Apolipoprotein B-100 Kinetics Research Articles

Effects of PNPLA3 I148M on hepatic lipid and very-low-density lipoprotein metabolism in humans.

The phospholipase domain-containing 3 gene (PNPLA3)-148M variant is associated with liver steatosis but its influence on the metabolism of triglyceride-rich lipoproteins remains unclear. Here, we investigated the kinetics of large, triglyceride-rich very-low-density lipoprotein (VLDL), (VLDL1 ), and smaller VLDL2 in homozygotes for the PNPLA3-148M variant. The kinetics of apolipoprotein (apo) B100 (apoB100) and triglyceride in VLDL subfractions were analysed in nine subjects homozygous for PNPLA3-148M and nine subjects homozygous for PNPLA3-148I (controls). Liver fat was >3-fold higher in the 148M subjects. Production rates for apoB100 and triglyceride in VLDL1 did not differ significantly between the two groups. Likewise, production rates for VLDL2 -apoB100 and -triglyceride, and fractional clearance rates for both apoB100 and triglyceride in VLDL1 and VLDL2 , were not significantly different. Despite the higher liver fat content in PNPLA3 148M homozygotes, there was no increase in VLDL production. Equally, VLDL production was maintained at normal levels despite the putative impairment in cytosolic lipid hydrolysis in these subjects.

Effects of TM6SF2 E167K on hepatic lipid and very low-density lipoprotein metabolism in humans.

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic lipid accumulation. The transmembrane 6 superfamily member 2 (TM6SF2) E167K genetic variant associates with NAFLD and with reduced plasma triglyceride levels in humans. However, the molecular mechanisms underlying these associations remain unclear. We hypothesized that TM6SF2 E167K affects hepatic very low-density lipoprotein (VLDL) secretion and studied the kinetics of apolipoprotein B100 (apoB100) and triglyceride metabolism in VLDL in homozygous subjects. In 10 homozygote TM6SF2 E167K carriers and 10 matched controls, we employed stable-isotope tracer and compartmental modeling techniques to determine apoB100 and triglyceride kinetics in the 2 major VLDL subfractions: large triglyceride-rich VLDL1 and smaller, less triglyceride-rich VLDL2. VLDL1-apoB100 production was markedly reduced in homozygote TM6SF2 E167K carriers compared with controls. Likewise, VLDL1-triglyceride production was 35% lower in the TM6SF2 E167K carriers. In contrast, the direct production rates for VLDL2-apoB100 and triglyceride were not different between carriers and controls. In conclusion, the TM6SF2 E167K genetic variant was linked to a specific reduction in hepatic secretion of large triglyceride-rich VLDL1. The impaired secretion of VLDL1 explains the reduced plasma triglyceride concentration and provides a basis for understanding the lower risk of cardiovascular disease associated with the TM6SF2 E167K genetic variant.

Lipoprotein (a) and Low-density lipoprotein apolipoprotein B metabolism following apheresis in patients with elevated lipoprotein(a) and coronary artery disease.

Lipoprotein apheresis effectively lowers lipoprotein(a) [Lp(a)] and low-density lipoprotein (LDL) by approximately 60%-70%. The rebound of LDL and Lp(a) particle concentrations following lipoprotein apheresis allows the determination of fractional catabolic rate (FCR) and hence production rate (PR) during non-steady state conditions. We aimed to investigate the kinetics of Lp(a) and LDL apolipoprotein B-100 (apoB) particles in patients with elevated Lp(a) and coronary artery disease undergoing regular apheresis. A cross-sectional study was carried out in 13 patients with elevated Lp(a) concentration (>500mg/L) and coronary artery disease. Lp(a) and LDL-apoB metabolic parameters, including FCR and PR were derived by the fit of a compartment model to the Lp(a) and LDL-apoB concentration data following lipoprotein apheresis. The FCR of Lp(a) was significantly lower than that of LDL-apoB (0.39 [0.31, 0.49] vs 0.57 [0.46, 0.71] pools/day, P=0.03) with no significant differences in the corresponding PR (14.80 [11.34, 19.32] vs 15.73 [11.93, 20.75] mg/kg/day, P=0.80). No significant associations were observed between the FCR and PR of Lp(a) and LDL-apoB. In patients with elevated Lp(a), the fractional catabolism of Lp(a) is slower than that of LDL-apoB particles, implying that different metabolic pathways are involved in the catabolism of these lipoproteins. These findings have implications for new therapies for lowering apolipoprotein(a) and apoB to prevent atherosclerotic cardiovascular disease.

