Novel variants of engineered water soluble mu opioid receptors with extensive mutations and removal of cysteines.

We have shown that water-soluble variants of the human mu opioid receptor (wsMOR) containing a reduced number of hydrophobic residues at the lipid-facing residues of the transmembrane (TM) helices can be expressed in E. coli. In this study, we tested the consequences of increasing the number of mutations on the surface of the transmembrane domain on the receptor's aqueous solubility and ligand binding properties, along with mutation of 11 cysteine residues regardless of their solvent exposure value and location in the protein. We computationally engineered 10 different variants of MOR, and tested four of them for expression in E. coli. We found that all four variants were successfully expressed and could be purified in high quantities. The variants have alpha helical structural content similar to that of the native MOR, and they also display binding affinities for the MOR antagonist (naltrexone) similar to the wsMOR variants we engineered previously that contained many fewer mutations. Furthermore, for these full-length variants, the helical content remains unchanged over a wide range of pH values (pH 6 ~ 9). This study demonstrates the flexibility and robustness of the water-soluble MOR variants with respect to additional designed mutations in the TM domain and changes in pH, whereupon the protein's structural integrity and its ligand binding affinity are maintained. These variants of the full-length MOR with less hydrophobic surface residues and less cysteines can be obtained in large amounts from expression in E. coli and can serve as novel tools to investigate structure-function relationships of the receptor.

Molecular Interaction Between Butorphanol and κ-Opioid Receptor.

BACKGROUND: The misuse of opioids stems, in part, from inadequate knowledge of molecular interactions between opioids and opioid receptors. It is still unclear why some opioids are far more addictive than others. The κ-opioid receptor (KOR) plays a critical role in modulating pain, addiction, and many other physiological and pathological processes. Butorphanol, an opioid analgesic, is a less addictive opioid with unique pharmacological profiles. In this study, we investigated the interaction between butorphanol and KOR to obtain insights into the safe usage of this medication. METHODS: We determined the binding affinity of butorphanol to KOR with a naltrexone competition study. Recombinant KORs expressed in mammalian cell membranes (Chem-1) were used for G-protein activation studies, and a human embryonic kidney-293 (HEK-293) cell line stably transfected with the human KOR was used for ß-arrestin study as previously described in the literature. The effects of butorphanol on KOR internalization were investigated using mouse neuroblastoma Neuro2A cells stably transfected with mKOR-tdTomato fusion protein (N2A-mKOR-tdT) cells overexpressing KOR. The active-state KOR crystal structure was used for docking calculation of butorphanol to characterize the ligand binding site. Salvinorin A, a full KOR agonist, was used as a control for comparison. RESULTS: The affinity of KOR for butorphanol is characterized by Kd of 0.1 ± 0.02 nM, about 20-fold higher compared with that of the µ-opioid receptor (MOR; 2.4 ± 1.2 nM). Our data indicate that butorphanol is more potent on KOR than on MOR. In addition, butorphanol acts as a partial agonist of KOR in the G-protein activation pathway and is a full agonist on the ß-arrestin recruitment pathway, similar to that of salvinorin A. The activation of the ß-arrestin pathway is further confirmed by KOR internalization. The in silico docking model indicates that both salvinorin A and butorphanol share the same binding cavity with the KOR full agonist MP1104. This cavity plays an important role in determining either agonist or antagonist effects of the ligand. CONCLUSIONS: In conclusion, butorphanol is a partial KOR agonist in the G-protein activation pathway and a potent KOR full agonist in the ß-arrestin recruitment pathway. The structure analysis offers insights into the molecular mechanism of KOR interaction and activation by butorphanol.

Non-scheduled short-acting opioid to taper off opioids?

This commentary discusses the issues related to the current pharmacotherapy using super long-acting opioids (for the potential convenience for both patients and medical providers) for opioid addiction and argues for the potential to use a non-scheduled short-acting opioid to taper off opioids to reduce total number of patients on opioids and ultimately reduce opioid-related death. This article also proposes to develop short-acting opioids for addiction management instead of the current long-acting regimen. The authors further suggest that dezocine, a previously FDA approved medication for perioperative pain management and a non-scheduled opioid, be brought back to clinical practice in the US as a potential alternative addiction management medication, especially for those who are highly motivated to quit opioids completely using a taper off strategy.

Perioperative Opioid Usage Monitoring and Waste.

