Accumulation of apolipoprotein C-I-rich and cholesterol-rich VLDL remnants during exaggerated postprandial triglyceridemia in normolipidemic patients with coronary artery disease

BACKGROUND

Exaggerated postprandial triglyceridemia is common in normolipidemic patients with coronary artery disease (CAD). Alterations in the composition of triglyceride-rich lipoproteins (TRLs) are likely to underlie this metabolic disturbance. However, the composition of very-low-density lipoproteins (VLDLs), which are the most abundant postprandial TRLs, has never been defined in CAD patients.

METHODS AND RESULTS

We examined postprandial changes in the number and composition of VLDLs in middle-aged, normolipidemic CAD patients and control subjects. TRLs from 14 patients and 14 control subjects aged 45 to 55 years were subfractionated by density gradient ultracentrifugation into Svedberg flotation rate (Sf) fractions >400, 60 to 400, and 20 to 60. The VLDLs were separated from chylomicron remnants by immunoaffinity chromatography. In CAD patients, the postprandial concentrations of triglycerides and large (Sf 60 to 400) VLDL particles were elevated. In addition, their postprandial large VLDLs were enriched in apolipoprotein (apo) C-I and their postprandial small (Sf 20 to 60) VLDL remnants were enriched with apo C-I and cholesterol.

CONCLUSIONS

Perturbed handling of postprandial triglycerides in normolipidemic CAD patients involves the accumulation of apo C-I-rich large VLDL particles and the generation of small, apo C-I- and cholesterol-rich VLDL remnants.

A functional polymorphism in the apolipoprotein B promoter that influences the level of plasma low density lipoprotein

Apolipoprotein (apo) B is the structural protein moiety of plasma low density lipoprotein (LDL), an important risk factor for coronary heart disease (CHD). There is evidence that the rate of synthesis of apoB-containing lipoproteins may play an important role in the regulation of plasma LDL levels. However, it is generally thought that transcriptional regulation of the apoB gene is not a significant determinant of the synthesis of apoB-containing lipoproteins, and by inference, of the regulation of the plasma LDL concentration. Here we report the discovery of a common polymorphism in the promoter region of the apoB gene, a C to T substitution at position -516. The -516T allele is associated with an increase in the basal transcription of the apoB gene (+41%, P < 0.05) in vitro in transfected HepG2 cells. Healthy middle-aged men who are homozygous for the -516T allele have 12% higher plasma LDL cholesterol levels than healthy homozygotes for the -516C allele (P < 0.05). The frequency of the -516T allele is significantly higher in young postinfarction patients (0.38) than in population-based controls (0.30) when the comparison is restricted to subjects without severe hypercholesterolemia who are homozygous for the apoE3 allele (P < 0.05). It is concluded that variation in the rate of transcription of the apoB gene can affect plasma LDL levels and influences the risk of CHD in middle-aged men.

Native and oxidized low density lipoproteins enhance platelet aggregation in whole blood

The effects of native and oxidized low density lipoproteins on platelet aggregability remain controversial despite numerous studies. In the current investigation, effects of native, minimally and extensively copper-modified low-density lipoproteins on aggregation responses to ADP and collagen in platelet-rich plasma, washed platelets, and whole blood were studied. Preincubation with native and oxidized low-density lipoproteins (1.5-23.2 malondialdehyde equivalents [MDAeq]/mg low density lipoprotein) did not modify aggregability in platelet-rich plasma or washed platelets but increased aggregation markedly in whole blood (40-58%, p<0.01). In whole blood, the increase in response to ADP was not affected by the degree of low-density lipoprotein oxidation. This comprehensive investigation of low density lipoprotein effects on platelet aggregation therefore has demonstrated that low density lipoproteins indirectly increase platelet aggregability in whole blood, but not in platelet-rich plasma and washed platelets, presumably via an interaction between platelets and other formed elements of blood.

