Reversal of Peripheral Neuropathic Pain by the Small-Molecule Natural Product Physalin F via Block of CaV2.3 (R-Type) and CaV2.2 (N-Type) Voltage-Gated Calcium Channels

Abstract

No universally efficacious therapy exists for chronic pain, a disease affecting one-fifth of the global population. An overreliance on the prescription of opioids for chronic pain despite their poor ability to improve function has led to a national opioid crisis. In 2018, the NIH launched a Helping to End Addiction Long-term plan to spur discovery and validation of novel targets and mechanisms to develop alternative nonaddictive treatment options. Phytochemicals with medicinal properties have long been used for various treatments worldwide. The natural product physalin F, isolated from the Physalis acutifolia (family: Solanaceae) herb, demonstrated antinociceptive effects in models of inflammatory pain, consistent with earlier reports of its anti-inflammatory and immunomodulatory activities. However, the target of action of physalin F remained unknown. Here, using whole-cell and slice electrophysiology, competition binding assays, and experimental models of neuropathic pain, we uncovered a molecular target for physalin F’s antinociceptive actions. We found that physalin F (i) blocks CaV2.3 (R-type) and CaV2.2 (N-type) voltage-gated calcium channels in dorsal root ganglion (DRG) neurons, (ii) does not affect CaV3 (T-type) voltage-gated calcium channels or voltage-gated sodium or potassium channels, (iii) does not bind G-protein coupled opioid receptors, (iv) inhibits the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in spinal cord slices, and (v) reverses tactile hypersensitivity in models of paclitaxel-induced peripheral neuropathy and spinal nerve ligation. Identifying CaV2.2 as a molecular target of physalin F may spur its use as a tool for mechanistic studies and position it as a structural template for future synthetic compounds.

Taxane‐induced neurotoxicity: Pathophysiology and therapeutic perspectives

“…Thus, betulinic acid may represent a promising alternative to treat taxane‐related peripheral neuropathy, without causing tolerance (Bellampalli et al, 2019). In a continuous effort to identify new analgesic drugs lacking abuse potential, Shan et al (2019) demonstrated that the small molecule physalin F, isolated from Physalis acutifolia , prevents paclitaxel‐induced tactile allodynia in rats when dosed intrathecally. The same study indicated that physalin F promotes analgesia by blocking R‐ and N‐type Ca v channels and excitatory postsynaptic currents, without any interaction with opioid receptors (Shan et al, 2019).…”

1-O-Acetylgeopyxin A, a derivative of a fungal metabolite, blocks tetrodotoxin-sensitive voltage-gated sodium, calcium channels and neuronal excitability which correlates with inhibition of neuropathic pain

“…The changes in [Ca 2+ ]c changes were examined with a ratio of F340/ F380, calculated after subtracting background from both channels. Recordings of total calcium currents were obtained using recording solutions and protocols (also illustrated in the figures) described earlier [18]. The internal solution consisted of (in mM): 150 CsCl 2 , 10 HEPES, 5 Mg-ATP, and 5 BAPTA (pH 7.3, mOsm/L = 290-310) and external solution contained (in mM): 110 NMDG, 10 BaCl 2 , 30 TEA-Cl, 10 HEPES, 10 glucose and 10 μM HEPES (pH 7.3, mosM/L = 310-315).…”

“…The internal solution consisted of (in mM): 150 CsCl 2 , 10 HEPES, 5 Mg-ATP, and 5 BAPTA (pH 7.3, mOsm/L = 290-310) and external solution contained (in mM): 110 NMDG, 10 BaCl 2 , 30 TEA-Cl, 10 HEPES, 10 glucose and 10 μM HEPES (pH 7.3, mosM/L = 310-315). The neurons were subjected to current−density (I − V) and activation/inactivation voltage protocols as previously described and shown in the figures [18].…”

“…The internal solution consisted of (in mM): 140 CsF, 10 NaCl, 1.1Cs-EGTA, and 15 HEPES (pH 7.3, mOsm/L = 290-310) and external solution contained (in mM): 140 NaCl, 30 tetraethylammonium chloride, 10 D-glucose, 3 KCl, 1 CaCl2, 0.5 CdCl 2 , 1 MgCl 2 , and 10 HEPES (pH 7.3, mosM/L = 310-315). The neurons were subjected to current−density (I− V) and activation/inactivation voltage protocols as previously described and shown in the figures [18,21]. Because of differential inactivation kinetics of TTX-R and TTX-S channels, the fast inactivation protocol permitted separation of electrically isolated TTX-R (current available following a − 40 mV prepulse) from the total current (current left after a − 120 mV prepulse), to obtain TTX-S currents, as previously reported [21].…”

“…Likewise, we identified two plant natural products: hardwickiic acid, isolated from Salvia wagneriana, and hautriwaic acid, isolated from Eremocarpus, both of which reversed pain behaviors in experimental models of HIV-induced and chemotherapy-induced neuropathies by inhibition of voltage-gated sodium (Na + ) channels [17]. In another study, we demonstrated that physalin F, a steroidal derivative isolated from Physalis acutifolia reversed tactile hypersensitivity in models of paclitaxel-induced peripheral neuropathy and spinal nerve ligation (SNL) via blockade of R-type and N-type voltage-gated Ca 2+ channels [18].…”