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Eur J Clin Invest 2011; 41 (9): 921–928 Abstract Background Reverse cholesterol transport (RCT) is an anti-atherogenic process by which cholesterol is effluxed from peripheral tissues by high-density lipoprotein (HDL) and returned to the liver for excretion into the bile and faeces. Dyslipidemia is thought to impair RCT through higher triglyceride-rich lipoprotein (TRL), low HDL-cholesterol and higher activity of cholesteryl ester transfer protein (CETP), which transfers cholesteryl esters from HDL to TRL for further hepatic uptake. As CETP pathway would represent a major route in human RCT, we therefore investigated whether diet-induced dyslipidemia impairs RCT in hamster, a CETP-expressing species. Materials and methods Golden Syrian hamsters were fed a chow or chow+0·3% cholesterol diet over 4 weeks. Biochemical parameters and in vivo VLDL-triglycerides secretion (Triton WR-1339 injection) were then measured. In vitro macrophage cholesterol efflux was measured, and in vivo macrophage-to-faeces RCT was also assessed after an intraperitoneal injection of 3H-cholesterol-labelled hamster primary macrophages. Results Cholesterol-enriched diet increased plasma total cholesterol (144%), triglycerides (101%), VLDL-triglycerides secretion (175%), CETP activity (44%) and reduced HDL-cholesterol/total cholesterol ratio by 20% (P

Apolipoprotein B100 (apoB100) is an essential component of very low density lipoprotein (VLDL) and low-density lipoprotein (LDL), both independent markers of cardiovascular risk. Nicotinic acid (NA) is an efficacious drug for decreasing VLDL and LDL, but the underlying mechanisms are unclear. For this purpose, six obese insulin-resistant dogs were given 350 mg/day of NA for 1 week and then 500 mg/day for 3 weeks. Turnover of apoB100-containing lipoproteins was investigated using stable isotope-labeled tracers. Multicompartmental modeling was used to derive kinetic parameters before and at the end of NA treatment. Hepatic diacylglycerol acyltransferase 2 (DGAT2), microsomal triglyceride transfer protein (MTP), hepatic lipase (HL), and adipose lipoprotein lipase (LPL) mRNA expression was also determined. NA treatment decreased plasma triglyceride (TG) (p < 0.001), VLDL-TG (p < 0.05), total cholesterol (p < 0.0001), and LDL cholesterol (p < 0.05), whereas plasma nonesterified fatty acids were unchanged. The decrease in VLDL-apoB100 concentration (p < 0.001) was the result of a lower absolute production rate (APR) (p < 0.001), despite a moderate decrease (p < 0.05) in fractional catabolic rate (FCR). LDL-apoB100 concentration was reduced (p < 0.05), an effect related to a decrease in LDL APR (p < 0.05) and no change in FCR. NA treatment reduced DGAT2 expression (p < 0.05), whereas MTP, HL, and LPL expression was unchanged. Our results suggest that NA treatment reduced VLDL and LDL concentration as a consequence of a decrease in VLDL production.

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

International audience; Aim Nicotinic acid (NA) treatment decreases plasma triglycerides and increases HDL cholesterol, but the mechanisms involved in these change are not fully understood. A reduction in cholesteryl ester transfer protein (CETP) activity has been advanced to explain most lipid-modulating effects of NA. However, due to the central role of CETP in reverse cholesterol transport in humans, other effects of NA may have been hidden. As dogs have no CETP activity, we conducted this study to examine the specific effects of extended-release niacin (NA) on lipids and high-density lipoprotein (HDL) cholesteryl ester (CE) turnover in obese Insulin-Resistant dogs with increase plasma triglycerides. Methods HDL kinetics were assessed in fasting dogs before and four weeks after NA treatment through endogenous labeling of cholesterol and apolipoprotein AI by simultaneous infusion of [1,2 C-13(2)] acetate and [5,5,5 H-2(3)] leucine for 8 h. Kinetic data were analyzed by compartmental modeling. In vitro cell cholesterol efflux of serum from NA-treated dogs was also measured. Results NA reduced plasma total cholesterol, low-density lipoprotein cholesterol, HDL cholesterol, triglycerides (TG), and very-low-density lipoprotein TG concentrations (p < 0.05). The kinetic study also showed a higher cholesterol esterification rate (p < 0.05). HDL-CE turnover was accelerated (p < 0.05) via HDL removal through endocytosis and selective CE uptake (p < 0.05). We measured an elevated in vitro cell cholesterol efflux (p < 0.05) with NA treatment in accordance with a higher cholesterol esterification. Conclusion NA decreased HDL cholesterol but promoted cholesterol efflux and esterification, leading to improved reverse cholesterol transport. These results highlight the CETP-independent effects of NA in changes of plasma lipid profile.

