Ascorbic acid inhibition

Inhibition of Nitrosamine Formation. Nitrites can react with secondary amines and A/-substituted amides under the acidic conditions of the stomach to form /V-nitrosamines and A/-nitrosamides. These compounds are collectively called N-nitroso compounds. There is strong circumstantial evidence that in vivo A/-nitroso compounds production contributes to the etiology of cancer of the stomach (135,136), esophagus (136,137), and nasopharynx (136,138). Ascorbic acid consumption is negatively correlated with the incidence of these cancers, due to ascorbic acid inhibition of in vivo A/-nitroso compound formation (139). The concentration of A/-nitroso compounds formed in the stomach depends on the nitrate and nitrite intake. 

To prevent oxidation of nitrous oxide to nitrogen tetraoxide, excess ascorbic acid must be used. Douglas et al (1978) has reviewed the numerous literature reports on ascorbic acid inhibition of nitrosamine formation in amine-nitrite systems. 

Ascorbic acid has been found to be the most effective and useful inhibitor of amine nitrosation [23]. Ascorbic acid inhibits the formation of DMN from oxytetracycline and nitrite, and also from aminophenazone (aminopyrine) and nitrite. Tannins are present in a variety of foods, competing with secondary amines for nitrite and thus leading to a reduction in the amount of nitrosamine formed [24]. 

The oxidation of DOPA and adrenaline to dopachrome and adrenochrome, respectively, by a horse radish peroxidase-H202 system has been reported by Herzmann.29,30 The oxidation process was activated by trace quantities of caffeic acid, its esters, and related compounds.30 Ascorbic acid inhibited the oxidation of adrenaline by this enzyme in the initial stages of the reaction, but later had a stimulatory effect.30... 

Ascorbic acid inhibits light-induced yellowing for a finite time, 1 to 2 hours when irradiated with near-uv light with an intensity of 9.2 mW/cm2 (6). This limitation has been attributed in part to photooxidation of ascorbic acid. In addition to air oxidation, ascorbic acid is oxidized by photochemically produced peroxyl radicals, superoxide radical anion and singlet oxygen (27,28). If ascorbic acid is to be an effective inhibitor of light-induced yellowing it s oxidation must be slowed. 

Holtz G, Bresnick E. 1988. Ascorbic acid inhibits the squamous metaplasia that results from treatment of tracheal explants with asbestos or benzo[a]pyrene-coated asbestos. Cancer Lett 42 23-28. 

Kimura, K. and Sidhu, A., Ascorbic acid inhibits 125I-SCH 23982 binding but increases the affinity of dopamine for D1 dopamine receptors,. Neurochem., 63[6], 2093, 1994. 

Mirvish, S.S. Ascorbic acid inhibition of A-nitroso compound formation in chemical, food and biological systems in Inhibition of tumor induction and development, edited by M.S. Zedeck and M. Lipkin, Plenum Publishing, New York, NY (1981) 101-126. 

When protein was low in cystine, the ascorbic acid inhibited LAL formation, but ascorbic acid was a less effective inhibitor at higher concentrations. The argument would suggest that at low concentration most of the cystine was reduced to cysteine and at... 

Ascorbic acid inhibits the oxidation quite efficiently for a long period and also neutralizes free nitrites which are a substrate for carcinogens. Vitamin C acts as a potent s)mergist in the presence of a-tocopherol and spares this antioxidant. 

Does Ascorbic Acid Inhibit the Sjrnthesis of Cortical Hormones . 87... 

Ascorbic acid inhibits catalase in concentrations as low as 2 X 10 moll. Very low concentration of Cu " " ions accelerates the rate of inhibition. The inhibition of ascorbic acid to catalase occurs in the presence of ions. The activity of catalase can be monitored by the decrease of H2O2 substrate or increase of O2. For fluorimetric detection of H2O2, the decrease in fluorescence of scopoletin or the increase in fluorescence of diaceyldichlorofluorescein upon reaction with H2O2 are preferably monitored. 

Monteiro, H. P., Ivaschenko, Y., Fischer, R., and Stem, A., 1993, Ascorbic acid inhibits protein tyrosine phosphatases in NIH 3T3 cells expressing human epidermal growth factor receptors, Int. J. Biochem. 25 1859-1864. 

Macrophages from mouse bone marrow showed increased PGE production when incubated with ascorbic acid (Siegel and Morton, 1984). In contrast, in renal medulla, ascorbic acid inhibited PG synthesis (Zenser and Davis, 1978). 

Animal studies to date have failed to show consistent evidence of an anticancer action of vitamin C. Holtz and Bresnick (1988) reported that ascorbic acid inhibited the squamous metaplasia that results from the treatment of tracheal explants with asbestos or benzo(a)pyrene-coated asbestos. Liehr et al. (1989) found that vitamin C could inhibit estrogen-induced renal carcinogenesis in male ham-... 

Redox phenomena seem to modulate activity of the NMDA subtype of glutamate receptors. Ascorbic acid inhibits binding of [ H]glutamate to the NMDA-receptor complex and impedes NMDA-gated currents in isolated neurons, whereas dithiothreitol-like reductants enhance NMDA-induced currents (Majewska et aL, 1990). The ability of reductants to alter function of the NMDA receptors is prevented by oxidation. This inhibitory effect of ascorbic acid on NMDA receptors may act to protect against excitotoxic insults to the neurons (Section 6). 

Indeed, there are some suggestions that ascorbic acid inhibits the glycation of hemoglobin by competition in vivo (Stolba et aL, 1987 Davie et aL, 1992). Ascorbic acid supplementation in nondiabetic individuals increases HBAi, a measure... 

Jialal, I., Vega, G. L., and Grundy, S. M., 1990, Physiologic levels of ascorbic acid inhibit the oxidative modification of LDL, Atherosclerosis 82 185-191. 

Kaya, R Belin, S. Bourgeois, R Micaleff, J. Blin, O. Fontes, M. 2007. Ascorbic acid inhibits PMP22 expression by reducing cAMP levels. Neuromuscul. Disord. 17(3) 248-253. 

Treatment of 5,6-0-isopropylidene-L-ascorbic acid with alkyl halides and NaHCOs in DMSO gave alkylation only at 0-3 the products were then hydrolysed to give 3-0-alkyl-ascorbic acids as free radical scavengers.78 The crown ether type of derivatives (68) of isopropylidene-L-ascorbic acid could be made by interaction with the appropriate ditosylate and K2CO3 in DMF the reaction was unsuccessful in the case of (68, n=2).79 The mechanism by which 3-0-dodecylcarboxymethyl-ascorbic acid inhibits lipid peroxidation. 

---