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The Journal of Nutrition Dec 1994To study effects of vitamin A status on retinol dynamics, male rats were fed purified diets varying in vitamin A concentration. Group 1 rats had marginal liver vitamin A...
To study effects of vitamin A status on retinol dynamics, male rats were fed purified diets varying in vitamin A concentration. Group 1 rats had marginal liver vitamin A levels (approximately 500 nmol) and were in a slight positive vitamin A balance; Group 2 had similar liver levels but were in a slight negative balance; Group 3 had lower liver levels (approximately 370 nmol) and were in a slight negative balance; Group 4 had depleted liver reserves (<10 nmol) and were in vitamin A balance. [3H]Retinol-labeled plasma was injected intravenously, and serial plasma samples were collected for 41 d while rats (six per group) consumed approximately 50 nmol retinol/d (Group 1) or -25 nmol/d (Groups 2-4). Plasma retinol was normal in Groups 1-3 (1.9-2.0 micromol/L) and lower in Group 4 (0.96 micromol/L). Plasma tracer data were fit to a three-compartment model. The central plasma retinol compartment (transit time, 1.5-1.7 h) exchanged with a fast turning-over extravascular vitamin A pool (transit time, 3-4.5 h; -40 nmol) and with a larger, slow turning-over extravascular pool (transit time, 5.5-10 d) that was the site of irreversible utilization of vitamin A. Irreversible utilization was 36 nmol/d (Group 1), 29 nmol/d (Groups 2 and 3) and 20 nmol/d (Group 4). The data indicate that in rats with low or marginal vitamin A status, vitamin A intake, vitamin A reserves and plasma retinol concentration all influence vitamin A utilization and other aspects of retinol dynamics.
Topics: Animals; Diet; Male; Nutritional Requirements; Rats; Rats, Sprague-Dawley; Vitamin A; Weaning
PubMed: 16856330
DOI: 10.1093/jn/124.12.477 -
Current Concepts in Nutrition 1983Although large doses of oral retinoids produce marked toxic effects in some circumstances, it appears there may be a potential for the use of synthetic retinoids in... (Review)
Review
Although large doses of oral retinoids produce marked toxic effects in some circumstances, it appears there may be a potential for the use of synthetic retinoids in cancer prevention and therapy in addition to the profoundly important benefits shown thus far in a variety of dermatological conditions. Furthermore, the wide diversity of retinoid effects on cell systems suggests that other, nondermatological, diseases may eventually be found to respond to this new class of therapeutic agents. This is to be expected particularly if newer retinoids show new tissue specificities. As was true of steroids in 1950, the potential of retinoids in 1982 is only partly visible, but very exciting.
Topics: Acne Vulgaris; Animals; Chemical Phenomena; Chemistry; Epithelium; Humans; Neoplasms; Psoriasis; Reproduction; Skin Diseases; Vitamin A
PubMed: 6221887
DOI: No ID Found -
Presse Medicale (Paris, France : 1983) Jun 1987Although vitamin A intervenes essentially in the mechanism of sight, its possible role in the prevention and treatment of cancer is widely discussed. Epidemiological... (Review)
Review
Although vitamin A intervenes essentially in the mechanism of sight, its possible role in the prevention and treatment of cancer is widely discussed. Epidemiological studies have demonstrated a correlation between vitamin A deficiency and an increase in the frequency of cancers in man. Several hypotheses have been put forward concerning the mechanism of interaction between vitamin A and cancer on the basis of experimental models showing that vitamin A exerts a protective action against spontaneous or induced neoplasias in animals. The toxicological aspects of vitamin A administration and the relevance of these experimental results to human oncology are discussed.
Topics: Cell Differentiation; Humans; Neoplasms; Vitamin A
PubMed: 2955341
DOI: No ID Found -
Journal of Controlled Release :... May 2000Burst release as well as sustained release has been reported for SLN suspensions. For dermal application, both features are of interest. Burst release can be useful to...
