Plasma endothelin-1 levels in patients with complex regional pain syndrome

Endothelin-1 Decreases Excitability of the Dorsal Root Ganglion Neurons via ETB Receptor

Endothelin-1 (ET-1) has been demonstrated to be a pro-nociceptive as well as an anti-nociceptive agent. However, underlying molecular mechanisms for these pain modulatory actions remain unclear. In the present study, we evaluated the ability of ET-1 to alter the nociceptor excitability using a patch clamp technique in acutely dissociated rat dorsal root ganglion (DRG) neurons. ET-1 produced an increase in threshold current to evoke an action potential (I _threshold) and hyperpolarization of resting membrane potential (RMP) indicating decreased excitability of DRG neurons. I _threshold increased from 0.25 ± 0.08 to 0.33 ± 0.07 nA and hyperpolarized RMP from -57.51 ± 1.70 to -67.41 ± 2.92 mV by ET-1 (100 nM). The hyperpolarizing effect of ET-1 appears to be orchestrated via modulation of membrane conductances, namely voltage-gated sodium current (I _Na) and outward transient potassium current (I _KT). ET-1, 30 and 100 nM, decreased the peak I _Na by 41.3 ± 6.8 and 74 ± 15.2%, respectively. Additionally, ET-1 (100 nM) significantly potentiated the transient component (I _KT) of the potassium currents. ET-1-induced effects were largely attenuated by BQ-788, a selective ET_BR blocker. However, a selective ET_AR blocker BQ-123 did not alter the effects of ET-1. A selective ET_BR agonist, IRL-1620, mimicked the effect of ET-1 on I _Na in a concentration-dependent manner (IC₅₀ 159.5 ± 92.6 μM). In conclusion, our results demonstrate that ET-1 hyperpolarizes nociceptors by blocking I _Na and potentiating I _KT through selective activation of ET_BR, which may represent one of the underlying mechanisms for reported anti-nociceptive effects of ET-1.

Correlations between plasma endothelin-1 levels and breakthrough pain in patients with cancer

Endothelin-1 (ET-1) may be involved in driving pain in patients with advanced cancer. However, a few studies focus on the role of ET-1 in breakthrough pain (BP). The aim of this pivotal study was to explore the correlation between the plasma (ET-1) level and BP intensity. A total of 40 patients were enrolled in the study, and they were divided into two groups: BP group and non-BP group. Moreover, 20 healthy adults were used as the normal control group. Pain intensity was measured using visual analog scale (VAS) scores of 1–10. Plasma ET-1 levels were detected by an ET radioimmunoassay kit. Subsequently, the correlation of ET-1 level with the VAS score and cancer types was analyzed by Pearson’s correlation coefficient. The plasma ET-1 level in the BP group (35.31±8.02 pg/mL) was higher than that in the non-BP group (29.51±6.78 pg/mL) and the normal control group (24.77±10.10 pg/mL, P<0.05). In addition, the VAS score in the BP group (7.45±0.82) was higher than that in the non-BP group (2.80±1.23, P<0.05). The plasma ET-1 level was positively correlated with the VAS score of the BP group (Pearson’s r=0.42). There was no significant correlation between the plasma ET-1 level and VAS score of the non-BP group (Pearson’s r=−0.22) or/and cancer types (P>0.05). The elevated plasma ET-1 levels were positively related to BP, and targeting ET-1 may provide a novel pain-reducing therapeutic treatment in BP.