BACKGROUND: The mechanisms involved in the decline of high-density lipoprotein (HDL) levels at a higher dose of atorvastatin have not yet been elucidated. We investigated the effects of atorvastatin on HDL-apolipoprotein (apo) A-I metabolism in dogs, a species lacking cholesteryl ester transfer protein activity. MATERIALS AND METHODS: Seven ovariectomized normolipidaemic female Beagle dogs underwent a primed constant infusion of [5,5,5-(2)H(3)] leucine to determine HDL-apo A-I kinetics before and after atorvastatin treatment (5 mg kg(-1) d(-1) for 6 weeks). Plasma lipoprotein profiles, activity of HDL-modifying enzymes involved in reverse cholesterol transport and hepatic scavenger receptor class B type I (SR-BI) expression were also studied. RESULTS: Atorvastatin treatment decreased HDL-cholesterol levels (3.56 +/- 0.24 vs. 2.64 +/- 0.15 mmol L(-1), P < 0.05). HDL-triglycerides were not affected. HDL-phospholipids levels were decreased (4.28 +/- 0.13 vs. 3.29 +/- 0.13 mmol L(-1), P < 0.05), as well as phospholipids transfer protein (PLTP) activity (0.83 +/- 0.05 vs. 0.60 +/- 0.05 pmol microL(-1) min(-1), P < 0.05). Activity of lecithin: cholesterol acyl transferase (LCAT), hepatic lipase (HL) and SR-BI expression did not change. HDL-apo A-I absolute production rate (APR) was higher after treatment (twofold, P < 0.05) as well as fractional catabolic rate (FCR) (threefold, P < 0.05). This resulted in lower HDL-apo A-I levels (2.36 +/- 0.03 vs. 1.55 +/- 0.04 g l(-1), P < 0.05). Plasma lipoprotein profiles showed a decrease in large HDL(1) levels, with lower apo A-I and higher apo E levels in this subfraction. CONCLUSIONS: Although a high dose of atorvastatin up-regulated HDL-apo A-I production, this drug also increased HDL-apo A-I FCR in dogs. This effect could be explained by a higher uptake of apo E-enriched HDL(1) by hepatic lipoprotein receptors.

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 [ 2 H 3 ] 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. Conclusion— 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.

Amongst the processes involved in the reverse cholesterol transport (RCT) from organs to liver, including high density lipoproteins-apolipoprotein AI (HDL-apoAI) dependent tissue uptake and cholesteryl ester transfer protein (CETP)-mediated transfers, the selective uptake of cholesteryl ester (CE) is of increasing interest through its antiatherogenic role. The purpose of this report is to develop a simple protocol allowing study of this process in an animal model with easier quantification of CE selective uptake. The dog was chosen essentially because this animal has a low CETP activity and an appropriate size to conduce a kinetic study. Tracer kinetics were performed to estimate in vivo the contributions of the pathways involved in HDL-CE turnover in dogs. Stable isotopes, 13C-acetate and D3-leucine as labeled precursors of CE and apoAI, were infused to fasting dogs. Isotopic enrichments were monitored in plasma unesterified cholesterol and in HDL-CE and apoAI by mass spectrometry. Kinetics were analyzed using compartmental modeling. Results concerned the measurement of the activity of cholesterol esterification (0.13+/-0.032 h(-1)), rate of HDL-apoAI catabolism (0.024+/-0.012 h(-1)), HDL-CE turnover (0.062+/-0.010 h(-1)) and CE selective uptake (0.038+/-0.014 h(-1)). Our results show that CE in dogs is mainly eliminated by selective uptake of HDL-CE (60% of HDL-CE turnover), unlike in other species studied by similar methods in our laboratory. This study shows that among species used to analyze cholesterol metabolism, the dog appears to be the animal in whom HDL-CE selective uptake represents the largest part of HDL-CE turnover.