Differential Effects of Estrogen and Progestin on Apolipoprotein B100 and B48 Kinetics in Postmenopausal Women.

The distinct effects of the estrogen and progestin components of hormonal therapy on the metabolism of apolipoprotein (apo) B-containing lipoproteins have not been studied. We enrolled eight healthy postmenopausal women in a placebo-controlled, randomized, double-blind crossover study. Each subject received placebo, conjugated equine estrogen (CEE, 0.625 mg/day) and CEE plus medroxyprogesterone acetate (MPA, 2.5 mg/day) for 8 weeks in a randomized order, with a 4-week washout between phases. Main outcomes were the fractional catabolic rate (FCR) and production rate (PR) of apo B100 in triglyceride-rich lipoproteins (TRL), intermediate-density lipoproteins (IDL) and low -density lipoprotein (LDL) and of apo B48 in TRL. Compared to placebo, CEE increased TRL apo B100 PR (p = 0.04). CEE also increased LDL apo B100 FCR (p = 0.02), but this effect was offset by a significant increase in LDL apo B100 PR (p = 0.04). Adding MPA to CEE negated the CEE effects resulting in no significant changes in TRL apo B100 PR and LDL apo B100 FCR and PR relative to placebo. Relative to placebo, during CEE there was a trend toward a reduction in plasma apo B48 concentrations and PR (p = 0.07 and p = 0.12, respectively). Compared with CEE, CEE + MPA significantly increased TRL apo B48 FCR (p = 0.02) as well as apo B48 PR (p = 0.01), resulting in no significant changes in apo B48 concentration. Estrogen and progestin have independent and opposing effects on the metabolism of the atherogenic apo B100- and apo B48-containing lipoproteins.

Dietary medium-chain triglyceride supplementation has no effect on apolipoprotein B-48 and apolipoprotein B-100 kinetics in insulin-resistant men

Medium-chain triglyceride (MCT) supplements are used by clinicians to treat patients with severe hypertriglyceridemia who are at risk of pancreatitis. However, the potential mechanisms underlying the effects of MCT on triglyceride-rich lipoprotein (TRL) metabolism have not yet been thoroughly examined in humans. This double-blind randomized crossover study compared the impact of 4 wk of supplementation with 20 g MCT oil/d or 20 g corn oil/d on the kinetics of apolipoprotein (apo) B-48-containing TRLs and apo B-100-containing very-low-density lipoprotein (VLDL), as well as on the expression of key intestinal genes involved in lipid metabolism in 28 obese, insulin-resistant men. The in vivo kinetics of TRL apo B-48 and VLDL apo B-100 were assessed by using a primed-constant infusion of l-[5,5,5-d3]leucine for 12 h in the fed state. Real-time polymerase chain reaction quantification was performed on duodenal biopsy samples taken at the end of each phase of supplementation. Compared with corn oil, MCT supplements had no significant effect on plasma lipoprotein profile or TRL apo B-48 and VLDL apo B-100 kinetics. Positive correlations were observed between the intestinal expression of several key genes involved in lipoprotein metabolism in a subgroup of participants (n = 16) after MCT supplementation. However, there was no difference between MCT and the corn oil control supplement in the intestinal messenger RNA expression levels of these key genes. These data indicate that short-term supplementation with MCT has a neutral effect on TRL apo B-48 and VLDL apo B-100 kinetics and on the intestinal expression of genes involved in lipid and fatty acid metabolism in men with insulin resistance. This trial was registered at www.clinicaltrials.gov as NCT01806142.

