Duell E A, Aström A, Griffiths C E, Chambon P, Voorhees J J
Department of Dermatology, University of Michigan, Ann Arbor 48109-0528.
J Clin Invest. 1992 Oct;90(4):1269-74. doi: 10.1172/JCI115990.
Metabolism of retinoic acid to a less active metabolite, 4-hydroxyretinoic acid, occurs via cytochrome P-450 isozyme(s). Effect of a pharmacological dose of retinoic acid on the level of retinoic acid in skin and on cytochrome P-450 activity was investigated. A cream containing 0.1% retinoic acid or cream alone was applied topically to adult human skin for four days under occlusion. Treated areas were removed by a keratome and a microsomal fraction was isolated from each biopsy. In vitro incubation of 3H-retinoic acid with microsomes from in vivo retinoic acid treated sites resulted in a 4.5-fold increase (P = 0.0001, n = 13) in its transformation to 4-hydroxyretinoic acid in comparison to in vitro incubations with microsomes from in vivo cream alone treated sites. This cytochrome P-450 mediated activity was oxygen- and NADPH-dependent and was inhibited 68% by 5 microM ketoconazole (P = 0.0035, n = 8) and 51% by carbon monoxide (P = 0.02, n = 6). Cotransfection of individual retinoic acid receptors (RARs) or retinoid X receptor-alpha (RXR-alpha) and a chloramphenicol acetyl transferase (CAT) reporter plasmid containing a retinoic acid responsive element into CV-1 cells was used to determine the ED50 values for stimulation of CAT activity by retinoic acid and its metabolites. Levels of all trans and 13-cis RA in RA-treated tissues were greater than the ED50 values determined for all three RARs with these compounds. Furthermore, the level of all trans RA was greater than the ED50 for RXR-alpha whereas the 4-OH RA level was greater than the ED50 for RAR-beta and RAR-gamma but less than for RAR-alpha and RXR-alpha. These data suggest that there are sufficient amounts of retinoic acid in treated skin to activate gene transcription over both RARs and RXR-alpha.
视黄酸通过细胞色素P-450同工酶代谢为活性较低的代谢产物4-羟基视黄酸。研究了药理剂量的视黄酸对皮肤中视黄酸水平和细胞色素P-450活性的影响。将含有0.1%视黄酸的乳膏或单独的乳膏在封闭条件下局部应用于成年人体皮肤四天。用角膜刀切除处理过的区域，并从每次活检中分离出微粒体部分。与用单独的体内乳膏处理部位的微粒体进行体外孵育相比，用来自体内视黄酸处理部位的微粒体对3H-视黄酸进行体外孵育，其转化为4-羟基视黄酸的量增加了4.5倍（P = 0.0001，n = 13）。这种细胞色素P-450介导的活性依赖于氧气和NADPH，并被5 microM酮康唑抑制68%（P = 0.0035，n = 8），被一氧化碳抑制51%（P = 0.02，n = 6）。将单个视黄酸受体（RARs）或类视黄醇X受体-α（RXR-α）与含有视黄酸反应元件的氯霉素乙酰转移酶（CAT）报告质粒共转染到CV-1细胞中，以确定视黄酸及其代谢产物刺激CAT活性的半数有效剂量（ED50）值。视黄酸处理组织中全反式和13-顺式视黄酸的水平高于用这些化合物测定的所有三种RARs的ED50值。此外，全反式视黄酸的水平高于RXR-α的ED50，而4-羟基视黄酸的水平高于RAR-β和RAR-γ的ED50，但低于RAR-α和RXR-α的ED50。这些数据表明，处理过的皮肤中有足够量的视黄酸来激活RARs和RXR-α的基因转录。
