The existence of a relationship between bile acid and triacylglycerol metabolism in humans has been established, but the underlying mechanism and its physiological relevance have remained unclear. We have studied the effects of bile acids on the secretion of very-low-density lipoprotein (VLDL)-associated triacylglycerol, using [3H]glycerol labeling technique, and apolipoprotein B (apoB) in human hepatocytes in primary culture. Human hepatocytes secrete nascent VLDL with an average diameter of about 40 nm. Lipid composition of the particles resembles that reported for plasma VLDL, with the exception of a markedly lower cholesterylester content. In 24-hour cultured human hepatocytes, physiological (i.e., portal) concentrations of taurocholic acid (10 to 200 mumol/L) suppressed [3H]triacylglycerol secretion dose dependently. The degree of inhibition highly correlated (r = .87, P < .01) with taurocholic acid content of the cells of different preparations (n = 7). ApoB secretion was inhibited by taurocholic acid to a similar extent as [3H]triacylglycerol secretion (r = .93, P < .01). Lipid composition of secreted VLDL particles did not change during taurocholic acid-induced suppression. No effects on intracellular apoB, [3H]triacylglycerol, triacylglycerol, and cholesterol mass were observed, nor did taurocholic acid affect protein synthesis, albumin secretion, or lactate dehydrogenase (LDH) release. Cellular cholesteryl ester (CHE) mass, however, was markedly reduced. Our results show that bile acids strongly interfere with the assembly or secretion of VLDL particles by human hepatocytes, suggesting a physiological function of the enterohepatic circulation of bile acids in the regulation of postprandial serum lipid levels.

BACKGROUND

Cardiovascular disease risk can be estimated in part on the basis of the plasma lipoprotein profile. Analysis of lipoprotein subclasses improves the risk evaluation, but the traditional methods are very time-consuming. Novel, rapid, and productive methods are therefore needed.

METHODS

We obtained plasma samples from 103 fasting people and determined the plasma lipoprotein subclass profiles by an established ultracentrifugation-based method. Proton nuclear magnetic resonance (NMR) spectra were obtained from replicate samples on a 600 MHz NMR spectrometer. From the ultracentrifugation-based reference data and the NMR spectra, we developed partial least-squares (PLS) regression models to predict cholesterol and triglyceride (TG) concentrations in plasma as well as in VLDL, intermediate-density lipoprotein (IDL), LDL, 3 LDL fractions, HDL, and 3 HDL subclasses.

RESULTS

The correlation coefficients (r) between the plasma TG and cholesterol concentrations measured by the 2 methods were 0.98 and 0.91, respectively. For LDL- and HDL-cholesterol concentrations, r = 0.90 and 0.94, respectively. For cholesterol concentrations in the LDL-1, LDL-2, and LDL-3 fractions, r = 0.74, 0.78, and 0.69, respectively, and for HDL subclasses HDL(2b), HDL(2a), and HDL(3), cholesterol concentrations were predicted with r = 0.92, 0.94, and 0.75, respectively. TG concentrations in VLDL, IDL, LDL, and HDL were predicted with correlations of 0.98, 0.85, 0.77, and 0.74, respectively. The cholesterol and TG concentrations in the main lipoprotein fractions and in LDL fractions and HDL subclasses predicted by the PLS models were 94%-100% of the concentrations obtained by ultracentrifugation.

CONCLUSIONS

NMR-based PLS regression models are appropriate for use in research in which analyses of the plasma lipoprotein profile, including LDL and HDL subclasses, are required in large numbers of samples.

Clear-cell renal cell carcinoma (RCC) is, in most cases, caused by loss of function of the tumor suppressor gene von Hippel-Lindau, resulting in constitutive activation of hypoxia-inducible factor (HIF)-1α and expression of hypoxia-induced genes in normoxic conditions. Clear-cell RCC cells are characterized histologically by accumulation of cholesterol, mainly in its ester form. The origin of the increased cholesterol remains unclear, but it is likely explained by an HIF-1α-driven imbalance between cholesterol uptake and excretion. Here, we showed that expression of the very low-density lipoprotein receptor (VLDL-R) was significantly increased in clear-cell RCC human biopsies compared with normal kidney tissue. Partial knockdown of HIF-1α in clear-cell RCC cells significantly reduced the VLDL-R expression, and knockdown of either HIF-1α or VLDL-R reduced the increased lipid accumulation observed in these cells. We also showed increased uptake of fluorescently labeled lipoproteins in clear-cell RCC cells, which was significantly reduced by knockdown of HIF-1α or VLDL-R. Taken together, our results support the concept that the pathological increase of HIF-1α in clear-cell RCC cells upregulates VLDL-R, which mediates increased uptake and accumulation of lipids. These results explain the morphological characteristics of clear-cell RCC, and open up novel possibilities for detection and treatment of clear-cell RCC.

