Regulation of the T-type Ca(2+) channel Cav3.2 by hydrogen sulfide: emerging controversies concerning the role of H2 S in nociception

T-type calcium channel modulation by hydrogen sulfide in neuropathic pain conditions

Neuropathic pain can appear as a direct or indirect nerve damage lesion or disease that affects the somatosensory nervous system. If the neurons are damaged or indirectly stimulated, immune cells contribute significantly to inflammatory and neuropathic pain. After nerve injury, peripheral macrophages/spinal microglia accumulate around damaged neurons, producing endogenous hydrogen sulfide (H₂S) through the cystathionine-γ-lyase (CSE) enzyme. H₂S has a pronociceptive modulation on the Ca_v3.2 subtype, the predominant Ca_v3 isoform involved in pain processes. The present review provides relevant information about H₂S modulation on the Ca_v3.2 T-type channels in neuropathic pain conditions. We have discussed that the dual effect of H₂S on T-type channels is concentration-dependent, that is, an inhibitory effect is seen at low concentrations of 10 µM and an augmentation effect on T-current at 100 µM. The modulation mechanism of the Ca_v3.2 channel by H₂S involves the direct participation of the redox/Zn²⁺ affinity site located in the His191 in the extracellular loop of domain I of the channel, involving a group of extracellular cysteines, comprising C114, C123, C128, and C1333, that can modify the local redox environment. The indirect interaction pathways involve the regulation of the Ca_v3.2 channel through cytokines, kinases, and post-translational regulators of channel expression. The findings conclude that the CSE/H₂S/Ca_v3.2 pathway could be a promising therapeutic target for neuropathic pain disorders.

TET1 involved in bisphenol A induced TM3 Leydig cell toxicity by regulating Cav3.3 hydroxymethylation

Bisphenol A (BPA), an important environmental pollutant, is known to damage reproductive development. However, the underlying epigenetic mechanism in Leydig cells during BPA exposure has not been explored in detail. In this study, TM3 Leydig cells were treated with BPA (0, 20, 40 and 80 μM) for 72 h. The differentially expressed TET1 cell model was constructed to explore the mechanism of BPA-induced cytotoxicity. Results showed that BPA exposure significantly inhibited cell viability and increased apoptosis of TM3 Leydig cells. Meanwhile, the mRNA of TET1, Cav3.2 and Cav3.3 decreased significantly with the increase of BPA exposure. Importantly, TET1 significantly promoted proliferation of TM3 Leydig cells and inhibited apoptosis. Differentially expressed TET1 significantly affected BPA-induced toxicity in TM3 Leydig cells. Notably, TET1 elevated the mRNA levels of Cav3.2 and Cav3.3. MeDIP and hMeDIP confirmed that TET1 regulated the expression of Cav3.3 through DNA hydroxymethylation. Our study firstly presented that TET1 participated in BPA-induced toxicity in TM3 Leydig cells through regulating Cav3.3 hydroxymethylation modification. These findings suggest that TET1 acts as a potential epigenetic marker for reproductive toxicity induced by BPA exposure and may provide a new direction for the research on male reproductive damage.

Change in Cav3.2 T-Type Calcium Channel Induced by Varicella-Zoster Virus Participates in the Maintenance of Herpetic Neuralgia

