Publications by authors named "Achim Schmidtko"

58 Publications

Lack of efficacy of a partial adenosine A1 receptor agonist in neuropathic pain models in mice.

Purinergic Signal 2021 Jul 27. Epub 2021 Jul 27.

Institute of Pharmacology and Clinical Pharmacy, Goethe University Frankfurt, 60438, Frankfurt am Main, Germany.

Previous studies suggest that adenosine A receptors (AR) modulate the processing of pain. The aim of this study was to characterize the distribution of AR in nociceptive tissues and to evaluate whether targeting AR with the partial agonist capadenoson may reduce neuropathic pain in mice. The cellular distribution of AR in dorsal root ganglia (DRG) and the spinal cord was analyzed using fluorescent in situ hybridization. In behavioral experiments, neuropathic pain was induced by spared nerve injury or intraperitoneal injection of paclitaxel, and tactile hypersensitivities were determined using a dynamic plantar aesthesiometer. Whole-cell patch-clamp recordings were performed to assess electrophysiological properties of dissociated DRG neurons. We found AR to be expressed in populations of DRG neurons and dorsal horn neurons involved in the processing of pain. However, administration of capadenoson at established in vivo doses (0.03-1.0 mg/kg) did not alter mechanical hypersensitivity in the spared nerve injury and paclitaxel models of neuropathic pain, whereas the standard analgesic pregabalin significantly inhibited the pain behavior. Moreover, capadenoson failed to affect potassium currents in DRG neurons, in contrast to a full AR agonist. Despite expression of AR in nociceptive neurons, our data do not support the hypothesis that pharmacological intervention with partial AR agonists might be a valuable approach for the treatment of neuropathic pain.
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http://dx.doi.org/10.1007/s11302-021-09806-6DOI Listing
July 2021

cGMP signalling in dorsal root ganglia and the spinal cord: Various functions in development and adulthood.

Br J Pharmacol 2021 May 3. Epub 2021 May 3.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, Frankfurt am Main, Germany.

Cyclic GMP (cGMP) is a second messenger that regulates numerous physiological and pathophysiological processes. In recent years, more and more studies have uncovered multiple roles of cGMP signalling pathways in the somatosensory system. Accumulating evidence suggests that cGMP regulates different cellular processes from embryonic development through to adulthood. During embryonic development, a cGMP-dependent signalling cascade in the trunk sensory system is essential for axon bifurcation, a specific form of branching of somatosensory axons. In adulthood, various cGMP signalling pathways in distinct cell populations of sensory neurons and dorsal horn neurons in the spinal cord play an important role in the processing of pain and itch. Some of the involved enzymes might serve as a target for future therapies. In this review, we summarise the knowledge regarding cGMP-dependent signalling pathways in dorsal root ganglia and the spinal cord during embryonic development and adulthood, and the potential of targeting these pathways.
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http://dx.doi.org/10.1111/bph.15514DOI Listing
May 2021

Nox4-dependent upregulation of S100A4 after peripheral nerve injury modulates neuropathic pain processing.

Free Radic Biol Med 2021 05 28;168:155-167. Epub 2021 Mar 28.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, 60438 Frankfurt am Main, Germany. Electronic address:

Previous studies suggested that reactive oxygen species (ROS) produced by NADPH oxidase 4 (Nox4) affect the processing of neuropathic pain. However, mechanisms underlying Nox4-dependent pain signaling are incompletely understood. In this study, we aimed to identify novel Nox4 downstream interactors in the nociceptive system. Mice lacking Nox4 specifically in sensory neurons were generated by crossing Advillin-Cre mice with Nox4 mice. Tissue-specific deletion of Nox4 in sensory neurons considerably reduced mechanical hypersensitivity and neuronal action potential firing after peripheral nerve injury. Using a proteomic approach, we detected various proteins that are regulated in a Nox4-dependent manner after injury, including the small calcium-binding protein S100A4. Immunofluorescence staining and Western blot experiments confirmed that S100A4 expression is massively up-regulated in peripheral nerves and dorsal root ganglia after injury. Furthermore, mice lacking S100A4 showed increased mechanical hypersensitivity after peripheral nerve injury and after delivery of a ROS donor. Our findings suggest that S100A4 expression is up-regulated after peripheral nerve injury in a Nox4-dependent manner and that deletion of S100A4 leads to an increased neuropathic pain hypersensitivity.
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http://dx.doi.org/10.1016/j.freeradbiomed.2021.03.021DOI Listing
May 2021

Functional Coupling of Slack Channels and P2X3 Receptors Contributes to Neuropathic Pain Processing.

Int J Mol Sci 2021 Jan 2;22(1). Epub 2021 Jan 2.

Institut für Pharmakologie und Klinische Pharmazie, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main, Hessen, Germany.

The sodium-activated potassium channel Slack (K1.1, Slo2.2, or Kcnt1) is highly expressed in populations of sensory neurons, where it mediates the sodium-activated potassium current (I) and modulates neuronal activity. Previous studies suggest that Slack is involved in the processing of neuropathic pain. However, mechanisms underlying the regulation of Slack activity in this context are poorly understood. Using whole-cell patch-clamp recordings we found that Slack-mediated I in sensory neurons of mice is reduced after peripheral nerve injury, thereby contributing to neuropathic pain hypersensitivity. Interestingly, Slack is closely associated with ATP-sensitive P2X3 receptors in a population of sensory neurons. In vitro experiments revealed that Slack-mediated I may be bidirectionally modulated in response to P2X3 activation. Moreover, mice lacking Slack show altered nocifensive responses to P2X3 stimulation. Our study identifies P2X3/Slack signaling as a mechanism contributing to hypersensitivity after peripheral nerve injury and proposes a potential novel strategy for treatment of neuropathic pain.
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http://dx.doi.org/10.3390/ijms22010405DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7795269PMC
January 2021

Design, Synthesis, and Structure-Activity Relationship Studies of Dual Inhibitors of Soluble Epoxide Hydrolase and 5-Lipoxygenase.

