Cholesterol and triglycerides (TG) received from dietary fats are insoluble in plasma, and therefore these compounds must be packed to lipoproteins when transported by the bloodstream. Apolipoproteins are a group of proteins that are bound to lipoprotein particles, serving as cofactors for enzymes or as ligands for cellular binding. Apolipoprotein B exists in two forms: ApoB48 secreted by the intestine and apoB100 synthesized in the liver.

Epidemiological studies have shown that elevated postprandial (non-fasting) TG concentrations are a significant risk for cardiovascular diseases (CVD). Previous studies have shown that apoB48 protein serves as a good marker for postprandial triglyceride-rich chylomicrons and VLDL particles.

Traditionally apoB48 has been measured with SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) method from lipoprotein fractions separated first by ultracentrifugation (UCF). This SDS-PAGE methodology used to determine the contribution of intestinal triglyceride-rich lipoproteins to postprandial lipemia has been very time consuming. A much less time-consuming method, the ELISA (enzyme-linked immunosorbent assay) method by which apoB48 protein can be determined directly from plasma samples became available about ten years ago. The aim of this thesis is to assess the comparability of these two methods used to measure apoB48.

The data for this method comparison was obtained from two clinical studies called the Fructose study and the Gere study. These studies included all-together 199 participants who all went through an 8-hour fat tolerance test at least once. In all, data consisted of 995 apoB48 measurements performed by both methods, SDS-PAGE and ELISA.

Current data show that the correlation coefficient of measured apoB48 concentrations (mg/l) between the methods varied from R = 0.563, P<0.001 to R = 0.844, P<0.001 depending on the concentration of apoB48 in the samples. Data also show that plasma apoB48 concentrations measured by ELISA method are 76 - 85 % higher than the apoB48 concentrations measured by the SDS-PAGE method from lipoprotein fractions. There was a strong positive correlation observed between the two methods R = 0.765, P<0.001.

This study confirmed the earlier findings made with a smaller amount of data. ApoB48 concentration measured with ELISA directly from plasma reflects well the apoB48 concentration measured from the lipoprotein fractions with SDS-PAGE. In the future, the less time-consuming apoB48 ELISA measurement could easily be implemented in clinical laboratories and used as a biological marker of intestinal chylomicron and VLDL particle number when evaluating the risk of CVD especially in hyper triglyceridemic patients.

All the laboratory work and clinical studies were carried out at Biomedicum Helsinki, Research Program Unit, Marja-Riitta Taskinen’s study group, Diabetes and Obesity, Clinical Research Institute, HUCH Ltd. The instructors of this thesis are Docent Niina Matikainen, M.D., Ph.D., specialist in endocrinology and internal medicine and Reetta Sihvonen, Lector.