Burst release as well as sustained release has been reported for SLN suspensions. For dermal application, both features are of interest. Burst release can be useful to improve the penetration of a drug. Sustained release becomes important with active ingredients that are irritating at high concentrations or to supply the skin over a prolonged period of time with a drug. Glyceryl behenate SLN were loaded with vitamin A and the release profiles were studied. Franz diffusion cells were used to assess the release kinetic over a period of 24 h. Within the first 6 h retinol SLN displayed controlled release. After longer periods (12-24 h) the release rate increased and even exceeded the release rate of comparable nanoemulsions. Pure SLN dispersions are characterised by low viscosity. In contrast to membranous vesicles, SLN can also be stably incorporated in convenient topical dosage forms like hydrogels or creams. In the Franz diffusion cell these preparations showed a controlled release over 12-18 h. Similar to SLN dispersions an increase in release rate over a 24-h period was found. A good correlation between polymorphic transitions and increased drug release was observed in this study. Sustained release was often related to the metastable beta' polymorph. Drug expulsion is explained by a reduction of amorphous regions in the carrier lattice due to a beta'-->beta(i) polymorphic transition. This transformation can be controlled with surfactant mixtures or, in the case of the hydrogel and oil/water cream, with humectants or gelling agents. Thus, the release rate for the topical route of application is adjustable.
Topics: Administration, Topical; Diterpenes; Drug Delivery Systems; Emulsions; Hydrogels; Lipids; Microspheres; Retinyl Esters; Vitamin A
PubMed: 10742573
DOI: 10.1016/s0168-3659(99)00223-0 -
The Journal of Nutrition Nov 2016Retinol isotope dilution (RID) equations are used to determine vitamin A status and the efficacy of vitamin A intervention programs. Recent work related to RID methods...
BACKGROUND
Retinol isotope dilution (RID) equations are used to determine vitamin A status and the efficacy of vitamin A intervention programs. Recent work related to RID methods has focused on modifying the "Olson equation" to improve the accuracy of predictions of vitamin A total body stores (TBS) in individual subjects.
OBJECTIVE
We investigated the hypothesis that short-term restriction of vitamin A intake would result in accurate RID prediction of vitamin A TBS in individuals.
METHODS
We applied model-based compartmental analysis to a 6-component model derived from published retinol kinetic studies on 12 individuals with a wide range of vitamin A stores and determined vitamin A TBS in the steady state. Then we simulated the impact of eliminating or strictly limiting vitamin A intake at the time of isotope administration, while maintaining plasma retinol homeostasis, on retinol specific activity in plasma (SA; fraction of dose/μmol retinol) and stores, and we calculated TBS using the simplified RID equation TBS = 0.75 × 1/SA, where the fractional absorption of tracer was set at 0.75 and SA was simulated 5 d after dosing.
RESULTS
When vitamin A intake was zero or strictly limited (0.25 μmol/d), mean TBS predicted by the equation at 5 d after dose administration divided by TBS determined by using the model was 1.00 (range: 0.959-1.04) or 1.02 (range: 0.983 - 1.06), respectively.
CONCLUSIONS
By eliminating or strictly limiting vitamin A input, isotopic equilibrium was reached by 5 d. At isotopic equilibrium, SA is the same as that in the body's exchangeable vitamin A pools; under these conditions, SA may be measured at any time from 5 d on and used to calculate TBS.
Topics: Adult; Humans; Indicator Dilution Techniques; Isotope Labeling; Models, Biological; Nutritional Status; Tissue Distribution; Vitamin A; Vitamin A Deficiency
PubMed: 27683870
DOI: 10.3945/jn.116.238899 -
The Journal of Nutrition Oct 1977Pregnant rats and rabbits were given excess vitamin A, in the form of retinyl acetate or retinoic acid, for the 3-day period just prior to palatal closure in the...
Pregnant rats and rabbits were given excess vitamin A, in the form of retinyl acetate or retinoic acid, for the 3-day period just prior to palatal closure in the fetuses. Twenty-four hours later, the various forms of vitamin A, and their levels, were determined in fetal liver and carcass and in maternal liver and serum by thin-layer chromatography. The predominant forms of vitamin A found in both fetal and maternal tissues were retinyl palmitate, retinol and retinoic acid. In both species, the tissues from the groups treated with retinoic acid contained levels of vitamin A similar to those found in control tissues. After retinyl acetate treatment in the rat, both of the maternal tissues studied had elevated vitamin A, whereas in the rabbit only maternal liver levels increased. In the groups treated with retinyl acetate, the ratio of the vitamin A levels in fetal liver: maternal serum reflected a species difference: the ratio was lower than the control value in the rabbit and higher than controls in the rat. Radiotracer studies in the rat, using either 3H-retinol or 14C-retinoic acid, demonstrated vitamin A transport across the placenta, with vitamin A concentrating in the fetal liver.
