Bone cancer pain has a strong impact on the quality of life of patients, but is difficult to treat. Better understanding of the pathogenic mechanisms underlying bone cancer pain will likely lead to the development of more effective treatments. In the present study, we investigated whether inhibition of KCNQ/M channels contributed to the hyperexcitability of primary sensory neurons and to the pathogenesis of bone cancer pain. By using a rat model of bone cancer pain based on intratibial injection of MRMT-1 tumour cells, we documented a prominent decrease in expression of KCNQ2 and KCNQ3 proteins and a reduction of M-current density in small-sized dorsal root ganglia (DRG) neurons, which were associated with enhanced excitability of these DRG neurons and the hyperalgesic behaviours in bone cancer rats. Coincidently, we found that inhibition of KCNQ/M channels with XE-991 caused a robust increase in the excitability of small-sized DRG neurons and produced an obvious mechanical allodynia in normal rats. On the contrary, activation of the KCNQ/M channels with retigabine not only inhibited the hyperexcitability of these small DRG neurons, but also alleviated mechanical allodynia and thermal hyperalgesia in bone cancer rats, and all of these effects of retigabine could be blocked by KCNQ/M-channel antagonist XE-991. These results suggest that repression of KCNQ/M channels leads to the hyperexcitability of primary sensory neurons, which in turn causes bone cancer pain. Thus, suppression of KCNQ/M channels in primary DRG neurons plays a crucial role in the development of bone cancer pain.

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BackgroundPrimary and metastatic cancers that affect bone are frequently associated with severe and intractable pain. The mechanisms underlying the development of bone cancer pain are largely unknown. The aim of this study was to determine whether enhanced excitability of primary sensory neurons contributed to peripheral sensitization and tumor-induced hyperalgesia during cancer condition. In this study, using techniques of whole-cell patch-clamp recording associated with immunofluorescent staining, single-cell reverse-transcriptase PCR and behavioral test, we investigated whether the intrinsic membrane properties and the excitability of small-sized dorsal root ganglion (DRG) neurons altered in a rat model of bone cancer pain, and whether suppression of DRG neurons activity inhibited the bone cancer-induced pain.ResultsOur present study showed that implantation of MRMT-1 tumor cells into the tibial canal in rats produced significant mechanical and thermal hyperalgesia in the ipsilateral hind paw. Moreover, implantation of tumor cells provoked spontaneous discharges and tonic excitatory discharges evoked by a depolarizing current pulse in small-sized DRG neurons. In line with these findings, alterations in intrinsic membrane properties that reflect the enhanced neuronal excitability were observed in small DRG neurons in bone cancer rats, of which including: 1) depolarized resting membrane potential (RMP); 2) decreased input resistance (Rin); 3) a marked reduction in current threshold (CT) and voltage threshold (TP) of action potential (AP); 4) a dramatic decrease in amplitude, overshot, and duration of evoked action potentials as well as in amplitude and duration of afterhyperpolarization (AHP); and 5) a significant increase in the firing frequency of evoked action potentials. Here, the decreased AP threshold and increased firing frequency of evoked action potentials implicate the occurrence of hyperexcitability in small-sized DRG neurons in bone cancer rats. In addiotion, immunofluorescent staining and single-cell reverse-transcriptase PCR revealed that in isolated small DRG neurons, most neurons were IB4-positive, or expressed TRPV1 or CGRP, indicating that most recorded small DRG neurons were nociceptive neurons. Finally, using in vivo behavioral test, we found that blockade of DRG neurons activity by TTX inhibited the tumor-evoked mechanical allodynia and thermal hyperalgesia in bone cancer rats, implicating that the enhanced excitability of primary sensory neurons underlied the development of bone cancer pain.ConclusionsOur present results suggest that implantation of tumor cells into the tibial canal in rats induces an enhanced excitability of small-sized DRG neurons that is probably as results of alterations in intrinsic electrogenic properties of these neurons. Therefore, alterations in intrinsic membrane properties associated with the hyperexcitability of primary sensory neurons likely contribute to the peripheral sensitization and tumor-induced hyperalgesia under cancer condition.

BackgroundDespite high prevalence of anxiety accompanying with chronic pain, the mechanisms underlying pain-related anxiety are largely unknown. With its well-documented role in pain and emotion processing, the amygdala may act as a key player in pathogenesis of neuropathic pain-related anxiety. Pain-related plasticity and sensitization of CeA (central nucleus of the amygdala) neurons have been shown in several models of chronic pain. In addition, firing pattern of neurons with spike output can powerfully affect functional output of the brain nucleus, and GABAergic neurons are crucial in the modulation of neuronal excitability. In this study, we first investigated whether pain-related plasticity (e.g. alteration of neuronal firing patterns) and sensitization of CeA neurons contribute to nerve injury-evoked anxiety in neuropathic rats. Furthermore, we explored whether GABAergic disinhibition is responsible for regulating firing patterns and intrinsic excitabilities of CeA neurons as well as for pain-related anxiety in neuropathic rats.ResultsWe discovered that spinal nerve ligation (SNL) produced neuropathic pain-related anxiety-like behaviors in rats, which could be specifically inhibited by intra-CeA administration of anti-anxiety drug diazepam. Moreover, we found potentiated plasticity and sensitization of CeA neurons in SNL-induced anxiety rats, of which including: 1) increased burst firing pattern and early-adapting firing pattern; 2) increased spike frequency and intrinsic excitability; 3) increased amplitude of both after-depolarized-potential (ADP) and sub-threshold membrane potential oscillation. In addition, we observed a remarkable reduction of GABAergic inhibition in CeA neurons in SNL-induced anxiety rats, which was proved to be important for altered firing patterns and hyperexcitability of CeA neurons, thereby greatly contributing to the development of neuropathic pain-related anxiety. Accordantly, activation of GABAergic inhibition by intra-CeA administration of muscimol, a selective GABAA receptors agonist, could inhibit SNL-induced anxiety-like behaviors in neuropathic rats. By contrast, suppression of GABAergic inhibition by intra-CeA administration of bicuculline, a selective GABAA receptors antagonist, produced anxiety-like behavior in normal rats.ConclusionsThis study suggests that reduction of GABAergic inhibition may be responsible for potentiated plasticity and sensitization of CeA neurons, which likely underlie the enhanced output of amygdala and neuropathic pain-related anxiety in SNL rats.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-014-0072-z) contains supplementary material, which is available to authorized users.

