Effect of gabapentin derivates on mechanical allodynia-like behaviour in a rat model of chronic sciatic constriction injury

A novel gabapentin analogue assuages neuropathic pain response in chronic sciatic nerve constriction model in rats

Gabapentin (GBP) is an established drug that has been used in the management of symptoms of neuropathy but it is associated with unwanted side effects such as sedation and motor incoordination. The goal of the study was to find out a drug with greater efficacy and safety for the treatment of neuropathic pain. Our previously synthesized GABA analogue (Gabapentsal, GPS) was tested (25-100 mg/kg, i.p) in chronic constriction injury (CCI) induced nociceptive model of static allodynia, dynamic allodynia, thermal hyperalgesia, mechanical hyperalgesia and cold allodynia in rats (Sprague Dawley). Open field and rotarod tests were performed to assess the impact of GPS on the motor performance of the animals. GBP (100 mg/kg, i.p) was used as a standard for comparison. GPS dose dependently reduced static (P <0.001) and dynamic allodynia (P <0.001), thermal hyperalgesia (P <0.001), mechanical hyperalgesia (P < 0.001) and cold allodynia (P < 0.001). In comparison to GBP, GPS failed to alter any significantly the motor performance of rats in both the open field and rotarod assays. These results suggest that GPS is effective in alleviating nociception in CCI neuropathic pain model but free from the side effect of motor discoordination seen in the treatment with GBP. In conclusion, GPS may prove to be a prospectively more effective and safer option in the management of neuropathic syndromes.

Synergistic interaction between haloperidol and gabapentin in a model of neuropathic nociception in rat

Preclinical studies have reported that sigma-1 receptor antagonists may have efficacy in neuropathic pain states. The sigma-1 receptor is a unique ligand-operated chaperone present in crucial areas for pain control, in both the peripheral and central nervous system. This study assesses the synergistic antihyperalgesic and antiallodynic effect of haloperidol, a sigma-1 antagonist, combined with gabapentin in rats with peripheral neuropathy. Wistar rats male were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of gabapentin and the sigma-1 receptor antagonist, haloperidol, were examined at 11 days post-CCI surgery. An analysis of Surface of Synergistic Interaction was used to determine whether the combination's effects were synergistic. Twelve combinations showed various degrees of interaction in the antihyperalgesic and antiallodynic effects. In hyperalgesia, three combinations showed additive effects, four combinations showed supra-additive effects, and three combinations produced an effect limited by the maximum effect. In allodynia, five combinations showed additive effects, two combinations showed supra-additive effects, and five combinations produced antihyperalgesic effects limited by the maximum effect. These findings indicate that the administration of some specific combination of gabapentin and haloperidol can synergistically reduce nerve injury-induced allodynia and hyperalgesia. This suggests that the haloperidol-gabapentin combination can improve the antiallodynic and antihyperalgesic effects in a neuropathic pain model.

Pregabalin reduces muscle and cutaneous hyperalgesia in two models of chronic muscle pain in rats

Pregabalin is used for treatment of neuropathic pain conditions. The present study evaluated effects of pregabalin in 2 rat models of muscle-induced hyperalgesia: Inflammatory and noninflammatory. Muscle hyperalgesia (withdrawal threshold to compression of the muscle) and cutaneous hyperalgesia of the paw (withdrawal threshold to von Frey filaments) were measured before and after induction of hyperalgesia and after treatment with pregabalin (saline, 10 to 100 mg/kg i.p.). In the inflammatory model, 3% carrageenan injected into 1 gastrocnemius muscle decreased the mechanical withdrawal threshold of the paw bilaterally and the compression withdrawal threshold of the muscle ipsilaterally 2 weeks later. Pregabalin (10 to 100 mg/kg) increased the compression withdrawal threshold of the inflamed muscle when compared with vehicle controls. Pregabalin also increased the mechanical withdrawal threshold of the paw bilaterally, but only with 100 mg/kg. In the noninflammatory model, 2 unilateral injections of acidic saline into the gastrocnemius muscle produced bilateral cutaneous and muscle hyperalgesia 24 hours after the second injection. Pregabalin (10 to 100 mg/kg i.p.) significantly increased the compression withdrawal thresholds of the muscle and the mechanical withdrawal threshold of the paw bilaterally when compared with vehicle. However, pregabalin also has significant motor effects at the higher doses (60 to 100 mg/kg). Therefore, pregabalin reduces both muscle and cutaneous hyperalgesia that occurs after muscle insult in 2 animal models of muscle pain at doses that do not produce ataxia.

PERSPECTIVE

This study shows that pregabalin reduces both cutaneous and muscle hyperalgesia in inflammatory and noninflammatory models of muscle pain. Thus, pregabalin may be an effective treatment for people with chronic muscle pain.

Carboxylate bioisosteres of gabapentin

A series of carboxylate bioisosteres of structures related to gabapentin 1 have been prepared. When the carboxylate was replaced by a tetrazole, this group was recognized by the alpha2-delta protein. Further characterization of alpha2-delta binding compounds 14a and 14b revealed a similar pattern of functional in vitro and in vivo activity to gabapentin 1.