Complex regional pain syndrome-significant progress in understanding

Research into complex regional pain syndrome (CRPS) has made significant progress. First, there was the implementation of the official IASP "Budapest" diagnostic criteria. It would be desirable to also define exclusion and outcome criteria that should be reported in studies. The next step was to recognize the complex pathophysiology. After trauma, some inflammation is physiological; in acute CRPS, this inflammation persists for months. There is an abundance of inflammatory and a lack of anti-inflammatory mediators. This proinflammatory network (cytokines and probably also other mediators) sensitizes the peripheral and spinal nociceptive system, it facilitates the release of neuropeptides from nociceptors inducing the visible signs of inflammation, and it stimulates bone cell or fibroblast proliferation, and endothelial dysfunction leading to vascular changes. Trauma may also expose nervous system structures to the immune system and triggers autoantibodies binding to adreno- and acetylcholine receptors. In an individual time frame, the pain in this inflammatory phase pushes the transition into "centralized" CRPS, which is dominated by neuronal plasticity and reorganization. Sensory-motor integration becomes disturbed, leading to a loss of motor function; the body representation is distorted leading to numbness and autonomic disturbances. In an attempt to avoid pain, patients neglect their limb and learn maladaptive nonuse. The final step will be to assess large cohorts and to analyze these data together with data from public resources using a bioinformatics approach. We could then develop diagnostic toolboxes for individual pathophysiology and select focused treatments or develop new ones.

Antiallodynic effect through spinal endothelin-B receptor antagonism in rat models of complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a very complicated chronic pain disorder that has been classified into two types (I and II). Endothelin (ET) receptors are involved in pain conditions at the spinal level. We investigated the role of spinal ET receptors in CRPS. Chronic post-ischemia pain (CPIP) was induced in male Sprague-Dawley rats as a model for CRPS-I by placing a tourniquet (O-ring) at the ankle joint for 3h, and removing it to allow reperfusion. Ligation of L5 and L6 spinal nerves to induce neuropathic pain was performed as a model for CRPS-II. After O-ring application and spinal nerve ligation, the paw withdrawal threshold was significantly decreased at injured sites. Intrathecal administration of the selective ET-B receptor antagonist BQ 788 dose-dependently increased the withdrawal threshold in both CRPS-I and CRPS-II. In contrast, ET-A receptor antagonist BQ 123 did not affect the withdrawal threshold in either CRPS type. The ET-1 levels of plasma and spinal cord increased in both CRPS types. Intrathecal BQ 788 decreased the spinal ET-1 level. These results suggest that ET-1 is involved in the development of mechanical allodynia in CRPS. Furthermore, the ET-B receptor appears to be involved in spinal cord-related CRPS.

Cerebral activation during von Frey filament stimulation in subjects with endothelin-1-induced mechanical hyperalgesia: a functional MRI study

Endothelin-1 (ET-1) is an endogenously expressed potent peptide vasoconstrictor. There is growing evidence that ET-1 plays a role in the pain signaling system and triggers overt nociception in humans. The underlying neuronal pathways are still a matter of great debate. In the present study, we applied an intradermal ET-1 sensitization model to induce mechanical hyperalgesia in healthy subjects. Functional magnetic resonance imaging (fMRI) was used to tease out the cortical regions associated with the processing of ET-1-induced punctate hyperalgesia, as compared to a nonnoxious mechanical stimulation of the contralateral arm. Von Frey hair testing revealed the presence of increased responsiveness to punctate stimulation in all subjects. Activational patterns between nonpainful control stimulation and hyperalgesic stimulation were compared. Two major observations were made: (1) all cortical areas that showed activation during the control stimulation were also present during hyperalgesic stimulation, but in addition, some areas showed bilateral activation only during hyperalgesic stimulation, and (2) some brain areas showed significantly higher signal changes during hyperalgesic stimulation. Our findings suggest that injection of ET-1 leads to a state of punctate hyperalgesia, which in turn causes the activation of multiple brain regions. This indicates that ET-1 activates an extended neuronal pathway.

Inflammation in complex regional pain syndrome: a systematic review and meta-analysis

OBJECTIVES

We conducted a systematic review of the literature with meta-analysis to determine whether complex regional pain syndrome (CRPS) is associated with a specific inflammatory profile and whether this is dependent on the duration of the condition.

METHODS

Comprehensive searches of the literature using MEDLINE, Embase, Scopus, Web of Science, and reference lists from published reviews identified articles that measured inflammatory factors in CRPS. Two independent investigators screened titles and abstracts, and performed data extraction and risk of bias assessments. Studies were subgrouped by medium (blood, blister fluid, and CSF) and duration (acute and chronic CRPS). Where possible, meta-analyses of inflammatory factor concentrations were performed and pooled effect sizes were calculated using random-effects models.