Pain, as the most prevalent neurological complication of herpes zoster (HZ), may occur before or during the rash onset or even after the rash has recovered. Particularly, postherpetic neuralgia (PHN) is a refractory chronic condition, usually defined as pain persisting for 3 months or longer from the onset of HZ. Pain evoked by HZ impairs the normal physical and emotional functions of the patients, severely reducing their quality of life. However, how zoster-associated pain occurs and develops into PHN are elusive, making PHN difficult to predict. Uncovering the pathogenesis of zoster-associated pain (or HN) helps us to better understand the onset of PHN and supports developing more effective treatments. In this study, we successfully constructed a model for zoster-associated pain through varicella-zoster virus (VZV) infections of mouse footpads and pain behavior assessments. Next, we used the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Gene Ontology (GO) to analyze PHN rodent dorsal root ganglion (DRG) gene microarray data and found that calcium signal disorder might be involved in the onset of PHN. By using reverse transcription real-time fluorescent quantitative PCR (RT-qPCR) and Western blotting, we confirmed that VZV infection could significantly upregulate the expression of T-type calcium channel Cav3.2 in DRG and spinal dorsal horn (SDH). Intrathecal administration of Cav3.2 blocker (2R/S)-6-prenylnaringenin (6-PNG) relieved mechanical and thermal hyperalgesia induced by VZV. Taken together, our data indicated that VZV might participate in the occurrence and development of HN by upregulating the expression of Cav3.2 in DRG and SDH. These findings will help to reveal the underlying mechanisms on long-lasting pain and PHN formation, providing a new insight that Cav3.2 can be the promising drug target for remitting PHN.

Pain pathways and potential new targets for pain relief

Pain is an unpleasant sensory and emotional experience that affects a sizable percentage of people on a daily basis. Sensory neurons known as nociceptors built specifically to detect damaging stimuli can be found throughout the body. They transmit information about noxious stimuli from mechanical, thermal, and chemical sources to the central nervous system and higher brain centers via electrical signals. Nociceptors express various channels and receptors such as voltage-gated sodium and calcium channels, transient receptor potential channels, and opioid receptors that allow them to respond in a highly specific manner to noxious stimuli. Attenuating the pain response can be achieved by inhibiting or altering the expression of these pain targets. Achieving a deeper understanding of how these receptors can be affected at the molecular level can lead to the development of novel pain therapies. This review will discuss the mechanisms of pain, introduce the various receptors that are responsible for detecting pain, and future directions in pharmacological therapies.

Hydrogen Sulfide-Evoked Intracellular Ca2+ Signals in Primary Cultures of Metastatic Colorectal Cancer Cells

Simple Summary

Colorectal cancer (CRC) is the most common type of gastrointestinal cancer and the third most predominant cancer in the world. CRC is potentially curable with surgical resection of the primary tumor. The clinical problem of colorectal cancer, however, is the spread and outgrowth of metastases, which are difficult to eradicate and lead to a patient’s death. The failure of conventional treatment to significantly improved outcomes in mCRC has prompted the search for alternative molecular targets with the goal of ameliorating the prognosis of these patients. The present investigation revealed that exogenous delivery of hydrogen sulfide (H₂S) suppresses proliferation in metastatic colorectal cancer cells by inducing an increase in intracellular Ca²⁺ concentration. H₂S was effective on metastatic, but not normal, cells. Therefore, we propose that exogenous administration of H₂S to patients affected by metastatic colorectal carcinoma could represent a promising therapeutic alternative.

Abstract

Exogenous administration of hydrogen sulfide (H₂S) is emerging as an alternative anticancer treatment. H₂S-releasing compounds have been shown to exert a strong anticancer effect by suppressing proliferation and/or inducing apoptosis in several cancer cell types, including colorectal carcinoma (CRC). The mechanism whereby exogenous H₂S affects CRC cell proliferation is yet to be clearly elucidated, but it could involve an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i). Herein, we sought to assess for the first time whether (and how) sodium hydrosulfide (NaHS), one of the most widely employed H₂S donors, induced intracellular Ca²⁺ signals in primary cultures of human metastatic CRC (mCRC) cells. We provided the evidence that NaHS induced extracellular Ca²⁺ entry in mCRC cells by activating the Ca²⁺-permeable channel Transient Receptor Potential Vanilloid 1 (TRPV1) followed by the Na⁺-dependent recruitment of the reverse-mode of the Na⁺/Ca²⁺ (NCX) exchanger. In agreement with these observations, TRPV1 protein was expressed and capsaicin, a selective TRPV1 agonist, induced Ca²⁺ influx by engaging both TRPV1 and NCX in mCRC cells. Finally, NaHS reduced mCRC cell proliferation, but did not promote apoptosis or aberrant mitochondrial depolarization. These data support the notion that exogenous administration of H₂S may prevent mCRC cell proliferation through an increase in [Ca²⁺]_i, which is triggered by TRPV1.

