Myelin barrier breakdown, mechanical hypersensitivity, and painfulness in polyneuropathy with claudin-12 deficiency.

BACKGROUND: The blood-nerve and myelin barrier shield peripheral neurons and their axons. These barriers are sealed by tight junction proteins, which control the passage of potentially noxious molecules including proinflammatory cytokines via paracellular pathways. Peripheral nerve barrier breakdown occurs in various neuropathies, such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and traumatic neuropathy. Here, we studied the functional role of the tight junction protein claudin-12 in regulating peripheral nerve barrier integrity and CIDP pathogenesis. METHODS: Sections from sural nerve biopsies from 23 patients with CIDP and non-inflammatory idiopathic polyneuropathy (PNP) were analyzed for claudin-12 and -19 immunoreactivity. Cldn12-KO mice were generated and subjected to the chronic constriction injury (CCI) model of neuropathy. These mice were then characterized using a battery of barrier and behavioral tests, histology, immunohistochemistry, and mRNA/protein expression. In phenotype rescue experiments, the proinflammatory cytokine TNFα was neutralized with the anti-TNFα antibody etanercept; the peripheral nerve barrier was stabilized with the sonic hedgehog agonist smoothened (SAG). RESULTS: Compared to those without pain, patients with painful neuropathy exhibited reduced claudin-12 expression independently of fiber loss. Accordingly, global Cldn12-KO in male mice, but not fertile female mice, selectively caused mechanical allodynia associated with a leaky myelin barrier, increased TNFα, decreased sonic hedgehog (SHH), and loss of small axons accompanied by reduced peripheral myelin protein 22 (Pmp22). Other barriers and neurological functions remained intact. The Cldn12-KO phenotype could be rescued either by neutralizing TNFα with etanercept or stabilizing the barrier with SAG, which both also upregulated the Schwann cell barrier proteins Cldn19 and Pmp22. CONCLUSION: These results point to a critical role for claudin-12 in maintaining the myelin barrier presumably via Pmp22 and highlight restoration of the hedgehog pathway as a potential treatment strategy for painful inflammatory neuropathy.

A Novel Approach for the Control of Inflammatory Pain: Prostaglandin E2 Complexation by Randomly Methylated ß-Cyclodextrins.

BACKGROUND: Inhibitors of cyclooxygenase, which block the formation of prostaglandin (PG) E2, are the standard treatment of inflammatory pain. These drugs, however, have serious gastrointestinal, renal, and cardiovascular side effects that limit their clinical use. Cyclodextrins are neutral glucose oligomers that form a hydrophilic outer and a hydrophobic interior cavity used to carry hydrophilic substances. Methyl-ß-cyclodextrins are used currently in several drugs as enhancers and also to deliver PGs. We therefore hypothesized that randomly methylated ß-cyclodextrins (RAMEB) could be used for pain treatment. METHODS: An in silico screening for important inflammatory mediators (eg, PGE2, substance P, bradykinin, and calcitonin gene-related peptide) was performed to predict the probability of these molecules binding to RAMEB. Thereafter, a comprehensive in vitro study investigated the complexation affinity of the best target toward RAMEB or its RAMEB-fraction L (FL) using capillary electrophoresis.Wistar rats were injected intraplantarly with complete Freund's adjuvant (CFA) for 96 hours to induce inflammatory hyperalgesia. Subsequently, rats were treated intraplantarly or intravenously either with RAMEB or RAMEB FL and compared with the respective controls. Parecoxib was used as positive control. Mechanical (paw pressure threshold, PPT) and thermal (paw withdrawal latency) nociceptive thresholds were determined before injection and at the indicated time points thereafter. Paw tissue was collected after treatments, and PGE2 and PGD2 contents were measured. Analysis of variance was used for data analysis followed by appropriate post hoc comparisons. RESULTS: In silico screening indicated that PGE2, with the highest affinity, was the best candidate for RAMEB binding. Likewise, in capillary electrophoresis experiments, RAMEB had a high affinity to form inclusion complexes with the PGE2 (stability constant [K], 360 1/M; 95% confidence interval [C]: 347.58-372.42 M). Local treatment with RAMEB alleviated CFA-induced mechanical (PPT: 76.25 g; 95% CI: 56.24-96.25 g) and thermal hyperalgesia (PPT: 8.50 seconds; 95% CI: 6.76-10.23 seconds). Moreover, a systemic administration of RAMEB decreased CFA-induced mechanical (PPT: 126.66 g; 95% CI: 114.54-138.77 g) and thermal hyperalgesia (paw withdrawal latency: 11.47 seconds; 95% CI: 9.26-13.68 seconds). RAMEB FL resulted in greater in vitro PGE2-binding capacity and decreased PG content as well as hyperalgesia in vivo to a similar extent. Motor activity of the rats was not altered by RAMEB or RAMEB FL. CONCLUSIONS: Capture of PGs by cyclodextrins could be a novel and innovative tool for the treatment of inflammatory pain and bypassing some unwanted side effects of cyclooxygenase inhibitors.

