Spinal Mechanisms of Pain and Analgesia

Pain Control for Sickle Cell Crisis, a Novel Approach? A Retrospective Study

Background and Objectives: Pain management poses a significant challenge for patients experiencing vaso-occlusive crisis (VOC) in sickle cell disease (SCD). While opioid therapy is highly effective, its efficacy can be impeded by undesirable side effects. Local regional anesthesia (LRA), involving the deposition of a perineural anesthetic, provides a nociceptive blockade, local vasodilation and reduces the inflammatory response. However, the effectiveness of this therapeutic approach for VOC in SCD patients has been rarely reported up to now. The objective of this study was to assess the effectiveness of a single-shot local regional anesthesia (LRA) in reducing pain and consequently enhancing the management of severe vaso-occlusive crisis (VOC) in adults with sickle cell disease (SCD) unresponsive to conventional analgesic therapy. Materials and Methods: We first collected consecutive episodes of VOC in critical care (ICU and emergency room) for six months in 2022 in a French University hospital with a large population of sickle cell patients in the West Indies population. We also performed a systematic review of the use of LRA in SCD. The primary outcome was defined using a numeric pain score (NPS) and/or percentage of change in opioid use. Results: We enrolled nine SCD adults (28 years old, 4 females) for ten episodes of VOC in whom LRA was used for pain management. Opioid reduction within the first 24 h post block was -75% (50 to 96%). Similarly, the NPS decreased from 9/10 pre-block to 0-1/10 post-block. Five studies, including one case series with three patients and four case reports, employed peripheral nerve blocks for regional anesthesia. In general, local regional anesthesia (LRA) exhibited a reduction in pain and symptoms, along with a decrease in opioid consumption post-procedure. Conclusions: LRA improves pain scores, reduces opioid consumption in SCD patients with refractory pain, and may mitigate opioid-related side effects while facilitating the transition to oral analgesics. Furthermore, LRA is a safe and effective procedure.

Targeted Drug Delivery for Chronic Nonmalignant Pain: Longitudinal Data From the Product Surveillance Registry

OBJECTIVES

To assist in assessment of therapy risks and benefits of targeted drug delivery (TDD) for chronic nonmalignant pain using registry data on product performance, adverse events, and elective device replacement.

MATERIALS AND METHODS

The Product Surveillance Registry (PSR) (NCT01524276) is an ongoing prospective, long-term, multicenter registry enrolling consented patients implanted with an intrathecal drug delivery system. Patients are followed prospectively with participating investigators providing pump and catheter performance data for events related to the device, procedure, and therapy. Event descriptions include patient symptoms and outcomes.

RESULTS

Registry data from the 4646 patients (59.7% female) treated with TDD for chronic, nonmalignant pain at 59 registry sites between August 2003 and October 2019, with over 17,000 patient-years (4646 patients with 44 months average follow-up), were analyzed. Registry discontinuation was largely (46.2% of discontinued patients) due to study site closure and patient death; exit due to an adverse or device event was limited to 10.2%.

CONCLUSIONS

Treating chronic pain with escalating doses of strong systemic opioids often leads to inconsistent pain control, impaired function, untenable side effects, and reduced quality of life and this practice has contributed to the current opioid crisis in the United States. TDD has been an available therapy for these patients for greater than 30 years, and data from this real-world registry offer supporting evidence to the long-term safety of this therapy as an alternative to systemic opioids, as well as insights into patient acceptance and satisfaction.

Intrathecal Analgesia in Cancer Pain

The number of new cancer cases has been increasing globally over the last several decades.

Synthesis of Michael Adducts as Key Building Blocks for Potential Analgesic Drugs: In vitro, in vivo and in silico Explorations

Background

Organocatalytic asymmetric Michael addition is a strong approach for C-C bond formation. The objective of the study is to design molecules by exploiting the efficiency of Michael Adducts. We proceeded with the synthesis of Michael adducts by tailoring the substitution pattern on maleimide and trans-β-nitro styrene as Michael acceptors. The synthesized compounds were evaluated for dual cyclooxygenases (COX) and lipoxygenase (LOX) inhibition.

