Dehydroascorbic acid is the principal form for the cellular uptake by blood cells of vitamin C. Since previous studies from this laboratory had shown a higher content of ascorbic acid and dehydroascorbic acid (DHA) in chronic lymphocytic leukemia (CLL) lymphocytes when compared to their normal counterparts, DHA uptake was characterized using these cells. The affinities of CLL and normal lymphocytes for DHA uptake were similar, as demonstrated by the Km values of 3.7 and 3.5 mm, respectively. Differences were found in other kinetic constants of DHA uptake. The Vmax for normal lymphocytes, 634 µmol/liter cell H2O/min, was approximately twice that of CLL cells, 392 µmol/liter cell H2O/min. In addition, the initial velocity and the maximal DHA uptake by normal lymphocytes were greater than that of CLL lymphocytes. These differences were not simply a reflection of lymphocyte subsets since CLL B-cells demonstrated lower uptake rates than did normal B-cells whereas CLL T-cells were similar to their normal counterparts. The alterations appear to be specific for the leukemic B-cell since they were not shared by neoplastic cells from two patients with T-cell CLL. When analyzed in light of the 3-fold greater cellular DHA and ascorbic acid content in B-cell CLL as compared to normal lymphocytes, these kinetic parameters support the occurrence of a concentration-dependent transport system for DHA. We conclude that the DHA uptake properties of CLL lymphocytes of B-cell origin serves to distinguish this lineage from T-cell CLL or normal lymphocytes.
This work was supported by NIH Grant CA28376.