Two distinct uptake mechanisms for ascorbate and dehydroascorbate in human lymphoblasts and their interaction with...

Area of Science:

• Biochemistry
• Cell Biology
• Nutritional Science

Background:

• Cardiovascular complications in diabetes are a major cause of mortality.
• Low antioxidant levels, including vitamin C (ascorbic acid), are associated with these complications.
• Mechanisms of ascorbic acid and dehydroascorbic acid uptake in human lymphoid cells are not well understood.

Purpose of the Study:

• To investigate the uptake mechanisms of ascorbic acid (AA) and dehydroascorbic acid (DHA) in human lymphoblasts.
• To determine the influence of glucose on these uptake pathways.

Main Methods:

• Utilized HPLC mass assays to quantify AA and DHA uptake in human lymphoblasts.
• Implemented precautions to prevent AA oxidation and account for DHA instability.
• Investigated the effects of Na+, ouabain, phloretin, cytochalasin B, glucose, and phorbol esters on uptake.

Main Results:

• Human lymphoblasts possess distinct Na+-dependent (AA) and Na+-independent (DHA) uptake mechanisms.
• Glucose competitively inhibits DHA uptake (Ki = 2.2 mM) and, at high concentrations, reduces DHA uptake capacity.
• High glucose levels impair DHA uptake, potentially affecting cellular AA storage and recycling in diabetes.

Conclusions:

• Distinct transporters mediate ascorbic acid and dehydroascorbic acid uptake in human lymphoblasts.
• High glucose levels, characteristic of diabetes, acutely inhibit DHA uptake and chronically down-regulate its transport.
• Impaired DHA uptake in diabetes may compromise the cellular antioxidant defense system by limiting vitamin C recycling.