Methods

The compounds (4, 9–11) were synthesized through Michael additions. The cyclooxygenases (COX-1 and 2) and lipoxygenase (5-LOX) assays were used for in vitro evaluations of compounds. After the acute toxicity studies, the in vivo analgesic potential was determined with acetic acid induced writhing, tail immersion, and formalin tests. Furthermore, the possible roles of adrenergic and dopaminergic receptors were also studied. Extensive computational studies were performed to get a better understanding regarding the binding of this compound with protein target.

Results

Four Michael adducts (4, 9–11) were synthesized. Compound 4 was obtained in enantio- and diastereopure form. The stereopure compound 4 showed encouraging COX-1 and-2 inhibitions with IC₅₀ values of 128 and 65 μM with SI of 1.94. Benzyl derivative 11 showed excellent COX-2 inhibition with the IC₅₀ value of 5.79 μM and SI value 7.96. Compounds 4 and 11 showed good results in in vivo models of analgesia like acetic acid test, tail immersion, and formalin tests. Our compounds were not active in dopaminergic and adrenergic pathways and so were acting centrally. Through extensive computational studies, we computed binding energies, and pharmacokinetic predictions.

Conclusion

Our findings conclude that our synthesized Michael products (pyrrolidinedione 4 and nitroalkane 11) can be potent centrally acting analgesics. Our in silico predictions suggested that the compounds have excellent pharmacokinetic properties. It is concluded here that dual inhibition of COX/LOX pathways provides a convincing step towards the discovery of safe lead analgesic molecules.

Triple Intrathecal Combination Therapy for End-Stage Cancer-Related Refractory Pain: A Prospective Observational Study with Two-Month Follow-Up

INTRODUCTION

In cancer-related pain refractory to systemic opioids, intrathecal (IT) administration of morphine can be a useful strategy. In clinical practice, IT morphine is usually combined with other drugs with different mechanisms of action, in order to obtain a synergistic analgesic effect. However, the discussion on efficacy and safety of IT combination therapy is still ongoing. The aim of this observational study was to report the effects of an IT combination of low doses of ziconotide, morphine, and levobupivacaine in end-stage cancer refractory pain.

METHODS

Sixty adult patients, 21 females and 39 males, were enrolled to an IT device implant. The mean visual analogue scale of pain intensity (VASPI) score was 88 ± 20 mm. All patients started with a triple combination therapy: the initial IT dose of morphine was calculated for each patient based on the equivalent daily dose of morphine; an oral/IT ratio of 400/1 was used. For ziconotide, a standard slow titration schedule was started at 1.2 μg/day and the initial dose of levobupivacaine was 3 mg/day.

RESULTS

The initial IT mean doses of morphine, ziconotide, and levobupivacaine were 0.8 ± 0.3 mg/day, 1.2 mcg/day and 3 mg/day, respectively. At day 2, a significant reduction in VASPI score was registered (49 ± 17, p < 0.001), and this significant reduction persisted at 56 days (mean VASPI score 44 ± 9, p < 0.001), with mean doses of morphine 2 ± 1 mg/day, ziconotide 2.8 ± 1 mcg/day, and levobupivacaine 3.8 ± 2 mg/day. Very few adverse effects (AEs) were observed. Patients' satisfaction was very high during the entire study period.

CONCLUSIONS

Our results, within the limit of the study design, suggest that the IT combination of ziconotide, morphine, and levobupivacaine, at low doses, allows safe and rapid control of refractory cancer pain, with high levels of patient satisfaction.

Spinal α2 -adrenoceptors and neuropathic pain modulation; therapeutic target

Neuropathic pain can arise from disease or damage to the nervous system. The most common symptoms of neuropathic pain include spontaneous pain, allodynia, and hyperalgesia. There is still limited knowledge about the factors that initiate and maintain neuropathic pain. However, ample evidence has proved the antinociceptive role of spinal α-adrenoceptors following nerve injury. It is well-documented that noradrenergic descending pathways from supraspinal loci exert an inhibitory influence on the spinal cord nociceptive neurons, mostly through the activation of spinal α₂ -adrenoceptors. This, in turn, suppresses transmission of pain input and the hyperexcitability of spinal dorsal horn neurons. There is considerable evidence demonstrating that spinal application of α₂ -adrenoceptor agonists leads to analgesic effects in animal models of neuropathic pain. Today, despite the recent rapid development of neuroscience and drug discovery, effective drugs with clear basic mechanisms have remained a mystery. Here, we give an overview of the cellular mechanisms through which brainstem adrenergic descending inhibitory processing can alter spinal pain transmission to the higher centres, and how these pathways change in neuropathic pain conditions focusing on the role of spinal α₂ -adrenoceptors in the spinal dorsal horn. We then suggest that α₂ -adrenoceptor agonist may be useful to treat neuropathic pain. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

