Background: Alteration in the protein composition of high-density lipoprotein (HDL) has been proposed as a mechanism for the development of coronary heart disease (CHD). In HDL, an increase in serum amyloid A protein (SAA) accompanying the decrease in apolipoprotein A-I (apoA-I) has been found during the acute inflammation period. However, whether this phenomenon persists in CHD patients, a disease related to inflammation, is unknown. The purpose of the present study was to explore the relationship between SAA and apoA-I in HDL isolated from CHD patients.
Methods: Overall, 98 patients with confirmed stable CHD and 90 control subjects matched for age and gender were enrolled in this case-control study. Potassium bromide (KBr) density gradient ultracentrifugation was used to isolate HDL from plasma. The levels of SAA and apoA-I in the HDL samples were detected by enzyme-linked immunosorbent assay kits. Pearson's correlation and general linear models were used in the analysis.
Results: Compared with controls, patients with CHD had a significant decrease in the amount of apoA-I ((14.21 ± 8.44) µg/ml vs. (10.95 ± 5.95) µg/ml, P = 0.003) in HDL and a significant increase in the amount of log SAA (1.21 ± 0.46 vs. 1.51 ± 0.55, P < 0.00001). Differences were independent of age, body mass index (BMI), HDL cholesterol (HDL-C), and other factors. An independently and statistically significant positive correlation between log SAA and apoA-I in HDL was observed only in the CHD group (β = 2.0, P = 0.026). In the general linear model, changes in log(SAA), age, age2, gender, BMI and HDL-C could explain a statistically significant 43% of the variance in apoA-I.
Conclusions: This study provides direct evidence for the first time that there was an independent positive correlation between log SAA and apoA-I in the HDL of CHD patients, indicating the alteration of protein composition in HDL. However, the question of whether this alteration in HDL is associated with impairment of HDL functions requires further research.