Rabbits fed a 1% cholesterol diet with or without the antioxidant butylated hydroxytoluene (BHT) developed typical atherosclerotic lesions. The addition of BHT gave higher levels of total cholesterol (+40%), triglycerides (+250%), low density lipoprotein (LDL), and very low density lipoprotein (VLDL) in plasma. Despite the lower plasma lipid levels, the degree of atherosclerosis of the aortic surface was considerably higher in rabbits fed cholesterol than in the group treated with cholesterol and BHT. The mean atherosclerotic involvement was 18.6 +/- 4.4% in the former group and 5.9 +/- 1.7% in the latter group (p = 0.02). In all animals, there was a high correlation between the area of the arterial lesion and cholesterol content (r = 0.96). Serum levels of cholesterol autooxidation products (7-ketocholesterol and cholesterol 5 alpha,6 alpha-epoxide) were lower in the group of rabbits treated with BHT (p less than 0.005). Serum levels of vitamin E were slightly higher in the BHT group. There was no significant difference in the clearance of beta-VLDL between the two treatment groups after using either beta-VLDL from cholesterol-fed animals or beta-VLDL from BHT-fed animals. The results are in accord with the contention that oxidative modification of lipoproteins is important for the development of atherosclerosis and that antioxidants may have a protective effect. At present, however, other explanations cannot be completely excluded, for example, effects of antioxidants on immunologic factors or monocyte adhesion.

Overweight individuals with reduced insulin sensitivity often have mild to moderate hypertriglyceridemia. To investigate the role of apolipoprotein (apo)C-III metabolism in the etiology of hypertriglyceridemia in these individuals, we investigated 10 male subjects with different body weights (body mass index, 24-34 kg/m(2)) and insulin sensitivity (homeostasis model assessment, 4.7-35.0). Total plasma and very-low-density lipoprotein (VLDL) apoC-III kinetics, as well as VLDL triglyceride (TG) and VLDL apoB kinetics, were measured with iv injected stable isotopes. The apoC-III, TG, and apoB levels in VLDL ranged from 2.9-18.2 mg/dl, 0.49-2.89 mmol/liter, and 6.7-29.3 mg/dl, respectively. Mean production rates (PRs) were: VLDL apoC-III, 20.2 +/- 4.1 micromol/d (range, 8.0-44.8); VLDL TG, 26.9 +/- 4.6 mmol/d (range, 10.2-51.1); and VLDL apoB, 4.4 +/- 0.8 micromol/d (range, 1.5-9.1). VLDL apoC-III PRs were significantly correlated with body mass index, homeostasis model assessment, and plasma TG (r = 0.66, P < 0.05; r = 0.80, P < 0.01; r = 0.95, P < 0.001, respectively). Similar correlations were found for plasma apoC-III PRs (r = 0.70, P < 0.05; r = 0.67, P < 0.05; r = 0.80, P < 0.01, respectively). Fractional catabolic rates (FCRs) were not significantly related to metabolic variables. VLDL TG levels were strongly related to VLDL apoC-III levels (r = 0.99, P < 0.001) and VLDL apoC-III PRs (r = 0.94, P < 0.001). VLDL apoC-III levels were more strongly correlated with VLDL TG PRs (r = 0.81, P < 0.01) than with VLDL TG FCRs or VLDL apoB FCRs (r = -0.53, P = 0.12; r = -0.37, P = 0.29). These results suggest that increased hepatic production of VLDL apoC-III is characteristic of subjects with higher body weights and lower levels of insulin sensitivity and is strongly related to the plasma concentration and level of production of VLDL TG.

Rat and human very low density lipoproteins (VLDL) were fractionated by zonal ultracentrifugation, yielding sharply defined fractions with narrow sedimentation limits. Sedimentation coefficients for the individual fractions were determined at two densities with the analytical ultracentrifuge, and the results were analyzed to yield buoyant densities and molecular weights for the particles in each fraction. For the rat lipoproteins, the weight concentrations of triglycerides, cholesterol, phospholipid, and protein were determined for each fraction, and their molar concentrations of apolipoprotein B were measured with a radioimmunoassay. For the human lipoproteins the corresponding values were taken from Patsch et al. (Patsch, W., J. R. Patsch, G. M. Kostner, S. Sailer, and H. Braunsteiner. 1978. Isolation of subfractions of human very low density lipoproteins by zonal ultracentrifugation. J. Biol. Chem. 253:4911-4915). From these data, a ratio of the number of apoB peptides to the number of lipoprotein particles was calculated for each fraction. This ratio was close to 1 for all VLDL fractions, ranging in particle diameter from about 40 to 80 mm and 30 to 50 mm, respectively, for rat and human VLDL. The majority rat VLDL contain B-48 rather than B-100 as their (single) apoB peptide. Based on these data, we proposed that only a single copy of B-48 is required for VLDL assembly in rat liver, unless nascent hepatic VLDL contain additional apoB peptides which are uniformly lost from the plasma VLDL particles when they are analyzed.

beta-Sitosterol and campesterol were measured in serum lipoproteins of 17 subjects from two families. The serum levels of the two phytosterols were closely correlated with each other (r = 0.974), less consistently with serum cholesterol (r = 0.489), and not at all with serum triglycerides. As compared to cholesterol, serum free and esterified phytosterols tended to be accumulated in HDL where the phytosterol/cholesterol ratios were almost 40% higher than in VLDL and LDL. The serum phytosterol concentrations, the phytosterol/cholesterol ratios, especially in VLDL and LDL, and the fractional absorption of cholesterol were higher in women than in men. The levels of the phytosterols in whole serum and in each lipoprotein were significantly correlated with the percentage absorption of dietary cholesterol but were independent of the amount of dietary cholesterol and plant sterols. Our findings suggest that, in general, serum levels of noncholesterol sterols are effectively determined by the absorption which in turn is proportionate to the fractional absorption of cholesterol.

