Pregabalin as a Pain Therapeutic: Beyond Calcium Channels

Gabapentinoids for the treatment of stroke

ABSTRACT

Gabapentinoid drugs (pregabalin and gabapentin) have been successfully used in the treatment of neuropathic pain and in focal seizure prevention. Recent research has demonstrated their potent activities in modulating neurotransmitter release in neuronal tissue, oxidative stress, and inflammation, which matches the mechanism of action via voltage-gated calcium channels. In this review, we briefly elaborate on the medicinal history and ligand-binding sites of gabapentinoids. We systematically summarize the preclinical and clinical research on gabapentinoids in stroke, including ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, seizures after stroke, cortical spreading depolarization after stroke, pain after stroke, and nerve regeneration after stroke. This review also discusses the potential targets of gabapentinoids in stroke; however, the existing results are still uncertain regarding the effect of gabapentinoids on stroke and related diseases. Further preclinical and clinical trials are needed to test the therapeutic potential of gabapentinoids in stroke. Therefore, gabapentinoids have both opportunities and challenges in the treatment of stroke.

The Effect of Pregabalin on Microglia Differentiation in Rat with Neuropathic pain: A Preliminary Study

This study investigated the effects of pregabalin on microglial differentiation in rats with neuropathic pain (NP) induced by sciatic nerve ligation and transection. After confirming NP, the rats were randomly allocated to either a pregabalin or control group. The pregabalin group received intraperitoneal injections of 10 mg/kg pregabalin, while the control group received an equivalent volume of normal saline following surgery. On postoperative day 28, neuronal damage, microglial activity, and microglial differentiation were assessed. The pregabalin group exhibited significantly less neuronal damage compared to the control group, along with a significant decrease in activated microglial expression in both the brain and spinal cord. Pregabalin treatment also significantly altered the microglial phenotype expression, with a decrease in the M1 phenotype percentage and an increase in the M2 phenotype percentage in both the brain (M1 phenotype: 43.52 ± 12.16% and 18.00 ± 8.57% in the control and pregabalin groups, respectively; difference: 27.26 [15.18-42.10], p = 0.002; M2 phenotype: 16.88 ± 6.47% and 39.63 ± 5.82% in the control and pregabalin groups, respectively; difference 22.04 [17.17-32.70], p < 0.001) and the spinal cord ipsilateral to nerve injury (M1 phenotype: 44.35 ± 12.12% and 13.78 ± 5.39% in the control and pregabalin groups, respectively; difference 30.46 [21.73-44.45], p < 0.001; M2 phenotype: 7.64 ± 3.91% and 33.66 ± 7.95% in the control and pregabalin groups, respectively; difference 27.41 [21.21-36.30], p < 0.001). Overall, pregabalin treatment significantly decreased the microglial M1 phenotype while increasing the microglial M2 phenotype in NP rats.

A next generation peripherally restricted Cavα2δ-1 ligand with inhibitory action on Cav2.2 channels and utility in neuropathic pain

The Voltage-Gated Calcium Channel (VGCC) auxiliary subunit Cavα2δ-1 (CACNA2D1) is the target/receptor of gabapentinoids which are known therapeutics in epilepsy and neuropathic pain. Following damage to the peripheral sensory nervous system, Cavα2δ-1 is upregulated in dorsal root ganglion (DRG) neurons in several animal models of chronic neuropathic pain. Gabapentinoids, such as gabapentin and pregabalin, engage with Cavα2δ-1 via binding an arginine residue (R241) within an RRR motif located at the N-terminus of human Cavα2δ-1. A novel, next generation gabapentinoid, engineered not to penetrate the brain, was able to generate a strong analgesic response in Chronic Constriction Injury animal model of chronic neuropathic pain and showed binding specificity for Cavα2δ-1 versus the Cavα2δ-2 subunit. This novel non-brain penetrant gabapentinoid, binds to R241 and a novel binding site on Cavα2δ-1, which is located within the VGCC_α2 domain, identified as a lysine residue within an IKAK amino acid motif (K634). The overall whole cell current amplitudes were diminished by the compound, with these inhibitory effects being diminished in R241A mutant Cavα2δ-1 subunits. The functional effects occurred at lower concentrations than those needed for inhibition by gabapentin or pregabalin, which apparently bound the Cavα2δ-1 subunit only on the R241 and not on the K634 residue. Our work sets the stage for the identification and characterisation of novel compounds with therapeutic properties in neuropathic pain and possibly in other disorders and conditions which require engagement of the Cavα2δ-1 target.

Recent advances in the understanding and management of chronic pancreatitis pain

Abdominal pain is the most common symptom of chronic pancreatitis (CP) and is often debilitating for patients and very difficult to treat. To date, there exists no cure for the disease. Treatment strategies focus on symptom management and on mitigation of disease progression by reducing toxin exposure and avoiding recurrent inflammatory events. Traditional treatment protocols start with medical management followed by consideration of procedural or surgical intervention on selected patients with severe and persistent pain. The incorporation of adjuvant therapies to treat comorbidities including psychiatric disorders, exocrine pancreatic insufficiency, mineral bone disease, frailty, and malnutrition, are in its early stages. Recent clinical studies and animal models have been designed to improve investigation into the pathophysiology of CP pain, as well as to improve pain management. Despite the array of tools available, many therapeutic options for the management of CP pain provide incomplete relief. There still remains much to discover about the neural regulation of pancreas-related pain. In this review, we will discuss research from the last 5 years that has provided new insights into novel methods of pain phenotyping and the pathophysiology of CP pain. These discoveries have led to improvements in patient selection for optimization of outcomes for both medical and procedural management, and identification of potential future therapies.

