Preparation of a stable fresh frozen primary lipoproteina (Lpa) standard

LPa is one of the most atherogenic lipoproteins consisting of an LDL-like core particle and a covalently linked glycoprotein of variable size. Due to its structural features, its heterogeneity and instability, there are great difficulties in standardizing quantitative immunochemical Lpa assays. One particular problem is the preparation of a pure primary standard, which is sufficiently stable to be used for value assignment of secondary reference material. Here we describe a method to purify Lpa to virtual homogeneity. When mixed with glycerol at a ratio of 1:1, the preparation is stable in the deep frozen state for more than 12 months. This latter material gave dose;-response curves in several immunochemical assays that were parallel to fresh or frozen sera, freshly prepared Lpa, and other proposed reference materials. After determination of the protein content by amino acid analysis, it was possible to assign concentrations in molar and mass units to these preparations considering the theoretical molecular weights of the particular apoa isoform. Thus we propose to use this procedure for preparation of a "gold standard" for Lpa assays.