C.G. Vinagre

Chylomicron metabolism is markedly altered in systemic lupus erythematosus

OBJECTIVE To verify the in vivo status of chylomicron metabolism in systemic lupus erythematosus (SLE) since there is a high incidence of atherosclerosis in this disease and chylomicrons may have an important role in atherogenesis. METHODS A chylomicron-like emulsion labeled with 14C-cholesteryl esters and 3H-triglycerides was injected intravenously into 10 female patients with inactive SLE and 10 healthy age- and sex-matched control subjects to determine the plasma kinetics of the emulsion lipids from consecutive plasma samples taken at regular intervals for 1 hour. Lipolytic activity was determined in vitro after incubation of the labeled emulsion with postheparin plasma. RESULTS The decay curves for the emulsion were markedly slowed in SLE. Chylomicron lipolysis, indicated by the fractional clearance rate (FCR) of emulsion 3H-triglyceride, was 2-fold smaller in SLE patients than in controls (mean +/- SD 0.023 +/- 0.011 versus 0.047 +/-0.015 minute(-1); P = 0.010). Chylomicron removal, indicated by emulsion 14C-cholesteryl ester FCR, was 3-fold smaller in SLE patients than in controls (0.007 +/-0.007 versus 0.023 +/- 0.011 minute(-1); P = 0.009). In vitro lipolysis in SLE patients was nearly half that of the controls (mean +/- SD 10,199 +/- 2,959 versus 6,598 +/-2,215; P = 0.014). Higher levels of very-low-density lipoprotein cholesterol and triglycerides and lower levels of high-density lipoprotein cholesterol and apolipoprotein A-I were also observed in the SLE patients. CONCLUSION SLE patients have disturbances in chylomicron metabolism that are characterized by decreased lipolysis and chylomicron remnant removal from the plasma. This finding, together with other alterations in lipid profiles that were confirmed in the present study, is largely accountable for the accelerated atherosclerotic process of the disease.

Plasma kinetics of a chylomicron-like emulsion in patients with coronary artery disease

Chylomicron catabolism in the bloodstream consists of lipolysis by lipoprotein lipase and uptake of remnants by the liver. In rats, triglyceride-rich emulsions can mimic chylomicron metabolism. To further validate this model in man, the emulsion was injected intravenously into fasting and into subjects previously fed a test fatty meal. The plasma kinetic curves of the emulsion 3H-triglyceride and 14C-cholesteryl ester were determined. The fractional clearance rate (FCR) of both labels was markedly reduced in the fed subjects (triglycerides: fed = 0.018 +/- 0.007; fasting = 0.105 +/- 0.013 min-1, P < 0.001; cholesteryl ester: fed = 0.016 +/- 0.001; fasting = 0.040 +/- 0.006 min-1; P < 0.05) indicating that the emulsion and chylomicrons generated from the testinal lipid absorption compete for the same catabolic processes, confirming the validity of the method. The emulsion was injected into 11 patients with CAD and into 11 controls. All had plasma cholesterol < 240 and triglycerides < 250 mg/dl. FCR of triglycerides was 5-fold smaller in CAD compared to controls (0.028 +/- 0.004 and 0.141 +/- 0.069 min-1, respectively, P < 0.01). FCR of cholesteryl ester was 4-fold smaller in CAD than in controls (0.015 +/- 0.004 and 0.056 +/- 0.067 min-1 respectively, P < 0.05). These results indicate that both chylomicron lipolysis and remnant removal are diminished in CAD.

Increased apolipoprotein B serum concentration in Alzheimer's disease

Objective ‐ To investigate the lipoprotein profile in a group of Alzheimers disease (AD) patients. Patients und methods ‐ Twenty‐four patients with AD and 32 elderly controls were evaluated. Fasting blood samples were obtained for determination of total VLDL, HDL and LDL cholesterol, lipoprotein (a), triglycerides, apolipoprotein A1 and apolipoprotein B. Results ‐ Significantly higher levels of apolipoprotein B were found in AD patients (P=0.004), whereas the concentration of lipoprotein (a) and plasma lipids was not statistically different. Apo B levels were similar between AD patients with or without leukoaraiosis on CT scan. Conclusion ‐ AD patients had high serum concentration of apolipoprotein B. This finding suggests that apolipoprotein E may not be the single factor in lipid metabolism to play a role in AD pathogenesis.

