Vitamine A

Résumé

La vitamine A est une vitamine liposoluble. Dans l'organisme, elle existe sous forme de rétinol, de rétinal, d'acide rétinoïque (trétinoïne) et de phosphate de rétinyle. Ces molécules sont altérées par l'oxygène de l'air, altérations accélérées par la lumière et la chaleur. Les aliments d'origine animale (viandes, produits laitiers et surtout foie) contiennent du rétinol et des esters de rétinol alors que les végétaux contiennent essentiellement des carotènes qui sont des précurseurs du rétinol. Une molécule de bêta-carotène, par hydrolyse de la liaison 15-15′ sous l'influence d'un caroténoïde mono-oxygénase (β-carotène 15,15′ mono-oxygénase), donne deux molécules de vitamine A. Par contre, les deux autres carotènes (alpha et gamma) ne donnent naissance qu'à une seule molécule de vitamine A. Les besoins quotidiens en vitamine A pour un adulte sont estimés à (femme, femme enceinte exceptée) ou à (homme) soit de environ. Une unité internationale de vitamine A correspond à de

Source officielle

https://fr.wikipedia.org/wiki/Vitamine_A

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (7)

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (83)

Concepts associés

Chargement

Cours associés (3)

Cours associés

Chargement

Séances de cours associées (3)

Séances de cours associées

Chargement

Opportunities in Critical Rare Earth Metal Recycling Value Chains for Economic Growth with Sustainable Technological Innovations

Christian Ludwig, Ajay Bhagwan Patil, Rudolf Paul Wilhelm Jozef Struis

Rare earth elements (REEs) are often referred to as the industrial vitamins and the key drivers of the industry 4.0 revolution. The current global supply chain of REEs for green and high-tech applications with more than 220 metric kilotons per year involves a huge environmental impact (backpack) as well as the piling up of radioactive by-products to about 1.5 times the amount of REEs produced. E-wastes and municipal solid waste streams are attractive secondary resources. The current opinion paper discusses the recycling of rare earth metals along the value chain with the opportunities and challenges associated with it. The way to mitigate the economic constraints has been pointed out in terms of competitive quality and recovery of the REEs when compared with the mineral exploration options in the market. It is also emphasised that the technical complexity, capital expenditures and operating expenses need to fit the economic boundary conditions to make the recycling viable. In future, the appropriate REE-rich feedstocks such as fluorescent lamp e-waste powders and magnets can be potential secondary sources of the critical raw materials necessary for the green transition. The success of the viable recycling approaches and technologies will largely depend on the public–private partnerships based on hybrid financing models and local know-how generation to compete with quasi-monopoly in the REE supply chains. However, to break the monopolies, it will not be sufficient to only recycle the REEs; it will also be relevant to diversify the industries that produce REE-containing goods from recycled waste streams.

2022

Chargement

Effective treatment of mitochondrial myopathy by nicotinamide riboside, a vitamin B3

Johan Auwerx, Eija Riitta Pirinen

Nutrient availability is the major regulator of life and reproduction, and a complex cellular signaling network has evolved to adapt organisms to fasting. These sensor pathways monitor cellular energy metabolism, especially mitochondrial ATP production and NAD+/NADH ratio, as major signals for nutritional state. We hypothesized that these signals would be modified by mitochondrial respiratory chain disease, because of inefficient NADH utilization and ATP production. Oral administration of nicotinamide riboside (NR), a vitamin B3 and NAD+ precursor, was previously shown to boost NAD+ levels in mice and to induce mitochondrial biogenesis. Here, we treated mitochondrial myopathy mice with NR. This vitamin effectively delayed early- and late-stage disease progression, by robustly inducing mitochondrial biogenesis in skeletal muscle and brown adipose tissue, preventing mitochondrial ultrastructure abnormalities and mtDNA deletion formation. NR further stimulated mitochondrial unfolded protein response, suggesting its protective role in mitochondrial disease. These results indicate that NR and strategies boosting NAD+ levels are a promising treatment strategy for mitochondrial myopathy.

Wiley Open Access2014

Chargement

, ,

The vitamin D endocrine system has many extraskeletal targets, including adipose tissue. 1,25-Dihydroxyvitamin D-3, the active form of vitamin D, not only increases adipogenesis and the expression of typical adipocyte genes but also decreases the expression of uncoupling proteins. Mice with disrupted vitamin D action-owing to gene deletion of the nuclear receptor vitamin D receptor (Vdr) or the gene encoding 1 alpha-hydroxylase (Cyp27b1)-lose fat mass over time owing to an increase in energy expenditure, whereas mice with increased Vdr-mediated signalling in adipose tissue become obese. The resistance to diet-induced obesity in mice with disrupted Vdr signalling is caused at least partially by increased expression of uncoupling proteins in white adipose tissue. However, the bile acid pool is also increased in these animals, and bile acids are known to be potent inducers of energy expenditure through activation of several nuclear receptors, including Vdr, and G-protein-coupled receptors, such as GPBAR1 (also known as TGR5). By contrast, in humans, obesity is strongly associated with poor vitamin D status. A causal link has not been firmly proven, but most intervention studies have failed to demonstrate a beneficial effect of vitamin D supplementation on body weight. The reasons for the major discrepancy between mouse and human data are unclear, but understanding the link between vitamin D status and energy homeostasis could potentially be very important for the human epidemic of obesity and the metabolic syndrome.

Nature Publishing Group2014

Chargement