Modulation of low density lipoprotein subclasses by alimentary lipemia in control and normotriglyceridemic non-insulin-dependent diabetic subjects

Pre-exercise meal on oxidation of energy substrates during maximal exercise test in non-trained individuals

Objective

This study aimed to compare the influence of a high carbohydrate meal versus high-fat meal on the oxidation of substrates during an exercise incremental test.

Materials and methods

Ten untrained male subjects underwent two days of the protocol. Randomly, they received a high carbohydrate meal or a high-fat meal, receiving the other one in the next protocol. On both days, they performed an incremental treadmill test, with heart rate and maximal oxygen consumption to estimate the oxidation of substrates.

Results

The high-fat meal showed an increase in the absolute amount of oxidized fat along with the incremental test (P < 0.05; effect size = 0.9528), and a reduction in the respiratory exchange ratio at low intensities (P < 0.05; effect size = 0.7765).

Conclusion

The meals presented no difference when compared to maximum oxidation point of substrates, the oxidation rate of substrates over time, and heart rate. A pre-test high-fat meal in untrained individuals was shown to be a modulating factor of total oxidized fats throughout the exercise, although it did not exert a significant effect on the rate of this oxidation over time.

Association between Small Dense Low-Density Lipoproteins and High-Density Phospolipid Content in Patients with Coronary Artery Disease with or without Diabetes

OBJECTIVE

To evaluate the phospholipid profile in total plasma, non-high-density lipoprotein (HDL), and HDL fractions. We tried to correlate the phospholipid profile to low-density lipoprotein (LDL) size, as reflected by cholesterol content in each LDL subclass.

METHODS

We measured small dense LDL-C levels after heparin-magnesium precipitation and measured high-density lipoprotein phospholipid (HDL-P) levels using a colorimetric enzymatic method.

RESULTS

The correlation of the phospholipid profile to small dense LDL-C (sdLDL-C) in patients with coronary problems showed a negative association between small dense low-density lipoprotein (sdLDL) and HDL-P (r = -0.73; P = .02). Moreover, a strong positive correlation was detected between TG and the ratio HDL-P/HDL-C (r = 0.83; P <.001).

CONCLUSIONS

HDL phospholipid has an antiatherogenic effect in coronary artery disease with or without diabetes. Further, large LDL modulation seems to be associated with diabetes rather than coronaropathy.

Plasma proprotein convertase subtilisin/kexin type 9 is associated with Lp(a) in type 2 diabetic patients

AIM

Recent in vitro researches have shown that plasma Lp(a) can be reduced using a proprotein convertase subtilisin/kexin type 9 (PCSK9)-inhibitory monoclonal antibody. In our clinical study we tried to investigate the association between plasma Lp(a) and PCSK9 in Type 2 diabetic patients with elevated plasma Lp(a), and to check whether such an association would be related to LDL-receptor (LDL-R) levels.

METHODS

Plasma PCSK9 and LDL-R concentrations were measured by sandwich ELISA methods using recombinant human PCSK9 protein and LDL-R protein as standards in a cohort with type 2 diabetic patients (n=50) compared to an age- and sex-matched control group (n=50). Both clinical and biochemical parameters were determined in all patients.

RESULTS

Plasma PCSK9 level was significantly elevated in T2DM patients compared to controls (44.61±14.44 and 33.22±11.79ng/mL, respectively, P<0.0001). However LDL-R levels did not differ between the two groups. Remarkably, plasma PCSK9 levels were positively correlated with Lp(a) levels in whole population (r=+0.227, P=0.03) as well as in T2DM group (r=+0.398, P=0.0061) but not in control group. Multiple linear regression analysis showed that plasma Lp(a) levels were independently associated to those of PCSK9.

CONCLUSION

Lp(a) has been proposed as a contributing factor to the accelerated development of macrovascular complications in T2DM. Its synergic effect with PCSK9 may explain the enhanced atherogenicity in T2DM patients.

HOMA-IR and non-HDL-C as predictors of high cholesteryl ester transfer protein activity in patients at risk for type 2 diabetes

BACKGROUND AND AIMS

Metabolic syndrome (MS) and type 2 diabetes are highly associated with an abnormal lipoprotein profile, which may be generated and accentuated by high cholesteryl ester transfer protein (CETP) activity. Given the difficulty in measuring CETP activity, the aim was to identify simple biochemical predictors of high CETP activity.

