High-Concentration L-Menthol Exhibits Counter-Irritancy to Neurogenic Inflammation, Thermal and Mechanical Hyperalgesia Caused by Trans-cinnamaldehyde.
The transient receptor potential cation channel subfamily M 8 (TRPM8) agonist L-menthol has been used traditionally for its topical counterirritant properties. Although the use of topical L-menthol for pain is casuistically established, evidence regarding its efficacy is negligible. This study aimed to characterize the effect of L-menthol as a counterirritant on cutaneous pain and hyperalgesia provoked by topical application of the transient receptor potential cation channel, subfamily A, member 1 (TRPA1) agonist trans-cinnamaldehyde (CA). In a randomized, double-blinded study CA was applied to a 3 × 3-cm area of the volar forearm evoking neurogenic inflammation, pain, mechanical, and thermal hyperalgesia in 14 healthy volunteers. In different sessions, 10% CA alone or 40% L-menthol applied simultaneously with 10% CA were administered for 20 minutes, throughout which the subjects rated the pain intensity on a visual analogue scale of 0 to 10. Extensive quantitative sensory testing was conducted and superficial blood flow (neurogenic inflammation) was recorded. Administration of CA evoked spontaneous pain, neurogenic inflammation, thermal hyperalgesia, and primary and secondary mechanical hyperalgesia. Coadministration of topical L-menthol reduced spontaneous pain intensity (P < .01), neurogenic inflammation (P < .01), primary mechanical hyperalgesia (P < .05), secondary mechanical hyperalgesia (P < .05), and heat hyperalgesia (P < .05), but not cold hyperalgesia. L-menthol exhibited inhibitory effects on simultaneously established pain, hypersensitivity, and neurogenic inflammation in a human TRPA1-induced pain model. Potent TRPM8 agonists could be useful as topical antihyperalgesics. The study and the trial protocol is registered and approved by the local research ethics committee under the jurisdiction of the Danish Medicines Agency number N-20130005. The protocol also is registered at Clinicaltrials.gov under NCT02653703.



Drugs interacting with transient receptor potential channels are of great therapeutic potential. In the present study we established cutaneous pain and hyperalgesia using the TRPA1 agonist CA. Subsequently, we showed that the frequently used topical counterirritant and TRPM8 agonist, L-menthol, decreased evoked pain, hyperalgesia, and inflammation, indicating direct and indirect antinociceptive mechanisms.
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
Hjalte H
HH
Andersen
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
Parisa
P
Gazerani
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark. Electronic address: LAN@hst.aau.dk.
Lars
L
Arendt-Nielsen
D000171:Acrolein / Q000009:adverse effects / Q000031:analogs & derivatives; D000328:Adult; D000972:Antineoplastic Agents, Phytogenic / Q000009:adverse effects; D000982:Antipruritics / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy*; D008297:Male; D008715:Methionine / Q000627:therapeutic use*; D020078:Neurogenic Inflammation / Q000139:chemically induced / Q000188:drug therapy*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects*; D010812:Physical Stimulation; D013696:Temperature; D064232:Visual Analog Scale; D055815:Young Adult
D000972:Antineoplastic Agents, Phytogenic; D000982:Antipruritics; D000171:Acrolein; D008715:Methionine; C012843:cinnamaldehyde
Human surrogate pain model; L-menthol; TRPA1; TRPM8; hyperalgesia; trans-cinnamaldehyde