A method for measuring multiple cytokines from small samples

Role of edaravone in managemant of septic peritonitis

BACKGROUND AND AIMS

Sepsis is a complex rapidly progressive infectious disease that remain a major cause of morbidity and mortality in surgical patients and trauma victims. Edaravone a novel free radical scavenger was approved in 2001 in Japan for treatment of acute cerebral and myocardial infarction. Hence, in this work we attempt to evaluate its role in cases of septic peritonitis (SP).

MATERIAL AND METHODS

This is a prospective randomized observer-blinded study carried out in surgical Intensive Care Unit (ICU) after approval by Hospital Ethical Committee. After admission to ICU patients were randomly divided into two groups of thirty patients each-Group (C): Control group managed according to the routine protocol of sepsis and Group (E): Edaravone treated SP managed according to the routine protocol of sepsis + edaravone at dose of 30 mg/12 h intravenous infusion for 2 weeks. All patients were monitored for invasive blood pressure, central venous pressure, heart rate, temperature, urine output, total fluid balance, and routine investigation. Blood sample was taken weekly for 2 weeks to measure the following parameters: Nuclear transcription factor kappa B activity (NFKB), mitogen-activated protein kinase (MAPK), heat shock protein 72 (HSP 72) and total antioxidant capacity (TAC).

RESULTS

There was significant decrease (P < 0.05) in serum level of NFKB, MAPK in Group E in comparison with Group C. While serum level of HSP 72 and TAC showed significant increase (P < 0.05) in Group E compared with Group C with better outcome.

CONCLUSION

SP treatment with edaravone could significantly improve the inflammatory and oxidative states with better patient outcomes.

HIV infection is associated with higher levels of monocyte chemoattractant protein-1 and eotaxin among people with recent hepatitis C virus infection

Background

Human immunodeficiency virus (HIV) infection leads to more rapid progression of hepatitis C virus (HCV)-related liver fibrosis, which could be linked to differences in the severity of liver inflammation among HIV/HCV co-infected individuals compared to HCV mono-infected individuals.

This study assessed the association of HIV co-infection with pro-inflammatory and pro-fibrogenic cytokines and chemokines during recent HCV infection.

Methods

Participants from the ATAHC study, a prospective cohort of recent HCV infection, with detectable HCV RNA at the time of acute HCV detection were included. Concentrations of 27 plasma cytokines and chemokines were measured by multiplex immunoassays and compared between those with, and without, HIV co-infection.

Results

Out of 117 individuals with recent HCV infection included in analysis, 73 had HCV mono-infection and 44 had HIV/HCV co-infection. Individuals with HIV/HCV co-infection had significantly higher mean levels of eotaxin (1.79 vs. 1.62 log pg/mL; P < 0.001), monocyte chemotactic protein 1 (MCP-1; 2.10 vs. 1.98 log pg/mL; P < 0.001), and interferon-gamma inducible protein-10 (IP-10; 3.11 vs. 2.98 log pg/mL; P = 0.013). Linear regression analyses adjusting for age, alanine transaminase (ALT), HCV RNA levels, and assay run, higher eotaxin levels were independently associated with HIV/HCV co-infection (adjusted β: 0.12; 95%CI: 0.01, 0.24; P = 0.039). Higher MCP-1 levels were also independently associated with HIV/HCV co-infection in adjusted analysis (adjusted β: 0.11; 95%CI: 0.03, 0.18; P = 0.009).

Conclusions

During recent HCV, those with HIV/HCV co-infection had a stronger pro-fibrogenic mediator profile compared to those with HCV mono-infection. These findings may provide a potential explanation for accelerated liver fibrosis in HIV/HCV co-infection.

Trial registration

Australian Trial in Acute Hepatitis C (ATAHC) study was registered with ClinicalTrials.gov registry on September 11, 2005. NCT00192569.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1567-2) contains supplementary material, which is available to authorized users.