J Med Chem 2020 10 12;63(20):11498-11521. Epub 2020 Oct 12.

Institute of Pharmaceutical Chemistry, Goethe-University of Frankfurt, Max-von-Laue Str. 9 D-60438 Frankfurt a.M., Germany.

Inhibition of multiple enzymes of the arachidonic acid cascade leads to synergistic anti-inflammatory effects. Merging of 5-lipoxygenase (5-LOX) and soluble epoxide hydrolase (sEH) pharmacophores led to the discovery of a dual 5-LOX/sEH inhibitor, which was subsequently optimized in terms of potency toward both targets and metabolic stability. The optimized lead structure displayed cellular activity in human polymorphonuclear leukocytes, oral bioavailability, and target engagement in vivo and demonstrated profound anti-inflammatory and anti-fibrotic efficiency in a kidney injury model caused by unilateral ureteral obstruction in mice. These results pave the way for investigating the therapeutic potential of dual 5-LOX/sEH inhibitors in other inflammation- and fibrosis-related disease models.
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http://dx.doi.org/10.1021/acs.jmedchem.0c00561DOI Listing
October 2020

Rab27a Contributes to the Processing of Inflammatory Pain in Mice.

Cells 2020 06 18;9(6). Epub 2020 Jun 18.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, 60438 Frankfurt am Main, Germany.

Tissue injury and inflammation may result in chronic pain, a severe debilitating disease that is associated with great impairment of quality of life. An increasing body of evidence indicates that members of the Rab family of small GTPases contribute to pain processing; however, their specific functions remain poorly understood. Here, we found using immunofluorescence staining and in situ hybridization that the small GTPase Rab27a is highly expressed in sensory neurons and in the superficial dorsal horn of the spinal cord of mice. Rab27a mutant mice, which carry a single-nucleotide missense mutation of Rab27a leading to the expression of a nonfunctional protein, show reduced mechanical hyperalgesia and spontaneous pain behavior in inflammatory pain models, while their responses to acute noxious mechanical and thermal stimuli is not affected. Our study uncovers a previously unrecognized function of Rab27a in the processing of persistent inflammatory pain in mice.
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http://dx.doi.org/10.3390/cells9061488DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7349490PMC
June 2020

Neuropathic and cAMP-induced pain behavior is ameliorated in mice lacking CNGB1.

Neuropharmacology 2020 07 6;171:108087. Epub 2020 Apr 6.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, 60438, Frankfurt am Main, Germany.

Cyclic nucleotide-gated (CNG) channels, which are directly activated by cAMP and cGMP, have long been known to play a key role in retinal and olfactory signal transduction. Emerging evidence indicates that CNG channels are also involved in signaling pathways important for pain processing. Here, we found that the expression of the channel subunits CNGA2, CNGA3, CNGA4 and CNGB1 in dorsal root ganglia, and of CNGA2 in the spinal cord, is transiently altered after peripheral nerve injury in mice. Specifically, we show using in situ hybridization and quantitative real-time RT-PCR that CNG channels containing the CNGB1b subunit are localized to populations of sensory neurons and predominantly excitatory interneurons in the spinal dorsal horn. In CNGB1 knockout (CNGB1) mice, neuropathic pain behavior is considerably attenuated whereas inflammatory pain behavior is normal. Finally, we provide evidence to support CNGB1 as a downstream mediator of cAMP signaling in pain pathways. Altogether, our data suggest that CNGB1-positive CNG channels specifically contribute to neuropathic pain processing after peripheral nerve injury.
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http://dx.doi.org/10.1016/j.neuropharm.2020.108087DOI Listing
July 2020

Redox regulation of soluble epoxide hydrolase does not affect pain behavior in mice.

Neurosci Lett 2020 03 30;721:134798. Epub 2020 Jan 30.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, 60438 Frankfurt am Main, Germany. Electronic address:

Signaling mediated by soluble epoxide hydrolase (sEH) has been reported to play an important role in pain processing. Previous studies revealed that sEH activity is inhibited by specific binding of electrophiles to a redox-sensitive thiol (Cys521) adjacent to the catalytic center of the hydrolase. Here, we investigated if this redox-dependent modification of sEH is involved in pain processing using "redox-dead" knockin-mice (sEH-KI), in which the redox-sensitive cysteine is replaced by serine. However, behavioral characterization of sEH-KI mice in various animal models revealed that acute nociceptive, inflammatory, neuropathic, and visceral pain processing is not altered in sEH-KI mice. Thus, our results suggest that redox-dependent modifications of sEH are not critically involved in endogenous pain signaling in mice.
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http://dx.doi.org/10.1016/j.neulet.2020.134798DOI Listing
March 2020

cGMP: a unique 2nd messenger molecule - recent developments in cGMP research and development.

Naunyn Schmiedebergs Arch Pharmacol 2020 02 18;393(2):287-302. Epub 2019 Dec 18.

Institute of Pharmacology and Clinical Pharmacy, Goethe University, Max-von-Laue-Str. 9, D-60438, Frankfurt am Main, Germany.