OBJECTIVE

The objective of this study was to examine the associations between the severity of hepatic steatosis and dyslipidemia in type 2 diabetes, including circulating apolipoprotein B100 (apoB) concentrations and lipoprotein particle size and numbers.

METHODS

Computed tomography imaging was used to assess hepatic fat content and adipose tissue distribution in 67 men and women with type 2 diabetes, withdrawn from antidiabetic medications preceding the study. Fasting serum lipoprotein number and size was determined by nuclear magnetic resonance. Insulin sensitivity was measured with a glucose clamp and a [6,6-(2)H(2)]glucose isotope infusion.

RESULTS

Two-thirds of the cohort had fatty liver. Hepatic steatosis correlated with serum triglycerides (r = 0.40, P < 0.01) and lower HDL cholesterol (r = -0.31, P < 0.05). ApoB and LDL cholesterol did not, being virtually identical in those with or without steatosis. The association between serum triglycerides and hepatic steatosis was largely accounted for by greater triglyceride enrichment in VLDL particles, which were larger. Severe steatosis was also associated with 70% higher small, dense LDL concentrations. Visceral obesity did not fully explain these associations, and hepatic steatosis was better correlated with triglycerides than with hyperglycemia or hepatic insulin resistance (P>> 0.05).

CONCLUSIONS

The presence of hepatic steatosis in type 2 diabetes does not appear to affect apoB levels, but potentially increases atherogenesis by increasing triglycerides, reducing HDL levels, and increasing small, dense LDL.

OBJECTIVE

In an animal model VLDL-triglyceride secretion is highly dependent on stearoyl-coA desaturase (SCD) activity and could explain abdominal fattening. The aim was to assess the relationship of plasma palmitoleic acid content, a product of SCD activity, with triglyceridemia and abdominal adiposity in humans.

METHODS

We evaluated 134 healthy men. Plasma palmitoleic acid content was used as an indirect measurement of SCD activity because that enzyme catalyzes the desaturation from saturated to monounsaturated fatty acids and palmitoleic acid intake is very small.

RESULTS

Subjects with triglycerides>> or =75th percentile had a higher palmitoleic acid content than those with triglycerides <75th percentile (3.8+/-0.8 vs 2.8+/-0.9%, p<0.0001). Triglyceridemia was strongly correlated with palmitoleic acid content (PAC) (r=0.533, p<0.001). Mean triglyceridemia was 114% higher (1.43+/-0.75 vs 0.67+/-0.22 mmol/l) in the fourth quartile than in the first quartile of palmitoleic acid content. In a stepwise logistic regression analysis, palmitoleic acid content was the most strongly and independently associated parameter with triglyceridemia, and also with waist circumference when triglyceridemia was not included in the analysis.

CONCLUSIONS

Plasma palmitoleic acid content, a product of SCD activity, is an independent marker of triglyceridemia and abdominal adiposity in men. This enzyme (SCD) could represent a target for prevention and treatment of these metabolic disorders in particular in subjects at risk of developing a metabolic syndrome.

BACKGROUND

Plasma and adipose tissue concentrations of carotenoids are thought to reflect short- and long-term intakes of carotenoids, respectively. The ability of adipose tissue carotenoid concentrations to reflect dietary intake in population studies is unknown.

OBJECTIVE

We examined the relation between intakes of the major dietary carotenoids and their concentrations in plasma and adipose tissue.

METHODS

A blood sample and an adipose tissue biopsy sample were collected from 115 women and 344 men in Costa Rica after they had fasted overnight, and a dietary interview based on a 135-item food-frequency questionnaire was administered. After carotenoid intake was adjusted for total energy intake and plasma concentrations were adjusted for HDL-, LDL-, and VLDL-cholesterol concentrations, we calculated partial Spearman correlation coefficients that were adjusted for age, sex, smoking, and body mass index.

RESULTS

In women, the correlations (r) between intakes and concentrations of alpha-carotene, beta-carotene, beta-cryptoxanthin, and lutein+zeaxanthin were 0.25, 0.29, 0.44, and 0.17, respectively (P < 0.05 for r>> or = 0.19), in adipose tissue and 0.26, 0.13, 0.55, and 0.22 in plasma. In men, these values were 0.04, 0.07, 0.23, and 0.06 in adipose tissue and 0.24, 0.22, 0.44, and 0.20 in plasma. In women and men, correlations for lycopene were higher in plasma (r = 0.19 and 0.35, respectively) than in adipose tissue (r = 0.14 and 0.26). The relative abundance of each carotenoid in the diet was similar to its distribution in plasma but not in adipose tissue.

CONCLUSIONS

The usefulness of adipose tissue and plasma carotenoids as biomarkers of intake is similar, although correlations for individual carotenoids vary substantially.

