Peripheral Interaction of Resolvin D1 and E1 with Opioid Receptor Antagonists for Antinociception in Inflammatory Pain in Rats

Antinociceptive pathways are activated in the periphery in inflammatory pain, for instance resolvins and opioid peptides. Resolvins are biosynthesized from omega-3 polyunsaturated fatty acids such as eicosapentaenoic acid and docosahexaenoic acid. Resolvin D1 (RvD1) and resolvin E1 (RvE1) initiate the resolution of inflammation and control of hypersensitivity via induction of anti-inflammatory signaling cascades. RvD1 binds to lipoxin A4/annexin-A1 receptor/formyl-peptide receptor 2 (ALX/FPR2), RvE1 to chemerin receptor 23 (ChemR23). Antinociception of RvD1 is mediated by interaction with transient receptor potential channels ankyrin 1 (TRPA1). Endogenous opioid peptides are synthesized and released from leukocytes in the tissue and bind to opioid receptors on nociceptor terminals. Here, we further explored peripheral mechanisms of RvD1 and chemerin (Chem), the ligand of ChemR23, in complete Freund’s adjuvant (CFA)-induced hindpaw inflammation in male Wistar rats. RvD1 and Chem ameliorated CFA-induced hypersensitivity in early and late inflammatory phases. This was prevented by peripheral blockade of the μ-opioid peptide receptor (MOR) using low dose local naloxone or by local injection of anti-β-endorphin and anti-met-enkephalin (anti-ENK) antibodies. Naloxone also hindered antinociception by the TRPA1 inhibitor HC-030031. RvD1 did not stimulate the release of β-endorphin from macrophages and neutrophils, nor did RvD1 itself activate G-proteins coupled MOR or initiate β-arrestin recruitment to the membrane. TRPA1 blockade by HC-030031 in inflammation in vivo as well as inhibition of the TRPA1-mediated calcium influx in dorsal root ganglia neurons in vitro was hampered by naloxone. Peripheral application of naloxone alone in vivo already lowered mechanical nociceptive thresholds. Therefore, either a perturbation of the balance of endogenous pro- and antinociceptive mechanisms in early and late inflammation, or an interaction of TRPA1 and opioid receptors weaken the antinociceptive potency of RvD1 and TRPA1 blockers.

CXCL10 controls inflammatory pain via opioid peptide-containing macrophages in electroacupuncture

Acupuncture is widely used for pain treatment in patients with osteoarthritis or low back pain, but molecular mechanisms remain largely enigmatic. In the early phase of inflammation neutrophilic chemokines direct opioid-containing neutrophils in the inflamed tissue and stimulate opioid peptide release and antinociception. In this study the molecular pathway and neuroimmune connections in complete Freund's adjuvant (CFA)-induced hind paw inflammation and electroacupuncture for peripheral pain control were analyzed. Free moving Wistar rats with hind paw inflammation were treated twice with electroacupuncture at GB30 (Huan Tiao - gall bladder meridian) (day 0 and 1) and analyzed for mechanical and thermal nociceptive thresholds. The cytokine profiles as well as the expression of opioid peptides were quantified in the inflamed paw. Electroacupuncture elicited long-term antinociception blocked by local injection of anti-opioid peptide antibodies (beta-endorphin, met-enkephalin, dynorphin A). The treatment altered the cytokine profile towards an anti-inflammatory pattern but augmented interferon (IFN)-gamma and the chemokine CXCL10 (IP-10: interferon gamma-inducible protein) protein and mRNA expression with concomitant increased numbers of opioid peptide-containing CXCR3⁺ macrophages. In rats with CFA hind paw inflammation without acupuncture repeated injection of CXCL10 triggered opioid-mediated antinociception and increase opioid-containing macrophages. Conversely, neutralization of CXCL10 time-dependently decreased electroacupuncture-induced antinociception and the number of infiltrating opioid peptide-expressing CXCR3⁺ macrophages. In summary, we describe a novel function of the chemokine CXCL10 - as a regulator for an increase of opioid-containing macrophages and antinociceptive mediator in inflammatory pain and as a key chemokine regulated by electroacupuncture.

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 β-endorphin (β-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 β-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.

The molecular link between C-C-chemokine ligand 2-induced leukocyte recruitment and hyperalgesia

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.

PERSPECTIVE

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.

Long-term antinociception by electroacupuncture is mediated via peripheral opioid receptors in free-moving rats with inflammatory hyperalgesia

BACKGROUND

Electroacupuncture (EA) has been widely accepted and applied as an important acupuncture-related technique for acupuncture analgesia (AA) research. The involvement of opioid peptides and receptors in acute AA has been shown via pre-EA application of opioid receptor/peptide antagonists. In this study, we intended to reproducibly institute acupoint position and needling excluding influences from anaesthesia or restrainers on rats with complete Freund's adjuvant (CFA) hind paw inflammatory pain, as well as to explore opioid-dependency and anti-inflammatory effects in sustained acupuncture analgesia.

