TRPA1 mediates spinal antinociception induced by acetaminophen and the cannabinoid Δ(9)-tetrahydrocannabiorcol

Structural basis of THC analog activity at the Cannabinoid 1 receptor

Tetrahydrocannabinol (THC) is the principal psychoactive compound derived from the cannabis plant Cannabis sativa and approved for emetic conditions, appetite stimulation and sleep apnea relief. THC's psychoactive actions are mediated primarily by the cannabinoid receptor CB1. Here, we determine the cryo-EM structure of HU210, a THC analog and widely used tool compound, bound to CB1 and its primary transducer, Gi1. We leverage this structure for docking and 1000 ns molecular dynamics simulations of THC and 10 structural analogs delineating their spatiotemporal interactions at the molecular level. Furthermore, we pharmacologically profile their recruitment of Gi and β-arrestins and reversibility of binding from an active complex. By combining detailed CB1 structural information with molecular models and signaling data we uncover the differential spatiotemporal interactions these ligands make to receptors governing potency, efficacy, bias and kinetics. This may help explain the actions of abused substances, advance fundamental receptor activation studies and design better medicines.

Paracetamol metabolism by endothelial cells - Potential mechanism underlying intravenous paracetamol-induced hypotension

It was shown previously that a metabolite of acetaminophen (APAP), N-acetyl-p-benzoquinone imine (NAPQI), is a potent vasodilator, which could underlie the hypotension observed when APAP is administered intravenously. However, it is unknown whether APAP metabolism to NAPQI is possible in the vasculature. In this study, we examine the hypothesis that APAP is metabolized by cytochrome P450 enzymes within the endothelium, which may be accelerated in critically ill patients by the presence of elevated myeloperoxidase (MPO). Exposure of human coronary artery endothelial cells (HCAECs) to APAP resulted in the formation of protein-bound APAP adducts. Proteomic analysis of HCAECs exposed to APAP showed upregulation of CYP20A1, together with proteins involved in the pentose phosphate pathway and maintaining redox homeostasis. Proteomic analyses of mesenteric arteries from rats administered intravenous APAP are consistent with a key role of the vascular wall in APAP metabolism, with similar proteomic pathway changes identified in HCAECs. These changes occurred over a short timeframe and were not seen in the corresponding proteomic analyses of liver tissue. Intracellular thiols were depleted in HCAECs upon APAP treatment, which was partially attenuated by ketoconazole, consistent with the involvement of cytochrome P450 enzymes in the metabolism of APAP to a thiol-reactive metabolite such as NAPQI. Evidence was also obtained for the metabolism of APAP to a thiol-reactive intermediate by MPO in the absence of chloride ions, consistent with NAPQI formation. Taken together, these data provide a putative mechanism to explain the presentation of hypotension in critically ill patients following IV APAP administration.

Acute ingestion of acetaminophen improves cognitive and repeated high intensity short-term maximal performance in well-trained female athletes: a randomized placebo-controlled trial

This study examined the effect of acute acetaminophen (ACTP) ingestion on physical performance during the 5 m shuttle run test (5mSRT), attention, mood states, and the perception of perceived exertion (RPE), pain (PP), recovery (PRS), and delayed onset of muscle soreness (DOMS) in well-trained female athletes. In a randomized, placebo-controlled, double-blind, crossover trial, fifteen well-trained female athletes (age 21 ± 2 years, height 165 ± 6 cm, body mass 62 ± 5 kg) swallowed either 1.5 g of ACTP or 1.5 g of placebo. The profile of mood states (POMS) and digit cancellation (DCT) were assessed 45 min postingestion, and 5mSRT was performed 60 min postingestion. The RPE and PP were determined immediately after each 30-s repetition of the 5mSRT, and the PRS and DOMS were recorded at 5 min and 24 h post-5mSRT. For the 5mSRT, ACTP ingestion improved the greatest distance (+ 10.88%, p < 0.001), total distance (+ 11.33%, p = 0.0007) and fatigue index (+ 21.43%, p = 0.0003) compared to PLA. Likewise, the DCT score was better on the ACTP (p = 0.0007) than on the PLA. RPE, PP, PRS, and DOMS scores were improved after ACTP ingestion (p < 0.01 for all comparisons) compared to PLA. POMS scores were enhanced with ACTP ingestion compared to PLA (p < 0.01). In conclusion, this study indicates that acute acetaminophen ingestion can improve repeated high intensity short-term maximal performance, attention, mood states, and perceptions of exertion, pain, recovery, and muscle soreness in well-trained female athletes, suggesting potential benefits for their overall athletic performance and mood state.

TRPA1-Related Diseases and Applications of Nanotherapy

Transient receptor potential (TRP) channels, first identified in Drosophila in 1969, are multifunctional ion channels expressed in various cell types. Structurally, TRP channels consist of six membrane segments and are classified into seven subfamilies. Transient receptor potential ankyrin 1 (TRPA1), the first member of the TRPA family, is a calcium ion affinity non-selective cation channel involved in sensory transduction and responds to odors, tastes, and chemicals. It also regulates temperature and responses to stimuli. Recent studies have linked TRPA1 to several disorders, including chronic pain, inflammatory diseases, allergies, and respiratory problems, owing to its activation by environmental toxins. Mutations in TRPA1 can affect the sensory nerves and microvasculature, potentially causing nerve pain and vascular problems. Understanding the function of TRPA1 is important for the development of treatments for these diseases. Recent developments in nanomedicines that target various ion channels, including TRPA1, have had a significant impact on disease treatment, providing innovative alternatives to traditional disease treatments by overcoming various adverse effects.

Remote neurostimulation through an endogenous ion channel using a near-infrared light-activatable nanoagonist

The development of noninvasive approaches to precisely control neural activity in mammals is highly desirable. Here, we used the ion channel transient receptor potential ankyrin-repeat 1 (TRPA1) as a proof of principle, demonstrating remote near-infrared (NIR) activation of endogenous neuronal channels in mice through an engineered nanoagonist. This achievement enables specific neurostimulation in nongenetically modified mice. Initially, target-based screening identified flavins as photopharmacological agonists, allowing for the photoactivation of TRPA1 in sensory neurons upon ultraviolet A/blue light illumination. Subsequently, upconversion nanoparticles (UCNPs) were customized with an emission spectrum aligned to flavin absorption and conjugated with flavin adenine dinucleotide, creating a nanoagonist capable of NIR activation of TRPA1. Following the intrathecal injection of the nanoagonist, noninvasive NIR stimulation allows precise bidirectional control of nociception in mice through remote activation of spinal TRPA1. This study demonstrates a noninvasive NIR neurostimulation method with the potential for adaptation to various endogenous ion channels and neural processes by combining photochemical toolboxes with customized UCNPs.

A triple cysteine motif as major determinant of the modulation of neuronal KV7 channels by the paracetamol metabolite N-acetyl-p-benzo quinone imine

BACKGROUND AND PURPOSE

The analgesic action of paracetamol involves KV7 channels, and its metabolite N-acetyl-p-benzo quinone imine (NAPQI), a cysteine modifying reagent, was shown to increase currents through such channels in nociceptors. Modification of cysteine residues by N-ethylmaleimide, H2O2, or nitric oxide has been found to modulate currents through KV7 channels. The study aims to identify whether, and if so which, cysteine residues in neuronal KV7 channels might be responsible for the effects of NAPQI.

EXPERIMENTAL APPROACH

To address this question, we used a combination of perforated patch-clamp recordings, site-directed mutagenesis, and mass spectrometry applied to recombinant KV7.1 to KV7.5 channels.

KEY RESULTS

Currents through the cardiac subtype KV7.1 were reduced by NAPQI. Currents through all other subtypes were increased, either by an isolated shift of the channel voltage dependence to more negative values (KV7.3) or by such a shift combined with increased maximal current levels (KV7.2, KV7.4, KV7.5). A stretch of three cysteine residues in the S2-S3 linker region of KV7.2 was necessary and sufficient to mediate these effects.

CONCLUSION AND IMPLICATION

The paracetamol metabolite N-acetyl-p-benzo quinone imine (NAPQI) modifies cysteine residues of KV7 subunits and reinforces channel gating in homomeric and heteromeric KV7.2 to KV7.5, but not in KV7.1 channels. In KV7.2, a triple cysteine motif located within the S2-S3 linker region mediates this reinforcement that can be expected to reduce the excitability of nociceptors and to mediate antinociceptive actions of paracetamol.

Increased Postoperative Opioid Consumption in the Presence of Coadministration of 5-Hydroxytryptamine Type 3 Antagonists with Acetaminophen: A Hospital Registry Study

BACKGROUND

Acetaminophen and 5-hydroxytryptamine type 3 (5-HT3) receptor antagonists are administered as standard prophylaxes for postoperative pain, nausea, and vomiting. Preclinical studies, however, suggest that 5-HT3 antagonists may compromise acetaminophen's analgesic effect. This hospital registry study investigates whether 5-HT3 antagonists mitigate the analgesic effect of prophylactic acetaminophen in a perioperative setting.

