Distribution of Ascorbic Acid, Metabolites and Analogues in Man and Animals

Hornig, D.

doi:10.1111/j.1749-6632.1975.tb29271.x

Cited by 412 publications

(198 citation statements)

References 43 publications

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“…Under cellular conditions, the repair of vitamin E chromanoxyl radical will not only be dependent on the absolute rate of electron transfer from the electron donors cited, but also on the actual concentrations of the reactants. The steadystate concentration of O~-in hepatocytes has been estimated to be about 10-11M [21], a value decidedly lower than the intracellular concentration of ascorbate (-3-4 x 10 -4 M) [22]. However, the biological relevance of the repair of phenoxyl radicals by O~-reported here cannot be assessed on the questionable assumption that the distribution of O~--or any other free radical species -is homogeneous within the cell.…”

Section: Discussionmentioning

confidence: 59%

Pulse radiolysis study on the reactivity of Trolox C phenoxyl radical with superoxide anion

1989

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The reaction between the phenoxyl radical of Trolox C, a water-soluble vitamin E analogue, and superoxide anion radical was examined by using the pulse radiolysis teelmique. The results indicate that the Trolox C phenoxyl radical may undergo a rapid one-electron transfer from superoxide radical [k=(4.5+0.5)x 108 M-Ls -1] to its reduced form. This finding indicates that superoxide radical might play a role in the repair of vitamin E phenoxyl radical.

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Section: Discussionmentioning

confidence: 59%

Pulse radiolysis study on the reactivity of Trolox C phenoxyl radical with superoxide anion

1989

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“…First, vitamin C concentrations in tumours are, on the average, 3 times higher than those in surrounding normal tissues (Langemann et al, 1989), presumably because tumour cells use membrane glucose transporters to internalize ascorbate (Agus et al, 1999). Secondly, tissue vitamin C concentrations in guinea pigs and humans exceed those in plasma by as much as 2 orders of magnitude (Hornig, 1975). Vitamin C may have a favourable therapeutic index, despite the high concentrations needed for cytotoxicity, if it accumulates in tumours and lacks systemic toxicity.…”

Section: Discussionmentioning

confidence: 99%

Cytotoxicity of ascorbate, lipoic acid, and other antioxidants in hollow fibre in vitro tumours

Casciari¹,

Riordan²,

Schmidt³

et al. 2001

Br J Cancer

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Summary Vitamin C (ascorbate) is toxic to tumour cells, and has been suggested as an adjuvant cancer treatment. Our goal was to determine if ascorbate, in combination with other antioxidants, could kill cells in the SW620 hollow fibre in vitro solid tumour model at clinically achievable concentrations. Ascorbate anti-cancer efficacy, alone or in combination with lipoic acid, vitamin K 3 , phenyl ascorbate, or doxorubicin, was assessed using annexin V staining and standard survival assays. 2-day treatments with 10 mM ascorbate increased the percentage of apoptotic cells in SW620 hollow fibre tumours. Lipoic acid synergistically enhanced ascorbate cytotoxicity, reducing the 2-day LC 50 in hollow fibre tumours from 34 mM to 4 mM. Lipoic acid, unlike ascorbate, was equally effective against proliferating and nonproliferating cells. Ascorbate levels in human blood plasma were measured during and after intravenous ascorbate infusions. Infusions of 60 g produced peak plasma concentrations exceeding 20 mM with an area under the curve (24 h) of 76 mM h. Thus, tumoricidal concentrations may be achievable in vivo. Ascorbate efficacy was enhanced in an additive fashion by phenyl ascorbate or vitamin K 3 . The effect of ascorbate on doxorubicin efficacy was concentration dependent; low doses were protective while high doses increased cell killing.

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“…Ascorbate concentrations in plasma are about 50 mM (Hornig, 1975), while the concentration in neurons is estimated to be 10 mM and levels of 1 mM in glia (Rice & Russo-Menna, 1998). The brain has a relative high rate of oxidative metabolic activity and low levels of protective antioxidant enzymes, for example, catalase and GSH peroxidase (Evans, 1993).…”

Section: Cellular Antioxidant Defencementioning

confidence: 99%