We characterized the human Na ؉ -ascorbic acid transporter SVCT2 and developed a basic model for the transport cycle that challenges the current view that it functions as a Na ؉ -dependent transporter.

Vitamin C is a wide spectrum antioxidant essential for humans, which are unable to synthesize the vitamin and must obtain it from dietary sources. There are two biologically important forms of vitamin C, the reduced form, ascorbic acid, and the oxidized form, dehydroascorbic acid. Vitamin C exerts most of its biological functions intracellularly and is acquired by cells with the participation of specific membrane transporters. This is a central issue because even in those species capable of synthesizing vitamin C, synthesis is restricted to the liver (and pancreas) from which is distributed to the organism. Most cells express two different transporter systems for vitamin C; a transporter system with absolute specificity for ascorbic acid and a second system that shows absolute specificity for dehydroascorbic acid. The dehydroascorbic acid transporters are members of the GLUT family of facilitative glucose transporters, of which at least three isoforms, GLUT1, GLUT3 and GLUT4, are dehydroascorbic acid transporters. Ascorbic acid is transported by the SVCT family of sodium-coupled transporters, with two isoforms molecularly cloned, the transporters SVCT1 y SVCT2, that show different functional properties and differential cell and tissue expression. In humans, the maintenance of a low daily requirement of vitamin C is attained through an efficient system for the recycling of the vitamin involving the two families of vitamin C transporters.

The study describes the current state of knowledge on nanotechnology and its utilization in medicine. The focus in this manuscript was on the properties, usage safety, and potentially valuable applications of chitosan-based nanomaterials. Chitosan nanoparticles have high importance in nanomedicine, biomedical engineering, discovery and development of new drugs. The manuscript reviewed the new studies regarding the use of chitosan-based nanoparticles for creating new release systems with improved bioavailability, increased specificity and sensitivity, and reduced pharmacological toxicity of drugs. Nowadays, effective cancer treatment is a global problem, and recent advances in nanomedicine are of great importance. Special attention was put on the application of chitosan nanoparticles in developing new system for anticancer drug delivery. Pre-clinical and clinical studies support the use of chitosan-based nanoparticles in nanomedicine. This manuscript overviews the last progresses regarding the utilization, stability, and bioavailability of drug nanoencapsulation with chitosan and their safety.

Cellular glutathione levels may exceed vitamin C levels by 10-fold, generating the question about the real antioxidant role that low intracellular concentrations of vitamin C can play in the presence of a vast molar excess of glutathione. We characterized the metabolism of vitamin C and its relationship with glutathione in primary cultures of human endothelial cells oxidatively challenged by treatment with hydrogen peroxide or with activated cells undergoing the respiratory burst, and analyzed the manner in which vitamin C interacts with glutathione to increase the antioxidant capacity of cells. Our data indicate that: (i) endothelial cells express transporters for reduced and oxidized vitamin C and accumulate ascorbic acid with participation of glutathione-dependent dehydroascorbic acid reductases, (ii) although increased intracellular levels of vitamin C or glutathione caused augmented resistance to oxidative stress, 10-times more glutathione than vitamin C was required, (iii) full antioxidant protection required the simultaneous presence of intracellular and extracellular vitamin C at concentrations normally found in vivo, and (iv) intracellular vitamin C cooperated in enhancing glutathione recovery after oxidative challenge thus providing cells with enhanced survival potential, while extracellular vitamin C was recycled through a mechanism involving the simultaneous neutralization of oxidant species. Therefore, in endothelial cells under oxidative challenge, vitamin C functions as an essential cellular antioxidant even in the presence of a vast molar excess of glutathione.Human cells contain two important water soluble antioxidants, vitamin C and the tripeptide glutathione (L-␥-glutamyl-L-cysteinyl-glycine). Vitamin C plays an important physiological role in cells as a reducing agent and antioxidant, free radical scavenger, and enzyme cofactor (1, 2). Glutathione is the most abundant non-protein thiol in mammalian cells and participates in multiple functions central to the physiology of cells, acting as a reducing agent, antioxidant, and free-radical scavenger and is involved in the metabolism and detoxification of xenobiotics, and alterations in GSH levels and metabolism have been associated with different human diseases (3, 4). Glutathione and vitamin C show a strong functional interdependence in vivo. Disruption of glutathione metabolism in vivo in rats and guinea pigs by treatment with buthionine-(SR)-sulfoximine (BSO), 5 a potent and specific glutathione synthesis inhibitor, revealed that the dysfunction and mortality associated with glutathione deficiency can be ameliorated by vitamin C supplementation (3, 5). Inversely, glutathione ester supplementation can protect or delay the effects of a vitamin C-free diet in newborn rats and guinea pigs unable to synthesize vitamin C (3, 6).Although a functional relationship between glutathione and vitamin C has been clearly established in rats and guinea pigs, we know little about how they cooperate in providing human cells with potent antioxidant defense mechan...

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