Journal
PAIN
Volume 158, Issue 9, Pages 1723-1732Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1097/j.pain.0000000000000979
Keywords
Human surrogate pain model; Hyperalgesia; Allodynia; Allyl isothiocyanate; Mustard oil; TRPA1; TRPV1
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Funding
- Danish Ministry of Higher Education and Science
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Despite being a ubiquitous animal pain model, the natural TRPA1-agonist allyl isothiocyanate (AITC, also known as mustard oil) has only been sparsely investigated as a potential human surrogate model of pain, sensitization, and neurogenic inflammation. Its dose-response as an algogenic, sensitizing irritant remains to be elucidated in human skin. Three concentrations of AITC (10%, 50%, and 90%) and vehicle (paraffin) were applied for 5 minutes to 333 cm areas on the volar forearms in 14 healthy volunteers, and evoked pain intensity (visual analog scale 0-100 mm) and pain quality were assessed. In addition, a comprehensive battery of quantitative sensory tests was conducted, including assessment of mechanical and thermal sensitivity. Neurogenic inflammation was quantified using full-field laser perfusion imaging. Erythema and hyperpigmentation were assessed before, immediately after, and approximate to 64 hours after AITC exposure. AITC induced significant dose-dependent, moderate-to-severe spontaneous burning pain, mechanical and heat hyperalgesia, and dynamic mechanical allodynia (P < 0.05). No significant differences in induced pain hypersensitivity were observed between the 50% and 90% AITC concentrations. Acute and prolonged inflammation was evoked by all concentrations, and assessments by full-field laser perfusion imaging demonstrated a significant dose-dependent increase with a ceiling effect from 50% to 90%. Topical AITC application produces pain and somatosensory sensitization in a dose-dependent manner with optimal concentrations recommended to be > 10% and <= 50%. The model is translatable to humans and could be useful in pharmacological proof-of-concept studies of TRPA1-antagonists, analgesics, and anti-inflammatory compounds or for exploratory clinical purposes, eg, loss-or gain-of-function in peripheral neuropathies.
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