Summary It is well known that nuclear factor-kappaB (NF-κB) regulates neuronal structures and functions by nuclear transcription. Here, we showed that phospho-p65 ( p -p65), an active form of NF-κB subunit, reversibly interacted with Na v 1.7 channels in the membrane of dorsal root ganglion (DRG) neurons of rats. The interaction increased Na v 1.7 currents by slowing inactivation of Na v 1.7 channels and facilitating their recovery from inactivation, which may increase the resting state of the channels ready for activation. In cultured DRG neurons TNF-α upregulated the membrane p -p65 and enhanced Na v 1.7 currents within 5 min but did not affect nuclear NF-κB within 40 min. This non-transcriptional effect on Na v 1.7 may underlie a rapid regulation of the sensibility of the somatosensory system. Both NF-κB and Na v 1.7 channels are critically implicated in many physiological functions and diseases. Our finding may shed new light on the investigation into the underlying mechanisms.

BackgroundOral administration of Bulleyaconitine A, an extracted diterpenoid alkaloid from Aconitum bulleyanum plants, is effective for treating chronic pain in rats and in human patients, but the underlying mechanisms are poorly understood.ResultsAs the hyperexcitability of dorsal root ganglion neurons resulting from the upregulation of voltage-gated sodium (Nav) channels has been proved critical for development of chronic pain, we tested the effects of Bulleyaconitine A on Nav channels in rat spared nerve injury model of neuropathic pain. We found that Bulleyaconitine A at 5 nM increased the threshold of action potentials and reduced the firing rate of dorsal root ganglion neurons in spared nerve injury rats but not in sham rats. Bulleyaconitine A preferably blocked tetrodotoxin-sensitive Nav channels over tetrodotoxin-resistant ones in dorsal root ganglion neurons of spared nerve injury rats. Bulleyaconitine A was more potent for blocking Nav1.3 and Nav1.7 than Nav1.8 in cell lines. The half maximal inhibitory concentration (IC50) values for resting Nav1.3, Nav1.7, and Nav1.8 were 995.6 ± 139.1 nM, 125.7 ± 18.6 nM, and 151.2 ± 15.4 μM, respectively, which were much higher than those for inactivated Nav1.3 (20.3 ± 3.4 pM), Nav1.7 (132.9 ± 25.5 pM), and Nav1.8 (18.0 ± 2.5 μM). The most profound use-dependent blocking effect of Bulleyaconitine A was observed on Nav1.7, less on Nav1.3, and least on Nav1.8 at IC50 concentrations. Bulleyaconitine A facilitated the inactivation of Nav channels in each subtype.ConclusionsPreferably blocking tetrodotoxin-sensitive Nav1.7 and Nav1.3 in dorsal root ganglion neurons may contribute to Bulleyaconitine A’s antineuropathic pain effect.

Bulleyaconitine A, a diterpenoid alkaloid isolated from Aconitum bulleyanum plants, has been used for the treatment of chronic pain in China since 1985. Clinical studies show that the oral administration of bulleyaconitine A is effective for treating different kinds of chronic pain, including back pain, joint pain, and neuropathic pain with minimal side effect in human patients. The experimental studies have revealed that bulleyaconitine A at therapeutic doses potently inhibits the peripheral sensitization and central sensitization that underlie chronic pain and has no effect on acute pain. Bulleyaconitine A preferably blocks tetrodotoxin-sensitive voltage-gated sodium channels in dorsal root ganglion neurons by inhibition of protein kinase C, and the effect is around 600 times more potent in neuropathic animals than in naïve ones. Bulleyaconitine A at 5 nM inhibits the hypersensitivity of dorsal root ganglion neurons in neuropathic rats but has no effect on excitability of dorsal root ganglion neurons in sham group. Bulleyaconitine A inhibits long-term potentiation at C-fiber synapses in spinal dorsal horn, a synaptic model of pathological pain, preferably in neuropathic pain rats over naïve rats. The following mechanisms may underlie the selective effect of bulleyaconitine A on chronic pain. (1) In neuropathic conditions, protein kinase C and voltage-gated sodium channels in dorsal root ganglion neurons are upregulated, which enhances bulleyaconitine A’s effect. (2) Bulleyaconitine A use-dependently blocks voltage-gated sodium channels and therefore inhibits the ectopic discharges that are important for neuropathic pain. (3) Bulleyaconitine A is shown to inhibit neuropathic pain by the modulation of spinal microglia, which are involved in the chronic pain but not in acute (nociceptive) pain. Moreover, bulleyaconitine A facilitates the anesthetic effect of morphine and inhibits morphine tolerance in rats. Together, bulleyaconitine A is able to inhibit chronic pain by targeting at multiple molecules. Further clinical and experimental studies are needed for evaluating the efficacy of bulleyaconitine A in different forms of chronic pain in patients and for exploring the underlying mechanisms.