Clinical Significance of Electronegative Low-Density Lipoprotein Cholesterol in Atherothrombosis

Abstract

Despite the numerous risk factors for atherosclerotic cardiovascular diseases (ASCVD), cumulative evidence shows that electronegative low-density lipoprotein (L5 LDL) cholesterol is a promising biomarker. Its toxicity may contribute to atherothrombotic events. Notably, plasma L5 LDL levels positively correlate with the increasing severity of cardiovascular diseases. In contrast, traditional markers such as LDL-cholesterol and triglyceride are the therapeutic goals in secondary prevention for ASCVD, but that is controversial in primary prevention for patients with low risk. In this review, we point out the clinical significance and pathophysiological mechanisms of L5 LDL, and the clinical applications of L5 LDL levels in ASCVD can be confidently addressed. Based on the previously defined cut-off value by receiver operating characteristic curve, the acceptable physiological range of L5 concentration is proposed to be below 1.7 mg/dL. When L5 LDL level surpass this threshold, clinically relevant ASCVD might be present, and further exams such as carotid intima-media thickness, pulse wave velocity, exercise stress test, or multidetector computed tomography are required. Notably, the ultimate goal of L5 LDL concentration is lower than 1.7 mg/dL. Instead, with L5 LDL greater than 1.7 mg/dL, lipid-lowering treatment may be required, including statin, ezetimibe or PCSK9 inhibitor, regardless of the low-density lipoprotein cholesterol (LDL-C) level. Since L5 LDL could be a promising biomarker, we propose that a high throughput, clinically feasible methodology is urgently required not only for conducting a prospective, large population study but for developing therapeutics strategies to decrease L5 LDL in the blood.

Keywords: L5 LDL; LDL(–); atherosclerosis; cardiovascular disease; electronegative low-density lipoprotein; oxLDL; oxidized LDL.

Figure 1

Schematic procedures of L5 LDL isolation. EDTA, antibiotics, and protease inhibitors are materials for the prevention of protein degradation. Samples undergo sequential density-based ultracentrifugation (10,000 rpm at 4 °C for 2 h; d = 1.004, 45,000 rpm at 4 °C for 24 h; d = 1.019, 45,000 rpm at 4 °C for 24 h; d = 1.063, 45,000 rpm at 4 °C for 48 h), and after that, LDL (d = 1.019~1.063) can be purified. Additional three times dialyzed against TRIS/EDTA buffer at pH 8.0 and later sterilized by 0.22 µm filter, the LDL sample can be further isolated into five subfractions by a fast-protein liquid chromatography (FPLC) system equipped with an UnoQ12 column. L5 LDL is the most electronegative subfraction. VLDL: very-low-density lipoprotein; IDL: intermediate-density lipoprotein; LDL: low-density lipoprotein; HDL: high-density lipoprotein; L5: electronegative LDL; FPLC: fast-protein liquid chromatography; rpm: revolutions per minute; 1× Protease Inhibitor: cOmplete™ (Roche Diagnostics, Basel, Switzerland).

Figure 2

Reference ranges of L5 LDL and the strategy of statin treatment. Examining the plasma levels of L5 LDL can be useful to determine (1) whether to receive statin or not, (2) more detailed physical exams for cardiovascular functions and lesions, (3) the treatment strategy and goal. Rx: medical prescription; CIMT: carotid intima-media thickness; PWV: pulse wave velocity; ankle-brachial index; CTA: computed tomography angiography.