Role of H2S in pain: Growing evidences of mystification

There have been studies suggesting the pain attenuating as well as pain inducing actions of hydrogen sulfide (H₂S). Exogenous administrated H₂S may be antinociceptive or pronociceptive, while the endogenous H₂S is pronociceptive. Experimental studies have shown that pharmacological inhibitors of H₂S biosynthetic enzymes may attenuate nociceptive as well as neuropathic pain. It suggests that nerve injury or inflammatory agents may induce the expression of H₂S biosynthetic enzymes to increase the endogenous production of H₂S, which acts as a pain neurotransmitter to produce pain. The endogenous H₂S may act through different mechanisms including opening of T-type calcium channels, activation of voltage-gated sodium channels, suppression of potassium channels, activation of TRPA1, TRPV1 and TRPC6 channels, upregulation of spinal NMDA receptors and sensitization of purinergic receptors. Exogenous administration of H₂S/precursors/donors attenuates or facilitates pain. It may be hypothesized that local administration of H₂S may cause pain; while it's systemic administration may attenuate pain. The doses of H₂S may also influence the pain response and H₂S in low doses may contribute in reducing pain, while H₂S in high doses may contribute in relieving pain. Accordingly, enzymatic inhibitors of H₂S synthesis or systemic administration of slow H₂S releasing agents/low dose H₂S donors may be useful in attenuating nociceptive and neuropathic pain. The present review describes the dual role of H₂S in pain attenuation and pain induction along with possible mechanisms.

Delineating an extracellular redox-sensitive module in T-type Ca2+ channels

T-type (Cav3) Ca²⁺ channels are important regulators of excitability and rhythmic activity of excitable cells. Among other voltage-gated Ca²⁺ channels, Cav3 channels are uniquely sensitive to oxidation and zinc. Using recombinant protein expression in HEK293 cells, patch clamp electrophysiology, site-directed mutagenesis, and homology modeling, we report here that modulation of Cav3.2 by redox agents and zinc is mediated by a unique extracellular module containing a high-affinity metal-binding site formed by the extracellular IS1–IS2 and IS3–IS4 loops of domain I and a cluster of extracellular cysteines in the IS1–IS2 loop. Patch clamp recording of recombinant Cav3.2 currents revealed that two cysteine-modifying agents, sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES) and N-ethylmaleimide, as well as a reactive oxygen species–producing neuropeptide, substance P (SP), inhibit Cav3.2 current to similar degrees and that this inhibition is reversed by a reducing agent and a zinc chelator. Pre-application of MTSES prevented further SP-mediated current inhibition. Substitution of the zinc-binding residue His¹⁹¹ in Cav3.2 reduced the channel's sensitivity to MTSES, and introduction of the corresponding histidine into Cav3.1 sensitized it to MTSES. Removal of extracellular cysteines from the IS1–IS2 loop of Cav3.2 reduced its sensitivity to MTSES and SP. We hypothesize that oxidative modification of IS1–IS2 loop cysteines induces allosteric changes in the zinc-binding site of Cav3.2 so that it becomes sensitive to ambient zinc.

Hydrogen sulfide downregulates colonic afferent sensitivity by a nitric oxide synthase-dependent mechanism in mice

BACKGROUND

The effect of hydrogen sulfide (H₂ S) on visceral nociception is elusive. The conflicting evidence of its pro- and antinociceptive effects raises a series of questions with respect to the effect of H₂ S on colonic afferent activity and the underlying mechanism, which was further elucidated in this study.

METHODS

Colonic mesenteric afferent nerve spikes of normal male C57BL/6J mice, Cbs^+/- mice, and Wistar rats were recorded in vitro. The abdominal withdrawal reflex (AWR) induced by colorectal distension (CRD) was evaluated in Cbs^+/- mice and WT littermates.