METHODS

Accurate position and needling approach on acupoint GB30 was modelled by computer-based three-dimensional (3D) images and followed by an optimal EA treatment protocol (100 Hz, 2-3 mA, 20 min) at 0 and 24 h post-CFA in conscious free-moving rats. Opioid receptor antagonists, naloxone (NLX) and naltrindole (NTI) were applied intraplantarly post-EA at late phase (96 h) of CFA. Nociceptive thresholds were assessed by paw pressure threshold (Randall-Sellito) or paw withdrawal latency (Hargreaves), and anti-inflammatory effects were evaluated by measurement of plantar temperature and paw volume.

RESULTS

EA elicited significant sustained mechanical and thermal antinociception up to 144 h. Mechanical antinociception of EA was suppressed by peripheral intraplantar application of NLX and NTI. EA also reduced paw temperature and volume during the same time frame indicating anti-inflammatory effects.

CONCLUSIONS

By employing a reproducible EA treatment model on GB30 in free-moving rats, we demonstrated the involvement of peripheral opioid receptors mediated EA-induced long-term antinociception. Future studies should examine the specific neuroimmunological connection of EA-induced sustained antinociception in inflammation.

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 β-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.

Recruitment of opioid peptide-containing neutrophils is independent of formyl peptide receptors

In complete Freund's adjuvants (CFA) inflammation opioid containing neutrophils release opioid peptides upon stimulation and mediate peripheral analgesia. Neutrophil migration is regulated partially by chemokines, but other mediators e.g. formyl peptides could also contribute. In vitro, formyl peptides but not Mycobacterium butyricum (CFA component) induced migration of neutrophils. In contrast, local formyl peptide injection did not induce leukocyte recruitment in vivo due to insufficient up-regulation of adhesion molecule expression. Furthermore, leukocyte recruitment and peripheral opioid-mediated analgesia were unaffected by systemic formyl peptide receptor blockade in CFA inflammation. Thus, while formyl peptides do not regulate migration they directly stimulate opioid peptide release.

Antinociception by neutrophil-derived opioid peptides in noninflamed tissue--role of hypertonicity and the perineurium

Inflammatory pain can be controlled by intraplantar opioid injection or by secretion of endogenous opioid peptides from leukocytes in inflamed rat paws. Antinociception requires binding of opioid peptides to opioid receptors on peripheral sensory nerve terminals. In the absence of inflammation, hydrophilic opioid peptides do not penetrate the perineurial barrier and, thus, do not elicit antinociception. This study was designed to examine the conditions under which endogenous, neutrophil-derived hydrophilic opioid peptides (i.e. Met-Enkephalin and beta-endorphin) can raise nociceptive thresholds in noninflamed tissue in rats. Intraplantar injection of the chemokine CXCL2/3 (macrophage inflammatory protein-2) induced selective neutrophil recruitment without overt signs of inflammation or changes in mechanical nociceptive thresholds (paw pressure threshold). Following intraplantar injection of hypertonic saline, the perineurial barrier was permeable for hours and intraplantar injection of opioid peptides increased mechanical nociceptive thresholds. While formyl-Met-Leu-Phe (fMLP) triggered opioid peptide release from neutrophils in vitro, nociceptive thresholds were unchanged in vivo. In vitro, hypertonicity interfered with fMLP-induced p38 mitogen activated kinase (MAPK) phosphorylation and opioid peptide release from neutrophils. These inhibitory effects were fully reversible by washout. In vivo, return to normotonicity occurred within 30min while the perineurium remained permeable for hours. Under these conditions, fMLP triggered MAPK phosphorylation and induced opioid peptide-mediated increases in nociceptive thresholds in the noninflamed paw. Taken together, antinociception mediated by endogenous opioids in noninflamed tissue has two important requirements: (i) opening of the perineurial barrier for opioid peptide access and (ii) opioid peptide release from neutrophils involving p38 MAPK.

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.

Activation of microglial poly(ADP-ribose)-polymerase-1 by cholesterol breakdown products during neuroinflammation: a link between demyelination and neuronal damage

Multiple sclerosis (MS) is a chronic demyelinating disease in which it has only recently been suggested that damage to neuronal structures plays a key role. Here, we uncovered a link between the release of lipid breakdown products, found in the brain and cerebrospinal fluid (CSF) of MS patients as well as in experimental autoimmune encephalomyelitis, and neuronal damage mediated by microglial activation. The concentrations of the breakdown product 7-ketocholesterol detected in the CSF of MS patients were capable of inducing neuronal damage via the activation and migration of microglial cells in living brain tissue. 7-ketocholesterol rapidly entered the nucleus and activated poly(ADP-ribose)-polymerase (PARP)-1, followed by the expression of migration-regulating integrins CD11a and intercellular adhesion molecule 1. These findings reveal a novel mechanism linking demyelination and progressive neuronal damage, which might represent an underlying insidious process driving disease beyond a primary white matter phenomenon and rendering the microglial PARP-1 a possible antiinflammatory therapeutic target.