METHODS

This study included 55,016 adult patients undergoing general anesthesia for ambulatory procedures at a tertiary healthcare center in Massachusetts from 2015 to 2022. Using binary exposure variables and a comprehensive selection of preplanned patient- and procedure-related covariates for confounder control, the authors investigated whether intraoperative 5-HT3 antagonists affected the association between pre- or intraoperative acetaminophen and postoperative opioid consumption, gauged by opioid dose in milligram oral morphine equivalents (OME) administered in the postanesthesia care unit. A multivariable, zero-inflated negative binomial regression model was applied.

RESULTS

A total of 3,166 patients (5.8%) received only acetaminophen, 15,438 (28.1%) only 5-HT3 antagonists, 31,850 (57.9%) both drugs, and 4,562 (8.3%) neither drug. The median postanesthesia care unit opioid dose was 7.5 mg OME (interquartile range, 7.5 to 14.3 mg OME) among 16,640 of 55,016 (30.2%) patients who received opioids, and the mean opioid dose was 3.2 mg OME across all patients (maximum cumulative dose, 20.4 mg OME). Acetaminophen administration was associated with a -5.5% (95% CI, -9.6 to -1.4%; P = 0.009; adjusted absolute difference, -0.19 mg OME; 95% CI, -0.33 to -0.05; P = 0.009) reduction in opioid consumption among patients who did not receive a 5-HT3 antagonist, while there was no effect in patients who received a 5-HT3 antagonist (adjusted absolute difference, 0.00 mg OME; 95% CI, -0.06 to 0.05; P = 0.93; P for interaction = 0.013).

CONCLUSIONS

A dose-dependent association of pre- or intraoperative acetaminophen with decreased postoperative opioid consumption was not observed when 5-HT3 antagonists were coadministered, suggesting that physicians might consider reserving 5-HT3 antagonists as rescue medication for postoperative nausea or vomiting when acetaminophen is administered for pain prophylaxis.

EDITOR’S PERSPECTIVE

Structural basis of Δ9-THC analog activity at the Cannabinoid 1 receptor

Δ9-tetrahydrocannabinol (THC) is the principal psychoactive compound derived from the cannabis plant Cannabis sativa and approved for emetic conditions, appetite stimulation and sleep apnea relief. THC's psychoactive actions are mediated primarily by the cannabinoid receptor CB1. Here, we determine the cryo-EM structure of HU210, a THC analog and widely used tool compound, bound to CB1 and its primary transducer, Gi1. We leverage this structure for docking and 1,000 ns molecular dynamics simulations of THC and 10 structural analogs delineating their spatiotemporal interactions at the molecular level. Furthermore, we pharmacologically profile their recruitment of Gi and β-arrestins and reversibility of binding from an active complex. By combining detailed CB1 structural information with molecular models and signaling data we uncover the differential spatiotemporal interactions these ligands make to receptors governing potency, efficacy, bias and kinetics. This may help explain the actions of abused substances, advance fundamental receptor activation studies and design better medicines.

Chemistry and pharmacological aspects of furanoid cannabinoids and related compounds: Is furanoid cannabinoids open a new dimension towards the non-psychoactive cannabinoids?

Cannabinoids have emerged as compelling candidates for medicinal applications, notably following the recent approval of non-psychoactive cannabidiol (CBD) as a medicine. This endorsement has stimulated a growing interest in this class of compounds for drug discovery. Within the cannabis plant, a rich reservoir of over 125 compounds exists. Tetrahydrocannabinol (THC), a member of the dibenzopyran class, is widely recognized for its psychoactive effects. Conversely, the furanoid class, represented by cannabielsoin-type (CBE) and cannabifuran-type (CBF) compounds, has not been reported with psychoactivity and demonstrates a spectrum of pharmacological potential. The transition from the pyran structure of THC to the furan structure of CBE seems to mark a shift from psychoactive to non-psychoactive properties, but a comprehensive examination of other members in this class is essential for a complete understanding. Building on these observations, our thorough review delves into the subject, offering a comprehensive exploration of furanoid cannabinoids, covering aspects such as their biosynthesis, classification, synthesis, and medicinal potential. The aim of this review is to encourage and catalyze increased research focus in this promising area of cannabinoid exploration.

Synthesis and Evaluation of Natural and Unnatural Tetrahydrocannabiorcol for Its Potential Use in Neuropathologies

(-)-trans-Δ9-Tetrahydrocannabinol (trans-(-)-Δ9-THC) has shown neuroprotective potential, but its medicinal benefits are not fully exploited due to the limitations of psychoactive properties. The lower homologues are non-psychoactive in nature but lack comprehensive scientific validation regarding neuroprotective potential. The present study describes the synthesis of non-psychoactive lower homologues of THC-type compounds and their neuroprotective potential. Both natural tetrahydro-cannabiorcol (trans-(-)-Δ9-THCO) and unnatural Δ9-tetrahydrocannabiorcol (trans-(+)-Δ9-THCO) were successfully synthesized starting from R-limonene and S-limonene, respectively, and investigated for neuroprotective potential in cellular models. The structures of both enantiomers were confirmed by NMR, HMBC, HQSC, NOESY, and COSY experiments. Results indicated that both enantiomers were nontoxic to the cells treated up to 50 μM. Neuroprotective properties of the enantiomers showed that treatments could significantly reverse the corticosterone-induced toxicity in SH-SY5Y cells and simultaneously cause elevated expression of brain-derived neurotrophic factor (BDNF). It was also observed that unnatural trans-(+)-Δ9-THCO displayed better activity than the natural enantiomer and can be further explored for its potential use in neuropathological ailments.

Hexahydrocannabinol and closely related semi-synthetic cannabinoids: A comprehensive review

Since the early 2000s, there has been a turmoil on the global illicit cannabinoid market. Parallel to legislative changes in some jurisdictions regarding herbal cannabis, unregulated and cheap synthetic cannabinoids with astonishing structural diversity have emerged. Recently, semi-synthetic cannabinoids manufactured from hemp extracts by simple chemical transformations have also appeared as recreational drugs. The burst of these semi-synthetic cannabinoids into the market was sparked by legislative changes in the United States, where cultivation of industrial hemp restarted. By now, hemp-derived cannabidiol (CBD), initially a blockbuster product on its own, became a "precursor" to semi-synthetic cannabinoids such as hexahydrocannabinol (HHC), which appeared on the drug market in 2021. The synthesis and cannabimimetic activity of HHC were first reported eight decades ago in quest for the psychoactive principles of marijuana and hashish. Current large-scale manufacture of HHC is based on hemp-derived CBD extract, which is converted first by cyclization into a Δ8 /Δ9 -THC mixture, followed by catalytic hydrogenation to afford a mixture of (9R)-HHC and (9S)-HHC epimers. Preclinical studies indicate that (9R)-HHC has THC-like pharmacological properties. The animal metabolism of HHC is partially clarified. The human pharmacology including metabolism of HHC is yet to be investigated, and (immuno)analytical methods for the rapid detection of HHC or its metabolites in urine are lacking. Herein, the legal background for the revitalization of hemp cultivation, and available information on the chemistry, analysis, and pharmacology of HHC and related analogs, including HHC acetate (HHC-O) is reviewed.

Hexahydrocannabinol poisoning reported to French poison centres

INTRODUCTION

Hexahydrocannabinol is a hexahydro derivative of cannabinol. Poisoning with hexahydrocannabinol was first observed in Europe in May 2022.

METHOD

This is a retrospective observational study of cases of self-reported hexahydrocannabinol exposure reported to French poison centres between 1 January 2022 and 31 May 2023.

RESULTS

There were 37 cases, including 19 in May 2023. The median age of the patients was 36 (interquartile range 28-43) years, and most were men. Eight patients had a history of substance use disorder. The route of exposure was ingestion in 24, inhalation (smoking or vaping) in 10, inhalation and ingestion in two and sublingual in one. Clinical features were neurological (85 per cent), cardiovascular (61 per cent), gastrointestinal (33 per cent), psychiatric (27 per cent) and ocular (21 per cent). Fifty-nine per cent of the patients were hospitalized. In four patients, the Poisoning Severity Score was 0 (asymptomatic); in 15 patients, the Score was 1 (minor); in 16, the Score was 2 (moderate); and in two cases, the Score was 3 (severe). In 70 per cent of patients, the outcome was known, and all recovered. Testing of biological samples was only undertaken in six cases. Five patients had positive blood or urine tests for hexahydrocannabinol; in two patients, tetrahydrocannabinol and metabolites were also detected. In addition, there was an additional patient in whom Δ8- and Δ9-tetrahydrocannabinol was detected in the substances used.

DISCUSSION

Clinical effects reported in this series included neuropsychiatric and somatic effects. Whilst these cases related to self-reported hexahydrocannabinol use, it is likely that tetrahydrocannabinol use also contributed to the effects in a substantial proportion of cases. This study has some limitations, such as the lack of available information due to the retrospective nature of the study. As a result, it probably overestimates the number of moderate and severe cases due to under-reporting of cases of little or no severity. Analysis of the patient's blood and urine was performed only in six patients, so we cannot be certain that the products consumed by the other patients were hexahydrocannabinol.

CONCLUSION

The clinical effects attributed to hexahydrocannabinol were neurological, cardiovascular, gastrointestinal, psychiatric and ocular predominantly and were sometimes serious.

