miR-124a and miR-155 enhance differentiation of regulatory T cells in patients with neuropathic pain

Background: Accumulating evidence indicates that neuropathic pain is a neuro-immune disorder with enhanced activation of the immune system. Recent data provided proof that neuropathic pain patients exhibit increased numbers of immunosuppressive regulatory T cells (Tregs), which may represent an endogenous attempt to limit inflammation and to reduce pain levels. We here investigate the molecular mechanisms underlying these alterations. Methods: Our experimental approach includes functional analyses of primary human T cells, 3'-UTR reporter assays, and expression analyses of neuropathic pain patients' samples. Results: We demonstrate that microRNAs (miRNAs) are involved in the differentiation of Tregs in neuropathic pain. We identify miR-124a and miR-155 as direct repressors of the histone deacetylase sirtuin1 (SIRT1) in primary human CD4+ cells. Targeting of SIRT1 by either specific siRNA or by these two miRNAs results in an increase of Foxp3 expression and, consecutively, of anti-inflammatory Tregs (siRNA: 1.7 +/- 0.4;miR-124a: 1.5 +/- 0.4;miR-155: 1.6 +/- 0.4;p < 0.01). As compared to healthy volunteers, neuropathic pain patients exhibited an increased expression of miR124a (2.5 +/- 0.7, p < 0.05) and miR-155 (1.3 +/- 0.3;p < 0.05) as well as a reduced expression of SIRT1 (0.5 +/- 0.2;p < 0.01). Moreover, the expression of these two miRNAs was inversely correlated with SIRT1 transcript levels. Conclusions: Our findings suggest that in neuropathic pain, enhanced targeting of SIRT1 by miR-124a and miR-155 induces a bias of CD4(+) T cell differentiation towards Tregs, thereby limiting pain-evoking inflammation. Deciphering miRNA-target interactions that influence inflammatory pathways in neuropathic pain may contribute to the discovery of new roads towards pain amelioration

Interaction of hyperalgesia and sensory loss in complex regional pain syndrome type I (CRPS I)

Sensory abnormalities are a key feature of Complex Regional Pain Syndrome (CRPS). In order to characterise these changes in patients suffering from acute or chronic CRPS I, we used Quantitative Sensory Testing (QST) in comparison to an age and gender matched control group

miR-124a and miR-155 enhance differentiation of regulatory T cells in patients with neuropathic pain

Background: Accumulating evidence indicates that neuropathic pain is a neuro-immune disorder with enhanced activation of the immune system. Recent data provided proof that neuropathic pain patients exhibit increased numbers of immunosuppressive regulatory T cells (Tregs), which may represent an endogenous attempt to limit inflammation and to reduce pain levels. We here investigate the molecular mechanisms underlying these alterations. Methods: Our experimental approach includes functional analyses of primary human T cells, 3'-UTR reporter assays, and expression analyses of neuropathic pain patients' samples. Results: We demonstrate that microRNAs (miRNAs) are involved in the differentiation of Tregs in neuropathic pain. We identify miR-124a and miR-155 as direct repressors of the histone deacetylase sirtuin1 (SIRT1) in primary human CD4+ cells. Targeting of SIRT1 by either specific siRNA or by these two miRNAs results in an increase of Foxp3 expression and, consecutively, of anti-inflammatory Tregs (siRNA: 1.7 +/- 0.4;miR-124a: 1.5 +/- 0.4;miR-155: 1.6 +/- 0.4;p < 0.01). As compared to healthy volunteers, neuropathic pain patients exhibited an increased expression of miR124a (2.5 +/- 0.7, p < 0.05) and miR-155 (1.3 +/- 0.3;p < 0.05) as well as a reduced expression of SIRT1 (0.5 +/- 0.2;p < 0.01). Moreover, the expression of these two miRNAs was inversely correlated with SIRT1 transcript levels. Conclusions: Our findings suggest that in neuropathic pain, enhanced targeting of SIRT1 by miR-124a and miR-155 induces a bias of CD4(+) T cell differentiation towards Tregs, thereby limiting pain-evoking inflammation. Deciphering miRNA-target interactions that influence inflammatory pathways in neuropathic pain may contribute to the discovery of new roads towards pain amelioration

