Pulsed electromagnetic fields (PEMF) as a valid tool in orthognathic surgery to reduce post-operative pain and swelling: a prospective study

PURPOSE

PEMF (pulsed electromagnetic fields) founds application in several medical fields to accelerate bone wounds healing and to reduce inflammation. The aim of our study was to evaluate the effectiveness of PEMF in reducing postoperative swelling and pain in patients undergoing orthognathic surgery.

METHODS

A prospective observational monocentric study was conducted on a sample of 30 patients undergone to orthognathic surgery in Maxillofacial Surgery Unit of University of Naples Federico II. The patients who followed these inclusion criteria were enrolled in the study: age ≥ 18 years, Class III malocclusion, Surgical procedure of Le Fort I osteotomy + Bilateral Sagittal Split Osteotomy (BSSO), Written informed consent. Patients were divided into two groups: Group SD) postoperative standard treatment with medical therapy and cryotherapy, Group SD + PEMF) postoperative standard therapy + PEMF. Each patient underwent a 3D facial scan, at one (1d) and four (4d) days after surgery to compare the swelling reduction. The pain score was assessed through VAS score and analgesics administration amount.

RESULTS

In SD + PEMF group, the facial volume reduction between 1d and 4d scan was on average 56.2 ml (6.23%), while in SD group, it was 23.6 ml (2.63%). The difference between the two groups was 3.6% (p = 0.0168). VAS pain values were significantly higher in SD group compared to SD + PEMF group in the second day after surgery (P = 0.021) and in the total 4 days (P = 0.008).

CONCLUSIONS

Our data suggest that PEMF is valid tool to promote faster postoperative swelling and pain reduction in patients undergoing orthognathic surgery.

Modelled cost-effectiveness analysis of the Support and Treatment After Replacement (STAR) care pathway for chronic pain after total knee replacement compared with usual care

BACKGROUND

The aim of the study was to estimate the long-term cost-effectiveness of the Support and Treatment After Replacement (STAR) care pathway for chronic pain after total knee replacement compared with usual postoperative care.

METHODS

Study design: A decision-analytic (cohort Markov) model was used for the simulation with time dependent annual transition probabilities and a time horizon of five years.

SETTING

Patients treated by National Health Service (NHS) hospitals in England and Wales.

STUDY POPULATION

Adults classified as having chronic pain three months after undergoing a total knee replacement.

INTERVENTION

The STAR care pathway following a total knee replacement.

COMPARATOR

Usual postoperative care following a total knee replacement.

PERSPECTIVE

The study was undertaken from the perspective of the NHS.

OUTCOME MEASURES

Quality-adjusted life years and healthcare costs. Discounting: A rate of 3.5% for both costs and health utility.

RESULTS

Model results indicate that the STAR intervention would dominate current practice by providing a gain in quality-adjusted life years (QALYs) of 0.086 and a reduction of £375 (per person) in costs over the first five years. The incremental net monetary benefit of the STAR intervention was estimated at £2,086 (at a threshold of £20,000 per QALY). Probabilistic sensitivity analysis suggests the STAR intervention is likely to be cost-effective with a probability of 0.62. The results remain robust to changes in model assumptions on comparator utility and the timing of the start of the intervention. If hospital admission costs are assumed not to be reduced by the STAR intervention, it would no longer be cost saving, but it would likely be cost-effective based on probabilistic sensitivity analysis (0.59).

CONCLUSION

Evidence from the economic model suggests that the STAR care pathway is likely to be cost-effective and potentially dominant from an NHS perspective.

TRIAL REGISTRATION

The STAR trial is registered with ISRCTN, ISRCTN92545361.

Chronic pain patients and time to sustained acceptable pain scores after major surgery - A retrospective registry analysis

STUDY OBJECTIVE

We tested the hypothesis that pre-existing chronic pain is associated with prolonged time to reach sustained acceptable pain scores after major surgery.

DESIGN

Retrospective study using the German Network for Safety in Regional Anaesthesia and Acute Pain Therapy registry.

SETTING

Operating rooms and surgical wards.