Alanine aminotransferase, HCV RNA levels and pro-inflammatory and pro-fibrogenic cytokines/chemokines during acute hepatitis C virus infection

Background

This study assessed the association of alanine-aminotransferase (ALT) and hepatitis C virus (HCV) RNA levels with pro-inflammatory and pro-fibrogenic cytokines and chemokines during acute HCV infection to provide further insight into the potential HCV immunopathogenesis.

Methods

Participants in the ATAHC study, a prospective study of recent HCV infection, with detectable HCV RNA at the time of HCV detection were included. Plasma levels of 27 cytokines and chemokines were measured and their correlation with ALT and HCV RNA levels were assessed. Log₁₀ transformed cytokines and ALT values were used in the analysis.

Results

Among 117 individuals, the plasma levels of interferon-gamma inducible protein-10 (IP-10) and macrophage inflammatory protein-1beta (MIP-1β) were positively correlated with ALT levels (IP-10: r = 0.42, P < 0.001; MIP-1β: r = 0.29, P = 0.001) and HCV RNA levels (IP-10: rs = 0.44, P < 0.001; MIP-1β: rs = 0.43, P < 0.001). Using linear regression, after adjusting for sex, age, infection duration, symptomatic infection, HIV co-infection, interferon-lambda rs12979860 genotype, HCV genotype, and assay run, higher ALT levels (β = 0.20; 95 % CI: 0.07, 0.32; P = 0.002) and HCV RNA levels >400,000 IU/mL (vs. <8,500 IU/mL; β = 0.16; 95 % CI: 0.03, 0.28; P = 0.014) were independently associated with higher IP-10 levels. HCV RNA levels >400,000 IU/mL (vs. <8,500 IU/mL; β = 0.16; 95 % CI: 0.01, 0.31; P = 0.036) were associated with higher MIP-1β levels.

Conclusions

During acute HCV infection, high ALT and HCV RNA levels were associated with increased IP-10 levels, while high HCV RNA levels were also associated with increased MIP-1β levels. These data suggest that IP-10 and MIP-1β may have a role in HCV immuno-pathogenesis starting early in acute HCV infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0482-x) contains supplementary material, which is available to authorized users.

ELISA rescue protocol: recovery of sample concentrations from an assay with an unsuccessful standard curve

The Enzyme-linked Immunosorbant Assay (ELISA) is a method commonly used to measure proteins in various biological matrices, due to its ease of performance and relatively low cost. In order for quantitative data to be generated, a reference standard curve must be prepared for each assay; however, due to investigator error or standard protein degradation, otherwise representative experimental sample data are rendered useless. Herein, we describe a protocol by which sample concentrations can be recovered from assays in which the standard curve fails. The ΔOD values of the experimental samples are used to generate a new standard curve, which is applied back to the original plate. For validation of this method, experimental sample concentrations obtained using acceptable standard curves were potted against those calculated using this new method. Using linear regression analysis, we show a near 1:1 correlation between sample concentrations, with r(2) values between 0.98 and 0.99 and slopes between 0.97 and 1.10. This method demonstrates that assays resulting in unusable standard curves do not require re-assay of all samples. Instead, the experimental sample concentrations can be retrieved saving the investigator the time and resources required to rerun samples or repeat entire experiments.

Prior laparotomy or corticosterone potentiates lipopolysaccharide-induced fever and sickness behaviors

Stimulating sensitized immune cells with a subsequent immune challenge results in potentiated pro-inflammatory responses translating into exacerbated sickness responses (i.e. fever, pain and lethargy). Both corticosterone (CORT) and laparotomy cause sensitization, leading to enhanced sickness-induced neuroinflammation or pain (respectively). However, it is unknown whether this sensitization affects all sickness behaviors and immune cell responses equally. We show that prior CORT and prior laparotomy potentiated LPS-induced fever but not lethargy. Prior CORT, like prior laparotomy, was able to potentiate sickness-induced pain. Release of nitric oxide (NO) from peritoneal macrophages stimulated ex vivo demonstrates that laparotomy, but not CORT sensitizes these cells.

