Effect of atorvastatin on apolipoprotein B100 containing lipoprotein metabolism in type-2 diabetes

Contribution of intestinal triglyceride-rich lipoproteins to residual atherosclerotic cardiovascular disease risk in individuals with type 2 diabetes on statin therapy

AIMS/HYPOTHESIS

This study explored the hypothesis that significant abnormalities in the metabolism of intestinally derived lipoproteins are present in individuals with type 2 diabetes on statin therapy. These abnormalities may contribute to residual CVD risk.

METHODS

To investigate the kinetics of ApoB-48- and ApoB-100-containing lipoproteins, we performed a secondary analysis of 11 overweight/obese individuals with type 2 diabetes who were treated with lifestyle counselling and on a stable dose of metformin who were from an earlier clinical study, and compared these with 11 control participants frequency-matched for age, BMI and sex. Participants in both groups were on a similar statin regimen during the study. Stable isotope tracers were used to determine the kinetics of the following in response to a standard fat-rich meal: (1) apolipoprotein (Apo)B-48 in chylomicrons and VLDL; (2) ApoB-100 in VLDL, intermediate-density lipoprotein (IDL) and LDL; and (3) triglyceride (TG) in VLDL.

RESULTS

The fasting lipid profile did not differ significantly between the two groups. Compared with control participants, in individuals with type 2 diabetes, chylomicron TG and ApoB-48 levels exhibited an approximately twofold higher response to the fat-rich meal, and a twofold higher increment was observed in ApoB-48 particles in the VLDL1 and VLDL2 density ranges (all p < 0.05). Again comparing control participants with individuals with type 2 diabetes, in the latter, total ApoB-48 production was 25% higher (556 ± 57 vs 446 ± 57 mg/day; p < 0.001), conversion (fractional transfer rate) of chylomicrons to VLDL was around 40% lower (35 ± 25 vs 82 ± 58 pools/day; p=0.034) and direct clearance of chylomicrons was 5.6-fold higher (5.6 ± 2.2 vs 1.0 ± 1.8 pools/day; p < 0.001). During the postprandial period, ApoB-48 particles accounted for a higher proportion of total VLDL in individuals with type 2 diabetes (44%) compared with control participants (25%), and these ApoB-48 VLDL particles exhibited a fivefold longer residence time in the circulation (p < 0.01). No between-group differences were seen in the kinetics of ApoB-100 and TG in VLDL, or in LDL ApoB-100 production, pool size and clearance rate. As compared with control participants, the IDL ApoB-100 pool in individuals with type 2 diabetes was higher due to increased conversion from VLDL2.

CONCLUSIONS/INTERPRETATION

Abnormalities in the metabolism of intestinally derived ApoB-48-containing lipoproteins in individuals with type 2 diabetes on statins may help to explain the residual risk of CVD and may be suitable targets for interventions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02948777.

Severe Hepatic Insulin Resistance Induces Vascular Dysfunction: Improvement by Liver-Specific Insulin Receptor Isoform A Gene Therapy in a Murine Diabetic Model

BACKGROUND

Cardiovascular dysfunction is linked to insulin-resistant states. In this paper, we analyzed whether the severe hepatic insulin resistance of an inducible liver-specific insulin receptor knockout (iLIRKO) might generate vascular insulin resistance and dysfunction, and whether insulin receptor (IR) isoforms gene therapy might revert it.

METHODS

We studied in vivo insulin signaling in aorta artery and heart from iLIRKO. Vascular reactivity and the mRNA levels of genes involved in vascular dysfunction were analyzed in thoracic aorta rings by qRT-PCR. Finally, iLIRKO mice were treated with hepatic-specific gene therapy to analyze vascular dysfunction improvement.

RESULTS

Our results suggest that severe hepatic insulin resistance was expanded to cardiovascular tissues. This vascular insulin resistance observed in aorta artery from iLIRKO mice correlated with a reduction in both PI3K/AKT/eNOS and p42/44 MAPK pathways, and it might be implicated in their vascular alterations characterized by endothelial dysfunction, hypercontractility and eNOS/iNOS levels' imbalance. Finally, regarding long-term hepatic expression of IR isoforms, IRA was more efficient than IRB in the improvement of vascular dysfunction observed in iLIRKO mice.

CONCLUSION

Severe hepatic insulin resistance is sufficient to produce cardiovascular insulin resistance and dysfunction. Long-term hepatic expression of IRA restored the vascular damage observed in iLIRKO mice.

Effects of Extended-Release Nicotinic Acid on Apolipoprotein (a) Kinetics in Hypertriglyceridemic Patients

OBJECTIVE

To determine the mechanisms by which extended-release nicotinic acid reduces circulating lipoprotein (a) concentrations in hypertriglyceridemic patients.

APPROACH AND RESULTS

Eight nondiabetic, obese male subjects (aged 48±12 years; body mass index, 31.2±1.8 kg/m(2)) with hypertriglyceridemia (triglycerides, 226±78 mg/dL) were enrolled in an 8 week, double blind, placebo-controlled cross-over study. At the end of each treatment phase, fasted subjects received a 10 µmol/L per kg bolus injection of [5,5,5-(2)H3]-l-Leucine immediately followed by constant infusion of [5,5,5-(2)H3]-l-Leucine (10 µmol L(-1) kg(-1) h(-1)) for 14 hours, and blood samples were collected. A liquid chromatography-tandem mass spectrometry method was used to study apolipoprotein (a) (Apo(a)) kinetics. The fractional catabolic rate of Apo(a) was calculated with a single compartmental model using the apolipoprotein B100 (ApoB100) containing very low density lipoprotein tracer enrichment as a precursor pool. Extended-release nicotinic acid decreased plasma triglycerides (-46%; P=0.023), raised high-density lipoprotein cholesterol (+20%; P=0.008), and decreased Apo(a) plasma concentrations (-20%; P=0.008). Extended-release nicotinic acid also decreased ApoB100 (22%; P=0.008) and proprotein convertase subtilisin/kexin type 9 (PCSK9, -29%; P=0.008) plasma concentrations. Apo(a) fractional catabolic rate and production rates were decreased by 37% (0.58±0.28 versus 0.36±0.19 pool/d; P=0.008) and 50% (1.4±0.8 versus 0.7±0.4 nmol/kg per day; P=0.008), respectively.

