Vitamin C recycling and function in human monocytic U-937 cells

Area of Science:

• Cell Biology
• Biochemistry
• Nutritional Science

Background:

• Ascorbic acid (vitamin C) plays crucial roles in cellular functions.
• Understanding the uptake and intracellular processing of vitamin C is vital for cellular health.
• Monocytic cells like U-937 are key players in immune responses and cellular metabolism.

Purpose of the Study:

• To investigate the uptake, recycling, and functional significance of ascorbic acid in U-937 monocytic cells.
• To elucidate the mechanisms governing dehydroascorbic acid and ascorbate transport into cells.
• To determine the role of intracellular ascorbate in cellular redox processes.

Main Methods:

• Cultured U-937 monocytic cells were used to study vitamin C metabolism.
• Experiments involved measuring the uptake of dehydroascorbic acid and ascorbate.
• Cellular redox activity was assessed by monitoring electron transfer to extracellular ferricyanide.

Main Results:

• Dehydroascorbic acid was more efficiently taken up and reduced to ascorbate than ascorbate itself.
• Ascorbate uptake was sodium- and energy-dependent, while dehydroascorbic acid utilized glucose transporters.
• Intracellular ascorbate significantly enhanced electron transfer to ferricyanide, independent of glutathione (GSH) or NADPH under physiological conditions.

Conclusions:

• U-937 cells effectively accumulate intracellular ascorbate from extracellular dehydroascorbic acid via a non-GSH/NADPH-dependent pathway.
• The accumulated intracellular ascorbate acts as a primary electron donor for extracellular redox reactions.
• This study highlights a unique mechanism for vitamin C utilization in monocytic cells, relevant to cellular defense and metabolism.