Unique Cytokine/Chemokine Signatures for HIV-1 and HCV Mono-infection versus Co-infection as Determined by the Luminex® Analyses

Liver disease caused by HIV-1/HCV co-infection is characterized by the inflammation and cell-death. The co-existence of these two chronic viral infections also alters the cytokine production in vivo. The ability to visualize changes in cytokine networks with the onset and progression of disease or treatment is critical to advance our understanding of the immune response to pathogens. The recent Luminex® technology has revolutionized the simultaneous detection and quantitation of several cytokines and chemokines in clinical samples that are generally available in small quantities. We have applied this technology to analyze the plasma samples from patients who have either HIV-1 or HCV mono-infection or HIV-1/HCV co-infection and monitored the presence of 23 cytokines and chemokines. Of these, 8 (IFN-α2, IL-2, IL-3, IL-6, IL-8, IL-12p70, IL-15 and RANTES) cytokines were expressed at higher levels in the co-infected individuals. Interestingly, in case of HIV-1 mono-infected individuals, the levels of the proinflammatory cytokines IFN-γ and TNF-α were increased. Standard correlation clustering of the normalized data demonstrated unique plasma cytokine signatures for HIV-1/HCV co-infected individuals. These signatures were characterized not only by an up regulation of the aforementioned antiviral mediators but also by a marked down regulation in the chemokines Eotaxin and MIP-1α when compared to mono-infected individuals. Luminex®- based analyses have proven to be a powerful tool for therapeutic immunomonitoring, but may have an even greater impact in the discovery of the underlying immune response at all phases of infection. The study presented herein has potential to offer insight into the underlying mechanisms of immunopathogenesis of HIV-1/HCV co-infection.

Evidence that intrathecal morphine-3-glucuronide may cause pain enhancement via toll-like receptor 4/MD-2 and interleukin-1beta

Morphine-3-glucoronide (M3G) is a major morphine metabolite detected in cerebrospinal fluid of humans receiving systemic morphine. M3G has little-to-no affinity for opioid receptors and induces pain by unknown mechanisms. The pain-enhancing effects of M3G have been proposed to significantly and progressively oppose morphine analgesia as metabolism ensues. We have recently documented that morphine activates toll-like receptor 4 (TLR4), beyond its classical actions on mu-opioid receptors. This suggests that M3G may similarly activate TLR4. This activation could provide a novel mechanism for M3G-mediated pain enhancement, as (a) TLR4 is predominantly expressed by microglia in spinal cord and (b) TLR4 activation releases pain-enhancing substances, including interleukin-1 (IL-1). We present in vitro evidence that M3G activates TLR4, an effect blocked by TLR4 inhibitors, and that M3G activates microglia to produce IL-1. In vivo, intrathecal M3G (0.75 microg) induced potent allodynia and hyperalgesia, blocked or reversed by interleukin-1 receptor antagonist, minocycline (microglial inhibitor), and (+)-and (-)-naloxone. This latter study extends our prior demonstrations that TLR4 signaling is inhibited by naloxone nonstereoselectively. These results with (+)-and (-)-naloxone also demonstrate that the effects cannot be accounted for by actions at classical, stereoselective opioid receptors. Hyperalgesia (allodynia was not tested) and in vitro M3G-induced TLR4 signaling were both blocked by 17-DMAG, an inhibitor of heat shock protein 90 (HSP90) that can contribute to TLR4 signaling. Providing further evidence of proinflammatory activation, M3G upregulated TLR4 and CD11b (microglial/macrophage activation marker) mRNAs in dorsal spinal cord as well as IL-1 protein in the lumbosacral cerebrospinal fluid. Finally, in silico and in vivo data support that the glucuronic acid moiety is capable of inducing TLR4/MD-2 activation and enhanced pain. These data provide the first evidence for a TLR4 and IL-1 mediated component to M3G-induced effects, likely of at least microglial origin.