CONCLUSIONS

Extended-release nicotinic acid treatment decreased Apo(a) plasma concentrations by 20%, production rates by 50%, and catabolism by 37%. ApoB100 and PCSK9 concentrations were also decreased by treatment, but no correlation was found with Apo(a) kinetic parameters.

New insights into the pathophysiology of dyslipidemia in type 2 diabetes

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality for patients with type 2 diabetes, despite recent significant advances in management strategies to lessen CVD risk factors. A major cause is the atherogenic dyslipidemia, which consists of elevated plasma concentrations of both fasting and postprandial triglyceride-rich lipoproteins (TRLs), small dense low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) cholesterol. The different components of diabetic dyslipidemia are not isolated abnormalities but closely linked to each other metabolically. The underlying disturbances are hepatic overproduction and delayed clearance of TRLs. Recent results have unequivocally shown that triglyceride-rich lipoproteins and their remnants are atherogenic. To develop novel strategies for the prevention and treatment of dyslipidaemia, it is essential to understand the pathophysiology of dyslipoproteinaemia in humans. Here, we review recent advances in our understanding of the pathophysiology of diabetic dyslipidemia.

Ectopic lipid storage and insulin resistance: a harmful relationship

Obesity increases the risk of metabolic diseases, including insulin resistance and type 2 diabetes, as well as cardiovascular disease. In addition to lipid accumulation in adipose tissue, obesity is associated with increased lipid storage in ectopic tissues, such as skeletal muscle and liver. Furthermore, lipid accumulation in the heart may result in cardiac dysfunction and heart failure. It has recently been demonstrated that intracellular lipid accumulation in ectopic tissues leads to pathological responses and impaired insulin signalling. Here, we will review the current understanding of how lipid storage and lipid droplet physiology affect the risk of developing metabolic diseases.

Temporal changes in concentrations of lipids and apolipoprotein B among adults with diagnosed and undiagnosed diabetes, prediabetes, and normoglycemia: findings from the National Health and Nutrition Examination Survey 1988-1991 to 2005-2008

Background

Diabetes is characterized by profound lipid abnormalities. The objective of this study was to examine changes in concentrations of lipids and apolipoprotein B among participants stratified by glycemic status (diabetes, undiagnosed diabetes, prediabetes, and normoglycemia) in the United States from 1988–1991 to 2005–2008.

Methods

We used data from 3202 participants aged ≥20 years from the National Health and Nutrition Examination Survey (NHANES) III (1988–1991) and 3949 participants aged ≥20 years from NHANES 2005–2008.

Results

Among participants of all four groups, unadjusted and adjusted mean concentrations of total cholesterol, low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol, and apolipoprotein B, but not triglycerides, decreased significantly. Among participants with prediabetes and normoglycemia, unadjusted and adjusted mean concentrations of high-density lipoprotein cholesterol increased significantly. Adjusted mean log-transformed concentrations of triglycerides decreased in adults with undiagnosed diabetes and prediabetes. During 2005–2008, unadjusted concentrations of apolipoprotein B ≥80 mg/dl were observed in 72.8% of participants with diagnosed diabetes, 87.9% of participants with undiagnosed diabetes, 86.6% of participants with prediabetes, and 77.2% of participants with normoglycemia. The unadjusted use of cholesterol-lowering medications rose rapidly, especially among participants with diabetes (from ~1% to ~49%, P <0.001). The use of fenofibrate, gemfibrozil, and niacin rose significantly only among adults with diagnosed diabetes (from ~2% to ~8%, P = 0.011).

Conclusion

Lipid profiles of adults with diabetes improved during the approximately 16-year study period. Nevertheless, large percentages of adults continue to have elevated concentrations of apolipoprotein B.

Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation

Apolipoprotein (apo) E mutants are associated with type III hyperlipoproteinemia characterized by high cholesterol and triglycerides levels. Autosomal dominant hypercholesterolemia (ADH), due to the mutations in the LDLR, APOB, or PCSK9 genes, is characterized by an isolated elevation of cholesterol due to the high levels of low-density lipoproteins (LDLs). We now report an exceptionally large family including 14 members with ADH. Through genome-wide mapping, analysis of regional/functional candidate genes, and whole exome sequencing, we identified a mutation in the APOE gene, c.500_502delTCC/p.Leu167del, previously reported associated with sea-blue histiocytosis and familial combined hyperlipidemia. We confirmed the involvement of the APOE p.Leu167del in ADH, with (1) a predicted destabilization of an alpha-helix in the binding domain, (2) a decreased apo E level in LDLs, and (3) a decreased catabolism of LDLs. Our results show that mutations in the APOE gene can be associated with bona fide ADH.

Low rate of production of apolipoproteins B100 and AI in 2 patients with Anderson disease (chylomicron retention disease)

OBJECTIVE

Anderson disease is a rare inherited lipid malabsorption syndrome associated with hypocholesterolemia and linked to SAR1B mutations. The aim of this article was to analyze the mechanisms responsible for the low plasma apolipoprotein Apo-B100 and Apo-AI in 2 patients with Anderson disease.

METHODS AND RESULTS

A primed constant infusion of (13)C-leucine was administered for 14 hours to determine the kinetics of lipoproteins. In the 2 patients, total cholesterol (77 and 85 mg/dL versus 155±32 mg/dL), triglycerides (36 and 59 versus 82±24 mg/dL), Apo-B100 (48 and 43 versus 71±5 mg/dL), and Apo-AI (47 and 62 versus 130±7 mg/dL) were lower compared with 6 healthy individuals. Very-low-density lipoprotein-B100 production rate of the patients was lower (4.08 and 5.52 mg/kg/day versus 12.96±2.88 mg/kg/day) as was the fractional catabolic rate (5.04 and 4.32 day(-1) versus 12.24±3.84 day(-1)). No difference was observed in intermediate-density lipoprotein-B100 and LDL-B100 kinetic data. The production rate of high-density lipoprotein Apo-AI was lower in the patients (7.92 and 8.64 versus 11.96±1.92 mg/kg/day) and the fractional catabolic rate was higher (0.38 and 0.29 versus 0.22±0.01 day(-1)).

CONCLUSIONS

The low plasma Apo-B100 and Apo-AI concentrations in the patients with Anderson disease were mainly related to low rates of production.