Linalyl acetate exerts analgesic effects by inhibiting nociceptive TRPA1 in mice

Clary sage essential oil (CSEO) is utilized in perfumery, aromatherapy, and skincare. Linalyl acetate (LA), a primary component of CSEO, possesses sedative, anxiolytic, and analgesic properties. However, the mechanism of its analgesic action is not clearly understood. Transient receptor potential ankyrin 1 (TRPA1) channel, a non-selective cation channel, is mainly expressed in sensory neurons and serves as a sensor of various irritants. In this study, we investigated the effects of LA on TRPA1 channel using heterologous expression system and isolated sensory neurons. To detect channel activity, we employed Ca2+ imaging and the whole-cell patch-clamp technique. The analgesic action of LA was measured in a pain-related behavioral mouse model. In cells that heterologously expressed TRPA1, LA diminished [Ca2+]i and current responses to allylisothiocyanate (AITC) and carvacrol: exogenous TRPA1 agonists, and the inhibitory effects were more pronounced for the former than for the latter. Moreover, LA suppressed [Ca2+] i and current responses to PGJ2: an endogenous TRPA1 agonist. Similar inhibitory actions were observed in native TRPA1 channels expressed in mouse sensory neurons. Furthermore, LA diminished PGJ2-induced nociceptive behaviors in mice. These findings suggest that analgesic effects of LA exert through inhibition of nociceptive TRPA1, making it a potential candidate for novel analgesic development.

Modulation of TRPV1 and TRPA1 Channels Function by Sea Anemones' Peptides Enhances the Viability of SH-SY5Y Cell Model of Parkinson's Disease

Cellular dysfunction during Parkinson's disease leads to neuroinflammation in various brain regions, inducing neuronal death and contributing to the progression of the disease. Different ion channels may influence the process of neurodegeneration. The peptides Ms 9a-1 and APHC3 can modulate the function of TRPA1 and TRPV1 channels, and we evaluated their cytoprotective effects in differentiated to dopaminergic neuron-like SH-SY5Y cells. We used the stable neuroblastoma cell lines SH-SY5Y, producing wild-type alpha-synuclein and its mutant A53T, which are prone to accumulation of thioflavin-S-positive aggregates. We analyzed the viability of cells, as well as the mRNA expression levels of TRPA1, TRPV1, ASIC1a channels, alpha-synuclein, and tyrosine hydroxylase after differentiation of these cell lines using RT-PCR. Overexpression of alpha-synuclein showed a neuroprotective effect and was accompanied by a reduction of tyrosine hydroxylase expression. A mutant alpha-synuclein A53T significantly increased the expression of the pro-apoptotic protein BAX and made cells more susceptible to apoptosis. Generally, overexpression of alpha-synuclein could be a model for the early stages of PD, while expression of mutant alpha-synuclein A53T mimics a genetic variant of PD. The peptides Ms 9a-1 and APHC3 significantly reduced the susceptibility to apoptosis of all cell lines but differentially influenced the expression of the genes of interest. Therefore, these modulators of TRPA1 and TRPV1 have the potential for the development of new therapeutic agents for neurodegenerative disease treatment.

Potentiating TRPA1 by Sea Anemone Peptide Ms 9a-1 Reduces Pain and Inflammation in a Model of Osteoarthritis

Progressive articular surface degradation during arthritis causes ongoing pain and hyperalgesia that lead to the development of functional disability. TRPA1 channel significantly contributes to the activation of sensory neurons that initiate neurogenic inflammation and mediates pain signal transduction to the central nervous system. Peptide Ms 9a-1 from the sea anemone Metridium senile is a positive allosteric modulator of TRPA1 and shows significant anti-inflammatory and analgesic activity in different models of pain. We used a model of monosodium iodoacetate (MIA)-induced osteoarthritis to evaluate the anti-inflammatory properties of Ms 9a-1 in comparison with APHC3 (a polypeptide modulator of TRPV1 channel) and non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam and ibuprofen. Administration of Ms 9a-1 (0.1 mg/kg, subcutaneously) significantly reversed joint swelling, disability, thermal and mechanical hypersensitivity, and grip strength impairment. The effect of Ms 9a-1 was equal to or better than that of reference drugs. Post-treatment histological analysis revealed that long-term administration of Ms9a-1 could reduce inflammatory changes in joints and prevent the progression of cartilage and bone destruction at the same level as meloxicam. Peptide Ms 9a-1 showed significant analgesic and anti-inflammatory effects in the model of MIA-induced OA, and therefore positive allosteric modulators could be considered for the alleviation of OA symptoms.

Saturated Cannabinoids: Update on Synthesis Strategies and Biological Studies of These Emerging Cannabinoid Analogs

Natural and non-natural hexahydrocannabinols (HHC) were first described in 1940 by Adam and in late 2021 arose on the drug market in the United States and in some European countries. A background on the discovery, synthesis, and pharmacology studies of hydrogenated and saturated cannabinoids is described. This is harmonized with a summary and comparison of the cannabinoid receptor affinities of various classical, hybrid, and non-classical saturated cannabinoids. A discussion of structure-activity relationships with the four different pharmacophores found in the cannabinoid scaffold is added to this review. According to laboratory studies in vitro, and in several animal species in vivo, HHC is reported to have broadly similar effects to Δ9-tetrahydrocannabinol (Δ9-THC), the main psychoactive substance in cannabis, as demonstrated both in vitro and in several animal species in vivo. However, the effects of HHC treatment have not been studied in humans, and thus a biological profile has not been established.

Synthetic Pathways to Non-Psychotropic Phytocannabinoids as Promising Molecules to Develop Novel Antibiotics: A Review

Due to the rapid emergence of multi drug resistant (MDR) pathogens against which current antibiotics are no longer functioning, severe infections are becoming practically untreatable. Consequently, the discovery of new classes of effective antimicrobial agents with novel mechanism of action is becoming increasingly urgent. The bioactivity of Cannabis sativa, an herbaceous plant used for millennia for medicinal and recreational purposes, is mainly due to its content in phytocannabinoids (PCs). Among the 180 PCs detected, cannabidiol (CBD), Δ⁸ and Δ⁹-tetrahydrocannabinols (Δ⁸-THC and Δ⁹-THC), cannabichromene (CBC), cannabigerol (CBG), cannabinol (CBN) and some of their acidic precursors have demonstrated from moderate to potent antibacterial effects against Gram-positive bacteria (MICs 0.5-8 µg/mL), including methicillin-resistant Staphylococcus aureus (MRSA), epidemic MRSA (EMRSA), as well as fluoroquinolone and tetracycline-resistant strains. Particularly, the non-psychotropic CBG was also capable to inhibit MRSA biofilm formation, to eradicate even mature biofilms, and to rapidly eliminate MRSA persiter cells. In this scenario, CBG, as well as other minor non-psychotropic PCs, such as CBD, and CBC could represent promising compounds for developing novel antibiotics with high therapeutic potential. Anyway, further studies are necessary, needing abundant quantities of such PCs, scarcely provided naturally by Cannabis plants. Here, after an extensive overture on cannabinoids including their reported antimicrobial effects, aiming at easing the synthetic production of the necessary amounts of CBG, CBC and CBD for further studies, we have, for the first time, systematically reviewed the synthetic pathways utilized for their synthesis, reporting both reaction schemes and experimental details.

TRPA1 activation in non-sensory supporting cells contributes to regulation of cochlear sensitivity after acoustic trauma

TRPA1 channels are expressed in nociceptive neurons, where they detect noxious stimuli, and in the mammalian cochlea, where their function is unknown. Here we show that TRPA1 activation in the supporting non-sensory Hensen's cells of the mouse cochlea causes prolonged Ca2+ responses, which propagate across the organ of Corti and cause long-lasting contractions of pillar and Deiters' cells. Caged Ca2+ experiments demonstrated that, similar to Deiters' cells, pillar cells also possess Ca2+-dependent contractile machinery. TRPA1 channels are activated by endogenous products of oxidative stress and extracellular ATP. Since both these stimuli are present in vivo after acoustic trauma, TRPA1 activation after noise may affect cochlear sensitivity through supporting cell contractions. Consistently, TRPA1 deficiency results in larger but less prolonged noise-induced temporary shift of hearing thresholds, accompanied by permanent changes of latency of the auditory brainstem responses. We conclude that TRPA1 contributes to the regulation of cochlear sensitivity after acoustic trauma.

Novel Therapeutic Targets for Migraine

Migraine, a primary headache disorder involving a dysfunctional trigeminal vascular system, remains a major debilitating neurological condition impacting many patients' quality of life. Despite the success of multiple new migraine therapies, not all patients achieve significant clinical benefits. The success of CGRP pathway-targeted therapy highlights the importance of translating the mechanistic understanding toward effective therapy. Ongoing research has identified multiple potential mechanisms in migraine signaling and nociception. In this narrative review, we discuss several potential emerging therapeutic targets, including pituitary adenylate cyclase-activating polypeptide (PACAP), adenosine, δ-opioid receptor (DOR), potassium channels, transient receptor potential ion channels (TRP), and acid-sensing ion channels (ASIC). A better understanding of these mechanisms facilitates the discovery of novel therapeutic targets and provides more treatment options for improved clinical care.

