Accumulation of Dietary Antioxidants in Normal and Cancer Cells

Some studies have shown that tumor cells accumulate more vitamin C than normal tissue following

Table 11.1 Accumulation of D-a-tocopheryl succinate (a-TS) in human cervical cancer cells (HeLa) and normal human fibroblasts after 24 hours of treatment with a-TS

Concentrations of a-TS Accumulation of a-TS (^g/mg protein)

Fibroblasts HeLa cells

Experiment 1 1.07 1.23

Experiment 1 1.38 1.87

Experiment 2 1.04 0.93

a-TS was extracted in hexane and a-tocopheryl acetate was used as an internal standard to determine the efficiency of extraction procedure. The a-TS levels for 24 hours were similar in both HeLa cells and normal fibroblasts. Each measurement was repeated twice and they were reproducible within the same experiment (43).

the administration of radioactively labeled vitamin C into animals carrying transplanted tumor (44). A similar observation was made earlier in patients with leukemia (37). Thus, increased accumulation of vitamin C by tumor cells following high-dose supplementation may be responsible for its anticancer activity. Our results show that human cervical cancer cells (HeLa cells) and normal human fibroblasts in culture accumulate similar levels of a-TS within 24 hours of treatment (Table 11.1). This suggests that tumor cells acquired increased sensitivity to a-TS for growth-inhibition, differentiation, and/or apoptosis during transformation. The relative uptake of other antioxidant micronutrients such as retinoids and carotenoids by normal and cancer cells in culture has not been studied.

The analysis of the basal levels of antioxidant micronutrients in human tumors and their adja cent normal tissues shows that the levels of individual antioxidant micronutrients in tumor tissue may be higher, lower, or the same in comparison to those found in the adjacent normal tissues (4548). The exact reasons for these variations are not known. Several factors may account for the above results. They include differences in the dietary intake, vascularity, and uptake and subsequent intracellular metabolism of antioxidant micronu-trients between normal and cancer cells.

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