Alterations in the metabolism of very-low- and low-density lipoproteins after partial ileal-bypass surgery in the Watanabe heritable hyperlipidaemic rabbit.
ABSTRACT: The influence of interruption of bile-acid enterohepatic circulation by partial ileal bypass (PIB) surgery on serum lipids, lipoproteins and the turnover of very-low- (VLDL) and low-density (LDL) lipoproteins was investigated in Watanabe heritable hyperlipidaemic (WHHL) rabbits. Compared with controls, total serum cholesterol was 48% lower after PIB (16.88 +/- 1.57 versus 8.79 +/- 1.66 mmol/l; P less than 0.01), owing to lower levels of cholesterol in VLDL (-23%), intermediate-density lipoprotein (IDL; -39%) and LDL (-72%); serum triacylglycerols were 32% higher (3.86 +/- 1.35 versus 5.11 +/- 0.82 mmol/l). The ratio of the percentages of mass of cholesteryl esters to triacylglycerols was 71% lower in VLDL and LDL and 67% lower in IDL (P less than 0.01). Compared with controls, the secretion rate of LDL was 33% lower (31.1 +/- 7.2 versus 20.7 +/- 6.9 mg/day per kg; P less than 0.05) and the fractional catabolic rate (FCR) of LDL was 33% higher (0.46 +/- 0.06 versus 0.61 +/- 0.12 pool/day; P less than 0.02). The VLDL turnover showed that after PIB there was a higher secretion rate of VLDL apolipoprotein B (63.9 versus 167.4 mg/day per kg), a higher FCR (3.84 versus 8.61 pools/day), a higher direct uptake (38.8 versus 146.4 mg/day per kg) and a higher conversion of VLDL into LDL (4.8 versus 9.0 mg/day per kg). Some 82% of LDL originated from direct synthesis in controls, and after PIB this was 59%. In both controls and treated rabbits there was a direct LDL synthesis, which was 52% lower after PIB (26.3 versus 12.6 mg/day per kg). It is concluded that LDL-cholesterol lowering by PIB is due to an increased uptake of LDL, a decreased synthesis of LDL, and cholesterol depletion of the LDL particles; the decreased LDL synthesis is due to a decreased direct production of LDL, which exceeds the increased conversion of VLDL into LDL.
Project description:We investigated the effects of the cholesteryl ester (CE) transfer protein inhibitor anacetrapib (ANA) on plasma lipids, lipoprotein subfraction concentrations, and lipoprotein composition in 30 healthy individuals. Participants (n = 30) were randomized to ANA 20 mg/day, 150 mg/day, or placebo for 2 weeks. Changes in concentration of lipoprotein subfractions were assessed using ion mobility, and compositional analyses were performed on fractions separated by density gradient ultracentrifugation. ANA 150 mg/day versus placebo resulted in significant decreases in LDL-cholesterol (26%) and apo B (29%) and increases in HDL-cholesterol (82%). Concentrations of medium and small VLDL, large intermediate density lipoprotein (IDL), and medium and small LDL (LDL2a, 2b, and 3a) decreased whereas levels of very small and dense LDL4b were increased. There was enrichment of triglycerides and reduction of CE in VLDL, IDL, and the densest LDL fraction. Levels of large buoyant HDL particles were substantially increased, and there was enrichment of CE, apo AI, and apoCIII, but not apoAII or apoE, in the mid-HDL density range. Changes in lipoprotein subfraction concentrations and composition with ANA 20 mg/day were similar to those for ANA 150 mg/day but were generally smaller in magnitude. The impact of these changes on cardiovascular risk remains to be determined.
Project description:It is well known that familial hypercholesterolemia (FH) is a common inherited disorder that can markedly elevate the level of plasma LDL cholesterol. However, little data exists regarding the clinical impact of the plasma triglyceride (TG)-rich lipoprotein fraction, including VLDL and IDL, in FH. Thus, we assessed the hypothesis that the mutations in the LDL receptor modulate lipoprotein metabolism other than the LDL fraction.We investigated plasma lipoprotein with a one-step ultracentrifugation method for 146 controls (mean age=61.4±17.1 yr, mean LDL cholesterol=92.7±61.2 mg/dl), 213 heterozygous mutation-determined FH subjects (mean age=46.0±18.0 yr, mean LDL cholesterol=225.1±61.2 mg/dl), and 16 homozygous/compound heterozygous mutation-determined FH subjects (mean age=26.9±17.1 yr, mean LDL cholesterol=428.6±86.1 mg/dl). In addition, we evaluated cholesterol/TG ratio in each lipoprotein fraction separated by ultracentrifugation.In addition to total cholesterol and LDL cholesterol levels, VLDL cholesterol (19.5±10.4, 25.2±19.3, 29.5±21.4 mg/dl, respectively) and IDL cholesterol (8.3±3.7, 16.8±11.5, 40.0±37.3 mg/dl, respectively) exhibited a tri-model distribution according to their status in LDL receptor mutation(s). Moreover, the ratios of cholesterol/TG of each lipoprotein fraction increased significantly in heterozygous FH and homozygous/compound heterozygous FH groups, compared with that of controls, suggesting that the abnormality in LDL receptor modulates the quality as well as the quantity of each lipoprotein fraction.Our results indicate that cholesterol in TG-rich lipoproteins, including VLDL and IDL, are significantly higher in FH subjects, revealing a tri-modal distribution according to the number of LDL receptor mutations.