Clinical side-effects based drug repositioning for anti-epileptic activity

Several generations of anti-epileptic drugs (AEDs) are available but have several associated side effects apart from a limited success rate. Drug repositioning strategies have gained importance in the last two decades owing to lower failure rates and economic burden. Drugs with similar side effect profiles may share a common mechanism of action and thus can be linked to other disease treatments. The present study was carried out to identify the newly approved drug candidate(s) as AEDs using clinical side-effects drug repositioning strategy. The clinical side effect similarity of drugs available in the SIDER v4.1 database was estimated against common side effects of 5 major marketed AEDs, using the 'dplyr' package library in the R. Further drugs were filtered based on Blood Brain Barrier permeability prediction and FDA-approval status. Molecular docking studies were performed for selected 26 hits (drugs) against previously identified epilepsy target receptors: Voltage-gated sodium channel α2 (Nav1.2), GABA receptor α1-β1 (GABAr α1-β1), and Voltage-gated calcium channel α-1 G (Cav3.1). Only 2 drugs (Ziprasidone and Paroxetine) showed better binding affinities against studied epilepsy receptors Nav1.2, GABAr α1-β1, and Cav3.1, than their corresponding standard AEDs, i.e. Carbamazepine, Clonazepam, and Pregabalin, respectively. Ziprasidone reportedly showed seizure-like symptoms in ∼3% of patients and was hence omitted from further study. The MDS study of docked complexes of Paroxetine with selected epilepsy target receptors showed stable RMSD values and better interaction energies. The study reveals Paroxetine as a potential candidate to be repurposed for 1st line epileptic seizure medication.Communicated by Ramaswamy H. Sarma.

Protective effect of pregabalin on renal and renal endothelial damage in sepsis induced by lipopolysaccharide

OBJECTIVE

We investigated the protective effects of pregabalin (PRG) on kidney and renal endothelial damage in sepsis induced by Lipopolysaccharide (LPS).

MATERIALS AND METHODS

Rats were randomly divided into three groups as control, LPS and LPS+PRG. Saline solution was administered 30 mg/kg orally and 5 mg/kg intraperitoneally (i.p.) to the control group. LPS was applied as 5 mg/kg, i.p. to the LPS group. In the LPS+PRG group, PRG at 30 mg/kg orally and one hour before LPS administration, one hour later 5 mg/kg i.p. LPS was applied. Rats were sacrificed 6 hours after LPS administration.

RESULTS

White Blood Cell (WBC), granulocyte, Blood Urea Nitrogen (BUN), creatinine, uric asid, Total Oxidant Status (TOS) and Oxidative Stress Index (OSI) significantly increased (p<0.05); platelets (PLT), activated partial thromboplastin time (aPTT) and Total Antioxidant Status (TAS) significantly decreased in the LPS group compared to the control group (p<0.05). In the LPS+PRG group WBC, granulocyte, BUN, creatinine, uric asid, TOS and OSI significantly decreased (p<0.05); PLT, aPTT and TAS significantly increased compared to the LPS group(p<0.05). Histopathological examinations showed that kidney and renal endothelial damage in the LPS group decreased in the LPS+PRG group. Immunohistochemically IL1-β, IL-6, IL-10, TNF-α expressions in kidney tissue and Toll-Like Receptors-4 (TLR-4) and NF-κB expressions in the renal endothelial tissue significantly increased in the LPS group compared to the control group and significantly decreased in the LPS+PRG group compared to the LPS group (p<0.001).

CONCLUSIONS

Sepsis causes kidney and renal endothelial damage and PRG reduces this damage. Therefore PRG can be used in prophylactic treatment in sepsis, supported by more studies.

Post-Procedure Analgesic Management

During the development of multimodal pain management protocols, practitioners need to consider the potential risks each treatment modality inherently carries in order to prevent or diminish harmful outcomes. As an example, the part dentists played in the early stages of the opioid epidemic in the United States of America should serve as a cautionary account. By understanding the roots of this crisis, as practitioners we are better equipped to implement the novel analgesic agents available today to optimize post-operative pain control while minimizing any risk of addiction and harm to our communities. It is therefore critical that our colleagues understand the variety of accessible options for pain management to assure that our profession is able to seek adequate and sustainable relief for our post-operative patients. This article will go in depth to explain the analgesic tools practitioners can implement for an effective low-risk protocol, including a combination of NSAIDS and acetaminophen approach, using long-acting local anesthetics such as Exparel, pregabalin, gabapentin, ketamine, dexmedetomidine, and corticosteroids, and enhanced recovery after surgery protocols.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain

BACKGROUNDS

Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain.

METHODS

Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM).

RESULTS

We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration.

CONCLUSIONS

Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

In silico approaches in carcinogenicity hazard assessment: case study of pregabalin, a nongenotoxic mouse carcinogen

In silico toxicology protocols are meant to support computationally-based assessments using principles that ensure that results can be generated, recorded, communicated, archived, and then evaluated in a uniform, consistent, and reproducible manner. We investigated the availability of in silico models to predict the carcinogenic potential of pregabalin using the ten key characteristics of carcinogens as a framework for organizing mechanistic studies. Pregabalin is a single-species carcinogen producing only one type of tumor, hemangiosarcomas in mice via a nongenotoxic mechanism. The overall goal of this exercise is to test the ability of in silico models to predict nongenotoxic carcinogenicity with pregabalin as a case study. The established mode of action (MOA) of pregabalin is triggered by tissue hypoxia, leading to oxidative stress (KC5), chronic inflammation (KC6), and increased cell proliferation (KC10) of endothelial cells. Of these KCs, in silico models are available only for selected endpoints in KC5, limiting the usefulness of computational tools in prediction of pregabalin carcinogenicity. KC1 (electrophilicity), KC2 (genotoxicity), and KC8 (receptor-mediated effects), for which predictive in silico models exist, do not play a role in this mode of action. Confidence in the overall assessments is considered to be medium to high for KCs 1, 2, 5, 6, 7 (immune system effects), 8, and 10 (cell proliferation), largely due to the high-quality experimental data. In order to move away from dependence on animal data, development of reliable in silico models for prediction of oxidative stress, chronic inflammation, immunosuppression, and cell proliferation will be critical for the ability to predict nongenotoxic compound carcinogenicity.