Chloroquine increases low-density lipoprotein removal from plasma in systemic lupus patients

Low-density lipoprotein (LDL) pathway in systemic lupus erythematosus (SLE) patients taking chloroquine diphosphate (CDP) was evaluated through the kinetic behavior of a radioactive cholesterol-rich nanoemulsion (LDE) that resembles the LDL lipidic structure. LDE was labeled with 14C-cholesteryl ester (14C-CE), then IV injected in inactive female SLE patients: 10 taking CDP (CDP), 10 without therapy (NO THERAPY); and 10 normal subjects (CONTROL). Groups were age-matched and followed rigorous selection criteria of conditions that interfere in the lipid profile. Blood samples were collected in pre-established intervals after infusion for radioactivity measurement. Fasting lipoproteins were determined in the beginning of kinetic studies. Fractional clearance rate (FCR) of 14C-CE was significantly different in the three groups (P = 0.03). In fact, a greater FCR of 14C-CE was observed in CDP compared to NO THERAPY (0.076 ± 0.037 versus 0.046 ± 0.021 h— 1; P < 0.05) and to CONTROL (0.0516 ± 0.0125 h— 1; P < 0.05). Accordingly, a significant lower total and LDL cholesterol were observed in CDP (156 ± 16 and 88 ± 16 mg/dl) compared to NO THERAPY (174 ± 15 and 108 ± 17 mg/dl; P < 0.05) and to CONTROL (200 ± 24 and 118 ± 23 mg/dl; P < 0.05). In contrast, no difference in (FCR) of 14C-CE of NO THERAPY and CONTROL groups was observed. This is the first in vivo demonstration that LDE removal by LDL receptor from plasma is increased in SLE patients taking CDP with a consequent beneficial decrease in LDL-c levels. Lupus (2007) 16, 273—278.

Chylomicron metabolism in patients submitted to cardiac transplantation.

BACKGROUND Development of coronary graft disease is the most important cause of late heart graft failure. Alterations in plasma lipid profile are frequent in heart transplant (HT) patients, but they seem not to be prominent. Currently, the metabolism of chylomicrons, the lipoproteins that carry dietary lipids absorbed by the intestine, was evaluated because chylomicron remnants are considered atherogenic. METHODS An emulsion labeled with 3H-triolein and 14C-cholesteryl oleate and known to mimic the metabolic behavior of chylomicrons was injected intravenously after a 12-hr fast into 34 HT patients, 24 patients with end-stage heart failure (ESHF), and 30 healthy normolipidemic subjects. The plasma disappearance curves of the radioisotopes were determined from blood samples collected over 1 hr. In some of the patients and in controls, in vitro postheparin lipolytic activity was measured and an oral fat load test with postprandial measurement of triglyceridemia was performed. RESULTS Fractional clearance rate (in m(-1), median [25%; 75%]) of both emulsion 3H-triolein and 14C-cholesteryl oleate was extremely diminished in HT patients (HT: 0.0114 [0.0114; 0.0179] and 0.2x10(-8) [0.2x10(-8); 0.0041, respectively]; ESHF: 0.0226 [0.0223; 0.0568] and 0.0160 [0.0055; 0.0189]; control subjects: 0.0270 [0.0226; 0.0392] and 0.0090 [0.0042; 0.0180], respectively, P<0.05). HT patients also had reduced postheparin lipolysis and marked elevation of postprandial triglyceridemia compared with the controls. CONCLUSIONS HT patients develop accumulation in the plasma of chylomicrons and their remnants. The observed alterations were so intense that they may suggest an important involvement of atherogenic chylomicron remnants in coronary graft disease.

Effects of etofibrate upon the metabolism of chylomicron-like emulsions in patients with coronary artery disease

Slow chylomicron intravascular catabolism has been associated with coronary artery disease and screening for drugs that can speed-up this process can be important. In this study, the effects of etofibrate upon chylomicron metabolism was tested by determination of the plasma kinetics of a chylomicron-like emulsion model in 12 patients with coronary artery disease, aged 59+/-11 years, (total cholesterol: 240+/-41 mg/dl; triglycerides: 188+/-42 mg/dl) submitted to a randomized, crossover, double-blind, placebo-controlled study with administration of 1 g per day etofibrate or placebo for 1-month. A 1-month washout period was inserted between the treatment periods. Patients were intravenously injected a chylomicron-like emulsion doubly labeled with 14C-cholesteryl oleate and 3H-triolein at baseline and after treatments. After etofibrate treatment, there was decrease of total cholesterol and triglyceride plasma levels and a trend to increase high-density lipoprotein cholesterol plasma levels. Etofibrate elicited 62% enhancement of post-heparin lipolytic activity and 100% increase of 3H-triglyceride fractional clearance rate compared with placebo treatment. 14C-cholesterol ester fractional clearance rate was 260% greater after etofibrate than after placebo. Therefore, a potent effect of etofibrate on both chylomicron lipolysis and remnant removal was achieved, indicating that this drug can be used to improve this metabolism in future prospective studies.

Resistance training changes LDL metabolism in normolipidemic subjects: A study with a nanoemulsion mimetic of LDL

OBJECTIVE To evaluate the effects of resistance training (RT) on the metabolism of an LDL-like nanoemulsion and on lipid transfer to HDL, an important step of HDL metabolism. METHODS LDL-like nanoemulsion plasma kinetics was studied in 15 healthy men under regular RT for 1-4 years (age = 25 ± 5 years, VO(2)peak = 50 ± 6 mL/kg/min) and in 15 healthy sedentary men (28 ± 7 years, VO(2)peak = 35 ± 9 mL/kg/min). LDL-like nanoemulsion labeled with (14)C-cholesteryl-ester and (3)H-free-cholesterol was injected intravenously, plasma samples were collected over 24-h to determine decay curves and fractional clearance rates (FCR). Lipid transfer to HDL was determined in vitro by incubating of plasma samples with nanoemulsions (lipid donors) labeled with radioactive free-cholesterol, cholesteryl-ester, triacylglycerols and phospholipids. HDL size, paraoxonase-1 activity and oxidized LDL levels were also determined. RESULTS The two groups showed similar LDL and HDL-cholesterol and triacylglycerols, but oxidized LDL was lower in RT (30 ± 9 vs. 61 ± 19 U/L, p = 0.0005). In RT, the nanoemulsion (14)C-cholesteryl-ester was removed twice as fast than in sedentary individuals (FCR: 0.068 ± 0.023 vs. 0.037 ± 0.028, p = 0.002), as well as (3)H-free-cholesterol (0.041 ± 0.025 vs. 0.022 ± 0.023, p = 0.04). While both nanoemulsion labels were removed at the same rate in sedentary individuals, RT (3)H-free-cholesterol was removed slower than (14)C-cholesteryl-ester (p = 0.005). HDL size, paraoxonase 1 and the transfer rates to HDL of the four lipids were the same in both groups. CONCLUSIONS RT accelerated the clearance of LDL-like nanoemulsion, which probably accounts for the oxidized LDL levels reduction in RT. RT also changed the balance of free and esterified cholesterol FCRs. However, RT had no effect on HDL metabolism related parameters.

Apolipoprotein and lipid abnormalities in chronic liver failure

Total serum lipids, as well as apolipoproteins A-I (apo A-I) and B (apo B), were determined in 74 patients with chronic liver failure without cholestasis and in 82 normal subjects. The VLDL, LDL and HDL lipid fractions were reduced in the liver failure group by 36%, 24% and 46%, respectively (P < 0.001). Apolipoproteins A-I and B were also reduced by 26% and 25%, respectively (P < 0.001). However, the reduction of HDL cholesterol (HDLc) was more pronounced than that of apo A-I and the HDLc:apo A-I ratio was significantly lower in the liver failure group. After separating these patients into groups with plasma albumin lower than 3.0, between 3.0 and 3.5, and higher than 3.5 g/dl, the HDLc:apo A-I ratio was proportional to plasma albumin, but the correlation was not statistically significant. When these patients were separated by the Child classification of liver function, there was a correlation between the HDLc:apo A-I ratio and liver function. The differences in the HDLc:apo A-I ratio between the Child groups B and C, and A and C were statistically significant (P < 0.05). We conclude that there is a more pronounced reduction in HDL cholesterol than in apo A-I in liver failure patients. Therefore, the HDLc:apo A-I ratio is a marker of liver function, probably because there is a decreased lecithin-cholesterol acyltransferase production by the diseased liver.

