Evaluation of the antinociceptive activities of several sodium channel blockers using veratrine test in mice

Wikstroemia indica (L.) C. A. Mey. Exerts analgesic activity by inhibiting NaV1.7 channel

ETHNOPHARMACOLOGICAL RELEVANCE

Wikstroemia indica (L.) C. A. Mey. is traditionally used for the treatment of gastrointestinal disorders, respiratory illnesses, skin infections, and inflammatory conditions. Despite extensive evidence of its biological potential, including antipyretic, antimicrobial, antifungal, anti-inflammatory, and diuretic properties, there are currently no reports indicating its analgesic effects.

AIM OF THE STUDY

Crude extracts from W. indica stems were examined for anti-nociceptive activity. Additionally, an in-depth investigation was conducted to uncover the molecular basis for the possible analgesic phenomenon.

MATERIALS AND METHODS

W. indica stems were subjected to ethanol extraction. To evaluate the in vivo analgesic activity, both chemical and physical-induced pain models were employed. Additionally, single-cell electrophysiological recordings were performed on human embryonic kidney 293T (HEK293T) cells expressing NaV1.7 channel.

RESULTS

Crude extracts derived from W. indica exhibited significant efficacy in mitigating the pain sensation, as evidenced by their substantial effects in both acetic acid-induced and heat-induced pain models. Further screening unveiled osthenol as a key bioactive compound responsible for mediating the analgesic properties of W. indica. Osthenol directly interacts with the pore domain of NaV1.7 channels, leading to channel inhibition. Importantly, this interaction is independent of any changes in the channel gating modifier domain.

CONCLUSION

Both W. indica and osthenol demonstrate potential as effective anti-nociceptive agents in preclinical studies. Their analgesic effects are likely achieved by inhibiting the NaV1.7 channel, which is crucial in pain initiation, transmission, and modulation. These results elucidate the molecular basis of the W. indica as a pain-relieving medication. Additionally, osthenol holds great potential in advancing the development of anti-nociceptive drugs targeting the NaV1.7 channel.

Fentanyl Analogs Exert Antinociceptive Effects via Sodium Channel Blockade in Mice

The formalin test is one approach to studying acute pain in rodents. Similar to formalin, injection with glutamate and veratrine can also produce a nociceptive response. This study investigated whether opioid-related compounds could suppress glutamate- and veratrine-induced nociceptive responses in mice at the same dose. The administration of morphine (3 mg/kg), hydromorphone (0.4 mg/kg), or fentanyl (0.03 mg/kg) suppressed glutamate-induced nociceptive response, but not veratrine-induced nociceptive response at the same doses. However, high doses of morphine (10 mg/kg), hydromorphone (2 mg/kg), or fentanyl (0.1 mg/kg) produced a significant reduction in the veratrine-induced nociceptive response. These results indicate that high doses are required when using morphine, hydromorphone, or fentanyl for sodium channel-related neuropathic pain, such as ectopic activity. As a result, concerns have arisen about overdose and abuse if the dose of opioids is steadily increased to relieve pain. In contrast, trimebutine (100 mg/kg) and fentanyl analog isobutyrylfentanyl (iBF; 0.1 mg/kg) suppressed both glutamate- and veratrine-induced nociceptive response. Furthermore, nor-isobutyrylfentanyl (nor-iBF; 1 mg/kg), which is a metabolite of iBF, suppressed veratrine-induced nociceptive response. Besides, the optimal antinociceptive dose of iBF, unlike fentanyl, only slightly increased locomotor activity and did not slow gastrointestinal transit. Cancer pain is a complex condition driven by inflammatory, neuropathic, and cancer-specific mechanisms. Thus, iBF may have the potential to be a superior analgesic than fentanyl.

Differences in the antinociceptive effects of serotonin-noradrenaline reuptake inhibitors via sodium channel blockade using the veratrine test in mice

Antidepressants exert their analgesic effects by inhibiting the reuptake of noradrenaline. Several antidepressants have been shown to block the sodium channels, which might contribute to their analgesic potency. The aim of this study was to determine whether serotonin-noradrenaline reuptake inhibitors (SNRIs) could produce antinociceptive effects via sodium channel blockade using the veratrine test in mice. Furthermore, the effects of these agents on the veratrine test were examined to elucidate the effects of several antidepressants and tramadol on sodium channels. The administration of duloxetine (10 mg/kg) and venlafaxine (30 mg/kg) suppressed cuff-induced mechanical allodynia; however, these antinociceptive effects were only partially suppressed by atipamezole. Furthermore, duloxetine and venlafaxine demonstrated antinociceptive effects via sodium channel blockade, as assayed by the veratrine test. In addition, several antidepressants, including amitriptyline, paroxetine and mirtazapine, reduced veratrine-induced nociception. In contrast, milnacipran and tramadol did not alter the veratrine-induced nociception. These results indicated that, in addition to the primary action of SNRIs on monoamine transporters, sodium channel blockade might be involved in the antinociceptive activities of duloxetine and venlafaxine, but not milnacipran.

Valproic acid interactions with the NavMs voltage-gated sodium channel

Valproic acid (VPA) is an anticonvulsant drug that is also used to treat migraines and bipolar disorder. Its proposed biological targets include human voltage-gated sodium channels, among other membrane proteins. We used the prokaryotic NavMs sodium channel, which has been shown to be a good exemplar for drug binding to human sodium channels, to examine the structural and functional interactions of VPA. Thermal melt synchrotron radiation circular dichroism spectroscopic binding studies of the full-length NavMs channel (which includes both pore and voltage sensor domains), and a pore-only construct, undertaken in the presence and absence of VPA, indicated that the drug binds to and destabilizes the channel, but not the pore-only construct. This is in contrast to other antiepileptic compounds that have previously been shown to bind in the central hydrophobic core of the pore region of the channel, and that tend to increase the thermal stability of both pore-only constructs and full-length channels. Molecular docking studies also indicated that the VPA binding site is associated with the voltage sensor, rather than the hydrophobic cavity of the pore domain. Electrophysiological studies show that VPA influences the block and inactivation rates of the NavMs channel, although with lower efficacy than classical channel-blocking compounds. It thus appears that, while VPA is capable of binding to these voltage-gated sodium channels, it has a very different mode and site of action than other anticonvulsant compounds.