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pharmacologic ascorbate as a prooxidant drug for therapeutic use.

Recently we reported that pharmacologic ascorbic acid concentrations produced H2O2 concentrations of ≥25 μM, causing cancer cell death in vitro

We found that H2O2 concentrations generated in vivo were those that caused cancer cell death in vitro

When ascorbate was given parenterally, Asc•−, the product of a loss of one electron from ascorbate, was detected preferentially in extracellular fluid compared with blood

Asc•− generation in extracellular fluid depended on the ascorbate dose and the resulting concentrations

With i.v. administration of ascorbate, Asc•− concentrations were as much as 12-fold greater in extracellular fluid compared to blood and approached 250 nM

In blood, such Asc•− concentrations were never produced and were always <50 nM

These data are all consistent with the hypothesis that pharmacologic ascorbate concentrations in vivo serve as a prodrug for selective delivery of H2O2 to the extracellular space

After oral ingestion, control of intracellular and extracellular ascorbate concentrations is mediated by three mechanisms: intestinal absorption, tissue transport, and renal reabsorption

intestinal absorption, or bioavailability, declines at doses >200 mg

corresponding to plasma concentrations of ≈60 μM

at approximately this concentration, the ascorbate tissue transporter SVCT2 approaches Vmax, and tissues appear to be saturated

also at ≈60 μM, renal reabsorption approaches saturation, and excess ascorbate is excreted in urine

Parenteral administration bypasses tight control

When tight control is bypassed, H2O2 forms in the extracellular space

in vivo validation of ascorbate as a prodrug for selective H2O2 formation

Temporarily bypassing tight control with parenteral administration of ascorbate allows H2O2 to form in discrete time periods only, decreasing likelihood of harm, and provides a pharmacologic basis for therapeutic use of i.v. ascorbate

H2O2 formation results in selective cytotoxicity

Tumor cells are killed with exposure to H2O2 for ≤30 min

In vitro, killing is mediated by H2O2 rather than Asc•−

In addition to cancer treatment, another potential therapeutic use is for treatment of infections. H2O2 concentrations of 25–50 μM are bacteriostatic

virally infected cells may also be candidates