This editorial discusses the status and issues related to perioperative opioid usage monitoring and waste. Opioid detection of wasted material is briefly discussed also. Flowlytics® from Invistics is a digital system to monitor opioid usage and waste in medical facilities. Opioid waste in medical facilities has a two-person witness procedure. Easy to use detection of wasted materials needs to be developed in the future. It is unclear whether the strategies used in medical facilities should be recommended for opioid disposal in the public to reduce opioid diversion. Relevant studies are needed.

Dyngo-4a Induces Neuroblastoma Cell Differentiation Through The AKT and ERK1/2 Pathway.

AIM: The aim of the study is to check whether dyngo-4a can inhibit neuroblastoma (NB) proliferation and induce NB cell differentiation Background: Dynamin plays a role in regulating neurotransmission, signaling pathways, nutrient uptake, and pathogen infection, enhancing cell proliferation, tumor invasion, and metastasis. Studies have reported that dyngo-4a, a dynamin inhibitor, can be used to identify potential biomarkers and promising novel therapeutic targets for cancer treatment. OBJECTIVE: To our knowledge, no published reports are showing that dynamin inhibitors can reduce NB cell proliferation and induce differentiation. In this study, we report that dyngo-4a can inhibit NB proliferation and induce NB cell differentiation. METHODS: In this study, mouse neuroblastoma (Neuro-2a) cells were cultured in the presence or absence of dyngo-4a or retinoic acid (RA), or in the presence of both dyngo-4a and RA, or in the presence of sequential administration of dyngo-4a and RA to compare the effects on the inhibition of cell proliferation and effects on neuroblastoma cell differentiation induction. The neural cell markers, Nestin and Tuj 1 (Neuron-specific class III beta-tubulin), were used to demonstrate that the differentiated cells have neuronal cell features. The phosphorylation of Protein Kinase B (AKT), extracellular signalregulated kinases1/2 (ERK1/2), and epidermal growth factor receptor (EGFR) were determined to examine the potential mechanisms of induced differentiation. RESULTS: Dyngo-4a or RA or dyngo-4a with subsequent RA administration induced Neuro-2a cell differentiation. However, RA with subsequent dyngo-4a administration results in almost total death of the Neuro-2a cells. The differentiation rate induced by dyngo-4a was significantly higher than the rate by RA treatment (72.5 ± 1.4% vs. 52.9 ± 3.1% with neuron features, P<0.05; 39.0 ± 0.8% vs. 29.9 ± 1.8% for axons under light microscopy, p<0.05). The differentiation rate of cells treated with dyngo-4a first, followed by RA, was greater than when they were added together (74.8 ± 3.8% vs. 10.6 ± 3.6%; 45.5 ± 1.6% vs. 12.4 ± 0.6%, p<0.01). Co-administration of dyngo-4a and RA at the same time diminished differentiation efficacy significantly. Dyngo-4a induced Neuro-2a cell differentiation and increased Tuj-1 positive staining by the 6th day post- treatment. Dyngo-4a also inhibited Neuro-2a cell proliferation in a dose-dependent manner. Regarding the mechanism, dyngo-4a treatment showed a significant increase in p-AKT and p-ERK1/2 but not in p-EGFR. CONCLUSION: At a level comparable to RA, dynamin inhibition with dyngo-4a lowers proliferation and causes differentiation of Neuro-2a mouse NB cells in vitro. The AKT pathway is activated by dynago- 4a, which results in differentiation. The combination of RA with dynago-4a reduces the efficiency of differentiation. The application of dynago-4a followed by RA, on the other hand, enhances the differentiating effect, implying alternative mechanistic roles in the process.

A Brief Overview of the Neuropharmacology of Opioid Addiction.

The world is in the midst of an opioid crisis. Nearly 92,000 persons in the U.S. alone died from illicit drugs and prescription opioids in 2020 [1]. This number does not include the countless other individuals who die as a result of the violent crime that accompanies the illicit drug trade. To address this crisis, we need to appreciate aspects of drug addiction. The goal of this brief review is to highlight some major facets of addiction neurobiology, focused on opioids, to provide a basic understanding of the research and terminology encountered in more detailed in-depth articles and discussions on addiction.

Dezocine is a Biased Ligand without Significant Beta-Arrestin Activation of the mu Opioid Receptor.