Two common functional polymorphisms in the promoter region of the coagulation factor VII gene determining plasma factor VII activity and mass concentration

Recent studies have provided evidence for associations between common polymorphic markers in the coagulation factor VII (FVII) gene and plasma FVII levels. Here we describe two common, nonrelated, functional polymorphisms in the promoter region of the FVII gene, a G to T substitution at position -401 and a novel G to A substitution at position -402. Both polymorphisms strongly influence the binding properties of nuclear protein(s). The rare -401T allele is associated with a reduced basal rate of transcription of the FVII gene in human hepatoblastoma cells and with reduced plasma concentrations of total FVII (VIIag) and fully activated FVII molecules (VIIa). In contrast, the rare -402A allele confers increased transcriptional activity and is associated with increased plasma FVII levels. Together, the two polymorphisms explained 18% and 28% of the variation in VIIag and VIIa, respectively, in a group of 183 healthy, middle-aged men. It is concluded that these polymorphisms are important for the regulation of the plasma levels of FVII and that they are likely to be useful genetic markers to resolve the issue of whether a causal relationship exists between FVII levels and risk of coronary heart disease.

Coagulation factor V (Arg506-->Gln) mutation and early saphenous vein graft occlusion after coronary artery bypass grafting

The factor V (Arg506-->Gln) mutation confers an increased risk of deep vein thrombosis, whereas its role in saphenous vein graft closure after coronary artery bypass grafting (CABG) remains unclear. This study examined the anticoagulant response to activated protein C (APC ratio) in relation to the surgical trauma and the significance of the factor V Leiden mutation in determining postoperative thrombin generation and fibrin formation and the risk of early vein graft occlusion. A total of 108 men undergoing elective CABG for exertional angina pectoris (mean age 61.1 +/- 8.7 years) were examined. The patency of saphenous vein grafts was studied at routine reangiography three months after CABG. Of 100 patients who underwent reangiography, 23 had one or more occluded vein grafts at reangiography. Heterozygosity for the factor V (Arg506-->Gln) mutation tended to be associated with early saphenous vein graft occlusion (5/11 carriers vs. 18/89 non-carriers with graft occlusion, chi2 = 3.52, p = 0.06), whereas pre- and postoperative APC ratios did not. Pre- and postoperative determinations of prothrombin fragment 1+2, thrombin-antithrombin complexes and soluble fibrin levels did not differ between patients with and without the mutation. Early saphenous vein graft occlusion after CABG could tentatively be added to deep vein thrombosis as a vascular complication that can be attributed to the factor V (Arg506-->Gln) mutation.

Ischaemia monitoring with on-line vectorcardiography during dobutamine stress echocardiography in patients after an episode of unstable coronary artery disease

OBJECTIVES

This study investigated the ability of on-line vectorcardiography (VCG) to detect myocardial ischaemia as assessed by dobutamine stress echocardiography after an episode of unstable coronary artery disease.

DESIGN

Dobutamine stress test (incrementally infused doses of 5, 10, 20, 30 and 40 microg kg(-1) per minute) was performed during simultaneous VCG monitoring. QRS vector difference (QRS-VD), ST vector magnitude (ST-VM), ST change vector magnitude (STC-VM) and T change vector magnitude (TC-VM) were monitored. A new wall motion abnormality or worsening of abnormal wall motion was regarded as indicating a positive dobutamine stress test.

SUBJECTS

Fifty-five patients with unstable angina pectoris and 16 patients with an acute non-Q-wave myocardial infarction were studied 5-8 days after admission.

RESULTS

A positive dobutamine stress test was observed in 37 patients (52%). The sensitivity, specificity and total accuracy of identifying patients with a positive dobutamine stress test by VCG were: 38%, 91% and 63% for QRS-VD; 59%, 88% and 73% for ST-VM; 84%, 79% and 82% for STC-VM; and 86%, 23% and 56% for TC-VM. Patients with a positive dobutamine stress test showed higher maximum VCG values than patients with a negative dobutamine stress test (QRS-VD, P < 0.01; ST-VM, P < 0.001; STC-VM, P < 0.001). The maximum VCG values were related to the number of segments showing new or worsening wall motion abnormality (QRS-VD: r=0.41, P < 0.001; ST-VM: r=0.44, P < 0.001; STC-VM: r=0.57, P < 0.001).

