44 / 2021-07-29 14:11:29

Research on the mechanism underlying the Kv7 Channel Opener QO-83 on Neuropathic Pain

Kv7 channel; neuropathic pain; thalamic pain; CCI, CFA, KCNQ2

Neuropathic pain (NP) can be caused by primary lesions, dysfunction, or temporary disturbances of the peripheral or central nervous system^[1]. The risk of developing central poststroke pain is highest in patients with thalamic infarctions, in particular lesions involving the anterior pulvinar region of the thalamus and the ventral posterolateral nucleus of the thalamus. Central pain occurs immediately after injury, or is delayed up to 6 to 12 months, or persists for life, leading to severe psychosocial and functional consequences ^[2-4]. It shows that the development of compounds with analgesic effect is worthy of further research.

Neuronal hyperexcitability is a feature of both inflammatory and neuropathic pain. K_V7 channel play a key role in regulating neuronal excitability, controlling the excitability of nociceptors^[5-7]. Retigabine (RTG), a potassium channel opener, was approved in June 2011by the US Food and Drug Administration (FDA) for the adjunctive treatment of partial-onset seizures in adult patients^[8]. In recent reports, it was found that RTG also showed excellent analgesic activity in rodents ^{[7, 9]}. However, the clinical analgesic effect is not very good. We modified the structure of RTG to explore whether QO-83 has analgesic activity. We found that compared with RTG, QO-83 has better chemical stability and blood-brain barrier permeability in our previous study. The selectivity to K_V7.2 is higher, and its EC₅₀ value is 0.56 μM, which is three times that of RTG. Therefore, we focused on the mechanism and effects of QO-83 on central and peripheral neuropathic pain.

METHOD

Thalamic pain is a primary cause of central post-stroke pain (CPSP). Clinical symptoms vary depending on the location of the infarction and frequently accompany several pain symptoms. Stereotaxic placement of guide cannula or Intraventricular injection (Collagenase 4: 0.01U) was conducted for the ventral posterior thalamic nuclei, with bregma as a reference: 1.7 mm posterior, 1.9 mm lateral and 3.4 mm ventral to the cortical surface. QO-83 0.75mg/kg and 1.5mg/kg were administered intraperitoneally for 14 days to observe the threshold of mechanical pain and thermal pain in C57 mice. Establish CCI and CFA peripheral neuropathic pain models and observe the analgesic activity of QO-83. Spontaneous discharge of the ventroposterolateral nucleus of the thalamus experiments and action potentials and M current of dissociated rat small-diameter DRG neurons were perform using AXON Multiclamp 700B patch-clamp amplifier amplification and AXON Digidata 1440A digital-to-analog converter. Western blot was used to observe the effect of QO-83 on the expression of K_V7.2 protein in various neuropathic pain model animals.

RESULT

The effect of compound qo-83 on C57 mice model of thalamic pain

Compound QO-83 can significantly reduce the mechanical and cold hyperalgesia of thalamic pain in model C57 mice but does not affect heat sensitivity. QO-83 significantly reduced the spontaneous firing of ventrolateral thalamic nucleus neurons. In addition, we found that the expression of K_V7.2 was significantly decreasing in the thalamic pain model group, and QO-83 increased the expression of K_V7.2 channel protein.

The effect of QO-83 on CCI and CFA model rats

In CCI and CFA models, compound QO-83 significantly increased the mechanical threshold of rats but did not respond to heat hypersensitivity. QO-83 can significantly inhibit the discharge of DRG neurons and enhance the M current in DRG neurons, which EC₅₀ value is 0.76 μM. QO-83 also antagonized the decreased expression of K_V7.2 channel protein induced by sciatic nerve ligation in the CCI model, while there was no such effect in the CFA model. No obvious depressive-like behavior was found in QO-83 in social experiments in the mice.

CONCLUSION

QO-83 can significantly alleviate the hyperalgesia caused by the central neuropathic pain model of thalamic pain and the peripheral neuropathic pain model of CCI and CFA. It can reduce the excitability of the ventral-posterolateral nucleus of the thalamus and DRG neurons by enhancing the M current. QO-83 can also reduce neuronal hypersensitivity by increasing the expression of K_V7.2 in the thalamic pain model and CCI model. These results indicate that QO-83 is effective in alleviating both central and peripheral neuropathic pain.