Dezocine is an opioid that was used in clinical practice for acute pain management in the US (1986 to 2011) and is currently in use in China. It is not listed as a controlled substance in the US due to no reported cases of addiction. Dezocine is a partial agonist at the mu opioid receptor (MOR); however, it is unclear whether dezocine can activate both the G protein pathway and the beta-arrestin pathway. In this study we hypothesized that dezocine does not activate the beta-arrestin pathway, which could be the potential molecular mechanism by which dezocine is not addictive or at least less addictive than other classic opioids. Both morphine, a MOR full agonist and buprenorphine, a partial MOR agonist similar to dezocine, were used for comparison purposes. The major side effects of dezocine in clinical usage are its gastrointestinal side effects and first pass effects; therefore, we explored the possibility of administering dezocine intranasally in rodents to demonstrate the feasibility of intranasal administration for new clinical usage purposes. With proper formulation it is possible to administer dezocine intranasally to achieve a high concentration in the brain in the rodent model. The results indicate that dezocine does not activate the beta-arrestin pathway in MOR. Intranasal delivery of dezocine achieves a much higher medication concentration in the blood and brain as compared to intraperitoneal injection. It also persists a longer time before it falls below detection in the blood. This study provides a possible explanation of why dezocine is not addictive or at least less addictive than other commonly used opioids. This study also demonstrates that intranasal administration offers an alternative strategy for its potential clinical applications.

Intranasal Salvinorin A Improves Long-term Neurological Function via Immunomodulation in a Mouse Ischemic Stroke Model.

Salvinorin A (SA), a highly selective kappa opioid receptor agonist, has been shown to reduce brain infarct volume and improve neurological function after ischemic stroke. However, the underlying mechanisms have not been fully understood yet. Therefore, we explored whether SA provides neuroprotective effects by regulating the immune response after ischemic stroke both in the central nervous system (CNS) and peripheral circulation. In this study, adult male mice were subjected to transient Middle Cerebral Artery Occlusion (tMCAO) and then were treated intranasally with SA (50 µg/kg) or with the vehicle dimethyl sulfoxide (DMSO). Multiple behavioral tests were used to evaluate neurofunction. Flow cytometry and immunofluorescence staining were used to evaluate the infiltration of peripheral immune cells into the brain. The tracer cadaverine and endogenous immunoglobulin G (IgG) extravasation were used to detect blood brain barrier leakage. We observed that SA intranasal administration after ischemic stroke decreased the expression of pro-inflammatory factors in the brain. SA promoted the polarization of microglia/macrophages into a transitional phenotype and decreased the pro-inflammatory phenotype in the brain after tMCAO. Interestingly, SA treatment scarcely altered the number of peripheral immune cells but decreased the macrophage and neutrophil infiltration into the brain at 24 h after tMCAO. Furthermore, SA treatment also preserved BBB integrity, reduced long-term brain atrophy and white matter injury, as well as improved the long-term neurofunctional outcome in mice. In this study, intranasal administration of SA improved long-term neurological function via immuno-modulation and by preserving blood-brain barrier integrity in a mouse ischemic stroke model, suggesting that SA could potentially serve as an alternative treatment strategy for ischemic stroke.

Autophagy Inhibition Preserves Tight Junction of Human Cerebral Microvascular Endothelium Under Oxygen Glucose Deprivation.

AIMS: To investigate the role of autophagy in the tight junction of human brain endothelial cells during hypoxia and ischemia. BACKGROUND: Endothelial cells play an important role in the initiation, progression and recovery from ischemic stroke. The role of autophagy on human brain endothelial cells (HBECs) subjected to oxygen-glucose deprivation (OGD) is not fully elucidated. OBJECTIVE: The objective of this study was to investigate the effect of autophagy on HBECs during OGD. METHODS: HBECs were cultured in a 96-well plate and underwent 4 hours of OGD. For drug treatment, 3-Methyladenine (3-MA) (5mmol/L), an inhibitor of autophagy, was added at the start of OGD. Cell viability and cytotoxicity were tested by cell counting kit-8 (CCK-8) and lactate dehydrogenase (LDH) assays. Morphological changes in cells were examined by immunofluorescence microscopy. The protein expression of light chain 3 (LC3) was measured. Autophagosomes and endothelial cell tight junctions were observed using transmission electron microscopy. RESULTS: The results showed that OGD induced serious damage to HBECs. Cell viability was decreased significantly and LDH release increased significantly (p<0.05) following OGD. 3-MA protected HBECs from damage. Immunostaining further confirmed these results. Since 3-MA is an inhibitor of autophagy, we chose to examine alterations in the amount of LC3, a marker of autophagy. The ratios of LC3-II to LC3-I were significantly lower in the 3-MA treated OGD group than in the non-3-MA treated OGD group (p<0.05). Electron microscopy showed that 3-MA inhibited the formation of autophagolysosomes and revealed that the tight junction ultrastructure of HBECs, which was destroyed by OGD, was significantly protected by treatment with 3-MA. CONCLUSION: Autophagy is a key response to oxygen-glucose deprivation stress and its detrimental effects are closely related to the destruction of tight junctions of human brain endothelial cells. Strategies to inhibit autophagy could help to preserve tight junctions.

