β‐Carotene transport in human lipoproteins. Comparisons with a‐tocopherol

AbstractThe purpose of this study was to investigate the temporal relationships of the transport of β‐carotene in human lipoproteins. We administered 60 mg β‐carotene with breakfast to nine fasting subjects, then blood samples were collected at intervals of up to 75 h, lipoproteins were isolated, and β‐carotene was quantitated. β‐Carotene concentrations in chylomicrons and very low density lipoproteins (VLDL) peaked at 6 and 9 h, respectively. Nonetheless, at all time points the majority of plasma β‐carotene was contained in low density lipoproteins (LDL), while high density lipoproteins (HDL) carried a smaller portion (at 24 h, 73±8% in LDL as compared with 23±5% in HDL). In three subjects, transport of β‐carotene was compred with the results of earlier studies on the transport of stereoisomers of α‐tocopherol. Unlike plasmaRRR‐α‐tocopherol concentrations, which are maintained by the preferential incorporation ofRRR‐α‐tocopherol into VLDL by the liver, β‐carotene increased and decreased in VLDL similarly toSRR‐α‐tocopherol, a stereoisomer whose concentrations are not maintained in plasma. In conclusion, β‐carotene is primarily transported in the plasma in LDL, but its incorporation by the liver into lipoproteins does not appear to be enhanced.