Metabolism of triglyceride-rich lipoproteins and transfer of lipids to high-density lipoproteins (HDL) in vegan and omnivore subjects.

BACKGROUND AND AIMS Vegan diet excludes all foodstuffs of animal origin and leads to cholesterol lowering and possibly reduction of cardiovascular disease risk. The aim was to investigate whether vegan diet improves the metabolic pathway of triglyceride-rich lipoproteins, consisting in lipoprotein lipolysis and removal from circulation of the resulting remnants and to verify whether the diet alters HDL metabolism by changing lipid transfers to this lipoprotein. METHODS AND RESULTS 21 vegan and 29 omnivores eutrophic and normolipidemic subjects were intravenously injected triglyceride-rich emulsions labeled with (14)C-cholesterol oleate and (3)H-triolein: fractional clearance rates (FCR, in min(-1)) were calculated from samples collected during 60 min for radioactive counting. Lipid transfer to HDL was assayed by incubating plasma samples with a donor nanoemulsion labeled with radioactive lipids; % lipids transferred to HDL were quantified in supernatant after chemical precipitation of non-HDL fractions and nanoemulsion. Serum LDL cholesterol was lower in vegans than in omnivores (2.1 ± 0.8, 2.7 ± 0.7 mmol/L, respectively, p < 0,05), but HDL cholesterol and triglycerides were equal. Cholesteryl ester FCR was greater in vegans than in omnivores (0.016 ± 0.012, 0.003 ± 0.003, p < 0.01), whereas triglyceride FCR was equal (0.024 ± 0.014, 0.030 ± 0.016, N.S.). Cholesteryl ester transfer to HDL was lower in vegans than in omnivores (2.7 ± 0.6, 3.5 ± 1.5%, p < 0,05). Free-cholesterol, triglyceride and phospholipid transfer were equal, as well as HDL size. CONCLUSION Remnant removal from circulation, estimated by cholesteryl oleate FCR was faster in vegans, but the lipolysis process, estimated by triglyceride FCR was equal. Increased removal of atherogenic remnants and diminution of cholesteryl ester transfer may favor atherosclerosis prevention by vegan diet.

Exercise training accelerates the removal from plasma of LDL-like nanoemulsion in moderately hypercholesterolemic subjects

OBJECTIVE Exercise training improves plasma lipid profile and diminishes risk of coronary heart disease. Previously, we showed that training increases LDL plasma clearance, as tested by an artificial LDL-like nanoemulsion method, presumably by increasing LDL receptor activity. In this study, we investigated whether training could also improve LDL clearance in hypercholesterolemic subjects (HCh) that are exposed to increased risk of cardiovascular events. METHODS Twenty sedentary HCh and 20 normolipidemic (NL) sedentary volunteers were divided into four groups: 12 HCh submitted to 4-month training program, 8 HCh with no exercise program, 12 NL submitted to 4-month training and 8 NL with no exercise program. An LDL-like nanoemulsion labeled with (14)C-cholesteryl ester was injected intravenously into all subjects and plasma samples were collected during 24 h after injection to determine the fractional clearance rate (FCR, in h(-1)) by compartmental analysis. The study was performed on the first and on the last day of the 4-month study period. RESULTS In both, trained HCh and NL groups, training increased nanoemulsion FCR by 36% (0.0443+/-0.0126; 0.0602+/-0.0187, p=0.0187 and 0.0503+/-0.0203; 0.0686+/-0.0216, p=0.0827, respectively). After training, LDL cholesterol diminished in both HCh and NL groups. In HCh, but not in NL group, LDL susceptibility to oxidation decreased, but oxidized LDL was unchanged. In both non-trained groups FCR was the same for the last and the 4-month previous evaluation. CONCLUSION In HCh, exercise training increased the removal of LDL as tested by the nanoemulsion, and this probably accounted for decreased LDL cholesterol and diminished LDL susceptibility to oxidation.