Composition and structure of lipopolysaccharide-human plasma low density lipoprotein complex. Analytical ultracentrifugation, 31P-NMR, ESR and fluorescence spectroscopy studies.
Level 5 - mechanism / opinion, no new human data
In vitro bench study of structural and biophysical properties without human clinical outcomes
PubMed 2548621 · doi:10.1016/0005-2736(89)90351-9
What was done
Salmonella typhimurium lipopolysaccharide (LPS) was complexed in vitro with human plasma low-density lipoprotein (LDL). The composition and structural properties of the resulting complexes were evaluated using analytical ultracentrifugation, 31P-NMR, electron spin resonance (ESR), and intrinsic apolipoprotein B (apoB) fluorescence spectroscopy, including quencher accessibility assays (I-, Cs+, acrylamide).
What was found
LPS-LDL complexes comprised approximately 0.24 mg LPS per mg LDL protein (~9-10 LPS molecules per LDL particle), with apolipoprotein apoB-100 remaining the predominant protein (>=90-95%). LPS insertion was accompanied by an ~11% reduction in phosphatidylcholine, a 2-fold increase in free fatty acids, and a shift toward higher particle density. ESR showed increased ordering of phospholipid hydrocarbon chains, and 31P-NMR showed restricted polar headgroup mobility in a monolayer arrangement. ApoB intrinsic fluorescence showed a slight 1-2 nm red-shift with no dramatic change in quencher accessibility, indicating apoB localization was largely preserved without significant screening by LPS oligosaccharide chains.
Why it matters
The findings demonstrate that human LDL can carry significant quantities of bacterial endotoxin while preserving overall particle and apolipoprotein architecture. This provides a mechanistic basis for how LDL-LPS complexes might interact with normal lipoprotein or scavenger receptors in vivo.
Limits
This was an entirely in vitro biophysical study using isolated components. The abstract does not report the number of plasma donors, and functional receptor binding, downstream immune signaling, and in vivo clearance kinetics were not directly tested.
Cited by
- contradicts Circulating lipopolysaccharide (LPS) binds to the ApoB region on LDL particles, preventing ApoB from being recognized and recycled by the liver, which prolongs the particle's circulation time.