Magnesium modifies fentanyl-induced local antinociception and hyperalgesia

Buprenorphine induced opioid withdrawal syndrome relieved by adjunctive Magnesium: A clinical trial

INTRODUCTION

Precipitated opioid withdrawal syndrome (OWS) is a severe and intolerable situation that may occur by a pharmaceutical agent. Reactivation of inhibited N-methyl-d-aspartate (NMDA) receptor in person with prolonged opioid use can led to severe OWS. We conducted a double-blind, randomized clinical trial to assess the effect of magnesium sulfate (MGSO4) as an NMDA receptor antagonist on OWS.

MATERIALS AND METHODS

The study randomly divided forty patients with precipitated OWS due to partial agonist (buprenorphine) use referred to the emergency unit of Toxicology Department of Mashhad University of Medical Sciences, Iran; into two groups. The control group received conventional therapies, including clonidine 0.1 mg tablet each hour, intravenous infusion of 10 mg diazepam every 30 min, and IV paracetamol (Acetaminophen) 1 g, while the intervention group received 3 g of MGSO4 in 20 min and then 10 mg/kg/h up to 2 h, in addition to the conventional treatment. The clinical opiate withdrawal scale (COWS) evaluated OWS at the start of the treatment, 30 min, and 2 h later.

RESULTS

Both groups had similar demographic, opiate types, and COWS severity at the start of the intervention. COWS was lower in the intervention than the control group at 30 min (11.20 ± 2.86 and 14.65 ± 2.36, respectively, P = 0.002) and at 2 h (3.2 ± 1.61 and 11.25 ± 3.27, respectively, P < 0.001) after treatment. The intervention group received lesser doses of clonidine (0.12 ± 0.51 and 0.17 ± 0.45 mg, P = 0.003) and Diazepam (13.50 ± 5.87, 24.0 ± 6.80 mg, P = 0.001) than the control group. Serum magnesium levels raised from 1.71 ± 0.13 mmol/L to 2.73 ± 0.13 mmol/L in the intervention group.

CONCLUSION

Magnesium can significantly reduce the severity of OWS. Additional studies are required to confirm these results.

Analysis of Ionomic Profiles of Spinal Cords in a Rat Model with Bone Cancer Pain

Background

Ionomics is used to study levels of ionome in different states of organisms and their correlations. Bone cancer pain (BCP) severely reduces quality of life of patients or their lifespan. However, the relationship between BCP and ionome remains unclear.

Methods

The BCP rat model was constructed through inoculation of Walker 256 cells into the left tibia. Von Frey test, whole-cell patch-clamp recording and inductively coupled plasma mass spectrometry (ICP-MS) technologies were conducted for measuring tactile hypersensitivity, the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) of neurons of spinal slices, and ionome of spinal cord samples, respectively. Principal component analysis (PCA) was used to explore ionomic patterns of the spinal cord.

Results

The BCP rat model was successfully constructed through implantation of Walker 256 cells into the left tibia. The frequency and amplitude of mEPSCs of neurons in the spinal cord slices from the BCP model rats were notably greater than those in the sham control. In terms of ionomics, the spinal cord levels of two macroelements (Ca and S), four microelements (Fe, Mn, Li and Sr) and the toxic element Ti in the BCP group of rats were significantly increased by inoculation of Walker 256 cancer cells, compared to the sham control. In addition, the correlation patterns between the elements were greatly changed between the sham control and BCP groups. PCA showed that inoculation of Walker 256 cells into the tibia altered the overall ionomic profiles of the spinal cord. There was a significant separation trend between the two groups.

Conclusion

Taken together, inoculation of Walker 256 cells into the left tibia contributes to BCP, which could be closely correlated by some elements. The findings provided novel information on the relationship between the ionome and BCP.

A single dose of ketamine relieves fentanyl-induced-hyperalgesia by reducing inflammation initiated by the TLR4/NF-κB pathway in rat spinal cord neurons

A large amount of clinical evidence has revealed that ketamine can relieve fentanyl-induced hyperalgesia. However, the underlying mechanism is still unclear. In the current study, a single dose of ketamine (5 mg/kg or 10 mg/kg), TAK-242 (3 mg/kg), or saline was intraperitoneally injected into rats 15 min before four subcutaneous injections of fentanyl. Results revealed that pre-administration of ketamine alleviated fentanyl-induced hyperalgesia according to hind paw-pressure and paw-withdrawal tests. High-dose ketamine can reverse the expression of toll-like receptor-dimer (d-TLR4), phospho- nuclear factor kappa-B (p-NF-κB, p-p65), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) 1 d after fentanyl injection in the spinal cord. Moreover, fentany-linduced-hyperalgesia and changes in the expression of the aforementioned proteins can be attenuated by TAK-242, an inhibitor of TLR4, as well as ketamine. Importantly, TLR4, p-p65, COX-2, and IL-1β were expressed in neurons but not in glial cells in the spinal cord 1 d after fentanyl injection. In conclusion, results suggested that a single dose of ketamine can relieve fentanyl-induced-hyperalgesia via the TLR4/NF-κB pathway in spinal cord neurons.