DESIGN AND METHODS

Eighty five subjects at risk for type 2 diabetes were classified according to the presence of MS. Lipoprotein profile, HOMA-IR and endogenous CETP activity were evaluated.

RESULTS

As expected, MS patients presented higher concentration of glucose, insulin, triglycerides and non-HDL-C and lower HDL-C levels. Moreover, MS patients exhibited increased HOMA-IR and CETP activity. Employing a ROC curve for MS, high CETP activity was defined as >250%ml⁻¹ h⁻¹. The predictive variables of high CETP were non-HDL-C≥160mg/dl (OR=11.1;95%IC=3.3-38.2;p<0.001) and HOMA-IR>2.1 (OR=4.4;95%IC=1.3-14.8;p<0.05).

CONCLUSIONS

High non-HDL-C and insulin resistance were predictors for increased CETP activity which measurement is not accessible for clinical laboratories.

Agreement Between Fasting and Postprandial LDL Cholesterol Measured with 3 Methods in Patients with Type 2 Diabetes Mellitus

BACKGROUND

LDL cholesterol (LDL-C) is a modifiable cardiovascular disease risk factor. We used 3 LDL-C methods to study the agreement between fasting and postprandial LDL-C in type 2 diabetes (T2DM) patients.

METHODS

We served 74 T2DM patients a standardized meal and sampled blood at fasting and 1.5, 3.0, 4.5, and 6.0 h postprandially. We measured LDL-C by use of modified β quantification (MBQ), the Friedewald equation (FE), and a direct homogeneous assay (DA). We evaluated agreement using 95% limits of agreement (LOA) within ±0.20 mmol/L (±7.7 mg/dL).

RESULTS

LDL-C concentrations at all postprandial times disagreed with those at fasting for all methods. In 66 patients who had complete measurements with all LDL-C methods, maximum mean differences (95% LOA) in postprandial vs fasting LDL-C were −0.16 mmol/L (−0.51; 0.19) [−6.2 mg/dL (−19.7; 7.3)] with MBQ at 3 h; −0.36 mmol/L (−0.89; 0.17) [−13.9 mg/dL (−34; 6.6)] with FE at 4.5 h; and −0.24 mmol/L (−0.62; 0.05) [−9.3 mg/dL (−24; 1.9)] with DA at 6.0 h. In postprandial samples, FE misclassified 38% of patients (two-thirds of statin users) into lower Adult Treatment Panel III (ATP III) risk categories. Greater disagreement between fasting and postprandial LDL-C was observed in individuals with postprandial triglyceride concentrations &gt;2.08 mmol/L (&gt;184 mg/dL) and in women (interactions: P ≤ 0.038).

CONCLUSIONS

Differences up to 0.89 mmol/L (34 mg/dL) between fasting and postprandial LDL-C concentrations, with postprandial LDL-C concentrations usually being lower, were found in T2DM by 3 different LDL-C methods. Such differences are potentially relevant clinically and suggest that, irrespective of measurement method, postprandial LDL-C concentrations should not be used to assess cardiovascular disease risk.

High density lipoprotein-anionic peptide factor effect on reverse cholesterol transport in type 2 diabetic patients with and without coronary artery disease

OBJECTIVES

To verify if HDL3 Anionic Peptide Factor (HDL3-APF) is as an apolipoprotein that promotes the reverse cholesterol transport.

DESIGN AND METHODS

We investigated a possible association between plasma HDL3-APF concentration, cholesterol efflux from Fu5AH cells and cholesteryl ester transfer protein (CETP) activity in type 2 diabetic patients with coronary artery disease (CAD) (n=36), those without CAD (n=20), and 37 healthy subjects.

RESULTS

Plasma APF concentrations were decreased in diabetics with CAD compared to controls (p<0.01). Cellular cholesterol efflux was decreased in diabetics without and with CAD, (p<0.01 and p<0.001 respectively). CETP activity was significantly elevated in all patient groups. Multiple linear regression analysis shows that cholesterol efflux was independently and positively related only to APF concentrations in controls.

CONCLUSIONS

APF is likely to be a key independent factor for promoting cellular cholesterol efflux in healthy subjects. However this association is altered in type 2 diabetes.

