Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo.
Ascorbate (ascorbic acid, vitamin C), in pharmacologic concentrations easily achieved in humans by i.v. administration, selectively kills some cancer cells but not normal cells. We proposed that pharmacologic ascorbate is a prodrug for preferential steady-state formation of ascorbate radical (Asc(*-)) and H(2)O(2) in the extracellular space compared with blood. Here we test this hypothesis in vivo. Rats were administered parenteral (i.v. or i.p.) or oral ascorbate in typical human pharmacologic doses ( approximately 0.25-0.5 mg per gram of body weight). After i.v. injection, ascorbate baseline concentrations of 50-100 microM in blood and extracellular fluid increased to peaks of >8 mM. After i.p. injection, peaks approached 3 mM in both fluids. By gavage, the same doses produced ascorbate concentrations of <150 microM in both fluids. In blood, Asc(*-) concentrations measured by EPR were undetectable with oral administration and always <50 nM with parenteral administration, even when corresponding ascorbate concentrations were >8 mM. After parenteral dosing, Asc(*-) concentrations in extracellular fluid were 4- to 12-fold higher than those in blood, were as high as 250 nM, and were a function of ascorbate concentrations. By using the synthesized probe peroxyxanthone, H(2)O(2) in extracellular fluid was detected only after parenteral administration of ascorbate and when Asc(*-) concentrations in extracellular fluid exceeded 100 nM. The data show that pharmacologic ascorbate is a prodrug for preferential steady-state formation of Asc(*-) and H(2)O(2) in the extracellular space but not blood. These data provide a foundation for pursuing pharmacologic ascorbate as a prooxidant therapeutic agent in cancer and infections.
Chen
Qi
Q
Molecular and Clinical Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Espey
Michael Graham
MG
Sun
Andrew Y
AY
Lee
Je-Hyuk
JH
Krishna
Murali C
MC
Shacter
Emily
E
Choyke
Peter L
PL
Pooput
Chaya
C
Kirk
Kenneth L
KL
Buettner
Garry R
GR
Levine
Mark
M
D000818:Animals; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D045604:Extracellular Fluid / Q000201:enzymology*; D005260:Female; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007263:Infusions, Parenteral; D008297:Male; D015394:Molecular Structure; D051381:Rats
D005609:Free Radicals; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid