Comparative uptake of α‐ and γ‐tocopherol by human endothelial cells

The intake of γ‐tocopherol by North Americans is generally higher than that of α‐tocopherol. However, the levels of α‐tocopherol in human blood have consistently been shown to be higher than those of γ‐tocopherol suggesting differential cellular retention of the two tocopherol forms. We sought to resolve this question by studying tocopherol metabolism by human endothelial cells in culture. The time‐ and dose‐dependent uptake of γ‐tocopherol by endothelial cells was similar to that of α‐tocopherol. To determine the comparative uptake between α‐ and γ‐tocopherol, we adopted two approaches in which cells were enriched with either increasing concentrations of an equimolar mixture of α‐ and γ‐tocopherol; or cells were enriched with a fixed concentration of tocopherols in which the α to γ ratio was varied. Our results indicated that there was a preferential uptake of γ‐tocopherol by the cells. When cells were enriched with either α‐ or γ‐tocopherol and the disappearance of individual tocopherols was monitored over time, γ‐tocopherol exhibited a faster rate of disappearance. The faster turnover of γ‐tocopherol can explain the discrepancy between high intake and low retention of γ‐tocopherol in man.