Possible involvement of the Sigma-1 receptor chaperone in chemotherapeutic-induced neuropathic pain

Sigma-1 receptor targeting inhibits connexin 43 based intercellular communication in chronic neuropathic pain

BACKGROUND AND OBJECTIVE

Neuropathic pain is a chronic condition characterized by aberrant signaling within the somatosensory system, affecting millions of people worldwide with limited treatment options. Herein, we aim at investigating the potential of a sigma-1 receptor (σ1R) antagonist in managing neuropathic pain.

METHODS

A Chronic Constriction Injury (CCI) model was used to induce neuropathic pain. The potential of (+)-MR200 was evaluated following daily subcutaneous injections of the compound. Its mechanism of action was confirmed by administration of a well-known σ1R agonist, PRE084.

RESULTS

(+)-MR200 demonstrated efficacy in protecting neurons from damage and alleviating pain hypersensitivity in CCI model. Our results suggest that (+)-MR200 reduced the activation of astrocytes and microglia, cells known to contribute to the neuroinflammatory process, suggesting that (+)-MR200 may not only address pain symptoms but also tackle the underlying cellular mechanism involved. Furthermore, (+)-MR200 treatment normalized levels of the gap junction (GJ)-forming protein connexin 43 (Cx43), suggesting a reduction in harmful intercellular communication that could fuel the chronicity of pain.

CONCLUSIONS

This approach could offer a neuroprotective strategy for managing neuropathic pain, addressing both pain symptoms and cellular processes driving the condition. Understanding the dynamics of σ1R expression and function in neuropathic pain is crucial for clinical intervention.

Novel drug treatments for pain in advanced cancer and serious illness: a focus on neuropathic pain and chemotherapy-induced peripheral neuropathy

Drugs that are commercially available but have novel mechanisms of action should be explored as analgesics. This review will discuss haloperidol, miragabalin, palmitoylethanolamide (PEA), and clonidine as adjuvant analgesics or analgesics. Haloperidol is a sigma-1 receptor antagonist. Under stress and neuropathic injury, sigma-1 receptors act as a chaperone protein, which downmodulates opioid receptor activities and opens several ion channels. Clinically, there is only low-grade evidence that haloperidol improves pain when combined with morphine, methadone, or tramadol in patients who have cancer, pain from fibrosis, radiation necrosis, or neuropathic pain. Miragabalin is a gabapentinoid approved for the treatment of neuropathic pain in Japan since 2019. In randomized trials, patients with diabetic neuropathy have responded to miragabalin. Its long binding half-life on the calcium channel subunit may provide an advantage over other gabapentinoids. PEA belongs to a group of endogenous bioactive lipids called ALIAmides (autocoid local injury antagonist amides), which have a sense role in modulating numerous biological processes in particular non-neuronal neuroinflammatory responses to neuropathic injury and systemic inflammation. Multiple randomized trials and meta-analyses have demonstrated PEA's effectiveness in reducing pain severity arising from diverse pain phenotypes. Clonidine is an alpha2 adrenoceptor agonist and an imidazoline2 receptor agonist, which is U.S. Federal Drug Administration approved for attention deficit hyperactivity disorder in children, Tourette's syndrome, adjunctive therapy for cancer-related pain, and hypertension. Clonidine activation at alpha2 adrenoceptors causes downstream activation of inhibitory G-proteins (Gi/Go), which inhibits cyclic Adenosine monophosphate (AMP) production and hyperpolarizes neuron membranes, thus reducing allodynia. Intravenous clonidine has been used in terminally ill patients with poorly controlled symptoms, in particular pain and agitation.

KM-408, a novel phenoxyalkyl derivative as a potential anticonvulsant and analgesic compound for the treatment of neuropathic pain

BACKGROUND

Epilepsy frequently coexists with neuropathic pain. Our approach is based on the search for active compounds with multitarget profiles beneficial in terms of potential side effects and on the implementation of screening for potential multidirectional central activity.

METHODS

Compounds were synthesized by means of chemical synthesis. After antiseizure and neurotoxicity screening in vivo, KM-408 and its enantiomers were chosen for analgesic activity evaluations. Further safety studies included acute toxicity in mice, the effect on normal electrocardiogram and on blood pressure in rats, whole body plethysmography in rats, and in vitro and biochemical assays. Pharmacokinetics has been studied in rats after iv and po administration. Metabolism has been studied in vivo in rat serum and urine. Radioligand binding studies were performed as part of the mechanism of action investigation.

