Storage of human plasma samples leads to alterations in the lipoprotein distribution of apoC-III and apoE

Abstract

The effect of frozen storage on lipoprotein distribution of apolipoprotein C-III (apoC-III) and apoE was investigated by measuring apoC-III and apoE by ELISA in HDL and apoB-containing lipoproteins of human plasma samples (n = 16) before and after 2 weeks of frozen storage (−20°C). HDLs were separated by heparin-manganese precipitation (HMP) or by fast-protein liquid chromatography (FPLC). Total plasma apoC-III and apoE levels were not affected by frozen storage. HDL-HMP apoC-III and apoE levels were significantly higher in frozen versus fresh samples: 7.7 ± 0.7 versus 6.7 ± 0.7 mg/dl (P < 0.05) and 2.0 ± 0.1 versus 1.2 ± 0.1 mg/dl (P < 0.001), respectively. HDL-FPLC apoC-III and apoE, but not triglyceride (TG) or cholesterol, levels were also higher in frozen samples: 12.0 ± 1.2 versus 7.5 ± 0.6 mg/dl (P < 0.001) and 2.7 ± 0.2 versus 1.6 ± 0.2 mg/dl (P < 0.001), respectively. Frozen storage led to a decrease in apoC-III (−17 ± 9%) and apoE (−19 ± 9%) in triglyceride-rich lipoprotein. Redistribution of apoC-III and apoE was most evident in samples with high TG levels. HDL apoC-III and apoE levels were also significantly higher when measured in plasma stored at −80°C.Our results demonstrate that lipoprotein distribution of apoC-III and apoE is affected by storage of human plasma, suggesting that analysis of frozen plasma should be avoided in studies relating lipoprotein levels of apoC-III and/or apoE to the incidence of coronary artery disease.

Keywords

• apolipoprotein
• atherosclerosis
• cholesterol
• coronary artery disease
• HDL
• remnants