Cellular permeation of large molecules mediated by TRPM8 channels

β-Lactam TRPM8 Antagonists Derived from Phe-Phenylalaninol Conjugates: Structure-Activity Relationships and Antiallodynic Activity

The protein transient receptor potential melastatin type 8 (TRPM8), a non-selective, calcium (Ca2+)-permeable ion channel is implicated in several pathological conditions, including neuropathic pain states. In our previous research endeavors, we have identified β-lactam derivatives with high hydrophobic character that exhibit potent and selective TRPM8 antagonist activity. This work describes the synthesis of novel derivatives featuring C-terminal amides and diversely substituted N'-terminal monobenzyl groups in an attempt to increase the total polar surface area (TPSA) in this family of compounds. The primary goal was to assess the influence of these substituents on the inhibition of menthol-induced cellular Ca2+ entry, thereby establishing critical structure-activity relationships. While the substitution of the tert-butyl ester by isobutyl amide moieties improved the antagonist activity, none of the N'-monobencyl derivatives, regardless of the substituent on the phenyl ring, achieved the activity of the model dibenzyl compound. The antagonist potency of the most effective compounds was subsequently verified using Patch-Clamp electrophysiology experiments. Furthermore, we evaluated the selectivity of one of these compounds against other members of the transient receptor potential (TRP) ion channel family and some receptors connected to peripheral pain pathways. This compound demonstrated specificity for TRPM8 channels. To better comprehend the potential mode of interaction, we conducted docking experiments to uncover plausible binding sites on the functionally active tetrameric protein. While the four main populated poses are located by the pore zone, a similar location to that described for the N-(3-aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)-benzamide (AMTB) antagonist cannot be discarded. Finally, in vivo experiments, involving a couple of selected compounds, revealed significant antinociceptive activity within a mice model of cold allodynia induced by oxaliplatin (OXA).

Peripheral nerves directly mediate the transneuronal translocation of silver nanomaterials from the gut to central nervous system

The blood circulation is considered the only way for the orally administered nanoparticles to enter the central nervous systems (CNS), whereas non-blood route-mediated nanoparticle translocation between organs is poorly understood. Here, we show that peripheral nerve fibers act as direct conduits for silver nanomaterials (Ag NMs) translocation from the gut to the CNS in both mice and rhesus monkeys. After oral gavage, Ag NMs are significantly enriched in the brain and spinal cord of mice with particle state however do not efficiently enter the blood. Using truncal vagotomy and selective posterior rhizotomy, we unravel that the vagus and spinal nerves mediate the transneuronal translocation of Ag NMs from the gut to the brain and spinal cord, respectively. Single-cell mass cytometry analysis revealed that enterocytes and enteric nerve cells take up significant levels of Ag NMs for subsequent transfer to the connected peripheral nerves. Our findings demonstrate nanoparticle transfer along a previously undocumented gut-CNS axis mediated by peripheral nerves.

Silencing of TRPV4-expressing sensory neurons attenuates temporomandibular disorders pain

Identification of potential therapeutic targets is needed for temporomandibular disorders (TMD) pain, the most common form of orofacial pain, because current treatments lack efficacy. Considering TMD pain is critically mediated by the trigeminal ganglion (TG) sensory neurons, functional blockade of nociceptive neurons in the TG may provide an effective approach for mitigating pain associated with TMD. We have previously shown that TRPV4, a polymodally-activated ion channel, is expressed in TG nociceptive neurons. Yet, it remains unexplored whether functional silencing of TRPV4-expressing TG neurons attenuates TMD pain. In this study, we demonstrated that co-application of a positively charged, membrane-impermeable lidocaine derivative QX-314 with the TRPV4 selective agonist GSK101 suppressed the excitability of TG neurons. Moreover, co-administration of QX-314 and GSK101 into the TG significantly attenuated pain in mouse models of temporomandibular joint (TMJ) inflammation and masseter muscle injury. Collectively, these results suggest TRPV4-expressing TG neurons represent a potential target for TMD pain.