Apolipoprotein E genotype as a most significant predictor of lipid response at lipid-lowering therapy: mechanistic and clinical studies

APOE alleles and apolipoprotein E isoforms control plasma cholesterol level on population level. Among three ɛ2, ɛ3, ɛ4 alleles, ɛ4 allele is associated with the increase in cholesterol level, risk of atherosclerosis and Alzheimer disease, while ɛ2 allele is associated with the decrease in cholesterol level and risk of atherosclerosis. The increase in plasma triglyceride is an independent risk factor of atherosclerosis and triglyceride-high density lipoprotein coupling determines the efficiency of reverse cholesterol transport. The impairment of this coupling specifically at hypertriglyceridemia may be followed by specific lipoprotein markers. The influence of major lipid-lowering drugs on lipoprotein metabolism and association of apoE isoforms with the efficiency of therapy by statins and fibrates are summarized both at isolated and combined increase in plasma triglyceride and cholesterol. APOE polymorphism seems to be a single genetic variant with a confirmed stratification both at candidate gene and at wide genome analyses.

Basal and insulin mediated VLDL-triglyceride kinetics in type 2 diabetic men

OBJECTIVE

Increased very-low-density lipoprotein triglycerides (VLDL-TG) concentration is a central feature of diabetic dyslipidemia. The objective was to compare basal and insulin mediated VLDL-TG kinetics, oxidation, and adipose tissue storage in type 2 diabetic and healthy (nondiabetic) men.

RESEARCH DESIGN AND METHODS

Eleven type 2 diabetic and 11 healthy men, matched for BMI and age, were included. Ex vivo-labeled VLDL-TG tracers, blood and breath samples, fat biopsies, indirect calorimetry, and body composition measures were applied to determine VLDL-TG kinetics, VLDL-TG fatty acids (FA) oxidation, and storage in regional adipose tissue before and during a hyperinsulinemic euglycaemic clamp.

RESULTS

VLDL-TG secretion was significantly greater in diabetic compared with healthy men (basal: 86.9 [31.0] vs. 61.9 [30.0] μmol/min, P = 0.03; clamp: 60.0 [26.2] vs. 34.2 [17.9] μmol · min⁻¹, P = 0.01). The insulin mediated suppression of VLDL-TG secretion was significant in both groups. VLDL-TG clearance was lower in diabetic men (basal: 84.6 [32.7] vs. 115.4 [44.3] ml · min⁻¹, P = 0.08; clamp: 76.3 [30.6] vs. 119.0 [50.2] ml · min⁻¹, P = 0.03). During hyperinsulinemia fractional VLDL-TG FA oxidation was comparable, but in percentage of energy expenditure (EE), significantly higher in diabetic men. Basal VLDL-TG storage was similar, but significantly greater in abdominal compared with leg fat.

CONCLUSIONS

Increased VLDL-TG in type 2 diabetic men is caused by greater VLDL-TG secretion and less so by lower VLDL-TG clearance. The ability of hyperinsulinemia to suppress VLDL-TG secretion appears preserved. During hyperinsulinemia VLDL-TG FA oxidation is significantly increased in proportion of EE in type 2 diabetic men. Greater basal abdominal VLDL-TG storage may help explain the accumulation of upper-body fat in insulin-resistant individuals.

Influence of simvastatin on apoB-100 secretion in non-obese subjects with mild hypercholesterolemia

Statins decrease apoB-100-containing lipoproteins by increasing their fractional catabolic rates through LDL receptor-mediated uptake. Their influence on hepatic secretion of these lipoproteins is controversial. The objective of the study was to examine the influence of simvastatin on the secretion of apoB-100-containing lipoproteins in fasting non-obese subjects. Turnover of apoB-100-containing lipoproteins was investigated using stable isotope-labeled tracers. Multicompartmental modeling was used to derive kinetic parameters. Eight male subjects (BMI 25 +/- 3 kg/m(2)) with mild hypercholesterolemia (LDL cholesterol 135 +/- 30 mg/dL) and normal triglycerides (111 +/- 44 mg/dL) were examined under no treatment (A), under chronic treatment with simvastatin 40 mg/day (B) and after an acute-on-chronic dosage of 80 mg simvastatin under chronic simvastatin treatment (C). Lipoprotein concentrations changed as expected under 40 mg/day simvastatin. Fractional catabolic rates increased in IDL and LDL but not in VLDL fractions versus control [VLDL +35% in B (n.s.) and +21% in C (n.s.); IDL +169% in B (P = 0.08) and +187% in C (P = 0.032); LDL +87% in B (P = 0.025) and +133% in C (P = 0.025)]. Chronic (B) and acute-on-chronic simvastatin treatment (C) did not affect lipoprotein production rates [VLDL -8 and -13%, IDL +47 and +38%, and LDL +19 and +30% in B and C, respectively (all comparisons n.s.)]. The data indicate that simvastatin does not influence the secretion of apoB-100-containing lipoproteins in non-obese subjects with near-normal LDL cholesterol concentrations.

PCSK9 dominant negative mutant results in increased LDL catabolic rate and familial hypobetalipoproteinemia

OBJECTIVE

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a central player in the regulation of cholesterol homeostasis, increasing the low-density lipoprotein (LDL) receptor degradation. Our study aimed at exploring the pathogenic consequences in vivo and in vitro of a PCSK9 prodomain mutation found in a family with hypobetalipoproteinemia (FHBL).

METHODS AND RESULTS

A white 49-year-old diabetic man had profound FBHL (LDLC: 16 mg/dL) whereas his daughter and sister displayed a milder phenotype (LDLC 44 mg/dL and 57 mg/dL, respectively), all otherwise healthy with a normal liver function. A monoallelic PCSK9 double-mutant R104C/V114A cosegregated with FBHL, with no mutation found at other FHBL-causing loci. A dose-effect was also found in FBHL relatives for plasma APOB and PCSK9 (very-low to undetectable in proband, approximately 50% decreased in sister and daughter) and LDL catabolic rate (256% and 88% increased in proband and daughter). Transient transfection in hepatocytes showed severely impaired processing and secretion of the double mutant which acted as a dominant negative over secretion of wild-type PCSK9.

CONCLUSIONS

These results show that heterozygous PCSK9 missense mutations may associate with profound hypobetalipoproteinemia and constitute the first direct evidence in human that decrease of plasma LDLC concentrations associated to PCSK9 LOF mutations are attributable to an increased clearance rate of LDL.

