Molecular Composition and Function of High-Density Lipoprotein Is Uniquely Altered After Kidney Transplantation.

Abstract

Background: Renal transplant recipients experience increased cardiovascular morbidity and mortality, largely unaffected by therapeutic measures such as statins: here we studied molecular composition and functionality of High-Density Lipoprotein (HDL) to explore a potential mechanism of this excessive cardiovascular risk. Methods: HDL from fresh human plasma of stable renal transplant (CKD I-IV) and end-stage renal disease (ESRD) patients as well as matched healthy controls was isolated by one-step density gradient ultracentrifugation. Protein composition was analyzed by shotgun proteomics and confirmed by immunoblot. Functional HDL modifications were determined by measurement of cholesterol-efflux, the membrane cholesterol concentration in peripheral blood mononuclear cells and paraoxonase-1 activity. Results: We found that distinct proteins like surfactant protein B, serum amyloid A, pigment epithelium-derived factor and alpha-1 microglobulin/bikunin precursor were enriched in HDL of renal transplant patients similar to ESRD patients indicating a characteristic disease-specific HDL proteome. Of note, alterations of HDL were virtually identical between patients with CKD I-II and III-IV and independent of transplant vintage. Furthermore, transplant HDL displayed decreased cholesterol acceptor capacity, but substantially increased free cholesterol within patient leukocytes. Finally, impaired anti-oxidative HDL function was demonstrated by decreased paraoxonase-1 activity in all transplant groups. Conclusion: We demonstrate unique alterations of HDL from renal transplant recipients at the molecular and functional level. Importantly, remodeling of HDL including enrichment of distinct proteins previously identified from uremic HDL was also observed in patients with excellent graft function independent of the transplant vintage. These data may therefore not only help to unravel the causes of the excessive cardiovascular risk in renal transplant patients, but may also pave the way for novel diagnostic and innovative therapeutic directions.