Project description:BACKGROUND: Assessment of cardiovascular disease (CVD) risk factors can predict clinical manifestations of atherosclerosis in adulthood. In this pilot study with hypercholesterolemic children and adolescents, we investigated the effects of a combination of plant sterols, fish oil and B vitamins on the levels of four independent risk factors for CVD; LDL-cholesterol, triacylglycerols, C-reactive protein and homocysteine. METHODS: Twenty five participants (mean age 16 y, BMI 23 kg/m2) received daily for a period of 16 weeks an emulsified preparation comprising plant sterols esters (1300 mg), fish oil (providing 1000 mg eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA)) and vitamins B12 (50 ?g), B6 (2.5 mg), folic acid (800 ?g) and coenzyme Q10 (3 mg). Atherogenic and inflammatory risk factors, plasma lipophilic vitamins, provitamins and fatty acids were measured at baseline, week 8 and 16. RESULTS: The serum total cholesterol, LDL- cholesterol, VLDL-cholesterol, subfractions LDL-2, IDL-1, IDL-2 and plasma homocysteine levels were significantly reduced at the end of the intervention period (p<0.05). The triacylglycerols levels decreased by 17.6%, but did not reach significance. No significant changes in high sensitivity C-reactive protein, HDL-cholesterol and apolipoprotein A-1 were observed during the study period. After standardisation for LDL cholesterol, there were no significant changes in the levels of plasma ?-tocopherol, ?-carotene and retinol, except for reduction in ?-tocopherol levels. The plasma levels of n-3 fatty acids increased significantly with the dietary supplementation (p<0.05). CONCLUSIONS: Daily intake of a combination of plant sterols, fish oil and B vitamins may modulate the lipid profile of hypercholesterolemic children and adolescents. TRIAL REGISTRATION: Current Controlled Trials ISRCTN89549017.
Project description:We have used adenovirus-mediated gene transfer in apolipoprotein (apo)E(-/-) mice to elucidate the molecular etiology of a dominant form of type III hyperlipoproteinemia (HLP) caused by the R142C substitution in apoE4. It was found that low doses of adenovirus expressing apoE4 cleared cholesterol, whereas comparable doses of apoE4[R142C] greatly increased plasma cholesterol, triglyceride, and apoE levels, caused accumulation of apoE in VLDL/IDL/LDL region, and promoted the formation of discoidal HDL. Co-expression of apoE4[R142C] with lecithin cholesterol acyltransferase (LCAT) or lipoprotein lipase (LPL) in apoE(-/-) mice partially corrected the apoE4[R142C]-induced dyslipidemia. High doses of C-terminally truncated apoE4[R142C]-202 partially cleared cholesterol in apoE(-/-) mice and promoted formation of discoidal HDL. The findings establish that apoE4[R142C] causes accumulation of apoE in VLDL/IDL/LDL region and affects in vivo the activity of LCAT and LPL, the maturation of HDL, and the clearance of triglyceride-rich lipoproteins. The prevention of apoE4[R142C]-induced dyslipidemia by deletion of the 203-299 residues suggests that, in the full-length protein, the R142C substitution may have altered the conformation of apoE bound to VLDL/IDL/LDL in ways that prevent triglyceride hydrolysis, cholesterol esterification, and receptor-mediated clearance in vivo.