MicroRNA-142-3p relieves neuropathic pain by targeting high mobility group box 1

MicroRNA (miRNA) are emerging as critical regulators of neuropathic pain development. Neuroinflammation contributes to the development of neuropathic pain. miR‑142‑3p has been characterized as an inflammation‑related miRNA in various pathological processes. However, little is known about the role of miR‑142‑3p in neuroinflammation and neuropathic pain. The present study aimed to investigate the function of miR‑142‑3p in neuropathic pain by creating a murine model using spinal nerve ligation (SNL). A significant reduction in miR‑142‑3p expression was observed in the dorsal root ganglion of mice with SNL (P<0.05) compared with control mice. Overexpression of miR‑142‑3p significantly inhibited neuropathic pain and neuroinflammation in mice with SNL (P<0.05). High mobility group box 1 (HMGB1) was identified as a direct target gene of miR‑142‑3p by bioinformatic analysis and dual‑luciferase reporter assays. Overexpression of miR‑142‑3p significantly reduced the mRNA and protein expression levels of HMGB1 in vitro and in vivo (P<0.05). In addition, HMGB1 mRNA expression and miR‑142‑3p expression were inversely correlated in mice with SNL. Furthermore, overexpression of HMGB1 significantly reversed the inhibitory effect of miR‑142‑3p on neuroinflammation and neuropathic pain development (P<0.05). Overall, these results suggest that miR‑142‑3p functions as a negative regulator of neuropathic pain development through the downregulation of HMGB1, indicating that miR‑142‑3p may serve as a potential therapeutic target for neuropathic pain.

Role of Buffers in Protein Formulations

Buffers comprise an integral component of protein formulations. Not only do they function to regulate shifts in pH, they also can stabilize proteins by a variety of mechanisms. The ability of buffers to stabilize therapeutic proteins whether in liquid formulations, frozen solutions, or the solid state is highlighted in this review. Addition of buffers can result in increased conformational stability of proteins, whether by ligand binding or by an excluded solute mechanism. In addition, they can alter the colloidal stability of proteins and modulate interfacial damage. Buffers can also lead to destabilization of proteins, and the stability of buffers themselves is presented. Furthermore, the potential safety and toxicity issues of buffers are discussed, with a special emphasis on the influence of buffers on the perceived pain upon injection. Finally, the interaction of buffers with other excipients is examined.

Liposomal bupivacaine incisional injection in single-level lumbar spine surgery

BACKGROUND CONTEXT

Postsurgical pain control is important in spine surgery as it can lead to earlier mobilization, decreased length of stay, decreased side effects from narcotic medications, and improved patient satisfaction. Liposomal bupivacaine (LB) is an injectable formulation of bupivacaine, providing prolonged local anesthesia, up to 72 hours postinjection. Although, LB has been used with increasing frequency following other musculoskeletal procedures, specifically total joint replacements, its pre-emptive analgesic effect following lumbar microdiscectomy has hitherto not been reported. If administration of LB as a pre-emptive analgesic agent at the end of microdiscectomy resulted in reduced postoperative pain, then this could minimize adverse events related to narcotic pain medication use and improve acute clinical outcomes.

PURPOSE

The aim of the present study was to determine the comparative efficacy of infiltration of a standard dose and volume of LB in a comparative cohort analysis of single-level microdiscectomy procedures.

DESIGN

The present study made use of mixed prospective/retrospective observational cohort analysis.

PATIENT SAMPLE

Adult patients presenting with lumbar or sacral compressive disc disease treated with single-level microdiscectomy, at one institution utilizing a standard surgical technique.

OUTCOME MEASURES

Time spent on intravenous (IV) narcotics postoperatively (primary outcome), postoperative visual analog score (VAS), total morphine equivalent dose of narcotic pain medications, and 30-day emergency room visits for pain control were measured.

