Apolipoprotein E (APO-E) binds to the beta-amyloid peptide and is present in senile neuritic plaques in Alzheimer's disease (AD). The epsilon 4 isoform of APO-E has been associated with both sporadic and familial late-onset AD, implying a causal role. Among patients and control subjects similar in age, gender, and ethnic group from the New York City community of Washington Heights-Inwood, we found that the odds ratio (OR) for AD associated with homozygosity for APO-epsilon 4 was 17.9 (95% confidence interval [CI], 4.6-69.8) and that associated with heterozygosity for APO-epsilon 4 was 4.2 (95% CI, 1.8-9.5) compared with persons with other APO-E genotypes. The association was stronger among patients with sporadic disease (OR = 10.3; 95% CI, 3.4-31.1) than among those with a family history of dementia in a first-degree relative (OR = 0.9; 95% CI, 0.1-13.5). The association between APO-epsilon 4 and AD did not differ according to age at onset (< 65 vs > or = 65), but appeared to vary across the 3 ethnic groups investigated (black, Hispanic, and white). Our data confirm the association between AD and APO-epsilon 4 and support the hypothesis that the APO-epsilon 4 allele either confers genetic susceptibility to AD or may be in linkage disequilibrium with another susceptibility locus. Ethnic variability in the allelic frequency of APO-epsilon 4 in the elderly warrants further investigation.

Background Alirocumab, a monoclonal antibody to proprotein convertase subtilisin/kexin type 9 (PCSK9), lowers plasma low density lipoprotein cholesterol (LDL-C) and apolipoprotein B100 (apoB). Although studies in mice and cells have identified increased hepatic LDL receptors as the basis for LDL lowering by PCSK9 inhibitors, there have been no human studies characterizing the effects of PCSK9 inhibitors on lipoprotein metabolism. In particular, it is not known if inhibition of PCSK9 has any effects on very low density lipoprotein (VLDL) or intermediate density lipoprotein (IDL) metabolism. Inhibition of PCSK9 also results in reductions of plasma Lp(a) levels. The regulation of plasma Lp(a) levels, including the role of LDL receptors (LDLRs) in the clearance of Lp(a), is poorly defined, and there have been no mechanistic studies of the Lp(a) lowering by alirocumab in humans. Methods Eighteen (10F, 8M) participants completed a placebo-controlled, two-period study. They received 2 doses of placebo, 2 weeks apart, followed by 5 doses of 150 mg of alirocumab, 2 weeks apart. At the end of each period, fractional clearance rates (FCR) and production rates (PR) of apoB and apo(a) were determined. In 10 participants, postprandial triglycerides (TG) and apoB48 levels were measured. Results Alirocumab reduced ultracentrifugally isolated LDL-C by 55.1%, LDL-apoB by 56.3%, and plasma Lp(a) by 18.7%. The fall in LDL-apoB was due to an 80.4% increase in LDL-apoB FCR and a 23.9% reduction in LDL-apoB PR. The latter was associated with a 46.1% increase in IDL-apoB FCR coupled with a 27.2% decrease in conversion of IDL to LDL. The FCR of apo(a) tended to increase (24.6%) without any change in apo(a) PR. Alirocumab had no effects on FCRs or PRs of VLDL-apoB and VLDL-TG, or on postprandial plasma TG or apoB48 concentrations. Conclusions Alirocumab decreased LDL-C and LDL-apoB by increasing IDL- and LDL-apoB FCRs, and decreasing LDL-apoB PR. These results are consistent with increases in LDLRs available to clear IDL and LDL from blood during PCSK9 inhibition. The possible increase in apo(a) FCR during alirocumab treatment suggests that increased LDLRs may also play a role in the reduction of plasma Lp(a). Clinical Trials Registration Clinical trials.gov # NCT01959971

Elevated plasma levels of VLDL triglycerides (TGs) are characteristic of patients with type 2 diabetes mellitus (T2DM) and are associated with increased production rates (PRs) of VLDL TGs and apoB. Lipoprotein lipase-mediated (LPL-mediated) lipolysis of VLDL TGs may also be reduced in T2DM if the level of LPL is decreased and/or the level of plasma apoC-III, an inhibitor of LPL-mediated lipolysis, is increased. We studied the effects of pioglitazone (Pio), a PPARgamma agonist that improves insulin sensitivity, on lipoprotein metabolism in patients with T2DM. Pio treatment reduced TG levels by increasing the fractional clearance rate (FCR) of VLDL TGs from the circulation, without changing direct removal of VLDL particles. This indicated increased lipolysis of VLDL TGs during Pio treatment, a mechanism supported by our finding of increased plasma LPL mass and decreased levels of plasma apoC-III. Lower apoC-III levels were due to reduced apoC-III PRs. We saw no effects of Pio on the PR of either VLDL TG or VLDL apoB. Thus, Pio, a PPARgamma agonist, reduced VLDL TG levels by increasing LPL mass and inhibiting apoC-III PR. These 2 changes were associated with an increased FCR of VLDL TGs, almost certainly due to increased LPL-mediated lipolysis.