A novel method for modeling facial allodynia associated with migraine in awake and freely moving rats

Migraine is a neurovascular disorder that induces debilitating headaches associated with multiple symptoms including facial allodynia, characterized by heightened responsivity to normally innocuous mechanical stimuli. It is now well accepted that immune activation and immune-derived inflammatory mediators enhance pain responsivity, including the trigeminal system. Nociceptive ("pain" responsive) trigeminal nerves densely innervate the cranial meninges. We have recently proposed that the meninges may serve as a previously unidentified, key interface between the peripheral immune system and the CNS with potential implications for understanding underlying migraine mechanisms. Our focus here is the development of a model for facial allodynia associated with migraine. We developed a model wherein an indwelling catheter is placed between the skull and dura, allowing immunogenic stimuli to be administered over the dura in awake and freely moving rats. Since the catheter does not contact the brain itself, any proinflammatory cytokines induced following manipulation derive from resident or recruited meningeal immune cells. While surgery alone does not alter immune activation markers, TNF or IL6 mRNA and/or protein, it does decrease gene expression and increase protein expression of IL-1 at 4 days after surgery. Using this model we show the induction of facial allodynia in response to supradural administration of either the HIV glycoprotein gp120 or inflammatory soup (bradykinin, histamine, serotonin, and prostaglandin E2), and the induction of hindpaw allodynia in our model after inflammatory soup. This model allows time- and dose-dependent assessment of the relationship between changes in meningeal inflammation and corresponding exaggerated pain behaviors.

Lipopolysaccharide-induced increases in cytokines in discrete mouse brain regions are detectable using Luminex xMAP technology

Methods to determine cytokine protein content in samples of interest, such as enzyme-linked immunosorbent assay (ELISA), are often labor-intensive and costly. Furthermore, because ELISA requires relatively large sample volumes and protein concentrations, it is difficult using this technique to determine protein content for multiple cytokines from individual samples. Recently, Luminex has developed an open source hardware platform combining flow cytometry- and bead-based antibody capture that is capable of detecting multiple analytes from a single sample. In the present study we employed the Luminex 200 platform to determine the cytokine protein content in discrete brain regions of C57BL/6J mice. In spike-and-recovery experiments, known concentrations of murine recombinant interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)alpha were added either singly or as a mixture of all three to whole brain homogenates containing known quantities of total protein. Spiked samples were assayed for either a single cytokine or for multiple cytokines using 1-plex or 3-plex assay kits, respectively. In whole mouse brain homogenate we recovered between 81% and 103% of the recombinant cytokines. We then injected C57BL/6J mice intraperitoneally with bacterial lipopolysaccharide (LPS) and sacrificed them 4h later. We detected in samples taken from LPS-stimulated mice 4- to 870-fold increases in serum or spleen cytokine protein, and 1.5- to 16-fold increases in cytokine protein in discrete brain regions, relative to protein content in samples obtained from vehicle-treated animals. These results indicate that multiple cytokines may be reliably assayed from discrete regions of mouse brain using a single sample.

Assessment of natural killer (NK) and NKT cells in murine spleens and livers

Natural killer (NK) cells part of innate immunity. NK cells have been assigned numerous functions, including the ability to serve as a bridge between innate and adaptive immunity. In evaluating NK cell function, two pathways need to be examined: their ability to kill certain tumors spontaneously and their ability to secrete cytokines, interferon-gamma (IFN-gamma), in particular. Although NK cells are distinct from T lymphocytes, a new lymphocyte subset, termed NKT cell, has been described. NKT cells express surface markers that are unique to NK cells (e.g., NK1.1) as well as markers that are unique to T cells (e.g., CD3). Most NKT cells recognize glycolipids and are thought to play an important immunoregulatory role. This chapter will detail the methodology needed for examination of NK and NKT cells in mice.