The accuracy of the Friedewald formula in estimating low-density lipoprotein (LDL) cholesterol was investigated in 47 alcoholic patients with liver disease (21 minimal-change, 26 cirrhotic) by comparing the results with those obtained by sequential preparative ultracentrifugation. In 14% of subjects with minimal-change disease, the error in the estimated LDL cholesterol was 50% +/- 9% (mean +/- SD; range 40-59%) and was related to the degree of attendant hypertriglyceridemia (r = 0.98; P < 0.001). A similar degree of error was observed in patients with cirrhosis, despite the absence of hypertriglyceridemia; an abnormal VLDL cholesterol: triglyceride ratio was the contributory factor in the discrepancy. We conclude that, as is the case in other clinical pathologies in which abnormalities of lipoprotein composition have been described (e.g., diabetes), the Friedewald formula to estimate LDL cholesterol may be inappropriate in chronic alcoholics, particularly those in whom a degree of hepatic dysfunction may be suspected.

BACKGROUND

Characterization of the normal degree of physiological variation in the metabolomic profiles of healthy humans is a necessary step in the development of metabolomics as both a clinical research and diagnostic tool. This study investigated the effects of the menstrual cycle on (1)H nuclear magnetic resonance (NMR) derived metabolomic profiles of urine and plasma from healthy women.

METHODS

In this study, 34 healthy women were recruited and a first void urine and fasting blood sample were collected from each woman at four different time points during one menstrual cycle. Serum hormone levels were used in combination with the menstrual calendar to classify the urine and plasma samples into five different phases i.e. menstrual, follicular, periovulatory, luteal and premenstrual. The urine and plasma samples were analysed using (1)H NMR spectroscopy and subsequent data were analysed using principal component analysis (PCA) and partial least squares discriminant analysis.

RESULTS

PCA of the urine spectra showed no separation of samples based on the phases of the menstrual cycle. Multivariate analysis of the plasma spectra showed a separation of the menstrual phase and the luteal phase samples (R(2) = 0.61, Q(2) = 0.41). Subsequent analysis revealed a significant decrease in levels of glutamine, glycine, alanine, lysine, serine and creatinine and a significant increase in levels of acetoacetate and very low density lipoprotein (VLDL CH(2)) during the luteal phase.

CONCLUSIONS

These results establish a need to control for metabolic changes that occur in plasma due to the menstrual cycle in the design of future metabolomic studies involving premenopausal women.

Diet is a major factor influencing the composition and metabolic activity of the gut microbiota.

This study investigated the effect of soy compared with dairy protein on the gut microbiota of hamsters to determine whether changes in microbiota could account for soy protein's lipid lowering properties.

Thirty-two 6- to 8-wk-old, male Golden Syrian hamsters were fed a Western diet containing 22% (%wt) milk protein isolate (MPI) as the single protein source for 3 wk followed by 6 wk of one of 4 diets containing either [22% protein (%wt)]: MPI, soy protein concentrate (SPC), partially hydrolyzed soy protein isolate (SPI1), or intact soy protein isolate. Serum lipids, hepatic gene expression, and gut microbial populations were evaluated.

Serum total and LDL-cholesterol concentrations were lower in the SPC-fed group (183 ± 9.0 and 50 ± 4.2 mg/dL, respectively) than in the MPI group (238 ± 8.7 and 72 ± 3.9 mg/dL, respectively) (P< 0.05). Triglyceride (TG) concentrations were lower (P< 0.05) in the SPI1-fed group (140 ± 20.8 mg/dL) than in the MPI-fed group (223 ± 14.2 mg/dL). VLDL and non-HDL-cholesterol concentrations were lower (by 40-49% and 17-33%, respectively) in all soy-fed groups than in the MPI-fed group (P< 0.05). Sequencing of the 16S ribosomal RNA gene revealed greater microbial diversity in each soy-fed group than in the MPI-fed group (P< 0.05). The cholesterol- and TG-lowering effect of soy protein was associated with higher expression of 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), lanosterol synthase (Lss), and farnesyl-diphosphosphate farnesyl-transferase 1 (Fdft1) (1.6-2.5-fold higher), and lower steroyl-CoA desaturase-1 (Scd1) expression (37-46% lower) in all soy-fed groups (P< 0.05) compared with the MPI-fed group. Gut microbes that showed significant diet differences were significantly correlated (ρ = -0.68 to 0.65,P< 0.05) with plasma lipids and hepatic gene expression.

Dietary protein sources in male Golden Syrian hamsters fed a Western diet affect the gut microbiota, and soy protein may reduce lipogenesis through alterations of the gut microbial community.