RESULTS

Twenty-two studies were included in the systematic review and 15 in the meta-analysis. In acute CRPS, the concentrations of interleukin (IL)-8 and soluble tumor necrosis factor receptors I (sTNF-RI) and II (sTNF-RII) were significantly increased in blood. In chronic CRPS, significant increases were found in 1) TNFα, bradykinin, sIL-1RI, IL-1Ra, IL-2, sIL-2Ra, IL-4, IL-7, interferon-γ, monocyte chemoattractant protein-1 (MCP-1), and sRAGE (soluble receptor for advanced glycation end products) in blood; 2) IL-1Ra, MCP-1, MIP-1β, and IL-6 in blister fluid; and 3) IL-1β and IL-6 in CSF. Chronic CRPS was also associated with significantly decreased 1) substance P, sE-selectin, sL-selectin, sP-selectin, and sGP130 in blood; and 2) soluble intercellular adhesion molecule-1 (sICAM-1) in CSF. Most studies failed to meet 3 or more of our quality criteria.

CONCLUSION

CRPS is associated with the presence of a proinflammatory state in the blood, blister fluid, and CSF. Different inflammatory profiles were found for acute and chronic cases.

Role of peripheral endothelin receptors in an animal model of complex regional pain syndrome type 1 (CRPS-I)

Chronic post-ischemic pain (CPIP) is an animal model of CRPS-I developed using a 3-h ischemia-reperfusion injury of the rodent hind paw. The contribution of local endothelin to nociception has been evaluated in CPIP mice by measuring sustained nociceptive behaviors (SNBs) following intraplantar injection of endothelin-1 or -2 (ET-1, ET-2). The effects of local BQ-123 (ETA-R antagonist), BQ-788 (ETB-R antagonist), IRL-1620 (ETB-R agonist) and naloxone (opioid antagonist) were assessed on ET-induced SNBs and/or mechanical and cold allodynia in CPIP mice. ETA-R and ETB-R expression was assessed using immunohistochemistry and Western blot analysis. Compared to shams, CPIP mice exhibited hypersensitivity to local ET-1 and ET-2. BQ-123 reduced ET-1- and ET-2-induced SNBs in both sham and CPIP animals, but not mechanical or cold allodynia. BQ-788 enhanced ET-1- and ET-2-induced SNBs in both sham and CPIP mice, and cold allodynia in CPIP mice. IRL-1620 displayed a non-opioid anti-nociceptive effect on ET-1- and ET-2-induced SNBs and mechanical allodynia in CPIP mice. The distribution of ETA-R and ETB-R was similar in plantar skin of sham and CPIP mice, but both receptors were over-expressed in plantar muscles of CPIP mice. This study shows that ETA-R and ETB-R have differing roles in nociception for sham and CPIP mice. CPIP mice exhibit more local endothelin-induced SNBs, develop a novel local ETB-R agonist-induced (non-opioid) analgesia, and exhibit over-expression of both receptors in plantar muscles, but not skin. The effectiveness of local ETB-R agonists as anti-allodynic treatments in CPIP mice holds promise for novel therapies in CRPS-I patients.

Analysis of cerebrospinal fluid inflammatory mediators in chronic complex regional pain syndrome related dystonia

OBJECTIVES

There is compelling evidence of central nervous system involvement in neuropathic pain and movement disorders in patients with complex regional pain syndrome (CRPS). Previously, elevated cerebrospinal fluid (CSF) levels of interleukin-1beta and interleukin-6 were found in CRPS patients with and without movement disorders. The aim of the present study was to replicate these findings and to search for additional CSF biomarkers in chronic CRPS patients with dystonia.

METHODS

CSF samples of 20 patients and 29 controls who underwent spinal anesthesia for surgical interventions participated. We measured interleukin-1beta, interleukin-6, interferon-gamma inducible protein-10, RANTES (regulated upon activation, normal T-cell expressed and secreted), complement C3, mannose-binding lectin, complement C1q, soluble intercellular adhesion molecule-1, endothelin-1, nitric oxide, human lactoferrin, and hypocretin-1 levels in these samples.

RESULTS

No differences in the CSF levels of these effector mediators between patients and controls were found.

