Pharmacology of capsaicin-, anandamide-, and N-arachidonoyl-dopamine-evoked cell death in a homogeneous transient receptor potential vanilloid subtype 1 receptor population.
BACKGROUND
Transient receptor potential vanilloid subtype 1 (TRPV1) receptor is a primary pain-sensing relay at peripheral sensory nerve endings and is also widespread in the brain, where it is implicated in neurodegeneration. Previous studies of TRPV1 neurotoxicity have utilized heterogeneous receptor populations, non-selective ligands, or non-neuronal cell types. Here, we explored the pharmacology of TRPV1-induced cytotoxicity in a homogeneous, neurone-like cellular environment.


METHODS
Cell death was examined in a human neurone-like cell line, stably expressing recombinant human TRPV1. Cytotoxicity was quantified in terms of nuclear morphology and mitochondrial complex II activity. Immunocytochemical markers of apoptotic cell death were also examined.


RESULTS
The TRPV1-selective agonist capsaicin, and the endovanilloids anandamide and N-arachidonoyl-dopamine (NADA), induced TRPV1-dependent delayed cell death in a concentration- and time-dependent manner. Capsaicin exposure time was significantly correlated with potency (r(2)=0.91, P=0.01). Release of cytochrome c from mitochondria, activation of caspase-3, and condensed nuclear chromatin were evident 6 h after capsaicin exposure, but cytotoxicity was unaffected by a pan-caspase inhibitor (zVAD-fmk, 50 microM).


CONCLUSIONS
We conclude that capsaicin, anandamide, and NADA can initiate TRPV1-dependent delayed cell death in neurone-like cells. This is an apoptosis-like process, but independent of caspase activity.
Davies
J W
JW
Division of Anaesthesia, Critical Care and Pain Management, Department of Cardiovascular Sciences (Pharmacology and Therapeutics Group), University of Leicester, Leicester Royal Infirmary, Leicester LE1 5WW, UK.
Hainsworth
A H
AH
Guerin
C J
CJ
Lambert
D G
DG
D017209:Apoptosis / Q000187:drug effects*; D001095:Arachidonic Acids / Q000494:pharmacology*; D002211:Capsaicin / Q000494:pharmacology*; D004298:Dopamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D006801:Humans; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology*; D050916:TRPV Cation Channels / Q000819:agonists / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured
D001095:Arachidonic Acids; D063388:Endocannabinoids; D053284:Polyunsaturated Alkamides; D050916:TRPV Cation Channels; C494484:TRPV1 receptor; C474941:arachidonyl dopamine; D002211:Capsaicin; C078814:anandamide; D004298:Dopamine