To understand the mechanism responsible for maternal hyperlipidemia, 25 healthy pregnant women were studied longitudinally during the three trimesters of gestation and at post-partum, and 11 were studied again at post-lactation. Triglyceride and cholesterol levels increased with gestation in all the lipoprotein fractions. However, the greatest change appeared in low density (LDL) and high density (HDL) lipoproteins, both of which showed an increase in their triglyceride/cholesterol ratio. The proportional distribution of HDL subfractions showed that the HDL2b fraction was the only one that increased with gestation, whereas both HDL3a and HDL3b had the greatest decrease. Cholesteryl ester transfer protein activity increased during the second trimester of gestation. While postheparin lipoprotein lipase activity decreased during the third trimester, postheparin hepatic lipase activity progressively decreased from the first trimester. The 17 beta-estradiol, progesterone, and prolactin hormones progressively increased from the first trimester of gestation. The lipoprotein-triglyceride values correlated linearly and negatively with the logarithm of either postheparin lipase activities, HDL-triglycerides showing the highest correlation coefficient when plotted against the hepatic lipase values (r = -0.757). It appeared that the highest correlation between any of the HDL subclasses and the activity of the enzymes was for hepatic lipase activity versus HDL2b (r = 0.456) or HDL3a (r = 0.519). A significant lineal correlation also appeared between the postheparin hepatic lipase activity and the logarithm of any of the sex hormones studied, the highest value corresponding to estradiol (r = -0.783). Therefore, during gestation, the effect of estrogen in enhancing very low density lipoprotein (VLDL) production and decreasing hepatic lipase activity plays a key role in the accumulation of triglycerides in lipoproteins of density higher than VLDL.

The native fibrin gel structure formed in vitro from plasma samples was examined by liquid permeation of hydrated fibrin gel networks in 38 unselected men who had suffered a myocardial infarction before the age of 45 years and in 88 age-matched population-based control men. Both the fibrin gel porosity (permeability coefficient, Ks) and the calculated fiber mass-length ratio varied considerably within the two groups, but were generally lower in the patients. Ks was 8.3 +/- 5.2 cm2 x 10(9) (mean +/- SD) in the patient group and 12.5 +/- 5.7 cm2 x 10(9) among controls (p < 0.001). The corresponding figures for fiber mass-length ratio were 13.1 +/- 7.7 and 16.5 +/- 7.5 Dalton/ cm x 10(-13), respectively (p < 0.01). Around 50% of the patients had Ks values below the 10th percentile of the control group. A strong inverse correlation was seen between plasma plasminogen activator inhibitor-1 (PAI-1) activity and Ks (r = -0.603, p < 0.001) or fiber mass-length ratio (r = -0.565, p < 0.001) in the patient group. Corresponding weaker associations of PAI-1 with fibrin gel properties were also present in the control group. In addition, inverse relationships of very low density lipoprotein (VLDL) triglyceride concentrations to Ks (r = -0.362, p < 0.001) and fiber mass-length ratio (r = -0.283, p < 0.01) were found among the controls. Proneness to formation of tight and rigid fibrin gel networks with abnormal architecture in vitro is in vivo associated with myocardial infarction at a young age. Impaired fibrinolytic function secondary to a raised plasma PAI-1 activity level is associated with abnormal fibrin gel structure.

Plasma choleste<em>r</em>yl este<em>r</em> t<em>r</em>ansfe<em>r</em> p<em>r</em>otein (CETP) facilitates int<em>r</em>avascula<em>r</em> lipop<em>r</em>otein <em>r</em>emodeling by p<em>r</em>omoting the hete<em>r</em>oexchange of neut<em>r</em>al lipids. To dete<em>r</em>mine whethe<em>r</em> the deg<em>r</em>ee of t<em>r</em>iglyce<em>r</em>idemia may influence the CETP-mediated <em>r</em>edist<em>r</em>ibution of HDL CE between athe<em>r</em>ogenic plasma lipop<em>r</em>otein pa<em>r</em>ticles in type 2 diabetes, we evaluated CE mass t<em>r</em>ansfe<em>r</em> f<em>r</em>om HDL to apoB-containing lipop<em>r</em>otein accepto<em>r</em>s in the plasma of type 2 diabetes subjects (n=38). In pa<em>r</em>allel, we investigated the potential <em>r</em>elationship between CE t<em>r</em>ansfe<em>r</em> and the appea<em>r</em>ance of an athe<em>r</em>ogenic dense LDL p<em>r</em>ofile. The diabetic population was divided into 3 subg<em>r</em>oups acco<em>r</em>ding to fasting plasma t<em>r</em>iglyce<em>r</em>ide (TG) levels: g<em>r</em>oup 1 (G1), TG<100 mg/dL; g<em>r</em>oup 2 (G2), 100<TG<200 mg/dL; and g<em>r</em>oup 3 (G3), TG>200 mg/dL. Type 2 diabetes patients displayed an asymmet<em>r</em>ical LDL p<em>r</em>ofile in which the dense LDL subf<em>r</em>actions p<em>r</em>edominated. Plasma levels of dense LDL subf<em>r</em>actions we<em>r</em>e st<em>r</em>ongly positively co<em>r</em><em>r</em>elated with those of plasma t<em>r</em>iglyce<em>r</em>ide (TG) (<em>r</em>=0.471; P:=0.0003). The <em>r</em>ate of CE mass t<em>r</em>ansfe<em>r</em> f<em>r</em>om HDL to apoB-containing lipop<em>r</em>oteins was significantly enhanced in G3 compa<em>r</em>ed with G2 o<em>r</em> G1 (46.2+/-8.1, 33.6+/-5.3, and 28.2+/-2.7 mic<em>r</em>og CE t<em>r</em>ansfe<em>r</em><em>r</em>ed. h(-1). mL(-1) in G3, G2, and G1, <em>r</em>espectively; P:<0.0001 G3 ve<em>r</em>sus G1, P:=0.0001 G2 ve<em>r</em>sus G1, and P:=0.02 G2 ve<em>r</em>sus G3). The <em>r</em>elative capacities of <em>VLDL</em> and LDL to act as accepto<em>r</em>s of CE f<em>r</em>om HDL we<em>r</em>e distinct between type 2 diabetes subg<em>r</em>oups. LDL pa<em>r</em>ticles <em>r</em>ep<em>r</em>esented the p<em>r</em>efe<em>r</em>ential CE accepto<em>r</em> in G1 and accounted fo<em>r</em> 74% of total CE t<em>r</em>ansfe<em>r</em><em>r</em>ed f<em>r</em>om HDL. By cont<em>r</em>ast, in G2 and G3, TG-<em>r</em>ich lipop<em>r</em>otein subf<em>r</em>actions accounted fo<em>r</em> 47% and 72% of total CE t<em>r</em>ansfe<em>r</em><em>r</em>ed f<em>r</em>om HDL, <em>r</em>espectively. Mo<em>r</em>eove<em>r</em>, the <em>r</em>elative p<em>r</em>opo<em>r</em>tion of CE t<em>r</em>ansfe<em>r</em><em>r</em>ed f<em>r</em>om HDL to <em>VLDL</em>(1) in type 2 diabetes patients inc<em>r</em>eased p<em>r</em>og<em>r</em>essively with inc<em>r</em>ease in plasma TG levels. The <em>VLDL</em>(1) subf<em>r</em>action accounted fo<em>r</em> 34%, 43%, and 52% of total CE t<em>r</em>ansfe<em>r</em><em>r</em>ed f<em>r</em>om HDL to TG-<em>r</em>ich lipop<em>r</em>oteins in patients f<em>r</em>om G1, G2, and G3, <em>r</em>espectively. Finally, dense LDL acqui<em>r</em>ed an ave<em>r</em>age of 45% of total CE t<em>r</em>ansfe<em>r</em><em>r</em>ed f<em>r</em>om HDL to LDL in type 2 diabetes patients. In conclusion, CETP cont<em>r</em>ibutes significantly to the fo<em>r</em>mation of small dense LDL pa<em>r</em>ticles in type 2 diabetes by a p<em>r</em>efe<em>r</em>ential CE t<em>r</em>ansfe<em>r</em> f<em>r</em>om HDL to small dense LDL, as well as th<em>r</em>ough an indi<em>r</em>ect mechanism involving an enhanced CE t<em>r</em>ansfe<em>r</em> f<em>r</em>om HDL to <em>VLDL</em>(1), the specific p<em>r</em>ecu<em>r</em>so<em>r</em>s of small dense LDL pa<em>r</em>ticles in plasma.

