Quantifying cholesterol synthesis in vivo using (2)H(2)O: enabling back-to-back studies in the same subject.

The advantages of using (2)H(2)O to quantify cholesterol synthesis include i) homogeneous precursor labeling, ii) incorporation of (2)H via multiple pathways, and iii) the ability to perform long-term studies in free-living subjects. However, there are two concerns. First, the t(1/2) of tracer in body water presents a challenge when there is a need to acutely replicate measurements in the same subject. Second, assumptions are made regarding the number of hydrogens (n) that are incorporated during de novo synthesis. Our primary objective was to determine whether a step-based approach could be used to repeatedly study cholesterol synthesis a subject. We observed comparable changes in the (2)H-labeling of plasma water and total plasma cholesterol in African-Green monkeys that received five oral doses of (2)H(2)O, each dose separated by one week. Similar rates of cholesterol synthesis were estimated when comparing data in the group over the different weeks, but better reproducibility was observed when comparing replicate determinations of cholesterol synthesis in the same nonhuman primate during the respective dosing periods. Our secondary objective was to determine whether n depends on nutritional status in vivo; we observed n of ∼25 and ∼27 in mice fed a high-carbohydrate (HC) versus carbohydrate-free (CF) diet, respectively. We conclude that it is possible to acutely repeat studies of cholesterol synthesis using (2)H(2)O and that n is relatively constant.

Effects of anacetrapib on plasma lipids, apolipoproteins and PCSK9 in healthy, lean rhesus macaques.

Inhibition of cholesteryl ester transfer protein (CETP) has been vigorously pursued as a potential therapy to treat patients who are at an elevated risk for coronary artery disease. Anacetrapib, a novel CETP inhibitor, has been shown clinically to raise HDL cholesterol and reduce LDL cholesterol when provided as monotherapy or when co-administered with a statin. Preclinically, the effects of anacetrapib on the functionality and composition of HDL have been extensively studied. In contrast, the effects of anacetrapib on other parameters related to lipoprotein metabolism and cardiovascular risk have been difficult to explore. The aim of the present investigation was to evaluate the effects of anacetrapib in rhesus macaques and to compare these to effects reported in dyslipidemic humans. Our results from two separate studies show that administration of anacetrapib (150 mg/kg q.d. for 10 days) to rhesus macaques results in alterations in CETP activity (reduced by more than 70%) and HDL cholesterol (increased by more than 110%) which are similar to those reported in dyslipidemic humans. Levels of LDL cholesterol were reduced by more than 60%, an effect slightly greater than what has been observed clinically. Treatment with anacetrapib in this model was also found to lead to statistically significant reductions in plasma PCSK9 and to reduce cholesterol excursion in the combined chylomicron and remnant lipoprotein fraction isolated from plasma by fast protein liquid chromatography. Collectively, these data suggest that rhesus macaques may be a useful translational model to study the mechanistic effects of CETP inhibition.