Abstract
Serum amyloid A protein (SAA) was prepared and purified by gel filtration from high density lipoprotein (HDL) obtained from the pooled plasma of patients with bronchiectasis and rheumatoid arthritis. Rabbits were repeatedly immunized with SAA, and the resulting antiserum IgG was rendered monospecific to apo SAA by absorption with normal human HDL and VLDL. Immunoblot analysis, using this monospecific anti-SAA, demonstrated the presence of apo SAA in HDL fractions obtained from the patients with acute myocardial infarction. Two-dimensional gel electrophoresis demonstrated the presence of 6 apo SAA isoforms with a molecular weight of approximately 12, 000, and two major isoelectric points of 6.3 and 5.9. Apo SAA in HDL fractions was determined during the course of acute myocaldial infarction. The apo SAA/apo A-I ratio increased sharply and peaked on the 3rd and 5th days after onset, with 0.90±0.58 (up to 1.68), and declined to an almost normal level on the 10th day. On the other hand, the decrease in plasma apo A-I/HDL-C and apo A-II/HDL-C ratio on the 3rd and 5th days was observed. And during the course, the apo SAA/apo A-I ratio in HDL correlated inversely with the plasma apo A-I/HDL-C and apo A-II/HDL-C ratio (r=-0.538; p<0.001, r=-0.566; p<0.001). In view of these results, the possibility that apo SAA as a constituent of HDL particles might actually change places with apo A-I and apo A-II was suggested. We conclude that these apo SAA-enriched HDL particles, i. e., a remodeled apolipoprotein structure, not only yield abnormal HDL metabolism but also may affect the metabolism of the other lipoproteins.
