Clinical trial NCT03587220: A Mechanistic Evaluation of the Nociceptive Desensitizing Properties of Topical Capsaicin
Official title: En undersøgelse af Mekanismerne Bag Nociceptiv Desensibilisering forårsaget af Topikal Capsaicin
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Capsaicin
Ultaviolet B Light Burn
Neuropathic Pain
Lidocaine
Lead sponsor: Aalborg University
Sponsor class: OTHER
First posted: 2018-07-16
Enrollment: 44
Sex: ALL
Minimum age (years): 18
Maximum age (years): 60
Standard ages: ADULT
Accepts healthy volunteers: yes
Allocation: RANDOMIZED
Intervention model: PARALLEL
Primary purpose: BASIC_SCIENCE

Brief summary: The aim of this project is to study the role of transient receptor potential (TRP-) channel V1 (TRPV1+) fibers in the development of cutaneous inflammation induced by epidermal Ultraviolet-B damage. Moreover, in this project the investigators want to evaluate if the capsaicin-desensitization action can still be induced in a skin area pretreated with topical, local anesthetic lidocaine.

Detailed description: In this project the Ultraviolet- B pain model, a model using type B ultraviolet rays to induce a first-degree sunburn, will be used to induce a non-specific inflammation in the skin. This model is well-known to produce both peripheral and central hyperalgesia through sensitization of peripheral and central nociceptors. Capsaicin, the active substance in chili peppers, is currently used to treat peripheral neuropathic pain, and prolonged application of 8% capsaicin patch causes profound desensitization to painful heat stimuli and itch provocations. Therefore, the investigators would like to monitor the development of unspecific UVB-cutaneous inflammation and consequent neurogenic flare in a capsaicin pre-treated area. Moreover the investigators want to test if pre-treating the skin with lidocaine can reduce the pain associated with the capsaicin application without affecting its desensitization action.

Eligibility criteria: Inclusion criteria:

* Healthy men and women
* 18-60 years
* Caucasian descent (only in sub-study 1)
* Speak and understand English

Exclusion criteria:

* Pregnancy or lactation
* Drug addiction defined as any use of cannabis, opioids or other drugs
* Previous or current neurologic, musculoskeletal or mental illnesses
* Lack of ability to cooperate
* Current use of medications that may affect the trial
* Skin diseases
* Consumption of alcohol or painkillers 24 hours before the study days and between these
* Moles or tattoos in the area to be treated or tested.
* Exposure of the irradiated area to UV radiation (e.g., sun) 48 hours before the study days and between these
* Acute or chronic pain
* Participation in other trials within 1 week of study entry (4 weeks in the case of pharmaceutical trials)
* Known history of anaphylactic shock, or local allergy (contact dermatitis) to lidocaine, prilocaine or other local anaesthetics of the amide type.

Primary outcomes:
measure: Superficial blood perfusion measured by a Speckle contrast imager (FLPI, Moor Instruments, England).
timeFrame: Changes from baseline to 7 days after intervention
measure: Measurement of Warm Detection Thresholds and Heat thresholds by using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device.
timeFrame: Changes from baseline to 7 days after intervention
measure: Measurement of Pain to Supra-threshold Heat Stimuli by using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device.
timeFrame: Changes from baseline to 7 days after intervention
measure: Measurement of Mechanical Pain Thresholds and Sensitivity using a pin-prick set consisting of 8 needles each having a diameter of 0.6 mm and different force applications: 0.8, 1.6, 3.2, 6.4, 12.8, 25.6, 50.1 and 60.0 g.
timeFrame: Changes from baseline to 7 days after intervention
measure: Trans-epidermal Water Loss (TEWL) using a 2x2 cm probe to measure the humidity gradient of the skin.
timeFrame: Changes from baseline to 7 days after intervention
Secondary outcomes:
measure: assessment of pain rating by using a visual analog scales (VAS)
timeFrame: Change from baseline to 24 h
measure: Itch rating by using a visual analog scales (VAS)
timeFrame: Changes from baseline to 7 days after intervention
Other outcomes:
Locations:
city: Aalborg
country: Denmark
facility: Silvia Lo Vecchio
state: Nordjylland
Study officials:
References: