Do gabapentin or pregabalin directly modulate the µ receptor?

Mechanism of gabapentinoid potentiation of opioid effects on cyclic AMP signaling in neuropathic pain

Over half of spinal cord injury (SCI) patients develop opioid-resistant chronic neuropathic pain. Safer alternatives to opioids for treatment of neuropathic pain are gabapentinoids (e.g., pregabalin and gabapentin). Clinically, gabapentinoids appear to amplify opioid effects, increasing analgesia and overdose-related adverse outcomes, but in vitro proof of this amplification and its mechanism are lacking. We previously showed that after SCI, sensitivity to opioids is reduced by fourfold to sixfold in rat sensory neurons. Here, we demonstrate that after injury, gabapentinoids restore normal sensitivity of opioid inhibition of cyclic AMP (cAMP) generation, while reducing nociceptor hyperexcitability by inhibiting voltage-gated calcium channels (VGCCs). Increasing intracellular Ca2+ or activation of L-type VGCCs (L-VGCCs) suffices to mimic SCI effects on opioid sensitivity, in a manner dependent on the activity of the Raf1 proto-oncogene, serine/threonine-protein kinase C-Raf, but independent of neuronal depolarization. Together, our results provide a mechanism for potentiation of opioid effects by gabapentinoids after injury, via reduction of calcium influx through L-VGCCs, and suggest that other inhibitors targeting these channels may similarly enhance opioid treatment of neuropathic pain.

Effects of Gabapentinoids on Heroin-Induced Ventilatory Depression and Reversal by Naloxone

Despite an increasing prevalence of gabapentinoids (gabapentin and pregabalin) in opioid overdose deaths, little research has evaluated potentially harmful interactions between gabapentinoids and opioids. This study sought to determine the effects of gabapentinoids on the ventilatory depressive effects of heroin and their reversal by naloxone. Rats were given gabapentin, pregabalin, or saline prior to receiving increasing doses of heroin while ventilation was monitored using whole-body plethysmography. In some sessions naloxone was administered following the largest dose of heroin. The primary outcomes of this study were minute volume and Pause. Heroin dose-dependently reduced minute volume and increased Pause. Administration of naloxone dose-dependently reversed the effects of heroin on ventilation. Gabapentinoids did not alter the ventilatory depressive effects of heroin alone but reduced the potency of naloxone to reverse heroin-induced ventilatory depression. These preliminary findings emphasize the need for further research evaluating interactions between gabapentinoids and opioids related to substance misuse and overdose.

Mirogabalin Decreases Pain-like Behaviours and Improves Opioid and Ketamine Antinociception in a Mouse Model of Neuropathic Pain

Neuropathic pain remains a difficult clinical challenge due to its diverse aetiology and complex pathomechanisms, which are yet to be fully understood. Despite the variety of available therapies, many patients suffer from ineffective pain relief; hence, the search for more efficacious treatments continues. The new gabapentinoid, mirogabalin has recently been approved for clinical use. Although its main mechanism of action occurs at the α2σ-1 and α2σ-2 subunits of calcium channels and is well documented, how the drug affects the disturbed neuropathic interactions at the spinal cord level has not been clarified, which is crucial information from a clinical perspective. The findings of our study suggest that several indirect mechanisms may be responsible for the beneficial analgesic effect of mirogabalin. This is the first study to report that mirogabalin enhances the mRNA expression of spinal antinociceptive factors, such as IL-10 and IL-18BP, and reduces the concentration of the pronociceptive substance P. Importantly, mirogabalin improves the morphine-, buprenorphine-, oxycodone-, and ketamine-induced antinociceptive effects in a neuropathic pain model. Our findings support the hypothesis that enhancing opioid and ketamine analgesia by combining these drugs with mirogabalin may represent a new strategy for the effective pharmacotherapy of neuropathic pain.