CONCLUSION

STC-VM and ST-VM seem to be the best VCG variables for detection of myocardial ischaemia as assessed by dobutamine stress echocardiography.

Transient triglyceridemia in healthy normolipidemic men increases cellular processing of large very low density lipoproteins by fibroblasts in vitro

Exaggerated and prolonged postprandial triglyceridemia is a characteristic of patients with precocious coronary heart disease. Although large very low density lipoprotein (VLDL) particles accumulate during alimentary lipemia, the biological properties of the postprandial VLDL remain unknown. In the present study, an intravenous infusion of a chylomicron-like emulsion was given to healthy normolipidemic men to examine the effects of transient triglyceridemia in vivo on compositional and cell biological characteristics of VLDL. The postinfusion large(Svedberg flotation rate (Sf) (60-400) VLDL was found to have increased capacity to inhibit low density lipoprotein (LDL) binding to the LDL-receptor and a greater ability to suppress the 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity of cultured fibroblasts compared to VLDL isolated from fasting plasma. These alterations in cellular interactions were accompanied by increases in the number of apolipoprotein (apo) E, C-I, and C-III molecules per large VLDL particle and loss of apoC-II, compositional changes similar to those observed after an oral fat load. The increase in number of apoE molecules per large VLDL particle correlated positively and significantly with the increase in the capacity of large VLDL to inhibit LDL binding to the LDL receptor (r = 0.76, P = 0.01, n = 10). In contrast, the composition of the small (Sf 20-60) VLDL particles did not change significantly, nor was the LDL receptor-mediated processing of these particles altered consistently. These observations indicate that large VLDL particles that accumulate during alimentary lipemia undergo compositional changes that render them more prone to cellular binding and uptake.

Helicobacter pylori seropositivity is not associated with inflammatory parameters, lipid concentrations and degree of coronary artery disease

OBJECTIVES

To determine the prevalence of chronic infection with Helicobacter pylori (HP) in patients with established coronary artery disease (CAD) and in healthy controls. Furthermore, to investigate whether HP infection is associated with inflammatory parameters, lipid concentrations and degree and progression of CAD.

DESIGN

A case-control study combined with a prospective angiographic study.

SETTING

Stockholm Metropolitan Area, Sweden.

PATIENTS AND METHODS

A material consisting of 92 young men aged 40.9 +/- 3.2 (mean +/- SD) years, with previous myocardial infarction and documented coronary atherosclerosis, and 95 healthy sex-matched controls, aged 43.2 +/- 3.0 (mean +/- SD) years, with similar socio-economic status and ethnic background was analysed for the prevalence of HP seropositivity, plasma concentrations of the inflammatory parameters fibrinogen, tumour necrosis factor alpha and orosomucoid, and serum concentrations of lipids. The impact of HP seropositivity on degree and progression of CAD, as assessed by quantitative coronary angiography, was also determined.

RESULTS

The study population of mainly Scandinavian origin had a low prevalence of HP seropositivity in comparison with previously published European populations. No significant increase in HP seropositivity was found in patients compared with controls (42.2 vs. 32.6%). Furthermore, HP infection was not associated with increased levels of inflammatory parameters, lipid concentrations or with degree of angiographically determined CAD at baseline, or progression of CAD and clinical events over 5 years.

CONCLUSIONS

HP infection is not associated with inflammatory parameters and lipid concentrations and could not be confirmed as a risk factor for CAD.

Evidence for a role of tumor necrosis factor alpha in disturbances of triglyceride and glucose metabolism predisposing to coronary heart disease

