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Pain research

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Current projects

Development of novel analgesics without side effects

Figure signaling Fluorfentanyl pH
pH dependent opioid receptor signaling (copyright AG Stein, Giovanna Del Vecchio)

Christoph Stein, Halina Machelska 

Currently available drugs to treat severe pain are mu-opioid receptor ligands (e.g., morphine, fentanyl) that are limited by adverse effects such as sedation, cognitive impairment, apnoea, constipation, and addiction. Our goal is to develop new painkillers devoid of untoward side effects by using mathematical modelling, and to examine them in vitro and in vivo in models of pathological pain (Stein. Annu Rev Med 2016; Spahn, Del Vecchio et al., Science 2017)

Group members involved: Viola Spahn, Dominika Labuz, Antonio Rodriguez-Gaztelumendi, Giovanna Del Vecchio, Julia Temp, Michael Kloner, Sandeep Dembla 

Collaborators: M. Weber, O. Scharkoi, P. Deuflhard, M. Reidelbach, V. Durmaz, P. Sabri (Mathematics, Zuse Institut, Berlin) 

Funding: BMBF

Regulation of µ-opioid receptor function in inflammation

Regulation of µ-opioid receptor function in inflammation (copyright AG Stein, Johanna Meyer)

Christoph Stein

The analgesic potency of peripherally applied opioids is strongly increased in inflamed tissue. In this project we investigate how the function of the µ-opioid receptor is modulated by changes in pH as observed in the pathological state of inflammation. Following a multidisciplinary approach we combine methods from molecular and cellular biology with molecular simulations to elucidate the mechanisms underlying observations from behavioral experiments. Identifying disease-specific regulatory mechanisms will help to design novel opioids with reduced side-effects. 

Group members involved: Johanna Meyer, Giovanna Del Vecchio, Viola Spahn

Collaborator: M. Weber, V. Durmaz (Mathematics, Zuse Institute, Berlin)

Control of pain in experimental osteoarthritis

Figure Osteoarthritis
Regulation of pain in experimental osteoarthritis - the impact training on endogeneous proalgesic and analgesic mechanisms (copyright AG Machelska, Julia Temp)

Halina Machelska

Osteoarthritis (OA) is a common chronic degenerative disease of the joints, and the knee is most often affected. OA affects millions of people worldwide and its risk increases with age. Pain is the major debilitating sign of OA; it impairs function and quality of life. Current pharmacological and surgical treatments are unsatisfactory and produce serious complications. In this project we focus on a non-pharmacological, non-invasive approach to ameliorate OA pain, namely vibration-based exercise. We aim to elucidate the mechanisms underlying the analgesia resulting from whole body vibration. Since OA pain involves peripheral and central nervous system mechanisms, we investigate the impact of vibration on pain-promoting and pain-inhibiting mediators in the knee, peripheral neurons, spinal cord, and brain. 

Group members involved: Julia Temp, Dominika Labuz, M. Özgür Celik

Collaborators: OVERLOAD-PrevOP consortium

Funding: BMBF (OVERLOAD-Prev-OP)

Intraarticular application of opioids in chronic arthritis

Christoph Stein

We investigate pain and inflammatory parameters (cytokines, immune cells) in knee joint tissue of chronic arthritis patients following intraarticular (i.a.) injections of morphine, a standard steroid or placebo. The primary hypothesis is that i.a. morphine results in significantly lower pain scores and supplemental analgesic consumption than placebo during the first week after injection, an efficacy comparable to standard i.a. steroid (dexamethasone) medication.

