Regulation of Two-Pore-Domain Potassium TREK Channels and their Involvement in Pain Perception and Migraine

Discovery of ONO-TR-772 (VU6018042): A Highly Selective and CNS Penetrant TREK Inhibitor in Vivo Tool Compound

Herein we describe our continuing work on the K2P family of potassium ion channels with the chemical optimization of a selective and CNS penetrant series of TREK inhibitors, culminating in the discovery of ONO-TR-772 (VU6018042). From an HTS hit harboring a benzyl ether linker, SAR proved intractable until an acetylene linker was identified as an isosteric replacement. Robust SAR was then observed, and a key fluorination to enhance PK and CNS penetration provided ONO-TR-772 (VU6018042), a potent (TREK-1 IC50 = 15 nM), selective (>10 μM versus other K2P channels except TREK-2), and CNS penetrant (rat K p = 0.98) TREK inhibitor. ONO-TR-772 (VU6018042) demonstrated robust efficacy in an MK-801 challenge NOR paradigm, with an MED of 10 mg/kg.

Discovery of Isobenzofuran-1(3H)-one Derivatives as Selective TREK-1 Inhibitors with In Vitro and In Vivo Neuroprotective Effects

TREK-1 regulates neuronal excitability and neuronal cell apoptosis, and inhibition of TREK-1 is a potential strategy to prevent cell death and achieve neuroprotection in an ischemic stroke. In this work, a series of novel isobenzofuran-1(3H)-one derivatives were designed and synthesized as TREK-1 inhibitors, and extensive structure-activity relationships led to the discovery of potent and selective TREK-1 inhibitors having IC50 values of a low micromolar level. Among them, Cpd8l potently and selectively inhibited TREK-1 (IC50 = 0.81 μM, selectivity >30 fold over other K+, Na+, and TRP channels). Cpd8l remarkably reduced the neuron death in the OGD/R-induced cortical neuronal injury model, while adenovirus silencing TREK-1 reduced its neuroprotective effect. Furthermore, Cpd8l could effectively ameliorate brain injury in MCAO/R model mice. Collectively, this work demonstrates that Cpd8l may serve as a novel lead compound to develop a highly potent and selective TREK-1 inhibitor for ischemic stroke treatment.

Language errors in pain medicine: An umbrella review

Errors in language are common in pain medicine, but the extent of such errors has not been systematically measured. This pre-registered umbrella review explored Embase, PubMed, Medline and CINAHL and seeks to quantify the prevalence of errors in language in review articles since the last IASP definition revision. To be eligible, studies must have met the following criteria: 1) Primary aim was stated as to provide neurophysiological explanations of nociception and/or pain in humans in context of a pathology/condition; 2) Any type of review article; 3) Written in English; 4) Published in a peer-reviewed journal. Studies were excluded if they met any of the following criteria: 5) Published prior to the last revision of the IASP definition; 6) Published after May 2023; 7) Published in a predatory journal. Out of 5470 articles screened, 48 review articles met the inclusion criteria. All articles contained at least one error in language, there were no differences in the proportions of errors in language in review articles between years of publication, and various predictors were mostly not associated with a higher or lower number of errors in language counts in articles. Our findings reveal the need for heightened awareness among researchers, clinicians, journals and editorial boards regarding the prevalence and impact of these errors. Given our findings and their limitations, further research should focus on examining the contextual influence of misnomer usage and replication of these results. PERSPECTIVE: This umbrella review explored the main biomedical databases to see how many review articles contained language errors. Our findings underscore the imperative for prompt action in regulating pain medicine terminology. PRE-REGISTRATION: This umbrella review was pre-registered on OSF registries (https://doi.org/10.17605/osf.io/kau8m). ONLINE MATERIAL: https://osf.io/kdweg/.

Insights into the structure and modulation of human TWIK-2

The T andem of pore domain in a W eak I nward R ectifying K + channel 2 (TWIK-2; KCNK6) is a member of the Two-Pore Domain K + (K2P) channel family, which is associated with pulmonary hypertension, lung injury, and inflammation. The structure and regulatory mechanisms of TWIK-2 remain largely unknown. Here, we present the cryo-electron microscopy (cryo-EM) structure of human TWIK-2 at ~3.7 Å and highlight its conserved and unique features. Using automated whole-cell patch clamp recordings, we demonstrate that gating in TWIK-2 is voltage-dependent and insensitive to changes in the extracellular pH. We identify key residues that influence TWIK-2 activity by employing structure and sequence-guided site-directed mutagenesis and provide insights into the possible mechanism of TWIK-2 regulation. Additionally, we demonstrate the application of high-throughput automated whole-cell patch clamp platforms to screen small molecule modulators of TWIK-2. Our work serves as a foundation for designing high-throughput small molecule screening campaigns to identify specific high-affinity TWIK-2 modulators, including promising new anti-inflammatory therapeutics.

