Evaluation of a method for study of kinetics of autologous apolipoprotein A-I.

Apolipoprotein A-I (apoA-I) participates in transport of plasma cholesterol. Concentrations of apoA-I depend on the balance between production and fractional clearance. To elucidate factors influencing apoA-I levels, accurate estimates of apoA-I turnover rates may be valuable. We describe a method for isolation of autologous apoA-I and its use in turnover studies. Free apoA-I was isolated from high density lipoproteins (HDL) by treatment with guanidine hydrochloride. This free apoA-I was radioiodinated with 131I and injected into eleven subjects simultaneously with HDL labeled with 125I. Plasma die-away curves of free apoA-I (131I) and HDL apoA-I (125I) were compared; fractional clearance rates averaged 0.256 +/- 0.019 (SEM) and 0.254 +/- 0.017 pools/day, respectively. Although slight differences between the two die-away curves were noted for some of the patients, the differences were relatively small; for the group as a whole, average fractional catabolic rates were not significantly different. Thus, by isolation of autologous apoA-I under the conditions described, free apoA-I seemingly provides a valid method for estimating apoA-I turnover.