TRP Channels: Recent Development in Translational Research and Potential Therapeutic Targets in Migraine

Migraine is a chronic neurological disorder that affects approximately 12% of the population. The cause of migraine headaches is not yet known, however, when the trigeminal system is activated, neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P (SP) are released, which cause neurogenic inflammation and sensitization. Advances in the understanding of migraine pathophysiology have identified new potential pharmacological targets. In recent years, transient receptor potential (TRP) channels have been the focus of attention in the pathophysiology of various pain disorders, including primary headaches. Genetic and pharmacological data suggest the role of TRP channels in pain sensation and the activation and sensitization of dural afferents. In addition, TRP channels are widely expressed in the trigeminal system and brain regions which are associated with the pathophysiology of migraine and furthermore, co-localize several neuropeptides that are implicated in the development of migraine attacks. Moreover, there are several migraine trigger agents known to activate TRP channels. Based on these, TRP channels have an essential role in migraine pain and associated symptoms, such as hyperalgesia and allodynia. In this review, we discuss the role of the certain TRP channels in migraine pathophysiology and their therapeutic applicability.

Analgesic Action of Acetaminophen via Kv7 Channels

The mechanism of acetaminophen (APAP) analgesia is at least partially unknown. Previously, we showed that the APAP metabolite N-acetyl-p-benzoquinone imine (NAPQI) activated Kv7 channels in neurons in vitro, and this activation of Kv7 channels dampened neuronal firing. Here, the effect of the Kv7 channel blocker XE991 on APAP-induced analgesia was investigated in vivo. APAP had no effect on naive animals. Induction of inflammation with λ-carrageenan lowered mechanical and thermal thresholds. Systemic treatment with APAP reduced mechanical hyperalgesia, and co-application of XE991 reduced APAP's analgesic effect on mechanical pain. In a second experiment, the analgesic effect of systemic APAP was not antagonized by intrathecal XE991 application. Analysis of liver samples revealed APAP and glutathione-coupled APAP indicative of metabolization. However, there were no relevant levels of these metabolites in cerebrospinal fluid, suggesting no relevant APAP metabolite formation in the CNS. In summary, the results support an analgesic action of APAP by activating Kv7 channels at a peripheral site through formation of the metabolite NAPQI.

Cannabinoid non-cannabidiol site modulation of TRPV2 structure and function

TRPV2 is a ligand-operated temperature sensor with poorly defined pharmacology. Here, we combine calcium imaging and patch-clamp electrophysiology with cryo-electron microscopy (cryo-EM) to explore how TRPV2 activity is modulated by the phytocannabinoid Δ⁹-tetrahydrocannabiorcol (C16) and by probenecid. C16 and probenecid act in concert to stimulate TRPV2 responses including histamine release from rat and human mast cells. Each ligand causes distinct conformational changes in TRPV2 as revealed by cryo-EM. Although the binding for probenecid remains elusive, C16 associates within the vanilloid pocket. As such, the C16 binding location is distinct from that of cannabidiol, partially overlapping with the binding site of the TRPV2 inhibitor piperlongumine. Taken together, we discover a new cannabinoid binding site in TRPV2 that is under the influence of allosteric control by probenecid. This molecular insight into ligand modulation enhances our understanding of TRPV2 in normal and pathophysiology.

Potent Activation of Human but Not Mouse TRPA1 by JT010

Transient receptor potential (TRP) ankyrin repeat 1 (TRPA1), which is involved in inflammatory pain sensation, is activated by endogenous factors, such as intracellular Zn²⁺ and hydrogen peroxide, and by irritant chemical compounds. The synthetic compound JT010 potently and selectively activates human TRPA1 (hTRPA1) among the TRPs. Therefore, JT010 is a useful tool for analyzing TRPA1 functions in biological systems. Here, we show that JT010 is a potent activator of hTRPA1, but not mouse TRPA1 (mTRPA1) in human embryonic kidney (HEK) cells expressing hTRPA1 and mTRPA1. Application of 0.3-100 nM of JT010 to HEK cells with hTRPA1 induced large Ca²⁺ responses. However, in HEK cells with mTRPA1, the response was small. In contrast, both TRPA1s were effectively activated by allyl isothiocyanate (AITC) at 10-100 μM. Similar selective activation of hTRPA1 by JT010 was observed in electrophysiological experiments. Additionally, JT010 activated TRPA1 in human fibroblast-like synoviocytes with inflammation, but not TRPA1 in mouse dorsal root ganglion cells. As cysteine at 621 (C621) of hTRPA1, a critical cysteine for interaction with JT010, is conserved in mTRPA1, we applied JT010 to HEK cells with mutations in mTRPA1, where the different residue of mTRPA1 with tyrosine at 60 (Y60), with histidine at 1023 (H1023), and with asparagine at 1027 (N1027) were substituted with cysteine in hTRPA1. However, these mutants showed low sensitivity to JT010. In contrast, the mutation of hTRPA1 at position 669 from phenylalanine to methionine (F669M), comprising methionine at 670 in mTRPA1 (M670), significantly reduced the response to JT010. Moreover, the double mutant at S669 and M670 of mTRPA1 to S669E and M670F, respectively, induced slight but substantial sensitivity to 30 and 100 nM JT010. Taken together, our findings demonstrate that JT010 potently and selectively activates hTRPA1 but not mTRPA1.

Neuroprotective effect of low-dose paracetamol treatment against cognitive dysfunction in d-galactose-induced aging mice

Background

Aging is closely associated to several deleterious conditions and cognitive impairment. Administration of low-dose paracetamol (APAP) has previously been reported to improve cognitive performance in both human and animal studies. However, the altered cognitive effects of low-dose APAP treatment in the aging brain have not been elucidated.

Objectives

The purpose of this study was to determine whether low-dose APAP treatment improves cognitive dysfunction in a d-galactose (d-gal)-induced aging model.

Materials and methods

APAP (15 and 50 mg/kg p.o.) and vitamin E (Vit E 100 mg/kg p.o.) were administered once daily to d-gal-injected mice (200 mg/kg s.c.) for 6 weeks. The elevated plus maze (EPM), open field, novel object recognition (NOR), and Morris water maze (MWM) tests, respectively, were used to measure altered neurobehavioral functions, including anxiety-like behavior and exploratory locomotor activity, as well as learning and memory performance. The gene transcription of brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling in brain tissues was evaluated by real-time polymerase chain reaction.

Results

Compared to the control, d-gal significantly decreased exploratory locomotor activity and NOR and MWM performance but did not significantly change the activity in the EPM test. However, APAP50 and Vit E significantly reversed the effects of d-gal injection on exploratory locomotor activity. In addition, low-dose APAP (15 and 50 mg/kg) and Vit E significantly improved the reduction in NOR and MWM performance induced by d-gal. Real-time polymerase chain reaction analysis revealed that the mRNA expression of BDNF, neurotrophic tyrosine receptor kinase (NTRK), which is the gene coding TrkB receptor, and cAMP response element-binding protein (CREB) was significantly decreased in the frontal cortex and hippocampus of the d-gal mice. However, APAP50 and Vit E significantly increased BDNF and NTRK mRNA expression in both the frontal cortex and the hippocampus. A lower dose of APAP (15 mg/kg) significantly elevated the mRNA expression of NTRK, but only in the hippocampus. Moreover, APAP50 significantly increased CREB mRNA expression in the frontal cortex and hippocampus.

Conclusion

Low-dose APAP treatment has a neuroprotective effect on cognitive dysfunction in the d-gal aging model, and the underlying molecular mechanisms depend on the activation of BDNF/TrkB signaling.

Analysis of Structural Determinants of Peptide MS 9a-1 Essential for Potentiating of TRPA1 Channel

The TRPA1 channel is involved in a variety of physiological processes and its activation leads to pain perception and the development of inflammation. Peptide Ms 9a-1 from sea anemone Metridium senile is a positive modulator of TRPA1 and causes significant analgesic and anti-inflammatory effects by desensitization of TRPA1-expressing sensory neurons. For structural and functional analysis of Ms 9a-1, we produced four peptides—Ms 9a-1 without C-terminal domain (abbreviated as N-Ms), short C-terminal domain Ms 9a-1 alone (C-Ms), and two homologous peptides (Ms 9a-2 and Ms 9a-3). All tested peptides possessed a reduced potentiating effect on TRPA1 compared to Ms 9a-1 in vitro. None of the peptides reproduced analgesic and anti-inflammatory properties of Ms 9a-1 in vivo. Peptides N-Ms and C-Ms were able to reduce pain induced by AITC (selective TRPA1 agonist) but did not decrease AITC-induced paw edema development. Fragments of Ms 9a-1 did not effectively reverse CFA-induced thermal hyperalgesia and paw edema. Ms 9a-2 and Ms 9a-3 possessed significant effects and anti-inflammatory properties in some doses, but their unexpected efficacy and bell-shape dose–responses support the hypothesis of other targets involved in their effects in vivo. Therefore, activity comparison of Ms 9a-1 fragments and homologues peptides revealed structural determinants important for TRPA1 modulation, as well as analgesic and anti-inflammatory properties of Ms9a-1.