Many studies have shown that obesity and low insulin sensitivity are associated with lipoprotein abnormalities, which are risk factors for coronary heart disease. The effects of insulin resistance on lipoprotein metabolism were investigated in hyperenergetic-fed beagle dogs, a new model of insulin resistance. Insulin resistance was assessed by the 3-hour euglycemic-hyperinsulinemic glucose clamp technique. Lipoproteins were separated by fast-protein liquid chromatography (FPLC) and lipid composition of the different lipoproteins was determined by enzymatic methods. Hyperenergetic diet was associated with a 43% ± 5% increase in dog body weight and a reduction in insulin-mediated glucose uptake (28 ± 3 to 16 ± 1 mg · kg−1 · min−1, P

Summary Many studies have shown that in humans insulin resistance (IR) is associated with obesity and hypertriglyceridaemia. The aim of our study was to develop slowly dietary-induced obesity in dogs through long-term overfeeding of a high-fat diet, and to characterize this IR, hypertriglyceridaemic and normotensive model. Insulin resistance was assessed by the euglycaemic hyperinsulinaemic clamp technique. The contribution of hepatic glucose production during the clamp was evaluated using a constant stable-isotope-labelled glucose infusion. Overfeeding a high-fat diet for 7 months was associated with a 43 ± 5% body weight increase. Insulin resistance was characterized by hyperinsulinaemia in the unfed state (10 ± 1 vs. 24 ± 1 μU/ml, in healthy and obese dogs, respectively, p

The effect of a dietary fish oil supplementation on metabolism of HDL was studied in type II diabetes mellitus. Endogenous labeling of HDL-apo AI was performed using a 14 h primed infusion of D3-leucine in five diabetic patients before and 2 months after treatment with maxEPA(R). Isotopic enrichment curves were analyzed using a monoexponential function. After treatment, plasma cholesterol level remained unchanged (205.4+/-41.9 vs. 206.8+/-30.7 mg/dl, NS), whereas plasma triglycerides were decreased (155.4+/-67.9 vs. 202.6+/-32.2 mg/dl, P=0.06). Plasma apo AI was similar under maxEPA(R) (116.0+/-25.6 vs. 111.8+/-25.4 mg/dl, NS), and HDL-cholesterol and HDL-triglycerides were also not markedly changed (30.2+/-10.0 vs. 27.1+/-10 mg/dl, and 15.3+/-9.8 vs. 19.2+/-10.4 mg/dl, NS). HDL-apo AI fractional catabolic rate (FCR) and absolute production rate (APR) were significantly decreased after treatment with maxEPA(R) (0.27+/-0.09 vs. 0.37+/-0.08 pool day, P

The aim of this study was to delineate the role of lipoprotein lipase (LPL) activity in the kinetic alterations of high density lipoprotein (HDL) metabolism in patients with type II diabetes mellitus compared with controls. The kinetics of HDL were studied by endogenous labeling of HDL apolipoprotein AI (HDL-apo AI) using a primed infusion of D(3)-leucine. The HDL-apo AI fractional catabolic rate (FCR) was significantly increased (0.32 +/- 0.07 vs. 0.23 +/- 0.05 pool/day; P < 0.01), and HDL composition was changed [HDL cholesterol, 0.77 +/- 0.16 vs. 1.19 +/- 0.37 mmol/L (P < 0.05); HDL triglycerides, 0.19 +/- 0.12 vs. 0.10 +/- 0.03 mmol/L (P < 0.05)] in diabetic patients compared with healthy subjects. HDL-apo AI FCR was correlated to plasma and HDL triglyceride concentrations (r = 0.82; P < 0.05 and r = 0.80; P < 0.05, respectively) and to homeostasis model assessment (r = 0.78; P < 0.05). Postheparin plasma LPL activity was decreased in type II diabetes (6.8 +/- 2.8 vs. 18.1 +/- 5.2 micromol/mL postheparin plasma.h; P < 0.005) compared with that in healthy subjects and was correlated to the FCR of HDL-apo AI (r = -0.63; P < 0.05). LPL activity was also correlated with HDL cholesterol (r = 0.78; P < 0.05), plasma and HDL triglycerides (r = -0.87; P < 0.005 and r = -0.83; P < 0.05, respectively), and homeostasis model assessment (r = -0.79; P < 0.05). In addition, the LPL to hepatic lipase ratio was correlated with the catabolic rate of HDL (r = -0.76; P < 0.06). These results suggest that a decrease in the LPL to hepatic lipase ratio in type II diabetes mellitus, mainly related to lowered LPL activity, could induce an increase in HDL catabolism. These alterations in HDL kinetics in type II diabetes proceed to some extent from changes in their composition, probably linked to an increase in triglyceride transfer from very low density lipoprotein particles, in close relationship with LPL activity and resistance to insulin.

