Handbook of Vitamin C Research

Prefacexiprovided or is contradictory. Many studies show an inverse relationship between mortalityand vitamin C intake indicating a protective antioxidant activity. On the other side severalreports show no significant relationship after controlling for confounding variables. Thereforethere is still debate on whether supplements of vitamin C could act as antioxidant or prooxidantin vivo. Recent research suggests that 3 factors are responsible for the pro- orantioxidant behaviour of vitamin C in biological systems, e.g., cellular environment: 1.) theredox potential of the cellular environment (oxidosis/redosis), 2.) the presence or absence oftransition metals, and 3.) the local concentration of ascorbate. This may also explain theobserved quite specific pro-oxidant activity of high dose intravenous vitamin C against metalreach malignant tumours. In this paper possible pro- and antioxidant effects of vitamin C willbe presented and their impact on human health will be discussed.Chapter VI - Vitamin C, also known as ascorbic acid, is a very important water-solublevitamin. It is essential for preserving optimal health and it is used by the body for manypurposes. Vitamin C promotes collagen biosynthesis, provides photoprotection, causesmelanin reduction, enhances the immunity (anti-virus effect), etc. Vitamin C is a highlyeffective antioxidant. Even in small amounts vitamin C can protect indispensable moleculesin the body, such as proteins, lipids (fats), carbohydrates, and nucleic acids (DNA and RNA)from damage by free radicals and reactive oxygen species that can be generated duringnormal metabolism as well as through exposure to toxins and pollutants (e.g., smoking).Vitamin C may be involved in the reduction of the risk of certain types of cancer. A numberof in vitro and in vivo experiments have been performed in order to evaluate the ability ofascorbic acid to prevent the adverse effects, increase the effects of, and decrease resistance tochemotherapeutic agents. The problem is that ascorbic acid is very unstable to air, light, heat,moisture, metal ions, oxygen, and base, and it easily decomposes into biologically inactivecompounds such as 2,3-diketo-L-gulonic acid, oxalic acid, L-threonic acid, L-xylonic acidand L-lyxonic acid. This makes its use very limited in the field of pharmaceuticals,dermatologicals and cosmetics. In order to overcome the chemical instability of the ascorbicacid numerous researches have been staged toward its encapsulation or immobilization. Theascorbic acid introduced in the body in the greater portion is isolated from the body.However, the encapsulated ascorbic acid within, for example, the polymeric matrix shouldhave significantly higher efficiency. The present review attempts to address some importantissues related to various methods which are employed to encapsulate ascorbic acid, such asthermal phase separation, melt dispersion, solvent evaporation, spray drying, homogenizationof water and organic phases, etc. This review also gives a comparation of the characteristicsof ascorbic acid nano and microparticles prepared by different methods. The materials inwhich ascorbic acid can be successfully encapsulated are poly (DL-lactide-co-glycolide),tripolyphosphate cross-linked chitosan, liposomes, maltodextrin, dendrimers, etc.Encapsulation efficiency, release rate, size distribution of particles with encapsulatedascorbic acid, are some of the parameters which are used for evaluating encapsulation systemcharacteristics.Chapter VII - Under circumstances of an adequate dietary content in ascorbic acid, theavailability of this vitamin for cells is still not ensured. The reason could be poor intestinalabsorption or impaired access to cells in different tissues because, owing to the markedhydrophylicity of this molecule, the rate of free diffusion across plasma membranes is low.