Functional and structural characterization of axonal opioid receptors as targets for analgesia.

BACKGROUND: Opioids are the gold standard for the treatment of acute pain despite serious side effects in the central and enteric nervous system. µ-opioid receptors (MOPs) are expressed and functional at the terminals of sensory axons, when activated by exogenous or endogenous ligands. However, the presence and function of MOP along nociceptive axons remains controversial particularly in naïve animals. Here, we characterized axonal MOPs by immunofluorescence, ultrastructural, and functional analyses. Furthermore, we evaluated hypertonic saline as a possible enhancer of opioid receptor function. RESULTS: Comparative immunolabeling showed that, among several tested antibodies, which all provided specific MOP detection in the rat central nervous system (CNS), only one monoclonal MOP-antibody yielded specificity and reproducibility for MOP detection in the rat peripheral nervous system including the sciatic nerve. Double immunolabeling documented that MOP immunoreactivity was confined to calcitonin gene-related peptide (CGRP) positive fibers and fiber bundles. Almost identical labeling and double labeling patterns were found using mcherry-immunolabeling on sciatic nerves of mice producing a MOP-mcherry fusion protein (MOP-mcherry knock-in mice). Preembedding immunogold electron microscopy on MOP-mcherry knock-in sciatic nerves indicated presence of MOP in cytoplasm and at membranes of unmyelinated axons. Application of [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin (DAMGO) or fentanyl dose-dependently inhibited depolarization-induced CGRP release from rat sciatic nerve axons ex vivo, which was blocked by naloxone. When the lipophilic opioid fentanyl was applied perisciatically in naïve Wistar rats, mechanical nociceptive thresholds increased. Subthreshold doses of fentanyl or the hydrophilic opioid DAMGO were only effective if injected together with hypertonic saline. In vitro, using ß-arrestin-2/MOP double-transfected human embryonic kidney cells, DAMGO as well as fentanyl lead to a recruitment of ß-arrestin-2 to the membrane followed by a ß-arrestin-2 reappearance in the cytosol and MOP internalization. Pretreatment with hypertonic saline prevented MOP internalization. CONCLUSION: MOPs are present and functional in the axonal membrane from naïve animals. Hypertonic saline acutely decreases ligand-induced internalization of MOP and thereby might improve MOP function. Further studies should explore potential clinical applications of opioids together with enhancers for regional analgesia.

Transient opening of the perineurial barrier for analgesic drug delivery.

Selective targeting of sensory or nociceptive neurons in peripheral nerves remains a clinically desirable goal. Delivery of promising analgesic drugs is often impeded by the perineurium, which functions as a diffusion barrier attributable to tight junctions. We used perineurial injection of hypertonic saline as a tool to open the perineurial barrier transiently in rats and elucidated the molecular action principle in mechanistic detail: Hypertonic saline acts via metalloproteinase 9 (MMP9). The noncatalytic hemopexin domain of MMP9 binds to the low-density lipoprotein receptor-related protein-1, triggers phosphorylation of extracellular signal-regulated kinase 1/2, and induces down-regulation of the barrier-forming tight junction protein claudin-1. Perisciatic injection of any component of this pathway, including MMP9 hemopexin domain or claudin-1 siRNA, enables an opioid peptide ([D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin) and a selective sodium channel (NaV1.7)-blocking toxin (ProToxin-II) to exert antinociceptive effects without motor impairment. The latter, as well as the classic TTX, blocked compound action potentials in isolated nerves only after disruption of the perineurial barrier, which, in return, allowed endoneurally released calcitonin gene-related peptide to pass through the nerve sheaths. Our data establish the function and regulation of claudin-1 in the perineurium as the major sealing component, which could be modulated to facilitate drug delivery or, potentially, reseal the barrier under pathological conditions.

