Quantifying Lipoprotein Secretion in Mice

After an overnight fast, mice were given an intraperitoneal injection of 200 µCi of [³⁵S] methionine/cysteine protein labeling mix (NEG772002MC, Perkin Elmer) combined with 1,000 mg/kg pluronic F127 poloxamer-407 (BASF, P2443, Sigma-Aldrich) to inhibit lipoprotein clearance from plasma as previously described^{58 (link)}. Triglyceride secretion was calculated using plasma collected at 2 h post-injection. Total plasma apoB100 and apoB48 secretion was determined by taking 2 µl of plasma from the 2 h time point and separating the proteins by SDS-PAGE gel electrophoresis followed by densitometric quantification using ImageJ. Plasma from Apobec1^−/− mice (which express only apo B100) was used as control to identify apoB100 and apoB48 bands^{59 (link),60 (link)}.