[Apolipoprotein (a) isoform size determination. Value and limits of high resolution phenotyping by agarose gel...

High-resolution methods using agarose gel electrophoresis followed by immunoblotting have been recently developed for the measurement of the apolipoprotein (a) size isoforms. Despite the high sensitivity of these methods, a variable proportion of isoforms remain undetected. Four primary antibodies were compared for their ability to detect a large number of isoforms, and were found to express equal reactivity irrespective of the apo (a) size. Comparison of the data obtained both by phenotyping and by genotyping led to the identification of 15 artefactual bands. All these nonspecific bands were of low intensity and occurred when more than 50 ng of Lp (a) were loaded on the gel. The visualization of the isoforms was performed by labelling apo (a) with a peroxidase conjugated antibody coupled to a luminescent substrate, thereby allowing quantification of the relative expression of each isoform by densitometry. There is currently no standardized nomenclature for the apo (a) isoforms: a procedure is proposed using a commercially available standard to express the results in kringle number.