Aggregation of human plasma low density lipoproteins by means of poly(ethylene glycol)

The aggregation of LDL induced by PEG was investigated by turbidity measurements at increasing concentration of PEG. Aggregation occurs over a narrow range of PEG concentration. The PEG concentration required to induce aggregation is shifted toward lower values as the LDL concentration is increased, the molecular weight of PEG is increased, the pH is decreased, and positively charged molecules such as chlorpromazine are added. The results are compared with the properties of the aggregation of proteins and liposomes. The data are interpreted on the basis of the volume exclusion principle and assuming the exclusion of PEG from the LDL surface. The influences of pH and the change of the surface charge on aggregation can be explained by the analysis of the repulsive and attractive forces.