Toll like receptor (TLR)-4 as a regulator of peripheral endogenous opioid-mediated analgesia in inflammation.

BACKGROUND: Leukocytes containing opioid peptides locally control inflammatory pain. In the early phase of complete Freund's adjuvant (CFA)-induced hind paw inflammation, formyl peptides (derived e.g. from Mycobacterium butyricum) trigger the release of opioid peptides from neutrophils contributing to tonic basal antinociception. In the later phase we hypothesized that toll-like-receptor-(TLR)-4 activation of monocytes/macrophages triggers opioid peptide release and thereby stimulates peripheral opioid-dependent antinociception. RESULTS: In Wistar rats with CFA hind paw inflammation in the later inflammatory phase (48-96 h) systemic leukocyte depletion by cyclophosphamide (CTX) or locally injected naloxone (NLX) further decreased mechanical and thermal nociceptive thresholds. In vitro ß-endorphin (ß-END) content increased during human monocyte differentiation as well as in anti-inflammatory CD14+CD16- or non-classical M2 macrophages. Monocytes expressing TLR4 dose-dependently released ß-END after stimulation with lipopolysaccharide (LPS) dependent on intracellular calcium. Despite TLR4 expression proinflammatory M1 and anti-inflammatory M2 macrophages only secreted opioid peptides in response to ionomycin, a calcium ionophore. Intraplantar injection of LPS as a TLR4 agonist into the inflamed paw elicited an immediate opioid- and dose-dependent antinociception, which was blocked by TAK-242, a small-molecule inhibitor of TLR4, or by peripheral applied NLX. In the later phase LPS lowered mechanical and thermal nociceptive thresholds. Furthermore, local peripheral TLR4 blockade worsened thermal and mechanical nociceptive pain thresholds in CFA inflammation. CONCLUSION: Endogenous opioids from monocytes/macrophages mediate endogenous antinociception in the late phase of inflammation. Peripheral TLR4 stimulation acts as a transient counter-regulatory mechanism for inflammatory pain in vivo, and increases the release of opioid peptides from monocytes in vitro. TLR4 antagonists as new treatments for sepsis and neuropathic pain might unexpectedly transiently enhance pain by impairing peripheral opioid analgesia.

Thoracic epidural anesthesia decreases endotoxin-induced endothelial injury.

BACKGROUND: The sympathetic nervous system is considered to modulate the endotoxin-induced activation of immune cells. Here we investigate whether thoracic epidural anesthesia with its regional symapathetic blocking effect alters endotoxin-induced leukocyte-endothelium activation and interaction with subsequent endothelial injury. METHODS: Sprague Dawley rats were anesthetized, cannulated and hemodynamically monitored. E. coli lipopolysaccharide (Serotype 0127:B8, 1.5 mg x kg(-1) x h(-1)) or isotonic saline (controls) was infused for 300 minutes. An epidural catheter was inserted for continuous application of lidocaine or normal saline in endotoxemic animals and saline in controls. After 300 minutes we measured catecholamine and cytokine plasma concentrations, adhesion molecule expression, leukocyte adhesion, and intestinal tissue edema. RESULTS: In endotoxemic animals with epidural saline, LPS significantly increased the interleukin-1ß plasma concentration (48%), the expression of endothelial adhesion molecules E-selectin (34%) and ICAM-1 (42%), and the number of adherent leukocytes (40%) with an increase in intestinal myeloperoxidase activity (26%) and tissue edema (75%) when compared to healthy controls. In endotoxemic animals with epidural infusion of lidocaine the values were similar to those in control animals, while epinephrine plasma concentration was 32% lower compared to endotoxemic animals with epidural saline. CONCLUSIONS: Thoracic epidural anesthesia attenuated the endotoxin-induced increase of IL-1ß concentration, adhesion molecule expression and leukocyte-adhesion with subsequent endothelial injury. A potential mechanism is the reduction in the plasma concentration of epinephrine.

