Metabolism of apolipoprotein C-I in normolipoproteinemic human subjects

Labeling of apolipoprotein C-I by the Bolton and Hunter reagent allowed a study of the kinetics of this peptide in normolipidemic human volunteers. After its intravenous injection the appearance of radioactivity of the labeled apoprotein was followed in plasma, lipoprotein fractions, and urine for 15 days. Apolipoprotein C-I was quickly associated with HDL and to a smaller extent with VLDL in in vitro and in vivo incubation. Kinetic parameters of apolipoprotein C-I were compared with those of apo A-I. Fractional catabolic rates are respectively 0.422 +/- 0.044 vs 0.240 +/- 0.003 pools/day, residence times through the whole system 3.24 +/- 0.27 vs 6.31 +/- 0.27 days and production rates 1.79 +/- 0.18 vs 13.2 +/- 2.1 mg/kg X day. Two explanations for these differences are proposed.