Freezing does not affect the susceptibility of low density lipoprotein (LDL) to oxidation

The aims of this study were to determine the effect of sample freezing on the susceptibility of LDL to oxidation and to determine mtra-assay and intra-subject variability. LDL oxidative susceptibility was determined by the analysis of thiobarbituric acid reactive substances (TBARSl generated during incubation of LDL with Cu²⁺. Blood was drawn from healthy postmenopausal subjects and separated into two fresh aliquots (FRIA and FR1B) which were immediately assayed for LDL oxidation susceptibility, while a third aliquot was frozen (FROZ) for 2-4 weeks at -30°C before analysis Subjects returned 2-4 weeks later for a second blood draw and LDL oxidation was measured the same day (FR2) LDL oxidation values were 28 4 ± 10 0. 27 6 ± 7 n. 32 0 ± 69 0 and 29.7 ± 03 {mean ± SD. n - 8) for FRIA, FRIB, FRO/ and FR2 respectively There were no significant differences among treatments. Significant correlations (P <' 0 03) were found between FRIA and FR1B (r = 0.97); the mean of FRIA and FRIB vs FR2 and FROZ (r = 0.71, r = 0.78 respectively) These results demonstrate that sample freezing had no effect on the susceptibility of LDL to oxidation and that there is no significant variation between samples taken at different time periods for the same individual.