RESULTS

Selected results for KM-408: K_i sigma = 7.2*10^-8; K_i 5-HT_1A = 8.0*10^-7; ED₅₀ MES (mice, ip) = 13.3 mg/kg; formalin test (I phase, mice, ip)-active at 30 mg/kg; SNL (rats, ip)-active at 6 mg/kg; STZ-induced pain (mice, ip)-active at 1 mg/kg (von Frey) and 10 mg/kg (hot plate); hot plate test (mice, ip)-active at 30 mg/kg; ED₅₀ capsaicin test (mice, ip) = 18.99 mg/kg; tail immersion test (mice)-active at 0.5%; corneal anesthesia (guinea pigs)-active at 0.125%; infiltration anesthesia (guinea pigs)-active at 0.125%.

CONCLUSIONS

Within the presented study a novel compound, R,S-2-((2-(2-chloro-6-methylphenoxy)ethyl)amino)butan-1-ol hydrochloride (KM-408) with dual antiseizure and analgesic activity has been developed for potential use in neuropathic pain treatment.

Neuro-immune interactions in paclitaxel-induced peripheral neuropathy

BACKGROUND

Paclitaxel is a taxane-based chemotherapeutic agent used as a treatment in breast cancer. There is no effective prevention or treatment strategy for the most common side effect of peripheral neuropathy. In this manuscript, we reviewed the molecular mechanisms that contribute to paclitaxel-induced peripheral neuropathy (PIPN) with an emphasis on immune-related processes.

METHODS

A systematic search of the literature was conducted in PubMed, EMBASE and Cochrane Library. The SYRCLE's risk of bias tool was used to assess internal validity.

RESULTS

156 studies conducted with rodent models were included. The risk of bias was high due to unclear methodology. Paclitaxel induces changes in myelinated axons, mitochondrial dysfunction, and mechanical hypersensitivity by affecting ion channels expression and function and facilitating spinal transmission. Paclitaxel-induced inflammatory responses are important contributors to PIPN.

CONCLUSION

Immune-related processes are an important mechanism contributing to PIPN. Studies in humans that validate these mechanistic data are highly needed to facilitate the development of therapeutic strategies.

Therapeutic Agents for Oxaliplatin-Induced Peripheral Neuropathy; Experimental and Clinical Evidence

Oxaliplatin is an essential drug in the chemotherapy of colorectal, gastric, and pancreatic cancers, but it frequently causes peripheral neuropathy as a dose-limiting factor. So far, animal models of oxaliplatin-induced peripheral neuropathy have been established. The mechanisms of development of neuropathy induced by oxaliplatin have been elucidated, and many drugs and agents have been proven to have neuroprotective effects in basic studies. In addition, some of these drugs have been validated in clinical studies for their inhibitory effects on neuropathy. In this review, we summarize the basic and clinical evidence for the therapeutic effects of oxaliplatin. In basic research, there are many reports of neuropathy inhibitors that target oxidative stress, inflammatory response, sodium channel, transient receptor potential (TRP) channel, glutamate nervous system, and monoamine nervous system. Alternatively, very few drugs have clearly demonstrated the efficacy for oxaliplatin-induced peripheral neuropathy in clinical trials. It is important to activate translational research in order to translate basic research into clinical research.

Therapeutic Agents for Oxaliplatin-Induced Peripheral Neuropathy; Experimental and Clinical Evidence

Oxaliplatin is an essential drug in the chemotherapy of colorectal, gastric, and pancreatic cancers, but it frequently causes peripheral neuropathy as a dose-limiting factor. So far, animal models of oxaliplatin-induced peripheral neuropathy have been established. The mechanisms of development of neuropathy induced by oxaliplatin have been elucidated, and many drugs and agents have been proven to have neuroprotective effects in basic studies. In addition, some of these drugs have been validated in clinical studies for their inhibitory effects on neuropathy. In this review, we summarize the basic and clinical evidence for the therapeutic effects of oxaliplatin. In basic research, there are many reports of neuropathy inhibitors that target oxidative stress, inflammatory response, sodium channel, transient receptor potential (TRP) channel, glutamate nervous system, and monoamine nervous system. Alternatively, very few drugs have clearly demonstrated the efficacy for oxaliplatin-induced peripheral neuropathy in clinical trials. It is important to activate translational research in order to translate basic research into clinical research.

