A human surrogate model of itch utilizing the TRPA1 agonist trans-cinnamaldehyde

The thermoreceptive transient receptor potential ankyrin 1 (TRPA1) is important in the transmission of itch, and its agonist trans-cinnamaldehyde has occasionally been reported to be a pruritogen in humans. However, no studies have accurately quantified the capabilities of trans-cinnamaldehyde to induce itch and related dysesthetic sensations. The present study examined alterations in somatosensory and vasomotor parameters in response to topical trans-cinnamaldehyde 5% and vehicle (ethanol) in 24 healthy subjects. During the study the following parameters were recorded: itch area and intensity, hyperknesis, alloknesis, neurogenic flare, skin blood flow and temperature. Trans-cinnamaldehyde evoked moderate itch sensation, flare, hyperknesis and alloknesis (p < 0.001). Blood flow and skin temperature were elevated in the area of trans-cinnamaldehyde application (p < 0.001). Significant positive correlations were found between blood flow and skin temperature, itch area and blood flow, and itch area and skin temperature. Topical trans-cinnamaldehyde proved feasible as a human itch model with applicability in studying itch mechanisms or anti-pruritic drug profiling.