The acute reduction of low-density lipoprotein (LDL) cholesterol obtained by LDL-apheresis allows the role of the high level of circulating LDL on lipoprotein metabolism in heterozygous familial hypercholesterolemia (heterozygous FH) to be addressed. We studied apolipoprotein B (apoB) kinetics in five heterozygous FH patients before and the day after an apheresis treatment using endogenous labeling with [2H3]leucine. Compared with younger control subjects, heterozygous FH patients before apheresis showed a significant decrease in the fractional catabolic rate of LDL (0.24 ± 0.08 vs. 0.65 ± 0.22 day−1; P < 0.01), and LDL production was increased in heterozygous FH patients (18.9 ± 7.0 vs. 9.9 ± 4.2 mg/kg·day; P< 0.05). The modeling of postapheresis apoB kinetics was performed using a nonsteady state condition, taking into account the changing pool size of very low density lipoprotein (VLDL), intermediate density lipoprotein, and LDL apoB. The postapheresis kinetic parameters did not show statistical differences compared with preapheresis parameters in heterozygous FH patients; however, a trend for increases in fractional catabolic rate of LDL (0.24 ± 0.08 vs. 0.35± 0.09 day−1; P = 0.067) and the production of VLDL (13.7 ± 8.3 vs. 21.9 ± 1.6 mg/kg·day; P = 0.076) was observed. These results suggested that the marked decrease in plasma LDL obtained a short time after LDL-apheresis is able to stimulate LDL receptor activity and VLDL production in heterozygous FH.

The effects of the new hypolipidemic agent, F2833 or (chloro 2' (1-1') biphenyl-4)-2 propanol-2, on cholesterol metabolism were studied in genetically hyperlipidemic rats (RICO). Cholesterolemia decreased after 2 days of treatment to 60% of its initial value (1.20+/-0.10 g/l vs. 1.99+/-0.08, P < 0.001) and then stabilised within 10 days. This hypocholesterolemic action was effective for as long as 3 months. Concerning the different classes of lipoproteins, a significant drop was observed in HDL (high density lipoproteins) (25%, 0.49 +/- 0.02 g/l vs. 0.66 +/- 0.007, P < 0.01) and particularly in LDL (low density lipoproteins) (70%, 0.30 +/- 0.04 g/l vs. 0.92 +/- 0.05, P < 0.001). Whole body cholesterol showed a higher fractional catabolic rate (0.25 +/- 0.02 vs. 0.17 +/- 0.005 day(-1), P < 0.01) together with an increased cholesterol synthesis (60 +/- 5 vs. 36 +/- 4 mg/day, P < 0.01). LDL kinetics showed that the decrease in these lipoproteins is essentially caused by an increase in the fractional catabolic rate (10.6 +/-0.1%/h vs. 5.2 +/- 0.1%/h, P < 0.001) and by a lesser decrease in the LDL production rate. This cholesterol metabolic profile created by treatment suggests an effect through stimulation of cholesterol output (biliary cholesterol elimination or cholesterol transformation into bile acids).

Kinetic disturbances of lipoprotein metabolism are important to know for a better understanding of lipid diseases or effects of drugs. These kinetic aspects were previously studied with radioactive tracers. The ethical concerns related to these tracers can be now overcome at a reasonable cost with the new development of small bench top mass spectrometers and the increased production of stable isotope tracers. In this review, we will discuss some methodological aspects related to stable isotope tracers and the analysis of the data with non-compartmental or compartmental models.

Incorporation of amino acids labeled with stable isotopes in apoliproproteins is used to estimate kinetic aspects of lipoprotein metabolism. In this study two deuterated tracers, [5,5,5-2H3]leucine and [ring-2H5]phenylalanine, were compared. Isolation and acid hydrolysis of apolipoproteins are required for mass spectrometric analysis. When apolipoprotein B100 of very low density liproproteins was prepared with this procedure, a loss of deuterium was observed on deuterated phenylalanine with 10 and 6 M HCl hydrolysis but not with deuterated leucine or when 4 M HCl hydrolysis was used. This study stre sses the effect of acid hydrolysis on [ring-2H5]phenylalanine. This tracer must be used with caution in studies of specific protein synthesis.

