TRPV1 activation power can switch an action mode for its polypeptide ligands

Abstract

TRPV1 (vanilloid) receptors are activated by different types of stimuli including capsaicin, acidification and heat. Various ligands demonstrate stimulus-dependent action on TRPV1. In the present work we studied the action of polypeptides isolated from sea anemone Heteractis crispa (APHC1, APHC2 and APHC3) on rat TRPV1 receptors stably expressed in CHO cells using electrophysiological recordings, fluorescent Ca2+ measurements and molecular modeling. The APHCs potentiated TRPV1 responses to low (3–300 nM) concentrations of capsaicin but inhibited responses to high (>3.0 μM) concentrations. The activity-dependent action was also found for TRPV1 responses to 2APB and acidification. Thus the action mode of APHCs is bimodal and depended on the activation stimuli strength—potentiation of low-amplitude responses and no effect/inhibition of high-amplitude responses. The double-gate model of TRPV1 activation suggests that APHC-polypeptides may stabilize an intermediate state during the receptor activation. Molecular modeling revealed putative binding site at the outer loops of TRPV1. Binding to this site can directly affect activation by protons and can be allosterically coupled with capsaicin site. The results are important for further investigations of both TRPV1 and its ligands for potential therapeutic use.

Animal Toxins Providing Insights into TRPV1 Activation Mechanism

“…All three toxins were shown to be partial, but potent, antagonists, with APHC3 displaying the highest level of inhibition (71% of 3 µM capsaicin), and the lowest IC 50 value (18 nM) [ 78 ]. As is common with molecules presenting with partial antagonistic characteristics, a bimodal mechanism of action of APHC on TRPV1 activity was recently described [ 79 ]. In the presence of saturating concentrations of capsaicin (3 µM), APHC acts as an inhibitor, whereas current produced by very low concentrations (3 nM) of capsaicin are potentiated in the presence of the toxin [ 79 ].…”

“…As is common with molecules presenting with partial antagonistic characteristics, a bimodal mechanism of action of APHC on TRPV1 activity was recently described [ 79 ]. In the presence of saturating concentrations of capsaicin (3 µM), APHC acts as an inhibitor, whereas current produced by very low concentrations (3 nM) of capsaicin are potentiated in the presence of the toxin [ 79 ]. Interestingly, APHC1 showed the highest levels of potentiation, showing an increase of 250% of the capsaicin - evoked current [ 79 ].…”

“…In the presence of saturating concentrations of capsaicin (3 µM), APHC acts as an inhibitor, whereas current produced by very low concentrations (3 nM) of capsaicin are potentiated in the presence of the toxin [ 79 ]. Interestingly, APHC1 showed the highest levels of potentiation, showing an increase of 250% of the capsaicin - evoked current [ 79 ]. Furthermore, APHC3 potentiated TRPV1 activation in response to slightly acidic (pH 6.2) solution, whereas no inhibition was observed at highly acidic (pH 4.5) solutions [ 79 ].…”

“…Interestingly, APHC1 showed the highest levels of potentiation, showing an increase of 250% of the capsaicin - evoked current [ 79 ]. Furthermore, APHC3 potentiated TRPV1 activation in response to slightly acidic (pH 6.2) solution, whereas no inhibition was observed at highly acidic (pH 4.5) solutions [ 79 ]. Likewise, low concentrations of the synthetic molecule 2-aminoethoxydiphenyl borate (2APB) were subject to APHC potentiation, while high concentrations were unaffected [ 79 ].…”

TRPV1 antagonists that cause hypothermia, instead of hyperthermia, in rodents: Compounds’ pharmacological profiles, in vivo targets, thermoeffectors recruited and implications for drug development

“…The list of hypothermia‐inducing compounds includes several small‐molecule antagonists, viz., 5′‐iodo‐resiniferatoxin (5′‐I‐RTX), Amgen's AMG7905 and AMG8562, Abbott Laboratories’ A‐425619, AbbVie's Compound 3 and Schwarz Pharma's JYL1421, as well as at least 1 polypeptide antagonist, APHC3 . In agreement with the fact that TRPV1 agonists also cause hypothermia, several hypothermia‐causing TRPV1 antagonists, viz., 5′‐I‐RTX and Compound 3, were found to be partial agonists, whereas the partial antagonist APHC3 was found to potentiate the effects of low concentrations of capsaicin . However, several other hypothermia‐inducing TRPV1 antagonists, viz., A‐425619, AMG7905 and AMG8562 and JYL1421, showed no TRPV1 agonistic or capsaicin‐potentiating activity.…”