To assess genetic variation of murine lipoprotein profiles, plasma lipoproteins of 11 inbred strains, AKR/J, BALB/cByJ, C3H/HeJ, C57BL/6J, C57BL/6ByJ, C57L/J, DBA/1LacJ, 129/J, NZB/B1NJ, PL/J, and SWR/J, were analyzed by gel-permeation chromatography (fast peptide liquid chromatography) and nondenaturing gradient gel electrophoresis. Vena caval blood was drawn after 18 to 20 hours of fasting. Plasma triglyceride and cholesterol concentrations ranged from 12.9 mg/dL (C57BL/6ByJ) to 66.9 mg/dL (C3H/HeJ) and from 54.8 mg/dL (AKR/J) to 128.5 mg/dL (NZB/B1NJ), respectively. Mouse strain-related heterogeneities of very low-, low-, and high-density lipoprotein (VLDL, LDL, and HDL, respectively) concentrations were documented; VLDL-triglyceride concentrations ranged from 7.5 mg/dL to 38.8 mg/dL, LDL cholesterol from 12.0 mg/dL to 39.6 mg/dL, and HDL cholesterol from 41.3 mg/dL to 92.4 mg/dL. Hyper-VLDL-triglyceridemia was present in C3H/HeJ and SWR/J strains and hyper-LDL-cholesterolemia in NZB/B1NJ, C3H/HeJ, and DBA/1LacJ. VLDL cholesterol/VLDL triglyceride ratios also ranged widely among strains (0.13 to 0.43), with C57BL/6J, C57BL/6ByJ, and C57L/J, the strains particularly susceptible to diet-induced atherosclerosis, having the highest VLDL-lipid ratio. LDL and HDL size heterogeneities were also observed. LDL and HDL diameters ranged between 24.1 nm and 29.4 nm, and between 9.24 nm and 10.32 nm, respectively. Although LDL sizes showed no segregation, HDL sizes fell into two groups. C57L/J and C57BL/6J possessed low HDL-cholesterol concentrations and small-sized HDL. HDL sizes were positively correlated with HDL-cholesterol concentrations (r = .90, P less than .001) and LDL-cholesterol concentrations (r = .85, P less than .001), but LDL sizes did not correlate with lipoprotein concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum levels of total cholesterol, triglycerides, lipoproteins, lipid peroxides (TBARS) and erythrocyte antioxidant enzyme activities were measured in 105 non insulin dependent diabetic patients, among whom 38 had microvascular complications (MVC) of diabetes. All the diabetic patients had higher concentrations of glycated hemoglobin (HbA1) compared to controls (10.51 +/- 2.42% vs 6.31 +/- 0.85% P <0.001). Significant increase of serum triglycerides (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) and very low density lipoprotein cholesterol (VLDL-C) and a significant decrease of high density lipoprotein cholesterol (HDL-C) were observed in the diabetic patients compared to controls (TG: 2.31 +/- 0.9 mmol/l vs 1.53 +/- 0.48 mmol/l P <0. 001; TC: 5.94 +/- 1.4 mmol/l vs 4.3 +/- 0.85 mmol/l P <0.001; LDL-C: 3.96 +/- 1.33 mmol/l vs 2.39 +/- 0.8 mmol/l P <0.001; VLDL-C: 0.46 +/- 0.2 mmol/l vs 0.3 +/- 0.09 mmol/l P <0.001; HDL-C: 0.81 +/- 0.24 mmol/l vs 1.04 +/- 0.18 mmol/l P <0.001). Significantly increased levels of serum TBARS were observed in diabetic patients compared to those in controls (TBARS: 6.7 +/- 1.5 mmol/l vs 5.14 +/- 0.61 mmol/l P <0.001). Erythrocyte catalase (CAT) activity was increased and Glutathione peroxidase (GPx) activity was decreased in diabetic patients compared to controls, but no significant change in Superoxide dismutase (SOD) activity was observed in diabetic patients (CAT: 104.94 +/- 37.1 KU/g Hb vs 85.8 +/- 23.6 KU/g Hb, P <0.01; GPx: 30 +/- 9.7 U/g Hb/min vs 40.84 +/- 12.3 U/g Hb/min, P <0. 001; SOD: 2.4 +/- 1.2 U/mg Hb/min vs 2.55 +/- 0.84 U/mg Hb/min, P=NS). In comparison with the diabetic group without MVC, the diabetic group with MVC had decreased GPx and SOD activities, while no difference was observed between these two groups regarding CAT activity (GPx: 25.32 +/- 8.4 U/g Hb/min vs 34.5 +/- 8.8 U/g Hb/min, P <0.001; SOD: 1.83 +/- 0.53 U/mg Hb/min vs 2.84 +/- 1.4 U/mg Hb/min, P<0.001; CAT: 106.3 +/- 39.9 KU/g Hb vs 103 +/- 34.9 KU/g Hb, P =NS). TBARS concentrations were significantly increased in the group with MVC compared to the group without these complications, indicating a positive relationship between TBARS and MVC of diabetes (7.05 +/- 1.23 mmol/l vs 6.3 +/- 1.02 mmol/l, P <0.001). Serum triglycerides, LDL and VLDL cholesterol concentration were significantly higher in diabetics with MVC than in diabetics without the complications (TG: 2.7 +/- 0.98 mmol/l vs 2.13 +/- 0.82 mmol/l, P<0.01; LDL - C: 4.45 +/- 1.3 mmol/l vs 3.67 +/- 1.3 mmol/l, P <0. 02; VLDL-C: 0.53 +/- 0.19 mmol/l vs 0.43 +/- 0.16 mmol/l, P <0.01), and the serum levels of TC in the group with MVC showed a positive correlation with their lipid peroxide levels (r =0.368, P <0.001). The increase in TBARS and the decreased GPx and SOD activities in diabetics with MVC in this study indicate that these factors may contribute to the occurrence of micro vascular complications in NIDDM patients.