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

Reverse cholesterol transport (RCT) is an anti-atherogenic process by which cholesterol is effluxed from peripheral tissues by high-density lipoprotein (HDL) and returned to the liver for excretion into the bile and faeces. Dyslipidemia is thought to impair RCT through higher triglyceride-rich lipoprotein (TRL), low HDL-cholesterol and higher activity of cholesteryl ester transfer protein (CETP), which transfers cholesteryl esters from HDL to TRL for further hepatic uptake. As CETP pathway would represent a major route in human RCT, we therefore investigated whether diet-induced dyslipidemia impairs RCT in hamster, a CETP-expressing species.Golden Syrian hamsters were fed a chow or chow+0·3% cholesterol diet over 4 weeks. Biochemical parameters and in vivo VLDL-triglycerides secretion (Triton WR-1339 injection) were then measured. In vitro macrophage cholesterol efflux was measured, and in vivo macrophage-to-faeces RCT was also assessed after an intraperitoneal injection of (3) H-cholesterol-labelled hamster primary macrophages.Cholesterol-enriched diet increased plasma total cholesterol (144%), triglycerides (101%), VLDL-triglycerides secretion (175%), CETP activity (44%) and reduced HDL-cholesterol/total cholesterol ratio by 20% (P0·01 vs. chow). Cholesterol-enriched diet significantly increased hepatic total cholesterol and triglycerides by 459 and 118% and increased aortic total cholesterol content by 304%. In vitro cholesterol efflux from macrophages to plasma was significantly reduced by 25% with plasma from cholesterol-fed hamsters. In vivo RCT experiments showed a significant 75% reduction of macrophage-derived cholesterol faecal excretion in cholesterol-fed hamsters.Overall, these data demonstrate that diet-induced dyslipidemia severely impairs in vivo RCT in hamsters.

In humans, obesity is closely associated with insulin resistance (IR) and dyslipidaemia. The purpose of this study was to explore the effect of age on metabolic disturbances related to obesity in dogs (n = 25). Three age-groups of dogs (puppies, young adults and mature adults) were overfed to induce obesity, and body composition, insulin sensitivity index (I(IS)) (euglycaemic-hyperinsulinaemic glucose clamp) and plasma lipids were measured. Fat mass was similar in the three obese groups (30 +/- 1% in puppies, 34 +/- 1% in young adults and 39 +/- 1% in mature adults). In mature adults, body weight (BW) increased (+45%, p < 0.001) and I(IS) decreased (-60%, p < 0.001) over 22 weeks. In young adults, BW gain was similar but slower (60 weeks) and I(IS) decreased to a lesser extent (-49%, p < 0.001). Overfed puppies weighed 30% more (p < 0.01) than normally-fed control puppies, but there was no change in I(IS). Unlike young and mature adults, obese puppies did not exhibit significant changes in triglycerides (TG) and free fatty acid concentrations. In conclusion, as in humans, obese dogs develop IR that is associated with high TG levels; however, younger animals may be better able to balance energy needs with energy consumption.

As in man, canine obesity is associated with insulin resistance, dyslipidaemia and other chronic diseases. This study was designed to examine the effects of a nutritional supplement (green tea) on insulin sensitivity and plasma lipid concentrations in an obese insulin-resistant dog model. We also determined mRNA expression of two transcription factors, PPARγ and PPARα, and some of their target genes, including GLUT4, lipoprotein lipase (LPL) and adiponectin. Obese dogs were divided into two groups: a green tea group (n 6); a control group (n 4). Dogs in the green tea group were given green tea extract (80 mg/kg per d) orally, just before their single daily meal, for 12 weeks. Insulin sensitivity (using a euglycaemic–hyperinsulinaemic clamp) and concentrations of plasma TAG, total cholesterol and NEFA were assessed in each group. Gene expression was measured in visceral and subcutaneous adipose tissues and in liver and skeletal muscle, by real-time PCR. At 12 weeks in the green tea group, mean insulin sensitivity index was 60 (sem 11) % higher (P sem 10) % lower (P