Sensory TRP Channels in Three Dimensions

Transient receptor potential (TRP) ion channels are sophisticated signaling machines that detect a wide variety of environmental and physiological signals. Every cell in the body expresses one or more members of the extended TRP channel family, which consists of over 30 subtypes, each likely possessing distinct pharmacological, biophysical, and/or structural attributes. While the function of some TRP subtypes remains enigmatic, those involved in sensory signaling are perhaps best characterized and have served as models for understanding how these excitatory ion channels serve as polymodal signal integrators. With the recent resolution revolution in cryo-electron microscopy, these and other TRP channel subtypes are now yielding their secrets to detailed atomic analysis, which is beginning to reveal structural underpinnings of stimulus detection and gating, ion permeation, and allosteric mechanisms governing signal integration. These insights are providing a framework for designing and evaluating modality-specific pharmacological agents for treating sensory and other TRP channel-associated disorders.

Evaluating methods and protocols of ferritin-based magnetogenetics

FeRIC (Ferritin iron Redistribution to Ion Channels) is a magnetogenetic technique that uses radiofrequency (RF) alternating magnetic fields to activate the transient receptor potential channels, TRPV1 and TRPV4, coupled to cellular ferritins. In cells expressing ferritin-tagged TRPV, RF stimulation increases the cytosolic Ca²⁺ levels via a biochemical pathway. The interaction between RF and ferritin increases the free cytosolic iron levels that, in turn, trigger chemical reactions producing reactive oxygen species and oxidized lipids that activate the ferritin-tagged TRPV. In this pathway, it is expected that experimental factors that disturb the ferritin expression, the ferritin iron load, the TRPV functional expression, or the cellular redox state will impact the efficiency of RF in activating ferritin-tagged TRPV. Here, we examined several experimental factors that either enhance or abolish the RF control of ferritin-tagged TRPV. The findings may help optimize and establish reproducible magnetogenetic protocols.

Contribution of non-selective membrane channels and receptors in epilepsy

Overcoming refractory epilepsy's resistance to the combination of antiepileptic drugs (AED), mitigating side effects, and preventing sudden unexpected death in epilepsy are critical goals for therapy of this disorder. Current therapeutic strategies are based primarily on neurocentric mechanisms, overlooking the participation of astrocytes and microglia in the pathophysiology of epilepsy. This review is focused on a set of non-selective membrane channels (permeable to ions and small molecules), including channels and ionotropic receptors of neurons, astrocytes, and microglia, such as: the hemichannels formed by Cx43 and Panx1; the purinergic P2X7 receptors; the transient receptor potential vanilloid (TRPV1 and TRPV4) channels; calcium homeostasis modulators (CALHMs); transient receptor potential canonical (TRPC) channels; transient receptor potential melastatin (TRPM) channels; voltage-dependent anion channels (VDACs) and volume-regulated anion channels (VRACs), which all have in common being activated by epileptic activity and the capacity to exacerbate seizure intensity. Specifically, we highlight evidence for the activation of these channels/receptors during epilepsy including neuroinflammation and oxidative stress, discuss signaling pathways and feedback mechanisms, and propose the functions of each of them in acute and chronic epilepsy. Studying the role of these non-selective membrane channels in epilepsy and identifying appropriate blockers for one or more of them could provide complementary therapies to better alleviate the disease.

Nociceptive afferent phenotyping reveals that transient receptor potential ankyrin 1 promotes cold pain through neurogenic inflammation upstream of the neurotrophic factor receptor GFRα3 and the menthol receptor transient receptor potential melastatin 8