PATIENTS

107,412 patients recovering from major surgery who were cared for by an acute pain service. 3.3% of the treatments were in patients who reported chronic pain with functional or psychological impairment.

INTERVENTIONS AND MEASUREMENT

We compared time to sustained adequacy of postoperative pain control defined by numeric rating scores <4 at rest and with movement in patients with and without chronic pain using an adjusted cox proportional hazard regression model and Kaplan-Meier analysis. The observation period was censored at 10 days and propensity score matching was used as a sensitivity analysis.

MAIN RESULTS

Postoperative pain at rest took significantly longer to resolve in patients with chronic pain than in those without (adjusted hazard ratio HR 1.42, 95% CI 1.36-1.49, P < 0.001). Postoperative pain with movement took even longer to resolve in patients with chronic pain (adjusted HR 1.65, 95%CI 1.56-1.75, P < 0.001).

CONCLUSIONS

Patients with chronic pain sustain more surgical pain than those without, and the pain takes longer to resolve. Clinicians providing postoperative pain management should consider the special needs of chronic pain patients.

Comparison of preemptive etoricoxib and dexamethasone in third molar surgery - a randomized controlled clinical trial of patient-reported and clinical outcomes

OBJECTIVES

To compare preemptive single-dose etoricoxib and dexamethasone on postoperative patient satisfaction (pPS) and clinical parameters following the impacted mandibular third molar (IMTM) extraction.

MATERIALS AND METHODS

A parallel-group, triple-blinded, controlled clinical study included a total of 90 patients (n = 30), randomized to receive: etoricoxib 90 mg, dexamethasone 4 mg, or no premedication (control group) 1 h before surgery. Paracetamol 500 mg was prescribed as rescue medication (RM). Check-ups were scheduled at 24 h, 48 h, and day 7 post-surgery. At each time point, pPS was assessed using the 5-point Likert scale. RM parameters, swelling, trismus, and the occurrence of adverse events were also recorded, and patients were instructed to rate the perceived pain on Visual Analogue Scale.

RESULTS

In all the follow-up periods, data indicated significantly higher pPS scores in the preemptive medication groups when compared to the control group (p < 0.05). Both regimens delayed the first RM intake when compared to controls. In the etoricoxib group, a significantly lower total RM consumption was observed (p < 0.05). Dexamethasone significantly decreased swelling at each check-up and increased mouth opening at day 7 after the surgery (p < 0.05).

CONCLUSIONS

Preemptive etoricoxib and dexamethasone elevate pPS after IMTM surgery. Etoricoxib improves RM parameters, while dexamethasone ameliorates the patient's postoperative functional ability.

CLINICAL RELEVANCE

Preemptive etoricoxib and dexamethasone use may decrease patients' discomfort following the impacted mandibular third molar extraction.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05791721. Date of Registration: 28/03/2023 (retrospectively registered).

Treatment of Acute Pain in Patients on Naltrexone: A Narrative Review

PURPOSE OF REVIEW

The tissue damage and trauma associated with surgery almost always result in acute postoperative pain. The intensity of postoperative pain can range from mild to severe. Naltrexone is suitable for patients who do not wish to be on an agonist treatment such as methadone or buprenorphine. However, naltrexone has been shown to complicate postoperative pain management.

RECENT FINDINGS

Multiple studies have found that the use of naltrexone can increase the opioid requirement for postoperative pain control. Other modalities exist that can help outside of opioids such as ketamine, lidocaine/bupivacaine, duloxetine, and non-pharmacological management can help manage pain. Multimodal pain regiments should also be employed in patients. In addition to traditional methods for postoperative pain management, other methods of acute pain control exist that can help mitigate opioid dependence and help control pain in patients who use naltrexone for their substance use disorders.