OBJECTIVE

As an important risk factor for coronary atherosclerosis, elevated plasma total homocysteine (t-hcy) concentration has recently received greater attention than have conventional risk factors. Though less reactive than homocysteine, cysteine (cys) is the most abundant plasma thiol and may function as an extracellular regulating factor of thiol/disulfide exchange in order to maintain an adequate redox status. An increase in the total amount of this compound may be noxious depending on environmental conditions. In the present study, the aim was to investigate changes of plasma total cysteine, homocysteine and other determinants in different types of coronary heart disease.

METHODS

Plasma total homocysteine (t-hcy), cysteine (t-cys), cysteinylglycine (t-cysgly), folic acid, vitamin B(12), lipid parameters, total protein, albumin and creatinine levels were studied in plasma from 68 patients with coronary heart disease and 42 healthy controls. After reduction of disulfide bonds with tri-n-buthylphosphine, plasma total thiols were assayed using high performance liquid chromatography (HPLC) and fluorescence detection following derivatization of sulfhydryl groups with 7-fluoro-benzo-2-oxa-1,3-diazole-4-sulfonate (SBD-F). Other parameters were determined by using commercial kits.

RESULTS

Plasma t-hcy and t-cys levels were higher in patients (P<0.0001) than in controls, but t-cysgly was unchanged. Hcy and cys levels were correlated with age in the whole study population (r=0.49, r=0.46, P<0.01). Plasma t-hcy positively correlated with plasma t-cys (r=0.53, P<0.01) and t-cysgly (r=0.49, P<0.01) in patients, and with plasma t-cys (r=0.57, P<0.01) in controls. Postmenopausal women had higher t-cys and t-hcy levels than premenopausal women among the controls (P<0.01). Folate and vitamin B(12) levels were similar in both patients and controls. Patients with vitamin B(12) levels below normal had higher plasma t-cys and t-cysgly levels (P<0.05). Interestingly, control subjects with lower vitamin B(12) levels had lower plasma t-hcy levels (P<0.05). Plasma total cholesterol, HDL-cholesterol, LDL-cholesterol, total protein, albumin and creatinine levels in patients and controls were within the normal range, but only HDL-cholesterol levels in patients were lower than in controls (P<0.0001). Triglyceride and VLDL levels of patients were also higher than those of controls (P<0.0001).

CONCLUSIONS

Higher plasma total cysteine levels are as important as higher plasma total homocysteine levels. Both parameters are intercorrelated and may act synergistically. To discern their respective roles in atherosclerotic disease, these aminothiol levels have to be considered together.

BACKGROUND

Biochemical evidence has linked the coordinate control of fatty acid (FA) synthesis with the activity of stearoyl-CoA desaturase-1 (SCD1). The ratio of 16:1n-7 to 16:0 [SCD1₁₆] in plasma triacylglycerol FA has been used as an index to reflect liver SCD1₁₆ activity and has been proposed as a biomarker of FA synthesis, although this use has not been validated by comparison with isotopically measured de novo lipogenesis (DNL(Meas)).

OBJECTIVE

We investigated plasma lipid 16:1n-7 and FA indexes of elongation and desaturation in relation to lipogenesis.

METHODS

In this cross-sectional investigation of metabolism, 24 overweight adults, who were likely to have elevated DNL, consumed D2O for 10 d and had liver fat (LF) measured by magnetic resonance spectroscopy. Very-low-density lipoprotein (VLDL)-triacylglycerols and plasma free FA [nonesterified fatty acids (NEFAs)] were analyzed by using gas chromatography for the FA composition (molar percentage) and gas chromatography-mass spectrometry and gas chromatography-combustion isotope ratio mass spectrometry for deuterium enrichment.

RESULTS

In all subjects, VLDL-triacylglycerol 16:1n-7 was significantly (P < 0.01) related to DNL(Meas) (r = 0.56), liver fat (r = 0.53), and adipose insulin resistance (r = 0.56); similar positive relations were shown with the SCD1₁₆ index, and the pattern in NEFAs echoed that of VLDL-triacylglycerols. Compared with subjects with low LF (3.1 ± 2.7%; n = 11), subjects with high LF (18.4 ± 3.6%; n = 13) exhibited a 45% higher VLDL-triacylglycerol 16:1n-7 molar percentage (P < 0.01), 16% of subjects had lower 18:2n-6 (P = 0.01), and 27% of subjects had higher DNL as assessed by using a published DNL index (ratio of 16:0 to 18:2n-6; P = 0.03), which was isotopically confirmed by DNL(Meas) (increased 2.5-fold; P < 0.01). Compared with 16:0 in the diet, the low amount of dietary 16:1n-7 in VLDL-triacylglycerols corresponded to a stronger signal of elevated DNL.

CONCLUSIONS

The current data provide support for the use of the VLDL-triacylglycerol 16:1n-7 molar percentage as a biomarker for elevated liver fat when isotope use is not feasible; however, larger-scale confirmatory studies are needed.