Neuronal and non-neuronal TRPA1 as therapeutic targets for pain and headache relief

The transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily of channels, has a major role in different types of pain. TRPA1 is primarily localized to a subpopulation of primary sensory neurons of the trigeminal, vagal, and dorsal root ganglia. This subset of nociceptors produces and releases the neuropeptide substance P (SP) and calcitonin gene-related peptide (CGRP), which mediate neurogenic inflammation. TRPA1 is characterized by unique sensitivity for an unprecedented number of reactive byproducts of oxidative, nitrative, and carbonylic stress and to be activated by several chemically heterogenous, exogenous, and endogenous compounds. Recent preclinical evidence has revealed that expression of TRPA1 is not limited to neurons, but its functional role has been reported in central and peripheral glial cells. In particular, Schwann cell TRPA1 was recently implicated in sustaining mechanical and thermal (cold) hypersensitivity in mouse models of macrophage-dependent and macrophage-independent inflammatory, neuropathic, cancer, and migraine pain. Some analgesics and herbal medicines/natural products widely used for the acute treatment of pain and headache have shown some inhibitory action at TRPA1. A series of high affinity and selective TRPA1 antagonists have been developed and are currently being tested in phase I and phase II clinical trials for different diseases with a prominent pain component. Abbreviations: 4-HNE, 4-hydroxynonenal; ADH-2, alcohol dehydrogenase-2; AITC, allyl isothiocyanate; ANKTD, ankyrin-like protein with transmembrane domains protein 1; B2 receptor, bradykinin 2 receptor; CIPN, chemotherapeutic-induced peripheral neuropathy; CGRP, calcitonin gene related peptide; CRISPR, clustered regularly interspaced short palindromic repeats; CNS, central nervous system; COOH, carboxylic terminal; CpG, C-phosphate-G; DRG, dorsal root ganglia; EP, prostaglandins; GPCR, G-protein-coupled receptors; GTN, glyceryl trinitrate; MAPK, mitogen-activated protein kinase; M-CSF, macrophage-colony stimulating factor; NAPQI, N-Acetyl parabenzoquinone-imine; NGF, nerve growth factor; NH2, amino terminal; NKA, neurokinin A; NO, nitric oxide; NRS, numerical rating scale; PAR2, protease-activated receptor 2; PMA, periorbital mechanical allodynia; PLC, phospholipase C; PKC, protein kinase C; pSNL, partial sciatic nerve ligation; RCS, reactive carbonyl species; ROS, reactive oxygen species; RNS, nitrogen oxygen species; SP, substance P; TG, trigeminal ganglion; THC, Δ9-tetrahydrocannabinol; TrkA, neurotrophic receptor tyrosine kinase A; TRP, transient receptor potential; TRPC, TRP canonical; TRPM, TRP melastatin; TRPP, TRP polycystin; TRPM, TRP mucolipin; TRPA, TRP ankyrin; TRPV, TRP vanilloid; VG, vagal ganglion.

Isobolographic analysis of antinociceptive effect of ketorolac, indomethacin, and paracetamol after simultaneous peripheral local and systemic administration

This study was designed to characterize the type of interaction (subadditive, additive, or synergistic) after simultaneous administration by two different routes (intraperitoneal plus peripheral local) of the same nonsteroidal anti-inflammatory drugs (NSAID) ketorolac and indomethacin or paracetamol. The antinociceptive effects of locally or intraperitoneally delivery of NSAIDs or paracetamol, and the simultaneous administration by the two routes at fixed-dose ratio combination were evaluated using the formalin test. Pain-related behavior was quantified as the number of flinches of the injected paw. Isobolographic analysis was used to characterize the interaction between the two routes. ED30 values were estimated for individual drugs, and isobolograms were constructed. Ketorolac, indomethacin, or paracetamol and fixed-dose ratio combinations produced a dose-dependent antinociceptive effect in the second but not in the first phase of the formalin test. The analysis of interaction type after simultaneous administration by the two routes the same NSAID or paracetamol (on basis of their ED30), revealed that the simultaneous administration of ketorolac or paracetamol was additive and for indomethacin was synergistic. Since the mechanisms underlying the additive effect of ketorolac or paracetamol and the synergistic effect of indomethacin were not explored; it is possible that the peripheral and central mechanism is occurring at several anatomical sites. The significance of these findings for theory and pain pharmacotherapy practice indicates that the combination of one analgesic drug given simultaneously by two different administration routes could be an additive or it could lead to a synergistic interaction.

The role of TRP ion channels in migraine and headache

Migraine afflicts more than 10% of the general population. Although its mechanism is poorly understood, recent preclinical and clinical evidence has identified calcitonin gene related peptide (CGRP) as a major mediator of migraine pain. CGRP, which is predominantly expressed in a subset of primary sensory neurons, including trigeminal afferents, when released from peripheral terminals of nociceptors, elicits arteriolar vasodilation and mechanical allodynia, a hallmark of migraine attack. Transient receptor potential (TRP) channels include several cationic channels with pleiotropic functions and ubiquitous distribution in various cells and tissues. Some members of the TRP channel family, such as the ankyrin 1 (TRPA1), vanilloid 1 and 4 (TRPV1 and TRPV4, respectively), and TRPM3, are abundantly expressed in primary sensory neurons and are recognized as sensors of chemical-, heat- and mechanical-induced pain, and play a primary role in several models of pain diseases, including inflammatory, neuropathic cancer pain, and migraine pain. In addition, TRP channel stimulation results in CGRP release, which can be activated or sensitized by various endogenous and exogenous stimuli, some of which have been proven to trigger or worsen migraine attacks. Moreover, some antimigraine medications seem to act through TRPA1 antagonism. Here we review the preclinical and clinical evidence that highlights the role of TRP channels, and mainly TRPA1, in migraine pathophysiology and may be proposed as new targets for its treatment.

TRPA1: Pharmacology, natural activators and role in obesity prevention

Transient receptor potential ankyrin 1 (TRPA1) channel is a calcium permeable, non-selective cation channel, expressed in the sensory neurons and non-neuronal cells of different tissues. Initially studied for its role in pain and inflammation, TRPA1 has now functionally involved in multiple other physiological functions. TRPA1 channel has been extensively studied for modulation by pungent compounds present in the spices and herbs. In the last decade, the role of TRPA1 agonism in body weight reduction, secretion of hunger and satiety hormones, insulin secretion and thermogenesis, has unveiled the potential of the TRPA1 channel to be used as a preventive target to tackle obesity and associated comorbidities including insulin resistance in type 2 diabetes. In this review, we summarized the recent findings of TRPA1 based dietary/non-dietary modulation for its role in obesity prevention and therapeutics.

Paracetamol use during pregnancy - a call for precautionary action

Paracetamol (N-acetyl-p-aminophenol (APAP), otherwise known as acetaminophen) is the active ingredient in more than 600 medications used to relieve mild to moderate pain and reduce fever. APAP is widely used by pregnant women as governmental agencies, including the FDA and EMA, have long considered APAP appropriate for use during pregnancy when used as directed. However, increasing experimental and epidemiological research suggests that prenatal exposure to APAP might alter fetal development, which could increase the risks of some neurodevelopmental, reproductive and urogenital disorders. Here we summarize this evidence and call for precautionary action through a focused research effort and by increasing awareness among health professionals and pregnant women. APAP is an important medication and alternatives for treatment of high fever and severe pain are limited. We recommend that pregnant women should be cautioned at the beginning of pregnancy to: forego APAP unless its use is medically indicated; consult with a physician or pharmacist if they are uncertain whether use is indicated and before using on a long-term basis; and minimize exposure by using the lowest effective dose for the shortest possible time. We suggest specific actions to implement these recommendations. This Consensus Statement reflects our concerns and is currently supported by 91 scientists, clinicians and public health professionals from across the globe.

Systematic Review of Systemic and Neuraxial Effects of Acetaminophen in Preclinical Models of Nociceptive Processing

Acetaminophen (APAP) in humans has robust effects with a high therapeutic index in altering postoperative and inflammatory pain states in clinical and experimental pain paradigms with no known abuse potential. This review considers the literature reflecting the preclinical actions of acetaminophen in a variety of pain models. Significant observations arising from this review are as follows: 1) acetaminophen has little effect upon acute nociceptive thresholds; 2) acetaminophen robustly reduces facilitated states as generated by mechanical and thermal hyperalgesic end points in mouse and rat models of carrageenan and complete Freund’s adjuvant evoked inflammation; 3) an antihyperalgesic effect is observed in models of facilitated processing with minimal inflammation (eg, phase II intraplantar formalin); and 4) potent anti-hyperpathic effects on the thermal hyperalgesia, mechanical and cold allodynia, allodynic thresholds in rat and mouse models of polyneuropathy and mononeuropathies and bone cancer pain. These results reflect a surprisingly robust drug effect upon a variety of facilitated states that clearly translate into a wide range of efficacy in preclinical models and to important end points in human therapy. The specific systems upon which acetaminophen may act based on targeted delivery suggest both a spinal and a supraspinal action. Review of current targets for this molecule excludes a role of cyclooxygenase inhibitor but includes effects that may be mediated through metabolites acting on the TRPV1 channel, or by effect upon cannabinoid and serotonin signaling. These findings suggest that the mode of action of acetaminophen, a drug with a long therapeutic history of utilization, has surprisingly robust effects on a variety of pain states in clinical patients and in preclinical models with a good therapeutic index, but in spite of its extensive use, its mechanisms of action are yet poorly understood.