Plasma lipoprotein concentration, composition, and size were evaluated in two common familial forms of hypertriglyceridemia and compared with those in normal subjects. The very low density lipoproteins (VLDL) were triglyceride-enriched in familial hypertriglyceridemia (triglyceride/apoprotein B ratio: 25.7 +/- 8.9) as compared to normal (9.6 +/- 12.2, P < 0.001) or familial combined hyperlipidemia (9.7 +/- 3.3, P < 0.001). The diameter of VLDL was larger in familial hypertriglyceridemia (3.27 +/- 0.28 pm) than in familial combined hyperlipidemia (2.87 +/- 0.16 pm, P < 0.02). Although in familial hypertriglyceridemia VLDL tended to be larger, and in familial combined hyperlipidemia VLDL tended to be smaller than normal (3.08 +/- 0.48 pm), neither of these differences were significant. While VLDL was normally distributed in the control population, the size was skewed to larger particles in familial hypertriglyceridemia with fewer small particles (P < 0.05) and skewed to smaller particles in familial combined hyperlipidemia with fewer large particles (P < 0.05). VLDL was reciprocally related to low density lipoproteins (LDL) in familial combined hyperlipidemia (r = -0.80 to -0.87) suggesting that the concentrations of these individual lipoprotein groups were somehow interrelated. There was no significant relationship between these two lipoprotein classes in familial hypertriglyceridemia or in normals. In familial combined hyperlipidemia, the apoprotein A-I/A-II ratio was below normal (P < 0.01) suggestive of low HDL(2) levels. This change in apoprotein composition was independent of VLDL or LDL concentration. In familial hypertriglyceridemia, high density lipoprotein (HDL) cholesterol was reduced (33% below mean normal) and HDL triglyceride was increased (by 46%), while the concentration of apoA-I and apoA-II was normal. VLDL triglyceride was inversely related to HDL cholesterol in familial hypertriglyceridemia (r = -0.74, P < 0.005), but not in familial combined hyperlipidemia. The large, triglyceride-enriched VLDL observed in familial hypertriglyceridemia is compatible with the reported increase in VLDL triglyceride synthesis seen in this disorder. The increase in VLDL apoprotein B synthesis previously reported in familial combined hyperlipidemia was associated with VLDL of normal composition. The changes in HDL cholesterol in these two disorders might reflect exchange of triglyceride between VLDL and HDL or could be related to transfer of surface components during the catabolism of VLDL. The reciprocal relationship between various components of VLDL and LDL seen in familial combined hyperlipidemia, but not in familial hypertriglyceridemia or in normal subjects, might provide some insight into the pathological abnormalities in these disorders. The differences between these two common familial forms of hypertriglyceridemia provide further support that they are distinct entities.-Brunzell, J. D., J. J. Albers, A. Chait, S. M. Grundy, E. Groszek, and G. B. McDonald. Plasma lipoproteins in familial combined hyperlipidemia and monogenic familial hypertriglyceridemia.

The association between coronary heart disease and subclinical hypothyroidism (SCH) is unclear. We aimed to determine hs-CRP concentrations in patients with SCH. Seventy-seven patients (age 34.6 +/- 13.7 yr) with SCH (TSH>> 4.2 microIU/ml and serum free thyroxine level between 0.932-1.71 ng/dL), and 80 control subjects (age 33.9 +/- 13.3 yr) were studied. Thyroid hormones, C-reactive protein, insulin, glucose, total, HDL, LDL and VLDL-cholesterol levels and HOMA-IR index were also determined. TSH levels of SCH group were higher than control (7.4 +/- 2.9 and 1.55 +/- 0.78 microIU/ml, respectively, p = 0.0001). However, FT4 levels were lower than control subjects (1.18 +/- 0.22 ng/dL and 1.38 +/- 0.26, respectively, p = 0.001). Serum hs-CRP levels of subjects with SCH were higher than control subjects (4.2 +/- 0.8 mg/l and 1.05 +/- 0.3 mg/l respectively, p = 0.0001). Insulin levels of SCH group were higher than control (8.5 +/- 4.3 microU/ml and 7.1 +/- 3.1 microU/ml respectively, p<0.02) but, Homa-IR levels of the two groups were not different. Mean total and LDL-cholesterol levels of SCH group were higher than control (p = 0.01 and p<0.02). We also found a positive correlation between hs-CRP levels and insulin (r = 0.362, p = 0.002 in men, r = 0.358, p = 0.0001 in women), TSH (r = 0.611, p = 0.0001 in men, r = 0.411 p = 0.0001 in women), and prolactin (r = 0.340, p = 0.01 in men r = 0.553, p = 0.0001 in women).

CONCLUSIONS

Patients with SCH, irrespective of gender, have higher serum hs-CRP, insulin, total and LDL-cholesterol levels than healthy subjects. 2- High hs-CRP level, and thereby low grade inflammation may be associated with fasting hyperinsulinemia before insulin resistance becomes evident in patients with SCH.