Molecular and clinical markers of pain relief in complex regional pain syndrome: An observational study.

BACKGROUND: Complex regional pain syndrome (CRPS) is marked by disproportionate pain after trauma. Whilst the long-term outcome is crucial to patients, predictors or biomarkers of the course of pain or CRPS symptoms are still lacking. In particular, microRNAs, such as miR-223, decreased in CRPS, have been described only in cross-sectional studies. METHODS: In this study, we characterised CRPS patients over a course of 2.5 years of standard treatment. The patient underwent clinical examination including pain measurement, symptom questionnaires, quantitative sensory testing (QST) and blood sampling. Exosomal microRNA levels were measured via qPCR. After follow-up, patients were stratified into 'pain relief' (mean pain reduced by ≥2 numeric rating scale) or 'persistence' (mean pain unchanged or worsened). The primary outcome was miR-223 and miR-939 expression, secondary outcomes were differences in clinical parameters between groups and time points. RESULTS: Thirty-nine patients were included, 33 of whom qualified for stratification. Overall, patients reported lower pain and improved clinical characteristics after 2.5 years, but no significant changes in QST or miR-223 and miR-939 expression levels. 16 patients met the criteria for pain relief. This was associated with stable exosomal miR-223 expression, whilst levels further decreased in pain persistence. Clinically, pain relief was marked by shorter disease duration and correlated positively with high initial pain. CONCLUSION: We identified progressively reduced miR-223 as a putative biomarker of chronic CRPS pain. Clinically, this study underlines the importance of early diagnosis and treatment showing that high initial pain does not predict an unfavourable outcome. Finally, pain relief and recovery of sensory disturbances seem independent processes.

Development and Evaluation of an MRI Artifact-Free Aneurysm Clip.

BACKGROUND AND OBJECTIVES: The digital subtraction angiography is still the gold standard in the follow-up after aneurysm surgery, although it remains a repeating invasive technique with accumulating X-ray exposure. An alternative magnetic resonance angiography has the disadvantage of metal-related artifacts. A metal-free aneurysm clip could overcome this problem. Recent advances in manufacturing technologies of fiber-reinforced plastics might allow developing a prototype of a metal-free clip. METHODS: The prototype was formed out of carbon fiber-reinforced polyetheretherketone (CF-PEEK) in accordance with the standard clip design. In vivo and in vitro studies were performed to analyze the central nervous system biocompatibility. The prototype was tested in a phantom in a 3 T MRI scanner and microtomography scanner. For in vivo assessment, the left renal artery of rats was either ligated with a suture, clipped with a regular titanium clip or with the CF-PEEK prototype clip. The animals underwent standard MRI sequences and magnetic resonance angiography and assessment by a blinded neuroradiologist. RESULTS: Phantom studies showed no signs of artifacts. The prototype showed a reliable clamping and reopening after clip application, although the clamping force was reduced. In vivo studies showed a successful occlusion of the renal artery in all cases in the magnetic resonance angiography. Clip artifacts were statistically significant reduced in the prototype group (P < .01). CF-PEEK showed no signs of impaired biocompatibility compared with the titanium samples in vitro and in vivo. CONCLUSION: Former attempts of metal-free aneurysm clips did not meet the criteria of the standard clip design. In this study, the practicability of this new CF-PEEK artifact-free aneurysm clip has been proven. The further fabrication developments should overcome the problem of a reduced clamping force in the future. After clinical approval, it will improve the magnetic resonance image quality and might help to reduce the amount of digital subtraction angiography in the follow-up.

A peptidomimetic tight junction modulator to improve regional analgesia.