The ELISA Standard Save: calculation of sample concentrations in assays with a failed standard curve

The enzyme-linked immunosorbent assay (ELISA) is often used to measure protein levels in plasma and other solutions. In order for the assay to be quantitative, a standard curve must be prepared for each assay. Technical blunders in preparing the standard curve can render otherwise representative sample values useless. In order to recover these data, a protocol has been developed whereby a new standard curve is generated using the DeltaOD values of the samples. This new standard is applied to the original plate in order to determine sample concentrations. To validate this method, sample concentrations obtained using an acceptable standard curve were plotted against those obtained using the new standard curve. Linear regression analysis showed a 1:1 correlation between concentrations, with r(2) values ranging from 0.98-0.99 and slopes ranging from 0.97-1.10. In this manner, data for these samples are preserved, saving the investigator the time and money involved in repeating experiments.

Interleukin-6 mediates low-threshold mechanical allodynia induced by intrathecal HIV-1 envelope glycoprotein gp120

Spinal cord glia (microglia and astrocytes) contribute to enhanced pain states. One model that has been used to study this phenomenon is intrathecal (i.t.) administration of gp120, an envelope glycoprotein of HIV-1 known to activate spinal cord glia and thereby induce low-threshold mechanical allodynia, a pain symptom where normally innocuous (non-painful) stimuli are perceived as painful. Previous studies have shown that i.t. gp120-induced allodynia is mediated via the release of the glial pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF), and interleukin-1beta (IL-1). As we have recently reported that i.t. gp120 induces the release of interleukin-6 (IL-6), in addition to IL-1 and TNF, the present study tested whether this IL-6 release in spinal cord contributes to gp120-induced mechanical allodynia and/or to gp120-induced increases in TNF and IL-1. An i.t. anti-rat IL-6 neutralizing antibody was used to block IL-6 actions upon its release by i.t. gp120. This IL-6 blockade abolished gp120-induced mechanical allodynia. While the literature predominantly documents the cascade of pro-inflammatory cytokines as beginning with TNF, followed by the stimulation of IL-1, and finally TNF plus IL-1 stimulating the release of IL-6, the present findings indicate that a blockade of IL-6 inhibits the gp120-induced elevations of TNF, IL-1, and IL-6 mRNA in dorsal spinal cord, elevation of IL-1 protein in lumbar dorsal spinal cord, and TNF and IL-1 protein release into the surrounding lumbosacral cerebrospinal fluid. These results would suggest that IL-6 induces pain facilitation, and may do so in part by stimulating the production and release of other pro-inflammatory cytokines.

Multiplex bead array assay for detection of 25 soluble cytokines in blister fluid of patients with complex regional pain syndrome type 1

Inflammatory processes are known to be involved at least in the early phase of complex regional pain syndrome type 1 (CRPS1). Blister fluid obtained from the involved extremities displayed increased amounts of proinflammatory cytokines IL-6 and TNFα compared with the noninvolved extremities. The aim of this paper is to investigate the involvement of mediators by measurement of several other cytokines using new detection techniques that enable multiple cytokine measurement in small samples. The use of a multiplex-25 bead array cytokine assay and Luminex technology enabled simultaneous measurement of representative (1) proinflammatory cytokines such as GM-CSF, IL-1β, IL-1RA, IL-6, IL-8, and TNF-α; (2) Th1/Th2 distinguishing cytokines IFN-γ, IL-2, IL-2R, IL-4, IL-5, and IL-10; (3) nonspecific acting cytokines IFN-α, IL-7, IL-12p40/p70, IL-13, IL-15, and IL-17; and (4) chemokines eotaxin, IP-10, MCP-1, MIP-1α, MIP-1β, MIG, and RANTES. Although minimal detection levels are significantly higher in the bead array system than those in common ELISA assays, in blister fluid, IL-1RA, IL-6, IL-8, TNF-α, IL-12p40/p70, MCP-1, and MIP-1β were detectable and increased in CRPS1 affected extremities. Levels of IL-6 and TNF-α simultaneously measured by ELISA (Sanquin Compact kit) and by multiplex-25 bead array assay (Biosource) were highly correlated (r = 0.85, P < .001 for IL-6 and r = 0.88, P < .001 for TNF-α). Furthermore, IP-10 and eotaxin were detectable but diminished in CRPS1, whereas detectable amounts of IL-10 were similar in involved and noninvolved extremities. Multiplex bead array assays are useful systems to establish the involvement of cytokines in inflammatory processes by measurements in blister fluids of CRPS1. Ten representative cytokines were detectable. However, detection levels and amounts measured are at least 3 times higher in the multiplex-25 array assay than in the ELISA assays used simultaneously for the measurement of cytokines.