Sustained postprandial decrease in plasma levels of LDL cholesterol in patients with type-2 diabetes mellitus

OBJECTIVE

Low density lipoprotein cholesterol (LDL-C) is an independent and modifiable risk factor for development of cardiovascular disease (CVD). Postprandial lipid metabolism has been linked to CVD, but little is known about the postprandial LDL-C profile in patients with type-2 diabetes (T2DM). We aimed to study the postprandial levels of LDL-C in T2DM patients.

MATERIAL AND METHODS

After an overnight fast, 74 T2DM patients, mean age approximately 60 years, were served a standard fat-rich meal of 3515 kJ containing 54% fat, 13 % protein and 33 % carbohydrates. Only drinking water was allowed postprandially. Blood samples were drawn at times 0 (fasting), 1.5, 3.0, 4.5 and 6.0 h (postprandial). In all samples, LDL-C was measured with modified beta quantification (separation by ultracentrifugation followed by measurement of infranate high density lipoprotein cholesterol (HLD-C) using a homogeneous assay).

RESULTS

At all postprandial times, levels of LDL-C showed highly significant (p < 0.005) decreases compared to time 0 (mean [95% CI] maximum change in LDL-C levels at 3.0 h: -0.16 mmol/L [-0.12; -0.20]; p < 0.001). Independently of fasting LDL-C levels and ongoing statin therapy, LDL-C decreased significantly more in female compared to male patients postprandially (mean [95% CI] maximum unadjusted change versus time 0 in LDL-C for men [n=56] at 3.0 h: -0.14 mmol/L [-0.19; -0.10], p < 0.001; for women [n=18] at 4.5 h: -0.26 mmol/L [-0.35; -0.18], p < 0.001; -0.14 mmol/L [-0.24; -0.05], p = 0.005 between genders for the mean [95% CI] fasting adjusted difference at 4.5 h in the change versus time 0 in LDL-C; gender by time interaction: p = 0.007 (repeated measures mixed model)).

CONCLUSIONS

In T2DM patients served a fat-rich meal, levels of LDL-C decreased significantly more in women compared to men postprandially, irrespective of fasting levels or ongoing statin therapy. This might have implications in the atherosclerotic process and on any difference in the risk of CVD between genders.

Post-prandial alterations in LDL size and subclasses in patients with growth hormone deficiency

OBJECTIVE

Several studies have suggested that lipoproteins generated during the post-prandial phase are highly atherogenic, with modifications in low-density lipoproteins (LDL) size and density. In the present study we assessed post-prandial variations in LDL size and subclasses in patients with growth hormone deficiency (GHD).

DESIGN

We studied in 12 hypopituitary patients with GHD and 10 healthy control subjects matched for gender, age and body mass index (BMI) post-prandial variations after a standardized meal consisting of 35% fat, 45% carbohydrate and 20% of protein (Clinutren Mix, Nestlé) and containing calories corresponding to 1/3 of estimated basal metabolic rate. Blood samples were collected at baseline and after 2 and 4h to measure plasma lipids and LDL size and subclasses by nondenaturing polyacrylamide gradient gel electrophoresis.

RESULTS

At baseline patients had similar plasma lipids than controls, with the exception of higher triglycerides (1.2+/-0.8 vs. 0.7+/-0.4mmol/L, p=.0024). Baseline LDL size was similar between the two groups and LDL subclass analysis revealed a small increase in LDL-IIIA (p=.0046). During post-prandial phase no significant differences were found in LDL size and subclasses in patients vs. controls with the sole exception of increased levels of LDL-IVB after 2h (p=.0295) and LDL-IIIB after 4h (p=.0478).

CONCLUSIONS

It is, therefore, unlikely that a post-prandial variation in levels of small, dense LDL may significantly contribute to the atherogenic potential in hypopituitary patients with GHD.

