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Electrical stimulation models and mediators conveying pruritus in allergic contact dermatitis and urticaria patients
Elke Weisshaar, Martin Metz, Roman Rukwied
Slowly depolarizing electrical stimuli induce pain in healthy volunteers but pruritus in about 30 % of patients suffering chronic itch. Notably, electrically induced pain and itch ameliorates with ongoing stimulation (habituation). In the present project proposal, we aim to develop and establish an electrical stimulation paradigm that continuously evokes itch without habituation in patients with chronic pruritus, enabling neurophysiological basic research in various itch entity. At first, the stimulation paradigm will be developed in healthy human subjects, validated in single nerve fiber recordings in the pig in vivo, and after establishment of the protocol applied in patients with allergic contact eczema and chronic spontaneous urticaria.
We will deliver the stimulation protocol to all projects of the research unit investigating chronic inflammatory, systemic and neuropathic pruritus. The duration and intensity of electrically evoked itch will be correlated with structural parameters of the skin, i. e. the intra-epidermal nerve fiber density and their neuronal branching pattern. These parameters will be identified in skin punch biopsies obtained from lesional and non-lesional skin of patients with contact eczema and urticaria, respectively. In addition, interstitial fluid will be collected by intradermal microdialysis from these skin sites and analyzed for interleukin-31, a cytokine that is associated with chronic pruritus. The dialysate of contact allergy patients will be analyzed for non-cellular microRNA. Free circulating microRNA was identified as biomarker in various chronic painful and pruritic conditions. The analyzed microRNA in lesional and non-lesional skin of contact allergy patients will be compared to healthy control subjects and with data from the literature described for atopic eczema and psoriasis. In chronic urticaria patients, we will explore the sensitization level of skin mast cells. Mast cells express the mas-related G protein-coupled receptor X2 (MRGPRX2) and have been attributed to play a pivotal role in the pathology of urticaria. In affected and non-affected skin of chronic spontaneous and induced urticarial skin we will deliver with pinprick the MRGPRX2 agonisten ciprofloxacin and measure by means of intradermal microdialysis the release of tryptase and histamine. A differential MRGPRX2-induced release of these mediators would indicate a sensitized activation of skin mast cells and provide new therapeutic approaches in the treatment of urticaria.