Tohoku J. Exp. Med., 2003, 201 (1)

Quantitative Analysis of Apolipoprotein E Secretion by
Human Monocyte-Derived Macrophages in Culture

KAZUMI YAMATO, NAOKI TAMASAWA, HIROSHI MURAKAMI, JING-ZHI GUAN,
JUTAROU TANABE, JUN MATSUI, TOSHIHIRO SUDA¹ and MINORU YASUJIMA²

¹Third Department of Internal Medicine and ²Laboratory Medicine, Hirosaki University School of Medicine, Zaifu-5, Hirosaki 036-8562

Apolipoprotein E (apo E) has an impact on lipid metabolism and its production by macrophages is considered to play a protective role against atherosclerosis. Apo A-I stimulates secretion of apo E from macrophages. We developed a new method to evaluate the ability of human monocyte-derived macrophages to secrete apo E, and the effects of factors such as apo A-I were examined. Monocytes separated from peripheral venous blood were cultured. The levels of apo E in macrophage-conditioned medium were quantified by immunoblotting with an anti-human apo E antiserum conjugated with alkaline phosphatase. The basal levels of apo E secretion and the response to exogenous apo A-I in macrophages from 10 healthy volunteers were measured. Sufficient accuracy and sensitivity were confirmed and coefficient of variation of the method was 18±11% (n=10). It was confirmed that macrophage secreted apo E in a concentration-dependent manner in response to M-CSF and apo A-I. The average apo E concentration in the conditioned medium of macrophages from 10 healthy subjects was 30.9±14.7 ng/mg cell protein. After the addition of apoA-I, the average apo E concentration increased, by about 60%, to 49.4±29.7 ng/mg cell protein (p<0.05). There was a positive correlation between the apo A-I-induced increase and plasma LDL cholesterol levels (r=+0.54, p<0.05).

keywords —— atherosclerosis; macrophage; apolipoprotein E; apolipoprotein A-I

© 2003 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2003, 201, 47-54

Address for reprints: Dr. Naoki Tamasawa, M.D., Third Department of Internal Medicine, Hirosaki University School of Medicine, Zaifu-5, Hirosaki, 036-8562, Japan

e-mail: tmsw@cc.hirosaki-u.ac.jp