Reverse cholesterol transport (RCT) is considered as the most important antiatherogenic role of high-density lipoproteins (HDL), but interventions based on RCT have failed to reduce the risk of coronary heart disease. In contrast to RCT, important evidence suggests that HDL deliver lipids to peripheral cells. Therefore, in this paper, we investigated whether HDL could improve endothelial function by delivering lipids to the cells. Internalization kinetics using cholesterol and apolipoprotein (apo) AI fluorescent double-labeled reconstituted HDL (rHDL), and human dermal microvascular endothelial cells-1 (HMEC-1) showed a fast cholesterol influx (10 min) and a slower HDL protein internalization as determined by confocal microscopy and flow cytometry. Sphingomyelin kinetics overlapped that of apo AI, indicating that only cholesterol became dissociated from rHDL during internalization. rHDL apo AI internalization was scavenger receptor class B type I (SR-BI)-dependent, whereas HDL cholesterol influx was independent of SR-BI and was not completely inhibited by the presence of low-density lipoproteins (LDL). HDL sphingomyelin was fundamental for intercellular adhesion molecule-1 (ICAM-1) downregulation in HMEC-1. However, vascular cell adhesion protein-1 (VCAM-1) was not inhibited by rHDL, suggesting that components such as apolipoproteins other than apo AI participate in HDL’s regulation of this adhesion molecule. rHDL also induced endothelial nitric oxide synthase eNOS S1177 phosphorylation in HMEC-1 but only when the particle contained sphingomyelin. In conclusion, the internalization of HDL implies the dissociation of lipoprotein components and a SR-BI-independent fast delivery of cholesterol to endothelial cells. HDL internalization had functional implications that were mainly dependent on sphingomyelin. These results suggest a new role of HDL as lipid vectors to the cells, which could be congruent with the antiatherogenic properties of these lipoproteins.

Background: High-density lipoproteins (HDL) exert protective effects on the endothelium, which are impaired in type 2 diabetes (T2D). Although monocyte-derived multipotential cells (MOMCs) can be differentiated into the endothelial lineage, it remains unclear whether HDL glycation, size, and composition could affect MOMCs differentiation. Methods: Twenty normoglycemic (49 years, 35% male), 20 prediabetic (52 years, 35% male), and 20 newly diagnosed T2D participants (51 years, 50% male) were recruited. HDL were isolated from each study group. The size, composition, and early, intermediate, or advanced glycation products of HDL were determined. CD14+ MOMCs were isolated from healthy volunteers and incubated with HDL from each group. Endothelial phenotypic expression was assessed by CD14⁺/KDR⁺ expression. Results: Compared with normoglycemic and prediabetic individuals, T2D patients had higher concentrations of early (4.4, 4.6, vs. 5.2 µmol/mg of protein, respectively; p = 0.049) and advanced (7.7, 8.7, vs. 14.3 µg-BSA-AGEs/mg of protein, respectively; p < 0.02) glycation products in HDL. HDL composition was similar among groups. The CD14+/KDR+ expression in MOMCs incubated with HDL from T2D patients was lower than that observed in prediabetes and normoglycemic individuals (46% vs. 52% and 61%, respectively; p = 0.002). Advanced glycation end products in HDL inversely correlated with CD14+/KDR+ cells (r = −0.418, p = 0.002), adjusting for other HDL characteristics. Conclusions: In T2D patients, increased HDL-advanced glycation impairs the endothelial phenotypic expression of MOMCs, independently of other HDL characteristics. Since advanced glycation leads to greater biological damage, these findings highlight the importance of preserving HDL integrity in T2D patients to support endothelial repair and potentially delay vascular complications.