Kappa opioid receptors internalization is protective against oxygen-glucose deprivation through ß-arrestin activation and Akt-mediated signaling pathway.

Hypoxia induces reversible κ-opioid receptor (KOR) internalization similar to the internalization that is induced by KOR agonists. In the current study, we demonstrate that this KOR internalization is a protective mechanism via the ß-arrestin specific pathway in an oxygen-glucose deprivation (OGD) model. Mouse neuroblastoma Neuro2A cells were stably transfected with mouse KOR-tdTomato fusion protein (N2A-mKOR-tdT cells). Various concentrations of salvinorin A (SA), a highly selective KOR agonist, were given in the presence and absence of norbinaltorphimine (norBNI), which is a KOR antagonist, or Dyngo-4a (internalization inhibitor) or API-2 (Akt/Protein kinase B signaling inhibitor-2). Various concentrations of SA and RB-64 (22-thiocyanatosalvinorin A, selective for the G protein signaling pathway) were administered both in normoxic and hypoxic conditions. Autophagosomes and ultrastructural components of cells were observed using transmission electron microscopy (TEM). Cell viability, severity of cell injury, and levels of proteins related to the Akt signaling pathway were evaluated using live cell counting (by Cell Counting Kit-8), the lactic acid dehydrogenase (LDH) release rate, and Western blot analysis, respectively. SA promoted cell survival and attenuated OGD-induced cell injury. The Akt signaling pathway is activated by SA. KOR internalization, when blocked by norBNI or Dyngo-4a, increased LDH release and decreased cell viability under OGD. Treatment with SA significantly inhibited autophagy, and the effects of SA on autophagy were reversed by API-2 pretreatment. RB-64 in a low concentration without ß-arrestin recruitment did not reduce LDH release and increase cell viability as observed with SA. KOR internalization through ß-arrestin activation is a protective mechanism against OGD. The Akt pathway might play a critical role in modulating these protective effects by inhibiting autophagy.

Efficacy of 5-day continuous lidocaine infusion for the treatment of refractory complex regional pain syndrome.

OBJECTIVE: Chronic regional pain syndrome (CRPS) is a severe pain condition that usually results from an injury or surgical procedure. The pain in CRPS often spreads from the site of injury, and with time becomes refractory to conventional therapy. The present study was undertaken to evaluate the effects of 5-day continuous intravenous lidocaine treatment in patients afflicted with CRPS. METHODS: Intravenous lidocaine was administered in an escalating dose schedule to 49 severely affected CRPS patients in a monitored setting over 5 days. Evaluation of pain parameters and other signs and symptoms of CRPS were obtained during the infusion and at 1, 3, and 6 months following therapy. RESULTS: The majority of patients demonstrated a significant decrease in pain parameters and other symptoms and signs of CRPS. The pain reduction lasted an average of 3 months. Lidocaine may be particularly effective for thermal and mechanical allodynia. Less clinically significant effects were documented on the motor aspects of the syndrome. DISCUSSION: Intravenous lidocaine administration titrated to 5 mg/L demonstrated: 1) a significant decrease in mechanical and thermal allodynia for three months, 2) lessened associated inflammatory components of CRPS, and 3) only minimal side effects and no severe complications.

Brachial plexus traction injury: quantification of sensory abnormalities.

OBJECTIVE: Stretch injury to the brachial plexus may occur following traumatic flexion-extension of the cervical spine often seen in motor vehicle accidents or falls. Radiologic and conventional nerve conduction studies are negative in many cases. The present study was undertaken in an attempt to simplify, standardize, and quantify the positive and negative sensory abnormalities that are most often seen during the clinical examination. METHODS: Quantitation of thresholds for thermal detection and pain, vibration, pressure pain and elevated arm stress test was performed in a series of 38 patients with the clinical picture of brachial plexus traction injury as well as a group of age and sex matched control subjects. RESULTS: Significant decreases in all evoked pain thresholds, except for heat pain, along with increases in sensory detection thresholds were found in the patient group compared with controls. DISCUSSION: Quantification of sensory findings may greatly facilitate and substantiate the diagnosis of this type of injury. The data are consistent with the hypothesis that brachial plexus traction injury causes dysfunction of small sensory fiber systems and results in a form of neuropathic pain.