Improving well-being for individuals with persistent pain after surgery for breast cancer, lobular carcinoma in situ, or ductal carcinoma in situ: A randomized clinical trial

>276,000 Americans will be diagnosed with invasive breast cancer, lobular carcinoma in situ, or ductal carcinoma in situ this year and most will undergo breast surgery as part of their care. Although prognosis is excellent, many patients experience persistent post-surgical pain (PSP), which has no satisfactory pharmacological treatment. The causal contributions of pain-associated psychological factors (e.g., catastrophic thoughts about pain, psychological flexibility, self-efficacy) to the continuing burden of PSP have not yet been determined and may be opportune intervention targets. The randomized trial described here will compare the benefits of three manualized behavioral interventions for individuals with PSP. Participants will receive either: 1) self-guided health education (SGHE); 2) interventionist-guided health education (IGHE); or 3) interventionist-guided pain coping skills training with elements of acceptance and commitment therapy that specially target catastrophic thoughts about pain, self-efficacy, and psychological flexibility (CST-PSP). Participants will prospectively complete validated assessments of primary outcomes (PSP severity and interference) at baseline (pre-intervention) and 3-, 6-, and 12-months later. Validated measures of emotional distress and cancer-specific distress will be assessed as secondary outcomes. To test their roles as drivers of PSP, catastrophic thoughts about pain, self-efficacy, and psychological flexibility, will be assessed and statistically analyzed as mediators of hypothesized beneficial effects. The interventions' impacts on pain sensitivity and central sensitization will be investigated to test these physiological pathways as proximal drivers of PSP. To better characterize the patient experience, additional validated measures will be explored for associations with PSP, along with demographic and clinical factors. Trial registration: https://clinicaltrials.gov/ct2/show/NCT04225585, registered January 13, 2020.

The effectiveness of battlefield acupuncture in addition to standard physical therapy treatment after shoulder surgery: a protocol for a randomized clinical trial

INTRODUCTION

There is a large incidence of shoulder instability among active young athletes and military personnel. Shoulder stabilization surgery is the commonly employed intervention for treating individuals with instability. Following surgery, a substantial proportion of individuals experience acute post-operative pain, which is usually managed with opioid pain medications. Unfortunately, the extended use of opioid medications can have adverse effects that impair function and reduce military operational readiness, but there are currently few alternatives. However, battlefield acupuncture (BFA) is a minimally invasive therapy demonstrating promise as a non-pharmaceutical intervention for managing acute post-operative pain.

METHODS

This is a parallel, two-arm, single-blind randomized clinical trial. The two independent variables are intervention (2 levels, standard physical therapy and standard physical therapy plus battlefield acupuncture) and time (5 levels, 24 h, 48 h, 72 h, 1 week, and 4 weeks post shoulder stabilization surgery). The primary dependent variables are worst and average pain as measured on the visual analog scale. Secondary outcomes include medication usage, Profile of Mood States, and Global Rating of Change.

DISCUSSION

The magnitude of the effect of BFA is uncertain; current studies report confidence intervals of between-group differences that include minimal clinically important differences between intervention and control groups. The results of this study may help determine if BFA is an effective adjunct to physical therapy in reducing pain and opioid usage in acute pain conditions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04094246 . Registered on 16 September 2019.

Sensory profiles in women with neuropathic pain after breast cancer surgery

Purpose

We performed a detailed analysis of sensory function in patients with chronic post-surgical neuropathic pain (NP) after breast cancer treatments by quantitative sensory testing (QST) with DFNS (German Research Network on Neuropathic Pain) protocol and bed side examination (BE). The nature of sensory changes in peripheral NP may reflect distinct pathophysiological backgrounds that can guide the treatment choices. NP with sensory gain (i.e., hyperesthesia, hyperalgesia, allodynia) has been shown to respond to Na⁺-channel blockers (e.g., oxcarbazepine).

Methods

104 patients with at least “probable” NP in the surgical area were included. All patients had been treated for breast cancer 4–9 years ago and the handling of the intercostobrachial nerve (ICBN) was verified by the surgeon. QST was conducted at the site of NP in the surgical or nearby area and the corresponding contralateral area. BE covered the upper body and sensory abnormalities were marked on body maps and digitalized for area calculation. The outcomes of BE and QST were compared to assess the value of QST in the sensory examination of this patient group.