Aims: In reverse cholesterol transport (RCT), hepatic Scavenger Receptor class B type I (SR-BI) plays an important role by mediating the selective uptake of high-density lipoprotein cholesteryl ester (HDL-CE). However, little is known about this antiatherogenic mechanism in insulin resistance. HDL-CE selective uptake represents the main process for HDL-CE turnover in dog, a species lacking cholesteryl ester transfer protein activity. We therefore investigate the effects of diet induced insulin resistance on RCT. Methods: Five beagle dogs, in healthy and insulin resistant states, underwent a primed constant infusion of [1,213C2]acetate and [5,5,5-2H3]leucine, as labelled precursors of CE and apolipoprotein (apo) A-I, respectively. Data were analysed using modelling methods. Results: HDL-apo A-I concentration did not change in insulin resistant state but apo A-I absolute production rate (APR) and fractional catabolic rate (FCR) were both higher (2.2- and 2.4-fold, respectively, p

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.

Amongst the processes involved in the reverse cholesterol transport (RCT) from organs to liver, including high density lipoproteins-apolipoprotein AI (HDL-apoAI) dependent tissue uptake and cholesteryl ester transfer protein (CETP)-mediated transfers, the selective uptake of cholesteryl ester (CE) is of increasing interest through its antiatherogenic role. The purpose of this report is to develop a simple protocol allowing study of this process in an animal model with easier quantification of CE selective uptake. The dog was chosen essentially because this animal has a low CETP activity and an appropriate size to conduce a kinetic study. Tracer kinetics were performed to estimate in vivo the contributions of the pathways involved in HDL-CE turnover in dogs. Stable isotopes, 13C-acetate and D3-leucine as labeled precursors of CE and apoAI, were infused to fasting dogs. Isotopic enrichments were monitored in plasma unesterified cholesterol and in HDL-CE and apoAI by mass spectrometry. Kinetics were analyzed using compartmental modeling. Results concerned the measurement of the activity of cholesterol esterification (0.13+/-0.032 h(-1)), rate of HDL-apoAI catabolism (0.024+/-0.012 h(-1)), HDL-CE turnover (0.062+/-0.010 h(-1)) and CE selective uptake (0.038+/-0.014 h(-1)). Our results show that CE in dogs is mainly eliminated by selective uptake of HDL-CE (60% of HDL-CE turnover), unlike in other species studied by similar methods in our laboratory. This study shows that among species used to analyze cholesterol metabolism, the dog appears to be the animal in whom HDL-CE selective uptake represents the largest part of HDL-CE turnover.

Seven hypertriglyceridemic patients with type-2 diabetes were treated with atorvastatin (40 mg/day) for 2 months. Kinetics of apolipoprotein B100 (apoB100)-containing lipoproteins were determined before and after atorvastatin treatment and compared with data obtained in five normolipidemic volunteers. ApoB100 metabolism was studied using stable isotopes and multicompartmental modeling. Compared with normolipidemic obese subjects, type-2 diabetic patients had a higher apoB100 concentration in very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), and low-density lipoproteins (LDL) (P < 0.005). Kinetic analysis showed an increase in the total apoB100 production rate (P < 0.005) related to VLDL apoB100 overproduction (P < 0.005). Patients were also characterized by a lower fractional catabolic rate (FCR) in VLDL (not significant) or IDL (P < 0.005) mainly related to a decrease in VLDL and IDL delipidation rate (P < 0.005). Catabolism of LDL was also lower in diabetic patients (P < 0.05). Atorvastatin treatment significantly decreased plasma triglycerides (P < 0.05), total and LDL cholesterol (P < 0.05), apoB100 in LDL, IDL, and VLDL (P < 0.05). Treatment significantly decreased total apoB100 production rate (P < 0.05), but only for VLDL (P < 0.05). Treatment normalized FCR in IDL and LDL (P < 0.05). We concluded that atorvastatin improved lipid abnormalities in type-2 diabetic patients not only by increasing the clearance of apoB100-containing lipoproteins but also by decreasing VLDL production.

