Cholesteryl ester transfer protein genotypes associated with venous thrombosis and dyslipoproteinemia in males

The association of genetic variants in the cholesteryl ester transfer protein gene with hemostatic factors and a first venous thrombosis

BACKGROUND

Cholesteryl ester transfer protein (CETP) plays an important role in lipoprotein metabolism. Previous studies have suggested that the CETP TaqI B1/B2 allele is associated with the risk of venous thrombosis (VT).

AIM

To investigate the associations between genetically determined CETP concentrations and 22 hemostatic factors in healthy individuals, and the risk of a first VT event, in a large VT case-control study.

METHODS

Analyses were performed in the Multiple Environmental and Genetic Assessment of Risk Factors for Venous Thrombosis (MEGA) case-control study. CETP unweighted/weighted genetic risk scores (GRSs) were derived from three single-nucleotide polymorphisms that were identified from a recent genome-wide association study on serum CETP concentrations. The associations between CETP GRSs and 22 hemostatic factors (procoagulant/anticoagulant and fibrinolytic factors) were assessed by linear regression from an additive model in controls (n = 2813). The associations between CETP GRSs and the risk of a first VT were assessed by logistic regression analyses in 3950 VT cases and 4765 controls.

RESULTS

In the controls (median age, 49 years; 53% women), both unweighted and weighted GRSs showed that factor VII activity was negatively associated with the genetically determined CETP concentration (weighted GRS β -3.08 IU/dL per μg/mL genetically determined CETP, 95% confidence interval -5.73 to -0.42). No association was observed with the risk of a first VT.

CONCLUSIONS

Genetically determined CETP concentrations only showed a weak negative association with factor VII activity. However, this did not lead to an association with the risk of a first VT.

Elevated CETP Lipid Transfer Activity is Associated with the Risk of Venous Thromboembolism

Aim: Cholesteryl ester transfer protein (CETP) is an important lipid transfer factor in plasma that enhances prothrombinase activity in purified systems. This study was conducted to test the association of plasma CETP activity with venous thrombosis (VTE) and to address the procoagulant mechanism of CETP activity in prothrombinase assays.

Methods: We measured CETP lipid transfer activity in plasmas of 49 male VTE patients and in plasmas of matched controls. CETP procoagulant activity was tested in purified prothrombinase systems.

Results: CETP lipid transfer activity levels were significantly higher in VTE patients than in controls (p = 0.0008). A subset of patients carrying the CETP mutations Ala373Pro and Arg451Gln, which were also linked to the VTE risk, showed significantly higher plasma CETP activity than the non-carriers. The plasma CETP activity negatively correlated with APTT, suggesting that the CETP activity is associated with plasma coagulability. Recombinant (r) CETP bound to both factor Xa (Kd = 15 nM) and Gla-domainless factor Xa (Kd = 59 nM), whereas rCETP enhanced prothrombin activation by factor Xa, but not by Gla-domainless factor Xa. rCETP also required factor Va for enhancement of prothrombinase activity. When we addressed the effects of mutations in CETP on prothrombinase activity, Gln451-rCETP was found to have five-fold higher thrombin generation activity than wt-rCETP or Pro373-rCETP.

Conclusions: Elevated CETP lipid transfer activity in plasma was associated with the risk of VTE. Gln451-CETP, which is linked to VTE, has much higher procoagulant activity than wt-CETP. CETP might act as a physiologic procoagulant by mechanisms that involve its direct binding to factor Xa.

Crystal structures of cholesteryl ester transfer protein in complex with inhibitors

Human plasma cholesteryl ester transfer protein (CETP) transports cholesteryl ester from the antiatherogenic high-density lipoproteins (HDL) to the proatherogenic low-density and very low-density lipoproteins (LDL and VLDL). Inhibition of CETP has been shown to raise human plasma HDL cholesterol (HDL-C) levels and is potentially a novel approach for the prevention of cardiovascular diseases. Here, we report the crystal structures of CETP in complex with torcetrapib, a CETP inhibitor that has been tested in phase 3 clinical trials, and compound 2, an analog from a structurally distinct inhibitor series. In both crystal structures, the inhibitors are buried deeply within the protein, shifting the bound cholesteryl ester in the N-terminal pocket of the long hydrophobic tunnel and displacing the phospholipid from that pocket. The lipids in the C-terminal pocket of the hydrophobic tunnel remain unchanged. The inhibitors are positioned near the narrowing neck of the hydrophobic tunnel of CETP and thus block the connection between the N- and C-terminal pockets. These structures illuminate the unusual inhibition mechanism of these compounds and support the tunnel mechanism for neutral lipid transfer by CETP. These highly lipophilic inhibitors bind mainly through extensive hydrophobic interactions with the protein and the shifted cholesteryl ester molecule. However, polar residues, such as Ser-230 and His-232, are also found in the inhibitor binding site. An enhanced understanding of the inhibitor binding site may provide opportunities to design novel CETP inhibitors possessing more drug-like physical properties, distinct modes of action, or alternative pharmacological profiles.