Effects of 20 mg rosuvastatin on VLDL1-, VLDL2-, IDL- and LDL-ApoB kinetics in type 2 diabetes

AIMS/HYPOTHESIS

In addition to its efficacy in reducing LDL-cholesterol, rosuvastatin has been shown to significantly decrease plasma triacylglycerol. The use of rosuvastatin may be beneficial in patients with type 2 diabetes, who usually have increased triacylglycerol levels. However, its effects on the metabolism of triacylglycerol-rich lipoproteins in type 2 diabetic patients remains unknown.

METHODS

We performed a randomised double-blind crossover trial of 6-week treatment with placebo or rosuvastatin 20 mg in eight patients with type 2 diabetes who were being treated with oral glucose-lowering agents. In each patient, an in vivo kinetic study of apolipoprotein B (ApoB)-containing lipoproteins with [13C]leucine was performed at the end of each treatment period. A central randomisation centre used computer-generated tables to allocate treatments. Participants, caregivers and those assessing the outcomes were blinded to group assignment.

RESULTS

Rosuvastatin 20 mg significantly reduced plasma LDL-cholesterol, triacylglycerol and total ApoB. It also significantly reduced ApoB pool sizes of larger triacylglycerol-rich VLDL particles (VLDL1; p = 0.011), smaller VLDL particles (VLDL2; p = 0.011), intermediate density lipoprotein (IDL; p = 0.011) and LDL (p = 0.011). This reduction was associated with a significant increase in the total fractional catabolic rate of VLDL1-ApoB (6.70 +/- 3.24 vs 4.52 +/- 2.34 pool/day, p = 0.049), VLDL2-ApoB (8.72 +/- 3.37 vs 5.36 +/- 2.64, p = 0.011), IDL-ApoB (7.06 +/- 1.68 vs 4.21 +/- 1.51, p = 0.011) and LDL-ApoB (1.02 +/- 0.27 vs 0.59 +/- 0.13, p = 0.011). Rosuvastatin did not change the production rates of VLDL2-, IDL- or LDL-, but did reduce VLDL1-ApoB production rate (12.4 +/- 4.5 vs 19.5 +/- 8.4 mg kg(-1) day(-1), p = 0.035). No side effects of rosuvastatin were observed during the study.

CONCLUSIONS/INTERPRETATION

In type 2 diabetic patients rosuvastatin 20 mg not only induces a significant increase of LDL-ApoB catabolism (73%), but also has favourable effects on the catabolism of triacylglycerol-rich lipoproteins, e.g. a significant increase in the catabolism of VLDL1-ApoB (48%), VLDL2-ApoB (63%) and IDL-ApoB (68%), and a reduction in the production rate of VLDL1-ApoB (-36%). The effects of rosuvastatin on the metabolism of triacylglycerol-rich lipoproteins may be beneficial for prevention of atherosclerosis in type 2 diabetic patients.

Overproduction of very low-density lipoproteins is the hallmark of the dyslipidemia in the metabolic syndrome

Insulin resistance is a key feature of the metabolic syndrome and often progresses to type 2 diabetes. Both insulin resistance and type 2 diabetes are characterized by dyslipidemia, which is an important and common risk factor for cardiovascular disease. Diabetic dyslipidemia is a cluster of potentially atherogenic lipid and lipoprotein abnormalities that are metabolically interrelated. Recent evidence suggests that a fundamental defect is an overproduction of large very low-density lipoprotein (VLDL) particles, which initiates a sequence of lipoprotein changes, resulting in higher levels of remnant particles, smaller LDL, and lower levels of high-density liporotein (HDL) cholesterol. These atherogenic lipid abnormalities precede the diagnosis of type 2 diabetes by several years, and it is thus important to elucidate the mechanisms involved in the overproduction of large VLDL particles. Here, we review the pathophysiology of VLDL biosynthesis and metabolism in the metabolic syndrome. We also review recent research investigating the relation between hepatic accumulation of lipids and insulin resistance, and sources of fatty acids for liver fat and VLDL biosynthesis. Finally, we briefly discuss current treatments for lipid management of dyslipidemia and potential future therapeutic targets.

The hyperenergetic-fed obese dog, a model of disturbance of apolipoprotein B-100 metabolism associated with insulin resistance: kinetic study using stable isotopes

The hyperenergetic-fed beagle dog model of obesity-associated insulin resistance has previously demonstrated lipoprotein abnormalities similar to those of obese insulin-resistant humans. The aim of this study was to check, in the insulin-resistant dog, the mechanism leading to abnormalities in the mass of apolipoprotein B-100 (apo B-100) containing lipoproteins. Six healthy male beagle dogs were overfed with a high-fat diet for 28 +/- 2.5 weeks. Obesity was associated with insulin resistance as assessed by the euglycemic hyperinsulinemic clamp technique. The kinetics of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) apo B-100 were recorded in dogs, at healthy and insulin-resistant states, using a primed constant infusion of [5,5,5-D(3)]leucine. Isotopic enrichment was measured by gas chromatography-mass spectrometry (GC-MS). A multicompartmental model was used for the analysis of tracer kinetics data. Apolipoprotein B-100 concentration was higher in VLDL (2.8-fold, P < .05) but lower in LDL (2-fold, P < .05) in the insulin-resistant compared to the healthy state. Kinetic analysis showed a higher VLDL apo B-100 production (1.7-fold, P < .05). The fractional catabolic rate of VLDL did not change significantly, but the lipolysis was decreased significantly (3-fold, P < .05). The lower LDL apo B-100 level in insulin-resistant dogs was explained by a higher LDL fractional catabolic rate (2.5-fold, P < .05). The mechanisms leading to hypertriglyceridemia (higher production rate and lower lipolysis of VLDL) in insulin-resistant dogs were similar to those described in the insulin-resistant humans.

Dose-dependent effect of rosuvastatin on apolipoprotein B-100 kinetics in the metabolic syndrome

In a randomized, double-blind, crossover trial of 5-week treatment period with placebo or rosuvastatin (10 or 40 mg/day) with 2-week placebo wash-outs between treatments, the dose-dependent effect of rosuvastatin on apolipoprotein (apo) B-100 kinetics in metabolic syndrome subjects were studied. Compared with placebo, there was a significant dose-dependent decrease with rosuvastatin in plasma cholesterol, triglycerides, LDL cholesterol, apoB and apoC-III concentrations and in the apoB/apoA-I ratio, lathosterol:cholesterol ratio, HDL cholesterol concentration and campesterol:cholesterol ratio also increased significantly. Rosuvastatin significantly increased the fractional catabolic rates (FCR) of very-low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and LDL-apoB and decreased the corresponding pool sizes, with evidence of a dose-related effect. LDL apoB production rate (PR) fell significantly with rosuvastatin 40 mg/day with no change in VLDL and IDL-apoB PR. Changes in triglycerides were significantly correlated with changes in VLDL apoB FCR and apoC-III concentration, and changes in lathosterol:cholesterol ratio were correlated with changes in LDL apoB FCR, the associations being more significant with the higher dose of rosuvastatin. In the metabolic syndrome, rosuvastatin decreases the plasma concentration of apoB-containing lipoproteins by a dose-dependent mechanism that increases their rates of catabolism. Higher dose rosuvastatin may also decrease LDL apoB production. The findings provide a dose-related mechanism for the benefits of rosuvastatin on cardiovascular disease in the metabolic syndrome.