Mini-review: The nociceptive sensory functions of the polymodal receptor Transient Receptor Potential Ankyrin Type 1 (TRPA1)

Over the last 17 years since its cloning in 2003, the receptor-channel TRPA1 has received increasing attention due to its polymodal features and prominent role in pain signaling in a variety of human disease states. While evidence has been accumulating for non-neuronal TRPA1 expression, it is the presence of this channel in nociceptive nerve endings which has taken centre stage, due to its potential clinical ramifications. As a consequence, we shall focus in this review on the sensory functions of TRPA1 related to its expression in the peripheral nervous system. While substantial research has been focused on the putative role of TRPA1 in detecting irritant compounds, noxious cold and mechanical stimuli, the current overall picture is, to some extent, still cloudy. The chemosensory function of the channel is well demonstrated, as well as its involvement in the detection of oxidative and nitrosative stress; however, the other sensory features of TRPA1 have not been fully elucidated yet. The current state of the experimental evidence for these physiological roles of TRPA1 in mammals, and particularly in humans, will be discussed in this review.

Major Phytocannabinoids and Their Related Compounds: Should We Only Search for Drugs That Act on Cannabinoid Receptors?

The most important discoveries in pharmacology, such as certain classes of analgesics or chemotherapeutics, started from natural extracts which have been found to have effects in traditional medicine. Cannabis, traditionally used in Asia for the treatment of pain, nausea, spasms, sleep, depression, and low appetite, is still a good candidate for the development of new compounds. If initially all attention was directed to the endocannabinoid system, recent studies suggest that many of the clinically proven effects are based on an intrinsic chain of mechanisms that do not necessarily involve only cannabinoid receptors. Recent research has shown that major phytocannabinoids and their derivatives also interact with non-cannabinoid receptors such as vanilloid receptor 1, transient receptor ankyrin 1 potential, peroxisome proliferator-activated receptor-gamma or glitazone receptor, G55 protein-coupled receptor, and nuclear receptor, producing pharmacological effects in diseases such as Alzheimer's, epilepsy, depression, neuropathic pain, cancer, and diabetes. Nonetheless, further studies are needed to elucidate the precise mechanisms of these compounds. Structure modulation of phytocannabinoids, in order to improve pharmacological effects, should not be limited to the exploration of cannabinoid receptors, and it should target other courses of action discovered through recent research.

Paracetamol (Acetaminophen) and the Developing Brain

Paracetamol is commonly used to treat fever and pain in pregnant women, but there are growing concerns that this may cause attention deficit hyperactivity disorder and autism spectrum disorder in the offspring. A growing number of epidemiological studies suggests that relative risks for these disorders increase by an average of about 25% following intrauterine paracetamol exposure. The data analyzed point to a dose-effect relationship but cannot fully account for unmeasured confounders, notably indication and genetic transmission. Only few experimental investigations have addressed this issue. Altered behavior has been demonstrated in offspring of paracetamol-gavaged pregnant rats, and paracetamol given at or prior to day 10 of life to newborn mice resulted in altered locomotor activity in response to a novel home environment in adulthood and blunted the analgesic effect of paracetamol given to adult animals. The molecular mechanisms that might mediate these effects are unknown. Paracetamol has diverse pharmacologic actions. It reduces prostaglandin formation via competitive inhibition of the peroxidase moiety of prostaglandin H2 synthase, while its metabolite N-arachidonoyl-phenolamine activates transient vanilloid-subtype 1 receptors and interferes with cannabinoid receptor signaling. The metabolite N-acetyl-p-benzo-quinone-imine, which is pivotal for liver damage after overdosing, exerts oxidative stress and depletes glutathione in the brain already at dosages below the hepatic toxicity threshold. Given the widespread use of paracetamol during pregnancy and the lack of safe alternatives, its impact on the developing brain deserves further investigation.

Synergistic interaction between amitriptyline and paracetamol in persistent and neuropathic pain models: An isobolografic analysis

The current study was designed to evaluate the transient antinociceptive interaction between amitriptyline and paracetamol in the formalin test. In addition, considering other long-term neuroprotective mechanisms of these drugs, we hypothesized that this combination might exert some synergistic effects on neuropathic pain linked with its possible ability to prevent Wallerian degeneration (WD). The effects of individual and fixed-ratio of 1:1 combinations of orally administered amitriptyline and paracetamol were assayed in the two phases of the formalin test and in the chronic constriction injury (CCI) model in rats. Isobolographic analysis was employed to characterize the synergism produced by the combinations. Amitriptyline, paracetamol, and fixed-ratio amitriptyline-paracetamol combinations produced dose-dependent antinociceptive effects mainly on the inflammatory tonic phase. Repeated doses of individual drugs and their combination decreased CCI-induced mechanical allodynia in a dose-dependent manner. ED₃₀ (formalin) and ED₅₀ (CCI) values were estimated for the individual drugs, and isobolograms were constructed. Theoretical ED_30/50 values for the combination estimated from the isobolograms were 16.5 ± 3.9 mg/kg and 26.0 ± 7.2 mg/kg for the single and repeated doses in persistent and neuropathic pain models, respectively. These values were significantly higher than the actually observed ED_30/50 values, which were 0.39 ± 0.1 mg/kg and 8.2 ± 0.8 mg/kg in each model, respectively, indicating a synergistic interaction. Remarkably, CCI-induced sciatic nerve WD-related histopathological changes were prevented by this combination compared to either drug administered alone.

Acetaminophen Interactions with Phospholipid Vesicles Induced Changes in Morphology and Lipid Dynamics

Acetaminophen (APAP) or paracetamol, despite its wide and common use for pain and fever symptoms, shows a variety of side effects, toxic effects, and overdose effects. The most common form of toxic effects of APAP is in the liver where phosphatidylcholine is the major component of the cell membrane with additional associated functionalities. Although this is the case, the effects of APAP on pure phospholipid membranes have been largely ignored. Here, we used 1,2-di-(octadecenoyl)-sn-glycero-3-phosphocholine (DOPC), a commonly found phospholipid in mammalian cell membranes, to synthesize large unilamellar vesicles to investigate how the incorporation of APAP changes the pure lipid vesicle structure, morphology, and fluidity at different concentrations. We used a combination of dynamic light scattering, small-angle neutron and X-ray scattering (SANS, SAXS), and cryo-TEM for structural characterization, and neutron spin-echo (NSE) spectroscopy to investigate the dynamics. We showed that the incorporation of APAP in the lipid bilayer significantly impacts the spherical phospholipid self-assembly in terms of its morphology and influences the lipid content in the bilayer, causing a decrease in bending rigidity. We observe a decrease in the number of lipids per vesicle by almost 28% (0.06 wt % APAP) and 19% (0.12 wt % APAP) compared to the pure DOPC (0 wt % APAP). Our results showed that the incorporation of APAP reduces the membrane rigidity by almost 50% and changes the spherical unilamellar vesicles into much more irregularly shaped vesicles. Although the bilayer structure did not show much change when observed by SAXS, NSE and cryo-TEM results showed the lipid dynamics change with the addition of APAP in the bilayer, which causes the overall decreased membrane rigidity. A strong effect on the lipid tail motion showed that the space explored by the lipid tails increases by a factor of 1.45 (for 0.06 wt % APAP) and 1.75 (for 0.12 wt % APAP) compared to DOPC without the drug.

Striatal TRPV1 activation by acetaminophen ameliorates dopamine D2 receptor antagonist-induced orofacial dyskinesia

Antipsychotics often cause tardive dyskinesia, an adverse symptom of involuntary hyperkinetic movements. Analysis of the US Food and Drug Administration Adverse Event Reporting System and JMDC insurance claims revealed that acetaminophen prevented the dyskinesia induced by dopamine D₂ receptor antagonists. In vivo experiments further showed that a 21-day treatment with haloperidol increased the number of vacuous chewing movements (VCMs) in rats, an effect that was inhibited by oral acetaminophen treatment or intracerebroventricular injection of N-(4-hydroxyphenyl)-arachidonylamide (AM404), an acetaminophen metabolite that acts as an activator of the transient receptor potential vanilloid 1 (TRPV1). In mice, haloperidol-induced VCMs were also mitigated by treatment with AM404 applied to the dorsal striatum, an effect not seen in TRPV1-deficient mice. Acetaminophen prevented the haloperidol-induced decrease in the number of c-Fos⁺preproenkephalin⁺ striatal neurons in wild-type mice but not in TRPV1-deficient mice. Finally, chemogenetic stimulation of indirect pathway medium spiny neurons in the dorsal striatum decreased haloperidol-induced VCMs. These results suggest that acetaminophen activates the indirect pathway neurons by activating TRPV1 channels via AM404.

Synergism between oral paracetamol and nefopam in a murine model of postoperative pain

BACKGROUND

The use of paracetamol or nefopam for postoperative pain control is limited by the need of high doses associated with unwanted effects. Previous works suggest positive interactions between both compounds that may be exploited to obtain potentiation of antinociception.