Cyclic guanosine monophosphate (cGMP) is a unique second messenger molecule formed in different cell types and tissues. cGMP targets a variety of downstream effector molecules and, thus, elicits a very broad variety of cellular effects. Its production is triggered by stimulation of either soluble guanylyl cyclase (sGC) or particulate guanylyl cyclase (pGC); both enzymes exist in different isoforms. cGMP-induced effects are regulated by endogenous receptor ligands such as nitric oxide (NO) and natriuretic peptides (NPs). Depending on the distribution of sGC and pGC and the formation of ligands, this pathway regulates not only the cardiovascular system but also the kidney, lung, liver, and brain function; in addition, the cGMP pathway is involved in the pathogenesis of fibrosis, inflammation, or neurodegeneration and may also play a role in infectious diseases such as malaria. Moreover, new pharmacological approaches are being developed which target sGC- and pGC-dependent pathways for the treatment of various diseases. Therefore, it is of key interest to understand this pathway from scratch, beginning with the molecular basis of cGMP generation, the structure and function of both guanylyl cyclases and cGMP downstream targets; research efforts also focus on the subsequent signaling cascades, their potential crosstalk, and also the translational and, ultimately, the clinical implications of cGMP modulation. This review tries to summarize the contributions to the "9th International cGMP Conference on cGMP Generators, Effectors and Therapeutic Implications" held in Mainz in 2019. Presented data will be discussed and extended also in light of recent landmark findings and ongoing activities in the field of preclinical and clinical cGMP research.
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http://dx.doi.org/10.1007/s00210-019-01779-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7260148PMC
February 2020

Loxapine for Treatment of Patients With Refractory, Chemotherapy-Induced Neuropathic Pain: A Prematurely Terminated Pilot Study Showing Efficacy But Limited Tolerability.

Front Pharmacol 2019 25;10:838. Epub 2019 Jul 25.

Institute of Pharmacology and Toxicology, Centre for Biomedical Education and Research (ZBAF), School of Medicine, Faculty of Health, Witten/Herdecke University, Witten, Germany.

Neuropathic pain is a debilitating and commonly treatment-refractory condition requiring novel therapeutic options. Accumulating preclinical studies indicate that the potassium channel Slack (K1.1) contributes to the processing of neuropathic pain, and that Slack activators, when injected into mice, ameliorate pain-related hypersensitivity. However, whether Slack activation might reduce neuropathic pain in humans remains elusive. Here, we evaluated the tolerability and analgesic efficacy of loxapine, a first-generation antipsychotic drug and Slack activator, in neuropathic pain patients. We aimed to treat 12 patients with chronic chemotherapy-induced, treatment-refractory neuropathic pain (pain severity ≥ 4 units on an 11-point numerical rating scale) in a monocentric, open label, proof-of-principle study. Patients received loxapine orally as add-on analgesic in a dose-escalating manner (four treatment episodes for 14 days, daily dose: 20, 30, 40, or 60 mg loxapine) depending on tolerability and analgesic efficacy. Patient-reported outcomes of pain intensity and/or relief were recorded daily. After enrolling four patients, this study was prematurely terminated due to adverse events typically occurring with first-generation antipsychotic drugs that were reported by all patients. In two patients receiving loxapine for at least two treatment episodes, a clinically relevant analgesic effect was found at a daily dose of 20-30 mg of loxapine. Another two patients tolerated loxapine only for a few days. Together, our data further support the hypothesis that Slack activation might be a novel strategy for neuropathic pain therapy. However, loxapine is no valid treatment option for painful polyneuropathy due to profound dopamine and histamine receptor-related side effects. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02820519.
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http://dx.doi.org/10.3389/fphar.2019.00838DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6669235PMC
July 2019

Narciclasine exerts anti-inflammatory actions by blocking leukocyte-endothelial cell interactions and down-regulation of the endothelial TNF receptor 1.

FASEB J 2019 08 24;33(8):8771-8781. Epub 2019 Apr 24.

Institute of Pharmaceutical Biology, Faculty of Biochemistry, Chemistry, and Pharmacy, Goethe University Frankfurt, Frankfurt, Germany.

The alkaloid narciclasine has been characterized extensively as an anticancer compound. Accumulating evidence suggests that narciclasine has anti-inflammatory potential; however, the underlying mechanism remains poorly understood. We hypothesized that narciclasine affects the activation of endothelial cells (ECs), a hallmark of inflammatory processes, which is a prerequisite for leukocyte-EC interaction. Thus, we aimed to investigate narciclasine's action on this process and to analyze the underlying mechanisms . In a murine peritonitis model, narciclasine reduced leukocyte infiltration, proinflammatory cytokine expression, and inflammation-associated abdominal pain. Moreover, narciclasine decreased rolling and blocked adhesion and transmigration of leukocytes . In cultured ECs, narciclasine inhibited the expression of cell adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin and blocked crucial steps of the NF-κB activation cascade: NF-κB promotor activity, p65 nuclear translocation, inhibitor of κB α (IκBα) phosphorylation and degradation, and IκBα kinase β and TGF-β-activated kinase 1 phosphorylation. Interestingly, these effects were based on the narciclasine-triggered loss of TNF receptor 1 (TNFR1). Our study highlights narciclasine as an interesting anti-inflammatory compound that effectively inhibits the interaction of leukocytes with ECs by blocking endothelial activation processes. Most importantly, we showed that the observed inhibitory action of narciclasine on TNF-triggered signaling pathways is based on the loss of TNFR1.-Stark, A., Schwenk, R., Wack, G., Zuchtriegel, G., Hatemler, M. G., Bräutigam, J., Schmidtko, A., Reichel, C. A., Bischoff, I., Fürst, R. Narciclasine exerts anti-inflammatory actions by blocking leukocyte-endothelial cell interactions and down-regulation of the endothelial TNF receptor 1.
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http://dx.doi.org/10.1096/fj.201802440RDOI Listing
August 2019

Distinct functions of soluble guanylyl cyclase isoforms NO-GC1 and NO-GC2 in inflammatory and neuropathic pain processing.

