Kynurenic acid and zaprinast diminished CXCL17-evoked pain-related behaviour and enhanced morphine analgesia in a mouse neuropathic pain model.

BACKGROUND: The G protein-coupled receptor 35 (GPR35), is considered important for nociceptive transmission, as suggested by accumulating evidence. This receptor was discovered in 1998; however, a lack of pharmacological tools prevented a complete understanding of its function and how to exploit it therapeutically. We studied the influence of CXCL17, kynurenic acid and zaprinast on nociceptive transmission in naïve and neuropathic mice. Additionally, we investigated the influence of kynurenic acid and zaprinast on morphine effectiveness in neuropathic pain. METHODS: The chronic constriction injury (CCI) of the sciatic nerve in Swiss mice was performed. The CXCL17, kynurenic acid, zaprinast and morphine were injected intrathecally into naive and CCI-exposed mice at day 14. To evaluate tactile and thermal hypersensitivity, the von Frey and cold plate tests were used, respectively. RESULTS: Our results have shown, for the first time, that administration of CXCL17 in naïve mice induced strong pain-related behaviours, as measured by von Frey and cold plate tests. Moreover, we demonstrated that kynurenic acid and zaprinast diminished CXCL17-evoked pain-related behaviours in both tests. Kynurenic acid and zaprinast reduced thermal and tactile hypersensitivity developed by sciatic nerve injury and strongly enhanced the effectiveness of morphine in neuropathy. CONCLUSIONS: Our study highlights the importance of GPR35 as a receptor involved in neuropathic pain development. Therefore, these results suggest that the modulation of GPR35 could become a potential strategy for the treatment of neuropathic pain.

Effects of SDF-1alpha and gp120IIIB on apoptotic pathways in SK-N-SH neuroblastoma cells.

CXCR4, a chemokine receptor constitutively expressed in the brain, binds both ligands, the chemokine SDF-1alpha and the HIV envelope glycoprotein gp120(IIIB). There seem to be intracellular differences between the neuronal apoptosis induced by SDF-1alpha and that induced by gp120(IIIB), but the apoptotic pathways involved have not been compared in human neuronal cells. In this study, we characterized the apoptotic intracellular pathways activated by neurotoxic concentrations of SDF-1alpha and gp120(IIIB) in human neuroblastoma cells SK-N-SH. SDF-1alpha (10 nM) and gp120(IIIB) (2 nM) induced similar levels of apoptosis after 24 h of incubation (49 +/- 4% and 48 +/- 3%, respectively, of the neurons were apoptotic). SDF1alpha-induced apoptosis was completely abolished by the inhibition of Src phosphorylation by PP2. Exposure to SDF-1alpha (10 nM) triggered an increase in Src phosphorylation, with a maximum after 20 min of incubation (1.80 +/- 0.24 times higher than control, P = 0.01). NMDA calcium flux was enhanced only if cells were incubated with SDF-1alpha for 20 min before applying NMDA. By contrast, gp120(IIIB)-induced apoptosis was not affected by the inhibition of Src phosphorylation. Moreover, gp120(IIIB) enhanced NMDA calcium flux immediately, without modifying Src phosphorylation status. Finally, levels of phospho-JNK increased following exposure to gp120(IIIB) (by a factor of 1.46 +/- 0.4 at 120 min, P = 0.03), but not after exposure to SDF-1alpha. Thus, SDF-1alpha and gp120(IIIB) induced a similar level of neuronal apoptosis, but by activating different intracellular pathways. SDF-1alpha enhanced NMDA activity indirectly via Src phosphorylation, whereas gp120(IIIB) probably activated the NMDA receptor directly and phosphorylated JNK.

Direct hepatotoxic effect of KC chemokine in the liver without infiltration of neutrophils.

KC is a mouse homolog of human chemokine gro-alpha (CXCL1), expression of which is increased in liver diseases. We show that activated, but not quiescent, hepatic stellate cells (HSCs) express KC. Hepatic stellate cells constitutively express the KC receptor, CXCR2. Addition of recombinant KC to HSCs undergoing activation in culture increases secretion and processing of Type I collagen. Overexpression of endogenous KC in the mouse liver could be achieved by an intraperitoneal injection of CCl(4), followed after 24 hrs by an injection of recombinant KC into circulation. This protocol resulted in about a 14-fold increase in concentration of KC protein in the liver. Overexpression of KC was associated with upregulation of the mRNA for CXCR2 and MIP-2 and with necrosis and increased synthesis of Type I collagen. This suggests that KC has a direct hepatotoxic effect, which led to a massive liver necrosis after 48 hrs. No accumulation of neutrophils was seen in the livers as judged by histology and reverse transcriptase-polymerase chain reaction analysis of myeloperoxidase mRNA. Autostimulation of KC and CXCR2 expression by recombinant KC protein in the mice with preexisting liver injury indicates a positive feedback regulation. Such regulation and direct hepatotoxicity of KC with increased collagen synthesis represent novel findings about the role of KC/ gro-alpha in liver pathology.