METHODS

Under an approved process improvement project, immediate outcome and process measures for a prospective cohort of 40 patients who received LB field blocks following single-level lumbar microdiscectomy were compared with a historical cohort of 40 patients who underwent the same surgical procedure but did not receive postsurgical infiltration of local anesthetic. All patients received a standard open surgical technique and postoperative convalescence protocol, which included overnight admission, oral narcotic pain medication as needed, scheduled IV ketorolac and IV narcotic pain medication for breakthrough.

RESULTS

Data from 80 subjects (67 males) operated on between January 2014 and 2015 were compared, including 40 cases, which occurred prior to using LB, and 40 cases after. There was no significant difference between mean age or body mass index (BMI) between groups. Patients who received LB infiltration spent significantly less time using IV narcotics in the postoperative period (LB patients 13.0±2.1 hours vs. non-LB patients 23.3±2.1 hours, p<.001). There was no significant difference noted between VAS at any point in the postoperative period, total injectable morphine equivalent doses, or 30-day emergency room visits for pain.

CONCLUSIONS

We found that patients who received LB field blocks required IV narcotic pain medication for a significantly decreased length of time (average delta=10.3 hours). Although this is a surrogate for earlier discharge, within the numbers studied, this did not translate into a significantdifference in VAS scores or total morphine equivalents. It is uncertain, if the independent effect of LB may have been masked by the multimodal postoperative pain control protocol in use. Further study is required to best understand the potential benefit of pre-emptive analgesia in elective spine surgery. Its impact would likely be more significant in more invasive procedures.

SOCS1 regulates neuropathic pain by inhibiting neuronal sensitization and glial activation in mouse spinal cord

Neuropathic pain is still a basic science and clinical challenge now, the neuronal sensitization and glial activation in the spinal cord (SC) level are more far-reaching for contributing to pain hypersensitivity following chronic constriction injury (CCI). Accumulating evidence indicates that astrocytes and microglia are activated in the spinal cord dorsal horn (SCDH) after CCI. Suppressor of cytokine signaling 1 (SOCS1) plays an important role in regulating of neuronal inflammation. Here, we investigated the role of SOCS1 in SC played in neuropathic pain. We find SOCS1 was persistently downregulated in the spinal neurons after CCI in mice. On the contrary, overexpression of SOCS1 in the SC reversed CCI-induced pain behavioral, activation of neurons, astrocytes, microglia, and the expression of proinflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β) and IL-6. Over all, these results demonstrate that downregulation of SOCS1 contributed to the development and maintenance of neuropathic pain via activating of neurons, astrocytes, microglia, and proinflammatory cytokines. SOCS1 may be developed into a potential target for treating neuropathic pain.

CE: Intrathecal Pumps for Managing Cancer Pain

: It is estimated that more than 1.6 million new cases of cancer were diagnosed in the United States in 2014. Among patients with cancer, moderate to severe pain is prevalent and can be refractory, even with the use of systemic opioids, which may cause adverse effects that are difficult to manage at the doses required to control pain. When delivered intrathecally, however, opioids and adjuvant analgesics may provide greater pain relief at dramatically lower doses and with fewer adverse effects. Although the use of intrathecal drug delivery systems for cancer pain management has increased dramatically over the past several years and is expected to continue growing, patients with intrathecal pumps often report interactions with nurses unfamiliar with the technology. This article provides an overview of intrathecal pump therapy and explains how it prolongs duration of action and improves the efficacy of certain analgesics while reducing their adverse effects. The author discusses the costs involved, the patients most likely to derive benefit, the types of pumps currently used in the United States, the medications that can be delivered intrathecally, the potential risks and complications associated with intrathecal therapy, and the nursing care required by patients who use an intrathecal pump.

Management of refractory pain in hospitalized adolescents with sickle cell disease: changing from intravenous opioids to continuous infusion epidural analgesia

BACKGROUND

Prolonged hospitalizations for sickle cell disease painful episodes are not uncommon, as analgesic options are often suboptimal.

OBSERVATIONS

Seven patients (15.4 ± 3.7 y, 6 females) were treated with epidural analgesia for refractory pain. The median duration of epidural catheter placement was 4 days (interquartile range, 3 to 6 d). Mean pain scores changed from 6.8 ± 2.7 to 4.8 ± 2.2, whereas mean daily parenteral opioid requirements changed from 79.7 ± 100.4 to 13.0 ± 13.1 mg of morphine equivalents.