Pain 2019 Mar;160(3):607-618

Pharmakologisches Institut für Naturwissenschaftler, Goethe-Universität, Frankfurt am Main, Germany.

A large body of evidence indicates that nitric oxide (NO)/cGMP signaling essentially contributes to the processing of chronic pain. In general, NO-induced cGMP formation is catalyzed by 2 isoforms of guanylyl cyclase, NO-sensitive guanylyl cyclase 1 (NO-GC1) and 2 (NO-GC2). However, the specific functions of the 2 isoforms in pain processing remain elusive. Here, we investigated the distribution of NO-GC1 and NO-GC2 in the spinal cord and dorsal root ganglia, and we characterized the behavior of mice lacking either isoform in animal models of pain. Using immunohistochemistry and in situ hybridization, we demonstrate that both isoforms are localized to interneurons in the spinal dorsal horn with NO-GC1 being enriched in inhibitory interneurons. In dorsal root ganglia, the distribution of NO-GC1 and NO-GC2 is restricted to non-neuronal cells with NO-GC2 being the major isoform in satellite glial cells. Mice lacking NO-GC1 demonstrated reduced hypersensitivity in models of neuropathic pain, whereas their behavior in models of inflammatory pain was normal. By contrast, mice lacking NO-GC2 exhibited increased hypersensitivity in models of inflammatory pain, but their neuropathic pain behavior was unaltered. Cre-mediated deletion of NO-GC1 or NO-GC2 in spinal dorsal horn neurons recapitulated the behavioral phenotypes observed in the global knockout. Together, these results indicate that cGMP produced by NO-GC1 or NO-GC2 in spinal dorsal horn neurons exert distinct, and partly opposing, functions in chronic pain processing.
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http://dx.doi.org/10.1097/j.pain.0000000000001440DOI Listing
March 2019

Human adenovirus type 17 from species D transduces endothelial cells and human CD46 is involved in cell entry.

Sci Rep 2018 09 7;8(1):13442. Epub 2018 Sep 7.

Institute for Virology and Microbiology, Center for Biomedical Education and Research (ZBAF), Witten/Herdecke University, Witten, Germany.

More than 70 human adenoviruses with type-dependent pathogenicity have been identified but biological information about the majority of these virus types is scarce. Here we employed multiple sequence alignments and structural information to predict receptor usage for the development of an adenoviral vector with novel biological features. We report the generation of a cloned adenovirus based on human adenovirus type 17 (HAdV17) with high sequence homology to the well characterized human adenovirus type 37 (HAdV37) that causes epidemic keratoconjunctivitis (EKC). Our study revealed that human CD46 (CD46) is involved in cell entry of HAdV17. Moreover, we found that HAdV17 infects endothelial cells (EC) in vitro including primary cells at higher efficiencies compared to the commonly used human adenovirus type 5 (HAdV5). Using a human CD46 transgenic mouse model, we observed that HAdV17 displays a broad tropism in vivo after systemic injection and that it transduces ECs in this mouse model. We conclude that the HAdV17-based vector may provide a novel platform for gene therapy.
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http://dx.doi.org/10.1038/s41598-018-31713-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6128842PMC
September 2018

cGMP Imaging in Brain Slices Reveals Brain Region-Specific Activity of NO-Sensitive Guanylyl Cyclases (NO-GCs) and NO-GC Stimulators.

Int J Mol Sci 2018 Aug 7;19(8). Epub 2018 Aug 7.

Interfakultäres Institut für Biochemie, University of Tübingen, 72076 Tübingen, Germany.

Impaired NO-cGMP signaling has been linked to several neurological disorders. NO-sensitive guanylyl cyclase (NO-GC), of which two isoforms-NO-GC1 and NO-GC2-are known, represents a promising drug target to increase cGMP in the brain. Drug-like small molecules have been discovered that work synergistically with NO to stimulate NO-GC activity. However, the effects of NO-GC stimulators in the brain are not well understood. In the present study, we used Förster/fluorescence resonance energy transfer (FRET)-based real-time imaging of cGMP in acute brain slices and primary neurons of cGMP sensor mice to comparatively assess the activity of two structurally different NO-GC stimulators, IWP-051 and BAY 41-2272, in the cerebellum, striatum and hippocampus. BAY 41-2272 potentiated an elevation of cGMP induced by the NO donor DEA/NO in all tested brain regions. Interestingly, IWP-051 potentiated DEA/NO-induced cGMP increases in the cerebellum and striatum, but not in the hippocampal CA1 area or primary hippocampal neurons. The brain-region-selective activity of IWP-051 suggested that it might act in a NO-GC isoform-selective manner. Results of mRNA in situ hybridization indicated that the cerebellum and striatum express NO-GC1 and NO-GC2, while the hippocampal CA1 area expresses mainly NO-GC2. IWP-051-potentiated DEA/NO-induced cGMP signals in the striatum of NO-GC2 knockout mice but was ineffective in the striatum of NO-GC1 knockout mice. These results indicate that IWP-051 preferentially stimulates NO-GC1 signaling in brain slices. Interestingly, no evidence for an isoform-specific effect of IWP-051 was observed when the cGMP-forming activity of whole brain homogenates was measured. This apparent discrepancy suggests that the method and conditions of cGMP measurement can influence results with NO-GC stimulators. Nevertheless, it is clear that NO-GC stimulators enhance cGMP signaling in the brain and should be further developed for the treatment of neurological diseases.
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http://dx.doi.org/10.3390/ijms19082313DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6122017PMC
August 2018

Boosting Anti-Inflammatory Potency of Zafirlukast by Designed Polypharmacology.

J Med Chem 2018 07 22;61(13):5758-5764. Epub 2018 Jun 22.