ABSTRACT

The proper detection and behavioral response to painfully cold temperatures is critical for avoiding potentially harmful tissue damage. Cold allodynia and hyperalgesia, pain associated with innocuous cooling and exaggerated pain with noxious cold, respectively, are common in patients with chronic pain. In peripheral somatosensory afferents, the ion channels transient receptor potential melastatin 8 (TRPM8) and transient receptor potential ankyrin 1 (TRPA1) are candidate receptors for innocuous and noxious cold temperatures, respectively. However, the role of TRPA1 as a cold sensor has remained controversial, and recent evidence suggests that TRPM8 channels and afferents mediate the detection of both pleasant and painful cold. To determine the role of TRPA1 afferents in cold-induced mouse behaviors in vivo, we used functional phenotyping by targeted nerve conduction block with the cell-impermeant lidocaine derivative QX-314. Surprisingly, we find that injection of QX-314 with TRPA1 agonists reduces cold-induced behaviors in mice, but does so in a TRPM8-dependent manner. Moreover, this effect is sexually dimorphic and requires the glial cell line-derived neurotrophic factor receptor GFRα3, as does cold hypersensitivity produced by the activation of TRPA1 channels. Taken together, these results suggest that under conditions of neurogenic inflammation, TRPA1 works upstream of GFRα3 and TRPM8 to produce cold hypersensitivity, providing novel insights into the role of TRPA1 channels in cold pain.

Quaternary Lidocaine Derivatives: Past, Present, and Future

Local anesthetics have the advantage of complete analgesia with fewer side effects compared to systemic analgesics. However, their clinical use is limited due to their short duration of action. Thus, local anesthetics with fast onset, long duration of action, selective nociceptive block, and low local and systemic toxicity are highly desirable. In the past electrophysiological studies, quaternary lidocaine derivatives (QLDs) showed these characteristics. Here, we review electrophysiological properties of QLDs and their pharmacodynamic characteristics to shed light on potential problems.

Selective cold pain inhibition by targeted block of TRPM8-expressing neurons with quaternary lidocaine derivative QX-314

Treatment of pain with local anesthetics leads to an unfavorable decrease in general sensory acuity due to their indiscriminate block of both pain sensing (nociceptors) and non-pain sensing nerves. However, the cell impermeant lidocaine derivative QX-314 can be selectively targeted to only nociceptors by permeation through ligand-gated cation channels. Here we show that localized injection of QX-314 with agonists for the menthol receptor TRPM8 specifically blocks cold-evoked behaviors in mice, including cold allodynia and hyperalgesia. Remarkably, cooling stimuli also promotes QX-314-mediated inhibition of cold behaviors, and can be used to block cold allodynia, while retaining relatively normal cold sensation. The effects of both agonist and thermally evoked uptake of QX-314 are TRPM8-dependent, results demonstrating an effective approach to treat localized cold pain without altering general somatosensation.

Serra Ongun, Angela Sarkisian and David McKemy show that localized co-injection of lidocaine derivative QX-314 and receptor agonists is able to block cold sensitivity in mice in a targeted way, with implications for treating cold pain associated with injury and disease.

Targeting dorsal root ganglia and primary sensory neurons for the treatment of chronic pain

INTRODUCTION

Currently the treatment of chronic pain is inadequate and compromised by debilitating central nervous system side effects. Here we discuss new therapeutic strategies that target dorsal root ganglia (DRGs) in the peripheral nervous system for a better and safer treatment of chronic pain. Areas covered: The DRGs contain the cell bodies of primary sensory neurons including nociceptive neurons. After painful injuries, primary sensory neurons demonstrate maladaptive molecular changes in DRG cell bodies and in their axons. These changes result in hypersensitivity and hyperexcitability of sensory neurons (peripheral sensitization) and are crucial for the onset and maintenance of chronic pain. We discuss the following new strategies to target DRGs and primary sensory neurons as a means of alleviating chronic pain and minimizing side effects: inhibition of sensory neuron-expressing ion channels such as TRPA1, TRPV1, and Nav1.7, selective blockade of C- and Aβ-afferent fibers, gene therapy, and implantation of bone marrow stem cells. Expert opinion: These peripheral pharmacological treatments, as well as gene and cell therapies, aimed at DRG tissues and primary sensory neurons can offer better and safer treatments for inflammatory, neuropathic, cancer, and other chronic pain states.