Low density lipoprotein heterogeneity in spontaneously hypercholesterolemic pigs.

We previously described a strain of spontaneously hypercholesterolemic pigs carrying an apo-B allele termed Lpb5. Lpb5 pigs are heterogeneous with respect to the severity of their hypercholesterolemia. We have termed Lpb5 pigs with severe hypercholesterolemia Lpb 5.1 pigs, and those with moderate hypercholesterolemia Lpb 5.2, Lpb 5.1 animals have a dramatic increase in buoyant LDL relative to dense LDL, with a buoyant-to-dense LDL ratio of 2.2. In contrast, Lpb 5.2 and control pigs have buoyant-to-dense LDL ratios of 0.7 and 0.5 respectively. This ratio appears to be a stable characteristic of the Lpb 5.1 phenotype because sexually mature boars have a dramatic decrease in total plasma cholesterol concentration with no decrease in their ratio of buoyant-to-dense LDL. We have previously demonstrated a fourteen-fold overproduction of buoyant LDL in the Lpb 5.1 pigs, with very little conversion of dense LDL to buoyant LDL. In the current work, very low density lipoprotein (VLDL) turnover experiments were conducted to determine whether VLDL conversion to buoyant LDL was increased in the Lpb 5.1 pigs. VLDL conversion to buoyant LDL could not account for the increased production of buoyant LDL in Lpb 5.1 pigs. Thus, we cannot account for the increased production of buoyant LDL in the Lpb 5.1 pigs from any measurable plasma lipoprotein source. We have therefore termed this production of buoyant LDL in the Lpb 5.1 pigs direct buoyant LDL production.