Association of remnant-like particle cholesterol with coronary artery disease in patients with normal total cholesterol levels

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.

Very low density lipoprotein cholesterol associates with coronary artery calcification in type 2 diabetes beyond circulating levels of triglycerides

OBJECTIVE

While recent genomic studies have focused attention on triglyceride (TG) rich lipoproteins in cardiovascular disease (CVD), little is known of very low-density lipoprotein cholesterol (VLDL-C) relationship with atherosclerosis and CVD. We examined, in a high-risk type-2 diabetic population, the association of plasma VLDL-C with coronary artery calcification (CAC).

METHODS

The Penn Diabetes Heart Study (PDHS) is a cross-sectional study of CVD risk factors in type-2 diabetics (n = 2118, mean age 59.1 years, 36.5% female, 34.1% Black). Plasma lipids including VLDL-C were calculated (n = 1879) after ultracentrifugation.

RESULTS

In Tobit regression, VLDL-C levels were positively associated with increasing CAC after adjusting for age, race, gender, Framingham risk score, body mass index, C-reactive protein, exercise, medication and alcohol use, hemoglobin A1c, and diabetes duration [Tobit ratio (TR) and 95% confidence interval (CI) 0.38 (0.12-0.65), P = 0.005] and even after inclusion of apolipoprotein B data [TR 0.31 (0.03-0.58), P = 0.030]. Approximately 3-fold stronger effect was observed in women [TR 0.75 (0.16-1.34), P = 0.013] than men [TR 0.20 (-0.10-0.50), P = 0.189; gender interaction P = 0.034]. Plasma VLDL-C was related more strongly to CAC scores than TG levels (e.g., Akaike information criteria of 7263.65 vs. 7263.94) and had stronger CAC association in individuals with TGs >150 mg/dl (TR 0.80, P = 0.010) vs. those with TGs <150 mg/dl (TR 0.27, P = 0.185).

CONCLUSIONS

In PDHS, VLDL-C is associated with CAC independent of established CVD risk factors, particularly in women, and may have value even beyond apolipoprotein B levels and in patients with elevated TGs.

How do elevated triglycerides and low HDL-cholesterol affect inflammation and atherothrombosis?

This review article summarizes recent research into the mechanisms as to how elevated levels of triglyceride (TG) and low levels of high- density- lipoprotein cholesterol (HDL-C) contribute to inflammation and atherosclerosis. Evidence supports the role of TG-rich lipoproteins in signaling mechanisms via apolipoproteins C-III and free fatty acids leading to activation of NFKβ, VCAM-1 and other inflammatory mediators which lead to fatty streak formation and advanced atherosclerosis. Moreover, the cholesterol content in TG-rich lipoproteins has been shown to predict CAD risk better than LDL-C. In addition to reverse cholesterol transport, HDL has many other cardioprotective effects which include regulating immune function. The "functionality" of HDL appears more important than the level of HDL-C. Insulin resistance and central obesity underlie the pathophysiology of elevated TG and low HDL-C in metabolic syndrome and type 2 diabetes. Lifestyle recommendations including exercise and weight loss remain first line therapy in ameliorating insulin resistance and the adverse signaling processes from elevated levels of TG-rich lipoproteins and low HDL-C.

Acute effect of orlistat on post-prandial lipaemia and free fatty acids in overweight patients with Type 2 diabetes mellitus

AIMS

Post-prandial lipaemia is prolonged and exaggerated in patients with Type 2 diabetes mellitus, with an accumulation of atherogenic triglyceride-rich lipoprotein remnants. We postulate that orlistat, a gastrointestinal lipase inhibitor, may cause changes in post-prandial lipoprotein metabolism by reducing dietary triglyceride absorption.

METHODS

The acute effect of a single dose of 120 mg orlistat on post-prandial glucose, lipids, remnant lipoproteins and free fatty acids (FFA) was evaluated in a randomized, double-blind, placebo-controlled cross-over study of 63 overweight patients with Type 2 diabetes mellitus (body mass index 30.4 +/- 3.8 kg/m2). Either a single dose of orlistat or placebo was given before a standard mixed meal containing 70 g of fat and plasma triglyceride (TG), remnant-like particles cholesterol (RLP-C) and FFA were sampled at 2-h intervals for 8 h. RLP-C was measured by an immunoseparation assay and FFA by an enzymatic colorimetric method.

RESULTS

The concentrations of plasma TG (P < 0.0001), RLP-C (P = 0.003), and FFA (P < 0.0001) were significantly lower at 2 h after orlistat compared with placebo. Both plasma RLP-C (P = 0.04) and FFA (P < 0.0001) remained lower after orlistat than placebo at 4 h. The incremental area under the curve (iAUC) above baseline fasting level for both TG and RLP-C was significantly more reduced after orlistat than placebo (iAUC-TG 5.8 (3.7-8.2) mmol/l x h-1 vs. 5.7 (4.1-10.9), respectively, P = 0.04; iAUC-RLP-C: 0.53 (0.23-1.04) mmol/l x h-1 vs. 0.56 (0.35-1.40), respectively, P = 0.02). The test meal was well tolerated by all subjects, with only three subjects reporting faecal urgency after orlistat.

CONCLUSIONS

Orlistat has a beneficial effect on post-prandial lipaemia in overweight Type 2 diabetic patients and lowers plasma TG, RLP-C and FFA in the early post-prandial period.