Activation and desensitization of TRPV1 channels in sensory neurons by the PPARα agonist palmitoylethanolamide.
OBJECTIVE
Palmitoylethanolamide (PEA) is an endogenous fatty acid amide displaying anti-inflammatory and analgesic actions. To investigate the molecular mechanism responsible for these effects, the ability of PEA and of pain-inducing stimuli such as capsaicin (CAP) or bradykinin (BK) to influence intracellular calcium concentrations ([Ca²⁺](i)) in peripheral sensory neurons, has been assessed in the present study. The potential involvement of the transcription factor PPARα and of TRPV1 channels in PEA-induced effects was also studied.


METHODS
[Ca²⁺](i) was evaluated by single-cell microfluorimetry in differentiated F11 cells. Activation of TRPV1 channels was assessed by imaging and patch-clamp techniques in CHO cells transiently-transfected with rat TRPV1 cDNA.


RESULTS
In F11 cells, PEA (1-30 μM) dose-dependently increased [Ca²⁺](i). The TRPV1 antagonists capsazepine (1 μM) and SB-366791 (1 μM), as well as the PPARα antagonist GW-6471 (10 μM), inhibited PEA-induced [Ca²⁺](i) increase; blockers of cannabinoid receptors were ineffective. PEA activated TRPV1 channels heterologously expressed in CHO cells; this effect appeared to be mediated at least in part by PPARα. When compared with CAP, PEA showed similar potency and lower efficacy, and caused stronger TRPV1 currents desensitization. Sub-effective PEA concentrations, closer to those found in vivo, counteracted CAP- and BK-induced [Ca²⁺](i) transients, as well as CAP-induced TRPV1 activation.


CONCLUSIONS
Activation of PPARα and TRPV1 channels, rather than of cannabinoid receptors, largely mediate PEA-induced [Ca²⁺](i) transients in sensory neurons. Differential TRPV1 activation and desensitization by CAP and PEA might contribute to their distinct pharmacological profile, possibly translating into potentially relevant clinical differences.
Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
Paolo
P
Ambrosino
Maria Virginia
MV
Soldovieri
Claudio
C
Russo
Maurizio
M
Taglialatela
D000200:Action Potentials / Q000187:drug effects; D000577:Amides; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D016466:CHO Cells; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004336:Drug Antagonism; D063388:Endocannabinoids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004983:Ethanolamines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D049990:Membrane Transport Modulators / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D047493:PPAR alpha / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000378:metabolism; D010169:Palmitic Acids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D011994:Recombinant Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D050916:TRPV Cation Channels / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013618:Tachyphylaxis
D000577:Amides; D000894:Anti-Inflammatory Agents, Non-Steroidal; D063388:Endocannabinoids; D004983:Ethanolamines; D049990:Membrane Transport Modulators; D009419:Nerve Tissue Proteins; D047493:PPAR alpha; D010169:Palmitic Acids; D011994:Recombinant Proteins; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; C493922:Trpv1 protein, rat; C005958:palmidrol