Enhancing KCC2 function counteracts morphine-induced hyperalgesia

Abstract

Morphine-induced hyperalgesia (MIH) is a severe adverse effect accompanying repeated morphine treatment, causing a paradoxical decrease in nociceptive threshold. Previous reports associated MIH with a decreased expression of the Cl− extruder KCC2 in the superficial dorsal horn (SDH) of the spinal cord, weakening spinal GABAA/glycine-mediated postsynaptic inhibition. Here, we tested whether the administration of small molecules enhancing KCC2, CLP257 and its pro-drug CLP290, may counteract MIH. MIH was typically expressed within 6–8 days of morphine treatment. Morphine-treated rats exhibited decreased withdrawal threshold to mechanical stimulation and increased vocalizing behavior to subcutaneous injections. Chloride extrusion was impaired in SDH neurons measured as a depolarizing shift in E GABA under Cl− load. Delivering CLP257 to spinal cord slices obtained from morphine-treated rats was sufficient to restore Cl− extrusion capacity in SDH neurons. In vivo co-treatment with morphine and oral CLP290 prevented membrane KCC2 downregulation in SDH neurons. Concurrently, co-treatment with CLP290 significantly mitigated MIH and acute administration of CLP257 in established MIH restored normal nociceptive behavior. Our data indicate that enhancing KCC2 activity is a viable therapeutic approach for counteracting MIH. Chloride extrusion enhancers may represent an effective co-adjuvant therapy to improve morphine analgesia by preventing and reversing MIH.

Neurobiological Correlates of Pain Avoidance-Like Behavior in Morphine-Dependent and Non-Dependent Rats

“…Similar morphine regimens reliably induce analgesic and other forms of tolerance, in addition to central sensitization (e.g., Enrico et al, 1997; Walker et al, 1997; Craft et al, 1999; Haugan et al, 2008; Ferrini et al, 2017). To determine if the escalating morphine regimen (10-20 mg/kg) increased mechanical hypersensitivity during morphine withdrawal, we measured paw withdrawal thresholds (von Frey) at the end of weeks 1 & 2 of treatment.…”

Opioid and nondopamine reward circuitry and state‐dependent mechanisms

“…Repeated morphine treatment disrupted intraneuronal chloride ion homeostasis in the superficial dorsal horn in the spinal cord in rats that exhibited morphine‐induced hyperalgesia, and hyperalgesia was counteracted by enhancing KCC2 function . Thus, changes in intraneuronal chloride homeostasis that were caused by lower KCC2 expression might be commonly induced by chronic opioid treatment, and these changes might be an important mechanism that contributes to opioid dependence.…”

Enhancing KCC2 activity decreases hyperreflexia and spasticity after chronic SCI

“…Following chronic SCI, there is a ~10-20% decrease in motoneuronal KCC2 expression, and the translocation of KCC2 to the somatic membrane of motoneurons is significantly reduced (Boulenguez et al, 2010;Bos et al, 2013). As CLP257 works post-translationally to increase KCC2 membrane expression (Gagnon et al, 2013;Ferrini et al, 2017), we compared the ratio of membrane KCC2 to cytosolic KCC2 immuno-labelling between groups. Figure 7 shows KCC2 immunoreactivity in lumbar motoneurons after chronic SCI in animals that received CLP257 ( Fig.…”

“…Recently, a family of selective KCC2 activators known as CLPs was developed, allowing us to directly target KCC2 activity (Gagnon et al, 2013;Kahle et al, 2014;Ferrini et al, 2017). CLPs have been shown to restore impaired KCC2-mediated Clextrusion in neurons in vitro and in vivo (Gagnon et al, 2013), and were later shown to increase KCC2 activity in various disease models in which KCC2 is pathologically decreased (Gagnon et al, 2013;Ostroumov et al, 2016;Ferrini et al, 2017;Chen et al, 2018;Thomas et al, 2018;Lizhnyak et al, 2019).…”