Sortilin-Mediated Inhibition of TREK1/2 Channels in Primary Sensory Neurons Promotes Prediabetic Neuropathic Pain

Neuropathic pain can occur during the prediabetic stage, even in the absence of hyperglycemia. The presence of prediabetic neuropathic pain (PDNP) poses challenges to the management of individuals with prediabetes. However, the mechanisms underlying this pain remain unclear. This study aims to investigate the underlying mechanism and identify potential therapeutic targets of PDNP. A prediabetic animal model induced by a high-energy diet exhibits both mechanical allodynia and thermal hyperalgesia. Furthermore, hyperexcitability and decreased potassium currents are observed in the dorsal root ganglion (DRG) neurons of these rats. TREK1 and TREK2 channels, which belong to the two-pore-domain K+ channel (K2P) family and play an important role in controlling cellular excitability, are downregulated in DRG neurons. Moreover, this alteration is modulated by Sortilin, a molecular partner that modulates the expression of TREK1. The overexpression of Sortilin negatively affects the expression of TREK1 and TREK2, leading to increased neuronal excitability in the DRG and enhanced peripheral pain sensitivity in rats. Moreover, the downregulation of Sortilin or activation of TREK1 and TREK2 channels by genetic or pharmacological approaches can alleviate PDNP. Therefore, targeting the Sortilin-mediated TREK1/2 pathway may provide a therapeutic approach for ameliorating PDNP.

Mechanosensitive receptors in migraine: a systematic review

BACKGROUND

Migraine is a debilitating neurological disorder with pain profile, suggesting exaggerated mechanosensation. Mechanosensitive receptors of different families, which specifically respond to various mechanical stimuli, have gathered increasing attention due to their potential role in migraine related nociception. Understanding these mechanisms is of principal importance for improved therapeutic strategies. This systematic review comprehensively examines the involvement of mechanosensitive mechanisms in migraine pain pathways.

METHODS

A systematic search across the Cochrane Library, Scopus, Web of Science, and Medline was conducted on 8th August 2023 for the period from 2000 to 2023, according to PRISMA guidelines. The review was constructed following a meticulous evaluation by two authors who independently applied rigorous inclusion criteria and quality assessments to the selected studies, upon which all authors collectively wrote the review.

RESULTS

We identified 36 relevant studies with our analysis. Additionally, 3 more studies were selected by literature search. The 39 papers included in this systematic review cover the role of the putative mechanosensitive Piezo and K2P, as well as ASICs, NMDA, and TRP family of channels in the migraine pain cascade. The outcome of the available knowledge, including mainly preclinical animal models of migraine and few clinical studies, underscores the intricate relationship between mechanosensitive receptors and migraine pain symptoms. The review presents the mechanisms of activation of mechanosensitive receptors that may be involved in the generation of nociceptive signals and migraine associated clinical symptoms. The gender differences of targeting these receptors as potential therapeutic interventions are also acknowledged as well as the challenges related to respective drug development.

CONCLUSIONS

Overall, this analysis identified key molecular players and uncovered significant gaps in our understanding of mechanotransduction in migraine. This review offers a foundation for filling these gaps and suggests novel therapeutic options for migraine treatments based on achievements in the emerging field of mechano-neurobiology.

Autonomic Nervous System Dysfunction Is Related to Chronic Prostatitis/Chronic Pelvic Pain Syndrome

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a common and non-lethal urological condition with painful symptoms. The complexity of CP/CPPS's pathogenesis and lack of efficient etiological diagnosis results in incomplete treatment and recurrent episodes, causing long-term mental and psychological suffering in patients. Recent findings indicate that the autonomic nervous system involves in CP/CPPS, including sensory, sympathetic, parasympathetic, and central nervous systems. Neuro-inflammation and sensitization of sensory nerves lead to persistent inflammation and pain. Sympathetic and parasympathetic alterations affect the cardiovascular and reproductive systems and the development of prostatitis. Central sensitization lowers pain thresholds and increases pelvic pain perception in chronic prostatitis. Therefore, this review summarized the detailed processes and mechanisms of the critical role of the autonomic nervous system in developing CP/CPPS. Furthermore, it describes the neurologically relevant substances and channels or receptors involved in this process, which provides new perspectives for new therapeutic approaches to CP/CPPS.

Association between dietary potassium intake and severe headache or migraine in US adults: a population-based analysis

Background

Migraine is a prevalent neurovascular headache disorder. The link between dietary potassium and blood pressure has been established. We sought to delineate the relationship between dietary potassium intake and the prevalence of migraines.

Methods

We conducted a cross-sectional analysis using data from the National Health and Nutrition Examination Survey (NHANES) spanning 1999-2004, comprising 10,254 participants aged ≥20 years. Participants who reported severe headaches or migraine in the self-report questionnaire were identified as migraineurs. A 24-h dietary recall methodology was used to assess dietary potassium intake. Multivariate regression analysis and restricted cubic spline (RCS) modeling were utilized to elucidate the relationship between dietary potassium and migraines.