OBJECTIVE

This study aimed (a) to investigate the relationship between the degree of obesity and serum adiponectin, tumor necrosis factor (TNF)-α, leptin, insulin levels and the lipid profile; (b) to clarify the relationship between insulin resistance/glucose tolerance and adipocytokine levels; and (c) to investigate the value of adipocytokine levels as a marker of metabolic syndrome (MS).

METHODS

We studied 151 obese children and adolescents (86 boys and 65 girls; mean age was 12.3±2.4 years). We defined obesity as a body-mass index (BMI) z-score more than 2 SD above the mean for age and sex. The control group consisted of 100 children (48 boys, 52 girls, mean age 12.4±2.5 years). Fasting glucose, insulin levels and lipid profiles were measured in all cases and controls after a 12-hour fast. Adiponectin, TNF-α, and leptin levels were measured in the subjects who participated in the adipocytokine branch of the study. An oral glucose tolerance test (OGTT) was also performed in all obese patients. Obese patients were grouped into three subgroups according to their glucose tolerance and insulin sensitivity assessment, and also according to whether they were grouped as MS or not.

RESULTS

Serum levels of total cholesterol, LDL and VLDL cholesterol, log triglyceride, insulin, leptin and TNF-α were higher, whereas HDL and square root adiponectin levels were lower in the obese group when compared with controls. Multiple regression analysis among BMI-z score, LDL, triglyceride, HOMA-IR, leptin and TNF-α as determinants of adiponectin revealed that BMI-z score was the only determinant for adiponectin (r:-0.45, p<0.0001). Adiponectin levels in hyperinsulinemic and impaired glucose tolerance groups (IGT) tended to be lower than in normoinsulinemic obese children, however, the difference was not significant. There was a weak negative correlation between adiponectin levels and increasing severity of insulin resistance (r=-0.23, p=0.005) in the groups of obese subjects. Mean serum adiponectin level in subjects with MS was lower than in subjects without MS (p=0.008).

CONCLUSIONS

Evaluation of serum adiponectin levels might contribute to an early intervention in obese children with MS.

We investigated the interaction between genetic and environmental factors in the regulation of plasma HDL cholesterol concentration by determining TaqI and EcoN I restriction fragment length polymorphisms at the cholesteryl ester transfer protein (CETP) gene locus in 93 male alcohol drinkers and 82 control men. The highest plasma CETP activity and the lowest HDL cholesterol concentration were in the control subjects who were homozygous for the presence of the TaqI B restriction site (genotype 1-1). The lowest CETP activity and the highest HDL cholesterol among the control subjects were in those with genotype 2-2. These associations were, however, evident only in the non-smokers (P = 0.03 for CETP activity and P = 0.05 for HDL cholesterol). The non-smoking control subjects with genotype 1-1 had 19% higher CETP activity and 16% lower HDL cholesterol than those with genotype 2-2 (mean +/- S.D., 113 +/- 25 nmol/h/ml and 1.16 +/- 0.30 mmol/l vs. 95 +/- 16 nmol/h/ml and 1.38 +/- 0.34 mmol/l, respectively), and CETP activity and HDL cholesterol were negatively correlated (r = -0.280, P = 0.03, n = 59). The alcohol drinkers had 30% lower CETP activity (P < 0.001) and 48% higher HDL cholesterol (P < 0.001) than the controls. CETP activity was not affected by the TaqI B genotype in the alcohol drinkers. The lowest HDL cholesterol was in subjects with genotype 1-1 (1.68 +/- 0.60 mmol/l), but those with genotype 2-2 had lower HDL cholesterol than those with genotype 1-2 (1.78 +/- 0.59 and 1.93 +/- 0.66 mmol/l, respectively). The data of the alcohol drinkers fitted better with the quadratic regression model than with the linear one, suggesting a trend towards a curved relationship between the TaqI B genotype and HDL cholesterol in both the non-smoking and smoking alcohol drinkers. Total, LDL or VLDL cholesterol, total or VLDL triglycerides did not differ between the TaqI B genotypes either in the alcohol drinkers or the controls. Lipid and lipoprotein levels and CETP activities were likewise similar in the TaqI A and EcoN I polymorphisms. Our data indicate that CETP TaqI B polymorphism is related to plasma CETP activity and HDL cholesterol concentration in non-smoking men, but these associations are affected by smoking and alcohol drinking.