Differential expression of P2X7 receptor and IL-1 beta in nociceptive and neuropathic pain

Background: Despite substantial progress, pathogenesis and therapy of chronic pain are still the focus of many investigations. The ATP-gated P2X7 receptor (P2X7R) has previously been shown to play a central role in animal models of nociceptive inflammatory and neuropathic pain. Recently, we found that the adaptive immune system is involved in the pathophysiology of chronic nociceptive and neuropathic pain in humans. So far, data regarding P2X7R expression patterns on cells of the adaptive immune system of pain patients are scarce. We therefore analyzed the P2X7R expression on peripheral blood lymphocytes and monocytes, as well as serum levels of IL-1 beta in patients suffering from chronic nociceptive and neuropathic pain in comparison to healthy volunteers in order to identify individuals who might benefit from a P2X7R modulating therapy. Methods: P2X7R messenger RNA (mRNA) and protein expression were determined in patients with either chronic nociceptive low back pain (CLBP) or neuropathic pain (NeP), and in healthy volunteers by quantitative real-time PCR (qPCR) and by fluorescence-assisted cell-sorting (FACS), respectively. IL-1 beta serum levels were measured with a multiplex cytokine assay. Results: Compared to healthy volunteers, P2X7R mRNA (1.6-fold, p = 0.038) and protein levels were significantly increased on monocytes (NeP: 24.6 +/- 6.2, healthy volunteers: 17.0 +/- 5.4;p = 0.002) and lymphocytes (NeP: 21.8 +/- 6.5, healthy volunteers: 15.6 +/- 5.2;p = 0.009) of patients with NeP, but not in patients with CLBP. Similarly, IL-1 beta serum concentrations were significantly elevated only in NeP patients (1.4-fold, p = 0.04). Conclusions: A significant upregulation of P2X7R and increased IL-1 beta release seems to be a particular phenomenon in patients with NeP. P2X7R inhibitors may therefore represent a potential option for the treatment of this frequently intractable type of pain

Effects of low-dose intranasal (S)-ketamine in patients with neuropathic pain

a b s t r a c t Background: NMDA receptors are involved in the development and maintenance of neuropathic pain. We evaluated the efficacy and safety of intranasal (S)-ketamine, one of the most potent clinically available NMDA receptor antagonists. Methods: Sixteen patients with neuropathic pain of various origins were randomized into two treatment groups: (S)-ketamine 0.2 mg/kg (group 1); (S)-ketamine 0.4 mg/kg (group 2). Plasma concentrations of (S)-ketamine and (S)-norketamine were measured over 6 h by High Performance Liquid Chromatography combined with mass spectrometry. Quantitative sensory testing (QST) was conducted before, during and after treatment. Side effects and amount of pain reduction were recorded. Results: Intranasal (S)-ketamine administration lead to peak plasma concentrations of 27.7 ± 5.9 ng/ml at 10 ± 6.3 min (group 1) and 34.3 ± 22.2 ng/ml at 13.8 ± 4.8 min after application (group 2). Maximal plasma concentrations of (S)-norketamine were 18.3 ± 14.9 ng/ml at 81 ± 59 min (group 1) and 34.3 ± 5.5 ng/ml at 75 ± 40 min (group 2). Pain scores decreased significantly in both groups with minimal pain at 60 min after drug administration (70 ± 10% and 61 ± 13% of initial pain in groups 1 and 2). The time course of pain decrease was significantly correlated with plasma concentrations of (S)-ketamine and (S)-norketamine (partial correlations: (S)-norketamine: À0.90 and À0.86; (S)-ketamine: À0.72 and À0.71 for group 1 and group 2, respectively). Higher dosing elicited significantly more side effects. Intranasal (S)-ketamine had no significant impact on thermal or mechanical detection and pain thresholds in normal or symptomatic skin areas. Conclusions: Intranasal administration of low dose (S)-ketamine rapidly induces adequate plasma concentrations of (S)-ketamine and subsequently of its metabolite (S)-norketamine. The time course of analgesia correlated with plasma concentrations

The major brain endocannabinoid 2-AG controls neuropathic pain and mechanical hyperalgesia in patients with neuromyelitis optica.