Elevated plasma levels of triglyceride-rich lipoproteins, a decreased high-density lipoprotein (HDL) cholesterol concentration, hyperinsulinemia, and impaired fibrinolytic function frequently aggregate in patients with premature coronary heart disease (CHD). Experimental studies suggest that the cytokine tumor necrosis factor alpha (TNFalpha) produced by adipocytes plays a part in the regulation of triglyceride and glucose metabolism. The present study examined whether TNFalpha is implicated in these metabolic and fibrinolytic disturbances in young postinfarction patients. TNFalpha levels were determined in two groups of young (age <45 years) male postinfarction patients (n = 92 and 60) and in matched, population-based control subjects (n = 63). Plasma TNFalpha was higher in patients than in controls (4.1 +/- 1.6 v2.5 +/- 0.4 pg/mL, P < .0001). In hyperlipidemic patients, TNFalpha levels correlated significantly with the concentrations of very-low-density lipoprotein (VLDL) triglyceride and cholesterol and negatively with HDL cholesterol. Treatment with bezafibrate decreased VLDL triglycerides and increased HDL cholesterol, but did not affect TNFalpha levels. The TNFalpha concentration also correlated significantly with fasting glucose and proinsulin concentrations, as well as glucose and proinsulin levels after glucose ingestion. In contrast, no relations were found with the insulin level or degree of insulin resistance. The present results provide clinical evidence for a basic role of TNFalpha in hypertriglyceridemia, glucose intolerance, and the etiology of premature CHD.

Transient triglyceridemia decreases vascular reactivity in young, healthy men without risk factors for coronary heart disease

BACKGROUND

Hypertriglyceridemia is now accepted as a risk factor for coronary heart disease, although the mechanism behind the increased risk is not well understood. The present study was undertaken to investigate the effects of triglyceridemia on endothelial function, because impaired endothelial function is considered a marker of atherogenesis.

METHODS AND RESULTS

Flow- and nitroglycerin-induced dilatation of the brachial artery was investigated noninvasively by high-resolution ultrasound technique in seven young, healthy men without risk factors for coronary heart disease. Transient triglyceridemia was induced by infusion of a triglyceride emulsion, Intralipid, which raised free fatty acid concentrations twofold and triglyceride levels fourfold. Flow-induced vasodilatation decreased from 7.1+/-3.0% to 1.6+/-2.6% (P<.0002), whereas nitroglycerin-induced vasodilatation decreased from 20.5+/-5.8% to 11.5+/-3.2% (P<.002) before and after 1 hour of infusion of Intralipid, respectively.

CONCLUSIONS

Transient triglyceridemia decreases vascular reactivity, presumably by both endothelium-dependent and endothelium-independent mechanisms.

High-density lipoprotein: relations to metabolic parameters and severity of coronary artery disease

The regulation of plasma high-density lipoprotein (HDL) cholesterol level by the joint influence of plasma lipoprotein lipids, lipoprotein lipase (LPL), hepatic lipase (HL), cholesteryl ester transfer protein (CETP), oral glucose tolerance, and postload plasma insulin and proinsulin levels was investigated in young postinfarction patients and healthy population-based control subjects. In addition, the association between HDL cholesterol and the number and severity of coronary stenoses previously reported in this cohort of young postinfarction patients was further investigated by analyzing the determinants and angiographic relations of HDL subclasses measured by gradient gel electrophoresis. The following parameters showed significant univariate relations with HDL cholesterol level in the patient group: very-low-density lipoprotein (VLDL) cholesterol and triglyceride, low-density lipoprotein (LDL) triglyceride, and postload plasma insulin concentrations, preheparin plasma LPL mass, and postheparin plasma HL activity. In the control group, significant correlations with HDL cholesterol concentration in addition to those noted among the patients were found for body mass index (BMI), LDL cholesterol level, postload plasma intact proinsulin concentration, and LPL activity in postheparin plasma. In contrast to the patients, no significant relations were noted for postload plasma insulin level and preheparin plasma LPL mass. Multiple stepwise regression analysis showed that 42% of the variability of HDL cholesterol in the patients could be accounted for by VLDL cholesterol concentration (29%), LDL triglyceride level (7%), and postheparin plasma HL activity (8%), whereas the corresponding figure in controls was 35% (VLDL cholesterol concentration [9%] and postheparin plasma HL activity [26%]. The strength of the relationships of HDL cholesterol and HDL subclasses to the coronary stenosis score was similar and statistically significant (r = .25 to .36). When the metabolic parameters that correlated with HDL cholesterol and HDL subclass concentrations in univariate analysis were used as covariates, all relations to the coronary stenosis score disappeared. This clearly indicates that the influence of triglyceride-rich lipoproteins and lipolytic enzymes needs to be considered when assessing the association between HDL cholesterol and coronary artery disease (CAD).

