Prioritizing the Role of Major Lipoproteins and Subfractions as Risk Factors for Peripheral Artery Disease

Abstract

BackgroundCirculating lipid and lipoprotein levels have consistently been identified as risk factors for atherosclerotic cardiovascular disease (ASCVD), largely on the basis of studies focused on coronary artery disease (CAD). The relative contributions of specific lipoproteins to risk of peripheral artery disease (PAD) have not been well-defined. Here, we leveraged large scale genetic association data to identify genetic proxies for circulating lipoprotein-related traits, and employed Mendelian randomization analyses to investigate their effects on PAD risk.MethodsGenome-wide association study summary statistics for PAD (Veterans Affairs Million Veteran Program, 31,307 cases) and CAD (CARDIoGRAMplusC4D, 60,801 cases) were used in the Mendelian Randomization Bayesian model averaging (MR-BMA) framework to prioritize the most likely causal major lipoprotein and subfraction risk factors for PAD and CAD. Mendelian randomization was used to estimate the effect of apolipoprotein B lowering on PAD risk using gene regions that proxy potential lipid-lowering drug targets. Transcriptome-wide association studies were performed to identify genes relevant to circulating levels of prioritized lipoprotein subfractions.ResultsApoB was identified as the most likely causal lipoprotein-related risk factor for both PAD (marginal inclusion probability 0.86, p = 0.003) and CAD (marginal inclusion probability 0.92, p = 0.005). Genetic proxies for ApoB-lowering medications were associated with reduced risk of both PAD (OR 0.87 per 1 standard deviation decrease in ApoB, 95% CI 0.84 to 0.91, p = 9 × 10−10) and CAD (OR 0.66, 95% CI 0.63 to 0.69, p = 4 × 10−73), with a stronger predicted effect of ApoB-lowering on CAD (ratio of ORs 1.33, 95% CI 1.25 to 1.42, p = 9 × 10−19). Among ApoB-containing subfractions, extra-small VLDL particle concentration (XS.VLDL.P) was identified as the most likely subfraction associated with PAD risk (marginal inclusion probability 0.91, p = 2.3 × 10−4), while large LDL particle concentration (L.LDL.P) was the most likely subfraction associated with CAD risk (marginal inclusion probability 0.95, p = 0.011). Genes associated with XS.VLDL.P and L.LDL.P included canonical ApoB-pathway components, although gene-specific effects varied across the lipoprotein subfractions.ConclusionApoB was prioritized as the major lipoprotein fraction causally responsible for both PAD and CAD risk. However, diverse effects of ApoB-lowering drug targets and ApoB-containing lipoprotein subfractions on ASCVD, and distinct subfraction-associated genes suggest possible biologic differences in the role of lipoproteins in the pathogenesis of PAD and CAD.

Remnant Lipoproteins as a Target for Atherosclerosis Risk Reduction

“…13,14 Similarly, hydrolysis of triglycerides (which are more abundant on VLDL particles) liberates free fatty acids, which may lead to increased inflammation, predisposing to atherogenesis and lesion instability that results in myocardial infarction. Observational and mendelian randomization studies have suggested that atherogenic lipoproteins may not uniformly influence atherosclerotic risk across vascular beds 15,16 and that triglycerides but not LDL-C are associated with markers of systemic inflammation. 17 Future mechanistic studies will be required to characterize the specific interactions between lipoproteins and the arterial wall that may contribute to these differences.…”

“…[18][19][20] CGPS participants were also nonfasting, which may have influenced the assessed lipoprotein profile. Although it is likely that VLDL and triglyceride-rich particles represent causal effectors (rather than merely biomarkers) of increased cardiovascular risk based on genetic epidemiology, mendelian randomization, and clinical trial data of triglyceride-lowering therapies, 7,16,[21][22][23] future randomized trials will be required to definitively establish the therapeutic potential of targeting these subfractions. More broadly, these results are consistent with mendelian randomization studies which have prioritized apoB as the causal lipoprotein risk factor for atherosclerosis, 6,16,24 but future studies will be needed to delineate the causal roles of the specific components of each lipoprotein fraction and subfraction.…”