Physiological role of hepatic NPC1L1 in human cholesterol and lipoprotein metabolism: New perspectives and open questions

The importance of the cholesterol transporter Niemann-Pick C1 like protein 1 (NPC1L1)in the small intestine for efficient absorption of cholesterol is well documented and its physiological importance is clear (1). Similarly, the drug ezetimibe (Zetia™), which blocks function of this transporter, reduces plasma cholesterol, primarily LDL, by dramatically reducing intestinal absorption of dietary and biliary cholesterol (2). There are controversies about the exact mechanism by which NPC1L1 functions: whether the protein is on the apical cell membrane or intracellular vesicles or both (3–5), and whether ezetimibe directly blocks NPC1L1 or interrupts its association with other proteins in the sterol absorption and transport pathway (6–8). Nevertheless, it is now accepted that this protein is the key player in sterol absorption, although other transporters may play ancillary roles (9, 10).

Apolipoprotein B-100 and ApoA-II Kinetics as Determinants of Cellular Cholesterol Efflux

Cellular cholesterol efflux is a key step in reverse cholesterol transport and may depend on the metabolism of apolipoprotein (apo) B-100, apoA-I, and apoA-II. We examined the associations between cholesterol efflux and plasma concentrations and kinetics of very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL)-apoB-100, high-density lipoprotein (HDL)-apoA-I, and HDL-apoA-II in men. DESIGN, SUBJECTS, AND METHODS: Thirty men were recruited from the community with a wide range of body mass index. The capacity of plasma and HDL to efflux cholesterol was measured ex vivo. Apolipoprotein kinetics were measured using stable isotope techniques and multicompartmental modeling. Cholesterol efflux to whole plasma was correlated with plasma levels of cholesterol, triglyceride, apoB-100, insulin, cholesteryl ester transfer protein, and lecithin-cholesterol acyltransferase, body mass index and waist circumference (P < 0.05 in all). Cholesterol efflux was inversely correlated with the fractional catabolic rate (FCR) of VLDL (r = -0.728), IDL (r = -0.662), and LDL-apoB-100 (r = -0.479) but positively correlated with the FCR (r = 0.438) and production rate (r = 0.468) of HDL-apoA-II. In multiple regression analysis, the concentration and FCR of VLDL-apoB-100 (β-coefficient = 0.708 and -0.518, respectively) and IDL-apoB-100 (β-coefficient = 0.354 and -0.447, respectively) were independent predictors of cholesterol efflux. The association of cholesterol efflux with apoB-100 metabolism was diminished after removal of apoB-100-containing lipoproteins from plasma prior to efflux. All associations, except for cholesteryl ester transfer protein, were lost when cholesterol efflux to isolated HDL was tested. The plasma concentration and kinetics of apoB-100-containing lipoproteins are significant predictors of the capacity of whole plasma to effect cellular cholesterol efflux.

Effects of Acute Hyperglucagonemia on Hepatic and Intestinal Lipoprotein Production and Clearance in Healthy Humans

OBJECTIVEThe metabolism of hepatic- and intestinally derived lipoproteins is regulated in a complex fashion by nutrients, hormones, and neurologic and other factors. Recent studies in animal models suggest an important role for glucagon acting via the glucagon receptor in regulating hepatic triglyceride (TG) secretion. Here we examined the direct effects of glucagon on regulation of hepatic and intestinal lipoprotein metabolism in humans.RESEARCH DESIGN AND METHODSEight healthy men underwent two studies each, in random order, 4–6 weeks apart in which de novo lipogenesis, kinetics of larger VLDL1 TG, and kinetics of VLDL1 and smaller VLDL2 apolipoprotein (apo)B100 and B48 were studied using established stable isotope enrichment methods. Subjects were studied in the constant fed state under conditions of a pancreatic clamp (with infusion of somatostatin, insulin, and growth hormone) at either basal glucagon (BG study, 64.5 ± 2.1 pg/mL) or hyperglucagonemia (high glucagon [HG] study, 183.2 ± 5.1 pg/mL).RESULTSThere were no significant differences in plasma concentration of VLDL1 or VLDL2 TG, apoB100 or apoB48 between BG and HG studies. There was, however, lower (P < 0.05) VLDL1 apoB100 fractional catabolic rate (−39%) and production rate (−30%) in HG versus BG, but no difference in de novo lipogenesis or TG turnover, and glucagon had no effect on intestinal (B48-containing) lipoprotein metabolism.CONCLUSIONSGlucagon acutely regulates hepatic but not intestinal lipoprotein particle metabolism in humans both by decreasing hepatic lipoprotein particle production as well as by inhibiting particle clearance, with no net effect on particle concentration.