Repeated intrathecal injections of plasmid DNA encoding interleukin-10 produce prolonged reversal of neuropathic pain

Neuropathic pain is a major clinical problem unresolved by available therapeutics. Spinal cord glia play a pivotal role in neuropathic pain, via the release of proinflammatory cytokines. Anti-inflammatory cytokines, like interleukin-10 (IL-10), suppress proinflammatory cytokines. Thus, IL-10 may provide a means for controlling glial amplification of pain. We recently documented that intrathecal IL-10 protein resolves neuropathic pain, albeit briefly (approximately 2-3 h), given its short half-life. Intrathecal gene therapy using viruses encoding IL-10 can also resolve neuropathic pain, but for only approximately 2 weeks. Here, we report a novel approach that dramatically increases the efficacy of intrathecal IL-10 gene therapy. Repeated intrathecal delivery of plasmid DNA vectors encoding IL-10 (pDNA-IL-10) abolished neuropathic pain for greater than 40 days. Naked pDNA-IL-10 reversed chronic constriction injury (CCI)-induced allodynia both shortly after nerve injury as well as 2 months later. This supports that spinal proinflammatory cytokines are important in both the initiation and maintenance of neuropathic pain. Importantly, pDNA-IL-10 gene therapy reversed mechanical allodynia induced by CCI, returning rats to normal pain responsiveness, without additional analgesia. Together, these data suggest that intrathecal IL-10 gene therapy may provide a novel approach for prolonged clinical pain control.

Sequential ELISA to profile multiple cytokines from small volumes

Due to the low cost and relative effectiveness the enzyme-linked immunosorbent assay (ELISA) is widely used to measure the concentration of inflammatory cytokines in plasma and other sources. Blood volume represents a limiting factor in those mouse models requiring repeated sample collection at multiple time intervals to monitor the trajectory of inflammatory processes. The small blood volumes in such scenarios restrict the array of cytokines that can be measured using the traditional ELISA. The implementation of the sequential ELISA protocol presented here can dramatically increase the number of measured cytokines, since the plasma samples are not discarded after the initial assay but re-used to measure additional selected inflammatory proteins in consecutive tests. From the original 20 mul of blood volume collected, up to fifteen cytokines can be successfully assayed in five consecutive cycles. With more unstable cytokines analyzed in the initial cycles, no inter-assay interference and/or deterioration of samples occurs. The sequential ELISA technique based on commercially-available antibody pairs can be an attractive alternative to more advanced, costly methods. Given the simplistic validation procedure, the proposed sequential ELISA protocol has a wide potential for further modifications to include other inflammation-related targets.

Involvement of spinal cord nuclear factor κB activation in rat models of proinflammatory cytokine-mediated pain facilitation