An orally bioavailable acyl coenzyme A:cholesterol acyltransferase (ACAT) inhibitor, avasimibe (CI-1011), was used to test the hypothesis that inhibition of cholesterol esterification, in vivo, would reduce hepatic very low density (VLDL) apolipoprotein (apo) B secretion into plasma. ApoB kinetic studies were carried out in 10 control miniature pigs, and in 10 animals treated with avasimibe (10 mg/kg/d, n = 6; 25 mg/kg/d, n = 4). Pigs were fed a diet containing fat (34% of calories) and cholesterol (400 mg/d; 0.1%). Avasimibe decreased the plasma concentrations of total triglyceride, VLDL triglyceride, and VLDL cholesterol by 31;-40% 39-48%, and 31;-35%, respectively. Significant reductions in plasma total cholesterol (35%) and low density lipoprotein (LDL) cholesterol (51%) concentrations were observed only with high dose avasimibe. Autologous 131I-labeled VLDL, 125I-labeled LDL, and [3H]leucine were injected simultaneously into each pig and apoB kinetic data were analyzed using multicompartmental analysis (SAAM II). Avasimibe decreased the VLDL apoB pool size by 40;-43% and the hepatic secretion rate of VLDL apoB by 38;-41%, but did not alter its fractional catabolism. Avasimibe decreased the LDL apoB pool size by 13;-57%, largely due to a dose-dependent 25;-63% in the LDL apoB production rate. Hepatic LDL receptor mRNA abundances were unchanged, consistent with a marginal decrease in LDL apoB FCRs. Hepatic ACAT activity was decreased by 51% (P = 0.050) and 68% (P = 0.087) by low and high dose avasimibe, respectively. The decrease in total apoB secretion correlated with the decrease in hepatic ACAT activity (r = 0.495; P = 0.026). We conclude that inhibition of hepatic ACAT by avasimibe reduces both plasma VLDL and LDL apoB concentrations, primarily by decreasing apoB secretion.

OBJECTIVE

To compare the binding to cultured endothelial cells of mononuclear cells isolated from healthy volunteers and patients with NIDDM.

METHODS

Mononuclear cells were isolated from healthy volunteers (n = 11) and patients with NIDDM (n = 14) and incubated with ECV 304 cells, a human umbilical endothelial cell-derived transformed cell line. Following a period of incubation, the adherence of mononuclear cells to endothelial cells was determined.

RESULTS

Adherence of mononuclear cells from patients with NIDDM was significantly greater (P < 0.05) than that of cells isolated from the healthy volunteers, and this difference persisted when adjusted for age, sex, and degree of obesity. Mononuclear cell binding to ECV 304 cells correlated significantly with fasting plasma glucose (r = 0.52, P < 0.01), insulin (r = 0.51, P < 0.01), triglyceride (r = 0.54, P < 0.01), and VLDL (r = 0.54, P < 0.01) and HDL cholesterol (r = -0.45, P < 0.05) levels, but not with either total or LDL cholesterol levels or blood pressure.

CONCLUSIONS

Since the adherence of mononuclear cells to the endothelium represents the earliest step in atherogenesis, the observation that mononuclear cells from patients with NIDDM bind more avidly to cultured endothelial cells may help explain why accelerated atherosclerosis occurs in patients with NIDDM. The metabolic abnormality, or abnormalities, present in patients with NIDDM that is responsible for the enhanced adhesiveness of mononuclear cells requires further examination.

Sixteen hyperlipidemic men were enrolled in a randomized, placebo-controlled, double-blind, cross-over study to evaluate the effect of ezetimibe 10 mg and simvastatin 40 mg, coadministered and alone, on the in vivo kinetics of apolipoprotein (apo) B-48 and B-100 in humans. Subjects underwent a primed-constant infusion of a stable isotope in the fed state. The coadministration of simvastatin and ezetimibe significantly reduced plasma concentrations of cholesterol (-43.0%), LDL-C (-53.6%), and triglycerides (-44.0%). Triglyceride-rich lipoproteins (TRL) apoB-48 pool size (PS) was significantly decreased (-48.9%) following combination therapy mainly through a significant reduction in TRL apoB-48 production rate (PR) (-38.0%). The fractional catabolic rate (FCR) of VLDL and LDL apoB-100 were significantly increased with all treatment modalities compared with placebo, leading to a significant reduction in the PS of these fractions. We also observed a positive correlation between changes in TRL apoB-48 PS and changes in TRL apoB-48 PR (r = 0.85; P < 0.0001) with combination therapy. Our results indicate that treatment with simvastatin plus ezetimibe is effective in reducing plasma TRL apoB-48 levels and that this effect is most likely mediated by a reduction in the intestinal secretion of TRL apoB-48. Our study also indicated that the reduction in LDL-C concentration following combination therapy is mainly driven by an increase in FCR of apoB-100 containing lipoproteins.