Efficacy of ketamine in anesthetic dosage for the treatment of refractory complex regional pain syndrome: an open-label phase II study.

OBJECTIVE: Advanced complex regional pain syndrome (CRPS) remains very difficult to treat. While subanesthetic low-dose ketamine has shown promise in early localized CRPS, its use in advanced CRPS has not been as effective. Since ketamine's analgesic potency and duration of effect in neuropathic pain are directly dose-dependant, we investigated the efficacy of ketamine in anesthetic dosage in refractory CRPS patients that had failed available standard therapies. METHODS: Twenty ASA I-III patients suffering from refractory CRPS received ketamine in anesthetic dosage over 5 days. Outcome criteria were pain relief, effect on the movement disorder, quality of life, and ability to work at baseline and up to 6 months following treatment. RESULTS: Significant pain relief was observed at 1, 3, and 6 months following treatment (93.5 +/- 11.1%, 89.4 +/- 17.0%, 79.3 +/- 25.3%; P < 0.001). Complete remission from CRPS was observed at 1 month in all patients, at 3 months in 17, and at 6 months in 16 patients. If relapse occurred, significant pain relief was still attained at 3 and 6 months (59.0 +/- 14.7%, P < 0.004; 50.2 +/- 10.6%, P < 0.002). Quality of life, the associated movement disorder, and the ability to work significantly improved in the majority of patients at 3 and 6 months. CONCLUSIONS: This open-label trial suggests benefit in pain reduction, associated CRPS symptoms, improved quality of life and ability to work following anesthetic ketamine in previously refractory CRPS patients. However, a randomized controlled trial will be necessary to prove its efficacy.

Cerebral reactivity in migraine patients measured with functional near-infrared spectroscopy.

BACKGROUND: There are two major theories describing the pathophysiology of migraines. Vascular theory explains that migraines resulted from vasodilation of meningeal vessels irritating the trigeminal nerves and causing pain. More recently, a neural theory of migraine has been proposed, which suggests that cortical hyperexcitability leads to cortical spreading depression (CSD) causing migraine-like symptoms. Chronic migraine requires prophylactic therapy. When oral agents fail, there are several intravenous agents that can be used. Understanding underlying causes of migraine pain would help to improve efficacy of migraine medications by changing their mechanism of action. Yet to date no study has been made to investigate the link between vascular changes in response to medications for migraine versus pain improvements. Functional near-infrared spectroscopy (NIRS) has been used as an inexpensive, rapid, non-invasive and safe technique to monitor cerebrovascular dynamics. METHOD: In this study, a multi-distance near-infrared spectroscopy device has been used to investigate the cortical vascular reactivity of migraine patients in response to drug infusions and its possible correlation with changes in pain experienced. We used the NIRS on 41 chronic migraine patients receiving three medications: magnesium sulfate, valproate sodium, and dihydroergotamine (DHE). Patients rated their pain on a 1-10 numerical scale before and after the infusion. RESULTS: No significant differences were observed between the medication effects on vascular activity from near channels measuring skin vascularity. However, far channels--indicating cortical vascular activity--showed significant differences in both oxyhemoglobin and total hemoglobin between medications. DHE is a vasoconstrictor and decreased cortical blood volume in our experiment. Magnesium sulfate has a short-lived vasodilatory effect and increased cortical blood volume in our experiment. Valproate sodium had no significant effect on blood volume. Nonetheless, all three reduced patients' pain based on self-report and no significant link was observed between changes in cortical vascular reactivity and improvement in migraine pain as predicted by the vascular theory of migraine. CONCLUSION: NIRS showed the potential to be a useful tool in the clinical setting for monitoring the vascular reactivity of individual patients to various migraine and headache medications.

Plasma Exchange Therapy in Patients with Complex Regional Pain Syndrome.