Differential effect of fenofibrate and atorvastatin on in vivo kinetics of apolipoproteins B-100 and B-48 in subjects with type 2 diabetes mellitus with marked hypertriglyceridemia

The specific impact of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors and fibrates on the in vivo metabolism of apolipoprotein (apo) B has not been systematically investigated in patients with type 2 diabetes mellitus with high plasma triglyceride (TG) levels. Therefore, the objective of this 2-group parallel study was to examine the differential effects of a 6-week treatment with atorvastatin or fenofibrate on in vivo kinetics of apo B-48 and B-100 in men with type 2 diabetes mellitus with marked hypertriglyceridemia. Apolipoprotein B kinetics were assessed at baseline and at the end of the intervention using a primed constant infusion of [5,5,5-D(3)]-l-leucine for 12 hours in the fed state. Fenofibrate significantly decreased plasma TG levels with no significant change in plasma low-density lipoprotein cholesterol (LDL-C) and apo B levels. On the other hand, atorvastatin significantly reduced plasma levels of TG, LDL-C, and apo B. After treatment with fenofibrate, very low-density lipoprotein (VLDL) apo B-100 pool size (PS) was decreased because of an increase in the fractional catabolic rate (FCR) of VLDL apo B-100. No significant change was observed in the kinetics of LDL apo B-100. Moreover, fenofibrate significantly decreased TG-rich lipoprotein (TRL) apo B-48 PS because of a significant increase in TRL apo B-48 FCR. After treatment with atorvastatin, VLDL and IDL apo B-100 PSs were significantly decreased because of significant elevations in the FCR of these subfractions. Low-density lipoprotein apo B-100 PS was significantly lowered because of a tendency toward decreased LDL apo B-100 production rate (PR). Finally, atorvastatin reduced TRL apo B-48 PS because of a significant decrease in the PR of this subfraction. These results indicate that fenofibrate increases TRL apo B-48 as well as VLDL apo B-100 clearance in men with type 2 diabetes mellitus with marked hypertriglyceridemia, whereas atorvastatin increases both VLDL and IDL apo B-100 clearance and decreases TRL apo B-48 and LDL apo B-100 PR.

Hepatic insulin resistance is sufficient to produce dyslipidemia and susceptibility to atherosclerosis

Insulin resistance plays a central role in the development of the metabolic syndrome, but how it relates to cardiovascular disease remains controversial. Liver insulin receptor knockout (LIRKO) mice have pure hepatic insulin resistance. On a standard chow diet, LIRKO mice have a proatherogenic lipoprotein profile with reduced high-density lipoprotein (HDL) cholesterol and very low-density lipoprotein (VLDL) particles that are markedly enriched in cholesterol. This is due to increased secretion and decreased clearance of apolipoprotein B-containing lipoproteins, coupled with decreased triglyceride secretion secondary to increased expression of Pgc-1 beta (Ppargc-1b), which promotes VLDL secretion, but decreased expression of Srebp-1c (Srebf1), Srebp-2 (Srebf2), and their targets, the lipogenic enzymes and the LDL receptor. Within 12 weeks on an atherogenic diet, LIRKO mice show marked hypercholesterolemia, and 100% of LIRKO mice, but 0% of controls, develop severe atherosclerosis. Thus, insulin resistance at the level of the liver is sufficient to produce the dyslipidemia and increased risk of atherosclerosis associated with the metabolic syndrome.

Effects of different doses of atorvastatin on human apolipoprotein B-100, B-48, and A-I metabolism

Nine hypercholesterolemic and hypertriglyceridemic subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study to test the effect of atorvastatin 20 mg/day and 80 mg/day on the kinetics of apolipoprotein B-100 (apoB-100) in triglyceride-rich lipoprotein (TRL), intermediate density lipoprotein (IDL), and LDL, of apoB-48 in TRL, and of apoA-I in HDL. Compared with placebo, atorvastatin 20 mg/day was associated with significant reductions in TRL, IDL, and LDL apoB-100 pool size as a result of significant increases in fractional catabolic rate (FCR) without changes in production rate (PR). Compared with the 20 mg/day dose, atorvastatin 80 mg/day caused a further significant reduction in the LDL apoB-100 pool size as a result of a further increase in FCR. ApoB-48 pool size was reduced significantly by both atorvastatin doses, and this reduction was associated with nonsignificant increases in FCR. The lathosterol-campesterol ratio was decreased by atorvastatin treatment, and changes in this ratio were inversely correlated with changes in TRL apoB-100 and apoB-48 PR. No significant effect on apoA-I kinetics was observed at either dose of atorvastatin. Our data indicate that atorvastatin reduces apoB-100- and apoB-48-containing lipoproteins by increasing their catabolism and has a dose-dependent effect on LDL apoB-100 kinetics. Atorvastatin-mediated changes in cholesterol homeostasis may contribute to apoB PR regulation.

