title: Formaldehyde up-regulates TRPV1 through MAPK and PI3K signaling pathways in a rat model of bone cancer pain.
abstract: OBJECTIVE
  Our previous study showed that tumor tissue-derived formaldehyde at low concentrations plays an important role in bone cancer pain through activating transient receptor potential vanilloid subfamily member 1 (TRPV1). The present study further explored whether this tumor tissue-derived endogenous formaldehyde regulates TRPV1 expression in a rat model of bone cancer pain, and if so, what the possible signal pathways are during the development of this type of pain.
  
  
  METHODS
  A rat model of bone cancer pain was established by injecting living MRMT-1 tumor cells into the tibia. The formaldehyde levels were determined by high performance liquid chromatography, and the expression of TRPV1 was examined with Western blot and RT-PCR. In primary cultured dorsal root ganglion (DRG) neurons, the expression of TRPV1 was assessed after treatment with 100 µmol/L formaldehyde with or without pre-addition of PD98059 [an inhibitor for extracellular signal-regulated kinase], SB203580 (a p38 inhibitor), SP600125 [an inhibitor for c-Jun N-terminal kinase], BIM [a protein kinase C (PKC) inhibitor] or LY294002 [a phosphatidylinositol 3-kinase (PI3K) inhibitor].
  
  
  RESULTS
  In the rat model of bone cancer pain, formaldehyde concentration increased in blood plasma, bone marrow and the spinal cord. TRPV1 protein expression was also increased in the DRG. In primary cultured DRG neurons, 100 μmol/L formaldehyde significantly increased the TRPV1 expression level. Pre-incubation with PD98059, SB203580, SP600125 or LY294002, but not BIM, inhibited the formaldehyde-induced increase of TRPV1 expression.
  
  
  CONCLUSIONS
  Formaldehyde at a very low concentration up-regulates TRPV1 expression through mitogen-activated protein kinase and PI3K, but not PKC, signaling pathways. These results further support our previous finding that TRPV1 in peripheral afferents plays a role in bone cancer pain.
authors.affiliation: Neuroscience Research Institute, The Ministry of Education/The Ministry of Health, Peking University, Beijing 100191, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Han
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Xing
authors.initials: X
authors.lastname: Xiao
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Xiang-Ling
authors.initials: XL
authors.lastname: Meng
authors.forename: Feng-Yu
authors.initials: FY
authors.lastname: Liu
authors.forename: Guo-Gang
authors.initials: GG
authors.lastname: Xing
authors.forename: You
authors.initials: Y
authors.lastname: Wan
mesh_terms: D000818:Animals; D001859:Bone Neoplasms / Q000150:complications*; D004195:Disease Models, Animal; D005260:Female; D005557:Formaldehyde / Q000097:blood / Q000134:cerebrospinal fluid / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000187:drug effects / Q000503:physiopathology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D010148:Intractable Pain / Q000139:chemically induced*; D061251:Primary Cell Culture; D051381:Rats; D017207:Rats, Sprague-Dawley; D050916:TRPV Cation Channels / Q000819:agonists / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects* / Q000502:physiology
chemical_list: D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D005557:Formaldehyde