Pregabalin alters reproductive performance in male mice and causes congenital anomalies in offspring

CONTEXT

Pregabalin is an anticonvulsant drug with analgesic activity for the treatment of neuropathic pain.

AIMS

To valuate the toxicity of pregabalin in reproductive parameters, spermatogenesis, and teratogenicity in the offspring of mice.

METHODS

Twenty male mice were randomly distributed into two groups: PGB group and group C (n =10 per group). The animals in the PGB group received, via gavage, 200mg/kg of pregabalin diluted in distilled water daily, for a period of 45days. Group C received distilled water under the same experimental design.

KEY RESULTS

In the paternal parameters of the PGB group, there was a significant increase in the size of the testicles, morphological alterations in the spermatozoa, a decrease in the Johnsen score, an increase in the Leydig cells, and a decrease in the serum level of testosterone. In the intrauterine development parameters of females mated with males from the PGB group, a significant decrease in placental weight, weight and length of fetuses, and fetal viability rate was observed. There was a significant increase in the number of resorptions and post-implantation losses. The significant anomalies observed in the offspring were alteration in the size of the kidneys, absent metacarpals and phalanges, alteration in the sternum, and supernumerary thoracic vertebrae.

CONCLUSION

Results suggest that pregabalin had toxic effects on the reproductive function of male mice and teratogenic potential.

IMPLICATIONS

The findings of this study may provide new hypotheses, taking into account the risk-benefit ratio for male reproduction and offspring health.

Pregabalin-Tolperisone Combination to Treat Neuropathic Pain: Improved Analgesia and Reduced Side Effects in Rats

The current treatment of neuropathic pain (NP) is unsatisfactory; therefore, effective novel agents or combination-based analgesic therapies are needed. Herein, oral tolperisone, pregabalin, and duloxetine were tested for their antinociceptive effect against rat partial sciatic nerve ligation (pSNL)-induced tactile allodynia described by a decrease in the paw withdrawal threshold (PWT) measured by a dynamic plantar aesthesiometer. On day 7 after the operation, PWTs were assessed at 60, 120, and 180 min post-treatment. Chronic treatment was continued for 2 weeks, and again, PWTs were measured on day 14 and 21. None of the test compounds produced an acute antiallodynic effect. In contrast, after chronic treatment, tolperisone and pregabalin alleviated allodynia. In other experiments, on day 14, the acute antiallodynic effect of the tolperisone/pregabalin or duloxetine combination was measured. As a novel finding, a single dose of the tolperisone/pregabalin combination could remarkably alleviate allodynia acutely. It also restored the neuropathy-induced elevated CSF glutamate content. Furthermore, the combination is devoid of adverse effects related to motor and gastrointestinal transit functions. Tolperisone and pregabalin target voltage-gated sodium and calcium channels, respectively. The dual blockade effect of the combination might explain its advantageous acute analgesic effect in the present work.

The effect of pregabalin on postoperative pain after anterior cruciate ligament reconstruction: A systematic review of randomized clinical trials

Background

Despite the enormous success of anterior cruciate ligament (ACL) reconstruction, acute neuropathic pain can develop postoperatively and is both distressing and difficult to treat once established. Pregabalin, an anticonvulsant agent that selectively affects the nociceptive process, has been used as a pain relief agent. The purpose of this systematic review of randomized controlled trials (RCTs) was to evaluate the pain control effect of pregabalin versus placebo after ACL reconstruction.

Method

A search of the literature was performed from inception to June 2022, using PubMed, Scopus, Google Scholar, Web of Science, Cochrane and EBSCO. Studies considered for inclusion were RCTs that reported relevant outcomes (postoperative pain scores, cumulative opioid consumption, adverse events) following administration of pregabalin in patients undergoing ACL reconstruction.

Result

Five placebo-controlled RCTs involving 272 participants met the inclusion criteria. 75 mg and 150 mg oral pregabalin was used in included trials. Two studies used a single dose of pregabalin one hour before anesthesia induction. Two studies used pregabalin 1 hour before anesthesia induction and 12 hours after. One study used daily pregabalin 7 days before and 7 days after surgery. Out of five papers, three papers found significantly lower pain intensity and cumulative opioid consumption in pregabalin group compared with placebo group. However, a decrease in pain scores was found in all trials. Pregabalin administration was associated with dizziness and nausea.

Conclusion

The use of pregabalin may be a valuable asset in pain management after ACL reconstruction. However, future studies with larger sample size and longer follow-up period are required.

The immunomodulatory effects of ethosuximide and sodium butyrate on experimentally induced fibromyalgia: The interaction between IL-4, synaptophysin, and TGF-β1/NF-κB signaling

BACKGROUND AND AIMS

Fibromyalgia is a widespread chronic pain syndrome associated with several comorbid conditions that affect the quality of patients' life. Its pathogenesis is complex, and the treatment strategies are limited by partial efficacy and potential adverse effects. So, our aim was to investigate the possible ameliorative effects of ethosuximide and sodium butyrate on fibromyalgia and compare their effects to pregabalin.

MATERIALS AND METHODS

In a mouse model of reserpine induced fibromyalgia, the effect of ethosuximide, sodium butyrate, and pregabalin was investigated. Evaluation of mechanical allodynia, cold hypersensitivity, anxiety, cognitive impairment, and depression was performed. Also, the brain and spinal cord tissue serotonin, dopamine and glutamate in addition to the serum levels of interleukin (IL)-4 and transforming growth factor beta 1 (TGF-β1) were assayed. Moreover, the expression of nuclear factor kappa B (NF-κB) synaptophysin was immunoassayed in the hippocampal tissues.

