Both all-trans retinoic acid and cytochrome P450 (CYP26)  inhibitors affect the expression of vitamin A metabolizing enzymes and Retinoic biomarkers in organotypic epidermis

• The biosynthesis of retinoic acid (RA) from retinol is controlled by several enzymes, e.g. dehydrogenases (RalDH2, RoDH-4) and   retinol-esterifying enzyme (LRAT), whereas its degradation mainly   involves CYP26 enzymes. In keratinocytes, RA activates the nuclear   retinoid-receptors inducing the transcription of many genes. Here, we  examined the effects of RA and the CYP26 inhibitors, liarozole and talarozole, on retinoid metabolism and RA-regulated genes in organotypic epidermis. RA induced the expression of CYP26 enzymes   already after 8 h, whereas LRAT exhibited a later response and peaked   at 48 h, indicating a feedback induction of retinol esterification. In   line with a reduced biosynthesis of RA from retinol after exogenous RA,   the expression of RDH16 reduced 80% in response to exogenous RA. The   mRNA expression of RA-regulated genes (KRT2, KRT4, CRABPII and HBEGF)   was altered within 24 h after RA exposure. In contrast, the CYP26   inhibitors caused only minor effects, except for a clear-cut induction  of CYP26A1 only when combined with minute amounts of exogenous RA.   Cellular accumulation of exogenous [H-3]RA was higher after talarozole  than after liarozole, probably indicating a greater CYP26-inhibitory   potency of the former drug. The present study shows that CYP26A1  expression is extremely sensitive to both exogenous RA and increased   endogenous RA levels, i.e. due to CYP26 inhibition, and thus an excellent biomarker for retinoid signalling in organotypic epidermis.

Keyword

CYP26

RAMBA

Metabolism

MEDICINE

MEDICIN

Publication and Content Type

ref (subject category)

art (subject category)