Proinflammatory cytokines, such as interleukin-1beta and tumour necrosis factor-alpha, are released by activated glial cells in the spinal cord and play a major role in pain facilitation. These cytokines exert their actions, at least partially, through the activation of the transcription factor, nuclear factor kappaB (NF-kappaB). In turn, NF-kappaB regulates the transcription of many inflammatory mediators, including cytokines. We have previously shown that intrathecal injection of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein, gp120, induces mechanical allodynia via the release of proinflammatory cytokines. Here, we investigated whether NF-kappaB is involved in gp120-induced pain behaviour in Sprague-Dawley rats. Intrathecal administration of NF-kappaB inhibitors, pyrrolidinedithiocarbamate (PDTC) and SN50, prior to gp120 partially attenuated gp120-induced allodynia. In addition, PDTC delayed and reversed allodynia in a model of neuropathic pain induced by sciatic nerve inflammation. These observations suggest that intrathecal gp120 may lead to activation of NF-kappaB within the spinal cord. To reveal NF-kappaB activation, we assessed inhibitory factor kappaBalpha (IkappaBalpha) mRNA expression by in situ hybridization, as NF-kappaB activation up-regulates IkappaBalpha gene expression as part of an autoregulatory feedback loop. No or low levels of IkappaBalpha mRNA were detected in the lumbar spinal cord of vehicle-injected rats, whereas IkappaBalpha mRNA expression was markedly induced in the spinal cord following intrathecal gp120 in predominantly astrocytes and endothelial cells. Moreover, IkappaBalpha mRNA expression positively correlated with proinflammatory cytokine protein levels in lumbosacral cerebrospinal fluid. Together, these results demonstrate that spinal cord NF-kappaB activation is involved, at least in part, in exaggerated pain states.

Controlling pathological pain by adenovirally driven spinal production of the anti-inflammatory cytokine, interleukin-10

Gene therapy for the control of pain has, to date, targeted neurons. However, recent evidence supports that spinal cord glia are critical to the creation and maintenance of pain facilitation through the release of proinflammatory cytokines. Because of the ability of interleukin-10 (IL-10) to suppress proinflammatory cytokines, we tested whether an adenoviral vector encoding human IL-10 (AD-h-IL10) would block and reverse pain facilitation. Three pain models were examined, all of which are mediated by spinal pro-inflammatory cytokines. Acute intrathecal administration of rat IL-10 protein itself briefly reversed chronic constriction injury-induced mechanical allodynia and thermal hyperalgesia. The transient reversal caused by IL-10 protein paralleled the half-life of human IL-10 protein in the intrathecal space (t(1/2) approximately 2 h). IL-10 gene therapy both prevented and reversed thermal hyperalgesia and mechanical allodynia, without affecting basal responses to thermal or mechanical stimuli. Extra-territorial, as well as territorial, pain changes were reversed by this treatment. Intrathecal AD-h-IL10 injected over lumbosacral spinal cord led to elevated lumbosacral cerebrospinal fluid (CSF) levels of human IL-10, with far less human IL-10 observed in cervical CSF. In keeping with IL-10's known anti-inflammatory actions, AD-h-IL10 lowered CSF levels of IL-1, relative to control AD. These studies support that this gene therapy approach provides an alternative to neuronally focused drug and gene therapies for clinical pain control.

Minocycline attenuates mechanical allodynia and proinflammatory cytokine expression in rat models of pain facilitation

Activated glial cells (microglia and astroglia) in the spinal cord play a major role in mediating enhanced pain states by releasing proinflammatory cytokines and other substances thought to facilitate pain transmission. In the present study, we report that intrathecal administration of minocycline, a selective inhibitor of microglial cell activation, inhibits low threshold mechanical allodynia, as measured by the von Frey test, in two models of pain facilitation. In a rat model of neuropathic pain induced by sciatic nerve inflammation (sciatic inflammatory neuropathy, SIN), minocycline delayed the induction of allodynia in both acute and persistent paradigms. Moreover, minocycline was able to attenuate established SIN-induced allodynia 1 day, but not 1 week later, suggesting a limited role of microglial activation in more perseverative pain states. Our data are consistent with a crucial role for microglial cells in initiating, rather than maintaining, enhanced pain responses. In a model of spinal immune activation by intrathecal HIV-1 gp120, we show that the anti-allodynic effects of minocycline are associated with decreased microglial activation, attenuated mRNA expression of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-1beta-converting enzyme, TNF-alpha-converting enzyme, IL-1 receptor antagonist and IL-10 in lumbar dorsal spinal cord, and reduced IL-1beta and TNF-alpha levels in the CSF. In contrast, no significant effects of minocycline were observed on gp120-induced IL-6 and cyclooxygenase-2 expression in spinal cord or CSF IL-6 levels. Taken together these data highlight the importance of microglial activation in the development of exaggerated pain states.