Genetic determinants of apolipoprotein B-100 kinetics

We review stable isotope tracer studies of apolipoprotein B-100 (apoB) kinetics concerning genetic polymorphisms and mutations that affect human lipoprotein metabolism. In obese men, the allelic combination of the apoB signal peptide, SP24, and cholesteryl ester transfer protein, CETP B1B1, is independently associated with lower VLDL apoB secretion. Microsomal triglyceride transfer protein -493G/T carriers have reduced IDL apoB and LDL apoB production as compared with controls. Mutations in cholesterol transporters (ATP-binding cassette transporter G8 and Niemann-Pick C1 Like 1) are associated with reduced VLDL apoB secretion and increased LDL apoB production and catabolism. The ATP-binding cassette transporter G8 400K variant is a significant, independent predictor of VLDL apoB secretion. Mutations in lipases (lipoprotein lipase and hepatic lipase) and transfer proteins (lecithin-cholesterol acyltransferase and cholesteryl ester transfer protein) alter their functional activity, which impact on VLDL and LDL kinetics. Mutations in genes that regulate intrahepatic apoB assembly and lipid substrate availability to the liver impact on VLDL apoB secretion. Lipoprotein tracer studies can provide functional insight into the potential impact of genetic polymorphisms in regulating apoB metabolism in humans.

Effect of Ezetimibe on Hepatic Fat, Inflammatory Markers, and Apolipoprotein B-100 Kinetics in Insulin-Resistant Obese Subjects on a Weight Loss Diet

OBJECTIVENonalcoholic fatty liver disease is highly prevalent in obese and type 2 diabetic individuals and is strongly associated with dyslipidemia and inflammation. Weight loss and/or pharmacotherapy are commonly used to correct these abnormalities.RESEARCH DESIGN AND METHODSWe performed a 16-week intervention trial of a hypocaloric, low-fat diet plus 10 mg/day ezetimibe (n = 15) versus a hypocaloric, low-fat diet alone (n = 10) on intrahepatic triglyceride (IHTG) content, plasma high sensitivity–C-reactive protein (hs-CRP), adipocytokines, and fetuin-A concentrations and apolipoprotein (apo)B-100 kinetics in obese subjects. ApoB-100 metabolism was assessed using stable isotope tracer kinetics and compartmental modeling; liver and abdominal fat contents were determined by magnetic resonance techniques.RESULTSBoth weight loss and ezetimibe plus weight loss significantly (all P < 0.05) reduced body weight, visceral and subcutaneous adipose tissues, insulin resistance and plasma triglycerides, VLDL–apoB-100, apoC-III, fetuin-A, and retinol-binding protein-4 and increased plasma adiponectin concentrations. Compared with weight loss alone, ezetimibe plus weight loss significantly (all P < 0.05) decreased IHTG content (−18%), plasma hs-CRP (−53%), interleukin-6 (−24%), LDL cholesterol (−18%), campesterol (−59%), and apoB-100 (−14%) levels, with a significant increase in plasma lathosterol concentrations (+43%). The LDL–apoB-100 concentration also significantly fell with ezetimibe plus weight loss (−12%), chiefly owing to an increase in the corresponding fractional catabolic rate (+29%). The VLDL–apoB-100 secretion rate fell with both interventions, with no significant independent effect of ezetimibe.CONCLUSIONSAddition of ezetimibe to a moderate weight loss diet in obese subjects can significantly improve hepatic steatosis, inflammation, and LDL–apoB-100 metabolism.