KEY RESULTS

Sodium hydrosulfide (NaHS) significantly decreased colonic afferent spontaneous discharge, chemosensitivity to bradykinin, mechanosensitivity to ramp distention, and intraluminal pressure in mice. Reducing the relaxant action of NaHS on intestinal smooth muscle using the nonspecific K⁺ channel blocker TEA (10 mmol/L) did not block the inhibition of NaHS on afferent nerve activity. The inhibitory effects of NaHS (0.5 mmol/L) on colonic afferent sensitivity were largely eliminated by the pretreatment with nonspecific NOS inhibitor N^G -Methyl-l-arginine acetate salt (1 mmol/L), the specific nNOS inhibitor NPLA (1 μmol/L), or N-type Ca²⁺ channel blocker ω-conotoxin GVIA (1 μmol/L). Compared with WT mice, Cbs^+/- mice showed increased mesenteric afferent sensitivity to colonic distention and enhanced hyperalgesic response to CRD. Intraperitoneal administration of NaHS (60 μmol/kg) alleviated the nociception response to CRD in both Cbs^+/- and WT mice.

CONCLUSIONS AND INFERENCES

H₂ S downregulates colonic mesenteric afferent sensitivity by a nNOS-dependent mechanism in mice. Our findings may demonstrate a new mechanism for the antinociceptive effect of H₂ S in colon.

Functional Exploration Of T-Type Calcium Channels (Cav3.2 And Cav3.3) And Their Sensitivity To Zinc

Introduction:

T-type Ca²⁺ channels (TTCC) are low Voltage-gated calcium channels, expressed in various tissues such as the brain and heart, and contribute to a variety of physiological functions including neuronal excitability, hormone secretion, muscle contraction, and pacemaker activity. At high concentrations, Zinc (Zn²⁺) is naturally attached to cell membranes and is therefore considered a reversible inhibitor of calcium. Zinc is also involved in the kinetics of sodium and potassium currents. Zinc is essential for many functions. A low zinc tenor is associated with emotional instability, digestive disorders, slow-growing and alteration of protein synthesis.

Material and Methods:

For the Cell Culture we used HEK-293/tsA-201, and for transfection, the pCDNA3 plasmid constructs encoding human CaV3.2, and CaV3.3 subunits. Electrophysiological experiments were performed using the whole cell configuration of the patch-clamp technique. T-type currents were recorded using a test pulse from a holding potential at (-100mV) to (-30 mV), data Acquisition and Analysis for Current-voltage relationships (I-V curves) were recorded for the two cloned T-type Ca²⁺ channels (Cav3.2, Cav3.3).

Results:

Our studies describe the behavior of these channels Cav3.2 and Cav3.3 and also their current sensitivity to Zinc (Zn²⁺) in transfected HEK-293/tsA-201cells. Our results show that Zn²⁺ applies a modulatory effect on T-type calcium channels. We observe that Zn²⁺ differentially modulates the CaV3.2 and CaV3.3 channels. Zn²⁺ preferably inhibits Cav3.2.

Conclusion:

We have demonstrated that Zn²⁺ differentially modulates two CaV3 channels (Cav3.2 and Cav3.3): It is a preferential blocker of CaV3.2 channels and it alters the gating behaviour of CaV3.3 channels.

Role of Transient Receptor Potential Ankyrin 1 Ion Channel and Somatostatin sst4 Receptor in the Antinociceptive and Anti-inflammatory Effects of Sodium Polysulfide and Dimethyl Trisulfide

