New strategy for atopic dermatitis therapy with modulation of calcium ion channels.

Background: Intracellular Ca²⁺ signaling via various calcium channels, such as Orai1, Transient receptor potential (TRP)A1, TRPV1, and TRPV3, has been shown to directly modulate not only inflammation but also barrier homeostasis, and inflammation. Ca²⁺ influx through these channels eventually generates intracellular Ca²⁺ signaling that results in different outcomes dependent on the individual Ca²⁺channel type, for example, keratinocyte proliferation and migration through Orai1, epidermal barrier formation and keratinocyte differentiation through TRPA1, and keratinocyte cornification through TRPV3. Therefore, a specific agonist/antagonist for each calcium channel is required for maintaining skin barrier homeostasis and for the treatment of atopic dermatitis.

Objectives: To identify applicable topical botanically derived chemicals for the treatment of atopic dermatitis.

Method: Novel modulators of Orai1, TRPA1, TRPV1, and TRPV3 were identified were identified by screening the 70% methanol (MeOH) extracts (plus their fractions) of 30 medicinal herbs and their constituents. The potencies of the activating and inhibitory compounds of each channel were determined by an automated patch clamp system. The biophysical properties of channel modulation by hit products were re-analyzed using conventional whole-cell patch clamp and fluorometric calcium imaging.

Results:We prepared 70% MeOH extracts of 30 medicinal herbs, performed bioassay-guided fractionation of the active extracts, and then isolated and identified the bioactive constituents. By performing the combination of automated and conventional whole-cell patch clamp studies, we found eight medicinal herb fractions for Orai1, four for TRPV1, two for TRPA1, and one for TRPV3 that showed >50% inhibition rates at 30 μg/mL. We also found three fractions with TRPA1 agonist activity. Further, we also identified chemical constituents that inhibit Orai1 (compound V: 95 ± 5% inhibition at 90 μM) and TRPV1 (compound M: 93.9 ± 2.45% inhibition at 90 μM; compound CYP: 61 ± 5% inhibition at 90 μM). Chemical constituents that showed agonist/antagonistic effects on TRPA1 and TRPV3 also will be discussed.

Conclusions:Considering that most regional plants have not been investigated chemically or pharmaceutically, they remain as untapped potential sources of topical agents for drugs and other application. We found major active components and chemical constituents of plant extracts for the modulation of various calcium ion channels, which may have potential clinical applications for atopic dermatitis.

Limitations:Extensive clinical studies of the lead compounds are needed to develop topical agents for atopic dermatitis that relate to skin barrier functions.