Nonalcoholic Fatty Liver Disease as the Transducer of Hepatic Oversecretion of Very-Low-Density Lipoprotein–Apolipoprotein B-100 in Obesity

To examine the association between liver fat content and very low-density lipoprotein (VLDL)-apolipoprotein (apo) B-100 kinetics and the corresponding responses to weight loss in obese subjects. VLDL-apoB-100 kinetics were assessed using stable isotope tracers, and the fat content of the liver and abdomen was determined by magnetic resonance techniques in 25 obese subjects. In univariate analysis, liver fat content was significantly (P<0.05 in all) associated with body mass index (r=0.65), visceral fat area (r=0.45), triglycerides (r=0.40), homeostasis model assessment score (r=0.40), VLDL-apoB-100 concentrations (r=0.44), and secretion rate (r=0.45). However, liver fat content was not associated with plasma concentrations of retinol-binding protein 4, fetuin A, adiponectin, interleukin-6, and tumor necrosis factor-alpha. Of these 25 subjects, 9 diagnosed as having nonalcoholic fatty liver disease (which is highly prevalent in obese individuals and strongly associated with dyslipidemia) underwent a weight loss program. The low-fat diet achieved significant reduction in body weight, body mass index, liver fat, visceral and subcutaneous fat areas, homeostasis model assessment score, triglycerides, VLDL-apoB-100 concentrations, and VLDL-apoB-100 secretion rate. The percentage reduction of liver fat with weight loss was significantly associated with the corresponding decreases in VLDL-apoB-100 secretion (r=0.67) and visceral fat (r=0.84). In patients with obesity, hepatic steatosis increases VLDL-apoB-100 secretion. Weight loss can help reduce this abnormality.

Chronic kidney disease delays VLDL-apoB-100 particle catabolism: potential role of apolipoprotein C-III

To determine the relative contribution of obesity and/or insulin resistance (IR) in the development of dyslipidemia in chronic kidney disease (CKD), we investigated the transport of apolipoprotein (apo) B-100 in nonobese, nondiabetic, nonnephrotic CKD subjects and healthy controls (HC). We determined total VLDL, VLDL(1), VLDL(2), intermediate density lipoprotein (IDL), and LDL-apoB-100 using intravenous D3-leucine, GC-MS, and multicompartmental modeling. Plasma apoC-III and apoB-48 were immunoassayed. In this case control study, we report higher plasma triglyceride, IDL-, VLDL-, VLDL(1)-, and VLDL(2)-apoB-100 concentrations in CKD compared with HC (P < 0.05). This was associated with decreased fractional catabolic rates [FCRs (pools/day)] [IDL:CKD 3.4 (1.6) vs. HC 5.0 (3.2), P < 0.0001; VLDL:CKD 4.8 (5.2) vs. HC 7.8 (4.8), P = 0.038; VLDL(1):CKD 10.1 (8.5) vs. HC 29.5 (45.1), P = 0.007; VLDL(2):CKD 5.4 (4.6) vs. HC 10.4 (3.4), P = 0.001] with no difference in production rates. Plasma apoC-III and apoB-48 were significantly higher in CKD (P < 0.001) and both correlated with impaired FCRs of VLDL, VLDL(1), and VLDL(2) apoB-100 (P < 0.05). In CKD, apoC-III concentration was the only independent predictor of clearance defects in VLDL and its subfractions. Moderate CKD in the absence of central adiposity and IR is associated with mild hypertriglyceridemia due to delayed catabolism of triglyceride rich lipoproteins, IDL, and VLDL, without changes in production rate. Altered apoC-III metabolism may contribute to dyslipidemia in CKD, and this requires further investigation.

Disturbance of Apolipoprotein B100 Containing Lipoprotein Metabolism in Severe Hyperlipidemic and Lipodystrophic HIV Patients on Combined Antiretroviral Therapy: Evidences of Insulin Resistance Effect

