Metabolism of the serum amyloid A proteins (SSA) in high-density lipoproteins and chylomicrons of nonhuman primates (vervet monkey).

Serum amyloid protein (SAA) has been reported to be an apoprotein of high-density lipoprotein (HDL), but little is known concerning its metabolism. In this study, apoSAA was induced in nonhuman primate plasma HDL and thoracic duct lymph chylomicra by overnight chair restraint of the animals. There was a 3-6-fold increase in plasma HDL apoSAA in chair-restrained animals when compared with caged (control) animals. Lymph chylomicrons of chaired animals also contained significant amounts (approximately 20% of total protein) of apoSAA. For study of the metabolism of HDL apoSAA, animals were given injections of 131I-labeled lymph chylomicrons and autologous 125I-HDL. HDL were isolated from the plasma of recipient animals between 1 minute and 5 days after injection, and the specific activity of the apoSAA was determined. The turnover of apoSAA from plasma was biphasic, the initial phase having a t1/2 (0.39-0.48 days) similar regardless of the source (chylomicrons versus HDL) of the injected dose. The second phase of the turnover was significantly faster (t1/2 = 2.5 days) for apoSAA of 125I-HDL origin than that of 131I-chylomicron origin (t1/2 = 4.3 days). This difference also was suggested by the fractional catabolic rates (FCR) of 125I-HDL and 131I-chylomicron apoSAA (1.02 versus 0.74 d-1, respectively). From these studies it was concluded that 1) apoSAA can be rapidly induced in plasma HDL and lymph chylomicrons of nonhuman primates by chair restraint; 2) HDL apoSAA is catabolized more rapidly than HDL apoA-I and apoA-II; 3) and the catabolic rate of HDL apoSAA may be determined, in part, by its lipoprotein origin (chylomicrons versus HDL).