Low-density lipoproteins generated during an oral fat load in mild hypertriglyceridemic and healthy subjects are smaller, denser, and have an increased low-density lipoprotein receptor binding affinity

Triglyceride-rich lipoproteins generated during the postprandial phase are atherogenic. Large very low-density lipoproteins (LDLs) or chylomicrons (CMs) are not as atherogenic as their remnants (Rem). Small and dense LDLs are associated with cardiovascular disease. Low-density lipoprotein size is partly under genetic control and is considered as a relatively stable LDL feature. In this article, we present data on retinyl palmitate kinetics correlated with the modification of LDL features in terms of size, density, and in vitro receptor binding affinity after an oral fat load. Six nondiabetic, hypertriglyceridemic (HTG) patients and 6 healthy controls were examined. Low-density lipoprotein size was assessed by gradient gel electrophoresis, and LDL density by density gradient ultracentrifugation. Low-density lipoprotein binding affinity was tested by in vitro competition binding assay on normal human skin fibroblasts (HSFs) and hepatoma cells (HepG2). Kinetic parameters were estimated in CM and Rem fractions by compartmental modeling. Hypertriglyceridemic patients showed significantly higher triglyceride area and a slower CM fractional catabolic rate. Postprandial LDL density increased both in HTG patients and in the control group with a significant difference between groups at 6 hours. Fasting LDL size was lower in HTG patients vs controls but decreased similarly in the postprandial phase. Low-density lipoprotein size and density postprandial modifications were not correlated with any investigated parameter. Postprandial LDLs were internalized more efficiently by HSF than baseline LDL only in the HTG group. In conclusion, postprandial LDLs are smaller and denser compared with fasting LDLs after an oral fat load. Postprandial LDLs also slightly increased their affinity to the HSF cell receptors.

Postprandial changes in LDL phenotypes in patients with myocardial infarction

BACKGROUND

Low-density lipoprotein (LDL) particle size is strongly affected by both fasting and postprandial triglyceride levels. We report here that the LDL phenotype shifts toward the smaller phenotype during oral fat tolerance tests (OFTTs) in some patients with myocardial infarction (MI); a condition closely associated with postprandial increases of triglyceride and remnant-like particles (RLPs).

METHODS

Oral fat tolerance tests were performed on 63 MI patients with fasting serum triglyceride levels of less than 2.25 mmol L-1 (= 200 mg dL-1). Remnant-like particles and other serum lipids were compared among patients characterized by three LDL phenotypes based on nondenaturing gradient gel electrophoresis: pattern A (large LDLs, peak LDL particle size > or = 260 A), pattern I (intermediate-sized LDLs, LDL size > 255 A, < 260 A), and pattern B (small, dense LDLs, LDL size < or = 255 A).

RESULTS

The LDL size decreased significantly in patients with the highest tertile of areas under the incremental curves (AUICs) of triglycerides above the fasting levels. The LDL phenotype shifted toward the smaller phenotype after a fat load in three of eight patients with pattern A and in seven of 35 patients with pattern I. The AUICs of triglyceride-rich lipoproteins were significantly higher in these patients than in the patients exhibiting little change in LDL size, whereas the fasting metabolic parameters were similar among the patients of the same LDL phenotype in the fasting state.

CONCLUSION

These results suggest that alimentary lipaemia plays an important role in the remodeling of LDL particles into the more atherogenic small, dense LDLs in patients with MI.

Association between LDL particle size and postprandial increase of remnant-like particles in Japanese type 2 diabetic patients

Small, dense LDL, as well as chylomicron- and VLDL-remnant lipoproteins, are known to be important risk factors for coronary heart disease in patients with type 2 diabetes mellitus. The aim of this study was to clarify the relationship between LDL particle size and postprandial remnant lipoprotein levels in Japanese type 2 diabetic patients. Forty-six patients with type 2 diabetes mellitus were divided into tertiles according to LDL particle size. The peak LDL particle diameter was <26.30 nm in tertile 1, 26.30-26.85 nm in tertile 2, and >26.85 nm in tertile 3. After a test meal, tertile 1 had a significantly greater increment of triglycerides (TG), remnant-like particle (RLP)-TG, and RLP-cholesterol (RLP-C) than tertiles 2 and 3. There was a negative correlation between LDL particle size and the postprandial increases of TG, RLP-TG, and RLP-C. These results indicate that smaller sized LDL particles may be a marker of fasting state for an exaggerated postprandial increase of remnant lipoproteins as well as an increase of TG-rich lipoproteins.

