Retinyl esters application

It should be elucidated to what extent the "topical" application of retinyl esters on the respiratory epithelium, especially with BDP, can contribute to the replenishment of the lung stores and thus leading to the improvement of the clinical outcome. 

These results show that retinyl esters in respiratory epithelium and in alveolar cells form a pool of vitamin A, which can be used physiologically by the tissue. The formation of retinol and at least RA from retinyl esters is strictly controlled. So far an unphysiological formation of RA and a subsequent toxicity seems not possible. Retinyl esters, however, are biochemically inert with respect to gene expression or vitamin A activity as long as they are not hydrolyzed. Consequently, the inhalative application, especially in cases of insufficient lung development, could represent a true alternative. The oral contribution is hardly successful because of the poor RBP s)mthesis of the liver and the lack of availability of a parenteral solution is currently not available. 

The obtained results confirm earlier findings where vitamin A-deficient rats were used to prove the uptake of retinyl esters into lung, liver, kidney, and plasma after inhalation thereof (Biesalski, 1996). However, long-term topical administration of high vitamin A concentrations is a well-established therapy in atrophic rhinitis, rhinitis sicca, and metaplastic changes in the nasal or ocular epithelium (Deshpande et ah, 1997 Simm, 1980). The application leads to the normalization of mucous membranes and reappearance of a normal function with no side effects. 

Gerlach, T., Biesalski, H. K., Weiser, H., Haeussermann, B., and Baessler, K. H. (1989). Vitamin A in parenteral nutrition Uptake and distribution of retinyl esters after intravenous application. Am. ]. Clin. Nutr. 50,1029-1038. 

Additional noteworthy applications of CEC include natural products such as the plant flavonoids hesperetin and hesperidin [160], anthraquinones extracted from rhubarb and from Chinese medicine [161], and heterocyclic compounds present in oils of bergamot, mandarin, and sweet orange [162], The CEC analysis of retinyl esters has been investigated by Roed et al. in nonaqueous mode for the separation of liver extracts of arctic seal [163]. Carotenoid isomers were also separated on C30 stationary phases by nonaqueous CEC [164]. It was found that CEC offered increased resolution compared to HPLC, and in CEC... 

A wide variety of liquid chromatography-mass spectrometry (LC-MS) techniques have been reported for retinoid analysis including direct liquid introduction with Cl (281,282,299-301), particle beam (302-304), thermospray (305-307), electrospray (308,309), and atmospheric pressure chemical ionization (APCI) (310). Because many of the early LC-MS applications to retinoids carried out hydrolysis of retinyl esters and then derivatization of retinoic acid and related retinoids, Wyss (141) predicted in a review of retinoid analysis that derivatization of retinoids would be necessary for all LC-MS techniques, even the anticipated application of atmospheric pressure chemical ionization (APCI). Recently, LC-MS analyses of retinoids have been carried out using APCI (310) and electrospray (308,309), and highly sensitive LC-MS analyses of retinoic acid and retinyl esters were achieved without hydrolysis or derivatization. 

Analytical SEC has found application for the assay of vitamin E in oils (151,153,183,184), seeds (163), and deodorizer distillates (172), mostly in combination with that of other fat soluble compounds such as retinyl esters, triglycerides, sterols, and fatty acids. This technique has also been used for the determination of a-tocopheryl acetate in pharmaceutical preparations (164,165). SEC can be conducted either on capillary GC columns with EID detection (151,153,163, 172, 184,185) or, alternatively, on EC columns with EID (165) or UV detection (144,164,183). 

The application of SCF to the extraction of vitamins has been widely reported. Thus, retinyl palmitate and tocopherol acetate have been extracted from a hydrophobic ointment with supercritical CO2 at 40°C and 196 bar for 4 min, the extract analysis being performed by SFC (137). The calibration graphs were linear from 0.5 to 2.5 pg and the recoveries were quantitative. On the other hand, water-soluble vitamins can be extracted mixing them with low substituted hydroxypropil cellulose. Portions were placed in a column to which a reversed micellar extractant was delivered (138). Extraction of vitamins A and E and their esters from tablet preparations prior to FIPLC was performed in the dynamic mode with CO2 at 40°C and 253 bar for 15 min (139). Calibration graphs were linear from 0.02 to 0.8 and from 0.005 to 0.2 mg/mL of vitamins E and A, respectively. The corresponding RSDs (six... 

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