A simple and convenient method to determine plasma cholesterol profiles in individual mouse plasma samples is not presently available. With commonly used methods, plasma samples from several animals in a study group must often be pooled and analyzed, usually by the fast phase liquid chromatography (FPLC) method. The Column Lipoprotein Profile (or CLiP) method described here is a modification of the FPLC method that provides a simple and convenient procedure for determining plasma lipoprotein cholesterol profiles in small sample volumes, allowing determination of profiles from individual animals rather than from pooled plasma. The CLiP method is reproducible; a human sample measured five times over several days produced coefficients of variation as follows: VLDL, 10.0%; LDL, 0.93%; and HDL, 2.51%. CLiP-derived total cholesterol values of five different human samples (with total cholesterol levels ranging from 198 to 263 mg/dL) differed from VAP-II by -1.88% +/- 2.57%. Linearity of differing concentrations for each of the lipoprotein classes was determined by measuring the same sample with different aliquot sizes. The linear regression from VLDL had an r value of 0.996, while LDL, HDL, and total cholesterol all had r values of greater than 0.999. We present a direct comparison of plasma cholesterol profiles from several mouse models with gene modification or expression of transgenic proteins. In conclusion, the CLiP method provides a simple, reliable, and reproducible procedure for determination of plasma cholesterol profiles from individual plasma samples with very low sample volumes, using readily available equipment and reagents.

Syndrome X, or the syndrome of insulin resistance, is a cluster of related metabolic abnormalities of hyperinsulinemia, glucose intolerance, increased very low density lipoprotein (VLDL), decreased high density lipoprotein (HDL), and hypertension in nonobese adults and plays an important role in the genesis of cardiovascular disease. The aim of the present study was to examine the relationships among insulin sensitivity, plasma lipid levels, and body composition in the pediatric age group to determine whether these associations are present in childhood. Twenty healthy Caucasian Tanner stage I (TI) children (age, 10.7 +/- 0.3 yr; body mass index, 18.9 +/- 0.8 kg/m2) and 22 pubertal Tanner stage II-IV (TII-IV) adolescents (age, 14.0 +/- 0.3 yr; body mass index, 20.0 +/- 0.4 kg/m2) were studied. In vivo insulin-mediated glucose disposal (Rd) was evaluated during a 40 mu/m2. min hyperinsulinemic-euglycemic clamp. Body composition was assessed isotopically by the H218O dilution principle. Fasting blood was obtained for cholesterol, triglyceride (TG), VLDL, low density lipoprotein (LDL), and HDL determinations. In both groups, the strongest correlation of Rd was with percent body fat (%BF) (TI: r = -0.82; P < 0.001; TII-IV: r = -0.73; P < 0.001). In addition, in TI, Rd was correlated with TG (r = 0.64; P = 0.001), VLDL (r = 0.64; P = 0.001), and diastolic blood pressure (r = -0.50; P = 0.01). There were no such correlations in TII-IV. In TI, % BF correlated positively with LDL and negatively with TG and VLDL. In TII-IV, % BF correlated positively with cholesterol and LDL. After correcting for %BF, partial correlation analysis revealed no relationship between Rd and lipid levels in either group. This suggests that the relationship of insulin sensitivity to lipid levels was secondary to the effect of body composition on lipid levels. However, regardless of body composition, the basal insulin level was correlated with TG (r = 0.38; P = 0.04) and VLDL (r = 0.40; P = 0.04) in TII-IV subjects. We conclude that 1) the primary correlate of insulin sensitivity is %BF in both prepubertal and pubertal subjects, with no relationship to plasma lipids; 2) in prepubertal children, diastolic blood pressure is negatively correlated with insulin sensitivity and positively with insulin levels, independent of adiposity; and 3) after the onset of puberty, basal insulin levels are positively correlated with VLDL and TG regardless of the degree of adiposity. This observation could be a very early manifestation of the genesis of syndrome X in childhood.

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.

RESULTS

In vivo kinetics of apolipoprotein B100-containing lipoproteins using a 14-hour primed constant infusion of [2H3] 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.

CONCLUSIONS

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.

Niacin, the first lipid lowering drug shown to improve survival after myocardial infarction, decreases LDL and increases HDL cholesterol levels. These effects cannot fully be explained by its suspected mechanism of action, inhibition of lipolysis and hepatic VLDL synthesis. Niacin has also been shown to interfere with the cyclic AMP (cAMP)/protein kinase A (PKA) pathway and massively stimulate prostaglandin D2 (PGD2) formation. The major metabolite of PGD2, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), was recently identified as the most potent endogenous PPARgamma activator. We, therefore, studied the effects of niacin on the PPARgamma- and cAMP-dependent expression of receptors promoting reverse cholesterol transport. The transcription of PPARgamma-, HDL-, LDL- and scavenger-receptors and the sterol exporter ABCA1, were measured by quantitative RT-PCR and cellular cholesterol efflux and PPARgamma activation studied in macrophage and hepatocyte models. Niacin stimulated the translocation of PPARgamma and the transcription of PPARgamma, CD36 and ABCA1 in monocytoid cells, whereas the LDL-receptor (LDL-R) was unchanged. Thereby niacin enhanced HDL-mediated cholesterol efflux from the cells resulting in a reduced cellular cholesterol content. The niacin effect on CD36 but not on ABCA1 was prevented by cyclooxygenase inhibition, whereas the niacin effect on ABCA1 but not on CD36 was prevented by PKA inhibition, suggesting mediation by the 15d-PGJ2/PPARgamma and the cAMP/PKA pathways, respectively. These new actions of niacin on several key effectors of reverse cholesterol transport out of the vessel wall provide a rational to expect regression of atherosclerosis and test the combination of niacin with statins for an overadditive clinical benefit.

