JNK in Spinal Cord Facilitates Bone Cancer Pain in Rats through Modulation of CXCL1

In patients with advanced cancer, cancer-induced bone pain（CIBP） is a severe and common problem that is difficult to manage and explain. As c-Jun N-terminal kinase（JNK） and chemokine（C-X-C motif） ligand 1（CXCL1） have been shown to participate in several chronic pain processes, we investigated the role of JNK and CXCL1 in CIBP and the relationship between them. A rat bone cancer pain model was established by intramedullary injection of Walker 256 rat gland mammary carcinoma cells into the left tibia of Sprague-Dawley rats. As a result, intramedullary injection of Walker 256 carcinoma cells induced significant bone destruction and persistent pain. Both phosphorylated JNK1（p JNK1） and p JNK2 showed time-dependent increases in the ipsilateral spinal cord from day 7 to day 18 after tumor injection. Inhibition of JNK activation by intrathecal administration of SP600125, a selective p JNK inhibitor, attenuated mechanical allodynia and heat hyperalgesia caused by tumor inoculation. Tumor cell inoculation also induced robust CXCL1 upregulation in the ipsilateral spinal cord on day 18 after tumor injection. Inhibition of CXCL1 by intrathecal administration of CXCL1 neutralizing antibody showed a stable analgesic effect. Intrathecal administration of SP600125 reduced CXCL1 increase in the spinal cord, whereas inhibition of CXCL1 in the spinal cord showed no influence on JNK activation. Taken together, these results suggested that JNK activation in spinal cord contributed to the maintenance of CIBP, which may act through modulation of CXCL1. Inhibition of the p JNK/CXCL1 pathway may provide a new choice for treatment of CIBP.

Targeting the nitric oxide/cGMP signaling pathway to treat chronic pain

Nitric oxide(NO)/cyclic guanosine 3′,5′-monophosphate(cGMP) signaling has been shown to act as a mediator involved in pain transmission and processing. In this review, we summarize and discuss the mechanisms of the NO/cGMP signaling pathway involved in chronic pain, including neuropathic pain, bone cancer pain, inflammatory pain, and morphine tolerance. The main process in the NO/cGMP signaling pathway in cells involves NO activating soluble guanylate cyclase, which leads to subsequent production of cGMP. cGMP then activates cGMP-dependent protein kinase(PKG), resulting in the activation of multiple targets such as the opening of ATP-sensitive K+ channels. The activation of NO/cGMP signaling in the spinal cord evidently induces upregulation of downstream molecules, as well as reactive astrogliosis and microglial polarization which participate in the process of chronic pain. In dorsal root ganglion neurons, natriuretic peptide binds to particulate guanylyl cyclase, generating and further activating the cGMP/PKG pathway, and it also contributes to the development of chronic pain. Upregulation of multiple receptors is involved in activation of the NO/cGMP signaling pathway in various pain models. Notably the NO/cGMP signaling pathway induces expression of downstream effectors, exerting both algesic and analgesic effects in neuropathic pain and inflammatory pain. These findings suggest that activation of NO/cGMP signaling plays a constituent role in the development of chronic pain, and this signaling pathway with dual effects is an interesting and promising target for chronic pain therapy.

The effects of Yishen Qutong granula on pain sensitization and bone destruction of rats with bone cancer pain

Objective:To study the effects of Yishen Qutong granula on pain sensitization and bone destruction of rats with bone cancer pain.Methods:Walker256 cells were passaged in ascites and injected into the tibia of female Wistar rats to prepare the bone cancer pain model.On the 14th day after model establishment,60 rats were randomly divided into model group,sham-operated group,Yishen Qutong granula low,middle,high dose group and tramadol hydrochloride positive control group.After continuous administration for 14 days,the mechanical pain threshold,thermal threshold and weight-bearing difference of both hind limbs were observed.Results:Compared with the model group,Yishen Qutong groups increased the mechanical pain threshold,thermal pain threshold and reduced the weight difference of both hind limbs(P<0.05).Compared with the positive drug group,there was no significant difference in increasing the mechanical pain threshold and thermal pain threshold of rats in the medium dose group of Yishen Qutong(P>0.05),and Yishen Qutong granula significantly reduced the weight-bearing difference of hind limbs in all groups(P<0.05).Conclusion:Yishen Qutong granula can relieve pain sensitization and alleviate bone damage in rats with bone cancer pain.