Results

Among the 10,254 participants, 20.1% were identified with migraine or severe headaches. The adjusted odds ratio (OR) for migraine occurrence in the Q2 dietary potassium intake (1771-2,476 mg/d) was 0.84 (95% CI: 0.73-0.97, p = 0.021) compared to the lowest quartile (Q1, ≤ 1771 mg/d). The relationship between dietary potassium and migraine exhibited an L-shaped pattern (non-linear, p = 0.016) with an inflection at approximately 1439.3 mg/d. In the subgroup analysis, when compared to Q1, who had the lowest dietary potassium intake, the adjusted OR for Q2 in females, those in the medium-high household income group, and with a Body Mass Index (BMI) ≥ 25 kg/m2 were as follows: (OR, 0.82; 95% CI, 0.69-0.98), (OR, 0.79; 95% CI, 0.66-0.95), and (OR, 0.78; 95% CI, 0.66-0.93), respectively. No significant interaction was observed across groups after adjusting for all possible covariates.

Conclusion

The relationship between dietary potassium intake and migraine prevalence among US adults appears to follow an L-shaped curve.

Xenon's Sedative Effect Is Mediated by Interaction with the Cyclic Nucleotide-Binding Domain (CNBD) of HCN2 Channels Expressed by Thalamocortical Neurons of the Ventrobasal Nucleus in Mice

Previous studies have shown that xenon reduces hyperpolarization-activated cyclic nucleotide-gated channels type-2 (HCN2) channel-mediated current (I_h) amplitude and shifts the half-maximal activation voltage (V1/2) in thalamocortical circuits of acute brain slices to more hyperpolarized potentials. HCN2 channels are dually gated by the membrane voltage and via cyclic nucleotides binding to the cyclic nucleotide-binding domain (CNBD) on the channel. In this study, we hypothesize that xenon interferes with the HCN2 CNBD to mediate its effect. Using the transgenic mice model HCN2EA, in which the binding of cAMP to HCN2 was abolished by two amino acid mutations (R591E, T592A), we performed ex-vivo patch-clamp recordings and in-vivo open-field test to prove this hypothesis. Our data showed that xenon (1.9 mM) application to brain slices shifts the V1/2 of I_h to more hyperpolarized potentials in wild-type thalamocortical neurons (TC) (V1/2: -97.09 [-99.56--95.04] mV compared to control -85.67 [-94.47--82.10] mV; p = 0.0005). These effects were abolished in HCN2EA neurons (TC), whereby the V1/2 reached only -92.56 [-93.16- -89.68] mV with xenon compared to -90.03 [-98.99--84.59] mV in the control (p = 0.84). After application of a xenon mixture (70% xenon, 30% O₂), wild-type mice activity in the open-field test decreased to 5 [2-10] while in HCN2EA mice it remained at 30 [15-42]%, (p = 0.0006). In conclusion, we show that xenon impairs HCN2 channel function by interfering with the HCN2 CNBD site and provide in-vivo evidence that this mechanism contributes to xenon-mediated hypnotic properties.

Histamine bidirectionally regulates the intrinsic excitability of parvalbumin-positive neurons in the lateral globus pallidus and promotes motor behaviour

BACKGROUND AND PURPOSE

Parvalbumin (PV)-positive neurons are a type of neuron in the lateral globus pallidus (LGP) which plays an important role in motor control. The present study investigated the effect of histamine on LGP^PV neurons and motor behaviour.

EXPERIMENTAL APPROACH

Histamine levels in LGP as well as its histaminergic innervation were determined through brain stimulation, microdialysis, anterograde tracing and immunostaining. Mechanisms of histamine action were detected by immunostaining, single-cell qPCR, whole-cell patch-clamp recording, optogenetic stimulation and CRISPR/Cas9 gene-editing techniques. The effect of histamine on motor behaviour was detected by animal behavioural tests.

KEY RESULTS

A direct histaminergic innervation in LGP from the tuberomammillary nucleus (TMN) and a histamine-induced increase in the intrinsic excitability of LGP^PV neurons were determined by pharmacological blockade or by genetic knockout of the histamine H₁ receptor (H₁ R)-coupled TWIK-related potassium channel-1 (TREK-1) and the small-conductance calcium-activated potassium channel (SK3), as well as by activation or overexpression of the histamine H₂ receptor (H₂ R)-coupled hyperpolarization-activated cyclic nucleotide-gated channel (HCN2). Histamine negatively regulated the STN → LGP^Glu transmission in LGP^PV neurons via the histamine H₃ receptor (H₃ R), whereas blockage or knockout of H₃ R increased the intrinsic excitability of LGP^PV neurons.

CONCLUSIONS AND IMPLICATIONS

Our results indicated that the endogenous histaminergic innervation in the LGP can bidirectionally promote motor control by increasing the intrinsic excitability of LGP^PV neurons through postsynaptic H₁ R and H₂ R, albeit its action was negatively regulated by the presynaptic H₃ R, thereby suggesting possible role of histamine in motor deficits manifested in Parkinson's disease (PD).