Results

Loss of function in both small and large fibers was a prominent feature in QST in the area of post-surgical NP. QST profiles did not differ between spared and resected ICBN. In BE, hypoesthesia on multiple modalities was highly prevalent. The presence of sensory gain in BE was associated with more intense pain.

Conclusions

Extensive sensory loss is characteristic for chronic post-surgical NP several years after treatment for breast cancer. These patients are unlikely to respond to Na⁺-channel blockers.

Perception of pain in post-surgical patients in intensive care units

INTRODUCTION

Pain assessment and treatment are essential for ensuring quality of care as well as for improving patient's satisfaction and clinical outcomes.

OBJECTIVES

1) To describe pain perception of surgical patients admitted to our Intensive Care Unit(ICU). 2) To compare the patients' pain perception with the assessment carried out by nurses. 3) To correlate International Pain Outcomes Questionnaire results with socio-demographical data.

METHODOLOGY

A prospective descriptive observational study was carried out in the ICU of a third level university hospital over a period of 3 months. Surgical patients' pain-perception was assessed 24hours after their admission to the ICU using the Spanish translation of International Pain Outcomes Questionnaire.

RESULTS

The highest pain score recorded among 109 patients by nurses was 4.47±2.75, while, the lowest was .69±1,25. However, the highest and lowest pain scores reported by patients were 5.59±2.72 and 2.13±2.03, which showed significant differences (P <0.001). The highest pain score seemed to be related to the type of surgery (P <0.027). There are significant variations in the lowest pain score depending on age (P=0.005 r=-0.270). Likewise, the worst pain score correlated with the patients' sex (P=0.004). Patients who reported that pain made them feel very anxious or helpless scored highest with the worst pain, 7.35±1.98, 7.44±1.85 respectively. These differences were statistically significant (P=0.001, P <0.001). Regarding to the score of less pain, there is an association with feeling anxiety (P=0.032) and not with feeling helpless (P=-0.088).

CONCLUSIONS

The post-surgical patients reported pain during the first 24hours following admission to ICU (max score 5.59±.26). The nurses underestimated the patients' reported pain. Improving nurses' education would provide them with assessment strategies for better pain management. Age, sex, anxiety and helplessness caused by pain, were variables that significantly influenced pain.

Comparison of intradermal Dexmedmotidine and subcutaneous Ketamine for post-surgical pain management in patients with abdominal hysterectomy

Hysterectomy after cesarean section is the second most commonly used surgery for women in the United States. One of the most common problem after hysterectomy is pain. We decided to compare the effects of dexmedmotidine or ketamine on pain in patients by a double blind randomized clinical trial on 126 female candidates for abdominal hysterectomy in three groups of 42 persons referred to Taleghani hospital in Arak. For the first group, 50 micrograms of intradermal dexmedmotidine were injected, while in the second group, patients were injected with 100 mg of subcutaneous ketamine and the third group received 5 cc normal saline. Data were next analyzed by SPSS version 19. The mean age and body mass index of the patients were not significantly different in the three groups. The mean scores of pain during recovery of patients in ketamine, dexmedmotidine and placebo groups were 4.2±0.77, 2.6±0.89 and 1.3±0.87, respectively (p = 0.001). Scores of pain in patients at 4 and 8 hours after surgery showed also significant differences. In conclusion, ketamine and dexmedmotidine significantly reduce the severity of pain, but ketamine has a lower effect.

Association of G472A allele of membrane bound catechol-O-methyltransferase gene with chronic post-sternotomy pain

Chronic persistent surgical pain (CPSP) is a complex disease with strong genetic component. The studies on revealed association of mutations in membrane bound catechol-O-methyltransferase gene with CPSP were reported indifferent ethnic populations across the globe. We identify that one out of four patients who underwent sternotomy procedure showed CPSP even after 3 months of surgery. The Mb.COMT gene sequence analysis revealed of the four patients, three patients had no mutation in Mb.COMT gene, while in one patient exhibited G472A mutation. Interestingly, this patient showed CPSP even after 90 days of surgery. The magnitude of the CPSP was evaluated with pain questionnaires' at the end of 3 months after discharge from the hospital. In this study 25% (1/4) showed presence G472A allele correlating with CPSP. Further the study suggested that evaluation of G472A allele of Mb.COMT gene in the patients undergoing sternotomy for monitoring pain in pre and post-surgical events.

