Vitamine C | EPFL Graph Search

La vitamine C est une vitamine hydrosoluble sensible à la chaleur et à la lumière jouant un rôle important dans le métabolisme de l'être humain et de nombreux autres mammifères. Chimiquement parlant, il s'agit de l'acide L-ascorbique, un des stéréoisomères de l'acide ascorbique, et de ses sels, les ascorbates. Les plus courants sont l'ascorbate de sodium et l'ascorbate de calcium. On parle d'acide ascorbique ou acide L-(+)-ascorbique donc dextrogyre de numéro CAS et il est le seul autorisé à porter le nom de « vitamine C ». L'acide ascorbique lévogyre (acide D-(–)-ascorbique) n'a pas d'effet vitaminique suffisant. Propriétés chimiques Acide ascorbique Conservation Très fragile en solution, elle est détruite au contact de l'air (par oxydation) ou sous l'exposition à la lumière (par action des ultraviolets) et la chaleur accélère ces processus. La cuisson des aliments détruit progressivement la vitamine C, il faut donc privilégier une cuisson courte et à basse t

Study of the influence of over-the-counter vitamin supplement intake on urine fluorescence to optimize cancer detection by fluorescence cystoscopy

Carla Martoccia, Hubert van den Bergh, Georges Wagnières, Matthieu Zellweger

Fluorescence cystoscopy (FC) efficiently enhances the detection and improves the therapeutic management of early bladder cancer. During an FC, about 150 ml of water is needed to inflate the bladder. The water is quickly diluted by urine which can be fluorescent. If this bladder washout fluid (BWF) becomes fluorescent, the FC images are frequently degraded. Unfortunately, it is unclear which elements of the diet may contribute to this background fluorescence. We propose to start this exploration with over-the-counter (OTC) vitamin supplements. To this end, we measured excitation-emission matrices of urine samples and the kinetics of modifications of urine fluorescence obtained from nine healthy volunteers before, during, and after intake of a commercially available OTC vitamin supplement. The pharmacokinetics shows that the BWF fluorescence values reach a maximum 8 to 10 h after vitamin intake. They decrease in the half-day that follows and reach values close to baseline similar to 1 day afterward. Based on these results, we conclude that, in order to avoid degradations of fluorescence images, it is likely best that the intake of OTC vitamin supplements be avoided during the week preceding an FC. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Spie-Soc Photo-Optical Instrumentation Engineers2015

Functional characterization of a vitamin B12-dependent methylmalonyl pathway in Mycobacterium tuberculosis: implications for propionate metabolism during growth on fatty acids

John McKinney

Mycobacterium tuberculosis is predicted to subsist on alternative carbon sources during persistence within the human host. Catabolism of odd- and branched-chain fatty acids, branched-chain amino acids, and cholesterol generates propionyl-coenzyme A (CoA) as a terminal, three-carbon (C(3)) product. Propionate constitutes a key precursor in lipid biosynthesis but is toxic if accumulated, potentially implicating its metabolism in M. tuberculosis pathogenesis. In addition to the well-characterized methylcitrate cycle, the M. tuberculosis genome contains a complete methylmalonyl pathway, including a mutAB-encoded methylmalonyl-CoA mutase (MCM) that requires a vitamin B(12)-derived cofactor for activity. Here, we demonstrate the ability of M. tuberculosis to utilize propionate as the sole carbon source in the absence of a functional methylcitrate cycle, provided that vitamin B(12) is supplied exogenously. We show that this ability is dependent on mutAB and, furthermore, that an active methylmalonyl pathway allows the bypass of the glyoxylate cycle during growth on propionate in vitro. Importantly, although the glyoxylate and methylcitrate cycles supported robust growth of M. tuberculosis on the C(17) fatty acid heptadecanoate, growth on valerate (C(5)) was significantly enhanced through vitamin B(12) supplementation. Moreover, both wild-type and methylcitrate cycle mutant strains grew on B(12)-supplemented valerate in the presence of 3-nitropropionate, an inhibitor of the glyoxylate cycle enzyme isocitrate lyase, indicating an anaplerotic role for the methylmalonyl pathway. The demonstrated functionality of MCM reinforces the potential relevance of vitamin B(12) to mycobacterial pathogenesis and suggests that vitamin B(12) availability in vivo might resolve the paradoxical dispensability of the methylcitrate cycle for the growth and persistence of M. tuberculosis in mice.

2008

Functional characterization of a vitamin B12-dependent methylmalonyl pathway in Mycobacterium tuberculosis: implications for propionate metabolism during growth on fatty acids

John McKinney

2008