Vitamin E is delivered to cells via the high affinity receptor for low-density lipoprotein

The high affinity receptor for low-density lipoprotein (LDL) is demonstrated to function as a mechanism for delivery of vitamin E to cells. After incubation for 24 h with lipoprotein-depleted serum (which induces LDL receptor synthesis), and then incubation for 24 h with an increasing amount of LDL (from 10 to 250 micrograms of protein per ml), the tocopherol contents of normal fibroblasts increased in a saturable fashion from 19 to 103 ng of tocopherol per mg cell protein. In contrast, similarly incubated LDL receptor-negative fibroblasts (from a patient with the homozygous form of familial hypercholesterolemia) only increased from 18 to 39 ng of tocopherol per mg. Estimation of the amount of LDL degraded from the cellular tocopherol uptake by normal cells yielded values virtually identical to the actual values of protein degradation as measured using 125I-LDL.