HIV-induced metalloproteinase processing of the chemokine stromal cell derived factor-1 causes neurodegeneration.

The mechanisms of neurodegeneration that result in human immunodeficiency virus (HIV) type 1 dementia have not yet been identified. Here, we report that HIV-infected macrophages secrete the zymogen matrix metalloproteinase-2 (MMP-2), which is activated by exposure to MT1-MMP on neurons. Stromal cell-derived factor 1 alpha (SDF-1), a chemokine overexpressed by astrocytes during HIV infection, was converted to a highly neurotoxic protein after precise proteolytic processing by active MMP-2, which removed the N-terminal tetrapeptide. Implantation of cleaved SDF-1(5-67) into the basal ganglia of mice resulted in neuronal death and inflammation with ensuing neurobehavioral deficits that were abrogated by neutralizing antibodies to SDF-1 and an MMP inhibitor drug. Hence, this study identifies a new in vivo neurotoxic pathway in which cleavage of a chemokine by an induced metalloproteinase results in neuronal apoptosis that leads to neurodegeneration.

Brain-derived neurotrophic factor inhibits human immunodeficiency virus-1/gp120-mediated cerebellar granule cell death by preventing gp120 internalization.

The human immunodeficiency virus type 1 (HIV-1) envelope protein gp120 has been implicated in the pathogenesis of HIV-1 dementia. Thus, inhibition of gp120 activity could reduce HIV toxicity in the brain. We have used primary cultures of rat cerebellar granule cells to examine mechanisms whereby gp120 causes cell death and to characterize neuroprotective agents. gp120 induced a time- and concentration-dependent apoptotic cell death, which was caspase-3-mediated but caspase-1 independent, and was totally blocked by the irreversible caspase-3-like protease inhibitor N-acetyl-Asp-Glu-Val-Asp-chloromethylketone. Caspase-3 activation was observed only in neurons that internalize gp120, indicating that internalization is key to gp120 toxicity. Because brain-derived neurotrophic factor (BDNF) prevents caspase-3-mediated neuronal cell death, we examined whether BDNF could prevent gp120-mediated apoptosis. Preincubation of neurons with BDNF before the addition of gp120 reduced caspase-3 activation, and consequently rescued 80% of neurons from apoptosis. Most importantly, BDNF reduced the levels of CXC chemokine receptor-4 (CXCR4), a receptor that mediates HIV-1 gp120-induced apoptosis. This effect correlated with the ability of BDNF to reduce gp120 internalization and apoptosis. Moreover, BDNF blocked the neurotoxic effect of stromal-derived factor-1alpha, a natural ligand for CXCR4, further establishing a correlation between neuroprotection and downregulation of CXCR4. We propose that BDNF may be a valid therapy to slow down the progression of HIV/gp120-mediated neurotoxicity.

Suradista NSC 651016 inhibits the angiogenic activity of CXCL12-stromal cell-derived factor 1alpha.

CXCL12 (stromal cell-derived factor 1alpha), a ligand for CXCR4, has been shown to induce endothelial cell chemotaxis and to stimulate angiogenesis, suggesting that it may be a significant target for antiangiogenic therapy. Here we have tested suradista NSC 651016, a compound known to inhibit CXCL12-induced monocyte chemotaxis, for its ability to inhibit CXCL12-induced angiogenic activity. NSC 651016 inhibited CXCL12-mediated endothelial cell chemotaxis in a dose-dependent manner. In addition, new vessel sprouting, by both rat and chick aorta in an angiogenesis model, was inhibited. Additionally, in vitro capillary-like structure formation induced by CXCL12 was inhibited by NSC 651016. Furthermore, NSC 651016 inhibited CXCL12-mediated angiogenesis in an in vivo s.c. assay. These data indicate that suradista NSC 651016 possesses in vitro and in vivo antiangiogenic activity and has the potential to interfere with neovacularization of tumors and their metastases.

Recombinant mouse granulocyte chemotactic protein-2: production in bacteria, characterization, and systemic effects on leukocytes.

