Investigational Drugs for the Treatment of Postherpetic Neuralgia: Systematic Review of Randomized Controlled Trials.

The pharmacological treatment of postherpetic neuralgia (PHN) is unsatisfactory, and there is a clinical need for new approaches. Several drugs under advanced clinical development are addressed in this review. A systematic literature search was conducted in three electronic databases (Medline, Web of Science, Scopus) and in the ClinicalTrials.gov register from 1 January 2016 to 1 June 2023 to identify Phase II, III and IV clinical trials evaluating drugs for the treatment of PHN. A total of 18 clinical trials were selected evaluating 15 molecules with pharmacological actions on nine different molecular targets: Angiotensin Type 2 Receptor (AT2R) antagonism (olodanrigan), Voltage-Gated Calcium Channel (VGCC) α2δ subunit inhibition (crisugabalin, mirogabalin and pregabalin), Voltage-Gated Sodium Channel (VGSC) blockade (funapide and lidocaine), Cyclooxygenase-1 (COX-1) inhibition (TRK-700), Adaptor-Associated Kinase 1 (AAK1) inhibition (LX9211), Lanthionine Synthetase C-Like Protein (LANCL) activation (LAT8881), N-Methyl-D-Aspartate (NMDA) receptor antagonism (esketamine), mu opioid receptor agonism (tramadol, oxycodone and hydromorphone) and Nerve Growth Factor (NGF) inhibition (fulranumab). In brief, there are several drugs in advanced clinical development for treating PHN with some of them reporting promising results. AT2R antagonism, AAK1 inhibition, LANCL activation and NGF inhibition are considered first-in-class analgesics. Hopefully, these trials will result in a better clinical management of PHN.

Antinociceptive and modulatory effect of pathoplastic changes in spinal glia of a TLR4/CD14 blocking molecule in two models of pain in rat.

The role of spinal glia in the development and maintenance of chronic pain has become over the last years a subject of increasing interest. In this regard, toll-like receptor 4 (TLR4) signaling has been proposed as a major trigger mechanism. Hence, in this study we explored the implications of TLR4 inhibition in the periphery and primarily in the CNS, focusing on the impact this inhibition renders in pain development and glia activation in the dorsal horn in two models of pain. Making use of a synthetic cluster of differentiation 14 (CD14)/TLR4 antagonist, the effect of TLR4 blockade on tactile allodynia and heat hyperalgesia was evaluated in osteoarthritic and postoperative rat models. An in vitro parallel artificial membrane permeation assay was performed to determine the proneness of the drug to permeate the blood-brain barrier prior to systemic and central administration. Findings suggest a dominant role of peripheral TLR4 in the model of incisional pain, whilst both peripheral and central TLR4 seem to be responsible for osteoarthritic pain. That is, central and peripheral TLR4 may be differently involved in the etiopathology of diverse types of pain what potentially seems a promising approach in the management of pain.

SGK1.1 isoform is involved in nociceptive modulation, offering a protective effect against noxious cold stimulus in a sexually dimorphic manner.

The serum and glucocorticoid-regulated kinase 1 (SGK1) is a widely expressed protein in the Central Nervous System (CNS), involved in regulating the activity of a wide variety of ion channels and transporters and physiological functions, such as neuronal excitability. SGK1.1 is a neuronal splice isoform of SGK1, expressed exclusively in the CNS, distributed in brain and cerebellum, that decreases neuronal excitability via up-regulation of M-current, linked to Kv7.2/3 potassium channels. Strategies to maintain increased SGK1.1 activity could be helpful in decreasing neuronal hyperexcitability, as occurs in neuropathic pain. Transgenic mice overexpressing SGK1.1 (B6.Tg.sgk1) offer a particularly relevant opportunity to assess the physiological involvement of this protein in nociception. Behavior and physiological nociception were evaluated in male and female B6.Tg.sgk1 and wild-type mice (B6.WT), characterizing nociceptive thresholds to different nociceptive stimuli (thermal, chemical and mechanical), as well as the electrophysiological properties of cutaneous sensory Aδ-fibres isolated from the saphenous nerve. The acute antinociceptive effect of morphine was also evaluated. Compared with B6.WT animals, male and female B6.Tg.sgk1 mice showed increased spontaneous locomotor activity. Regarding nociception, there were no differences between transgenic and wild-type mice in heat, chemical and mechanical thresholds, but interestingly, male B6.Tg.sgk1 mice were less sensitive to cold stimulus; B6.Tg.sgk1 animals showed lower sensitivity to morphine. Electrophysiological properties of cutaneous primary afferent fibres were maintained. This is the first demonstration that the SGK1.1 isoform is involved in nociceptive modulation, offering a protective effect against noxious cold stimulus in a sexually dimorphic manner. B6.Tg.sgk1 mice offer a particularly relevant opportunity to further analyze the involvement of this protein in nociception, and studies in models of chronic, neuropathic pain are warranted.