Group members involved: M. Özgür Celik

Collaborators: Joachim Sieper, Hildrun Haibel, Anja Kühl (Rheumatology, Charité CBF), Peter Martus (Clinical Epidemiology and applied Biostatistics, University Tübingen)


Regulation of neuropathic pain by opioid peptides and receptors in immune cells

Leukocyte opioid receptors mediate analgesia via Ca-regulated release of opioid peptides (copyright AG Machelska, Özgür Celik)

Halina Machelska

Neuropathic pain often results from nerve injury (e.g., amputation, compression), which can lead to inflammation (neuritis). Previously we found that damaged nerves express opioid receptors and are infiltrated by opioid peptide-containing immune cells (Labuz et al., J Clin Invest 2009; Labuz et al., Brain Behav Immun 2010; Schmidt et al., PloS One 2013). The traditional view is that opioids produce analgesia by acting at opioid receptors in neurons. We have now discovered that pain can be inhibited by activation of opioid receptors in immune cells. In contrast to the action of neuronal receptors which leads to the inhibition of the release of pain-inducing mediators (e.g., substance P), the activation of leukocyte opioid receptors results in the secretion of opioid peptides. The released opioid peptides act at local neuronal receptors and decrease neuropathy-triggered mechanical, but not heat pain (Celik et al., Brain Behav Immun 2016; Labuz et al., Sci Rep 2016). These data offer a previously unknown explanation for the effective analgesia of opioids applied to tissue infiltrated by immune cells in patients with postoperative pain and in animal models of neuropathic pain (Stein et al., J Clin Invest 1996; Labuz et al., J Pharmacol Exp Ther 2013). Our findings have broad clinical implications, since most painful conditions are associated with immune responses, including inflammatory neuropathies, arthritis, cancer, and postoperative pain. In several ongoing projects we investigate various populations of immune cells, including pro-inflammatory M1 and anti-inflammatory M2 macrophages. 

Group members involved: M. Özgür Celik, Dominika Labuz, Karen Henning

Collaborators: A. Zimmer (Institute of Molecular Psychiatry, Universitätsklinikum Bonn, Germany), B. Kieffer (McGill University, Montreal, Canada), C. Gavériaux-Ruff (University of Strasbourg, Ilkrich, France)

Funding: DFG

Neuropathic pain: genetic biomarkers and novel analgesics for individualized therapy

Quantitativ sensory testing (QST)
extensive phenotyping: Quantitativ sensory testing (picture: copyright TU München)

Christoph Stein

Up to 8% of the population suffers from neuropathic pain due to lesions in the peripheral or central nervous system. To enable "personalized" medicine, only a strict separation of neuropathic from other chronic pain syndromes allows individualized therapy. At present, diagnosis is based on medical history, subjective description of somatosensory symptoms and application of non-genetic diagnostic tests. Conventional pain medications are not sufficiently effective and limited by serious side effects. The search for new analgesics is extremely difficult because of the poor predictive validity of animal models and the high inter-individual variability of neuropathic pain manifestations and treatment responses. In collaboration with an interdisciplinary group of European pain researchers (NeuroPain consortium) we pursue the following aims:

  • Examination of phenotype-genotype associations predictive for neuropathic pain by extensive phenotyping
  • Investigation of the analgesic effect of a novel phytocannabinoid in a cohort of HIV-associated painful neuropathy
  • Pharmacogenomic studies in patients to evaluate genetic characteristics of responders and non-responders to this novel substance


Group members involved: Simone Scheffel, Luca Eibach, Madeleine Cardebring, Marie Lettau, M. Özgür Celik 

Collaborators: NeuroPain Consortium (particularly Helsinki University Central Hospital, Finland; DeCODE Genetics, Iceland; Imperial College London and GW Pharmaceuticals, England)

Funding: European Commission FP7 (NeuroPain), CRU, BIH

Transcriptional regulation and processing of opioid peptides in immune cells

Figure POMC
POMC mRNA expression (copyright AG Stein, Sitte N. et al. 2007)

Christoph Stein

Immune cell-derived beta-endorphin is a potent inhibitor of inflammatory pain in animals and in patients with arthritis. In lymph nodes of rats draining an inflamed hind paw the amounts of signal sequence-encoding (exon 2-3) proopiomelanocortin (POMC) mRNA and beta-endorphin increase. We are interested in factors that induce POMC gene expression in immune cells and that regulate posttranslational processing of POMC resulting in the production of beta-endorphin (Busch-Dienstfertig et al., Mol Pain 2012; Busch-Dienstfertig and González-Rodríguez, JAKSTAT 2013; Maddila et al., J Neuroimmune Pharm 2017). 