Pharmacological Interventions for Opioid-Induced Hyperalgesia: A Scoping Review of Preclinical Trials

BACKGROUND

Opioid analgesics are the most effective pharmacological agents for moderate and severe pain. However, opioid use has several limitations such as opioid-induced hyperalgesia (OIH), which refers to the increased pain sensitivity that occurs once analgesia wears off after opioid administration. Several pharmacological interventions have been suggested for OIH, but the current literature does not provide guidelines on which interventions are the most effective and whether they differ depending on the opioid that induces hyperalgesia. This scoping review aimed to identify and describe all the preclinical trials investigating pharmacological interventions for OIH caused by remifentanil, fentanyl, or morphine as the first step towards evaluating whether the most effective OIH interventions are different for different opioids.

METHODS

Electronic database searches were carried out in Embase, PubMed, and Web of Science. Detailed data extraction was conducted on the eligible trials.

RESULTS

72 trials were eligible for the review. Of these, 27 trials investigated remifentanil, 14 trials investigated fentanyl, and 31 trials investigated morphine. A total of 82 interventions were identified. The most studied interventions were ketamine (eight trials) and gabapentin (four trials). The majority of the interventions were studied in only one trial. The most common mechanism suggested for the interventions was inhibition of N-methyl-D-aspartate (NMDA) receptors.

CONCLUSION

This scoping review identified plenty of preclinical trials investigating pharmacological interventions for OIH. Using the current literature, it is not possible to directly compare the effectiveness of the interventions. Hence, to identify the most effective interventions for each opioid, the interventions must be indirectly compared in a meta-analysis.

Intravenous Magnesium - Lidocaine - Ketorolac Cocktail for Postoperative Opioid Resistant Pain: A Case Series of Novel Rescue Therapy

BACKGROUND

Severe postoperative pain is principally managed by opioids. While effective, opioids do not provide adequate relief in many patients and cause many side effects, including antinociceptive tolerance and opioid-induced hyperalgesia. To evaluate if a combination of intravenous Magnesium, Lidocaine, Ketorolac (MLK cocktail) is a useful rescue therapy through synergistic pharmacological mechanisms for acute pain relief. We present the intravenous combination of magnesium, lidocaine, and ketorolac (MLK cocktail) as a possible rescue for opioid insensitive severe post-operative pain.

MATERIALS AND METHODS

The principal settings were the post-operative care unit (PACU) and the surgical ward. We retrospectively analyzed the electronic medical record and anesthesia documents of 14 patients experiencing severe postoperative pain, >7/10 visual-analogue pain score (VAS), despite receiving at least 8 mg of intravenous morphine milligram equivalents (MME) after arrival in the LAC+USC Medical Center PACU between September 2012 and January 2013. The data reviewed included patients' demographics, disease etiology, surgical procedure, opioids received perioperatively, and visual-analogue pain scores before and after each analgesic received, and after the MLK cocktail. The a priori primary outcome and a posteriori secondary outcome of this study are mean visual-analogue pain score and morphine milligram equivalent dose administered per hour, respectively. The main tool evaluated has been VAS score.

RESULTS

In patients who failed to respond to opioid analgesics, administration of the MLK cocktail improved the VAS pain scores immediately from 9.4 ± 1.0 to 3.6 ± 3.5. The MLK cocktail also decreased the MME doses/hour in the immediate 12 hours postoperative period from 12.4 ± 5.6 to 1.1 ± 0.9.

CONCLUSION

In patients experiencing opioid-resistant severe postoperative pain, the magnesium, lidocaine, and ketorolac combination may be an effective nonopioid rescue therapy. Additionally, magnesium, lidocaine, and ketorolac may be utilized in cases complicated by either antinociceptive tolerance or opioid-induced hyperalgesia and can restore opioid responsiveness.

