Antipruritic effect of curcumin on histamine-induced itching in mice

Itching is a common clinical symptom of skin disease that significantly affects a patient's quality of life. Transient receptor potential vanilloid 1 (TRPV1) receptors of keratinocytes and peripheral nerve fibers in skin are involved in the regulation of itching as well as pain. In this study, we investigated whether curcumin, which acts on TRPV1 receptors, affects histamine-induced itching in mice, using behavioral tests and electrophysiological approaches. We found that histamine-induced itching was blocked by topical application of curcumin in a concentration-dependent manner. In ex-vivo recordings, histamine-induced discharges of peripheral nerves were reduced by the application of curcumin, indicating that curcumin acts directly on peripheral nerves. Additionally, curcumin blocked the histamine-induced inward current via activation of TRPV1 (curcumin IC₅₀=523 nM). However, it did not alter chloroquine-induced itching behavior in mice, which is associated with transient receptor potential ankyrin 1 (TRPA1). Taken together, our results suggest that histamine-induced itching can be blocked by topical application of curcumin through the inhibitory action of curcumin on TRPV1 receptors in peripheral nerves.

Changes of Transepidermal Water Loss (TEWL) in Psoriatic Plaques during D-PUVA Therapy

BACKGROUND: Psoriatic lesions have reduced water-holding capacity and show increased transepidermal water loss (TEWL). The effect of D-PUVA therapy, which combines topical calcipotriol and PUVA therapy, on epidermal barrier function has not yet been evaluated. OBJECTIVE: The purpose of this study was to verify the change of TEWL in lesional and normal skin according to D-PUVA therapy in psoriasis patients. METHODS: TEWL was measured consecutively by TEWAMETER TM210®, in 13 psoriasis patients who received D-PUVA therapy. Clinical grading was done according to psoriasis severity index (PSI). RESULTS: TEWL of psoriatic lesion decreased as D-PUVA continued. TEWL of normal-looking skin gradually increased, although the increase was trivial. Clinical grading of scale and in-filtration followed the pattern of PSI in the decrease of TEWL, while that of erythema did not. CONCLUSION: In psoriatic plaques, TEWL was decreased according to the improvement. In normal-looking skin, D-PUVA therapy caused only a little effect on TEWL.