Clinical symptoms, lipoprotein patterns, and apoE phenotypes were determined in 17 individuals with type III hyperlipoproteinemia (type III HLP) and in their relatives and spouses. The apoE phenotype E2/2 occurred in 15 type III HLP probands (88%) and the apoE phenotype E4/2 was found in 2 probands. In each of the families studied, the apoE phenotype inheritance was compatible with a model we previously proposed in which apoE is determined at a single genetic locus with three common alleles. The apoE phenotypes E4/4, E3/3, and E2/2 represent homozygosity for the apoE alleles epsilon4, epsilon3, and epsilon2, respectively, whereas the apoE phenotypes E4/3, E3/2, and E4/2 represent heterozygosity for the apoE alleles epsilon4/epsilon3, epsilon3/epsilon2, and epsilon4/epsilon2, respectively. Plasma lipids in 69 relatives of type III HLP probands were analyzed by apoE phenotype and revealed no significant differences between phenotypes in the levels of cholesterol, triglyceride, or HDL cholesterol. However, there were differences between the apoE phenotypes in LDL cholesterol levels (P = 0.01) and in the ratio of VLDL cholesterol/total triglyceride (ratio) (P < 0.01). Relatives with the apoE phenotype E2/2 had the lowest LDL cholesterol levels and the highest ratios. Of these eleven individuals with the apoE phenotype E2/2 who were not type III HLP probands, two males were taking lipid-lowering drugs, one male had mild angina at age 59, five individuals had ratios >0.25 and two had ratios >0.30 with the ratios for males (0.28 +/- 0.06) significantly greater than the ratios for females (0.17 +/- 0.06) (P < 0.01), and seven had evidence of floating betaVLDL on lipoprotein electrophoresis. In addition, when compared to a control group in the general population, the whole group of relatives had normal cholesterol and HDL cholesterol levels, slightly low LDL cholesterol levels, and almost twice elevated triglyceride levels. In summary, a) a very strong but not invariate association exists between type III HLP and the apoE phenotype E2/2 with some type III HLP individuals having the apoE phenotype E4/2; b) apoE phenotype inheritance is determined by three alleles at a single genetic locus; c) relatives of type III HLP probands, no matter what their apoE phenotype, have on the average nearly twofold elevated plasma triglyceride levels compared to a control population; and d) non-proband type III HLP individuals with the apoE phenotype E2/2 have been identified. As a group these individuals, particularly the males, show a tendency to express type III HLP, but clearly genetic or environmental factors other than the apoE phenotype E2/2 are required for the full phenotypic expression of this disease.-Breslow, J. L., V. I. Zannis, T. R. SanGiacomo, J. L. H. C. Third, T. Tracy, and C. J. Glueck. Studies of familial type III hyperlipoproteinemia using as a genetic marker the apoE phenotype E2/2.

Plasma net cholesteryl ester (CE) transfer and optimum cholesteryl ester transfer protein (CETP) activity were determined in primary hypertriglyceridemic (n = 11) and normolipidemic (n = 15) individuals. The hypertriglyceridemic group demonstrated threefold greater net CE transfer leading to enhanced accumulation of CE in VLDL. This increased net transfer was not accompanied by a change in CETP activity. In normolipidemia, but not in hypertriglyceridemia, net CE transfer correlated with VLDL triglyceride (r = 0.92, P less than 0.001). In contrast, net CE transfer in hypertriglyceridemia, but not in normolipidemia, correlated with CETP activity (r = 0.73, P less than 0.01). Correction of hypertriglyceridemia with bezafibrate reduced net CE transfer towards normal and restored the correlation with VLDL triglyceride (r = 0.90, P less than 0.005) while suppressing the correlation with CETP activity. That net CE transfer depends on VLDL concentration was confirmed by an increase of net CE transfer in normolipidemic plasma supplemented with purified VLDL. Supplementation of purified CETP to normolipidemic plasma did not stimulate net CE transfer. In contrast, net CE transfer was enhanced by addition of CETP to both plasma supplemented with VLDL and hypertriglyceridemic plasma. Thus, in normal subjects, VLDL concentration determines the rate of net CE transfer. CETP becomes rate limiting as VLDL concentration increases, i.e., in hypertriglyceridemia.

Autologous 131I-labelled very low density lipoprotein (VLDL) and 125I-labelled low density lipoprotein (LDL) were injected into seven normal subjects and into forty-three hyperlipidaemic patients, classified into groups on the basis of family studies and clinical findings, to quantitate VLDL and LDL apolipoprotein B kinetics. In normal subjects, mean VLDL-B peptide synthetic rate was 15 . 1 mg kg-1 day-1, mean LDL-B peptide synthetic rate 7 . 7 mg kg-1 day-1 and mean LDL-B fractional catabolic rate (FCR) 0 . 31 day-1. In heterozygous familial hypercholesterolaemia (n = 14) VLDL-B peptide production was normal in patients with normal triglyceride levels; in those with high triglyceride levels there was either VLDL overproduction or a catabolic defect. LDL-B peptide synthetic rates ranged from high normal to increased (8 . 5--18 . 0 mg kg-1 day-1) and LDL-B peptide FCR values were markedly reduced (0 . 14--0 . 28 day-1) confirming the presence of a defect in LDL catabolism but indicating over-production as well. In familial combined hyperlipidaemia (n = 11) VLDL-B peptide production ranged from normal to elevated (13 . 9--44 . 4 mg kg-1 day-1, mean 23 . 8 mg kg-1 day-1) correlating with the VLDl triglyceride level (i.e. with the phenotypic expression of the disorder). LDL-B peptide production ranged from high normal to markedly increased (8 . 9--19 . 5 mg kg-1 day-1, mean 12 . 2 mg kg-1 day-1) and correlated with LDL cholesterol levels (i.e. the phenotype), (r = +0 . 66, P < 0 . 05). Three patients with unclassified hypercholesterolaemia had increased LDL-B peptide synthetic rates. One patient with remnant hyperlipoproteinaemia (type III) had a high normal VLDL-B peptide synthetic rate, 17 . 3 mg kg-1 day-1, and a strikingly low FCR of VLDL-B. In familial hypertriglyceridaemia (three patients) there was a low VLDL-B peptide FCR. In unclassified hypertriglyceridaemia VLDL over-production was the finding in seven patients but four patients appeared to have catabolic defects only. Overall there were significant hyperbolic relationships between VLCL-B peptide FCR and VLDL-B peptide concentration (r = -0 . 78, P < 0 . 001, for the log/log relationship) and between LDL-B peptide FCR and LDL cholesterol (r = -0 . 88, P < 0 . 001 for the log/log relationship.)