Male Syrian hamsters consumed diets containing incremental increases in dietary n-3 fatty acids from fish oil with either low (0.015% w/w) or moderate (0.1% w/w) dietary cholesterol content. Animals consuming diets containing moderate cholesterol, but not animals consuming diets containing low cholesterol, had increased plasma very low (VLDL)- and low density lipoprotein (LDL)-cholesterol levels with increasing fish oil consumption. The plasma concentration of high density lipoprotein (HDL)-cholesterol decreased by 43 and 32% with the consumption of the highest fish oil diets in the low and moderate dietary cholesterol groups, respectively. Hepatic LDL-receptor binding activity did not change with the consumption of low cholesterol diets, but gradually decreased with fish oil consumption in animals consuming the moderate cholesterol diets. Hepatic LDL-receptor binding and plasma LDL-cholesterol levels of the different dietary fish oil groups were highly correlated (r = -0.91). Fish oil consumption also caused an increase in hepatic free cholesterol but a decreased cholesteryl ester content. Therefore, in the Syrian hamster, the consumption of n-3 fatty acids increases LDL-cholesterol levels which can be partially explained by decreased hepatic LDL-receptor binding and this response to dietary n-3 fatty acids is dependent on the dietary cholesterol content. However, the effects of dietary n-3 fatty acids on HDL-cholesterol are independent of dietary cholesterol content.

We used [2-13C1]glycerol to characterize very low density lipoprotein (VLDL)-triglyceride kinetics and intrahepatic glycerol metabolism in normal men (n = 4) after alcohol (EtOH) ingestion. [2-13C1]glycerol was infused before and after the consumption of 48 g EtOH or a placebo. Three additional subjects also received [1-13C1]acetate in addition to the [2-13C1]glycerol with EtOH treatment. Incorporation of tracer into the glycerol or fatty acid moiety of VLDL-triglyceride was measured by gas chromatography-mass spectrometry and used to calculate VLDL-triglyceride production rates. Intrahepatic triose-phosphate enrichments were also calculated based on mass isotopomer distribution analysis of plasma glucose. There was no difference in VLDL-triglyceride production rates after 48 g EtOH (11.9 +/- 3.7 mg/kg/h) or placebo (14.7 +/- 3. 3 mg/kg/h). The VLDL-triglyceride rate constants calculated by kinetic modeling using the glycerol and acetate tracers in the combined isotope infusion subjects were very closely correlated (r 2 = 0.94). The peak VLDL-glycerol enrichments after EtOH were 22.5 +/- 3.3% versus 7.6 +/- 0.8% after placebo (P < 0.001), while intrahepatic triose-phosphate enrichments were 19.8 +/- 1.3% and 13. 1 +/- 1.2% (P < 0.001), respectively. Moreover, the calculated asymptotic VLDL-glycerol enrichments (representing the hepatic alpha-glycerol phosphate enrichment) were significantly higher after EtOH than placebo. The higher ratio of VLDL-glycerol to triose-phosphate labeling after EtOH suggests a metabolic block at glycerol 3-phosphate dehydrogenase. We conclude that consumption of 48 g EtOH does not increase VLDL-triglyceride production in normal men but does cause accumulation of tracer in hepatic alpha-glycerol phosphate.

The effects of 9 weeks of aerobic exercise training with maintenance of stable body weight upon insulin sensitivity and upon glucose, lipid, and lipoprotein concentrations were studied in 10 middle-aged men with mild hypertriglyceridemia. Following training, mean maximum oxygen consumption improved from 33.5 +/- 1.9 to 39.3 +/- 1.9 mL/kg/min (means +/- SEM), (P less than 0.01). Glucose concentrations, both fasting and during oral glucose tolerance testing, remained stable but both fasting insulin concentrations and insulin responses to oral glucose decreased (P less than 0.1 and less than 0.01, respectively). In vivo insulin sensitivity improved 25 +/- 6.1% (P less than 0.01) following training. Exercise training resulted in decreases in fasting serum triglyceride concentrations from 203 +/- 12.6 to 126 +/- 9.0 mg/dL (P less than 0.01), primarily as a result of the reduction in VLDL-triglycerides (P less than 0.01). The magnitude in percentage decrease of VLDL-triglycerides was found to be significantly correlated (r = 0.71, P less than 0.05) with the magnitude in percent increase in max VO2. Serum cholesterol levels declined from 211 +/- 8.9 to 193 +/- 11.9 mg/dL (P less than 0.01), and the ratio of HDL-cholesterol to total cholesterol was improved. This study demonstrates that exercise training at a level of intensity feasible for many middle-aged men has beneficial effects on several factors that have been associated with an increased risk of cardiovascular disease.

