Bilateral downregulation of Nav1.8 in dorsal root ganglia of rats with bone cancer pain induced by inoculation with Walker 256 breast tumor cells.
BACKGROUND
Rapid and effective treatment of cancer-induced bone pain remains a clinical challenge and patients with bone metastasis are more likely to experience severe pain. The voltage-gated sodium channel Nav1.8 plays a critical role in many aspects of nociceptor function. Therefore, we characterized a rat model of cancer pain and investigated the potential role of Nav1.8.


METHODS
Adult female Wistar rats were used for the study. Cancer pain was induced by inoculation of Walker 256 breast carcinosarcoma cells into the tibia. After surgery, mechanical and thermal hyperalgesia and ambulation scores were evaluated to identify pain-related behavior. We used real-time RT-PCR to determine Nav1.8 mRNA expression in bilateral L4/L5 dorsal root ganglia (DRG) at 16-19 days after surgery. Western blotting and immunofluorescence were used to compare the expression and distribution of Nav1.8 in L4/L5 DRG between tumor-bearing and sham rats. Antisense oligodeoxynucleotides (ODNs) against Nav1.8 were administered intrathecally at 14-16 days after surgery to knock down Nav1.8 protein expression and changes in pain-related behavior were observed.


RESULTS
Tumor-bearing rats exhibited mechanical hyperalgesia and ambulatory-evoked pain from day 7 after inoculation of Walker 256 cells. In the advanced stage of cancer pain (days 16-19 after surgery), normalized Nav1.8 mRNA levels assessed by real-time RT-PCR were significantly lower in ipsilateral L4/L5 DRG of tumor-bearing rats compared with the sham group. Western-blot showed that the total expression of Nav1.8 protein significantly decreased bilaterally in DRG of tumor-bearing rats. Furthermore, as revealed by immunofluorescence, only the expression of Nav1.8 protein in small neurons down regulated significantly in bilateral DRG of cancer pain rats. After administration of antisense ODNs against Nav1.8, Nav1.8 protein expression decreased significantly and tumor-bearing rats showed alleviated mechanical hyperalgesia and ambulatory-evoked pain.


CONCLUSIONS
These findings suggest that Nav1.8 plays a role in the development and maintenance of bone cancer pain.
Miao
Xue-Rong
XR
Department of Anesthesiology, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China.
Gao
Xiao-Fei
XF
Wu
Jing-Xiang
JX
Lu
Zhi-Jie
ZJ
Huang
Zhang-Xiang
ZX
Li
Xiao-Qing
XQ
He
Cheng
C
Yu
Wei-Feng
WF
D000818:Animals; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000378:metabolism / Q000556:secondary*; D002279:Carcinoma 256, Walker / Q000378:metabolism / Q000556:secondary*; D015536:Down-Regulation; D005260:Female; D005455:Fluorescent Antibody Technique; D005727:Ganglia, Spinal / Q000378:metabolism* / Q000503:physiopathology; D055785:Gene Knockdown Techniques; D006930:Hyperalgesia / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology / Q000517:prevention & control; D007278:Injections, Spinal; D015674:Mammary Neoplasms, Animal / Q000378:metabolism / Q000473:pathology*; D062559:NAV1.8 Voltage-Gated Sodium Channel; D016376:Oligonucleotides, Antisense / Q000008:administration & dosage; D010146:Pain / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology / Q000517:prevention & control; D010147:Pain Measurement; D017288:Pain Threshold; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D013977:Tibia / Q000473:pathology*; D013997:Time Factors
D062559:NAV1.8 Voltage-Gated Sodium Channel; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; C568319:Scn10a protein, rat; D015222:Sodium Channels