Mechanism of inhibition defines CETP activity: a mathematical model for CETP in vitro.

Because cholesteryl ester transfer protein (CETP) inhibition is a potential HDL-raising therapy, interest has been raised in the mechanisms and consequences of CETP activity. To explore these mechanisms and the dynamics of CETP in vitro, a mechanistic mathematical model was developed based upon the shuttle mechanism for lipid transfer. Model parameters were estimated from eight published experimental datasets, and the resulting model captures observed dynamics of CETP in vitro. Simulations suggest the shuttle mechanism yields behaviors consistent with experimental observations. Three key findings predicted from model simulations are: 1) net CE transfer activity from HDL to VLDL and LDL can be significantly altered by changing the balance of homoexchange versus heteroexchange of neutral lipids via CETP; 2) lipemia-induced increases in CETP activity are more likely caused by increases in lipoprotein particle size than particle number; and 3) the inhibition mechanisms of the CETP inhibitors torcetrapib and JTT-705 are significantly more potent than a classic competitive inhibition mechanism with the irreversible binding mechanism having the most robust response. In summary, the model provides a plausible representation of CETP activity in vitro, corroborates strong evidence for the shuttle hypothesis, and provides new insights into the consequences of CETP activity and inhibition on lipoproteins.

Pharmacological effects of lipid-lowering drugs recapitulate with a larger amplitude the phenotypic effects of common variants within their target genes.

BACKGROUND: A major expectation underlying the search for novel susceptibility genes for common diseases using genome-wide association studies (GWAS) is that these discoveries will lead to new drug targets. This claim has not been verified yet. Here, we tested the hypothesis that common single nucleotide polymorphisms (SNPs) within drug target genes are associated with the corresponding phenotypes, using a population-based GWAS dataset and lipid-lowering drugs as a test case. METHODS: We examined the association between 36 genotyped and 193 imputed SNPs within four lipid-lowering drug target genes (HMGCR, PPARA, HM74A/GPR109A and CETP) and four non-lipid drug target genes (ACE, AGTR1, P2RY12, and ATP4B) and lipid phenotypes, blood pressure, and coronary artery disease in 5635 adult participants of the Lausanne, Switzerland, CoLaus study, genotyped using the Affymetrix 500K SNP chip technology. RESULTS: The phenotypes associated with SNPs within drug target genes recapitulated to a certain extent the pharmacological effects of the drug. The amplitude of the SNP effect was about 10 times smaller than the pharmacological effect of the corresponding drug. In particular, several CETP SNPs were associated with an elevation in HDL-cholesterol levels, yet a lower diastolic blood pressure, providing evidence that the blood pressure elevation induced by the CETP inhibitor torcetrapib is more likely compound specific than class specific. CONCLUSION: Pharmacological modulation of lipid-lowering drug targets recapitulates, and markedly amplifies, the phenotypic effects of common SNPs within these target genes. This data provides indirect evidence that, with certain limitations, large-scale GWAS represent a new tool for the discovery and the development of innovative drugs.

Inhibition of lipoprotein-associated phospholipase A2 reduces complex coronary atherosclerotic plaque development.

Increased lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) activity is associated with increased risk of cardiac events, but it is not known whether Lp-PLA(2) is a causative agent. Here we show that selective inhibition of Lp-PLA(2) with darapladib reduced development of advanced coronary atherosclerosis in diabetic and hypercholesterolemic swine. Darapladib markedly inhibited plasma and lesion Lp-PLA(2) activity and reduced lesion lysophosphatidylcholine content. Analysis of coronary gene expression showed that darapladib exerted a general anti-inflammatory action, substantially reducing the expression of 24 genes associated with macrophage and T lymphocyte functioning. Darapladib treatment resulted in a considerable decrease in plaque area and, notably, a markedly reduced necrotic core area and reduced medial destruction, resulting in fewer lesions with an unstable phenotype. These data show that selective inhibition of Lp-PLA(2) inhibits progression to advanced coronary atherosclerotic lesions and confirms a crucial role of vascular inflammation independent from hypercholesterolemia in the development of lesions implicated in the pathogenesis of myocardial infarction and stroke.