The paracellular flux of solutes through tissue barriers is limited by transmembrane tight junction proteins. Within the family of tight junction proteins, claudin-1 seems to be a key protein for tightness formation and integrity. In the peripheral nervous system, the nerve fibers are surrounded with a barrier formed by the perineurium which expresses claudin-1. To enhance the access of hydrophilic pharmaceutical agents via the paracellular route, a claudin-1 specific modulator was developed. For this purpose, we designed and investigated the claudin-1 derived peptide C1C2. It transiently increased the paracellular permeability for ions and high and low molecular weight compounds through a cellular barrier model. Structural studies revealed a ß-sheet potential for the functionality of the peptide. Perineurial injection of C1C2 in rats facilitated the effect of hydrophilic antinociceptive agents and raised mechanical nociceptive thresholds. The mechanism is related to the internalization of C1C2 and to a vesicle-like distribution within the cells. The peptide mainly colocalized with intracellular claudin-1. C1C2 decreased membrane-localized claudin-1 of cells in culture and in vivo in the perineurium of rats after perineurial injection. In conclusion, a novel tool was developed to improve the delivery of pharmaceutical agents through the perineurial barrier by transient modulation of claudin-1.

Modulation of tight junction proteins in the perineurium to facilitate peripheral opioid analgesia.

BACKGROUND: Peripheral application of opioids reduces inflammatory pain but is less effective in noninflamed tissue of rats and human patients. Hypertonic solutions can facilitate the antinociceptive activity of hydrophilic opioids in noninflamed tissue in vivo. However, the underlying mechanisms are not well understood. We hypothesized that the enhanced efficacy of opioids may be because of opening of the perineurial barrier formed by tight junction-proteins like claudin-1. METHODS: Male Wistar rats were treated intraplantarly with 10% NaCl. Pain behavior (n = 6) and electrophysiological recordings (n = 9 or more) from skin-nerve preparations after local application of the opioid [d-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO) were explored. Tight junction-proteins as well as permeability of the barrier were examined by immunohistochemistry and Western blot (n = 3 or more). RESULTS: Local administration of 10% NaCl facilitated increased mechanical nociceptive thresholds in response to DAMGO, penetration of horseradish peroxidase into the nerve, as well as a reduced response of C- but not Aδ-nociceptors to mechanical stimulation after application of DAMGO in the skin-nerve preparation. In noninflamed paw tissue, claudin-1 was expressed in the epidermis, blood vessels, and the perineurium, surrounding neurons immunoreactive for calcitonin gene-related peptide or protein gene product 9.5. Claudin-1 but not claudin-5 or occludin was significantly reduced after pretreatment with 10% NaCl. Intraplantar application of a metalloproteinase inhibitor (GM6001) completely reversed these effects. CONCLUSION: Hypertonic saline opens the perineurial barrier via metalloproteinase activation and claudin-1 regulation, thereby allowing access of hydrophilic drugs to peripheral opioid receptors. This principle may be used to specifically target hydrophilic drugs to peripheral neurons.

Chronic morphine use does not induce peripheral tolerance in a rat model of inflammatory pain.

Although opioids are highly effective analgesics, they are also known to induce cellular adaptations resulting in tolerance. Experimental studies are often performed in the absence of painful tissue injury, which precludes extrapolation to the clinical situation. Here we show that rats with chronic morphine treatment do not develop signs of tolerance at peripheral mu-opioid receptors (micro-receptors) in the presence of painful CFA-induced paw inflammation. In sensory neurons of these animals, internalization of mu-receptors was significantly increased and G protein coupling of mu-receptors as well as inhibition of cAMP accumulation were preserved. Opioid receptor trafficking and signaling were reduced, and tolerance was restored when endogenous opioid peptides in inflamed tissue were removed by antibodies or by depleting opioid-producing granulocytes, monocytes, and lymphocytes with cyclophosphamide (CTX). Our data indicate that the continuous availability of endogenous opioids in inflamed tissue increases recycling and preserves signaling of mu-receptors in sensory neurons, thereby counteracting the development of peripheral opioid tolerance. These findings infer that the use of peripherally acting opioids for the prolonged treatment of inflammatory pain associated with diseases such as chronic arthritis, inflammatory neuropathy, or cancer, is not necessarily accompanied by opioid tolerance.

Mycobacteria attenuate nociceptive responses by formyl peptide receptor triggered opioid peptide release from neutrophils.

