Fig. 6.

Functional analysis of flash-frozen HDL. HDL was isolated from the serum of four healthy donors by density gradient ultracentrifugation and pooled for functional analysis. HDL in the presence or absence of cryoprotectants (10% glycerol or 5% sucrose) was either frozen directly at −70°C or flash-frozen with liquid nitrogen and subsequently stored at −70°C. Aliquots were analyzed for their ability to promote cholesterol efflux (A) or for their HDL associated paraoxonase 1 activity (B). The dashed lines indicate the control value measured right after the isolation of HDL and were used for normalization to 100%. The labeling on the x axis indicates weeks of storage. Results represent the combined analysis of two independent experiments performed in triplicate. *P < 0.05 versus control.