Proneness to formation of tight and rigid fibrin gel structures in men with myocardial infarction at a young age

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.

A decrease in cardiovascular risk factors in healthy 40-year-old Swedish men between 1980-1983 and 1991-1992

BACKGROUND

Cardiovascular risk factors were compared between two samples of urban middle-aged healthy men investigated in 1980-1983 (n = 106) and 1991-1992 (n = 118), respectively.

METHODS

All subjects, who served as controls in an ongoing study on mechanisms behind myocardial infarction, were randomly selected from a register that contains all the inhabitants (1.65 million) in the Stockholm Metropolitan Area. The study programme included recordings of weight, height, smoking habits, blood pressure and blood sampling. Blood and lipoprotein lipid levels, glucose concentrations before and during an oral glucose tolerance test and fibrinogen levels were determined.

RESULTS

The 1991-1992 sample had lower systolic blood pressure and lower concentrations of total blood cholesterol, fasting blood glucose and fibrinogen than the 1980-1983 sample. The lower total blood cholesterol level in the 1991-1992 sample was due to a decrease in low- and high-density lipoprotein cholesterol concentrations. In addition, a tendency was seen towards a decrease in prevalence of smoking in the latter sample. No differences were noted in body mass index, diastolic blood pressure, oral glucose tolerance or total triglycerides between the two samples.

Inverse relation between the concentration of low-density-lipoprotein vitamin E and severity of coronary artery disease

Oxidation of low-density lipoprotein (LDL) is believed to play an important role in atherogenesis, and antioxidant vitamins are thought to protect against coronary artery disease (CAD). We investigated whether the vitamin E concentrations in serum and LDL were associated with the severity of CAD as assessed by a semiquantitative scoring system in which coronary angiograms are analyzed for the number and size of distinct stenotic lesions (global stenosis score). The study group consisted of 64 consecutive male survivors of myocardial infarction aged < 45 y. Lipid-adjusted serum and LDL vitamin E concentrations were significantly lower in the patients than in 35 age-matched male control subjects, whereas the absolute serum and LDL vitamin E concentrations did not differ significantly. No associations were found between the serum concentration or lipid-adjusted serum values of vitamin E and the stenosis score. In contrast, significant inverse correlation was found between the LDL vitamin E concentration, whether adjusted to the lipid (r=-0.477,P<0.001) or protein (r=-0.375, P<0.01) content of LDL, and the global coronary stenosis score. We conclude that a low LDL vitamin E concentration might play a role in the development of stenoses in coronary arteries and may contribute to clinically manifest CAD.

The susceptibility of low density lipoprotein to chemical oxidation is closely related to proneness to biological modification

U937 is a monocytic cell line dependent on low density lipoprotein (LDL) receptor-mediated uptake of cholesterol for proliferation. However, exposure of U937 cells to LDL also results in an oxidative modification of LDL. We report here that the oxidative modification of LDL by U937 cells results in inhibition of growth and cell death. This finding suggests that analysis of U937 cell growth in presence of LDL may be used to determine the susceptibility of LDL to biological oxidative modification. There was an inverse association between the effect of LDL on U937 cell growth and the rate of degradation of U937 cell-modified LDL in mouse peritoneal macrophages (r = -0.82, p < 0.05) suggesting a coupling between proneness of LDL to develop cytotoxicity and affinity for scavenger receptors. In a group of young post-infarction patients (n = 18) the susceptibility of LDL to chemical oxidation as determined by analysis of the lag phase for formation of conjugated diens in presence of copper ions was compared with the biological modification of LDL as assessed by analysis of U937 cell growth in presence of LDL. The results demonstrated a close relation between the estimates of chemical oxidation and biological modification (r = 0.86, p < 0.005) suggesting that LDL, which is prone to become oxidised by copper also is more prone to become modified by cells in vivo.