KEY FINDINGS

Ethosuximide and sodium butyrate restored the behavioral tests to the normal values except for the antidepressant effect which was evident only with ethosuximide. Both drugs elevated the levels of the anti-inflammatory cytokines IL-4 and TGF-β1, reduced the hippocampal NF-κB, and increased synaptophysin expression with superiority of sodium butyrate. Ethosuximide reduced only spinal cord and brain glutamate while improved brain dopamine while sodium butyrate elevated spinal cord dopamine and serotonin with no effect on glutamate. Also, sodium butyrate elevated brain serotonin and reduced glutamate with no effect on brain dopamine.

SIGNIFICANCE

Each of sodium butyrate and ethosuximide would serve as a promising therapeutic modality for management of fibromyalgia and its comorbid conditions.

Pregabalin Silences Oxaliplatin-Activated Sensory Neurons to Relieve Cold Allodynia

Oxaliplatin is a platinum-based chemotherapeutic agent that causes cold and mechanical allodynia in up to 90% of patients. Silent Nav1.8-positive nociceptive cold sensors have been shown to be unmasked by oxaliplatin, and this event has been causally linked to the development of cold allodynia. We examined the effects of pregabalin on oxaliplatin-evoked unmasking of cold sensitive neurons using mice expressing GCaMP-3 in all sensory neurons. Intravenous injection of pregabalin significantly ameliorates cold allodynia, while decreasing the number of cold sensitive neurons by altering their excitability and temperature thresholds. The silenced neurons are predominantly medium/large mechano-cold sensitive neurons, corresponding to the "silent" cold sensors activated during neuropathy. Deletion of α2δ1 subunits abolished the effects of pregabalin on both cold allodynia and the silencing of sensory neurons. Thus, these results define a novel, peripheral inhibitory effect of pregabalin on the excitability of "silent" cold-sensing neurons in a model of oxaliplatin-dependent cold allodynia.

Modulation of GABAA receptors and of GABAergic synapses by the natural alkaloid gelsemine

The Gelsemium elegans plant preparations have shown beneficial activity against common diseases, including chronic pain and anxiety. Nevertheless, their clinical uses are limited by their toxicity. Gelsemine, one of the most abundant alkaloids in the Gelsemium plants, have replicated these therapeutic and toxic actions in experimental behavioral models. However, the molecular targets underlying these biological effects remain unclear. The behavioral activity profile of gelsemine suggests the involvement of GABA_A receptors (GABA_ARs), which are the main biological targets of benzodiazepines (BDZs), a group of drugs with anxiolytic, hypnotic, and analgesic properties. Here, we aim to define the modulation of GABA_ARs by gelsemine, with a special focus on the subtypes involved in the BDZ actions. The gelsemine actions were determined by electrophysiological recordings of recombinant GABA_ARs expressed in HEK293 cells, and of native receptors in cortical neurons. Gelsemine inhibited the agonist-evoked currents of recombinant and native receptors. The functional inhibition was not associated with the BDZ binding site. We determined in addition that gelsemine diminished the frequency of GABAergic synaptic events, likely through a presynaptic modulation. Our findings establish gelsemine as a negative modulator of GABA_ARs and of GABAergic synaptic function. These pharmacological features discard direct anxiolytic or analgesic actions of gelsemine through GABA_ARs but support a role of GABA_ARs on the alkaloid induced toxicity. On the other hand, the presynaptic effects of the alkaloid provide an additional mechanism to explain their beneficial effects. Collectively, our results contribute novel information to improve understanding of gelsemine actions in the mammalian nervous system.

Traumatic neuromas of peripheral nerves: Diagnosis, management and future perspectives

Traumatic neuromas are infrequent in clinical settings but are prevalent following trauma or surgery. A traumatic neuroma is not a true malignancy, rather, it is a hyperplastic, reparative nerve reaction after injury and typically manifests as a nodular mass. The most common clinical manifestations include painful hypersensitivity and the presence of a trigger point that causes neuralgic pain, which could seriously decrease the living standards of patients. While various studies are conducted aiming to improve current diagnosis and management strategies via the induction of emerging imaging tools and surgical or conservative treatment. However, researchers and clinicians have yet to reach a consensus regarding traumatic neuromas. In this review, we aim to start with the possible underlying mechanisms of traumatic neuromas, elaborate on the diagnosis, treatment, and prevention schemes, and discuss the current experiment models and advances in research for the future management of traumatic neuromas.

Treatment of Pain in Rats, Mice, and Prairie Dogs

Recent myomorph and scuiromorph rodent analgesia studies are reviewed and evaluated for potential clinical application. Differences between laboratory animal studies and clinical use in diseased animals are discussed. Analgesia classes reviewed include local anesthetics, nonsteroidal anti-inflammatories, acetaminophen, opioids, and adjuvants such as anticonvulsants. Routes of administration including sustained-release mechanisms are discussed, as are reversal agents. Drug interactions are reviewed in the context of beneficial multimodal analgesia as well as potential adverse effects. Dosage recommendations for clinical patients are explored.

Management of Pain after Photorefractive Keratectomy: A Report by the American Academy of Ophthalmology

OBJECTIVE

To evaluate current best practices for postoperative photorefractive keratectomy (PRK) pain control.

METHODS

Literature searches in the PubMed database were last conducted in October 2021 and were restricted to publications in English. This search identified 219 citations, of which 84 were reviewed in full text for their relevance to the scope of this assessment. Fifty-one articles met the criteria for inclusion; 16 studies were rated level I, 33 studies were rated level II, and 2 studies were rated level III.

