Hypertriglyceridaemic insulin-resistant obese dog model: effects of high-fat diet depending on age.

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.

Effect of low-density lipoprotein apheresis on kinetics of apolipoprotein B in heterozygous familial hypercholesterolemia.

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 [(2)H(3)]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.

In vivo evidence for the role of lipoprotein lipase activity in the regulation of apolipoprotein AI metabolism: a kinetic study in control subjects and patients with type II diabetes mellitus.

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.

Metabolism of intestinal triglyceride-rich lipoproteins in the genetically hypercholesterolemic rat (RICO)

Experiments were carried out to compare the catabolism of intestinal lipoproteins between genetically hypercholesterolemic (RICO) and normocholesterolemic (SW) rats. Kinetics of plasma cholesteryl ester were studied after injection of cholesterol-labeled chylomicrons or VLDL. The chylomicron clearance is reduced in the RICO rat (rate constant, K = 7.2 +/- 0.1 h-1 vs. 10.7 +/- 0.1 h-1 in SW rat), while a much more minor alteration was observed in the catabolism of lymph VLDL (K = 4.3 +/- 0.6 h-1 in the RICO rat vs. 5.1 +/- 0.4 h-1). The injection of chylomicrons from SW rats to RICO rats and from RICO rats to SW rats showed that the fall in the rate of catabolism of chylomicrons in RICO rats was not secondary to an increase in the production rate, but was related to the lipoprotein particle itself without any alteration of the catabolic system. The reduction in the rate of catabolism of chylomicrons in the RICO rat could be related to a change in their apolipoprotein composition (increase in the proportion of apolipoprotein E = 12 +/- 2% vs. 3 +/- 1% in the SW rat).

Effect of dietary omega-3 fatty acids on high-density lipoprotein apolipoprotein AI kinetics in type II diabetes mellitus.

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<0.05, and 12.1+/-2.8 vs. 16.1+/-3.3 mg/kg per day, P<0.05). These findings showed an effect of maxEPA(R) on kinetics of apolipoprotein AI in type II diabetes mellitus, probably linked to changes in plasma triglyceride level.

Metabolism of plasma lipoproteins in the genetically hypercholesterolemic rat (RICO).

Experiments were performed to determine the turnover processes of plasma cholesterol in genetically hypercholesterolemic rats (RICO). Specific activity of plasma cholesterol was monitored during 4 months following an intravenous injection of tritiated cholesterol. The results were subjected to two-pool model analysis. Cholesterol production in the RICO rat was significantly higher (28.9 +/- 1.7 mg/d) than in the SW control (18.5 +/- 0.7, P < .01). The study also revealed a 30% decrease in the rate constant for cholesterol movement from the plasma toward the majority of organs in the RICO rat versus the SW control. Very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) turnover were investigated following injection of labeled lipoproteins (on cholesteryl ester or apolipoproteins). Results from these experiments showed that the higher HDL cholesterol concentration in the RICO rat as compared with the control is due to the greater production rate of esterified cholesterol in these lipoproteins (1.3 +/- 0.05 mg/h v 0.8 +/- 0.03 in the control, P < .001). The fractional catabolic rate (FCR) or production rate for VLDL were not significantly different between the two groups (3.4 +/- 0.01 and 3.6 +/- 0.01 h-1 and 2.6 +/- 0.4 and 3.3 +/- 0.1 mg/h, respectively). However, radioactivity of VLDL recovered in LDL at death was considerably higher in RICO rats (14% +/- 1% v 6% +/- 1%, P < .01). The greater concentration of LDL cholesterol in RICO rats is due to a higher LDL production (0.40 +/- 0.05 v 0.19 +/- 0.03 mg/h, P < .01) together with a lower catabolism (FCR, 5.5 +/- 0.6 v 7.9 +/- 0.8%/h, P < .05). Cross-injection experiments showed that this lower catabolism of LDL is partly due to the nature of the lipoprotein particle. Taken together, these data are consistent with the hypothesis of a reduced uptake of apolipoprotein (apo)E-containing lipoproteins (VLDL and LDL), which results in a higher LDL cholesterol concentration in RICO rats.