This study was designed to examine the effect of a high-fat (primarily saturated), refined-carbohydrate (sucrose) diet (HFS), which is known to induce obesity and hyperlipidemia, on adipose tissue and skeletal muscle lipoprotein lipase (LPL) and very-low density lipoprotein receptor (VLDL-R) protein expressions. Female Fischer rats were placed on either a HFS or a low-fat, complex-carbohydrate (LFCC) diet for 22 months beginning at 2 months of age. After 20 months, a subgroup of the HFS rats were switched to the LFCC diet for 2 months (HFS/LFCC). Body weight, feed efficiency, plasma total cholesterol, VLDL-C, low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) concentrations and LDL-C to high-density lipoprotein cholesterol ratio were all significantly raised by the HFS diet and improved by conversion to the LFCC diet. Adipose tissue heparin-releasable, extractable and total LPL activity expressed per cell were significantly increased in the HFS-fed group. However, LPL protein abundance normalized against total cellular protein was unchanged in the HFS group. This observation is consistent with the presence of adipose tissue hypertrophy. Skeletal muscle LPL protein abundance and heparin-releasable activity were reduced by the HFS diet and improved after switching to the LFCC diet. Both adipose tissue and skeletal muscle VLDL-R protein levels were significantly reduced by the HFS diet and increased after conversion to the LFCC diet. We conclude that an HFS diet induces changes in LPL and VLDL-R in a manner which favors shunting of dietary fat from skeletal muscle to adipose tissue and decreases TG-rich lipoprotein clearance contributing to increased plasma lipids and obesity. Conversion to a LFCC diet can ameliorate the dyslipidemia and tissue changes induced by long-term HFS diet consumption.

Cholesterol net transport, esterification, and cholesteryl ester transfer have been determined in plasma during fasting, and postprandially, after a high fat-cholesterol meal. Significant rises in plasma triglyceride, phospholipid, and free cholesterol were associated with increases in cholesterol net transport, esterification, and transfer (all P less than 0.005), which were well correlated in individual subjects (r greater than 0.60). Essentially, the whole of free cholesterol required for such increased esterification was derived from cell membranes, when cultured fibroblasts were present, despite the increased level of free cholesterol in postprandial plasma; most of the additional cholesteryl ester generated was transferred to the low and very low density lipoproteins (LDL and VLDL) of plasma. Postprandial LDL (the major carrier of free and ester cholesterol and phospholipids among the acceptor lipoproteins) contained significantly decreased ratios of free cholesterol to phospholipid (P less than 0.001), which may modulate the increased transfer of cholesteryl ester to VLDL and LDL. These data suggest that the presence of postprandial acceptor lipoproteins in plasma may play an important role in stimulating the "reverse" transport of cholesterol from peripheral cells for hepatic degradation, which is effective even after the ingestion of dietary cholesterol.

Hypertriglyceridemia is considered a cardiovascular risk factor in diabetic and nondiabetic subjects. In this study, we aimed to determine potential regulators of very low density lipoprotein-triglyceride (TG) production. VLDL-TG kinetics were measured in 13 men and 12 women [body mass index [mean (range)]: 24.8 (20.2-35.6) kg/m(2)]. VLDL-TG production was assessed from the plasma decay of a bolus injection of ex vivo labeled VLDL particles ([1-(14)C]triolein-VLDL-TG). Similar VLDL-TG production (micromol/min) was found in men and women. VLDL-TG production was not significantly correlated with palmitate flux ([9,10-(3)H]palmitate) (r = 0.09, P = 0.67) or palmitate concentration (r = -0.29, P = 0.2) but was correlated significantly with fasting insulin concentration (r = 0.46, P < 0.05) and resting energy expenditure (REE) (r = 0.45, P < 0.05). The latter correlation improved when adjusted for sex. The best multivariate model with VLDL-TG production as the dependent variable and REE, body composition, hormones, and substrate levels as independent variables included fasting insulin (P = 0.02) and REE (P = 0.02) (r(2) = 0.32, P < 0.001). We conclude that VLDL kinetics are similar in men and women and that REE and plasma insulin are significant independent predictors of VLDL-TG production. FFA availability and body fat distribution are unrelated to VLDL production. We suggest that REE plays a greater role in VLDL-TG production than previously anticipated. REE and insulin should be taken into account when VLDL-TG production comparisons between groups are made.

Fat intake leads to generation of potentially atherogenic triglyceride-rich lipoproteins (TRL). To investigate the relationship between early atherosclerotic changes and accumulation of hepatic and intestinal TRL after oral fat intake, an estimate of the intima-media thickness (IMT) was made using ultrasound of the common carotid artery, and postprandial TRL was quantified during a standardized oral fat tolerance test in 30 healthy normo- and hypertriglyceridemic middle-aged men. At base line the expected positive association between the LDL cholesterol level and the IMT of the common carotid artery was observed (r = 0.53, P<0.01). In addition, postprandial plasma triglycerides, in particular those measured late (6 h) after intake of the test meal, correlated positively with the IMT (r = 0.44, P<0.05). Of note, this latter correlation was independent of both the LDL cholesterol and the fasting plasma triglyceride concentrations. In a multivariate analysis, 39% of the total variability for the common carotid IMT were explained by age, LDL cholesterol and the postprandial triglyceride level. In univariate analysis, few statistically significant relations were found between common carotid IMT and postprandial levels of chylomicron remnants, VLDL and VLDL remnants of different particle size, the latter determined by specific measurements of ApoB-48 and ApoB-100 in subfractions of TRL. Therefore, in healthy middle-aged men, elevated postprandial triglyceride levels might identify a metabolic state related to early atherosclerosis.