BACKGROUND

Hyperinsulinemia has been considered to be a potent cardiovascular risk factor. The present investigation examines persistently elevated fasting insulin levels from childhood to young adulthood and its influence on cardiovascular risk factors.

RESULTS

A longitudinal cohort was constructed from two cross-sectional surveys in a community-based population over an 8-year period: 1606 individuals (39% were black) aged 5 to 23 years participated in the first survey. Stability in rankings (persistence) of insulin levels was shown by the presence of significant correlations between year 1 and year 8 values (r=.23 to .36, P<.0001), with a greater magnitude in older subjects. Compared with subjects with levels of insulin consistently in the lowest quartile, those with levels always in the highest quartile showed higher (P<.001) levels of body mass index (+9 kg/m2), triglycerides (+58 mg/dL), LDL cholesterol (+11 mg/dL), VLDL cholesterol (+8 mg/dL), glucose (+9 mg/dL), systolic blood pressure (+7 mm Hg), and diastolic blood pressure (+3 mm Hg); lower (P<.001) levels of HDL cholesterol (-4 mg/dL): and higher (P<.05) prevalence of parental history of diabetes (3.3-fold) and hypertension (1.2-fold). There were 739 young adults aged 20 to 31 years at follow-up. As adults, individuals with consistently elevated insulin versus those with consistently decreased insulin had increased (P<.05) prevalence of obesity (36-fold), hypertension (2.5-fold), and dyslipidemia (3-fold), which was attributed to both baseline insulin and change of insulin from baseline to follow-up. In addition, clustering of these risk factors was stronger (P<.05) in adults with persistent insulin elevation.

CONCLUSIONS

Elevated insulin levels persist from childhood through young adulthood, resulting in a clinically relevant adverse cardiovascular risk profile in young adults.

Apolipoprotein B (apoB) metabolism was investigated in 20 men with plasma triglyceride 0.66-2.40 mmol/l and plasma cholesterol 3.95-6. 95 mmol/l. Kinetics of VLDL(1) (S(f) 60-400), VLDL(2) (S(f) 20-60), IDL (S(f) 12-20), and LDL (S(f) 0;-12) apoB were analyzed using a trideuterated leucine tracer and a multicompartmental model which allowed input into each fraction. VLDL(1) apoB production varied widely (from 5.4 to 26.6 mg/kg/d) as did VLDL(2) apoB production (from 0.18 to 8.4 mg/kg/d) but the two were not correlated. IDL plus LDL apoB direct production accounted for up to half of total apoB production and was inversely related to plasma triglyceride (r = -0.54, P = 0.009). Percent of direct apoB production into the IDL/LDL density range (r = 0.50, P < 0.02) was positively related to the LDL apoB fractional catabolic rate (FCR). Plasma triglyceride in these subjects was determined principally by VLDL(1) and VLDL(2) apoB fractional transfer rates (FTR), i.e., lipolysis. IDL apoB concentration was regulated mainly by the IDL to LDL FTR (r = -0.71, P < 0.0001). LDL apoB concentration correlated with VLDL(2) apoB production (r = 0.48, P = 0.018) and the LDL FCR (r = -0.77, P < 0. 001) but not with VLDL(1), IDL, or LDL apoB production. Subjects with predominantly small, dense LDL (pattern B) had lower VLDL(1) and VLDL(2) apoB FTRs, higher VLDL(2) apoB production, and a lower LDL apoB FCR than those with large LDL (pattern A). Thus, the metabolic conditions that favored appearance of small, dense LDL were diminished lipolysis of VLDL, resulting in a raised plasma triglyceride above the putative threshold of 1.5 mmol/l, and a prolonged residence time for LDL. This latter condition presumably permitted sufficient time for the processes of lipid exchange and lipolysis to generate small LDL particles.

Although metabolic disturbances are often observed in obese patients, increased accumulation of visceral adipose tissue (AT) has been shown to be more closely associated with high fasting triglyceride (TG) and insulin levels as well as with low HDL cholesterol concentrations than with excess body fatness per se. Interestingly, the fasting concentration of plasma TGs has been shown to be an important determinant of the magnitude and duration of the postprandial TG response. Yet little is known about the respective contributions of obesity versus excess visceral AT to the variation in postprandial TG clearance. In the present study, we examined potential differences in postprandial triglyceride-rich lipoprotein (TRL) responses in subjects characterized by high versus low levels of visceral AT. In a sample of 43 men (mean age: 41.3 +/- 9.6 years), we found that both excess body fat and visceral obesity were associated with increased postprandial TG responses in total TRL (r = 0.33-0.45). We also found a strong relationship between fasting plasma TG levels and postprandial total TRL-TG concentrations (r = 0.79, P < 0.0001). When matched for total body fat mass, individuals with high levels of visceral AT >> or =130 cm2; n = 10) as assessed by computed tomography were characterized by increased medium- and small-TRL-TG responses (P < 0.05) compared with subjects with low visceral AT accumulation (<130 cm2; n = 10). Moreover, this elevated response of small-TRL triglycerides noted in men with high levels of visceral AT was not accompanied by a concomitant increased retinyl palmitate response in this TRL fraction, suggesting that visceral obesity in men is accompanied by higher postprandial VLDL production than is found in obese men with lower levels of visceral AT. Increased postprandial insulin and free fatty acid (FFA) responses were also noted in men with high levels of visceral AT. Finally, postheparin plasma lipoprotein lipase activity was negatively correlated with the total-TRL-TG response in a subsample of 32 individuals (r = -0.37, P < 0.05). The results of the present study suggest that visceral obesity is associated with an impaired postprandial TG clearance. Furthermore, the exaggerated postprandial FFA response observed in subjects with high visceral AT suggests that visceral obesity may contribute to fasting and postprandial hypertriglyceridemia by altering FFA metabolism in the postprandial state.