Elevated plasma levels of VLDL triglycerides (TGs) are characteristic of patients with type 2 diabetes mellitus (T2DM) and are associated with increased production rates (PRs) of VLDL TGs and apoB. Lipoprotein lipase-mediated (LPL-mediated) lipolysis of VLDL TGs may also be reduced in T2DM if the level of LPL is decreased and/or the level of plasma apoC-III, an inhibitor of LPL-mediated lipolysis, is increased. We studied the effects of pioglitazone (Pio), a PPARγ agonist that improves insulin sensitivity, on lipoprotein metabolism in patients with T2DM. Pio treatment reduced TG levels by increasing the fractional clearance rate (FCR) of VLDL TGs from the circulation, without changing direct removal of VLDL particles. This indicated increased lipolysis of VLDL TGs during Pio treatment, a mechanism supported by our finding of increased plasma LPL mass and decreased levels of plasma apoC-III. Lower apoC-III levels were due to reduced apoC-III PRs. We saw no effects of Pio on the PR of either VLDL TG or VLDL apoB. Thus, Pio, a PPARγ agonist, reduced VLDL TG levels by increasing LPL mass and inhibiting apoC-III PR. These 2 changes were associated with an increased FCR of VLDL TGs, almost certainly due to increased LPL-mediated lipolysis.

Objective: Apolipoprotein (apo)CIII inhibits lipoprotein lipase (LpL)-mediated lipolysis of very low density lipoprotein (VLDL) TG and decreases hepatic uptake of VLDL remnants. The discovery that 5% of Lancaster Old Order Amish are heterozygous for the APOC3 R19X null mutation provided the opportunity to determine the effects of a naturally occurring reduction in apoC-III levels on the metabolism of atherogenic containing lipoproteins. Approach and Results: We conducted stable isotope studies of VLDL-TG and apoB100 in five individuals heterozygous for the null mutation APOC3 R19X (CT) and their unaffected (CC) siblings. Fractional clearance rates (FCRs) and production rates (PRs) of VLDL-TG and apoB100 in VLDL, intermediate density lipoprotein (IDL), low density lipoprotein (LDL), apoCIII and apoCII were determined. Affected (CT) individuals had 49% reduction in plasma apoCIII levels compared to CCs (p<0.01) and reduced plasma levels of TG (35%, p<0.02), VLDL TG (45%, p<0.02), and VLDL-apoB100 (36%,p<0.05). These changes were due to higher FCRs of VLDL-TG and VLDL-apoB100 with no differences in PRs. CTs had higher rates of the conversion of VLDL remnants to LDL compared to CCs. In contrast, rates of direct removal of VLDL remnants did not differ between the groups. As a result, the flux of apoB100 from VLDL to LDL did not change, and the plasma levels of LDL-chol and LDL-apoB100 were not lower in the CT group. ApoCIII PR was lower in CTs compared to CCs, whereas apoCII PR was not different between the two groups. The FCRs of both apoCIII and apoCII were higher in CTs than CCs. Conclusions: These studies demonstrate that 50% reductions in plasma apoCIII, in otherwise healthy subjects, results in a significantly higher rate of conversion of VLDL to LDL, with little effect on direct hepatic uptake of VLDL. When put in the context of studies demonstrating significant protection from cardiovascular events in individuals with loss of function variants in the APOC3 gene, our results provide strong evidence that therapies which increase the efficiency of conversion of VLDL to LDL, thereby reducing remnant concentrations, should reduce the risk of cardiovascular disease.

