Ascorbic acid factors affecting

In addition to the well-known iron effects on peroxidative processes, there are also other mechanisms of iron-initiated free radical damage, one of them, the effect of iron ions on calcium metabolism. It has been shown that an increase in free cytosolic calcium may affect cellular redox balance. Stoyanovsky and Cederbaum [174] showed that in the presence of NADPH or ascorbic acid iron ions induced calcium release from liver microsomes. Calcium release occurred only under aerobic conditions and was inhibited by antioxidants Trolox C, glutathione, and ascorbate. It was suggested that the activation of calcium releasing channels by the redox cycling of iron ions may be an important factor in the stimulation of various hepatic disorders in humans with iron overload. 

One example is the known interference by reducing compounds that affect the chemical conversion of substrate to a colored indicator. This is especially true for the tetrazolium assays (Ulukaya, Colakogullari, and Wood 2004 Chakrabarti et al. 2000 Pagliacci et al. 1993 Collier and Pritsos 2003). The growing list of interfering compounds includes ascorbic acid and sulfhydryl reagents such as glutathione, coenzyme A, dithiothreitol, etc. Similar interferences by compounds that affect the oxidation and reduction chemistry of cells are likely to cause artifacts with the resazurin reduction assay. Assays that measure markers of metabolism also can be influenced by the pH of the culture medium and other factors that may stimulate or stress the metabolic rates of cells. 

Whether this increased oxalate excretion has consequences in terms of stone formation depends very much on the dosage and duration of treatment. In a small study in healthy individuals short-term, high-dose ascorbic acid (4 g in 5 days) did not affect the risk factors associated with calcium oxalate kidney stone formation (8). A prospective study of the association between doses of pyri-doxine and ascorbic acid and the risk of symptomatic kidney stones was undertaken in a large cohort of US nurses. Ascorbic acid was not associated with a higher risk of stone formation (25). 

Other factors in the diet have also been found to modify the effect of phosphorus on iron and zinc metabolism. One such factor is ascorbic acid. Peters, et al. (35) observed that when human subjects were fed a solution of iron chloride, they absorbed very little iron if ascorbic acid was not present in the solution (Table IV). In fact, if ascorbic acid was not present, absorption of iron was so low it was difficult to tell whether dietary factors, such as phosphorus, affected the absorption of iron. However, ascorbic acid may also counteract the effect of dietary phosphorus on the absorption of nonheme iron. Investigators have demonstrated that the addition of ascorbic acid to a diet counteracted the effect of the phosphoprotein in egg yolk on iron absorption (17. 18). 

Many factors have been identified as influencing the absorption of iron. In addition to changes within the host which affect iron absorption and the form of the iron salt, various dietary constituents which may increase or decrease iron bioavailability have also been studied. As diets become more plant product oriented and less iron is provided by animal products, the occurrence of these other dietary factors is also likely to change. Factors which have been implicated include the following amount of heme iron, ascorbic acid level, dietary protein,... 

The influence of ascorbic acid on tyrosine metabolism in man and intact animals has been discussed under alkaptonuria and tyrosinosis q.v.). Ty-rosyluria, also called hydroxyphenyluria, i.e., the excretion of p-hydroxy-phenyl compounds in the urine, can be affected by factors other than ascor-... 

Lll. Lewis, W. R., Chiang, J. L., and Gross, S., Factors affecting the determination of bound ascorbic acid in blood serum or animal tissues. Arch. Biochem. Biophys. 89, 21-26 (1960). 

Factors Affecting Blood Levels of Ascorbic Acid and Glutathione. 71... 

Watts, B. M., and Wong, R. 1951. Some factors affecting the antioxidant behavior of ascorbic acid with unsaturated fats. Arch. Biochem. 30, 110. 

Bendich, A., and Cohen, M., 1990, Ascorbic acid safety Analysis of factors affecting iron absorption,... 

Many factors that affect calcium absorption have a similar effect on the absorption of iron. Absorption is promoted by ascorbic acid possibly because it reduces ferric to ferrous iron. Absorption is augmented in iron deficiency and depressed when stores are increased. Thus when, after a haemorrhage, erthyropoiesis is accelerated, iron absorption is enhanced and, under conditions in which erythropoiesis is reduced, e.g. starvation or descent from a high altitude, absorption is reduced. 

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