Does high triglycerides with low HDL cholesterol reflect increased triglyceride-rich lipoprotein traffic and HDL remodeling?

The co-occurrence of high triglycerides (TG) and low high-density lipoprotein cholesterol (HDL-C) is a classic clinical phenotype. Rather than representing two independent lipid abnormalities, this combined profile is a dynamic, coordinated metabolic process driven by increased triglyceride-rich lipoprotein traffic and active intravascular remodeling.

Mechanistic pathways of lipid remodeling

• VLDL and CETP activity: Elevated levels of circulating TG-rich very-low-density lipoproteins (VLDL) drive the activity of cholesteryl ester transfer protein (CETP). CETP facilitates a reciprocal lipid exchange, transferring cholesteryl esters from HDL to VLDL in exchange for triglycerides, resulting in TG-enriched, cholesteryl ester-depleted HDL.
• Hepatic lipase hydrolysis: These TG-rich HDL particles serve as highly favorable substrates for hepatic lipase, which hydrolyzes the core triglycerides and surface phospholipids.
• ApoA-I dissociation and clearance: This lipolytic hydrolysis shrinks the HDL particles into smaller, denser forms. This structural contraction causes apolipoprotein A-I (apoA-I) to dissociate from the particle shell. The free apoA-I is rapidly cleared from circulation by the kidneys and liver, increasing the fractional catabolic rate of HDL and lowering overall steady-state HDL-C levels.

Clinical implications

• Atherogenic lipid profile: This remodeling pathway not only reduces cardioprotective HDL-C but also transforms VLDL remnants into highly atherogenic, cholesterol-rich particles.
• Surrogate marker: The TG/HDL ratio serves as a reliable surrogate marker for these underlying kinetics, indicating accelerated intravascular lipid exchange and remodeling rather than simple static lipid concentrations.

Bottom line

• High triglycerides and low HDL-C directly reflect increased VLDL traffic driving CETP-mediated lipid exchange. This process enriches HDL with triglycerides, allowing hepatic lipase to shrink the particles and accelerate apoA-I clearance, ultimately lowering circulating HDL-C levels and promoting an atherogenic lipid profile.