Abstract
Although lipoproteins are conventionally separated into a few classes using density gradient centrifugation, there may be a much higher number of physical classes that differ in origin or phase. Comprehensive knowledge of the classes of lipoproteins is rather limited, which hinders both the study of their functions and the identification of the primary causes of related diseases. This study aims to determine the number of classes of lipoproteins that can be practically distinguishable and identify the differences between them. We separated rat serum samples by gel filtration. The elution was continuously monitored for triglyceride (TG), cholesterol, and protein, and fractionated for further SDS–PAGE and immunological detection of apoprotein A-I (ApoA1) and apoprotein B (ApoB). The elution patterns were analyzed using a parsimonious method, i.e., the estimation of the least number of classes. Ten classes were recognized that contained different amounts of TG and cholesterol, as well as a unique protein content. Each of the classes contained much more protein than that observed previously, especially in low-density lipoproteins (LDL) classes. In particular, two major antiproteases formed complexes with specific classes of LDL; because these classes exclusively carry cholesterol and antiproteases, they may lead to the progression of atheroma by supplying materials that enlarge fatty streaks and protecting thrombi from enzymatic digestion. The separated classes may have specific biological functions. The attribution of protein species to certain classes will help understand the functions. A distinction among lipoprotein classes may provide important information in the field of vascular pathology.
Highlights
Animals retrieve lipids from foods, or synthesize them in the liver and supply them to the whole body through the bloodstream [1,2,3,4]
In addition to correcting the misidentification of lipoprotein classes reported in rat studies [29], these results showed that the protein content of all lipoproteins was much higher than that observed previously, which raises questions regarding classification based on differences in density
Curve fitting was performed by identifying the time and range parameters for each distribution, and a parameter of magnitude was determined for each component
Summary
Animals retrieve lipids from foods, or synthesize them in the liver and supply them to the whole body through the bloodstream [1,2,3,4]. The classes are traditionally isolated using density gradient centrifugation in biochemical studies [6,7,8,9,10] and clinical measurements [11]. This is a rather unique process that repeats a series of isopycnic centrifugations. Very-low-density lipoproteins (VLDL), LDL, and high-density lipoproteins (HDL) are collected step-by-step by repeating the gradient-formation process using more concentrated media
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