers have EQUAL effects on glia [-]-Methadone: Active Agonist at Glial Opioid Receptor [+]-Methadone: Active Agonist at Glial Opioid Receptor Glial opioid receptor -- Fits BOTH [-] & [+]-enantiomers 19

20 What if Glial Non-Stereoselectivity Extends to Opioid Antagonists? [-]-Naloxone: Active Antagonist at Glial Opioid receptor [+]-Naloxone: Active Antagonist at Glial Opioid receptor [+]-Naloxone should POTENTIATE morphine analgesia by: (a) NOT blocking morphine effects on neurons, yet (b) Removing glial activation that OPPOSES analgesia! Neuronally INACTIVE [+]-Naloxone Potentiates Morphine Analgesia! Suggests Effects on Glia & Neurons May be Separable! Hutchinson et al., MS in prep 08 20

21 Neuronally INACTIVE (+)-Naltrexone Potentiates Morphine Analgesia, Too! 100 Morphine alone Morphine + (+)-Naltrexone ** *** *** *** *** * ** * IL1ra 0 BL Time (min post IT drug admin) Hutchinson et al., MS in prep 08 Opioid Activation of Glia Suppresses Analgesia ANALGESIA Analgesia TLR4 21

22 Opioid Activation of Glia Suppresses Analgesia: Blockade by (+)-Naloxone (+)-naloxone TLR4 ANALGESIA Why is This Important? This Difference Predicts: Morphine effects on neurons & glia should be separable! ) 22

23 Why is This Important? This Difference Predicts: Morphine effects on neurons & glia ) should be separable! To increase the efficacy of opioids: * structurally modify opioids to prevent glial activation, or * create a long-lasting version of (+)-naloxone that only blocks glia Soooooo. What s s the mystery opioid receptor on glia? To target it, one must know what it is Toll-Like Receptors (TLRs): Classically. not me, not right, not OK receptors Toll-Like Receptors (TLRs) detect: *pathogens (bacteria, viruses, etc.) *endogenous danger signals (damage/death) * All classes of opioids used clinically Hutchinson et al., TheScientificWorldJournal

24 This isn t t just morphine! All major classes of clinically utilized opioid analgesics are TLR4 agonists 4,5-epoxymorphinans: morphine, oxycodone, buprenorphine 3,3-diphenylpropylamine: methadone 4-phenylpiperidine: pethadine 4-amilinopiperidine: fentanyl Hutchinson et al., MS in prep 08 TLR4 Induced Glial Activation TLR4 expression is upregulated by: * Neuropathy * Opioids, non-stereoselectively TLR4 is activated by: * Neuropathy * Opioid agonists, non-stereoselectively TLR4 is blocked by: * Naloxone, non-stereoselectively Hutchinson et al., TheScientificWorldJournal

25 Toll Like Receptor-4 (TLR4): (+)-Naloxone, a TLR4 antagonist, non-stereoselectively reverses neuropathic pain Hutchinson et al., in review (+)-Naloxone Reverses CCI Neuropathy-Induced Microglial Activation Each Panel: Spinal cord dorsal horn ipsilateral to nerve injury Saline (+)-Naloxone 25

26 Neuropathy-Induced Glial Activation & Pain: TLR4 is Key Glial activation in spinal dorsal horn & neuropathic pain are suppressed in TLR4 KOs TLR4 Knock Outs Wild Type Tanga et al. PNAS 05 TLR induced glial activation: Opioids Glia TLR4 Neuronal Consequences Neuron 26

27 TLR induced glial activation: Endogenous danger signals Glia Neuron Neuronal Consequences Neuron TLR induced glial activation: Endog. danger signals + Opioids Neuron Glia Naïve Tolerance Neuronal Consequences Neuron 27

28 Conclusions - 1 So, Taken Together The Data Predict That Suppressing Glial Activation Will: Suppress neuropathic pain, etc. Improve opioid analgesia Suppress opioid tolerance Suppress opioid dependence Suppress opioid reward linked to drug craving/drug seeking Suppress other negative side effects 28

29 Conclusions - 2 Opioid Activation of Glia is Fundamentally Different Than Neurons: Glial opioid receptors: not stereoselective Opioid effects on glia must be via different receptors than for neurons: TLR4 Effects on glia & neurons should be separable To increase the efficacy of opioids: * Modify opioids so they don t bind glia &/or * Create long-lasting versions of [+]-naloxone Conclusions - 3 TLR4: Pivotal for Glial Activation by BOTH Opioids & Neuropathic Pain TLR4: Activated by both opioids & neuropathic pain Activation of TLR4 by nerve injury: endogenous danger signals released by stressed/injured cells (+)-Naloxone as a stand alone drug, treats neuropathic pain as a TLR4 antagonist 29

30 Colorado - High on Science! AV411 Suppresses Chronic Morphine Induced Glial Activation (Hutchinson et al. MS in review) Morphine+Vehicle Morphine + AV411 PAG Trigem. Nuclei 30