Improved Outcomes Associated With the Use of Intravenous Acetaminophen for Management of Acute Post-Surgical Pain in Cesarean Sections and Hysterectomies

Background

Post-surgical pain impacts many patient outcomes. Effective pain management increasingly relies on multimodal analgesia regimens in which acetaminophen (APAP) is a key component. The aim of our study was to examine the impact of oral APAP versus intravenous (IV) APAP as a component of post-surgical pain management after Cesarean sections and hysterectomies.

Methods

A retrospective analysis of the Cerner HealthFacts® database (from January, 2011 to December, 2015) was conducted to compare outcomes of Cesarean section and hysterectomy surgery patients who received oral APAP to those who received IV APAP post-surgically. Length of stay (LOS), daily morphine milligram equivalent (MME) consumption, the presence of potential opioid-related adverse events (ORADEs), and total pharmacy costs were assessed. Adjusted results were derived using inverse probability weighted regression adjustment (IPW-RA) estimators based on covariates that included demographics, comorbidities, patient clinical characteristics, and hospital characteristics.

Results

The study identified 29,124 Cesarean section patients (24,612 oral APAP; 4,512 IV APAP) and 9,767 hysterectomy surgery patients (5,586 oral APAP; 4,181 IV APAP). Compared to the oral APAP group, the IV APAP group had reductions in adjusted LOS (Cesarean section: -11.7% days (P < 0.001), hysterectomy: -11.8% days (P = 0.005)), lowered adjusted daily MME consumption from day 0 to day 3 (Cesarean section: -1.6 mg (P < 0.001), hysterectomy: -1.7 mg (P = 0.014)), and reduced risk of ORADEs for Cesarean sections (relative risk of 0.45, P < 0.001). Total pharmacy costs were not significantly different between the two APAP groups.

Conclusions

Post-surgical pain managed with IV APAP in patients undergoing Cesarean section or hysterectomy was associated with shorter LOS, reduced risk of ORADEs, and lower opioid consumption compared to patients managed with oral APAP, without adversely impacting total pharmacy costs.

Pre-surgery beliefs about pain and surgery as predictors of acute and chronic post-surgical pain: A prospective cohort study

BACKGROUND

Chronic pain post-surgical pain (CPSP) is common and has far-reaching negative consequences for patients, yet relatively few studies have evaluated the impact of both deficit- and resource-based beliefs about pain and surgery on subjective intensities of acute and chronic post-surgical pain. To address this issue a prospective cohort study was performed.

METHOD

259 consecutive surgery patients from general surgery, gynecology, and thoracic departments completed a self-report battery of demographics, pain experiences, and psychological factors 24 h before surgery (T1) and provided follow-up pain intensity ratings 48 h-72 h after surgery (T2), and at a 4-month follow-up (T3).

RESULTS

In the hierarchical regression model for acute post-operative pain intensity, pre-surgery pain self-efficacy beliefs made a significant unique contribution independent of all other pre-surgery and surgery-related factors (i.e., age, presence of pre-surgical pain, type of anesthesia, surgery duration). In the prediction model for intensity of chronic post-surgical pain, beliefs about long-term effects of surgery had a unique impact after controlling other significant pre-surgery and surgery influences (gender, education, surgery time).

CONCLUSION

Results underscored the potential utility of considering specific pre-surgery pain- and surgery-related beliefs as factors that predict patient experiences of acute and chronic post-operative pain.

