Comparison of behaviour of very low density lipoproteins of type III hyperlipoproteinaemia on electrophoresis on paper and on agarose gel with a note on a late (slow) pre-beta VLDL liproprotein.

The diagnosis of type III hyperlipoproteinaemia is based on the presence of a very low density lipoprotein (VLDL) that on electrophoresis has beta instead of the usual pre-beta mobility. This definition is based on paper electrophoresis. Lipoproteins of type III sera were studied by simultaneous electrophoresis on paper and on agarose gel. On paper the ultracentrifugally isolated VLDL had beta mobility, but on agarose gel their mobility was slightly more rapid than beta. It is thus important to consider the electrophoretic conditions in the diagnosis of type III. The diagnosis of type III is further complicated by the presence of agarose gel electrophoresis - contrary to paper - of a second, a 'late pre-beta VLDL' lipoprotein (LPbeta) in 20-30 per cent of both normal and hyperlipoproteinaemic sera. Quantitative lipoprotein analysis of 609 consecutive sera showed that when LPbeta was present, both in normo- and hyperlipoproteinaemia, certain significant lipoprotein changes occurred. Thus VLDL had a high cholesterol content and a raised cholesterol to triglyceride ratio. Furthermore, the triglyceride content of low density lipoproteins (LDL) was increased. These lipoprotein abnormalities are also seen in type III hyperlipoproteinaemia. With regard both to chemical composition of VLDL and LDL and to electrophoretic mobility on agarose gel of VLDL, type III hyperlipoproteinaemia and LPbeta are similar. The possibility of a metabolic relation is discussed.