The aim was to study the mechanisms involved in the dyslipidemia associated with lipodystrophy in HIV infected patients on antiretroviral therapy (ART). We investigated the in vivo kinetics of apolipoprotein B100 (apoB) containing lipoproteins using a 14 h primed constant infusion of [5,5,5, (2)H(3)] leucine and compartmental modelling in normolipidemic without lipodystrophy (7 patients, NLD) or dyslipidemic with lipodystrophy (7 patients, LD) treated with ART. Subjects in group LD showed higher plasma triglycerides (5.73+/-3.58 vs 1.29+/-0.54 g/L, p<0.005), total cholesterol (2.98+/-0.95 vs 1.74+/-0.26 g/L, p<0.05), apoB (1.49+/-1.11 vs 0.51+/-0.11 g/L, p<0.005) and apolipoprotein CIII in apoB containing lipoproteins (117.7+/-42.2 vs 22.6+/-23.9 g/L, p<0.005). LD subjects exhibited an insulin resistant as observed by higher HOMA (3.44+/-1.62 vs 1.60+/-0.61, p<0.05). They exhibited an increase in VLDL (1.24+/-0.33 vs 0.80+/-0.21 mg/kg/h, p<0.05), decrease in IDL (0.20+/-0.10 vs 0.48+/-0.24 mg/kg/h, p<0.05) and no difference in LDL (0.38+/-0.19 vs 0.45+/-0.25 mg/kg/h) production rate. LD subject also showed a dramatic decrease in transformation of VLDL to IDL (0.013+/-0.010 vs 0.258+/-0.206 h(-1), p<0.005) and IDL to LDL (0.088+/-0.093 vs 0.366+/-0.189 h(-1), p<0.05) and a decrease in fractional catabolic rate (FCR) of VLDL (0.199+/-0.132 vs 0.555+/-0.398 h(-1), p<0.05), IDL (0.110+/-0.08 vs 0.523+/-0.275 h(-1), p<0.05) and LDL (0.010+/-0.005 vs 0.025+/-0.014 h(-1), p<0.05). These disturbances, overproduction and an overall delayed catabolism of apoB, are similar to those observed using the same protocol in insulin resistant subjects. Our study suggests that metabolic disturbance of apoB100 observed in lipodystrophic HIV in combined antiretroviral therapy are consecutive to insulin resistance induced by the treatment.

Inhibition of apoB secretion from HepG2 cells by insulin is amplified by naringenin, independent of the insulin receptor

Hepatic overproduction of apolipoprotein B (apoB)-containing lipoproteins is characteristic of the dyslipidemia associated with insulin resistance. Recently, we demonstrated that the flavonoid naringenin, like insulin, decreased apoB secretion from HepG2 cells by activation of both the phosphoinositide-3-kinase (PI3-K) pathway and the mitogen-activated protein kinase/extracellular-regulated kinase (MAPK(erk)) pathway. In the present study, we determined whether naringenin-induced signaling required the insulin receptor (IR) and sensitized the cell to the effects of insulin, and whether the kinetics of apoB assembly and secretion in cells exposed to naringenin were similar to those of insulin. Immunoblot analysis revealed that insulin stimulated maximal phosphorylation of IR and IR substrate-1 after 10 min, whereas naringenin did not affect either at any time point up to 60 min. The combination of naringenin and submaximal concentrations of insulin potentiated extracellular-regulated kinase 1/2 activation and enhanced upregulation of the LDL receptor, downregulation of microsomal triglyceride transfer protein expression, and inhibition of apoB-100 secretion. Multicompartmental modeling of apoB pulse-chase studies revealed that attenuation of secreted radiolabeled apoB in naringenin- or insulin-treated cells was similar under lipoprotein-deficient or oleate-stimulated conditions. Naringenin and insulin both stimulated intracellular apoB degradation via a kinetically defined rapid pathway. Therefore, naringenin, like insulin, inhibits apoB secretion through activation of both PI3-K and MAPK(erk) signaling, resulting in similar kinetics of apoB secretion. However, the mechanism for naringenin-induced signaling is independent of the IR. Naringenin represents a possible strategy for reduction of hepatic apoB secretion, particularly in the setting of insulin resistance.

Lipoprotein separation in a novel iodixanol density gradient, for composition, density, and phenotype analysis

Separation of lipoproteins by traditional sequential salt density floatation is a prolonged process ( approximately 72 h) with variable recovery, whereas iodixanol-based, self-generating density gradients provide a rapid ( approximately 4 h) alternative. A novel, three-layered iodixanol gradient was evaluated for its ability to separate lipoprotein fractions in 63 subjects with varying degrees of dyslipidemia. Lipoprotein cholesterol, triglycerides, and apolipoproteins were measured in 21 successive iodixanol density fractions. Iodixanol fractionation was compared with sequential floatation ultracentrifugation. Iodixanol gradient formation showed a coefficient of variation of 0.29% and total lipid recovery from the gradient of 95.4% for cholesterol and 84.7% for triglyceride. Recoveries for VLDL-, LDL-, and HDL-cholesterol, triglycerides, and apolipoproteins were approximately 10% higher with iodixanol compared with sequential floatation. The iodixanol gradient effectively discriminated classic lipoproteins and their subfractions, and there was evidence for improved resolution of lipoproteins with the iodixanol gradient. LDL particles subfractionated by the gradient showed good correlation between density and particle size with small, dense LDL (<25.5 nm) separated in fractions with density >1.028 g/dl. The new iodixanol density gradient enabled rapid separation with improved resolution and recovery of all lipoproteins and their subfractions, providing important information with regard to LDL phenotype from a single centrifugation step with minimal in-vitro modification of lipoproteins.

