Separating extracellular vesicles and lipoproteins via acoustofluidics

Extracellular vesicles (EVs) and lipoproteins are abundant and co-exist in blood. Both have been proven to be valuable as diagnostic biomarkers and for therapeutics. However, EVs and lipoproteins are both on the submicron scale and overlap in size distributions. Conventional methods to separate EVs and lipoproteins are inefficient and time-consuming. Here we present an acoustofluidic-based separation technique that is based on the acoustic property differences of EVs and lipoproteins. By using the acoustofluidic technology, EVs and subgroups of lipoproteins are separated in a label-free, contact-free, and continuous manner. With its ability for simple, rapid, efficient, continuous-flow isolation, our acoustofluidic technology could be a valuable tool for health monitoring, disease diagnosis, and personalized medicine.

Serum butyrylcholinesterase and the risk of future type 2 diabetes: the Kansai Healthcare Study

OBJECTIVE

Butyrylcholinesterase is synthesized in the liver. The serum butyrylcholinesterase level has been cross-sectionally reported to be higher in patients with diabetes, hyperlipidaemia, obesity and fatty liver than in those without them. It is not known whether serum butyrylcholinesterase is associated with the risk of future type 2 diabetes.

DESIGN

A prospective cohort study.

PARTICIPANTS

A total of 8470 Japanese men aged 40-55 years without type 2 diabetes at baseline.

MEASUREMENTS

Type 2 diabetes was diagnosed if a fasting plasma glucose (FPG) level was ≥7·0 mmol/l, if a HbA1 c level was ≥6·5% or if participants were taking oral hypoglycaemic medication or insulin.

RESULTS

During the 42,227 person-years of follow-up, 868 cases had developed type 2 diabetes. Serum butyrylcholinesterase was significantly positively correlated with body mass index (BMI), FPG, alanine aminotransferase (ALT), γ-glutamyltransferase (GGT) and triglycerides (TG), whereas negatively with high-density lipoprotein (HDL) cholesterol. In Cox proportional hazards models, after adjusting for age, BMI, FPG, alcohol consumption, smoking habit, walk to work, regular leisure-time physical activity and family history of diabetes, the highest quartile (398-806 IU/l) of serum butyrylcholinesterase increased the risk of type 2 diabetes compared with the lowest quartile (56-311 IU/l) [hazard ratio (HR) 1·41 (95% confidence interval (CI), 1·14-1·74)]. After further adjusting for ALT and GGT, this association remained [HR 1·40 (95% CI, 1·13-1·73)]. Furthermore, this association was significant independent of TG and HDL cholesterol.

CONCLUSIONS

Elevated serum butyrylcholinesterase was independently associated with an increased risk of future type 2 diabetes.

Optimized negative-staining electron microscopy for lipoprotein studies

BACKGROUND

Negative-staining (NS), a rapid, simple and conventional technique of electron microscopy (EM), has been commonly used to initially study the morphology and structure of proteins for half a century. Certain NS protocols however can cause artifacts, especially for structurally flexible or lipid-related proteins, such as lipoproteins. Lipoproteins were often observed in the form of rouleau as lipoprotein particles appeared to be stacked together by conventional NS protocols. The flexible components of lipoproteins, i.e. lipids and amphipathic apolipoproteins, resulted in the lipoprotein structure being sensitive to the NS sample preparation parameters, such as operational procedures, salt concentrations, and the staining reagents.

SCOPE OF REVIEW

The most popular NS protocols that have been used to examine lipoprotein morphology and structure were reviewed.

MAJOR CONCLUSIONS

The comparisons show that an optimized NS (OpNS) protocol can eliminate the rouleau artifacts of lipoproteins, and that the lipoproteins are similar in size and shape as statistically measured from two EM methods, OpNS and cryo-electron microscopy (cryo-EM). OpNS is a high-throughput, high-contrast and high-resolution (near 1nm, but rarely better than 1nm) method which has been used to discover the mechanics of a small protein, 53kDa cholesterol ester transfer protein (CETP), and the structure of an individual particle of a single protein by individual-particle electron tomography (IPET), i.e. a 14Å-resolution IgG antibody three-dimensional map.

GENERAL SIGNIFICANCE

It is suggested that OpNS can be used as a general protocol to study the structure of proteins, especially highly dynamic proteins with equilibrium-fluctuating structures.

Negative staining and cryo-negative staining of macromolecules and viruses for TEM

In this review we cover the technical background to negative staining of biomolecules and viruses, and then expand upon the different possibilities and limitations. Topics range from conventional air-dry negative staining of samples adsorbed to carbon support films, the variant termed the "negative staining-carbon film" technique and negative staining of samples spread across the holes of holey-carbon support films, to a consideration of dynamic/time-dependent negative staining. For each of these approaches examples of attainable data are given. The cryo-negative staining technique for the specimen preparation of frozen-hydrated/vitrified samples is also presented. A detailed protocol to successfully achieve cryo-negative staining with ammonium molybdate is given, as well as examples of data, which support the claim that cryo-negative staining provides a useful approach for the high-resolution study of macromolecular and viral structure.