METHODS

Mechanical and heat antinociception induced by oral doses of paracetamol, nefopam or their combination was studied by isobolographic analysis in a murine model of postsurgical pain. The effective doses that produced 50% antinociception (ED₅₀ ) were calculated from the log dose-response curves for each compound. Subsequently, the effects of ED_8.7 s, ED_12.5 s, ED_17.5 s and ED₃₅ s of nefopam and paracetamol combined were assessed.

RESULTS

Oral paracetamol induced dose-dependent relief of postoperative sensitivity and showed higher efficacy reducing mechanical hypersensitivity (ED₅₀ 177.3 ± 15.4 mg/kg) than heat hyperalgesia (ED₅₀ 278.6 ± 43 mg/kg). Oral nefopam induced dose-dependent antinociception with similar efficacy for mechanical and heat hypersensitivity (ED₅₀ s 5.42 ± 0.81 vs. 5.83 ± 0.72). Combinations of increasing isoeffective doses revealed that combined ED_17.5 s (85.76 mg/kg paracetamol and 1.9 mg/kg nefopam) and ED₃₅ s (132.67 mg/kg and 3.73 mg/kg) showed synergistic effects leading to 75% and 90% mechanical antinociception, respectively. These mixtures were defined by interaction indexes of 0.43 and 0.41 and ratios 45:1 and 35:1 paracetamol:nefopam, respectively. The same combinations showed additive effects for the inhibition of incisional thermal hyperalgesia.

CONCLUSIONS AND LIMITATIONS

This work describes a synergistic antinociceptive interaction between low doses of nefopam and paracetamol for the treatment of postoperative hypersensitivity to peripheral stimuli. The promising results obtained on reflexive nociceptive responses of young male mice subjected to plantar surgery highlight the interest of further research evaluating the effects of this mixture on the affective-motivational component of pain and in females and additional age groups. Confirmation of pain-relieving efficacy and safety of this oral combination clinically available in European and Asian countries could provide a useful tool for postsurgical pain management.

SIGNIFICANCE

Early postoperative pain is currently undertreated and has been recognized as a relevant source of chronic postsurgical pain. Oral efficient treatments could facilitate fast-track surgeries and patient recovery at home. Here, we identify in a mouse model of postoperative pain a potent synergistic oral combination consisting of low paracetamol and nefopam doses that provides relief of postsurgical hypersensitivity to mechanical and thermal stimuli. Oral multimodal paracetamol-nefopam mixtures represent a potential clinically available pharmacological strategy for the relief of incisional sensitivity and the promotion of patient recovery.

TRP channels in cancer pain

Chronic pain is a common symptom experienced during cancer progression. Additionally, some patients experience bone pain caused by cancer metastasis, which further complicates the prognosis. Cancer pain is often treated using opioid-based pharmacotherapy, but these drugs possess several adverse effects. Accordingly, new mechanisms for cancer pain management are being explored, including transient receptor potential channels (TRPs). TRP ion channels are expressed in several tissues and play a key role in pain detection, especially TRP vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1). In the present review, we describe the role of TRPV1 and TRPA1 involved in cancer pain mechanisms. Several studies have revealed that the administration of TRPV1 or TRPA1 agonists/antagonists and TRPV1 or TRPA1 knockdown reduced sensitivity to nociception in cancer pain models. TRPV1 was also found to be involved in various models of cancer-induced bone pain (CIBP), with TRPV1 expression reportedly enhanced in some models. These studies have demonstrated the TRPV1 or TRPA1 association with cancer pain in models induced by tumour cell inoculation into the bone cavity, hind paw, mammary fat pad, and sciatic nerve in mice or rats. To date, only resiniferatoxin, a TRPV1 agonist, has been evaluated in clinical trials for cancer pain and showed preliminary positive results. Thus, TRP channels are potential targets for managing cancer-related pain syndromes.

TRPV1 antagonist BCTC inhibits pH 6.0-induced pain in human skin

Tissue acidosis due to ischemia occurs under several pathological conditions and is believed to contribute to pain in these circumstances. TRPV1, TRPA1, and ASICs are known to be sensitive to acidic pH. Addressing their possible role in acidosis perception, the respective antagonists BCTC, A-967079, and amiloride were injected in the volar forearm skin of 32 healthy volunteers. To investigate possible redundancies between channels, a full-factorial study design was used. Injections were performed in a prerandomized, double-blind, and balanced design. Each injection included a three-step pH protocol from pH 7.0 over pH 6.5 to pH 6.0 with a step duration of 90 seconds. Pain was reported by volunteers on a numerical scale every 10 seconds during injections. Confirming the primary hypothesis, the combination of all 3 antagonists reduced acid-induced pain at pH 6.0. Because of the full-factorial design, it could be concluded that BCTC alone, but not A-967079 or amiloride, or any combination thereof, was responsible for the observed effects, suggesting TRPV1 as primary sensor for pH 6.0-induced pain. Surprisingly, A-967079 even enhanced pain induced by pH 6.0. In cultured mouse dorsal root ganglion neurons, TPRV1 dependence of pH 6-induced calcium responses could be confirmed. Responses of hTRPV1 to acidic stimulation showed a maximum around pH6, providing an explanation for the pH-dependent inhibition by BCTC. A-967079 sensitizes pH responses is a TRPA1-responsive dorsal root ganglion neuron population, and a direct effect of A-967079 on hTRPA1 and hTRPV1 was excluded. In conclusion, inhibiting TRPV1-mediated acidosis-induced pain could be a symptomatic and potentially also a disease-modifying approach.

Petasin and isopetasin reduce CGRP release from trigeminal afferents indicating an inhibitory effect on TRPA1 and TRPV1 receptor channels

Background

Butterbur root extract with its active ingredients petasin and isopetasin has been used in the prophylactic treatment of migraine for years, while its sites of action are not completely clear. Calcitonin gene-related peptide (CGRP) is known as a biomarker and promoting factor of migraine. We set out to investigate the impact of petasins on the CGRP release from trigeminal afferents induced by activation of the calcium conducting transient receptor potential channels (TRPs) of the subtypes TRPA1 and TRPV1.

Methods

We used well-established in vitro preparations, the hemisected rodent skull and dissected trigeminal ganglia, to examine the CGRP release from rat and mouse cranial dura mater and trigeminal ganglion neurons, respectively, after pre-incubation with petasin and isopetasin. Mustard oil and capsaicin were used to stimulate TRPA1 and TRPV1 receptor channels. CGRP concentrations were measured with a CGRP enzyme immunoassay.

Results

Pre-incubation with either petasin or isopetasin reduced mustard oil- and capsaicin-evoked CGRP release compared to vehicle in an approximately dose-dependent manner. These results were validated by additional experiments with mice expressing functionally deleted TRPA1 or TRPV1 receptor channels.

Conclusions

Earlier findings of TRPA1 receptor channels being involved in the site of action of petasin and isopetasin are confirmed. Furthermore, we suggest an important inhibitory effect on TRPV1 receptor channels and assume a cooperative action between the two TRP receptors. These mechanisms may contribute to the migraine prophylactic effect of petasins.

Thiazoline-related innate fear stimuli orchestrate hypothermia and anti-hypoxia via sensory TRPA1 activation

Thiazoline-related innate fear-eliciting compounds (tFOs) orchestrate hypothermia, hypometabolism, and anti-hypoxia, which enable survival in lethal hypoxic conditions. Here, we show that most of these effects are severely attenuated in transient receptor potential ankyrin 1 (Trpa1) knockout mice. TFO-induced hypothermia involves the Trpa1-mediated trigeminal/vagal pathways and non-Trpa1 olfactory pathway. TFOs activate Trpa1-positive sensory pathways projecting from trigeminal and vagal ganglia to the spinal trigeminal nucleus (Sp5) and nucleus of the solitary tract (NTS), and their artificial activation induces hypothermia. TFO presentation activates the NTS-Parabrachial nucleus pathway to induce hypothermia and hypometabolism; this activation was suppressed in Trpa1 knockout mice. TRPA1 activation is insufficient to trigger tFO-mediated anti-hypoxic effects; Sp5/NTS activation is also necessary. Accordingly, we find a novel molecule that enables mice to survive in a lethal hypoxic condition ten times longer than known tFOs. Combinations of appropriate tFOs and TRPA1 command intrinsic physiological responses relevant to survival fate.