Associations between genetic and epigenetic variations in cytokine genes and mild persistent breast pain in women following breast cancer surgery

Persistent pain following breast cancer surgery is a significant problem. Both inherited and acquired mechanisms of inflammation appear to play a role in the development and maintenance of persistent pain. In this longitudinal study, growth mixture modeling was used to identify persistent breast pain phenotypes based on pain assessments obtained prior to and monthly for 6months following breast cancer surgery. Associations between the "no pain" and "mild pain" phenotypes and single nucleotide polymorphisms (SNPs) spanning 15 cytokine genes were evaluated. The methylation status of the CpG sites found in the promoters of genes associated with pain group membership was determined using bisulfite sequencing. In the multivariate analysis, three SNPs (i.e., interleukin 6 (IL6) rs2069840, C-X-C motif chemokine ligand 8 (CXCL8) rs4073, tumor necrosis factor (TNF) rs1800610) and two TNF CpG sites (i.e., c.-350C, c.-344C) were associated with pain group membership. These findings suggest that variations in IL6, CXCL8, and TNF are associated with the development and maintenance of mild persistent breast pain. CpG methylation within the TNF promoter may provide an additional mechanism through which TNF alters the risk for mild persistent breast pain after breast cancer surgery. These genetic and epigenetic variations may help to identify individuals who are predisposed to the development of mild levels of persistent breast pain following breast cancer surgery.

Exploring the Interplay between Rescue Drugs, Data Imputation, and Study Outcomes: Conceptual Review and Qualitative Analysis of an Acute Pain Data Set

In placebo-controlled acute surgical pain studies, provisions must be made for study subjects to receive adequate analgesic therapy. As such, most protocols allow study subjects to receive a pre-specified regimen of open-label analgesic drugs (rescue drugs) as needed. The selection of an appropriate rescue regimen is a critical experimental design choice. We hypothesized that a rescue regimen that is too liberal could lead to all study arms receiving similar levels of pain relief (thereby confounding experimental results), while a regimen that is too stringent could lead to a high subject dropout rate (giving rise to a preponderance of missing data). Despite the importance of rescue regimen as a study design feature, there exist no published review articles or meta-analysis focusing on the impact of rescue therapy on experimental outcomes. Therefore, when selecting a rescue regimen, researchers must rely on clinical factors (what analgesics do patients usually receive in similar surgical scenarios) and/or anecdotal evidence. In the following article, we attempt to bridge this gap by reviewing and discussing the experimental impacts of rescue therapy on a common acute surgical pain population: first metatarsal bunionectomy. The function of this analysis is to (1) create a framework for discussion and future exploration of rescue as a methodological study design feature, (2) discuss the interplay between data imputation techniques and rescue drugs, and (3) inform the readership regarding the impact of data imputation techniques on the validity of study conclusions. Our findings indicate that liberal rescue may degrade assay sensitivity, while stringent rescue may lead to unacceptably high dropout rates.

A feasibility study to determine the benefits of upper extremity virtual rehabilitation therapy for coping with chronic pain post-cancer surgery

BACKGROUND

Persistent pain in shoulder and arm following post-surgical breast cancer treatment can lead to cognitive and physical deficits. Depression is also common in breast cancer survivors. Virtual reality therapy with integrative cognitive and physical rehabilitation has not been clinically trialed for this population. The novel BrightArm Duo technology improved cognition and upper extremity (UE) function for other diagnoses and has great potential to benefit individuals coping with post-surgical breast cancer pain.

OBJECTIVES

The aim of this study was to explore the feasibility of BrightArm Duo therapy for coping with post-surgical chronic pain and associated disability in breast cancer survivors with depression.

METHODS

BrightArm Duo is a robotic rehabilitation table modulating gravity loading on supported forearms. It tracks arm position and grasping strength while patients play three-dimensional (3D) custom integrative rehabilitation games. Community-dwelling women (N = 6) with post-surgical breast cancer pain in the upper arm trained on the system twice a week for 8 weeks. Training difficulty increased progressively in game complexity, table tilt and session length (20-50 minutes). Standardized assessments were performed before and after therapy for pain, cognition, emotion, UE function and activities of daily living.

RESULTS

Subjects averaged upwards of 1300 arm repetitions and 850 hand grasps per session. Pain intensity showed a 20% downward trend (p = 0.1) that was corroborated by therapist observations and participant feedback. A total of 10 out of 11 cognitive metrics improved post-training (p = 0.01) with a significant 8.3-point reduction in depression severity (p = 0.04). A total of 17 of 18 range of motion metrics increased (p < 0.01), with five affected-side shoulder improvements above the Minimal Clinically Important Difference (8°). In all, 13 out of 15 strength and function metrics improved (p = 0.02) with lateral deltoid strength increasing 7.4 N on the affected side (p = 0.05).

