Small dense low density lipoprotein has increased affinity for LDL receptor-independent cell surface binding sites: a potential mechanism for increased atherogenicity.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study evaluating LDL binding kinetics in cultured fibroblasts
What was done
In vitro binding and association experiments compared small dense low-density lipoprotein (LDL) with normal LDL in normal and LDL receptor-negative fibroblasts at 4 °C and 37 °C across concentrations from <10 µg/mL to ≥100 µg/mL. The researchers tested the effects of anti-apoB monoclonal antibodies, enzymatic treatments (proteases, chondroitinase, neuraminidase, heparinase, and heparitinase), and sodium chlorate (an inhibitor of proteoglycan sulfation) on LDL cell surface binding.
What was found
At low concentrations (<10 µg/mL), small dense LDL showed reduced LDL receptor binding in normal fibroblasts at 4 °C, but a 2-fold higher binding to LDL receptor-independent sites compared to normal LDL. At 100 µg/mL, receptor-independent binding was 4.5-fold higher in normal fibroblasts and 2- to 14-fold higher in receptor-negative fibroblasts. At 37 °C, small dense LDL showed 3-fold higher cell association in receptor-negative fibroblasts without effective degradation. Binding was not modified by anti-apoB antibodies, proteases, chondroitinase, or neuraminidase. Pretreatment with heparinase and heparitinase decreased LDL binding by 35% in normal and 50% in receptor-negative fibroblasts, while sodium chlorate decreased binding by approximately 45%.
Why it matters
The study outlines a cellular mechanism for why small dense LDL is particularly atherogenic: reduced clearance by classic LDL receptors combined with increased trapping at extrahepatic cell surfaces via cell surface proteoglycans.
Limits
This study was conducted entirely in cultured fibroblasts in vitro, which may not fully reflect in vivo arterial wall biology. The abstract does not report the number of independent biological replicates, donor characteristics, or statistical variance.
Cited by
- supports As LDL particles shrink in size, the apoB receptor recognition site becomes obscured, giving smaller LDL particles lower binding affinity for the LDL receptor.