Previously, based on distinct requirement of microsomal triglyceride transfer protein (MTP) and kinetics of triglyceride (TG) utilization, we concluded that assembly of very low density lipoproteins (VLDL) containing B48 or B100 was achieved through different paths (Wang, Y. , McLeod, R. S., and Yao, Z. (1997) J. Biol. Chem. 272, 12272-12278). To test if the apparent dual mechanisms were accounted for by apolipoprotein B (apoB) length, we studied VLDL assembly using transfected cells expressing various apoB forms (e.g. B64, B72, B80, and B100). For each apoB, enlargement of lipoprotein to form VLDL via bulk TG incorporation was induced by exogenous oleate, which could be blocked by MTP inhibitor BMS-197636 treatment. While particle enlargement was readily demonstrable by density ultracentrifugation for B64- and B72-VLDL, it was not obvious for B80- and B100-VLDL unless the VLDL was further resolved by cumulative rate flotation into VLDL(1) (S(f)>> 100) and VLDL(2) (S(f) 20-100). BMS-197636 diminished B100 secretion in a dose-dependent manner (0.05-0.5 microM) and also blocked the particle enlargement from small to large B100-lipoproteins. These results yield a unified model that can accommodate VLDL assembly with all apoB forms, which invalidates our previous conclusion. To gain a better understanding of the MTP action, we examined the effect of BMS-197636 on lipid and apoB synthesis during VLDL assembly. While BMS-197636 (0.2 microM) entirely abolished B100-VLDL(1) assembly/secretion, it did not affect B100 translation or translocation across the microsomal membrane, nor did it affect TG synthesis and cell TG mass. However, BMS-197636 drastically decreased accumulation of [(3)H]glycerol-labeled TG and TG mass within microsomal lumen. The decreased TG accumulation was not a result of impaired B100-VLDL assembly, because in cells treated with brefeldin A (0.2 microgram/ml), the assembly of B100-VLDL was blocked yet lumenal TG accumulation was normal. Thus, MTP plays a role in facilitating accumulation of TG within microsomes, a prerequisite for the post-translational assembly of TG-enriched VLDL.

OBJECTIVE

To search for determinants of endothelial dysfunction in type 2 diabetes.

METHODS

We performed a comprehensive analysis of cardiovascular risk markers and measured blood flow responses to endothelium-dependent (acetylcholine [ACh] and NG-monomethyl-L-arginine) and -independent (sodium nitroprusside [SNP]) vasoactive agents in 30 nonsmoking men with type 2 diabetes (age 51 +/- 1 years, BMI 27.8 +/- 0.4 kg/m2, HbA1c 7.4 +/- 0.3%) and 12 matched normal control men.

RESULTS

ACh-induced vasodilation was 37% lower in type 2 diabetic (6.1 +/- 0.5) than in normal subjects (9.7 +/- 1.5 ml.dl-1.min-1, P < 0.01), while flows during SNP were similar (9.1 +/- 0.6 vs. 9.9 +/- 1.3 ml.dl-1.min-1, NS). The ratio of endothelium-dependent vs. -independent flow (ACh:SNP ratio) was 31% lower in type 2 diabetic (0.70 +/- 0.05) than in normal subjects (1.10 +/- 0.18, P < 0.01). Total (2.2 +/- 0.4 vs. 1.3 +/- 0.2 mmol/l, P < 0.05), VLDL, and intermediate-density lipoprotein triglycerides were significantly higher, and the mean LDL particle diameter was significantly smaller in type 2 diabetic than in normal subjects. The lag times for LDL oxidation by Cu2+ in vitro were similar in patients with type 2 diabetes (183 +/- 7) and in normal subjects (183 +/- 9 min, NS). Measured and calculated (sum of concentration of individual antioxidants in serum) total peroxyl radical-trapping capacities (TRAPs) were comparable between the groups. In the patients with type 2 diabetes, LDL size was significantly correlated with endothelium-dependent vasodilation (r = 0.43, P < 0.05), serum triglycerides (r = -0.75, P < 0.001), and the lag time for LDL oxidation in vitro (r = 0.38, P < 0.05). HbA1c was inversely correlated with the lag time for LDL oxidation in vitro (r = -0.41, P < 0.05) and TRAP.

CONCLUSIONS

In summary, patients with type 2 diabetes exhibited impaired endothelium-dependent vasodilation in vivo, elevated serum triglycerides, decreased LDL size, and normal antioxidant capacity. Of these parameters, LDL size was significantly correlated with endothelial function.

Dietary n-3 fatty acids (FAs) found in fish oils markedly lower plasma triglyceride (TG) and very low density lipoprotein (VLDL) levels in both normal and hypertriglyceridemic subjects. The present study examined the mechanism of this effect. Ten subjects with widely different plasma triglyceride levels (82 to 1002 mg/dl) were fed metabolically controlled diets containing 20% fat. The control diet contained a blend of cocoa butter and peanut oil (P/S = 0.8). The test diet contained fish oil (P/S = 1.1) and provided 10-17 g of n-3 FAs per day (depending on calorie intake). After 3 to 5 weeks of each diet, the kinetics of VLDL-TG were determined over a 48-h period after the injection of [3H]glycerol. The fish oil diet reduced the VLDL-TG synthetic rate from 23 +/- 14.3 (mean +/- SD) to 12.6 +/- 7.5 mg/h per kg ideal weight (P less than 0.005) and increased the fractional catabolic rate (FCR) for VLDL-TG from 0.23 +/- 0.12 to 0.38 +/- 0.16 h -1 (P less than 0.005). At the same time, there was a 66% reduction of plasma triglyceride levels, resulting largely from a 78% decrease in VLDL-TG levels (398 +/- 317 to 87 +/- 77 mg/dl; P less than 0.005). There was a strong correlation (r = 0.83; P less than 0.01) between the change in synthetic rates and pool sizes, but there was no correlation (r = 0.24; NS) between changes in FCRs and pool sizes. The VLDL cholesterol: triglyceride ratio increased during the n-3 diet suggesting that smaller VLDL particles were present. These particles would be expected to leave the VLDL fraction more rapidly than larger particles producing a higher FCR. We conclude that the hypotriglyceridemic effect of fish oil appears to be caused primarily by an inhibition of very low density lipoprotein-triglyceride synthesis, but an additional, independent effect upon VLDL catabolism cannot be ruled out.