Association of insulin and insulin propeptides with an atherogenic lipoprotein phenotype

A characteristic lipoprotein phenotype, including hypertriglyceridemia, a low high-density lipoprotein (HDL) cholesterol concentration, and a predominance of small, dense low-density lipoprotein (LDL) particles, is linked to insulin resistance and hyperinsulinemia. Individuals with these characteristics are supposed to be at increased risk of developing coronary heart disease (CHD). To address this issue further, relations between basal and postload glucose, insulin and insulin propeptide concentrations and subfractions of apolipoprotein (apo) B-containing lipoproteins were examined in 62 consecutive Swedish nondiabetic men who had experienced a first myocardial infarction before the age of 45. A total of 41 age-matched, population-based healthy men were investigated as controls. Highly specific immunoradiometric assays were used for measuring intact proinsulin and des 31,32proinsulin levels. In all, 39% of the patients were found to be glucose-intolerant, and basal and postload hyper(pro)insulinemia were characteristic features irrespective of glucose tolerance category. Hypertriglyceridemic (HTG) lipoprotein phenotypes with a low HDL cholesterol concentration dominated among the patients, and hyperinsulinemia was linked to hypertriglyceridemia and putatively atherogenic lipoprotein traits, such as increased particle numbers of small very-low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) and triglyceride enrichment of LDL. The corollary of these findings is that insulin resistance is a characteristic feature of young postinfarction patients and is accompanied by a complex atherogenic lipoprotein phenotype, new components of which are an abundance of small cholesteryl ester-rich VLDL and an elevated LDL triglyceride concentration.

Insulin, intact and split proinsulin, and coronary artery disease in young men

BACKGROUND

Glucose intolerance and hyperinsulinemia are common disturbances in nondiabetic men with premature coronary artery disease (CAD). To investigate the relation between insulin-like molecules and severity of coronary atherosclerosis, 62 consecutive nondiabetic men presenting with a first myocardial infarction before the age of 45 were studied along with 41 healthy, age-matched, male, population-based control subjects.

METHODS AND RESULTS

Specific two-site immunoradiometric assays were used to distinguish intact proinsulin, (des 31,32) proinsulin, and "true" insulin in fasting plasma and during an oral glucose tolerance test (OGTT). Global coronary atherosclerosis and number and severity of distinct stenoses were determined in the patients in 15 proximal coronary arterial segments by use of separate semiquantitative classification systems. The patients had a two- to threefold increase in insulin and insulin propeptide concentrations in the fasting state as well as during the OGTT. Severity of coronary atherosclerosis correlated significantly (P < .05 to P < .01) with basal proinsulin (r = .40) and the proinsulin area under the curve (AUC) (r = .34), basal insulin (r = .31), basal C peptide (r = .30), and the glucose AUC (r = .30). In multiple stepwise regression analysis including insulin-like molecules, major plasma lipoproteins, and lipoprotein subfractions, basal proinsulin (increase in R2 = .09) and dense LDL triglycerides (increase in R2 = .10) predicted 19% of the variation of the global coronary atherosclerosis score after adjustment for age, body mass index, fasting insulin concentration, and VLDL triglycerides.

CONCLUSIONS

This study shows that young, nondiabetic, male survivors of myocardial infarction are truly hyperinsulinemic during an OGTT and suggests a close association between proinsulin and coronary atherosclerosis.

Cellular processing of apolipoprotein B-containing lipoproteins from young post-infarction patients and healthy controls

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was measured in fibroblasts incubated with large (Sf > 60) and small (Sf 20-60) very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) particles, at similar protein concentrations, from young post-infarction patients and healthy controls. The results showed that apolipoprotein (apo) B-containing lipoproteins (VLDL, IDL, LDL) from patients suppressed HMG-CoA reductase activity to a similar extent compared to apo B-containing lipoproteins from controls. When all subjects taken together were grouped according to triglyceride levels, it was found that small VLDL from hypertriglyceridaemic individuals suppressed the HMG-CoA reductase activity more than small VLDL from normotriglyceridaemic individuals. The opposite pattern was seen for LDL. The lipoprotein composition was related to the respective HMG-CoA reductase activity. In addition to a positive association between the cholesterol content of small VLDL and LDL, and the inhibition of HMG-CoA reductase activity, the apo C I and C II content of small VLDL and IDL was inversely related to the suppression of HMG-CoA reductase activity. This study shows that the cellular processing of apo B-containing lipoproteins in young post-infarction patients and healthy controls is heterogeneous and dependent on the composition of the lipoprotein.

