Control of inflammatory pain by chemokine-mediated recruitment of opioid-containing polymorphonuclear cells

Abstract

Opioid-containing leukocytes can counteract inflammatory hyperalgesia. Under stress or after local injection of corticotropin releasing factor (CRF), opioid peptides are released from leukocytes, bind to opioid receptors on peripheral sensory neurons and mediate antinociception. Since polymorphonuclear cells (PMN) are the predominant opioid-containing leukocyte subpopulation in early inflammation, we hypothesized that PMN and their recruitment by chemokines are important for peripheral opioid-mediated antinociception at this stage. Rats were intraplantarly injected with complete Freund's adjuvant (CFA). Using flow cytometry, immunohistochemistry, and ELISA, leukocyte subpopulations, chemokine receptor (CXCR2) expression on opioid-containing leukocytes and the CXCR2 ligands keratinocyte-derived chemokine (KC), macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant-2 (CINC-2) were quantified. Paw pressure threshold (PPT) was determined before and after intraplantar and subcutaneous injection of CRF with or without naloxone. PMN depletion was achieved by intravenous injection of an antiserum. Chemokines were blocked by intraplantar injection of anti-MIP-2 and/or anti-KC antiserum. We found that at 2 h post CFA (i) intraplantar but not subcutaneous injection of CRF produced dose-dependent and naloxone-reversible antinociception (P<0.05, ANOVA). (ii) Opioid-containing leukocytes in the paw and CRF-induced antinociception were reduced after PMN depletion (P<0.05, t-test). (iii) Opioid-containing leukocytes mostly expressed CXCR2. MIP-2 and KC, but not CINC-2 were detectable in inflamed but not in noninflamed tissue (P<0.05, ANOVA). (iv) Combined but not single blockade of MIP-2 and KC reduced the number of opioid-containing leukocytes and peripheral opioid-mediated antinociception (P<0.05, t-test; P>0.05, ANOVA). In summary, in early inflammation peripheral opioid-mediated antinociception is critically dependent on PMN and their recruitment by CXCR2 chemokines.

CD11b+Ly6G−myeloid cells mediate mechanical inflammatory pain hypersensitivity

“…Many of these studies used myeloperoxidase activity as a surrogate for neutrophil infiltration, even though flow cytometry provides a more accurate picture of the presence/absence of these cells. Intraplantar injection of chemokines has also been used to recruit neutrophils into the hind paw, but this might result in a different activation state of the cells than that caused by CFA or an incisional wound (56,59).…”

Modulation of Peripheral Sensory Neurons by the Immune System: Implications for Pain Therapy

“…Blocking selectins, ICAM-1, integrins ␣ 4 and ␤ 2 , or chemokines CXCL1 and CXCL2/3 in vivo substantially decreased opioid-producing immune cells in inflamed tissue or injured nerves (Machelska et al, 1998(Machelska et al, , 2004Brack et al, 2004c;Labuz et al, 2009). In addition, the recruitment of opioid-containing cells is dependent on neurokinin-1 receptors (which bind substance P) (Rittner et al, 2007b), on sensory and sympathetic neurons (Kager et al, 2010), and may be regulated by adhesion to neurons (Hua et al, 2006).…”

“…In inflamed rat paws it was shown that L-selectin, integrin ␤ 2 , and the CXC chemokine receptor 2 (CXCR2) are coexpressed by opioid peptide-containing leukocytes (Mousa et al, 2000;Brack et al, 2004c;Machelska et al, 2004). Blocking selectins, ICAM-1, integrins ␣ 4 and ␤ 2 , or chemokines CXCL1 and CXCL2/3 in vivo substantially decreased opioid-producing immune cells in inflamed tissue or injured nerves (Machelska et al, 1998(Machelska et al, , 2004Brack et al, 2004c;Labuz et al, 2009).…”

“…When applied to peripheral injured tissue, all the releasing agents mentioned in section II.B.4 can produce opioid-mediated antinociceptive effects in vivo. Depending on the agent, stage, and type of inflammation, these effects are mediated by different opioid peptides (Schä fer et al, 1994;Mousa et al, 2003;Binder et al, 2004;Brack et al, 2004c;Labuz et al, 2006Labuz et al, , 2009. Recent studies have suggested that ␣ 2 -adrenergic agonists and serine proteases can also induce antinociception via enhanced production and release of endogenous opioids in models of inflammation (Ansah and Pertovaara, 2007;Martin et al, 2009).…”

“…Recent studies have suggested that ␣ 2 -adrenergic agonists and serine proteases can also induce antinociception via enhanced production and release of endogenous opioids in models of inflammation (Ansah and Pertovaara, 2007;Martin et al, 2009). Various immunosuppressive treatments (e.g., cyclosporine A, depletion of granulocytes, blockade of chemokines or formyl peptide receptors, anti-selectin, anti-ICAM-1) reduce opioid-containing cells, opioidmediated antinociception, and/or baseline nociceptive thresholds in inflamed tissue (Schä fer et al, 1994;Machelska et al, 1998Machelska et al, , 2002Brack et al, 2004c;Rittner et al, 2006aRittner et al, , 2009aLabuz et al, 2009). Conversely, by transfer of allogenic lymphocytes (Hermanussen et al, 2004) or granulocytes (Rittner et al, 2006a), such impaired antinociception can be restored.…”