Three different forms of stress all resulted in acute reduction of plasma triglyceride concentrations. Pyrogen reactions in two hypertriglyceridemic men resulted in the lowering of very-low-density lipoprotein (VLDL) triglyceride levels by 93% and 73% due to decreased secretion of this lipoprotein into plasma. More modest reductions in plasma triglycerides were observed after 2-deoxyglucose-induced intracellular glucopenia and insulin-induced hypoglycemia. With hypoglycemia, the lowering of plasma triglyceride concentration correlated significantly with the stimulation of urinary epinephrine output (r = 0.86) but with neither the urinary norepinephrine response nor with the increase in plasma immunoreactive glucagon levels. To further test whether these changes in plasma triglyceride levels were mediated via the sympathetic nervous system, hypoglycemia was evoked by insulin in subjects with traumatic spinal cord transactions. Two such subjects, who demonstrated sympathetic stimulation in response to hypoglycemia, had evidence of reduced VLDL secretion into plasma, while in two who had no evidence of an adrenergic response. VLDL secretion was not inhibited. Thus, acute lowering of plasma triglyceride concentrations by certain forms of stress appears to be mediated via the sympathetic nervous system.

BACKGROUND

Patients and animals with nephrotic syndrome and those with chronic renal failure (CRF) often exhibit hypertriglyceridemia and impaired very low-density lipoprotein (VLDL) clearance. Imai rats that were originally derived from Sprague-Dawley rats develop spontaneous proteinuria, hyperlipidemia, progressive renal insufficiency and histologic changes of focal glomerulosclerosis (FGS), closely resembling human FGS. This study was undertaken to test the hypothesis that elevation of plasma triglyceride and VLDL concentrations in the Imai rats is associated with deficiency of lipoprotein lipase (LPL) and VLDL receptor which are the main pathways of triglyceride-rich lipoprotein clearance.

METHODS

Male Imai and Sprague-Dawley control rats were fed regular rat chow and studied at 10 and 34 weeks of age. Tissue LPL and VLDL-r protein abundance (Western analysis) and post-heparin lipolytic activity were determined.

RESULTS

At 10 weeks of age, Imai rats showed mild proteinuria, moderate hyperlipidemia, normal creatinine clearance and blood pressure. By 34 weeks of age, the study animal exhibited severe proteinuria, marked hyperlipidemia, significant renal insufficiency and hypertension. This was associated with a severe progressive reduction in skeletal muscle and adipose tissue LPL and VLDL-r protein abundance and depressed plasma post heparin, lipolytic activity.

CONCLUSIONS

Progressive hyperlipidemia in the Imai rats with spontaneous FGS is accompanied by severe combined LPL and VLDL-r deficiencies that can, in part, account for the associated hypertriglyceridemia and elevated plasma VLDL concentrations.

Apolipoprotein L-I (apoL-I) is present on a subset of HDL particles and is positively correlated with plasma triglycerides (TGs). We measured plasma apoL-I levels in coronary artery disease (CAD) subjects with low HDL who were enrolled in an angiographic CAD prevention trial. At baseline, apoL-I levels (n = 136; range, 2.2-64.1 mug/ml) were right skewed with a large degree of variability. Multivariate analysis for biological determinants of apoL-I revealed that the log of VLDL-TG (+0.17; P < 0.05) and hyperglycemia (HG; +0.26; P < 0.005) independently predicted apoL-I level. Hyperglycemic patients (n = 24) had mean apoL-I levels >50% higher than normoglycemic subjects (n = 112; 13.2 vs. 8.3 mug/ml, respectively; P < 0.001). No relationship between apoL-I level and change in CAD was found (r = 0.06, P = 0.49). Simvastatin-niacin therapy did not alter apoL-I levels (n = 34; P = 0.27), whereas antioxidant vitamins alone increased apoL-I by >50% (n = 36; P < 0.01). Genotyping of a known apoL-I polymorphism (Lys166Glu) did not independently account for any of the variability in apoL-I levels. In conclusion, we found TG and HG to be the strongest predictors of apoL-I within a dyslipidemic CAD population. These data provide further characterization of the novel HDL-associated apoL-I.