Transient receptor potential ankyrin 1 (TRPA1) non-selective ligand-gated cation channels are mostly expressed in primary sensory neurons. Polysulfides (POLYs) are Janus-faced substances interacting with numerous target proteins and associated with both protective and detrimental processes. Activation of TRPA1 in sensory neurons, consequent somatostatin (SOM) liberation and action on sst4 receptors have recently emerged as mediators of the antinociceptive effect of organic trisulfide dimethyl trisulfide (DMTS). In the frame of the present study, we set out to compare the participation of this mechanism in antinociceptive and anti-inflammatory effects of inorganic sodium POLY and DMTS in carrageenan-evoked hind-paw inflammation. Inflammation of murine hind paws was induced by intraplantar injection of carrageenan (3% in 30 µL saline). Animals were treated intraperitoneally with POLY (17 µmol/kg) or DMTS (250 µmol/kg) or their respective vehicles 30 min prior paw challenge and six times afterward every 60 min. Mechanical pain threshold and swelling of the paws were measured by dynamic plantar aesthesiometry and plethysmometry at 2, 4, and 6 h after initiation of inflammation. Myeloperoxidase (MPO) activity in the hind paws were detected 6 h after challenge by luminescent imaging. Mice genetically lacking TRPA1 ion channels, sst4 receptors and their wild-type counterparts were used to examine the participation of these proteins in POLY and DMTS effects. POLY counteracted carrageenan-evoked mechanical hyperalgesia in a TRPA1 and sst4 receptor-dependent manner. POLY did not influence paw swelling and MPO activity. DMTS ameliorated all examined inflammatory parameters. Mitigation of mechanical hyperalgesia and paw swelling by DMTS were mediated through sst4 receptors. These effects were present in TRPA1 knockout animals, too. DMTS inhibited MPO activity with no participation of the sensory neuron-SOM axis. While antinociceptive effects of POLY are transmitted by activation of peptidergic nerves via TRPA1, release of SOM and its effect on sst4 receptors, those of DMTS partially rely on SOM release triggered by other routes. SOM is responsible for the inhibition of paw swelling by DMTS, but TRPA1 does not contribute to its release. Modulation of MPO activity by DMTS is independent of TRPA1 and sst4.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

Regulation of the CaV3.2 calcium channels in health and disease Regulácia CaV3.2 vápnikových kanálov v zdraví a chorobe

Family of T-type or low-voltage activated calcium channels consists of three members: CaV3.1, CaV3.2, and CaV3.3. CaV3.2 channel has almost identical biophysical properties as the CaV3.1 channel, but is distinguished by a specific tissue expression profile and a prominent role in several pathologies, including neuropathic pain, epilepsy, and dysregulation of cardiac rhythm. Further, it may be involved in phenotype of autism spectrum disorders, and amyotrophic lateral sclerosis. It represents a promising target for future pharmacotherapies.

Redox-Dependent Modulation of T-Type Ca(2+) Channels in Sensory Neurons Contributes to Acute Anti-Nociceptive Effect of Substance P

AIMS

Neuropeptide substance P (SP) is produced and released by a subset of peripheral sensory neurons that respond to tissue damage (nociceptors). SP exerts excitatory effects in the central nervous system, but peripheral SP actions are still poorly understood; therefore, here, we aimed at investigating these peripheral mechanisms.

RESULTS

SP acutely inhibited T-type voltage-gated Ca(2+) channels in nociceptors. The effect was mediated by neurokinin 1 (NK1) receptor-induced stimulation of intracellular release of reactive oxygen species (ROS), as it can be prevented or reversed by the reducing agent dithiothreitol and mimicked by exogenous or endogenous ROS. This redox-mediated T-type Ca(2+) channel inhibition operated through the modulation of CaV3.2 channel sensitivity to ambient zinc, as it can be prevented or reversed by zinc chelation and mimicked by exogenous zinc. Elimination of the zinc-binding site in CaV3.2 rendered the channel insensitive to SP-mediated inhibition. Importantly, peripherally applied SP significantly reduced bradykinin-induced nociception in rats in vivo; knock-down of CaV3.2 significantly reduced this anti-nociceptive effect. This atypical signaling cascade shared the initial steps with the SP-mediated augmentation of M-type K(+) channels described earlier.

INNOVATION

Our study established a mechanism underlying the peripheral anti-nociceptive effect of SP whereby this neuropeptide produces ROS-dependent inhibition of pro-algesic T-type Ca(2+) current and concurrent enhancement of anti-algesic M-type K(+) current. These findings will lead to a better understanding of mechanisms of endogenous analgesia.

CONCLUSION

SP modulates T-type channel activity in nociceptors by a redox-dependent tuning of channel sensitivity to zinc; this novel modulatory pathway contributes to the peripheral anti-nociceptive effect of SP. Antioxid. Redox Signal. 25, 233-251.