Capsaicin-induced neurotoxicity in cultured dorsal root ganglion neurons: involvement of calcium-activated proteases.
We examined the mechanism by which capsaicin produces its toxic effects on cultures of rat sensory neurons. Capsaicin caused a robust increase in [Ca2+]i in a subpopulation of cultured rat dorsal root ganglion neurons. Similarly, a brief exposure to capsaicin resulted in delayed degeneration of a subpopulation of the cells. This subpopulation (about 35% of the cells present) was characterized by a capsaicin-induced uptake of Co2+, which could be detected cytochemically. Both capsaicin-induced Co2+ uptake and capsaicin-induced cell death were blocked by the capsaicin antagonist Ruthenium Red. Cell death was also prevented by removal of external calcium or by inhibiting calcium-activated proteases such as calpain. Evidence that calpain activity was increased was provided by examining the amount of degradation of the preferred calpain substrate alpha-spectrin. Capsaicin treatment produced a significant increase in the levels of the 150,000 molecular weight spectrin breakdown product. Furthermore, applying the protease inhibitors E64 or MDL 28,170 reduced capsaicin-mediated cell death. It is concluded that capsaicin kills a subpopulation of sensory neurons by activating a receptor-operated channel. The consequent Ca2+ ion influx causes large increases in [Ca2+]i and subsequent activation of Ca(2+)-sensitive proteases. This model provides support for the role of [Ca2+]i as the orchestrator of delayed neuronal degeneration.
Chard
P S
PS
Department of Pharmacological and Physiological Sciences, University of Chicago, IL 60637, USA.
Bleakman
D
D
Savidge
J R
JR
Miller
R J
RJ
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002118:Calcium / Q000502:physiology*; D002154:Calpain / Q000502:physiology*; D002211:Capsaicin / Q000633:toxicity*; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D003592:Cytophotometry; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D016257:Fura-2; D005727:Ganglia, Spinal / Q000166:cytology* / Q000187:drug effects; D006651:Histocytochemistry; D009474:Neurons / Q000187:drug effects*; D009498:Neurotoxins / Q000633:toxicity*; D018408:Patch-Clamp Techniques; D051381:Rats
D009498:Neurotoxins; D002154:Calpain; D002211:Capsaicin; D002118:Calcium; D016257:Fura-2