Hypothesis II: The majority of VLDL-apoB48 remnants in postprandial plasma are derived from the liver, not from the intestine.

We have long thought that remnant lipoproteins (RLP) in the postprandial plasma contain CM remnants (exogenous remnants; RLP-apoB48) and VLDL remnants (endogenous remnants; RLP-apoB100) of different origin, i.e. produced in the intestine and liver, respectively. However, the majority of CM remnants incorporated into liver from the circulation are degraded in liver and may be reused for the remodeling of VLDL. Namely, the most of the apoB48 in CM remnants are smoothly incorporated into the liver after fat intake along with lipids and other apolipoproteins via the LDL receptor and LDL-receptor-related protein (LRP). Subsequently, apoB48 may be reconstituted in VLDL as VLDL apoB48 through an essential physiological pathway similar or the same to that of VLDL apoB100 formation in the liver and secreted into the circulation as VLDL apoB48 to form their remnants. Because those particles are newly reconstituted in liver as a portion of VLDL, we propose that both RLP-apoB100 and RLP-apoB48 are endogenous VLDL remnants produced in liver after fat intake. Also we predict the presence of a new pathway for the formation of VLDL apoB48 along with VLDL apoB100 in liver in humans similar in mice and rats.