The low-density lipoprotein (LDL) receptor (LDL-R) family members (LDL-R, LRP, megalin, VLDL-R, apoERR and LRP play important roles in plasma cholesterol homeostasis and fetal development. Megalin is an antigenic determinant for Heymann nephritis in rats and may be important for re-absorption of various molecules by the kidney. VLDL-R homologue in chicken is essential for female fertility. This receptor and apoERR gene family contain several complement-type and EGF precursor-like repeats, and single transmembrane and cytoplasmic domain. Cysteine-rich complement-type repeats containing DxSDE sequences at the C-termini constitute ligand-binding domains. In contrast to the ligand binding domains, receptor-binding domains in different ligands do not share sequence homology. It has been proposed that positive electrostatic surface potentials, not the primary sequences, in different ligands constitute receptor-binding domains. The EGF precursor homology repeats in receptors are important for the dissociation of ligands from receptors in endocytic vesicles. The transmembrane domain is necessary for anchoring to membranes and the cytoplasmic domain is required for their targeting to coated pits and subsequent internalization. The receptor-mediated endocytosis involves recognition of the NPXY motif by clathrin. Recently, this motif has also been implicated in signaling pathways that are crucial in brain development. The signaling process involves the recognition of the NPXY motif by Disabled-1 protein and possibly other proteins involved in intracellular signaling cascade. The LDL-R gene family has provided important insights into the mechanisms of ligand catabolism and may serve as new targets for the treatment of different cardiovascular and neuronal disorders. In the future, their role in signaling may provide novel insights into brain development and neuronal layering.

Patients with systemic lupus erythematosus (SLE) are at high risk of cardiovascular disease (CVD). Tumour necrosis factor-alpha (TNF-alpha) has been implicated in the pathophysiological processes of both SLE and CVD. This study focuses on the role of TNF-alpha and its soluble receptors in SLE-related CVD. In summary, 26 women (52 +/- 8.2 years) with SLE and a history of CVD (SLE cases) we compared with 26 age-matched women with SLE and no clinical manifestations of CVD (SLE controls) and 26 age-matched population-based control women (population controls). Plasma concentrations of circulating TNF-alpha, TNF-alpha receptor 1 (sTNFR1) and TNF-a receptor 2 (sTNFR2) were determined by ELISA. TNF-alpha, sTNFR1 and sTNFR2 were raised in SLE cases as compared to SLE controls (P = 0.009; P = 0.001; P = 0.001, respectively), and SLE controls had higher levels than population controls (P = 0.001; P = 0.02; P = 0.001, respectively). Exclusively in the SLE case group there was a striking positive correlation between TNF-alpha and plasma triglycerides (r = 0.57, P < 0.002), VLDL triglycerides (r = 0.54, P = 0.004) and VLDL cholesterol (r = 0.58, P = 0.002). Furthermore, TNF-alpha correlated with the waist-hip ratio but not with estimated insulin resistance. TNF-alpha may thus be a major factor in SLE-related CVD acting both by contributing to hypertriglyceridaemia and by promoting atherosclerosis-related inflammation. sTNFR1 and sTNFR2 are strongly associated with CVD in SLE but their exact roles in disease development remain to be elucidated.

We have generated transgenic mice expressing the human apolipoprotein CII (apoCII) gene under the transcriptional control of the human cytochrome P-450 IA1 (CYPIA1) promoter. Human apoCII transgenic (HuCIITg) mice exhibited significant basal expression of the transgene (plasma apoCII level = 26.1 +/- 4 mg/dl) and showed further induction of transgene expression after treatment with beta-naphthoflavone. Unexpectedly, HuCIITg mice were hypertriglyceridemic and human apoCII levels correlated strongly to triglyceride levels (R = 0.89, P < 0.0001). Triglyceride levels (mg/dl +/- SEM) were elevated compared to controls in both the fed (804 +/- 113 vs 146 +/- 18, P < 0.001) and fasted (273 +/- 39 vs 61 +/- 4, P < 0.001) states. HuCIITg mice accumulated triglyceride-rich very low density lipoproteins (VLDL) with an increased apoC/apoE ratio. Tracer kinetic studies indicated delayed clearance of VLDL-triglyceride, and studies using Triton inhibition of VLDL clearance showed no increase in VLDL production. Plasma from these mice activated mouse lipoprotein lipase normally and radiolabeled VLDL were normally hydrolyzed. However, HuCIITg VLDL showed markedly decreased binding to heparin-Sepharose, suggesting that apoCII-rich, apoE-poor lipoprotein may be less accessible to cell surface lipases or receptors within their glycosaminoglycan matrices. HuCIITg mice are a promising model of hypertriglyceridemia that suggests a more complex role for apoCII in the metabolism of plasma triglycerides.

OBJECTIVE

To investigate cholesterol metabolism in obesity with and without diabetes.

METHODS

We performed cross-sectional metabolic studies in obese individuals with and without type 2 diabetes. The study population consisted of 16 obese (BMI >30 kg/m(2)) diabetic subjects with a mean age of 52 +/- 2 years (SE) and 16 nondiabetic control subjects of similar age and weight. Cholesterol absorption efficiency was measured with peroral dual isotopes and cholesterol synthesis with sterol balance.

RESULTS

Serum total cholesterol did not differ between the groups, but LDL and HDL cholesterol were significantly lower and VLDL cholesterol and serum total and VLDL triglycerides were higher in the diabetic group than in the control group. Cholesterol absorption efficiency was 29 +/- 1% in diabetic subjects vs. 42 +/- 2% in the control subjects (P < 0.01). Cholesterol synthesis was higher (17 +/- 1 vs. 14 +/- 1 mg. kg(-1). day(-1); P < 0.05) and neutral sterol and bile acid excretion and cholesterol turnover tended to be higher in the diabetic group than in the control group. Blood glucose was positively related to cholesterol synthesis in the diabetic group (r = +0.663, P < 0.01) and in the control group (r = +0.590, P < 0.05), suggesting that the higher blood glucose level, the higher the cholesterol synthesis. In addition, blood glucose was significantly positively related to fecal neutral sterol excretion in both groups.

CONCLUSIONS

Cholesterol absorption efficiency was lower and cholesterol synthesis was higher in obese subjects with diabetes than in those without diabetes, suggesting that diabetes modulates cholesterol metabolism more than obesity alone.

