Genome-wide expression profiling of complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a chronic, progressive, and devastating pain syndrome characterized by spontaneous pain, hyperalgesia, allodynia, altered skin temperature, and motor dysfunction. Although previous gene expression profiling studies have been conducted in animal pain models, there genome-wide expression profiling in the whole blood of CRPS patients has not been reported yet. Here, we successfully identified certain pain-related genes through genome-wide expression profiling in the blood from CRPS patients. We found that 80 genes were differentially expressed between 4 CRPS patients (2 CRPS I and 2 CRPS II) and 5 controls (cut-off value: 1.5-fold change and p<0.05). Most of those genes were associated with signal transduction, developmental processes, cell structure and motility, and immunity and defense. The expression levels of major histocompatibility complex class I A subtype (HLA-A29.1), matrix metalloproteinase 9 (MMP9), alanine aminopeptidase N (ANPEP), l-histidine decarboxylase (HDC), granulocyte colony-stimulating factor 3 receptor (G-CSF3R), and signal transducer and activator of transcription 3 (STAT3) genes selected from the microarray were confirmed in 24 CRPS patients and 18 controls by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). We focused on the MMP9 gene that, by qRT-PCR, showed a statistically significant difference in expression in CRPS patients compared to controls with the highest relative fold change (4.0±1.23 times and p = 1.4×10⁻⁴). The up-regulation of MMP9 gene in the blood may be related to the pain progression in CRPS patients. Our findings, which offer a valuable contribution to the understanding of the differential gene expression in CRPS may help in the understanding of the pathophysiology of CRPS pain progression.

Targeting peripheral opioid receptors to promote analgesic and anti-inflammatory actions

Mechanisms of endogenous pain control are significant. Increasing studies have clearly produced evidence for the clinical usefulness of opioids in peripheral analgesia. The immune system uses mechanisms of cell migration not only to fight pathogens but also to control pain and inflammation within injured tissue. It has been demonstrated that peripheral inflammatory pain can be effectively controlled by an interaction of immune cell-derived opioid peptides with opioid receptors on peripheral sensory nerve terminals. Experimental and clinical studies have clearly shown that activation of peripheral opioid receptors with exogenous opioid agonists and endogenous opioid peptides are able to produce significant analgesic and anti-inflammatory effects, without central opioid mediated side effects (e.g., respiratory depression, sedation, tolerance, dependence). This article will focus on the role of opioids in peripheral inflammatory conditions and the clinical implications of targeting peripheral opioid receptors.

Targeting inflammation and wound healing by opioids

Opioid receptors are expressed on peripheral sensory nerve endings, cutaneous cells, and immune cells; and local application of opioids is used for the treatment of inflammatory pain in arthritis, burns, skin grafts, and chronic wounds. However, peripherally active opioids can also directly modulate the inflammatory process and wound healing. Here, we discuss the underlying mechanisms of opioid action and the conceivable therapeutic approaches for opioid treatment, as investigated in experimental and clinical studies. A large number of in vitro experiments and animal model investigations have produced evidence that peripherally active opioids can reduce plasma extravasation, vasodilation, proinflammatory neuropeptides, immune mediators, and tissue destruction. In contrast to currently available anti-inflammatory agents, opioids have not demonstrated organ toxicity, thus making them interesting candidates for drug development. Few clinical studies have tapped into this potential to date.

Opioids, sensory systems and chronic pain

Opioids are the oldest and most potent drugs for the treatment of severe pain. Their clinical application is undisputed in acute pain (e.g. associated with trauma or surgery) but their long-term use in chronic pain has met increasing scrutiny. Therefore, this article will review sensory mechanisms related to opioid analgesia and side effects with a special emphasis on chronic pain. Central and peripheral sites of analgesic actions and side effects, as well as conventional and novel opioid compounds will be discussed. Since pain is a complex bio-psycho-social phenomenon, non-pharmacological considerations important for the understanding of opioid analgesic efficacy are also included. Finally, examples of challenging clinical situations such as the perioperative management of patients receiving long-term opioid treatment are illustrated.

JAK-STAT1/3-induced expression of signal sequence-encoding proopiomelanocortin mRNA in lymphocytes reduces inflammatory pain in rats

BACKGROUND

Proopiomelanocortin (POMC)-derived beta-endorphin1-31 from immune cells can inhibit inflammatory pain. Here we investigated cytokine signaling pathways regulating POMC gene expression and beta-endorphin production in lymphocytes to augment such analgesic effects.

RESULTS

Interleukin-4 dose-dependently elevated POMC mRNA expression in naïve lymph node-derived cells in vitro, as determined by real-time PCR. This effect was neutralized by janus kinase (JAK) inhibitors. Transfection of Signal Transducer and Activator of Transcription (STAT) 1/3 but not of STAT6 decoy oligonucleotides abolished interleukin-4 induced POMC gene expression. STAT3 was phosphorylated in in vitro interleukin-4 stimulated lymphocytes and in lymph nodes draining inflamed paws in vivo. Cellular beta-endorphin increased after combined stimulation with interleukin-4 and concanavalin A. Consistently, in vivo reduction of inflammatory pain by passively transferred T cells improved significantly when donor cells were pretreated with interleukin-4 plus concanavalin A. This effect was blocked by naloxone-methiodide.

CONCLUSION

Interleukin-4 can amplify endogenous opioid peptide expression mediated by JAK-STAT1/3 activation in mitogen-activated lymphocytes. Transfer of these cells leads to inhibition of inflammatory pain via activation of peripheral opioid receptors.