Effect of n-3 fatty acids on metabolism of apoB100-containing lipoprotein in type 2 diabetic subjects

The effect of long-chain n-3 PUFA on the metabolism of apoB100-containing lipoprotein in diabetic subjects is not fully understood. The objective of the present study was to determine the effect of a daily intake of 1080 mg EPA and 720 mg DHA for diabetic subjects on the kinetics of apoB100-containing lipoprotein in the fasting state. A kinetic study was undertaken to determine the mechanisms involved in the effects of n-3 fatty acids in terms of a decrease in triacylglycerol level in type 2 diabetic patients. We have studied the effect of fish oils on the metabolism of apoB100 endogenously labelled by [5,5,5-2H3]-leucine in type 2 diabetic patients in the fasting state. The kinetic parameters of apoB100 in VLDL, intermediate-density lipoprotein and LDL were determined by compartmental modelling in five diabetic subjects before and 8 weeks after n-3 fatty acid treatment. Treatment did not change the plasma cholesterol level (0.801 (sd 0.120) v. 0.793 (sd 0.163) mmol/l) but lowered the plasma triacylglycerol level (1.776 (sd 0.280) v.1.356 (sd 0.595) mmol/l; P < 0.05). Treated patients showed a decrease in VLDL apoB100 concentration (0.366 (sd 0.030) v.0.174 (sd 0.036) g/l; P < 0.05) related to a decrease in VLDL 1 production (1.49 (sd 0.23) v.0.44 (sd 0.19) mg/kg per h; P < 0.05) and an increase in the VLDL conversion rate (0.031 (sd 0.024) v.0.052 (sd 0.040) per h; P < 0.05), with no change in fractional catabolic rates. Treatment led to a higher direct production of intermediate-density lipoprotein (0.02 (sd 0.01) v.0.24 (sd 0.12) mg/kg per h; P < 0.05). In conclusion, the present study, conducted in the fasting state, showed that supplementation with n-3 fatty acids in type 2 diabetic patients induced beneficial changes in the metabolism of apoB100-containing lipoprotein.

Effects of atorvastatin and apoA-I/phosphatidylcholine discs on triglyceride-rich lipoprotein subfractions as characterized by capillary isotachophoresis

BACKGROUND

The present study examined the effects of atorvastatin and the in vitro effect of apolipoprotein (apo) A-I/phosphatidylcholine (POPC) discs on charge-based triglyceride-rich lipoprotein (TRL) subfractions in a patient with type III hyperlipoproteinemia (HLP) and the apoE2/2 phenotype.

METHODS

Charge-based lipoprotein subfractions were characterized by capillary isotachophoresis (cITP). cITP analysis was performed using plasma that had been prestained with a lipophilic dye on a Beckman P/ACE MDQ system.

RESULTS

Treatment with atorvastatin for 4 weeks markedly decreased the slow (s)-migrating TRL subfraction and both fast- and slow-migrating low-density lipoprotein (LDL) subfractions, but did not affect the fast (f)-migrating TRL subfraction in this patient. ApoA-I/POPC discs consisted of two major charge-based subfractions that had the mobility of cITP fTRL and sTRL. Incubation of plasma from this patient in the presence of apoA-I/POPC discs caused not only a reduction in cITP fast- and intermediate-migrating HDL and an increase in cITP sHDL but also a reduction in fTRL and sTRL and an increase in sLDL.

CONCLUSION

Atorvastatin and apoA-I/POPC discs decreased cITP TRL subfractions in a complementary manner, suggesting that the combination of apoA-I/POPC discs and atorvastatin could be a promising therapeutic approach for hypertriglyceridemia.

Thematic review series: patient-oriented research. What we have learned about VLDL and LDL metabolism from human kinetics studies

Lipoprotein metabolism is the result of a complex network of many individual components. Abnormal lipoprotein concentrations can result from changes in the production, conversion, or catabolism of lipoprotein particles. Studies in hypolipoproteinemia and hyperlipoproteinemia have elucidated the processes that control VLDL secretion as well as VLDL and LDL catabolism. Here, we review the current knowledge regarding apolipoprotein B (apoB) metabolism, focusing on selected clinically relevant conditions. In hypobetalipoproteinemia attributable to truncations in apoB, the rate of secretion is closely linked to the length of apoB. On the other hand, in patients with the metabolic syndrome, it appears that substrate, in the form of free fatty acids, coupled to the state of insulin resistance can induce hypersecretion of VLDL-apoB. Studies in patients with familial hypercholesterolemia, familial defective apoB, and mutant forms of proprotein convertase subtilisin/kexin type 9 show that mutations in the LDL receptor, the ligand for the receptor, or an intracellular chaperone for the receptor are the most important determinants in regulating LDL catabolism. This review also demonstrates the variance of results within similar, or even the same, phenotypic conditions. This underscores the sensitivity of metabolic studies to methodological aspects and thus the importance of the inclusion of adequate controls in studies.

Recent studies of lipoprotein kinetics in the metabolic syndrome and related disorders

PURPOSE OF REVIEW

Dyslipoproteinemia is a cardinal feature of the metabolic syndrome that accelerates atherosclerosis. Recent in-vivo kinetic studies of dyslipidemia in the metabolic syndrome are reviewed here.

RECENT FINDINGS

The dysregulation of lipoprotein metabolism may be caused by a combination of overproduction of VLDL apolipoprotein B-100, decreased catabolism of apolipoprotein B-containing particles, and increased catabolism of HDL apolipoprotein A-I particles. Nutritional modifications and increased physical exercise may favourably alter lipoprotein transport by collectively decreasing the hepatic secretion of VLDL apolipoprotein B and the catabolism of HDL apolipoprotein A-I, as well as by increasing the clearance of LDL apolipoprotein B. Conventional and new pharmacological treatments, such as statins, fibrates and cholesteryl ester transfer protein inhibitors, can also correct dyslipidemia by several mechanisms, including decreased secretion and increased catabolism of apolipoprotein B, as well as increased secretion and decreased catabolism of apolipoprotein A-I.

SUMMARY

Kinetic studies provide a mechanistic insight into the dysregulation and therapy of lipid and lipoprotein disorders. Future research mandates the development of new tracer methodologies with practicable in-vivo protocols for investigating fatty acid turnover, macrophage reverse cholesterol transport, cholesterol transport in plasma, corporeal cholesterol balance, and the turnover of several subpopulations of HDL particles.

REVIEW: Efficacy and mechanisms of action of statins in the treatment of diabetic dyslipidemia

CONTEXT

The Adult Treatment Panel III recommends 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, as first-line lipid-altering therapy for all adult patients with diabetes mellitus. This is based on the well-characterized efficacy and safety profiles of this class of agents as well as several clinical trials demonstrating that statin treatment reduces the risk of cardiovascular events.

EVIDENCE ACQUISITION

This review provides an overview of the effectiveness and mechanisms of action of statins in patients with diabetes mellitus using small efficacy trials and large clinical outcomes trials as well as studies of the effects of statins on apolipoprotein B (apoB) metabolism.

EVIDENCE SYNTHESIS

The major findings presented are a review of mechanistic studies of selected subjects with diabetes mellitus and dyslipidemia and a compilation of results from large-scale clinical trials of patients with diabetes.