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.

Relationships between changes in plasma lipid transfer proteins and apolipoprotein B-100 kinetics during fenofibrate treatment in the metabolic syndrome

Volume 111 (2006), pp. 193–199In Table 2, the values for PLTP activity were incorrect, due to a dilution error; however, this error did not alter the findings significantly. The correct values appear in the Table below.

Rapid turnover of apolipoprotein C-III-containing triglyceride-rich lipoproteins contributing to the formation of LDL subfractions

The atherogenicity theory for triglyceride-rich lipoproteins (TRLs; VLDL + intermediate density lipoprotein) generally cites the action of apolipoprotein C-III (apoC-III), a component of some TRLs, to retard their metabolism in plasma. We studied the kinetics of multiple TRL and LDL subfractions according to the content of apoC-III and apoE in 11 hypertriglyceridemic and normolipidemic persons. The liver secretes mainly two types of apoB lipoproteins: TRL with apoC-III and LDL without apoC-III. Approximately 45% of TRLs with apoC-III are secreted together with apoE. Contrary to expectation, TRLs with apoC-III but not apoE have fast catabolism, losing some or all of their apoC-III and becoming LDL. In contrast, apoE directs TRL flux toward rapid clearance, limiting LDL formation. Direct clearance of TRL with apoC-III is suppressed among particles also containing apoE. TRLs without apoC-III or apoE are a minor, slow-metabolizing precursor of LDL with little direct removal. Increased VLDL apoC-III levels are correlated with increased VLDL production rather than with slow particle turnover. Finally, hypertriglyceridemic subjects have significantly greater production of apoC-III-containing VLDL and global prolongation in residence time of all particle types. ApoE may be the key determinant of the metabolic fate of atherogenic apoC-III-containing TRLs in plasma, channeling them toward removal from the circulation and reducing the formation of LDLs, both those with apoC-III and the main type without apoC-III.

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.

The molecular mechanisms underlying the reduction of LDL apoB-100 by ezetimibe plus simvastatin

The combination of ezetimibe, an inhibitor of Niemann-Pick C1-like 1 protein (NPC1L1), and an HMG-CoA reductase inhibitor decreases cholesterol absorption and synthesis. In clinical trials, ezetimibe plus simvastatin produces greater LDL-cholesterol reductions than does monotherapy. The molecular mechanism for this enhanced efficacy has not been defined. Apolipoprotein B-100 (apoB-100) kinetics were determined in miniature pigs treated with ezetimibe (0.1 mg/kg/day), ezetimibe plus simvastatin (10 mg/kg/day), or placebo (n = 7/group). Ezetimibe decreased cholesterol absorption (-79%) and plasma phytosterols (-91%), which were not affected further by simvastatin. Ezetimibe increased plasma lathosterol (+65%), which was prevented by addition of simvastatin. The combination decreased total cholesterol (-35%) and LDL-cholesterol (-47%). VLDL apoB pool size decreased 26%, due to a 35% decrease in VLDL apoB production. LDL apoB pool size decreased 34% due to an 81% increase in the fractional catabolic rate, both of which were significantly greater than monotherapy. Combination treatment decreased hepatic microsomal cholesterol (-29%) and cholesteryl ester (-65%) and increased LDL receptor (LDLR) expression by 240%. The combination increased NPC1L1 expression in liver and intestine, consistent with increased SREBP2 expression. Ezetimibe plus simvastatin decreases VLDL and LDL apoB-100 concentrations through reduced VLDL production and upregulation of LDLR-mediated LDL clearance.