Histamine- and Pruritogen-induced Itch is Inhibited By a TRPM8 Agonist: a Randomized Vehicle-controlled Human Trial

Background: Allergies often present challenges in managing itch and the effects of histamine. Cooling agents that act via transient receptor potential melastatin 8 (TRPM8) agonism have shown potential in itch management. However, animal studies on itch have limitations, as animals cannot communicate subjective events and their fur-coated skin differs from that of humans. Human studies offer more direct and reliable information.

Objectives: To investigate the effects of a specific TRPM8 agonist gel (cryosim-1) on itch induced by various pruritogens in human skin.

Methods: Calcium imaging experiments determined the binding of cryosim-1 and histamine to their respective receptors. Thirty healthy volunteers underwent skin prick tests with pruritogens and a control vehicle. Itch and pain intensity were measured using a numerical rating scale (NRS) across 10 min. Participants were randomly assigned to pretreatments with vehicle or TRPM8 agonist gel. Tests were repeated at a later date, and skin moisture, transepidermal water loss and mechanical sensitivity were measured.

Results: The in vitro study confirmed that histamine is not a TRPM8 agonist and cryosim-1 does not act as an agonist or antagonist on the human histamine 1 receptor. The TRPM8 agonist gel significantly reduced the itch intensity for all pruritogens compared with the vehicle-only gel. It also reduced itch NRS and the integrated itch score. Mechanical sensitivity was also reduced.

Conclusions: The specific TRPM8 agonist gel effectively suppressed human skin itch induced by various pruritogens. These versatile actions suggest that cooling agents may be promising treatments for multiple forms of itch stimuli.