CONCLUSIONS

Statins are highly efficacious as low-density lipoprotein cholesterol-lowering agents and have more modest effects on very low-density lipoprotein triglyceride and high-density lipoprotein cholesterol levels. The effects of statins on plasma lipids and lipoproteins result from their ability to both increase the efficiency with which very low-density lipoprotein and low-density lipoprotein are cleared from the circulation and reduce the production of apoB-containing lipoproteins by the liver. Additional investigations are needed to clarify the mechanisms by which statins reduce apoB secretion from the liver.

The effect of high-dose simvastatin on triglyceride-rich lipoprotein metabolism in patients with type 2 diabetes mellitus

Statins decrease triglycerides (TGs) in addition to decreasing low density lipoprotein-cholesterol. Although the mechanism for the latter effect is well understood, it is still unclear how TG decrease is achieved with statin therapy. Because hypertriglyceridemia is common in obese patients with type 2 diabetes mellitus, we studied triglyceride-rich lipoprotein triglyceride (TRL-TG) turnover in 12 such subjects using stable isotopically labeled glycerol. The diabetic subjects were studied after 12 weeks of placebo and after a similar course of therapy with simvastatin (80 mg daily) in a single-blind design. The results were compared with those from six nonobese nondiabetic control subjects. Simvastatin therapy reduced serum TGs by 35% in the diabetic subjects. Compared with the control subjects, TRL-TG secretion was almost 2-fold higher in the diabetic subjects (45.4 +/- 4.9 vs. 24.4 +/- 1.9 micromol/min; P < 0.002) and was unaffected by simvastatin therapy. However, TRL-TG clearance was significantly increased in the diabetic subjects during simvastatin treatment compared with placebo (0.25 +/- 0.03 vs. 0.16 +/- 0.02 pools/h; P < 0.002). This change was accompanied by a 49% increase in preheparin plasma lipase activity (P < 0.03) and a 21% increase in postheparin LPL activity (P < 0.01). Together, these findings provide strong evidence that the effect of statins on serum TGs is related to an increase in LPL activity, resulting in accelerated delipidation of TRL particles. The effect of high-dose simvastatin on triglyceride-rich lipoprotein metabolism in patients with type 2 diabetes mellitus.

Treatment with high-dose simvastatin reduces secretion of apolipoprotein B-lipoproteins in patients with diabetic dyslipidemia

HMG-CoA reductase inhibitors (statins) are effective lipid-altering drugs for the treatment of dyslipidemia in patients with type 2 diabetes mellitus. We conducted a randomized, double-blind, placebo-controlled, crossover design trial to determine the effects of simvastatin, 80 mg/day, on plasma lipid and lipoprotein levels and on the metabolism of apolipoprotein B (apoB) in VLDL, intermediate density lipoprotein (IDL), and LDL and of triglycerides (TGs) in VLDL. Simvastatin therapy decreased TG, cholesterol, and apoB significantly in VLDL, IDL, and LDL. These effects were associated with reduced production of LDL-apoB, mainly as a result of reduced secretion of apoB-lipoproteins directly into the LDL density range. Statin therapy also reduced hepatic production of VLDL-TG. There were no effects of simvastatin on the fractional catabolic rates of VLDL-apoB or -TG or LDL-apoB. The basis for decreased VLDL-TG secretion during simvastatin treatment is not clear, but recent studies suggest that statins may activate peroxisomal proliferator-activated receptor alpha (PPARalpha). Activation of PPARalpha could lead to increased hepatic oxidation of fatty acids and less synthesis of TG for VLDL assembly.

Enhanced Conversion of Triglyceride-Rich Lipoproteins and Increased Low-Density Lipoprotein Removal in LPLS447X Carriers

OBJECTIVE

Lipoprotein lipase (LPL) exerts 2 principal actions, comprising enzymatic hydrolysis of triglyceride-rich lipoproteins (TRLs) and nonenzymatic ligand capacity for enhancing lipoprotein removal. The common LPLS447X variant has been associated with cardiovascular protection, for which the mechanism is unknown. We therefore evaluated enzymatic and nonenzymatic consequences of this LPL variant on TRL metabolism.

METHODS AND RESULTS

TRL apolipoprotein B100 (apoB100) metabolism was determined in 5 homozygous LPLS447X carriers and 5 controls. Subjects were continuously fed and received infusion of stable isotope l-[1-(13C)]-valine. Results were analyzed by SAAMII modeling. Also, preheparin and postheparin LPL concentration and activity were measured. Compared with controls, carriers presented increased very low-density lipoprotein 1 (VLDL1) to VLDL2 apoB100 flux (P=0.04), increased VLDL2 to intermediate-density lipoprotein (IDL) apoB100 flux (P=0.02), increased IDL to low-density lipoprotein (LDL) apoB100 flux (P=0.049), as well as an increased LDL clearance (P=0.04). Additionally, IDL apoB100 synthesis was attenuated (P=0.05). Preheparin LPL concentration was 4-fold higher compared with controls (P=0.01), and a correlation was observed between preheparin LPL concentration and LDL clearance (r2=0.92; P=0.01).

CONCLUSIONS

Enhanced TRL conversion and enhanced LDL removal combined with increased preheparin LPL concentration suggest increased enzymatic consequences as well as increased nonenzymatic consequences of LPL in LPLS447X carriers, which might both contribute to the cardiovascular benefit of this LPL variant.

Influence of atorvastatin on apolipoprotein E and AI kinetics in patients with type 2 diabetes

