Abstract
β-carotene is the most abundant provitamin A carotenoid in human diet and tissues. It exerts a number of beneficial functions in mammals, including humans, owing to its ability to generate vitamin A as well as to emerging crucial signaling functions of its metabolites. Even though β-carotene is generally considered a safer form of vitamin A due to its highly regulated intestinal absorption, detrimental effects have also been ascribed to its intake, at least under specific circumstances. A better understanding of the metabolism of β-carotene is still needed to unequivocally discriminate the conditions under which it may exert beneficial or detrimental effects on human health and thus to enable the formulation of dietary recommendations adequate for different groups of individuals and populations worldwide. Here we provide a general overview of the metabolism of this vitamin A precursor in mammals with the aim of identifying the gaps in knowledge that call for immediate attention. We highlight the main questions that remain to be answered in regards to the cleavage, uptake, extracellular and intracellular transport of β-carotene as well as the interactions between the metabolism of β-carotene and that of other macronutrients such as lipids.
Highlights
Carotenoids are C40 tetraterpenoid pigments that are found in plants, fungi and bacteria
Lintig and colleagues provided evidence that CMOII alone does not significantly contribute to β-carotene homeostasis in vivo and suggested that it is unlikely that the asymmetric cleavage enzyme is a component of a pathway for the production of β-apocarotenoid signaling molecules that could interact with nuclear receptors [45]
Similar mechanisms are employed by invertebrates, such as the silkworms, to deliver lutein to the silk gland where a specific cell surface uptake protein, Cameo2, and a specific carotenoid binding protein, CBP, are needed [124,125]. This year marks the century of vitamin A research, there are still various aspects of the mammalian metabolism of its main precursor, β-carotene, which are not fully understood. β-Carotene bioconversion by its cleavage enzymes has been studied extensively
Summary
Carotenoids are C40 tetraterpenoid pigments that are found in plants, fungi and bacteria. Mammals obtain carotenoids predominantly through foods of plant origin [1] In plants, these compounds accumulate in the plastids giving the characteristic bright yellow, red and orange color to many fruits and vegetables [1]. A complete understanding of the metabolism of these compounds is still needed to unequivocally determine the conditions under which these compounds may exert either beneficial or detrimental effects on human health. This knowledge will generate dietary recommendations adequate to different groups of individuals and populations worldwide. We will provide a general overview of the main aspects of β-carotene metabolism in mammals to highlight what we believe are the major questions still left to be answered in this field of research
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