Project description:To characterize human triglyceride-rich lipoproteins (TRL) with and without apoA-II and to study their metabolism in vivo.Plasma from 11 participants on a controlled diet given a bolus infusion of [D5]l-phenylalanine to label apoB was combined into four pools and applied to anti-apoA-II immunoaffinity columns. Fractions with and without apoA-II were separated into VLDL and IDL by ultracentrifugation; lipids and apolipoproteins were measured. For kinetic measurements, apoB was isolated and hydrolyzed to the constituent amino acids. Tracer enrichment was measured by GCMS. Metabolic rates were determined by SAAM-II.VLDL and IDL with apoA-II comprised 7% and 9% of total VLDL and IDL apoB respectively. VLDL with apoA-II was enriched in apoC-III, apoE, and cholesterol compared to VLDL without apoA-II. Mean apoB FCR of VLDL with apoA-II was significantly lower than for VLDL without apoA-II (2.80 ± 0.96 pools/day v.s. 5.09 ± 1.69 pools/day, P = 0.009). A higher percentage of VLDL with apoA-II was converted to IDL than was cleared from circulation, compared to VLDL without apoA-II (96 ± 8% vs. 45 ± 22%; P = 0.007). The rate constants for conversion of VLDL to IDL were similar for VLDL with and without apoA-II. Thus, a very low rate constant for clearance accounted for the lower FCR of VLDL with apoA-II.VLDL with apoA-II represents a small pool of VLDL particles that has a slow FCR and is predominantly converted to IDL rather than cleared from the circulation.
Project description:We investigated the impact of lipoprotein lipase (LPL) gene mutations on apolipoprotein B (apoB)-100 metabolism.We studied 3 subjects with familial LPL deficiency; 14 subjects heterozygous for the LPL gene mutations Gly188Glu, Trp64Stop, and Ile194Thr; and 10 control subjects. Very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL)-apoB-100 kinetics were determined in the fed state using stable isotope methods and compartmental modeling. Compared with controls, familial LPL deficiency had markedly elevated plasma triglycerides and lower VLDL-apoB-100 fractional catabolic rate (FCR), IDL-apoB-100 FCR, VLDL-to-IDL conversion, and VLDL-apoB-100 production rate (P<0.01). Compared with controls, Gly188Glu had higher plasma triglyceride and VLDL- and IDL-apoB-100 concentrations and lower VLDL- and IDL-apoB-100 FCR (P<0.05). Plasma triglycerides were not different, but IDL-apoB-100 concentration and production rate and VLDL-to-IDL conversion were lower in Trp64Stop compared with controls (P<0.05). No differences between controls and Ile194Thr were observed.Our results confirm that hypertriglyceridemia is a key feature of familial LPL deficiency. This is due to impaired VLDL- and IDL-apoB-100 catabolism and VLDL-to-IDL conversion. Single-allele mutations of the LPL gene result in modest to elevated plasma triglycerides. The changes in plasma triglycerides and apoB-100 kinetics are attributable to the effects of the LPL genotype.
Project description:BACKGROUND AND AIMS:Sitosterolemia displays high plasma total sterols [high plant sterols (PS) + normal to high total cholesterol (TC)] with normal to moderately elevated low-density lipoprotein (LDL) levels. High LDL, intermediate-density lipoprotein (IDL) and very low-density lipoprotein (VLDL) particles, low high-density lipoprotein (HDL), and increased non-HDL and the ratios of TC and triglycerides (TG) to HDL can increase the risk for atherosclerosis. Ezetimibe (EZE) can reduce plasma PS and TC levels in sitosterolemia, but its effect on lipoprotein subclasses has not been previously reported. METHODS:Sitosterolemia patients (n = 8) were taken off EZE for 14 weeks (OFF EZE) and placed on EZE (10 mg/d) for 14 weeks (ON EZE). Serum lipids were measured enzymatically and lipoprotein subclasses were assessed by polyacrylamide gel electrophoresis. RESULTS:EZE reduced (p < 0.05) total sterols (-12.5 ± 4.1%) and LDL-sterol (-22.7 ± 5.7%) and its sterol mass of large VLDL (-24.4 ± 4.5%), VLDL remnants (-21.1 ± 7.9%) and large IDL (-22.4 ± 7.2%) compared to OFF EZE. EZE did not affect large LDL subclasses or mean LDL particle size (273.8 ± 0.6 vs. 274.6 ± 0.3 Å). EZE increased HDL-sterol (25.5 ± 8.0%, p = 0.008) including intermediate (34 ± 14%, p = 0.02) and large (33 ± 16%, p = 0.06) HDL. EZE reduced non-HDL-sterol (-21.8± 5.0%), total sterols/HDL (-28.2 ± 5.5%) and TG/HDL (-27.4 ± 6.5%, all p < 0.01). CONCLUSIONS:EZE improves VLDL and HDL subfraction distribution, thereby reducing the atherogenic lipid profile, thus providing potential clinical benefit in sitosterolemia beyond TC and PS reduction.
