Intrathecal transplantation of autologous macrophages genetically modified to secrete proenkephalin ameliorated hyperalgesia and allodynia following peripheral nerve injury in rats

Altered Gene Expression of RNF34 and PACAP Possibly Involved in Mechanism of Exercise-Induced Analgesia for Neuropathic Pain in Rats

Despite the availability of several modalities of treatment, including surgery, pharmacological agents, and nerve blocks, neuropathic pain is often unresponsive and sometimes progresses to intractable chronic pain. Although exercise therapy is a candidate for treatment of neuropathic pain, the mechanism underlying its efficacy has not been elucidated. To clarify the molecular mechanism for pain relief induced by exercise, we measured Rnf34 and Pacap mRNA levels in the spinal cord dorsal horn of SNL rats, a model of neuropathic pain. SNL model rats exhibited stable mechanical hyperalgesia for at least 6 weeks. When the rats were forced to exercise on a treadmill, mechanical and thermal hyperalgesia were significantly ameliorated compared with the non-exercise group. Accordingly, gene expression level of Rnf34 and Pacap were also significantly altered in the time course analysis after surgery. These results suggest that exercise therapy possibly involves pain relief in SNL rats by suppressing Rnf34 and Pacap expression in the spinal cord.

Adoptive transfer of cytokine-induced immunomodulatory adult microglia attenuates experimental autoimmune encephalomyelitis in DBA/1 mice

Microglia are resident antigen-presenting cells in the central nervous system (CNS) that either suppress or promote disease depending on their activation phenotype and the microenvironment. Multiple sclerosis (MS) is a chronic inflammatory disease causing demyelination and nerve loss in the CNS, and experimental autoimmune encephalomyelitis (EAE) is an animal model of MS that is widely used to investigate pathogenic mechanisms and therapeutic effects. We isolated and cultured microglia from adult mouse brains and exposed them to specific combinations of stimulatory molecules and cytokines, the combination of IL-4, IL-10, and TGF-β yielding the optimal regime for induction of an immunosuppressive phenotype (M2). M2 microglia were characterized by decreased expression or production of CD86, PD-L1, nitric oxide, and IL-6, increased expression of PD-L2, and having a potent capacity to retain their phenotype on secondary proinflammatory stimulation. M2 microglia induced regulatory T cells, suppressed T-cell proliferation, and downmodulated M1-associated receptor expression in M1 macrophages. Myelin oligodendrocyte glycoprotein (MOG)-induced EAE was induced in DBA/1 mice and at different time points (0, 5, 12, or 15 days postimmunization) 3 × 10⁵ M2 microglia were transferred intranasally. A single transfer of M2 microglia attenuated the severity of established EAE, which was particularly obvious when the cells were injected at 15 days postimmunization. M2 microglia-treated mice had reduced inflammatory responses and less demyelination in the CNS. Our findings demonstrate that adult M2 microglia therapy represents a novel intervention that alleviated established EAE and that this therapeutic principle may have relevance for treatment of MS patients.

Different analgesic effects of adenosine between postoperative and neuropathic pain

BACKGROUND

Adenosine is an endogenous neuromodulator in both the peripheral and central nervous systems. Adenosine inhibits pain signals by hyperpolarizing neuronal membrane.

METHODS

To clarify the effects of adenosine on pain signals, we tested intrathecal adenosine injection in two neuropathic pains (spinal cord compression and chronic constriction of sciatic nerve) and postoperative pain (plantar incision).

RESULTS

In all three kinds of pain models, significant shortening of withdrawal latencies to thermal stimulation were detected from 24 h to 1 week after the surgery. Significant improvements of pain sensation were observed in all three models after intrathecal injection of Cl-adenosine 24 h after surgery. At 72 h after surgery, intrathecal Cl-adenosine injection inhibited hyperalgesia in the two neuropathic pain models but not in the postoperative pain model. Adenosine A1R messenger RNA (mRNA) expression significantly decreased in the plantar incision model. Adenosine A1R protein levels also decreased compared with the other two models and normal control.

CONCLUSIONS

These results suggest that adenosine effectively inhibits pain signals in neuropathic pain but is less effective in postoperative pain because of the decrease in adenosine A1 receptors.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Gene therapy for the treatment of chronic peripheral nervous system pain

Chronic pain is a major health concern affecting 80 million Americans at some time in their lives with significant associated morbidity and effects on individual quality of life. Chronic pain can result from a variety of inflammatory and nerve damaging events that include cancer, infectious diseases, autoimmune-related syndromes and surgery. Current pharmacotherapies have not provided an effective long-term solution as they are limited by drug tolerance and potential abuse. These concerns have led to the development and testing of gene therapy approaches to treat chronic pain. The potential efficacy of gene therapy for pain has been reported in numerous pre-clinical studies that demonstrate pain control at the level of the spinal cord. This promise has been recently supported by a Phase-I human trial in which a replication-defective herpes simplex virus (HSV) vector was used to deliver the human pre-proenkephalin (hPPE) gene, encoding the natural opioid peptides met- and leu-enkephalin (ENK), to cancer patients with intractable pain resulting from bone metastases (Fink et al., 2011). The study showed that the therapy was well tolerated and that patients receiving the higher doses of therapeutic vector experienced a substantial reduction in their overall pain scores for up to a month post vector injection. These exciting early clinical results await further patient testing to demonstrate treatment efficacy and will likely pave the way for other gene therapies to treat chronic pain.

Peripheral immune contributions to the maintenance of central glial activation underlying neuropathic pain

Recent evidence implicates an adaptive immune response in the central nervous system (CNS) mechanisms of neuropathic pain. This review identifies how neuropathic pain alters CNS immune privilege to facilitate T cell infiltration. Once in the CNS, T cells may interact with the local antigen presenting cells, microglia, via the major histocompatibility complex and the costimulatory molecules CD40 and B7. In this way, T cells may contribute to the maintenance of neuropathic pain through pro-inflammatory interactions with microglia and by facilitating the activation of astrocytes in the spinal dorsal horn. Based on the evidence presented in this review, we suggest that this bidirectional, pro-inflammatory system of neurons, glia and T cells in neuropathic pain should be renamed the pentapartite synapse, and identifies the latest member as a potential disease-modifying therapeutic target.

Cell based therapy for the management of chronic pain

The management of chronic pain, particularly neuropathic pain, still has significant unmet needs. In addition to inadequate symptomatic relief, there are concerns about adverse effects and addiction associated with treatments. The transplantation of cells that secrete neuroactive substances with analgesic properties into the central nervous system has only become of practical interest in more recent years, but provides a novel strategy to challenge current approaches in treating chronic pain. This review covers pre-clinical and clinical studies from both allogeneic and xenogeneic sources for management of chronic refractory pain.

Non-surgical therapies for peripheral nerve injury

BACKGROUND

Non-surgical approaches have been developed to enhance nerve recovery, which are complementary to surgery and are an adjunct to the reinnervation process.

SOURCES OF DATA

A search of PubMed, Medline, CINAHL, DH data and Embase databases was performed using the keywords 'peripheral nerve injury' and 'treatment'.

AREAS OF CONTROVERSY

Most of the conservative therapies are focused to control neuropathic pain after nerve tissue damage. Only physical therapy modalities have been studied in humans and their effectiveness is not proved.

GROWING POINTS

Many modalities have been experimented with to promote nerve healing and restore function in animal models and in vitro studies. Despite this, none have been actually translated into clinical practice.

AREAS TIMELY FOR DEVELOPING RESEARCH

The hypotheses proved in animals and in vitro should be translated to human clinical practice.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).