Atorvastatin reduces both plasma cholesterol and triglyceride concentrations in patients with type 2 diabetes, but mechanisms underlying triglyceride decrease and the effect of atorvastatin on high density lipoprotein (HDL) still remain unclear. Apolipoprotein (apo) E plays a crucial role in modulating production and clearance of triglyceride-rich very low density lipoprotein (VLDL). The main effect of apoAI is to modulate HDL metabolism. The aim of this work was to study the influence of atorvastatin on apoAI and apoE kinetics and to determine whether its hypocholesterolemic and hypotriglyceridemic effects could be related to changes in this apolipoprotein metabolism. Plasma VLDL-apoE, HDL-apoE, and HDL-apoAI were studied in seven patients with diabetes with mixed hyperlipidemia using a stable isotope labeling technique ([(2)H3]leucine-primed constant infusion) and monocompartmental model before and after 2 months of treatment with 40 mg/day of atorvastatin. Plasma apoE concentration was significantly reduced (44.1 +/- 19.1 versus 32 +/- 11.6 mg/l, p < 0.05) after treatment. This decrease was associated with a diminution of HDL-apoE concentration (17.46 +/- 6.71 versus 13.37 +/- 6.05 mg/l, p < 0.05) and production rate (0.202 +/- 0.085 versus 0.119 +/- 0.047 mg/kg/day, p < 0.05), whereas an increase in VLDL-apoE concentration (6.44 +/- 2.16 before versus 9.23 +/- 4.02 mg/l after, p < 0.05) and production rate (0.827 +/- 0.367 versus 1.524 +/- 0.664 mg/kg/day, p < 0.05) was observed. No significant difference was observed after treatment for apoAI parameters. We conclude that atorvastatin treatment promotes different apoE distribution between HDL and VLDL, favoring VLDL apoE content. The increased number of apoE per VLDL particle suggests that atorvastatin could enhance the direct catabolism of triglyceride-rich VLDL through apoE receptor pathways.

Metabolism of cholesterol ester of apolipoprotein B100-containing lipoproteins in dogs: evidence for disregarding cholesterol ester transfer

BACKGROUND

It has been shown that dogs exhibit no cholesterol ester transfer protein (CETP) activity in vitro, in contrast to humans. The aim of our study was to determine modalities of in vivo plasma cholesterol ester turnover in this species, using a kinetic approach with stable isotopes.

MATERIALS AND METHODS

Kinetics of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) were studied in seven adult male Beagle dogs using a dual isotope approach through endogenous labelling of both their cholesterol moiety and their protein moiety. A primed constant infusion of both [1,2(13)C]acetate and [5,5,5-2H3]leucine enabled us to obtain measurable deuterium enrichments by gas chromatography-mass spectrometry for plasma leucine and apoB100, as well as measurable 13C enrichment by gas chromatography-combustion-isotopic ratio mass spectrometry for unesterified cholesterol and cholesterol ester in the VLDL and LDL. Two identical multicompartmental models (SAAM II) were used together for the analysis of tracer kinetics' data of proteins and cholesterol.

RESULTS

Characterization of the apoB100-containing lipoprotein cholesterol ester model allowed determination of kinetic parameters of VLDL and LDL cholesterol ester metabolism. We succeeded in modelling VLDL and LDL cholesterol ester metabolism and apoB100 metabolism simultaneously. Fractional catabolic rate (FCR) of apoB100 and CE had the same values. Introducing cholesterol ester transfer between lipoproteins in the model did not significantly improve the fit. Total VLDL FCR was 2.97 +/- 01.47 h(-1). Approximately one-quarter corresponded to the direct removal of VLDL (0.81 +/- 00.34 h(-1)) and the remaining three-quarters corresponded to the fraction of VLDL converted to LDL, which represented a conversion of VLDL into LDL of 2.16 +/- 01.16 h(-1). Low-density lipoproteins were produced exclusively from VLDL conversion and were then removed (0.031 +/- 0.004 h(-1)) from plasma.

CONCLUSION

These kinetic data showed that VLDL cholesterol ester and LDL cholesterol ester metabolism followed VLDL and LDL apoB100 metabolism, and that consequently there is no in vivo transfer of cholesterol ester in dogs.

Phenotypes, genotypes and response to statin therapy

PURPOSE OF REVIEW

Response to statin treatment can vary widely from person to person as a result of inherited traits (genotype) and acquired characteristics such as obesity (phenotype). The aim of this review is to describe what is known about factors that determine a patient's response, and to offer a mechanism to explain how plasma triglyceride influences the nature and magnitude of lipid lowering on statin therapy.

RECENT FINDINGS

In normotriglyceridemic individuals statins have little impact on the concentration of large VLDL, but as basal plasma triglyceride rises there is an increasing tendency for large VLDL, chylomicrons, chylomicron remnants and small, dense LDL to fall on treatment. These phenotype-dependent effects are in contrast to the phenotype-independent actions on IDL and LDL. Recent studies have also revealed that the principal mechanism by which statins lower VLDL (and LDL) in hypertriglyceridemic individuals is by stimulation of lipoprotein clearance. Individuals with low HDL-cholesterol are increasingly treated with statins. The increase in this lipoprotein affects the subfraction distribution, with a specific increase in alpha1 HDL components. Polymorphism in the promoter for the ABCG8 gene has been linked to variations in response to statins; individuals with the rarer D19H genotype exhibit a greater reduction in LDL-cholesterol. Similarly, the magnitude of the statin-induced increase in HDL-cholesterol has been linked to a polymorphism in the promoter for apolipoprotein A1.

SUMMARY

Statins are administered to a wide range of individuals on an empirical basis. Investigation of the phenotype and genotype influences on treatment response will allow a more tailored use of these drugs.

Apolipoprotein B100 metabolism in autosomal-dominant hypercholesterolemia related to mutations in PCSK9

OBJECTIVE

We have reported further heterogeneity in familial autosomal-dominant hypercholesterolemia (FH) related to mutation in proprotein convertase subtilisin/kexin type 9 (PCSK9) gene previously named neural apoptosis regulated convertase 1 (Narc-1). Our aim was to define the metabolic bases of this new form of hypercholesterolemia.

METHODS AND RESULTS

In vivo kinetics of apolipoprotein B100-containing lipoproteins using a 14-hour primed constant infusion of [2H3] leucine was conducted in 2 subjects carrying the mutation S127R in PCSK9, controls subjects, and FH subjects with known mutations on the low-density lipoprotein (LDL) receptor gene (LDL-R). Apo B100 production, catabolism, and transfer rates were estimated from very LDL (VLDL), intermediate-density lipoprotein (IDL), and LDL tracer enrichments by compartmental analysis. PCSK9 mutation dramatically increased the production rate of apolipoprotein B100 (3-fold) compared with controls or LDL-R mutated subjects, related to direct overproduction of VLDL (3-fold), IDL (3-fold), and LDL (5-fold). The 2 subjects also showed a decrease in VLDL and IDL conversion (10% to 30% of the controls). LDL fractional catabolic rate was slightly decreased (by 30%) compared with controls but still higher than LDL-R-mutated subjects.

CONCLUSIONS

These results showed that the effect of the S127R mutation of PCSK9 on plasma cholesterol homeostasis is mainly related to an overproduction of apolipoprotein B100.