A new labeling approach using stable isotopes to study in vivo plasma cholesterol metabolism in humans.

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-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-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-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.

Effect of low-density lipoproteins on apolipoprotein AI kinetics in heterozygous familial hypercholesterolemia.

In patients with heterozygous familial hypercholesterolemia (FH), both synthetic and clearance rates of high-density lipoproteins (HDL) are increased compared with control subjects. According to in vitro data on hepatocytes, the expanded pool size of low-density lipoproteins (LDL) in FH could partly explain the enhanced HDL production. Therefore, we have tested the hypothesis that a reduction of LDL pool size, achieved by LDL-apheresis, is associated with a downregulation of HDL synthesis. We studied the kinetics of HDL by infusing [5,5,5-(2)H(3)]-leucine in 7 heterozygous FH patients before and after 3 biweekly LDL-apheresis using dextran sulfate columns. Both plasma and LDL-cholesterol levels were decreased after LDL-apheresis (169 +/- 35 v 422 +/- 27 mg/dL, P <.05, and 85 +/- 19 v 327 +/- 52 mg/dL, P <.05, respectively). Plasma triglyceride level was unaffected (162 +/- 43 v 176 +/- 35 mg/dL, not significant [NS]) and HDL composition remained stable (HDL-cholesterol 29 +/- 6 v 37 +/- 7 mg/dL, NS, and HDL-triglyceride 20 +/- 6 v 19 +/- 8 mg/dL, NS). Plasma apolipoprotein AI (apo AI) was also similar (122 +/- 20 v 115 +/- 18 mg/dL, NS). Mean HDL-apo AI fractional catabolic rate (FCR) was slightly higher (0.41 +/- 0.07 v 0.36 +/- 0.14 pool/d, NS), and absolute production rate (APR) was increased (22.1 +/- 5.7 v 18.0 +/- 5.7 mg/kg/d, P <.05) after LDL-apheresis. These human kinetic data suggest that LDL do not play a major role on HDL production in heterozygous FH patients.

Effects of F2833 on cholesterol metabolism in the genetically hyperlipidemic rat.

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).

A minimal model using stable isotopes to study the metabolism of apolipoprotein B-containing lipoproteins in humans.

A protocol using stable isotopes, developed to measure apolipoprotein B turnover in humans, was tested by intravenous infusion of [2H3]-leucine into 5 normolipidemic volunteers during a 14-h fast. Tracer-to-tracee ratio curves were analyzed by four different approaches: linear regression, monoexponential regression, a minimal compartmental model (3 compartments) and a complex model (4 compartments and two shunt pathways). The three-compartment model was validated by qualitative analysis of data obtained after injection of a [2H3]-leucine bolus. This simple model gave an FCR of 0.48 +/- 0.05 h-1 for VLDL, 0.62 +/- 0.08 h-1 for IDL and 0.022 +/- 0.002 h-1 for LDL. The total production rate of apolipoprotein B in plasma was 24.8 +/- 6.5 mg.kg-1.day-1. Kinetic parameters were similar for the complex model which showed no improvement in fit. Lower estimates were observed with the non-compartmental approaches.

In vivo effect of simvastatin on lipoprotein cholesteryl ester metabolism in normocholesterolemic volunteers.

A kinetic study on lipoprotein cholesteryl ester metabolism was carried out in 4 normolipidemic volunteers before and after treatment with simvastatin. They received LDL labelled with 3H-cholesteryl linoleate. A lipoprotein cholesteryl ester model was developed that fit the radioactivity in LDL, HDL and VLDL cholesteryl ester during 24 hours following injection. Before treatment, the model is consistent with previously reported data. Moreover our results suggest that, in normal fasting subjects, the efflux of plasma cholesteryl ester is almost exclusively derived from LDL. Administration of drug decreased LDL cholesteryl ester concentration by 35%. After treatment, the rate constant concerning LDL catabolism was increased by 25% and the model required the existence of a direct removal of VLDL cholesteryl ester (40% of total VLDL turnover). Our results suggest that the reduction in the LDL cholesteryl ester concentration induced by treatment with simvastatin is due to an increase in the uptake of LDL and LDL precursors (VLDL, VLDL remnants) by LDL receptors.