Comparison of two homogeneous HDL cholesterol methods in a large population study

OBJECTIVES

High-density lipoprotein cholesterol (HDL-C) is an independent risk factor for coronary heart disease. Data are lacking on the performance of homogeneous methods using a large number of samples.

DESIGN AND METHODS

We compared the performance of two HDL-C direct assays, the Dimension RxL (the Dade method) and the COBAS INTEGRA (the Roche method), for population screening. Performance was assessed using 4214 sera obtained from the International Collaborative Study on Atherosclerosis and Stroke In Asia (InterASIA) participants.

RESULTS

The method comparison results demonstrated that both methods were highly correlated (r = 0.972). Deming regression analysis showed a slope of 1.009 +/- 0.007, an intercept of 0.048 +/- 0.009 and a S(y/x) of 0.08. The means were 1.29 +/- 0.33 and 1.23 +/- 0.33 mmol/l for the Roche and Dade methods, respectively, and the range of observed values were 0.30-3.05 and 0.19-2.86 mmol/l, respectively. The 95% confidence interval for the mean of the method differences was -0.10 to 0.22 mmol/l. Percentages of low (> or = 1.55 mmol/l), normal (1.03-1.54 mmol/l), and high risk (< 1.03 mmol/l) results were 15.5, 55.4, 29.0 for the Dade and 19.3, 59.3, 21.4 for the Roche method. The percentage of concordantly classified subjects at each cut point was 77.1%, 84.4%, and 95.5%. The percentage of overall consistency subjects was 85.4%. Thirteen percent of subjects were discordantly classified into the higher-risk group while the 1.6% of subjects were discordantly classified into the lower-risk group.

CONCLUSIONS

Both homogeneous HDL-C methods were correlated and agree well with one another. The percentage of concordantly classified subjects was high. Thus, either method is suitable for large population studies.

Simplified method for the diameter sizing of serum low-density lipoprotein using polyacrylamide gradient gel electrophoresis

The appearance of small, dense, low-density lipoprotein in serum has been demonstrated to be associated with increased risk of coronary artery disease. The molecular diameter of low-density lipoprotein is usually measured on the basis of mobility differences on polyacrylamide gel electrophoresis. However, since mobility assessed by this method is seriously affected by the increased levels of serum free fatty acids associated with hypertriglyceridemia, we used polyacrylamide gradient gel electrophoresis to eliminate the interference by fatty acids and devised a simple, precise method of polyacrylamide gradient gel electrophoresis to measure the diameter of small, dense, low-density lipoproteins in serum. We used apoferritin and thyroglobulin, which have a molecular diameter of 12.2 nm and 17.0 nm, respectively, and standard low-density lipoprotein particles having a diameter of 25.7 and 27.0 nm as calibrators, estimated by measurement of negative staining of electron microscopy. We also included apoferritin as an internal standard for polyacrylamide gradient gel electrophoresis. The only stain used was Coomassie brilliant blue, and it was used for lipoprotein staining. When we used low-density lipoprotein of 25.73 nm in diameter as a quality control specimen, the coefficient of variation of the size measurements obtained by our method was less than 1.2%. The new method markedly improved the laboratory procedure for measuring the diameter of low-density lipoproteins.

Evolution of Methods for Measurement of HDL-Cholesterol: From Ultracentrifugation to Homogeneous Assays

Background: Adoption of automated homogeneous assays for HDL-cholesterol (HDL-C) is increasing, driven by the need of clinical laboratories to cope with increasing workloads while containing costs. However, performance characteristics of homogeneous assays often differ in important aspects from those of the earlier precipitation methods. This review provides an overview of the new generation of homogeneous assays for HDL-C within the historical context of the evolution of methods and the efforts to standardize measurements of the lipoproteins.

Approach: This is a narrative review based on method evaluations conducted in the laboratories of the authors as well as on relevant publications, especially comparative evaluation studies, from the literature. Publications considered here have been collected by the authors over the past 30 years of involvement as methods for HDL-C made the transition from their early use in lipid research laboratories to clinical laboratories and the recent emergence of homogeneous assays.

Content: The presentation includes descriptions of methodologies, including homogeneous, precipitation, electrophoresis, and ultracentrifugation assays. Reference methods and recommended approaches for assessing accuracy are described. Accuracy and imprecision are summarized in the context of the National Cholesterol Education Program (NCEP) standards for analytical performance. The effects of interfering substances and preanalytical sources of variation are presented.

Summary: Homogeneous assays have been shown to be reasonably well suited for use in routine clinical laboratories, generally meeting the NCEP criteria for precision, accuracy, and total error. However, discrepant results compared with the reference methods have been observed with some of the assays, and the sources of discrepancies are not well characterized. Some homogeneous reagents have not been thoroughly evaluated. At least three of the reagents have experienced successive adjustments in formulation; hence, the reagents may not yet be fully optimized. For these reasons, the homogeneous assays cannot be confidently recommended for use in long-term clinical trials and other research applications without thorough validation.