In inflammation, pain is regulated by a balance of pro- and analgesic mediators. Analgesic mediators include opioid peptides which are secreted by neutrophils at the site of inflammation, leading to activation of opioid receptors on peripheral sensory neurons. In humans, local opioids and opioid peptides significantly downregulate postoperative as well as arthritic pain. In rats, inflammatory pain is induced by intraplantar injection of heat inactivated Mycobacterium butyricum, a component of complete Freund's adjuvant. We hypothesized that mycobacterially derived formyl peptide receptor (FPR) and/or toll like receptor (TLR) agonists could activate neutrophils, leading to opioid peptide release and inhibition of inflammatory pain. In complete Freund's adjuvant-induced inflammation, thermal and mechanical nociceptive thresholds of the paw were quantified (Hargreaves and Randall-Selitto methods, respectively). Withdrawal time to heat was decreased following systemic neutrophil depletion as well as local injection of opioid receptor antagonists or anti-opioid peptide (i.e. Met-enkephalin, beta-endorphin) antibodies indicating an increase in pain. In vitro, opioid peptide release from human and rat neutrophils was measured by radioimmunoassay. Met-enkephalin release was triggered by Mycobacterium butyricum and formyl peptides but not by TLR-2 or TLR-4 agonists. Mycobacterium butyricum induced a rise in intracellular calcium as determined by FURA loading and calcium imaging. Opioid peptide release was blocked by intracellular calcium chelation as well as phosphoinositol-3-kinase inhibition. The FPR antagonists Boc-FLFLF and cyclosporine H reduced opioid peptide release in vitro and increased inflammatory pain in vivo while TLR 2/4 did not appear to be involved. In summary, mycobacteria activate FPR on neutrophils, resulting in tonic secretion of opioid peptides from neutrophils and in a decrease in inflammatory pain. Future therapeutic strategies may aim at selective FPR agonists to boost endogenous analgesia.

[Acute pain therapy for non opioid-naive patients]. / Der chronische Schmerzpatient als Notfall. Akutschmerztherapie bei opioidgewöhnten Patienten.

Patients used to opioids belong to 2 groups: patients under opioid therapy due to tumor pain or chronic non malignant pain and, second, opioid addicts with current uncontrolled abuse, under substitution therapy or former opioid addicts ("clean"). Perioperatively these patients are difficult to manage because of the complex medical as well as psychosocial factors. Despite these problems, these patients have a right to receive sufficient perioperative pain therapy and this should not be withheld. Due to the lack of controlled studies this review summarizes standardized examples and alternatives in the acute pain treatment of patients using opioids. Early interdisciplinary cooperation, prevention of withdrawal through substitution of opioids and alternative treatment strategies like regional analgesia or ketamine as well as carefully titration of opioids are the essential components of the treatment of these patients. Furthermore, these patients require a clear and empathic guidance by medical and nursing staff.

Selective blood-nerve barrier leakiness with claudin-1 and vessel-associated macrophage loss in diabetic polyneuropathy.

Diabetic polyneuropathy (DPN) is the most common complication in diabetes and can be painful in up to 26% of all diabetic patients. Peripheral nerves are shielded by the blood-nerve barrier (BNB) consisting of the perineurium and endoneurial vessels. So far, there are conflicting results regarding the role and function of the BNB in the pathophysiology of DPN. In this study, we analyzed the spatiotemporal tight junction protein profile, barrier permeability, and vessel-associated macrophages in Wistar rats with streptozotocin-induced DPN. In these rats, mechanical hypersensitivity developed after 2 weeks and loss of motor function after 8 weeks, while the BNB and the blood-DRG barrier were leakier for small, but not for large molecules after 8 weeks only. The blood-spinal cord barrier remained sealed throughout the observation period. No gross changes in tight junction protein or cytokine expression were observed in all barriers to blood. However, expression of Cldn1 mRNA in perineurium was specifically downregulated in conjunction with weaker vessel-associated macrophage shielding of the BNB. Our results underline the role of specific tight junction proteins and BNB breakdown in DPN maintenance and differentiate DPN from traumatic nerve injury. Targeting claudins and sealing the BNB could stabilize pain and prevent further nerve damage. KEY MESSAGES: • In diabetic painful neuropathy in rats: • Blood nerve barrier and blood DRG barrier are leaky for micromolecules. • Perineurial Cldn1 sealing the blood nerve barrier is specifically downregulated. • Endoneurial vessel-associated macrophages are also decreased. • These changes occur after onset of hyperalgesia thereby maintaining rather than inducing pain.