Metabolism of high density lipoprotein apolipoprotein A-I and cholesteryl ester in insulin resistant dog: a stable isotope study.

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 [1,2(13)C(2)]acetate and [5,5,5-(2)H(3)]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 < 0.05). HDL-CE levels were lower (1.2-fold, p < 0.05). HDL-CE APR and FCR were both lower (2.3- and 2-fold, respectively, p < 0.05), as well as selective uptake (2.6-fold, p < 0.05). CONCLUSIONS: Lower HDL-CE selective uptake suggests that RCT is impaired in obese insulin resistant dog.

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 on high-density lipoprotein apolipoprotein A-I metabolism in dogs.

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.

Kinetics of prebeta1 HDL and alphaHDL in type II diabetic patients.

BACKGROUND: The aim of this study was to analyze the recycling of high density lipoprotein (HDL) in six type II diabetic patients compared with six control subjects by endogenous labelling of apolipoprotein A-I (Apo A-I) with stable isotope Apo A. MATERIALS AND METHODS: The -I-HDL kinetics were performed by infusion of (5.5.5-(2)H3)-leucine for 14 h. The prebeta1 and alphaHDL were separated by gel filtration fast protein liquid chromatrography system (FPLC). Kinetics of isotopic enrichment of Apo A-I were analyzed with a multi-compartmental model software (SAAM II, SAAM Institute, Seattle, WA). RESULTS: Plasma Apo A-I concentration was decreased in patients with type II diabetes as a result of a decrease in Apo A-I-alphaHDL (P < 0.05). Diabetic patients were also characterized by an increased relative contribution of Apo A-I in prebeta1 HDL (18.3 +/- 2.8% vs 11.9 +/- 3.7%, P < 0.01). The synthetic rate of prebeta1 HDL was slightly increased in diabetic patients compared with control (NS) and an increase of recycling rate of alpha to prebeta1 HDL was observed (11.67 +/- 3.14 d(-1) vs 7.09 +/- 4.51 d(-1), P < 0.05). The clearance rate of Apo A-I was higher in diabetic patients (P < 0.05 for Apo A-I-prebeta1 HDL and P < 0.005 for Apo A-I-alphaHDL). CONCLUSION: This study suggests that the usual increase in prebeta1 HDL in type II diabetic patients is mainly related to an increased conversion rate of alpha to prebeta1 HDL.

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.

Kinetic study of apo B100 containing lipoprotein metabolism using amino acids labeled with stable isotopes: methodological aspects.

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.

Turnover of [14C] sucrose HDL and uptake by organs in the normal or genetically hypercholesterolemic (RICO) rat using a constant infusion method.

The turnover and tissular uptake of HDL (d 1.095-1.21) have been compared in normocholesterolemic or genetically hypercholesterolemic rats by a constant infusion method of [14C] sucrose labelled HDL for 8 h. The HDL clearance rate was not significantly smaller in the RICO than in the normocholesterolemic animal (320 +/- 22 microliters.h-1 versus 366 +/- 24 microliters.h-1 per 100 g of rat). It was the same case for the fractional catabolic rate, respectively equal to 7.8 and 9.4 +/- 0.6%.h-1. For both strains, liver and skeletal muscle were the main catabolic sites for HDL. The HDL uptake rates in intestine or kidney were 3-4-fold smaller than those in the liver. In the RICO rat, intestine, testis and adrenals showed a lesser HDL uptake capacity (expressed per g of organ) than the normocholesterolemic rat.

Overestimation of the lipoprotein fractional catabolic rate (FCR) measured in short duration experiments.

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.