CONCLUSION

Continuous epidural analgesia is an alternative to continuing intravenous opioids in sickle cell disease patients with refractory pain, and may reduce opioid-related side effects and facilitate transition to oral analgesics.

Mechanism of dorsal column stimulation to treat neuropathic but not nociceptive pain: analysis with a computational model

OBJECTIVE

Stimulation of axons within the dorsal columns of the human spinal cord has become a widely used therapy to treat refractory neuropathic pain. The mechanisms have yet to be fully elucidated and may even be contrary to standard "gate control theory." Our hypothesis is that a computational model provides a plausible description of the mechanism by which dorsal column stimulation (DCS) inhibits wide dynamic range (WDR) cell output in a neuropathic model but not in a nociceptive pain model.

MATERIALS AND METHODS

We created a computational model of the human spinal cord involving approximately 360,000 individual neurons and dendritic processing of some 60 million synapses--the most elaborate dynamic computational model of the human spinal cord to date. Neuropathic and nociceptive "pain" signals were created by activating topographically isolated regions of excitatory interneurons and high-threshold nociceptive fiber inputs, driving analogous regions of WDR neurons. Dorsal column fiber activity was then added at clinically relevant levels (e.g., Aβ firing rate between 0 and 110 Hz by using a 210-μsec pulse width, 50-150 Hz frequency, at 1-3 V amplitude).

RESULTS

Analysis of the nociceptive pain, neuropathic pain, and modulated circuits shows that, in contradiction to gate control theory, 1) nociceptive and neuropathic pain signaling must be distinct, and 2) DCS neuromodulation predominantly affects the neuropathic signal only, inhibiting centrally sensitized pathological neuron groups and ultimately the WDR pain transmission cells.

CONCLUSION

We offer a different set of necessary premises than gate control theory to explain neuropathic pain inhibition and the relative lack of nociceptive pain inhibition by using retrograde DCS. Hypotheses regarding not only the pain relief mechanisms of DCS were made but also regarding the circuitry of pain itself, both nociceptive and neuropathic. These hypotheses and further use of the model may lead to novel stimulation paradigms.

Liposomal bupivacaine and clinical outcomes

In the multimodal approach to the management of postoperative pain, local infiltration and regional blocks have been increasingly utilized for pain control. One of the limitations of local anesthetics in the postoperative setting is its relatively short duration of action. Multivesicular liposomes containing bupivacaine have been increasingly utilized for their increased duration of action. Compared with bupivacaine HCl, local infiltration of liposomal bupivacaine has shown to have an increase in duration of action and causes delay in peak plasma concentration. In this article, we attempt to review the clinical literature surrounding liposomal bupivacaine and its evolving role in perioperative analgesia. This new bupivacaine formation may have promising implications in postoperative pain control, resulting in increased patient satisfaction and a decrease in both hospital stay and opioid-induced adverse events (AEs). Although more studies are needed, the preliminary clinical trials suggest that liposomal bupivacaine has predictable pharmacokinetics, a similar side effect profile compared with bupivacaine HCl, and is effective in providing increased postoperative pain control.

Intrathecal drug administration in chronic pain syndromes

Chronic pain may recur after initial response to strong opioids in both patients with cancer and patients without cancer or therapy may be complicated by intolerable side effects. When minimally invasive interventional pain management techniques also fail to provide satisfactory pain relief, continuous intrathecal analgesic administration may be considered. Only 3 products have been officially approved for long-term intrathecal administration: morphine, baclofen, and ziconotide. The efficacy of intrathecal ziconotide for the management of patients with severe chronic refractory noncancer pain was illustrated in 3 placebo-controlled trials. A randomized study showed this treatment option to be effective over a short follow-up period for patients with pain due to cancer or AIDS. The efficacy of intrathecal opioid administration for the management of chronic noncancer pain is mainly derived from prospective and retrospective noncontrolled trials. The effect of intrathecal morphine administration in patients with pain due to cancer was compared with oral or transdermal treatment in a randomized controlled trial, which found better pain control and fewer side effects with intrathecal opioids. Other evidence is derived from cohort studies. Side effects of chronic intrathecal therapy may either be technical (catheter or pump malfunction) or biological (infection). The most troublesome complication is, however, the possibility of granuloma formation at the catheter tip that may induce neurological damage. Given limited studies, the evidence for intrathecal drug administration in patients suffering from cancer-related pain is more compelling than that of chronic noncancer pain.