Measurements of transport of triglycerides (TG) in very low density lipoproteins (VLDL) were carried out in 59 patients by injection of radioactive glycerol, determinations of specific activities of VLDL-TG for 48 h thereafter, and treatment of the data by multicompartmental analysis. The patients were divided into three groups: normal weight (89-120% ideal weight), mildly obese (120-135% ideal weight), and markedly obese (135% ideal weight). They had varying levels of VLDL-TG ranging from normal to markedly elevated. In many subjects, there was a positive correlation between concentrations and transport of VLDL indicating that overproduction of VLDL-TG contributed to hypertriglyceridemia. In others, and particularly in several markedly obese subjects, transport rates were greatly increased without significant hypertriglyceridemia, suggesting that they had enhanced capacity to clear TG. In all groups, however, there were patients whose degree of hypertriglyceridemia seemed out of proportion to their transport rates. This finding and the fact that many patients have increased secretion of VLDL-TG without elevated plasma TG suggests that both overproduction of VLDL-TG and insufficient enhancement of clearance contributed to the development of hypertriglyceridemia.The data showed a poor correlation between transport rates determined by our multicompartment analysis and single-exponential analysis used previously by other investigators (r = 0.46); this comparison was not improved by segregating patients according to their degree of obesity. Although two conversion pathways (fast and slow synthetic paths) were required to fit the data, there was no correlation between transport rates and the ratio of the two pathways. Also, despite the known pathway of conversion of VLDL to low density lipoprotein, no correlation was found between VLDL-TG transport rates and estimated low density lipoprotein-cholesterol concentrations.

Familial hypobetalipoproteinemia (FHBL) subjects may develop fatty liver. Liver fat was assessed in 21 FHBL with six different apolipoprotein B (apoB) truncations (apoB-4 to apoB-89) and 14 controls by magnetic resonance spectroscopy (MRS). Liver fat percentages were 16.7 +/- 11.5 and 3.3 +/- 2.9 (mean +/- SD) (P = 0.001). Liver fat percentage was positively correlated with body mass index, waist circumference, and areas under the insulin curves of 2 h glucose tolerance tests, suggesting that obesity may affect the severity of liver fat accumulation in both groups. Despite 5-fold differences in liver fat percentage, mean values for obesity and insulin indexes were similar. Thus, for similar degrees of obesity, FHBL subjects have more hepatic fat. VLDL-triglyceride (TG)-fatty acids arise from plasma and nonplasma sources (liver and splanchnic tissues). To assess the relative contributions of each, [2H2]palmitate was infused over 12 h in 13 FHBL subjects and 11 controls. Isotopic enrichment of plasma free palmitate and VLDL-TG-palmitate was determined by mass spectrometry. Non-plasma sources contributed 51 +/- 15% in FHBL and 37 +/- 13% in controls (P = 0.02). Correlations of liver fat percentage and percent VLDL-TG-palmitate from liver were r = 0.89 (P = 0.0001) for FHBL subjects and r = 0.69 (P = 0.01) for controls. Thus, apoB truncation-producing mutations result in fatty liver and in altered assembly of VLDL-TG.

Combined hyperlipidemia (CHL) is characterized by a concomitant elevation of plasma levels of triglyceride-rich, very low density lipoproteins (VLDLs) and cholesterol-rich, low density lipoproteins (LDLs). The predominance of small, dense LDLs contributes significantly to the premature development of coronary artery disease in patients with this atherogenic dyslipoproteinemia. In the present study, we evaluated the impact of atorvastatin, a newly developed inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, on the cholesteryl ester transfer protein (CETP)-mediated remodeling of apolipoprotein (apo) B-containing lipoprotein subspecies, and more specifically, the particle subpopulations of VLDL and LDL in CHL. In parallel, we evaluated the atorvastatin-induced modulation of the quantitative and qualitative features of atherogenic apo B-containing and cardioprotective apo AI-containing lipoprotein subspecies. Atorvastatin therapy (10 mg/d for a 6-week period) in patients with a lipid phenotype typical of CHL (n=18) induced reductions of 31% (P<0.0001) and 36% (P<0.0001) in plasma total cholesterol and LDL cholesterol, respectively. In addition, atorvastatin significantly reduced VLDL cholesterol, triglycerides, and apo B levels by 43% (P<0.0001), 27% (P=0.0006), and 31% (P<0.0001), respectively. The plasma concentrations of triglyceride-rich lipoproteins (VLDLVLDLrmediate density lipoproteins, Sf 12 to 20) and of LDL, as determined by chemical analysis, were markedly diminished after drug therapy (-30% and -28%, respectively; P<0.0007). Atorvastatin significantly reduced circulating levels of all major LDL subspecies, ie, light (-28%, P<0.0008), intermediate (-27%, P<0.0008), and dense (-32%, P<0.0008) LDL; moreover, in terms of absolute lipoprotein mass, the reduction in dense LDL levels (mean -62 mg/dL) was preponderant. In addition, the reduction in plasma dense LDL concentration after therapy was significantly correlated with a reduction in plasma VLDLr=0.429, P=0.0218). Atorvastatin induced a significant reduction (-7%, P=0.0039) in total CETP-dependent CET activity, which accurately reflects a reduction in plasma CETP mass concentration. Total CETP-mediated CET from high density lipoproteins to apo B-containing lipoproteins was significantly reduced (-26%, P<0.0001) with drug therapy. Furthermore, CETP activity was significantly correlated with the atorvastatin-induced reduction in plasma VLDLr=0.456, P=0. 0138). Indeed, atorvastatin significantly and preferentially decreased CET from HDL to the VLDLraction (-37%, P=0.0064), thereby reducing both the levels (-37%, P=0.0001) and the CE content (-20%, P<0.005) of VLDLrpret our data to indicate that 2 independent but complementary mechanisms may be operative in the atorvastatin-induced reduction of atherogenic LDL levels in CHL: first, a significant degree of normalization of both the circulating levels and the quality of their key precursors, ie, VLDLr LDL particle subclasses (ie, light, intermediate, and dense LDL) due to upregulation of hepatic LDL receptors.