[Treatment of euthyroid struma. Comparable volume reduction with 400 micrograms iodine, 100 micrograms levothyroxine combined with 100 micrograms iodine or individually dosed levothyroxine]

AIM

In patients with euthyroid goitre, the efficacy of treatment with 400 micrograms iodine and 100 micrograms levothyroxine combined with 100 micrograms iodine was compared to that of the previous standard of therapy, individually dosed levothyroxine.

PATIENTS AND METHODS

A total of 78 patients presenting with euthyroid diffuse goitre (> or = 25 ml) were prospectively enrolled, randomised and treated for 6 months. The course of thyroid volume was followed using thyroid volumetry.

RESULTS

Data of 69 patients were included in the final evaluation (57 women, 12 men, age 31 +/- 1 years, thyroid volume 31.5 +/- 1.4 ml, 23 per treatment group). In the patients treated with individually dosed levothyroxine, the thyroid volume decreased by about 39% (95%-confidence limit [CL]-31% to -41%). However, the volume reductions achieved in the patients treated with 400 micrograms iodine or 100 micrograms levothyroxine/100 micrograms iodine were not significantly different (p = 0.35, variance analysis, mono-iodine -34%, 95%-CL -29% to -43%, 100 micrograms levothyroxine/100 micrograms iodine -39%, 95%-CL -32% to -45%).

CONCLUSIONS

In patients with euthyroid diffuse goitre, treatment with mono-iodine or combination of levothyroxine with iodine should have principally the same status as the previous standard of therapy, individually dosed levothyroxine. In the view of the authors, its preferential treatment with mono-iodine appears most reasonable.

[The prevention of the recurrence of endemic goiter. The efficacy of a once-a-week dose of 1.53 mg iodide]

OBJECTIVE

To investigate the efficacy of 1.53 mg iodide administered once weekly in the prophylaxis of goitre recurrence in patients with endemic euthyroid goitre after initial treatment to reduce the goitre size.

PATIENTS AND METHODS

46 consecutive patients who had undergone initial L-thyroxine, iodide or combined treatment were included in the prospective study. Thyroid volume was measured sonographically at the beginning as well as 6 and 18 months later. An increase in thyroid volume of more than 15% was taken as recurrence.

RESULTS

The study was concluded in 41 patients. During the prophylaxis mean thyroid volume increased from initially 21.7 +/- 9.9 ml to 22 +/- 10.9 ml after 6 months and to 24.5 +/- 12.1 ml after 18 months (P < 0.01). While thyroid volume remained unchanged in at least two thirds of patients, a recurrence occurred in 32% (n = 13; from initially 22.7 +/- 9.7 ml, to 26.3 +/- 11.3 ml at 6 months and to 29.7 +/- 12.3 ml at 18 months). In all patients with a recurrence a doubling of the iodide dosage to twice weekly 1.53 mg for 6 months reduced thyroid volume again (mean of 25.7 +/- 10.0 ml; P < 0.01).

CONCLUSIONS

In at least two third of patients a once-weekly dose of 1.53 mg iodide is a reliable means of preventing a recurrence of endemic euthyroid goitre, but in the remainder the same dose must be increased to twice weekly.

Quantitative analysis of right and left ventricular infarction in the presence of postinfarction ventricular septal defect

To quantitate the amount of right and left ventricular infarction in patients dying with postinfarction ventricular septal defect (PIVSD), hearts from 54 patients with anterior or inferior myocardial infarction were studied at autopsy. Fifteen hearts had myocardial infarction with PIVSD and 39 hearts had infarction without PIVSD and were used as a comparison group. All infarcts were sized histologically and the percent of each ventricle infarcted was quantitated by computer-assisted planimetry. The pathologic substrate for PIVSD was diffuse coronary artery disease with acute thrombosis resulting in transmural confluent infarction. Within the PIVSD group, there was significantly more left ventricle involved in anterior infarctions than in inferior infarctions (p less than .04). Conversely, there was more right ventricular infarction in inferiorly located myocardial infarctions with resulting PIVSD (p = .059). When infarctions resulting in PIVSD were compared with infarctions not resulting in PIVSD, the PIVSD group was characterized by larger left and right ventricular infarcts irrespective of infarct location (p less than .003). The incidence of right ventricular infarction was 100% in the PIVSD group (p less than .0001). Twelve of the 15 patients with PIVSD (80%) developed cardiogenic shock within 48 hr of septal rupture. The high incidence of shock and the rapid deterioration may have been secondary to right ventricular infarction in these patients. Therefore, infarcts resulting in PIVSD and subsequent death are characterized by a high incidence of right ventricular infarction. Significantly more infarction of the right ventricle is seen in either anterior or inferior infarctions resulting in PIVSD compared with infarctions not resulting in PIVSD. PIVSD complicating inferior infarctions is associated with the greatest amount of right ventricular infarction.