Granulocyte chemotactic protein-2 (GCP-2) is an important neutrophil chemotactic factor in the mouse that belongs to the CXC chemokine family. Although the local tissular effects of chemokines are well known, only recently has the systemic regulation of leukocytes become accepted. To study the pharmacokinetics of mouse GCP-2 and the systemic effects on leukocytes, we expressed a potent natural isoform of mouse GCP-2, GCP-2(9-78), in Escherichia coli and produced electrophoretically pure material. GCP-2(9-78) was 10-fold more potent to chemoattract neutrophils than recombinant GCP-2(5-78). After intravenous (i.v.) injection in mice, GCP-2(9-78) persisted in the circulation with an average half-life of 42 min. When a bolus of 1 mg/kg recombinant mouse GCP-2(9-78) was injected systemically, a significant effect on circulating leukocytes was observed. After a neutropenic phase, at its height at 1 h after injection, neutrophil numbers increased to a maximum at 4 h postinjection, and a concomitant decrease in lymphocyte numbers was observed. In control mice injected with isotonic saline, changes in leukocyte numbers were less pronounced and followed a different kinetic. Whereas tissular neutrophil chemotaxis to GCP-2 is influenced by gelatinase B, the systemic effects on neutrophilia and lymphopenia were not different in gelatinase B-deficient and wild-type mice. These data reinforce the idea that chemokines, including GCP-2, influence the homeostasis of circulating leukocyte numbers.

Fractalkine modulates TNF-alpha secretion and neurotoxicity induced by microglial activation.

Among the chemokine family, fractalkine shows unusual properties: it exists as a membrane-bound and soluble protein, and both fractalkine and its receptor CX(3)CR1 are expressed predominantly in the central nervous system. In rat cell culture models, the chemokine fractalkine was expressed in neurons and microglia, but not in astrocytes and its receptor exclusively localized to microglial cells, where its expression was downregulated by treatment with the bacterial endotoxin (LPS). In microglial cultures, LPS (10 ng/ml) induced a marked increase in the release of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). The effects of LPS on TNF-alpha secretion were partially blocked (30%) by fractalkine and the effects of fractalkine were reversed by a polyclonal anti-fractalkine antibody. When microglial-associated fractalkine was neutralized by anti-fractalkine antibody, the LPS response was increased by 80%, suggesting tonic activation of microglial fractalkine receptors by endogenous fractalkine. The effects of the antibody were antagonized by the addition of fractalkine. LPS-activated microglia were neurotoxic when added to neuronal hippocampal culture, producing 20% neuronal death, as measured by NeuN-positive cell counting. An anti-fractalkine antibody produced neurotoxic effects of similar magnitude in this co-culture system and also markedly potentiated the neurotoxic effects of LPS-activated microglia (40% neuronal death). These results suggest that endogenous fractalkine might act tonically as an anti-inflammatory chemokine in cerebral tissue through its ability to control and suppress certain aspects of microglial activation. These data may have relevance to degenerative conditions such as multiple sclerosis, in which cerebral inflammatory processes may be activated.

Fractalkine-mediated endothelial cell injury by NK cells.

Endothelial cells (ECs) are primary targets of immunological attack, and their injury can lead to vasculopathy and organ dysfunction in vascular leak syndrome and in rejection of allografts or xenografts. A newly identified CX3C-chemokine, fractalkine, expressed on activated ECs plays an important role in leukocyte adhesion and migration. In this study we examined the functional roles of fractalkine on NK cell activity and NK cell-mediated endothelial cell injury. Freshly separated NK cells expressed the fractalkine receptor (CX3CR1) determined by FACS analysis and efficiently adhered to immobilized full-length fractalkine, but not to the truncated forms of the chemokine domain or mucin domain, suggesting that fractalkine functions as an adhesion molecule on the interaction between NK cells and ECs. Soluble fractalkine enhanced NK cell cytolytic activity against K562 target cells in a dose- and time-dependent manner. This enhancement correlated well with increased granular exocytosis from NK cells, which was completely inhibited by the G protein inhibitor, pertussis toxin. Transfection of fractalkine cDNA into ECV304 cells or HUVECs resulted in increased adhesion of NK cells and susceptibility to NK cell-mediated cytolysis compared with control transfection. Moreover, both enhanced adhesion and susceptibility of fractalkine-transfected cells were markedly suppressed by soluble fractalkine or anti-CX3CR1 Ab. Our results suggest that fractalkine plays an important role not only in the binding of NK cells to endothelial cells, but also in NK cell-mediated endothelium damage, which may result in vascular injury.