Impact of postprandial variation in triglyceridemia on low-density lipoprotein particle size

The fasting atherogenic dyslipidemia of visceral obesity, which includes the presence of small, dense low-density lipoprotein (LDL) particles, is predictive of an increased risk of coronary heart disease (CHD). It has also been suggested that progression of atherosclerosis may be accelerated in the presence of postprandial hyperlipidemia independently from the fasting dyslipidemic state. Studies have shown that the best predictor of postprandial hyperlipidemia and of the small, dense LDL phenotype is fasting triglyceride (TG) concentration. In the present study, we evaluated the impact of postprandial hypertriglyceridemia on the variation in LDL particle size. Fasting (0 hour) and postprandial changes (2, 4, 6, and 8 hours) in LDL particle size were measured by nondenaturing 2% to 16% polyacrylamide gel electrophoresis in a sample of 49 men (mean age +/- SD: 46.6 +/- 9.2 years) who underwent a standardized breakfast with a high-fat (64% calories as fat) content. The postprandial increase in TG levels was associated with a transient reduction in LDL particle size, the most substantial reduction being observed 4 hours (-1.0 +/- 2.4 A) after the oral fat load. Although there were strong correlations between TG-rich lipoprotein (TRL)-TG levels and LDL particle size in the fasting state (r=-0.71, P<.0001) as well as 4 hours after the oral fat load (r=-0.70, P<.0001), changes in TRL-TG concentrations during the postprandial state (from time 0 to 4 hours) were not associated with changes in LDL particle size during this period (r=-0.04, not significant [NS]). However, among subgroups of men matched for similar fasting TRL-TG levels (n=12), subjects with the highest total area under the curve (AUC) of TRL-TG after the fat load were characterized by smaller LDL particle size at 6 and 8 hours compared with men with the lowest AUC TRL-TG (P<.02). Men displaying the highest postprandial AUC TRL-TG were also characterized by the greatest accumulation of visceral adipose tissue (AT) (P<.05). These results indicate that the hypertriglyceridemic (hyperTG) state induced by a high-fat meal is associated with a transient reduction in LDL peak particle diameter, which is not proportionate, however, to the level of TG achieved in the postprandial state. Furthermore, despite similar TG levels at baseline, viscerally obese men with an impaired postprandial lipemia had smaller LDL particles at the end of the oral fat load than obese men with a lower accumulation of visceral AT.

Postprandial lipidemia is normal in non-obese type 2 diabetic patients with relatively preserved insulin secretion

To assess postprandial lipidemia in normotriglyceridaemic type 2 diabetic patients treated with diet only, 12 non-obese patients (8 males, hemoglobin A(1c) [HbA(1c)] 6.80 +/- 0.67%) and 14 controls of similar age, body mass index (BMI), and fasting triglyceride (Tg) were given a test meal (58 g fat, 100,000 IU vitamin A). Fasting low-density lipoprotein (LDL) cholesterol (LDLc), high-density lipoprotein (HDL) cholesterol (HDLc), free fatty acids, and apolipoprotein B (apoB), and fasting and postprandial Tg, retinylpalmitate (RP), LDL size, glucose, and insulin were measured. The homeostasis assessment model (HOMA) index and lipoprotein (Lpl) and hepatic (HL) lipase activities were estimated. Patients showed lower fasting HDLc (1.12 +/- 0.26 v 1.40 +/- 0.28 mmol/L, P =.02) and a trend towards smaller LDL particles, which was significant 4 hours postprandially (25.86 +/- 0.40 v 26.16 +/- 0.30 nm, P =.04). The area under the curve of Tg (AUC-Tg) and RP, and Lpl were similar, but HL was higher in patients (156.63 +/- 23.89 v 118 +/- 43.27 U/L, P =.011). HL correlated inversely with LDL size and directly with the HOMA index. In conclusion, normotriglyceridemic type 2 diabetic patients with insulin resistance but relatively preserved insulin secretion show low fasting HDLc and increased HL, but normal postprandial lipidemia.

Effects of nateglinide and glibenclamide on postprandial lipid and glucose metabolism in type 2 diabetes

BACKGROUND

Postprandial hyperlipemia and small, dense LDL particles are features of dyslipidemia in type 2 diabetes. The purpose of this study was (1) to determine whether the oral insulinotropic drugs, nateglinide and glibenclamide, can overcome the defect of insulin action to suppress the hepatic VLDL release after a meal and decrease the postprandial lipemia and (2) to evaluate the acute effect of postprandial hypertriglyceridemia on LDL particle size in subjects with type 2 diabetes.