RESULTS

Systemic opioid and nonsteroidal anti-inflammatory drugs (NSAIDs); topical NSAIDs; postoperative cold patches; bandage soft contact lenses (BCLs), notably senofilcon A contact lenses; and topical anesthetics were demonstrated to offer significantly better pain control than comparison treatments. Some other commonly reported pain mitigation interventions such as systemic gabapentinoids, chilled intraoperative balanced salt solution (BSS) irrigation, cycloplegia, and specific surface ablation technique strategies offered limited improvement in pain control over control treatments.

CONCLUSIONS

Systemic NSAIDs and opioid medications, topical NSAIDs, cold patches, BCLs, and topical anesthetics have been shown to provide improved pain control over alternative strategies and allow PRK-associated pain to be more tolerable for patients.

Case report: A comatose patient with pregabalin overdose successfully treated with continuous renal replacement therapy

Pregabalin (PB) overdose causes mild symptoms and coma is rarely seen unless the patient has also ingested sedatives and/or has preexisting renal disease. We present a case report of a suicide attempt with PB where the patient presented in a comatose state that was successfully treated with continuous renal replacement therapy (CRRT). Treatment of PB overdose is usually supportive. However, previous reports of PB overdose have been treated with intermittent hemodialysis (IHD) in patients with preexisting renal disease. The problem with IHD is that it is only available in specialist centers and unsuitable for unstable patients. In the following case report, the patient presented to the emergency department (ED) unconscious and hypotensive. It was thought that the patient tried to commit suicide by taking an overdose of zopiclone tablets, as empty packets of zopiclone tablets were found beside the patient. There was no effect with flumazenil treatment, so the patient was intubated, mechanically ventilated, and admitted to the intensive care unit (ICU) where inotropic support was started. Despite supportive therapy, there was no improvement in the patient's condition. Further investigation into the patient's medical records uncovered prescriptions of PB. Based on this finding, plasma PB levels were measured and found to be 20 times the upper limit of the therapeutic reference range. CRRT was instituted and after 6 h of treatment the patient woke up. Hospitals with ICUs often have CRRT available in their units whereas IHD is less readily available. This case report demonstrates that CRRT is an effective method for treating PB overdose in an unconscious unstable patient that was unsuitable for transfer to another hospital.

Promising Advances in Pharmacotherapy for Patients with Spinal Cord Injury-A Review of Studies Performed In Vivo with Modern Drugs

Spinal cord injury (SCI) is a pathological neurological condition that leads to significant motor dysfunction. It is a condition that occurs as a result of tragic accidents, violent acts, or as a consequence of chronic diseases or degenerative changes. The current treatments for patients with SCI have moderate efficacy. They improve the quality of life of patients, but they are still doomed to long-term disability. In response to the modern directions of research on possible therapeutic methods that allow for the recovery of patients with SCI, a scientific review publication is needed to summarize the recent developments in this topic. The following review is focused on the available pharmacological treatments for SCIs and the problems that patients face depending on the location of the injury. In the following review, the research team describes problems related to spasticity and neuropathic pain; possible therapeutic pathways are also described for neuroprotection and the improvement of neurotransmission within the injured spinal cord, and the review focuses on issues related to oxidative stress.

Pregabalin Mediates Retinal Ganglion Cell Survival From Retinal Ischemia/Reperfusion Injury Via the Akt/GSK3β/β-Catenin Signaling Pathway

Purpose

Progressive retinal ganglion cell (RGC) loss induced by retinal ischemia/reperfusion (RIR) injury leads to irreversible visual impairment. Pregabalin (PGB) is a promising drug for neurodegenerative diseases. However, with regard to RGC survival, its specific role and exact mechanism after RIR injury remain unclear. In this study, we sought to investigate whether PGB could protect RGCs from mitochondria-related apoptosis induced by RIR and explore the possible mechanisms.

Methods

C57BL/6J mice and primary RGCs were pretreated with PGB prior to ischemia/reperfusion modeling. The retinal structure and cell morphology were assessed by immunochemical assays and optical coherence tomography. CCK8 was used to assay cell viability, and an electroretinogram was performed to detect RGC function. Mitochondrial damage was assessed by a reactive oxygen species (ROS) assay kit and transmission electron microscopy. Western blot and immunofluorescence assays quantified the expression of proteins associated with the Akt/GSK3β/β-catenin pathway.

Results

Treatment with PGB increased the viability of RGCs in vitro. Consistently, PGB preserved the normal thickness of the retina, upregulated Bcl-2, reduced the ratio of cleaved caspase-3/caspase-3 and the expression of Bax in vivo. Meanwhile, PGB improved mitochondrial structure and prevented excessive ROS production. Moreover, PGB restored the amplitudes of oscillatory potentials and photopic negative responses following RIR. The mechanisms underlying its neuroprotective effects were attributed to upregulation of the Akt/GSK3β/β-catenin pathway. However, PGB-mediated neuroprotection was suppressed when using MK2206 (an Akt inhibitor), whereas it was preserved when treated with TWS119 (a GSK3β inhibitor).

Conclusions

PGB exerts a protective effect against RGC apoptosis induced by RIR injury, mediated by the Akt/GSK3β/β-catenin pathway.

Ion channel long non-coding RNAs in neuropathic pain

Neuropathic pain is one of the primary forms of chronic pain and is the consequence of the somatosensory system's direct injury or disease. It is a relevant public health problem that affects about 10% of the world's general population. In neuropathic pain, alteration in neurotransmission occurs at various levels, including the dorsal root ganglia, the spinal cord, and the brain, resulting from the malfunction of diverse molecules such as receptors, ion channels, and elements of specific intracellular signaling pathways. In this context, there have been exciting advances in elucidating neuropathic pain's cellular and molecular mechanisms in the last decade, including the possible role that long non-coding RNAs (lncRNAs) may play, which open up new alternatives for the development of diagnostic and therapeutic strategies for this condition. This review focuses on recent studies associated with the possible relevance of lncRNAs in the development and maintenance of neuropathic pain through their actions on the functional expression of ion channels. Recognizing the changes in the function and spatio-temporal patterns of expression of these membrane proteins is crucial to understanding the control of neuronal excitability in chronic pain syndromes.