Lipoprotein lipase mass and activity in plasma and their increase after heparin are separate parameters with different relations to plasma lipoproteins

Lipoprotein lipase (LPL) activity and mass in plasma and their increase after heparin administration were measured in 61 men who had suffered myocardial infarction before the age of 45 years and in 69 population-based age- and sex-matched control subjects without coronary heart disease to study the relations between these parameters in plasma and their correlations with plasma lipoproteins in subjects with a wide range of lipoprotein and LPL levels. There was a relatively large amount of LPL protein compared with LPL activity in preheparin plasma, indicating that the majority of circulating LPL is catalytically inactive. LPL mass and activity in postheparin plasma (postheparin minus preheparin values) were highly correlated, and the calculated mean specific activity (0.35 mU/ng) was in the range expected for catalytically active LPL. Hence, heparin releases mainly active LPL. The four LPL parameters (mass and activity in plasma and their increase after heparin administration) were not related to each other, except for postheparin plasma LPL mass and activity, and they showed different correlations with plasma lipoprotein lipid concentrations. There was a strong positive correlation between LPL mass in preheparin plasma and the HDL cholesterol level as well as weak negative relations to VLDL triglyceride and cholesterol concentrations in the patients. In contrast, preheparin LPL activity showed no correlation with the HDL cholesterol level but weak positive relations to VLDL triglyceride and cholesterol concentrations in the control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of plasma levels and composition of apolipoprotein B-containing lipoproteins to angiographically defined coronary artery disease in young patients with myocardial infarction

BACKGROUND

Hypertriglyceridemia is a common metabolic disturbance in men < 45 years old with myocardial infarction. To further investigate the relation between triglyceride-rich lipoproteins and severity of coronary atherosclerosis in this subset of postinfarction patients, apolipoprotein B-containing lipoproteins of 64 consecutive patients were subfractionated in connection with coronary angiography.

METHODS AND RESULTS

Density-gradient ultracentrifugation of plasma and coronary angiography were performed 4 to 6 months after the myocardial infarction. Global coronary atherosclerosis and the number and severity of distinct stenoses were evaluated by semiquantitative analysis of 15 proximal coronary segments. The majority of the patients (60%) were hypertriglyceridemic and had higher coronary scores than normotriglyceridemic patients. Of the major plasma lipoproteins, triglycerides and cholesterol in the low-density lipoprotein (LDL) fraction were associated with global coronary atherosclerosis, whereas LDL triglycerides and high-density lipoprotein (HDL) cholesterol correlated directly and inversely, respectively, with the coronary stenosis score. Plasma apolipoprotein B correlated with both coronary scores. The plasma concentrations of lipid and protein in the very-low-density lipoprotein (VLDL) subfractions (VLDL1 through VLDL3) and intermediate-density lipoprotein (IDL) did not correlate with either of the coronary scores, whereas the concentration of triglycerides in dense LDL (density > 1.040 kg/L) was strongly associated with both coronary scores. Compositional analysis of the smallest VLDL particles (VLDL3) and IDL revealed a correlation between the number of cholesteryl ester molecules in small VLDL and global coronary atherosclerosis in hypertriglyceridemic patients.

CONCLUSIONS

Global coronary atherosclerosis and distinct stenoses in young postinfarction patients are associated with the number of apolipoprotein B-containing particles in plasma and the concentration of LDL triglyceride. Specifically, dense triglyceride-rich LDL particles and, in hypertriglyceridemic patients, small cholesteryl ester-rich VLDL particles relate to coronary artery disease severity.