CONCLUSION

This pilot study demonstrated feasibility of using the BrightArm Duo Rehabilitation System to treat cancer survivors coping with upper body chronic pain. Outcomes indicate improvement in cognition, shoulder range, strength, function and depression.

Evaluating the Analgesic Effect of the GLS Inhibitor 6-Diazo-5-Oxo-L-Norleucine in Vivo

Glutamate is an excitatory neurotransmitter, produced by its synthetic enzyme, glutaminase (GLS), and packaged by vesicular transporters (VGluT2) into synaptic vesicles. Primary sensory peripheral nerve and spinal synaptic terminals release glutamate during nociceptive (pain) signaling. In post-incisional and inflammation models in rats, GLS and VGluT2 production is elevated in dorsal root ganglion neuronal cell bodies and transported to peripheral and spinal terminals for increased glutamate synthesis and release. 6-Diazo-5-oxo-l-norleucine (DON) is a GLS inhibitor that produces long lasting pain relief when applied to the inflamed paw of arthritic rats, but its effect in a post-incisional model has not been evaluated. In this study, we examined the analgesic efficacy of DON in a surgical incision model by measuring thermal latency and mechanical allodynia. Following behavioral evaluation, we examined the skin for VGluT2, GLS and glutamate immunoreactivity (ir). Our findings revealed that VGluT2-ir is elevated in the stratum lucidum by approximately 19%, 64 hours post-surgical incision and attenuated by approximately 5.4% after the administration of DON. During that same period GLS-ir was elevated in dermal nerve fibers by 52% and was attenuated by approximately 27.9% after the application of DON. Additionally, glutamate-ir was elevated in epidermal nerve fibers by 35% after incision and attenuated by approximately 23% after the administration of DON. Behavioral testing 24 and 48 hours after a single local administration of DON showed five out of six animals having an analgesic response to mechanical allodynia, but not to thermal hyperalgesia. Following a surgical incision, the area of injury shows increased VGluT2-, GLS-, glutamate-ir, mechanical allodynia and no change in thermal latency. After the application of the GLS inhibitor, DON, nerve fiber of the skin showed decreased VGluT2, GLS, and glutamate-ir. Furthermore, post-incision DON treated animals exhibited decreased mechanical allodynia with no change in thermal latency when compared to control animals.

Evaluating the Toxicity of the Analgesic Glutaminase Inhibitor 6-Diazo-5-Oxo-L-Norleucine in vitro and on Rat Dermal Skin Fibroblasts

6-diazo-5-oxo-l-norleucine (DON) is a glutamine antagonist produced naturally by Streptomyces. It inhibits several glutamine-dependent enzyme pathways. Of particular note is its inhibitory effect on the mitochondrial enzyme, glutaminase (GLS), the primary producer of neuronal glutamate. Glutamate is an excitatory neurotransmitter released by primary sensory peripheral nerve terminals and spinal synaptic terminals during pain signaling. Previous work using the tail incision and inflammatory models of pain has demonstrated that a single application of the glutaminase inhibitor, DON, into a surgical incision or the paw of arthritic animals results in pain relief. Even though this compound shows promise as a therapeutic agent, limited data exist regarding its dermal toxicity. As a first approach, we evaluated the effect of several concentrations of DON, on the viability, mitochondrial oxidative capacity and proliferation of rat skin fibroblasts, and then examined the effect of DON after incubation with human liver microsomes on proliferation. Finally, we evaluated DON treated rat skin (tail and hind paw) for cellular necrosis, inflammation and mitotic bodies. No significant effects (p > 0.05) of DON were noted on apoptosis, necrosis, and mitochondrial activity in experiments with cultured rat skin fibroblasts. Flow cytometry revealed the absence of apoptosis in cells treated at the IC₅₀ of 232.5 μM. Enhanced toxicity post-exposure to human microsomes was not observed when compared to DON alone. The H&E staining of the rat skin revealed no obvious pathology in the DON treatment group (10 mM). DON has no/minimal cellular toxicity in vitro on dermal fibroblasts at concentrations that effectively provide analgesia. The local application of concentrations greater than the in vitro IC₅₀ for DON revealed no in vivo skin toxicity. These data provide results indicating zero-to-minimal cellular toxicity with DON and support the further investigation of DON as an analgesic.

