Laure Dumont

Apolipoprotein CI deficiency markedly augments plasma lipoprotein changes mediated by human cholesteryl ester transfer protein (CETP) in CETP transgenic/ApoCI-knocked out mice.

Transgenic mice expressing human cholesteryl ester transfer protein (HuCETPTg mice) were crossed with apolipoprotein CI-knocked out (apoCI-KO) mice. Although total cholesterol levels tended to be reduced as the result of CETP expression in HuCETPTg heterozygotes compared with C57BL6 control mice (−13%, not significant), a more pronounced decrease (−28%,p < 0.05) was observed when human CETP was expressed in an apoCI-deficient background (HuCETPTg/apoCI-KO mice). Gel permeation chromatography analysis revealed a significant, 6.1-fold rise (p < 0.05) in the cholesteryl ester content of very low density lipoproteins in HuCETPTg/apoCI-KO mice compared with control mice, whereas the 2.7-fold increase in HuCETPTg mice did not reach the significance level in these experiments. Approximately 50% decreases in the cholesteryl ester content and cholesteryl ester to triglyceride ratio of high density lipoproteins (HDL) were observed in HuCETPTg/apoCI-KO mice compared with controls (p < 0.05 in both cases), with intermediate −20% changes in HuCETPTg mice. The cholesteryl ester depletion of HDL was accompanied with a significant reduction in their mean apparent diameter (8.68 ± 0.04 nm in HuCETPTg/apoCI-KO miceversus 8.83 ± 0.02 nm in control mice;p < 0.05), again with intermediate values in HuCETPTg mice (8.77 ± 0.04 nm). In vitro purified apoCI was able to inhibit cholesteryl ester exchange when added to either total plasma or reconstituted HDL-free mixtures, and coincidently, the specific activity of CETP was significantly increased in the apoCI-deficient state (173 ± 75 pmol/μg/h in HuCETPTg/apoCI-KO mice versus 72 ± 19 pmol/μg/h in HuCETPTg,p < 0.05). Finally, HDL from apoCI-KO mice were shown to interact more readily with purified CETP than control HDL that differ only by their apoCI content. Overall, the present observations provide direct support for a potent specific inhibition of CETP by plasma apoCI in vivo.

Molecular Mechanism of the Blockade of Plasma Cholesteryl Ester Transfer Protein by Its Physiological Inhibitor Apolipoprotein CI

Genetically engineered mice demonstrated that apolipoprotein (apo) CI is a potent, physiological inhibitor of plasma cholesteryl ester transfer protein (CETP) activity. The goal of this study was to determine the molecular mechanism of the apoCI-mediated blockade of CETP activity. Kinetic analyses revealed that the inhibitory property of apoCI is independent of the amount of active CETP, but it is tightly dependent on the amount of high density lipoproteins (HDL) in the incubation mixtures. The electrostatic charge of HDL, i.e. the main carrier of apoCI in human plasma, is gradually modified with increasing amounts of apoCI, and the neutralization of apoCI lysine residues by acetylation produces a marked reduction in its inhibitory potential. The inhibitory property of full-length apoCI is shared by its C-terminal α-helix with significant electrostratic properties, whereas its N-terminal α-helix with no CETP inhibitory property has no effect on HDL electronegativity. Finally, binding experiments demonstrated that apoCI and to a lower extent its C-terminal α-helix are able to disrupt CETP-lipoprotein complexes in a concentration-dependent manner. It was concluded that the inhibition of CETP activity by apoCI is in direct link with its specific electrostatic properties, and the apoCI-mediated reduction in the binding properties of lipoproteins results in weaker CETP-HDL interactions and fewer cholesteryl ester transfers.

Titanate nanotubes: towards a novel and safer nanovector for cardiomyocytes.

Abstract Actively contractile cardiomyocyte (CM) monolayer represents an interesting tool to study both cardiac diseases and injuries. However, this model is poorly transfectable with conventional agents. Consequently, there is a need to develop new carriers that could overcome this problem. Titanate nanotubes (TiONts) could be a potential candidate due to possibly higher cell uptake as a direct consequence of their shape. On the basis of this rationale, TiONts were assessed for their cytotoxicity and internalization pathways. Cytotoxicity was assessed for TiONts either functionalized with PEI or unfunctionalized and its spherical counterpart P25 TiO2. No cytotoxic effect was observed under TiONts, TiONts-PEI1800 and P25 TiO2 exposed conditions. The tubular morphology was found to be an important parameter promoting internalization while reversing the charge was assessed as non-additional. Internalization was found to occur by endocytosis and diffusion through the membrane. A preliminary transfection study indicated the potential of TiONts as a nanocarrier.

Apolipoprotein CI is a physiological regulator of cholesteryl ester transfer protein activity in human plasma but not in rabbit plasma.

Plasma cholesteryl ester transfer protein (CETP) activity is high in rabbits, intermediate in humans, and nondetectable in rodents. Human apolipoprotein CI (apoCI) was found to be a potent inhibitor of CETP. The aim of this study was to compare the ability of rabbit and human apoCI to modulate the interaction of CETP with HDLs and to evaluate to which extent apoCI contributes to plasma cholesteryl ester transfer rate in normolipidemic humans and rabbits. Rabbit apoCI gene was cloned and sequenced, rabbit and human apoCI were purified to homogeneity, and their ability to modify the surface charge properties and the CETP inhibitory potential of HDL were compared. It is demonstrated that unlike human apoCI, rabbit apoCI does not modulate cholesteryl ester transfer rate in total plasma. Whereas both human and rabbit apoCI readily associate with HDL, only human apoCI was found to modify the electrostatic charge of HDL. In humans, both CETP and apoCI at normal, physiological levels contribute significantly to the plasma cholesteryl ester transfer rate. In contrast, CETP is the sole major determinant of cholesteryl ester transfer in normolipidemic rabbit plasma as a result of the inability of rabbit apoCI to change HDL electronegativity.

Plasma Phospholipid Transfer Protein Deficiency in Mice Is Associated With a Reduced Thrombotic Response to Acute Intravascular Oxidative Stress

Objective—Earlier in vitro studies suggested a putative role for the plasma phospholipid transfer protein (PLTP) in the modulation of blood coagulation. The effect of PLTP expression on blood coagulation under both basal and oxidative stress conditions was compared here in wild-type and PLTP-deficient (PLTP−/−) mice. Methods and Results—Under basal conditions, PLTP deficiency was associated with an extended tail bleeding time despite a significant depletion of vascular &agr;-tocopherol content and an impairment of endothelial function. When acute oxidative stress was generated in vivo in the brain vasculature, the steady state levels of oxidized lipid derivatives, the extent of blood vessel occlusion, and the volume of ischemic lesions were more severe in wild-type than in PLTP−/− mice. Conclusion—In addition to its recognized hyperlipidemic, proinflammatory, and proatherogenic properties, PLTP increases blood coagulation and worsens the extent of ischemic lesions in response to acute oxidative stress. Thus, PLTP arises here as a cardiovascular risk factor for the late thrombotic events occurring in the acute phase of atherosclerosis.