Vitamin A and postulated mechanisms of its effects on cancer
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Abstract
In recent years vitamin A has been closely examined as a potential anti-cancer agent. Some studies report a vitamin A inhibitory effect on carcinogenesis, others report a vitamin A enhancing effect, some report no effect at all. Part I of this thesis deals with some background on normal physiological vitamin A activity, followed by an overview of cancer. Some of the probable mechanisms of vitamin A action are discussed such as vitamin A metabolism, the two physiological forms of vitamin A, vitamin A's interaction with the chromatin and its influence on gene expression, vitamin A interaction in the membrane, and vitamin A action being cell cycle-dependent. Also discussed are histologic changes in vitamin A deficiency and excess. This is followed by the overview on cancer. Part II discusses vitamin A effects on the carcinogenic process. Two major categories are presented: vitamin A deficiency and vitamin A excess. Each category discusses the inhibitory and the enhancing effects of that particular vitamin A status. The mechanisms discussed include direct-acting carcinogens vs. metabolically activated carcinogens, the site of action not being reached, the cell maintaining its vitamin A-deficient state, transcription, actual inhibition of the carcinogen by vitamin A, mechanisms in the membrane, cell cycle phases, and the protein kinase-c system.
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Thesis (M.A.)--Boston University
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