Therapeutic Agents for Oxaliplatin-Induced Peripheral Neuropathy; Experimental and Clinical Evidence

Oxaliplatin is an essential drug in the chemotherapy of colorectal, gastric, and pancreatic cancers, but it frequently causes peripheral neuropathy as a dose-limiting factor. So far, animal models of oxaliplatin-induced peripheral neuropathy have been established. The mechanisms of development of neuropathy induced by oxaliplatin have been elucidated, and many drugs and agents have been proven to have neuroprotective effects in basic studies. In addition, some of these drugs have been validated in clinical studies for their inhibitory effects on neuropathy. In this review, we summarize the basic and clinical evidence for the therapeutic effects of oxaliplatin. In basic research, there are many reports of neuropathy inhibitors that target oxidative stress, inflammatory response, sodium channel, transient receptor potential (TRP) channel, glutamate nervous system, and monoamine nervous system. Alternatively, very few drugs have clearly demonstrated the efficacy for oxaliplatin-induced peripheral neuropathy in clinical trials. It is important to activate translational research in order to translate basic research into clinical research.

Activation of Sigma-1 Receptor Enhanced Pericyte Survival via the Interplay Between Apoptosis and Autophagy: Implications for Blood-Brain Barrier Integrity in Stroke

Stroke is a cerebrovascular disorder that affects many people worldwide. Pericytes play an important role in stroke progression and recovery. The sigma-1 receptor (σ-1R) signaling pathway has been suggested as having promising neuroprotective potential in treating stroke; however, whether σ-1R activation regulates pericyte function remains unknown. The aim of this study was to elucidate the role of σ-1R and a novel σ-1R agonist in pericytes following ischemic stroke. An ischemic stroke animal model was induced by photothrombotic middle cerebral artery occlusion (pMCAO) in σ-1R knockout (KO) and wild-type (WT) mice. After pMCAO, there was significant pericyte loss and coverage in σ-1R KO mice compared with WT mice as determined using transmission electron microscopy, immunofluorescence staining, and western blot. Interestingly, a novel σ-1R agonist decreased infarct volume and blood-brain barrier damage with a concomitant amelioration of pericyte loss, as determined by western blot. Further studies indicated that cell apoptosis and autophagy were induced in an in vivo pMCAO ischemic stroke animal model and an in vitro oxygen glucose deprivation-treatment group. Inhibition of autophagy using a pharmacological approach significantly mitigated pericyte apoptosis, suggesting that autophagy was upstream of apoptosis in pericytes. Both in vivo and in vitro studies indicated that the σ-1R agonist significantly decreased cell apoptosis via inhibition of autophagy with a subsequent enhancement of pericyte survival. This study identified the unique roles for σ-1R in mediating pericyte survival via the regulation of the interplay between apoptosis and autophagy, suggesting that a novel σ-1R agonist may be a promising therapeutic agent for the treatment of stroke patients.

An Increase of Sigma-1 Receptor in the Penumbra Neuron after Acute Ischemic Stroke

BACKGROUND

Penumbra salvage from infarction by early reperfusion within the time window is the target of acute ischemic stroke therapies. Although the penumbral imaging is potently usable in clinic trial, additional work needs to be performed to advancing the field with better-defined, evaluated, and validated imaging measures.

METHODS

Mice were subjected to permanent stroke by right middle cerebral artery (MCA) occlusion. Multimodel magnetic resonance imaging (MRI) method was assessed to define the penumbra as that brain region in which the perfusion and diffusion-weighted MR images are mismatched (perfusion-weighted imaging [PWI]-diffusion-weighted imaging [DWI] mismatch). MRI measurements were performed at 1 hour after MCA occlusion (MCAO). Sigma-1 receptor expression was assessed by immunoblotting and immunostaining in PWI-DWI-defined penumbra and core compared with sham or contralateral slice. Penumbral sigma-1 receptor identified the correlation with the neuron, astrocyte, and microglia by immuno-colocalization.

