title: The molecular link between C-C-chemokine ligand 2-induced leukocyte recruitment and hyperalgesia.
abstract: The chemokine C-C-chemokine ligand 2 (CCL2) (formerly known as MCP, macrophage chemotactic protein) is one of the important genes upregulated in different types of pain both in animals and humans. CCL2 governs the recruitment of C-C chemokine receptor 2-expressing monocytes into inflamed tissue. In contrast to neutrophilic chemokines, intraplantar injection of CCL2 in Wistar rats recruited macrophages and neutrophils and simultaneously lowered nociceptive thresholds. CCL2-induced hyperalgesia was abolished by prior systemic leukocyte depletion by cyclophosphamide and was reconstituted by local adoptive transfer of donor macrophages but not of neutrophils. Antagonists against transient receptor potential vannilloid 1 inhibited thermal and against transient receptor potential ankyrin 1 blocked mechanical hyperalgesia. Peripheral but not central activation of cyclooxygenase-2 (Cox-2) were critical for CCL2-induced hyperalgesia. In vitro CCL2 did not directly stimulate Cox-2 expression or prostaglandin E2 formation but slightly enhanced the formation of reactive oxygen species in monocytes and macrophages. In vivo, increased immunoreactivity for 4-hydroxy-2-nonenal (4-HNE), a downstream product of reactive oxygen species and known inducer of Cox-2, was observed and colocalized with Cox-2 in ED1 (CD68) positive infiltrating cells. No hyperalgesia, 4-HNE, or Cox-2 immunoreactivity was seen in leukocyte-depleted rats that were reconstituted with macrophages in the absence of CCL2, supporting the important role of CCL2.
  
  
  CONCLUSIONS
  CCL2 plays a dual role: 1) promoting monocyte/macrophage recruitment into tissue; and 2) potentially stimulating macrophages in the tissue to produce 4-HNE and subsequently Cox-2, all resulting in the induction of hyperalgesia via transient receptor potential vannilloid 1 and transient receptor potential ankyrin 1. This encourages pharmacological efforts targeting CCL2/C-C chemokine receptor 2 and macrophages for treatment of inflammatory pain.
authors.affiliation: Department of Anesthesiology, University Hospital of Würzburg, Würzburg, Germany.
authors.forename: Diana
authors.initials: D
authors.lastname: Pflücke
authors.forename: Dagmar
authors.initials: D
authors.lastname: Hackel
authors.forename: Shaaban A
authors.initials: SA
authors.lastname: Mousa
authors.forename: Anna
authors.initials: A
authors.lastname: Partheil
authors.forename: Annick
authors.initials: A
authors.lastname: Neumann
authors.forename: Alexander
authors.initials: A
authors.lastname: Brack
authors.forename: Heike L
authors.initials: HL
authors.lastname: Rittner
mesh_terms: D000447:Aldehydes / Q000494:pharmacology; D000818:Animals; D018932:Chemokine CCL2 / Q000633:toxicity*; D002922:Ciguatoxins / Q000633:toxicity; D003520:Cyclophosphamide / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000473:pathology*; D007166:Immunosuppressive Agents / Q000633:toxicity*; D007962:Leukocytes / Q000187:drug effects*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008297:Male; D017288:Pain Threshold / Q000187:drug effects*; D010812:Physical Stimulation / Q000009:adverse effects; D011719:Pyrazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D054390:Receptors, CCR2 / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D000447:Aldehydes; C515336:Ccr2 protein, rat; D018932:Chemokine CCL2; D007166:Immunosuppressive Agents; C475772:N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamide; D011719:Pyrazines; D011725:Pyridines; D017382:Reactive Oxygen Species; D054390:Receptors, CCR2; D002922:Ciguatoxins; D003520:Cyclophosphamide; C027576:4-hydroxy-2-nonenal
keywords: CCL2; cyclooxygenase-2; electrophysiology; macrophages; reactive oxygen species; transient receptor potential ankyrin 1; transient receptor potential vannilloid 1