The influence of training-induced adaptations in skeletal muscle tissue on lipoprotein metabolism was investigated in six healthy men. The knee extensors were studied at rest and during exercise after 8 wk of dynamic exercise training of the knee extensors of one leg, while the other leg served as a control. The trained and nontrained thighs were investigated on different occasions. In the trained knee extensors, muscle (m) lipoprotein lipase activity (LPLA) was 70 +/- 29% higher compared with the nontrained (P less than 0.05), and correlated positively with the capillary density (r = 0.84). At rest there was a markedly higher arteriovenous (A-V) VLDL triacylglycerol (TG) difference over the trained thigh, averaging 55 mumol/liter (range 30-123), than over the nontrained, averaging 30 mumol/liter (4-72). In addition to the higher LPLA and VLDL-TG uptake in the trained thigh, a higher production of HDL cholesterol (C) and HDL2-C was also observed (P less than 0.05). Positive correlations between m-LPLA and A-V differences of VLDL-TG (r = 0.90; P less than 0.05) were observed only in the trained thigh. During exercise with the trained thigh the venous concentration of HDL2-C was invariably higher than the arterial, and after 110 min of exercise a production of 88 mumol/min (54-199) of HDL2-C was revealed. Even though a consistent degradation of VLDL-TG was not found during exercise, the total production of HDL-C across the trained and nontrained thigh, estimated from A-V differences times venous blood flow for the whole exercise period, correlated closely with the total estimated degradation of VLDL-TG (r = 0.91). At the end of 2 h of exercise m-LPLA did not differ from the preexercise value in either the nontrained or the trained muscle. We conclude that changes in the lipoprotein profile associated with endurance training to a large extent are explainable by training-induced adaptations in skeletal muscle tissue.

An antioxidant defense system consisting of enzymes and non-enzymatic compounds prevents oxidative damage of lipoproteins in the plasma. When the activity of this system decreases or the reactive oxygen species (ROS) production increases, an oxidative stress may occur. Since fatty acids and triglyceride-rich emulsions can stimulate leukocytes to produce ROS, it is conceivable that raised plasma triglyceride-rich lipoproteins such as very low density lipoprotein (VLDL) may overload the antioxidant system. To test this hypothesis, we selected 14 patients with combined hyperlipidemia (HLP), in whom low density lipoprotein (LDL) and VLDL levels are elevated, as well as 18 hypercholesterolemic patients (HCH) with increased LDL levels and 19 controls (NL) to examine the trend for an imbalance between the production of oxidative species and the antioxidant defense system as challenged by increased plasma lipids. With this goal, plasma lipoprotein lipid fractions were determined and correlated with the release of ROS by leukocytes monitored by luminol-enhanced chemiluminescence. Plasma beta-carotene, alpha-tocopherol, lycopene and the lipoprotein lipid hydroperoxides were determined by high pressure liquid chromatography with electrochemical detection. HLP had lower plasma superoxide dismutase (SOD) activity (0.04 and 0.11 U/mg protein; P < 0.05) as well as lower concentrations of lycopene (0.1 and 0.2 nmol/mg cholesterol; P < 0.05) and beta-carotene (0.8 and 2.7 nmol/mg cholesterol; P < 0.05) in the plasma, as compared with NL. Moreover, HLP showed the highest ROS production by resting mononuclear leukocytes (MN) among the three study groups. When the results of the subjects of the three groups were taken together, the plasma triglyceride concentration was positively correlated to ROS release by resting polymorphonuclear leukocytes (PMN, r = 0.38, P = 0.04) and MN (r = 0.56, P < 0.005). Moreover, ROS release by resting MN was positively correlated with VLDL (r = 0.47, P = 0.02) and LDL (r = 0.57, P = 0.01) triglycerides. There was also a positive correlation between ROS release by stimulated PMN and VLDL (r = 0.44, P = 0.03) as well as LDL (r = 0.53, P = 0.01) triglycerides. High density lipoprotein (HDL) cholesterol showed a negative correlation with ROS release by resting MN (r = -0.48, P = 0.02) and resting PMN (r = -0.49, P = 0.01). VLDL susceptibility to copper (II) oxidation was not different among the three groups. Regarding LDL, there was an increased oxidizability in HLP group.(ABSTRACT TRUNCATED AT 400 WORDS)

We have produced gene knockout mice by targeted disruption of the apobec-1 gene. As recently reported by Hirano et al. (Hirano, K.-I., Young, S. G., Farese, R. V., Jr., Ng, J., Sande, E., Warburton, C., Powell-Braxton, L. M., and Davidson, N. O. (1996) J. Biol. Chem. 271, 9887-9890), these animals do not edit apolipoprotein (apo) B mRNA or produce apoB-48. In this study we have performed a detailed analysis of the lipoprotein phenotypic effects of apobec-1 gene disruption that were not examined in the previous study. We first analyzed the plasma lipoproteins in knockout animals with a wild-type genetic background. Although there was no difference in plasma cholesterol between apobec-1(-/-), +/-, or +/+ mice, there was a marked (176%) increase in plasma apoB-100, from 1.8 +/- 1.2 mg/dl in apobec-1(+/+) mice to 2.7 +/- 0.6 mg/dl in apobec-1(+/-) and 5.0 +/- 1.4 mg/dl in apobec-1(-/-) mice. Plasma apoE was similar in these animals. By fast protein liquid chromatography (FPLC) analysis, there was a significant decrease in plasma high density lipoprotein (HDL) cholesterol in apobec-1(-/-) mice. We further fractionated the plasma lipoproteins into d < 1.006, 1.006-1.02, 1.02-1.05, 1.05-1.08, 1.08-1.10, and 1.10-1.21 g/ml classes, and found a marked (30-40%) reduction in the cholesterol and protein content in the (d 1.08-1.10 and 1.10-1.21) HDL fractions, corroborating the FPLC data. SDS-gel analysis revealed an absence of apoB-48, an increase in apoB-100 in the very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions, and a small decrease in apoA-I in the HDL fractions in the apobec-1(-/-) samples. We next raised the basal plasma apoB levels in the apobec-1(-/-) animals by cross-breeding them with human apoB transgenic (TgB) mice. The plasma apoB-100 was 3-fold higher in apobec-1(-/-)/TgB+/- mice (26.6 +/- 18.3 mg/dl) than in apobec-1(+/+)/TgB+/- mice (9.8 +/- 3.9 mg/dl, p < 0.05). The apobec-1(-/-)/TgB+/- mice had a plasma cholesterol levels of 170 +/- 28 mg/dl and triglyceride levels of 106 +/- 31 mg/dl, which are 80% and 58% higher, respectively, than the corresponding values of 94 +/- 21 mg/dl and 67 +/- 11 mg/dl in apobec+/+/TgB+/- mice. By FPLC, the apobec-1(-/-)/TgB+/- animals developed markedly elevated plasma LDL cholesterol (518.5 +/- 329.5 microg/ml) that is 373% that of apobec1(+/+)/TgB+/- mice (139.0 +/- 87.0 microg/ml) (p < 0.05). The elevated plasma triglyceride was accounted for mainly by a 97% increase in VLDL triglyceride in the apobec1(-/-)/TgB+/- mice. We conclude that apobec-1(-/-) animals have a distinctive lipoprotein phenotype characterized by significant hyperapoB-100 and HDL deficiency in mice with a wild-type genetic background. Furthermore, the abolition of apoB mRNA editing elevates plasma total cholesterol and LDL cholesterol in apobec-1(-/-) animals with a TgB background. Finally, to exclude the possibility that absence of apoB mRNA editing was a secondary effect of chronic Apobec-1 deficiency, we treated apobec-1(-/-) mice with a replication-defective mouse Apobec-1 adenoviral vector and found that we could acutely restore apoB mRNA editing in the liver. These experiments indicate that Apobec-1 is an essential component of the apoB mRNA editing machinery and absence of editing in the knockout animals is a direct consequence of the absence of functional Apobec-1.