Magnesium sulphate attenuate remifentanil-induced postoperative hyperalgesia via regulating tyrosine phosphorylation of the NR2B subunit of the NMDA receptor in the spinal cord

BACKGROUND

Remifentanil induced hyperalgesia (RIH) is characterized by stimulation evoked pain including allodynia and thermal hyperalgesia after remifentanil infusion. N-methyl-D-aspartate (NMDA) receptor was reported to be involved in the progress of RIH. We hypothesized that intrathecal MgSO₄ could relieve hyperalgesia after remifentanil infusion via regulating phosphorylation of NMDA receptor NR₂B subunit activity in this study.

METHODS

Thirty two rats were randomly allocated into control group, model of RIH group, RIH plus 100ug MgSO₄ group, RIH plus 300ug MgSO₄ group. Mechanical and thermal hyperalgesia were tested at -24^th h, 2^nd h, 6^th h, 24^th h, 48^th h after remifentanil infusion. Following sacrifice of rats after the last behavioral test, we performed the western blot to detect the expression of spinal phosphorylated NMDA receptor NR₂B subunit (pNR₂B) in the L₄-L₅ segments.

RESULTS

Intrathecal MgSO₄ (100, 300 μg) dose-dependently reduced thermal and mechanical hyperalgesia from 2 h to 48 h after remifentanil infusion. Remifentanil infusion remarkably stimulated the expression of pNR₂B. Nevertheless, the increased amount of pNR₂B by RIH was dose-dependently suppressed by intrathecal infusion of MgSO₄ in rats.

CONCLUSIONS

Remifentanil induced hyperalgesia/allodynia could be ameliorated by Mg-mediated blockade targeting the NR₂B subunit in NMDA receptors.

A comparison of intrathecal magnesium and ketamine in attenuating remifentanil-induced hyperalgesia in rats

Background

Activation of NMDA receptors play an important role in the development of remifentanil-induced hyperalgesia. We hypothesized that in addition to ketamine, intrathecal MgSO₄ could also relieve thermal and mechanical hyperalgesia in rats.

Methods

Initially, 24 Sprague–Dawley rats were divided into control group, remifentanil group, surgical incision group and remifentanil combined with surgical incision group to create an experimental model. Subsequently, 40 rats were divided into control group, model group, model group plus 100 μg MgSO₄, 300 μg MgSO₄ and 10 μg ketamine respectively. Paw withdrawal mechanical thresholds and paw withdrawal thermal latency tests were performed at −24 h, 2 h, 6 h, 24 h, 48 h, 72 h and 7 day after the surgical procedure. After behavior assessment on the 7th day, remifentanil was given again to ascertain whether or not NMDA antagonists could suppress the re-exposure of remifentanil-induced hyperalgesia.

Results

Remifentanil administration plus surgical incision induced significant postoperative hyperalgesia, as indicated by decreased paw withdrawal mechanical thresholds and paw withdrawal thermal latency to mechanical and thermal stimulation. In addition to ketamine, intrathecal MgSO₄ (100, 300 μg) dose-dependently reduced remifentanil-induced mechanical and thermal hyperalgesia. Ketamine had less mechanical hyperalgesia in 6 h (p = 0.018), 24 h (p = 0.014) and 48 h (p = 0.011) than 300 μg MgSO₄. There was no difference in inhibiting thermal hyperalgesia between the group ketamine and group MgSO₄ (300 μg). The rats were given remifentanil again 7 days later after the first exposure of remifentanil. The hyperalgesic effect induced by re-exposure of remifentanil was not reversed in any groups of MgSO₄ or ketamine.

Conclusions

In addition to ketamine, intrathecal administration of MgSO₄ dose-dependently reduced remifentanil-induced hyperalgesia in a surgical incision mode. Re-exposure to remifentanil 1 week later again produced hyperalgesia, and this was not altered by the prior intrathecal treatments in any 4 groups treated with MgSO₄ or ketamine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-016-0235-9) contains supplementary material, which is available to authorized users.

Opioid withdrawal increases transient receptor potential vanilloid 1 activity in a protein kinase A-dependent manner

Hyperalgesia is a cardinal symptom of opioid withdrawal. The transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated ion channel expressed on sensory neurons responding to noxious heat, protons, and chemical stimuli such as capsaicin. TRPV1 can be inhibited via μ-opioid receptor (MOR)-mediated reduced activity of adenylyl cyclases (ACs) and decreased cyclic adenosine monophosphate (cAMP) levels. In contrast, opioid withdrawal following chronic activation of MOR uncovers AC superactivation and subsequent increases in cAMP and protein kinase A (PKA) activity. Here we investigated (1) whether an increase in cAMP during opioid withdrawal increases the activity of TRPV1 and (2) how opioid withdrawal modulates capsaicin-induced nocifensive behavior in rats. We applied whole-cell patch clamp, microfluorimetry, cAMP assays, radioligand binding, site-directed mutagenesis, and behavioral experiments. Opioid withdrawal significantly increased cAMP levels and capsaicin-induced TRPV1 activity in both transfected human embryonic kidney 293 cells and dissociated dorsal root ganglion (DRG) neurons. Inhibition of AC and PKA, as well as mutations of the PKA phosphorylation sites threonine 144 and serine 774, prevented the enhanced TRPV1 activity. Finally, capsaicin-induced nocifensive behavior was increased during opioid withdrawal in vivo. In summary, our results demonstrate an increased activity of TRPV1 in DRG neurons as a new mechanism contributing to opioid withdrawal-induced hyperalgesia.

