Cholesteryl Ester Transfer Protein (CETP) is a hydrophobic glycoprotein secreted mainly from the liver and circulates in plasma, bound mainly to HDL. It reduces circulating HDL cholesterol levels by promoting the transfer of cholesteryl esters from antiatherogenic HDLs to proatherogenic apolipoprotein B (apoB)–containing lipoproteins, including VLDLs, VLDL remnants, IDLs, and LDLs in exchange for triglyceride. Its activity is associated with conditions linked with accelerated atherosclerosis including diabetes, metabolic syndrome and the dyslipidaemia typically found in myocardial infarction survivors. CETP is a member of a family of proteins expressed in species including man and rabbit, which are susceptible to atherosclerosis, but not in rats, which are resistant to atherogenesis. Dalcetrapib and Torcetrapib (Axon 1962 and Axon 2047 respectively) both inhibit CETP activity, resulting in increased levels of HDL cholesterol, and decreased levels of LDL cholesterol. However, in case of Torcetrapib, not Dalcetrapib, the beneficial pharmacological effects are accompanied by an increased risk of cardiovascular events leading to mortality and morbidity.
The microsomal triglyceride transfer protein (MTP) plays a crucial role in the assembly of triglycerides (TG), cholesterol esters, and phospholipids into ApoB-containing lipoproteins and is integral in the assembly of very low-density lipoprotein-cholesterol (VLDL-C) in the liver. As a result, inhibition of hepatic MTP could be a promising alternative strategy for the control of circulating levels of LDL-C and TG.
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