Stabilization of Delphinidin in Complex with Sulfobutylether-ß-Cyclodextrin Allows for Antinociception in Inflammatory Pain.

Aims: Delphinidin (DEL) is a plant-derived antioxidant with clinical potential to treat inflammatory pain but suffers from poor solubility and low bioavailability. The aim of the study was to develop a well-tolerated cyclodextrin (CD)-DEL complex with enhanced bioavailability and to investigate the mechanisms behind its antinociceptive effects in a preclinical model of inflammatory pain. Results: CD-DEL was highly soluble and stable in aqueous solution, and was nontoxic. Systemic administration of CD-DEL reversed mechanical and heat hyperalgesia, while its local application into the complete Freund's adjuvant (CFA)-induced inflamed paw dose-dependently reduced mechanical hyperalgesia, paw volume, formation of the lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE), and tissue migration of CD68+ macrophages. CD-DEL also directly prevented 4-HNE-induced mechanical hyperalgesia, cold allodynia, and an increase in the intracellular calcium concentration into transient receptor potential ankyrin 1 expressing cells. Both 4-HNE- and CFA-induced reactive oxygen species (ROS) levels were sensitive to CD-DEL, while its capacity to scavenge superoxide anion radicals (inhibitory concentration 50 [IC50]: 70 ± 5 µM) was higher than that observed for hydroxyl radicals (IC50: 600 ± 50 µM). Finally, CD-DEL upregulated heme oxygenase 1 that was prevented by HMOX-1 siRNA in vitro. Innovation:In vivo application of DEL to treat inflammatory pain is facilitated by complexation with CD. Apart from its antioxidant effects, the CD-DEL has a unique second antioxidative mechanism involving capturing of 4-HNE into the CD cavity followed by displacement and release of the ROS scavenger DEL. Conclusion: CD-DEL has antinociceptive, antioxidative, and anti-inflammatory effects making it a promising formulation for the local treatment of inflammatory pain.

T lymphocytes containing ß-endorphin ameliorate mechanical hypersensitivity following nerve injury.

Neuropathic pain is a debilitating consequence of nerve injuries and is frequently resistant to classical therapies. T lymphocytes mediate adaptive immune responses and have been suggested to generate neuropathic pain. In contrast, in this study we investigated T cells as a source of opioidergic analgesic ß-endorphin for the control of augmented tactile sensitivity following neuropathy. We employed in vivo nociceptive (von Frey) testing, flow cytometry and immunofluorescence in wild-type and mice with severe combined immunodeficiency (SCID) subjected to a chronic constriction injury of the sciatic nerve. In wild-type mice, T lymphocytes constituted approximately 11% of all immune cells infiltrating the injury site, and they expressed ß-endorphin and receptors for corticotropin-releasing factor (CRF), an agent releasing opioids from leukocytes. CRF applied at the nerve injury site fully reversed neuropathy-induced mechanical hypersensitivity in wild-type animals. In SCID mice, T cells expressing ß-endorphin and CRF receptors were absent at the damaged nerve. Consequently, these animals had substantially reduced CRF-mediated antinociception. Importantly, the decreased antinociception was fully restored by transfer of wild-type mice-derived T lymphocytes in SCID mice. The re-established CRF antinociception could be reversed by co-injection of an antibody against ß-endorphin or an opioid receptor antagonist with limited access to the central nervous system. We propose that, in response to CRF stimulation, T lymphocytes accumulating at the injured nerves utilize ß-endorphin for activation of local neuronal opioid receptors to reduce neuropathy-induced mechanical hypersensitivity. Our findings reveal ß-endorphin-containing T cells as a crucial component of beneficial adaptive immune responses associated with painful peripheral nerve injuries.

The clinical (ir)relevance of opioid-induced immune suppression.

