Desensitization of Nociceptive Afferents by Application of Topical Capsaicin, Trans-cinnamaldehyde and L-menthol

Aalborg University

Status: Unknown

Conditions: Dermatology/Skin - Other; Neuropathic Pain; Pain; Pruritus

Treatments: Drug: Trans-cinnamaldehyde; Drug: Vehicle patch; Drug: L-Menthol; Drug: Capsaicin

Study type: Interventional

Funder types: Other

Identifiers

NCT03132142

N-20170018

Details and patient eligibility

About

The purpose of this study is to investigate the potential desensitising effects of repeated applications of capsaicin, trans-cinnamaldehyde and L-menthol on thermal, mechanical and chemical sensory stimulations.

Full description

Capsaicin, the compound responsible for the pungency of chili peppers, can induce desensitization to nociceptive (1) and pruriceptive (2) stimuli when topically applied. The purpose of this study is to determine whether repeated topical applications of trans-cinnamaldehyde and L-menthol result in decreased responses to various nociceptive and non-nociceptive thermal and mechanical stimuli and to compare potential alterations with those caused by repeated topical application of capsaicin. Furthermore, this study investigates the temporal profile of said alterations.

Capsaicin 8% patches, trans-cinnamaldehyde 10%, L-menthol 40% and inert vehicle patches will each be applied to 4 4x4 cm predefined areas on the skin of the volar forearms for 1 hour 4 times on 4 consecutive days. Before each application and the day after the last application, cold detection threshold (CDT), warmth detection threshold (WDT), cold pain threshold (CPT) and heat pain threshold (HPT) will be assessed using a Medoc Pathway (Medoc, Israel) equipped with a 3x3 cm contact thermode. On the last day, mechanical detection threshold (MDT) is assessed using a series of von Frey filaments and mechanical pain threshold (MPT) and mechanical pain sensitivity (MPS) is assessed using a series of standardized pinprick stimulators (Aalborg University).

Furthermore, full-field laser perfusion imaging (FLPI) will be used to assess the degree of neurogenic inflammation in each predefined area before and after each substance application and at the last session.

1. F. Henrich et al. 2015 "Capsaicin-sensitive C- and A-fibre nociceptors control long-term potentiation-like pain amplification in humans"
2. H.H. Andersen et al. 2017 "Antipruritic effect of pretreatment with 8% topical capsaicin on histamine- and cowhage-evoked itch in healthy volunteers - a randomized placebo-blinded proof-of-concept trial"

Enrollment: 22 estimated patients

Sex: All

Ages: 18 to 60 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Healthy
• Speaks and understands English or Danish
• 18-60 years

Exclusion criteria

• Pregnancy or lactation
• Drug addiction
• Previous or current dermatological, neurological, musculoskeletal or mental illnesses
• Lack of ability to cooperate
• Current use of medications that may affect the trial

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Single Blind

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22 participants in 4 patient groups, including a placebo group

Capsaicin

Experimental group

Description:

Capsacin (8%) patches applied topically 4 times for 1 hour to a 4x4 cm predefined area on the skin of the volar forearms.

Treatment:

Drug: Capsaicin

Trans-cinnamaldehyde

Experimental group

Description:

Trans-cinnamaldehyde (10%, dissolved in 90% ethanol) applied topically 4 times for 1 hour to a 4x4 cm predefined area on the skin of the volar forearms on a cotton ball placed in a plastic chamber to limit evaporation.

Treatment:

Drug: Trans-cinnamaldehyde

L-menthol

Experimental group

Description:

L-menthol (40%, dissolved in 96% ethanol) applied topically 4 times for 1 hour to a 4x4 cm predefined area on the skin of the volar forearms on a cotton ball placed in a plastic chamber to limit evaporation.

Treatment:

Drug: L-Menthol

Vehicle patch

Placebo Comparator group

Description:

Inert vehicle patches applied topically 4 times for 1 hour to a 4x4 cm predefined area on the skin of the volar forearms.

Treatment:

Drug: Vehicle patch