The relations of high density lipoprotein (HDL) subclasses to severity and rate of progression of coronary atherosclerosis were investigated in 60 men who had survived a myocardial infarction before the age of 45 years and who had subsequently undergone two coronary angiographies, with an intervening time interval of 4-7 years between angiographies. Five HDL subclasses with different particle sizes were determined by gradient gel electrophoresis, and the major serum lipoprotein classes were separated by preparative ultracentrifugation in connection with the second angiography. Highly significant inverse correlations were found between the plasma levels of the largest HDL particles, the HDL2b subclass, and both disease severity as observed on the second coronary angiogram (r = -0.53, p less than 0.001) and progression of coronary lesions between angiographies (r = -0.38, p less than 0.01). Grouping the patients according to the presence or absence of very low density lipoprotein (VLDL) triglyceride elevation revealed striking differences in the relations of HDL subspecies to coronary atherosclerosis between normotriglyceridemic and hypertriglyceridemic subjects. There were strong inverse correlations between the plasma HDL2b concentration and both severity of lesions (r = -0.72, p less than 0.001) and rate of lesion progression (r = -0.58, p less than 0.01) in the normotriglyceridemic patients, whereas this relation was absent in subjects with hypertriglyceridemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatitis C virus-like particles (HCV-LPs) containing the structural proteins of HCV H77 strain (1a genotype) was used as a model for HCV virion to study virus-cell interaction. HCV-LPs showed a buoyant density of 1.17 to 1.22 g/cm(3) in a sucrose gradient and formed double-shelled particles 35 to 49 nm in diameter. Flow cytometry analysis by an indirect method (detection with anti-E2 antibody) and a direct method (use of dye-labeled HCV-LPs) showed that HCV-LPs binds to several human hepatic (primary hepatocytes, HepG2, HuH7, and NKNT-3) and T-cell (Molt-4) lines. HCV-LPs binding to cells occurred in a dose- and calcium-dependent manner and was not mediated by CD81. Scatchard plot analysis suggests the presence of two binding sites for HCV-LPs with high (K(d) approximately 1 microg/ml) and low (K(d) approximately 50 to 60 microg/ml) affinities of binding. Anti-E1 and -E2 antibodies inhibited HCV-LPs binding to cells. While preincubation of HCV-LPs with very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), or high-density lipoprotein (HDL) blocked its binding to cells, preincubation of cells with VLDL, LDL, HDL, or anti-LDL-R antibody did not. Confocal microscopy analysis showed that, after binding to cells, dye-labeled HCV-LPs were internalized into the cytoplasm. This process could be inhibited with anti-E1 or anti-E2 antibodies, suggesting that E1 and E2 proteins mediate HCV-LPs binding and, subsequently, their entry into cells. Altogether, our results indicate that HCV-LPs can be used to further characterize the mechanisms involved in the early steps of HCV infection.

