4-oxoretinoic-acid and retinol-palmitate

HaCaT keratinocytes differ from normal human epidermal keratinocytes (HEK) by constitutive expression of differentiation markers which are normally suppressed by vitamin A. In search of an explanation for this discrepancy we compared the vitamin A content, the expression of retinoid-binding proteins, and the vitamin A metabolism in the two cell types. The concentrations of retinol and 3,4-didehydroretinol in cultured HaCaT cells were less than one-fifth those in HEK, and the content of fatty acyl esters was even lower. Similarly, the concentrations of cellular retinol-binding protein and cellular retinoic acid-binding protein (CRBPI and CRABPII, respectively) were 10-30 times lower in HaCaT cells than in HEK corresponding to a reduced mRNA expression of these proteins. Unexpectedly, HaCaT cells expressed RARbeta in addition to RARalpha, RARgamma and RXRalpha, which are nuclear receptors normally found in HEK. Radioactive retinol added to the culture medium appeared only transiently in HaCaT cells, and pulse labeling confirmed a defective cellular retention of retinyl esters. After 24 h of incubation with [3H]retinol, cell-associated radioactivity corresponding to retinol, 3,4-didehydroretinol, all-trans-retinoic acid and 3,4-didehydroretinoic acid was found in both HaCaT cells and HEK. [3H]Retinoic acid showed a more rapid metabolism to 4-hydroxy/4-keto-retinoic acid in HaCaT cells than in HEK, which could be explained by a higher expression of cytochrome p450RAI in the former cells. In conclusion, the abnormal uptake of vitamin A and low levels of retinoid binding proteins in HaCaT cells, linked with an aberrant metabolism of retinol, may help to explain why these cells differentiate also in the presence of retinoids.

Topics: Biomarkers; Carrier Proteins; Cell Differentiation; Cell Line; Cytochrome P-450 Enzyme System; Diterpenes; Humans; Keratinocytes; Receptors, Retinoic Acid; Reference Values; Retinoic Acid 4-Hydroxylase; Retinoids; Retinyl Esters; Tretinoin; Vitamin A

Patients with retinitis pigmentosa have been suggested to benefit from treatment with moderate doses of retinyl palmitate. Retinyl palmitate is not an active retinoid in itself but is metabolised to active components in the body. To find out which metabolites of retinyl palmitate were formed and at which concentrations, we measured the concentrations of retinol, retinyl palmitate, retinoic acids and tocopherol in serum of patients treated with oral retinyl palmitate for retinitis pigmentosa.. Nine male patients and one female diagnosed as having retinitis pigmentosa after a complete ophthalmological examination including a full-field electroretinogram were given vitamin A at their own request as one daily morning dose of 16600 IU vitamin A. Blood samples were obtained before and after > 2 weeks of treatment. The concentrations of retinoids and tocopherol were measured with established methods.. The patients were not deficient in vitamin A or vitamin E as judged from the serum vitamin concentrations. Treatment with retinyl palmitate significantly increased the serum concentration of retinyl palmitate and of 13-cis-retinoic acid but not of retinol, tocopherol or all-trans-retinoic acid.. Neither retinyl palmitate nor 13-cis-retinoic acid, are known to be biologically active. However, 13-cis-retinoic acid can isomerise to the active vitamin A derivative, all-trans-retinoic acid. It is suggested that patients may be treated with a small dose of 13-cis-retinoic acid instead, to avoid the relatively long metabolic detour from retinyl palmitate.

Topics: Administration, Oral; Adult; Aged; Anticarcinogenic Agents; Chromatography, High Pressure Liquid; Diterpenes; Electroretinography; Female; Humans; Male; Middle Aged; Retinitis Pigmentosa; Retinoids; Retinyl Esters; Tretinoin; Vitamin A; Vitamin E

Plasma concentrations of retinyl esters, retinol, retinol-binding protein and the polar retinol metabolites all-trans-retinoic acid, 13-cis-retinoic acid, all-trans-4-oxoretinoic acid and 13-cis-4-oxoretinoic acid were measured for six male volunteers who received 0.46 mg retinyl palmitate per kilogram body weight as oily drops (equivalent to 0.25 mg retinol per kilogram body weight) once daily over a 20-d period. Retinol and retinol-binding protein levels remained virtually constant throughout the study. Following absorption of vitamin A, retinyl esters as well as all-trans-retinoic acid and 13-cis-retinoic acid were transiently increased in plasma. 13-cis-4-Oxoretinoic acid increased gradually to a steady state level present on d 10 or 20. All-trans-4-oxoretinoic acid was not detected in plasma of the volunteers, with the exception of one on d 10 of the study. Plasma pharmacokinetic profiles of retinyl esters and polar metabolites of retinol displayed great interindividual differences (peak concentrations, time to peak, area-under-the-concentration-time curve values) among the volunteers. Because of the relatively high and consistent steady state concentrations of plasma 13-cis-4-oxoretinoic acid, we suggest that this compound be further investigated as a biochemical marker of vitamin A uptake in humans.

Topics: Administration, Oral; Adult; Chromatography, High Pressure Liquid; Diterpenes; Humans; Male; Retinol-Binding Proteins; Retinol-Binding Proteins, Plasma; Retinyl Esters; Stereoisomerism; Tretinoin; Vitamin A