Institute of Pharmaceutical Chemistry , Goethe University Frankfurt , Max-von-Laue-Straße 9 , D-60438 Frankfurt , Germany.

Multitarget design offers access to bioactive small molecules with potentially superior efficacy and safety. Particularly multifactorial chronic inflammatory diseases demand multiple pharmacological interventions for stable treatment. By minor structural changes, we have developed a close analogue of the cysteinyl-leukotriene receptor antagonist zafirlukast that simultaneously inhibits soluble epoxide hydrolase and activates peroxisome proliferator-activated receptor γ. The triple modulator exhibits robust anti-inflammatory activity in vivo and highlights the therapeutic potential of designed multitarget agents.
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http://dx.doi.org/10.1021/acs.jmedchem.8b00458DOI Listing
July 2018

The Absence of Sensory Axon Bifurcation Affects Nociception and Termination Fields of Afferents in the Spinal Cord.

Front Mol Neurosci 2018 8;11:19. Epub 2018 Feb 8.

Developmental Neurobiology, Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.

A cGMP signaling cascade composed of C-type natriuretic peptide, the guanylyl cyclase receptor Npr2 and cGMP-dependent protein kinase I (cGKI) controls the bifurcation of sensory axons upon entering the spinal cord during embryonic development. However, the impact of axon bifurcation on sensory processing in adulthood remains poorly understood. To investigate the functional consequences of impaired axon bifurcation during adult stages we generated conditional mouse mutants of Npr2 and cGKI ( and ) that lack sensory axon bifurcation in the absence of additional phenotypes observed in the global knockout mice. Cholera toxin labeling in digits of the hind paw demonstrated an altered shape of sensory neuron termination fields in the spinal cord of conditional Npr2 mouse mutants. Behavioral testing of both sexes indicated that noxious heat sensation and nociception induced by chemical irritants are impaired in the mutants, whereas responses to cold sensation, mechanical stimulation, and motor coordination are not affected. Recordings from C-fiber nociceptors in the hind limb skin showed that Npr2 function was not required to maintain normal heat sensitivity of peripheral nociceptors. Thus, the altered behavioral responses to noxious heat found in mice is not due to an impaired C-fiber function. Overall, these data point to a critical role of axonal bifurcation for the processing of pain induced by heat or chemical stimuli.
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http://dx.doi.org/10.3389/fnmol.2018.00019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5809486PMC
February 2018

Correction to: Meeting report of the 8 International Conference on "cGMP BcGMP: generators, effectors, and therapeutic implications" at Bamberg, Germany, from June 23 to 25, 2017.

Naunyn Schmiedebergs Arch Pharmacol 2018 03;391(3):347

Institute of Pharmacology, College of Pharmacy, Goethe University, Max-von-Laue-Str. 9, 60438, Frankfurt, Germany.

The article "Meeting report of the 8 International Conference on "cGMP BcGMP: generators, effectors, and therapeutic implications" at Bamberg, Germany, from June 23 to 25, 2017" was originally published Online First without open access. After publication in volume 390, issue 12, pages 1177-1188, the author decided to opt for Open Choice and to make the article an open access publication.
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http://dx.doi.org/10.1007/s00210-018-1472-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6828335PMC
March 2018

Meeting report of the 8 International Conference on cGMP "cGMP: generators, effectors, and therapeutic implications" at Bamberg, Germany, from June 23 to 25, 2017.

Naunyn Schmiedebergs Arch Pharmacol 2017 Dec 10;390(12):1177-1188. Epub 2017 Oct 10.

Institute of Pharmacology, College of Pharmacy, Goethe University, Max-von-Laue-Str. 9, 60438, Frankfurt, Germany.

Although the Nobel Prize for the discovery of nitric oxide (NO) dates back almost 20 years now, the knowledge about cGMP signaling is still constantly increasing. It looks even so that our understanding of the role of the soluble guanylyl cyclase (sGC) and particulate guanylyl cyclase (pGC) in health and disease is in many aspects at the beginning and far from being understood. This holds even true for the therapeutic impact of innovative drugs acting on both the NO/sGC and the pGC pathways. Since cGMP, as second messenger, is involved in the pathogenesis of numerous diseases within the cardiovascular, pulmonary, renal, and endocrine systems and also plays a role in neuronal, sensory, and tumor processes, drug applications might be quite broad. On the 8th International Conference on cGMP, held in Bamberg, Germany, world leading experts came together to discuss these topics. All aspects of cGMP research from the basic understanding of cGMP signaling to clinical applicability were discussed in depth. In addition, present and future therapeutic applications of cGMP-modulating pharmacotherapy were presented ( http://www.cyclicgmp.net/index.html ).
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http://dx.doi.org/10.1007/s00210-017-1429-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783999PMC
December 2017

K3.1 channels modulate the processing of noxious chemical stimuli in mice.

Neuropharmacology 2017 Oct 18;125:386-395. Epub 2017 Aug 18.

Pharmakologisches Institut für Naturwissenschaftler, Goethe-Universität, Fachbereich Biochemie, Chemie und Pharmazie, 60438 Frankfurt am Main, Germany; Institut für Pharmakologie und Toxikologie, Universität Witten/Herdecke, ZBAF, 58453 Witten, Germany.

