Acid-sensing ion channels (ASICs) have been known as sensors of a local pH change within both physiological and pathological conditions. ASIC-targeting peptide toxins could be potent molecular tools for ASIC-manipulating in vitro, and for pathology treatment in animal test studies. Two sea anemone toxins, native Hmg 1b-2 and recombinant Hmg 1b-4, both related to APETx-like peptides, inhibited the transient current component of human ASIC3-Δ20 expressed in Xenopus laevis oocytes, but only Hmg 1b-2 inhibited the rat ASIC3 transient current. The Hmg 1b-4 action on rASIC3 as a potentiator was confirmed once again. Both peptides are non-toxic molecules for rodents. In open field and elevated plus maze tests, Hmg 1b-2 had more of an excitatory effect and Hmg 1b-4 had more of an anxiolytic effect on mouse behavior. The analgesic activity of peptides was similar and comparable to diclofenac activity in an acid-induced muscle pain model. In models of acute local inflammation induced by λ-carrageenan or complete Freund’s adjuvant, Hmg 1b-4 had more pronounced and statistically significant anti-inflammatory effects than Hmg 1b-2. It exceeded the effect of diclofenac and, at a dose of 0.1 mg/kg, reduced the volume of the paw almost to the initial volume. Our data highlight the importance of a comprehensive study of novel ASIC-targeting ligands, and in particular, peptide toxins, and present the slightly different biological activity of the two similar toxins.

A novel peptide AnmTX Sco 9a-1 with the β-hairpin fold was isolated from the swimming sea anemone Stomphia coccinea (Actinostolidae family). The peptide consists of 28 amino acid residues, including modified hydroxyproline residue, and its measured molecular mass is 2960 Da. The peptide was not toxic on mice; however, it stimulated their exploratory motivation and active search behavior, and demonstrated an anti-anxiety effect. AnmTX Sco 9a-1 at doses of 0.1 and 1 mg/kg reduced the volume of edema during 24 h better than the nonsteroidal anti-inflammatory drug, Diclofenac, at dose of 1 mg/kg in a model of acute local λ-carrageenan-induced inflammation. ELISA analysis of the animal’s blood showed that peptide at a dose of 1 mg/kg reduced the content of tumor necrosis factor-α (TNF-α), a pro-inflammatory mediator responsible in the edema development, up to the level of TNF-α in the intact group. Besides, AnmTX Sco 9a-1 demonstrated a significant analgesic effect on acute pain sensitivity in the carrageenan-induced thermal hyperalgesia model at doses of 0.1 and 1 mg/kg. Activity of AnmTX Sco 9a-1 was shown not to be associated with modulation of nociceptive ASIC channels.

TRPA1 is a homotetrameric non-selective calcium-permeable channel. It contributes to chemical and temperature sensitivity, acute pain sensation, and development of inflammation. HCIQ2c1 is a peptide from the sea anemone Heteractis magnifica that inhibits serine proteases. Here, we showed that HCIQ2c1 significantly reduces AITC- and capsaicin-induced pain and inflammation in mice. Electrophysiology recordings in Xenopus oocytes expressing rat TRPA1 channel revealed that HCIQ2c1 binds to open TRPA1 and prevents its transition to closed and inhibitor-insensitive ‘hyperactivated’ states. NMR study of the ¹⁵N-labeled recombinant HCIQ2c1 analog described a classical Kunitz-type structure and revealed two dynamic hot-spots (loops responsible for protease binding and regions near the N- and C-termini) that exhibit simultaneous mobility on two timescales (ps–ns and μs–ms). In modelled HCIQ2c1/TRPA1 complex, the peptide interacts simultaneously with one voltage-sensing-like domain and two pore domain fragments from different channel’s subunits, and with lipid molecules. The model explains stabilization of the channel in the open conformation and the restriction of ‘hyperactivation’, which are probably responsible for the observed analgetic activity. HCIQ2c1 is the third peptide ligand of TRPA1 from sea anemones and the first Kunitz-type ligand of this channel. HCIQ2c1 is a prototype of efficient analgesic and anti-inflammatory drugs.

Inflammation is a physiological response of the immune system to infectious agents or tissue injury, which involves a cascade of vascular and cellular events and the activation of biochemical pathways depending on the type of harmful agent and the stimulus generated. The Kunitz peptide HCIQ2c1 of sea anemone Heteractis magnifica is a strong protease inhibitor and exhibits neuroprotective and analgesic activities. In this study, we investigated the anti-inflammatory potential of HCIQ2c1 in histamine- and lipopolysaccharide (LPS)-activated RAW 264.7 macrophages as well as in LPS-induced systemic inflammation and carrageenan-induced paw edema models in CD-1 mice. We found that 10 μM HCIQ2c1 dramatically decreases histamine-induced intracellular Ca²⁺ release and LPS-induced reactive oxygen species (ROS) production in RAW 264.7 macrophages. Moreover, HCIQ2c1 significantly inhibited the production of LPS-induced tumor necrosis factor α (TNF-α), inducible NO-synthase (iNOS), and 5-lipoxygenase (5-LO) but slightly influenced the IL-1β and cyclooxygenase-2 (COX-2) expression level in macrophages. Furthermore, intravenous administration by HCIQ2c1 at 0.1 mg/kg dose reduced LPS-induced TNF-α, IL-1β, COX-2, and iNOS gene expression in CD-1 mice. The subplantar administration of HCIQ2c1 at 0.1 mg/kg dose to mice significantly reduced carrageenan-induced paw edema by a factor of two, which is comparable to the effect of diclofenac at 1 mg/kg dose. Thus, peptide HCIQ2c1 has a strong anti-inflammatory potential by the attenuation of systemic and local inflammatory effects through the inhibition of intracellular Ca²⁺ release, the production of ROS and pro-inflammatory cytokines, and enzymes involved in arachidonic acid metabolism.

Psoriasis and allergic contact dermatitis (ACD) are the most common chronic inflammatory diseases, which are accompanied by epithelial alterations and a T cell-mediated immunopathology. In this study, we investigated the anti-ACD and anti-psoriasis effects of sea anemone Heteractis magnifica peptide HCRG21, a blocker of the TRPV1 channel, in 2,4-dinitrofluorobenzene (DNFB)- and imiquimod (IMQ)-induced mouse models, respectively. We found that topical application of 0.005–0.1% HCRG21 gels normalized hematological and immunological blood parameters in mice, significantly reduced the severity of ACD- and psoriasiform-like skin lesions, and increased the rate of tissue repair. The use of 0.005 and 0.05% HCRG21 gels decreased the production of IL-23-A and macrophage-derived chemokine (MDC) proteins in blood plasma, reduced the expression of Tnf, Il1β, Il6, Il23a, and Il17a genes, but increased the levels of the Il10 gene in scabs and/or blood of IMQ-treated mice. On the other hand, topical application of 0.05 and 0.1% HCRG21 reduced the expression of Il6 and Il23a in the DNFB-treated mice’s blood and it had no significant effects on TNF-α and IL-1β production. Thus, HCRG21 has the potential to be a treatment for psoriasis and dermatitis due to its potent anti-inflammatory properties. This effect is achieved by reducing pro-inflammatory cytokines associated with TRPV1 and normalizing immune cell levels in the bloodstream. This, in turn, leads to a decrease in clinical symptoms and an improvement in skin healing.