132. Lipids: LDL Physiology & Function with Dr. Peter Toth


CardioNerds Academy Chief Fellows Dr. Rick Ferraro (FIT, Johns Hopkins) and Dr. Tommy Das (FIT, Cleveland Clinic) join Academy fellow Dr. Jessie Holtzman (soon, chief resident at UCSF internal medicine residency) to learn all about LDL physiology and function from Dr. Peter Toth!

Low-density lipoprotein cholesterol (LDL-C) has been well established as a risk factor for atherosclerotic cardiovascular disease with an ever growing armamentarium of medications to lower LDL-C plasma levels. Yet, LDL-C also plays a number of key physiologic roles across mammalian species, such as cell membrane formation, bile acid synthesis, and steroid hormone production. In this episode, we discuss the definitions of high, normal, low, and ultra-low LDL-C, what functional assays are used to measure LDL-C, and what is considered the safe lower-limit of LDL-C, if there is one at all. Drawing upon experience from rare genetic conditions including abetalipoproteinemia and loss-of-function variants of the PCSK9 gene, we glean pearls that clarify  the risks and benefits of low LDL-C.

Relevant disclosure: Dr. Toth has served as a consultant to Amarin, Amgen, Kowa, Resverlogix, and Theravance; and has served on the Speakers Bureau for Amarin, Amgen, Esperion, and Novo Nordisk.

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Pearls

1. Lipoproteins are processed via two major pathways in mammals: 1) exogenous fat metabolism that digests ingested lipids and 2) endogenous fat metabolism that synthesizes lipids in the liver and small intestine. High density lipoprotein (HDL)-mediated reverse transport also brings lipids from the periphery back to the liver.

2. LDL-C comprises ~70% of plasma cholesterol due to its long half-life of 2-3 days. It is one of 5 major lipid particles in plasma including chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), LDL, and HDL.