Profiling the Plasma Apolipoproteome of Normo- and Hyperlipidemic Mice by Targeted Mass Spectrometry.

Atherosclerotic cardiovascular disease is the leading cause of death worldwide. For decades, mouse modeling of atherosclerosis has been the mainstay for preclinical testing of genetic and pharmacological intervention. Mouse models of atherosclerosis depend on supraphysiological levels of circulating cholesterol carried in lipoprotein particles. Lipoprotein particles vary in atherogenicity, and it is critical to monitor lipoprotein levels during preclinical interventions in mice. Unfortunately, the small plasma volumes typically harvested during preclinical experiments limit analyses to measuring total cholesterol and triglyceride levels. Here we developed a high-throughput, low-cost targeted multiple reaction monitoring (MRM) stable isotope dilution (SID) mass spectrometry assay for simultaneous relative quantification of nine apolipoproteins using a few microliters of mouse plasma. We applied the MRM assay to investigate the plasma apolipoproteome of two atherosclerosis models: the widely used ApoE knockout model and the emerging recombinant adeno-associated virus-mediated hepatic Pcsk9 overexpression model. By applying the assay on size-exclusion chromatography-separated plasma pools, we provide in-depth characterization of apolipoprotein distribution across lipoprotein species in these models, and finally, we use the assay to quantify apolipoprotein deposition in mouse atherosclerotic plaques. Taken together, we report development and application of an MRM assay that can be adopted by fellow researchers to monitor the mouse plasma apolipoproteome during preclinical investigations.

Hyperlipidemia does not affect development of elastase-induced abdominal aortic aneurysm in mice.

BACKGROUND AND AIMS: Hyperlipidemia is a suggested risk factor for abdominal aortic aneurysm (AAA). However, whether hyperlipidemia is causally involved in AAA progression remains elusive. Here, we tested the hypothesis that hyperlipidemia aggravates AAA formation in the widely used porcine pancreatic elastase (PPE) model of AAA in mice with varying levels of plasma lipids. METHODS: Prior to PPE-surgery, 8-week-old male C57BL/6J mice (n = 32) received 1·1011 viral genomes of rAAV8-D377Y-mPcsk9 or control rAAV8 via the tail vein. Mice were fed either western type diet or regular chow. At baseline and during the 28 days following PPE-surgery, mice underwent weekly ultrasonic assessment of AAA progression. Experiments were repeated using Apolipoprotein E knockout (ApoE-/-) mice (n = 7) and wildtype C57BL/6J mice (n = 5). RESULTS: At sacrifice, maximal intergroup plasma cholesterol and non-HDL/HDL ratio differences were >5-fold and >20-fold, respectively. AAA diameters expanded to 150% of baseline, but no intergroup differences were detected. This was verified in an independent experiment comparing 8-week-old male ApoE-/- mice with wildtype mice. Histological evaluation of experimental AAA lesions revealed accumulated lipid in neointimal and medial layers, and analysis of human AAA lesions (n = 5) obtained from open repair showed medial lipid deposition. CONCLUSIONS: In summary, we find that lipid deposition in the aortic wall is a feature of PPE-induced AAA in mice as well as human AAA lesions. Despite, our data do not support the hypothesis that hyperlipidemia contributes to AAA progression.