Electron cryomicroscopy and digital image processing of lipoprotein(a)

Developing Electron Microscopy Tools for Profiling Plasma Lipoproteins Using Methyl Cellulose Embedment, Machine Learning and Immunodetection of Apolipoprotein B and Apolipoprotein(a)

Plasma lipoproteins are important carriers of cholesterol and have been linked strongly to cardiovascular disease (CVD). Our study aimed to achieve fine-grained measurements of lipoprotein subpopulations such as low-density lipoprotein (LDL), lipoprotein(a) (Lp(a), or remnant lipoproteins (RLP) using electron microscopy combined with machine learning tools from microliter samples of human plasma. In the reported method, lipoproteins were absorbed onto electron microscopy (EM) support films from diluted plasma and embedded in thin films of methyl cellulose (MC) containing mixed metal stains, providing intense edge contrast. The results show that LPs have a continuous frequency distribution of sizes, extending from LDL (> 15 nm) to intermediate density lipoprotein (IDL) and very low-density lipoproteins (VLDL). Furthermore, mixed metal staining produces striking “positive” contrast of specific antibodies attached to lipoproteins providing quantitative data on apolipoprotein(a)-positive Lp(a) or apolipoprotein B (ApoB)-positive particles. To enable automatic particle characterization, we also demonstrated efficient segmentation of lipoprotein particles using deep learning software characterized by a Mask Region-based Convolutional Neural Networks (R-CNN) architecture with transfer learning. In future, EM and machine learning could be combined with microarray deposition and automated imaging for higher throughput quantitation of lipoproteins associated with CVD risk.

Quantification of lipoprotein(a): comparison of an automated latex-enhanced nephelometric assay with an immunoenzymometric method

Several studies indicate the relevance of lipoprotein(a) (Lp(a)) in the genesis of premature coronary artery disease. A simple method for determining the concentration of Lp(a) is therefore of great interest for assessing the risk of coronary artery disease in patients. We compared a new latex-enhanced immunonephelometric assay (Behringwerke AG, Marburg, Germany), using the Behring Nephelometer System 100, with an established immunoenzymometric assay (Immuno, Heidelberg, Germany). A total of 163 patients was studied. Intra- and inter-assay coefficients of variation were between 2.2% and 7.1%, and between 3.4% and 8.6%, depending on the concentration of Lp(a). The correlation between the studied assays was excellent (r = 0.93, y = 0.98x -1.57, Spearman rank, Passing & Bablok). When values above 1000 mg/l for Lp(a) were excluded, the correlation was even higher. Increased light scattering with particle size, which hitherto has been a disadvantage of the nephelometric technique, seems to be negligible using the improved latex-enhanced approach. In patients with triacylglycerol values above 4.5 mmol/l (n = 19) there was no interference with the Behring system, i.e. the results of the nephelometric method were not increasing, and they agreed with those of the immunoenzymometric assay. In conclusion, this new latex-enhanced nephelometric immunoassay represents a rapid and precise method for the quantification of Lp(a).