Inclusion of calcium during isolation of high-density lipoprotein from plasma maintains antioxidant function

We investigated how inclusion of calcium during isolation of high-density lipoprotein (HDL) affected its antioxidant function. Following isolation, HDL was dialyzed against 0.154 M NaCl without or with added calcium (1mM). HDL's paraoxonase 1 activity was unaffected by calcium treatment (87 ± 11% of normal vs. 89 ± 16% of normal, P=0.826). In contrast, whereas HDL dialyzed with calcium inhibited oxidation of low-density lipoprotein (LDL) by 87 ± 10%, HDL dialyzed without calcium inhibited oxidation by only 58 ± 19% (P=0.004). Thus, inclusion of calcium during isolation is important for maintaining HDL's antioxidant function.