Group members involved: Santhosh Chandar Maddila, Nicole Vogel, Charlotte Jacobi 

Funding: BMBF (NEUROIMPA, ImmunoPain)

Development of kappa-opioid nanocarriers for pain control without side effects

Halina Machelska, Christoph Stein

The most commonly used analgesics are cyclooxygenase inhibitors (NSAIDs) and mu-opioid receptor agonists (e.g., morphine), which are limited by severe side effects such as stomach bleeding or ulcers, hypertension, kidney problems, constipation, respiratory failure, and addiction. To overcome these problems, selective kappa-opioid receptor agonists (e.g., U50,488H) have been developed. However, they were found to produce sedation, depressive-like behaviors and hallucinations, which result from kappa-receptor activation in the brain. In this collaborative, interdisciplinary project involving pain researches, biochemists and veterinarians, we develop and investigate nanocarriers (González-Rodríguez et al., eLife 2017) to deliver kappa-opioids selectively to peripheral inflamed tissue to inhibit pain at the site of its origin, without adverse effects produced by classical opioids, in rodent models and in veterinary practice.   

Group members involved: Dominika Labuz, Roger Negrete 

Collaborators: R. Haag (Chemistry, Freie Universität Berlin), S. Moré (DendroPharm GmbH) 

Funding: Investitionsbank Berlin, Europäische Fonds für regionale Entwicklung (EFRE), Charité

Opioid modulation of ion channels in peripheral sensory neurons

Figure GIRK staining
GIRK1 and GIRK2 staining in human skin (copyright AG Stein, Nockemann D. et al. 2013)

Christoph Stein, Halina Machelska

Opioids act through G-inhibitory protein-coupled opioid receptors located on central and peripheral pain-sensing neurons. Mechanisms involved in opioid analgesia include activation of G-protein-gated inwardly rectifying K+ (GIRK) channels and inhibition of voltage-gated Ca2+ channels. We examine GIRK/opioid receptor coupling in peripheral sensory neurons and its impact on peripheral opioid analgesia in inflammatory pain (Nockemann et al., EMBO Mol Med 2013; Stötzner et al. Front Pharmacol 2018). We also investigate other ion channels such as transient receptor potential A (TRPA) and the interactions between opioid receptors and vanilloid receptor type 1 (TRPV1) during withdrawal of chronically applied opioid as well as in the peripheral inhibition of neuropathic pain. We utilize in vivo analgesia testing, ex vivo electrophysiological patch clamp recordings, Ca2+- and K+-imaging in naïve and pathological pain conditions (Spahn et al., Pain 2013; Spahn et al., Mol Pharmacol 2014; Spahn et al., Methods Mol Biol 2015; Labuz et al., Neuropharmacology 2016).   

Group members involved: Dinah Nockemann, Viola Spahn, Philip Stötzner

Funding: DFG, BMBF (MedSys, NoPain)

Modeling pain switches

Figure Modelling Pain Switches
Modelling Pain Switches (copyright AG Stein, Viola Spahn)

Christoph Stein

This program project applies mathematical models of signaling switches involved in pain sensitization, optimizes and expands them by reflection on molecular, cellular as well as behavioral experiments, to finally apply their predictive power to enable a mechanism-based pain therapy in humans. Our project tests mathematical models electrophysiologically in primary sensory neurons and in in vivo models. Ultimately, testing in human patients with suitable sensory modality profiles is anticipated. 

Group members involved: Marian Brackmann, Viola Spahn

Collaborators: T. Hucho (Uni Köln), H. Seitz (Fraunhofer Inst. Potsdam), R. Baron (Uni Kiel), P. Reeh (Uni Erlangen), W. Marwan (Uni Magdeburg), M. Heiner (Uni Cottbus), F. Herberg (Uni Kassel) 

Funding: BMBF (e:Bio)

Previous projects

Role of kinin receptors B1 and B2 in the generation and inhibition of pain

Cecile Cayla

Kinins are produced in response to tissue trauma and inflammation and are involved in the initiation of pain and in the development of hypersensitivity. They act through two G protein coupled receptors, the constitutively expressed B2 receptor and the injury-induced B1 receptor. Our major research interest is to better understand the role of kinins in painful processes and answer the following questions: 

·         What are their overall contributions to hypersensitivity and pain?

