Apolipoproteins and lipoproteins of human plasma: significance in health and in disease

Abstract

When DeLalla and Gofman (1954) presented their work "Ultracentrifugal Analysis of Serum Lipoproteins" more than 25 years ago, we were thinking about lipoproteins in terms of density fractions. In the 1970s the electrophoresis concept was pushed by Fredrickson and his colleagues (Fredrickson et al., 1967). There is no doubt that both these lipoprotein research centers have fertilized entire investigations in this field and still have a tremendous impact on our current knowledge. It was, however, not until 1966, when Gustafson, Alaupovic, and Furmann first described the presence of a third lipoprotein family, LpC, that researchers in this area became aware of the dominant role of apolipoproteins in the transport and metabolism of plasma lipids. Lipoprotein density fractions and electrophoretic classes in the mean time have not lost their importance; they still exist and the application of methods yielding those fractions is still going on in lipoprotein laboratories. Yet we need to recognize that the whole lipid transport system is far more complex than was believed some 10 or 20 years ago. Lipoprotein density fractions consist of varying numbers of families; some of them comigrate upon electrophoresis, and the protein moiety of them is mostly composed of nonidentical polypeptides. There are a number of inborn errors of metabolism, for example, ABL, Tangier disease, and enzyme defects, which have taught us a lot about the functions and interplay of the complex apolipoprotein system. In dyslipoproteinemia, abnormal lipoproteins occur in the plasma and apolipoproteins, which are hardly recognized in normal fasting plasma, suddenly become prominent. There still exist, however, apolipoproteins and lipoproteins, one of which certainly is Lp(a), whose function and biological significance remains completely unknown. The structure and the molecular arrangement of lipids and apolipoproteins within a lipoprotein particle has been the subject of intensive investigations, and almost every physicochemical method available has been applied to reveal the morphology of individual lipoproteins in closest detail. Lipoproteins and apolipoproteins have often also served as model substances for cell membranes. After the purification of individual apolipoproteins succeeded in many laboratories and specific antibodies were available, clinical chemists and epidemiologists became interested in this area of research. Apolipoprotein quantification currently is most prominent for the prediction of atherosclerotic risk in preventive medicine.(ABSTRACT TRUNCATED AT 400 WORDS)