Intermediate conductance calcium-activated potassium channels (K3.1) have been recently implicated in pain processing. However, the functional role and localization of K3.1 in the nociceptive system are largely unknown. We here characterized the behavior of mice lacking K3.1 (K3.1) in various pain models and analyzed the expression pattern of K3.1 in dorsal root ganglia (DRG) and the spinal cord. K3.1 mice demonstrated normal behavioral responses in models of acute nociceptive, persistent inflammatory, and persistent neuropathic pain. However, their behavioral responses to noxious chemical stimuli such as formalin and capsaicin were increased. Accordingly, formalin-induced nociceptive behavior was increased in wild-type mice after administration of the K3.1 inhibitor TRAM-34. In situ hybridization experiments detected K3.1 in most DRG satellite glial cells, in a minority of DRG neurons, and in ependymal cells lining the central canal of the spinal cord. Together, our data point to a specific inhibitory role of K3.1 for the processing of noxious chemical stimuli.
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http://dx.doi.org/10.1016/j.neuropharm.2017.08.021DOI Listing
October 2017

Rab7-a novel redox target that modulates inflammatory pain processing.

Pain 2017 07;158(7):1354-1365

Institute of Pharmacology, College of Pharmacy, Goethe University, Frankfurt am Main, Germany.

Chronic pain is accompanied by production of reactive oxygen species (ROS) in various cells that are important for nociceptive processing. Recent data indicate that ROS can trigger specific redox-dependent signaling processes, but the molecular targets of ROS signaling in the nociceptive system remain largely elusive. Here, we performed a proteome screen for pain-dependent redox regulation using an OxICAT approach, thereby identifying the small GTPase Rab7 as a redox-modified target during inflammatory pain in mice. Prevention of Rab7 oxidation by replacement of the redox-sensing thiols modulates its GTPase activity. Immunofluorescence studies revealed Rab7 expression to be enriched in central terminals of sensory neurons. Knockout mice lacking Rab7 in sensory neurons showed normal responses to noxious thermal and mechanical stimuli; however, their pain behavior during inflammatory pain and in response to ROS donors was reduced. The data suggest that redox-dependent changes in Rab7 activity modulate inflammatory pain sensitivity.
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http://dx.doi.org/10.1097/j.pain.0000000000000920DOI Listing
July 2017

The H2S-producing enzyme CSE is dispensable for the processing of inflammatory and neuropathic pain.

Brain Res 2015 Oct 10;1624:380-389. Epub 2015 Aug 10.

Pharmazentrum Frankfurt/ZAFES, Institute of Clinical Pharmacology, Goethe University, Frankfurt am Main, Germany. Electronic address:

Accumulating lines of evidence indicate that hydrogen sulfide (H2S) contributes to the processing of chronic pain. However, the sources of H2S production in the nociceptive system are poorly understood. Here we investigated the expression of the H2S releasing enzyme cystathionine γ-lyase (CSE) in the nociceptive system and characterized its role in chronic pain signaling using CSE deficient mice. We show that paw inflammation and peripheral nerve injury led to upregulation of CSE expression in dorsal root ganglia. However, conditional knockout mice lacking CSE in sensory neurons as well as global CSE knockout mice demonstrated normal pain behaviors in inflammatory and neuropathic pain models as compared to WT littermates. Thus, our results suggest that CSE is not critically involved in chronic pain signaling in mice and that sources different from CSE mediate the pain relevant effects of H2S.
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http://dx.doi.org/10.1016/j.brainres.2015.07.058DOI Listing
October 2015

Nitric oxide-mediated pain processing in the spinal cord.

Authors:
Achim Schmidtko

Handb Exp Pharmacol 2015 ;227:103-17

Institut für Pharmakologie und Toxikologie, Universität Witten/Herdecke, ZBAF, Stockumer Str. 10, 58453, Witten, Germany,

A large body of evidence indicates that nitric oxide (NO) plays an important role in the processing of persistent inflammatory and neuropathic pain in the spinal cord. Several animal studies revealed that inhibition or knockout of NO synthesis ameliorates persistent pain. However, spinal delivery of NO donors caused dual pronociceptive and antinociceptive effects, pointing to multiple downstream signaling mechanisms of NO. This review summarizes the localization and function of NO-dependent signaling mechanisms in the spinal cord, taking account of the recent progress made in this field.
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http://dx.doi.org/10.1007/978-3-662-46450-2_6DOI Listing
July 2015

Slack channels expressed in sensory neurons control neuropathic pain in mice.

J Neurosci 2015 Jan;35(3):1125-35

Institut für Pharmakologie und Toxikologie, Universität Witten/Herdecke, Zentrum für Biomedizinische Ausbildung und Forschung, 58453 Witten, Germany, Pharmazentrum Frankfurt/Zentrum für Arzneimittelforschung, Entwicklung und Sicherheit, Institut für Klinische Pharmakologie, Universitätsklinikum Frankfurt, 60590 Frankfurt am Main, Germany,

Slack (Slo2.2) is a sodium-activated potassium channel that regulates neuronal firing activities and patterns. Previous studies identified Slack in sensory neurons, but its contribution to acute and chronic pain in vivo remains elusive. Here we generated global and sensory neuron-specific Slack mutant mice and analyzed their behavior in various animal models of pain. Global ablation of Slack led to increased hypersensitivity in models of neuropathic pain, whereas the behavior in models of inflammatory and acute nociceptive pain was normal. Neuropathic pain behaviors were also exaggerated after ablation of Slack selectively in sensory neurons. Notably, the Slack opener loxapine ameliorated persisting neuropathic pain behaviors. In conclusion, Slack selectively controls the sensory input in neuropathic pain states, suggesting that modulating its activity might represent a novel strategy for management of neuropathic pain.
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http://dx.doi.org/10.1523/JNEUROSCI.2423-14.2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6605535PMC
January 2015

Nox2-dependent signaling between macrophages and sensory neurons contributes to neuropathic pain hypersensitivity.

Pain 2014 Oct 17;155(10):2161-70. Epub 2014 Aug 17.