A method to study reverse cholesterol transport in humans was developed using stable isotopes and kinetic analysis. Three normolipidemic subjects received simultaneous intravenous infusions of deuterated leucine and 13 C-acetate for 14 and 8 hours, respectively. Deuterium enrichment was measured in protein-bound leucine in apolipoproteins (apo) B-100 and A-I (using gas chromatography coupled with mass spectrometry [GCMS]) and 13 C-enrichment in unesterified cholesterol and cholesteryl ester (using gas chromatography coupled to isotope ratio mass spectrometry [GC-C-IRMS]) in very[ndash ]low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) during the tracer infusion. Curves were analyzed using multicompartmental analysis. This protocol is suitable to quantify the different processes involved in reverse cholesterol transport (RCT) in humans, including cholesterol esterification, transfer of cholesteryl ester from HDL towards apo B-100[ndash ]containing lipoproteins, and the contribution of VLDL, LDL, and HDL in the final steps of RCT. In agreement with previous data from kinetic analysis of radiotracer experiments, our results suggest that in fasting normolipidemic subjects the major fraction of cholesteryl ester enters plasma through esterification in HDL (more than 95%). The major fraction of cholesteryl ester disappears through apo B-100[ndash ]containing lipoproteins (VLDL and LDL) catabolism (mean of 82%) rather than through removal from HDL (mean of 18% with approximately an equal part for apo AI-dependent and independent catabolism, respectively, 7% and 11%). We conclude that this protocol could be applied to study the modulation of these processes by nutrition, diseases, or pharmacologic treatments.

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Abstract In vitro data suggested that albumin is a key factor controlling apolipoprotein (apo) synthesis by hepatocytes. Studies in analbuminemic rats have shown an increase in secretion of apoB-containing lipoprotein from the liver. We studied the kinetic aspects of apoB- and apoAI-containing lipoprotein metabolism in two sisters with analbuminemia using a constant 14-hour infusion of leucine labeled with stable isotopes. Compared with control subjects, total cholesterol was higher in the two patients (432 and 461 versus 155±14 mg/dL), as was apoB (257 and 230 versus 72±7 mg/dL). Triglycerides were slightly increased (134 and 105 versus 89±9 mg/dL), whereas apoAI was lower (109 and 105 versus 124±6 mg/dL). VLDL–apoB production was higher, as was the production of IDL–apoB and LDL–apoB (32.8 and 36.0 versus 24.8±5.9, 32.1 and 27.2 versus 16.4±2.3, and 14.1 and 17.6 versus 10.3±1.2 mg · kg −1 · d −1 , respectively). The fractional catabolic rate of all the apoB-containing lipoproteins was decreased (0.23 and 0.37 versus 0.48±0.05, 0.27 and 0.28 versus 0.62±0.08, and 0.012 and 0.009 versus 0.022±0.002 · h −1 , respectively). A similar mechanism could explain the dyslipidemia observed in other conditions associated with low albumin levels, such as nephrotic syndrome.

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International audience

International audience

We have previously shown in a 2-yr controlled trial that hypercholesterolemia, frequent in primary biliary cirrhosis, is lowered by ursodeoxycholic acid (13 to 15 mg daily). To further investigate this effect, we analyzed the influence of long-term ursodeoxycholic acid administration on serum lipids, lipoproteins and bile acids. The study involved a subgroup of 33 noncirrhotic patients (17 received ursodeoxycholic acid and 16 received a placebo) analyzed at inclusion and after 2 yr. The total serum cholesterol concentration was markedly reduced in the ursodeoxycholic acid-treated patients in comparison with the controls (mean +/- S.E.M. = 7.49 +/- 0.42 mmol/L and 7.07 +/- 0.23 mmol/L at entry and 4.44 +/- 0.40 mmol/L and 6.89 +/- 0.27 mmol/L at 2 yr in the ursodeoxycholic acid and placebo groups, respectively; p < 0.02). Quantitatively, this decrease was mainly caused by a fall in low-density-lipoprotein cholesterol, but very low density-lipoprotein cholesterol levels also fell significantly. High-density-lipoprotein cholesterol levels remained stable in both groups, but the high-density-lipoprotein2/high-density-lipoprotein3 cholesterol ratio fell significantly during ursodeoxycholic acid treatment. No significant change occurred in total triglyceride or total phospholipid levels. In the treated group, the proportion of ursodeoxycholic acid increased (up to 60% of total circulating bile acids), whereas that of cholic and chenodeoxycholic acids fell significantly. In conclusion, the cholesterol-lowering effect of ursodeoxycholic acid could be related to an improvement of cholestasis, modifications in cholesterol metabolism or both. Changes in endogenous bile acid composition induced by ursodeoxycholic acid might be the common denominator of these two mechanisms.