CONCLUSION

Our CSF findings do not support a role of a variety of inflammatory mediators or hypocretin-1 in chronic CRPS patients with dystonia.

Age- and Sex-Specific Nociceptive Response to Endothelin-1

Endothelin-1 (ET-1) is a chemical mediator released by the body at sites of injury and disease. This study tests the hypothesis that ET-1-induced nociception changes with age and sex. Intraplantar ET-1 (1.1 and 3.3 nmol) produced age-specific paw flinching and licking (postnatal day 7 > 21 > 60). The onset and duration of the nociceptive responses was dependent on age. Postnatal day (P) 21 and 60 rats displayed an immediate onset of behavior that subsided with time, whereas the P7 rats had a delayed behavioral response that onset at 20 minutes after ET-1 administration and continued beyond the 75 minute observation period. P7 males showed greater paw flinching compared with females. In addition to spontaneous nociceptive behaviors, ET-1 produced mechanical allodynia in all ages. As with spontaneous nociception, ET-1-induced mechanical allodynia was of a longer duration in the younger aged rats compared with adult rats. These findings show that ET-1 produces both spontaneous nociceptive behaviors and evoked mechanical allodynia in both young and adult rats but that the temporal profile and the size of the responses are age- and sex-dependent. These findings are the first description of age- and sex-specific ET-1-induced nociception.

PERSPECTIVE

Endothelin-1 is a vasoactive peptide released into the systemic circulation after stress and cold pain as well as locally in tissue after injury and disease. These findings suggest greater pain to stimuli that release endogenous endothelin in younger versus older organisms. This developmental approach to studying ET-1-induced pain further illustrates the need for understanding pain mechanisms as a function of the development of the organism so as to better treat pain across the life span.

Applied information retrieval and multidisciplinary research: new mechanistic hypotheses in complex regional pain syndrome

Background

Collaborative efforts of physicians and basic scientists are often necessary in the investigation of complex disorders. Difficulties can arise, however, when large amounts of information need to reviewed. Advanced information retrieval can be beneficial in combining and reviewing data obtained from the various scientific fields. In this paper, a team of investigators with varying backgrounds has applied advanced information retrieval methods, in the form of text mining and entity relationship tools, to review the current literature, with the intention to generate new insights into the molecular mechanisms underlying a complex disorder. As an example of such a disorder the Complex Regional Pain Syndrome (CRPS) was chosen. CRPS is a painful and debilitating syndrome with a complex etiology that is still unraveled for a considerable part, resulting in suboptimal diagnosis and treatment.

Results

A text mining based approach combined with a simple network analysis identified Nuclear Factor kappa B (NFκB) as a possible central mediator in both the initiation and progression of CRPS.

Conclusion

The result shows the added value of a multidisciplinary approach combined with information retrieval in hypothesis discovery in biomedical research. The new hypothesis, which was derived in silico, provides a framework for further mechanistic studies into the underlying molecular mechanisms of CRPS and requires evaluation in clinical and epidemiological studies.

Increased endothelin-1 and diminished nitric oxide levels in blister fluids of patients with intermediate cold type complex regional pain syndrome type 1

Background

In complex regional pain syndrome type 1 (CRPS1) pro-inflammatory mediators and vascular changes play an important role in the sustained development and outcome of the disease. The aim of this study was to determine the involvement of vasoactive substances endothelin-1 (ET-1) and nitric oxide (NO) during early chronic CRPS1.

Methods

Included were 29 patients with CRPS 1 who were diagnosed during the acute stage of their disease and observed during follow-up visits. Disease activity and impairment were determined and artificial suction blisters were made on the CRPS1 and the contralateral extremities for measurements of IL-6, TNF-α, ET-1 and nitrate/nitrite (NOx).

Results

The levels of IL-6, TNF-α and ET-1 in blister fluid in the CRPS1 extremity versus the contralateral extremity were significantly increased and correlated with each other, whereas NOx levels were decreased.

Conclusion

The NOx/ET-1 ratio appears to be disturbed in the intermediate stage of CRPS, resulting in vasoconstriction and consequently in a diminished tissue blood distribution.