Medication-overuse headache and opioid-induced hyperalgesia: A review of mechanisms, a neuroimmune hypothesis and a novel approach to treatment

Introduction

Patients with chronic headache who consume large amounts of analgesics are often encountered in clinical practice. Excessive intake of analgesics is now considered to be a cause, rather than simply a consequence, of frequent headaches, and as such the diagnosis “medication-overuse headache” (MOH) has been formulated. Despite the prevalence and clinical impact of MOH, the pathophysiology behind this disorder remains unclear and specific mechanism-based treatment options are lacking.

Discussion

Although most acute headache treatments have been alleged to cause MOH, here we conclude from the literature that opioids are a particularly problematic drug class consistently associated with worsening headache. MOH may not be a single entity, as each class of drug implicated may cause MOH via a different mechanism. Recent evidence indicates that chronic opioid administration may exacerbate pain in the long term by activating toll-like receptor-4 on glial cells, resulting in a pro-inflammatory state that manifests clinically as increased pain. Thus, from the available evidence it seems opioid-overuse headache is a phenomenon similar to opioid-induced hyperalgesia, which derives from a cumulative interaction between central sensitisation, due to repeated activation of nociceptive pathways by recurrent headaches, and pain facilitation due to glial activation.

Conclusion

Treatment strategies directed at inhibiting glial activation may be of benefit alongside medication withdrawal in the management of MOH.

Comparison of actions of systemically and locally administrated local anaesthetics in diabetic rats with painful neuropathy

Nothing is known about actions of levobupivacaine, a long-acting local anaesthetic belonging to the amino amide group, in diabetes-induced neuropathic pain conditions. In this study, we therefore investigated the possible antihyperalgesic and antiallodynic effects of levobupivacaine in diabetic animal model. Actions of systemically (intraperitoneal) or locally (intraplantar) administrated levobupivacaine on streptozotocin-induced diabetic rats with painful neuropathy were examined using a thermal plantar test and a dynamic plantar aesthesiometer. Effects of levobupivacaine were compared with those of a well-known amide local anaesthetic lidocaine. Levobupivacaine was more potent than lidocaine in all tests employed on diabetic rats. After intraperitoneal injections to diabetic rats, levobupivacaine, but not lidocaine, produced pronounced antihyperalgesic and antiallodynic effects. However, intraplantar administration of both levobupivacaine and lidocaine produced antihyperalgesic and antiallodynic action in diabetic rats. In contrast to the transient effects of lidocaine (30 min), antihyperalgesic and antiallodynic actions of levobupivacaine gradually disappeared within 120 min after intraplantar injections. Intraperitoneal or intraplantar administrations of levobupivacaine or lidocaine at the effective dose had no effect on any parameters in intact rats. Findings revealed that antiallodynic and antihyperalgesic potency of levobupivacaine was higher in comparison with that of lidocaine after their intraperitoneal or intraplantar administration to diabetic animals. Furthermore, locally administrated levobupivacaine has the greatest antihyperalgesic and antiallodynic actions in diabetic rats.

Opioid-induced hyperalgesia: clinically relevant or extraneous research phenomenon?

Opioids have become the unequivocal therapy of choice in treating many varieties of chronic pain. With the increased prescription of opioids, some unintended consequences have occurred. After prolonged opioid exposure, opioid-induced hyperalgesia (OIH), the paradoxical effect that opioid therapy may in fact enhance or aggravate preexisting pain, may occur. Over the past several decades, an increasing number of laboratory and clinical reports have suggested lowered pain thresholds and heightened atypical pain unrelated to the original perceived pain sensations as hallmarks of OIH. However, not all evidence supports the clinical importance of OIH, and some question whether the phenomenon exists at all. Here, we present a nonexhaustive, brief review of the recent literature. OIH will be reviewed in terms of preclinical and clinical evidence for and against its existence; recommendations for clinical evaluation and intervention also will be discussed.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).