Cholesteryl ester-rich beta-very low density lipoproteins (beta-VLDL) are beta-migrating lipoproteins that accumulate in the d < 1.006 g/ml fraction of plasma from cholesterol-fed animals and from patients with Type III hyperlipoproteinemia. They can be separated from pre-beta-migrating very low density lipoproteins in the d 1.006 g/ml fraction by Geon-Pevikon block electrophoresis. The beta-VLDL have a general property of stimulating cholesteryl ester synthesis and accumulation in macrophages. In the present study, we demonstrated that beta-VLDL obtained from cholesterol-fed dogs fasted for 16 hr were heterogeneous and that two subpopulations of particles, referred to as Fractions I and II, could be isolated from the whole beta-VLDL fraction using gel filtration chromatography. These fractions of beta-VLDL were similar in that both were cholesteryl ester rich, had beta-electrophoretic mobility on Geon-Pevikon electrophoresis, and possessed the B and E apoproteins as major constituents. However, Fractions I and II differed in size, shape, electrophoretic mobility, chemical composition, and apoprotein B type. (Fraction I vs. Fraction II: size: 90 to 300 nm vs. 20 to 70 nm; shape: irregular with redundant surface vs. spherical; electrophoretic mobility on paper: origin vs. beta; chemical composition: rich in phospholipid and poor in protein vs. rich in protein and poor in triglycerides; apoprotein B types: equal amounts of the high and low molecular weight forms vs. predominantly the high molecular weight form.) Furthermore, Fraction I was 3- to 15-fold more active than Fraction II in stimulating cholesteryl ester formation in mouse peritoneal macrophages. The concentration of Fraction I, but not Fraction II, was diminished in plasma by prolonged fasting, and Fraction I transported more intestinal-absorbed retinol than Fraction II. In addition, the plasma clearance of Fraction I injected into cholesterol-fed dogs was distinctly different from the clearance of Fraction II, and the in vivo dieaway of Fraction I resembled that of chylomicrons and chylomicron remnants. These findings suggest that beta-VLDL in dogs are composed of cholesteryl ester-rich chylomicron remnants (Fraction I) and cholesteryl ester-rich lipoproteins, probably of liver origin (Fraction II). Finally, in studies of two patients with Type III hyperlipoproteinemia, we also identified the existence of two fractions in the beta-VLDL with characteristics similar to Fractions I and II of cholesterol-fed dogs.-Fainaru, M., R. W. Mahley, R. L. Hamilton, and T. L. Innerarity. Structural and metabolic heterogeneity of beta-very low density lipoproteins from cholesterol-fed dogs and from humans with Type III hyperlipoproteinemia.

The activity of two triglyceride lipases was determined by an immunochemical method in the postheparin plasma of 60 diabetic patients and of 47 age- and sex-matched nondiabetic control subjects. The results were related to the type of diabetes, to plasma triglyceride and insulin concentrations, to removal of exogenous fat from the blood, and to turnover of VLDL-triglycerides . The mean postheparin plasma lipoprotein lipase (LPL) activity was decreased by 44 per cent (p less than 0.001) in patients with untreated ketotic diabetes and by 20 per cent (p less than 0.01) in patients with untreated mild to moderate nonketotic early-onset diabetes. Insulin treatment of ketotic diabetes resulted in a rapid increase in the activity of LPL and decrease in serum triglycerdie level, whereas sulfonylurea treatment of non-insulin-requiring diabetics did not significantly influence the enzyme activity. In insulin-treated chronic diabetics the average postheparin plasma LPL activity was not different from that of nondiabetic controls, but some of these patients had high LPL values. In normolipidemic maturity-onset-type diabetics the LPL activity was within normal range, but in those having hypertriglyceridemia the average LPL value was decreased by an average of 26 per cent (p less than 0.01). The LPL activity showed a significant negative correlation with the logarithm of serum triglyceride concentration (r = -0.62) and a positive correlation with fractional removal of Intralipid (r = +0.64) and fractional turnover of V triglyceride (r = +0.40). The activity of LPL was correlated to basal plasma insulin concen tration in the insulin-deficient diabetes r = +0.34) but not in patients with maturity-onset-type diabetes. The hepatic lipase (HL) activity of postheparin plasma was similar in diabetes and controls, with the exception of hypertriglyceridemic maturity-onset diabetics, who had higher mean HL activity than the corresponding control group (p greater than 0.01). The activity of HL was not related to triglyceride removal but showed a significant correlation to VLDL-triglyceride production rate. On the basis of these results it seems that a deficiency of LPL accounts for a great deal of the elevation of serum triglyceride in insulin-deficient human diabetes but has a smaller role in the pathogenesis of the hypertriglyceridemia that is associated with maturity-onset diabetes. The latter abnormality is caused mainly by an increased secretion of triglycerides into the blood even though a decreased LPL may contribute to development of hyperlipemia in cases with gross elevation of serum triglycerides.

To study the mechanisms of discrimination between various forms of vitamin E, four normal subjects, one patient with lipoprotein lipase deficiency, and three patients with abnormal apolipoprotein B-100 production were given an oral dose containing three tocopherols labeled with differing amounts of deuterium (2R,4'R,8'R-alpha-(5,7-(C2H3)2)tocopheryl acetate (d6-RRR-alpha-tocopheryl acetate), 2S,4'R,8'R-alpha-5-(C2H3)tocopheryl acetate (d3-SRR-alpha-tocopheryl acetate), and 2R,4'R,8'R-gamma-(3,4-2H)tocopherol (d2-RRR-gamma-tocopherol). The tocopherol contents of plasma, red cells, and lipoproteins were measured up to 76 h after the dose. In normal subjects all three tocopherols were absorbed and secreted in chylomicrons with equal efficiencies. Both d2-gamma- and d3-SRR-alpha-tocopherols peaked at similar concentrations in the other lipoprotein fractions, then decreased similarly, but 2-4 times more rapidly than did d6-RRR-alpha-tocopherol. A lipoprotein lipase-deficient patient and a patient with prolonged production of chylomicrons with absent apolipoprotein B-100 also demonstrated the lack of discrimination between tocopherols during absorption. Despite abnormal apolipoprotein B-100 production in two patients, the "VLDL" was preferentially enriched in d6-RRR-alpha-tocopherol. Our results show that there is no discrimination between the three tocopherols during absorption and secretion in chylomicrons, but subsequently there is a preferential enrichment of very low density lipoprotein (VLDL) with RRR-alpha-tocopherol. Catabolism of this VLDL results in the maintenance of plasma RRR-alpha-tocopherol concentrations.