Inflammatory bowel disease (IBD) such as Crohn's disease and ulcerative colitis is a chronic autoimmune disease affecting nearly five million people worldwide. Among all drug delivery system, oral administration is the most preferable route for colon-specific targeting and the treatment of IBD. Herein, an amphiphilic curcumin polymer (PCur) composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic curcumin (Cur) linked by disulfide bond was synthesized and characterized. The sufficient solubility, nano-scaled size and close to the neutral surface potential of PCur lead to preferential accumulation of the active drug in the inflamed regions of the gut. Moreover, PCur showed limited drug release and enhanced robustness under the physiological pH of the gastrointestinal tract (GIT), and a significantly elevated release was observed when responding to a bacterial reduction in the colon. Furthermore, cellular studies confirmed PCur had low cytotoxicity and increased transmembrane permeability, resulting in improved oral bioavailability evidenced by in vivo pharmacokinetics of rats. Finally, with DSS-induced murine model of IBD, we demonstrated that orally administered PCur ameliorated the inflammatory progression in the colon and could protect mice from IBD. In conclusion, it is illustrated that the developed PCur conjugate could potentially be employed as a colon-specific candidate for IBD treatment.

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Primary and metastatic cancers that affect bone are frequently associated with severe and intractable pain. The mechanisms underlying the development of bone cancer pain are largely unknown. In this study, we first demonstrated that a functional upregulation of P2X3 receptors in dorsal root ganglion (DRG) neurons is closely associated with the neuronal hyperexcitability and the cancer-induced bone pain in MRMT-1 tumor cell-inoculated rats. Second, we revealed that visinin-like protein 1 (VILIP-1), a member of visinin-like proteins that belong to the family of neuronal calcium sensor proteins is responsible for the observed upregulation of P2X3 receptors in DRG neurons. The interaction between the amino terminus of VLIP-1 and the carboxyl terminus of the P2X3 receptor is critical for the surface expression and functional enhancement of the receptor. Finally, overexpression of VILIP-1 increases the expression of functional P2X3 receptors and enhances the neuronal excitability in naive rat DRG neurons. In contrast, knockdown of VILIP-1 inhibits the development of bone cancer pain via downregulation of P2X3 receptors and repression of DRG excitability in MRMT-1 rats. Taken together, these results suggest that functional upregulation of P2X3 receptors by VILIP-1 in DRG neurons contributes to the development of cancer-induced bone pain in MRMT-1 rats. Hence, P2X3 receptors and VILIP-1 could serve as potential targets for therapeutic interventions in cancer patients for pain management. Pharmacological blockade of P2X3 receptors or knockdown of VILIP-1 in DRGs would be used as innovative strategies for the treatment of bone cancer pain.

BackgroundKnockdown of Akt1 promotes Epithelial-to-Mesenchymal Transition in breast cancer cells. However, the mechanisms are not completely understood.MethodsWestern blotting, immunofluorescence, luciferase assay, real time PCR, ELISA and Matrigel invasion assay were used to investigate how Akt1 inhibition promotes breast cancer cell invasion in vitro. Mouse model of lung metastasis was used to measure in vivo efficacy of Akt inhibitor MK2206 and its combination with Gefitinib.ResultsKnockdown of Akt1 stimulated β-catenin nuclear accumulation, resulting in breast cancer cell invasion. β-catenin nuclear accumulation induced by Akt1 inhibition depended on the prolonged activation of EGFR signaling pathway in breast cancer cells. Mechanistic experiments documented that knockdown of Akt1 inactivates PIKfyve via dephosphorylating of PIKfyve at Ser318 site, resulting in a decreased degradation of EGFR signaling pathway. Inhibition of Akt1 using MK2206 could induce an increase in the expression of EGFR and β-catenin in breast cancer cells. In addition, MK2206 at a low dosage enhance breast cancer metastasis in a mouse model of lung metastasis, while an inhibitor of EGFR tyrosine kinase Gefitinib could potentially suppress breast cancer metastasis induced by Akt1 inhibition.ConclusionEGFR-mediated β-catenin nuclear accumulation is critical for Akt1 inhibition-induced breast cancer metastasis.