Voltage-dependent CaV3.2 and CaV2.2 channels in nociceptive pathways

Noxious stimuli like cold, heat, pH change, tissue damage, and inflammation depolarize a membrane of peripheral endings of specialized nociceptive neurons which eventually results in the generation of an action potential. The electrical signal is carried along a long axon of nociceptive neurons from peripheral organs to soma located in dorsal root ganglions and further to the dorsal horn of the spinal cord where it is transmitted through a chemical synapse and is carried through the spinal thalamic tract into the brain. Two subtypes of voltage-activated calcium play a major role in signal transmission: a low voltage-activated Ca_V3.2 channel and a high voltage-activated Ca_V2.2 channel. The Ca_V3.2 channel contributes mainly to the signal conductance along nociceptive neurons while the principal role of the Ca_V2.2 channel is in the synaptic transmission at the dorsal horn. Both channels contribute to the signal initiation at peripheral nerve endings. This review summarizes current knowledge about the expression and distribution of these channels in a nociceptive pathway, the regulation of their expression and gating during pain pathology, and their suitability as targets for pharmacological therapy.

Pathogenic Mechanism of Dry Eye-Induced Chronic Ocular Pain and a Mechanism-Based Therapeutic Approach

Purpose

Dry eye–induced chronic ocular pain is also called ocular neuropathic pain. However, details of the pathogenic mechanism remain unknown. The purpose of this study was to elucidate the pathogenic mechanism of dry eye–induced chronic pain in the anterior eye area and develop a pathophysiology-based therapeutic strategy.

Methods

We used a rat dry eye model with lacrimal gland excision (LGE) to elucidate the pathogenic mechanism of ocular neuropathic pain. Corneal epithelial damage, hypersensitivity, and hyperalgesia were evaluated on the LGE side and compared with the sham surgery side. We analyzed neuronal activity, microglial and astrocytic activity, α₂δ–1 subunit expression, and inhibitory interneurons in the trigeminal nucleus. We also evaluated the therapeutic effects of ophthalmic treatment and chronic pregabalin administration on dry eye–induced ocular neuropathic pain.

Results

Dry eye caused hypersensitivity and hyperalgesia on the LGE side. In the trigeminal nucleus of the LGE side, neuronal hyperactivation, transient activation of microglia, persistent activation of astrocytes, α₂δ–1 subunit upregulation, and reduced numbers of inhibitory interneurons were observed. Ophthalmic treatment alone did not improve hyperalgesia. In contrast, continuous treatment with pregabalin effectively ameliorated hypersensitivity and hyperalgesia and normalized neural activity, α₂δ–1 subunit upregulation, and astrocyte activation.

Conclusions

These results suggest that dry eye–induced hypersensitivity and hyperalgesia are caused by central sensitization in the trigeminal nucleus with upregulation of the α₂δ–1 subunit. Here, we showed that pregabalin is effective for treating dry eye–induced ocular neuropathic pain even after chronic pain has been established.

Pharmacotherapy of Painful Diabetic Neuropathy: A Clinical Update

The rising prevalence of diabetes mellitus (DM) leads on to an increase in chronic diabetic complications. Diabetic peripheral neuropathies (DPNs) are common chronic complications of diabetes. Distal symmetric polyneuropathy is the most prevalent form. Most patients with DPN will remain pain-free; however, painful DPN (PDPN) occurs in 6-34% of all DM patients and is associated with reduced health-related-quality-of-life and substantial economic burden. Symptomatic treatment of PDPN and diabetic autonomic neuropathy is the key treatment goals. Using certain patient related characteristics, subjects with PDPN can be stratified and assigned targeted therapies to produce better pain outcomes. The aim of this review is to discuss the various pathogenetic mechanisms of DPN with special reference to the mechanisms leading to PDPN and the various pharmacological and non-pharmacological therapies available for its management. Recommended pharmacological therapies include anticonvulsants, antidepressants, opioid analgesics, and topical medications.

Piperazinyl Bicyclic Derivatives as Selective Ligands of the α2δ-1 Subunit of Voltage-Gated Calcium Channels

The synthesis and pharmacological activities of a new series of piperazinyl quinazolin-4-(3H)-one derivatives acting toward the α2δ-1 subunit of voltage-gated calcium channels (Ca_vα2δ-1) are reported. Different positions of a micromolar HTS hit were explored, and best activities were obtained for compounds containing a small alkyl group in position 3 of the quinazolin-4-(3H)-one scaffold and a 3-methyl-piperazin-1-yl- or 3,5-dimethyl-piperazin-1-yl-butyl group in position 2. The activity was shown to reside in the R enantiomer of the chain in position 2, and several eutomers reached single digit nanomolar affinities. Final modification of the central scaffold to reduce lipophilicity provided the pyrido[4,3-d]pyrimidin-4(3H)-one 16RR, which showed high selectivity for Ca_vα2δ-1 versus Ca_vα2δ-2, probably linked to its improved analgesic efficacy-safety ratio in mice over pregabalin.

Brain circuits for pain and its treatment

[Figure: see text].

The gabapentinoid drugs and their abuse potential

The gabapentinoid drugs, gabapentin and pregabalin, are first-line treatments for neuropathic pain. The epidemics of chronic pain and opioid misuse have given rise to the widespread use of non-opioid drugs such as the gabapentinoids for treatment. Unfortunately, the widespread use of gabapentinoid drugs has resulted in reports of misuse and abuse. Here we summarize the clinical reports of gabapentinoid abuse in different patient populations to help inform clinical practice of chronic pain management.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

The effect of pregabalin on postdural puncture headache among patients undergoing elective cesarean section: A randomized controlled trial

INTRODUCTION

Post-dural puncture headache (PDPH) is one of the most common problems of cesarean section. The present study aimed to evaluate the effect of pregabalin on PDPH among patients undergoing elective cesarean section.

