Synthesis and activity of the salicylic acid ester of bakuchiol in psoriasis-surrogate keratinocytes and skin substitutes

Background: Topical retinoids are effective in retarding skin ageing and restoring homeostasis in skin conditions such as psoriasis. However their adverse effects (AEs), which include irritation (retinoid dermatitis), photosensitivity and teratogenicity, limit their use and patient compliance. Development of retinoid analogues with minimal AEs would allow a broader and more compliant use. Aim: To synthesise a novel molecule, bakuchiol salicylate (bakusylan), with a modulatory gene expression profile similar to retinoids, using as reference three prescription retinoids: tretinoin, tazarotene and adapalene. Methods: We hypothesized that because bakuchiol salicylate has a structure entirely different from existing retinoids, there would be at least a partial uncoupling of AEs from the skin-normalizing activity of this retinoid. This hypothesis was tested at the transcriptional level in psoriatic cytokine-treated cultures of keratinocytes and organotypic skin substitutes, using DNA microarrays and custom PCR arrays. Results: Evaluation of the gene expression profile of bakuchiol salicylate revealed elimination of several components of the retinoid-like proinflammatory response and teratogenic signature, without a substantial loss of normalizing potential. A possible mechanism of action, consisting of keratinocyte desensitization to psoriatic cytokine signalling through inhibition of the signal transducer and regulator of transcription (STAT)1/3/interferon inflammatory signal transduction axis was also identified. Conclusion: Bipartite materials obtained by merging two skin-active entities with specific, complementary bioactivities, such as bakuchiol and salicylic acid, may yield a new class of functional retinoids.