RESULTS

Sigma-1 receptor was significantly upregulated in penumbra or peri-infarct compared with sham and core tissue at 1 hour and 24 hours after MCAO. There was a colocalization of sigma-1 receptor and neuron in penumbra at 1 hour after stroke. Sigma-1 receptor is specifically increased in ischemic penumbral neuron at 1 hour after MCAO.

CONCLUSIONS

Sigma-1 receptor may act as an endogenous marker of penumbra after acute ischemic stroke.

Pharmacological Modulation of the Sigma 1 Receptor and the Treatment of Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy with respect to existing therapies and reduce their unwanted effects. Current preclinical evidence supports the modulatory role of sigma-1 receptors (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pains of different etiologies. σ1R is highly expressed in different pain areas of the CNS and the periphery (particularly dorsal root ganglia), and interacts and modulates the functionality of different receptors and ion channels . The antagonism of σ1R leads to decreased amplification of pain signaling within the spinal cord (central sensitization), but recent data also support a role at the periphery. σ1R antagonists have consistently demonstrated efficacy in neuropathic pain , but also in other types of pain including inflammatory, orofacial, visceral, and post-operative pain. Apart from acting alone, when combined with opioids, σ1R antagonists enhance opioid analgesia but not opioid-induced unwanted effects. Interestingly, unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitive effects in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. Accordingly, σ1R antagonists are not strictly analgesics; they are antiallodynic and antihyperalgesic drugs acting when the system is sensitized following prolonged noxious stimulation or persistent abnormal afferent input (e.g., secondary to nerve injury). These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain .

Sigma-1 Receptor and Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy respect to existing therapies and/or reduce their unwanted effects. Current preclinical evidence supports the modulatory role of the sigma-1 receptor (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pain of different etiology, very consistently in neuropathic pain, but also in nociceptive, inflammatory, and visceral pain. σ1R is highly expressed in different pain areas of the CNS and the periphery, particularly dorsal root ganglia (DRG), and interacts and modulates the functionality of different receptors and ion channels. Accordingly, antinociceptive effects of σ1R antagonists both acting alone and in combination with other analgesics have been reported at both central and peripheral sites. At the central level, behavioral, electrophysiological, neurochemical, and molecular findings support a role for σ1R antagonists in inhibiting augmented excitability secondary to sustained afferent input. Moreover, the involvement of σ1R in mechanisms regulating pain at the periphery has been recently confirmed. Unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitivity effects (antihyperalgesic and antiallodynic) in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain.

Antinociception by Sigma-1 Receptor Antagonists: Central and Peripheral Effects

There is plenty of evidence supporting the modulatory role of sigma-1 receptors (σ1Rs) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists, particularly in nonacute sensitizing conditions involving sustained afferent drive, activity-dependent plasticity/sensitization, and ultimately pain hypersensitivity, as it is the case in chronic pains of different etiology. Antinociceptive effects of σ1R antagonists both when acting alone and in combination with opioids (to enhance opioid analgesia) have been reported at both central and peripheral sites. At the central level, findings at the behavioral (animal pain models), electrophysiological (spinal wind-up recordings), neurochemical (spinal release of neurotransmitters) and molecular (NMDAR function) level supports a role for σ1R antagonists in inhibiting augmented excitability secondary to sustained afferent input. Attenuation of activity-induced plastic changes (central sensitization) following tissue injury/inflammation or nerve damage could thus underlie the central inhibitory effect of σ1R antagonists. Moreover, recent pieces of information confirm the involvement of σ1R in mechanisms regulating pain at the periphery, where σ1Rs are highly expressed, particularly in dorsal root ganglia. Indeed, local peripheral administration of σ1R antagonists reduces inflammatory hyperalgesia. Potentiation of opioid analgesia is also supported, particularly at supraspinal sites and at the periphery, where locally administered σ1R antagonists unmask opioid analgesia. Altogether, whereas σ1R activation is coupled to pain facilitation and inhibition of opioid antinociception, σ1R antagonism inhibits pain hypersensitivity and "releases the brake" enabling opioids to exert enhanced antinociceptive effects, both at the central nervous system and at the periphery.