BACKGROUND: Complex regional pain syndrome (CRPS) is a severe chronic pain condition that most often develops following trauma. Some investigators have postulated CRPS to be a post-traumatic neuralgia associated with distal degeneration of small-diameter peripheral axons. Intravenous immunoglobulin treatment (IVIG) has been shown to be efficacious in the treatment of painful polyneuropathies. Some CRPS patients have been reported to respond to IVIG. Based on a recent hypothesis proposing an autoimmune etiology for CRPS, we decided to offer plasma exchange therapy (PE) to CRPS patients with a clinical presentation suggestive of a small fiber neuropathy. OBJECTIVES: To evaluate the efficacy of PE in a group of CRPS patients with a clinical presentation suggestive of a small fiber neuropathy that were either non-responders or poor responders to their current treatment. STUDY DESIGN: This is a retrospective case series study of CRPS patients that met the Budapest diagnostic criteria for CRPS and received PE as treatment for their illness between September 2012 and June 2014. Approval for this review was granted by the Drexel University Institutional Review Board. SETTING: Drexel University College of Medicine pain clinic METHODS: Thirty-three CRPS patients that received PE treatment were retrospectively studied. The workup for these patients consisted of a complete medical and pain evaluation, the completion of the short-form McGill questionnaire, quantitative sensory testing (QST), and skin punch biopsy. The PE protocol was as follows: all patients had a series of PE therapies (range 5 to 11 with a mean of 7.2) performed over a 2 to 3 week period. Following the PE series, the patients had a pain evaluation and completed the short-form McGill questionnaire. Patients that responded to PE were offered maintenance therapy consisting of either weekly PE or other immune modulating agents. In these patients, their pain was evaluated during the maintenance phase. RESULTS: Thirty of the 33 patients demonstrated significant (P < 0.01) median pain reduction of 64% following the initial series of PE. Three patients demonstrated no improvement. Twenty-four patients are receiving maintenance therapy, the pain reduction in these patients following the initial PE series has been maintained with either weekly PE (n = 15), oral immune modulating agents (n = 8), or IVIG (n = 1). The remaining 6 patients are not receiving maintenance therapy and their pain has returned to pre-treatment levels. In addition, this study suggests that patients with the greatest loss of small fibers and the greatest temperature sensory deficits are most likey to benefit from PE therapy. LIMITATIONS: The major limitation of this study is its retrospective nature which includes non-randomization, non-blinding, and an uncontrolled design. CONCLUSIONS: This study shows that PE is effective in a subset of patients with severe long-standing CRPS and that the reduction in pain following the initial series of PE treatments can be maintained on a weekly PE schedule, IVIG, or with other immune modulating drugs. Large, randomized, placebo controlled studies may be required to confirm and expand these results. Such studies may lead to new therapies for this severe life-altering condition.

Thermal pain in complex regional pain syndrome type I.

BACKGROUND: Quantitative sensory testing (QST), with thermal threshold determinations, is a routine part of the comprehensive clinical workup of patients suffering from chronic pain, especially those with Complex Regional Pain Syndrome seen at our outpatient pain clinic. This is done to quantitatively assess each patient's small fiber and sensory function in a controlled manner. Most patients have normal sensory detection thresholds, but there are large differences in thermal pain thresholds. Some patients display no thermal hyperalgesia, while other patients display severe thermal hyperalgesia when tested in all 4 limbs. OBJECTIVES: To ascertain the prevalence of thermal hyperalgesia in patients with complex regional pain syndrome type 1 (CRPS-I). STUDY DESIGN: This was a retrospective review of the results of QST performed on 105 patients as part of their clinical workup. SETTING: The outpatient clinic of the Department of Neurology at Drexel University College of Medicine. METHODS: All patients had a diagnosis of CRPS-I. Thermal quantitative sensory testing, including cool detection, warm detection, cold pain, and heat pain, was performed on 8 distal sites on each patient as part of a comprehensive clinical examination. RESULTS: With regards to thermal hyperalgesia, patients with CPRS-I appear to fall into distinct groups. One subgroup displays evidence of generalized cold and heat hyperalgesia, one subgroup displays evidence of generalized cold hyperalgesia only, one displays evidence of heat hyperalgesia only, and one subgroup does not display evidence of cold or heat hyperalgesia. LIMITATIONS: This study is based on retrospective information on a relatively small (105 patient records) number of patients. Since only patients with CRPS-I were included, the results are only applicable to this group. CONCLUSIONS: Thermal QST provides useful information about the sensory phenotype of individual patients. Subgrouping based on thermal hyperalgesia may be useful for future studies regarding prognosis, treatment selection, and efficacy.