Effects of p38 MAPK inhibitor on the rat pain behavior and proinflammatory cytokines in a metastatic bone cancer pain model

Objective： To observe the effects of p38 mitogen activated protein kinase （MAPK） inhibitor SB203580 by intrathecal injection on the pain behavior and the spinal proinflammatory cytokines in a rat model of bone cancer pain induced by breast cancer cells. Methods： Eleven rats were used to establish the models of bone cancer pain, six rats were treated by intrathecal SB203580 injection, and the other 5 were as the controls. The paw withdrawal latency （PWL）, histology and the spinal levels of IL-1β and TNF-α were detected. Results： All the 11 rats presented evident bone destruction and thermal hyperalgesia after intra-tibial injection of breast cancer cells. No effect of SB203580 on the bone destruction was observed. However, following intrathecal injection of SB203580, the left PWLs （12.12± 1.26 s at 16 days and 12.99 ± 1.65 s at 19 days） were significant higher than that of controls （9.05 ± 1.08 s at 16 days and 8.55 ± 1.60 s at 19 days）, P 〈 0.05. Meanwhile, inkathecal injection of SB203580 evidently reduced the levels of spinal IL-1β and TNF-α. Conclusion： Intrathecal injection of SB203580 in a rat model of bone cancer pain cannot prevent the tibial destruction but significantly depress the thermalgia sensitivity, which might result from inhibiting inkacellular p38 MAPK signaling transduction, and thereby reducing the release of the proinflammatory cytokines.

Modulation of Na_v1.8 by Lysophosphatidic Acid in the Induction of Bone Cancer Pain

Given that lysophosphatidic acid（LPA） and the tetrodotoxin-resistant sodium channel Na_v1.8 are both involved in bone cancer pain, the present study was designed to investigate whether crosstalk between the LPA receptor LPA_1（also known as EDG2） and Na_v1.8 in the dorsal root ganglion（DRG） contributes to the induction of bone cancer pain. We showed that the EDG2 antagonist Ki16198 blocked the mechanical allodynia induced by intrathecal LPA in na？ve rats and attenuated mechanical allodynia in a rat model of bone cancer. EDG2 and Na_v1.8expression in L_（4-6）DRGs was upregulated following intrathecal or hindpaw injection of LPA. EDG2 and Na_v1.8expression in ipsilateral L_（4-6）DRGs increased with the development of bone cancer. Furthermore, we showed that EDG2 co-localized with Na_v1.8 and LPA remarkably enhanced Na_v1.8 currents in DRG neurons, and this was blocked by either a protein kinase C（PKC） inhibitor or a PKCe inhibitor. Overall, we demonstrated the modulation of Na_v1.8 by LPA in DRG neurons, and that this probably underlies the peripheral mechanism by which bone cancer pain is induced.

Mechanisms of treatment of cancer pain with a topical Chinese herbal formula in rats

Background Pain has a substantial impact on patients＇ activities and overall quality of life, but current conventional drugs have debilitating side effects, including gastrointestinal disorders. Thus there is a pressing need for new therapies with fewer side effects to alleviate cancer pain. We recently developed a topical herbal formula Xiaotan Tongluo analgesic gel （X＇I-IL gel） based on the principles of traditional Chinese herbalism, and we have received positive feedback from bone cancer pain patients. The aim of this study was to determine the analgesic effects and explore the mechanisms of XTI-L gel in a rat model of bone cancer pain. Methods The rat model of bone cancer pain was established by inoculating Walker-256 rat carcinoma cells directly into the right tibial medullary cavity of Wistar rats. The rats were randomly assigned to three groups （n=-10 per group）： （1） sham bone cancer control （sham group）： vehicle （PBS） inoculation without carcinoma cells plus topical administration of blank gel; （2） Sham treatment control （vehicle group）： Walker-256 cell inoculation plus topical administration of blank gel; （3） XTTL gel treatment （treatment group）： Walker-256 cell inoculation plus topical administration of XTTL gel. XTTL gel treatments were applied daily for 7 days starting on day 14 following inoculation. Outcomes were assessed 21 days after inoculation by mechanical allodynia, histological staining, and by measuring concentrations of type I collagen carboxy-terminal telopeptide （ICTP） and bone-specific alkaline phosphatase （BAP） in serum. Results Fourteen days after cancer cell incubation, significant mechanical allodynia in the ipsilateral hind paw and tumor growth in proximal end of the tibia were observed in the vehicle and treatment groups but not in the sham group. At day 21, mechanical withdrawal thresholds in treatment group rats were significantly higher （（4.8557±0.8336） g） compared with those of the vehicle group （（1.8630±1.4369） g, P 〈0.05）. ICTP and BAP levels increased significantly in vehicle group rats （（101.5176±11.0694） U/L and （370.7838±12.8273） U/L, respectively） compared with those of the sham group （（11.7553±1.1885） U/L and （185.7338±3.6761） U/L, respectively; P 〈0.05）. XTTL gel decreased the level of blood serum ICTP （（41.8998±6.4970） U/L, P 〈0.05） but had little effect on blood serum BAP （（365.5338±18.5361） U/L, P 〉0.05）. Conclusion Topical use of XTTL gel may have an analgesic effect on bone cancer pain, an effect mediated by lowering of ICTP levels and inhibiting bone resorption. Chin Med J 2009; 122（17）：2027-2031