All-trans-Retinoic Acid Regulates Retinol and 3,4-Didehydroretinol Metabolism in Cultured Human Epidermal Keratinocytes

Abstract

The potential for all-trans-retinoic acid to regulate the metabolism of 3H-retinol and 3H-3,4-didehydroretinol was examined in cultured human epidermal keratinocytes. Confluent cultures were treated daily with medium containing 5% fetal bovine serum or the same medium supplemented with nanomolar concentrations of all-trans-retinoic acid for up to 3 d. During the last 24 of treatment, cells were incubated with 3H-retinol or 3H-3,4-didehydroretinol for 24 h (isotopic steady state) to label the endogenous retinoids. After the labeling period, one group of cells was harvested and another group was allowed to incubate for an additional 24 h in the absence of medium retinol for the determination of endogenous 3H-retinoid utilization. The 3H-retinoids present in cells were extracted and quantitated by reverse-phased high-pressure liquid chromatography. Keratinocytes treated with retinoic acid and labeled with 3H-retinol exhibited time- and concentration-dependent (i) increases in retinyl ester mass, (ii) increases in the rate of retinyl ester synthesis, (iii) decreases in retinyl ester utilization, and (iv) decreases in the cellular concentrations of retinoic and 3,4-didehydroretinoic acids. There was no effect of exogenous retinoic acid on its own metabolism. Cells labeled with 3H-3,4-didehydroretinol exhibited exclusive labeling of vitamin A2-related retinoids suggesting that the A1 to A2 conversion is not reversible. Treatment of cells with low nanomolar concentrations of retinoic acid decreased the utilization of 3,4-didehydroretinyl esters, decreased the production of 3,4-didehydroretinoic acid but had no effect on the synthesis of 3,4-didehydroretinol or its esters. The results demonstrate that keratinocytes respond to extracellular retinoic acid by decreasing endogenous production of active retinoids, sequestering extracellular substrate retinol as retinyl ester, and decreasing ester utilization.

The Effects of Vitamin A Compounds on Hyaluronic Acid Released from Cultured Rabbit Corneal Epithelial Cells and Keratocytes

“…It has been reported that VApal is converted into reti- nol in the skin of mammals and humans (34,35) and that retinol is metabolized and converted into retinal and retinoic acid (36,37). Considering that retinol is converted into retinoic acid in cultured corneal epithelial cells and in rabbit corneas, as it also is in skin (38,39), it is reasonable to assume that in our study, hyaluronic acid production by retinoic acid and VApal in the cornea was promoted through nuclear receptors of retinoic acid and HAS gene expression.…”

Keratinocyte differentiation induced by calcium, phorbol ester or interferon-γ elicits distinct changes in the retinoid signalling pathways

“…First-strand cDNA was synthesized from 3 µg of total RNA in a 30-µl reaction mixture using oligo-d(T) 15 as primer and M-MLV reverse transcriptase (Invitrogen). The cDNA was diluted with 30 µl dH 2 O to obtain a concentration of 50 ng cDNA/µl.…”

“…The effects of natural vitamin A are mediated by its active metabolite all-trans-retinoic acid (RA) [1] and possibly also 3,4-didehydroretinoic acid (ddRA), a substance found exclusively in human keratinocytes and with similar properties to RA [2,3]. The conversion of retinol (ROH) to RA and ddRA in cultured human keratinocytes is well established [2,4], and this process is probably linked to the state of differentiation, with production of RA and ddRA occurring primarily in differentiated cells [2,5].…”

The Holistic Scarless Rejuvenation of the Face

“…[3] However, vitamin A is rapidly destroyed by exposure to light because it is in fact a natural sunscreen and absorbs UVA and UVB rays [4]. As a result our skin develops a chronic, progressive and unrelenting deficiency of vitamin A that manifests as pigmented blotches, wrinkles, thin skin, and pre-cancerous lesions that eventually develop into skin cancer.…”

“…As a result, when used topically at adequate dosage, it affords us the most acceptable method of vitamin A replacement. Research shows us that Retinyl palmitate plays a role in preventing skin cancer [5] and squamous skin cancer cells have an impaired ability to esterify retinol [6] Doctors generally think retinoic acid is the only effective vitamin A but retinyl palmitate, as described above, is the major form of vitamin A in the human body and skin [3]. Retinyl esters are de-esterified to retinol, which is then oxidised by alcohol dehydrogenases to retinal and finally retinoic acid [7].…”