Pharmacological Inhibition of the Voltage-Gated Sodium Channel Na_V1.7 Alleviates Chronic Visceral Pain in a Rodent Model of Irritable Bowel Syndrome

Abstract

The human nociceptor-specific voltage-gated sodium channel 1.7 (hNaV1.7) is critical for sensing various types of somatic pain, but it appears not to play a primary role in acute visceral pain. However, its role in chronic visceral pain remains to be determined. We used assay-guided fractionation to isolate a novel hNaV1.7 inhibitor, Tsp1a, from tarantula venom. Tsp1a is 28-residue peptide that potently inhibits hNaV1.7 (IC50 = 10 nM), with greater than 100-fold selectivity over hNaV1.3–hNaV1.6, 45-fold selectivity over hNaV1.1, and 24-fold selectivity over hNaV1.2. Tsp1a is a gating modifier that inhibits NaV1.7 by inducing a hyperpolarizing shift in the voltage-dependence of channel inactivation and slowing recovery from fast inactivation. NMR studies revealed that Tsp1a adopts a classical knottin fold, and like many knottin peptides, it is exceptionally stable in human serum. Remarkably, intracolonic administration of Tsp1a completely reversed chronic visceral hypersensitivity in a mouse model of irritable bowel syndrome. The ability of Tsp1a to reduce visceral hypersensitivity in a model of irritable bowel syndrome suggests that pharmacological inhibition of hNaV1.7 at peripheral sensory nerve endings might be a viable approach for eliciting analgesia in patients suffering from chronic visceral pain.

Structural Modeling of Peptide Toxin - Ion Channel Interactions using RosettaDock

“…Huwentoxin-IV (HWTX-IV) and Protoxin-II (ProTx-II) from tarantula venom are peptide toxins that have subtype selectivity for and state-dependent antagonist activity against human Na V 1.7 channel (Schmalhofer et al, 2008; Xiao et al, 2010) that play a key role in the transmission of pain signals (Bennett et al, 2019). HWTX-IV and ProTx-II peptides have been used as scaffolds for optimization of peptides targeting NaV1.7 to develop novel therapeutics to treat pain (Adams et al, 2022; Flinspach et al, 2017; Jiang et al, 2021c; Lawrence et al, 2019; Neff and Wickenden, 2021; Neff et al, 2020). ProTx-II and HWTX-IV inhibit activation of Na V 1.7 by trapping the VSDII in a deactivated state (IC 50 ∼ 1 nM for ProTx-II and ∼20 nM for HWTX-IV) (Park et al, 2014; Peng et al, 2002; Schmalhofer et al, 2008; Sokolov et al, 2008; Xiao et al, 2010, 2011; Xu et al, 2019).…”

The voltage-gated sodium channel NaV1.7 underlies endometriosis-associated chronic pelvic pain

“…In this study we addressed this by investigating the role of NaV1.7 in normal vaginal mechanosensitivity and endometriosis-associated vaginal mechanical hypersensitivity. We decided to target this channel because: (i) NaV1.7 is TTX-sensitive; (ii) it is abundantly expressed (98-100%) in sensory neurons that innervate pelvic organs affected by endometriosis, including the vagina [16], colon [38], and bladder [32]; (iii) we have unique access to selective modulators of NaV1.7 [23; 41]; (iv) we recently demonstrated a role for NaV1.7 in chronic visceral pain [41] First, we demonstrated that activation of NaV1.7 with OD1, a α-highly selective NaV1.7 agonist [23], dramatically enhanced the responsiveness of vaginal afferents from Sham control mice to three different types of mechanical stimuli. Interestingly, we observed that whilst OD1 failed to elicit AP discharge in the absence of mechanical stimuli (direct activation of afferents), half of the afferents incubated with OD1 continued to fire APs after cessation of the mechanical stimulus.…”

Voltage-Gated Sodium Channel Modulation by a New Spider Toxin Ssp1a Isolated From an Australian Theraphosid

“…Gating modifier spider ICK peptides can modulate the channel conductance by targeting neurotoxin Site 3 (domain IV) and Site 4 (domain II) in either the 1) down state of DII S4 (closed channel), 2) up state of DII S4 (open channel), and 3) down state of DIV S4 (open channel) (Dongol et al, 2019). Recently, the spider ICK peptide Tsp1a was reported to stabilize the inactivated state of the channel in the up state of DIV S4 (closed channel) (Jiang et al, 2021). Although rSsp1a's effect on channel activation and inactivation at the three subtypes tested was independent of membrane potential, the extent of inhibition was voltage dependent (Figure 7C) and at saturating concentrations of rSsp1a, inward currents were fully inhibited at moderate depolarizations, while depolarizations above +50 mV partially restored current (Figures 7A,B).…”

“…Recently, the spider toxin Hm1a was used to investigate the role of Na V 1.1 in chronic visceral pain and mechanical hypersensitivity (Osteen et al, 2016) but many more provide new molecular tools to help define the role and molecular pharmacology of Na V channels. Increasingly, structure-function studies of these spider toxins are providing valuable new opportunities to rationally design potential drug leads with improved selectivity and potency (Xiao et al, 2010;Rong et al, 2011;Xiao et al, 2011;Cai et al, 2015;Wingerd et al, 2017;Xu et al, 2019;Jiang et al, 2021), especially NaSpTx1-3 family toxins ProTx-II (Flinspach et al, 2017), Pn3a (Deuis et al, 2017a;Mueller et al, 2019), HnTx-IV (Liu et al, 2014b), HwTx-IV (Liu et al, 2014a), and Ca2a (Zhang et al, 2018). In this study, we report the discovery of Ssp1a from an Australian theraphosid Selenotypus species and investigate its mode of action and selectivity across hNa V 1.1-1.8.…”