Metabolism of ascorbic acid and ascorbic-2-sulfate in man and the subhuman primate

Area of Science:

• Biochemistry
• Comparative Physiology
• Nutritional Science

Background:

• Humans do not catabolize ascorbate (vitamin C) to carbon dioxide (CO2).
• Monkeys catabolize ascorbate and ascorbate sulfate to CO2 when administered orally.
• Scurvy development time is similar in humans and monkeys.

Purpose of the Study:

• To investigate the comparative metabolism, storage, and utilization of ascorbate in humans and monkeys.
• To understand the implications of differing ascorbate metabolic pathways on scurvy development.

Main Methods:

• Oral administration of ascorbate and ascorbate sulfate to monkeys.
• Isotope studies using labeled ascorbic acid (ascorbic-1-14C and ascorbic-6-14C) in monkeys.
• Intravenous administration of ascorbic acid to monkeys.
• Monitoring of scurvy signs and blood ascorbate levels.

Main Results:

• Monkeys catabolize orally administered ascorbate and ascorbate sulfate to CO2.
• Despite different metabolic pathways, scurvy onset is similar in humans and monkeys.
• Only a small fraction of labeled ascorbate or ascorbate sulfate equilibrates with body stores in monkeys.
• Monkeys require 250 mg/day of ascorbate to resolve scurvy and normalize blood levels.
• Intravenously administered ascorbic acid equilibrates fully with monkey ascorbate pools.
• Ascorbate sulfate is a urinary metabolite in monkeys fed labeled ascorbic acid.

Conclusions:

• Comparative ascorbate storage, utilization rate, and metabolism appear similar between humans and monkeys.
• The catabolism of ascorbate to CO2 in monkeys does not significantly alter the rate of scurvy development compared to humans.
• Published ascorbic acid requirements align with experimental findings, indicating a need for substantial dietary intake.