Introduction Le syndrome metabolique est caracterise par une augmentation des TG et une baisse du HDL-CH. Chez ces patients, les omega 3 baissent les TG des VLDL sans modifier les LDL. Le but du travail est de mesurer le transport inverse de cholesterol (RCT), en utilisant un protocole developpe au laboratoire par marquage simultane des apolipoproteines et du cholesterol. Patients et Methodes Une etude cinetique du metabolisme des lipoproteines a ete entreprise chez 6 sujets atteints de syndrome metabolique avant et apres un traitement de 8 semaines aux omega 3 (3 g/j). Pendant les 14 h de perfusion de [ 2 H 3 ] leucine et du 13C acetate, des prelevements de sang ont ete realises et l'enrichissement isotopique des apolipoproteines et du cholesterol des VLDL, IDL et LDL d'une part et celui de l'apoAI et du choleterol des HDL d'autre part a ete determine. Les courbes cinetiques ont ete analysees par modelisation multicompartimentale. Resultats Les omega 3 entrainent une baisse significative des TG des VLDL. liee a une baisse de la production des VLDL (0,62 ± 0,33 vs 0,43 ± 0,23 mg/kg/h). La transformation des VLDL vers les LDL augmente de maniere significative (0,063 ± 0,037 vs 0,093 ± 0,040 h-1, p -1 . H -1 , p -1 , p -1 , p -1 , p Conclusion Les omega 3 entrainent un effet hypotriglyceridemiant par diminution de production de VLDL et par stimulation de la lipolyse. Les resultats montrent un effet stimulant sur le transport inverse du cholesterol par stimulation de la LCAT associe a une augmentation du transfert du CE vers LDL via la CETP.

The aim of the study was to compare two methods classically used in rats to determine the fractional catabolic rate (FCR) of labeled high or low density lipoproteins: constant infusion and single pulse. The FC of [14C]-sucrose HDL (High density lipoprotein) was studied. For the short term experiment (8 hours), both methods gave similar FCR determined 8 hours after HDL constant infusion (9.4%.h-1 +/- 0.6) or single pulse (8.5%.h-1 +/- 0.4), values significantly higher than those measured 24 hr after the single pulse (6.2%.h-1 +/- 0.3). The identification and simulation of the model representing HDL movements between an intravascular and extravascular pool, after single pulse and constant infusion methods, demonstrated that FCR of lipoproteins cannot be precisely measured with techniques involving excessively short observation periods.

International audience

Heterozygous familial hypercholesterolemia (FH) is associated with a moderate decrease of plasma apoA-I and HDL-cholesterol levels. The aim of the study was to test the hypothesis that these abnormalities were related to an increase of HDL-apoA-I fractional catabolic rate (FCR). We performed a 14-h infusion of (5,5,5- 2 H 3 )leucine in seven control subjects and seven heterozygous FH patients (plasma total cholesterol 422 6 27 vs. 186 6 42 mg/dL, P , 0.001, respectively). Plasma apoA-I concentration was not changed in FH compared to controls (respectively 115 6 18 vs. 122 6 15 mg/dL, NS), and HDL-cholesterol level was decreased (37 6 7 vs. 46 6 19 mg/dL, NS). Kinetics of HDL metabolism were modeled as a single compartment as no differences were observed between HDL 2 and HDL 3 subclasses. Both mean apoA-I FCR and absolute production rate (APR) were increased in FH (respectively, 0.36 6 0.14 vs. 0.22 6 0.05 pool/d, P , 0.05, and 18.0 6 7.7 and 11.2 6 2.3 mg/kg/d, P , 0.05). Higher HDL-triglyceride and HDL- apoE levels were observed in patients with heterozygous FH. (Respectively 19 6 8 vs. 8 6 3 mg/dL, P , 0.05, and 5.3 6 0.8 vs. 3.7 6 0.9 mg/dL, P , 0.05). We conclude that the catabolism of HDL-apoA-I is increased in heterozy- gous FH patients. However, plasma apoA-I concentration was maintained because of an increased HDL-apoA-I pro- duction rate. —Frenais, R., K. Ouguerram, C. Maugeais, J. S. Marchini, P. Benlian, J. M. Bard, T. Magot, and M. Krempf. Apolipoprotein A-I kinetics in heterozygous familial hyper- cholesterolemia: a stable isotope study. J. Lipid Res. 1999. 40 : 1506-1511.