Monoclonal Antibodies for Chronic Pain Treatment: Present and Future.

Chronic pain remains a major problem worldwide, despite the availability of various non-pharmacological and pharmacological treatment options. Therefore, new analgesics with novel mechanisms of action are needed. Monoclonal antibodies (mAbs) are directed against specific, targeted molecules involved in pain signaling and processing pathways that look to be very effective and promising as a novel therapy in pain management. Thus, there are mAbs against tumor necrosis factor (TNF), nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), or interleukin-6 (IL-6), among others, which are already recommended in the treatment of chronic pain conditions such as osteoarthritis, chronic lower back pain, migraine, or rheumatoid arthritis that are under preclinical research. This narrative review summarizes the preclinical and clinical evidence supporting the use of these agents in the treatment of chronic pain.

Maternal separation affects the electrophysiological properties of Aδ-fibres and nociceptive behaviours in male and female mice.

AIM: Early life adverse effects have been associated with an increased risk of suffering pain syndromes in adulthood. Although animal models are of great importance to study modifications of pain sensitivity, up to date the results obtained are contradicting due to the varied methodologies used. Therefore, the aim of the present study was to characterise, as a whole, possible modifications in visceral and somatic nociceptive responses in male and female ICR mice, submitted to two different protocols of maternal separation (MS), and possible modifications in the electrophysiological properties of peripheral nociceptive Aδ-primary afferents. MAIN METHODS: Male and female mice were submitted to 3 or 4-8 hr of daily MS from postnatal day (PND) 2-17 and early weaned. On PND 67 von Frey, hot plate and writhing tests were performed. Afterwards electrophysiological recordings were carried out, using the in vitro skin-saphenous nerve preparation in males. KEY FINDINGS: The short separation protocol of MS did not modify nociceptive sensitivity; but when mice were separated from their dams for the long separation, mechanical pain thresholds were modified in male and female mice and visceral nociception was increased in female mice. Electrophysiological recordings showed that cutaneous Aδ-fibres were sensitised and their mechanotransduction properties were altered in both MS protocols. SIGNIFICANCE: Although MS increases the activity and the mechanosensitivity of cutaneous Aδ-afferent fibres at both short and long periods of separation, only the longer interval of time induces nociceptive sensitivity alterations during adulthood. These results highlight the possible influence of a stress free environment during childhood to reduce nociceptive alterations in adulthood.

May a sigma-1 antagonist improve neuropathic signs induced by cisplatin and vincristine in rats?

BACKGROUND: The antineoplastic drugs cisplatin and vincristine induce peripheral neuropathies. The sigma-1 receptor (σ1R) is expressed in areas of pain control, and its blockade with the novel selective antagonist MR-309 has shown efficacy in nociceptive and neuropathic pain models. Our goal was to test whether this compound reduces neuropathic signs provoked by these antitumoural drugs. METHODS: Rats were treated with cisplatin or vincristine to induce neuropathies. The effects of acute or repeated administration of MR-309 were tested on mechanical and thermal sensitivity, electrophysiological activity of Aδ-primary afferents in the rat skin-saphenous nerve preparation, and gastrointestinal or cardiovascular functions. RESULTS: Rats treated with antitumourals developed tactile allodynia, while those treated with vincristine also developed mechanical hyperalgesia. These in vivo modifications correlated with electrophysiological hyperactivity (increased spontaneous activity and hyperresponsiveness to innocuous and noxious mechanical stimulation). Animals treated with cisplatin showed gastrointestinal impairment and those receiving vincristine showed cardiovascular toxicity. A single dose of MR-309 strongly reduced both nociceptive behaviour and electrophysiological changes. Moreover, its concomitant administration with the antitumourals blocked the development of neuropathic symptoms, thus restoring mechanical sensitivity, improving the impairment of feeding behaviour and gastrointestinal transit in the cisplatin-treated group along with ameliorating the altered vascular reactivity recorded in rats treated with vincristine. CONCLUSION: σ1R antagonist, MR-309, reduces sensorial and electrophysiological neuropathic signs in rats treated with cisplatin or vincristine and, in addition, reduces gastrointestinal and cardiovascular side effects. SIGNIFICANCE: σ1R antagonism could be an interesting and new option to palliate antitumoural neuropathies.