Mechanical allodynia triggered by cold exposure in mice with the Scn11a p.R222S mutation: a novel model of drug therapy for neuropathic pain related to NaV1.9

Mutations within the SCN11A gene which encodes the voltage-gated sodium channel NaV1.9 mainly expressed in small fiber sensory neurons have been associated with neuropathic disorders; however, suitable medications have not been fully investigated. To develop drug therapies against NaV1.9-related neuropathic pain, we aimed to establish a novel model using mice carrying the Scn11a p.R222S mutation initially identified in patients with familial episodic limb pain that is characterized by paroxysmal pain induced by fatigue or bad weather conditions. We investigated the influence of cold exposure (4 °C, overnight) on the behavioral and biochemical phenotypes of Scn11a p.R222S mutant (R222S) and wild type C57BL/6N (WT) mice. We also tested the effects of acetaminophen (125, 250 mg/kg, perorally, p.o.) and traditional Japanese medicine, goshajinkigan (0.5 or 1.0 g/kg, p.o.), which are analgesic drugs prescribed to patients with neuropathic pain, in this model of cold-induced mechanical allodynia in R222S mice.Cold-exposed R222S mice exhibited enhanced mechanical allodynia and thermal hypersensitivity compared with WT mice. The decrease of the mechanical withdrawal threshold in R222S mice was reversible 24 h after housing at room temperature. There was no significant change in the levels of interleukin-1β, interleukin-6, tumor necrosis factor-α, or interferon-γ in the plasma or spinal cords of WT and R222S mice after cold exposure. Both acetaminophen (250 mg/kg) and goshajinkigan (1.0 g/kg) significantly attenuated mechanical allodynia in R222S mice. The model of cold-induced mechanical allodynia in mice with the Scn11a p.R222S mutation is novel and useful for evaluating analgesic drugs for intractable neuropathies related to NaV1.9.

Anti-Inflammatory and Analgesic Effects of TRPV1 Polypeptide Modulator APHC3 in Models of Osteo- and Rheumatoid Arthritis

Arthritis is a widespread inflammatory disease associated with progressive articular surface degradation, ongoing pain, and hyperalgesia causing the development of functional limitations and disability. TRPV1 channel is one of the high-potential targets for the treatment of inflammatory diseases. Polypeptide APHC3 from sea anemone Heteractis crispa is a mode-selective TRPV1 antagonist that causes mild hypothermia and shows significant anti-inflammatory and analgesic activity in different models of pain. We evaluated the anti-inflammatory properties of APHC3 in models of monosodium iodoacetate (MIA)-induced osteoarthritis and complete Freund’s adjuvant (CFA)-induced rheumatoid monoarthritis in comparison with commonly used non-steroidal anti-inflammatory drugs (NSAIDs) such as diclofenac, ibuprofen, and meloxicam. Subcutaneous administration of APHC3 (0.1 mg/kg) significantly reversed joint swelling, disability, grip strength impairment, and thermal and mechanical hypersensitivity. The effect of APHC3 was equal to or better than that of reference NSAIDs. Protracted treatment with APHC3 decreased IL-1b concentration in synovial fluid, reduced inflammatory changes in joints, and prevented the progression of cartilage degradation. Therefore, polypeptide APHC3 has the potential to be an analgesic and anti-inflammatory substance for the alleviation of arthritis symptoms.

N-acetylcysteine dose-dependently improves the analgesic effect of acetaminophen on the rat hot plate test

BACKGROUND

Acetaminophen (APAP) induced hepatotoxicity is a clinically important problem. Up to now, interventive therapy with n-acetylcysteine (NAC) has been considered as a gold-standard treatment for APAP overdose. However, no study has focused on the efficacy of these drugs' concurrent administration on probable enhancing therapeutic outcomes. Thus, this study was aimed to investigate the analgesic effect of co-administration of NAC and acetaminophen in male rats. The NAC-APAP drug formulation may demonstrate the stranger antinociceptive effect.

METHODS

Forty-eight male Sprague-Dawley rats (12-14 weeks) randomly divided into six equal groups; control, APAP (received 300 mg/kg APAP), NAC (received 600 mg/kg NAC) and APAP+ NAC groups that received simultaneously 300 mg/kg APAP with 200-600 mg/kg NAC (AN200, AN400, AN600). All administrations were done orally for once. The antinociceptive effect was recorded by measurement of latency period on a hot plate in 30, 60, and 90 min after administrations.

RESULTS

The results showed that NAC's concurrent administration with APAP, dose-dependently increased APAP analgesic effects (p< 0.0001). Moreover, NAC treatment exhibited an antinociceptive effect in 60 and 90 min, per se. The treatments had no adverse effect on liver enzymes and oxidative stress.

CONCLUSION

Co-administration of NAC with APAP can improve the antinociceptive effect of APAP. It is suggested that this compound can enhance analgesic effects of APAP and eventually lead to a reduction in acetaminophen dose. Further studies are needed to evaluate the molecular mechanism of this hyper analgesic effect.

Paracetamol - An old drug with new mechanisms of action

Paracetamol (acetaminophen) is the most commonly used over-the-counter (OTC) drug in the world. Despite its popularity and use for many years, the safety of its application and its mechanism of action are still unclear. Currently, it is believed that paracetamol is a multidirectional drug and at least several metabolic pathways are involved in its analgesic and antipyretic action. The mechanism of paracetamol action consists in inhibition of cyclooxygenases (COX-1, COX-2, and COX-3) and involvement in the endocannabinoid system and serotonergic pathways. Additionally, paracetamol influences transient receptor potential (TRP) channels and voltage-gated Kv7 potassium channels and inhibits T-type Cav3.2 calcium channels. It also exerts an impact on L-arginine in the nitric oxide (NO) synthesis pathway. However, not all of these effects have been clearly confirmed. Therefore, the aim of our paper was to summarize the current state of knowledge of the mechanism of paracetamol action with special attention to its safety concerns.

Implications of Transient Receptor Potential Cation Channels in Migraine Pathophysiology

Migraine is a common and debilitating headache disorder. Although its pathogenesis remains elusive, abnormal trigeminal and central nervous system activity is likely to play an important role. Transient receptor potential (TRP) channels, which transduce noxious stimuli into pain signals, are expressed in trigeminal ganglion neurons and brain regions closely associated with the pathophysiology of migraine. In the trigeminal ganglion, TRP channels co-localize with calcitonin gene-related peptide, a neuropeptide crucially implicated in migraine pathophysiology. Many preclinical and clinical data support the roles of TRP channels in migraine. In particular, activation of TRP cation channel V1 has been shown to regulate calcitonin gene-related peptide release from trigeminal nerves. Intriguingly, several effective anti-migraine therapies, including botulinum neurotoxin type A, affect the functions of TRP cation channels. Here, we discuss currently available data regarding the roles of major TRP cation channels in the pathophysiology of migraine and the therapeutic applicability thereof.

Analgesic Effect of Acetaminophen: A Review of Known and Novel Mechanisms of Action

Acetaminophen is one of the most commonly used analgesic agents for treating acute and chronic pain. However, its metabolism is complex, and its analgesic mechanisms have not been completely understood. Previously, it was believed that acetaminophen induces analgesia by inhibiting cyclooxygenase enzymes; however, it has been considered recently that the main analgesic mechanism of acetaminophen is its metabolization to N-acylphenolamine (AM404), which then acts on the transient receptor potential vanilloid 1 (TRPV1) and cannabinoid 1 receptors in the brain. We also recently revealed that the acetaminophen metabolite AM404 directly induces analgesia via TRPV1 receptors on terminals of C-fibers in the spinal dorsal horn. It is known that, similar to the brain, the spinal dorsal horn is critical to pain pathways and modulates nociceptive transmission. Therefore, acetaminophen induces analgesia by acting not only on the brain but also the spinal cord. In addition, acetaminophen is not considered to possess any anti-inflammatory activity because of its weak inhibition of cyclooxygenase (COX). However, we also revealed that AM404 induces analgesia via TRPV1 receptors on the spinal dorsal horn in an inflammatory pain rat model, and these analgesic effects were stronger in the model than in naïve rats. The purpose of this review was to summarize the previous and new issues related to the analgesic mechanisms of acetaminophen. We believe that it will allow clinicians to consider new pain management techniques involving acetaminophen.

Analgesic Effects of Topical Amitriptyline in Patients With Chemotherapy-Induced Peripheral Neuropathy: Mechanistic Insights From Studies in Mice

Oral amitriptyline hydrochloride (amitriptyline) is ineffective against some forms of chronic pain and is often associated with dose-limiting adverse events. We evaluated the potential effectiveness of high-dose topical amitriptyline in a preliminary case series of chemotherapy-induced peripheral neuropathy patients and investigated whether local or systemic adverse events associated with the use of amitriptyline were present in these patients. We also investigated the mechanism of action of topically administered amitriptyline in mice. Our case series suggested that topical 10% amitriptyline treatment was associated with pain relief in chemotherapy-induced peripheral neuropathy patients, without the side effects associated with systemic absorption. Topical amitriptyline significantly increased mechanical withdrawal thresholds when applied to the hind paw of mice, and inhibited the firing responses of C-, Aβ- and Aδ-type peripheral nerve fibers in ex vivo skin-saphenous nerve preparations. Whole-cell patch-clamp recordings on cultured sensory neurons revealed that amitriptyline was a potent inhibitor of the main voltage-gated sodium channels (Nav1.7, Nav1.8, and Nav1.9) found in nociceptors. Calcium imaging showed that amitriptyline activated the transient receptor potential cation channel, TRPA1. Our case series indicated that high-dose 10% topical amitriptyline could alleviate neuropathic pain without adverse local or systemic effects. This analgesic action appeared to be mediated through local inhibition of voltage-gated sodium channels. PERSPECTIVE: Our preliminary case series suggested that topical amitriptyline could provide effective pain relief for chemotherapy-induced peripheral neuropathy patients without any systemic or local adverse events. Investigation of the mechanism of this analgesic action in mice revealed that this activity was mediated through local inhibition of nociceptor Nav channels.