Recurrent myelitis is one of the predominant characteristics in patients with neuromyelitis optica (NMO). While paresis, visual loss, sensory deficits, and bladder dysfunction are well known symptoms in NMO patients, pain has been recognized only recently as another key symptom of the disease. Although spinal cord inflammation is a defining aspect of neuromyelitis, there is an almost complete lack of data on altered somatosensory function, including pain. Therefore, eleven consecutive patients with NMO were investigated regarding the presence and clinical characteristics of pain. All patients were examined clinically as well as by Quantitative Sensory Testing (QST) following the protocol of the German Research Network on Neuropathic Pain (DFNS). Additionally, plasma endocannabinoid levels and signs of chronic stress and depression were determined. Almost all patients (10/11) suffered from NMO-associated neuropathic pain for the last three months, and 8 out of 11 patients indicated relevant pain at the time of examination. Symptoms of neuropathic pain were reported in the vast majority of patients with NMO. Psychological testing revealed signs of marked depression. Compared to age and gender-matched healthy controls, QST revealed pronounced mechanical and thermal sensory loss, strongly correlated to ongoing pain suggesting the presence of deafferentation-induced neuropathic pain. Thermal hyperalgesia correlated to MRI-verified signs of spinal cord lesion. Heat hyperalgesia was highly correlated to the time since last relapse of NMO. Patients with NMO exhibited significant mechanical and thermal dysesthesia, namely dynamic mechanical allodynia and paradoxical heat sensation. Moreover, they presented frequently with either abnormal mechanical hypoalgesia or hyperalgesia, which depended significantly on plasma levels of the endogenous cannabinoid 2-arachidonoylglycerole (2-AG). These data emphasize the high prevalence of neuropathic pain and hyperalgesia in patients with NMO. The degree of mechanical hyperalgesia reflecting central sensitization of nociceptive pathways seems to be controlled by the major brain endocannabinoid 2-AG

Clinical characteristics of neuropathic pain.

<p>Clinical characteristics of neuropathic pain.</p

Pattern of sensory changes in patients with NMO (normalized to mean and standard deviation of healthy control group).

<p>A: The sensory profile by comprehensive quantitative sensory testing (QST) shows significant sensory loss (negative z-values) for thermal detection (CDT, WDT, TSL) and vibration detection (VDT) in both extremities, significant sensory gain (positive z-values) for noxious heat (HPT) in the hand dorsum. B: Patients with NMO experienced pronounced dysesthesia to non-noxious mechanical and thermal stimulation in both extremities, namely pain to stroking with non-noxious light tactile stimuli (dynamic mechanical allodynia DMA) and paradoxical heat sensation (PHS) to stimulation with non-noxious cold stimuli during the TSL procedure (alternating cold and warm stimuli). *p<0.05, **p<0.01, ***p<0.001, t-test.</p

Thermal thresholds in NMO.

<p>A: Heat pain thresholds in patients with NMO (NMO) compared to healthy controls (HC) differed significantly in the hands, but not feet. <b>B</b>: Patients with NMO (NMO) in patients with an acute MRI-verified cervical lesion (NMO w) were significantly more heat pain-sensitive in both extremities and also tended to be more cold pain-sensitive than patients without (NMO w/o). For both thermal pain modalities the hyperalgesia tended to be more pronounced in the hands than feet. <b>C</b>: Collapsing data from both extremities revealed that patients with an acute MRI-verified cervical lesion (NMO w) were significantly more cold pain-sensitive than patients without (NMO w/o). <b>D</b>: Correlations of heat pain thresholds to the time span since the last relapse of an acute NMO attack was high in the hand (closed circles; r = 0.77) and feet (open circles; r = 0.68). This correlation also persisted at the same level, when normalized for gender and age. The correlations indicated that NMO relapses may have induced a severe heat hyperalgesia that subsided slowly during the course of remission. ⁽*⁾p<0.10, *p<0.05, **p<0.01, ***p<0.001, t-test.</p