Microsomal triglyceride transfer protein-mediated transfer of β-carotene from donor to acceptor vesicles in vitro.

Dietary β-carotene is the most abundant vitamin A precursor. Once absorbed by the enterocytes, the provitamin A carotenoid can either be cleaved into retinoids (vitamin A and its derivatives) or incorporated in its intact form within chylomicrons to be distributed throughout the body for utilization and/or storage by other tissues. From the liver, together with endogenous lipids, intact β-carotene can also be incorporated within very low-density lipoprotein/low-density lipoprotein (VLDL/LDL) for transport to other tissues and organs. Microsomal triglyceride transfer protein (MTP) is a key regulator of lipoprotein biosynthesis in intestine and liver as it facilitates the incorporation of dietary and endogenous lipids into nascent lipoproteins. MTP is also critical for transferring β-carotene into lipoprotein particles for secretion. Here, we present an in vitro method to assess the transfer of β-carotene by MTP from donor to acceptor vesicles. This transfer can be assessed by precipitating donor vesicles and measuring amounts of β-carotene transferred to acceptor vesicles. The levels of transferred β-carotene are quantified by HPLC analysis and intrinsic fluorescence of β-carotene. This chapter demonstrates the feasibility of this method which is also useful to study the role of MTP for incorporation of other carotenoids that are known to be carried within VLDL/LDL and chylomicrons for organ distribution.