Sea-anemone toxin ATX-II elicits A-fiber-dependent pain and enhances resurgent and persistent sodium currents in large sensory neurons

<p>Abstract</p> <p>Background</p> <p>Gain-of-function mutations of the nociceptive voltage-gated sodium channel Nav1.7 lead to inherited pain syndromes, such as paroxysmal extreme pain disorder (PEPD). One characteristic of these mutations is slowed fast-inactivation kinetics, which may give rise to resurgent sodium currents. It is long known that toxins from <it>Anemonia sulcata</it>, such as ATX-II, slow fast inactivation and skin contact for example during diving leads to various symptoms such as pain and itch. Here, we investigated if ATX-II induces resurgent currents in sensory neurons of the dorsal root ganglion (DRGs) and how this may translate into human sensations.</p> <p>Results</p> <p>In large A-fiber related DRGs ATX-II (5 nM) enhances persistent and resurgent sodium currents, but failed to do so in small C-fiber linked DRGs when investigated using the whole-cell patch-clamp technique. Resurgent currents are thought to depend on the presence of the sodium channel β4-subunit. Using RT-qPCR experiments, we show that small DRGs express significantly less β4 mRNA than large sensory neurons. With the β4-C-terminus peptide in the pipette solution, it was possible to evoke resurgent currents in small DRGs and in Nav1.7 or Nav1.6 expressing HEK293/N1E115 cells, which were enhanced by the presence of extracellular ATX-II. When injected into the skin of healthy volunteers, ATX-II induces painful and itch-like sensations which were abolished by mechanical nerve block. Increase in superficial blood flow of the skin, measured by Laser doppler imaging is limited to the injection site, so no axon reflex erythema as a correlate for C-fiber activation was detected.</p> <p>Conclusion</p> <p>ATX-II enhances persistent and resurgent sodium currents in large diameter DRGs, whereas small DRGs depend on the addition of β4-peptide to the pipette recording solution for ATX-II to affect resurgent currents. Mechanical A-fiber blockade abolishes all ATX-II effects in human skin (e.g. painful and itch-like paraesthesias), suggesting that it mediates its effects mainly via activation of A-fibers.</p

Safety and efficacy of transdermal buprenorphine for the relief of cancer pain

Purpose: This study aimed to synthesize the available evidence on the efficacy and safety of transdermal (TD) buprenorphine. Methods: We searched studies in electronic databases. Randomized controlled trials (RCTs) assessing the efficacy of TD buprenorphine comparing with placebo or other comparator drug in relieving cancer pain were included. The primary end points are patient-reported pain intensity and pain relief. For dichotomous data, the summary relative risk (RR) and its 95 % confidence interval (CI) were derived using random-effect model in view of heterogeneity testing. Results: Eight clinical trials (n = 909) were included in the analysis. Only a few studies reported the same outcome in similar way, which created difficulty in the pooling of outcome data. Two studies (n = 288) assessed 'responders' and showed a significant difference between TD buprenorphine and placebo in all three doses of TD buprenorphine, 35.5, 52.5, or 70 μg/h (RR 1.74, 95 % CI 1.31-2.32; I 2 0 %); the numbers-needed-to-treat was 5.8 (3.9-11). Two studies (n = 331) showed a comparable requirement for rescue SL buprenorphine between TD buprenorphine and placebo (RR 1.25, 95 % CI 0.84-1.88; I 2 0 %). The preferred outcome measure '50 % pain relief' was not reported in any included studies. On the basis of summary quality, further research is likely to have an important impact on our confidence in the estimate. Conclusion: Transdermal buprenorphine has an increasing role for the relief of cancer pain. Further research in this field is needed. Multicentre studies in this field using a common protocol and strict supervision will be more practicable