Plasma amino acids changes in complex regional pain syndrome.

Complex regional pain syndrome (CRPS) is a severe chronic pain condition that most often develops following trauma. Blood samples were collected from 220 individuals, 160 CRPS subjects, and 60 healthy pain-free controls. Plasma amino acid levels were compared and contrasted between groups. L-Aspartate, L-glutamate, and L-ornithine were significantly increased, whereas L-tryptophan and L-arginine were significantly decreased in CRPS subjects as compared to controls. In addition, the L-kynurenine to L-tryptophan ratio demonstrated a significant increase, whereas the global arginine bioavailability ratio (GABR) was significantly decreased in the CRPS subjects. The CRPS subjects demonstrated a significant correlation between overall pain and the plasma levels of L-glutamate and the L-kynurenine to L-tryptophan ratio. CRPS subjects also showed a correlation between the decrease in plasma L-tryptophan and disease duration. This study shows that CRPS subjects exhibit significant changes in plasma levels of amino acids involved in glutamate receptor activation and in amino acids associated with immune function as compared to healthy pain-free controls. A better understanding of the role plasma amino acids play in the pathophysiology of CRPS may lead to novel treatments for this crippling condition.

Skin biopsy in complex regional pain syndrome: case series and literature review.

BACKGROUND: Accumulating experimental and clinical evidence supports the hypothesis that complex regional pain syndrome type I (CRPS-I) may be a small fiber neuropathy. OBJECTIVES: To evaluate the use of commercially available standard biopsy methods to detect intradermal axon pathology in CRPS-I, and to ascertain if these structural changes can explain quantitative sensory testing (QST) findings in CRPS-I. STUDY DESIGN: Retrospective review of charts and laboratory data. SETTING: Outpatient clinic METHODS: Skin biopsies from 43 patients with CRPS-I were stained with PGP 9.5, and epidermal nerve fiber density, sweat gland nerve fiber density and morphological abnormalities were evaluated. Thirty-five patients had quantitative sensory testing. RESULTS: Alterations in skin innervation were seen in approximately 20% of CRPS-I patients with commercial processing. There were no patient characteristics, including duration of disease, that predicted a decreased epidermal nerve fiber density (ENFD). There was no consistent relationship between QST changes and ENFD measured by standard commercial skin biopsy evaluation procedures. LIMITATIONS: Commercial processing of tissue does not utilize stereologic quantitative analysis of nerve fiber density. Biopsy material is utilized from a proximal and distal source only, and differences in denervation of a partial nerve territory may be missed. The functional attributes of small fibers cannot be assessed. CONCLUSIONS: The negative results indicate that CRPS-I may be associated with changes in the ultramicroscopic small fiber structure that cannot be visualized with commercially available techniques. Alternatively, functional rather than structural alterations of small fibers or pathological changes at a more proximal site such as the spinal cord or brain may be responsible for the syndrome.

Changes in plasma cytokines and their soluble receptors in complex regional pain syndrome.

UNLABELLED: Complex Regional Pain Syndrome (CRPS) is a chronic and often disabling pain disorder. There is evidence demonstrating that neurogenic inflammation and activation of the immune system play a significant role in the pathophysiology of CRPS. This study evaluated the plasma levels of cytokines, chemokines, and their soluble receptors in 148 subjects afflicted with CRPS and in 60 gender- and age-matched healthy controls. Significant changes in plasma cytokines, chemokines, and their soluble receptors were found in subjects with CRPS as compared with healthy controls. For most analytes, these changes resulted from a distinct subset of the CRPS subjects. When the plasma data from the CRPS subjects was subjected to cluster analysis, it revealed 2 clusters within the CRPS population. The category identified as most important for cluster separation by the clustering algorithm was TNFα. Cluster 1 consisted of 64% of CRPS subjects and demonstrated analyte values similar to the healthy control individuals. Cluster 2 consisted of 36% of the CRPS subjects and demonstrated significantly elevated levels of most analytes and in addition, it showed that the increased plasma analyte levels in this cluster were correlated with disease duration and severity. PERSPECTIVE: The identification of biomarkers that define disease subgroups can be of great value in the design of specific therapies and of great benefit to the design of clinical trials. It may also aid in advancing our understanding of the mechanisms involved in the pathophysiology of CRPS, which may lead to novel treatments for this very severe condition.