MATERIALS AND METHODS

This double-blind clinical trial was performed on 136 patients undergoing elective cesarean section referred to Shahid Motahari Teaching Hospital in Urmia in northwestern Iran from February 1 to December 20, 2020. Patients were selected by convenience sampling method and randomly divided into two groups of intervention and control (N = 68 people each group). The presence of PDPH and its severity were recorded in the checklist based on the VAS, and conventional treatments were prescribed in the case of occurrence of the PDPH. The PDPH severity was also assessed by the patient using the 10-cm Visual Analog Scale (VAS).

RESULTS

The mean age of participants was 27.82 years. A total of 29 people suffered from hypotension. Regarding pain severity, the mean pain score in the intervention group was significantly lower than the control group (p = 0.01). Results also showed that the frequency of PDPH in the intervention group was significantly lower than the placebo group (4.4% vs. 11.8%; p = 0.019). There was no significant difference between intervention and control groups in terms of demographic characteristics (p > 0.05).

CONCLUSION

Results of the present study showed the use of oral pregabalin at night before spinal anesthesia in patients undergoing elective cesarean(C-) section had a preventive effect on the severity and incidence of PDPH.

α-Phellandrene exhibits antinociceptive and tumor-reducing effects in a mouse model of oncologic pain

Medical reports indicate a prevalence of pain in 50% of patients with cancer. In this context, this article investigated the antinociceptive activity of α-PHE using in vivo Sarcoma-180-induced hypernociception in mice to detail its mechanism(s) of antinociception under different conditions of treatment and tumor progression. Firsty, in vitro cytotoxic action was assessed using melanoma B-16/F-10 and S-180 murine cells and colorimetric MTT assays. For in vivo studies, acute treatment with α-PHE (6.25, 12.5, 25 and 50 mg/kg orally by gavage) was performed on the 1st day after S-180 inoculation. Subacute treatments were performed for 8 days starting on the next day (early protocol) or on day 8 after S-180 inoculation (late protocol). For all procedures, mechanical nociceptive evaluations were carried out by von Frey's technique in the subaxillary region peritumoral tissue (direct nociception) and in right legs of S-180-bearing mice (indirect nociception). α-PHE showed in vitro cytotoxic action on B-16/F-10 and S-180 (CI₅₀ values of 436.0 and 217.9 μg/mL), inhibition of in vivo tumor growth (ranging from 47.3 to 82.7%) and decreased direct (peritumoral tissue in subaxillary region) and indirect (right leg) mechanical nociception in Sarcoma 180-bearing mice with early and advanced tumors under acute or subacute conditions of treatment especially at doses of 25 and 50 mg/kg. It improved serum levels of GSH as well as diminished systemic lipid peroxidation, blood cytokines (interleukin-1β, -4, -6, and tumor necrosis factor-α). Such outcomes highlight α-PHE as a promising lead compound that combines antinociceptive and antineoplasic properties. Its structural simplicity make it a cost-effective alternative, justifying further mechanistic investigations and the development of pharmaceutical formulations. Moreover, the protocols developed and standardized here make it possible to use Sarcoma-180 hypernociception model to evaluate the capacity of new antinociceptive molecules under conditions of cancer-related allodynia.

Oral Pregabalin in Cardiac Surgery: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background

Pregabalin has received wide clinical attention as a new type of analgesic. We undertake a systematic review and meta-analysis to evaluate the effect of pregabalin on postoperative pain in patients undergoing cardiac surgery.

Methods

We searched PubMed, Embase, and Cochrane Library (from inception to July 2020) for eligible studies. The primary outcomes were the total morphine consumption at 24 h. A secondary outcome was intraoperative fentanyl consumption, extubation time postoperative, and length of stay in hospital. We calculated pooled weighted mean difference (WMD) or odds ratio (OR) and 95% CIs using random- or fixed-effects models.

Results

Seven trials involving 463 patients were listed. Meta-analysis showed that the total morphine consumption at 24 h in the pregabalin group was significantly less than the control group (WMD: -5.44, 95% CI: -10.42–0.46, P = 0.03). We found that there is no significant difference between the two groups in intraoperative fentanyl consumption. Compared with the control group, the length of stay in hospital in the pregabalin group was significantly shorter (WMD = -0.87, 95% CI: -1.42−0.32, P = 0.002). And we found that there were no significant differences between the two groups in extubation time (WMD: 17.24, 95% CI: -24.36−58.84, P = 0.42).

Conclusions

Oral pregabalin for cardiac surgery patients can effectively reduce the patient's 24-hour morphine consumption after surgery, shorten the patient's hospital stay, and is more conducive to early postoperative recovery.

Role of α2δ3 in Cellular Synchronization of the Suprachiasmatic Nucleus Under Constant Light Conditions

By the effort to identify candidate signaling molecules important for the formation of robust circadian rhythms in the suprachiasmatic nucleus (SCN), the mammalian circadian center, here we characterize the role of α2δ proteins, synaptic molecules initially identified as an auxiliary subunit of the voltage dependent calcium channel, in circadian rhythm formation. In situ hybridization study demonstrated that type 3 α2δ gene (α2δ3) was strongly expressed in the SCN. Mice without this isoform (Cacna2d3^-/-) did not maintain proper circadian locomotor activity rhythms under a constant light (LL) condition, whereas under a constant dark (DD) condition, these mice showed a similar period length and similar light-responsiveness as compared to wild type mice. Reflecting this behavioral phenotype, Cacna2d3^-/- mice showed a severely impaired Per1 expression rhythm in the SCN under LL, but not under DD. Cultured SCN slices from Per1-luc transgenic Cacna2d3^-/- mice revealed reduced synchrony of Per1-luc gene expression rhythms among SCN neurons. These findings suggest that α2δ3 is essential for synchronized cellular oscillations in the SCN and thereby contributes to enhancing the sustainability of circadian rhythms in behavior.