Pharmazentrum Frankfurt/ZAFES, Institute of Clinical Pharmacology, Goethe University Medical School, Frankfurt am Main, Germany; Institute of Pharmacology and Toxicology, ZBAF, Witten/Herdecke University, Witten, Germany. Electronic address:

Emerging lines of evidence indicate that production of reactive oxygen species (ROS) at distinct sites of the nociceptive system contributes to the processing of neuropathic pain. However, the mechanisms underlying ROS production during neuropathic pain processing are not fully understood. We here detected the ROS-generating nicotinamide adenine dinucleotide phosphate oxidase isoform Nox2 in macrophages of dorsal root ganglia (DRG) in mice. In response to peripheral nerve injury, Nox2-positive macrophages were recruited to DRG, and ROS production was increased in a Nox2-dependent manner. Nox2-deficient mice displayed reduced neuropathic pain behavior after peripheral nerve injury, whereas their immediate responses to noxious stimuli were normal. Moreover, injury-induced upregulation of tumor necrosis factor α was absent, and activating transcription factor 3 induction was reduced in DRG of Nox2-deficient mice, suggesting an attenuated macrophage-neuron signaling. These data suggest that Nox2-dependent ROS production in macrophages recruited to DRG contributes to neuropathic pain hypersensitivity, underlining the observation that Nox-derived ROS exert specific functions during the processing of pain.
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http://dx.doi.org/10.1016/j.pain.2014.08.013DOI Listing
October 2014

Lack of effect of a P2Y6 receptor antagonist on neuropathic pain behavior in mice.

Pharmacol Biochem Behav 2014 Sep 18;124:389-95. Epub 2014 Jul 18.

Pharmazentrum Frankfurt/ZAFES, Institut für Klinische Pharmakologie, Universitätsklinikum Frankfurt, 60590 Frankfurt am Main, Germany; Institut für Pharmakologie und Toxikologie, ZBAF, Universität Witten/Herdecke, 58453 Witten, Germany. Electronic address:

Accumulating evidence indicates that various subtypes of purinergic receptors (P2X and P2Y receptor families) play an essential role in the development and the maintenance of neuropathic pain. However, there is only limited data available about the role of P2Y6 receptors in pain processing. Here we detected P2Y6 receptor immunoreactivity in primary afferent neurons of mice and observed an upregulation in response to peripheral nerve injury. However, systemic and intrathecal administration of the P2Y6 receptor antagonist MRS2578 failed to affect the injury-induced neuropathic pain behavior. Our results suggest that P2Y6 receptors, in contrast to other purinergic receptor subtypes, are not critically involved in nerve injury-induced neuropathic pain processing in mice.
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http://dx.doi.org/10.1016/j.pbb.2014.07.009DOI Listing
September 2014

Phosphodiesterase 2A localized in the spinal cord contributes to inflammatory pain processing.

Anesthesiology 2014 Aug;121(2):372-82

From the Pharmazentrum Frankfurt/Zentrum für Arzneimittelforschung, -entwicklung und -sicherheit, Institut für Klinische Pharmakologie, Universitätsklinikum Frankfurt, Frankfurt am Main, Germany (W.K-.G., R.L., A.B., D.T., J.E.L., N.L., N.F., G.G., A.S.); Institut für Pharmakologie und Toxikologie, Zentrum für Biomedizinische Ausbildung und Forschung, Universität Witten/Herdecke, Witten, Germany (R.L., C.I.R., A.S.); and Institut für Klinische Neuroanatomie, Neuroscience Center, Goethe-Universität, Frankfurt am Main, Germany (J.S., D.D.T.). Current address: Institut für Neuroradiologie, Universitätsklinikum Frankfurt, Frankfurt am Main, Germany (A.B.).

Background: Phosphodiesterase 2A (PDE2A) is an evolutionarily conserved enzyme that catalyzes the degradation of the cyclic nucleotides, cyclic adenosine monophosphate, and/or cyclic guanosine monophosphate. Recent studies reported the expression of PDE2A in the dorsal horn of the spinal cord, pointing to a potential contribution to the processing of pain. However, the functions of PDE2A in spinal pain processing in vivo remained elusive.

Methods: Immunohistochemistry, laser microdissection, and quantitative real-time reverse transcription polymerase chain reaction experiments were performed to characterize the localization and regulation of PDE2A protein and messenger RNA in the mouse spinal cord. Effects of the selective PDE2A inhibitor, BAY 60-7550 (Cayman Chemical, Ann Arbor, MI), in animal models of inflammatory pain (n = 6 to 10), neuropathic pain (n = 5 to 6), and after intrathecal injection of cyclic nucleotides (n = 6 to 8) were examined. Also, cyclic adenosine monophosphate and cyclic guanosine monophosphate levels in spinal cord tissues were measured by liquid chromatography tandem mass spectrometry.

Results: The authors here demonstrate that PDE2A is distinctly expressed in neurons of the superficial dorsal horn of the spinal cord, and that its spinal expression is upregulated in response to hind paw inflammation. Administration of the selective PDE2A inhibitor, BAY 60-7550, increased the nociceptive behavior of mice in animal models of inflammatory pain. Moreover, BAY 60-7550 increased the pain hypersensitivity induced by intrathecal delivery of cyclic adenosine monophosphate, but not of cyclic guanosine monophosphate, and it increased the cyclic adenosine monophosphate levels in spinal cord tissues.

Conclusion: Our findings indicate that PDE2A contributes to the processing of inflammatory pain in the spinal cord.
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http://dx.doi.org/10.1097/ALN.0000000000000270DOI Listing
August 2014

Oxidant-induced activation of cGMP-dependent protein kinase Iα mediates neuropathic pain after peripheral nerve injury.

Antioxid Redox Signal 2014 Oct 5;21(10):1504-15. Epub 2014 Mar 5.