·         What are the specific roles of each receptor?

·         Are kinin receptors also involved in antihyperalgesic mechanisms associated with inflammation and injury?

Group members involved: Katharina Kuschfeldt, Barbara Trampenau, Dominika Labuz

Collaborator: M. Bader (MDC, Berlin-Buch)

Funding: DFG, CA 793/1-1 (C. Cayla)


Immune cell-derived opioids and neuropathic pain

Halina Machelska

Neuropathic pain is a common consequence of peripheral nerve injuries such as amputation, diabetes, entrapment or compression, and represents one of the most devastating forms of chronic pain. This pain can persist long after the initiating nerve damaging event has healed, and is often refractory to conventional treatments. In addition to neuronal changes the activation of the immune system as a component of nerve injury is gaining increasing attention. The prevalent opinion points to immune cells as generators of neuropathic pain. In contrast, we have shown that leukocytes (CD45+ hematopoetic cells) containing opioid peptides contribute to the attenuation of pain in neuritis. In a model of neuropathic pain we demonstrated that these cells infiltrate the site of nerve damage. Following application of corticotropin-releasing factor (CRF) the immune cells secrete opioid peptides (beta-endorphin, Met-enkephalin, dynorphin A), which activate local neuronal opioid receptors (mu, delta, kappa) to produce analgesia. Moreover, we found that T lymphocytes represent an essential CD45+ cell population, which mediates analgesia in advanced neuropathy. These data define opioid peptide-containing immune cells as a new component of beneficial effects of neuroinflammation. 

Group members involved: Dominika Labuz, Yvonne Schmidt, Anja Schreiter

Funding: DFG, KFO 100/2, Project 1, MA 2437/1-4 (H. Machelska)


Enhancement of endogenous opioid function in experimental inflammatory pain

Halina Machelska, Christoph Stein

This project explores novel ways of pain control without adverse effects associated with classical anti-inflammatory drugs and centrally acting opioids. Immune cells infiltrating inflamed tissue produce and release opioid peptides. These peptides activate opioid receptors on peripheral terminals of sensory nerves and inhibit neuronal excitability, resulting in analgesia. Compared to conventional exogenous agonists, endogenous opioids have a reduced potential of inducing receptor downregulation, tolerance or paradoxical excitatory effects due to unphysiologically high exogenous agonist concentrations at the receptor. Here we blocked the peptidase-induced degradation of opioids in peripheral injured tissue to locally augment this physiological system. In a model of inflammatory pain we found that the peptidases (aminopeptidase N and neutral endopeptidase) are present and metabolically active in macrophages, granulocytes, and sciatic nerves from inflamed tissue. Blocking both peptidases by their selective inhibitors prevented the degradation of endogenous opioid peptides and decreased inflammatory pain.  Thus, leukocytes and peripheral nerves are important sources of peptidases in inflamed tissue, and their blockade promotes peripheral opioid analgesia.

Group members involved: Anja Schreiter, Stephanie Miceli, Dominika Labuz

Collaborators: B. Roques (Université Paris Descartes), J. Sieper (Rheumatologie, Charité Campus Benjamin Franklin), M. Schmelz (Institut für Anästhesiologie, Fakultät für Klinische Medizin Mannheim, Universität Heidelberg)

Funding: DFG, MA 243/2-1 (H. Machelska); DFG, STE 477/9-1 (C. Stein)


Machelska H, Stein C. Endogene Opioide: Ihre Wirkung kann man deutlich verstärken. AINS (Anästhesiologie, Intensivmedizin, Notfallmedizin, Schmerztherapie) 2013, 3:142-143

