Characterization of New Human Models of Non-histaminergic Itch

Aalborg University

Status: Completed

Conditions: Itch; Skin Prick Test (SPT); Papain

Treatments: Drug: Papain 5 SPT; Drug: Papain 1 SPT; Drug: Papain 100 µg; Drug: Papain 50 µg; Other: Cowhage; Other: Vehicle; Drug: Papain 25 SPT; Drug: Papain 10 µg

Study type: Interventional

Funder types: Other

Identifiers

NCT04515056

N-20200005

Details and patient eligibility

About

In this experiment the investigators would like to test a new new human itch model based on papain, and to characterize the sensory quality and temporary aspects of papain skin prick test (SPT) in comparison to the inactivated-cowhage delivery system.

Full description

The most used model of non-histaminergic itch is cowhage but this models presents several problems, such us the impossibility of standardizing the amount of the spicules inserted in the skin and the difficulty of obtaining the substance. These aspects bring us the necessity to find a new and more standardized model of non-histaminergic itch.

Papain is a cysteine protease extracted from papaya plant that is known to cause itch if applied to the skin. For these reasons the investigators would like to test a new new human itch model based on papain, and to characterize the sensory quality and temporary aspects of papain skin prick test (SPT) in comparison to the inactivated-cowhage delivery system.

Enrollment: 20 patients

Sex: All

Ages: 18 to 60 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Healthy men and women
• 18-60 years
• Speak and understand English

Exclusion criteria

• Pregnancy or lactation
• Drug addiction defined as any use of cannabis, opioids or other addictive drugs
• Previous or current history of neurological, dermatological, immunological musculoskeletal, cardiac disorder or mental illnesses that may affect the results (e.g. neuropathy, muscular pain in the upper extremities, etc.).
• Lack of ability to cooperate
• Current use of medications that may affect the trial such as antihistamines, antipsychotics and pain killers, as well as systemic or topical steroids.
• Skin diseases
• Moles, scars or tattoos in the area to be treated or tested.
• Hypersensitivity to papaya and mango fruit, cashew nuts, rubber latex
• Consumption of alcohol or painkillers 24 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)

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Single Group Assignment

Masking: Single Blind

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20 participants in 2 patient groups

Papain dosage

Experimental group

Description:

In the 1st session, each of the middle forearms of the subject will be divided into two squared areas (4x4 cm). The two areas will be located 4 cm apart. Three areas will be exposed to 10, 50 or 100 µg of papain, while the last area will be used as control (exposed to a vehicle).

Treatment:

Drug: Papain 50 µg

Drug: Papain 10 µg

Drug: Papain 100 µg

Other: Vehicle

Papain SPT

Experimental group

Description:

Each forearm of the subject will be divided into two squared areas (4x4 cm). The provocations of three areas will be performed with 100 µg of papain by SPT lancets. To assess the potential importance of repeated pricks, papain will be applied by 1, 5 or 25 SPT pricks thought the skin. The last area will be exposed to cowage spicules (made chemically inert by autoclaving) soaked in 5 mg/ml papain solution.

Treatment:

Drug: Papain 25 SPT

Other: Cowhage

Drug: Papain 1 SPT

Drug: Papain 5 SPT