Very low density lipoprotein receptor (VLDL-R) was found to be expressed in bovine mammary gland and the human breast carcinoma cell line MCF-7 as an M(r) 105,000 variant, and in Chinese hamster ovary (CHO) cells transfected with human VLDL-R cDNA as an M(r) 130,000 variant. The receptor was purified by ligand affinity chromatography with immobilized M(r) 40,000 receptor-associated protein (RAP). The purified receptor was found to bind urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex (u-PA.PAI-1), while there was no or very weak binding of active site blocked u-PA (DFP-u-PA), PAI-1 or u-PA-type-2 plasminogen activator inhibitor complex. The binding of u-PA.PAI-1 was blocked by RAP. The transfected CHO cells had an efficient, RAP-sensitive endocytosis of u-PA.PAI-1, severalfold higher than non-transfected parental CHO cells. u-PA.PAI-1 endocytosis was partially inhibited by DFP-u-PA, which blocks binding of the complex to the u-PA receptor. RAP and DFP-u-PA sensitive u-PA.PAI-1 endocytosis was also observed in MCF-7 cells, which were without detectable levels of other RAP-binding endocytosis receptors. These results show that VLDL-R represents a novel endocytosis mechanism for u-PA receptor-bound u-PA.PAI-1.

We examined the association between rate of cholesterol esterification in plasma depleted of apolipoprotein B-containing lipoproteins (FER(HDL)), atherogenic index of plasma (AIP) [(log (TG/HDL-C)], concentrations, and size of lipoproteins and changes in coronary artery stenosis in participants in the HDL-Atherosclerosis Treatment Study. A total of 160 patients was treated with simvastatin (S), niacin (N), antioxidants (A) and placebo (P) in four regimens. FER(HDL) was measured using a radioassay; the size and concentration of lipoprotein subclasses were determined by nuclear magnetic resonance spectroscopy. The S+N and S+N+A therapy decreased AIP and FER(HDL), reduced total VLDL (mostly the large and medium size particles), decreased total LDL particles (mostly the small size), and increased total HDL particles (mostly the large size). FER(HDL) and AIP correlated negatively with particle sizes of HDL and LDL, positively with VLDL particle size, and closely with each other (r = 0.729). Changes in the proportions of small and large lipoprotein particles, which were reflected by FER(HDL) and AIP, corresponded with findings on coronary angiography. Logistic regression analysis of the changes in the coronary stenosis showed that probability of progression was best explained by FER(HDL) (P = 0.005). FER(HDL) and AIP reflect the actual composition of the lipoprotein spectrum and thus predict both the cardiovascular risk and effectiveness of therapy. AIP is already available for use in clinical practice as it can be readily calculated from the routine lipid profile.

We have developed a high resolution microvolume Vertical Auto Profile (VAP) method for the simultaneous measurement of cholesterol in all lipoprotein classes, including lipoprotein[a] (Lp[a]) and intermediate density lipoprotein (IDL). This method, designated as VAP-II, uses a non-segmented continuous flow (controlled-dispersion flow) analyzer for the enzymatic analysis of cholesterol in lipoprotein classes separated by a short spin (47 min) single vertical ultracentrifugation. Cholesterol concentrations of high (HDL), low (LDL), very low (VLDL), and intermediate (IDL) density lipoproteins, as well as Lp[a], are determined by decomposing the spectrophotometric absorbance curve, obtained from the continuous analysis of the centrifuged sample, into its components using software developed in this laboratory. Analysis by VAP-II is rapid and sensitive (as little as 40 microliters plasma is required per assay). The resolution of lipoprotein peaks is considerably enhanced in the present analyzer compared to the previous analyzer (VAP-I, which used the Technicon AutoAnalyzer); improvement is especially noticeable for Lp[a] and IDL. Total and lipoprotein cholesterol values obtained by VAP-II correlated well with the values obtained by Northwest Lipid Research Laboratories (NWLRL). VAP-II Lp[a] cholesterol values also correlated well with the Lp[a] mass values obtained by an immunoassay technique performed at NWLRL (r = 0.907). The reproducibility and accuracy of the method are within the requirements of the CDC-NHLBI (Centers for Disease Control-National Heart, Lung, and Blood Institute) Lipid Standardization Program.

OBJECTIVE

Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme in monounsaturated fatty acid synthesis. It is imperative for the assembly of VLDL particles, which transport triacylglycerol (TG) from liver to adipose tissue and other sites. We aimed to determine the role of hepatic SCD1 activity in human glucose and lipid metabolism.

METHODS

We studied 54 people participating in a lifestyle intervention programme with diet modification and increased physical activity. Insulin sensitivity was determined during a euglycaemic-hyperinsulinaemic clamp and estimated from an OGTT. Liver fat was quantified by (1)H-magnetic resonance spectroscopy at baseline and after 9 months of intervention. The pattern of fatty acids in serum VLDL-TGs was determined by ultracentrifugation followed by thin layer and gas chromatography, with the 18:1 n-9: 18:0 ratio providing an index of hepatic SCD1 activity.

RESULTS

The hepatic SCD1 activity index correlated negatively with liver fat (r= -0.29, p=0.04) and positively with insulin sensitivity, both OGTT-derived (r=0.42, p=0.003) and clamp-derived (r=0.27, p=0.07). These correlations depended on overall adiposity. They were absent in leaner participants (n=27, liver fat: p=0.34, insulin sensitivity [OGTT]: p=0.75, insulin sensitivity [clamp]: p=0.24), but were strong in obese individuals (n=27, p=0.004, p=0.0002 and p=0.006, respectively). Furthermore, during intervention a high SCD1 activity index at baseline predicted a decrease in liver fat only in obese participants (r= -0.46, p=0.02).

CONCLUSIONS

Our data suggest that high hepatic SCD1 activity may regulate fat accumulation in the liver and possibly protects from insulin resistance in obesity.