Opioid actions on nociceptor function following nerve damage and inflammation

Halina Machelska, Christoph Stein

Peripheral nerve injuries or inflammation often trigger a hypersensitivity to mechanical stimulation. Behavioral studies demonstrated efficient and side effect-free analgesia mediated by opioid receptors on peripheral sensory neurons. However, mechanistic approaches addressing such opioid properties in chronic pain are lacking. We employ immunohistochemical and electrophysiological in vitro skin-nerve recordings in models of neuropathic and inflammatory pain. The goal is to examine how peripheral tissue damage affects properties of peripheral sensory fibers and how opioids modulate these properties. In neuropathic pain model we found that behaviorally manifested neuropathy-induced mechanosensitivity does not require a sensitized state of cutaneous nociceptors in damaged nerves. In contrast, in inflammation the nociceptors were sensitized to mechanical stimulation. In both models, μ-opioid receptor agonists (DAMGO or fentanyl) applied on the nociceptor cutaneous receptive fields significantly elevated the mechanical thresholds and diminished the mechanically evoked discharges of Aδ and C nociceptors in injured tissue. Prevention of action potential generation or propagation in nociceptors might represent a cellular mechanism underlying peripheral opioid-mediated alleviation of mechanical hypersensitivity in neuropathy and somatic inflammation.

Group members involved: Yvonne Schmidt, Rabih A. Moshourab, Dominika Labuz

Funding: DFG, KFO 100/2, Project 1, MA 2437/1-4 (H. Machelska)


Subcellular pathways of opioid peptide synthesis, processing and release from leukocytes

Christoph Stein

This project examines the posttranslational processing of pro-opiomelanocortin, proenkephalin and prodynorphin in immune cells under conditions of painful inflammation. Knock-out mice lacking processing enzymes are used. These mice show defective changes in beta-endorphin, Met-enkephalin and/or dynorphin processing in the pituitary gland and the brain. We examine mechanisms of opioid peptide processing and release in immune cells from these animals.

Collaborator: S.A. Mousa, Charité Campus Virchow-Klinikum

Funding: DFG, KFO 100/2, Teilprojekt: Opioid peptide expression, processing and release from immune cells (S.A. Mousa, C. Stein)


Topical morphine for analgesia in patients with skin and mucosal lesions

Christoph Stein

Topically applied opioids have provided effective and safe analgesia when applied onto skin wounds. In animal models, opioids have been shown to enhance wound healing. This study has two arms: clinical and experimental. The clinical arm looks at the effect of morphine gel on analgesia when applied onto skin-graft wounds or oral mucosal lesions. We are also developing an animal model for assessing analgesia and wound healing in response to topical opioids. 

Group members involved: Ruth Zaslansky

Collaborators: M. Schäfer-Korting (Pharmacy, FU Berlin), A. Kopf (Anesthesiology, Charité Campus Benjamin Franklin), Y. Ullman & O. Fishelzon (Rambam Medical Center, Haifa, Israel), I. Kager and R. Likar (Landeskrankenhaus Klagenfurt, Austria), A.M. Schmidt-Westhausen (Oral Medicine, Charité Campus Benjamin Franklin)

Funding: International Anesthesia Research Society, Clinical Scholar Research Award 2006 (R. Zaslansky)


Differentiating peripherally from centrally mediated opioid analgesia

Christoph Stein, Halina Machelska

Peripherally mediated opioid analgesia may be achieved without adverse effects of centrally acting opioids. Efforts are made to design opioid agonists which do not pass the blood-brain barrier. Animal studies have shown that up to 50% of antinociceptive effects elicited by systemically applied conventional opioids can be attributed to peripheral opioid receptors. This project aims at defining the relative contribution of peripheral opioid receptors to morphine analgesia in clinical and experimental pain. In a clinical trial we found that following the selective blockade of peripheral opioid receptors by methylnaltrexone (MNX), a peripherally restricted opioid receptor antagonist, the patients' demand for morphine to achieve satisfactory postoperative pain relief was strongly increased (by about 40%). Thus, a significant proportion of analgesia produced by systemically administered morphine is mediated by peripheral opioid receptors in clinical postoperative pain. Drugs that selectively activate such receptors should have the potential to produce powerful clinical pain relief.

Group members involved: Dominika Labuz, Leonie Lang, Christina Jagla

Collaborators: M. Brandl, A. Okach, A. Timmermann, E. Nickel (Helios Kliniken Berlin), J. Eberitsch, K. Günther (Sana Kliniken Sommerfeld)

Funding: International Anesthesia Research Society, Clinical Scholar Research Award 2009 (L. Lang).