Apolipoprotein E polymorphisms are important determinants of blood lipid levels and have been associated with longevity and atherosclerosis. However, information is limited on the effects of apo E variation on the lipids of nonwhite and elderly individuals. We tested the hypothesis that apo E polymorphisms are associated with plasma lipid levels in an elderly, multiethnic population. Cross-sectional data from 1068 noninstitutionalized individuals from northern Manhattan over the age of 64 who were not on a lipid-lowering diet or drug were analyzed. The ethnic distribution was 34% African-Americans, 47% Hispanics, and 19% non-Hispanic Caucasians. In the entire group, the most prevalent apo E allele was epsilon 3 (76%), followed by epsilon 4 (16%) and epsilon 2 (8%); epsilon 4 was more prevalent in African-Americans (21%) than in non-Hispanic Caucasians (12%) or Hispanics (14%). The apo epsilon 2 allele was the most important correlate of plasma lipids, but association varied across ethnoracial groups. After being adjusted for age, sex, obesity, diabetes mellitus, and alcohol intake, LDL cholesterol levels declined with each apo epsilon 2 allele by 8.8 mg/dL in Hispanics and by 25.6 and 18.1 mg/dL in non-Hispanic Caucasians and African-Americans, respectively (P < .001). No significant independent effect was noted for any apo E genotype on HDL cholesterol. Overall, there was a reduction in the total/HDL cholesterol ratio, per apo epsilon 2 allele, of 0.82 in non-Hispanic Caucasians and 0.43 and 0.48 in African-American and Hispanic individuals, respectively (P < .05). In a multivariate model, apo epsilon 4 did not significantly affect plasma lipid levels. Plasma triglyceride levels were inversely correlated with the number of apo epsilon 4 alleles (175, 159, and 143 mg/dL with 0, 1, and 2 alleles, respectively; P =.002), and this effect increased with age. Thus, in an elderly, multiethnic population, apolipoprotein E polymorphisms were important determinants of blood lipids, with differing effects depending on ethnicity. The presence of apo epsilon 2 was associated with lower LDL cholesterol levels and total/HDL cholesterol ratio, although apo epsilon genotype did not influence HDL cholesterol levels. Prospective studies are needed to test whether apo epsilon 2 protects against incident cardiovascular disease in the elderly.

Objective Anacetrapib, an inhibitor of cholesteryl ester transfer protein (CETP) activity, increases plasma concentrations of HDL-C, apoA-I, apoA-II, and CETP. The mechanisms responsible for these treatment-related increases in apolipoproteins and plasma CETP are unknown. We performed a randomized, placebo-controlled, double-blind, fixed-sequence study to examine the effects of anacetrapib on the metabolism of HDL apoA-I and apoA-II and plasma CETP. Approach and Results Twenty-nine participants received atorvastatin 20mg/day plus placebo for four weeks, followed by atorvastatin plus anacetrapib 100 mg/day for 8 weeks (ATV-ANA). Ten participants received double placebo for four weeks followed by placebo plus anacetrapib for 8 weeks (PBO-ANA). At the end of each treatment, we examined the kinetics of HDL apoA-I, HDL apoA-II and plasma CETP after D3-leucine administration as well as 2D gel analysis of HDL subspecies. In the combined ATV-ANA and PBO-ANA groups, anacetrapib treatment increased plasma HDL-C (63.0%, P < 0.001) and apoA-I levels (29.5%, P < 0.001). These increases were associated with reductions in HDL apoA-I fractional clearance rate (FCR) (18.2%, P = 0.002) without changes in production rate (PR). Although the apoA-II levels increased by 12.6% (P < 0.001), we could not discern significant changes in either apoA-II FCR or PR. CETP levels increased 102% (P < 0.001) on anacetrapib due to a significant reduction in the FCR of CETP (57.6%, P < 0.001) with no change in CETP PR. Conclusion Anacetrapib treatment increases HDL apoA-I and CETP levels by decreasing the fractional clearance rate of each protein. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT00990808

Mipomersen is a 20mer antisense oligonucleotide (ASO) that inhibits apolipoprotein B (apoB) synthesis; its low-density lipoprotein (LDL)–lowering effects should therefore result from reduced secretion of very-low-density lipoprotein (VLDL). We enrolled 17 healthy volunteers who received placebo injections weekly for 3 weeks followed by mipomersen weekly for 7 to 9 weeks. Stable isotopes were used after each treatment to determine fractional catabolic rates and production rates of apoB in VLDL, IDL (intermediate-density lipoprotein), and LDL, and of triglycerides in VLDL. Mipomersen significantly reduced apoB in VLDL, IDL, and LDL, which was associated with increases in fractional catabolic rates of VLDL and LDL apoB and reductions in production rates of IDL and LDL apoB. Unexpectedly, the production rates of VLDL apoB and VLDL triglycerides were unaffected. Small interfering RNA–mediated knockdown of apoB expression in human liver cells demonstrated preservation of apoB secretion across a range of apoB synthesis. Titrated ASO knockdown of apoB mRNA in chow-fed mice preserved both apoB and triglyceride secretion. In contrast, titrated ASO knockdown of apoB mRNA in high-fat–fed mice resulted in stepwise reductions in both apoB and triglyceride secretion. Mipomersen lowered all apoB lipoproteins without reducing the production rate of either VLDL apoB or triglyceride. Our human data are consistent with longstanding models of posttranscriptional and posttranslational regulation of apoB secretion and are supported by in vitro and in vivo experiments. Targeting apoB synthesis may lower levels of apoB lipoproteins without necessarily reducing VLDL secretion, thereby lowering the risk of steatosis associated with this therapeutic strategy.