Topics: Animals; Female; Fetus; Liver; Maternal-Fetal Exchange; Pregnancy; Pregnancy Complications; Rabbits; Rats; Species Specificity; Tretinoin; Vitamin A
PubMed: 903826
DOI: 10.1093/jn/107.10.1816 -
The Journal of Nutrition Jun 2002
Topics: Animals; Carnivora; Diet; Diterpenes; Female; Ferrets; Kidney; Liver; Retinol-Binding Proteins; Retinyl Esters; Tissue Distribution; Vitamin A
PubMed: 12042529
DOI: 10.1093/jn/132.6.1787S -
Strahlentherapie Und Onkologie : Organ... Feb 1995Retinoids are a class of compounds structurally related to vitamin A which have been found to be active agents experimentally as well as clinically in the prevention and... (Review)
Review
PURPOSE
Retinoids are a class of compounds structurally related to vitamin A which have been found to be active agents experimentally as well as clinically in the prevention and treatment of tumors. The data available suggest to study whether they might improve treatment results if combined with irradiation.
METHODS
The clinical results in the prevention and treatment of cancer with retinoids are reviewed. In the context of experimental studies evaluating the antiproliferative effects of retinoids, cytokines and radiation alone or in combination our own experimental investigations analyzing a combination of all-trans-retinoic acid, interferon-alpha (IFN-alpha) and ionizing radiation in squamous cell carcinoma cell lines are described.
RESULTS
There is a solid body of experimental and clinical data to combine retinoids with cytokines (e.g.IFN-alpha). Since it is known that vitamin A alters the radiation response in experimental tumors our analyses further support the combination of retinoids and IFN-alpha with ionizing radiation.
CONCLUSIONS
We emphasize further clinical investigations evaluating the combined treatment with retinoids/IFN-alpha and ionizing radiation in squamous cell carcinomas such as head and neck tumors and cervical cancer.
Topics: Animals; Combined Modality Therapy; Humans; Neoplasms; Retinoids; Vitamin A
PubMed: 7863423
DOI: No ID Found -
Pakistan Journal of Biological Sciences... Jul 2008The vitamin A status of 101 pregnant women attending clinic at the University of Calabar Teaching Hospital (UCTH), Calabar, Nigeria was assessed based on 24 h dietary...
The vitamin A status of 101 pregnant women attending clinic at the University of Calabar Teaching Hospital (UCTH), Calabar, Nigeria was assessed based on 24 h dietary recall, serum retinol concentration, history of night blindness, physical appearance and clinical eye signs. The study revealed that the mean dietary vitamin A intake of the respondents (2645.31 +/- 188.91 microg RE) and their mean serum retinol concentration (31.18 +/- 2.94 microg dL(-1)) were significantly (p < 0.05) higher than the FAO/WHO recommended intake and cutoff level for VAD. No case of night blindness, physical signs and symptoms, or clinical eye signs attributable to VAD was observed. There was a significant (p < 0.01) correlation between the amount of 24 h vitamin A intake of the women and their serum retinol concentration (r = 0.31). Also, women who had above 50% of their vitamin A intake from provitamin A sources had a significantly (p < 0.05) lower serum retinol concentration (23.10 +/- 21.12 microg dL(-1)) than those who had above 50% intake from preformed sources (49.54 +/- 42.63 microg dL(-1)) and those with about equal intake from both sources (55.75 +/- 30.80 microg dL(-1)). There was a significant (p < 0.05) and steady decline in serum retinol concentration in the women from the first trimester (37.79 +/- 6.65 microg dL(-1)), through the second trimester (35.12 +/- 4.72 microg dL(-1)), to the third trimester (21.54 +/- 1.46 microg dL(-1)) of pregnancy.
Topics: Diet; Female; Gestational Age; Humans; Nigeria; Pregnancy; Vitamin A
PubMed: 18819622
DOI: 10.3923/pjbs.2008.1702.1707 -
Toxicon : Official Journal of the... Jul 1967
Topics: Animals; Carnivora; Cats; Fishes; Liver; Rats; Sharks; Vitamin A
PubMed: 6036254
DOI: 10.1016/0041-0101(67)90121-3