A role for proinflammatory cytokines and fractalkine in analgesia, tolerance, and subsequent pain facilitation induced by chronic intrathecal morphine

The present experiments examined the role of spinal proinflammatory cytokines [interleukin-1beta (IL-1)] and chemokines (fractalkine) in acute analgesia and in the development of analgesic tolerance, thermal hyperalgesia, and tactile allodynia in response to chronic intrathecal morphine. Chronic (5 d), but not acute (1 d), intrathecal morphine was associated with a rapid increase in proinflammatory cytokine protein and/or mRNA in dorsal spinal cord and lumbosacral CSF. To determine whether IL-1 release modulates the effects of morphine, intrathecal morphine was coadministered with intrathecal IL-1 receptor antagonist (IL-1ra). This regimen potentiated acute morphine analgesia and inhibited the development of hyperalgesia, allodynia, and analgesic tolerance. Similarly, intrathecal IL-1ra administered after the establishment of morphine tolerance reversed hyperalgesia and prevented the additional development of tolerance and allodynia. Fractalkine also appears to modulate the effects of intrathecal morphine because coadministration of morphine with intrathecal neutralizing antibody against the fractalkine receptor (CX3CR1) potentiated acute morphine analgesia and attenuated the development of tolerance, hyperalgesia, and allodynia. Fractalkine may be exerting these effects via IL-1 because fractalkine (CX3CL1) induced the release of IL-1 from acutely isolated dorsal spinal cord in vitro. Finally, gene therapy with an adenoviral vector encoding for the release of the anti-inflammatory cytokine IL-10 also potentiated acute morphine analgesia and attenuated the development of tolerance, hyperalgesia, and allodynia. Taken together, these results suggest that IL-1 and fractalkine are endogenous regulators of morphine analgesia and are involved in the increases in pain sensitivity that occur after chronic opiates.

Spinal gap junctions: Potential involvement in pain facilitation

Glia are now recognized as important contributors in pathological pain creation and maintenance. Spinal cord glia exhibit extensive gap junctional connectivity, raising the possibility that glia are involved in the contralateral spread of excitation resulting in mirror image pain. In the present experiments, the gap junction decoupler carbenoxolone was administered intrathecally after induction of neuropathic pain in response to sciatic nerve inflammation (sciatic inflammatory neuropathy) or partial nerve injury (chronic constriction injury). In both neuropathic pain models, a low dose of carbenoxolone reversed mirror image mechanical allodynia, while leaving ipsilateral mechanical allodynia unaffected. Ipsilateral thermal hyperalgesia was briefly attenuated. Critically, blockade of mechanical allodynia and thermal hyperalgesia was not observed in response to intrathecal glycyrrhizic acid, a compound similar to carbenoxolone in all respects but it does not decouple gap junctions. Thus, blockade of mechanical allodynia and thermal hyperalgesia by carbenoxolone does appear to reflect an effect on gap junctions. Examination of carbenoxolone's effects on intrathecal human immunodeficiency virus type 1 gp120 showed that blockade of pain facilitation might result, at least in part, via suppression of interleukin-1 and, in turn, interleukin-6. These data provide the first suggestion that spread of excitation via gap junctions might contribute importantly to inflammatory and traumatic neuropathic pain.

PERSPECTIVE

The current studies provide evidence for involvement of gap junctions in spinal cord pain facilitation. Intrathecal carbenoxolone, a gap junction decoupler, reversed neuropathy-induced mirror image pain and intrathecal gp120-induced allodynia. In addition, it decreased gp120-induced proinflammatory cytokines. This suggests gap junction activation might lead to proinflammatory cytokine release by distantly activated glia.