1 Pharmazentrum Frankfurt/ZAFES, Institut für Klinische Pharmakologie, Universitätsklinikum Frankfurt , Frankfurt am Main, Germany .

Aims: Emerging lines of evidence indicate that oxidants such as hydrogen peroxide exert specific signaling functions during the processing of chronic pain. However, the mechanisms by which oxidants regulate pain processing in vivo remain poorly understood. Here, we investigated whether cyclic guanosine monophosphate (cGMP)-dependent protein kinase Iα (cGKIα), which can be activated by oxidants independently of cGMP, serves as a primary redox target during pain processing.

Results: After peripheral nerve injury, oxidant-induced cGKIα activation is increased in dorsal root ganglia of mice. Knock-in (KI) mice in which cGKIα cannot transduce oxidant signals demonstrated reduced neuropathic pain behaviors after peripheral nerve injury, and reduced pain behaviors after intrathecal delivery of oxidants. In contrast, acute nociceptive, inflammatory, and cGMP-induced pain behaviors were not impaired in these mice.

Innovation: Studying cGKIα KI mice, we provide the first evidence that oxidants activate cGKIα in sensory neurons after peripheral nerve injury in vivo.

Conclusion: Our results suggest that oxidant-induced activation of cGKIα specifically contributes to neuropathic pain processing, and that prevention of cGKIα redox activation could be a potential novel strategy to manage neuropathic pain.
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http://dx.doi.org/10.1089/ars.2013.5585DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4158966PMC
October 2014

BKCa channels expressed in sensory neurons modulate inflammatory pain in mice.

Pain 2014 Mar 11;155(3):556-565. Epub 2013 Dec 11.

Pharmazentrum Frankfurt/ZAFES, Institut für Klinische Pharmakologie, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany Pharmakologie, Toxikologie und Klinische Pharmazie, Institut für Pharmazie, Tübingen, Germany Pharmakologisches Institut, Universität Heidelberg, Heidelberg, Germany.

Large conductance calcium-activated potassium (BKCa) channels are important regulators of neuronal excitability. Although there is electrophysiological evidence for BKCa channel expression in sensory neurons, their in vivo functions in pain processing have not been fully defined. Using a specific antibody, we demonstrate here that BKCa channels are expressed in subpopulations of peptidergic and nonpeptidergic nociceptors. To test a functional association of BKCa channel activity in sensory neurons with particular pain modalities, we generated mice in which BKCa channels are ablated specifically from sensory neurons and analyzed their behavior in various models of pain. Mutant mice showed increased nociceptive behavior in models of persistent inflammatory pain. However, their behavior in models of neuropathic or acute nociceptive pain was normal. Moreover, systemic administration of the BKCa channel opener, NS1619, inhibited persistent inflammatory pain. Our investigations provide in vivo evidence that BKCa channels expressed in sensory neurons exert inhibitory control on sensory input in inflammatory pain states.
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http://dx.doi.org/10.1016/j.pain.2013.12.005DOI Listing
March 2014

Direct intrathecal drug delivery in mice for detecting in vivo effects of cGMP on pain processing.

Methods Mol Biol 2013 ;1020:215-21

Pharmazentrum Frankfurt/ZAFES, Institut für Klinische Pharmakologie, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany.

Intrathecal delivery of drugs is an important method in pain research in order to investigate pain-relevant effects in the spinal cord in vivo. Here, we describe a method of intrathecal drug delivery by direct lumbar puncture in mice. The procedure does not require surgery, is rapidly performed, and does not produce neurological deficits. If cGMP analogs are injected, a state of transient hindpaw hypersensitivity can be induced which is quantifiable by measurement of hindpaw withdrawal latency in response to mechanical stimulation.
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http://dx.doi.org/10.1007/978-1-62703-459-3_14DOI Listing
December 2013

Antioxidant activity of sestrin 2 controls neuropathic pain after peripheral nerve injury.

Antioxid Redox Signal 2013 Dec 19;19(17):2013-23. Epub 2013 Apr 19.

1 Pharmazentrum Frankfurt/ZAFES, Institute of Clinical Pharmacology, Goethe University Medical School , Frankfurt am Main, Germany .

Aims: Neuropathic pain is a chronic debilitating disease that is often unresponsive to currently available treatments. Emerging lines of evidence indicate that reactive oxygen species (ROS) are required for the development and maintenance of neuropathic pain. However, little is known about endogenous mechanisms that neutralize the pain-relevant effects of ROS. In the present study, we tested whether the stress-responsive antioxidant protein Sestrin 2 (Sesn2) blocks the ROS-induced neuropathic pain processing in vivo.

Results: We observed that Sesn2 mRNA and protein expression was up-regulated in peripheral nerves after spared nerve injury, a well-characterized model of neuropathic pain. Sesn2 knockout (Sesn2(-/-)) mice exhibited considerably increased late-phase neuropathic pain behavior, while their behavior in acute nociceptive and in inflammatory pain models remained unaffected. The exacerbated neuropathic pain behavior of Sesn2(-/-) mice was associated with elevated ROS levels and an enhanced activating transcription factor 3 up-regulation in sensory neurons, and it was reversed by the ROS scavenger N-tert-Butyl-α-phenylnitrone. In contrast, administration of the ROS donor tert-butyl hydroperoxide induced a prolonged pain behavior in naive Sesn2(-/-) mice.

Innovation: We show that the antioxidant function of Sesn2 limits neuropathic pain processing in vivo.

Conclusion: Sesn2 controls ROS-dependent neuropathic pain signaling after peripheral nerve injury and may, thus, provide a potential new target for the clinical management of chronic neuropathic pain conditions.
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http://dx.doi.org/10.1089/ars.2012.4958DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3869453PMC
December 2013
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