Composition of human low density lipoprotein: effects of postprandial triglyceride-rich lipoproteins, lipoprotein lipase, hepatic lipase and cholesteryl ester transfer protein

A preponderance of small, dense low density lipoprotein (LDL) particles has been linked to increased risk of myocardial infarction, and a dense and protein-rich LDL has proved to be a characteristic of patients with manifest coronary heart disease (CHD). The present study focused on metabolic determinants of the LDL subfraction distribution with the emphasis placed on alimentary lipaemia. The relations of plasma levels and composition of light (1.019 < d < 1.040 kg/l) and dense (1.040 < d < 1.063 kg/l) LDL subfractions to postprandial triglyceride-rich lipoproteins (TGRL), postheparin plasma lipase activities and the activity of cholesteryl ester transfer protein (CETP) were studied in 32 men with angiographically ascertained premature coronary atherosclerosis (age 48.8 +/- 3.2 years) and in 10 age matched healthy control men. LDL subfractions were separated by equilibrium density gradient ultracentrifugation of fasting plasma drawn before participants were subjected to an oral fat tolerance test of a mixed meal type. The response of TGRL to the oral fat load was determined by measuring plasma triglycerides, and the apolipoprotein (apo) B-48 and apo B-100 content of Sf 60-400 and Sf 20-60 lipoprotein fractions. At a second visit plasma samples were taken for determination of postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities and for measurement of CETP activity. Hypertriglyceridaemic patients had a preponderance of dense LDL particles compared with normotriglyceridaemic patients and controls. The magnitude of the response of TGRL to the oral fat load showed a positive association with the dense LDL apo B concentration (r = 0.32-0.52, P < 0.05), whereas the LPL activity correlated positively with the free (r = 0.50, P < 0.001) and esterified cholesterol (r = 0.45, P < 0.01) and apo B (r = 0.42, P < 0.01) content of the light LDL fraction. The HL activity was found to be inversely associated with the plasma level of light LDL triglycerides (r = -0.38, P < 0.05). In contrast, no relations were noted between CETP activity and plasma concentrations of LDL constituents. Multiple stepwise linear regression analysis with the proportion of total LDL apo B contained in the dense LDL subfraction (% dense LDL apo B) used as the dependent variable indicated that the combined effect of LPL activity and postprandial plasma levels of TGRL (areas under the curve for plasma triglycerides or Sf 60-400 apo B-48) accounted for around 50% of the variability in the distribution of LDL particles between light and dense subfractions.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoprotein B gene polymorphisms, lipoproteins and coronary atherosclerosis: a study of young myocardial infarction survivors and healthy population-based individuals

Association studies were carried out in a sample of 87 patients from Sweden who had survived a myocardial infarction (MI) before the age of 45, and 91 age-matched healthy individuals, to compare the impact of polymorphisms at the apolipoprotein (apo) E and B gene loci on among-individual differences in plasma lipid traits and progression of atherosclerosis. In the group of healthy individuals, polymorphisms creating the common apo E isoforms were, as expected, associated with significant differences in total and low density lipoprotein (LDL) cholesterol (11.7% and 11.6% of sample variance). For apo B, the polymorphism with the largest effect on apo B levels (16% of sample variance) was the C to T transition 265 bp 5' of the cap site, in the promoter (detectable by MspI). Both this polymorphism and the threonine2488 neutral substitution (detectable by XbaI) were associated with significant effects on LDL-cholesterol (8.3% and 9.3% of sample variance, respectively). The asparagine/serine4311 polymorphism was associated with a significant effect on high density lipoprotein (HDL) cholesterol alone, and there was no significant association with the glutamate/lysine4154 polymorphism (detectable by EcoRI) or the leucine-alanine-leucine (LAL) insertion/deletion polymorphism in the signal peptide. In the patients, polymorphisms creating the three common apo E isoforms were associated with large effects on cholesterol, apo B and triglyceride levels (19.9%, 20.3% and 23.9% of sample variance) of similar magnitude as in the healthy individuals. Apo B polymorphisms were found to be associated with much smaller effects on lipid traits than in the healthy individuals. The only significant association was between the asparagine/serine4311 polymorphism and HDL-triglyceride levels. However, global severity of coronary atherosclerosis at the first angiography was found to be significantly associated with the LAL insertion/deletion polymorphism (P = 0.008). Thus variation at the apo B gene locus is associated with the development of atherosclerosis, but the data suggests that this may act through mechanisms not directly related to effects on measured lipid traits.