The combined analgesic effect of pregabalin and morphine in the treatment of pancreatic cancer pain, a retrospective study

BACKGROUND

Pregabalin is commonly used to relieve neuropathic pain. However, data are lacking on its efficacy for the treatment of chronic cancer pain. The purpose of this study was to determine the analgesic efficacy of pregabalin combined with morphine in the management of pancreatic cancer pain.

METHODS

This study reviewed patients who were prescribed morphine and 150 mg/d pregabalin between 1 January 2017 and 10 November 2018 in our institute. The primary outcomes of this study were the average pain score and dose of morphine. Secondary outcomes included characters of breakthrough cancer pain, functional interference related to pain, anxiety/depression status, and incidence of treatment-related adverse events during the study.

RESULTS

A total of 240 patients with pain related to pancreatic cancer were included in the study. The results showed that patients of both combination therapy group (pregabalin+morphine) and monotherapy group (morphine) achieved similar analgesic efficacy, demonstrated by NRS (2.4 ± 0.9 vs. 2.6 ± 0.9; combination vs. monotherapy) at the end of the study. Mean daily dose of morphine used in the combination group was significant lower compared to monotherapy group (39.5 ± 16.0 mg vs. 61.5 ± 19.3 mg, net difference 23.5, 95% CI: 18.4-28.6, p <  0.001). The change of functional interference score related to pain was significantly different between combination and monotherapy group (12.0 ± 0.4 vs. 9.8 ± 4.9; net difference, 2.3; 95% CI: 1.1-3.3; p < 0.001). Patients in combination therapy group had experienced shorter duration of breakthrough cancer pain than those in monotherapy group (X² p < 0.001, Cramer's V:0.36). The incidence of somnolence, dizziness, and cognitive dysfunction were significantly higher in the combination group compared to monotherapy group. No serious treatment-related side effects were observed.

CONCLUSIONS

The findings of this study supported the use of pregabalin with morphine to relieve pain in patients of pancreatic cancer.

Neurotoxic effects of pregabalin dependence on the brain frontal cortex in adult male albino rats

Pregabalin (PGB) is an analog of the inhibitory neurotransmitter gamma-aminobutyric acid. The currently available evidence favors the misuse and abuse potential of PGB. However, its neurotoxicity remains unclear. Therefore, this study assessed the toxic effects of chronic pregabalin dependence as well as withdrawal on the cortical neurons of the frontal lobe. This study included eighty adult male albino rats which were divided into three groups. Group I (Control) included 40 rats and was further subdivided into two equal subgroups (IA and IB) as negative and positive controls. Group II (PGB-dependent) included 20 rats which received PGB starting with the therapeutic dose (300 mg/day), then the doses were gradually increased until they reached the dependent dose (3400 mg/day) by the end of the first month. Further, the dependent dose was given daily for another 2 months. Group III (PGB withdrawal) included 20 rats which received PGB as described in group II. After that, administration of PGB was stopped and the rats were kept for another one month. By the end of the experiment, all animals were sacrificed by cervical decapitation. The specimens were taken from the frontal cortex for histologic and immunohistochemical staining as well as morphometric analysis. Sections of the frontal cortex of group II showed changes in the form of disturbed architectural pattern of cortical layers, apoptotic cells, weak immunoexpression of Bcl-2 and VEGF as well as moderate-strong immunoexpression of iNOS and nestin. These expressions were significantly different from the control groups, but they were non-significant in comparison with group III. These findings indicate that chronic PGB dependence induces neurotoxic effects mainly in the form of neuronal apoptosis, gliosis, and oxidative stress injury of the frontal cortex. The PGB- induced neurotoxic effects persisted after withdrawal. The influence of these neurotoxic effects and their relevance to the cognitive or neurologic disorders in PGB-dependent individuals warrants further research. Furthermore, it is recommended to quantify the behavioral changes related to PGB dependence as well as withdrawal in future studies.

Efficacy of pregabalin as a monotherapy versus combined pregabalin and milnacipran in the management of fibromyalgia

AIM

To compare the efficacy and tolerability of combined pregabalin (PGB) and milnacipran (MLN) in female patients with fibromyalgia (FM) versus PGB as a monotherapy.

METHODS

The present randomized open study included 58 female patients diagnosed with FM (registered on 4/2/19: NCT03905486). Patients were randomly divided into 2 groups (2:2); group 1 included 29 patients who received PGB monotherapy (150 mg twice daily) and group 2 included 29 patients who received combined PGB (150 mg twice daily) and MLN (50 mg twice daily) for 3 months. At the initial visit, patients were subjected to demographic data collection and assessed by the visual analog scale (VAS) for pain and the FM impact questionnaire (FIQ). Outcome measures after 3 months: FIQ, VAS and Leeds Sleep Evaluation Questionnaire.

RESULTS

The median disease duration was 2 years in group 1 (6 months to 5 years) and 2 years in group 2 (6 months to 12 years). The dropout rate was 20.7% in group 1 (n = 6) and 10.3% in group 2 (n = 3). At the follow-up evaluation, a statistically significant improvement was observed in VAS and FIQ scores in both groups (P < 0.001). Although the percentage of patients demonstrating significant improvement in pain, disease impact and sleep pattern were higher in group 2, this did not reach statistical significance.

CONCLUSION

Although PGB as a monotherapy and in combination with MLN have both shown adequate efficacy in the treatment of patients with FM, the combined therapy did not demonstrate superiority over the monotherapy.