Project description:Paraoxonase-1 (PON1) and lipoprotein phospholipase A2 (Lp-PLA2) may exert an important protective role by preventing the oxidative transformation of high- and low-density lipoproteins (HDL and LDL, respectively). The activity of both enzymes is influenced by lipidome and proteome of the lipoprotein carriers. T2DM typically presents significant changes in the molecular composition of the lipoprotein subclasses. Thus, it becomes relevant to understand the interaction of PON1 and Lp-PLA2 with the subspecies of HDL, LDL, and other lipoproteins in T2DM. Serum levels of PON1-arylesterase and PON1-lactonase and Lp-PLA2 activities and lipoprotein subclasses were measured in 202 nondiabetic subjects (controls) and 92 T2DM outpatients. Arylesterase, but not lactonase or Lp-PLA2 activities, was inversely associated with TD2M after adjusting for potential confounding factors such as age, sex, smoking, body mass index, hypertension, and lipoprotein subclasses (odds ratio?=?3.389, 95% confidence interval 1.069-14.756). Marked difference between controls and T2DM subjects emerged from the analyses of the associations of the three enzyme activities and lipoprotein subclasses. Arylesterase was independently related with large HDL-C and small intermediate-density lipoprotein cholesterol (IDL-C) in controls while, along with lactonase, it was related with small low-density lipoprotein cholesterol LDL-C, all IDL-C subspecies, and very low-density lipoprotein cholesterol (VLDL-C) in T2DM (p < 0.05 for all). Concerning Lp-PLA2, there were significant relationships with small LDL-C, large IDL-C, and VLDL-C only among T2DM subjects. Our study showed that T2DM subjects have lower levels of PON1-arylesterase compared to controls and that T2DM occurrence may coincide with a shift of PON1 and Lp-PLA2 towards the more proatherogenic lipoprotein subclasses. The possibility of a link between the two observed phenomena requires further investigations.
Project description:OBJECTIVE:We aimed to clarify the influence of apolipoprotein C-III (apoCIII) on human apolipoprotein B metabolism. METHODS AND RESULTS:We studied the kinetics of 4 very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) types containing: (1) otherApos-CIII-: none of apoCIII, apoAII, apoCI, apoCII, or apoE; (2) otherApos+CIII-: no apoCIII but at least one of the others; (3) otherApos-CIII+: apoCIII, but not any others; and (4) otherApos+CIII+: apoCIII and at least one other. VLDL and IDL otherApos-CIII+ and otherApos-CIII- had similar rates of lipolytic conversion to smaller particles. However, light LDL otherApos-CIII+ compared with otherApos-CIII- had much faster conversion to dense LDL as did light LDL otherApos+CIII+ compared with otherApos+CIII-. VLDL and IDL otherApos-CIII+ had minimal direct removal from circulation, whereas VLDL and IDL otherApos+CIII-, rich in apoE, showed fast clearance. Lipoproteins in fraction otherApos+CIII+ also rich in apoE had very low clearance. CONCLUSIONS:The results suggest that apoCIII strongly inhibits hepatic uptake of VLDL and IDL overriding the opposite influence of apoE when both are present. The presence of apoCIII on dense VLDL is not associated with slow conversion to IDL, a lipoprotein lipase-dependent process; but when on light LDL, apoCIII is associated with enhanced conversion to dense LDL, a process involving hepatic lipase.
Project description:MDCO-216, a complex of dimeric recombinant apoA-IMilano (apoA-IM) and palmitoyl-oleoyl-phosphatidylcholine (POPC), was administered to cynomolgus monkeys at 30, 100, and 300 mg/kg every other day for a total of 21 infusions, and effects on lipids, (apo)lipoproteins, and ex-vivo cholesterol efflux capacity were monitored. After 7 or 20 infusions, free cholesterol (FC) and phospholipids (PL) were strongly increased, and HDL-cholesterol (HDL-C), apoA-I, and apoA-II were strongly decreased. We then measured short-term effects on apoA-IM, lipids, and (apo)lipoproteins after the first or the last infusion. After the first infusion, PL and FC went up in the HDL region and also in the LDL and VLDL regions. ApoE shifted from HDL to LDL and VLDL regions, while ApoA-IM remained located in the HDL region. On day 41, ApoE levels were 8-fold higher than on day 1, and FC, PL, and apoE resided mostly in LDL and VLDL regions. Drug infusion quickly decreased the endogenous cholesterol esterification rate. ABCA1-mediated cholesterol efflux on day 41 was markedly increased, whereas scavenger receptor type B1 (SRB1) and ABCG1-mediated effluxes were only weakly increased. Strong increase of FC is due to sustained stimulation of ABCA1-mediated efflux, and drop in HDL and formation of large apoE-rich particles are due to lack of LCAT activation.