Niacin potently lowers triglycerides, mildly decreases LDL-cholesterol, and largely increases HDL-cholesterol. Despite evidence for an atheroprotective effect of niacin from previous small clinical studies, the large outcome trials, AIM-HIGH and HPS2-THRIVE did not reveal additional beneficial effects of niacin (alone or in combination with laropiprant) on top of statin treatment. We aimed to address this apparent discrepancy by investigating the effects of niacin without and with simvastatin on atherosclerosis development and determine the underlying mechanisms, in APOE*3Leiden.CETP mice, a model for familial dysbetalipoproteinemia (FD).

Mice were fed a western-type diet containing cholesterol without or with niacin (120 mg/kg/day), simvastatin (36 mg/kg/day) or their combination for 18 weeks. Similarly as in FD patients, niacin reduced total cholesterol by -39% and triglycerides by -50%, (both P<0.001). Simvastatin and the combination reduced total cholesterol (-30%; -55%, P<0.001) where the combination revealed a greater reduction compared to simvastatin (-36%, P<0.001). Niacin decreased total cholesterol and triglycerides primarily by increasing VLDL clearance. Niacin increased HDL-cholesterol (+28%, P<0.01) and mildly increased reverse cholesterol transport. All treatments reduced monocyte adhesion to the endothelium (-46%; -47%, P<0.01; -53%, P<0.001), atherosclerotic lesion area (-78%; -49%, P<0.01; -87%, P<0.001) and severity. Compared to simvastatin, the combination increased plaque stability index [(SMC+collagen)/macrophages] (3-fold, P<0.01). Niacin and the combination reduced T cells in the aortic root (-71%, P<0.01; -81%, P<0.001). Lesion area was strongly predicted by nonHDL-cholesterol (R(2) = 0.69, P<0.001) and to a much lesser extent by HDL-cholesterol (R(2) = 0.20, P<0.001).

Niacin decreases atherosclerosis development mainly by reducing nonHDL-cholesterol with modest HDL-cholesterol-raising and additional anti-inflammatory effects. The additive effect of niacin on top of simvastatin is mostly dependent on its nonHDL-cholesterol-lowering capacities. These data suggest that clinical beneficial effects of niacin are largely dependent on its ability to lower LDL-cholesterol on top of concomitant lipid-lowering therapy.

Surgical trauma initiates a complex series of metabolic host responses designed to maintain homeostasis and ensure survival. (1)H NMR spectroscopy was applied to intraoperative urine and plasma samples as part of a strategy to analyze the metabolic response of Wistar rats to a laparotomy model. Spectral data were analyzed by multivariate statistical analysis. Principal component analysis (PCA) confirmed that surgical injury is responsible for the majority of the metabolic variability demonstrated between animals (R² Urine = 81.2% R² plasma = 80%). Further statistical analysis by orthogonal projection to latent structure discriminant analysis (OPLS-DA) allowed the identification of novel urinary metabolic markers of surgical trauma. Urinary levels of taurine, glucose, urea, creatine, allantoin, and trimethylamine-N-oxide (TMAO) were significantly increased after surgery whereas citrate and 2-oxoglutarate (2-OG) negatively correlated with the intraoperative state as did plasma levels of betaine and tyrosine. Plasma levels of lipoproteins such as VLDL and LDL also rose with the duration of surgery. Moreover, the microbial cometabolites 3-hydroxyphenylpropionate, phenylacetylglycine, and hippurate correlated with the surgical insult, indicating that the gut microbiota are highly sensitive to the global homeostatic state of the host. Metabonomic profiling provides a global overview of surgical trauma that has the potential to provide novel biomarkers for personalized surgical optimization and outcome prediction.

OBJECTIVE

Obesity and overweight are related to unfavourable lipoprotein subclass profiles. Here we studied the relation between weight change and lipoprotein particle concentrations and sizes in a general population cohort in a longitudinal setting.

METHODS

The cohort included 683 adults with a 6.5-year follow-up. Lipoprotein particle subclasses and mean particle sizes of VLDL, LDL, and HDL were measured by nuclear magnetic resonance spectroscopy.

RESULTS

During the follow-up period, a weight loss of at least 5% was associated with decreased particle concentrations of all apoB-containing subclasses and increased concentrations of large HDL particles. Coherently, weight gain (≥5%) was associated with increases in all apoB-containing subclasses and decreases in total and medium HDL particle concentrations. The relatively largest increase occurred for large HDL particle concentration (24.1%, 95% CI 15.8-32.5) in weight loss and for large VLDL particle concentration (33.0%, 19.6-46.4) in weight gain. Weight change correlated positively with changes in apoB-containing lipoprotein particle concentrations and also with the change in average VLDL particle size. Negative correlations were found between weight change and the change in average LDL (r = -0.10) and HDL (r = -0.32) particle size, but not between weight change and total HDL particle concentration.

CONCLUSIONS

Moderate weight loss is related to favourable and weight gain to unfavourable changes in lipoprotein subclass profiles. These population level findings underline the importance of weight control as a modifier of cardiovascular risk factors.