METHODS

Forty-three subjects with type 2 diabetes and mean baseline HbA(1c) 7.6% (95% CI 7.3 to 7.9) were treated with nateglinide 120 mg three times daily or glibenclamide 5 mg once or twice daily for 12 weeks in a double-blind randomised trial. Insulin, glucose, and lipoprotein responses to a mixed fat-rich meal were determined for 8 h postprandially at baseline and at 12 weeks on-trial.

RESULTS

Nateglinide and glibenclamide significantly augmented the maximal response in serum insulin at 60 min postprandially compared with the response without the drug [additional increase 25.0 mU/l (95% CI 11.2-38.8) p = 0.001 and 12.5 mU/l (95% CI 4.6-20.3) p = 0.003, respectively] and reduced hyperglycemia. Neither drug affected fasting or postprandial lipid or lipoprotein levels. LDL size did not significantly change in the 8-h postprandial period.

CONCLUSIONS

Although nateglinide and glibenclamide increase postprandial insulin secretion and attenuate hyperglycemia, they do not alleviate postprandial lipemia in subjects with type 2 diabetes and good glycemic control. Although small LDL particle size is associated with chronic hypertriglyceridemia, LDL size does not change during acute postprandial hypertriglyceridemia.

Changes in LDL particle composition after the consumption of meals containing different amounts and types of fat

BACKGROUND

Remodeling of lipoprotein particles in the postprandial period is considered to be an important source of atherogenic particles, but acute changes occurring after meals have been little studied.

OBJECTIVE

We sought to characterize changes in LDL particle composition occurring after a single meal, with particular reference to potential lipid exchange with particles carrying dietary fatty acids.

DESIGN

In a balanced design, 8 healthy subjects ingested isoenergetic meals of different fat content: low-fat, rich in saturated fatty acids (SFAs), and rich in polyunsaturated fatty acids (PUFAs). We investigated changes in LDL composition 4 and 6 h after meal ingestion.

RESULTS

The LDL triacylglycerol-to-protein ratio closely mirrored the plasma triacylglycerol concentrations after each of the meals, and there was a strong association between these variables in both the fasting and postprandial states (P < 0.001). A postprandial increase in LDL triacylglycerol was associated with a decrease in LDL cholesterol. There were no effects of the ingestion of a single meal on the LDL density profiles for protein or for any of the lipid components. The fatty acid composition of total LDL lipids changed in the postprandial period, with an enrichment in PUFA after the PUFA-rich meal and in SFA after the SFA-rich meal.

CONCLUSIONS

The changes observed in LDL composition after single meals are in accord with the proposition that there is neutral lipid exchange in the postprandial period, with triacylglycerol enrichment of LDL particles at the expense of cholesteryl esters. The change in the fatty acid composition of LDL particles implies significant lipid exchange with particles containing dietary fat.

The db/db mouse, a model for diabetic dyslipidemia: molecular characterization and effects of Western diet feeding

Diabetic dyslipidemia is a major factor contributing to the accelerated atherosclerosis in type 2 diabetes mellitus. Although several mouse models are available, the plasma lipoproteins in response to diet have not been fully characterized in these animals. In this study, we have characterized the plasma lipoproteins and related apolipoproteins, as well as the vascular lipases, in diabetes (db/db) mice and their nondiabetic controls (+/?) in the C57BL/KsJ strain. Within 6 weeks of age, db/db mice developed significant obesity, fasting hyperglycemia, and hyperinsulinemia. By FPLC analysis, db/db mice showed a prominent peak in the low-density lipoprotein (LDL) range that was absent in +/? mice, although high-density lipoprotein (HDL) was the predominant species in both groups of animals. Postheparin lipoprotein lipase (LPL) activity in db/db mice was 28% of the level in +/? mice. Upon feeding a human-like 0.15% (wt/wt) cholesterol and 21% (wt/wt) fat "Western" diet, db/db mice developed elevated plasma cholesterol, accompanied by an exaggerated apolipoprotein E (apoE) response compared with +/? mice. FPLC analysis showed that the marked hypercholesterolemic response in db/db mice was the result of a massive increase in the LDL region, which overshadowed a moderate increase in HDL. We next isolated lipoproteins by ultracentrifugation and characterized them by nondenaturing gradient gel electrophoresis. With regular chow, db/db mice had almost exclusively small dense LDL with a peak size at 21.4 nm, as compared with 26.6 nm in nondiabetic controls. On the Western diet, the small dense LDLs persisted but larger particles also appeared in db/db mice, whereas the size distribution in +/? mice was unchanged by the diet. Our results suggest that db/db mice fed a Western diet have a plasma lipoprotein phenotype that shows some similarities to that in patients with type 2 diabetes mellitus, and that db/db mice are a useful model to study the pathogenesis and treatment of diabetic dyslipidemia.