Expression of Glutaminase and Vesicular Glutamate Transporter Type 2 Immunoreactivity in Rat Sacral Dorsal Root Ganglia Following a Surgical Tail Incision

Glutamate is an excitatory neurotransmitter, released by primary sensory peripheral nerve and spinal synaptic terminals during nociceptive (pain) signaling. The primary source of neurotransmitter, glutamate, is provided from its synthetic enzyme, glutaminase (GLS). Neurotransmitter glutamate is packaged into synaptic vesicles in nociceptive neurons by the vesicular glutamate transporter 2 (VGluT2). Little is known, however, what effect a surgical incision has on GLS and VGluT2 in primary afferent neurons. In this study, an aseptic, midline incision in the proximal one-third of the rat-tail was examined to determine whether sacral dorsal root ganglia innervate the area of surgical incision, utilizing the retrograde tracer Fluoro-Gold™. Subsequently, the amount of VGluT2 and GLS immunoreactivity (IR) in sacral dorsal root ganglia (DRG) was evaluated using immunofluorescence with image analysis and Western immunoblotting with density analysis. GLS messenger RNA (mRNA) changes were evaluated using real-time reverse transcriptase polymerase chain reaction (RT²-PCR). Our findings revealed that sacral-1 (S₁) DRG neurons innervate the area of surgical incision. Both GLS and VGluT2-ir are elevated post-surgical incision in S₁ DRG neurons for up to 72 hours, while GLS mRNA levels rapidly decreased post-incision and remain depressed for at least 96 hours. Following a surgical incision of the tail, sacral DRGs rapidly deplete their available supply of GLS mRNA and alter their production of the synthetic enzyme, GLS and the vesicular transporter, VGluT2. The rapid use of GLS mRNA and subsequent elevation of GLS protein, along with VGluT2 protein may result in both increased glutamate production and release at peripheral and central processes contributing to primary and secondary sensitization, respectively.

Activation of mesocorticolimbic reward circuits for assessment of relief of ongoing pain: a potential biomarker of efficacy

Preclinical assessment of pain has increasingly explored operant methods that may allow behavioral assessment of ongoing pain. In animals with incisional injury, peripheral nerve block produces conditioned place preference (CPP) and activates the mesolimbic dopaminergic reward pathway. We hypothesized that activation of this circuit could serve as a neurochemical output measure of relief of ongoing pain. Medications commonly used clinically, including gabapentin and nonsteroidal anti-inflammatory drugs (NSAIDs), were evaluated in models of post-surgical (1 day after incision) or neuropathic (14 days after spinal nerve ligation [SNL]) pain to determine whether the clinical efficacy profile of these drugs in these pain conditions was reflected by extracellular dopamine (DA) release in the nucleus accumbens (NAc) shell. Microdialysis was performed in awake rats. Basal DA levels were not significantly different between experimental groups, and no significant treatment effects were seen in sham-operated animals. Consistent with clinical observation, spinal clonidine produced CPP and produced a dose-related increase in net NAc DA release in SNL rats. Gabapentin, commonly used to treat neuropathic pain, produced increased NAc DA in rats with SNL but not in animals with incisional, injury. In contrast, ketorolac or naproxen produced increased NAc DA in animals with incisional but not neuropathic pain. Increased extracellular NAc DA release was consistent with CPP and was observed selectively with treatments commonly used clinically for post-surgical or neuropathic pain. Evaluation of NAc DA efflux in animal pain models may represent an objective neurochemical assay that may serve as a biomarker of efficacy for novel pain-relieving mechanisms.