PURPOSE OF REVIEW: Opioid-induced immune suppression has been demonstrated in cell culture experiments and in animal models. This review examines whether opioids also increase the risk of infections in the perioperative setting or on the ICU. RECENT FINDINGS: Only a few studies are available. Patients receiving higher doses of systemic opioids had an increased risk of developing a pneumonia perioperatively. However, these results only occurred if laparoscopic vs. open surgery or epidural vs. systemic opioid therapy were compared. These differences are thought to reflect the better quality of analgesia and the improved ability to clear secretions. Alternatively, systemic opioids could induce an immune suppression leading to infectious complications. In intensive care patients, opioid use correlated with infectious complications in patients with burn injuries but did not increase the rate of sepsis in neonates. One retrospective study indicated that opioid withdrawal might be an important risk factor. At present, it remains unclear whether the choice of an opioid, its dose, and mode of withdrawal influence infectious complications. SUMMARY: In contrast to in-vitro studies and to animal models, conclusive evidence is currently lacking that opioids induce clinically relevant infectious complications in patients. However, these findings should be interpreted with great caution, as almost no adequately designed trials have been performed. Peripherally selective opioid receptor antagonists might be useful if opioid-induced immune suppression should prove to be clinically relevant.

[Opioid induced cough: Do we know its pathophysiology and can it be eliminated?]. / Leser fragen - Experten antworten - Hustenreiz nach intravenöser Applikation von Opioiden.

The (intravenous) administration of opioids is frequently associated with the induction of cough. This phenomenon is usually neither harmful for the patient nor bothersome. However, in some situations a severe cough may interfere with imaging, diagnostic or therapeutic procedures and thus, anesthesiologists may want to know effective preventive measures. The existing literature is extremely diverse and the results of clinical trials are sometimes conflicting. Based on experimental investigations in accordance with clinical findings this systematic review of the existing evidence helps to guide the management strategy if opioid induced cough should be avoided. Promising strategies - among others - in order to achieve this aim consist for instance of decreasing the injection speed in conjunction with pre-administration of lidocaine or clonidine.

Pain Control by Targeting Oxidized Phospholipids: Functions, Mechanisms, Perspectives.

Within the lipidome oxidized phospholipids (OxPL) form a class of chemically highly reactive metabolites. OxPL are acutely produced in inflamed tissue and act as endogenous, proalgesic (pain-inducing) metabolites. They excite sensory, nociceptive neurons by activating transient receptor potential ion channels, specifically TRPA1 and TRPV1. Under inflammatory conditions, OxPL-mediated receptor potentials even potentiate the action potential firing rate of nociceptors. Targeting OxPL with D-4F, an apolipoprotein A-I mimetic peptide or antibodies like E06, specifically binding oxidized headgroups of phospholipids, can be used to control acute, inflammatory pain syndromes, at least in rodents. With a focus on proalgesic specificities of OxPL, this article discusses, how targeting defined substances of the epilipidome can contribute to mechanism-based therapies against primary and secondary chronic inflammatory or possibly also neuropathic pain.

COVID-19 Induced Acute Respiratory Distress Syndrome-A Multicenter Observational Study.

Background: Proportions of patients dying from the coronavirus disease-19 (COVID-19) vary between different countries. We report the characteristics; clinical course and outcome of patients requiring intensive care due to COVID-19 induced acute respiratory distress syndrome (ARDS). Methods: This is a retrospective, observational multicentre study in five German secondary or tertiary care hospitals. All patients consecutively admitted to the intensive care unit (ICU) in any of the participating hospitals between March 12 and May 4, 2020 with a COVID-19 induced ARDS were included. Results: A total of 106 ICU patients were treated for COVID-19 induced ARDS, whereas severe ARDS was present in the majority of cases. Survival of ICU treatment was 65.0%. Median duration of ICU treatment was 11 days; median duration of mechanical ventilation was 9 days. The majority of ICU treated patients (75.5%) did not receive any antiviral or anti-inflammatory therapies. Venovenous (vv) ECMO was utilized in 16.3%. ICU triage with population-level decision making was not necessary at any time. Univariate analysis associated older age, diabetes mellitus or a higher SOFA score on admission with non-survival during ICU stay. Conclusions: A high level of care adhering to standard ARDS treatments lead to a good outcome in critically ill COVID-19 patients.