Effect of infusion of a triacylglycerol emulsion on low-density lipoprotein composition and oxidizability

Six, healthy, male volunteers aged 19-48 years received a 4-h infusion of a triacylgycerol emulsion (Intralipid 10%) after an overnight fast. Plasma triacylglycerol (TAG) and low-density lipoprotein (LDL) -TAG, -protein and -phospholipid concentrations all rose significantly during the course of the infusion and remained elevated 90 min after its end. The weight/weight ratio of LDL-TAG to -protein also increased significantly (from 0.43+/-0.14 to 0.79+/-0.30 at 4 h and 0.63+/-0.31 90 min later), indicating TAG-enrichment of LDL particles. There were no significant changes in LDL particle density. Susceptibility of LDL to copper-induced oxidation, as measured by the lag time for conjugated diene formation, was less at the end of and 90 min after the end of the infusion than in the fasting state (59.3+/-16.5, 47.4+/-17.4 and 34.8+/-19.6 min, respectively). Lag time was positively correlated with LDL TAG in the fasting state (rS=0.900, P < 0.0001) and the correlation continued with the post-infusion TAG-enriched LDL (rs=0.886, P < 0.05). Acute hypertriglyceridaemia induced by infusion of Intralipid therefore causes TAG-enrichment and a decrease in the susceptibility to oxidation of LDL. TAG-enrichment of LDL may lead to subsequent potentially atherogenic changes in LDL following TAG hydrolysis.

Insulin resistance is not a major determinant of low-density lipoprotein particle size

The relationship between low-density lipoprotein (LDL) peak particle diameter and insulin sensitivity, very-low-density lipoprotein (VLDL) + intermediate-density lipoprotein (LDL) triglyceride, cholesterol, and apoprotein B, postprandial lipemia, and LDL + high-density lipoprotein (HDL) triglyceride was assessed. The subjects were 101 healthy males aged 15 to 45 years. Sixty-one subjects (60.4%) were offspring of a parent with coronary artery disease before age 60, and 40 subjects (39.6%) had no parental history of coronary artery disease. LDL peak particle diameter was measured following polyacrylamide gradient gel electrophoresis. An insulin sensitivity index (Si) was determined from a frequently sampled intravenous glucose tolerance test using a minimal modeling method. A fat tolerance test was performed with a test meal containing 70 g/m2 fat, with triglyceride concentrations measured hourly for 12 hours. LDL peak particle diameter was significantly correlated with body mass index (BMI) (r = -.282, P < .01), waist to hip ratio (r = -.291, P < .01), fasting triglyceride (logarithmically [log] transformed) (r = -.566, P < .001), area under the postprandial triglyceride curve (log transformed) (r = -.562, P < .001), VLDL + IDL triglyceride (log transformed) (r = -.462, P < .001), VLDL + IDL cholesterol (log transformed) (r = -.477, P < .001), VLDL + IDL apoprotein B (log transformed) (r = -.321, P < .001), LDL + HDL triglyceride (log transformed) (r = .583, P < .001), and HDL cholesterol (r = .347, P < .001), but there was no significant correlation with Si. Using stepwise regression analysis, LDL + HDL triglyceride showed the strongest relationship to LDL peak particle diameter, accounting for 34% of the variation in size. Si was not an independent predictor of LDL particle size. In conclusion, insulin sensitivity appears to have little influence on LDL particle size. The importance of LDL + HDL triglyceride should be considered a preliminary finding warranting verification in this and other populations.